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Application of titanate nanotubes silicon dioxide (TNTSiO2) nanocomposite for the adsorption heavy metal (copper (II) ion) in aqueous solution

THAI NGUYEN UNIVERSITY
UNIVERSITY OF AGRICULTURE AND FORESTRY

NGUYEN THUY TRANG

APPLICATION OF TITANATE NANOTUBES-SILICON DIOXIDE
(TNT@SiO2) NANOCOMPOSITE FOR THE ADSORPTION HEAVY METAL
(COPPER (II) ION) IN AQUEOUS SOLUTION

BACHELOR THESIS
Study Mode: Full-time
Major: Environmental Science and Management
Faculty: International Training and Development Center
Batch: 2012-2016

Thai Nguyen, 20/07/2016


Thai Nguyen University of Agriculture and Forestry
Degree Program


Bachelor of Environmental Science and Management

Student name

Nguyen Thuy Trang

Student ID

DTN1253060015

Thesis Title

Application of Titanate nanotubes-Silicon dioxide (TNT@SiO2)
nanocomposite for the adsorption heavy metal (Copper (II) ion)
in aqueous solution.

Supervisor(s)

Prof. Dr. Ruey- an Doong- National Tsing Hua University,
Taiwan.
Assoc. Prof. Dr. Tran Thi Thu Ha- Thai Nguyen University of
Agriculture and Forestry, Vietnam.

Abstract:
The objective of this study was to fabricate TNT@SiO2 nanocomposite material
with specific surface areas, pore structure for the adsorption heavy metal- Cu(II) ion
in aqueous solution. With a large amount of SiO2 was contained in waste display
panel glass combined with TiO2 have the unique morphology, strong oxidative
properties, low cost, non-toxicity, chemical and thermal stability through a
hydrothermal method. The morphology changed when mixing SiO2 with TiO2 and
then the TNT surface area improved, -O-Ti-O-Si- linkage is formed. In addition,
TNT@SiO2 nanocomposite is an effective adsorbent heavy metal in aqueous
solution. The results demonstrated that 100% Cu(II) ion is absorbed by TNT@SiO2
nanocomposite and separated out of aqueous solution within 30 minutes reaction.
Results obtained in this study clearly show TNT@SiO2 nanocomposite is successful
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for the adsorption heavy metals ion in solution.
Keywords



TNT@SiO2 nanocomposite , hydrothermal method,
adsorption, heavy metal, Cu(II) ion.

Number of pages

56

Date of submission 30th August, 2016
Supervisor’s
signature

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ACKNOWLEAGEMENT
Firstly, I would like to say thanks to the cooperation between Thai Nguyen
University of Agriculture and Forestry and National Tsing Hua University for
providing me an amazing opportunity to internship in Taiwan. It brings me great
pleasure to work and submit my thesis for graduation.
I would like to express my deeply gratitude to Prof. Dr. Ruey- an Doong
whose guidance, encouragement, suggestion and very constructive criticism have
contributed immensely to the evolution of my ideas during the project. Without his
guidance, I may not have this thesis.
I sincerely thanks to Assoc. Prof. Dr. Tran Thi Thu Ha for her advices,
assistance, sharing experiences before and after I went to Taiwan, helping me to
understand and complete proposal and thesis.
I am also thankful to Mr. Nguyen Thanh Binh (PhD) and Ms. Khuat Thi
Thanh Huyen for teaching me the synthesis of nanotubes and various other
techniques and methods used in environmental field. They were very helpful in
providing me constructive feedback and suggestions on my project and helping me to
successful complete several of my experiments and report. Without them help and
devotion, I would not be able to reach this stage.
I am really fortunate to be in Prof. Dr. Ruey- an Doong’s lab. Thanks to all the
members in Professor Doong’s laboratory who hearty help me a lot when I work in
there.

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I also thank to my family for providing me emotional, unceasing
encouragement and physical and financial support. At last, I would like to thank all
those other persons who helped me in completing this report. Because of my lack
knowledge, the mistake is inevitable, I am very grateful if I receive the comments and
opinions from teachers and others to contribute my report.
Sincerely,

Nguyen Thuy Trang

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TABLE OF CONTENT
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 .......................................................................................... 5
1.3. Research questions.............................................................................................. 6
1.4. Limitations ......................................................................................................... 6

PART II. LITERATURE REVIEW ................................................................................ 7
2.1. Heavy metals ...................................................................................................... 7
2.1.1.Definition and sources of heavy metals: ...................................................... 7
2.1.2.Characteristics of heavy metals: .................................................................. 7
2.1.3.Heavy metals pollution in the world and Vietnam. ...................................... 8
2.1.3.1. Heavy metals pollution in the soil. ..................................................... 8
2.1.3.2. Heavy metals pollution in coastal, marine environment . ................... 9
2.1.4.Effecting of heavy metals to environment and human’s health .................. 10
2.1.5.The characteristics and health effects of Copper........................................ 12
2.1.6.Method for treament heavy metals in aqueous solutions............................ 13
2.2. Nanomaterials: .................................................................................................. 13
2.2.1.Titanate nanotubes ( TNT) : ...................................................................... 15
2.2.1.1. Overview of Titanium dioxide: ........................................................ 15
2.2.1.1.1.Titanium oxidation structures and properties: ........................... 15
2.2.1.1.2.Titanate nanotubes(TNT).......................................................... 16
2.2.2.Overview of SiO2: ..................................................................................... 17
2.2.3.Overview of nanocomposite...................................................................... 18
2.2.3.1. Definition and characteristics of nanocomposite .............................. 18
2.2.3.2. SiO2@TNT nanocomposite ............................................................. 19
PART III. MATERIALS AND METHODS ...................................................................... 20
3.1. Materials ........................................................................................................... 20
3.2. Methods: ........................................................................................................... 22
3.2.1.The synthesis of TNT:............................................................................... 22
3.2.2.The synthesis of TNT@SiO2 nanocomposite ............................................ 23
3.2.3.Adsorption experiment:............................................................................. 23
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3.2.4.The methods for determining the characteristics of materials. ................... 24
3.2.4.1. X-ray Diffraction ( XRD) ................................................................ 25
3.2.4.2. Scanning Electron Microscopy ( SEM) .......................................... 26
3.2.4.3. Transmission Electron Microscopy ( TEM) ................................... 28
3.2.4.4. Fourier transform infrared spectroscopy ( FTIR).............................. 29
3.2.4.5. Zeta potential (ZP) ........................................................................... 30
3.2.4.6. Atomic absorption spectroscopy ...................................................... 32
PART IV. RESULTS............................................................................................................. 33
4.1. The X-ray diffraction of TNT, SiO2 and SiO2@TNT composite. ...................... 33
4.2. Morphology of TNT, SiO2 and TNT@SiO2 composite. .................................... 34
4.3. Fourier transform infrared (FTIR) spectrum of SiO2, the synthesis TNT and
TNT@SiO2................................................................................................................ 37
4.4. Zeta potential .................................................................................................... 38
4.5. Application of TNT@SiO2 for the adsorption Cu(II) ion................................... 39
PART V. DISCUSSION AND CONCLUSION ................................................................. 41
5.1. Discussion ........................................................................................................ 41
5.2. Conclusion ........................................................................................................ 42
REFERENCES ...................................................................................................................... 43

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LIST OF FIGURES
Figure 2.2.1.1.1: Crystal structure of the three forms of titanium dioxide .............................. 15
Figure 2.2.2 : Crystal structure of SiO2 .................................................................................... 17
Figure 3.1.2: Some instruments used for this study. ................................................................ 21
Figure 3.2.1: Schematic of the synthesis TNT ......................................................................... 22
Figure 3.2.2: Schematic of the synthesis TNT@SiO2 ............................................................. 23
Figure 3.2.3 : The samples of Cu(II) ion (10mg/L) and TNT@SiO2 of the adsorption
experiment at pH=5 in the different times............................................................................... 24
Figure 3.2.4.1: Schematics of X-ray diffractometer technique used for crystal structure
analysis. .................................................................................................................................... 26
Figure 3.2.4.2: Schematic diagram of SEM ............................................................................ 28
Figure 3.2.4.3: Schematic diagram of TEM............................................................................. 29
Figure 3.2.4.5: The effect of pH on Zeta potential ................................................................... 31
Figure 3.2.4.6: Schematic of an atomic-absorption experiment............................................... 32
Figure 4.1: XRD patterns of TNT, SiO2 and SiO2@TNT composite...................................... 33
Figure 4.2 A: SEM images of the synthesis TNT(a) and TNT@SiO2 composite (b). ........... 34
Figure 4.2 B: TEM images of SiO2, the synthesis TNT and TNT@SiO2 composite.............. 36
Figure 4.3: FTIR spectrum of SiO2, the synthesis TNT and TNT@SiO2....................... 37
Figure 4.4: The effect of pH to zeta potential of SiO2@TNT ................................................. 38
Figure 4.5: The adsorption Cu (II) ion (10mg/L) by TNT@ SiO2 at pH=5 in aqueous solution
at room temperature.................................................................................................................. 39

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LIST OF TABLES

Table 3.1.1: Sources of chemical materials.............................................................................. 20

2


LIST OF ABBREVIATIONS
TNT

TiO2/ Titanate nanotubes

SiO2@TNT or

SiO2 + TiO2 nano composite

TNT@SiO2

TiO2 + SiO2 nano composite

XRD

X-Ray Diffraction

SEM

Scanning Electron Microscopy

TEM

Transmission Electron Microscopy

FTIR

Fourier transform infrared spectroscopy

ZP

Zeta Potential

AAS

Atomic absorption spectroscopy

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PART I. INTRODUCTION
1.1 Research rationale:

Economic and social development have produced many benefits – raising standards
of living and improving quality of life across the world – it has also resulted in the
depletion of natural resources, the degradation of ecosystems and environmental
issues. Environmental pollution is a controversial issue not only in Vietnam but also in
the world.
With about 70% of the earth’s cover being water, it undeniably becomes one of our
greatest resources. Furthermore, roughly 70% of an adult’s body made up of water. So,
water is very important for human. Water pollution is an appalling issue, powerful
enough to lead the world on a path of destruction. Water is an easy solvent, enabling
most pollutants to dissolve in it easily and contaminate it. The most basic effect of
water pollution is directly suffered by the organisms and vegetation that survive in
water, including amphibians. On a human level, several people die each day due to
consumption of polluted water contained heavy metals. Heavy metals are particularly
problematic because, unlike most organic contaminants, they are non-biodegradable
and can accumulate in living tissues, posing great threat to both human health and
ecological environment. The most common heavy metals mainly include mercury,
cadmium, lead, chromium, arsenic, zinc, copper, nickel, cobalt, etc. To date, various
methods have been proposed for efficient heavy metal removal from waters, including
but not limited to coagulation, chemical precipitation, membrane filtration, reverse
osmosis, solvent extraction, flotation, ion exchange and adsorption. But, adsorption is
one of the highly selective methods for removing heavy metals from aqueous
solutions. This is an economical technique which also offers numerous advantages
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resulting from the vast number of available adsorbents. With the development of
modern technologies, a very wide range of materials have come to be used as
hazardous metal adsorbents, from natural substances to highly selective synthetic
systems.
Titanium oxide nanotube (TiO2 nanotube/ TNT) is one of the nanostructured
oxides with tubular structure. TiO2 is well known as a wide gap semiconductor oxide,
high photocatalytic activity, inexpensive, chemically stable, harmless, large specific
surface area and high pore volume, has no absorption in the visible light region, and a
potential material for the adsorption of metal ions in aqueous solution.
SiO2 was contained in waste panel glass of television, notebook, smartphone etc,.
To contribute for protecting the environment, with efforts are being done in recent year
to coat TiO2 on high surface area supports such as silica (SiO2) and alumina (Al2O3) to
improve surface area of TiO2(Hanprasopwattana A et al.,1997; Yuranova T et
al.,2006). Recent studies showed that TiO2-SiO2 mixed oxides might be good
combination to become one of the best catalyst for oxidation reactions ( Yoshida H et
al., 2000). Thus, SiO2@TNT nano composite with high specific surface area of TNT is
promising in treating contaminated aqueous solution.
Considering all aspects and issues mentioned above, I propose research:
“Application of Titanate nanotubes-Silicon dioxide (TNT@SiO2) nanocomposite for
the adsorption heavy metal ( Copper (II) ion) in aqueous solution.”
1.2.

Research’s objectives

The objective of this study was to fabricate, investigate and develop of
TNT@SiO2 nano composite for the adsorption of Cu (II) ion from aqueous solution.

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To further approach and understand about the synthesis process, nanostructures,
formation mechanism, various physicochemical characteristics, and evaluate the
properties and application for the adsorption of TNT@SiO2 nano composite through a
hydrothermal method.
Estimation of the adsorption capacity of some heavy metal ions in aqueous
solutions.
The characteristics of nano composite materials were determined by XRD,
TEM, SEM, FTIR, and AAS.
The fabrication of new materials TNT@ SiO2 nano composite will make a
significant contribution in waste water treatment and improve the domestic water
efficiency as well as contribute to the environmental protection.
1.3.

Research questions

What is the characteristics of TNT@SiO2 nano composite?
How about the adsorption capacity Cu (II) ion of TNT@SiO2 nano composite
in aqueous solution?
1.4.

Limitations

Because the time for an internship was too short, this research project cannot
perform any other experiments.

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PART II. LITERATURE REVIEW
2.1.

Heavy metals

2.1.1. Definition and sources of heavy metals:
There is not clearly about definition of a heavy metal. But the high densities of
native metals such as copper, iron and gold may have been noticed in prehistory
(Raymond 1984, p. 9). Heavy metals are found naturally in the earth, and become
concentrated as a result of human caused activities. Common sources are from mining
and industrial wastes; vehicle emissions; lead-acid batteries; fertilisers; paints; treated
woods; aging water supply infrastructure ( Harvey, Handley & Taylor 2015); and
microplastics floating in the world's oceans ( Howell et al., 2012; Cole et al., 2011,
pp. 2589‒2590).
Heavy metals have a high atomic weight and a density at least 5 times greater than
that of water. Heavy metals can be classified into three different types including toxic
metals (such as Hg, Cr, Pb, Zn, Cu, Ni, Cd, As, Co, Sn, etc.), precious metals (such as
Pd, Pt, Ag, Au, Ru etc.) and radionuclides (such as U, Th, Ra, Am) ( Bishop.,2012).
And toxic metals are the most impact to human’s health and life.
2.1.2. Characteristics of heavy metals:
Heavy metals are a natural constituent on earth commonly known with properties
such as having persistence, high toxicity and also serving as non-biodegradable
pollutants when they accumulate in the ecosystem. Heavy metals can create adverse
effects on environmental and human health due to their toxicity. Some heavy metals
are found in the body and essential for human health, such as iron, zinc, magnesium,
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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. Heavy metals enter plant, animal and human tissues via air inhalation, diet and
manual handling. Thus, heavy metals can bind to vital cellular components, such as
structural proteins, enzymes, and nucleic acids, and interfere with their functioning.
Symptoms and effects can vary according to the metal or metal compound, and the
dose involved. Broadly, long-term exposure to toxic heavy metals can have
carcinogenic, central and peripheral nervous system and circulatory effects.
2.1.3. Heavy metals pollution in the world and Vietnam.
Nowadays, pollution becomes increasingly prevalent in our daily life. In some
areas, it has a fairly negative impact on our health. Among all the pollutions, heavy
metal is an important part which should never be neglected.
2.1.3.1.

Heavy metals pollution in the soil.

Heavy metals contamination of soils currently has become one of the most
serious environmental problems. Some of the heavy metals are micronutrients
necessary for plant growth, such as Zn, Cu, Mn, Ni and Co, while others have no
known function, such as Cd, Pb and As. In a national survey commissioned by the
United Kingdom, the Department of the Environment analysed samples collected from
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November 1981 to June 1982 from 53 locations in England, Scotland, and Wales
(Thornton et al., 1990). The results showed that 93 % of the garden soils exceeded
2,000 mg·kg-1 Pb. In Derbyshire, the Pb concentration was within the range of 1,180 –
22,100 mg·kg-1 , while the Pb concentration in the vegetable plot soil the range was
1,140 – 26,500 mg·kg-1. Several studies reported that the Cd content in soils near the
smelter or metallurgical factories were very high. For example, in Poland, at a site
located 600 m away from a metallurgical factory, the Cd content in soil was 250
mg·kg-1 (Greszta and Godzik, 1969). In Vietnam, by using wastewater for the
irrigation of crops, the land might have been exposed to heavy metals contamination
(Nguyen et al., 2001). According to Le and Nguyen (1998) and to Ho and Nguyen
(2003), most of the soil pollutions with Pb and Cu are caused by the traditional craft
villages and heavy metal recycling activities.
2.1.3.2.

Heavy metals pollution in coastal, marine environment .

Heavy metals contamination in coastal and marine environments is becoming
an increasingly serious threat to both the naturally stressed marine ecosystems and
humans that rely on marine resources for food, industry and recreation. Heavy metals
are introduced to coastal and marine environments through a variety of sources and
activities including sewage and industrial effluents, brine discharges, coastal
modifications and oil pollution. There is an increasing trend of heavy metal pollution
in sediments of several coastal waters in the western part of Indonesia. Heavy metals
such as Pb, Cd, Cu, Cr and Zn in sediments were recorded relatively high in
concentration. Variation for each metal were in the following: 0.42 -101.28 mg Pb kg-1
dry weight (dw), 0.03 -9.86 mg Cd kg-1 , 0.10 -61.34 mg Cu kg -1 , 0.99 -42.10 mg Cr
9


kg

-1

and 0.46 -122.00 mg Zn kg

-1

(Zainal Arifin., 2001). While in the water of the

Yangtze River Basin, China, the concentrations of Cd, Cu, Pb and Zn are 0.080, 7.91,
15.7 and 18.7 microg/l, respectively. This metals come from human activities,
industrial emission, wastewater and solid waste. These contaminants pollute drinking
water and food, and threaten human health. Some diseases resulting from pollution of
geological and environmental origin, were observed with long-term and non-reversible
effects (Cheng S., 2003). In Vietnam, in four surveyed stations from Quang Ninh
province to Thai Binh province, the concentration of some metals, such as copper,
exceeded the permissible concentrations (0.01 mg/litre), reaching concentrations of
0.017–0.048 mg/litre of dissolved copper. Mercury contamination may prove very
harmful to aquatic organisms, one third of the samples exceeded permissible
concentrations. In the water layer near the bottom of Bach Dang and Thai Binh river
mouths it was 0.005 mg/litre and in other stations it is now 0.0002 mg/litre. In some
areas, Fe2+ exceeded the permissible concentration (0.50 mg/litre), reaching Fe2+
concentrations of 1.20–1.65 mg/litre (FAO/NACA., 1995)
2.1.4. Effecting of heavy metals to environment and human’s health
Environmental pollution due to toxicity of heavy metals cause ecological
imbalance, decrease crop yield , degrade many populations organisms, and effect to
human's health have been found in many countries around the world. In the mining
areas located in the districts of Jajpur, Keonjhar, Mayurbhanj and Sundargarh districts
of Odisha in India, nearly 45% to 67% of iron and 45% to 54% of chromium
contamination are reported. This high concentration of salts and metals acts as stress to
plants affecting the yield of crops and viability of flora and fauna adversely not only in
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the area of location but all adjoining areas by spreading thus raising concern. The
major effects of heavy metals on seeds are manifested by overall abnormalities and
decrease in germination, reduced root and shoot elongation, dry weight, total soluble
protein level, oxidative damage, membrane alteration, altered sugar and protein
metabolisms, nutrient loss all contributing to seed toxicity and productivity loss (Sunil
Kumar Sethy & Shyamasree Ghosh., 2013). Besides, fish are relatively situated at the
top of the aquatic food chain. The concentrations of heavy metals (Cu, Zn, Pb, Cd, Fe
and Mn) were measured in the liver, gills and muscles of fourteen benthic and pelagic
fish species collected from three main landing areas (Shalateen, Hurghada and Suez)
in the Egyptian Red Sea. The levels of heavy metals varied significantly among fish
species and organs. Thus, the content of toxic heavy metals in fish affected to fish
populations, especially, to human’s health as renal failure, liver damage,
cardiovascular diseases and even death. (Kh. M. El-Moselhy et al., 2014)
The main threats to human health from heavy metals are associated with
exposure to lead, mercury, cadmium, arsenic, copper, zinc, and chromium. Exposure
to arsenic is mainly via intake of food and drinking water, food being the most
important source in most populations. Long-term exposure to arsenic in drinking-water
is mainly related to increased risks of skin cancer, but also some other cancers, as well
as other skin lesions such as hyperkeratosis and pigmentation changes. Occupational
exposure to arsenic, primarily by inhalation, is causally associated with lung cancer.
Clear exposure-response relationships and high risks have been observed. Cadmium
affected to kidney damage but possibly also bone effects and fractures. Mercury can
cause mutations and genetic damage, while copper, lead can cause brain and bone
11


damage. In Thai Nguyen province of Vietnam, people living around Pb-Zn mining
areas occurred some sign of heavy metal poisoning even cancer disease. And in a lead
recycling village in Hung Yen province of Vietnam, a lot of children became less
intelligent than the children in other places of this province (Ha, C. T., 2011).
2.1.5. The characteristics and health effects of Copper.
Characteristics of Copper
Copper was one of the earliest elements known to man. At one time, it could be
found lying on the ground in its native state or uncombined state. Copper's distinctive
red color made it easy to identify. However, the commonly encountered compounds
are copper (II) salts, which often impart blue or green colors. Copper is obtained from
minerals such as azurite, or basic copper carbonate (Cu2(OH)2CO3 ); chalcocite, or
copper glance or copper sulfide (Cu2S); chalcopyrite, or copper pyrites or copper iron
sulfide (CuFeS2 ); cuprite, or copper oxide (Cu2O); and malachite, or basic copper
carbonate (Cu2(OH)2CO3 ). And copper forms a rich variety of compounds, usually
with oxidation states +1 and +2, which are often called cuprous and cupric,
respectively (Holleman, A. F et al., 2001).
Health effects
Copper is an essential micronutrient for both plants and animals. A
micronutrient is an element needed in minute amounts to maintain good health in an
organism. A healthy human has no more than about 2 milligrams of copper for
every kilogram of body weight. However, a large amounts of copper in the human
body are usually a problem. One exception is the condition known as Wilson's disease.
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Some people are born without the ability to eliminate copper from their bodies. The
amount of copper they retain increases. The copper level can become so great it begins
to affect a person's brain, liver, or kidneys. Mental illness and death can result.
(Chemistry Explained, 2016)
2.1.6. Method for treament heavy metals in aqueous solutions
Environmental pollution by heavy metal is arising as the most endangering
tasks to both water sources and atmosphere quality today. Revelation to heavy metals,
even at trace levels, is harmful to human beings. Thus, removal of undesirable metals
from water sources is considered as an important task that is still threatening to
human's health and the environment. There are some effective methods for the
removal of heavy metal ions from water sources such as: chemical precipitation,
membrane filtration, reverse osmosis, solvent extraction, flotation, ion exchange and
adsorption. Among these methods, adsorption offers flexibility in design and operation
and, in many cases it generates high-quality treated effluents. In addition, owing to the
reversible nature of most adsorption processes, adsorbents could be regenerated by
suitable desorption processes for multiple use (B.J. Pan et al., 2009). In addition, many
desorption processes are of low maintenance cost, high efficiency, and ease of
operation (S.P. Mishra, et al., 1996). Therefore, the adsorption process is considered as
one of the major suitable technique for heavy metals removal from water/wastewater
sources.
2.2.

Nanomaterials:

The rapid growth in nanotechnology has spurred significant interest in the
environmental applications of nanomaterials. Nanomaterials are excellent adsorbents
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and catalysts (Khin et al., 2012). Since nanomaterials offer significant improvement
with extremely high specific surface area, numerous associated sorption sites, low
temperature modification, short intraparticle diffusion distance, tunable pore size and
surface chemistry compared to other materials (Ju-Nam and Lead, 2008; Qu et al.,
2013; Chen et al., 2007), extensive research have been carried out to remove heavy
metals from wastewater by developing and using various nanomaterials.
Although traditional sorbents could remove heavy metal ions from waste water
the low sorption capacities and efficiencies limit their application deeply. To solve
these defects of traditional sorbents nanomaterials are used as the novel ones to
remove heavy metal ions in waste water. Compared with traditional materials nanostructure adsorbents have exhibited much higher efficiency and faster rates in water
treatment. Nanomaterials used as sorbents for removing heavy metal ions in waste
water should satisfy the following criterions; (a) the nano sorbents themselves should
be non toxic; (b) the sorbent should have relatively high sorption capacities and
selectivity to the low concentration of pollutants; (c) the adsorbed pollutant should be
removed from the surface of the nano adsorbent easily; (d) the sorbents should be
infinitely recycled. So far, a variety of nanomaterials such as carbon nanotubes, carbon
based material composites, graphene, nano metal or metal oxides, and polymeric
sorbents have been studied in the removal of heavy metal ions from aqueous solution,
and the results indicate that these nanomaterials show high adsorption capacity.

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2.2.1.Titanate nanotubes ( TNT) :

2.2.1.1. Overview of Titanium dioxide:
2.2.1.1.1. Titanium oxidation structures and properties:
Titanium dioxide, also known as titanium (IV) oxide or titania, is the naturally
occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is
called titanium white, Pigment White 6 (PW6), or CI 77891, or CI 77891.
TiO2 is polymorphous and it exits in three types of crystal structure: rutile,
anatase and brookite. The most common are anatase and rutile, since brookite is rather
unstable. Anatase can be transformed into rutile at high temperatures(Floriano et al.,
2014). Brookite with its orthorhombic crystal system can be transformed into rutile
with the application of heat (Kadam et al., 2015).
In all three forms, titanium (Ti4+) atoms are coordinated to six oxygen (O2−)
atoms, forming TiO6 octahedral(Pelaez et al., 2012).
Figure 2.2.1.1.1 was shown the crystal structure of the three forms of titanium
dioxide (Shanon.,2012)

Figure 2.2.1.1.1: Crystal structure of the three forms of titanium dioxide (Source:
Shanon.,2012) ( Ti: Grey; O: Red)

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Titanium dioxide is an n-type semiconductor that has a band gap of 3.2 eV for
anatase, 3.0 eV for rutile, and ~3.2 eV for brookite(Goswami Pallabi., 2012). Titanium
dioxide (TiO2) is the most widely investigated photocatalyst due to its strong oxidative
properties, low cost, non-toxicity, chemical and thermal stability.
2.2.1.1.2. Titanate nanotubes(TNT)
Inspired by the discovery of carbon nanotubes, one dimensional nanostructured
materials have become a research topic owing to their unusual properties and potential
applications. Among the various semiconductors, titanate nanotubes (TNTs) have been
subject of interest because of their cheap fabrication, unique one-dimensional
nanostructure, high surface area and electrical conductivity (D.V. Bavykin et al., 2009;
H.-H. Ou et al., 2007). Titanium dioxide has been intensively investigated as a
potential sorbent due to its high chemical stability in the pH range 2- 14 and because
the process is simple with a fast rate of adsorption and desorption.
Titanate nanotubes (TNT) were prepared by hydrothermal method. These welldefined and uniformly tubular materials are characterized by high specific surface
areas and pore volumes, and they possess good ion-exchange properties (Q. Chen et
al., 2007). Particularly, TNT have many functional hydroxyl groups. All the protons of
these hydroxyl groups may be readily exchanged with heavy metal ions in aqueous
solutions (D.V. Bavykin et al., 2006). Moreover, the hydrothermal method is very
simple with high yield and reusable alkali solutions (Q. Chen et al., 2002). Therefore,
TNT may have great potential to adsorb heavy metals. Doong et al., (2012) fabricated
titanate nanotubes (TNT) using an alkaline hydrothermal method and then calcined at

16


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.
2.2.2. Overview of SiO2:
Silicon dioxide, the most abundant material in the world is also known as silica.
Silica can be found in different forms such as sand, quartz, sandstone, and granite.
In the majority of silicates, the Si atom shows tetrahedral coordination, with 4
oxygen atoms surrounding a central Si atom. In each of the most thermodynamically
stable crystalline forms of silica, on average, all 4 of the vertices (or oxygen atoms) of
the SiO4 tetrahedra are shared with others, yielding the net chemical formula: SiO2.
Figure 2.2.2 shows the crystal structure of SiO2.

Figure 2.2.2 : Crystal structure of SiO2
(Source: Kyawthetlatt., 2013)

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Silica is used primarily in the production of glass, optical fibers for
telecommunications, whiteware ceramics (earthenware, stoneware, and porcelain).
Silica is used as a desiccant. It is the soul material for the semiconductor industry as it
has good thermal and dielectric property. Silicon dioxide also used as the supporting
material of titanium dioxide to enhance the surface areas and the photocatalytic
activity for the adsorption heavy metals.
2.2.3. Overview of nanocomposite
2.2.3.1. Definition and characteristics of nanocomposite
A conbination of two or more materials with different physical and chemical
properties and distinguishable interface defined, that is a composite. With many
advantages of composites over many metal compounds, such as high toughness, high
specific stiffness, high specific strength, gas barrier characteristics, flame retardancy,
corrosion resistance, low density, and thermal insulation.made nanomaterials, in
particular nanocomposites, have diversified applications in different areas such as
biological

sciences,

drug delivery systems,

and

wastewater

treatment.

In

nanocomposites, the nanoparticles were incorporated within different functionalized
materials such as multiwalled carbon nanotubes, activated carbon, reduced graphene
oxide, and different polymeric matrices.
In recent years, water pollution is a huge issue and caused by the pollutants that
result in severe environmental problems. In recent years, various methods for heavy
metal detection from water have been extensively studied. One of the most effective
methods is using nanocomposite. These nanocomposites provide high surface area and

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