Nghiên cứu cải thiện khả năng quang xúc tác của g-C3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)

Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)Nghiên cứu cải thiện khả năng quang xúc tác của gC3N4 biến tính với kim loại (Fe, Co, Mg, Ag) và oxit bán dẫn (TiO2, ZnO)

MINISTRY OF EDUCATION AND TRAINING HANOI NATIONAL UNIVERSITY OF EDUCATION

-

LAM THI HANG

INVESTIGATING THE ENHANCEMENT OF

MODIFIED WITH METALS (Fe, Co, Mg, Ag) AND

Specialization: Solid State Physics

Code: 9.44.07.04

SUMMARY OF THE DOCTORY OF PHYSICS

Hanoi, 2024

HANOI NATIONAL UNIVERSITY OF EDUCATION

Science instructor:

1: Prof Dr Nguyen Van Minh 2: Assoc Prof Dr Do Danh Bich

Review 1: Assoc Prof Du Thi Xuan Thao – Phenikaa University

Review 2: Assoc Prof Nguyen Dinh Lam – VNU University of Engineering and Technology

Review 3: Assoc Prof Pham Van Hai - Hanoi National University

of Education

The thesis has been defended before the School-level Thesis Judging Committee meeting at Hanoi National University of Education

on 2024

Thesis can be found at the library:

- National Library, Hanoi

- Library of Hanoi National University of Education

PREAMBLE

In the last few decades, on planet Earth, the rapidly growing textile, dyeing, tanning, organic chemical and petrochemical industries have contributed significantly to organic pollution of water resources Organic toxins often released from these industries are pesticides, herbicides, organic dyes, etc., which mix directly with clean water and pollute water sources Synthetic organic dyes used in the textile, leather and paper industries are highly toxic, mutagenic, carcinogenic and seriously affect aquatic ecosystems and have the potential to cause health problems serious problems related to human health Nowadays, the treatment of environmental pollution, especially the treatment of water pollution, has become a hot and concerned issue worldwide and the treatment of polluted water is a major persistent challenge by scientists around the world Therefore, in the field of water treatment, researchers have constantly made efforts and persistently discovered modern and effective technologies to remove toxic organic substances from polluted water In particular, the technology of decomposing toxic organic substances by photocatalysis is a widely used environmentally benign technique, using clean energy sources (natural light) to decompose substances organic pollutants into non-toxic or less toxic products and thus effectively overcome environmental pollution However, photocatalytic water treatment also faces some challenges because its effectiveness depends on many different factors such as the type of catalyst, wavelength of light, and bandgap of the substance catalysis

Using semiconductor materials as catalysts in the process of treating water pollution

is a highly appreciated idea in the green chemistry industry (researching chemicals to treat environmental pollution) Some popular types of materials that are currently being researched include metal oxides (TiO2, ZnO, WO3 ), ferroelectric materials with ABO3

perovskite structure(BiFeO3, BaTiO3, SrTiO3), ABO4 semiconductor compounds (ZnWO4, SnWO4) … However, most of these materials have a large band gap (> 3.2 eV), so they almost only absorb light in the ultraviolet region, accounting for about 4% of the solar spectrum Currently, finding semiconductor materials with small band gaps is a topic that attracts great attention from research groups around the world with the goal of taking advantage of sunlight sources in applications photocatalysis, helping to expand application scale, reduce costs and increase convenience Besides, narrow band semiconductor materials also have great potential in the field of energy conversion or clean fuel production such as Hydrogen and Oxygen To meet the goal of using sunlight, semiconductor materials need

to meet a number of requirements such as: (i) band gap less than 3.2 eV (380nm); (ii) large contact surface area and (iii) small electron and hole recombination rate

Recently, the material g-C3N4, a non-metallic organic semiconductor with unique electronic structure and optical properties with a small band gap (on the order of 2.7 eV), has received attention Extensive research by scientists around the world The g-C3N4

material possesses a number of superior physical properties such as high hardness, toxicity, chemical and temperature stability in different environmental conditions, large specific surface area, and high efficiency relatively high quantum and biocompatible, Therefore, this material has potential applications in a number of fields such as photoelectric conversion, temperature sensing, chemical sensing, biomedicine, and especially in the field

non-of photocatalysis to extract H2 fuel from water, decompose CO2 gas and clean organic pollution in the water environment

So far, g-C3N4 materials with diverse morphologies such as nanosheets, nanowires, porous nanostructures and thin films have been researched and manufactured using different technological processes such as vapor phase deposition ( CVD and PVD), solvothermal, and pyrolysis from C- and N-rich precursors, etc Unlike metal-containing semiconductor photocatalysts, g-C3N4 can be easily synthesized by thermal polymerization from C and N rich precursors such as dicyanamide, cyanamide, melamine and urea However, research shows that g-C3N4 material also has low quantum efficiency due to the high electron-hole recombination rate; The absorption edge is at about 460 nm, so it only absorbs the blue light region of the solar spectrum Besides, g-C3N4 particlestend to cluster together, reducing the specific surface area, leading to reduced photocatalytic efficiency Recently, research on modifying g-C3N4 materials to increase the lifetime of electron-hole pairs, reduce the band gap energy and increase the specific surface area is the top priority solution for the research

of g-C3N4 materials

Some basic measures to improve quantum efficiency and promote photocatalytic activity of g-C3N4 materials include: (i) controlling surface morphology, creating thin nanoleaf structures, porous structures or quantum dots, quantum wires, to increase the specific surface area; (ii) combine the material with some other semiconductors to increase the lifetime of the electron-hole pair, while reducing the band gap of the material; (iii) coating the g-C3N4 surface with some metal nanoparticles that act as electron reservoirs (Pt,

Ag or Au nanoparticles); (iv) doping non-metal elements (P, S, O), transition metals (Fe,

Cu, Zn) to reduce the band gap while creating an electron capture center from the g-C3N4

crystal

In Vietnam, research direction based on g-C3N4 materials is still quite new Currently, the material g-C3N4 has been initially deployed in the research group of Professor Dr Vo Vien belongs to Quy Nhon University The research team focuses on the technology of manufacturing g-C3N4 material from melamine precursor and doping some non-metallic elements (O, S) to enhance photocatalytic activity under visible light of material g-C3N4 In addition, the group also developed composite materials between g-C3N4 and GaN-ZnO or

Ta2O5 Research results show that the photocatalytic activity of composite materials increases significantly compared to that of the component materials The research team's results supported two PhD students to successfully defend their PhD thesis in Chemistry In

2018, the research group of Prof Dr Nguyen Ngoc Ha - Department of Chemistry, Hanoi University of Education received funding from the National Foundation for Science and Technology Development (Nafosted) for material research nano composite materials based

on g-C3N4 and diatomite to effectively treat reactive dyes In 2022, the PhD thesis of author Dang Thi Ngoc Hoa of Hue University also researched the synthesis of g-C3N4 composite for application in electrochemistry and photocatalysis The author focuses on researching composite materials such as ZIF-67/g-C3N4, ZIF-67/Fe2O3/g-C3N4, TiO2/g-C3N4 with precursors for making g-C3N4 is melamine and focuses on photocatalytic decomposition of Methylene Blue (MB), Diclofenac (DCF), Auramine O (AO)

To our knowledge, apart from the above research groups, g-C3N4 material has not yet been researched or widely announced in Vietnam In this thesis, we choose to research the production of g-C3N4 material from urea precursor using simple pyrolysis method, this is a cheap chemical, easy to find, friendly and process research Manufacturing technology to achieve thin, well-crystallized foil samples, suitable for laboratory conditions of the Department of Physics, Hanoi University of Education From there, a good quality sample

was selected to conduct " Investigating the enhancement of photocatalytic performance of g-C3N4 modified with metals (Fe, Co, Mg, Ag) " These metals are

cheap, chemically simple, have good conductivity and have been shown to have good results in improving the photocatalytic ability of g-C3N4 Besides, we also chose to modify

with "semiconducting oxides (TiO 2 , ZnO)" because these are two promising photocatalytic

materials for environmental applications with outstanding properties such as: Good photocatalytic properties, low cost, easy to manufacture and non-toxic

Objectives of the thesis: (i) Research the influence of sample manufacturing

conditions on the structure, physical properties and photocatalytic ability of g-C3N4 material, from which to select methods and conditions Suitable technological conditions to manufacture g-C3N4 thin-leaf material with good nano-crystalline size (ii) Improve the photocatalytic ability of g-C3N4 base material by modifying with metal elements (Fe, Co,

Mg, Ag) and combining materials with semiconducting oxides (TiO2, ZnO) to reduce the band gap while creating an electron capture center, increasing the lifetime of the electron-hole pair From there, evaluate the influence of the concentration of modified metals as well

as the percentage of combined samples on the photocatalytic ability of g-C3N4 material

Research subjects:

- Nano sheet material g-C3N4

- Nanomaterial g-C3N4 modified with metals Fe, Co, Mg, Ag

- Nanomaterial g-C3N4 combined with semiconductors TiO2 , ZnO

Research Methods: The thesis is based on experimental methods, the sample is

manufactured mainly by polymerization through pyrolysis of N-rich organic precursors A number of manufacturing technologies are applied to synthesize the material materials such

as pyrolysis in a noble gas environment, pyrolysis in an air environment

Materials were manufactured at the Department of Physics and Center for Nano Science and Technology, Hanoi University of Education Fabricated samples are analyzed for crystal structure and physical properties using a number of techniques such as: X-ray diffraction (XRD), scanning electron microscopy (SEM, FE-SEM), electron microscopy transmittance (TEM) and high resolution transmittance (HRTEM), infrared absorption spectroscopy (FTIR), surface area and pore volume measurement (BET), UV-Vis absorption spectroscopy, fluorescence spectroscopy (PL), photoelectron spectroscopy (XPS), Raman scattering spectroscopy

The fabricated samples were used to perform photocatalytic processes for decomposing 10 ppm RhB solution The concentration of remaining organic compounds was measured indirectly through UV-Vis optical absorption spectroscopy

In addition, the thesis also uses a number of software to exploit and analyze and calculate physical parameters of materials from experimental data such as Origin, UniCell, ImageJ, JCPDS standard card library

Scientific and practical significance of the project: With the orientation of

researching and applying g-C3N4 materialsin the field of photocatalysis, the thesis has built

a process for manufacturing g-C3N4 base materials using the A simple method is urea pyrolysis This is a cheap but highly effective method of using precursors This contributes

to proposing a technological process for effectively manufacturing semiconductor materials that can be applied in the field of treating some organic waste in the aquatic environment Modifying the material by doping metals and combining it with other semiconductors increases the photocatalytic ability of the g-C3N4 base material The material has good photocatalytic ability to decompose some organic compounds such as RhB, oriented for application in decomposing some toxic organic substances in wastewater samples in domestic and craft villages; Actively contribute to the process of cleaning the living environment

The content of the thesis includes: Overview of g-C3N4 materials, experimental techniques, research results and analysis of the effects of sample manufacturing conditions; The influence of Fe, Co, Mg, Ag metals on the structure, optical properties of materials and photocatalytic ability of g-C3N4 base materials; Results of studying the structure and properties of g-C3N4 materialscombined with semiconductor TiO2 and ZnO

Layout of the thesis: The thesis is presented in 145 pages with 22 tables and 109

figures, including an introduction, 5 content chapters, a conclusion, a list of research works and references As follows:

Introduction: Introduces the reason for choosing the topic, the object and purpose of the research, and the scientific significance of the thesis

Chapter 1: Presents an overview of the structural properties, morphology, physical properties and some research on photocatalytic orientation of g-C3N4 materials The typical properties of g-C3N4 materialsare the basis for analyzing results on pure g-C3N4 and g-C3N4

model systemsdenatured with metals and g-C3N4 combination in chapters 3, 4 and 5

Chapter 2: Presents methods and procedures for sample fabrication, process for evaluating photocatalytic ability, principles of measurements used in analyzing material properties used in the thesis

Chapter 3: Research on the effects of technological conditions on the crystal structure, physical properties and photocatalytic ability of g-C3N4 materials

Chapter 4: Research on physical properties and photocatalytic ability of g-C3N4

materialmodified with metals Fe, Co, Mg, Ag

Chapter 5: Research on physical properties and photocatalytic ability of g-C3N4

materialcombined with semiconductors TiO2, ZnO

Conclusion: Presents the main results of the thesis

The main results of the thesis have been published in 07 scientific works (including 04 articles published in international specialized journals, 03 articles

published in domestic specialized journals)

Chapter 1 OVERVIEW 1.1 Material g-C 3 N 4

1.1.1 Structural properties

g-C3N4 crystal has a hexagonal structure, belonging to the P 6̅m2 space group According to the research results, the base unit cell of the g-C3N4 crystal has 56 atoms, including 32 N atoms and 24 C atoms

Figure 1.2 (a) Unit cell and (b) AB-type layered structure of the crystal of g-C 3 N 4

1.1.3 Surface morphology of g-C3N4 material

Figure 1.6 TEM images of g-C 3 N 4 material from different precursors

The produced g-C3N4 material is usually in the form of a porous material However, the pore volume, pore size distribution and specific surface area of g-C3N4

depend on the precursor and material fabrication method

1.1.4 Optical properties of g-C3N4 materials

The g-C3N4 layer unit with the gh-heptazine structure is a semiconductor with an indirect band gap Accordingly, the band gap value is 2.76 eV with the valence band maximum (VBM) at point Γ and conduction band minimum (CBM) located at point

M Meanwhile, the band gap energy in real The experimental range is from 2.67 eV

to 2.95 eV

1.1.5 Photocatalytic properties of g-C3N4 materials

The photocatalytic ability of g-C3N4 can be applied to treat organic pollutants such as: Rhodamine B (RhB), Methylene Blue (MB), Methyl Orange (MO), Phenol,

1.2 Photocatalysis mechanism and application potential of g-C 3 N 4 materials

1.2.1 Photocatalytic mechanism of g-C3N4 materials

1.2.2 Application potential of g-C3N4 materials

1.3 Some manufacturing methods of g-C 3 N 4 materials

1.3.1 Sol-gel method

1.3.2 Hydrothermal method

1.3.3 Heat polymerization method

1.4 Some research directions to improve photocatalytic properties of g-C 3 N 4 materials

1.4.1 Combination of g-C3N4 with other materials

heterosemiconductor materials such as: TiO2, WO3, ZnO, Ag2WO4 Studies show that the modification of g-C3N4 materials by uniform combination aims to reduce the recombination of electron-hole pairs in the material to enhance the photocatalytic ability

1.4.2 Modification of g-C3N4 with metallic elements

Modification of g-C3N4 material by doping elements Fe, Co, Mg, Cu, Na, K,

Zr, Mn or coating metal nanoparticles such as Au, Ag, Pt on the surface material surface g-C3N4 has been studied by several groups These studies show that modifying g-C3N4 material by uniform doping gives better photocatalytic ability than pure g-C3N4 material

Chapter 2 EXPERIENCE 2.1 Material manufacturing process

2.1.1 C fabrication of pure g-C3N4 material

2.1.2 Fabrication of g-C3N4 doped Fe/Co/Mg

2.1.3 Fabrication of g-C3N4 materials coated with Ag metal nanoparticles

2.1.4 The model systems are fabricated and studied in the thesis

Table 2.1 Symbols of the model systems used in the thesis

Pure g-C 3 N 4 model system was made in Ar gas environment

Temper

ature

change

450 o C 500 o C 550 o C 600 o C 650 o C gCN(Ar450 gCN(Ar)500 gCN(Ar)550 gCN(Ar)600 gCN(Ar)650

Change

time

gCN(Ar)0.5h gCN(Ar)1.0h gCN(Ar)1.5h gCN(Ar)2.0h gCN(Ar)2.5h

Sample system g-C 3 N 4 purified in air environment

gCN/Ag 0.005M

gCN/Ag 0.007M

gCN/Ag 0.01M

gCN/Ag 0.03M

gCN/Ag 0.05M

gCN/Ag 0.1M

gCN/Au 0.003M

gCN/Au 0.005M

gCN/Au 0.007M

gCN/Au 0.009M

2.2 Photocatalytic testing of organic matter decomposition

2.3 Methods for investigating the physical properties of model systems

Measurements taken to analyze the properties of materials include: X-ray diffraction measurements; Scanning electron microscopy measurement; High resolution transmission and transmission electron microscopy; Raman scattering

spectroscopy; Infrared absorption spectrometry; Method of measuring absorption spectroscopy; X-ray photoelectron spectroscopy method; Fluorescence spectroscopy method; Differential thermal analysis method; Nitrogen adsorption-desorption isotherm method

Chapter 3 RESEARCH IN FABRICATION OF GRAPHITIC CARBON

3.1 The g-C 3 N 4 system was manufactured in an Ar atmosphere

3.1.1 Effect of calcination temperature

3.1.1.1 Crystal structure

Figure 3.1 (a) XRD diagram of g-C 3 N 4 sample system made from Urea precursor in Ar atmosphere at different temperatures ; (b) Change in crystal lattice constant according to

sample heating temperature

The XRD pattern shows 3 diffraction peaks at the angle 2θ about 12.47°; 24.59°and 27.17° The diffraction intensity increased sharply from the calcination temperature of 450 oC to 550 oC and gradually decreased as the calcination temperature continued to increase

3.1.1.2 Surface morphology

Figure 3.2 SEM of g-C 3 N 4 sample system fabricated from Urea in Ar atmosphere at varying

temperatures (a) 450, (b) 500, (c) 550 and (d) 600 C °for 2 time now

Figure 3.2 shows that the sample calcined at a temperature of 450 °C has a morphology similar to a large, uneven membrane with holes and many folds on the surface

Figure 3.3 (a) Nitrogen adsorption-desorption isotherm and (b)

Barrett-Joyner-Halenda (BJH) pore volume distribution curve of g-C 3 N 4 material

c) Chemical composition analysis

Figure 3.4a presents the composite XPS spectrum of sample gCN(Ar)550 showing characteristic peaks of elements C, N and O at energies of 288 eV, 400 eV and

All samples show absorption margins at about 450 nm This absorption edge corresponds to the region-to-band transition between the top of the valence band and the bottom of the conduction band

f) Luminescence properties

Figure 3.9 (a) Fluorescence emission spectra of the g-C 3 N 4 material system calcined for 2 h at different temperatures and (b) the component fluorescence emission peaks

of the gCN(Ar)500 sample

The fluorescence intensity increased as the calcination temperature increased from 450 oC to 500 oC then gradually decreased as the calcination temperature continued to increase

Figure 3.12 (a) Adsorption properties and photocatalytic activity of RhB decomposition of

the g-C 3 N 4 model system calcination for 2 h at different temperatures and (b) RhB

decomposition rate over time

When the calcination temperature is 550 oC, the decrease in RhB solution concentration becomes very strong, completely decomposing 10 ppm RhB solution in

2 hours

3.1.2 Effect of sample heating time

The results show that when keeping the

calcination temperature at 550 oCand increasing the

calcination time, the g-C3N4 crystals become more

ordered with a decreasing lattice constant Large

calcination time changes the surface morphology of

the material, the g-C3N4 sheets become smaller,

thinner and more porous Besides, the width of the

optical band gap also tends to decrease as the

heating time increases The changes in structure,

morphology and physical properties greatly affect

the photocatalytic activity of g-C3N4 materials

Sample g-C3N4 heated at 550 o C for 2 hours or more exhibits strong photocatalytic activity, almost completely decomposing RhB after 2 hours of illumination with Xenon lamp

3.2 The g-C 3 N 4 system is made in air

Similar to the model system calcined in the noble gas environment Ar, the model system calcined in air was also researched, manufactured and investigated when changing two factors: calcination temperature and calcination time The first system is the gCN-T system, in which the calcination time is kept constant for 2

second system is the gCN-t system, in which the calcination temperature is kept fixed

at 550 oC and the calcination time is changed from 0.5 hours to 2.5 hours The physical and photocatalytic properties of the materials are analyzed to come to a conclusion which model system best suits the material's photocatalytic application goals

gCN sample heated at 550 oC

for 2 hours almost completely

decomposes RhB in 180 minutes of

illumination under Xenon lamp

light (Figure 3.28a ) For the

calcination times (Figure 3.28b), the

photocatalytic ability depends on

the sample calcination time The

photocatalytic ability of the samples

is in the order gCN-1.5 < gCN-2.5 < gCN-0.5 < gCN-1.0 < gCN-2.0

In the two atmospheres of Ar gas and air, when Urea is heated at 550 oC for 2 hours, the material g-C3N4 exhibits the best photocatalytic performance Therefore, in the next research directions, we choose the calcination condition to make the g-C3N4

material is 550 oC for 2 hours g-C3N4 materials fabricated at a temperature of 550 oC for 2 hours in an Ar noble gas atmosphere gave higher photocatalytic efficiency, completely decomposing RhB solution in 120 minutes of lamp illumination Xenon Meanwhile, the sample fabricated in air at the same conditions completely decomposed RhB in 180 min

Table 3.7 Compare the photocatalytic results of pure g-C 3 N 4 of the thesis author with

some results published by other authors

Author Thesis author Dong et al [28] Sun et al [93]

180 minutes

100%

decomposition of RhB 5 ppm after

300 minutes

Decompose 78.9

% RhB 10 ppm after 120 minutes

Chapter 4 INCREASING THE PHOTOCATATIC ABILITY OF g-C 3 N 4

MATERIALS BY METAL DOPING 4.1 The g-C 3 N 4 system doped with Fe metal

4.1.1 Structural properties

All samples did not exhibit any diffraction peaks of Fe crystals The (101) and (002) diffraction peaks shift slightly to the left as the Fe concentration increases (Figure 4.2b) The lattice constants are calculated as (a = b = 4.97 Å, c = 6.47 ) and (a

= b = 4.98 Å, c = 6.48 ) for the doped samples, respectively FeCN3 and FeCN5 The increase in crystal structure parameters shows a certain change of the g-C3N4 crystal upon Fe doping, leading to a less dense structural pattern in the crystal lattice This change can be due to the alternating doping configuration of large radius Fe ions in the g-C3N4 crystal by chemically bonding with the six unpaired electron-paired nitrogen atoms as shown in Figure 4.2, leading to crystal lattice expansion

4.1.2 Fluctuating nature

The intensity of all absorption peaks increased as the Fe content increased Magnification of the FTIR absorption peaks (Figure 4.3b) shows a slight shift of the

Magnification of the FTIR absorption peaks (Figure 4.3b) shows a slight shift of the

813, and 813.9 cm-1 for the g-C3N4, FeCN5

and FeCN7 samples Meanwhile, the peaks at

1240 cm-¹ and 1320 cm-¹ almost do not change

position This further shows that the influence

of Fe impurity on the g-C3N4 lattice structure ,

although very small, leads to a slight

expansion of the benzene ring as observed in

the XRD analysis

4.1.3 Nitrogen BET adsorption - desorption

spectroscopy results

The BET surface areas are 91, 100, 132 and

104 m2/g for g-C3N4, FeCN5, FeCN7 and

FeCN10, respectively This result shows that

the specific surface area increases slightly when

doping Fe into the g-C3N4 crystal lattice This

result shows that the specific surface area