STUDY ON SYNTHESIS AND CHARACTERIZATION OF NEW MATERIALS BASED NANOSTRUCTURES OF GRAPHENE APPLIED IN ENVIRONMENTAL TREATMENT

In recent years, carbon materials and the carbon based materials are widely used as effficient adsorbent because of high specific surface, stabilization and resistance to chemical and th

Major: Theoretical chemistry and physical chemistry

Code: 62.44.01.19

SUMMARY OF CHEMICAL DOCTORAL THESIS

Hanoi – 2016

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INTRODUCTION

1 The urgency of the thesis

While industry dramatically develops, agriculture also pays the main role in the expansion of national economy However, as a consequence of expanding ecomomy, water resouces are effected by the toxic agents coming from planting and feeding These poisons can be biologicallly deposited in the water, which leads to harm the life of uder water creatures as well as the human life Therefore, not only heightenned the environment protection attitude, Government should find the way to remove the contaminants (heavy metal ions, dye, pesticide…) from aqueus solution

In recent years, carbon materials and the carbon based materials are widely used as effficient adsorbent because of high specific surface, stabilization and resistance to chemical and thermal agent Moreover, this type of material is easy modified, which leads

to create the new chemical and physical properites such as decomposating the dye and heavy metal ions Further more, the modified material can increase the adsorption capacity and selectivity for removal of the toxic agents in the waste

The nano structured carbon materials, such as carbon nano tubes, are familiar with people Because of the high cost in producing, it is limited for the application So, investigation of new adsorbents based on carbon material has received a great of interest Graphene and Graphene based material are the answers Actually, graphene is introduced in 2004 but it received a Nobel price for this material in 2010 This material is more and more popular and it is used in the various field: Electronics, photo electronics, electrical chemistry, mechanics and optics are examples

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The graphene is a new carbon material Basically, it is defined as one carbon atomic or several carbon layers with sp2 bonding which forms the crystallization type like honey bee Thank to their unique physical and chemical properties, graphene and GO (grapahene oxide) have many applications, including adsorption area Although many studies on synthesis and application ability of graphene based material are reported The studies of the modifed graphene still less focused and investigated Moreover, the technique which produced and modifies GO from graphene oxide layer by using microwave and the reduction from GO to rGO by using thermal reduction still less reported

Thus, regarding the reasons mentionned above, we choose the

subject of the thesis: “Study on synthesis and characterization of new materials based nanostructures of graphene applied in environmental treatment”

2 Objectives of the thesis

Synthesis and characterization of the GO (exfoliation by using the microwave (GOVS) and ultrasonic (GOSA) technigues), rGO, Fe3O4-GO, Fe-Fe3O4-GO and evaluation of these adsorbents for removal of activated dyes, asenic and heavy metal ions

3 Main contents of the thesis

- The parameters affect on the GO synthesis by using microwave and ultrasonication; reduction GO to rGO Characterizing the sythesized GO, rGO and Graphite oxide

- The factors affect on the synthesis Fe3O4-GOVS material such as

pH, concentration ratio Fe3+/Fe2+, temperature and stir speed

- Synthesi of Fe-Fe3O4-GOVS

Chapter 2:: Investigating method and experiment

Chapter 3: Results and Dicussions

Conclusion

List of works has been published

New findings of the thesis

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CHAPTER 2: EXPERIMENT AND INVESTIGATION METHOD

There are 22 pages in this chapter which consist of:

- Synthesizing Fe-Fe3O4-GO by chemical reduction method by using NaBH4 as reducing agent

- Eveluation of the adsorption ability of synthesized materials for RR195, Cd(II), Cu(II) and As(V) Adsorption by Langmuir and Feundlich model

- In order to investigate the kinetics of adsorption based on the pseudo-first-order and pseudo-second-order equations

2.2 Characterization methods

- Chemical determination composition: EDX, XPS, UV-Vis, AAS

- Characterizing material method: XRD, TEM, HR-TEM, BET, FTIR, XPS, FE-SEM, VMS (vibration magnetometer system)

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CHAPTER 3: RESULTS AND DISCUSSION

This chapter contains 72 pages The details are:

3.1 The factors affect on the synthesis of GO and rGO

3.1.1 XRD results of Graphite before and after oxidation

The XRD results show that for Graphite-Sigma Aldrich the peak 2θ = 26,5o is existed, characterizing the Graphite material Moreover, the peak 2θ = 11o is the evidence of the oxygen bonding formation between Graphite layers, which leads to the formation of

GO structure

3.1.2 The factors affect on the exfoliation of GO by microwave and ultrasonic technique

* The effect of microwave time: 1,2,3 and 4 minutes

Conditions: microwave power 700 W, graphite oxide weight 1g Basing on the recovery efficiency and XRD results of all

samples, the suitable microwave time is 2 minutes

* The effect of microwave power: 216, 700, 1000 and 1200 W

Conditions: graphite oxide weight 1g, microwave time: 2 minutes with different microwave powers The results of XRD, FTIR show that the microwave power is 700 W

* The effect of ultrasonic time on the GOSA process from graphite oxide: 30, 60 and 120 minutes

On this investigation, the ratio Graphite oxide/H2O at 2 mg/mL, the graphite oxide weight at 0,1 g and power 40 W are fixed According to the XRD and HR-TEM results, the suitable ultrasonic

time is 60 minutes

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3.1.4 The effect of temperature on the reduction of GOVS to rGO

The thermal reduction performed at 400, 600, 800 and 1000 oC with heating rate 20 oC/minute and N2 gas flow 15-20 mL/minute Combining with the purpose of saving energy, the results of XRD and FTIR give 600 oC as the best temperature for reduction The yield of this process is in the range of 50 - 60%

3.2 The characterization of synthesized GO and rGO

3.2.1 X-ray Diffraction methods (XRD)

In the XRD patterns of GOVS and GOSA there are characteristic peaks at 2 = 11,5o and 11,2o, respectively, while for rGO it show a peak

at 2 = 25,8o, which confirm the structure of GO and rGO

3.2.2 Fourier transform infrared spectroscopy (FTIR)

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Thank to these spectroscopies, there is the carbony group – C=O (in range 1700 -1730 cm-1) in the samples Beside the carbony group, there are other groups existed in these samples C–O in the range of 1200-1250 cm-1, C=C in aromatic compound in the range of 1500-1600 cm-1 and C-O-C in the range of 1060 cm-1 are examples Moreover, beacause of the peak from 3400 – 3850 cm-1, OH group is existed, which is slightly changed to the range of 3460 – 3500 cm-1after supersonic process Moreover, the peak of other groups are also undergone the change within this process More detail is C=C at

1633 cm-1, C-O at 1168 cm-1 and carbonyl at 1728 cm-1 It is interesting that, after thermal reduction, the FTIR result of rGO does not contain the characterized peaks of GO (fig 3.9) which demonstrates the loss of huge amount of the functional group on GO surface

3.2.3 High Resolution Transmission Electron Microscope (HR – TEM)

The calculation from HR-TEM indicates that the number of layers of GOSA, GOSV and rGO are 10, 7-8 and 5-6, respectively Moreover, the gap between each layer is about 0,4 nm for rGO, 0,6 nm

3.2.4 N 2 adsorption–desorption isotherms (BET)

This method determines the specific area, pore size, volume and the pore distribution of material The BET results of synthesized

material are in table 3.3

Table 3.3 The parameters of GOSA, GOVS and rGO

Micro-capillary volume (cm3/g) 0,0004 0,0015 0,018 Total capillary volume (cm3/g) 0,283 1,719 1,596 Average of capillary diameter (nm) 9,6 - 21,4 7,8 - 21,2 8,8 - 22,5

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From the Table 3.3, the GOVS and rGO have the high specific

area and these are 6 times higher than that of GOSA

3.2.5 X-ray photoelectron spectroscopy (XPS)

As the results of XPS:

- There are huge amount of oxygen in the functional group existing

on GOSV and GOSA and the number of these group is dramatically decreased in rGO

- The thermal reduction from GO to rGO are clearly demonstrated by the peak of π→π* in the aromatic compound at 291,5 eV

- On the thermal reduction process from GO to rGO, the ratio of C/O increases from 2,32 (GOSA) and 2,98 (GOVS) to 6,15 and 10,89, respectively

The composition of elements in GOVS, GOSA and rGO is in table 3.4

Table 3.4 The composition of elements in GOVS, GOSA and rGO (%At)

3.3 The factors effect on the Fe 3 O 4 -GOVS synthesizing

In this part, we focus on synthesizing and evaluating the properties

of Fe3O4-GOVS synthesized by co-participation method By this way, the products have the small particle size, fine distribution and easy to recover

by the external magnetic field

3.3.1 The effect of co-participation reaction temperature

For clearly showing the effect of co-participation reaction temperature on the morphology, phase change and size of Fe3O4-GOVS Nano, the samples are made under the various temperature: 30

oC (GF1), 50 oC (GF2) and 80 oC (GF3) The characterized methods are used: XRD, XPS and TEM While the XRD shows the increase of

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particle size Fe3O4 nano on GOVS with increasing temperature, XPS results demonstrate that there is only Fe3O4 on GOVS (without γ-Fe2O3) Therefore, in the reaction temperature range from 30 to 80 oC, the synthesized materials are purity (only phase Fe3O4 on GOVS) TEMs of GF1, GF2 and GF3 give the shape of Fe3O4 on GOVS This shape is spherical and it is fine distribution, especially the sample at 80

oC The particle size of GF1, GF2 and GF3 has the increasing trend with 8 nm for GF1, 13 nm for GF2 and 15 nm for GF3 The XPS also conclude that the sample with 80 oC acheives the highest Fe concentraion (17,23%) In brielfly, 80 oC is chosen

3.3.2 The effect of precursor concentration

Making samples with the different concentration ratios Fe3+/Fe2+:

N (0,01M/0,005M), GF3 (0,1M/0,05M), N1 (1M/0,5M) và N2 (2M/1M), with the reaction temperature at 80 oC, pH = 10 and stir speed 500 rpm

The particle size increases with the rise of concentration ratio, basing on the XRD results The particle size is determined with Scheerer equation which is collected in Table 3.7

Tabke 3.7 Paticle size of Fe 3 O 4 -GOVS synthesizing

When comparing the TEM results of all sample, we see that it easily distinguishes the change in particle size For example, the particle size in N, GF3, N1 and N2 is 8 nm, 15 nm, 25 nm and 40 nm, respectively Moreover, Fe3O4 is in the spherical shape, fine distribution and posited at the space between each layer However, for high recovery efficiency, we need the high saturated sample Two sample GF3 and N1 belong to the highest group So, the choice is GF3

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3.3.3 The effect of pH

For studying, we make the samples with the different pH: pH

= 8 (GF4), pH =10 (GF3), pH = 12 (GF5), and the reaction temperature is 80 oC, Fe3+/Fe2+ concentration ratio = 0,1M/0,05M, stir

speed 500 rpm

The shape and size of particle are observed under FE-SEM spectroscopy Figure 3.21 is the FE-SEM spectroscopies of three Fe3O4-GOVS samples under different pH

Figure 3.21 FE-SEM images of Fe 3 O 4 -GOVS under different pH

GF3(a), GF4(b) và GF5(c)

Fig 3.21 shows the particle size of each sample For pH = 8 (GF4), the particle size is about 20 nm In comparison, sample with pH

= 10 (GF3) is about 15 nm and 18 nm is the particle size of sample pH

= 12 (GF5) The particle size increases with the increase of pH So, we choose the pH = 10

3.3.4 The effect of stir speed

The samples are made with the stir speed: 200 (V1), 350 (V2),

500 (GF3) and 1000 rpm (V4), pH = 10, reaction temperature 80 oC,

Fe3+/Fe2+ concentration ratio= 0,1M/0,05M

According to the XRD results, if the stir speed increases, the particle size decrease For example, the particle size of samples V1, V2, GF3 and V4 are 24,1 nm; 14,08 nm; 13,4 nm và 12,7 nm, respectively Moreover, this conclusion is tightened by the TEM results which give the average particle size of sample V1, V2, GF3 and V4 Those are 30 nm, 20 nm, 15 nm and14 nm Furthermore, for

(c)

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the range 500-1000 rpm, there is a slight decrease in particle size Therefore, we choose the stir speed 500 rpm

3.4 Synthesizing Fe 3 O 4 -GOVS and Fe-Fe 3 O 4 -GOVS material

- Procedure for synthesizing Fe 3 O 4 -GOVS

Figure 3.24 The procedue for synthesizing Fe 3 O 4 - GOVS

Basing on the above results, after geting Fe3O4-GOVS, we will make the Feo nano on this surface by using NaBH4 as a reducer agent and Fe3+ from (FeCl3.6H2O) The nitrogen is blown on this system (fig 2.5) By this method, the percentage of Feo on Fe3O4-GOVS surface is about 10% in weight

Figure 2.5 Procedure for synthesizing Fe-Fe 3 O 4 -GOVS

Figure 3.25 XRD patterns of Fe 3 O 4 -GOVS and Fe-Fe 3 O 4 -GOVS

XRD results show that there are the formation of Fe0 and Fe3O4 on the samples, which is the cause of existing the peaks 2θ at 45° and 68° These peaks are characterized for Feo

3.5.2 TEM and HR-TEM Spectroscopy

Figure 3.26 The TEM of Fe 3 O 4 -GOVS (a) and Fe-Fe 3 O 4 -GOVS (b,c)

(c)

3.5.3 FTIR Spectroscopy

According to FTIR

results, there is Fe3O4

nano on the surface of

GOSV, which leads to

the existance of peak at

578,2 cm-1 This is the

characterized peak for

Fe-O bonding in Fe3O4,

Fe-Fe3O4 and GOVS

While the peaks at 1230

cm-1 and 1576 cm-1 are

C=O and C-O, the peak

at 2342 cm-1 are the

bonding of CO2 with

Fe3O4-GOVS and Fe-Fe3O4-GOVS Furthermore, there is the formation of Feo nano on the Fe3O4-GOVS because of the characterized peak at 1048,5cm-1

3.5.4 EDX Spectroscopy of Fe-Fe 3 O 4 -GOVS and Fe 3 O 4 -GOVS

EDX Spectroscopy results in Table 3.8

Table 3.8 The element composition in Fe 3 O 4 -GOVS and

Fe-Fe 3 O 4 -GOVS

% weight % atom % weight % atom

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From Table 3.8, the percentage of Fe in Fe3O4-GOVS is about 48,59% in weight and 18% in atom, which is close to the initial calculation ( 50% in weight and 20 % in atom) After adding to Feowith 10% in weight on the Fe3O4-GOVS, the percentage of Fe in weight reaches to 57,68% (~ 9.1% in weight) It is close to the initial calculation

3.5.5 N 2 adsorption–desorption isotherms (BET) of Fe-Fe 3 O 4 -GOVS and Fe 3 O 4 -GOVS

The BET results show that these materials belong to the layer structure form From Table 3.9, Fe-Fe3O4-GO has a high specific area and high pore volumn and these are higher than that of Fe3O4-GOVS Moreover, these two material belongs to average capillary system (average capillary system is 99%, while the micro capillary system is about 1%) The capillary diameter is in the range from 8-13 nm

Table 3.9 Textual characteristics of Fe-Fe 3 O 4 -GOVS and Fe 3 O 4 -GOVS

Micro-capillary volume (cm3/g) 0,0033 0,0043 Total capillary volume (cm3/g) 0,499 0,523 Average of capillary diameter (nm) 8,8 - 12,1 8,9 - 12,3

3.5.6 XPS spectra of Fe-Fe 3 O 4 -GOVS and Fe 3 O 4 -GOVS

XPS spectroscopy results (Fig 3.30) demonstrate the purity of Fe3O4 on the GO because there are the characterized peaks at 711 eV and 725 eV For Fe-Fe3O4-GOVS, beside the peaks of Fe3O4, two other peaks at 719 and 733 eV are existed It can be explained by the reaction between Feo and Fe3O4-GOVS, which is conduct to the formation of Fe2O3, FeOOH Moreover, because of the peak at 706 eV, the particle size of Feo nano is predicted about less than 10 nm Although these XPS