A study on wastewater treatment by adsorption technique using hierarchical porous materials derived from aquatic waste

Dissertation objectives - Content 1: Producing activated carbon from shrimp shells by activating using KOH - Content 2: Characterizing the synthesized activated carbons by different anal

LITERATURE REVIEW

Overview of water pollution

Water is essential for the survival of all living organisms and serves as a symbol of life The quality of water, whether polluted or pure, greatly affects the health of these organisms Historically, humans have settled near abundant water resources, but the exploitation of these resources, combined with population growth, has resulted in severe pollution issues that endanger both aquatic ecosystems and human health.

Access to clean drinking water is a critical challenge, especially in developing nations like Vietnam, where 47% of the global population currently lacks a reliable supply of safe water, a figure expected to rise to 57% by 2050 The consequences of inadequate water quality can severely disrupt ecosystems Vietnam's history includes significant exposure to harmful chemicals, notably from the use of Agent Orange during the war, which devastated natural forests and contaminated water sources The Vietnamese government estimates that around four million people were exposed to this defoliant, with up to three million experiencing related health issues.

As Vietnam's economy undergoes industrialization and modernization, pollution levels have escalated significantly The contamination of water supplies is exacerbated by industrial and urban residential wastewater, particularly in the suburbs of major cities such as Hanoi and Ho Chi Minh City, as well as in regions with dense industrial production.

In recent decades, heavy metal water pollution has become a critical environmental issue, alongside chemical and microbiological contamination A notable case is the Hinckley incident, where Pacific Gas and Electric used hexavalent chromium from 1952 to 1966 to prevent corrosion in their cooling tower system The discharge of contaminated water into open ponds led to significant groundwater pollution over an area of 3.2 by 1.6 km, affecting local drinking water sources This chromium contamination has caused serious health problems for residents, including increased rates of Hodgkin’s disease, miscarriages, and various cancers, with ongoing efforts for groundwater remediation.

Heavy metal contamination is a serious threat to the environment and human health due to the long-lasting presence of toxic elements in ecosystems Industrial activities, including mining, smelting, and manufacturing, along with agricultural practices and improper electronic waste disposal, are the primary sources of heavy metal release Once these metals, such as lead, mercury, cadmium, and arsenic, enter the environment, they can contaminate soil, water, and air, leading to a cascade of harmful effects.

Human activities have significantly increased the presence of heavy metals (HMs) in water systems worldwide This rise is primarily attributed to the use of sewage sludge-based amendments, pesticides, herbicides, and phosphate fertilizers in irrigation practices, which elevate HM concentrations in soil As a result, water systems become contaminated through runoff and leaching Additionally, factors such as livestock manure, atmospheric deposition, wastewater, and the use of polluted water for irrigation further exacerbate the spread of heavy metals.

Common hazardous metals found in water include Cadmium (Cd), Copper (Cu), Nickel (Ni), Chromium (Cr), Cobalt (Co), Mercury (Hg), and Lead (Pb) These metals are deemed safe when their concentrations stay within established permissible limits For detailed standards regarding heavy metal content in water, refer to Table 1.1.

Table 1.1 Permissible limits of some heavy metals in water according to WHO [10].

Metal As Cu Ni Pb Hg Fe Mn

Additionally, water samples collected from various locations across Asia, which demonstrate the extent of water pollution caused by heavy metals, are summarized in Table 1.2.

Table 1.2.Heavy metal concentrations in water in different places around Asia

Heavy metals, due to their solubility in water and ability to be easily absorbed by living organisms, can accumulate over time, posing serious health risks to humans This accumulation can lead to significant health issues, including damage to the brain, kidneys, and respiratory systems, as well as the degradation of natural waterways A summary of the toxic effects of various heavy metals on human health is presented in Table 1.3.

Table 1.3.The toxicity of several heavy metals on human health

Hg Nervous system disorders (memory, sensory functions, coordination) [14]

Pb Nervous system disorders, liver and kidney disorders, fertility decrease [14]

Ni Respiratory diseases, asthma, congenital malformations, cancers [14]

Fe Hemochromatosis, eye disorder, cancer, and heart diseases [15]

Copper Menkes, Wilson, Alzheimer’s, Parkinson’s diseases, damages for eye [14]

Organic dyes are colorants used for textiles, paper, leather, and other materials, typically characterized by their water solubility and carbon content They are categorized into two primary types: natural dyes, sourced from plants, invertebrates, or minerals—such as madder for red, saffron for yellow, and indigo for blue—and synthetic dyes, which are artificially created with complex chemical structures, including anionic dyes like Congo Red and cationic dyes like Methylene Blue.

The use of organic dyes poses significant risks to human health and the environment, as some dyes are toxic or carcinogenic, leading to medical issues like nausea, skin irritation, respiratory problems, and cancer Additionally, their biodegradation can produce harmful compounds, contributing to water pollution that adversely affects aquatic life and plants Furthermore, these dyes can contaminate soil, impacting agriculture and food production.

Effluents containing organic dyes can be found in every waterway on the global scale: China [21], Canada [22], Italy [23] Common organic dyes encountered include:

Cationic dyes, also known as basic dyes, are a type of dye that dissociates into positively charged ions in aqueous solutions These dyes form strong salt complexes with the negatively charged groups on fiber molecules, resulting in effective dyeing of the fibers Common categories of cationic dyes include azo dyes, triarylmethane dyes, anthraquinone dyes, and heterocyclic compounds Notable examples of basic dyes are methylene blue, toluidine blue, thionine, and crystal violet.

The release of effluents containing dyes into aquatic ecosystems can lead to harmful effects, including increased water turbidity, the development of foul odors, and reduced sunlight penetration in water bodies.

Cationic dyes in wastewater from textile washing can significantly disrupt photosynthesis and oxygen circulation, leading to detrimental effects on marine life and the ecological balance of aquatic environments.

Cationic dyes and their degradation products are highly toxic and can pose serious health risks to humans, potentially leading to mutagenic and carcinogenic effects Exposure may result in various adverse health issues, including hyperactivity, behavioral changes like irritability and depression, as well as allergic reactions such as hives, asthma, sneezing, watery eyes, and skin irritation.

Anionic dyes, commonly known as acid dyes, are highly soluble in water due to their anionic characteristics and the presence of acidic groups like -SO3H and -COOH These dyes are extensively used on natural fibers such as wool and silk, as well as synthetic fibers like nylon The dyeing process involves the formation of an ionic bond between the protonated -NH2 group on the fiber and the acid group of the dye, which effectively fixes the dye onto the fiber surface.

Contaminant removal methods

Water pollution poses a significant threat to the environment and adversely affects human health In response, the scientific community is actively developing innovative, eco-friendly, and cost-effective strategies to remove contaminants from water bodies, utilizing both chemical and physical methods.

Scientists can develop a versatile removal tool by integrating different chemical functional groups into a targeted material Research has identified three effective chemical mechanisms—precipitation, coagulation, flocculation, and electrochemical processes—for the removal of heavy metals.

Chemical precipitation is an effective technique for eliminating heavy metals from wastewater by transforming soluble heavy metal ions into insoluble precipitates such as hydroxides, sulfides, carbonates, and phosphates These precipitates can be easily separated from the wastewater due to their heterogeneous nature Among these methods, hydroxide treatment is the most prevalent due to its simplicity, low cost of reagents, and the ease of automated pH control Various studies demonstrating the effectiveness of precipitation in treating heavy metals and dyes are summarized in Table 1.4.

Table 1.4.Studies into treating heavy metals and dyes by precipitation method

Precipitation method Precipitants Contaminants Removing efficiency

Polymergrafted magnetic iron oxide nanoparticles

Cr(VI) Alizarin Red S (ARS)

CaCO3and Ca(OH)2from gastropod shells

Acid orange II Direct yellow R

The coagulation-flocculation method is a well-established pre-treatment process that significantly improves the efficiency of secondary and post-treatment techniques in wastewater treatment This approach is especially effective for removing heavy metals and organic dyes, relying on the electrostatic interactions between pollutants and coagulant-flocculant agents.

In the treatment of heavy metals, coagulants such as ferric chloride, alum, and anionic polymer significantly improve the removal efficiencies of metals including chromium, copper, zinc, and nickel Research indicates that these coagulants can enhance heavy metal removal by over 200% for chromium, copper, zinc, and nickel, and by an impressive 475% for lead, when compared to traditional primary treatment methods.

In organic dye treatment, coagulants like alum, polyaluminium chloride (PACl), and MgCl2, along with an anionic coagulant aid, are utilized to treat aqueous solutions with different ratios of commercial disperse and reactive dyes Research indicates that PACl outperforms both MgCl2 and alum, achieving over 99% color removal and a 96.3% reduction in chemical oxygen demand (COD) while using a smaller amount of the coagulant.

In electrochemical systems, oxidation occurs at the anode, while reduction takes place at the cathode, collectively known as Redox processes, which are essential for metal removal from water during purification The electrochemical method has proven effective in treating organic dyes, such as permanent methylene blue, using an electrochemical cyclic ring reactor This approach is both user-friendly and eco-friendly, requiring less labor and energy for wastewater treatment However, the high cost of effective anode materials highlights the need for additional materials to balance cost and efficiency.

Chemical methods, although popular in the scientific community, have notable drawbacks, including the potential for secondary pollution and challenges related to waste disposal Despite their efficiency and time-saving advantages, there is a growing trend in research towards physical methods, which are increasingly recognized as more environmentally friendly and sustainable alternatives.

The ion-exchange method is a widely used technique for environmental treatment, particularly in the removal of heavy metals and dyes from wastewater [42].

The heavy metal removal process utilizes a column filled with resin beads to effectively extract heavy metal ions from wastewater As the water passes through, heavy metal ions bond to the resin, resulting in treated water exiting the column This method efficiently removes a range of heavy metals, and the ion exchangers can be easily regenerated for reuse.

The ion-exchange method is an effective technique for dye removal, utilizing strong interactions between functional groups on ion exchange resins and charged dye molecules The primary adsorption mechanisms include electrostatic attraction, ion exchange, and surface complexation This method is favored for its high removal efficiency, ease of operation, cost-effectiveness, and the recyclability of the adsorbents.

The membrane acts as an advanced filter, effectively trapping particles of various sizes through chemical interactions, particularly with small particles like metal ions and organic dyes By incorporating functional groups into the polymer membrane's pore walls and surface, a membrane adsorbent is created that selectively attracts targeted pollutants, thereby enhancing filtration efficiency As water passes through the membrane, active binding sites function like a net, capturing contaminants The advantages and disadvantages of these filtration methods are detailed in Table 1.5.

Table 1.5.Benefits and drawbacks of several wastewater treatment methods

Simple Affordable Applicable for most metals

Sludge build-up Disposal cost

Large chemical consumption Sludge treatment

No chemical required High selectivity High efficiency

High initial capital cost Initial pH solution required

High regeneration of metals High selectivity

High cost Low efficiency pH adjustment is required

Low solid waste Low chemical consumption

High initial capital cost High maintenance and operation costs Membrane fouling Limited flow rates

Aquatic environment treatment requires a comprehensive solution, and adsorption emerges as a highly efficient and cost-effective method This approach is distinguished by its large adsorption capacity, rapid adsorption speed, and the potential for recyclability, making it an ideal choice for effective water treatment.

Adsorption is a mass transfer process that enables a substance to transition from a liquid phase to a solid surface through physical and chemical interactions This process involves adsorbents that can bind heavy metal ions either physically or chemically, with chemical adsorption being characterized by stronger bonds formed by chemical functional groups A notable feature of chemical adsorption is the ability of adsorbate materials to form monolayers Activated carbon and biosorbents are two primary materials utilized as effective adsorbents in this process.

Bio-adsorbents

Adsorption is an effective method for removing heavy metals and organic dyes from wastewater, but the high cost of materials and complex modification processes can hinder its economic feasibility To overcome these challenges, researchers are exploring bio-materials, which are abundant and possess numerous chemical functional groups that facilitate bonding This makes bio-materials a cost-effective and efficient alternative for wastewater treatment.

Many modifications have been established towards multiple bio-based materials with significant adsorption capacities Several examples are presented in the Table 1.6.

Table 1.6 Several example of previous studies about heavy metals and dyes removal by bio-adsorbents

Material Modified agent Adsorbates Adsorption capacity

Hawthorn fruits Sulfuric acid Methylene blue 151.5 [54]

Lignin Phosphoric acid Cu(II) 136 [55]

Banana peels Sodium hydroxide 10% Cr(II) 2.52 [56]

However, bio-adsorbents have poor pore size and small surface area Therefore, a due to its large surface area, pore structure, and high degree of surface reactivity [59].

Activated carbon (AC) features a customizable porous structure and surface chemistry that can be optimized for improved adsorption It is highly effective in wastewater treatment due to its straightforward process design and ease of implementation Additionally, AC demonstrates resilience against corrosive and toxic environments, offering significant adsorption capabilities for both gas and liquid purification, and serves as an effective supportive catalyst.

Activated carbon

Activated carbon (AC) is a versatile material derived from various carbon-rich sources such as coal, coconut shells, wood, and agricultural residues Its production involves activating these materials, which enhances their adsorptive properties and results in a high surface area and diverse pore structure These characteristics enable AC to effectively adsorb a wide range of substances, making it essential for applications including water purification and gas separation.

Activated carbon (AC) is a highly porous material formed through heat, resulting in an extensive surface area that enhances its adsorption capabilities For example, AC derived from Bambusa vulgaris has a surface area of 1042 m²/g, while corncob-derived AC reaches 1600 m²/g Additionally, activated carbon aerogels boast an impressive surface area of 2600 m²/g, and sugarcane bagasse AC offers an even larger surface area of 3555 m²/g This large surface area provides numerous contact points for effective adsorption, making AC highly efficient in removing target molecules from fluids or gases.

Activated carbon (AC) features a diverse range of pore sizes—micropores, mesopores, and macropores—enabling it to adsorb molecules of varying dimensions This diverse pore structure enhances AC's versatility across multiple applications Additionally, the strong adsorption capabilities and high selectivity of AC can be customized by altering its surface properties.

Activated carbon (AC) is a cost-effective option for adsorption applications, as it can be regenerated and reused through methods such as thermal regeneration or desorption, significantly extending its service life.

Activated carbon (AC) is a highly versatile material widely utilized for its unique properties in various applications It effectively purifies gases by removing air impurities and adsorbs dissolved organic contaminants in water, improving odour, taste, and colour AC plays a crucial role in metal extraction and the recovery of precious metals, especially gold In the medical field, it is employed in diverse treatments and is also essential in sewage treatment for pollutant removal, including organic dyes Additionally, AC is used in air filters for respirators, compressed air filtration, and solvent recovery.

AC in these applications is not only effective but also cost-efficient as it can be regenerated and reused.

Heavy metal adsorption by AC

Activated carbons (AC) derived from materials such as macadamia residue, corncobs, and modified sources are effective for heavy metal adsorption, particularly for metals like Zn(II), Cr(VI), and Pb(II) In Vietnam, macadamia residue serves as a sustainable agricultural waste, which, when ground and impregnated with K2CO3, produces AC with enhanced adsorptive properties The addition of ferrous sulfate and ferric chloride improves the AC's performance, resulting in a magnetic variant with a notable adsorption capacity for Zn(II) at 22.73 mg/g The proposed adsorption mechanism involves chemisorption, characterized by the formation of complexes between Zn²⁺ ions and carboxylic or hydroxyl groups on the AC surface.

Corncobs, often overlooked as waste, are rich in carbon and can be effectively used to produce activated carbon By grinding and filtering corncobs into fine particles, the charcoal is then activated using phosphoric acid, which increases the presence of carboxyl groups on its surface This enhancement significantly improves its ability to adsorb contaminants, achieving an impressive adsorption capacity of 9.985 mg/g for Cr(VI).

Activated carbon was modified through a series of reactions to oxidize carboxylic groups, while nitrogen-containing groups from ethylenediamine were immobilized on its surface This modification allowed Pb(II) to bind with hydroxyl or carboxyl groups and form complexes with amine groups, resulting in an increased adsorption capacity of 60.2 mg/g.

Dye adsorption by AC

Recent studies have demonstrated impressive dye adsorption capabilities, particularly using rice husk as a raw material rich in CaO and SiO2 Through steam activation involving a nitrogen and steam mixture, the BET surface area of activated carbon was enhanced to 770 m²/g, primarily due to the oxidation process Key functional groups identified include carboxylic, carbonyl, and phenolic, which provide numerous binding sites for cationic dye methylene blue (MB) and anionic dye AG 25 The maximum adsorption capacities achieved were 231.48 mg/g for MB and 84.03 mg/g for AG 25.

Precursor AC was chemically modified to attach carboxylic groups (–COOH) to its surface through mechanical friction, facilitated by sodium hydroxide and chloroacetic acid The material properties were evaluated using methyl blue (MB) and crystalline violet (CV) as testing agents, highlighting its adsorption capacity.

124 and 120 mg/g for MB and CV, respectively.

Alkaline methods for surface modification of activated carbon (AC) have been extensively studied, utilizing basic substances such as NaOH, KOH, and NH3 This chemical modification significantly enhances the surface area and increases the number of oxygen-containing functional groups in activated biochar, leading to improved porosity and efficiency for various applications The alkali metals and carbonates generated during activation play a crucial role in stabilizing and expanding the spaces between carbon-atom layers, which boosts the adsorption capacity of activated carbon Additionally, higher activation temperatures and increased ratios of NaOH to carbonized samples contribute to a larger surface area.

The activation of activated carbon (AC) using sodium hydroxide (NaOH) significantly increased the intensity at the hydroxyl (-OH) peak in FTIR analysis This enhancement led to improved adsorption capacities for Acid Red 14 (AC14) and Acid Blue 92 (AB92), with maximum adsorption values recorded at 13.276 mg/g for AC14 and 9.329 mg/g for AB92.

Objective of the thesis

Industrialization is a crucial step for nations aiming to modernize and transition from outdated agricultural systems to socialism It enhances the manufacturing sector by transforming production technologies and boosting labor productivity, thereby strengthening state control over economic output and shaping market dynamics Additionally, industrialization fosters socioeconomic growth, improves security and defense, and promotes a self-sufficient economy However, it is vital to recognize the associated risks, including climate change, ecological imbalance, and environmental degradation, particularly the contamination of water sources by heavy metals and dyes from industrial wastewater Various methods, such as membrane filtration, ion exchange, redox, and precipitation, have been explored for effectively removing these contaminants, with recent research focusing on the development of nanoscale materials with high specific surface areas for improved separation processes.

In recent years, Vietnam's fishing and aquaculture industries have significantly expanded to meet the rising demand for seafood both domestically and internationally, particularly in the shrimp sector This growth has resulted in a substantial increase in shrimp by-products, with shelled heads accounting for a large portion of the 325,000 tons of shrimp waste generated annually Without proper research and utilization, these by-products could harm the environment However, shrimp by-products hold potential as valuable protein sources for producing astaxanthin and chitin Recent studies have explored the use of shrimp shells as effective adsorbents for treating heavy metal-contaminated wastewater Currently, shrimp shells are mainly processed into animal feed, leaving many shells to be discarded.

There is an urgent necessity for research in our country focused on the use of modified shrimp shells for the effective adsorption of heavy metal ions and dyes in wastewater Consequently, I have chosen to explore the topic "A Study on Wastewater Treatment by Adsorption Technique Using Hierarchical Porous Materials Derived from Aquatic Waste." This study aims to tackle these pressing environmental issues comprehensively.

+ Producing activated carbon from shrimp shells by activating using KOH

+ Characterizing the synthesized activated carbons by different analytical methods

+ Investigating the adsorption capacity of the synthesized activated carbons

EXPERIMENTAL SECTION

Materials

The shrimp shells, sourced from Ca Mau Seafood Co., Ltd in Ca Mau, Vietnam, were meticulously cleaned with deionized water to eliminate contaminants before being oven-dried Following this process, the shells were forcefully crushed, dried, and sieved to achieve a size range of 125–212 mm.

Preparations of –activated carbon materials

The synthesis of activated carbon adsorbents was conducted using an improvised tubular furnace for carbonization and a KOH activation method, building on previous research Porcelain boats containing 10 g of shrimp shell powder were placed in the furnace, where the powder was carbonized under a nitrogen flow at 600°C for 2 hours After cooling, the biochar was mixed with KOH in ratios of 1:1 and 1:2 and treated in a tubular reactor at 750°C for 1.5 hours, using nitrogen as the carrier gas to produce activated carbon The activated carbon was then washed with 1M HCl and deionized water until a neutral pH was achieved, followed by drying at 80°C overnight The samples were labeled as "ACSS-0" for non-activated biochar, "ACSS-1" for the 1:1 KOH ratio, and "ACSS-2" for the 2:1 ratio.

Figure 2.1.Experimental process of preparation of activated carbon from shrimp shells

Characterization and analysis

The crystal structure was studied through X-ray diffraction (XRD) to understand its properties The Brunauer-Emmett-Teller (BET) method was employed to measure the specific surface areas of the samples by analyzing nitrogen absorption and desorption Furthermore, scanning electron microscopy (SEM) was utilized to investigate the morphologies of the samples.

X-ray diffraction (XRD) is a technique employed to analyze materials possessing a crystalline structure This non-destructive method provides valuable information about the crystal structure, phase, orientation, and other structural characteristics like average grain size or crystal defects To examine the properties of the crystallinity, X-ray diffraction (XRD) analysis was carried out by Shimadzu 6100 X-ray diffractomer (Japan) When an X-ray beam is diffracted at a specific angle from the surface of a lattice in a sample, it generates an X-ray diffraction peak Consequently, the periodic atomic arrangements within a given material can be identified through their XRD patterns For a wide range of crystalline materials, rapid phase identification can be achieved by referencing a standard online library of X-ray powder diffraction patterns. X-ray diffraction occurs when radiation is scattered by regularly spaced scattering centers that have a spacing corresponding to the wavelength of the diffracted radiation. X-ray diffraction finds extensive application in the identification of unknown crystalline materials such as minerals and inorganic compounds The identification of unknown solids is crucial in various fields of research, including geology, environmental science, materials science, engineering, and biology Some of the applications of X-ray diffraction testing include:

+ Identifying the composition of minerals.

2.3.2 Scanning Electron Microscope method – SEM-EDS

Scanning electron microscopy (SEM) is a powerful analytical technique that provides high-resolution images of sample surfaces It operates alongside energy-dispersive X-ray spectroscopy (EDS), which analyzes and identifies the elemental composition of samples through X-ray excitation Each element's unique atomic structure generates distinct peaks in its electromagnetic emission spectrum, enabling effective characterization This principle aligns with spectroscopy, where the peak positions are predicted using Moseley's law, enhancing the resolution beyond that of standard EDX instruments.

The working principle of a Scanning Electron Microscope (SEM) involves generating electrons through a heat-emitting and field-emitting electron gun These electrons are accelerated between 10kV to 50kV and focused into a narrow beam, ranging from several hundred to several nanometers, using magnetic lenses The focused beam is then scanned across the sample's surface with electrostatic scanning coils The resolution of the SEM is determined by the size of the electron beam on the sample Upon interacting with the sample surface, the electrons emit a cloud of secondary electrons, which are captured to produce signals for imaging.

Surface imaging and analysis techniques, including energy-dispersive X-ray spectroscopy (EDX), wavelength-dispersive X-ray spectroscopy (WDS), Auger spectroscopy, and cathode fluorescence spectroscopy, rely on specific electronic signals In scanning electron microscopy (SEM), secondary electrons and backscattered electrons are the two primary types of signals used for these applications.

SEM finds applications in several areas, including:

+ Morphological structure analysis, such as observing crystallization and grain size for microstructure examination.

+ Composition analysis, including phase composition, interactions between phases, distribution, and the ratio of structural components.

+ Chemical composition analysis of materials, including identification of compositional elements and their percentages.

The study utilized scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) using a JEOL JSM-IT200 microscope to investigate the porosity and surface morphology of gold-coated materials SEM provides significant advantages, including magnifications over 100,000 times, non-destructive analysis, and operation at normal vacuum levels, while also ensuring straightforward sample preparation and instrument control.

Porosity and pore structure are essential in geology and engineering, particularly for mudrocks and shales, as they affect multiphase movement, geomechanical behavior, and storage/sealing potential Various techniques exist to measure porosity, each with distinct advantages and limitations, leading to significant discrepancies in results, especially in shales that display macro-, meso-, and micro-porosity Common methods like petrography, X-ray micro-tomography, and Hg-intrusion porosimetry, while effective for conventional reservoir rocks, struggle to accurately quantify porosity in shales.

In this study, the specific surface area was determined using the Brunauer-Emmett-Teller (BET) method with the Nova4000e (Quantachrome) at 77K, employing 30 adsorption and 16 desorption points The increasing demand for porosity and pore structure data in shales, driven by the rise in shale hydrocarbon production over the past decade, has led the geoscience community to adopt successful techniques from other fields One such technique is nitrogen physisorption analysis, which measures the physical adsorption of nitrogen gas at liquid nitrogen temperature (77 K) This method quantifies the amount of gas adsorbed as a function of relative pressure, and the resulting isotherms provide valuable insights into pore volume and area distributions.

In addition to the N2 approach, CO2 physisorption analysis is commonly used for advantages over N2, it has not been extensively utilized for shale characterization thus far (Thommes and Cychosz, 2014).

2.3.4 Ultraviolet-visible spectroscopy method UV-VIS

Modern UV-VIS spectrophotometers consist of key components, including a radiation source, monochromator, sample cuvette, detector, and data logger The radiation source emits light that is split into narrow bands by the monochromator, directing monochromatic beams through the solvent and sample cells The detector measures the intensity of the radiation passing through the sample, converting it into an electrical signal to quantify results based on Lambert-Beer's law This data is typically logged and analyzed using specialized software on a connected computer, enabling effective calculations and comparisons of spectral data.

Conventional UV-VIS spectrometers typically capture spectra in the near ultraviolet and visible ranges, spanning from 200 nm to 800 nm Certain models extend their measurement capabilities into the near-infrared region, reaching approximately 1000 nm However, specialized spectrometers are required to measure the far ultraviolet or vacuum ultraviolet region, which includes wavelengths shorter than 200 nm.

The absorbance (A) of a sample is calculated using the logarithm of the ratio of the initial light intensity (Io) to the light intensity after passing through the sample Transmittance (T) represents the proportion of light that passes through the sample and is determined by the ratio I/Io To find the concentration (C) of the sample, the Lambert-Beer equation is applied, utilizing known values of molar absorptivity (ε) and path length (L), with absorbance (A) as a measured parameter Molar absorptivity (ε) is measured in L mol⁻¹·cm⁻¹, path length (L) in centimeters (cm), and concentration (C) in moles (mol).

L -1 The absorbance (A) itself is dimensionless, as it does not have any units.

Titration has been a long-standing method for determining chemical concentrations. compounds Instead, a reactant of known concentration is added to the dissolved sample until the conversion is complete.

Titration continues to be a popular method in chemical analysis due to its simplicity and speed, delivering accurate measurements in just minutes under optimal conditions With a relative standard deviation usually below 1%, it remains the preferred technique in many standards.

During titration, the solution's volume is accurately measured, and a correction factor is applied for improved accuracy A reagent of known concentration is slowly added from a burette until the equivalence point is reached Modern titrators utilize automated methods for precise titrant dosing, with the endpoint detected by a potentiometric sensor, typically a pH electrode To ensure consistency with manual titration results, the process targets a specific pH value that aligns with the intended color change.

Different types of titrations can be distinguished based on the chemical reaction involved:

Acid-base titration involves monitoring changes in pH during the process, which can be indicated by a color change or measured with a pH electrode In contrast, redox titration focuses on alterations in the oxidation level of the sample, utilizing an oxidizing or reducing agent, with the endpoint identified through a color change or an ORP electrode, such as a platinum electrode.

+ Precipitation titration: The added reagent causes the formation of a precipitate. This can be observed, for example, in silver nitrate titration through a color change or by using a silver electrode.

+ Complex titration: Metals are titrated using complex reagents Their response can be observed using ion-sensing electrodes or through an indicator.

Based on the equation below we can observe the concentration of the solution used to titrate by EDTA:

2.3.6 Point of zero charge (pHpzc)

The point of zero charge (pHpzc) is the pH level at which an adsorbent material or solid surface has no net charge, meaning that the positive and negative charges are balanced, leading to an overall neutral charge Determining the pHpzc requires a series of experimental procedures.

Chemicals and instrumentations

All the chemicals needed for the tests were bought commercially from AcrosOrganics, Fisher Chemical Guangdong Guanghua Sci-tech, and Shanghai ZhanyunChemical and utilized without pretreatment.

Table 2.1.List of chemicals purchased and used in the research

1 Copper (II) nitrate trihydrate Cu(NO3)2 3H2O Acros Organics

2 Nickel (II) nitrate hexahydrate Ni(NO3)2 6H2O Acros Organics

3 Iron (III) nitrate nonahydrate Fe(NO3)3 9H2O Fisher Chemical

4 Ammonia solution, 35% NH4OH Fisher Scientific

5 Ammonium chloride NH4Cl Xi Long Scientific

7 Ethylene glycol C2H6O2 Xi Long Scientific

9 Methylene blue C16H18ClN3S Shanghai Zhanyun

10 Congo Red C32H22N6Na2O6S2 Shanghai Zhanyun

Adsorption studies

2.5.1 The adsorption of Fe 3+ solution

2.5.1.1 The standard curve of Fe 3+ solution

Figure 2.2.Standard curve equation of Fe 3+

The Fe 3+ standard curve exhibits linearity with the equation y = 0.0241x + 0.0218,where x represents the solution concentration in mg/L and y represents the absorbance

To prepare a single-metal stock solution with an approximate concentration of

To prepare a 1000 ppm solution of Fe(NO3)3.9H2O, dissolve the specified amount of the metal salt in distilled water within a 1000 mL volumetric flask The concentration of the metal cation in the resulting solution is subsequently measured using the UV-Vis method This solution acts as a foundation for the preparation of additional solutions tailored to specific experimental needs.

The following steps are followed:

To prepare a solution of iron(III) nitrate nonahydrate, weigh 1g of Fe(NO3)3.9H2O and transfer it to a 1000 mL volumetric flask Next, add distilled water until the volume reaches the mark on the flask Finally, shake the flask thoroughly to ensure the contents are well mixed.

+ The resulting Fe 3+ solution has a concentration of 1000 mg/L and is stored in beakers covered with silver paper.

From the 1000 mg/L solution, further dilutions are made using distilled water to obtain concentrations of 50, 100, 200, 300, 400, and 500 mg/L These concentrations correspond to ion Fe 3+ concentrations of 6.9, 13.9, 27.7, 41.6, 55.4, and 69.3 ppm, respectively.

The solutions with specified concentrations are analyzed for optical absorbance at 300 nm using a UV-Vis Jasco V-730 spectrophotometer, enabling the construction of a standard curve.

Table 2.4.Experiment of constructing standard curve

2.5.1.2 The effects of adsorption time

In the experiment, seven clean 50 mL Erlenmeyer flasks were utilized, each containing 25 mL of a 200 mg/L Fe 3+ solution, equating to an approximate concentration of 27.7 mg/L Fe 3+ Additionally, 0.025 g of ACSS-1 and ACSS-2 samples were precisely measured and added to each flask.

A magnetic stirrer was utilized at room temperature (25°C) with varying stirring durations of 10, 20, 30, 40, 60, 90, 120, and 180 minutes To ensure accurate UV-Vis measurements and reduce potential errors, filter paper and a funnel were employed to remove any biochar from the sample The concentration of Fe 3+ remaining in the solution post-adsorption was assessed similarly to the standard line construction, enabling the identification of a stable and optimal adsorption time for further study.

Table 2.5.Experiment of investigating the optimal adsorption time

2.5.1.3 The effect of initial concentration of Fe 3+ ions

The experiment utilized an activated carbon sample with a KOH/AC ratio of 2, involving six clean 50 mL Erlenmeyer flasks Each flask received 0.025 g of activated carbon samples ACSS-1 and ACSS-2 Following this, 50 mL of Fe 3+ solution at varying concentrations of 50, 100, 200, 300, 400, and 500 mg/L was added to each flask for analysis.

The mixtures in the flasks underwent magnetic stirring at 200 rpm and were kept at a room temperature of 25°C to ensure optimal equilibration This equilibration period facilitates the adsorption process, allowing it to achieve a steady state.

The remaining concentration of Fe 3+ in each solution was determined, representing the relationship between Ce/q and Ce This data was then utilized to calculate the maximum adsorption capacity (qmax).

Table 2.6.Experiment of investigating the effect of initial concentration on adsorption capacity

2.5.2 The adsorption of Cu 2+ ions

The adsorption of Cu 2+ ions on two samples was investigated using Cu(NO3)2 solutions The solutions were agitated with activated carbon (AC) for different durations—1, 5, 20, 30, 40, and 60 minutes—to facilitate interaction with varying amounts of Cu 2+ ions The concentration of copper in the filtrate was measured through complexometric titration with EDTA.

To achieve a pH of 10 in the test samples, 10 drops (0.5 mL) of 35% NH3 solution and 5 mg of NH4Cl were utilized The titration process involved the addition of 5 mM EDTA and 5 mg of murexide, with the transition point marked by a color change from yellow to orange to pink.

The concentration of Cu 2+ ions adsorbed on activated carbon (AC) can be determined by comparing the filtrate concentrations with those of a reference sample that was not exposed to AC.

2.5.3 The adsorption of Ni 2+ ions

The study examined the adsorption of Ni 2+ ions from Ni(NO3)2 solutions onto two samples Various concentrations of Ni 2+ ions (0.2, 0.5, 1.0, 5.0, and 10.0 mM) were mixed with activated carbon (AC) and allowed to interact for different time periods (1, 5, 20, 30, 40, and 60 minutes) before filtration The concentration of nickel in the filtrate was quantified using complexometric titration with EDTA.

To achieve a pH of 10 in the test samples, 10 drops (0.5 mL) of 35% NH3 solution and 5 mg of NH4Cl were added The titration utilized 5 mM EDTA and 5 mg of murexide as indicators, leading to a color change from yellow to orange to pink.

The amount of Ni 2+ ions adsorbed on activated carbon (AC) was determined by comparing the concentrations found in the filtrate to those in a reference sample that had not been exposed to AC.

Batch adsorption experiments were conducted to analyze the interaction between dyes and ACSS-x, focusing on four key factors: pH, adsorption time, initial concentration of the adsorbate, and dosage of the adsorbent The study initially explored the effect of pH levels ranging from 2 to 12 Following this, adsorption times were varied between 10 and 180 minutes A range of dye solutions with initial concentrations from 200 to 800 ppm was tested, alongside different adsorbent quantities varying from 0.03 to 0.07 g.

Filtration of the solutions was conducted using filtration paper, followed by dye concentration determination with a UV-visible spectrophotometer at wavelengths of 664 nm for MB dye and 497 nm for CR dye All experiments were performed in triplicate, and mean values were calculated from the recorded data The quantities of dyes adsorbed by ACSS-x and their respective removal percentages were computed using specific equations designed for these calculations.

Reusability of adsorbent

The ACSS-x material exhibited a significant ability for regeneration, making it a promising option for minimizing secondary waste generation after adsorption This study initiated an evaluation of the reusability of ACSS-x following its adsorption process.

The study investigated the regeneration of activated carbon after dye adsorption using absolute ethanol, distilled water, and various ethanol-water mixtures The optimal regeneration was achieved with a 6:4 ethanol-water mixture For the regeneration experiments, MB-ACSS-x and CR-ACSS-x were immersed in this solution for 24 hours After immersion, the adsorbent was separated from the dye solution, washed with distilled water, and prepared for the next adsorption-desorption cycle.

RESULTS AND DISCUSSION

The physicochemical properties of material samples

Figure 3.1.SEM analyses for the surface morphology of ACSS-1 (a, b), ACSS-2

The external morphology of biochar and ACSS-x was examined and depicted

Following activation, the non-porous biochar transformed into porous activated carbon (AC), as shown in the SEM images (Fig 3.1 (c) - (f)) The SEM images of ACSS-1 and ACSS-2 samples revealed significant voids and pores, highlighting their rough and porous structure This morphological feature is anticipated to significantly improve the effectiveness of adsorption processes.

The activation of shrimp shells with potassium hydroxide (KOH) begins with the transformation of potassium carbonate (K2CO3) at temperatures starting from 400°C and concluding at 600°C During this pyrolysis process, K2CO3 reacts with carbon, resulting in the production of metallic potassium and carbon dioxide These chemical reactions play a crucial role in creating the porous structure evident in the SEM images of activated carbon derived from shrimp shells (ACSS-x).

The transformation of ACSS-x from a non-porous to a porous structure significantly enhances its adsorption capacity by increasing surface area and active sites for contaminant removal from water This rough, porous configuration improves accessibility and interaction between the adsorbent and adsorbate, leading to more efficient adsorption Additionally, the formation of metallic potassium compounds during activation may further enhance the adsorption performance of ACSS-x, as potassium-based compounds are known for their adsorbent properties.

The SEM analysis highlights the crucial morphological transformations during the activation of biochar into ACSS-x, showcasing a shift from a non-porous to a porous structure This transition, characterized by the formation of voids, pores, and potentially adsorbent metallic potassium compounds, significantly improves the adsorption capabilities of ACSS-x, positioning it as a highly promising material for diverse adsorption applications.

Table 3.1 EDS analysis of activated carbon derived from shrimp shell with several ratio.

Table 3.1 presents the elemental analysis results of the ACSS samples, revealing a high carbon content that underscores the purity of materials derived from shrimp shells This significant carbon presence is advantageous, as it reflects the carbon-rich characteristics of the activated carbon material.

The elemental analysis of ACSS samples indicates the presence of potassium, linked to the use of potassium hydroxide (KOH) as an activating agent during the activation process This confirms that potassium is integrated into the ACSS structure However, some potassium is expected to be partially removed during the washing step, which is designed to eliminate any remaining activating agents and impurities.

Elemental analysis reveals the presence of contaminants like sulfur and chlorine in ACSS samples, which can originate from the raw materials or the activation process The washing step effectively reduces these contaminants, demonstrating the purification process's efficiency in producing cleaner final ACSS samples.

The elemental analysis of ACSS samples indicates a carbon-rich composition derived from shrimp shells, with notable amounts of potassium, sulfur, and chlorine reflecting the activating agent's influence and potential contaminants The washing process effectively reduces these elements, enhancing the purity of the ACSS materials These insights are essential for evaluating the elemental composition and purity of ACSS, particularly regarding their applicability in adsorption processes.

Figure 3.2.TEM analyses of ACSS-2 with the magnification of a) 80kX and b)

The transmission electron microscopy (TEM) images in Fig 3.2 offer critical insights into the microstructural features of the activated carbon (AC) samples The analysis indicates that the main components of the AC samples are carbon particles, which tend to aggregate due to their small size, leading to a stacking behavior when dispersed in aqueous solutions.

TEM images reveal notable distinctions between light and dark zones, where light areas indicate the presence of carbon particles and dark zones signify regions of higher carbon density This contrast visually demonstrates the distribution and arrangement of carbon particles within the AC structure.

TEM analysis reveals that the fragment sizes in AC samples range from 2nm, contributing to the formation of various pore sizes within the AC structure, including micro, meso-, and macro pores This diverse pore size distribution enhances the adsorption capacity of the AC material, facilitating the effective removal of contaminants from aqueous solutions.

The varying sizes of pores in activated carbon (AC) samples significantly enhance their adsorption capacity Micro-sized pores allow for the adsorption of small molecules, while meso- and macro-sized pores accommodate larger molecules This hierarchical pore structure maximizes the availability of active sites, making the AC material highly effective for adsorbing contaminants of different sizes.

TEM images of the activated carbon (AC) samples show aggregated carbon particles, with distinct light and dark zones indicating varying carbon density within the structure The analysis reveals a range of fragment sizes, leading to diverse pore sizes—micro, meso, and macro—which enhance the adsorption capacity of the material.

AC material Understanding the microstructural characteristics of the AC samples provides valuable insights into their adsorption capabilities and supports their potential application in various adsorption processes.

Figure 3.3.XRD results of ACSS-0, ACSS-1, and ACSS-2

The X-ray diffraction (XRD) patterns obtained for ACSS-0, ACSS-1, and ACSS-2 and the impact of the activation and carbonization processes The analysis reveals distinct differences in the crystalline structures of these samples.

The XRD pattern of ACSS-0, the biochar precursor, reveals a significant level of crystallinity primarily due to calcium oxide (CaO) and calcium carbonate (CaCO3) content Distinct diffraction peaks for CaCO3 are observed at 2θ values of 23.022°, 29.405°, 35.965°, 39.401°, 43.145°, 47.123°, 48.517°, and 57.400°, while CaO peaks appear at 2θ values of 32.203°, 37.347°, 53.854°, 64.152°, and 67.373° These findings confirm the presence of these crystalline phases in ACSS-0, underscoring its structural characteristics.

In contrast, the XRD patterns of the activated carbon samples, ACSS-1 and ACSS-

Material synthesis efficiency

The efficiency of shrimp biochar synthesis: 75%

The efficiency of ACSS-1 synthesis from shrimp biochar: 17.3%

The efficiency of the synthesis of ACSS-2 from shrimp biochar: 12.4%

The low efficiency observed in the synthesis of ACSS-1 and ACSS-2 can be attributed to the high-temperature treating process involved.

The use of KOH in the synthesis process can cause intense burning and negative side effects, which diminish the efficiency and yield of the synthesis program To enhance the efficiency of ACSS-1 and ACSS-2 synthesis from shrimp biochar, it may be essential to optimize synthesis conditions by exploring alternative activation agents and adjusting relevant parameters.

The adsorption capacity of activated carbon on heavy metals

3.3.1.1 Effect of time on Fe(III) adsorption capacity

The adsorption equilibrium time is essential for determining the efficiency of adsorption processes, as it indicates how long it takes for the system to reach a stable state This time is significantly affected by the interplay between adsorption duration and capacity, exemplified by the uptake of Fe(III) onto ACSS-2.

The investigation demonstrated that the adsorption of Fe(III) onto ACSS-2 increased significantly within the first 40 minutes, indicating a rapid utilization of its adsorption capacity This quick uptake is primarily due to the abundance of vacant adsorption sites on ACSS-2 and the favorable interactions between Fe(III) ions and these active sites.

Figure 3.7 illustrates that the adsorption of Fe(III) onto ACSS-2 achieves equilibrium in about 40 minutes, indicating that at this point, the rate of adsorption equals the rate of desorption, leading to a stable adsorption capacity.

3.3.1.2 Effect of Fe 3+ concentration on the adsorption efficiency of AC

Figure 3.8.Effect of initial concentration on adsorption capacity

Figure 3.7 Effect of time on Fe 3+ adsorption capacity

Figure 3.9.Effect of initial concentration on adsorption efficiency

The assessment of ACSS-2 samples for Fe 3+ ion adsorption, illustrated in Fig 3.8, demonstrates that initial Fe 3+ concentration significantly influences adsorption capacity Higher concentrations of Fe 3+ ions enhance adsorption capacity due to increased diffusion of ions across the adsorbent's surface and into its capillaries Consequently, the results indicate a direct correlation between rising adsorption concentration and the improved adsorption capacity of ACSS-2 samples.

As the concentration of Fe 3+ increases, the adsorption efficiency of ACSS-2 initially remains high between 6.9 mg/L and 13.9 mg/L but gradually declines In contrast, from 27.7 mg/L to 69.3 mg/L, the adsorption efficiency shows a decreasing trend At lower initial concentrations, the adsorption capacity is high due to the availability of unfilled pores on the ACSS-2 surface However, once these pores become saturated with Fe 3+, the material's ability to adsorb decreases significantly Thus, an optimal concentration of 27.7 ppm is recommended for effective adsorption.

3.3.1.3 Effect of pH on Fe(III) adsorption capacity and % removal at optimal condition

The pH of a solution is critical in adsorption processes, as it affects chemical reactions and interactions To assess the impact of pH, specific variables were held constant based on optimal batch experiment conditions The initial concentration of Fe(III) ions was fixed at 27.73 mg/L, and the adsorption time was set to 40 minutes pH values were varied between 2 and 6 to evaluate their effect on the adsorption performance of ACSS-2.

In general, it was observed that higher pH values resulted in improved performance of ACSS-2 in Fe(III) adsorption This phenomenon can be attributed to several factors.

At lower pH levels, the adsorbent surface is positively charged, making cation adsorption unfavorable due to strong competition from hydrogen ions for active sites, which limits adsorption capacity Notably, the study revealed a peak in Fe(III) removal efficiency at a pH of 3, indicating a distinct chemical phenomenon influenced by this specific pH environment.

Increasing the pH enhances the adsorption capacity of positive ion Fe 3+, as it approaches the point of zero charge (pHpzc), facilitating easier adsorption of positive ions However, under the examined conditions, where pH remains below 6 and pHpzc, chemisorption on the surface is unlikely to occur.

As pH increases, the formation of Fe(OH)2+ complexes becomes less favorable, leading to a decrease in adsorption capacity beyond pH 3 Conversely, at higher pH levels, the negatively charged Fe(OH)4- complex forms, which can effectively adsorb onto the positively charged surfaces of adsorbents when the pH is below the pHpzc Consequently, the maximum adsorption capacity is observed at pH 3.

Figure 3.10 Effect of pH on Fe 3+ adsorption capacity and % removal at optimal condition (C0: 27.73 mg/L, t: 40mins, temperature: 25±1 o C)

3.3.1.4 Adsorption kinetics of ACSS-2 on Fe(III) adsorption

The adsorption kinetics of Fe(III) on ACSS-2 were analyzed using various models, including the pseudo-first order (PFO), pseudo-second order (PSO), and Elovich equations The pseudo-first order equation, introduced by Lagergren, is represented by the formula ln(qe - qt) = ln(qe) - k1t This study aims to provide a comprehensive understanding of the adsorption behavior of Fe(III) on ACSS-2, contributing valuable insights for environmental applications.

Figure 3.11 Pseudo-1 st order adsorption kinetic model for Fe(III) removal onto ACSS-2 at required conditions (pH: 3, C0: 27.73 mg/L, temperature: 25±1 o C)

Pseudo-2 nd order equation is: t q t = 1 k 2 q e 2 + 1 q e t (5)

Figure 3.12 Pseudo-2 nd order adsorption kinetic model for Fe(III) removal onto ACSS-2 at required conditions (pH: 3, C0: 27.73 mg/L, temperature: 25±1 o C)

Elovich equation is expressed as below: q t =1 βln αβ +1 β lnt (6)

Figure 3.13.Elovich adsorption kinetic model for Fe(III) removal onto ACSS-

2 at required conditions (pH = 3, C0= 27.73 mg/L, temperature: 25±1 o C)

In the kinetics modeling of Fe(III) adsorption onto ACSS-2, key parameters such as the rate constants k1 and k2 were used to measure the rates of adsorption and desorption The initial adsorption rate, α, indicates the adsorption speed at the process's onset, while the desorption constant, β, reflects the desorption rate from the adsorbent surface The adsorption capacity at equilibrium (qe) and at a specific time (qt) is quantified as the amount of Fe(III) adsorbed per unit mass of the adsorbent (mg/g), offering valuable insights into the adsorption process's efficiency and effectiveness over time.

To identify the most appropriate kinetics model, experimental results were thoroughly analyzed and compared Scatter plots of the experimental data, illustrated in Figures 3.11, 3.12, and 3.13, facilitate the assessment of various kinetics models Notably, the correlation coefficients for the pseudo-second order model were substantially higher than those for the pseudo-first order model and the Elovich model, indicating a stronger fit for the pseudo-second order kinetics.

The theoretical qe value, derived from the pseudo-second order model, closely aligns with the experimental qe value obtained from the data This correlation reinforces the effectiveness of the pseudo-second order kinetics model in accurately representing the adsorption process of Fe(III) onto ACSS-2.

The primary adsorption mechanism for Fe(III) onto ACSS-2 is identified as chemisorption, characterized by a strong chemical interaction between Fe(III) ions and the ACSS-2 adsorbent, often involving electron sharing or transfer The alignment of experimental and theoretical data from the pseudo-second order model reinforces this conclusion.

Table 3.3.Kinetic constants for Fe(III) adsorption

Pseudo – 1 st constant Pseudo – 2 nd constant Elovich constant qeexp

3.3.1.5 Adsorption isotherms of ACSS-2 on Fe(III) adsorption

This study explores the correlation between the adsorption capacity of ACSS-2 and varying concentrations of Fe(III) in solution By utilizing a fixed variable approach, the initial concentration of Fe(III) was selected as the primary variable, facilitating a detailed analysis of the adsorption isotherms.

Dye adsorption

The influence of pH on the adsorption process is closely linked to the point of zero charge (pHpzc) of the adsorbents, as well as the presence of Congo Red and Methylene Blue in the solution A graph was created to explore the relationship between final and initial pH, revealing that the pHpzc values for ACSS-1 and ACSS-2 are 4.4 and 6.32, respectively, based on the intersection point of the curve.

The pHpzc is an essential parameter that defines the pH level at which the adsorbent surface has a neutral charge When the pH exceeds the pHpzc, the adsorbent's surface acquires a negative charge, which plays a crucial role in the adsorption process by attracting and binding positively charged substances, such as Congo.

Red and Methylene Blue, onto the adsorbent surface.

Determining the pHpzc is crucial for understanding the electrochemical behavior of adsorbents and the mechanisms of adsorption across varying pH levels Knowledge of pHpzc allows researchers to predict and enhance the adsorption efficiency of these materials, especially in scenarios where the solution pH surpasses the adsorbent's pHpzc.

Figure 3.24.Determination of pH zero point of charge (pHpzc) by initial pH vs. final pH

3.4.2 Adsorption study of ACSS-1 and ACSS-2 on Congo Red and Methylene Blue

In the adsorption study, four key parameters were systematically varied during the experiments The initial conditions for the batch experiment included a concentration (C0) of 300 ppm, a mass of ACSS (mACSS) of 0.05g, a volume (V) of 100 mL, and a temperature (T) maintained at 25 ± 2°C Notably, the pH of the solution is crucial as it affects the charge of the adsorbent and the properties of the adsorbate Additionally, the pH influences the electrostatic interactions between the biosorbent's surface and the adsorbate molecules, highlighting its importance in the adsorption process.

Figure 3.25 illustrates the impact of pH levels, from 2.0 to 12, on the removal efficiency of CR and MB dyes using ACSS-x As pH increases, MB dye adsorption rises proportionally, indicating a favorable adsorption process Conversely, the adsorption efficiency of CR dye declines with increasing pH levels.

For CR adsorption, the optimal pH for both ACSS-1 and ACSS-2 is observed to be

The study reveals that the highest adsorption efficiency for Congo Red (CR) occurs under acidic conditions, while Methylene Blue (MB) shows optimal adsorption at pH 10, indicating a preference for alkaline conditions These results underscore the significant impact of solution pH on the adsorption behavior of different dyes, highlighting the necessity of pH adjustment for effective and selective dye adsorption onto ACSS materials.

Figure 3.25.The effect of pH on the removal of a) Congo red, b) Methylene

The pHpzc values of the adsorbate indicate that ACSS-2 has a value of 6.32, while another material has a pHpzc of 4.4, suggesting that cation adsorption is favored at pH levels above these values In acidic conditions, the ACSS material's surface charge becomes positive, which enhances the biosorption capacity as anion dyes become fully protonated This results in stronger electrostatic attractions between negatively charged dye molecules and the positively charged sites on the biosorbent However, as pH increases, the release of hydroxyl ions (OH-) occurs, which can compete with dye molecules due to its behavior as an anion functional group.

CR for the active sites [101] Consequently, the adsorption peak for CR is observed at pH 2.

In a basic environment, ACSS-x enhances the generation of hydroxyl ions, which reduces the dissociation of methylene blue (MB) and improves its removal rate as pH increases Furthermore, the dissociation of H+ from oxygen-containing functional groups on the ACSS surface creates anion groups, elevating the electronegativity of ACSS This increase in electronegativity strengthens the electrostatic attraction between the dye cation and ACSS, facilitating more effective dye removal.

The adsorption rate is determined by the amount of dye removed over a specific time period, highlighting the necessity for a thorough investigation into optimal contact time Figure 3.26 illustrates how the time interval affects dye removal efficiency, with ACSS demonstrating a preference for effective dye adsorption within the same timeframe.

The maximum adsorption capacities for methylene blue (MB) were 581.51 mg/g for ACSS-2 and 580.3 mg/g for ACSS-1 after 90 minutes In contrast, the adsorption capacity for Congo red (CR) showed a significant increase within the first 120 minutes, with minimal changes observed thereafter for both ACSS materials.

The optimal adsorption time for Congo Red (CR) was determined to be 120 minutes, highlighting the significant potential of Activated Carbon from Sugarcane Shells (ACSS) in treating both anionic and cationic dyes The data reveals a consistent trend in the adsorption behavior of ACSS for both CR and Methylene Blue (MB), with adsorption capacities showing a sharp increase until equilibrium is reached, followed by minimal changes This behavior is attributed to the initially abundant vacant active sites on ACSS, which become occupied as dye diffusion occurs, indicating a dynamic equilibrium between the adsorbed and desorbed dye on the biomaterial.

Figure 3.26.The effect of adsorption time on the removal of a) Congo red, b)

The study examines the relationship between the initial concentration of Methylene Blue dye and the adsorption capacity of activated carbon from sugarcane stalks (ACSS), with concentrations ranging from 200 to 800 ppm Results indicate that ACSS demonstrates a higher adsorption capacity at elevated dye concentrations, as a greater number of dye molecules increases the likelihood of occupying active sites on the adsorbent's surface This highlights the significance of initial concentration in enhancing the effectiveness of the adsorbent's sorption capacity.

The adsorption process initiates at the boundary layer, where dye molecules in the solution interact with the adsorbent's surface This is followed by surface diffusion, enabling the dye molecules to traverse the adsorbent's surface Ultimately, the process penetrates the porous structure of the adsorbent, facilitating additional sorption of dye molecules This intricate multi-step mechanism emphasizes the significance of the initial concentration parameter in enhancing the adsorption efficiency of the adsorbent.

Figure 3.27 The effect of initial concentration on the removal of a) Congo red, b)

The adsorption capacity of an adsorbent is essential for its effectiveness in removing dyes at varying concentrations This study found that increasing the mass of adsorbents significantly enhances dye removal rates This improvement is linked to the increased surface area, which results from a higher number of pores and adsorption sites Consequently, a larger surface area facilitates more interactions between dye molecules and the adsorbent, thereby boosting adsorption efficiency.

Increasing the dose of adsorbent enhances the likelihood of collisions between dye molecules and the adsorbent surface, thereby facilitating the adsorption process A larger mass of adsorbents provides more active sites for adsorption, enabling a greater number of dye molecules to be captured and eliminated from the solution This effect significantly improves the dye removal rate.

Recycle studies

To evaluate the efficiency and economic viability of activated carbon (AC) recovery, desorption trials were performed to assess the sustainability of regenerating AC The ACSS-2 variant, known for its exceptional adsorption capabilities for both anion and cation dyes, was chosen for these experiments The distinct desorption behaviors of ACSS-2 towards anion and cation dyes are illustrated in Fig 3.37.

Methylene Blue (MB) showed a 50% reduction in adsorption capacity, decreasing from 551.2 mg/g to 268.1 mg/g after five regeneration cycles, while Congo Red (CR) experienced a similar decline, dropping from 423.7 mg/g to 204.76 mg/g after four cycles Despite this gradual decrease in adsorption capacity for ACSS-2 with each recycling iteration, the removal percentage remained stable, indicating its ability to endure more cycles than initially assessed Notably, ACSS-2 retained significant adsorption capacity even after five and seven regeneration cycles This suggests that the dyes adsorbed onto ACSS-2 may alter the superficial structures, potentially leading to the loss or blockage of adsorption sites within the activated carbon.

Figure 3.37.Regeneration of ACSS-2 after adsorbing a) Congo Red and b)

CONCLUSIONS AND RECOMMENDATION

Conclusions

The research for my graduation thesis, "A Study on Wastewater Treatment by Adsorption Technique Using Hierarchical Porous Materials Derived from Aquatic Waste," has led to several important conclusions regarding the effectiveness of these materials in wastewater treatment.

A novel adsorbent material (AC) was successfully synthesized from black tiger shrimp shells sourced from Ca Mau, Vietnam This innovative material showcased an impressive specific surface area of 2291.3 m²/g, reflecting its high porosity and substantial adsorption capacity.

Under optimal conditions of 40 minutes, 27.7 ppm, and ambient temperature, the maximum adsorption capacity of ACSS-2 for Fe 3+ ions was found to be 66.67 mg/g The adsorption behavior of Fe 3+ ions was best described by the Langmuir isotherm and the pseudo-second-order model, as indicated by the adsorption isotherm and kinetics analysis.

The adsorption capacity of ACSS-2 for Cu 2+ ions reached a maximum of 68.03 mg/g under optimal conditions of 25 minutes, 0.5 mM concentration, and ambient temperature Analysis of the adsorption isotherm and kinetics revealed that the Freundlich isotherm and pseudo-first-order model best describe the adsorption process for Cu 2+ ions.

The maximum adsorption capacity of ACSS-2 for Ni 2+ ions was found to be 57.80 mg/g at 25 minutes, 0.5 mM concentration, and ambient temperature Analysis of adsorption isotherms and kinetics indicated that the Freundlich isotherm and pseudo-second-order model were the most suitable for describing the adsorption process of Ni 2+ ions.

ACSS-2 exhibited superior adsorption capabilities for Congo Red (CR) and Methylene Blue (MB) dyes when compared to ACSS-1, with predicted maximum adsorption capacities reaching 5000 for both dyes.

The adsorption of Congo Red (CR) on ACSS-1 and ACSS-2 adhered to the pseudo-first-order kinetic model, while the adsorption of Methylene Blue (MB) on both materials was more accurately represented by the pseudo-second-order kinetic model These findings indicate that the selected kinetic models effectively describe the adsorption dynamics of the dyes.

The Freundlich model demonstrated a better fit than the Langmuir model for the adsorption of CR and MB on ACSS, indicating that the adsorption process involves both physical and chemical mechanisms This suggests the occurrence of multilayer adsorption.

ACSS-2 displayed distinct desorption behaviors for both anion and cation dyes, with methylene blue (MB) showing a 50% decrease in adsorption capacity after five regeneration cycles, while Congo red (CR) experienced a similar reduction after four cycles Despite these declines, ACSS-2 showcased strong resilience in maintaining its adsorption efficiency, highlighting its suitability for multiple regeneration cycles.

Recommendations

Based on the conclusions drawn from this study, the following recommendations are proposed:

To identify the optimal adsorption capacity, it is essential to conduct further experiments under different conditions, including pH, temperature, and initial dye concentration Analyzing the interactions of these variables in continuous experiments will yield a comprehensive understanding of the adsorption behavior and capacity of ACSS-1 and ACSS-2.

⮚ Adsorption Mechanism: Further research should be conducted to investigate the underlying mechanisms responsible for the adsorption of heavy metals and dyes on ACSS-2 and ACSS-1.

To maximize the regeneration efficiency of ACSS-2, optimization studies are essential This includes exploring various desorption techniques, such as thermal and chemical regeneration, to improve activated carbon (AC) recovery and prolong its lifespan.

The study highlights the promising application of ACSS-2 in wastewater treatment for effectively removing heavy metals and dyes Future research should concentrate on scaling up the adsorption process and assessing its performance in practical, real-world environments.

[1] A K Tripathi and S N Pandey,Water pollution APH Publishing, 2009.

[2] U Wwap, World Water Assessment Programme: The United Nations World

Water Development Report 4: Managing Water under Uncertainty and Risk, ed:

[3] D Briggs, "Environmental pollution and the global burden of disease," British medical bulletin,vol 68, no 1, pp 1-24, 2003.

[4] M Hasanpour and M Hatami, "Application of three dimensional porous aerogels as adsorbent for removal of heavy metal ions from water/wastewater:

A review study," Advances in Colloid and Interface Science, vol 284, p.

[5] R Sutton, Chromium-6 in US tap water Environmental Working Group

[6] S Mishra et al., "Heavy metal contamination: an alarming threat to environment and human health,"Environmental biotechnology: For sustainable future,Springer, 2019, pp 103-125.

[7] M N Ripa, A Leone, M Garnier, and A L Porto, "Agricultural land use and best management practices to control nonpoint water pollution," Environmental Management,vol 38, pp 253-266, 2006.

[8] M Edelstein and M Ben-Hur, "Heavy metals and metalloids: Sources, risks and strategies to reduce their accumulation in horticultural crops," Scientia Horticulturae,vol 234, pp 431-444, 2018.

[9] A Gabrielyan, G Shahnazaryan, and S Minasyan, "Distribution and identification of sources of heavy metals in the Voghji River basin impacted by mining activities (Armenia),"Journal of Chemistry,vol 2018, 2018.

[10] O Musa, M Shaibu, and E Kudamnya, "Heavy metal concentration in groundwater around Obajana and its environs, Kogi State, North Central Nigeria,"Am Int J Contemp Res,vol 3, no 8, pp 170-177, 2013.

[11] J Buschmannet al., "Contamination of drinking water resources in the Mekong delta floodplains: Arsenic and other trace metals pose serious health risks to population,"Environment international,vol 34, no 6, pp 756-764, 2008.

A study by Gong, Chen, and Luo (2014) investigates the spatial distribution, temporal variation, and sources of heavy metal pollution in groundwater within a century-old nonferrous metal mining and smelting region in China The findings highlight significant environmental concerns related to heavy metal contamination in this area, emphasizing the need for ongoing monitoring and assessment of groundwater quality.

[13] M Halim et al., "Groundwater contamination with arsenic in Sherajdikhan,

Bangladesh: geochemical and hydrological implications," Environmental geology,vol 58, pp 73-84, 2009.

[14] M Mahurpawar, "Effects of heavy metals on human health," Int J Res

Heavy metal contamination in surface soils linked to iron ore mining in Pahang, Malaysia poses significant ecological and human health risks A study conducted by Diami, Kusin, and Madzin highlights the potential dangers associated with these pollutants, emphasizing the need for environmental monitoring and risk assessment in mining areas The findings, published in the Environmental Science and Pollution Research journal, underscore the importance of addressing heavy metal exposure to safeguard both ecosystems and public health.

[16] S Benkhaya, S M'rabet, and A El Harfi, "A review on classifications, recent synthesis and applications of textile dyes," Inorganic Chemistry Communications,vol 115, p 107891, 2020.

A recent study published in the International Journal of Environmental Science and Technology explores the adsorption of Congo red dye using carbon derived from the leaves and stems of water hyacinth The research, conducted by Extross et al., examines the equilibrium, kinetics, and thermodynamic aspects of this innovative approach The findings highlight the potential of water hyacinth biomass as an effective adsorbent for wastewater treatment, contributing valuable insights into sustainable environmental solutions.

[18] S Sudarshanet al., "Impact of textile dyes on human health and bioremediation of textile industry effluent using microorganisms: current status and future prospects,"Journal of Applied Microbiology,vol 134, no 2, p lxac064, 2023.

[19] T Islam, M R Repon, T Islam, Z Sarwar, and M M Rahman, "Impact of textile dyes on health and ecosystem: A review of structure, causes, and potential solutions,"Environmental Science and Pollution Research,vol 30, no.

[20] S Gita, A Hussan, and T Choudhury, "Impact of textile dyes waste on aquatic environments and its treatment,"Environ Ecol, vol 35, no 3C, pp 2349-2353, 2017.

Zhang et al (2012) developed a method for detecting malachite green and crystal violet in environmental water using temperature-controlled ionic liquid dispersive liquid-liquid microextraction This technique was coupled with high-performance liquid chromatography, enhancing the analysis of these compounds in water samples The study, published in Analytical Methods, highlights the effectiveness of this approach for environmental monitoring.

[22] R Maguire, "Occurrence and persistence of dyes in a Canadian river," Water

Science and Technology,vol 25, no 11, pp 270-270, 1992.

[23] R Loos, G Hanke, and S J Eisenreich, "Multi-component analysis of polar water pollutants using sequential solid-phase extraction followed by LC-ESI- MS,"Journal of Environmental Monitoring, vol 5, no 3, pp 384-394, 2003.

[24] A Tkaczyk, K Mitrowska, and A Posyniak, "Synthetic organic dyes as contaminants of the aquatic environment and their implications for ecosystems:

A review,"Science of the total environment,vol 717, p 137222, 2020.

[25] W Konicki, M Aleksandrzak, and E Mijowska, "Equilibrium, kinetic and thermodynamic studies on adsorption of cationic dyes from aqueous solutions using graphene oxide," Chemical Engineering Research and Design, vol 123, pp 35-49, 2017.

[26] A X P D’mello, T V Sylvester, V Ramya, F P Britto, P K Shetty, and S.

Jasphin, "Metachromasia and metachromatic dyes: a review," Int J Adv Health Sci,vol 2, no 10, pp 12-17, 2016.

[27] R Srivastava and I R Sofi, "Impact of synthetic dyes on human health and environment," in Impact of textile dyes on public health and the environment:

Flow significantly boosts photosynthesis in marine benthic autotrophs by promoting the release of oxygen from these organisms into the surrounding water This research, published in the Proceedings of the National Academy of Sciences, highlights the critical role of flow dynamics in enhancing the efficiency of photosynthetic processes in aquatic environments The findings underscore the importance of understanding the interactions between physical flow and biological productivity in marine ecosystems.

[29] F E R Simon and K J Simons, "H1 antihistamines: current status and future directions," World Allergy Organization Journal, vol 1, no 9, pp 145-155, 2008.

[30] M A M Salleh, D K Mahmoud, W A W A Karim, and A Idris, "Cationic and anionic dye adsorption by agricultural solid wastes: a comprehensive review,"Desalination,vol 280, no 1-3, pp 1-13, 2011.

[31] M A Khan, M I Khan, and S Zafar, "Removal of different anionic dyes from aqueous solution by anion exchange membrane,"Membr Water Treat,vol 8, no.

[32] A Pohl, "Removal of heavy metal ions from water and wastewaters by sulfur- containing precipitation agents,"Water, Air, & Soil Pollution,vol 231, no 10, p.

[33] F Fu and Q Wang, "Removal of heavy metal ions from wastewaters: a review,"

Journal of environmental management,vol 92, no 3, pp 407-418, 2011.

[34] S Hanif and A Shahzad, "Removal of chromium (VI) and dye Alizarin Red S

(ARS) using polymer-coated iron oxide (Fe 3 O 4) magnetic nanoparticles by co-precipitation method," Journal of nanoparticle research, vol 16, pp 1-15, 2014.

[35] N Oladoja, I Raji, S Olaseni, and T Onimisi, "In situ hybridization of waste dyes into growing particles of calcium derivatives synthesized from a Gastropod shell (Achatina achatina)," Chemical engineering journal, vol 171, no 3, pp 941-950, 2011.

[36] H Hu, X Li, P Huang, Q Zhang, and W Yuan, "Efficient removal of copper from wastewater by using mechanically activated calcium carbonate," Journal of environmental management,vol 203, pp 1-7, 2017.

[37] D Sakhi, Y Rakhila, A Elmchaouri, M Abouri, S Souabi, and A Jada,

The study focuses on optimizing the coagulation-flocculation process to effectively remove heavy metals from actual textile wastewater Published in the journal "Advanced Intelligent Systems for Sustainable Development" (AI2SD’2018), the research demonstrates innovative methods that enhance the efficiency of wastewater treatment The findings contribute to sustainable environmental practices by addressing the critical issue of heavy metal contamination in textile industries, providing valuable insights for future applications in wastewater management.

[38] P D Johnson, P Girinathannair, K N Ohlinger, S Ritchie, L Teuber, and J.

Kirby, "Enhanced removal of heavy metals in primary treatment using coagulation and flocculation," Water environment research, vol 80, no 5, pp. 472-479, 2008.

[39] P W Wong, T T Teng, and N A R N Norulaini, "Efficiency of the coagulation-flocculation method for the treatment of dye mixtures containing disperse and reactive dye,"Water Quality Research Journal, vol 42, no 1, pp.54-62, 2007.

[40] Q Ding, C Li, H Wang, C Xu, and H Kuang, "Electrochemical detection of heavy metal ions in water," Chemical communications, vol 57, no 59, pp. 7215-7231, 2021.

[41] A A Beddai, B A Badday, A M Al-Yaqoobi, M K Mejbel, Z S Al Hachim, and M K Mohammed, "Color removal of textile wastewater using electrochemical batch recirculation tubular upflow cell," International Journal of Chemical Engineering,vol 2022, 2022.

[42] A Da̧browski, Z Hubicki, P Podkościelny, and E Robens, "Selective removal of the heavy metal ions from waters and industrial wastewaters by ion- exchange method,"Chemosphere, vol 56, no 2, pp 91-106, 2004.

[43] Renu, M Agarwal, and K Singh, "Methodologies for removal of heavy metal ions from wastewater: an overview," Interdisciplinary Environmental Review, vol 18, no 2, pp 124-142, 2017.

[44] M Wawrzkiewicz and Z Hubicki, "Anion exchange resins as effective sorbents for removal of acid, reactive, and direct dyes from textile wastewaters," Ion Exchange-Studies and Applications,InTechOpen, 2015,pp 37-72.

[45] S Dutta, B Gupta, S K Srivastava, and A K Gupta, "Recent advances on the removal of dyes from wastewater using various adsorbents: A critical review,"

Materials Advances,vol 2, no 14, pp 4497-4531, 2021.

[46] K Khulbe and T Matsuura, "Removal of heavy metals and pollutants by membrane adsorption techniques,"Applied water science,vol 8, pp 1-30, 2018.

[47] H R Rashidi, N M N Sulaiman, N A Hashim, C R C Hassan, and M R.

Ramli, "Synthetic reactive dye wastewater treatment by using nano-membrane filtration,"Desalination and Water Treatment,vol 55, no 1, pp 86-95, 2015.

[48] H Xiang, X Min, C.-J Tang, M Sillanpọọ, and F Zhao, "Recent advances in membrane filtration for heavy metal removal from wastewater: A mini review,"

Journal of Water Process Engineering,vol 49, p 103023, 2022.

[49] A K Badawi, M Abd Elkodous, and G A Ali, "Recent advances in dye and metal ion removal using efficient adsorbents and novel nano-based materials: an overview,"RSC advances,vol 11, no 58, pp 36528-36553, 2021.

[50] S Afroze and T K Sen, "A review on heavy metal ions and dye adsorption from water by agricultural solid waste adsorbents,"Water, Air, & Soil Pollution, vol 229, pp 1-50, 2018.

[51] Q Wang, S Zhu, C Xi, and F Zhang, "A Review: Adsorption and removal of heavy metals based on polyamide-amines composites," Frontiers in Chemistry, vol 10, p 814643, 2022.

[52] A E Burakov et al., "Adsorption of heavy metals on conventional and nanostructured materials for wastewater treatment purposes: A review,"

Ecotoxicology and environmental safety,vol 148, pp 702-712, 2018.

[53] Y W Chiang et al., "Adsorption of multi-heavy metals onto water treatment residuals: Sorption capacities and applications,"Chemical Engineering Journal, vol 200, pp 405-415, 2012.

[54] Y Akkửz, R Coşkun, and A Delibaş, "Preparation and characterization of sulphonated bio-adsorbent from waste hawthorn kernel for dye (MB) removal,"

Journal of Molecular Liquids,vol 287, p 110988, 2019.

[55] A Kriaa, N Hamdi, and E Srasra, "Removal of Cu (II) from water pollutant with Tunisian activated lignin prepared by phosphoric acid activation,"

[56] A Ali and K Saeed, "Decontamination of Cr (VI) and Mn (II) from aqueous media by untreated and chemically treated banana peel: a comparative study,"

Desalination and Water Treatment,vol 53, no 13, pp 3586-3591, 2015.

The study by Ay, A S Erdoğan, and A Özcan focuses on the characterization of Punica granatum L peels, highlighting their potential for biosorption of lead (II) ions and Acid Blue 40 Published in Colloids and Surfaces B: Biointerfaces, this research quantitatively assesses the effectiveness of pomegranate peels in removing harmful substances from solutions, showcasing their environmental applications.

[58] T Bakalár and H Pavolová, "Application of organic waste for adsorption of Zn

(II) and Cd (II) ions,"Environment Protection Engineering, vol 45, no 2, 2019.

[59] Z Heidarinejad, M H Dehghani, M Heidari, G Javedan, I Ali, and M.

Sillanpọọ, "Methods for preparation and activation of activated carbon: a review,"Environmental Chemistry Letters,vol 18, pp 393-415, 2020.

[60] B Wang, J Lan, C Bo, B Gong, and J Ou, "Adsorption of heavy metal onto biomass-derived activated carbon," RSC advances, vol 13, no 7, pp 4275-

The study by Mistar et al (2018) focuses on the preparation and characterization of activated carbon derived from Bambusa vulgaris, emphasizing the effects of NaOH activation and varying pyrolysis temperatures The research, published in the IOP Conference Series: Materials Science and Engineering, highlights the significance of these factors in achieving a high surface area for the activated carbon, which is crucial for its application in various environmental and industrial processes.

[62] W Tsai, C Chang, S Wang, C Chang, S Chien, and H Sun, "Preparation of activated carbons from corn cob catalyzed by potassium salts and subsequent gasification with CO2," Bioresource technology, vol 78, no 2, pp 203-208, 2001.

[63] Y Hanzawa, K Kaneko, R Pekala, and M Dresselhaus, "Activated carbon aerogels,"Langmuir,vol 12, no 26, pp 6167-6169, 1996.

[64] M Dwiyaniti, A E Barruna, R M Naufal, I Subiyanto, R Setiabudy, and C.

Hudaya, "Extremely high surface area of activated carbon originated from sugarcane bagasse," in IOP Conference Series: Materials Science and Engineering, 2020, vol 909, no 1: IOP Publishing, p 012018.

[65] A Bhatnagar, W Hogland, M Marques, and M Sillanpọọ, "An overview of the modification methods of activated carbon for its water treatment applications,"

Chemical Engineering Journal,vol 219, pp 499-511, 2013.

[66] H Li, P Gao, J Cui, F Zhang, F Wang, and J Cheng, "Preparation and Cr (VI) removal performance of corncob activated carbon," Environmental Science and Pollution Research,vol 25, pp 20743-20755, 2018.

[67] J Zhu, J Yang, and B Deng, "Ethylenediamine-modified activated carbon for aqueous lead adsorption,"Environmental Chemistry Letters,vol 8, pp 277-282, 2010.

[68] A Youssef, U El-Bana, and A Ahmed, "Adsorption of cationic dye (MB) and anionic dye (AG 25) by physically and chemically activated carbons developed from rice husk,"Carbon letters,vol 13, no 2, pp 61-72, 2012.

[69] M S Gohr, A Abd-Elhamid, A A El-Shanshory, and H M Soliman,

Kinetics and thermodynamic study,"Journal of Molecular Liquids, vol 346, p.

[70] B Hayati and N M Mahmoodi, "Modification of activated carbon by the alkaline treatment to remove the dyes from wastewater: mechanism, isotherm and kinetic," Desalination and water treatment, vol 47, no 1-3, pp 322-333, 2012.

[71] Y Gao, Q Yue, B Gao, and A Li, "Insight into activated carbon from different kinds of chemical activating agents: A review," Science of the Total Environment,vol 746, p 141094, 2020.

[72] W M H Wan Ibrahim, M H Mohamad Amini, N S Sulaiman, and W R.

Wan Abdul Kadir, "Evaluation of alkaline-based activated carbon from Leucaena Leucocephala produced at different activation temperatures for cadmium adsorption,"Applied Water Science, vol 11, pp 1-13, 2021.

A comparative study by Esfandiar, Nasernejad, and Ebadi (2014) investigates the removal of manganese (Mn II) from groundwater using sugarcane bagasse and activated carbon The research employs response surface methodology (RSM) to optimize the removal process, highlighting the effectiveness of these materials in treating contaminated water Published in the Journal of Industrial and Engineering Chemistry, this study contributes valuable insights into sustainable water treatment solutions.

In a study published in the journal Carbon, Radovic et al (1997) conducted both experimental and theoretical research on the adsorption properties of activated carbons modified to interact with aromatic compounds The focus was on aromatics that possess either electron-withdrawing or electron-donating functional groups, revealing insights into the effectiveness of chemically modified activated carbons in capturing these specific molecules The findings contribute to the understanding of adsorption mechanisms in carbon materials, which is crucial for various applications in environmental and industrial processes.

[75] N Yousefi, M Jones, A Bismarck, and A Mautner, "Fungal chitin-glucan nanopapers with heavy metal adsorption properties for ultrafiltration of organic solvents and water,"Carbohydrate Polymers,vol 253, p 117273, 2021.

[76] L Muniandy, F Adam, A R Mohamed, and E.-P Ng, "The synthesis and characterization of high purity mixed microporous/mesoporous activated carbon from rice husk using chemical activation with NaOH and KOH,"

Microporous and Mesoporous Materials,vol 197, pp 316-323, 2014.

The article by T R Sahoo and B Prelot discusses the significant role of nanomaterials and nanotechnology in adsorption processes aimed at removing contaminants from wastewater It highlights innovative approaches and advancements in nanomaterials that enhance the efficiency of pollutant detection and removal, providing insights into their application in wastewater treatment This comprehensive analysis is featured in the book "Nanomaterials for the Detection and Removal of Wastewater Pollutants," published by Elsevier in 2020.

[78] J Liu, X Yang, H Liu, X Jia, and Y Bao, "Mixed biochar obtained by the co- pyrolysis of shrimp shell with corn straw: Co-pyrolysis characteristics and its adsorption capability,"Chemosphere,vol 282, p 131116, 2021.

[79] Y Xiao et al., "High-capacity porous carbons prepared by KOH activation of activated carbon for supercapacitors,"Chinese Chemical Letters, vol 25, no 6, pp 865-868, 2014.

[80] C Bouchelta, M S Medjram, O Bertrand, and J.-P Bellat, "Preparation and characterization of activated carbon from date stones by physical activation with steam,"Journal of Analytical and Applied Pyrolysis,vol 82, no 1, pp 70-

[81] M Aryal and M Liakopoulou-Kyriakides, "Binding mechanism and biosorption characteristics of Fe (III) by Pseudomonas sp cells," Journal of Water sustainability,vol 3, no 3, pp 117-131, 2013.

[82] K Dideriksen, J Baker, and S Stipp, "Iron isotopes in natural carbonate minerals determined by MC-ICP-MS with a 58Fe–54Fe double spike,"

Geochimica et Cosmochimica Acta,vol 70, no 1, pp 118-132, 2006.

Rudzinski and Plazinski (2006) explore the kinetics of solute adsorption at solid/solution interfaces, presenting a theoretical framework for the empirical pseudo-first and pseudo-second order kinetic rate equations Their research applies statistical rate theory to interfacial transport, contributing to a deeper understanding of adsorption processes in physical chemistry.

[84] Y Liu, "Some consideration on the Langmuir isotherm equation," Colloids and

Surfaces A: Physicochemical and Engineering Aspects, vol 274, no 1-3, pp. 34-36, 2006.

[85] E Okoniewska, J Lach, M Kacprzak, and E Neczaj, "The removal of manganese, iron and ammonium nitrogen on impregnated activated carbon,"

[86] C Ng, J N Losso, W E Marshall, and R M Rao, "Freundlich adsorption isotherms of agricultural by-product-based powdered activated carbons in a geosmin–water system," Bioresource technology, vol 85, no 2, pp 131-135,2002.

[87] A K Meena, G Mishra, P Rai, C Rajagopal, and P Nagar, "Removal of heavy metal ions from aqueous solutions using carbon aerogel as an adsorbent,"

Journal of hazardous materials,vol 122, no 1-2, pp 161-170, 2005.

[88] B Meroufel, O Benali, M Benyahia, Y Benmoussa, and M Zenasni,

"Adsorptive removal of anionic dye from aqueous solutions by Algerian kaolin: Characteristics, isotherm, kinetic and thermodynamic studies," J Mater. Environ Sci,vol 4, no 3, pp 482-491, 2013.

[89] H Yoshitake, T Yokoi, and T Tatsumi, "Adsorption behavior of arsenate at transition metal cations captured by amino-functionalized mesoporous silicas,"

Chemistry of Materials,vol 15, no 8, pp 1713-1721, 2003.

[90] L Benhaddad, N Belhouchat, A Gueddouri, M Hammache, and H Saighi,

"Hollow Sea Urchin-Shaped Polypyrrole Nanomaterial for Efficient Adsorption of Methylene Blue and Congo Red Dyes: A Comparative Study," Russian Journal of General Chemistry,vol 93, no 9, pp 2378-2392, 2023.

[91] L.-Y Guo et al., "Quaternary ammonium-functionalized magnetic chitosan microspheres as an effective green adsorbent to remove high-molecular-weight invert sugar alkaline degradation products (HISADPs)," Chemical Engineering Journal,vol 416, p 129084, 2021.

[92] A Abin-Bazaine, A C Trujillo, and M Olmos-Marquez, "Adsorption isotherms: enlightenment of the phenomenon of adsorption," Wastewater Treatment,InTechOpen, 2022, pp 1-15.

[93] C J Pursell, H Hartshorn, T Ward, B D Chandler, and F Boccuzzi,

"Application of the Temkin model to the adsorption of CO on gold," The Journal of Physical Chemistry C,vol 115, no 48, pp 23880-23892, 2011.

[94] E D Revellame, D L Fortela, W Sharp, R Hernandez, and M E Zappi,

"Adsorption kinetic modeling using pseudo-first order and pseudo-second order rate laws: A review," Cleaner Engineering and Technology, vol 1, p 100032, 2020.

[95] Y S Ho and G McKay, "The kinetics of sorption of divalent metal ions onto sphagnum moss peat,"Water research,vol 34, no 3, pp 735-742, 2000.

[96] C Aharoni and F Tompkins, "Kinetics of adsorption and desorption and the

Elovich equation," inAdvances in catalysis, vol 21: Elsevier, 1970, pp 1-49.

[97] M Mirzaeinejad, Y Mansoori, and M Amiri, "Amino functionalized ATRP- prepared polyacrylamide-g-magnetite nanoparticles for the effective removal of

Cu (II) ions: Kinetics investigations," Materials Chemistry and Physics, vol.