THAI NGUYEN UNIVERSITY
UNIVERSITY OF AGRICULTURAL AND FORESTRY
VU THI HOAI
TOPIC TITLE: DEVELOPMENT OF NOVEL TITANATE NANOTUBES/
REDUCED GRAPHENE OXIDE COMPOSITE FOR THE REMOVAL OF
HEAVY METALS FROM AQUEOUS SOLUTION
BACHELOR THESIS
Study Mode: Full-time
Major: Environmental Science and Management
Faculty: International Training and Development Center
Batch: 2010-2015
Thai Nguyen, 15/01/ 2015
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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
Supervisor(s)
Development of Novel Titanate Nanotubes/ Reduced
Graphene Oxide Composite for the Removal of Heavy
Metals from Aqueous Solution
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
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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
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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
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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
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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
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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
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LIST OF ABBREVIATIONS
Abbreviations
Full text content
TNT
Titanate nanotube
GO
Graphene oxide
TNT-rGO
Titanate nanotube and reduced graphene oxide
XRD
X-Ray Diffraction
TEM
Transmission Electron Microscopy
AAS
Atomic adsorption spectroscopy
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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.
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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.
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1.2. Research's Objectives
The primary objective of this study is to develop and investigate a graphene based
nano composite for the removal of toxic heavy metals from aqueous solution.
Titanium nanotubes and GO were assembled in basic medium via microwave-assisted
hydrothermal method.
Estimation of the adsorption capacity of some heavy metal ions in aqueous solutions.
Characterization of material composites using techniques like XRD, TEM, SEM,
FTIR, Raman Spectroscopy.
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.
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PART II. LITERATURE REVIEW
2.1. 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
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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
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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
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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
2.3.1. Arsenic (As)
Arsenic distributed in many places of environment, they are ranked No.20 in the
presence of many elements in the Earth’s crust, present less than Cu, Sn, but more than
Hg, Cd, Au, Ag, Sb, Se (Bissen& Frimmel, 2003). Source giant arsenic release into the
atmosphere by natural processes is of volcanic activity. During volcanic activity, a
large amount of approximately 17,150 tons of arsenic release into the atmosphere
(Matschullat, 2000).
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
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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.
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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 20x10-3
percent. 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.
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 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:
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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.
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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
15
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
16
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.
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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.
 Use of biomaterials.
Rahman et al. (2011) investigated phytoremediation of arsenic by common aquatic
macrophytes. Phytoremediation of contaminated water by aquatic macrophytes would
be a good option in long term. A large number of aquatic plant species have been
tested for the remediation of toxic elements from fresh water systems. Few aquatic
plants (mostly macrophytes) have shown the ability to accumulate high level of arsenic
from water. Among those aquatic plants, water hyacinth (E. crassipes), duckweed
(Lemna, Spirodela, and Wolffia), water fern (Azolla spp.), Hydrilla (H. verticillata),
and watercresses (N. officinale, N. microphyllum) have been proposed to be potential
for phytoremediation due to their arsenic hyperaccumulation ability and growth habit.
A number of studies revealed that phytoremediation of arsenic using aquatic
macrophytes would be a good option to clean polluted water.
18
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.
2.5.4. Titanate nanotubes
Titanium dioxide (TiO2) has been intensively investigated as potentially sorbent due to
its high chemical stability in the pH range 2 to 14; the process is simple with a fast rate
of adsorption and desorption. In addition, nano-size titanium dioxide possesses many
unique features, such as high surface area, more surface atoms, high surface reactivity,
unique catalytic activity and high suspension stability when compared to larger size
particles. Doong et al. (2012) fabricated titanate nanotubes (TNT) using an alkaline
hydrothermal method and then calcined at various temperatures ranging from 200 to
600oC in air for 4h for removal of bisphenol A and Cu(II) ion. The calcined TNT has
good Cu (II) adsorption capacity.
19
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
20
higher than either GO or TiO2. Nguyen -Phan et al. (2012) investigated the adsorption
capacity of rGO/TNT hybrid in water purification; the dye uptake reached the
maximum valuee over the hybrid in the shet structure 83.26 mg/g, higher than that of
the materials containing titanate nanotubes 75.36 mg/g. These values are nearly twice
higher than those obtained on pure sheet and tubular titanates.
2.6.3. Prospects of technological rGO-TNT composite in removal of heavy metals
in aqueous solution.
In terms of their future prospects, reduced graphene oxide and titanate nanotubes
hybrid can not only push the limits of achievable sensitivity and selectivity but can
also offer a number of multifunctionalities.
Till date, the composites are widely explored as highly efficient adsorbents for heavy
metal removal from water/wastewater. They exhibit various advantages such as fast
kinetics, high capacity, and preferable sorption toward heavy metals in water and
wastewater. Wastewaters from many industries such as metallurgical, mining,
chemical manufacturing and battery manufacturing industries contain many kinds of
toxic heavy metal ions. These functional groups are essential for the high sorption of
heavy metal ions. Considering the oxygen-containing functional groups on the
graphene oxide surfaces and high surface area, the graphene oxide nanosheets should
have high sorption capacity to remove of heavy metal ions from large volumes of
aqueous solutions. The main advantages of this removal procedure include simplicity,
cost effectiveness, rapidity, and higher removal efficiency of toxic metal ions. The
rGO-TNT composites can be regenerated readily with a solution and it has a long
lifetime. The composite was determined to be reproducible with a good metal
selectivity over other potentially interfering ions.
21
PART III. METHODS
3.1. Materal
3.1.1. Chemicals
All the chemicals are used as receive without further treatment. ST01 Titanate was
obtained from Ishihara Sangyo Ltd.(Tokyo, Japan), sodium hydroxide pellets (NaOH)
and copper(II) nitrate pentahemihydrate (Cu(NO3)2.2.5H2O,98%) were purchased from
Riedel-de Haen (Seelze,Germany). Hydrochloric acid (36.5-38.0%) was purchased
from J.T. Baker (Phillips-burg,NJ). Bisphenol A (99+% purity) was purchased from
Aldrich. Natural graphite power was obtained by Alfa Aesar Co.RB, sulphuric acid
(H2SO4), phosphoric acid (H3PO4), potassium permanganate (KMnO4), hydrogen
peroxide (H2O2), hydrochloric acid (HCl) and Deionized water (resistivity 18 MΩcm)
was utilized to prepare all aqueous solution and to rinse the specimens.
3.1.2. Instruments
X-ray powder diffraction (XRD) patterns were obtained using a Rigaku Ultima IV
diffractometer (Cu Kα radiation), Raman spectra was collected using a JY Horiba HR800 spectrophotometer. Transmission electron microscope (TEM) images, microwave,
Rotary Vacuum Evaporator, centrifuge, stirrer, and atomic absorption spectrometer –
spectra AA 100/200 – Varian –Australia was used to estimate the concentration of
various metal ions present in the solution.
22
3.2. Methods
3.2.1. Synthesis of TNT
Figure 3.1. Schematic of TNT synthesis.
The 1-D nanostructured titanate nanotubes were synthesized by a hydrothermal
method using ST01 TiO2 as the starting material. In general, 300 mg of ST01 TiO2
powders were dispersed into 10 mL of 10M NaOH in each centrifuge tube (we
prepared 6 tubes). After vigorous stirring by vortex machine, solutions were dispersed
and washed by filtered water for 1hour.
They were synthesized into three tubes by
scale. The synthesized TNTs were then calcined at 150oC. The microwave is
maintained at a power of 600w for 3 hours for the formation of titanate nanotubes.
Later, the products were added with 10ml 0.1M HCl and DI water (distilled water) and
then cooled down to room temperature by shaking incubator at 25 oC for two nights.
Later the hydrothermal products were washed with 5ml 0.1M HCl and 20ml DI water.
23
After vigorous stirring by Vortex machine, in order to disperse the solution and
balance the solution by scale, we put it in the Centrifuge for 5mins for deposition and
are then taken out and checked for the pH repeatedly. The pH of solution would be
around 6~8. The resulting white products were filtered and then washed with (20ml)
absolute ethanol and are finally dried in drying oven at 60oC for 6 h.
3.2.2. Synthesis of Graphene oxide
Figure 3.2. Schematic of GO synthesis.
Currently, most GO is synthesized by chemical oxidation and exfoliation of pristine
graphite using the Brodie, Staudenmaier or Hummers method or some variations of
these methods. In this report, Graphene oxide (GO) was prepared from graphite
powder according to the modified Hummer method (Hummers and Offemen, 1958).
In brief, 225 ml H2SO4 and 25ml H3PO4 and 2g of natural graphite is added in a round
bottom and mixed, stirred together by a magnetic stirrer. After that, add 5g KMnO 4
24
batch by batch and then heat to appropriate temperature 35oC for 10 hr. Later, the
solution is added into 225ml DI water in ice bath to exchange H2SO4 in the sheet
followed by 3ml H2O2 to reduce residual KMnO4 was added in beaker and mixed it
well at room temp. Solution will change into deep brown to bright brown color,
according to the oxidation degree. Washing with 1M HCl 15ml, then pH=11 PO43-/
HPO42- buffer 5ml + DI water 15ml was done sequentially. The procedure is repeated
for two or three times until pH will reach neutral. Finally, solution was dried by using
Rotary Vacuum Evaporate with water-bath at 45~ 600C and thus graphene oxide
sheets were obtained.
3.2.3. Synthesis of rGO-TNT Composite
TNT composite with GO were prepared through an alkaline hydrothermal treatment.
Firstly, 50mg of GO were dispersed in 10mL of 1M NaOH under an stirrer/ hot plate
over night to achieved uniform dispersion of GO. Next, 300 mg of ST-01(TiO2)
powder added slowly to the GO dispersions while stirring. The composite further
stirred for 1 hour to ensure complete mixing. Then, the composite transferred to the
Teflon-lined and heated in microwave at 150oC, 800W under static condition for 3
hours. The resultant gray colored gel washed with 0.1M HCl solution and stirred
overnight in shaking incubator at room temperature 25oC. And finally, the product
washed with DI water several times, centrifuged until the pH~ 7. The product rGOTNT was dried 40 hours in oven at 50oC.
3.2.4. Adsorption Experiment
Adsorption of Cu (II) ion by TNT, rGO-TNT composites in aqueous solutions was
investigated in centrifuge tubes.
25
Adsorption of Cu(II) by TNT
Adsorption of Cu(II) by rGO-TNT
Figure 3. 3. Adsorption experiment of Copper by TNT and rGO-TNT.
Firstly, 1000 mL buffer solution was prepared to resist changes in pH when quantities
of an acid or an alkali are added to it. I took 2.13g of C6H13NO4S (ethane sulfonic acid
(MES)) and 950 mL DI water into the beaker. In this case, the pH is 4.02. We added
more 5ml NaOH and 45 ml DI water to adjust pH value equal 5.0 ± 0.1.
For TNT experiment: after addition of 10 mg of TNT composites into the solutions
containing 20 mL Cu (II) ion, the pH value was controlled at 5.0 ± 0.1 by buffer
solution. After stirred by Vortex machine, they were analyzed by atomic adsorption
spectroscopy (AAS, Perkin Elmer model 100).
TNT or GO-TiO2 hybrid structure powders (10 mg) were added to 20 mL of heavy
metal ion solution (20 mg/L of Cu2+), followed by stirring. All samples were filtered
by centrifugal filters and analyzed by atomic absorption spectrometry (AAS, PerkinElmer model 100). The removal experiments were conducted in many different times.
The removal capacity (q, mg/g) is calculated by:
26
where C0 and Cfiltered is initial and filtered concentration by centrifugal tube for heavy
metal ions (mg/L), V is sample volume (L) and M is mass of adsorbent (g).
,
Figure 3.4. Atomic adsorption spectroscopy (AAS)
It was similar experiments with others heavy metal.
3.2.5. The method of determining the characteristics of the material
Characteristics of the formation and transformation of crystalline phase composites
were determined by Raman spectroscopy and X-ray diffraction. The function structure
was observed by Fourier transform infrared spectroscopy FTIR. The morphological
evolution was observed by transmission electron microscopy TEM and Scanning
electron microscopy SEM. And subscribe to the absorption of heavy metals by AAS.
3.2.5.1. Method of X-ray diffraction
Technique X-ray diffraction provides some essential information for research sample
materials such as: The existence of the crystalline phase of qualitative, quantitative,
27
lattice constants, lattice size, variable form, stretching the limits of the crystal lattice
due to defects in the crystal lattice caused (Hanno zur Loye. 2013).
The existence of phase qualitative, quantify are identified primarily based on location,
intensity, area obtained from the diffraction signal collected.
The crystal lattice constant: on the basis of the value of d (the distance between
adjacent lattice surfaces) obtained from the diagram X-ray diffraction we calculate the
lattice constant of the crystal through specific formula, with each crystal system. For
example, for cubic system, the form of this equation is:
Cubic system:
Where: h, k, l are the Miller indices of the Bragg plane. dhkl (Å) is the spacing between
the planes in the atomic lattice, identified on X-Ray diffraction diagram, a,b,c are
parameters need to identify.
The size of particles of crystals obtained from XRD is calculated Scherrer formula:
Where: λ (Å): is the X–Ray wavelength; K ≈ 0,9. r: is the mean size of the ordered
(crystalline) domains (Å); Bsize (radian): is the line broading at half the maximum
intensity, after subtracting the instrumental line broading, in radians; θB: is the Bragg
angle.
X-ray diffraction was recorded on a Siemens D5000 at the Laboratory of Biomedical
and Environmental Science, National Tsing Hua University.
3.2.5.2. Method of Raman spectroscopy
Raman spectroscopy is a widely used tool for the characterization of carbon products,
especially considering the fact that conjugated and double carbon-carbon bonds lead to
28
high Raman intensities (Kudin. 2008). It is possible to band-fit the spectra of
amorphous and diamond-like carbons for hard carbon films to decouple the
contributions of the "graphitic carbon" (G band) from the "disordered carbon" (D
band).
Figure 3.5. Raman spectroscopy
For Raman analysis of the hard carbon film properties are usually limits the spectral
region of analysis to the range between 800 and 1950 cm-1 (for nitrogenized films up to
2250 cm-1). The G band normally appears between 1480 and 1580cm-1, and the D band
occurs between 1320 and 1440cm-1. The bands are generally overlapping and their
actual positions are, to some extent, reliant on the laser excitation wavelength (Horiba
scientific. 2013).
29
3.2.5.3. Transmission Electron Microscopy (TEM)
Transmission Electron Microscopy (TEM) is a vital characterization tool for directly
imaging nanomaterials to obtain quantitative measures of particle and/or grain size,
size distribution, and morphology.
Figure 3.6. Schematic of TEM
TEM images the transmission of a focused beam of electrons through a sample,
forming an image in an analogous way to a light microscope (Figure 3.6). However,
because electrons are used rather than light to illuminate the sample, TEM imaging has
significantly higher resolution (by a factor of about 1000) than light-based imaging
techniques. Amplitude and phase variations in the transmitted beam provide imaging
contrast that is a function of the sample thickness (the amount of material that the
electron beam must pass through) and the sample material (heavier atoms scatter more
30
electrons and therefore have a smaller electron mean free path than lighter atoms)
(Roson Ct Ste Ksan Diego).
Successful imaging of materials using TEM depends on the contrast of the sample
relative to the background. Samples are prepared for imaging by drying on a copper
grid that is coated with a thin layer of carbon. Materials with electron densities that are
significantly higher than amorphous carbon are easily imaged.
Figure 3. 7. The process TEM characterization
31
PART IV. RESULTS
4.1. Characterization of GO and titanate nanotubes/rGO composite.
The presence of rGO component in the rGO-TNT composite and the structural
properties are confirmed by Raman spectroscopy and X-Ray diffraction technique.
Figure 4.1. Raman spectra of GO, rGO-TNT materials
Figure 4.1 shows the Raman spectra of Graphene Oxide and rGO-TNT composite. The
Raman active 98 cm-1, 138 cm-1, 190cm-1, 228 cm-1, 276 cm-1, 396 cm-1, 664 cm-1 and
865 cm-1 modes for the composites match with titanate structure (Habashi. 2009 and
Liu et al,. 2005). In addition, the peaks of the composite are broader and significantly
shifted 98 cm-1 to 228 cm-1. The peak blue shift and broadening of the Raman spectra
were analyzed using the most intense in this stage (228 cm-1 peak). The peak position
and broadening of Raman spectrum is mainly affected by the size of the nanomaterial
as well as defects and temperature.
32
Raman spectroscopy is also widely used for the characterization of the electronic
structure of carbon products. A change in Raman band intensity and blue shifts
provide information on the nature of carbon- carbon bonds and defects. The Raman
spectra in Figure 4.1 show the characteristic D and G bands at 1346 cm-1 and 1589 cm1
found in GO and the composite. The D band is common feature for sp3 defects in
carbon, and the G band provides information on plane vibrations of sp2 bonded
carbons. The intensity ratio of the D band to the G band usually reflects the order of
defects in GO or graphene. Compared to GO, rGO-TNT composites show two
differences in the Raman spectra. First, the calculated ID/IG of the rGO-TNT samples
were lower than that of GO, indicating a lower density of defects present in rGO.
Second, the G band shifts by ~ 5cm−1 in the rGO-TNT. Therefore, both the change in
Raman band intensity and the blue shift of the G band provide clear evidence for the
presence of graphene in the composite).
Intensity (a.u.)
GO
10
20
30
40
50
60
2 theta
Figure 4.2. XRD patterns of GO
33
X-ray diffraction can also provide information on the crystal structure of the GO,
TNTs and rGO-TNT. Figure 4.2 shows a XRD pattern of GO with a sharp peak at
about 2θ = 10.5o corresponding to (002) reflection was observed, giving an interlayer
spacing of 0.9 nm.
Intensity (a.u.)
rGO-TNT
TNT
10
20
30
40
50
60
70
80
2 theta
Figure 4.3. XRD patterns of TNT and rGO-TNT composite
The crystal structures of as-prepared TNT and RGO–TNT electrodes were analyzed by
XRD, as shown in Figure 4.3. The peaks present clearly represent the formation of
titanate nanostructures, derived from microwave-assisted hydrothermal conditions, can
be assigned as NaxH2-xTi3O7 in our TNT nanostructures. However, no apparent peaks
for graphene were observed in the rGO–TNT sample. Similar results were also
reported by others. However, the existence of graphene in our rGO–TNT electrode can
be clearly elucidated by the above Raman analysis and following TEM, SEM images.
34
4.2. Morphology of TNT, GO and rGO-TNT composite.
The morphological evolution of titanate in rGO-TNT composite was observed by
TEM (transmission electron microscopy) images.
Figure 4.5. TEM images of the synthesis TNT and rGO-TNT composite.
Figure 4.5a. show the TEM image of TNT before the attachment of rGO. The titanate
nanotube showed tubular structures with lengths around 200-250 nm. And, the TEM
observation in Figure 4.5b reveals numerous overlapped layers with high transparency,
implying very thin sheet- like structure. No trace of spherical titanate nanotubes
precursors was found in hybrid materials, implying the successful interaction of Ti
species in between carbonaceous layers and subsequent transform to sheet-like
structure. In addition, Raman spectra detected on large area showed the presence of
dominant Ti and O species together with small amount of C. It can be obviously three
components were well distributed in the hybrid material as shown in the mapping in
35
Figure 4.5c. Such characteristics demonstrate that the rGO sheets were assembled on
the titanate nanotubes.
4.3. Application into removal of heavy metal ions
The absorption capacity of Copper ion by the TNT and rGO/TNT composite were
examined.
Table 4.1. The results of Cu (II) adsorption experiment by TNT, was observed by
Atomic adsorption spectroscopy (AAS).
Cont.(mg/L)
1
2
5
10
20
0
0.317
0.332
0.383
0.447
0.591
10
0.303
0.303
0.304
0.306
0.31
30
0.303
0.304
0.305
0.31
0.306
60
0.303
0.303
0.306
0.306
0.306
180
0.301
0.301
0.302
0.305
0.303
Time(min)
1.0
TNT
1 ppm
2 ppm
5 ppm
10 ppm
20 ppm
0.8
0.6
C/C0
0.4
0.2
0.0
-0.2
-0.4
0
30
60
90
120
Time (min)
150
180
Figure 4.6. The adsorption of Cu(II) by TNT at pH=5 in aqueous solutionat room
temperature.
36
Figure 4.6 shows the absorbed amounts of Cu(II) ion by different concentration of
TNT including 1ppm, 2ppm, 5ppm, 10 and 20ppm, and different absorption time (10,
30 or 180 minutes). The adsorption of copper ion by titanate nanotubes increased
rapidly with the increase in the equilibrium Cu (II) concentration. The higher is the
concentration, more stronger is the adsorption capacity.
The amount of heavy metal has reduced from 0.591 mg/L to 0.31 mg/L at the
concentration is 20 ppm and mitigation under the next period.
Table 4.2. The results of Cu (II) adsorption experiment by rGO-TNT, was observed by
Atomic adsorption spectroscopy (AAS).
Cont.(mg/L)
1
2
5
10
20
0
0.317
0.332
0.383
0.447
0.591
10
0.303
0.303
0.302
0.306
0.305
30
0.303
0.303
0.303
0.304
0.304
60
0.304
0.303
0.303
0.304
0.303
180
0.301
0.301
0.301
0.301
0.302
Time(min)
rGO-TNT
1.0
1 ppm
2 ppm
5 ppm
10 ppm
20 ppm
0.8
C/C0
0.6
0.4
0.2
0.0
-0.2
-0.4
0
30
60
90
120
Time (min)
150
180
Figure 4.7. The adsorption of Cu(II) by rGO /TNT composite in aqueous solution at
room temperature.
37
When using the TNT / rGO composite, the ability to effectively absorb higher is
shown in Figure 4.7. The absorbed amounts of Cu(II) ion are also by different
concentration of TNT including 1ppm, 2ppm, 5ppm, 10 and 20ppm, and different
absorption time( 10, 30 or 180 minute). The adsorption of copper ion by titanate
nanotubes/reduced graphene oxide increased rapidly with the increase in the
equilibrium Cu(II) concentration. In the concentration of 1 ppm, the ability to absorb
copper after 10 minutes was 0.015 mg /L and was slightly increased from 0.001 to
0.003 mg/L at 180 minutes. When increasing the concentration to 20 ppm, the
beginning adsorption with no adsorbent was 0.591 mg/L and with 10 mg of TNT/rGO
composite in 10 minutes, the adsorption capacity was 0.305 mg/L and it was 0.302
mg/L, 180 minutes. When compared with TNT, the adsorption capacities of the
rGO/TNT composite reached higher than TNT. It is well known that adsorption
strongly depend on the pore structure and surface area as well as surface functionality
of rGO/TNT.
38
PART V. DISCUSSION AND CONCLUSION
5.1. Discussion
To summary, the study has developed a graphene-based nano composite for the
removal of toxic heavy metals from aqueous solution. Graphene has unique
morphology, chemical structure, and electronic properties. The main advantages of
this removal procedure include simplicity, cost effectiveness, rapidity, and higher
removal efficiency of TNT/rGO. In this study we have synthesized titanate nanotubes
by hydrothermal method, graphene oxide by Hummer method and titanate
nanotubes/reduced graphene oxide composite by hydrothermal method, and their
adsorption capacity was evaluated. XRD, TEM, and Raman spectroscopy studies
revealed the structural morphology of the synthesized material and confirmed the
formation of titanate nanotube of lengths 200-250 nm. The presence of rGO
component in the rGO-TNT composite and the structural properties were confirmed by
Raman spectroscopy and X-Ray diffraction.
Experimental results obtained in this study clearly demonstrate that TNT/rGO
composite are an effective adsorbent for heavy metals. The amount of heavy metal has
reduced from 0.591 mg/L to 0.304 mg/L at the concentration was 20 ppm in 30
minutes and mitigation under the next period. The experiment also compared the
absorption capacity between rGP/TNT and TNT, the results shows that the absorption
capacitie of the rGO/TNT was higher than TNT; it depends on the pore structure and
surface area as well as surface functionality of rGO/TNT. Thus, it is suggested that
TNT/rGO prepared here could be a promising candidate sorbent material for removing
heavy metal ions from aqueous solutions beyond the ordinary use of adsorbents. The
39
outstanding physicochemical properties of the TNT/rGO materials will play a very
important role in environmental pollution management in the future.
5.2. Conclusion
In conclusion, results shown in the thesis clearly indicate the morphology of TNT and
rGO by SEM and TEM. The adsorption of Cu ions by TNT/rGO composites was
examined and analyzed. The TNT/GO nanocomposites showed excellent adsorption
capacity toward Cu (II) adsorption and the adsorption can be complete within 30 min.
This finding is interest and can be extended to remove other toxic chemicals in waters
and soils.
* There still lies a necessity in continuing the research on the adsorption of titanate
nanotube/reduced graphene oxide on the other materials such as metals (Pb, As,
Hg,...).
* Researching the adsorption of heavy metal ions of TNT/rGO to large scale that
may have high practical applicability.
* Significant tests regarding the ability to remove other ions on TNT/rGO to be
used for a variety of different contaminated water environment.
Although every attempt has been made to make the review work presented in Section2 as up-to-date as possible, unintentional omission of important references if any, is
regretted. In this report, Graphene oxide (GO) was prepared from graphite powder
according to the modified Hummer method. The present study may be extended to
other methods for high quality Graphene oxide. In the present experiment, Cu(II) was
adsorbed by TNT and rGO-TNT, we have done only single metal (Cu) adsorbent.
However in future we can do with different heavy metals removal experiment.
40
Nanocomposite based other materials may be explored for its deployment in removal
of toxic heavy metals from aqueous solution.
41
REFERENCES
Alkorta, I., Hernández-Allica, J., & Garbisu, C. (2004). Plants against the global
epidemic of arsenic poisoning. Environment international, 30(7), 949-951.
Åström, M., & Björklund, A. (1995). Impact of acid sulfate soils on stream water
geochemistry in western Finland. Journal of Geochemical Exploration, 55(1),
163-170.
Bissen, M., & Frimmel, F. H. (2003). Arsenic—a review. Part I: occurrence, toxicity,
speciation, mobility. Acta hydrochimica et hydrobiologica, 31(1), 9-18.
Bryan, G. W., & Langston, W. J. (1992). Bioavailability, accumulation and effects of
heavy metals in sediments with special reference to United Kingdom estuaries:
a review. Environmental Pollution, 76(2), 89-131.
Chandra, V., Park, J., Chun, Y., Lee, J. W., Hwang, I. C., & Kim, K. S. (2010). Waterdispersible
magnetite-reduced graphene
oxide composites for arsenic
removal. ACS nano, 4(7), 3979-3986.
Clark, D. B., Pollock, N., Bukstein, O. G., Mezzich, A. C., Bromberger, J. T., &
Donovan, J. E. (1997). Gender and comorbid psychopathology in adolescents
with alcohol dependence. Journal of the American Academy of Child &
Adolescent Psychiatry, 36(9), 1195-1203.
Doong, R. A., Chang, S. M., & Tsai, C. W. (2013). Enhanced photoactivity of Cudeposited titanate nanotubes for removal of bisphenol A. Applied Catalysis B:
Environmental, 129, 48-55.
42
Doong, R. A., Tsai, C. W., & Liao, C. I. (2012). Coupled removal of bisphenol A and
copper ion by titanate nanotubes fabricated at different calcination
temperatures. Separation and Purification Technology, 91, 81-88.
Foulkes, W. D., Stefansson, I. M., Chappuis, P. O., Bégin, L. R., Goffin, J. R., Wong,
N., ... & Akslen, L. A. (2000). Germline BRCA1 mutations and a basal
epithelial phenotype in breast cancer. Journal of the National Cancer Institute,
95(19), 1482-1485.
Hanno zur Loye. (2013). X-Ray Diffraction-How it works. Retrieved from:
http://www.chem.sc.edu/faculty/zurloye/xrdtutorial_2013.pdf
(accessed
10
December 2014).
He, F., Fan, J., Ma, D., Zhang, L., Leung, C., & Chan, H. L. (2010). The attachment of
Fe< sub> 3</sub> O< sub> 4</sub> nanoparticles to graphene oxide by
covalent bonding. Carbon, 48(11), 3139-3144.
Horiba Scientific. (2013). Understanding Physical Parameters of Hard Carbon Films
Using Raman Spectra. Retrieved from:
http://www.azom.com/article.aspx?ArticleID=10105 (accessed on 10 December
2014).
Hummers Jr, W. S., & Offeman, R. E. (1958). Preparation of graphitic oxide.Journal of
the American Chemical Society, 80(6), 1339-1339.
Kudin, K. N., Ozbas, B., Schniepp, H. C., Prud'Homme, R. K., Aksay, I. A., & Car, R.
(2008). Raman spectra of graphite oxide and functionalized graphene
sheets. Nano letters, 8(1), 36-41.
43
Lee, Y. C., & Yang, J. W. (2012). Self-assembled flower-like TiO< sub> 2</sub> on
exfoliated graphite oxide for heavy metal removal. Journal of Industrial and
Engineering Chemistry, 18(3), 1178-1185.
Liu, X. Y., & Coville, N. J. (2005). A Raman study of titanate nanotubes. South
African Journal of Chemistry, 58, p-110.
Matschullat, J. (2000). Arsenic in the geosphere—a review. Science of the Total
Environment, 249(1), 297-312.
Nguyen-Phan, T. D., Pham, V. H., Kim, E. J., Oh, E. S., Hur, S. H., Chung, J. S., ... &
Shin, E. W. (2012). Reduced graphene oxide–titanate hybrids: Morphologic
evolution by alkali-solvothermal treatment and applications in water
purification. Applied Surface Science, 258(10), 4551-4557.
Perera, S. D., Mariano, R. G., Vu, K., Nour, N., Seitz, O., Chabal, Y., & Balkus Jr, K.
J. (2012). Hydrothermal synthesis of graphene-TiO2 nanotube composites with
enhanced photocatalytic activity. Acs Catalysis, 2(6), 949-956.
Rahman, M. A., & Hasegawa, H. (2011). Aquatic arsenic: phytoremediation using
floating macrophytes. Chemosphere, 83(5), 633-646.
Sreeprasad, T. S., Maliyekkal, S. M., Lisha, K. P., & Pradeep, T. (2011). Reduced
graphene oxide–metal/metal oxide composites: facile synthesis and application
in water purification. Journal of hazardous materials, 186(1), 921-931.
Tam, N. F. Y., & Wong, Y. S. (1996). Retention and distribution of heavy metals in
mangrove soils receiving wastewater. Environmental Pollution, 94(3), 283-291.
Yang, S. T., Chang, Y., Wang, H., Liu, G., Chen, S., Wang, Y., ... & Cao, A. (2010).
Folding/aggregation of graphene oxide and its application in Cu< sup>
2+</sup> removal. Journal of colloid and interface science, 351(1), 122-127.
Yifei, G. (2012). Nanomaterials as sorbents to remove heavy metal ions in wastewater
treatment. Journal of Environmental & Analytical Toxicology.
44
Zhang, Y., Chen, B., Zhang, L., Huang, J., Chen, F., Yang, Z., ... & Zhang, Z. (2011).
Controlled assembly of Fe 3 O 4 magnetic nanoparticles on graphene
oxide. Nanoscale, 3(4), 1446-1450.
Zhao, G., Li, J., Ren, X., Chen, C., & Wang, X. (2011). Few-layered graphene oxide
nanosheets
as
superior
sorbents
for
heavy
metal
ion
pollution
management. Environmental science & technology, 45(24), 10454-10462.
Zheng, W., & Lin, P. (1995). Accumulation and distribution of Cu, Pb, Zn and Cd in
Avicennia marina mangrove community of Futian in Shenzhen.Oceanologia et
Limnologia Sinica, 27(4), 388-393.
45