The design and synthesis of graphene oxide at iron oxide (GOFexOy) for catalytic application

Celeste Abstract: The thesis describes the oxidation of methylene blue, a basic dye of thiazine series using a Fenton reaction at normal laboratory temperature and at atmospheric pressur

THAI NGUYEN UNIVERSITY

UNIVERSITY OF AGRICULTURE AND FORESTRY

XAYALACK LASY

THE DESIGN AND SYNTHESIS OF GRAPHENE OXIDE

AT IRON OXIDE (GO@FE X O Y ) FOR CATALYTIC APPLICATION

BACHELOR THESIS

Study Mode: Full-time

Major: Environmental science and management

Faculty: International Training and Developing center

Batch: 43 Advance Education Program

Thai Nguyen, October 2015

DOCUMENTATION PAGE WITH ABSTRACT

Thai Nguyen University of Agriculture and Forestry

Degree Program Bachelor of Environment science and Management Student name Xayalack Lasy

Thesis title The design and synthesis of graphene oxide at iron

oxide (GO@FexOy) for catalytic application

Supervisors

Assoc Prof DR Tran Van Dien Assoc Prof Yu-Fen Huang PhD Student He YuePhD Student Celeste Abstract:

The thesis describes the oxidation of methylene blue, a basic dye of thiazine series using a Fenton reaction at normal laboratory temperature and at atmospheric pressure and the advantages in use of magnetic nanoparticles (MNPs), graphene oxide @iron oxide nanoparticles(GO@FexOy) in the reaction Oxidation by Fenton

reactions is proven and economically feasible process for destruction of a variety of hazardous pollutants in wastewater MNPs were synthesis via a thermal decomposition method and (GO@FexOy) via electrooxidation procedure The

synthesis of MNPs and (GO@FexOy) was characterized by several techniques,

Ultraviolet–visible spectroscopy (UV-Vis), and Transmission Electron Microscopy (TEM)

The concentrations of dye degradation were determined ectrophotometrically using Plate Readers at 665 nm, the absorption maximum of the dye

Keywords: Fenton reaction, nanocomposite, magnetic

nanocomposites, Graphene oxide @ iron oxide nanoparticles, absorption, methylene blue, H2O2.Number of pages: 40 pages

Date of submission: September 30, 2015

Supervisor’s signature

ACKNOWLEDGEMENT

First of all, we know that knowledge is just only can be proved by our works, and internship is one of the best opportunity for student whose can do their first project before they find their jobs to enroll in the future Besides that, we are not only improving ourselves by knowledge in company environment, institute or laboratory but also making more friends whose are having many experiences in environment, and

it will help us in the near future From my perspective, this internship is absolutely needed, helpful and important

Because of that, and be assigned by the International Training Center and also the allowed of Department of Biomedical Engineering and Environmental Science (National Tsing Hua University, Taiwan) To well done this thesis, I want to express profound gratitude to Advanced Education Program, the school administrators, the staffs in Department of Biomedical Engineering and Environmental Science, the staffs

of YF laboratory, and particularly my supervisor, Associate Prof DR Tran Van Dien and Associate Professor Huang Yu Fen whose is always support me every single time

I got troubles I would like to send both of supervisor a warmly thanks for the supporting me, and for their sacrifice for education, as same as environmental issues in Taiwan and Vietnam as all countries in the world

Finally, I would like to say that I have tried my best to finish this thesis in the best way, I guess However, to be honest, I partly believe that my thesis still have some problems because of the limitation of knowledge and reality experiences, especially in our environmental circumstances these days It is totally happy if I can get feedbacks and comments from you, my teachers, Professor, and Supervisor, to finish my thesis in a fantastic way, to get the best results

Sincerely,

Thai Nguyen, October, 2015

Student

Xayalack Lasy

STATEMENT BY THE AUTHOR

I hereby declare that this submission is my own work from doing my experimental research and to the best of my knowledge, it contains no material previously published, nor material which to a substantial extent has been accepted for the award of any other degree or diploma at any educational institution, except where due acknowledgement is made in the thesis

TABLE OF CONTENTS

CHAPTER I INTRODUCTION 1

1.1 Rationale .1

1.2 Objectives .2

CHAPTER II LITERATURE REVIEW 3

2.1 Nanotechnologies and Nanomaterial .3

2.1.1 Nanotechnologies .3

2.1.2 Nanomaterial .4

2.1.3 Methods synthesis of nanomaterial .6

2.1.4 Overview of research and application of nanomaterial and nanocomposite 8

2.1.5 Magnetic NPs and application of magnetic NPs in wastewater treatment 11

2.2 Fenton reaction in the degradation of methylene blue 13

2.3 The use of magnetic nanocomposites in catalytic degradation of methylene blue 14

2.4 The equipment used to determine the properties of gold nanoparticles and methylene blue degradation 15

2.4.1 Ultraviolet–visible spectroscopy (UV-Vis) 15

2.4.2 Transmission Electron Microscopy (TEM) 15

CHAPTER III METHODOLOGY 18

3.1 Preparation of magnetic nanoparticles and Graphene oxide@iron oxide 18

3.1.1 Method synthesis Fe3O4 NPs 18

3.1.2 Method synthesis FeOx, GO@FexOy andGO-Au,FeOx 19

3.2 Fenton reaction and the use of Magnetic NPs and Graphene oxide@

iron oxide NPs in in Fenton reaction for catalytic degradation of dye 21

3.2.1 Chemicals and equipment 21

3.2.2 Method preparation stock solution: 22

3.2.3 Procedure 25

CHAPTER IV RESULTS AND DISCUSSIONS 26

4.1 Characterizations 26

4.1.1 Magnetic nanoparticles 26

4.2 Magnetic NPs and Graphene@iron oxide NPs apply in Fenton reaction

degradation of methylene blue 27

4.2.1 Standard Fenton-like reaction for degradation of methylene blue 27

4.2.2 Application of magnetic nanoparticles,graphene oxide @iron-oxide on degradation of MB 31

4.2.3 The use of MNC, GO-FeOx in degradation of dye 34

CHAPTER V CONCLUSIONS AND RECOMMENDATION 36

5.1 Conclusions 36

5.2 Recommendation 36

REFERENCE 37

LIST OF FIGURES

Figure 1.1 Diagram of principle synthesis of nanomaterial 6

Figure 1.2 Ultraviolet–visible spectroscopy (UV-Vis) 15

Figure 1.3 Schematic diagram of a TEM Generally, TEM is divided into two main parts: illumination and imaging 17

Figure 1.4 Setup for synthesis MNC 18

Figure 1.5 Setup usingsonicators method 19

Figure 1.6 Setup for extract Fe3O4 NPs by centrifuging 19

Figure 1.7 Scheme for synthesis iron oxide, Graphen at iron

oxide and Graphen at gold,iron oxide nanoparticles 20

Figure 1.8 Using plastic tubes to containing the solutions of MB

degradation on the magnetic stirrer 25

Figure 1.9 TEM images of Fe3O4 NPs in different scale bar:

(a) 50 nm; (b) 100 nm 26

Figure 2.0 dynamic light-scattering (DLS) 27

Figure 2.1 UV–Vis spectra of 3.13×10-5 M methylene blue solution at 0 min (control) with absorption maximum at 665 nm 27

Figure 2.2 Temporal UV–Vis spectra absorption showing

changes the concentration of methyleneblue during Fenton reaction: a)

at 0min; b) at 60min 28

Figure 2.3 Degradation of methylene blue by Fe (II) (pH 2-3) 28

Figure 2.4 Effect of [Fe2+] on degradation of MB at 60 minutes 29

Figure 2.5 Effect of [H2O2] on degradation of MB at 30 minutes 30

Figure 2.6 Effect of pH on degradation of MB 30

Figure 2.7 Degradation of methylene blue by Fe (II); Fe (II) + Fe (III) and Fe (III) at pH 2-3 31

Figure 2.8 the degradation of MB by GO-FeOx 3h 32

Figure 2.9 the degradation of MB by GO-Au,FeOx 5V 32

Figure 3.0 Detection of Concentration of GO-FeOx 3h

and GO-Au, FeOx 5V 34

Figure 3.1 UV-vis absorption spectra of GO and GO-FeOx 35

Figure 3.2 recycle the degradation of GO-FeOx on MB 35

LIST OF TABLES

Table 1.1 Chemicals used in the experiment 21

Table 1.2 Preparation of Methylene blue stock solution 22

Table 1.3 Preparation of H2SO4 stock solution 22

Table 1.4 Preparation of Fe2+ within H2SO4(0.1M)stock solution 23

Table 1.5 Preparation of Fe2+ without H2SO4stock solution 23

Table 1.6 Preparation stock solution of Fe2+ 24

Table 1.7 Preparation stock solution of H2O2 25

Table 1.8 detection concentration of GO-FeOx 3h and GO-Au,FeOx 5V 33

MB Methylene Blue

Ppb Part per billion

Ppm Part per million

RO reverse osmosis SAM the scanning acoustic microscope STM Scanning Tunneling Microscope TEM Transmission Electron Microscopy UV-Vis Ultraviolet–visible spectroscopy

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CHAPTER I INTRODUCTION

1.1 Rationale

The Environment includes the natural resources and the artificial material factors, and they have a close relationship with each other, surrounded by humans, affecting to productive life, and the survival and the development of human and natural course

These days, with the advancement of science, engineering and technology, human has made great achievements in various fields As the increase of industrialization and urbanization in many developed cities, the requirement of removal of small amounts of toxic pollutants in the ppm or ppb level from industrial wastewater and contaminated groundwater is increasingly becoming significant Chemical industries, such as oil refineries, petrochemical units, dye and dye intermediate manufacturing industries, textile units, industries making paper, pharmaceuticals,cosmetics and synthetic detergents, and tanneries are the typical industries that discharge toxic organic compounds at low concentrations, thus making the water polluted (Kabita Dutta et al., 2001)

In this context, a new process for wastewater treatment in order to degrade or removing these compounds in textile industryeffluents is an important issue An extensively studied is the use of advanced oxidation processes (AOP) These processes are based on the formation of hydroxyl radicals, which are capable of oxidizing contaminutesants to smaller and less polluting molecules or even minuteseralize them, turning them into CO2, H2O, and inorganic ions from atoms Fenton’s chemistry is very well known and it is one of the high potential oxidation technologies because it produces a highly reactive species [OH•]

Currently, there is a lot of wastewater from industries causes the problem of the environmental management in the world in general and Vietnam in particular We have

to design collection systems and processing, and it is not only necessary for residential areas or factory area but also even the new place area planning to improve the urban environment and sustainable development nanotechnology is gradually changing

people's lives With its small nanometer size nanomaterials have very unique characteristics than other bulk materials with less mechanical strength, strong catalytic activity and the ability to absorb excess

According to the research results from domestic and foreign authors about the catalytic capacity of the magnetic nanocomposite preform good in Fenton reaction; the aim in this study was about to using the magnetic nanocomposite and Fenton reaction

to demonstrate the degradation in water pollutants, a study: “THE DESIGN AND

* Determine optimum of H2O2 concentration on degradation of methylene blue

by magnetic nanocomposite for degradation of dye in textiles industry

* Determine optimum of new chemical materials that suitable with researching experiment on degradation of Methylene blue

* Assess the efficiency of use magnetic nanocomposite in Fenton’s reaction to orientate the application in wastewater treatment technology

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CHAPTER II LITERATURE REVIEW

2.1 Nanotechnologies and Nanomaterial

2.1.1 Nanotechnologies

Nanotechnology (nanotech) is the manipulation of matter on

an atomic, molecular, and supramolecular scale The earliest, widespread description

of nanotechnology (Drexler & Eric, 1986) referred to the particular technological goal

of precisely manipulating atoms and molecules for fabrication of macro scale products, also now referred to as molecular nanotechnology A more generalized description of nanotechnology was subsequently established by the National Nanotechnology Initiative, which defines nanotechnology as the manipulation of matter with at least one dimension sized from 1 to 100 nanometers This definition reflects the fact that quantum mechanical effects are important at this quantum-realm scale, and so the definition shifted from a particular technological goal to a research category inclusive

of all types of research and technologies that deal with the special properties of matter that occur below the given size threshold It is therefore common to see the plural form

"nanotechnologies" as well as "Nanoscale technologies" to refer to the broad range of research and applications whose common trait is size Because of the variety of potential applications (including industrial and military), governments have invested billions of dollars in nanotechnology research Until 2012, through its National Nanotechnology Initiative, the USA has invested 3.7 billion dollars; the European Union has invested 1.2 billion and Japan 750 million dollars (Daily Star, 2012).

Nanotechnology as defined by size is naturally very broad, including fields of science as diverse as surface science, organic chemistry, molecular biology, semiconductor physics, Microfabrication, etc (Saini et al, 2010) The associated research and applications are equally diverse, ranging from extensions of conventional device physics to completely new approaches based upon molecular self-assembly, from developing new materials with dimensions on the Nanoscale to direct control of matter on the atomic scale

As a whole nanotechnology are technology sectors relevant to the analysis, design, fabrication and application of structures, devices and systems by controlling shape, size on the nanometer scale

According to National Nanotechnology Initiative-NNI of United State of America, nanotechnology includes:

- Research and development technology at the nanoscale with diameter size range from 1 nm to 100 nm

- Generating and use the structures, devices and systems with new properties and functions due to their very small size

2.1.2 Nanomaterial

Nanomaterials are materials in which at least one-dimensional nano-meter size Regarding the states of the material is divided into three states: solid, liquid and gas Currently, nanomaterials are studied mainly in solid state

About the shape material, it's splited into the following categories: dimension with nanoscale (nanoparticles, nano clusters), two-dimension with nanoscale (film), one-dimensional (thin wire) In addition, there are nanostructured materials or nanocompozit in which only a portion of nanoscale materials or its nano structures have no dimensional nanoscale

three-Therefore the nonmaterial includes subfields which develop or study materials having unique properties arising from their nanoscale dimensions (Narayan et al, 2004)

•Interface and colloid science has given rise to many materials which may be useful in nanotechnology, such as carbon nanotubes and other fullerenes, and various nanoparticles and nanorods Nanomaterials with fast ion transport are related also to nanoionics and nanoelectronics

•Nanoscale materials can also be used for bulk applications; most present commercial applications of nanotechnology are of this flavor

•Progress has been made in using these materials for medical applications; see Nanomedicine

•Recent applicationof nanomaterials include a range of biomedical applications, such as tissue engineering, drug delivery, andbiosensors (David et al., 2015)

2.1.2.1 Characteristics and properties of nanomaterials

An extremely important characteristic of nanomaterials is that the diameter size

is only in nanoscale Therefore, the total number of atoms on the surface distribution

of nanomaterials and the total surface area of the material is much greater than with conventional materials This has appeared in many feature nanomaterials anomalies, especially the ability to absorb catalyst With its small size at the molecular level, nanomaterials appear three main effects: quantum effects, surface effects, effect size

2.1.2.2 Nanocomposite

The term "nanocomposite" describes a group of composite materials, in which enhanced phase only at nanometer dimensions The presence of this enhanced phase was to generate major improvements in the physical and mechanical properties of nanocomposite materials (Kumar & Krishnamoorti, 2010).The nanocomposite either combining the precious nature of nanomaterials anomalies or it has separate nature of each of the constituents In composite materials based on goals that people made use

of different materials The presence of enhanced phase generates the products which their properties of the components are not at the original The nanocomposite is a material with many applications in many fields So studying on nano composite materials is an important direction and being strongly developed Enhanced phases in the nanocomposite usually are nanoparticles, colloidal particles, nano membrane fibers Carriers in the nanocomposite material often are polymers, carbon fiber, the salt, zeolite and silica, bentonite (Anh, 2007)

2.1.3 Methods synthesis of nanomaterial

Nanomaterials are made using two methods

- Top-down method (top-down), the method of nanoparticles from particles of larger size

- Bottom-up method (bottom-up), methods formed nanoparticles from atoms

Figure 1.1 Diagram of principle synthesis of nanomaterial

2.1.3.1 Top-down method

The principle of this method is crushing and deformation techniques for processing materials with organizing mass of coarse grain size of nanoparticles This method is simple, inexpensive but very effective, can be carried out for a variety of materials with relatively large size In the method of crushing, material in powder form mixed with balls made of very hard material and placed in a mortar Crusher can be crushed shaking, vibrating mill or mill spinning The hard balls collide and break down powders to nanoscale The result is non-dimensional nanomaterials (nanoparticles) Deformation method is used with a special technique to create extremely large deformation without destroying the material (probably > 10 nm) The temperature can be adjusted depending on each specific case If the process temperature is greater than the crystallization temperature is called the hot deformation, while the opposite is called cold deformation The result is a one-dimensional nanomaterials (nanowires) or bidirectional (nm layer thickness)

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However, the disadvantage of this method is that generate materials that are not homogeneous high energy-consuming and complex equipment (Bönnemann et al, 2004)

2.1.3.2 Bottom-up method

The principle of this method is the formation of nano materials from atoms or ions The method was developed from the bottom- up very strongly for flexibility and quality of the final product Most of the nanomaterials that we use today are made by this method The advantage of this method: convenience, the size of nanoparticles generated relatively small, uniform, equipment and service for this method is very simple Bottom-up method can be physical methods, chemical or a combination of both physico-chemical methods

* Physical methods:The method of creating nanomaterials from atoms or transition Atoms to form nanomaterials are created from physical methods such as thermal evaporation Method transition: the material is heated and then allowed to cool

at a faster rate in order to obtain an amorphous state, heat treatment to occur transformation of amorphous - crystalline (crystallized) Physical methods are often used to create nanoparticles, nano film

* Chemical methods: the method of creating nanomaterials from the ion Chemical methods are characterized by very diverse because, depending on the specific material that they have technical changes made accordingly However, we can classify the chemical methods into two categories: nanomaterials formed from the liquid phase (precipitation, sol-gel), and from the gas phase (pyrolysis) This method can produce nanoparticles, nanowires, nanotubes, nano film, nano powder

* Combined method: the method to create nanomaterials based on the principles

of physics and chemistry, such as electrolytic condensation from the gas phase this method can produce nanoparticles, nanowires, nanotubes, nano thin-film, nanopowders

•Synthetic chemical methods can also be used to create synthetic molecular motors, such as in a so-called nanocar

2.1.3.4 Biomimetic approaches

•Bionics or biomimicry seeks to apply biological methods and systems found in nature, to the study and design of engineering systems and modern technology.Biomineralization is one example of the systems studied

•Bionanotechnology is the use of biomolecules for applications in nanotechnology, including use of viruses and lipid assemblies (Mashaghi et al., 2013) Nanocellulose is a potential bulk-scale application

2.1.4 Overview of research and application of nanomaterial and nanocomposite

Nowadays, the research and applications of nanotechnology in the world are interested in many countries Some powers dominate the technology market currently such as the US, Japan, Taiwan, China, Germany, Russia and some European countries In these countries, government devoted a significant budget support for the research and practical applications of nano technology Not only laboratories in the universities with equipment-study scale but the production corporations also conduct research and development of nanotechnology with laboratory with total cost studies equivalent the government budget for nanotechnology

In Vietnam as in some countries that located in Asia, tend to approaching with nanotechnology in recent years has generated very charismatic movement on this field The government has spent a large budget for research programs nanotechnology national level with the participation of many universities and research institutes in the country, initially gained encouraging results The reason that nanotechnology is focused on developing due to magic applications that nanotechnology has been

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achieved in the field of science and technology The following is the application of nanotechnology has the advantage

2.1.4.1 Tool and Electronic Technology, Information Technology

There are several important modern developments The atomic force microscope (AFM) and the Scanning Tunneling Microscope (STM) are two early versions of scanning probes that launched nanotechnology There are other types of scanning probe microscopy Although conceptually similar to the scanning confocal microscope developed by Marvin Minskyin 1961 and the scanning acoustic microscope (SAM) developed by Calvin Quate and coworkers in the 1970s, newer scanning probe microscopes have much higher resolution, since they are not limited by the wavelength of sound or light

The tip of a scanning probe can also be used to manipulate nanostructures (a process called positional assembly) Feature-oriented scanning methodology may be a promising way to implement these Nano manipulations in automatic mode (Lapshin, 2004) However, this is still a slow process because of low scanning velocity of the microscope

In the information technology needs to use large memory capacity increasing Scientists have researched and generated computer chips with quantum dots called nano chip with very high integration level, allowing increased memory capacity of the computer Nanotechnology can also be applied in the fabrication of optoelectronic components in the liquid crystal display, laser transmitters, sensors with the precision of a few nanometers (Komatsu & Ogasawara, 2015)

* Biomedical

- Separation and selective cell: Based on the characteristic superparamagnetic of

magnetite nanoparticles, researchers have used it to conduct cell separation The process is split into two phases: biological marker that really need to study through the magnetic nanoparticles Then separating the entities marked out by an external magnetic field environment

- Drug delivery: When entering the body, drug is often scattered and unfocused affect healthy cells, producing side effects Therefore scientist use magnetic particles

as drug carriers to the desired location on the body (tumors, cancer ) by an external magnetic field

- Local hyperthermia: This method is used in cancer treatment The magnetic nanoparticles are dispersed in the diseased tissue, then use an external alternating magnetic field of sufficient intensity and frequency is applied to the ferromagnetic nanoparticles, the nanoparticles do respond and make the local thermal heating cancer cells (about 42°C) At this local temperature can kill the cancer cells (Cu & Chanh, 2004)

* New energy

With nanotechnology, it is possible to generate new battery capable of artificial photosynthesis, helping human to produce clean energy, or generate these devices consume less energy by using these materials soft material The film nano (with low production costs) promising absorb more solar energy than current photovoltaic materials This is the start of a revolution in the use of solar energy

2.1.4.2 Environmental treatment technology

Environmental treatment material is being concerned, especially materials used for water purification technology The filter was created by nanotechnology with the filter diameter hole just like nano film for reverse osmosis (RO), microfiltration membrane can filter bacteria and viruses in water and separated on 99.8% of all types of water-soluble substances (Tam, 2014)

Recently, Japanese scientists have discovered a bacteria eating suspended in water and the magnetic nanoparticles When the organisms were fed (organic pollutants and the magnetic nanoparticles) full, they will be deposited and separated from the water by an external magnetic field

substances-Nanomaterials have area and electronic distribution on the surface is much larger than the bulk materials Thus, nanomaterials appear more outstanding features, especially the ability to catalyze, absorb Taking advantage of that advantages, scientists have been studying in depth to explore generating advanced materials, used

in the field of environmental treatment: adsorbent, the material capable of catalytic processing of inorganic and organic compounds, and volatile gases

In environmental treatment technology, MNPs have absorbed capacity of two states of arsenate - As (III) and arsenit-As (V), capacity to absorb 200 times higher than bulk material (World Bank, 2005) Especially, it has catalytic capacity in wastewater treatment for degradation of organic pollutants in water

2.1.5.2 Application of Magnetic nanoparticles in wastewater treatment

Selection of the best method and material for wastewater treatment is a highly complex task, which should consider a number of factors, such as the quality standards

to be met and the efficiency as well as the cost (Huang et al., 2008) Therefore, the following four conditions must be considered in the decision on wastewater treatment technologies: (1) treatment flexibility and final efficiency (2) reuse of treatment agents, (3) environmental security and friendliness, and (4) low cost (Zhang & Fang

M, 2010) Fe3O4 MNPs are promising for industrial scale wastewater treatment, due to their low cost, strong adsorption capacity, easy separation and enhanced stability (Kumpiene et al., 2009) The ability of Fe3O4 MNPs to remove contaminants has been demonstrated at both laboratory and field scale tests (Mater, 2009) Current applications of Fe3O4 MNPs in contaminated water treatment can be divided into two groups: (a) technologies which use Fe3O4 MNPs as a kind of nanosorbent or immobilization carrier for removal efficiency enhancement (referred to here as adsorptive/ immobilization technologies), and (b) those which use Fe3O4 MNPs as photocatalysts to break down or to convert contaminants into a less toxic form (i.e

photocatalytic technologies) However, it should be noted that many technologies may utilize both processes

* Adsorptive technologies

- Magnetic NPs as nanosorbents for heavy metals:The majority of bench-scale research and field applications of materials for wastewater treatment has currently focused on magnetic NPs, carbon nanotubes, activated carbon, and zero-valent iron Among these, it seems that Fe3O4 MNPs, possessing the capability to treat large volume of wastewater and being convenient for magnetic separation, are most promising materials for heavy metal treatment ( Wang et al., 2010)

Fe3O4 MNPs could illustrate excellent superiority In a study performed by Nassar (2010), it was found that the maximum adsorption capacity for Pb (II) ions was 36.0 mg g−1 by Fe3O4 nanoparticles, which was much higher than that of reported low cost adsorbents The small size of Fe3O4 nanosorbents was favorable for the diffusion

of metal ions from solution onto the active sites of the adsorbents surface It recommended that Fe3O4 nanosorbents were effective and economical adsorbents for

rapid removal and recovery of metal ions from wastewater effluents

- Magnetic NPs as nanosorbents for organic contaminants:as a well-known separation process, adsorption has been widely applied to remove chemical pollutants from water It has numerous advantages in terms of cost, flexibility and simplicity of design/operation, and insensitivity to toxic pollutants Therefore, an effective and low-cost adsorbent with high adsorption capacity for organic pollutants removal is desirable Fe3O4 MNPs are currently being explored for organic contaminant adsorption, particularly for the efficient treatment of large-volume water samples and fast separation via employing a strong external magnetic field A lot of experiments have been undertaken to examine the removal efficiency of organic pollutants by using

Fe3O4 MNPs for organic pollutants (Zeng et al, 2007) For example, Fe3O4 hollow nanospheres were shown to be an effective sorbent for red dye (with the maximum adsorption capacity of 90 mg g−1) (Iram et al., 2010) The saturation magnetization of prepared nanospheres was observed to be 42 emu g−1, which was sufficient for magnetic separation with a magnet (critical value at 16.3 emu g−1) These proved that

Fe3O4 MNPs for the photocatalysis of toxic compounds: (a) the separation of materials after the treatment process tends to be expensive owing to man power, time and chemicals used for precipitation followed by centrifugation or decantation at the end of treatment process, and (b) the low quantum-yield of treatment process restricts the kinetics and efficiency

Fe3O4 MNPs can be a good photocatalyst absorbing visible light Compared with commonly applied TiO2, which mainly absorbs UV light with wavelengths of b380

nm (covering only 5% of the solar spectrum) due to its wide band-gap of 3.2 eV,

Fe2O3 with band-gap of 2.2 eV is an interesting n-type semiconducting material and a suitable candidate for photodegradation under visible light condition The better photocatalytic performance of Fe3O4 MNPs than TiO2 can be attributed to considerable generation of electron–hole pairs through the narrow band-gap illumination (Bandara

et al., 2007)

* Immobilization carriers

Fe3O4 MNPs have also shown considerable potential in the immobilization of biomass The biosorption capacity of a variety of macro and microbial biomass has been widely used to remove various pollutants Fe3O4 MNPs can offer larger surface areas and multiple sites for interaction or adsorption In particular, due to the advantage of chemical inertness and favorable biocompatibility, Fe3O4 MNPs has been widely used in immobilization technology

2.2 Fenton reaction in the degradation of methylene blue

A variety of physical, chemical and biological methods are presently available for the treatment of polluted water Biological treatment is a good and promising as well as cost effective technology but it has a number of disadvantages Physical

methods such as liquid-liquid extraction, ion exchange, GAC adsorption, air stripping etc are ineffective for pollutants which are not adsorbable or volatile similarly these technologies only transfer the pollutant from one phase to another phase In the light of limitations of these methods, the chemical oxidation methods are capable to almost complete mineralization of organic pollutants and effective to the wider range of pollutants (Sanjay, 2004)

Among the chemical oxidation methods, oxidation by Fenton’s reagent is popular method Advantages of Fenton’s reagent over other oxidizing treatment are numerous, including simplicity, suitability to treat a wide range of substance, no special equipment is needed etc (Arnold, 1995) Generally in Fenton’s process ferrous ion is commonly used with the H2O2 as a source of OH• radical in presence or absence

Methylene blue has been selected a refractory model compound in this oxidation process Methylene blue is a basic dye extensively used for dying and printing cotton, silk, etc It is also used as a medicinal dye because of its antiseptic properties (Sanjay, 2004)

2.3 The use of magnetic nanocomposites in catalytic degradation of methylene blue

Magnetic field was tentatively introduced into Fenton reactions system for the degradation and discoloration of methyl blue as the represent of organic chemical dye, which was a bio-refractory organic pollutant in industry wastewater It was found that under optimal Fenton reaction conditions, with the assistant of magnetic field in Fenton reactions, the degradation rate of methyl blue, the decomposition rate of H2O2

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and the conversion rate of Fe2+ were accelerated, the extent of them would be

improved by the increase of magnetic field intensity (Hao et al., 2009)

2.4 The equipment used to determine the properties of gold nanoparticles and methylene blue degradation

2.4.1 Ultraviolet–visible spectroscopy (UV-Vis)

The analytical method is widely used for a long time Ultraviolet and visible spectrum (UV-Vis) of organic compounds associated with electron transition between the energy levels of electrons in the molecule when the electron transfers from the energy low energy level high

Figure 1.2 Ultraviolet–visible spectroscopy (UV-Vis)

Energy transition: under normal conditions, the electrons in the molecule is in the ground state, the light stimulus with appropriate frequency, the electron will absorb energy and transfer to the excited state have a higher energy level

2.4.2 Transmission Electron Microscopy (TEM)

Transmission electron microscopy is a microscopy technique in which a beam of electrons is transmitted through an ultra-thin specimen, interacting with the specimen

as it passes through An image is formed from the interaction of the electrons transmitted through the specimen; the image is magnified and focused onto an imaging