Luận án nghiên cứu tổng hợp tio2 AC, tio2 GO và đưa lên gốm cordierite làm xúc tác cho quá trình quang phân hủy metyl da cam và phenol

To - Catalyst Program, for letting me be an official member of the sponsored research on modified TiO2 synthesis and methyl orange and phenol photocatalytic degradation at Hanoi Univers

MINISTRY OF EDUCATION AND TRAINING

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

Nguyen Trung Hieu

RESEARCH INTO TiO2/AC, TiO2/GO SYNTHESIS AND COATING ON

CORDIERITE CERAMIC APPLIED AS CATALYSTS FOR

PHOTODEGRADATION OF METHYL ORANGE AND PHENOL

DOCTORAL DISSERTATION IN CHEMICAL ENGINEERING

Hanoi – 2022

MINISTRY OF EDUCATION AND TRAINING

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

Nguyen Trung Hieu

RESEARCH INTO TiO2/AC, TiO2/GO SYNTHESIS AND COATING ON

CORDIERITE CERAMIC APPLIED AS CATALYSTS FOR

PHOTODEGRADATION OF METHYL ORANGE AND PHENOL

Major : Chemical Engineering Code No : 9520301

DOCTORAL DISSERTATION IN CHEMICAL ENGINEERING

ADVISOR: Prof Le Minh Thang

Hanoi – 2022

GUARANTEE

The study has been conducted at the School of Chemical Engineering (SCE), Germany and Vietnam catalyst research center (Gevicat), Hanoi University of Science and Technology (HUST)

I affirm that this is my own research The co-authors consented to the use of all the data and findings presented in the thesis and confirmed their veracity This study has not been published by anybody but me

ACKNOWLEDGEMENTS

I would like to express my sincerest and heartfelt gratitude to the following people and organizations whose valuable contributions and assistances have made my research possible:

To Hanoi University of Science and Technology, specifically to the School of Chemical Engineering, Department of Organic and Petrochemical Technology for

providing the laboratory instruments and the equipment for me to accomplish my research

To - Catalyst Program, for letting me be an official member of the sponsored

research on modified TiO2 synthesis and methyl orange and phenol photocatalytic

degradation at Hanoi University (HUST) and National Taiwan University (NTU).

To my thesis adviser, Prof Dr Le Minh Thang, for giving me guidance and

supervision as well as critiques and comments on my progress reports to bring me patience, finance, and power to finish this research

To Prof Dr Jeffrey Chi-Sheng Wu, for allowing me to be a part of his research team under the RoHan Program and for training me in his Lab at NTU

To my family and friends who always try to encourage and motivate me during

my thesis course, especially since it is the late gift for my father in heaven now

TABLE OF CONTENTS

GUARANTEE i

ACKNOWLEDGEMENTS ii

TABLE OF CONTENTS iii

LIST OF ABREVIATIONS vi

LIST OF TABLES vii

LIST OF FIGURES viii

INTRODUCTION 1

1 Necessity of the study 1

2 Objectives of the study 3

3 Content of the thesis 4

4 Methodologies of the study 4

5 Scope of the study 4

6 Scientific and practical meanings 5

7 Novelty of the study 5

8.Structure of the thesis 5

CHAPTER 1 LITERATURE REVIEW 6

1.1 Textile industry and Methyl Orange dye 6

1.2 Phenol in industry and its impact to the health 8

1.3 Titanium dioxide, TiO2 9

1.4 Principles of Precipitation, sol-gel and hydrothermal synthesis methods 13 1.4.1 Preparation of photocatalyst using sol-gel method 15

1.5 Support and thin films 19

1.5.1 Overview of Cordierite 19

1.5.2 Mesoporous TiO 2 and coating techniques 20

1.5.3 Catalyst Suspension and immobilization 21

1.6 TiO2/AC Materials 22

1.7 Graphene oxide (GO) 26

1.8 TiO2/GO Materials 28

1.9 MO photocatalytic degradation 31

1.10 Phenol photocatalysis degradation 36

1.11 Summary 38

CHAPTER 2 EXPERIMENTS 40

2.1 Materials and instruments 40

2.2 Catalyst preparation ……….42

2.2.1 Synthesis of mesoporous TiO 2 42

2.2.2 Synthesis of TiO 2 and AC/TiO 2 by Sol-gel method 45

2.2.3 Synthesis of TiO 2 GO by sol-gel method 46

2.2.4 Synthesis of TiO 2 films on cordierite 48

2.3 Characterization of the catalysts 54

2.3.1 Morphology on the surface 54

2.3.2 Elemental surface composition and traces of impurities 56

2.3.3 Specific surface area, pore volume, and average pore size 56

2.3.4 Crystal structures formed and the crystallite diameter 57

2.3.5 Absorbance 58

2.3.6 UV-Vis DSR 60

2.3.7 High-performance liquid chromatography analysis 60

2.4 Experimental set up 62

2.5 To calculate the efficiency of photocatalytic process 63

2.5.1 Construct calibration curve of methyl orange solution 63

2.5.2 Calculation the concentration via equation 64

CHAPTER 3 RESULTS AND DISSCUSSIONS 65

3.1 Mesoporous TiO2 synthesized by precipitation and hydrothermal with CTAB and P123 surfactants 65

3.1.1 Characterization results 65

3.1.2 MO photocatalytic degradation of mesoporous TiO 2 photocatalysts prepared by precipitation and hydrothermal methods with surfactants (CTAB and P123) 69

3.2 TiO2/AC catalyst synthesized using sol-gel method 74

3 2.1 Characterization Catalyst 74

3.2.2 Photocatalytic activity of the MO in water 77

3.3 GO-TiO2 catalysts by sol-gel method 83

3.3.1 Characterization 83

3.3.2 MO photocatalytic degradation by TiO2 – GO ……… …….86

3.4 TiO2 films 89

3.5 Phenol photocatalytic degradation 107 CHAPTER 4: CONCLUSIONS AND RECOMENDATONS 115 REFERENCES 116

FTIR Fourier transform infrared spectroscopy

EDX Energy-dispersive X-ray spectroscopy

P123 poly(ethylene glycol)-block-poly(propylene glycol)-block-poly

(ethylene glycol)

LPMOCVD Low pressure chemical vapor deposition

HPLC High-performance liquid chromatography

LIST OF TABLES

11

Table 1.2 Summary of TiO 2 and GO composites used as photocatalyst 30

Table 2.1: List of chemicals 40

Table 2.2: List of main instruments 41

Table 2.3: Catalyst synthesized by hydrothermal and precipitation methods using surfactant 44

Table 2.4 : AC to TiO 2 Ratio with Corresponding Theoretical % Weight AC in AC/TiO 2 catalyst 45

Table 2.5: Catalysis films and powders synthesized by various methods with the low concetration of PEG 50

Table 2.6: Catalyst films and powders synthesized by various methods with higher concentration of PEG 52

Table 3.1: The surface characteristics of catalysts synthesized by hydrothermal and precipitation methods 66

Table 3.2: Crystalline sizes of catalysts 68

Table 3.3: Surface area of two samples by sol-gel synthesis 75

Table 3.4: Crystalline sizes of catalysts 77

Table 3.5: Surface area of GO-TiO 2 catalysts 85

Table 3.6: Crystalline sizes of catalysts 86

Table 3.7: Effect of ratio mol TTIP:H 2 O to the catalyst mass coated 89

Table 3.8: Catalysts films coated cordierite 93

Table 3.9: Apparent first-order rate constant kapp and correlation coefficient R 2 for phenol degradation by catalysts synthesized by various methods 109

Table 3.10: Apparent first-order rate constant kapp and correlation coefficient R 2 for phenol degradation with various initial concentrations by P123-C25-450 catalyst 110

Table 3.11: Apparent first-order rate constant kapp and correlation coefficient R 2 for phenol degradation by P123-C25-450 catalyst with various concentrations H 2 O 2 112

Table 3.12: Apparent first-order rate constant kapp and correlation coefficient R 2 for phenol degradation in visible light condition 113

LIST OF FIGURES

Fig 1.1: Chemical structure of MO molecule [33,34] 7

Fig 1.2: TiO 2 Crystal Structures[44] 9

Fig 1.3: The mechanism of photocatalytic activity of TiO 2 [50] 11

Fig 1.4: Nanocrystalline Metal Oxide Preparation using Sol-Gel method 17

Fig 1.5: Structures of graphene, C60, CNT and graphite [109] 27

Fig 1.6: Structure of GO [110] 27

Fig 1.7: Possible mechanism of MO with TiO 2 [142] 34

Fig 1.8: Production Distributions from Phenol Decomposition Reaction [152] 38

Fig 2.1 Flowchart of TiO 2 synthesis using CTAB 42

Fig 2.2 Flowchart of TiO 2 synthesis using P123 43

Fig 2.3: Flowchart of GO synthesis 46

Fig 2.4: Flowchart of GO-TiO 2 (GO-ZnO) synthesis 47

Fig 2.5: Dip-coating TiO 2 on the surface of cordierite 49

Fig 2.6: Experimental LPCVD set-up 53

Fig 2.7: Simplified internal structure of FESEM 54

Fig 2.8: Energy band diagram of a semiconductor (Zeghbroeck, 2007) 60

Fig 2.9: Principle diagram of a HPLC system 61

Fig 2.10a: Photocatalytic exerimental setup with UV-C lamp 62

Fig 2.10 b: Principle diagram of visible photocatalytic exerimental setup 63

Fig 3.1: Nitrogen isotherm of CTAB-NE and P123 C25-450 66

Fig 3.2: Pore size distribution of CTAB-NE and P123 C25-450 67

Fig 3.3: XRD paterns of catalysts synthesized with surfactants CTAB and P123 68

Fig 3.4: FE-SEM images of CTAB-H (a) and P123 C25-450 (b) 69

Fig 3.5: Evaluation of the catalysts using CTAB by two hydrothermal and precipitation methods 70

Fig 3.6: The influence of citric acid amount to catalyst performance 71

Fig 3.7:The influence of Ethanol elimination method to catalyst performance 72

Fig 3.8: Comparing the best catalyst via hydrothermal and precipitation 73

Fig 3.9: Nitrogen isotherm of SG TiO 2 and SG AC1200 TiO 2 1/18 74

Fig 3.10: Pore size distribution of SG TiO 2 and SG AC1200 TiO 2 1/18 75

Fig 3.11: Morphology of SG AC-1200/Ti 1/18 (a) and SG AC-1200/Ti 3/1 (b) 76

Fig 3.12: EDX analysis results of samples: SG AC-1200/Ti 1/18 (a); SG AC-1200/Ti

2/1 (b); 76

Fig 3.13: XRD result of AC TiO 2 catalysts 77

Fig 3.14: MO dark adsorption of AC 78

Fig 3.15: MO photodegration is affected by activated carbon category 79

Fig 3.16: MO photodegradation via time of catalyst samples at pH=7 80

Fig 3.17: MO photodegrdation of samples at pH= 4 81

Fig 3.18: MO photodegradation of samples at pH= 10 82

Fig 3.19: Comparison the MO photodegradation SG AC1200 Ti/1/18 by pH 83

Fig 3.20: Nitrogen isotherm of G1/4, G1/18, G1/24 84

Fig 3.21: Pore distribution of SGGO Ti1/4, SG GO Ti1/18,SG GO Ti1/24 84

Fig 3.22: XRD analysis of GO catalyst 86

Fig 3.23: The effect of GO content to MO photocatalytic degradation 87

Fig 3.24: Photodegradation of TiO 2 GO catalysts with MO concentration 20 ppm in the full range Xenon lamp 88

Fig 3.25 Photodegradation of SG GO Ti/ 1/18 MO for various concentration 88

Fig 3.26: (a) SEM Cor-gel-200 and (b) SEM Cor-gel-CTAB 89

Fig 3.27: Investigate the efficiency of catalyst thin films by dip coating with low concentration of PEG 90

Fig 3.28: SEM characterization: (a) Cor-CTAB, (b) Corgel 200 (c) Cor-P123 92

Fig 3.29: SEM characterization of 2 samples Corgel-150AC (a) and Cor-P123 (b) after the first reaction 92

Fig 3.30: The photocatalytic degradation of four samples Corgel-150, Corgel-150AC, Corgel-200 and AC-gel powder 94

Fig 3.31: Surface of Corgel-150 (left) and Corgel-150AC (right) after reaction 94

Fig.3.32: (a) Surface of Corgel 150AC (left) and Corgel-200 (right);(b)Inside view of Corgel-150AC (left) và Corgel-200 ( right) 95

Fig 3.33: Photocatalytic performance of-P123 and Cor-P123 samples 96

Fig 3.34: MO Photodegradation by CTAB powder and Cor-CTAB 97

Fig 3.35: MO Photodegradation with three TiO 2 films coated on cordierite 98

Fig 3.36: The TiO2 film performance in the first and second times 99 Fig 3.37: SEM characterization of TiO2 on the surface of (a) glass, (b) aluminium, (c)

cordierite with 25,000 magnification; SEM characterization of TiO 2 on the surface of

(d) glass, (e) aluminum and (f) ceramic with 100,000 magnification EDS characterization of TiO 2 on the surface (g) glass, (h) aluminum and (i) c cordierite.

101

Fig 3.38: 10x Microscopy of TiO2 (a) 120oC; (b) 150oC; (c) 200oC; (d) 250oC; (e) 300oC 102

Fig 3.39: 10x Microscopy of TiO 2 thin film on glass substrate at 580 mm-bar pressure at position opposite (a) and next (b) nozzle 103

Fig.3.40: 10x Microscopy of TiO 2 thin film on glass substrate at 700 mm-bar pressure at position opposite (a) and next (b) nozzle 103

Fig 3.41: 10x Microscopy of TiO 2 thin film on glass substrate with carrying gas N 2 300 ml/min 104

Fig 3.42: Visual image of TiO 2 thin film on various substrates 104

Fig 3.43: 10x Microscopy of TiO 2 thin film on various substrates 104

Fig 3.44: TiO 2 thin film performance for MO photodegradation with UV-C 105

Fig 3.45: TiO 2 thin film performance for MO photodegradation with full range lamp 106

Fig 3.46: Phenol degradation evaluation and kinetics study in UV light 108

Fig 3.47: Effect of the initial concentration to the phenol degradation in UV condition and kinetics study by P123-C25-450 109

Fig 3.48: Effect of H 2 O 2 loading and kinetics study in phenol degradation process. 111

Fig 3.49: Phenol degradation process and kinetics study in visible light 113

INTRODUCTION

1 Necessity of the study

Soil and groundwater resource pollution are serious concerns in our nation One of the unavoidable effects of uncoordinated economic zone growth is the contamination of water sources with heavy metals and harmful, persistent organic compounds such as phenol and its derivatives The primary sources of phenol and phenol polluting compounds are the manufacture of synthetic plastics, insecticides, paints, and petroleum [1] Additionally, the textile sector emits a significant number of harmful chemical compounds into the atmosphere, including azo-based dyes, one of which is methyl orange As a result, the remediation of contaminated environments with two chemical compounds as phenol and methyl orange, is a hot topic not only in the nation, but also globally

Historically, remediation of polluted water has been mostly dependent on physicochemical and biological treatment approaches Among these, adsorption is one

of the most frequently used strategies for treating chemical contaminants in water due

to its ease of use and the broad application of a variety of adsorbents Another workable solution is biological treatment, which may eliminate around 90% of organic debris entirely However, this procedure is less efficient for compounds that are difficult to decompose, such as phenol and methyl orange Numerous extensive research studies have been undertaken to process the aforementioned chemicals, which include electrochemical methods, ion exchange, ozone, and adsorption on activated carbon [2, 3] In the other hand, these approaches are rarely used in reality due to their inherent constraints, which include heavy equipment systems, complex operation techniques, high initial and ongoing expenditures, and birth abnormalities It must include a sludge post-treatment step, otherwise the efficiency will remain poor results

Using photocatalysts to treat polluted water is one of the most environmentally friendly green treatment methods available, since it employs natural solar energy and is capable of degrading organic contaminants that are difficult to decompose Without the addition of extra chemicals or sludge buildup in the treatment system [4] TiO2, ZnO, and Fe2O3 are among the semiconductor materials that researchers are interested in as potential photocatalysts Due of titanium dioxide's (TiO2) outstanding characteristics, it

is the most investigated material It is ecologically safe, chemically and physiologically

inert, self-cleaning, and produces minimal byproducts during production [5]

TiO2 nanoparticles have played a key role in the photodegradation of organic pollutants; it seems to be the most investigated photocatalyst due to its cheap cost, photostability, abundance, and high oxidizing power against a wide range of organic pollutants [6,7] Despite these positive qualities, its use is limited due to its large band gap (3.2 eV), the difficulty in separating the catalyst TiO2 from the solution, and the recombination of the photogenerated electron-hole pairs, which results in low photocatalytic reaction efficiency [8] TiO2 is effective in decomposing a vast array of organic, inorganic, and toxic compounds in liquid and gas phase environments However, the 3,2 eV energy band gap of pure TiO2 limits its use to UV light (387 nm,

or about 4% of solar radiation) Numerous approaches have been used to improve the photocatalytic activity of TiO2, including two major classes of chemical treatments, including doping with non-metals, transition metals, dye sensitization, spatial structuring, and doping with rare earth metals [9] Alternative methods include infusing microwave or ultrasonic radiation into TiO2 photoreaction systems [10] Activated carbon may be an ideal substrate for evaluating the drawbacks of TiO2 when supported

by activated carbon

This new discovery has a great deal of potential as a result of the synergy between the photocatalytic activity of the catalyst and the adsorptivity of the activated carbon The use of commercial activated carbon as an effective adsorbent for the removal of organic pollutants from liquid phase [11] is well established However, due to the prohibitive cost involved, its use is severely limited Activated carbon may also be produced from waste products derived from agricultural by-products [12] and the wood industry, as well as non-conventional waste items from municipal and industrial operations The use of waste materials in the manufacturing of activated carbon may be

of significant benefit in minimizing waste disposal in the environment, which may have further impacts Activated carbon may be produced by using waste materials When using TiO2, one of the most important obstacles that must be overcome is separating the powder catalyst from the effluent at high concentrations, which might result in the coagulation of the catalyst as well as the creation of aggregates [13]

Activated carbon's high porosity, high surface area, high photostability, and appropriateness for use at room temperature are some of the benefits that accrue from

using TiO2 in conjunction with activated carbon Other advantages include the ease with which the catalyst can be extracted from the bulk solution Other materials than activated carbon, such as clays [14], zeolite [15], silica [18], alumina [16], and glass, were used

in an attempt to boost the photocatalytic efficacy of the catalyst; however, these other materials did not make a significant contribution It's possible that the synergistic effect

of activated carbon and TiO2 is what's responsible for the promising nature of the combo Sometimes the reaction between TiO2 and a specific pollutant can result in coagulation, which will prevent a significant amount of UV or solar radiation from reaching the catalyst's active core This can happen in a number of different ways This resulted in the reduction in the surface area of the catalyst, which in turn led in a decrease in its photocatalytic activity [17] Because the activated carbon at the surface of the TiO2

functions as an efficient adsorption trap for the organic pollutant, this results in the mass transfer of the pollutant to the surface of the catalyst, which is where the photoreaction takes place It has been shown that the higher adsorption of the substrate onto the surface

of the carbon in activated carbon contributes to the enhanced photocatalytic elimination

of pollutants [19,20] This effect is attributed to activated carbon

In order to broaden the absorption spectrum of the TiO2 catalyst to include the visible light area, which accounts for about 45 percent of solar energy, it is necessary to incorporate metal or nonmetallic alteration methods into the structure of the TiO2

material Since solar energy is a renewable and endless source of energy, this step is necessary because it is required to broaden the absorption spectrum of the TiO2 catalyst Recently, a number of researchers have begun using graphene oxide in an effort to enhance the performance of TiO2 photocatalysts This is owing to the multiple advantages that graphene oxide offers in terms of enhancing catalytic performance under circumstances of visible light [21-25]

2 Objectives of the study

The general objective of this study is to produce catalysts TiO2 modified with activated carbon and graphene oxide, coated on various materials to degrade organic pollutants in wastewater, which is represented by methyl orange and phenol as two harmful substances popular in many textile and other industrial factories, at Vietnam and in the world

The other aims are to investigate the process parameter in catalyst synthesis, to find out the optimum catalysts of each synthesis methods, to make the thin films of catalyst on various substrates to degrade methyl orange, to modify catalyst to have positive results in full range light condition

3 Content of the thesis

Firstly, literature review on previous studies will be investigated to select the preparation methods of the catalysts, materials to modify catalyst, coating techniques and model pollutants to conduct research

The photocatalyst TiO2 was synthesized by sol-gel, co-precipitation and hydrothermal methods After that, catalysts were modified with activated carbon and graphene oxide, silica gel then the catalysts were characterized by physical adsorption, SEM, XRD, UV-Vis

The catalytic activities of these catalysts were conducted for methyl orange and phenol, one stable organic compound, in UV-C and full range light condition

The main process parameters in phenol photodegradation of the optimum catalysts were evaluated and do kinetics study this process

4 Methodologies of the study

Literature review: it is a general section to collect related data from previous researches such as the catalyst composites with activated carbon and graphene oxide, the preparation methods, coating methods, methyl orange and phenol photodegradation Experiments: the catalysts were prepared by sol-gel, co-precipitation, and hydrothermal methods, then characterized by various techniques such as BET physical adsorption, SEM, XRD Finally, the photodegradation performances of these catalysts were evaluated using specific reactor systems combined with UV-Vis and HPLC methods

Data analysis and processing: the method is used to gather and determine the concentration of methyl orange and phenol based on the calibration curve of these substances

5 Scope of the study

Organic pollutants: Methyl orange and phenol were chosen to evaluate the catalyst performance since they are popular pollutants in wastewater

Catalyst thin films: Catalyst thin films made by dip coating and CVD methods on various substrates as cordierite, glass and aluminum are studied

6 Scientific and practical meanings

The thesis can provide a scientific background to synthesize the photocatalyst TiO2

in methyl orange and phenol in laboratory condition Since methyl orange and phenol are popular and difficult compounds to be degraded with aromatic compound, a catalyst with positive efficiency to degrade them will be certainly possible to photodegrade other pollutants

The catalysts were synthesized in thin films by dip coating and CVD methods The parameters and method in making thin films were investigated which can further apply

to treat industrial wastewater

7 Novelty of the study

The main innovations of this research include:

1 Process parameter optimization for catalysts synthesized via co-precipitation, hydrothermal, and sol-gel methods

2 Catalytic film formation optimization on various substrates using CVD (chemical vapor deposition) and dip coating

3 Research on the modification of catalysts synthesized by sol-gel and hydrothermal methods on activated carbon and graphene oxide carriers appliedd in the treatment of methyl orange and phenol

8.Structure of the thesis

The thesis consists of four main chapters The first chapter summarizes the literature on methyl orange (MO) and phenol contamination, and the methods for preparing titanium dioxide (TiO2) to improve its performance in the photocatalytic degradation of MO and phenol The second chapter describes the synthesis method to prepare the various catalysts, introduce basic principles of the physico-chemical methods used as well as the experimental set-up utilized in the thesis The third chapter focuses on evaluating the properties of the prepared catalysts, and the influence of different synthesis methods on the catalytic performance of the catalysts in the photodegradation of methyl orange and methyl orange phenol

Finally, the fourth chapter summarizes the main points of the thesis and gives some recommendations for future works

CHAPTER 1 LITERATURE REVIEW

This chapter presents the previous research that are related to this study as TiO2

catalyst, preparation method of photocatalyst, photodegradation for MO and phenol, TiO2/AC and TiO2/GO materials, coating techniques et al

1.1 Textile industry and Methyl Orange dye

The textiles and garment industry of Vietnam has been a critical area for the Vietnamese economy for a long time The industry employs over 3 million employees and has over 7,000 factories throughout the country As a sector relies heavily on water supply for its development and produces wastewater as a result, it is crucial for stakeholders in the sector to better understand the water threats they pose, their impacts and the possible approaches they provide to these challenges [26]

In the textile and dye business, wastewater is produced throughout the steps of sizing, cooking, bleaching, dying, and finishing These processes may be broken down into their individual stages here The quantity of wastewater produced is mostly attributable to the washing procedure that occurs after each cycle The amount of water that is required in a textile industry is quite high, although the amount varies greatly from item to item The examination of specialists indicates that the quantity of water used in the manufacturing stages amounts for 72.3% of the total, with the majority of this water coming from the dyeing and finishing stages of the goods One may do a rough calculation that places the water need for one meter of fabric anywhere in the range of 12–65 liters and the amount of water discharged somewhere between 10–40 liters Water contamination is the most significant environmental issue that the textile sector faces The textile dyeing business is regarded to be the most polluting of all industries when two parameters, namely the volume of wastewater and the types of pollutants that are included within the wastewater, are taken into consideration.[27,28] The primary contaminants in textile dyeing wastewater include persistent organic chemicals, dyes, surfactants, organic halogen compounds, neutral salts that enhance the total solids content, and temperature Due to the high alkalinity, the effluent pH is also high Among these, dyes are the most complex to process, particularly azo dyes, which account for 60-70 percent of the dye industry [29-32] During the dyeing process, the pigments in the dyes do not normally attach themselves to the fibers of the cloth; nonetheless, a certain quantity of the pigments still stays in the wastewater There may

be as much as fifty percent of the original quantity of color left in the material after it has been dyed [29-30] Because of this, the wastewater that is produced from the textile dyeing process has a strong color and a significant concentration of contaminants Methyl orange, often known as MO, is an anionic azo dye that has found widespread use in a variety of different sectors, including those dealing with textiles, printing, paper, pharmaceuticals, food, photography, and leather Methyl orange and the various compounds that come from it are responsible for significant amounts of pollution that are released into the environment It has been shown that this coloring agent may cause cancer as well as genetic mutations [33] In addition to being a dye that

is soluble in water, methyl orange is characterized by a high degree of stability as well

as unique color qualities This compound has an orange appearance when it is in a basic medium, but it has a red appearance when it is in an acidic media It was discovered that the reductive breakage of the azo bond (–N=N–) by the azo reductase enzyme that is present in liver creates aromatic amines, and that these aromatic amines may potentially contribute to intestinal cancer if they are taken by human humans [34]

Fig 1.1: Chemical structure of MO molecule [33,34]

Methyl orange, also known as (C14H14N3SO3Na), served as the model pollutant for the purpose of this investigation Methyl Orange is a typical kind of azo-dye that is used

in the industrial sector It is prized for the stability that it has Up to 70% of today's dyes are made up of azo-compounds, which are synthetic inorganic chemical chemicals These compounds are used to make colors It is believed that somewhere between 10 and 15 percent of the dye that is used in the production of textiles is wasted and emitted

as effluent The discharge of this effluent is referred to as "non-aesthetic pollution" since the concentrations that are visible in water sources are lower than 1 parts per million Although this is the major reason for degrading methyl orange, the dye waste water may also create harmful byproducts through other chemical processes such as oxidation and hydrolysis [35-37] Although this is the primary motive for degrading methyl orange, it

is not the only motivation These azo-compounds are quite stable, as was previously

said, and this is because the dye contains a significant amount of aromatics Biological treatments may not be able to degrade the dye effluents; instead, they could only change

the color of the effluents

The chemical compound known as phenol (C6H6OH) was found for the first time

in 1834 during the distillation of coal It was first referred to as a carbolic acid since coal distillation was the primary source of phenol synthesis up to the advent of the petrochemical industry At the moment, quite a few different chemical processes have been discovered that may be used to generate phenol In particular, a large number of steel plants discharge wastewater that contains phenol chemicals Pure phenol is either colorless or white in appearance In this state, phenols are solid crystals that may persist

in air for an extended period of time Partial oxidation of phenol causes the material to take on a pink hue and causes it to break down when it comes into contact with water vapor The concentration of phenol at which an odor can be detected begins at 0.04 ppm;

at this level, the phenol has an odor that may be described as mildly pungent and pungent Phenol plays a very important part in industry; it is the raw material that many factories use to produce plastics, chemical silk, agricultural pharmaceuticals, antiseptics, fungicides, pharmaceuticals, dyes, and explosives [38,39] In addition, phenol is the source material for many other industries that produce plastics

Phenol may enter the human body by inhalation as well as through contact with the skin, eyes, and mucous membranes When ingested, substances with a high phenol content will lead to a fatal phenomenon with symptoms such as convulsions, inability

to control, coma leads to respiratory disorders, blood changes in the body leading to a drop in blood pressure Phenol is considered to be extremely toxic to humans when it enters the body of a human through the mouth When a person is poisoned by phenol, it first affects their liver, and then it goes on to attack their heart When individuals were subjected to phenol for extended periods of time in a number of different trials, it was found that they experienced pain in their muscles and an enlargement of their livers Burns to the skin and irregular heartbeats are also side effects of phenol's contact with the skin The amount of phenol that may legally be present in a human body is capped

at 0.6 milligrams per kilogram of total body weight There are no studies on the effect

of phenol at low concentrations on the development of the body at this time; however, many scientists believe that chronic exposure to phenol can lead to growth retardation, cause abnormal changes in the next generation, and increase the rate of premature birth

in a pregnant woman [40-42]

In a nutshell, phenolic compounds are one of the most commonly used chemical compounds in the manufacturing industry On the other hand, they are also toxic compounds that can be extremely hazardous to both organisms and humans if they are not treated properly before being released into the environment Because the wastewater from the Formosa - Ha Tinh factory in Vietnam, which has been discharged into the marine environment, contains high levels of phenol, which has caused the death of a large number of fish in the coastal provinces in the central part of our country, it is necessary to take measures to thoroughly treat this phenomenon The level of chemical contaminants in waste water is rather high, particularly those that are long-lasting organic chemicals like phenol and its derivatives Because of this, phenol degradation is considered to be of critical significance not just in Vietnam but also across the whole globe [43]

1.3 Titanium dioxide, TiO2

Rutile Anatase Brookite

Titanium Dioxide, often known as TiO2 or titania, is a substance that has received

a significant amount of attention and study owing to the stability of its chemical structure, biocompatibility, as well as its physical, optical, and electrical characteristics TiO2 is a multipurpose substance that may be used in a wide variety of goods, including pigments for paint, sunscreen lotions, electrochemical electrodes, capacitors, solar cells, and even as a food coloring additive in toothpaste [45] TiO2 was created and put to use

in the previous two decades with the primary goal of ridding the environment of harmful chemical compounds, particularly those found in air and water TiO2 may be used to

lessen the amount of pollutant substances in the air, such as volatile organic compounds,

or perhaps get rid of them entirely In the presence of sunshine, the photocatalysis of titanium dioxide (TiO2) has the potential to break down and eliminate hazardous chemical molecules [46]

Figure 1.2 illustrates the arrangement of the various crystal structures of titanium dioxide There is one stable phase of TiO2 known as Rutile (tetragonal), as well as two meta-stable phases known as Anatase (tetragonal) and Brookite (orthorhombic), both of which have the potential to transform into Rutile when exposed to temperatures outside

of their normal range When compared to the Anatase form, the recombination rate of the surplus charged carriers in the Rutile structure is often seen to be greater In addition

to this, it is known to occupy the charged transfer that occurs between the catalyst and the potential reactants This provides a fundamental explanation for why rutile form of titanium dioxide (TiO2) is used in paint formulation rather than the anatase form, which has a much slower recombining rate but is far more efficient in charged transfer TiO2's anatase phase, which has a band gap of 3.2eV, has been shown to be TiO2's most active crystal structure This is largely due to the fact that it has favorable energy band positions and a high surface area [47, 48] Rutile, which has a band gap of 3.0, is used in a wide variety of applications, the majority of which are in the pigment industry Anatase has a band gap of 3.2eV and another thing to take into account is the wavelengths that correspond to the anatase and rutile phases of titanium dioxide, which are 388 for anatase and 410 for rutile, respectively

As a semiconductor, TiO2 may be photo-activated to create a redox environment that can destroy organic and inorganic contaminants In Table 1.1, we can see the overarching steps that occur throughout the photocatalytic reaction process on irradiated TiO2

Photodegradation of pollutants by TiO2 begins with UV radiation absorbed by the TiO2 particles, with a band gap value of 3.2eV for Anatase and 3.0eV for Rutile By doing so, holes and electron pairs are generated in the valence band (hole) and conduction band (electrons) of the semiconductor, respectively (Eq 1, Table 1.2) (electron) To clarify, although both Anatase and Rutile type TiO2 absorb UV radiation, Rutile type TiO2 may also absorb radiation that is closer to visible light In contrast to Rutile-type TiO2, Anatase-type TiO2 has more photocatalytic activity because of its conduction band location, which reveals better reducing power Both the absorbed energy and the kinetic energy of the recombining holes and electrons may be used in the

redox processes (Eq 5, Table 1.2) Electron donors and acceptors adsorbed on the semiconductor surface or even just close the double layer encircling the particle will participate in the redox reactions, which occur when an electron or hole with sufficient energy crosses the double layer

(semiconductor valence band

hole and conduction band

electron) Electron removal from

the conduction band

TiO2- + O2 + H+→ TiO2 + HO2

TiO2- + H2O2 + H+ → TiO2 + H2O+ OHTiO2-+ 2H+ → TiO2- + H2

The solid side of the junction between the semiconductor and the liquid creates an electrical field that separates the energized hole and electron pairs that are unable to recombine This allows the holes to migrate to the illuminated part of the TiO2 and the electrons to migrate to the unlit part of the TiO2 particle surface The failure of the pairs

to recombine results in the separation of the pairs The creation of a very reactive but short-lived hydroxyl radical (OH-) via hole-trapping is generally considered to be the first step in the process of photocatalytic degradation This theory is generally accepted Either the highly hydroxylated surface of the semiconductor or the direct oxidation of the pollutant molecules under the influence of UV radiation might result in the formation

of OH It is also possible that both of these ways of producing OH- occur concurrently

in certain situations This is another option This action takes place immediately after the reduction of adsorbed oxygen species, which may be generated either from dissolved oxygen molecules (in the aqueous system) or from other electron acceptors that are accessible in the aqueous system [50]

In the course of this research, the free radicals that are generated as a result of the photocatalytic activity will assault the organic component that is present in the polluted water MO and phenol will be used in the evaluation of the ability of TiO2 to be manufactured by sol-gel and other ways to play the role of a model chemical found in waste water TiO2 may be used in photocatalytic processes in one of two different ways: either it can be suspended in aqueous fluids or it can be immobilized on support materials Quartz sand, glass, activated carbon, zeolites, and noble metals are the materials that are used for the supports The fluidized bed reactor [40] and the fixed bed reactor [40,43] are two examples of various reactor designs that are possible Matthews and McEvoy discovered in 1992 that photocatalytic reactors using immobilized photocatalysts had a reduced efficiency compared to those that used dispersed titania particles [48]

It has been proposed that the lower efficiencies that can be achieved with immobilized photocatalyst can be attributed to the following: first, the decreased number

of activated sites in a given photoactivated volume that are available when the catalyst

is immobilized as compared to the same weight of catalyst that is freely suspended; and second, the mass transfer limitation that may become rate controlling at low flow rates This latter issue is especially problematic in the presence of intense illuminations because it is possible that the mass transport will be unable to keep up with the reaction occurring at the photoactivated surface, leading to the possibility that the reaction will become entirely mass-transfer limited When this occurs, the growing photon intensity

will not create a discernible change in the pace at which the reaction occurs

Akpan and Hameed conducted research on the influence of operational settings on the photocatalytic degradation of textile colors using TiO2-based photocatalysts[50] In addition to this, it has been shown that there are a variety of processes involved in the manufacturing of photocatalysts based on TiO2 The Sol–Gel process is quite popular because it makes it possible to produce nanometer-sized crystalline TiO2-based catalysts powder with a high degree of purity at a temperature that is very low

1.4 Principles of Precipitation, sol-gel and hydrothermal synthesis methods

❖ Precipitation

After thoroughly dissolving the precursors in water to make the homogeneous solution, the precipitant is added to the solution to precipitate the solid This completes the process of making the homogenous solution After that, the solids are extracted from the solution, washed to remove any contaminants, dried in an oven, and calcined at a high temperature to produce the materials This approach makes it possible to diffuse the reactant on an atomic size, which ultimately leads to an increase in the reactants' capacity to make contact with one another The fact that the desired ratio of elements in the product cannot be guaranteed to be achieved using this method is, however, one of

the method's major drawbacks [51]

❖ Sol-gel

The sol-gel method has seen a lot of action in recent years when it comes to the production of catalytic supports In preparations that begin with a metal alkoxide, the alkoxide is first hydrolyzed by the addition of water to an organic medium This is followed by polymerization of the hydrolyzed alkoxides by condensation of hydroxyl and/or alkoxy groups in the alkoxides The whole solution will become hard and a solid gel will be created when the level of polymerization and cross-linking of polymeric molecules becomes considerable The porosity of this gel, as well as the surface area, pore volume, pore size distribution, and thermal stability of the final oxide following calcinations, are all strongly impacted by the size and degree of branching of the inorganic polymer, as well as the level of cross-linking If the gel comprises polymeric chains that have a high amount of branching and cross-linking, the gel will, in general, have extensive void areas, will be structurally extremely stiff, and the oxide that will arise from calcinations will mostly have macropores and mesopores If the gel comprises polymeric chains that do not branch out much or have many cross-links, then the gel will have fewer void regions, will be structurally weak, and will thus easily collapse when calcinations are performed The oxide that is produced as a consequence consists

mostly of micropores and has a small surface area In spite of this, it is feasible to manufacture nano-material by employing the sol-gel process [52], which involves combining the reactants at the atomic range

The following are some of the many benefits that come with using the sol-gel process [53]:

(1) High-purity materials may be created by using synthetic chemicals rather than minerals, which makes this process possible

(2) It requires the use of liquid solutions in place of more traditional methods of combining raw components Because the liquids being mixed have a low viscosity, the process of homogenization may be completed in a very short amount of time and at the molecular level

(3) Because the precursors are well-mixed in the solutions, it is expected that they will be as well-mixed at the molecular level when the gel is created; as a result, chemical reaction will be simple and occur at a low temperature when the gel is heated

(4) It is possible to change the physical features of the material, such as the pore size distribution and the pore volume

(5) It is possible to include many different components into a single process step (6) It is possible to produce a variety of various samples in their physical shapes

❖ Hydrothermal method

The production of nanocrystalline inorganic materials by the use of hydrothermal processing is an unorthodox approach It is possible to tune the synthesis of nearly any material thanks to the existence of a direct precursor-product correlation, which does not need the inclusion of any additional structure guiding agents

The precursor substance is continually dissolved in the hydrothermal fluid while the hydrothermal environment is maintained at a certain temperature and pressure that

is suitable for the synthesis (for example, temperatures of around 300 degrees Celsius and water pressures of one kilobar) Even when alumosilicate materials are used, the production of gels is not noticed at any point throughout the process This is due to the fact that larger molecular units are hydrolyzed when the temperature and pressure are increased

In an aqueous solution, under autogeneous pressure conditions that are well below the critical point, different states of dissolution may be existent, and most importantly, not only the basic structural building units, but also colloidal states may be present This

is because the critical point is the point at which autogeneous pressure becomes critical

Because larger units that exceed the size that is present in true solutions are not stable under high pressure hydrothermal conditions, high pressure hydrothermal synthesis implements a first step of crackdown of possibly present "macromolecular" units by chemical reaction These "macromolecular" units could be present, for example, as a colloidal solution, as a precipitated colloidal solution (crystalline, partially crystalline (e.g gel), glassy and amorphous) or as solid state precursor materials Therefore, it is believed that a real solution will emerge, in which the smallest feasible structural building blocks, in addition to cations with their associated hydration spheres, will be transported [54]

1.4.1 Preparation of photocatalyst using sol-gel method

According to O Carp [55], TiO2 may be manufactured into powder, crystals, or thin films This versatility allows it to be used in a variety of applications Crystallites may range in size from a few nanometers to several micrometers, and they can be used

to generate powders, films, or both It is important to highlight that nanosized crystallites have a propensity to aggregate into larger structures A procedure known as

"deagglomeration" is often required in order to achieve the desired result of having nanoparticles that are distinct from one another Nanoparticles may be produced using

a variety of cutting-edge techniques that do not need an extra deagglomeration phase The nanosize titanium dioxide, also known as nano-TiO2, was produced using a procedure that began with the hydrolysis of titanium precursors and ended with annealing, flame synthesis, hydrothermal, and sol-gel processes The sol-gel approach has seen widespread use because it makes the synthesis of nanoparticles in conditions similar to those found in nature—that is, at room temperature and under the pressure of the atmosphere In addition to this, the set-up for this method is not very complex Sol-gel has all the advantages over other preparation techniques in terms of purity, homogeneity, flexibility in introducing dopants in large concentrations for stoichiometry control, and ease of processing and composition control since this method is a solution process Sol-gel also has all the advantages over other preparation techniques in terms

of stoichiometry control

Synthesis of solid materials carried out in a liquid medium and often carried out at low temperatures Particles in a dispersed condition in the solvent independent colloidal suspension (Sol) the colloidal particles are connected together to create a three-dimensional open grid (Gel) The typical molecular precursors are metallo-organic compounds such as alkoxides M(OR)n, where M is a metal such as Si, Ti, or another similar element R represents an alkyl group (R may be CH3, C2H5, or any other

combination of these) In a similarl way Ti(iOC3H7)4 is used in the manufacturing process for titanium dioxide the preparation of TiO2

Ti(OCH(CH3)2)4 + 2 H2O → TiO2 + 4 (CH3)2CHOH The Sol-Gel synthesis of TiO2-based products makes use of this reaction as one

of its building blocks In most cases, water is added to a solution containing an alkoxide that has been dissolved in an alcohol The presence of additives (such as acetic acid, for example), the quantity of water, and the mixing speed all have a role in determining the characteristics of the inorganic result Titanium (IV) (IV) The formation of chiral epoxides may be accomplished by a process known as the Sharpless epoxidation, which requires the use of isoproxide as an essential ingredient A water-soluble precursor molecule is hydrolyzed during the Sol-Gel synthesis, which results in the formation of

a dispersion of colloidal particles (the sol) The continuation of the reaction results in the formation of bonds between the sol particles, producing an endless network of particles (the gel) After that, the gel is heated in order to produce the required substance

in most cases This approach to the synthesis of inorganic materials provides a number

of benefits that are not shared by other, more traditional methods of synthetic synthesis For instance, very pure materials are able to be produced at temperatures that are lower

In addition to this, homogenous multi-component systems may be generated by combining precursor solutions; this makes it possible for the materials that have been prepared to have simple access to chemical doping In conclusion, the rheological characteristics of the sol and the gel may be employed in the processing of the material

in a variety of different ways, including the dip coating of thin films, the spinning of fibers, etc In order to provide a new generic method for the manufacture of nanostructures of semiconductors and other inorganic materials, the principles of Sol-Gel synthesis and the fabrication of templates for nano-materials are merged It is possible to do this by carrying out a Sol-Gel synthesis inside the pores of a variety of microporous and nanoporous membranes in order to generate mono-disperse tubules and fibrils of the material that is needed During the sol–gel synthesis of nano TiO2, a high water ratio was maintained This increased the nucleophilic attack of water on titanium (IV) isopropoxide and prevented the quick condensation of titanium (IV) isopropoxide species, which resulted in the production of TiO2 nanocrystals [56]

Xu presented a novel approach to the synthesis of titanium dioxide in the year 1991 [57] This approach included the use of a sol-gel technique, a cellulose membrane, and heat peptization in order to separate the by-product from the solvent, both of which were alcohol Compared to those that were dialyzed, the aggregation of the sols that underwent thermal peptization was much more dense The slow removal of protons from

highly charged particles is accomplished by the process of dialysis, which ultimately results in the aggregation of the particles This provides an explanation for the primary qualitative characteristic of aggregation and deposition, which is that the charges are completely screened by electrolyte ions and those driven by diffusion TiO2 that contains fewer particles reveals a greater surface area than does TiO2 that is densely packed Sol-gel processing is one of the most frequent ways used to generate photocatalyst TiO2 in both coatings and powder forms This approach may be used to make photocatalyst TiO2 in either form This method does not call for the use of a sophisticated apparatus and may produce nanoparticles at room temperature and under normal atmospheric pressure [58] It offers a straightforward and uncomplicated method of achieving the desired result When generating N-TiO2 using Titanium (IV) Isopropoxide

as the precursor material, Venkatchalam conducted research on the impact of hydrolyzing agents as well as the quantity of water used in the process The use of an acid as the hydrolyzing agent, which in this scenario was acetic acid, resulted in a more minute particle size for the TiO2 compound Because of this, rapid synthesis of Titanium Hydroxide and their condensation to form TiO2 nanoparticles was particularly well-favored in the presence of acetic acid

Fig 1.4: Nanocrystalline Metal Oxide Preparation using Sol-Gel method

In addition to this, the presence of an excessive amount of acetate anion adsorbed

on the surface of TiO2 has the potential to inhibit the development of TiO2 It is possible that the formation of this particular kind of acetate anion complex on the surface of anatase TiO2 during the process of sol-gel synthesis is to blame for the reduction in the crystallite size of TiO2 The study also made use of a high water ratio

in order to boost the nucleophilic attack of water on titanium (IV) isopropoxide and to slow down the fast condensation of titanium (IV) isopropoxide species in order to

produce TiO2 nanocrystals Both of these techniques were used in order to achieve the desired results Due to the presence of residual alkoxy groups, the rate of crystallization of TiO2 may be greatly slowed down, which in turn promotes the production of the less dense anatase phase exclusively The hydrolysis rates are low because there is a very little quantity of water, and the presence of an excess of titanium alkoxide in the solvent encourages the formation of Ti–O–Ti chains through alcoxolation The growth of Ti–O–Ti chains leads in the formation of three-dimensional polymeric skeletons with tight packing, which produces a high ratio of rutile phase This is due to the fact that each titanium atom is coordinated with four oxygen atoms

The process of calcination, on the other hand, is particularly significant for eliminating the organic molecules from the end products and finishing the crystallization process It is also a key parameter in the synthesis of catalysts, and it may play a significant role in regulating the final catalyst product's physicochemical qualities The temperature at which TiO2 films are calcined has been shown to have a significant impact on their photocatalytic activity [59-61] This has been reported in the past In the research carried out by Porkodi and Arokiamary, it was discovered that calcining TiO2 at temperatures lower than 520 degrees Celsius would result in the creation of anatase; however, at temperatures higher than that, a phase change from anatase to rutile will take place [62] In addition, the temperature at which the calcination process is carried out has an effect on the films' capacity to withstand mechanical stress Therefore, before designing a nano-photocatalyst, it is vital to understand the link between calcination temperature, photocatalytic activity, and mechanical stability of such coatings [63] This is because the nano-photocatalyst must

be able to withstand very high temperatures

The effects of acidic and basic hydrolysis catalysts on the photocatalytic activity and microstructures of bimodal mesoporous TiO2 were studied by Yu-Hsien [64] Titanium (IV) Isopropoxide was used as the starting material in the investigation, while NH4OH and HNO3 were used, respectively, as the basic and acidic catalysts The XRD was used to determine the crystal structures of the substance The investigation revealed that HNO3 promoted the development of brookite In addition,

NH4OH not only slowed down the phase change of the TiO2 powders from amorphous

to anatase and then from anatase to rutile, but it also prevented the development of brookite

Nikkanen investigated how acids change the crystal structure of TiO2 and found

some interesting results Nitric acid was used by the researchers so that the amorphous TiO2 could be converted into anatase and rutile structures [65] According to the findings, the quantity of anatase present in the catalysts increased in proportion to the degree to which the acid was diluted, whereas the proportion of rutile crystal structure increased in proportion to the degree to which the acid was concentrated Additionally, Zang conducted research in 2008 to investigate the influence that preparation techniques have on the structure and catalytic performance of TiO2/AC catalysts that were synthesized using the sol–gel method Titanium orthotitanate, also known as TBOT, served as the precursor material for the manufacture of titanium dioxide, which was exclusively applied to the outside of AC A modest alteration took place in the porous structure of AC [66]

Kanna looked into mixed TiO2 powders that had varying amounts of amorphous, anatase, and rutile in them [67] These powders were made using the acid-catalyzed sol–gel process and were heated to 80 degrees Celsius without calcination Titanium tetrachloride was the substance that was employed in the precursor stage In addition

to the precursor material, several acids, notably HCl, HNO3, H2SO4, CH3COOH, and

H3PO4, were also added TiO2 by itself and TiO2 that had been mixed with HCl, HNO3, and CH3COOH included a variety of structures that were amorphous, anatase, and rutile, according to the findings of an XRD analysis In addition, the BET findings demonstrated that the complete sample that was created did, in fact, contain comparable surface areas FT-IR analysis revealed that OH- groups were existing on the surface of the newly synthesized TiO2, as compared to the original Because of the presence of water and also the vibration of Ti-OH groups, every sample demonstrated the existence of OH- groups This was owing to both of these factors

1.5 Support and thin films

1.5.1 Overview of Cordierite

Cordierite is a material made of 3 components MgO–Al2O3–SiO2 The chemical composition of cordierite is 2MgO.2Al2O3.5SiO2 Cordierite contains 13.78% MgO, 34.86% Al2O3 and 51.36% SiO2, with this composition Cordierite belongs to the ceramic group with high mullite (3Al2O3.2SiO2) composition

Crystals of cordierite offer a number of beneficial features, including a low coefficient of thermal expansion and a low thermal loss Cordierite ceramic is a form of ceramic whose primary crystal is cordierite Because cordierite ceramic has great thermal stability and it is simple to generate porosity, it is frequently employed in sectors that experience fast temperature fluctuations, such as the manufacturing of filters for

motors mechanical, as a catalyst carrier, and as a lining material in arc welding Mag) technology mechanical, as a catalyst carrier, and as a lining material in arc welding (Mig-Mag) technology Because of its very limited temperature range during the firing process, cordierite ceramic is one of the most challenging types of ceramic to work with The reactions that take place during calcination are dependent on the maximum calcination temperature, the heating rate, the amount of time that is retained at the maximum calcination temperature, as well as the particle size and composition During the calcination process, another factor that plays a significant impact is the number of impurities present The reaction never quite reaches its destination since equilibration is such a difficult process to do In most cases, the only preparation that is necessary before use is heating to the desired temperature These preparations are carried out in accordance with the needs and objectives of the usage Objects that are clumped together and have a high mechanical strength, porosity, and a low water absorption capacity or bulk mass will be the biggest In general, materials that wish to solidify properly under normal circumstances must be heated to a temperature of not less than 0.8T (where T is the melting temperature) This means that the heating temperature must be over 1200°

(Mig-C for the intended result, which is cordierite [68]

1.5.2 Mesoporous TiO2 and coating techniques

It is essential for modern civilization to make advantage of porous materials in a variety of applications [69-71], including catalysis, adsorbents, optics, sensors, insulating lacquers, and ultralow-density materials, among others Porous materials are widely used in the field of catalysis and have a direct impact on the economy of the world This is because porous materials make it possible for reactions to take place under conditions that require less energy One example of this is the refining of petroleum, in which diverse microporous zeoliths play a prominent role in catalytic cracking reactions [72] Microporous materials, like zeolites, have restricted apertures, which prevents them from being used in demanding applications like oil refining This is one of the most significant limitations associated with these types of materials

Documentation has been provided by Stucky and colleagues [73] about the synthesis of large-pored, mesoporous metal oxide powders and films using P123 As a kind of inorganic starting material, metal chloride salts have been used in their studies

In order to postpone the crystallization of titanium, a non-hydrolytic approach that involves the breakage of carbon-oxygen bonds was developed This seems to be an essential step when creating the mesostructures in a controlled manner

Using TBT, TET, or TPT as precursors, Sanchez and colleagues conducted an

in-depth study on the function that water plays in the process [74] Condensation does not take place before the formation of the mesostructured hybrid stage because the condensation rate is very low when the water content is low On the other hand, condensation reactions, which take place in the presence of considerable amounts of water and contribute to the formation of oxo clusters, come before the formation of hybrid processes In spite of this, the addition of an excessive amount of water resulted

in the production of gels that lacked periodicity

For the synthesis of the mesoporous titanium that was employed in the EISA solution, CTAB and TET were used NBB, which self-assembles all around the micelles,

is the component of the hybrid process referred to as "titaniatropic." This assembly might be thought of as having interactions of the type Ti–OH+ –X– CTAB+, where X represents the CTAB bromide anion and/or HCl chloride ions that are involved in the synthesis Altering the solvents and co-solvents used allowed Yan and his team of researchers to discover that distinct phases of titanium could be produced The use of TiCl4, P123, or F127, together with changing the solvent from methanol to ethanol, 1-butanol, and 1-octanol, resulted in the production of a combination of anatase, rulia, and pure rutile anatase Clarification is provided on the variances in the ability to release atoms of chlorine As the length of the carbon chain increases, a greater quantity of chlorine is retained in the moieties of color alcohol [TiCl4x(OR)x], which results in an increase in the level of obstruction In phases, anatase normally forms when the acidity

is low, while rutile forms when the acidity is high [75]

A well-ordered TiO2 mesostructure was produced by using TiCl4 and TBT in conjunction with P123, as stated in reference number [70] Intriguingly, our investigation has produced pore walls that include a combination of rutiles and anatases

in their phase composition The mesoporous material has a surface area of 244 m2 per gram and was generated at a ratio of 0.2 to P123 / TBT mole [76] Citric acid was added

to the mixture that included TPT and F127 in order to produce mesoporous titania [77] The hydrophilic titanium surface of the nanoparticles is functionalized by the citric acid, which also increases the binding of the nanoparticles to the F127 ethylene oxide units The production of a titania-P123 mesostructure was followed by the addition of ethylenediamine, which resulted in the development of a mesoporous anatase that is thermally stable Following calcination at temperatures as high as 700 degrees Celsius, the en molecules bond to the surface of titanium nanoparticles This prevents the pores from collapsing and even prevents anatase from converting into rutiles [78]

1.5.3 Catalyst Suspension and immobilization

TiO2 catalyst powder has been suspended in water for use in a wide variety of

applications Due to the high cost of retrieving the catalyst, researchers have been looking at several ways that may immobilize catalyst particles in a substrate In spite of the fact that suspended TiO2 powder is effective because of the wide surface area of catalyst that is readily accessible for reaction, the procedure of recovering the catalyst is time consuming in addition to being a costly one In addition to this, suspended catalyst impeded the passage of ultraviolet light, which in turn decreased the effectiveness of the catalyst [79] Immobilizing the catalyst on a substrate, which is becoming more important in photocatalytic treatment of organic pollutants, is one approach to resolving this issue This is only one of several potential solutions

It is well known that the immobilized form of the TiO2 photocatalyst is inexpensive, has great stability, and does not show any signs of photocorrosion Additionally, immobilized TiO2 has great surface characteristics, making it an excellent candidate for the treatment of wastewater on a wider scale [80-82] Immobilizing TiO2

in a substrate has been possible via the use of a variety of different methods recently Anodization [83-84], the sol-gel method [85-86], reactive direct current magnitude 27 sputtering [87], chemical vapor deposition [81], electrostatic sol-spray deposition [86], and aerosol pyrolysis [87] are some of the processes that fall under this category When selecting a strategy for catalyst immobilization, several aspects, such as the nature of the catalyst substrate or support, the nature of the pollutant, and the surrounding environment, are taken into account (liquid or gas) When TiO2 is loaded onto a support, the photocatalytic characteristics of the support are altered, with the primary disadvantage being a decrease in the surface area of the support [88] Spraying, electrophoresis, inject printing, dip-coating, and spin coating are some of the techniques that may be used in the sol-gel process for the purpose of sol deposition on the substrate [89] In spin coating, a uniform coating was seen; the deposition of TiO2 particles under vacuum led to a hard coating, and the procedure eliminated residual air completely [90] Spin coating was successful in producing a uniform coating Even if it was discovered that TiO2 particles can be placed homogeneously on AC by utilizing vacuum and rotating, the dip coating process still provides numerous benefits over alternative deposition procedures owing to the fact that it uses extremely basic equipment [91] Glass, silicon, stainless steel, and titanium are just few of the substrates that have been used in the past When TiO2 was utilized as the starting material, various binders were added as additions to the suspension, and post-deposition annealing was also performed with the intention of improving the adherence [92] When compared to the binding approach, the direct creation method often produces crystals of worse quality [93-99]

1.6 TiO2/AC Materials

Fujishima and Honda made the discovery in 1972 that photocatalytic splitting of water may be accomplished on TiO2 electrodes Because of this occurrence,

a new stage for heterogeneous photocatalysis was established [100] that involves the exploitation of TiO2 as a semiconductor Recent research has shown that TiO2 may be used as a photocatalyst for the photodegradation of organic pollutants, which are substances that are thought to have a harmful influence on both the environment and human health The transformation of organic contaminants into less hazardous compounds is nonetheless still ongoing and contributes to the ongoing enhancement of its characteristics Controlling key factors, such as calcination temperatures, pH, and aging times, is one way to go in the right direction On the other hand, the inclusion of supporting material that contains titania would be an excellent strategy to improve the photocatalytic effectiveness of it As a result, on the basis of the assessment of the relevant literature, a number of fundamental criteria for choosing an appropriate catalyst load have been defined, including [94, 101]:

a The composite material should be transparent, or at the very least, should allow some ultraviolet radiation to flow through it Additionally, the material should

be chemically inert or non-reactive to pollutant molecules, their intermediates, and the surrounding aquatic system

b The composite material should be able to attach to the TiO2 in an adequate manner, either physically or chemically, without inhibiting the reactivity of the TiO2

c The composite material should have a large surface area as well as a significant adsorption affinity towards the contaminants (organic or inorganic substances) that need to be degraded This criteria decreases or eliminates the intermediates that are formed during the photocatalytic degradation, while simultaneously improving the mass transfer rates and processes for an effective photo-degradation

d The composite material should make it possible for photocatalysts to be recovered and reused in a quick and simple manner, with or without the need for regeneration

To make a composite catalyst, activated carbon and TiO2 are often combined This is done because activated carbon has excellent adsorptive characteristics Because

of its high surface area, good microporous structure, increased adsorption capabilities, and the ability to adjust its surface chemistry and porous structure during the preparation

or activation steps, activated carbon is a popular adsorbent that is used in the vast majority of industrial applications Because of this, when compared to adsorbents based

on other oxides, it has a number of advantages that make it stand out [101] Activated

carbons are extensively employed as an adsorbent in a broad variety of applications, including purifying, decolorizing, deodorizing, dechlorinating, detoxifying, filtering, removing or altering salts, separating, and concentrating for the purpose of recovery Titania's effectiveness as an adsorbent might be improved by combining it with activated carbon, which is known for its ability to remove contaminants from water During the process of photocatalysis, activated carbon allows for the migration of contaminants by diffusion; these pollutants are then further broken down into water and carbon dioxide Activated carbon and titanium dioxide were used as composite materials

in a research project that was carried out by Wang et al in 2007 [102] In the course of this research, TiO2 was manufactured using the Sol-gel technique, and composite material was manufactured before being calcined at a variety of temperatures Various amounts of the composites, including 20% by weight, 50% by weight, and 80% by weight (representing the weight proportion of the starting carbon content to the final TiO2 produced), were also subjected to testing When calcined at 450 degrees Celsius, the composite catalyst was able to display superior qualities in comparison to those calcined at temperatures either much lower or significantly higher The TG analysis demonstrated that the carbon content of the composite did not vary over its whole, which resulted in the composite maintaining its identical surface area However, when the composite was heated to higher degrees, a lower amount of carbon was discovered inside it, which led to a reduction in the surface area of the composite This weight reduction may be attributed to the carbon gasification that took place In addition, when the calcination temperature increased, the interphase contact grew more robust owing to the entrance and agglomeration of TiO2 in the pores of the activated carbon, as shown

in the SEM pictures This was the case This provides an explanation for why the surface area of the composite catalysts was reduced In addition, AC was effective as an adsorbent at temperatures below 450°C, especially 300°C However, at 450°C, a substantial interphase reaction occurred in the composite material, which was extremely obvious in the photodegradation of chromotrope 2R water pollutant In addition, the photo-activity of the composite catalyst was much greater than that of TiO2 Catalyst 80-AC-TiO2-450, which has the maximum capabilities in all pollutant concentrations, was calcined at a temperature of 450 degrees Celsius and contains 80% of the weight percentage of the original carbon content converted to TiO2

Together with titanium dioxide (TiO2), activated carbon fibers (ACF) were used

in Liu and colleagues' research The TiO2 that was deposited on the outside surface of ACFs seemed to be in the form of a film with close fractures rather than a thin, compact

coating The deposition of TiO2 and the following calcination procedure did not cause any harm to the micropore structure of ACFs, nor did it affect the high specific surface area of these materials The TiO2/ACFs system performed quite well, particularly when

it came to the breakdown of organic contaminants in wastewater that had a low molecular weight During the process of photocatalysis, the development of intermediate species was inhibited as a result of the synergistic action of the TiO2

photocatalyst and the ACFs Both photocatalytic activity and the capacity to regenerate are shown at high levels by the TiO2/ACFs catalyst Based on the findings of the XRD examination, it was determined that anatase was present, along with a little amount of rutile According to the findings of the BET analysis, the surface area of the ACFs was somewhat decreased as a consequence of the deposition of the catalyst, going from 1065

of ACFs to 845 of TiO2/ACFs In spite of this, the top layer of the film may still be defined as having a mesoporous structure The scanning electron micrographs (SEM) clearly demonstrated that the surface morphology of the composite materials were consistent across the board The TiO2/ACFs catalyst demonstrated a rather high capacity for the breakdown of MB The effectiveness of the breakdown reached 94% after just

40 minutes of reaction, and it reached 100% after only three hours of reaction According

to the findings, the TiO2/ACFs catalyst demonstrated greater breakdown activity than uncovered ACFs and pure TiO2 This is due to the fact that ACFs helped concentrate organic contaminants near TiO2, which is where they were degraded after being

concentrated [103]

Temperatures during calcination may have an effect on the structure of the catalyst [104] examined the removal of phenol from water using TiO2-mounted activated carbon The heat treatment ranged from 600 to 900 degrees Celsius The composite material was made by using hydrolytic precipitation as the preparation method The mounting of the TiO2, which blocked the pore entrances on the surface of the activated carbon, resulted in a reduction in the surface area of the activated carbon However, as the heat treatment progressed, the particle size of the TiO2 grew, which led

to a reduction in efficiency as a consequence of the clogging of pore entrances Because

of adsorption, the best phenol elimination occurred at a temperature of 900 degrees Celsius The use of activated carbon by itself served as a comparison for this Additionally, composite material that was calcined at temperatures higher than 700 degrees Celsius, specifically at 800 degrees Celsius, exhibited lower photocatalytic activity in the degradation of phenol This was because the crystalline structure of the TiO2 changed into a form that was less active (anatase to rutile)

TiO2-coated activated carbon composites and unadulterated TiO2 were both used

in a research that was conducted in 2007 by Li et al [105] The Sol-gel approach was used in the production of both the composite catalyst and the pure catalyst The calcination temperatures of the samples ranged from 300 degrees Celsius to 700 degrees Celsius, and a variety of characterization techniques were utilized in order to determine the impact that the AC matrix had on the TiO2 phase transformation, crystalline growth, morphology, and surface area of the composites The results of the XRD examination allowed for the determination of the ratio of anatase to rutile as well as the average crystal size After being calcined at temperatures ranging from 300 to 500 degrees Celsius, it was observed that the composite catalyst crystallites are anatase TiO2, and the same findings were reported for pure TiO2 At temperatures of 600 and 700 degrees Celsius, the anatase phase of the pure and composite catalysts underwent a phase transformation into rutile In addition to this, the development of the crystallites on the composite catalyst occurred at a slower rate in comparison to the growth on the pure TiO2 catalyst This is because the AC has a high surface area of 435 m2/g, which impedes the phase transformation from anatase to rutile This is because the large interfacial energy of the AC creates anti-calcination effects for the AC matrix, which in turn controls the growth of TiO2 particles and prevents agglomeration According to the findings of the BET study, the surface area of the composite catalyst rose when the calcination temperature was raised, in contrast to the pure TiO2, which had a decreasing surface area as the temperature was raised In addition, methylene blue was used in the testing process to determine the photocatalytic activity of both the composite and the pure catalyst At the end of the 200-minute test, the pure TiO2 had only removed 61%

of the substrate, whereas the composite catalyst had nearly completely removed all of the substrate This occurred because the AC in the composite has a large surface area, which concentrates the organic compound near the TiO2

1.7 Graphene oxide (GO)

Graphene, which is a single layer carbon sheet with a perfect sp2-hybridized dimensional structure (Fig 1.5), has attracted a tremendous amount of research attention ever since it was first discovered by Novoselov et al [100] This is due to the fact that graphene possesses a number of unique properties, such as a large specific surface area (2630m2.g-1), good optical transparency ( 97.7%), excellent thermal conductivity Graphene is a key building component that is used in the construction of other carbon compounds such as C60, graphite, and carbon nanotubes (CNTs) [106,107] In addition,

two-numerous techniques have been developed in order to synthesize graphene These techniques include chemical vapor deposition (CVD), epitaxial growth of graphene on silicon carbide, the arc discharge method, substrate-free gas-phase synthesis of graphene, chemical reduction of GO, electrochemical synthesis of graphene, unzipping CNTs for graphene nanoribbon, and many others [108] In addition, graphene-based films with the appropriate thickness and chemical compositions have been utilized in a variety of research areas, such as fuel cells, supercapacitors, hydrogen storage, lithium ion (Li-ion) batteries, solar cells, electrochemical sensors, fluorescent sensors, and many others [109] Due to the hydrophobic nature of pure graphene, its use in the area of water and wastewater treatment is very uncommon

Fig 1.5: Structures of graphene, C60, CNT and graphite [109]

Fig 1.6: Structure of GO [110]

GO is one of the most significant derivatives of graphene, which is created by the chemical oxidation of natural graphite [110,111] ( Figure 1.5) The Hummers technique, which is a powerful oxidation process that involves combining flake graphite, potassium permanganate (KMnO4) and concentrated sulfuric acid (H2SO4) [112,113], is the method that has been most commonly used for the synthesis of graphite oxide (GO) The presence of a significant number of oxygen-containing functional groups in the structure of GO, such as hydroxyl and carboxyl groups, confers hydrophilicity on GO and makes it an ideal supporter of inorganic nanoparticles [114] These groups include hydroxyl and carboxyl groups

Up to this point, a significant quantity of G/GO-based materials have been synthesized These materials include G/GO-metal composites, G/GO-metal oxide composites, G/GO-polymer composites, and so on and so forth [106] Ex-situ hybridization and in-situ crystallization are the two categories that may be used to describe the synthetic processes that are used to produce G/GO-based composites In addition, the chemical reduction, electroless deposition, sol-gel, hydrothermal, electrochemical deposition, thermal evaporation, and other processes are included in the in-situ crystallization technique [112]

In order to further improve the electrochemical and analytical characteristics of pure metals, G/GO sheets have been mixed with a variety of metals, such as silver, gold, platinum, palladium, nickel, copper, and others [108] For instance, in order to construct

a graphene-Pt composite, Liu and colleagues [114] mixed graphene sheets with Pt nanoparticles to create the material In comparison to the commercial catalyst, the composites demonstrated increased oxygen reduction activity owing to the greater electrochemical surface area The synthesis of graphene-gold composites was accomplished using the in-situ chemical reduction of chloroauric acid, which resulted

in the deposition of gold nanoparticles on RGO sheets [115] In addition, graphene-gold composites demonstrated an excellent photodegradation ability of RhB dye when exposed to visible light This was possible due to the unique properties of the composites, which included a high adsorption capacity for organic dyes, a slow charge recombination rate, and a strong interaction with dye chromophores

1.8 TiO2/GO Materials

In the last two decades, advanced oxidation (AOP) techniques, including photocatalysis, have attracted substantial attention In a number of environmental and non-environmental applications, such as energy storage and processing, photocatalytic