Effect of polystyrene nanospheres on photocatalytic properties of bismuth oxychloride

FTIR diagram of BiOCl synthesized by sol-gel method and PS90 synthesized by hard template method.... The photocatalytic process takes place on the surface of the semiconductor material t

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

GRADUATION PROJECT MAJOR: MATERIALS TECHNOLOGY

EFFECT OF POLYSTYRENE NANOSPHERES ON PHOTOCATALYTIC PROPERTIES OF BISMUTH

OXYCHLORIDE

ADVISOR: PHAM THANH TRUC STUDENT: TRAN TUAN ANH

S K L 0 1 1 7 9 9

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY OF APPLIED SCIENCES DEPARTMENT OF MATERIALS TECHNOLOGY

BACHELOR THESIS

STUDENT’S ID NUMBER: 19130004

Ho Chi Minh City, 08 – 2023 of dissertation

EFFECT OF POLYSTYRENE NANOSPHERES ON

PHOTOCATALYTIC PROPERTIES OF BISMUTH

OXYCHLORIDE

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY OF APPLIED SCIENCES DEPARTMENT OF MATERIALS TECHNOLOGY

BACHELOR THESIS EFFECT OF POLYSTYRENE NANOSPHERES ON

PHOTOCATALYTIC PROPERTIES OF BISMUTH

OXYCHLORIDE

STUDENT’S ID NUMBER: 19130004

Ho Chi Minh City, 08 – 2023 of dissertation

ACCKNOWLEDGEMENTS

First, I appreciate to personally express my sincere thanks to Dr Pham Thanh Truc has accompanied and supported my project throughout the process of my graduation thesis She is always enthusiastic to teach and answer questions as well as give directions so that I can complete the thesis in the best way

I’m grateful to the Faculty of Applied Sciences of Ho Chi Minh City University

of Technology and Education HCM has given me attention and support during the thesis course

I would also like to thank my family and classmates for coming together to support me when I encountered unexpected trouble during the experiment

Finally, in the process of implementation we could not avoid shortcomings I hope that will receive comments and contributions from teachers and friends to make the content of the thesis the most complete

Thank you all!

DECLARATION OF AUTHORSHIP

I assure you that this entire course is my own research under the guidance of

Dr Pham Thanh Truc The data, images, and results reported are truthful and have never been published in any other project The results and figures in the thesis belong

to the ownership of the author and instructor

Ho Chi Minh City, day month year 2023

Author Tran Tuan Anh

TABLE OF CONTENTS

ACCKNOWLEDGEMENTS i

DECLARATION OF AUTHORSHIP ii

TABLE OF CONTENTS iii

LIST OF ABBREVIATIONS vi

LIST OF FIGURES AND CHART viii

FOREWORD 1

CHAPTER 1: INTRODUCTION 2

1.1 Rationale 2

1.2 Studies on photocatalytic materials 2

1.2.1 In the world 2

1.2.2 In Vietnam 3

1.3 Aims and objectives of research 4

1.3.1 Aims of the research 4

1.3.2 Research objectives 4

CHAPTER 2: THEORETICAL BASIS 5

2.1 Overview of photocatalysis 5

2.1.1 Photocatalysis 5

2.1.2 Photocatalytic mechanism 5

2.2 Introdution of BiOCl 6

2.2.1 Overview 6

2.2.2 Structure 6

2.2.3 Properties 7

2.2.4 Synthesis method 8

2.4.1 Sol-gel method 8

2.4.2 Hydrothermal method 9

2.3 Introdution of nano Polystyrene 9

2.3.1 Overview 9

2.3.2 Structure 10

2.3.3 Properties 11

2.3.4 Synthesis method 12

2.4 Method of fabricating nanostructures with hard templates 14

2.5 Material Evaluation Methods 15

2.5.1 Fourier Transform Infrared Spectroscopy (FTIR) 15

2.5.2 Scanning Field Emission Electron Microscopy (FE-SEM) 15

2.5.3 Dynamic light scattering (DLS) 16

2.5.4 X-ray diffraction (XRD) 17

2.5.5 Brunauer – Emmett – Teller (BET) 17

2.4.6 Visible ultraviolet spectroscopy (UV-Vis) 19

2.4.7 Diffusion reflection spectroscopy (UV-Vis DRS) 20

CHAPTER 3: EXPERIMENTS 21

3.1 Materials 21

3.2 Apparatuses and equipment 22

3.3 Fabrication process 27

3.3.1 NPS synthesis process 27

3.2 BiOCl synthesis process 28

3.3 NPS-based BiOCl synthesis process 29

3.4 Characterization 31

3.5 Photocatalytic survey process 32

3.5.1 Calibration curve 32

3.5.2 Adsorption and photocatalytic activity measurements 33

CHAPTER 4: RESULTS AND DISCUSSIONS 34

4.1 Characterization of as-prepared NPS 34

4.1.1 (FTIR) Fourier Transform Infrared Spectroscopy 34

4.1.2 X-ray diffraction (XRD) 35

4.1.3 Dynamic light scattering (DLS) 35

4.1.4 FE SEM Analysis 36

4.2 Characterization of mesoporous BiOCl 36

4.2.1 (FTIR) Fourier Transform Infrared Spectroscopy 37

4.2.2 X-ray diffraction 38

4.2.3 BET Analysis 40

4.2.4 FE SEM Analysis 41

4.2.5 UV-Vis DRS spectrum 42

4.2.6 Photocatalytic results 44

CONCLUSION 50

RECOMMENDATION 50

REFERENCE 51

FE SEM Field emission scanning electron

microscope FTIR Fourier tranform infrared spectroscopy

NPS Nanospheres polystyrene PCS Photon correlation spectroscopy

SDS Sodium dodecylsulfate SSA Specific surface area TiO2 Titanium dioxide

UV-Vis DRS Ultraviolet visible diffuse reflectance

spectroscopy

LIST OF TABLES

Table 2.1 Physical property of polystyrene 11

Table 2.2 Mechanical properties of polystyrene 12

Table 3.2 Materials used in the project 21

Table 3.3 Apparatuses used in the project 22

Table 3.4 Appliances used in the project 24

Table 3.5 Samples were synthesized according to the proposed procedures 30

Table 3.6 Data used to draw the standard curve Rhb 32

Table 4.1 Average crystal size of BiOCl and PS90 39

Table 4.2 Surface area, pore diameter and pore volume of BiOCl and PS90 41

Table 4.3 The band gap energy value of BiOCl, PS50, PS90 44

Table 4.4 The value of the reaction rate constant of the samples 46

Table 4.5 Kinetic data for rhb adsorption 48

LIST OF FIGURES AND CHART

Figure 2.1 Diagram of the photocatalytic mechanism 6

Figure 2.2 Unit cell structure of BiOCl 7

Figure 2.3 Sol-gel method model 8

Figure 2.4 Model of hydrothermal method 9

Figure 2.5 The structure of polystyrene 10

Figure 2.6 Spatial structural forms of PS 11

Figure 2.7 Illustrating the hard template method 15

Figure 2.8 Forms of isothermal adsorption curves 19

Figure 3.1 Synthesis scheme of polystyrene 27

Figure 3.2 NPS synthesis process experiment 28

Figure 3.3 Diagram of synthesis of BiOCl by sol-gel method 28

Figure 3.4 NPS-based Biocl synthesis scheme 29

Figure 3.5 Experimental synthesis of BiOCl by sol gel and hard templatea method 30

Figure 3.6 BiOCl samples were synthesized 30

Figure 3.7 Sample NPS 31

Figure 3.8 Calibration curve plotted in origin 33

Figure 3.9 Rhb decomposition photochemical model 33

Figure 4.1 FTIR spectrum of NPS 34

Figure 4.2 X-ray diffraction diagram of NSP 35

Figure 4.3 NPS particle size distribution graph 35

Figure 4.4 SEM image of NPS at a) 100k magnification, b) 150K magnification 36

Figure 4.5 FTIR diagram of BiOCl synthesized by sol-gel method and PS90 synthesized by hard template method 37

Figure 4.6 X-ray diffraction diagram of BiOCl and PS90 38

Figure 4.7 Side 001 of BiOCl and PS90 magnified 39

Figure 4.8 Isothermal adsorption graph of N2 at a) BiOCl, b) PS90 40

Figure 4.9 Surface morphology of samples a) PS90, b) BiOCl 41

Figure 4.10 UV-Vis DRS spectrum of BiOCl, PS50, PS90 42

Figure 4.11 The band gap energy value of a) BiOCl, b) PS50, c) PS90 43

Figure 4.12 Photocatalytic graph of samples with Rbh concentration 10mg/L 44

Figure 4.13 Graph of the decline in Rhb concentration over time of the sample 45

Figure 4.15 Kinetic data of Rhb adsorption in the dark and (B) corresponding pseudo-second-order kinetic plots 47

Figure 4.16 Graph of time on the ability of PS90 to decrease Rhb concentration 49

FOREWORD

Water pollution in ponds, lakes, rivers, streams, canals is a sore issue in today's society The cause of pollution comes from wastes from nature, domestic and industrial waste In particular, industrial waste such as heavy metals, dyes, dangerous organic compounds is the main cause of water pollution and the process of treating them is also very difficult and costly The treatment of water pollutants from industrial waste can use methods such as filtration, flocculation, deposition, reverse osmosis Each method has its own advantages and disadvantages, such as fast pollutant treatment time but backlog disadvantages such as high cost, generation of secondary pollutants, etc One of the methods of interest in recent years is the use of photocatalysts to treat toxic organic substances, this method uses semiconductors to break down pollutants into water and CO2 under the action of sunlight The photocatalytic process takes place on the surface of the semiconductor material through oxidation, during this process the photocatalyst materials are not changed in structure, so this method is considered a green technology due to their cleanliness and

sustainability

Bismuth oxychloride (BiOCl) is a semiconductor material with high decomposition efficiency of organic pollutants thanks to its unique electronic and hierarchical structure, high redox ability, however, this material still has a few disadvantages that affect the photocatalytic performance To further enhance the photocatalytic efficiency of this material Polystyrene nanosphere (NPS) is used to develop BiOCl to increase the specific surface area, thereby improving the decomposition efficiency of toxic organic substances

Within the scope of this topic, We will focus on the influence of NPS on the photocatalytic properties of BiOCl, specifically will investigate the change in the mass percentage of NPS during BiOCl synthesis to improve the photocatalytic efficiency of

this material

CHAPTER 1: INTRODUCTION 1.1 Rationale

In recent years, many industrial parks have been built and operated in the territory of Vietnam, which have created benefits for our country economically but accompanied by water, soil and air pollution due to wastes generated from production activities Water pollution by manufacturing activities is one of the most painful and attention-intensive issues The waste from the textile, dyeing and paper industries contains many toxic organic substances and heavy metals they are considered an extremely dangerous to human health and the environment [1]

The total production of dyes in the world is about 800,000 tons per year and the amount of color loss is about 10-15% There are many dyes used in the world but generally they are synthetic in nature, non-biodegradable and potentially carcinogenic Finding solutions to be able to handle the negative effects that dyes cause on the environment is something that is researched and developed but encounters many challenges and difficulties [2]

There are many methods used to treat wastewater but there are still limitations such as the use of biological methods to decompose color due to the presence of toxic substances that reduce the growth of decomposing microorganisms, dyes are usually not biodegradable, so this method is considered less effective Or in the flocculation process used to recover water, they are also not considered feasible because of the high concentration of dyes into reverse osmosis systems Therefore, finding optimal and effective dye treatment solutions is a problem that attracts a lot of attention and exploitation for research, but so far there is no method that can completely remove the color and toxicity of dyes into the environment [3]

1.2 Studies on photocatalytic materials

1.2.1 In the world

In recent times, photocatalyst materials have been studied as TiO2 suspension solution in water under the action of UV radiation to decompose methyl red (MR), methylene blue (MR), congo red (CR), oxidizing dyes, converting toxic ions into harmless, decolorizing and detoxifying [4] Studies to improve the efficiency of TiO2

are also conducted by using acids for corrosion, phase control and crystallinity, creating a structure with a high surface area, optimizing reaction efficiency [5] Research on the doping of TiO2 with nonmetals boron, carbon, nitrogen, fluorine to improve catalytic activity under visible light conditions has also achieved positive

results [6]

Furthermore, ZnO synthesized by sol-gel method at many temperature ranges was used as an agent to decompose Azo color to achieve high performance and stability for a long time [7] The structural change that produces ZnO hollow nanospheres using polystyrene microspheres shows high absorption in the ultraviolet region and low in the visible region [8] Doping ZnO with nonmetals, transition metals, rare earth metals to narrow the band gap which hinders the application of ZnO

in sunlight shows that doping affects crystal structure, electronic properties, pore size, etc Photocatalytic properties [9]

Moreover, TiO2 and ZnO, BiOCl is also a semiconductor material that has gained a lot of attention in photocatalytic applications with its unique structure and electronics, a series of studies on this material have been conducted Doping F with BiOCl by hydrothermal method to decompose Rhb (rhodamine B) under visible light radiation, shows efficiency when crystal size decreases when doped with an amount of molar ratio of 3:4 while increasing light sensitivity, high stability when decomposing dyes [10] The synthesized Cd/CdS/BiOCl heterochromic structure shows better photochemical efficiency than pure Cd/CdS and BiOCl with color degradation up to 90% [11]

1.2.2 In Vietnam

Nguyen Huu Hieu of Ho Chi Minh City University of Natural Sciences has fabricated Fe2O3 – TiO2/GA composite material by hydrothermal method, achieving particle size at nanometer size, and at the same time resulting in MB decomposition under UV radiation reaching 97% [12]

Nguyen Thi Lan of Quy Nhon University fabricated TiO2 C-N-S-tridoped composite materials by hydrothermal method of materials prepared from ilmenite ore The material is synthesized for a large specific surface area, photochemical processes produce intermediate products that are eventually converted into CO2 and H2O The material shows stability after repeated reuse [13]

Nguyen Le Minh Tri of Ton Duc Thang University studied the doping of graphitic carbon nitride (g-C3N4) with Ag to treat wastewater from hospitals with an efficiency of approximately 97% under sunlight conditions, the doping improved the ability to absorb and separate photochemical carriers [14]

The team of authors Pham Van Viet from the University of Natural Sciences

Ho Chi Minh City makes Ag/TNTs materials by photoreduction method, giving antibacterial properties with greater than 99% efficiency [15]

1.3 Aims and objectives of research

1.3.1 Aims of the research

The research objectives of this thesis include the following:

Proposing a process for synthesizing BiOCl materials developed on NPS, using NPS as a hard template to create a hollow structure for BiOCl

Studying the effect of the mass percentage of NPS on the structure, surface area, adsorption capacity of BiOCl, thereby improving the photocatalyst product under sunlight conditions compared to BiOCl synthesized from other methods

Application of materials in the wastewater treatment process helps optimize costs and time, contributing to the protection of the water environment in Vietnam in particular and in the world in general

1.3.2 Research objectives

Thesis structure includes:

Overview of the topic

Research and synthesis NPS materials, BiOCl thereby developing BiOCl hollow materials based on NPS, investigating the change in NPS mass percentage to the properties and applications of BiOCl

Evaluating of the property structure of NPS, BiOCl and Hollow BiOCl based

on the following analyses, Field Emission Scanning Electron Microscope (FE-SEM), Dynamic Light Scattering (DLS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Ultraviolet–visible spectroscopy (UV-Vis), Surface Area Analysis Method (BET)

Investigated the photocatalytic properties of hollow BiOCl materials and BiOCl materials by Rhodamine B color decomposition reaction under visible light conditions for 30 minutes

CHAPTER 2: THEORETICAL BASIS 2.1 Overview of photocatalysis

2.1.1 Photocatalysis

Photocatalysis is a phenomenon of changing the speed of the reaction under the action of light Agents that change the reaction rate are called photocatalyst materials, basically most of them are made from semiconductor materials In the photocatalytic process, an electron-hole pair is formed when the semiconductor is exposed to light, from which redox occurs, causing the semiconductor material to be used as a catalyst

2.1.2 Photocatalytic mechanism

The photochemical process is shown in Figure 2.1 When light hits a

semiconductor material, a photon with an energy level higher than the semiconductor material's band gap appears and is absorbed by this material, this absorption process releases an electron that forms an electron pair - a hole Hole in the valence zone oxidizes water to OH* and h+ Meanwhile, electrons in the conductive region reduce

O2 to O2 −* Free radicals O2 −* reduce H2O to H2O2, under UV radiation H2O2

decomposes to 2OH* The energy of the free radical OH* is sufficient to be able to break the bonds of organic substances and eventually form CO2 and H2O according to the following equations [16]

Figure 2.1 Diagram of the photocatalytic mechanism 2.2 Introdution of BiOCl

2.2.1 Overview

Bismuth-based photocatalysts showing high efficiency and stability during photochemical reactions have won much attention in the field of photocatalytic materials development Currently many bismuth-based photocatalysts such as: Bi2O3, Bi2S3, BiVO4, BiOX (F, Cl, Br, I), M(BiO3)n has been studied The electronic structure of bismuth-based semiconductors consists of a valence range of Orbital 2p and Bi 6s Thanks to the 6s Bi orbital, the band gap width of the bonus ball is less than

3 eV They are often applied in environmental fields such as pollutants related to dyes, oxidizers NO, CO2, splitting water and other applications Among the compounds of

Bi, BiOX has a layered structure and unique electronic properties consisting of plates

Bi2O2 alternate with halogen atoms Typically, BiOCl this material has chemical stability, photochemical ability to achieve high efficiency There is enormous potential for the application of toxic organic substances that are dangerous to human health and the environment [17]

2.2.2 Structure

The photocatalytic properties and specific properties of BiOCl are expressed through the crystal structure BiOX is a 3rd order semiconductor consisting of the main group elements V-VI-VII, a PbFX-type quadrangular structure of the P4/nmm

space group Figure 2.2 Shows the unit cell structure of BiOCl, the Bi atom bonded

with the surrounding four O and Cl atoms to form an asymmetric quadrangular pyramidal structure This gives BiOCl a large space to polarize atoms and orbitals and easily creates an electrostatic field inside the structure In addition, BiOCl is a layered structure [Cl – Bi – O – Bi – Cl], these layers are interspersed by van der Waals forces holding the Cl atoms Research indicates that BiOCl has an open layered structure and has an indirect band of band energy This makes it easy for BiOCl to create hole electron pairs and minimizes the recombination of materials, contributing to improving photochemical efficiency [18]

Figure 2.2 Unit cell structure of BiOCl 2.2.3 Properties

BiOCl is studied as an indirect semiconductor material with an energy level of 3.37 eV, a wide conductive zone p-type semiconductor that can be excited by UV radiation With semiconductor materials with an indirect zone, photochemicalized

electrons must travel a certain distance before returning to the valence band and combining with the hole, which reduces the recombination ability of the electron-hole pair to a certain extent In addition, BiOCl also has a layered structure from these elements that makes BiOCl able to easily separate and move charge and improve the ability of photocatalysis to decompose organic molecules [18]

2.2.4 Synthesis method

BiOCl can be synthesized by various methods such as hydrothermal, template, sol-gel method In this thesis, sol-gel method and hard template will be used to synthesiz materials BiOCl

2.4.1 Sol-gel method

The sol-gel method is a wetchemical technique used to synthesize materials with different microstructures, mainly oxides of metals To carry out the sol-gel process, the precursor is dissolved in water, forming suspensions (colloidal solids in liquids) through hydrolysis and condensation reactions The product is dried depending on the properties of the material

The sol-gel method is a simple and cost-effective method, the process takes place at low temperatures, so it is easy to control the reaction process BiOCl is synthesized by sol-gel method usually from precursors BiCl3, Bi(NO3)3, Bi2O3

Solvents and catalysts are added to the reaction process to improve the hydrolysis efficiency, increasing the amount of sol The resulting product is processed at low temperatures, the result is powdered, which is an early method used to synthesize BiOCl Up to now, there are many other methods that can synthesize BiOCl such as microwave irradiation, hydrothermal, template method [18]

Figure 2.3 Sol-gel method model

2.4.2 Hydrothermal method

The hydrothermal method is a widely used method for the synthesis of nanostructured materials such as BiOCl Mechanical formation of nanomaterials by hydrothermal method consists of the following stages Dissolved metal ions are hydrated and hydrolyzed into hydroxide The hydroixide is then dehydrated at hydrothermal conditions to form a nanostructure precipitate The process of material formation is directly proportional to temperature Hydrothermal method is a method of good control of shape, structure, crystal phase of materials through synthesis at high temperature and pressure while increasing the reactivity of precursors to carry out reactions that are unlikely under normal conditions [18]

Figure 2.4 Model of hydrothermal method 2.3 Introdution of nano Polystyrene

2.3.1 Overview

Polystyrene is a synthetic plastic widely used in life fields and many different industries such as household appliances, electronics, automotive At smaller sizes, polystyrene nanoparticles exist in a microscopic state At this size, polystyrene shows the distinctive properties that bulk materials bring such as lower glass transition temperature compared to bulk materials, large surface area [19] NPS is easily synthesized in different sizes and controls charge, surface properties Research into NPS applications is widely conducted in many fields such as using them as a transporter in biological environments, or as a hard template for synthesizing materials

at the nanoscale In general, NPS shows a lot of potential for application and exploitation [20]

2.3.2 Structure

PS is made up of styrene polymerization also known as vinyl benzene, PS is a

linear chain hydrocarbon Figure 2.5 Phenyl group bonded to two carbon atoms, in the

chain only carbon and hydrogen atoms The circuits of the PS have a conditioning structure (tail connector) and are interconnected by the Waals valve force Because the structure of the phenyl group is quite bulky, PS is difficult to crystallize and belongs to the thermoplastic and amorphous type In the PS structure, hydrogen is flexibly bound

to 3rd order carbon, so they easily participate in oxidation reactions, so PS is not stable

in the presence of sunlight

Figure 2.5 The structure of polystyrene

The spatial structural forms of PS are shown in Figure 2.6 In an attactic state

phenyl groups are randomly arranged, syndiotactic functional groups are arranged in

an orderly manner, isotactic functional groups are arranged on one side of the polymer circuit The syndiotactic structural form gives PS the possibility of superior properties over the other two functional group arrangements due to its symmetrical and orderly structural properties, large molecular bonding forces Therefore, syndiotactic structures have superior mechanical and physical capabilities However, to synthesize this structure requires quite high requirements and difficulties, so they are usually only used for cases with high technical requirements [21]

Figure 2.6 Spatial structural forms of PS 2.3.3 Properties

❖ Physical property

The physical property parameters of PS are shown in Table 2.1 PS has low

molecular weight, has brittle properties, low tensile strength due to the bulky phenyl functional group, which makes the circuit less flexible PS has a high molecular weight that has increased mechanical and thermal strength properties The usable temperature range of PS fluctuates at 80°C, the burning point of this material is at 173°C and decomposes at a temperature of about 330°C In general, PS has a wide machining temperature range and is easy to process to shape products [21]

Table 2.1 Physical property of polystyrene

Molar mass (g/mol) 104.15 Melting entropy (KJ/mol) 0.0153 – 0.0168

Transition temperature (K) 373

Heat capacity (100K) (KJ/mol) 0.04737

Solubility parameter (MPa) 15.6 – 21.1

❖ Chemical properties

Polystyrene is basically white or transparent, they are non-biodegradable usually non-toxic without the use of additives, solvents They are also waterproof and insulating, being a non-polar substance that should be stable in polar solvents such as dilute cleaning solutions Less stable to solvents of non-polar nature like it such as aromatic hydrocarbons, toluene, chloroform

❖ Mechanical properties

The mechanical parameters of polystyrene are shown in Figure 2.2

Polystyrene is a thermoplastic, rigid plastic The specific gravity of PS can be changed when modified with other polymers to increase its properties according to the intended use Polystyrene can withstand continuous heat of about 59 – 79oC, too long heat resistance time will also affect the properties of this polymer [22]

Table 2.2 Mechanical properties of polystyrene

Density (g/cm3) 1.05 Tensile Strength (N/mm2) 32.4 – 56.5

Tensile modulus (N/mm2) 3103 -3276

Elongation at break (%) 1.2 – 3.6 Flexural modulus (N/mm2) 3103 -3448

advantage of this polymerization is that the process is quite simple and the product only exists unreacted monomer and polymer, so when removing the monomer, a highly purified product is obtained [23]

2.3.4.2 Solution polymerization

The solution polymerization technique uses solvents to dissolve monomers and initiators This polymerization process easily controls temperature and viscosity due to the presence of solvents However, the disadvantage of this technique is that it is difficult to remove the solvent from the product, the solvent used is often toxic and pollutes the environment, the resulting product has a low molecular weight due to the circuit transmission process [23]

2.3.4.3 Suspension polymerization

Suspension polymerization is a technique that uses monomers that disperse in water and form droplets and initiators that dissolve monomers, polymers that form suspensions in water and are easily obtained by filtration and washing This method uses water as a heat transfer medium, so heat is dispersed easily and efficiently, the solution viscosity is low, but this technique also requires the polymer to have a glass transition temperature lower than the polymerization temperature if Tg is higher, agglomeration will occur because the polymer exhibits flexibility, resulting in the polymer will be less stable[23]

2.3.4.4 Emulsion polymerization

This method uses monomer dispersed in the form of emulsion, the stability of the emulsion is controlled by adding surfactants or some others, the commonly used surfactant is organic fatty acid, they have the effect of reducing the surface tension of water to help disperse the monomers in water The solubility of surfactants is low so they disperse in the aqueous environment easily even at low concentrations, at a specific concentration insoluble surfactants form micelles At the highest concentration

of surfactants at which all molecules are in a dispersed state forming micelles is called the (CMC) critical micell concentration The micelle bead has a structure of one hydrophilic end and one hydrophobic head, the hydrophilic part will face outward and the hydrophobic part will be directed inward [23]

When the initiator introduced into the system approaches the surface of the micell, polymerization takes place from the outside of the micelle to the inside As polymerization takes place, the monomer is consumed and further diffused from the aqueous phase into the micelles This process continues until another free radical

appears and ends circuit development The amount of polymer formed collects and is surrounded by an emulsifier stably, evenly dispersed in water Emulsion polymerization minimizes the viscosity of the solution because, the product can be used directly However, heat transfer into the system is difficult due to the low viscosity of the polymer [23]

2.3.4.5 A quasi-emulsifier-free emulsion polymerization

During the polymerization of the emulsion, the control of the reaction process is difficult because the process is quite complex, thus resulting in the size of the polymer particles being unevenly dispersed This is caused by high concentrations of surfactants, which prolong reaction nucleation time and cause multi-dispersion In the emulsifier-free emulsion polymerization technique, there is little or even no appearance of surfactant, so nucleation takes place in a uniform manner [24]

The ogligomes formed in the reaction to a certain extent, they form a micelle, then the monomers will react inside this micelle to form a polymer Due to the absence

of surfactants, these particles are less stable and easily break down and form sized particles Therefore, synthesis by emulsification using surfactant content at concentrations that have not yet reached critical micelle concentrations will not result

larger-in secondary nucleation nor for the stability of obligomer-generated micelles

2.4 Method of fabricating nanostructures with hard templates

A hard template is a method of building nanostructures formed from hydrogen, chemical, or electrostatic bonds Inorganic substances grow above or inside the structure of the template by various methods such as electrochemical, precipitation,

etc Forming unique structures is illustrated in Figure 2.7 Hard templates are formed

from synthetic polymer microspheres The hard template method of fabricating materials creates porous structures and large specific surface areas This method offers superior material structure dimensional control and has great promise in nanomaterial structure fabrication [25]

Figure 2.7 Illustrating the hard template method

Synthetic polymers are often used as hard templates to make mesoporous materials with diameters below 100 nm They have a large molecular weight that is stable in structure and shape The use of polymers can control the rate of crystal growth as well as improve the morphology and distribution of particles [25]

2.5 Material Evaluation Methods

2.5.1 Fourier Transform Infrared Spectroscopy (FTIR)

Fourier transform infrared spectroscopy is an analysis that uses the Fourier transform to transfer outputs from an interferometer to an infrared spectrum This is a qualitative and quantitative analysis of both organic and inorganic materials, which takes place at a fast pace with a variety of samples (solid, liquid, gas) and does not destroy samples during analysis They express the transmittance (%) in units of wavelength (cm-1) Based on the rule that when a molecule in the process of selective absorption of radiation leads to a dipole moment change, the bonds in the structure have a different oscillation frequency corresponding to the energy level (E=hf) they absorb, where h is Planck's constant, f is the frequency [26]

In the infrared spectrum, absorption bands are represented by the number of waves at which absorption takes place characterizing chemical bonds, the intensity of absorption is directly proportional to the appearance of the bonds appearing in the sample The absorption bands of the infrared spectrum are divided into three regions (near infrared, middle infrared, and far infrared) [26]

This study used the middle infrared (MIR) region at the range of 4000 – 400

cm-1 to study the bonds present in the synthesized material

2.5.2 Scanning Field Emission Electron Microscopy (FE-SEM)

Scanning electron microscopy uses high-energy electrons as a source instead of using visible light like conventional electron microscopes, so SEM gives high-resolution results by accelerating electrons depending on the normal input voltage from 10kV – 40kV The interaction between the electron and the sample surface

reveals the characteristics of the surface shape and size of the material in the microstructure

The interaction of electrons with the sample includes secondary electrons They are generated when primary electrons from the source reach the sample surface, where electrons emitted from the source transfer some of the energy to the sample's surface and change the trajectory This process ionizes the sample electrons and causes them

to be released from the surface and is called the secondary electron, the dectector detects these secondary electrons and gives about the structural shape of the material Backscattered electrons, other cases when electrons from the source move from the source to the sample surface when interacting with atoms they will be scattered or reflected, depending on the atom, the scattering intensity of the electron will also change [27]

The medium used in SEM is usually a vacuum environment to create an environment where electrons can travel from the source to the sample in the most convenient way to limit the impact on the quality of the image When the source of electrons is provided by a field emission gun that allows the creation of electrons of shorter wavelengths, from which higher resolution images are obtained, they are called electron microscopes that scan for field emission

2.5.3 Dynamic light scattering (DLS)

The technique of analyzing materials by dynamic light cattering (DLS) is used

to study the morphology of nanoparticles in colloids, also known as photon correlation spectroscopy (PCS) Through the oscillating intensity of light scattering by nanoparticles in the system at a certain angle, the scattering intensity depends on the position of the particles relative to the direction of the incident and scattering light beam In colloidal systems, particles touch and move according to an uncertain rule called Brownian motion Large particles move more slowly than those of small size This results in a change in the scattering intensity, so a time correlation function is calculated by a computer to be able to process the resulting signal [28]

The radius and size of particles in the system can be calculated through the correlation between the diffusion coefficient and the particles related by the Stokes–Einstein equation:

𝐷 = 𝐾𝐵 × 𝑇6𝜋 × 𝜂 × 𝑅

KB is the Boltzmann constant, η is the viscosity of the system, T is the absolute temperature, R is the particle radius [28]

For the diffraction peak to occur, the angle of incidence of X-rays must satisfy the Bragg equation:

2𝑑 × sin 𝜃 = 𝑛𝜆 where d is the distance of the two crystal faces, n takes integer values from 1,2,3,

The size of the crystal is determined through the Scherrer equation:

𝐷 = 𝐾 × 𝜆

𝛽 × 𝑐𝑜𝑠𝜃

D is the crystal size (nm) ,

λ is the wavelength of X-rays (nm),

β is half the width of the diffraction peak (FWHM) (rad),

θ is the Bragg angle (rad),

K is the Scherrer constant, they range from 0.8 – 1.39 This constant depends on the crystal shape and diffraction line index [29]

2.5.5 Brunauer – Emmett – Teller (BET)

The method of measuring the specific surface area is a method of analyzing the structure of a material, this method indicates the adsorption capacity, specific surface

area, porosity, porous distribution of the material through BET theory Based on the determination of the amount of gas required to coat the surface of the monomolecular layer by means of an isothermal adsorption curve of nitrogen, argon or carbon dioxide Nitrogen is used mainly because they have inert, cheap properties, high purity and interact with many solids The amount of gas is physically absorbed on the surface

of the adsorbent at a given pressure condition From there, it is possible to calculate the adsorbed gas through volume or mass measurement Before analysis, the sample is heated and vacuumed to remove contaminants from the material [30]

The isothermal absorption line is divided into 6 types shown in Figure 2.8 In

type 1 represents single-layer adsorption materials, type 2 adsorption forms multiple layers of gas molecules on the surface of the adsorbent, type 4 appears capillary condensation characteristic for adsorption of porous objects Type 6 shows the ability

to adsorb multiple layers on uneven porous surfaces Types 3 and 5 represent adsorption whose adsorption heat is equal to or lower than the condensation heat of the adsorbed substance

The BET theory states that gas molecules on the adsorbent surface do not move freely nor interact with each other, can form multiple adsorption layers at many points but the surface area does not change The equation expressing the physical adsorption process is as follows:

𝑃𝑉(𝑃𝑜− 𝑃)=

an adsorption layer on the sample, C is the constant The specific surface area is calculated by the formula

𝑆𝑆𝐴 = 𝑉𝑚

𝑀 × 𝑚× 𝑁 × 𝐴

M is the gas molecular mass, m is the sample mass, A is the adsorption cross section, N is the Avogadro number

Figure 2.8 Forms of isothermal adsorption curves 2.4.6 Visible ultraviolet spectroscopy (UV-Vis)

The visible ultraviolet spectroscopy method is used to determine the absorption capacity of materials based on the absorption phenomenon when the material molecule interacts with electromagnetic radiation, UV-Vis spectroscopy is a quantitative analysis technique during non-destructive measurement of samples They are widely used to determine the content of materials When a beam of light of a certain wavelength is projected at the sample surface, they are diffused, reflected, or can cause resonance that changes the distribution of electron density When the material absorbs

a radiation they are excited to a higher energy level and quickly return to their original state, during which the material can emit corresponding energy levels The relationship