Applying activated carbon derived from coconut shell loaded by silver nanoparticles to remove methylene blue in aqueous solution

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURE AND FORESTRY VU THI THAO Applying activated carbon derived from coconut shell loaded by silver nanoparticles to remove methylene blue

THAI NGUYEN UNIVERSITY

UNIVERSITY OF AGRICULTURE AND FORESTRY

VU THI THAO

Applying activated carbon derived from coconut shell loaded

by silver nanoparticles to remove methylene blue in aqueous solution

BACHELOR THESIS

Study Mode : Full-Time

Major : Environmental Science and Management Faculty : Advanced Education Program

Thai Nguyen, 15/09/2018

DOCUMENTATION PAGE WITH ABSTRACT

Thai Nguyen University of Agriculture and Forestry

Degree program: Bachelor of Environmental Science and Management

Thesis Title:

APPLYING ACTIVATED CARBON DERIVED FROM COCONUT SHELL LOADED BY SILVER NANOPARTICLES TO REMOVE METHYLENE BLUE IN AQUEOUS SOLUTION

(Ag-pH 10, contact time of 120 minutes and adsorbent dose of 250 mg/25 mL solution

At this condition,the maximum adsorption capacity of MB onto Ag-NP-AC achieved

at 172.22 mg/g The adsorption equilibrium was represented with Langmuir, Freundlich and Sips models The Langmuir equations were found to have the correlation coefficient value (0.935) in good agreement The pseudo first and second order kinetic model agrees very well with the dynamic behavior of the adsorption of dye MB on Ag-NP-AC

in his department – Faculty of Environment and Earth Science, Thai Nguyen University

of Sciences (TNUS),

I gratefully acknowledge Dr Hoa, Laboratory of Physics, Thai Nguyen University of Science for helping and providing me necessary of equipment as well as knowledge for creating sliver nanoparticles

I also want to express my thanks to the Dean of Faculty of Environment and Earth Science, Prof Dr Ngo Van Gioi and Director of Thai Nguyen University of Sciences (TNUS), Prof Dr Le Thi Thanh Nhan who gave the permission to use all required equipment and the necessary materials to conduct my research in Laboratory of Faculty

of Environment and Earth Science, Thai Nguyen University of Sciences (TNUS)

I wish to thank the technicians who are Kien and Trung , Laboratory of Faculty

of Environment and Earth Science, Thai Nguyen University of Sciences (TNUS) for their help in tissue preparation

Special thanks to Luyen, Huyen, Quynh, Lan, Thien, Lan Anh, Minh, Giang and all people who helped me when I stayed in Thai Nguyen University of Science

My sincere thanks also go to all my classmates – K46N01 AEP for helping me finish this the study

Finally, I could like to thank my family, for their love and supporting me throughout my life

Thai Nguyen, September 15, 2018 Student

VU THI THAO

TABLE OF CONTENTS

LIST OF FIGURES viii

LIST OF TABLES x

LIST OF ABBREVIATIONS xi

PART I INTRODUCTION 1

1.1 Research rationale 1

1.2 Research’s objectives 2

1.3 Research questions and hypotheses 3

1.4 Limitations 3

PART II LITERATURE REVIEW 4

2.1 Textile Dyes Waste 4

2.1.1 Source of Textile Dyes Waste 4

2.1.2 Impact of Textile Dyes Waste 4

2.2 Methylene blue 5

2.2.1 Source of Methylene blue 5

2.2.2 Chemical and physical data of Methylene blue 6

2.2.3 Adverse effects of Methylene blue 8

2.3 Introduction to adsorption techniques 10

2.3.1 Concepts 10

2.3.2 Modeling and Interpretation of Adsorption Isotherms 11

2.3.2.1 Langmuir Isotherm 11

2.3.2.2 Freundlich Isotherm 12

2.3.2.3 Adsorption kinetics models 13

2.3.3 Factors Affecting Adsorption 13

2.4 Absorption material 14

2.4.1 Silver Nanoparticles 14

2.4.1.1 Definitions 14

2.4.1.2 Synthesis of silver nanoparticles 16

2.4.1.3 Applications 19

2.4.2 Coconut Shell Based Activated Carbon 20

2.4.2.1 Features 20

2.4.2.2 Specification of Coconut Shell Based Activated Carbon: 21

2.4.2.3 Coconut Shell Activated Carbon Types: 21

2.4.2.4 Applications 22

PART III MATERIALS AND METHODS 24

3.1 Materials 24

3.1.1 MB, Ag-NP-AC 24

3.1.3 Equipments 25

3.2 Methodology 26

3.2.1 Experimental method 26

3.2.1.1 Preparation of silver nanoparticles 26

3.2.1.2 Preparation of the AgNPs-loaded activated carbon (Ag-NP-AC) 26

3.2.2 Data processing methods 30

PART IV RESULTS AND DISCUSSION 33

4.1 Adsorbent property 33

4.2 Effect of impregnation ratio (Ag/AC) on Methylene blue adsorption 36

4.3 Effect of pH 37

4.4 Effect of contact time 39

4.5 Effect of absorbent dose 40

4.6 The effect of initial MB concentration 42

4.7 Adsorption isotherm 43

4.8 Adsorption kinetics of Ag-NP-AC 45

PART V CONCLUSION 47

REFERENCES 48

LIST OF FIGURES

Figure 2.1 Typical scanning electron microscope (SEM) and transmission electron microscope (TEM) image of different types of 0D NSMs, which is synthesized by several research groups (A) Quantum dots , (B) nanoparticles arrays, (C) core–shell nanoparticles, (D) hollow cubes, and (E) nanospheres Reprinted by permission of the Wiley-VCH Verlag GmbH & Co KGaA J.N Tiwari et al / Progress in Materials Science 57 (2012) 724–803 16Figure 4.1 SEM image of (a) AC and (b) AgNPs-loaded activated carbon (Ag-NP-AC), EDS spectra of (c) AC and (d) AgNPs-loaded activated carbon (Ag-NP-AC) 33Figure 4.2 XRD graph of (a) activated carbon from coconut shells (AC) and (b) AgNPs-loaded activated carbon (Ag-NP-AC) 34

Figure 4.3 FTIR graph of AC and Ag-NP-AC 35

Figure 4.4 The effect of the impregnation ratio on MB adsorption at concentration: 500 mg/L, adsorbent dose: 50 mg Ag-NP-AC/25 mL solution and temperature: 25oC 36Figure 4.5 Effect of pH on MB adsorption at concentration: 500 mg/L, adsorbent dose:

50 mg Ag-NP-AC/25 mL sulotion, time: 60 min, temperature: 25oC (a) and pHPZC of

AC, Ag-NP-AC before and after adsorption of MB (b) 38Figure 4.6 Effect of contact time on MB adsorption at pH 10, concentration: 500 mg/L, adsorbent dose: 50 mg Ag-NP-AC/25 mL solution and temperature: 25oC 39Figure 4.7 Effect of Ag-AC dosage on MB adsorption at pH 10, time: 120 min, 41

MB concentration: 500 mg/L, temperature: 25oC 41Figure 4.8 Effect of initial MB concentrations on the adsorption of MB by Ag-NP-AC at pH

10, time: 60 min, adsorbent dose: 250 mg/25 mL and temperature: 25oC 42

Figure 4.9 Adsorption isothermal equilibrium prediction of MB onto Ag-NP-AC at

contact time = 120 min, Ag-NP-AC dose = 250 mg/25mL) 44

Figure 4.10 Kinetics model of MB adsorption onto Ag-NP-AC (Co: 500mg/L; adsorbent dosage: 50 mg/25 mL; initial pH: 10, temperature: 25oC) 45

LIST OF TABLES

Table 2.1 shows a comparison of physical and chemical adsorption 11 Table 2.2: Specification of Coconut Shell Based Activated Carbon 21 Table 2.3: Physical and chemical analysis to the common coconut activated carbon: Inspection standard: GB/T 7702-1997 22 Table 4.1: Adsorption isothermal parameters and correlation coefficients of Langmuir, Freundlich and Sips models for sucrose adsorption on MAC 45 Table 4.2 Calculated kinetic parameters of models of MB adsorption on Ag-NP-AC 46

LIST OF ABBREVIATIONS

MB

AC AgNPs Ag-NP-AC

SEM TEM COD

Methylene Blue Activated carbon Siler Nanoparticles Activated Carbon loaded Silver Nanoparticles

Scanning Electron Microscope Transmission Electron Microscope Chemical Oxygen Demand

PART I INTRODUCTION 1.1 Research rationale

The high level of organic compounds from human activities usually causes harmful effective the living organism Dyes are one of the big challenges for water resources A lot of dyes are used in various industries such as textile, rubber, carpet, paper, printing, etc (Sara and Tushar 2014, Shu et al., 2015) The discharge

of dyes into a water resource leads to many serious environmental and health problems (Hamadi et al., 2017) Most of the dye cause water colourization at very low concentrations leading to serious ecological problems as destroying aquatic organisms and harming human (Stoyanova and Christoskova 2011, Chen et al., 2018) Numerous conventional treatment techniques have been applied to remove dye – containing wastewater, such as oxidation, electrochemical techniques, biological treatment, coagulation, and adsorption (De Castro et al., 2018) Among such existing methods, adsorption has been acknowledged to be the most economically favorable method for removing organic compounds from wastewater

Recently, nanotechnology is not only created a breakthrough in electronics (Kritika et al., 2010), informatics and biomedical technology (Ganau et al., 2018), but also is widely applied in our life Nano materials have excellent motorized and physical properties due to their extremely fine grain size and high grain boundary volume fraction (Krishnananda et al., 2017) Silver nanoparticles (AgNPs) have been used extensively in therapeutic applications such as catheters, surgical devices and wound dressings (Tang et al., 2017) However, the production of

AgNPs is expensive leading to a decrease in applied potential for removing pollutants from wastewater

Activated carbon with very large internal surface areas makes particularly attractive for removal of contaminants from water, soil and air (Kumar and Meikap, 2014) To date, the adsorption process is the simple and effective method for removing dye and other organic compounds from wastewater (Fontoura et al., 2017) Activated carbon was also modified with H P0 (Fierro et al., 2006),

H S0 (Singh et al., 2008), ZnCl (Yorgun et al., 2009), HNO (Lopes et al., 2015), NaOH (Vu et al., 2017) etc… to enhance the adsorption capacity However, there

is still no study focus on the mix of activated carbon and silver nanoparticles as a modified material for removing one kind of dye from aqueous solution With huge surface area and proper microspore, activated carbon is an ideal supporting material for loading AgNPs (Tang et al., 2017, Abe et al., 2000, Chingombe et al., 2006) This study therefore focuses on loaded AgPNs on the activated carbon to use as an adsorbent to remove methylene blue

1.3 Research questions and hypotheses

(Alternative Hypothesis): activated carbon derived from coconut shell loaded

by silver nanoparticles will adsorb Methylene blue in aqueous water

1.4 Limitations

In the laboratory do not have enough machines therefore some parts have to send to another laboratory in Hanoi to obtain the result

PART II LITERATURE REVIEW 2.1 Textile Dyes Waste

2.1.1 Source of Textile Dyes Waste

One of the oldest and most technologically complex of all industries is the textile production industry Textile product has also been raised dramatically because of the increasing demand of the population Textile mills and their waste water have been increasing proportionally, causing a major problem of pollution

in the world The textile industry accounts for two thirds of the total dyestuff market During dyeing process approximately 10-15% of the dyes used are released in to the waste water It is recognized as the root cause of environmental pollution Recently, much textile industries are located in developing countries such as India, Vietnam, etc often equipped with poor wastewater system However, India is one of the major contributors of textile waste water in south Asia In India, Maharashtra and Gujarat account for 90% of dye-stuff production due to the availability of raw materials and dominance of textile industry in these regions (CATR, 2018)

2.1.2 Impact of Textile Dyes Waste

A numerous chemicals used in the textile industry cause environmental and health problems Recently, in textile waste water are considered as important pollutants Globally, environmental problems related with the textile industry are those associated with water pollution caused by the direct discharge of untreated effluent and release of toxic chemicals in to the aquatic environment It drastically declines oxygen concentration in water body due to the presence of hydrosulfides and blocks the passage of light through water body which is detrimental to the

water ecosystem Untreated or incompletely treated textile effluent can be harmful

to both aquatic and terrestrial life by adversely affecting the natural ecosystem and causing long-term health effects Due to high thermal and photo stability to resist biodegradation dyes can remain in the environment for an extended period of time The greater environmental concern with dyes is their absorption and reflection of sunlight entering the water Light absorption diminishes photosynthetic activity of algae and influences the food chain High concentrations

of textile dyes in water bodies stop the oxygenation capacity of the receiving water and cut-off sunlight, thereby upsetting biological activity in aquatic life and also the photosynthesis process of aquatic plants or algae (Zaharia et al., 2009) The polluting effects of days against aquatic environment can be the result of toxic effects due to their long time presence in environment (i.e half-life time of several years), accumulation in sediments especially in fishes or other aquatic life forms, decomposition of pollutants in carcinogenic or mutagenic compounds and also low aerobic biodegradability Many dues and their break down products are carcinogenic, mutagenic and/or toxic to life The presence of very small amounts

of days in the water be highly visible, seriously affects the quality and transparency

of water bodies such as lakes, rivers and others, leading to damage to the aquatic environment

2.2.1 Source of Methylene blue

Methylene blue was originally synthesized in 1876 as an aniline-based dye for the textile industry (Berneth, 2008), but scientists such as Robert Koch and Paul Ehrlich were quick to realize its potential for use in microscopy stains

(Ehrlich, 1881; Oz et al., 2011) The observation of selective staining and inactivation of microbial species led to the testing of aniline-based dyes against tropical diseases (Oz et al., 2011) Methylene blue was the first such compound to

be administered to humans, and was shown to be effective in the treatment of malaria (Guttmann & Ehrlich, 1891; Oz et al., 2011) Methylene blue was also the first synthetic compound ever used as an antiseptic in clinical therapy, and the first antiseptic dye to be used therapeutically In fact, the use of methylene blue and its derivatives was widespread before the advent of sulfonamides and penicillin (Oz

Chem Abstr Serv Name: Phenothiazin- 5-ium, 3,7-bis(dimethylamino)-, chloride (O’Neil et al., 2006)

Synonyms: Aizen methylene blue; Basic blue 9 (8CI); Calcozine blue ZF; Chromosmon; C.I 52015; Methylthionine chloride; Methylthioninium chloride; Phenothiazine- 5-ium,3,7-bis, (dimethylamino)-, chloride; Swiss blue;

Tetramethylene blue; Tetramethyl thionine chloride (NTP., 2008; PubChem., 2013)

• Structural and molecular formulae and relative molecular mass

C H CIN S Relative molecular mass (anhydrous form): 319.85 (PubChem, 2013)

• Chemical and physical properties of the pure substance

Description: Dark green crystals or crystalline powder with bronze lustre, odourless, stable in air, deep blue solution in water or alcohol, forms double salts (PubChem., 2013)

Melting point: 100–110 °C (decomposition) (PubChem, 2013) Density: 1.0 g/mL at 20 °C (ChemNet, 2013) Solubility: 43.6 g/L in water at 25 °C; also soluble

in ethanol (PubChem., 2013)

Vapour pressure : 1.30 × 10 ! mm Hg at 25 °C (estimated) (PubChem., 2013)

• Technical products and impurities

Trade names: Desmoid piller; desmoidpillen; panatone; urolene blue; vitableu (NTP., 2008)

2.2.3 Adverse effects of Methylene blue

In humans, large doses of Methylene blue (~500 mg) have been reported to cause nausea, abdominal and chest pain, cyanosis, methaemoglobinaemia, sweating, dizziness, headache, and confusion (Clifton & Leikin., 2003; Oz et al., 2011) Toxicity in infants exposed to methylene blue during prenatal or perinatal diagnostic or therapeutic procedures is well documented: hyperbilirubinaemia,

haemolytic anaemia, formation of Heinz bodies, erythrocytic blister cells, skin discoloration, and photosensitization are the most commonly reported adverse effects (Sills & Zinkham, 1994; Porat et al., 1996; Cragan, 1999) A series of acute toxic effects have been described in animals exposed to methylene blue, including haemoconcentration, hypothermia, acidosis, hypercapnia, hypoxia, increases in blood pressure, changes in respiratory frequency and amplitude, corneal injury, conjunctival damage, and formation of Heinz bodies (Auerbach et al., 2010) Methylene blue is well absorbed, reduced, and is excreted largely in the urine

as the reduced form, leucomethylene blue Methylene blue and its N-demethylated metabolites, azure A, azure B, and azure C, have given positive results in an extensive series of standard in-vitro assays for genotoxicity, both in the absence and presence of exogenous metabolic activation At high doses, methylene blue oxidizes ferrous iron in haemoglobin to the ferric state, producing methaemoglobin Exposure to methylene blue results in haematological toxicity, including formation of Heinz bodies and haemolytic anaemia, in several species Photoactivation of methylene blue produces high-energy species that have the potential to damage DNA, proteins, and lipids, either directly or through the production of reactive oxygen species In the absence of light activation, the carcinogenicity of methylene blue is likely to arise from other mechanisms A potential mechanism is the inhibition of nitric oxide synthase, with possible generation of superoxide anions

2.3 Introduction to adsorption techniques

2.3.1 Concepts

Adsorption involves accumulation of substances at an interface, which can either be liquid-liquid, gas-liquid, gas-solid or liquid solid The material being adsorbed is termed the adsorbate and the adsorbing phase the adsorbent

• Physical Adsorption

Physisorption involves weak forces of van der walls, hydrogen bonding and dipoledipole interactions between the sorbent and sorbate It is reversible and resembles with condensation process The process of physisorption is exothermic with a heat of adsorption analogous to that of latent heat of condensation (Cooney and David, 1999) Equilibrium is attained quickly, followed by the intra-particle diffusion process of the adsorbate molecules inside the capillary pores of the sorbent structure The rate of sorption varies reciprocally with the square of the particle diameter but increases usually with the increasing concentration of the adsorbate and the temperature of the surroundings The rate of physisorption is inversely proportional with the molecular weight of the sorbate species (Eckenfelder, 2000) Physical adsorption represents comparatively weak adsorptive forces between sorbate and sorbent It proceeds with almost zero or negligible activation energy (Mattson and Mark, 1971)

• Chemical adsorption

Chemical adsorption proceeds by exchange or sharing of electrons between the sorbate and sorbent (Allen and Koumanova, 2005) It is non reversible and occurs at high temperature with significant activation energy Chemisorption is

characterized by

interaction between sorbate and specific functional groups attached on the surface

of the sorbent (Mattson and Mark, 1971) It may be exothermic or endothermic depending on the magnitude of the energy changes during the sorption process

Table 2.1 shows a comparison of physical and chemical adsorption

For removal of heavy metals, adsorption is considered as one of the most popular technique compared to other methods due to its low cost, abundant

availability, simple process design with high removal efficiency, easy mode of operation and biodegradability Moreover, it can treat pollutants in more

concentrated form (Arami et al., 2005) It does not produce large amount of toxic sludge (Crini, 2006)

2.3.2 Modeling and Interpretation of Adsorption Isotherms

2.3.2.1 Langmuir Isotherm

Langmuir adsorption which was primarily designed to describe gas-solid phase adsorption is also used to quantify and contrast the adsorptive capacity of various adsorbents (Elmorsi, 2011) Langmuir isotherm accounts for the surface coverage by balancing the relative rates of adsorption and desorption (dynamic equilibrium) Adsorption is proportional to the fraction of the surface of the

adsorbent that is open while desorption is proportional to the fraction of the adsorbent surface that is covered (Günay et al., 2007)

The Langmuir equation can be written in the following linear form (Da̧browski, 2001):

"# =

$"%&# +

"%where Ce is the equilibrium concentration in liquid phase (mg/l), qm is the monolayer adsorption capacity (mg/g) and b is the Langmuir constant related to the free adsorption energy (l/mg)

Heterogeneous surface energy systems can be described by the Freundlich model (Dada et al 2012) Freundlich was represented the following equation:

ln '( = ln )* +

+ln ,(where KF is a constant indicating of the adsorption capacity of the adsorbent (mg/g) and the constant 1/n indicates the intensity of the adsorption

The Sips model is the combination of both the Langmuir and Freundlich isotherm models The equation describes Sips isotherm model as follows:

The linear form of the Freundlich isotherm is as follows (Boparai et al., 2011):

Log q. = Log K= +

> Log C.

where K= is adsorption capacity (l/mg) and 1/n is adsorption intensity; it also indicates the relative distribution of the energy and the heterogeneity of the adsorbate sites

2.3.2.3 Adsorption kinetics models

Pseudo-first order, pseudo-second order and Elovich models was used to investigate the MB adsorption kinetics on Ag-NP-AC The linear form of pseudo-first order and pseudo-second order and Elovich equation are as follows, respectively:

t k q q

q e − t) = ln e− l

ln(

t q q k q

t

e e t

11

2 2

+

=

)ln(

q t =β αβ

where, the adsorption rate (kl) is calculated by linear regression analysis of pseudo first-order model from the slope of linear plot of experimental data, k2 is the constant of pseudo-second order rate; qe is the sorption capacity at equilibrium; and qt is the adsorption capacity at time t α is the initial adsorption rate (mg/g.min);

β is the adsorption constant (g/mg)

2.3.3 Factors Affecting Adsorption

The factors on which the extent of adsorption depends are:

• The effective surface area including appropriate pore size distribution of the adsorbent

• The solubility of the adsorbate in aqueous phase

• The nature of the active sites or surface functional groups on the surface

• The concentration of the liquid phase

• The nature of adsorbent or adsorbate

• The temperature of the surroundings

• pH of the system in case of liquid phase applications

In the past two decades, hundreds of novel NSMs have been obtained; therefore, the need in their classification is ripened NSMs as a subject of nanotechnology are low dimensional materials comprising of building units of a

submicron or nano scale size at least in one direction and exhibiting size effects The first classification idea of NSMs was given by Gleiter in 1995 (Gleiter, 2000) and further was explained by Skorokhod in 2000 (Skorokhod et al., 2001) However, Gleiter and Skorokhod scheme was not fully considered because of 0D, 1D, 2D, and 3D structures such as fullerenes, nanotubes, and nanoflowers were not taken into account Therefore, Pokropivny and Skorokhod (Fang et al., 2009) reported a modified classification scheme for NSMs, in which 0D, 1D, 2D and 3D NSMs are included Herein we classified the NSMs based on the scheme of Pokropivny et al scheme

A major feature that discriminates various types of nanostructures is their dimensionality The word ‘‘nano’’ stems from the Greek word ‘‘nanos’’, which means dwarf This word ‘‘nano’’ has been assigned to indicate the number 109 , i.e., one billionth of any unit In the past 10 years, significant progress has been made in the field of 0D NSMs A rich variety of physical and chemical methods have been developed for fabricating 0D NMSs with well-controlled dimensions Recently, 0D NSMs such as uniform particles arrays (quantum dots), heterogeneous particles arrays, core–shell quantum dots, onions, hollow spheres and nanolenses have been synthesized by several research groups ( Kim et al., 2010; Zhang et al., 2008; Wang et al., 2009; Gautam et al., 2005; Lee et al., 2009) Fig 1 shows the images of different types of 0D NSMs Moreover, 0D NSMs, such as quantum dots has been extensively studied in light emitting diodes (LEDs), solar cells, single-electron transistors, and lasers

Figure 2.1. Typical scanning electron microscope (SEM) and transmission electron microscope (TEM) image of different types of 0D NSMs, which is synthesized by several research groups (A) Quantum dots , (B) nanoparticles arrays, (C) core–shell nanoparticles, (D) hollow cubes, and (E) nanospheres Reprinted by permission of the Wiley-VCH Verlag GmbH & Co KGaA J.N

Tiwari et al / Progress in Materials Science 57 (2012) 724–803

2.4.1.2 Synthesis of silver nanoparticles

• Physical approach

In physical processes, metal nanoparticles are generally synthesized by evaporation–condensation, which could be carried out using a tube furnace at atmospheric pressure The source material within a boat centered at the furnace is vaporized into a carrier gas Nanoparticles of various materials, such as Ag, Au, PbS and fullerene, have previously been produced using the

evaporation/condensation technique (Gurav et al., 1994, Kruis et al., 2000, Magnusson et al., 1999, Schmidt-Ott, 1988)

However, the generation of silver nanoparticles (AgNPs) using a tube furnace has several drawbacks, because a tube furnace occupies a large space, consumes a great deal of energy while raising the environmental temperature around the source material, and requires a lot of time to achieve thermal stability A typical tube furnace requires power consumption of more than several kilowatts and a preheating time of several tens of minutes to attain a stable operating temperature Jung et al (2006) synthesized AgNPs via a small ceramic heater that has a local heating area Because the temperature gradient in the vicinity of the heater surface is very steep in comparison with that of a tube furnace, the evaporated vapor can cool at a suitably rapid rate This makes possible the synthesis of small nanoparticles in high concentration This method might be suitable for a variety of applications, including utilization as a nanoparticle generator for long-term experiments for inhalation toxicity study and as a calibration device for nanoparticle measurement equipment (Jung et al., 2006)

Moreover, AgNPs have been synthesized with laser ablation of metallic bulk materials in solution (Mafune et al., 2000, Mafune et al., 2001, Kabashin and Meunier, 2003, Sylvestre et al., 2004, Tsuji et al., 2002a, Tsuji et al., 2003, Compagnini et al., 2003, Chen and Yeh, 2002, Dolgaev et al., 2002) The characteristics of the metal particles formed and the ablation efficiency strongly depend upon many parameters such as the wavelength of the laser impinging the metallic target, the duration of the laser pulses (in the femto-, pico- and nanosecond

regime), the laser fluence, the ablation time duration and the effective liquid medium, with or without the presence of surfactants

• Chemical approach

Chemical reduction is the most frequently applied method for the preparation

of AgNPs as stable, colloidal dispersions in water or organic solvents Commonly used reductants are borohydride, citrate, ascorbate and elemental hydrogen The reduction of silver ions (Ag+) in aqueous solution generally yields colloidal silver with particle diameters of several nanometers Initially, the reduction of various complexes with Ag+ ions leads to the formation of silver atoms (Ag0), which is followed by agglomeration into oligomeric clusters These clusters eventually lead

to the formation of colloidal Ag particles (Tao et al., 2006) Also, AgNPs can be prepared inside microemulsion The synthesis of AgNPs in two-phase aqueous organic systems is based on the initial spatial separation of reactants (metal precursor and reducing agent) in two immiscible phases The rate of subsequent interaction between the metal precursor and the reducing agent is controlled by the interface between the two liquids and by the intensity of interphase transport between the aqueous and organic phases, which is mediated by a quaternary alkylammonium salt Metal clusters formed at the interface are stabilized, due to their surface being coated with stabilizer molecules occurring in the nonpolar aqueous medium, and transferred to the organic medium by the interphase transporter (Krutyakov et al., 2008)

This method allows preparation of uniform and size controllable nanoparticles However, a highly deleterious organic solvents is employed in this method Thus large amounts of surfactant and organic solvent, which are added to

the system, must be separated and removed from the final product As a result, it

is expensive to fabricate silver nanoparticles by this method Nevertheless, Zhang

et al used dodecane as oily phase which is a low deleterious and even nontoxic solvent Thus the prepared silver solution need not be separated from the reaction solution and it can be directly used for antibacterial activities (Petit et al., 1993, May and Ben-Shaul, 2001, Zhang et al., 2007)

2.4.1.3 Applications

AgNPs have been used extensively as anti-bacterial agents in the health industry, food storage, textile coatings and a number of environmental applications It is important to note that despite of decades of use, the evidence of toxicity of silver is still not clear Products made with AgNPs have been approved

by a range of accredited bodies, including the US FDA, US EPA, SIAA of Japan, Korea’s Testing and Research Institute for Chemical Industry and FITI Testing and Research Institute (Azonano, xxxx, Zhong et al., 2007, Deng and Chen, 2007, Wang et al., 2006, Wei et al., 2007, Jia et al., 2008, Bhattacharya and Mukherjee, 2008)

As anti-bacterial agents, AgNPs were applied in a wide range of applications from disinfecting medical devices and home appliances to water treatment (Bosetti

et al., 2002, Cho et al., 2005, Gupta and Silver, 1998, Jain and Pradeep, 2005, Li

et al., 2008) Moreover, this encouraged the textile industry to use AgNPs in different textile fabrics In this direction, silver nanocomposite fibers were prepared containing silver nanoparticles incorporated inside the fabric (Yeo et al., 2003) The cotton fibers containing AgNPs exhibited high antibacterial activity

against Escherichia coli (Yeo et al., 2003, Duran et al., 2007, Chen and Chiang, 2008)

Furthermore, the electrochemical properties of AgNPs incorporated them in nanoscale sensors that can offer faster response times and lower detection limits For instance, Manno et al (2008) electrodeposited AgNPs onto alumina plates gold micro-patterned electrode that showed a high sensitivity to hydrogen peroxide (Hahm and Lieber, 2004)

The optical properties of a metallic nanoparticle depend mainly on its surface plasmon resonance, where the plasmon refers to the collective oscillation of the free electrons within the metallic nanoparticle It is well known that the plasmon resonant peaks and line widths are sensitive to the size and shape of the nanoparticle, the metallic species and the surrounding medium For instance, nanoclusters composed of 2–8 silver atoms could be the basis for a new type of optical data storage Moreover, fluorescent emissions from the clusters could potentially also be used in biological labels and electroluminescent displays (Berciaud et al., 2005)

2.4.2 Coconut Shell Based Activated Carbon

2.4.2.1 Features

A highly porous adsorbent material, produced by heating organic matter, such as coal, wood and coconut shell, in the absence of air, which is then crushed into granules Activated carbon is positively charged and therefore able to remove negative ions from the water such as chlorine and dissolved organic solutes by absorption onto the activated carbon These are some features of Coconut Shell Granular Activated Carbon:

• Non-toxic, odourless

• Developed pores, large specific area

• Epigranular, little impurity content

• Large strength, long service life

• Good adsorption capacity

• Quick decoloration and deodorization

• Stable chemical properties, easy renewal

• Full range

2.4.2.2 Specification of Coconut Shell Based Activated Carbon:

Granular activated carbon is ideal for most air purification purposes Made from selected grades of coconut shell, its superior level of hardness makes it cleaner than most other carbons and gives it longer life expectancy This, combined with its high activity level, makes it well suited for use in any kind of carbon filter or system

Table 2.2: Specification of Coconut Shell Based Activated Carbon

2.4.2.3 Coconut Shell Activated Carbon Types:

• Coconut shell activated carbon for gold

• Coconut shell activated carbon water treatment

• Coconut active charcoal for gourmet powder treatment, used for mother liquor decoloration in gourmet powder production, also used for decoloration in fine chemicals

• Coconut active charcoal for petrochemical demercaptan treatment, used as catalyst carrier in refinery for gasoline demercaptan

• Coconut active charcoal for (vinylon) catalyst treatment, used as catalyst carrier

in chemical industry, used as VAM catalyst carrier for example

• Coconut active charcoal for ethylene desalted water

• Coconut active charcoal for cigarette filter tip, used in the cigarette filter tip to remove the tar and nicotine in the cigarettes

• Coconut active charcoal for citric acid treatment, used as decoloration, deflavour and refining for citric acid, amino acid and cystine

• Coconut active charcoal for protecting use, used in dipping charcoal production, percolator filling and chemical antitoxin appliance

Table 2.3: Physical and chemical analysis to the common coconut activated

carbon: Inspection standard: GB/T 7702-1997

2.4.2.4 Applications

Activated carbon from coconut shell has predominantly pores in micro pore range Almost 85-90% surface area of coconut shell activated carbon exists as

micro-pores These small pores match the size of contaminant molecules in drinking water and therefore are very effective in trapping them Peat and wood activated carbon has mostly meso and macro-pores which suit trapping of bigger molecules The pore structure of coal carbons falls between coconut shell and wood based carbons Macro-pores are considered as an access point to micropores Mesopores do not usually play an important role in the adsorption unless the surface area of these pores is large, 400 m /g or more The predominance of micro-pores in coconut shell carbon gives it tight structure and provides good mechanical strength and hardness and also high resistance to resist attrition or wearing away

by friction

The coconut activated carbon is widely used in food industry, medical treatment, mine, metallurgy, petrochemical, steel making, tobacco, fine chemicals and so on It is applied to high purity drinking water, industrial water and waste water for the purification such as dechlorinate, decoloration and deodorization, etc