Summary of doctor thesis: Research on effective treatment of DDT by photocatalyst method using Fe - CuOx /GO; SBA – 15 nanocomposite materials, Theoretical chemistry and physical chemistry

Objectives of the study: Focusing on studying how to incorporate of Fe and Cu atoms into GO and SBA-15 frameworks by atomic implantation method to create new, advanced and highly efficient nanocomposite catalysts for DDT treatment.

MINISTRY OF

EDUCATION AND TRAINING

VIETNAM ACADEMY OF SCIENCE AND

TECHNOLOGY

GRADATE UNIVERSITY OF SCIENCE AND TECHNOLOGY

- -

NGUYEN THANH TUAN

PHOTOCATALYTIC METHOD USING Fe-CuOx/GO; SBA – 15 NANOCOMPOSITE MATERIALS

Major: Theoretical Chemistry and Physical Chemistry

Code : 62.44.01.19

SUMMARY OF DOCTOR THESIS

Hanoi - 2019

The thesis was completed at Institute of Chemistry, Vietnam

Academy of Science and Technology

Supervisors:

1 Prof PhD Vu Anh Tuan

2 PhD Trịnh Khac Sau

Time: hour, date /month/2019

The thesis could be found at:

- National Library of Vietnam

- Library of Graduate University of Science and Technology

- Library of Institute of Chemistry

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INTRODUCTION

* The thesis necessity

Along with the economic development, Vietnam has been facing pollution problems arising from agricultural and industrial production activities In particular, Persistent Organic Pollutants (POPs) are halogenated organic compounds that are environmentally toxic and stable compounds They are capable of bioaccumulation through the food chain and stored for long periods of time with potential adverse impacts on human health and the environment Due to the hazardous potential of these compounds, 92 countries signed the Convention on May 22, 2001 in Stockholm (Sweden), commonly known as the Stockholm Convention to place a global ban on these particularly harmful and toxic compounds Initially, the Stockholm convention was designed to reduce and eliminate the 12 most dangerous POPs out of human life Among of the 12 POPs in the Stockholm Convention, up to 8 types of POPs-pesticides include Aldrin, chlordane, DDT, Dieldrin, Endrin, Hetachlor, Mirex and Toxaphene Then, at the sixth meeting (May 2013), the convention added a list of POPs up to the total 28 of persistent organic pollutants

In Vietnam, persistent organic pollutants such as Dioxin (due to war consequences, the burning of hazardous wastes, PVC, ), pesticides such as Chlordane, DDT, 2,4-D; 2,4,5-T as well as PCBs (from waste oil in transformers) cause serious pollution affecting human health, the environment and sustainable development

To remove these pollutants in water environment, many methods have been used such as: adsorption, biodegradation, chemical decomposition, advanced oxidation In which the adsorption method causes secondary pollution, biodegradation method requires

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long time and low efficiency Therefore, the advanced oxidation processes (AOPs) improved the removal efficiency using photochemical nanocatalysts such as Fe2O3, Fe3O4, FeOOH, Feo is being studied throughly Advanced oxidation processes (AOPs) refer

to an oxidation process through the formation of hydroxyl radicals (•OH) which is a promising approach to degrade primarily organic chemical contaminants in water treatment Advanced oxidation processes (AOPs) have shown many advantages such as cost-effectiveness, high efficiency, low toxicity and simple operation Several recent studies have shown that the simultaneous incorporation of different metals and metal oxides onto the same carrier to enhance efficiency of these composite catalysts Among the carriers, graphene and graphene oxide (GO) have been received a great interest due to their unique structure and physical-chemical properties such as high conductivities at room temperature, high specific surface and chemical stability, and high visible light absorption ability Unlike graphene, graphene oxide (GO) contains functional groups like hydroxyl, carbonyl, epoxi, carboxylic on the surface, so it is easy to form covalent bonds, strong chemical bonds with transition metal ions Therefore, GO is an ideal carrier in the synthesis of new composite nanomaterials Meanwhile, SBA-15 is a material with well-ordered hexagonal mesoporous silica structure which has a very large surface area (600 - 1000m2/g) However, the purely siliceous SBA-15 has a lack of functionality due to its electrically neutral framework, it can be used as adsorbent but not as acidic or redox catalysts In order to use as catalysts, SBA-15 can be modified by incorporation of transition metals into framework by direct synthesis and post-synthesis In this thesis, we focus on

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studying how to incorporate of Fe and Cu atoms into GO and

SBA-15 frameworks by atomic implantation method to create new, advanced and highly efficient nanocomposite catalysts for DDT treatment From the above arguments, we choose the thesis topic:

"Research on effective treatment of DDT by photocatalyst method using Fe - CuOx /GO; SBA – 15 nanocomposite materials" to

research and evaluate the catalytic activity of these new catalytic systems for DDT degradation

* Objectives of the study

Focusing on studying how to incorporate of Fe and Cu atoms into

GO and SBA-15 frameworks by atomic implantation method to create new, advanced and highly efficient nanocomposite catalysts for DDT treatment

* Main research contents of the thesis

- Synthesize some new and advanced nanocomposite materials based on metalic oxide combination with GO and SBA-15 as high-efficiency photocatalysts for toxic and persistent organic pollutants treatment by various methods such as co-precipitation, hydrothermal and especially atomic implantation method

- Study on structural characteristics, morphology and chemical properties of synthesized materials by modern methods such as XRD, FTIR, TEM, XPS, BET, UV-Vis

physic The photocatalytic activity of these novel materials under visible light for the removal of DDT from aqueous solution was investigated and discussed

- Study on the influencing factors such as pH, H2O2 concentration, DDT concentration, catalytic concentration to the DDT degradation efficiency

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- Research and propose reaction mechanism, decompose DDT through intermediate products formed in the process of DDT decomposition on synthesized catalytic systems

* Thesis structure

This thesis consists of 136 pages, 78 figures, 25 tables and 143 references including these main parts: introduction, three chapters in content and conclusion The main results were published on 6 journals: 02 articles was published on international journals, 04 article was published on national journals

Chapter 1 Literature review

Chapter 1 is presented in 36 pages, in which general introduction

of persistent organic pollutants (POPs), structure and toxicity of DDT

as representative for research in this thesis Also in this chapter, technologies to treat persistent organic substances in the world and in Vietnam are also explored Among the methods, Advanced Oxidation Processes (AOPs) have shown many advantages such as cost-effectiveness, high degradation efficiency, low toxicity and simple operation Therefore the advanced oxidation processes (AOPs) was mentioned in this chapter includes the theoretical basis and classification of the AOP, the theoretical basis of Fenton processes (Fenton homogeneous process, Fenton heterogeneous process, Fenton photo process) Chapter 1 also introduces some highly effective nanocomposite catalysts based on graphene, GO and SBA-

15 in the treatment of persistent organic pollutants in water environment Overview of synthetic methods, research and application of nanocomposite catalysts for advanced oxidation

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processes to treat persistent organic substances in water environment was introduced Evaluation and analysis of the applicability of these catalysts in environmental treatment: dye treatment; toxic organic substances and DDT

Chapter 2 Experimental

Chapter 2 is presented in 20 pages including:

2.1 Process of synthesizing materials

- Synthesis of Fe3O4, Fe3O4/GO nanocomposite materials by precipitation method

co Synthesis of TiO2/GO and Fe-TiO2/GO nanocomposite materials by hydrothermal method

- Synthesis of Fe-Cu/SBA-15 and Fe-Cu/GO nanocomposite materials by atomic implantation method The equipment for synthesis of Fe-Cu/GO nanocomposite by atomic implantation method is illustrated in Figure 2.6

Figure 2.6 Schematic illustrating the equipment for synthesis of

Cu/Fe/GO nanocomposite by atomic implantation method

- Study on photocatalytic process in the decomposition reaction of DDT by these synthesized catalysts

- Analysis and evaluation of intermediate products formed in the

2.3 Methods of evaluating the photocatalytic ability of materials

in the photocatalytic process of decomposing DDT

- Develop a model to assess the photocatalytic activity of materials in the reaction of DDT decomposition

- Methods of analysis and determination of removal efficiency in DDT decomposition process: GC-MS, TOC

Chapter 3 Results and Discussions

Chapter 3 is presented in 60 pages including:

3.1 Characteristics of structure and morphology of catalytic systems

3.1.1 X-ray diffraction (XRD)

Results of XRD for Fe3O4 and Fe3O4/GO samples (Figure 3.3) appear typical peaks of Fe3O4 at values of 2θ: 30.1 ° (220), 35.4 ° (311), 43, 05 ° (400), 54o (422), 62.51 ° (511) and 6395 ° (553) [88] Meanwhile, XRD patterns of GO, Fe/GO and Fe-Cu/GO samples (Figure 3.5) shows that the peak at position 2Ɵ ~ 11o is belong to GO material [42] When Fe3+ and Cu2+ was delivered on GO, the peak of

GO in this position decreased sharply As shown in XRD diagram of Fe/GO and Fe-Cu/GO, there are typical peaks such as: 24.1 ° (012), 33.1 ° (104), 36.5 ° (110), 40, 8 ° (113), 49.4 ° (024), 54.1 ° (116),

Figure 3.6 Small-angle X-ray scattering patterns (a) and wide-angle X-ray

scattering patterns (b) of SBA-15, 5Fe-2Cu/SBA-15, 10Fe-2Cu/SBA-15 and

15Fe-2Cu/SBA-15 samples

In figure 3.6, small-angle X-ray scattering patterns showed that all samples has three peaks, in which the peak intensity is sharp and strong at 2   0.8o and two peaks are smaller at 2 

 1.5o và 2   1.7o that can be indexed as the (100), (110), and (200) diffractions of 2D hexagonal p6mm symmetry of SBA-

15, respectively [20,28,32] The peak intensity of these samples

SEM image (Figure 3.9) and HR-TEM image (Figure 3.10) show that Fe3O4 nanoparticles have a spherical shape with the size of 15-20

nm which dispersed well on GO carriers From TEM images of TiO2/GO and Fe-TiO2 nanocomposite materials shown in Figure 3.11, we can see that Fe-TiO2 nanotubes are dispersed on the layers

Fe-of GO Fe-TiO2 nanotube structure has 8 - 12 nm diameter and the tube length is about 100-200 nm There are some bundles of Fe-TiO2

Figure 3.14 SEM and HR-TEM images of SBA-15(a); 5Fe-2Cu/SBA-15(b);

10Fe-2Cu/SBA-15(c) and 15Fe-2Cu/SBA-15(d)

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3.1.3 Energy-dispersive X-ray spectroscopy (EDX)

EDX mapping images and EDX analysis for the elemental composition (Figure 3.18 and 3.19) of nanocomposite Fe-Cu/GO showed that Fe content accounted for 17.87% by weight and Cu content only accounted for 1.84% by weight

Figure 3.18 EDX mapping images and Figure 3.19 EDX analysis

for the elemental composition of nanocomposite Fe-Cu/GO

EDX analysis of Fe-Cu/SBA-15 nanocomposite materials with different Fe/Cu ratios showed that when Fe, Cu with content <10%

by weight, content of Fe,Cu in Fe-Cu/SBA-15 nanocomposite is nearly equal to the caculated amount However, when Fe content is increased too much, Fe content in EDX ananlysis is lower than initial calculated amount

3.1.4 Fourier transform infrared spectroscopy (FTIR)

As seen in Figure 3.23, FTIR spectra of Cu-Fe/GO nanocomposite material showed the existence of carbonyl group C = O (in the range

1500 - 1730 cm-1) [109] The intense peak at 1230 cm−1 is related to

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the aromatic stretching vibration of C–O bond The peaks at about

2925 cm-1, 2850 cm-1 characterize the existence of the link –CH2– 23

In additional, peaks at 630 cm-1, 570 cm-1, 480 cm-1 corresponding to the formation of Fe-GO and Fe2O3-GO binding to the functional groups of GO Thus, these results revealed the interaction between

Feo, Fe2O3 and GO FTIR spectra of Cu-Fe/GO also showed low intensity peaks at 506 cm-1 and 430 cm-1 which assigned to the Cu2O,

Cu and CuO in the structure of Fe-Cu/GO composite [113]

Wavenumber (cm -1 )

500 1000 1500 2000 2500 3000

Figure 3.23 FTIR spectra of

GO, Fe/GO and Cu-Fe/GO

nanocomposite material

Figure 3.24 FTIR spectra of

SBA-15, Fe-Cu/SBA-15 samples with different Fe/Cu ratio

The FTIR spectra of SBA-15 and Fe-Cu/SBA-15 nanocomposite materials in Figure 3.24 are shown the stretching vibrations of the associated silanol groups (Si-OH) at 3,437 cm-1 and 1632 cm-1 The vibration bands centered at 1080 cm-1; 815 cm-1; 459 cm-1 were corresponded to Si-O-Si bending vibration of the silica frameworks [48,49,136] Observation of the FTIR spectra of Fe-Cu/SBA-15 nanocomposite samples revealed that the large peak at 660 cm-1 also attributed to the presence of Fe2O3 and CuO bound into SBA-15

frameworks [128]

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3.1.5 N 2 adsorption–desorption isotherms (BET)

It can be seen from the nitrogen adsorption–desorption isotherms

in figure 3.28, the graphs displayed type IV (according to IUPAC classification) which are featured of mesoporous structured materials Table 3.7 shows the structural parameters of the synthesized materials based on GO samples Table 3.11 shows the structural parameters of Fe-Cu/SBA-15 nanocomposite materials with different Fe/Cu ratio It can be seen that SBET surface area for the Fe-Cu/SBA-

15 samples slightly decreased with the increase of Fe and Cu content The capillary diameter (DBJH) and wall thickness (Wt) remarkably increased in the presence of Fe and Cu This clearly revealed that the substitution of metal ions (Fe or Cu) for Si in the SBA-15 network changed the formation of mesopores of nanocomposite materials

distribution (b) of Fe-Cu/GO nanocomposite material

Table 3.7 Structural parameters of synthesized materials based on

GO samples

Sample

parameters GO Fe 3 O 4 Fe 3 O 4 /GO

TiO 2 /GO Fe/GO

Cu/GO

Fe-S BET

8.6-Table 3.11 Structural parameters of SBA-15, 5Fe-2Cu/SBA-15,

10Fe-2Cu/SBA-15 and 15Fe-2Cu/SBA-15 samples

3.1.6 X-ray Photoelectron Spectroscopy (XPS)

As seen in Figure 3.31, XPS spectra showed that the occurrence

of peaks at binding energy of 931 eV; 943 eV and 951 eV ascribed to the formation of CuO in the material [44,88] The peak at 934 eV assigned to Cu2O [113,135] Moreover, the binding energy of Fe2p3/2

of the hybrid was located at 710 eV while the peak of Fe2p1/2appeared at 724 eV which indicated the existence of Fe2O3 [107] The peaks with low intensity at 715 eV and 730 eV could ascribe the formation of FeO in the material [32,135] The deconvolution of the C1s peak was consisted of three peaks at 284.4 eV, 285.6 eV and 288.3 eV, which were ascribed to the C-C, C-O, and C(O)O bonding

in GO sheets The XPS spectra in Figure 3.32 demonstrated the