Metallic nanoparticles supported on zeolite-added TiO2 and plasma-modified TiO2 Synthesis and photocatalytic oxidation applications

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VIETNAM NATIONAL UNIVERSITY - HO CHI MINH CITY HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

LE NGUYEN QUANG TU

METALLIC NANOPARTICLES SUPPORTED ON ZEOLITE- ADDED TiO2 AND PLASMA-MODIFIED TiO2: SYNTHESIS AND

PHOTOCATALYTIC OXIDATION APPLICATIONS

Major: Chemical Engineering

No.: 8520301

MASTER THESIS

HO CHI MINH CITY, 30 October 2019

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CƠNG TRÌNH ĐƯỢC HỒN THÀNH TẠI

TRUGNG DAI HOC BACH KHOA —DHQG -HCM

Cán bộ hướng dẫn khoa học: PGS TS Nguyén Quang Long TS Cù Thành Sơn

Cán bộ chấm nhận xét 1 : PGS TS Hồ Thị Thanh Vân

Cán bộ chấm nhận xét 2 : PGS TS Nguyễn Thị Phương Phong

Luận văn thạc sĩ được bảo vệ tại Trường Đại học Bách Khoa, ĐHQG Tp HCM ngày 25 tháng 10 năm 2019

Thành phần Hội đồng đánh giá luận văn thạc sĩ gồm: 1 GS TS Phan Thanh Sơn Nam

2 PGS TS Hé Thi Thanh Van

3 PGS TS Nguyén Thi Phuong Phong

4 TS Trần Thụy Tuyết Mai 5 TS Đặng Bảo Trung

Xác nhận của Chủ tịch Hội đồng đánh giá LV và Trưởng Khoa quản lý chuyên

ngành sau khi luận văn đã được sửa chữa (nếu cĩ)

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ĐẠI HỌC QUỐC GIA TP.HCM CỘNG HỊA XÃ HỘI CHỦ NGHĨA VIỆT NAM

TRUONG DAI HOC BACH KHOA Độc lập - Tự do - Hạnh phúc

NHIỆM VỤ LUẬN VĂN THẠC SĨ

Họ tên học VIÊN: .-.-G- nen ekvvs MSHV: Q se Ngày, tháng, năm sinh: .- s5 + Nơi sinh: .ceeeriieo Chuyên ngành: . 2c SSSsysse Mã sơ : .sse2

I TÊN ĐÈ TÀI:

HI NGÀY GIAO NHIỆM VỤ :

IV NGÀY HỒN THÀNH NHIỆM VỤ: V CÁN BỘ HƯỚNG DẪN

, , ; Tp HCM, ngay thang nam 20

CAN BO HUONG DAN CHU NHIEM BO MON DAO TAO

(Họ tên và chữ ký) (Họ tên và chữ ký)

TRƯỞNG KHOA

(Họ tên và chữ ký)

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ACKNOWLEDGEMENT

I would like to send my deepest gratitude to Associate Professor-Dr Nguyen Quang Long and Dr Cu Thanh Son, who had spent a lot of time, their great effort and dedication to communicate their valuable knowledge and experience in the process of completing this thesis Without their guidance and persistence help, this theisis would not have been possible

I would like to express my appreciation to the teachers of Department of Physico- Chemical Engineering - Faculty of Chemical Engineering of Ho Chi Minh University of Technology, who have communicated valuable knowledge to me while studying at the university This is a very important foundation for me to complete my thesis

I would like to thank the review committee, for spending time reading and giving

valuable comments on my thesis

Finally, I would like to send my sincere thanks to my family and friends, who have encouraged and helped me through the years at Ho Chi Minh University of Technology

Best regards

Ho Chi Minh City, Oct 2019

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ABSTRACT

This thesis studied the preparation of nanoparticles Au/TiO2-ZY and plasma- treated Au/TiO2 as catalysts for photocatalytic reaction which is a treatment of air pollutants VOCs The physicochemical properties of catalyst had been characterzied by

various methods, including XRD, SEM, TEM, FTIR, ICP, BET surface area

Within the thesis, toluene vapor was used as a typical VOC to evaluate the photo- catalytic activity under UV light The toluene concentrations before and after the reaction were analyzed by gas chromatography (GC) The effects of moisture concentration abd reaction temperature were investigated In each reaction, only one parameter was changed, while the other parameters were fixed

The catalytic performance of zeolite-added TiO2 was enhanced due to the support of high surface area in zeolite and the surface plasmon resonance of Au nanoparticles The photo-catalytic oxidation process was stable throughout the whole experiment and

was able to degrade 70% of toluene in the gas mixture

The presence of —OH functional group in plasma-treated samples enhance the toluene removal efficiency under low humid condition Furthermore, water content in gas mixture are less likely to effect the catalytic activity compared to non-treated TiO2

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TĨM TẮT

Luận văn này nghiên cứu quá trình tổng hợp nano Au/TiOa-ZY và Au/TiO; biến tính plasma làm chất xúc tác cho phản ứng quang hốt xử lý các chất gây ơ nhiễm khơng

khí VOCs Các tính chất hĩa lý của chất xúc tác đã được xác định bằng nhiều phương

pháp khác nhau, bao gồm XRD, SEM, TEM, FTIR, ICP, dién tich bé mat BET

Trong luận án, hoi toluene duoc st dung lam nguồn VOC điển hình để đánh giá

hoạt động xúc tác quang đưới ánh sáng tia cực tím Nồng độ toluene trước và sau phản

ứng được phân tích bằng sắc ký khí (GC) Ảnh hưởng của nơng độ âm, nhiệt độ phản

ứng đã được nghiên cứu Trong mỗi phản ứng, chỉ cĩ một tham số thay đổi, trong khi

các tham số khác được cố định

Đối với Au/TiO¿-ZY, hiệu suất xúc tác được tăng cường nhờ sự hỗ trợ của diện

tích bề mặt cao trong zeolite và cộng hưởng plasmon bề mặt của hạt nano Au Quá trình oxy hĩa xúc tác quang hĩa ỗn định trong tồn bộ thí nghiệm và cĩ thể làm giảm 70% lượng toluene trong hỗn hợp khí

Đối với Au/TiO; biến tính plasma, sự hiện diện của nhĩm chức -OH tăng cường hiệu quả loại bỏ toluene trong điều kiện độ âm thấp Hơn nữa, hàm lượng nước trong

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LỜI CAM ĐOAN CỦA TÁC GIÁ LUẬN VĂN

Tơi xin cam đoan những kết quả được trình bày trong Luận văn Thạc sĩ này là do chính tơi thực hiện từ kiên thức của chính mình Tơi khơng nộp luận văn này cho bất kỳ Trường, Viện nào đê được câp băng

ACKNOWLEDGMENT OF AUTHORIZATION

The results presented in this Master Thesis were made by myself from my own

knowledge I do not submit this thesis to any School or Institute to obtain a degree

Ho Chi Minh City, 01 October 2019 Author

Le Nguyen Quang Tu

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1.7 Hydrogenafed TỈO2 oo -o- o5 s5 5559223 555000 080999090968899966860999000600669096 16 VAN si3200)(t:dđiiiỔ 16 1.7.2 Plasma surface modIÍiCafIOT - s9 ng ng tre ve 18 1.8 Zeolite 18 1.9 Method of analyzing 20 CHAPTER 2: EXPERIMENT 25 2.1 Chemicals and equÏDIM€TI o- 5 5 5555 255 S 555 99999995 958589996665866996690800 806 25 2.2 Preparation 0Ÿ Ca{aÌysSf oo co c0 5 90009009990 098869999610868999060866009000000009 25 2.3 Characterization Of CafAÌyS o -ocoo son 20050506 0909996510888999660566899000000008 30 2.4 NĐeacfion sysfem oooooo 55555555599 89996.59686556688999999996666668800999905966056 31 2.5 Investigation of the effects of reactfion”s condÏfOIS o<sseessssssssse 33

CHAPTER 3: RESULT AND DISCUSSION .ccssccsssscsssossrsssccescocssoessesooeees 34

3.1 Characterization Of catalysts .cccccssssssssssssesssssssesssccsssessccsssssssscesssescoenss 34 3.1.1 X-ray diffraction pattern of Catalysts .ccccccsssscceeesssssseecsssssseeesssssssees 34 3.1.2 BET specific area - ICP amalysis cccccccesssseccsssscccsssesessssseesesaeeeessaaes 35 3.1.3 FTIR analysis of plasma treated Catalysts ccssssscccsssesessssscessssseeessaees 36 3.1.4 Scanning electron microscopy (SEM) and Transmission electron MICTOSCOPY (TEM) .ccccsssssccsssssseceessssssecevecsnnssccesesensecesensnseeeesessasseesessnsseesesenees 38 3.2 Catalytic performance of modified 'T¿ oo-se seo sssseeessssssseses 40 3.2.1 The effect of UV light on the depgradation of toÏuene - - 40 3.2.2 The effect of gold nanoparticles on the photo-catalytic performance of T1O2

T110 1110101 TT Họ kì 41

3.2.3 The catalytic performance of hydro-plasma-treated 'T1O2 43 3.2.3.1 The adsorption efficlency of plasma treated T1O2 samples 43 3.2.3.2 The effect of plasma treating tine on the photo-catalytic activity of plasma-treated T12 - - 1110111111 nh ng ng ng HH ng 44

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LIST OF FIGURES

Page Figure 1.1 Flow chart of bio-filtration System eee essseecssseceeseseecessneeeeesnateresenes 6 Figure 1.2 Schematic diagram of equipment used for condensing VOCS .4 6 Figure 1.3 Structure of activated carbonn - c1 HT ng kg 7 Figure 1.4 The diagram illustrates the photocatalytic mechamism of T1O2 10 Figure 1.5 Lattice structure of RutIÏÌ€ - 2c 131119 1 1 9 vn ng ngư 10 Figure 1.6 Lattice structure Of Ana{A$S€ .- n1 ng nh ng ng như 11 Figure 1.7 Photo-catalyst investigation TOUÍ€ . s1 x1 ng ng ngư 12 Figure 1.8 Au face-centered cubic Ïaftice struCfUT€ c5 vs sssvssssss 15 Figure 1.9 Illustration of the excitation of localized surface plasmon resonance 16 Figure 1.10 Spatial structure of zeolite Y (a) and frame structure of zeolite (b) 18

Figure 1.11 The angle of incidence and angle of reflection in XRD method 20

Figure 1.12 Diagram of principle XRD analys1s equIpmenf «+ + s«2 21 Figure 1.13 Gas chromatography SVS{€TN 2G n1 Y9 ng ngư 24

Eigure 2.1 Hydrogen plasma SYS{€TH LG 1Q TH ng vn 27 Figure 2.2 The process of preparing Au/'T 12 .- + «ng 28

Figure 2.3 The process of synthesis Zeolite YỂ cc 1 S3 series 29 Figure 2.4, The reaction sVSf€TH Q10 HH ng ng ng gà ng kh 31

Figure 3.1 XRD pattern of TiO2, Au/TiO2, TiO2-X and Zeolite Y -‹- 34

Eigure 3.2 FITIR spectrum of plasma treated T1O2 sarnpÌes . - - «+2 37 Figure 3.3 FTIR spectrum of plasma treated Au/T1O2 samples .- - - 37 Eigure 3.4 The SEM 1mages of Au/T1O2 sampÌ€s .- 5 1v sssrssseee 38

Figure 3.5 The TEM images of Au/TÌ2 - - + v3 1 vn nh 39

Figure 3.6 Au nanoparticles size đdistribution in Au/T1Oa sarnples ‹- 39 Figure 3.7 Energy distribution spectrum of Sankyo Denki FIOT8BLB (10W) 40 Figure 3.8 The effect of UV light on toluene removValÌ, ‹s s32 40 Figure 3.9 The effect of gold nanoparticles on the photo-catalytic activity of TiO2 41 Figure 3.10 a) Diagram illustrating the light absorption length/minority carrier

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Figure 3.11 An alternative route of photo-electron under the presence of AuNPs [13]

Figure 3.12 Toluene removal by adsorption of TiO2, plasma TiO2 and p-Au/TiO2 43 Figure 3.13 The toluene removal efficiency of TiO2-X samples with different plasma 0101611907525 ằee 44

Figure 3.14 The toluene removal efficiency of H-Au/TiO2 samples with different

3i; Rci00xn 0i 1177 ao a 45

Figure 3.15 The effect of humidity on the toluene removal efficiency of T1O2,

Au/T1O; p-T1O¿ and p-Au/TÌƯ2 - c5 1193211 3 31 v.v vn vn ren 46 Figure 3.16 The effect of temperature on the toluene removal efficiency of TiO2 and

Au/TiO2-ZY: 39°C (line) and 50°C (dash) 2G 0 n1 HH ng re 47 Figure 3.17 Toluene removal by adsorption of TiO2, Au/TiO2 and Au/TiO2-ZY .49

Figure 3.18 The effect of Au/TiO2:zeolite ratio on the toluene removal efficiency 50 Figure 3.19 The effect of humidity on the toluene removal efficiency of Ti02 and Au/TiO2-ZY: 60% (blue) and 15% (red|) -.- ‹ - ch 9 93133111111 1v vn vvre 51

Figure 3.20 The effect of temperature on the toluene removal efficiency 52 LIST OF TABLES

Page

Table 1.1 Overview of important sources and global annual emission rates of selected øroups of VOC per year (20U77).[ Ï] 7c c1 121 0 1911 v1 1119 1v ng ng ng nh 2 Table 1.2 Overview of average tropospheric lifetimes of VOC compound groups and some Selected VOCs as Examples c:ccccssscecsssssccsssseccssssccesssscessssscecsssneesessaesessessen ses 3 Table 1.3 Specific mass and energy of the restricted area 0Ÿ 'T1Ư2 -«s 11 Table 1.4 Some methods of modified metal and application - - 13

Table 1.5 Some methods of preparing hydrogenated T12 . - 5+5 17

Table 2.1 List of chermICaÌS, c1 211933011130 111 111 010 1 110 1 ng 25 Table 2.2 Investigation COndIfIOTS 7c 111 1S ng kg ngà 33 Table 3 Catalyst”S DrODeTẨ€S G ch TT ng ng ngà 35

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LIST OF ABBRIVIATIONS

VOCs Volatile organic compounds

p- TỉO› Plasma treated TiO2z

TEM Transmission electron microscopy

SEM Scanning electron microcospy

Crot Concentration of toluene, ppmy

Co2 Concentration of oxy, v%

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CHAPTER 1: OVERVIEW

1.1 Introduction

With the rapid development of society, people are living with life that is more comfortable However, along with the positive aspects, the process of industrialization - modernization has many negative effects Environmental pollution has become a global problem, especially air and water pollution

Vietnam is a developing country with a breakthrough in industry The emergence

of many industrial parks, factories is promoting the strong economic development of the country However, they were built near urban areas and not all factories are equipped with efficient waste treatment systems, especially gas and wastewater, before releasing into the environment Thus, the industrial activity is one of the major causes of air pollution

The development of the industry, especially the chemical industry, also contributes great values to human life Household products provide comfort and convenience to users Nevertheless, most products of this industry are using chemical

solvents and these substances are the source of indoor pollution and one of which is

volatile organic compounds (or VOCs) They appear in detergents, paints, etc in small quantities However, the accumulation of VOCs over time can harmfully affect human health, especially sensitive people such as children and the elderly Therefore, it is

necessary to eliminate this source of indoor pollution

1.2 Volatile organic compounds

Volatile organic compounds (VOCs) do not have a common definition It is used to refer to all organic compounds that exist in the atmosphere All activities, including cutting grass, making a fire, cooking and even breathing are also sources of VOCs such

as carbonyls, alcohols, alkanes, alkenes, esters, aromatics, ethers and amides However,

fuel combustion and industrial processes generate most of the VOCs released into the

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Sum of anthropogenic and oceanic emissions Alkanes 44 Alkenes 38 Aromatic compounds 25 Terrestrial plants 1180 Total 1287

The atmospheric lifetime of a VOC species can be determined using the overall rate of removal of that species from the atmosphere This rate can be derived by Summing the reaction rates with radical species, rates of photolysis and the wet and dry deposition rates

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1-Butene 10h Cyclic compounds Days-hours Cyclopentane 4 days Methylcyclohexane 2 days Cyclohexane 4h Aromatic compounds Weeks-—hours Benzene 2 weeks Toluene 2 days 1,3,5-Trimethylbenzene 75h Blogenic compounds Hours—minutes Isoprene 3h a-Pinene 4h

Today, human are more and more concerned about the quality of air indoor In recent reports, indoor air pollutants mainly contain nitrogen oxides (NOx), carbon oxides (CO and CO2), volatile organic compounds (VOCs) and particulates

1.3 Treatment of VOCs in the gas phase

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1.3.1 Decomposition technology 1.3.1.1 Oxidation technology

Thermal oxidation method (also known as combustion method) uses single chambers with ceramic blanket refractory lining the oxidizers and it is equipped with a

propane or natural gas burner In the chamber, burner capacities range between 0.4 to 2

(mil BTUs)/hr with high temperatures range from 760 to 870°C and a maximum gas residence time of 1 sec The modern heat oxidation equipment can treat 95% to 99% of

VOCs with a flow rate of 1000-500,000 ft?/min, concentrations from 100 to 2000 ppm

Non-combustible compounds or low input concentration, which requires the higher heat

and longer residence time in the chamber However, when the combustion temperature

is close to 870°C, nitrogen in the air can be converted into secondary oxide - pollutants, so further secondary treatment is required

Catalytic oxidation method is similar to thermal oxidation method However, due

to the presence of the catalyst, the system is operated at a lower temperature of about 370-480°C This method is suitable for low concentrations of 100-2000 ppm VOCs, with a flow rate of 1000-100000 ft?/min, whereby the maximum efficiency is 95% In spite of its outstanding advantage in reducing the energy costs, catalytic oxidation method still has many limitations such as the high cost of catalysts, more byproducts, catalyst after using can be poisoned if not properly treated and it is highly sensitive to non-VOCs (water, halogen and sulfur compounds) Therefore, current thermal oxidation methods are more commonly used than catalytic oxidation method

1.3.1.2 Biological filtration method

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shown to be effective in treating low levels of VOCs (few ppm) but with only simple organic compounds Microbes and supporting media TT Nutrient leeding VOC laden air ki e ceed (intermittent!) contro! unit = Nutrient Drain Figure 1.1 Flow chart of bio-filtration system 1.3.2 Recovery technology 1.3.2.1 VOCs condensation

Based on the principle of refrigeration or/and pressure compression, this method

is only suitable for organic compounds boiling above 38°C with a high concentration

of 5000 ppm It allows large amounts of organic compounds to be separated and

recovered, which can then be purchased and reused However, this is a method that

requires many bulky and modern equipments to ensure the safety In addition, water

after condensation needs to be treated, so the cost of condensation method is relatively

higher than the others

Coolant Outlet <= Coolant Inlet —

Figure 1.2 Schematic diagram of equipment used for condensing VOCs

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1.3.2.2 Absorption technology

Through direct contact with liquid solvents in the tower and tray, soluble organic compounds are absorbed Absorption systems can handle gas flow with rate of 2000 to 100000 ft?/min at concentrations of 500 to 5000 ppm Depending on the need for treatment, the characteristic of the pollution and processing conditions, the material is very variety in structure, size, surface as well as cost This method is particularly suited for high-moisture pollution (more than 50%) Due to the use of buffer material, the

pressure in the absorption tower should remain low, especially in the absence of dust or

impurities that may clog the column 1.3.2.3 Adsorption technology

Adsorption is categorized into two types: physical adsorption and chemical adsorption In VOCs recovery applications, physical adsorption exhibits superior performance The two most widely used materials for VOCs treatment are activated

carbon and zeolite

Due to its large surface area, flexibility, low cost and high recyclability, activated

carbon is most commonly used in VOCs recovery technology in particular and

adsorption in general This method is suitable for non-selective adsorption at room temperature with molecular weight of about 40 - 150 g/mol, boiling point of 38°C to 260°C However, the limitations of activated carbon include flammable, poor

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Many reports have shown that zeolite has many outstanding advantages that can replace activated carbon such as heat resistance, high selectivity and good moisture As

the Si/Al ratio increases, the heat resistance increases as well The zeolite with SiO2 is

100% resistant to 850°C Zeolite is also called a molecular sieve due to uniform capillary size, which allows the adsorption to be very selective In addition, the presence of water can reduce the adsorption capacity of zeolite, but the water vapor is almost unaffected The zeolite can withstand the gas flow, which has humidity up to 90% Although there are many precious properties but the cost of zeolite is still high, the application is still limited, only considered when activated carbon is not suitable 1.4 Photocatalytic oxidation of volatile organic compounds (VOCs)

Decomposition of VOCs has become one of the major directions studied by scientists around the world Commonly used methods have their disadvantages Adsorption using activated carbon merely transfers pollutants from gaseous phase to solid phase instead of decomposing them Bio-filtration method is slow and has no obvious effect Thermal oxidation destruction requires high temperatures of 200°C - 1200°C for efficient operation and expensive Moreover, all of these methods are ineffective with low and medium levels of processing or with a large number of different organic substances, recycling and re-using are not economically feasible

Therefore, this is great demand for scientists to find a more cost-effective, more efficient

and environmentally benign technology Photocatalytic oxidation (PCO) does not have such limitations and are cost-effective for treating low concentration pollutions It has been demonstrated that organics can be oxidized to harmless carbon dioxide, and water which makes PCO especially attractive for treating air indoor pollutants

1.5 Titanium dioxide

The development of new materials and their potential application form an important part of today's scientific research efforts Indeed, many areas of research and develop programs related to nanostructured materials Furthermore, it is estimated that

nanotechnology has invested millions of dollars in development and become the

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Among the photocatalyst potential, TiO2 is the most popular photocatalyst currently employed due to the hydrophilic properties of TiO2, which has ability to degrade organic compounds under irradiation of UV or near UV-light In addition, TiO2 is especially used for on PCO reaction because of its outstanding properties such as cheap cost, safety, high photoactivity and stability TiO2 is applied in such areas as: self-

cleaning surface material, gas treatment, water treatment, microbial treatment,

eliminating fog phenomenon [3]

The reaction mechanism of photocatalytic removal of toluene, a typical VOC compound, using the common TiO2 photocatalyst has been proposed [4-8]:

TiO2 + hy > e + ht (1)

OH: (surface) + ht — OH'aas (2)

H2Oads + h* — H*aas + OH" ads (3)

e€ + O2 ads > OF ads (4)

Ov ads + H* — HO?" (5)

2HO2" — H2O2a0s + Or (6)

H202 ads + O2 ads —- OH + OH” aas + O2 (7)

OF? ads + CoHs-CH3 ads > H20 + CoHsCHa’ ads (8)

CoHsCH 2’ ads + O2 ads — CoHsCH200 ads (9) CeHsCH200" ads + & — CeHsCHO ags + OH (10) CoHsCHO ads + (MOH" ads + NO2 ads)—> Oxidized compounds (11)

oxidized compounds + (KOH” ads + yO2 ads) —> (CO2, H20) (12)

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Adsorbed H,O Adsorbed ©+ UV Irradiation 4.< 390 mm Adsorbed pollutant (P) Adsorbed H,O, OH

Figure 1.4, The diagram illustrates the photocatalytic mechanism of TiOz TiO2 has three forms of crystalline structure: rutile, anatase and brookite; only two of the forms of TiO2 commonly used in photochemical catalysis are rutile and anatase, in which the anatase form has a higher catalytic activity

In both structures, each base unit is composed of titanium atoms surrounded by

Six oxygen atoms forming the orbital distortion Within each structure, the two bonds

between the titanium and oxygen at the symmetry axis of the orbit are longer All three

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Anatase `92.604°Y O làng [001] 4 [ 1) Ÿ

Figure 1.6 Lattice structure of Anatase

The difference between the Ti-O and Ti-Ti linkages, together with the order of octahedrons, leads to differing mass ratios and energies (Ebangap) for the Rutile and Anatase networks Table 1.3 Specific mass and energy of the restricted area of TiO2 Rutile Anatase Specific mass p (g/cm?) 4,250 3,894 Ebangap (eV) 3,1 3,2

In spite of being the most efficient catalyst for PCO processes, TiO2 still exhibits some major disadvantages Its limited photocatalytic region (A<400 nm) and poor affinity towards organic pollutants prevent this technology from being widely used Thus, the method to concentrate the target pollutants around the TiO2 surface requires consideration [10, 11] The low adsorption capacity of the TiO2 for H2O and toluene

due to the non-porous structure of the TiO2 materials also led to the low efficiency in

toluene removal in humid condition Moreover, many intermediate products are produced such as aldehydes and carboxylic acids which may adsorb and deactivate the photocatalysts The PCO process uses TiO2 to generate electron-hole pairs whichs are agents that produce the free radicals which will degrade the organic compounds

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However, the disadvantage of these pairs is their existence Before reaching the surface to interact with oxygen and water molecule, most of the electrons and holes recombine on the surface or in the bulk of the semiconducting material This process may occur

faster than the reaction to produce radicals [12, 13] Thus, it is possible to enhance the

photocatalytic efficiency of TiO: if the existing time of the electron-hole pair is longer

To overcome those limitations of Ti02-based photocatalyst, the following solutions have been adopted in previous studies: (1) modification of TiO2 catalyst, (2) enhancing surface area of TiO2 catalyst, (3) doping on the additional adsorbents, etc

This thesis will study the photo-catalytic performance of modified TiO2 The process of enhancing TiO? will consist of doping gold nanoparticles, mechanical mixing

with zeolite Y or plasma-treating TiOz (Figure 1.7.) Gold nanoparticles was chosen due

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1.6 Noble metal doping

1.6.1 Previous studies

Photochemical activity in the visible light region of metal doped TiO? is explained as the new energy level generated in the forbidden zone of TiO2 due to nanoparticle dispersion in the TiO2 network

Table 1.4 Some methods of modified metal and application Elements Synthesis Methods Application Ag [14] Fe [15] V [16]

AgNOs mixed with sodium citrate tribasic dehydrate, temperature reaction reached

80°C, continued to stir TTIP and HNO;

were then added, maintaining the

temperature reaction at 50 °C for 24 hours Sol was dried at 105°C for 24 hours and heated at 300°C

Magnetron method: 99.99% titanium beer

and 99.99% iron samples were made in the reactor, argon and oxygen were added to the tank during the exchange

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Au [17] Pt [18] Ce [19] dried at 150°C, milling and heating at 400°C for 0.5 hours

Titanium (IV) butoxide is dissolved in

absolute alcohol, then was added to a

solution containing tetrachloroauric acid

(HAuCl4.4H20), acetic acid and ethanol

The suspension was aged for 2 days, vacuum

drying, milling and heating at 650°C

Optical reduction process: TiO2 emulsified in a mixture of hexachloroplatinic acid in methanol The suspension is irradiated with a mercury lamp for 1 hour Pt-TiO2 was separated by filtration, washed with distilled water and dried at 100 °C for 24 hours

A proper amount of Ce(NOs3)3 and the titania

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1.6.2 Gold nanoparticles (AuNPs)

Nowadays, with the development of science and technology, many significant characteristics of gold under nano-scale have been discovered along with their practical applications Gold nanoparticles (AuNPs) catalysts began to be applied in 1991, when Hutching and his colleagues conducted hydrochlorination of acetylene [20]

1.6.2.1 Overview

Gold is the 79th element in the periodic table, denoted by Au, belonging to group IB, with configuration [Xe]5d’6s” The energy at 5d and 6s subclasses of Au are

approximately the same, so there is competition between these two subclasses Thus,

electrons are very flexible, able to move between both states, which creates a special

plasticity in Au and the complexity of optical spectrum

Au exhibits the metal characteristics which are soft, ductile and easy to laminate

The golden color of this metal can covert to black, ruby or purple when finely cut Gold is inert with most chemicals but dissolves in Aqua Regia forming cloroauric acid, as well as react with cyanide solutions of alkali metals

Different from bulk state, when in nano-scale, golden exhibits many special properties These include the ability to change color, change from golden to red or light purple This is explained by the fact that in gold nanoparticles absorb and scatter light

with wavelength spectral region differ from normal solid gold In addition, gold catalyst

is difficult to be poisoned, even under high sulfur condition

Gold (Au) has a face-centered cubic structure when in crystalline form Each Au atom is linked to 12 Au atoms around and has a network constant a = 4,0786 A

Figure 1.8 Au face-centered cubic lattice structure

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1.6.2.2 AuNPs optical characteristic

Optical properties are one of the outstanding properties of Au nanoparticles These nanoparticles absorb and scatter light with exceptional efficiency This phenomenon is

explained by the oscillation of conduction electrons on metal surfaces when they are

excited by light at a specific wavelength This oscillation is also known as “Surface plasmon resonance" and it causes Au nanoparticles to absorb and radiate light much better than non-plasmon nanoparticles of the same size This phenomenon can be tuned by controlling the particle size, shape and the local refractive index near the particle surface [21, 22] Electric field | Meta /” sphere Electron cloud Figure 1.9 Illustration of the excitation of localized surface plasmon resonance 1.7 Hydrogenated TiO» 1.7.1 Previous studies

Recently, hydrogen TiO2 modification processes have received a lot of attention thanks to the ability to expand the light absorption spectrum of TiO2 and enhance the

existence of photoelectron and holes [23, 24] Hydrogenated TiO2 can be prepared through many methods such as hydrogen thermal treatment [25], chemical reduction

and oxidation [26], electrochemical reduction [27], etc

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Table 1.5 Some methods of preparing hydrogenated T1O› Method Description Ref Hydrogen reduction Hydrogen plasma Chemical reduction Chemical oxidation

Hydrogenation or hydrogen reduction has

become a powerful tool to synthesize black TiO2 nanomaterials A variety of parameters, such as

source of raw TiO2, hydrogenation time and

temperature, H2 pressure, exposed crystal facet of

TiO2, and even reactor materials, will affect the

colorization, surface structure and groups, and photocatalytic performance of hydrogenated TiO2

nanomaterials

Hydrogen plasma technology has attracted increasing interest owing to its effectiveness in

engineering surface-disordered TiO2 nanomaterials

with a typical crystalline/amorphous core/shell Structure

Black TiO2 can be prepared using different

reducing agent such as aluminum, CaHz,

magnesium, NaBHy, lithium, etc This process is called chemical reduction

Most of these studies prepared black TiO2 by

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Electro- The electrochemically reduced black TIO2

chemical often possessed abundant Ti** species and oxygen [27, 45, 46]

reduction vacancies

These methods include: water-plasma-

Other assisted; nitrogen doping; electrochemical [4-52]

methods oxidation; ionothermal synthesis; laser irradiation;

proton implantation

1.7.2 Plasma surface modification

In spite of the remarkable findings of this material, the equipment and the general conditions lead to high costs Therefore, it is necessary to develop a simple method to effectively synthesize this advanced TiO2 material The hydrogenation TiO? technology by plasma is known for its ability to modify TiO2 surfaces without heat or high pressure and improving photocatalytic activity in the treatment of organic compound in the liquid

phase [53]

1.8 Zeolite

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The zeolite Y crystals formed during the crystallization of SiO4 and AlOa

tetrahedrons Each of the four adjacent tetrahedrons is connected by joining together atoms of oxygen at the top In tetrahedral AlO«, there is a coordinated number of 4, so the Al?* ion makes the AlO tetrahedron had negative charge, so that the negative charge will be compensated by a 1-cation metal cation which is usually a alkaline metal Therefore, the number of cations in the chemical element of the zeolite is equal to the number of aluminum atoms (Al) Then the crystal network of the zeolite will be balanced

Compensation cations (Na*, NH**, H*, ) are located inside the conduits, or

cavities of the zeolite to balance negative charges in the frame

Zeolite Y is usually made in the form NaY, mainly made from three sources:

Silicon (Sodium Silicate), Aluminum (Sodium Aluminate) and Sodium Hydroxyl The NaY crystallization process lasts from 8 hours to several days, depending on the

material, the crystallization conditions, the chemical composition of the zeolite NaY

have good SiOz / AlzO3 > 5, with a surface area of about 800m?/g, high crystallinity,

negligible impurities (using XRD test method)

Zeolites are widely used as catalysts for many reactions due to the following four properties [54]

Ion exchange capacity: Due to the crystal structure in the three-dimensional space, the zeolite frame does not swell during the ion exchange This is a precious property that other inorganic exchangers do not have

The zeolite after exchange with H* ion becomes a solid acid and it is capable of catalyzing the transformation process

The volume of porous hole in the zeolite is very large, allowing them to absorb large amounts of reactants As a result, the concentration of molecules around the active center will be greater than at the outer surface

With a uniform capillary structure of less than 10 A in diameter, zeolites exhibit

very high selectivity The diffusion of the reaction agents and the porous materials of the zeolite plays an important role in the catalytic reaction, affecting the rate of reaction

as well as the distribution of the product

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In these four properties, the activity and selectivity of the catalyst are determined by the surface acidity and the geometric selectivity of the zeolite This is also the basic condition for selecting the appropriate catalyst for each reaction process to achieve the

highest efficiency

In the process of reacting the diffusion capacity of molecules greatly influences Diffusion ability both depends on the molecular nature and depends on the size of the capillary in the zeolite, which represents the geometric selectivity of the zeolite With a special and very uniform structure of the capillaries, zeolite allows only smaller molecules to enter and exit its capillaries Therefore, the selective shape in the capillary is more important than the catalytic adsorption surface

1.9 Method of analyzing 1.9.1 X-ray Diffraction (XRD)

The principle of operation of the method is based on the phenomenon of X-ray

diffraction on the crystal lattice due to the periodicity of the structure to create the maximum and minimum diffraction At that point, each lattice node becomes a diffraction center The incoming rays and diffraction rays interfered with each other,

forming alternating light and dark veins

Figure 1.11 The angle of incidence and angle of reflection in XRD method

The law Vulf-Bragg: nA = 2d.sin@ Where in:

d: Distance between two atomic planes

0: The angle between the X-ray beam and the reflecting plane

n: diffraction degree (n is an integer) A: wavelength of the X-ray beam

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Each crystal phase corresponding to the characteristic distance d gives the diffraction peaks at certain angular values, so the X-ray diffraction spectrum is the dependence of the diffraction intensity BERYLLIUM TUNGSTEN GLASS WINDOW FILAMENT COOLING eet WATER -~-—— E E B TO TRANSFORMER TARGET

X-RAYS——” FOCUSING CUP VACUUM

SCHEMATIC CROSS SECTION OF AN X-RAY TUBE

Figure 1.12 Diagram of principle XRD analysis equipment

1.9.2 Analysis of surface area by adsorption N2 (BET)

According to the BET theory, adsorption molecules do not move freely on the

surface of the adsorbent and do not interact with each other, at different points may

form multiple adsorbent layers but the overall is constant Equation BET: 1 1 C-—1 P vŒ9/s— 1) =yc†v.cœ Where in:

P is the equilibrium pressure Po is the saturation pressure

V is the amount of adsorbed No Vm is the amount of mono-adsorbed No C is the BET constant

In the range of 0.05 < s < 0.35 then NI is the linear function of By Surface

area of the material by formula: S = =

Vm derived from the BET equation N is the Avogadro constant (6.023.107) A is the cross-sectional area of the adsorption cone (N2, 16.2 A?)

M is the molecular weight of the adsorbed particle

W is the mass of adsorbed material

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1.9.3 Scanning electron microscope (SEM)

This method uses a narrow beam of electrons to scan the surface of the sample to

produce a sample image, which can reach the desired magnification when it arrives at

the fluorescence screen The electron beam generated from the cathode through the two caustics will converge onto the sample When the electron beam hits the sample, the surface of the sample emits secondary electron beam Each of these electrons is accelerated by the accelerating voltage into the receiver, which changes into a light signal, amplifying the signal, and bringing it into the control network to create a brightness on the sample surface

1.9.4 Transmitted electron microscope (TEM)

This method allows for the observation of many of the nanoscale elements of the sample: shape, particle size, particle boundaries, etc using high energy electron beam through thin solid specimens and use magnetic lenses to produce images with great magnification (up to a million times), images can be produced on fluorescents, or on optical film, or recorded using digital cameras

1.9.5 FTIR analysis

When exposed to infrared radiation, sample molecules selectively absorb radiation of specific wavelengths which causes the change of dipole moment of sample molecules Consequently, the vibrational energy levels of sample molecules transfer from ground state to excited state The frequency of the absorption peak is determined by the vibrational energy gap The number of absorption peaks is related to the number of vibrational freedom of the molecule The intensity of absorption peaks is related to the change of dipole moment and the possibility of the transition of energy levels

Therefore, by analyzing the infrared spectrum, one can readily obtain abundant structure

information of a molecule What makes infrared absorption spectroscopy even more useful is the fact that it is capable to analyze all gas, liquid and solid samples The common used region for infrared absorption spectroscopy is 4000 ~ 400 cm”! because the absorption radiation of most organic compounds and inorganic ions is within this region

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1.9.6 Inductive coupled plasma (ICP)

ICP (Inductively Coupled Plasma) is an analytical technique used to detect elements in the fields of environment, geology, mineral, etc ICP spectrum is the type of emission spectrum using high frequency induction plasma generator Disperse

atoms/ions to emit electromagnetic waves at the characteristic wavelengths for each

element The intensity of this emission represents the concentration of the element in the sample

1.9.7 Gas Chromatography (GC)

The basis for separation by gas chromatography is the distribution of the sample between the two phases: the static phase has a large contact surface, the mobile phase is the permeate gas through the entire static surface If the static phase is solid then it is called gas-solid chromatography Columnar solids are usually silica gel, molecular sieve or activated carbon This process is mainly adsorbed If the static phase is liquid, we have gas-liquid chromatography The liquid envelops the surface of an inert solid,

called a carrier, to form a thin film The basis for the separation is the distribution of the sample in and out of this thin film[55]

Samples are injected in and follow the carrier gas (N2) to the chromatographic column (static phase) Sample through this column will be adsorbed on the static phase After that, the substances are separated from the column by the outflow of air that is detected by the probe From the received signals the computer will process and present the result by chromatogram Substances determined by the residence time value in the

chromatogram[56]

The gas chromatography system consists of the components[55]:

Carrier gas supply: can be used gas cylinders or gas appliances (the device separates N2 from the air, H2 gas from the distilled water, .)

Column furnace: used to control column temperature analysis

Sample Injection Unit: Used to put the sample into the analytic column with variable pump volume When injecting a sample into a column, split and splitless modes can be used There are 2 ways to put the sample into the column: by manual injection and auto ampler (Autosampler - with or without headspace)

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Catalysis Column: There are two types of columns are packed and capillary

Packed column: Static phase is packed into the column, the column is 2-4mm in diameter and 2-3m in length Capillary column: static phase is covered where in (thickness 0.2-0.5um), the column is 0.1 - 0.5mm in diameter and 30 - 100m in length

Probes: Use signaling to identify and quantify the substance to be analyzed There are different types of probes for different purposes such as FID-Flame Ionization

Detector, TCD-Thermal Conductivity Detector, ECD- Electronic Capture Detector,

FPD-Flame Photometric Detector, NPD - Nitrogen Phosphorus Detector, MS-Mass Spectrometry

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CHAPTER 2: EXPERIMENT 2.1 Chemicals for preparing the catalyst

Table 2.1 List of chemicals

Chemical name Composition Origin

Polyvinylalcohol 1 wt% solution Vietnam

Sodium borohydride 99.99% Germany

Sodium hydroxide Germany

Sodium aluminate Germany

Sodium metasillicate Germany

Chlocoauric acid 1000mg/L Germany

Titanium dioxide (P25) Germany

Ethanol 90 wt% Vietnam

Distilled water Vietnam

2.2 Preparation of catalyst

Hydrogenated TiOz TiO2 (P25-Degussa) purchased from Sigma-Aldrich was used in this study Hydrogen-plasma-treated TiOz was synthesized in plasma systems at the Institute Of Applied Materials Science (Figure 2.1.) The process of treating materials by plasma is carried out in a reactor made of quartz with an internal diameter of 10.6 mm, with a 1.6 mm diameter Wolfram electrode and a 1.7 mm thick dielectric layer (quartz tube) Materials before processing in plasma are dried under vacuum conditions, at a temperature of 110°C, 2 hours The material after drying is set inside the reactor and kept in the plasma The material handling process is carried out in H2/Ar gas flow (10% v/v), at a voltage of 7 kV The hydrogen plasma processing time is adjusted in the range of 0-60 minutes The samples are then denoted p-TiO2-X with X

= 0), 15, 30, 60 is the processing time

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Gold nanoparticle doping TiO2 Nanosized Au/TiQO2 catalysts were synthesized by a metal-sol method which was reported in our previous publication as a successful method to obtain nanosized metal on TiO2 [57-59] (Figure 2.2) 4 mL of HAuCl4 solution (0.0146 M) was to an Erlenmeyer flask containing 5 mL of PVA solution (1

wt%) and 20 mL of distilled water A freshly prepared solution of containing 15 mg of

NaBH was slowly added dropwise into the mixture Afterward, TiO2 was added into the flask and the mixture was stirred for another 4 hours at 60°C Amount of added Ti02 was calculated to obtain 0.5wt% noble metal in the final catalysts Then, the mixture was filtrated and washed with distilled water several times to remove CI ion The solid obtained after the filtration was dried overnight at 100°C Finally, the catalysts were

calcinated at 400°C for 2 hours

Zeolite Y Zeolite Y was synthesized by a hydrothermal method [60] (Figure 2.3.) A “seed gel” mixture was made up of 19.95 g of distilled water 4.07 g of NaOH and 2.09 g of NaAlOz This mixture was stirred in a beaker until completely dissolved After

that, 28.3 g of 40 wt% Na2SiO3 solution were added to the mixture and stirred at 1600

rpm for 30 minutes The mixture was aged for 24 hours at room temperature A “feedstock gel” mixture was formed by adding 131 mL of distilled water to 0.14 g NaOH and 13.0 g NaAlO2 The mixture was stirred in a beaker until it completely dissolved Then, 178 g of 40 wt% Na2SiO3 solution was added to the solution and stirred at 1600 rpm for 30 minutes After that, the “seed gel” mixture was added slowly to the “feedstock gel” mixture with stirring at 1600 rpm for 1 hour The mixture was hydrothermally treated at 100 ° C for 20 hours The mixture was then cooled, filtered and washed with distilled water several times until pH 9 Finally, the product was dried overnight at 100°C

Hydrogenated Au/TiO:2 In order to obtain hydrogenated Au/TiO2, Au/TiO2 was first prepared using the above procedure The sample was then treated using plasma under H2/Ar gas flow This phase was performed using the same system at at the Institute Of Applied Materials Science The samples were name Xp-Au/TiOz where X

is the plasma duration