Development of novel titanate nanotubes reduced graphene oxide composite for the removal of heavy metals from aqueous solution

DOCUMENTATION PAGE WITH ABSTRACT Thai Nguyen University of Agriculture and Forestry Degree Program Bachelor of environmental Science and Management Student name Vu Thi Hoai Student ID DT

1

THAI NGUYEN UNIVERSITY

UNIVERSITY OF AGRICULTURAL AND FORESTRY

Study Mode: Full-time

Major: Environmental Science and Management

Faculty: International Training and Development Center

Batch: 2010-2015

Thai Nguyen, 15/01/ 2015

DOCUMENTATION PAGE WITH ABSTRACT

Thai Nguyen University of Agriculture and Forestry

Degree Program Bachelor of environmental Science and Management

Student name Vu Thi Hoai

Student ID DTN1053110084

Thesis Tiltle Development of Novel Titanate Nanotubes/ Reduced

Graphene Oxide Composite for the Removal of Heavy Metals from Aqueous Solution

Supervisor(s) Prof Dr Nguyen The Dang, Thai Nguyen University of

Agriculture and Forestry, Vietnam Prof Ruey-an Doong, National Tsing Hua University Abstract

Graphene oxide (GO), is a two dimensional carbon nano-material which exhibits a great adsorption potential Graphene functionalized composites enhance its adsorption efficiency for toxic heavy-metals from contaminated waste water Titanium nanotubes and GO were assembled in basic medium via microwave-assisted hydrothermal method The strong anchoring of TNT on the surface of GO sheets can be easily observed by TEM (Transmission Electron Microscopy), XRD (X-ray Diffraction) Diffraction on GO sheets confirmed through D-band and G-band ration by Raman Spectroscopy As-synthesized TNT/rGO composite shows high efficiency and high selectivity toward heavy metals in aqueous solution The results indicated that TNT/rGO composite with high adsorption efficiency and fast adsorption equilibrium can be used as a practical adsorbent for heavy metals in aqueous solution

Keywords Titanate nanotube, Graphene oxide, composite,

hydrothermal, adsorption Number of papers 44 pages

Date of submission: 15/01/2015

ACKNOWLEDGEMENTS

I am deeply indebted to my research supervisor Prof Ruey-An Doong, whose

stimulating motivations and valuable ideas helped me to complete my thesis and I

would like to offer my sincere gratitude to prof Dr Nguyen The Dang for his

support throughout my thesis with his patience and knowledge whilst allowing me the room to work in my own way I attribute the level of my Bachelor degree to his

encouragement and effort

I am grateful to Rama Shanker Sahu (PhD) and Yen-Tung Yang (PhD) for

their valuable help, advices and constructive comments during all my experiments and writing thesis

I would like to thank Duncan, Sammy, Joyce (MS) for their great support in characterizing my samples, YC Ken Tsai (PhD) and Rudy (PhD) for their impressive

help in adsorption studies

I would also like to thank Khanh, Linh and all FATECOL members, Biomedical Engineering and Environmental Sciences, National Tsing-Hua University, Taiwan, who provided their ongoing support, questions and suggestions

Finally, I would like to express my love and gratitude to my beloved parents for their support & endless love

VU THI HOAI

TABLE OF CONTENTS

LIST OF FIGURES 1

LIST OF TABLES 2

LIST OF ABBREVIATIONS 3

PART I INTRODUCTION 4

1.1 Research rationale 4

1.2 Research's Objectives 6

PART II LITERATURE REVIEW 7

2.1 Overview of heavy metals 7

2.1.1 Definitions and sources of heavy metals 7

2.1.2 Characteristics of heavy metals 7

2.2 Heavy metal pollution in the world and Vietnam 8

2.2.1 In estuary, coastal and marine areas 8

2.2.2 In acid sulfate soil areas 9

2.3 Characteristics and hazards of some heavy metals 10

2.3.1 Arsenic (As) 10

2.3.2 Cadmium (Cd) 11

2.3.3 Lead (Pb) 12

2.3.4 Copper (Cu) 13

2.4 Effects of heavy metal to environmental and human health 14

2.5 Some of treatment methods for the removal of heavy metals from aqueous solution 15

2.5.1 Carbon materials 15

2.5.2 Phytoremediation 18

2.5.3 Nanomaterials 19

2.5.4 Titanate nanotubes 19

2.6 Overview of handling heavy metals in aqueous solution using Titanate

nanotube / reduced graphene oxide composite 20

2.6.1 Scientific Basis of handling heavy metals in aqueous solution by rGO-TNT composite 20

2.6.2 Some research results of absorption of heavy metals in water by rGO-TNT composite 20

2.6.3 Prospects of technological rGO-TNT composite in removal of heavy metals in aqueous solution 21

PART III METHODS 22

3.1 Materal 22

3.1.1 Chemicals 22

3.1.2 Instruments 22

3.2 Methods 23

3.2.1 Synthesis of TNT 23

3.2.2 Synthesis of Graphene oxide 24

3.2.3 Synthesis of rGO-TNT Composite 25

3.2.4 Adsorption Experiment 25

3.2.5 The method of determining the characteristics of the material 27

PART IV RESULTS 32

4.1 Characterization of GO and titanate nanotubes/rGO composite 32

4.2 Morphology of TNT, GO and rGO-TNT composite 35

4.3 Application into removal of heavy metal ions 36

PART V DISCUSSION AND CONCLUSION 39

5.1 Discussion 39

5.2 Conclusion 40

REFERENCES 42

LIST OF FIGURES

Figure 3.1 Schematic of TNT synthesis.……… …24

Figure 3.2 Schematic of GO synthesis…… ……… …… …… 25

Figure 3.3 Adsorption experiment of Copper by TNT and rGO-TNT ………27

Figure 3.4 Atomic adsorption spectroscopy (AAS)……… … …… 28

Figure 3.5 Raman spectroscopy……… 30

Figure 3.6 Schematic of TEM ……….……… …… 31

Figure 3 .7 The process TEM characterization…… ……… ….32

Figure 4.1 Raman spectra of GO, rGO-TNT materials……….……… …33

Figure 4.2 XRD patterns of GO……… 34

Figure 4.3 XRD patterns of TNT and rGO-TNT composite……… …… 35

Figure 4.5 TEM images of the synthesis TNT and rGO-TNT composite………… 36

Figure 4.6 The adsorption of Cu(II) by TNT at pH=5 in aqueous solution at room temperature.……….… … 37

Figure 4.7 The adsorption of Cu(II) by rGO /TNT composite in aqueous solution at room temperature.……… ……….… 38

LIST OF TABLES

Table 4.1 The results of Cu (II) adsorption experiment by TNT, was observed by Atomic adsorption spectroscopy (AAS) ………37 Table 4.2 The results of Cu (II) adsorption experiment by rGO-TNT, was observed by Atomic adsorption spectroscopy (AAS)……… 38

TEM Transmission Electron Microscopy

AAS Atomic adsorption spectroscopy

PART I INTRODUCTION

1.1 Research rationale

Pollution of air, water and soil is a worldwide issue for the eco-environment and human society Most of the earth's surface is covered by water, and most of the human body is composed of water These are the two facts illustrating the critical linkages between water, health and ecosystems It can be seen that, water is the most essential compound on the earth for the human activities Providing clean water is the prime requirement of the human being for their better health Since the fast growing sector of industries, expansion of population, and urbanization have largely contributed to the severe contamination of water, air and soil Chemical and fertilizers use in domestic and agricultural activities leads to the lifetime threatening diseases Intense use of heavy metals in industries for dyeing, paint etc is becoming one of the most serious environment problems globally Its presence in low concentration of heavy metals in various water resources could be harmful to human health The treatment of heavy metals is so important due to their persistence in the environment

In order to remove the heavy metals, various techniques have been developed The traditional treatment processes for heavy metals include chemical precipitation, electrolysis, adsorption, and ion exchange Among these methods, adsorption is an efficient technology, which has been widely used for the removal of metal ions in aqueous solutions A wide variety of adsorbents including activated carbon, water treatment sludge, zeolite, fly ash, and biomass have been reported to effectively adsorb metal ions, showing varying extent of effectiveness in removing the toxic pollutants from air, water and soil

More recently, one-dimensional (1-D) titanate nanotube (TNT) have been reported to

be an attractive adsorbent to effectively adsorb a wide variety of metal ions including

Cu, Pb, Cd, and Zn because of their large specific surface areas and layered structures TNT is considered as a modified structure in photo catalysis owing to its special electronic and mechanical properties, high photo catalytic activity, large specific surface area and high pore volume, a potential material for removal of metal ions in the aqueous solution

Besides, in the past few years, Graphene oxide (GO) have attracted tremendous interest in the world Graphene is a two-dimensional carbon nanomaterial with single layer of sp2 hybridized carbon atoms arranged in six membered rings Graphene has strong mechanical, thermal, and electrical properties with a theoretical value of specific surface area at 2630 m2/g GO is a functionalized graphene with varying oxygen containing groups Several views have been reported on applications of GO in different areas such as physics, chemistry, biology, and material science In particular, graphene based materials are used as adsorbents for pollutants removal since graphene oxide possesses several functional groups and has strong acidity, exhibiting high adsorption for basic compounds and cations Graphene also has a hydrophobic surface and presents high adsorption to chemicals due to strong π–π interaction

Among several physical, chemical and biological treatment techniques, the adsorption

is one of the simplest, fastest and most efficient processes or the removal of heavy metals Considering all aspects and issues mentioned above, I have paid attention to the preparation of titanate nanotube/reduced graphene oxide composite and subsequently used them as adsorbents

Synthesizing the TNT and performing the adsorption experiments to evaluate its properties

The fabrication of new materials Titanate nanotubes / reduced graphene oxide composite will make a significant contribution in wastewater treatment produced due

to mining in the country and improving the domestic water efficiency as well as contributing to the environmental protection

PART II LITERATURE REVIEW2.1 Overview of heavy metals

2.1.1 Definitions and sources of heavy metals

The origin of the term "heavy metal" is not clear An early use dates from 1817, when Gmelin divided the elements into nonmetals, light metals and heavy metals (Habashi F 2009) Light metals had densities of 0.860–5.0 gm/cm3; heavy metals 5.308–22.000 (Gmelin L 1849) Heavy metals are divided into three types: toxic metals (Hg, Cr, Pb,

Zn, Cu, Ni, Cd, As, Co, Sn etc.), precious metals (Pd, Pt, Au, Ag, Ru etc.), radioactive metals (U, Th, Ra, Am,etc.).The proportion of these metals is usually greater than 5g/cm3 (Bishop, 2002)

Heavy metals are found naturally in the earth, which become concentrated as a result

of human caused activities Common sources are from mining and industrial wastes; vehicle emissions; lead-acid batteries; fertilizers, paints and treated woods Lead is the most prevalent heavy metal contaminant

2.1.2 Characteristics of heavy metals

Heavy metals are not biodegradable (Tam & Wong, 1996) and are non-toxic in the form of elements, but are dangerous to living organisms when they are in the form of cations due to its linkage capacity with short carbon chain, which leads to the accumulation in the organism after several years For humans, approximately 12 elements of heavy metals cause toxic such as lead, mercury, aluminum, arsenic, cadmium, nickel Some heavy metals are found in the body and essential for human health, such as iron, zinc, magnesium, cobalt, manganese, molybdenum and copper, although the amount is very small but it is present in metabolism However, at excess

level of the essential elements can endanger the life of the organism (Foulkes, 2000) The remaining metal elements are unnecessary elements and can be highly toxic when present in the body; however, the toxic is only present when they enter the food chain These elements include mercury, nickel, lead, arsenic, cadmium, aluminum, platinum and copper in the form of metal ions They enter the body through the streets of the body to absorb as respiratory, gastrointestinal and through the skin If heavy metals enter the body and accumulate inside the cell is greater than the resolution of them, they will increase and the poisoning will appear (Foulkes, 2000) The toxicity of heavy metals is expressed through:

(1) Some of heavy metal can be moved from low to higher toxicity in the form of some environmental conditions, such as mercury

(2) Accumulation and biological amplification of these metals through the food chain may damaging the normal physiological activity and ultimately endanger human health

(3) Toxicity of these elements may be at a very low concentration of about 0.1-10 mg.L-1 (Alkorta et al., 2004)

2.2 Heavy metal pollution in the world and Vietnam

2.2.1 In estuary, coastal and marine areas

Metal pollution in the marine environment has increased in recent years due to increasing global population and industrial development Heavy metal pollution in many estuaries, coastal areas around the world have long been known by toxic threat

to the life of aquatic organisms, risk to human health

Pb and Zn pollution is one of great concern due to their toxic effects on the ecosystem

in the estuaries in Australia, with very high levels of 1000µg.g -1 Pb, 2000 µg.g-1 Zn

can be found in the contaminated sediments Bryan et al (1985) quoted in Bryan & Langston (1992) was determined the amount of inorganic lead in estuaries sediments

in the UK ranged from 25 μg.g-1 in non-contaminated areas to over 2700 μg.g-1 in estuary Gannel where get the waste from the mining of lead Concentrations of lead compounds are probably originated from the use of leaded petrol

Similarly Pb, As concentration has been identified in many estuaries, coastal areas in the world As concentrations in estuarine sediments were determined from 5 μg.g-1

in the Axe estuary to more than 1,000 μg.g-1

in the estuary Restronguet Creek, Cornwall where get wastewater from the mining area metal

Cd concentrations were determined in the UK in the estuary are not contaminated with levels of 0.2 μg.g-1

, in the estuaries were heavily polluted the concentration may be up

to 10 μg.g-1

(Bryan & Langston, 1992) Deule River in France is one of the rivers are serious polluted by suffered waste from metallurgical plants Metal concentrations in sediments of the river are very high (480mg.kg-1) Concentrations of heavy metals in sediments in estuaries, coastal areas in the world where there are mangroves also identified from less polluted to heavily polluted.Tam& Wong (1995) were determined

Pb concentration in sediments of mangrove Sai Keng, Hong Kong with concentration 58,2 µg.g-1 Zheng & Lin (1995) were determined Pb and Cd concentration in sediments of mangrove Avicennia marina, Shenzhen Bay with corresponding levels of 28,7 µg.g-1 and 0,136 µg.g-1 respectively

2.2.2 In acid sulfate soil areas

According Astrom & Bjorklund (1995) was shown that acid sulphate soil is source release of heavy metals make aqueous solution pollution When potential acid sulphate soil exposed to oxygen by natural phenomena or by artificial drainage, pyrite oxidized

creates acid sulfuric lowers pH When pH <4 protons are released to attack the clay minerals, dissolved some of metals that their concentration may be exceed concentration in soil without acid sulphate

2.3 Characteristics and hazards of some heavy metals

Sources of pollution due to human activity:

Mining ore (Cu, Ni, Pb, Zn), metallurgy releases into environmental a large amount of arsenic Approximately 62,000 tonnes of arsenic release into the environment every year from these activities

 Burning of fossil fuels from the household, from the power plant

 Use fungicides, herbicides, insecticides and industrial

 Since when put to use DDT in 1947 and the organic pesticides containing organic arsenic compounds

The harmful effects of arsenic on human health:

Toxicity of arsenic depends very much on the nature of the compounds that form, especially is valence Arsenic vanlence 3 is more toxic than vanlence 5 Toxicity of inorganic arsenic (arsenic tri-oxide) in humans has been known for a long time Lethal dose about 50-300mg but depend on the individual (Clark et al.,1997) The expression

of chronic arsenic poisoning include: weakness, loss of reflexes, tiredness, gastritis, colitis, anorexia, weight loss, hair loss, etc Human is poisoned Arsenic in long term through food or air leads to cardiovascular disease, disorders of the nervous system, circulatory, brittle nails brittle nails with horizontal white lines, liver dysfunction, kidney (Bissen & Frimmel, 2003) Acute arsenic poisoning can cause nausea, dry mouth, dry throat, pulled muscles, stomachache, itchy hands, itchy legs, blood circulation disorders, neurasthenia, etc

2.3.2 Cadmium (Cd)

Cd is present everywhere in the earth's crust with an average concentration about 0.1mg.kg-1 However, higher concentration can be found in sedimentary rocks such as marine sedimentary rock often contains about 15mg.kg Annually rivers transport a large amount of Cd approximately 15,000 tons into the ocean Concentration of Cd has been reported to be up to 5mg.kg-1 in the river and lake sediments, from 0.03 to 1 mg.kg-1 in the marine sediments

Source by human activity:

 The major application of Cd in the industry such as steel protective coating, stabilizer in PVC, pigments in plastics and glass, and in many components of the alloy is one of the causes release like Cd in the environment

 Concentration of Cd in phosphate fluctuates different, depending on the source

of phosphate rock Phosphate fertilizer is derived from North Carolina phosphate rock containing Cd 0.054g.kg-1, derived from Sechura rock containing concentration of Cd 0.012g.kg-1, whereas phosphate fertilizer is derived from phosphate rock Gafsa containing 0.07g.kg-1

The harmful effects of Cd on human health:

Cadmium is known to cause damage to the kidneys and bones at high doses Studied in

1021 men and women is infected Cd in Sweden showed that metal poisoning is related

to increased risk of fractures over the age of 50 Itai-itai disease is caused by the serious Cd poisoning All patients with this disease are all compromised kidney, bone pain become brittle and break easily

2.3.3 Lead (Pb)

The average of lead content in the lithosphere estimated 1,6x10-3weight percent, while the average land 10-3 percent and normal fluctuations around 0,2x10-3 to 20x10-3percent Lead is present naturally in soil with average content 10-84 ppm

Source by human activity:

 Lead is used in batteries, the battery, in some instruments conductivity Some lead compounds are added in paint, glass, ceramics, such as colorants, stabilizers, binder

 The waste products from the application of lead if not recycled properly, when released into the environment will increase the amount of this toxic metal Also some organic lead compounds such as lead tetrametyl or tetraetyl added in gasoline, especially in developing countries

The harmful effects of lead on human health:

In the human body, Pb in the blood associated with erythrocytes, and accumulated in the bone The ability to remove lead from the body is very slowly, primarily in the urine Half-life of lead in the blood is about a month, in bones of 20-30 years The organic lead compounds are sustainable, harmful to humans, can lead to death

The expression of acute lead poisoning, such as headache, irritability, excitability, and many different expressions related to the nervous system Humans infected long term may lead to memory loss, decreased ability to understand, reduced IQ, scrambling ability to synthesize hemoglobin can lead to anemia Lead is known to be the cause of lung cancer, stomach and gliomas Lead poisoning can cause harmful effects on reproductive capacity, miscarriage

2.3.4 Copper (Cu)

Copper is found naturally in minerals such as cuprite (Cu2O), malachite (Cu2CO3.Cu(OH)2), azurite (2CuCO3.Cu(OH)2), chalcopyrite (CuFeS2), chalcocite (Cu2S), and bornite (Cu5FeS4) and in many other organic compounds Ion Cu(II) Cu (II) linked through oxygen to the inorganic agents such as H2O, OH-, CO32-, SO42-, for organic agents across the group like phenolic and carboxylic, so most of copper in the natural complexes with organic compounds In the lava rock is co-variation from 4-200mg.kg-1, in sedimentary rock 2-90mg.kg-1

The harmful effects of Copper on human health:

Copper is considered to be one of the elements necessary for human development, but the accumulation of copper with high concentrations can be toxic to the body Cumings (1948) quoted in WHO (1998) discovered copper is actually toxic agents for Wilson patients and discover that the liver and brain of these patients contained metal content is very high

2.4 Effects of heavy metal to environmental and human health

Environmental pollution due to toxicity of heavy metals cause ecological imbalance, degrade many populations organisms have been found in many countries around the world The Severn Estuary is one of the largest rivers in Britain, is home and reproduction for many species of fish Decades, the river has suffered many pollutants from heavy metals such as lead, cadmium and other elements from various sources The effects of this pollution can be one of the causes make declining fish populations Fish population in the Severn Estuary river has increased again when the level of water pollution reduction

When organisms live in polluted environment, the ability to accumulation of pollutants

in their body is very high, especially is metal pollution, risk to the health of our consumers through the food chain Ohi et al (1974) quoted in WHO (1985) was determined the level of lead in the blood, in the femur and in the kidneys of pigeons were collected from rural and urban areas in Japan The results showed that the highest level of lead in the femur of pigeons with an average value ranged from 16.5 to 31.6 mg.kg-1 in urban areas While the average value of 2.0 and 3.2 mg.kg-1 in rural areas

In the blood, lead levels also have similar trends from 0.15 to 0.33 mg.L-1 in urban areas, and from 0.054 to 0.029 mg.L-1

In recent years, serious impacts of Arsenic on the human health also have been reported in India, China, Bangladesh Estimated that millions of people at risk of poisoned by poisoning As Vietnam has about 10 million people in the red river delta,

500 thousand to 1 million people in the mekong delta chronic poisoned by drinking water from drilled wells containing Arsenic Similarly, the accumulation of Cd in the liver and kidney of grazing animals in Australia and New Zealand affect the consumption of meat products in the country and export to foreign countries

2.5 Some of treatment methods for the removal of heavy metals from aqueous solution

There are many different technological solutions to water pollution treatment; however, when applying any solution to clean water should also interest in the effectiveness of the process is shown through the main aspects as follows:

 Ability to effectively apply in practice

 Reasonable price

 Method of conducting is simple, easy to operate

 Need of resources and energy to maintain the treatment process at a minimum

 Sustainability is high; reduce long-term risk to aquatic environment

 The processing time is fast

 The ability to easily accept the method

2.5.1 Carbon materials

2.5.1.1 Graphene

Graphene is a type carbon material as nanosorbent, which is a kind of one or several atomic layered graphites, possesses special two-dimensional structure and good mechanical, thermal properties Zhao et al (2011) synthesized the few-layered

graphene oxide nanosheets through the modified Hummers method, this graphene nanosheets are used as sorbents for the removal of Cd2+ and Co2+ ions from aqueous solution, results indicate that heavy metal ions sorption on nanosheets is dependent on

pH and ionic strength, and the abundant oxygen-containing functional groups on the surfaces of graphene oxide nanosheets played an important role on sorption (Chandra

et al, 2010) reported magnetite-graphene adsorbents with a particle size of ~10 nm give a high binding capacity for As3+ and As5+, and the results indicate that the high binding capacity is due to the increased adsorption sites in the graphene composite (Dana Fialova et al., 2010) was focused on isolation of heavy metals by nanomaterial approach with subsequent metal detection by electrochemical methods The aim of their experiment were to isolate cadmium from solution using adsorbents, such as the graphene, expanded carbon and multi-wall carbon nanotubes After 1 hour of interaction, it has been established that 99 % of cadmium was adsorbed on the surface

of graphene Graphene was evaluated as the most effective adsorbent that could be used for application in industrial field for example the decontamination of wastewater

2.5.1.2 Graphene oxide

Graphene oxide (GO) is chemically modified graphene prepared by oxidation and exfoliation Graphen oxide is a monolayer material with high oxygen content Thin membranes that allow water to pass through but block off harmful gases are a major use for GO

GO is a potential adsorption for metal ion complexation through both electrostatic and coordinate approaches Yang et al (2010) investigated Cu2+ GO interaction in aqueous solution and reported that Cu2+ causes GO sheets to be folded and also to form large

aggregates The coordination between Cu2+ and oxygen atoms on GO is the primary driving force and GO has Cu2+ adsorption capacity of 46.6 mg/g, higher than that of carbon nanotubes(28.5mg/g) and active carbon (4-5mg/g)

2.5.1.3 Reduced graphene oxide

The fabrication of reduced graphene oxide (rGO) and metal oxide composites has attracted enormous attention, especially in environmental remediation technology, because the material is easily prepare, inexpensive, environmental friendly and it is strongly developed worldwide Chandra et al (2010) applied magnetite-graphene hybrids to remove arsenic species, whose present in the drinking water in wide regions

of South Asia has been a huge problem They found that the high binding capacities, 3.35-4.23mg/g for As(V) and 6.21-7.81mg/g for As(III), were obtained over the composites due to the increased adsorption sited in the composite which occurred by reducing the aggregation of bare magnetite He et al (2010) successfully grafted surface-modified Fe3O4 nanoparticles onto GO by covalent bonding in order to improve the adsorption capacities for methylene blue and neutral red cationic dyes up

to 190.14 and 140.79mg/g, much higher than other adsorbents reported previously Zhang et al (2011) also applied this type of composite to eliminate tetracycline, a model antibiotic contaminant that is consumed in huge amount annually worldwide as well as discharged into soil and water The maximum amount of tetracycline adsorbed

on to 6 nm Fe3O4-rGO was determined to be 95mg/g Recently, Sreeprasad et al (2011) synthesized rGO-MnO2 and rGO-Ag composites to uptake Hg (II) in wastewater They gave a high distribution coefficient, greater than 10 l/g, as well as very good performance for removing heavy metal ions

2.5.2 Phytoremediation

Phytoremediation describes the treatment of environmental problems through the use

of plants that mitigate the environmental problem without the need to excavate the contaminant material and dispose of it elsewhere

The basis of this method is that the phenomenon of many species (aquatic plants, algae, fungi, bacteria etc.) has the ability to retaining on the surface or receiving into inside the cells of their bodies the existence of heavy metals in soil and water (Biosorption)

The biological methods for handling heavy metals include:

 Using anaerobic microorganisms and aerobic

 Use of aquatic plants

A number of studies revealed that phytoremediation of arsenic using aquatic macrophytes would be a good option to clean polluted water

2.5.3 Nanomaterials

With the development of nanotechnology, nanomaterials are used as the sorbents in wastewater treatment; several researches have proved that nanomaterials are the effective sorbents for the removal of heavy metal ions from wastewater due to their unique structure properties According Lee et al (2012) Used as sorbents for removing heavy metals ions in wastewater, nanomaterials should satisfy the following criterions:

 The nanosorbents themselves should be nontoxic

 The sorbents present relatively high sorption capacities and selectivity to the low concentration of pollutants

 The adsorbed pollutants could be removed from the surface of the nano adsorbent easily

 The sorbents could be infinitely recycled So far, a variety of nanomaterials have been studied in the removal of heavy metal ions from aqueous solution, and the results indicate that these nanomaterials show high adsorption capacity

600oC in air for 4h for removal of bisphenol A and Cu(II) ion The calcined TNT has good Cu (II) adsorption capacity

2.6 Overview of handling heavy metals in aqueous solution using Titanate

nanotube / reduced graphene oxide composite

2.6.1 Scientific Basis of handling heavy metals in aqueous solution by rGO-TNT composite

Nowadays, Thanks to development of high technology, Human being comprehends more about the chemistry, the physics of Titanate nanotube/ Graphene oxide composite Hence, we can use it to handling technology heavy metals pollution From the roles of TNT/rGO composite for handling water pollution, many scientist have studied about it, followed by they have a wide range of solution, result, to processing environmental pollution on the earth

On the other hand, in reality, heavy metals that can be very harmful to our health if found in your drinking water Severe effects include reduced growth and development, cancer, organ damage, nervous system damage, and in extreme cases, death Exposure

to some metals, such as mercury and lead, may also cause development of autoimmunity, in which a person's immune system attacks its own cells This can lead to joint diseases such as rheumatoid arthritis, and diseases of the kidneys, circulatory system Therefore, treatment technology heavy metals pollution by TNT/rGO composite in the water is a solution helping solve the problem of heavy metal pollution

2.6.2 Some research results of absorption of heavy metals in water by rGO-TNT composite

Graphene based nano composite for the removal of toxic heavy metals from aqueous solution was studied very extensively Lee and Yang (2012) prepared a flower-like TiO2 on GO hybrid (GO–TiO2) and applied for the removal of Zn2+, Cd2+ and Pb2+ions from water The adsorption capacities of the GO–TiO2 hybrid reached 88.9 mg/g for Zn2+, 72.8 mg/g for Cd2+, and 65.6 mg/g for Pb2+, respectively, at pH 5.6, which are