photocatalytic application of copper sulfide: effect of...

Ref. code: 25595710030635AWR

PHOTOCATALYTIC APPLICATION OF COPPER SULFIDE : EFFECT OF COPPER TO SULFUR RATIO

BY

MISS LADDAWAN BOONGLOMGLIN

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS

FOR THE DEGREE OF MASTER DEGREE OF ENGINEERING CHEMICAL ENGINEERING

DEPARTMENT OF CHEMICAL ENGINEERING FACULTY OF ENGINEERING THAMMASAT UNIVERSITY

ACADEMIC YEAR 2016 COPYRIGHT OF THAMMASAT UNIVERSITY

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หัวข้อวิทยานิพนธ์ การศึกษาปฏิกิริยาการถูกกระตุ้นด้วยแสงของตัวเร่งปฏิกิริยาคอปเปอร์ซัลไฟด์ระดับนาโนและอัตราส่วนระหว่างคอปเปอร์และซัลเฟอร์ในการสังเคราะห์

ชื่อผู้เขียน นางสาวลัดดาวรรณ บุญกล่อมกลิ่น ชื่อปริญญา วิศวกรรมศาสตรมหาบัณฑิต สาขาวิชา/คณะ/มหาวิทยาลัย วิศวกรรมเคมี

วิศวกรรมศาสตร์ มหาวิทยาลัยธรรมศาสตร์

อาจารย์ที่ปรึกษาวิทยานิพนธ์ รองศาสตราจารย์ ดร. นุรักษ์ กฤษดานุรักษ์ ปีการศึกษา 2559

บทคัดย่อ

งานวิจัยนี้ เป็นการสังเคราะห์ตัวเร่งปฏิกิริยาคอปเปอร์ซัลไฟด์ โครงสร้างระดับนาโนที่ ใช้ในการกระตุ้นด้วยแสง ในการศึกษานี้คอปเปอร์คลอไรด์และโซเดียมซัลเฟต ได้ถูกคัดเลือกเป็นวัตถุดิบในสัดส่วน 1 ต่อ 6 1 ต่อ 8 และ 1 ต่อ 10 โดยโมลตามล าดับ ภายใต้การ ใช้เฮกซะดีซิลไตรเมททิลแอมโมเนียมโบรมายด์เป็นตัวรีดิวซ์ โดยจะถูกไฮโดรเทอร์มัลที่อุณหภูมิ 130 องศาเซลเซียส เป็นเวลา 24 48 และ 72 ชั่วโมงตามล าดับ และจากการวิเคราะห์ด้วยเทคนิค เอ็กซ์อาร์ดีพบว่าตัวเร่งปฏิกิริยาคอปเปอร์ซัลไฟด์ที่สังเคราะห์ได้ท้ังหมดมีผลึกแบบเฮกซะโกนอล มีขนาดเฉลี่ย 25 ถึง 500 นาโนเมตรซึ่งได้จากการวิเคราะห์ด้วยเทคนิคเอสอีเอ็ม และ จากการวิเคราะห์ด้วยเทคนิค ยูวีดีอาร์เอสพบว่าแถบช่องว่างพลังงานที่อิเล็กตรอนใช้ในการเคลื่อนที่ภายในตัวเร่งปฏิกิริยาคอปเปอร์ซัลไฟด์มีขนาดเฉลี่ย 1.88 ถึง 2.04 อิเล็กตรอนโวลต์ เมื่อน าตัวเร่งปฏิกิริยาคอปเปอร์ซัลไฟด์ ที่สังเคราะห์ได้ไปทดสอบ ปฏิกิริยาการย่อยสลายพาราควอทภายใต้แสงวิซิเบิล พบว่าจลนพลศาสตร์ของการย่อยสลายของพาราควอทโดยใช้ตัวเร่งปฏิกิริยาคอปเปอร์ซัลไฟด์ที่สังเคราะห์ได้ในสัดส่วน 1 ต่อ 8 และถูกไฮโดรเทอร์มัล เป็นเวลา 72 ชั่วโมงจะมีพฤติกรรมแบบ LHHW และอันดับที่1 ตามความเข้มข้นที่ 40 ppm ของพาราควอท โดยมีค่าคงที่ปฏิกิริยาเท่ากับ 2.51x10-3 นาที-1 ค ำส ำคัญ: คอปเปอร์ซัลไฟด์, กระบวนการไฮโดรเทอร์มัล, พาราควอท, ปฏิกิริยาการย่อยสลายด้วยแสง, แสงวิซิเบิล

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Thesis Title PHOTOCATALYTIC APPLICATION OF COPPER SULFIDE : EFFECT OF COPPER TO SULFUR RATIO

Author Miss Laddawan Boonglomglin Degree Master of Engineering Department/Faculty/University Chemical Engineering

Faculty of Engineering Thammasat University

Thesis Advisor Assoc. Prof. Nurak Grisdanurak, Ph.D. Academic Years 2016

ABSTRACT

This research aimed to synthesize copper sulfide (CuS) nanocrystal from the solution of CuCl2·2H2O and Na2S·9H2O by hydrothermal method using hexadecyl trimethyl ammonium bromide (CTAB) as a reducing agent for photocatalytic activity. The ratios of copper to sulfur were in molar ratio of 1:6, 1:8 and 1:10. All synthesized

catalysts were obtained in an oven at 130C for 24, 48 and 72 hours, respectively. The result of CuS exists as hexagonal phase that was characterized by X-ray diffraction (XRD) and average crystallite size were in range 25 to 500 nm which characterized by scanning electron microscopy (SEM). Energy band gap of prepared CuS nanocrystals were 1.88 - 2.04 eV that were characterized by UV-Vis diffuse reflectance (UV-DRs). The photocatalytic performance for degradation 40 ppm of paraquat solution under visible light was investigated. The kinetic model of photocatalytic degradation of paraquat solution that using prepared CuS (1:8 obtained for 72 hours) was expressed by LHHW and pseudo 1st order, giving rate constant of 2.51x10-3 min-1. Keywords: Copper Sulfide, Hydrothermal, Paraquat, Photocatalytic activity, Visible light.

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ACKNOWLEDGEMENTS

During my Master’s Degree study entitled of “Photocatalytic application of copper sulfide: Effect of copper to sulfur ratio”, I would like to express my heartfelt gratitude to my thesis advisor, Associate Professor Dr. Nurak Grisdanurak, for his patience, encouragement, motivation, guidance and invaluable help throughout the course of my study.

I would like to thank the Center of Excellent in Environmental Catalysis and Adsorption (COE), Thammasat University and Faculty of Engineering, Thammasat University for the financial supports.

I am grateful to my special friend from Tunghai University, Taiwan, Ms. Hui-Chun Lee (Sanmao) during staying here in our Catalysis Laboratory for 3 months.

My sincere thanks also goes to Professor Dr. Philipina A. Marcelo, Dean of faculty of engineering and all members, that provided me an opportunity to join their faculty, suggest and kindly support about my work, also for warm welcome me in University of Santo Tomas, Manila, Philippines for 2 months.

I also wish my special thanks to Tak, Namtan, Tum, Pond, Aum, P’Kwan, P’Ekk, P’Eddie, P’A and all members of the Catalysis Laboratory. I thank my good friends during taking a course, Namtan, Mai, Nat, Tae and P’Tae. I thank my friend, Pokpong, CU. In particular, I am also grateful to a lovely sister, P’May for making a good time, supporting and loving me.

Finally, I would specially like to thank my beloved family, especially Mom and Dad, for teaching, supporting, and loving me unconditionally during my study.

Miss Laddawan Boonglomglin

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TABLE OF CONTENTS

Page ABSTRACT (1)

ACKNOWLEDGEMENTS (3)

LIST OF TABLES (7)

LIST OF FIGURES (8)

CHAPTER 1 INTRODUCTION 1

1.1 Background 1 1.2 Objectives of Study 2 1.3 Scopes of Research 2

CHAPTER 2 REVIEW OF LITERATURE 4

2.1 Paraquat 4 2.2 Heterogeneous Photocatalysis 6 2.3 Copper Sulfide (CuS) 7

2.3.1 Copper sulfide (CuS) as photocatalyst 8 CHAPTER 3 RESEARCH METHODOLOGY 14

3.1 Materials and Apparatus 14

3.1.1 Materials 14 3.1.2 Instrument and Apparatus 14

3.2 Synthesis of CuS 15

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3.3 Material Characterizations 16 3.3.1 X-Ray Diffraction (XRD) 17 3.3.2 Scanning Electron Microscope (SEM) 17 3.3.3 UV-Vis Diffuse Reflectance Spectroscopy (UV-DRs) 17

3.4 Photocatalytic Degradation Studies 18 3.4.1 Photodegradation of Paraquat over CuS 19 3.4.2 Effect of Initial Paraquat Concentrations 20 3.4.3 Kinetic study of photodegradation 21

CHAPTER 4 RESULTS AND DISCUSSION 22

4.1 Characterization of photocatalyst 22 4.1.1 X-Ray Diffraction (XRD) 22 4.1.2 Scanning Electron Microscope (SEM) 25 4.1.3 UV-Vis Diffuse Reflectance Spectroscopy (UV-DRs) 27

4.2 Photocatalytic Activities of Paraquat Degradation 30 4.2.1 Photocatalytic Degradation of Paraquat by using

various CuS 30

4.2.2 Photocatalytic Degradation of Paraquat by comparison between CuS and TiO2

32

4.3 Kinetic study 33 CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS 34

5.1 Conclusions 34 5.2 Recommendations 35

REFERENCES 36

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APPENDICES

APPENDIX A Raw data of the experiments and calculations 43 APPENDIX B Conference 54

BIOGRAPHY 61

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LIST OF TABLES

Tables Page 2.1 Properties of Paraquat 5 2.2 Photocatalysis studies of CuS (Covellite) 10 4.1 Average crystallite size (D) of synthesized CuS obtained at 130°C 24 4.2 Band gap energy (Eg) of synthesized CuS obtained at 130°C 27

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LIST OF FIGURES

Figures Page 1.1 Study chart 3 2.1 Chemical Structure of Paraquat 5 2.2 Schematic illustration of semiconductor photocatalysis 6 2.3 Growth mechanism for the CuS 8 3.1 Copper sulfide (CuS) nanocrystal preparations 16 3.2 The experimental set up for photocatalytic degradation under

visible light 19

4.1 XRD patterns of the synthesized CuS at 130°C 23 4.2 SEM images of the prepared CuS obtained at 130°C 26 4.3 UV-Vis Diffuse Reflectance spectra of the synthesized CuS obtained

at 130°C 28

4.4 Band gap energy spectra of the synthesized CuS obtained at 130°C 29 4.5 Photocatalytic degradations of 40 ppm paraquat solution over 9

synthesized copper sulfide (CuS) catalysts under visible light 31

4.6 Photocatalytic degradations of 40 ppm paraquat solution over a Cu:S = 1:10 with hydrothermal time 72 hours and TiO2 P25 with catalyst dosage 1.0 g/L and hydrogen peroxide dosage 0.22 M under visible light

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4.7 Plot of initial rate method for Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model

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CHAPTER 1 INTRODUCTION

1.1 Background

Copper sulfide has attracted interest because it has optical, electronic, physical and chemical properties(1). Copper sulfide has many formulas such as covellite (CuS), chalcocite (Cu2S) and villamaninite (CuS2). It can be applied to use in many applications such as p-type semiconductor in solar cell(2), adsorption and commonly applied as photocatalyst. Therefore many methods can be prepared copper sulfide such as solvothermal(3), microwave irradiation(4), sonication(5), sol-gel precipitation(6) and hydrothermal(7). In comparison with other methods used to synthesize copper sulfide, hydrothermal is a simpler, low cost and friendly to environment. Copper sulfide has a direct band gap of energy around 1.27 - 1.75 eV.(8) that is activated only under visible irradiation. The material was revealed the degradation performance over several dye solutions, such as methylene blue (MB), rhodamine B (RhB), malachite green (MG), methyl red (MR), methyl orange (MO) and eosin (E)(3). Saranya et al., reported that the photocatalytic activity was evaluated by the decolorization of methylene blue (20 ppm) under visible-light irradiation and results showed that 87% of the dye was degraded after 40 min(9). Gupta et al., used copper sulfide nanoparticles (CSNP) for the degradation of methylene blue (100 ppm) under sunlight, there was a removal of 40% of methylene blue after approximately 60 min(10) and He et al., studied the effect of Cu/S ratio on the photoactivity and found that stoichiometric CuS (Cu/S = 1:1) towards lower binding energies(11). However, copper sulfide has not been used to study on the photocatalytic reduction of herbicide.

Paraquat (1,1'-Dimethyl-4,4'-bipyridinium dichloride) is known to display some harmful effects on humans such as damage to the digestive system, kidneys and lungs. It is still used in developing countries in Southeast Asia such as Philippines and Thailand. Because of its known toxicity, degradation and removal of paraquat in

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waste water have been a matter of paramount importance(12). Therefore, many treatments including adsorption and photocatalysis reductions under Ultraviolet (UV) light have been applied to degrade paraquat concentrations to within acceptable levels(13). Cantavenera, M. J., et al. revealed that TiO2 completely degraded paraquat (20 ppm) under UV light within approximately 3 h(14).

In this research, factors influencing the synthesis of copper sulfide particles were investigated. Firstly, copper sulfide particles were fabricated by hydrothermal method. Characterizations of copper sulfide by XRD, SEM and UV-DR were applied to confirm the formulas and properties. In addition, photodegradable experiments on a paraquat aqueous solution as a pollutant probe were presented. Finally, temperature, time and ratio affecting copper sulfide synthesis were observed through its characteristics and photocatalytic activity. 1.2 Objectives of Study

1.2.1 To evaluate the dominant effect on synthesis of copper sulfide particles under hydrothermal method.

1.2.2 To test the photocatalytic activity of copper sulfide using paraquat probe contaminated in water.

1.3 Scopes of Research

1.3.1 Study the factors influencing synthesis of copper sulfide particles which utilized hydrothermal method

- The mole ratio between copper and sulfur 1:6, 1:8, 1:10 - Synthesis time 24, 48, 72 h - Synthesis temperature 130 oC 1.3.2 To test the photocatalytic activity of copper sulfide using paraquat

probe contaminated in water. - Concentration of paraquat solution 20-100 ppm

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- Time 0-240 min - Sample catalyst dosage 1 g/L - Visible light 6 W/m2 - Wavelength 257 nm

Fig.1.1 Study chart.

Hydrothermal

Method

CuCl2·2H2O +

Na2S·9H2O

SEM, XRD, UV-DRs

Paraquat

CuS Photocatalyst Characteristic

Photocatalytic Activity

Photodegradation under visible light

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CHAPTER 2 LITERATURE REVIEW

2.1 Paraquat Paraquat (1,1'-Dimethyl-4,4'-bipyridinium dichloride) is a quick acting and non-selective contact herbicide. It is one of the most extensively used herbicide in agricultural countries for the control of broad-leaved weeds and grasses in crop land and aquatic area due to its physical properties, such as high solubility in water, low vapor pressure. The chemical structure of paraquat is shown in Figure 2.1, and the properties of paraquat are shown in Table 2.1. As herbicide, paraquat has been available to farmers for over 40 years and the use of paraquat trends to be increased in the future due to its properties and application in order to control weeds effectively. Nowadays, it is present as an environmental pollutant both in soil and surface waters, due to its wide utilization(14). It is less (and usually much less) than 0.1% of applied paraquat will be present in the interstitial water(15). The minimum lethal dose of paraquat is stated to be about 35 mg/kg body weight for human beings(16). Many efforts have been prepared to remove it from the environment. The treatments to degrade contaminated paraquat in water are classified as physical, biological and chemical method. Physical method is adsorption onto spent diatomaceous earth(17), activated bleaching earth(18) and biochar adsorbent(19). Biological methods such as fungal decolonization(20), microbial degradation, adsorption by (living or dead) microbial biomass and bioremediation systems are commonly applied to the treatment of industrial effluents because many microorganisms such as bacteria, yeasts, algae and fungi are able to accumulate and degrade different pollutants(21). Chemical method is photochemical reduction(22) which is often used to remove the paraquat contaminate when compared with other physical and biological processes. Photocatalytic degradation under UV light Sorolla, M. G., et al. used Cu-TiO2/SBA-15 for degradation of paraquat (10 ppm); an almost complete removal of paraquat was achieved after approximately 8 hours(12), Marien,

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C. B. D., et al. used TiO2 nanotubes for degradation of paraquat (10 ppm); an almost complete removal of paraquat was achieved after approximately 90 minutes(23) and Cantavenera, M. J., et al. used TiO2 Degussa P25 for degradation of paraquat (20 ppm); an almost complete removal of paraquat was achieved after approximately 5 hours(14). Among those techniques, photocatalytic oxidation is quite a promising technique that effective only UV light irradiation. Table 2.1 Properties of Paraquat.

Properties

Chemical formula C12H14Cl2N2

IUPAC name 1,1'-Dimethyl-4,4'-bipyridinium dichloride CAS number 1910-42-5

Molecular weight 257.16 g/mol

Density 1.25 g/cm3 Physical state White to yellow powder

Boiling point > 300 °C (572°F) Melting point 175 - 180°C (347 - 356°F)

Vapor pressure < 0.0000001 mmHg (20°C)

Solubility in water 20°C 0.7 g/cm3

Figure 2.1 Chemical Structure of Paraquat.

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2.2 Heterogeneous photocatalysis Heterogeneous photocatalysis is one of the advanced oxidation processes that used for removal organic pollutants in aqueous solution in the presence of a catalyst. The photocatalysis commonly use semiconductor as a catalyst because it has band gap energy (Eg). The photocatalysis process is based on

adsorption of photons with energy (hν). Generation of excited energy states of an electron (e-) and a positive hole (h+) occurs when the band gap of semiconductor is irradiated greater than or equal to its band gap energy. It results in the promotion of e- in the conductive band and formation of h+ in the valence band as shown in (Eq. 2.1).

Semiconductor + hν → e- + h+ (2.1) The mechanism of photocatalysis semiconductor is shown in Figure 2.2: (I) the formation of charge carriers by a photon; (II) the charge carrier recombination to liberate heat; (III) the initiation of a reductive pathway by a conduction band electron; (IV) the initiation of an oxidative pathway by a valence band hole; (V) the further thermal (e.g., hydrolysis or reaction with active oxygen species) and photocatalytic reactions to yield mineralization products; (VI) the trapping of a conduction band electron in a dangling surficial bond; (VII) the trapping of a valence-band hole at the surface of the semiconductor(24).

Figure 2.2 Schematic illustration of semiconductor photocatalysis(24).

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The electron-hole recombination can be considered as one of the major factors limiting the efficiency of the photocatalysis. One of the most practical and interesting ways proposed to avoid this limitation is the use of Fenton-like heterogeneous catalytic wet peroxide oxidation(25) with semiconductor as photocatalyst and hydrogen peroxide (H2O2) as reducing agent. Addition of H2O2 as an electron acceptor on surface of semiconductor photocatalyst can enhance the photodegradation rate of organic pollutants due to overcomes the drawback of charge recombination(26). 2.3 Copper sulfide (CuS) Copper sulfide is a black powder and inorganic compound that is insoluble in water. The chemical compounds of copper sulfide are in the CuxSy formulas. Most formulas of the copper sulfide are covellite (CuS), chalcocite (Cu2S) and villamaninite (CuS2). All formulas of CuxSy have been identified as p-type semiconductor materials. Copper sulfide can be prepared by many methods such as sol-gel precipitation(27), microwave irradiation(28), sonication(29), solvothermal method(30) and hydrothermal method(31). In comparison with hydrothermal and other methods, hydrothermal route is a simpler, low cost, environment friendly because it just needs water as solvent instead of chemical solvent needed in solvothermal route. Copper sulfide with specific morphology and size such as nanowires(22), nanotubes(32), nanoplates(33) and nanoparticles(34) can be produced by different copper and sulfur sources with the aid of assisting agent. Tanveer, M., et al. used solvothermal method (Cu(NO3)2·3H2O, sulfur powder, Cu to S molar ratio = 1: 2) sythesis CuS at 140 °C to 160 °C, 180 °C, and 200 °C for 8 h, 12 h, and 24 h. They reported that the more complex hierarchical structures (high specific surface area) were obtained with increased synthesis reaction times and temperature, the schematic for CuS growth mechanism was shown in Figure 2.3(35). The CuS particle size has been decreased for increasing reaction time(36) and the form of CuS particles will change to plates (hierarchical structures) with increasing reaction temperature(4).

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Figure 2.3 Growth mechanism for the CuS. (SWCO, single wall cuboctahedra), (DWCO, double wall cuboctahedra), (MWCO, multiwall cuboctahedra) (SCCO, super complex cuboctahedra)(35). Copper sulfide (CuS) has attracted because it has excellent physical and chemical properties. Many research proposed many methods to synthesize copper sulfide, studied its optical properties and applied to use it in many applications such as p-type semiconductor in solar cell(37), chemical sensors(38), eyeglass coating(39), adsorption(40) and photocatalyst(35). Although CuS has a good chemical stability, absence of toxicity and good performance in photocatalyst work.

2.3.1 Copper sulfide (CuS) as photocatalyst Copper sulfide (CuS) is one of the photocatalyst that can used in photocatalysis often combine with Fenton-like reactions (adding H2O2). This process can overcome the recombination of electron (e-) and positive hole (h+) pairs then enhance the photodegradation rate of organic pollutants. There have many studies

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using CuS as a photocatalyst and hydrogen peroxide (H2O2) as reducing agent for degrading organic compounds that shown in Table 2.2. Moreover, CuS is one of the excellent photocatalysts for degradation of organic dye but just few studies degraded other organic contaminants such as Saranya, M., et al. synthesized CuS by hydrothermal method and reported that nitrobenzene and 4-nitrophenol were completely degraded after 60 min under visible light(41). So in this study, herbicide “paraquat” would be investigated utilize CuS as photocatalyst.

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Table 2.2-1 Photocatalysis studies of CuS (Covellite).

Methodology Morphology Band gap

Energy (eV) Results of photocatalyst work Reference

Hydrothermal method - Nanoplates 40 - 110 nm

2.08 - 100% of nitrobenzene was degraded after 60 min under visible light - 100% of 4-nitropheno was degraded after 60 min under visible light

(41)

Solvothermal method - Hierarchical particles 50 nm

1.45 - 98.23% of methylene blue (0.5 g/L) was degraded after 30 min under a 90 W Xenon lamp - 100% of methylene blue (0.5 g/L) was degraded after 30 min under a 160 W Mercury tungsten blended lamp

(42)

Solvothermal method - Nanoplates 10 - 40 nm

- - 90% of methylene blue (20 mg/L) was degraded after 90 min under solar light

(43)

Chemical dealloying method

- Particles 50 - 100 nm

1.60 - 1.70 - 100% of methylene blue (10 mg/L) was degraded after 40 s under a 500 W Xe lamp - 98% of methylene blue (1 g/L) was degraded after 16 min under a 500 W Xe lamp

(44)

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Solvothermal method - Nanoplates 400-500 nm - SWCO (8 h) - DWCO (12 h) - SCCO (24 h)

SWCO: 1.70 DWCO: 1.86 SCCO: 1.96

- SWCO: 60% of methylene blue was degraded after 60 min under natural light - DWCO: 72% of methylene blue was degraded after 60 min under natural light - SCCO: 96% of methylene blue was degraded after 60 min under natural light

(35)

Solvothermal method - Spheres 10–16 nm

3.38 - 25% of methylene blue (1.6 mg/L) was degraded after 40 min under visible light

(46)

Solvothermal method - Ball-flower

20–35 μm

- - 96% of methylene blue (10 mg/L) was degraded after 25 min under UV light

(49)

Hydrothermal method - Flake like aggregates - Spheres - Tubes 40 - 80 nm

1.63 - 1.87 - 87% of methylene blue (20 mg/L) was degraded after 40 min under visible light

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Mechanochemical ball milling method

- Quantum dots (QDs) <5 nm - Plates (NPs)

QDs: 1.87 NPs: 2.27

- 60% of rhodamine-b (10 mg/L) was degraded by QDs without H2O2 after 30 min under visible light. - 95% of rhodamine-b (10 mg/L) was degraded by QDs with H2O2 after 30 min under visible light. - 40% of rhodamine-b (10 mg/L) was degraded by NPs with H2O2 after 30 min under visible light.

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Hydrothermal method Solvothermal method

- Spheres 400 - 500 nm - Tubes

8 - 10 μm (L)

0.5 - 10 μm (D) - Plates 50 - 100 nm - Particles 10 - 25 nm

Spheres: 2.08 Tubes: 2.06 Plates: 2.16 Particles:

1.88

- Spheres: 97% of methylene blue (20 mg/L) in the dark was degraded after 25 min - Tubes: 94% of methylene blue (20 mg/L) in the dark was degraded after 25 min - Plates: 95% of methylene blue (20 mg/L) in the dark was degraded after 25 min - Particles: 97% of methylene blue (20 mg/L) in the dark was degraded after 25 min

(48)

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Ultrasonication - Hollow spheres 200 - 500 nm

1.27 - 95.6% of methylene blue (50 mg/L) was degraded after 30 min under visible light - 90.7% of rhodamine-b (50 mg/L) was degraded after 40 min under visible light

(45)

Solution (ion exchanging)

- Particles

3.10 - 32% of methylene orange (10 mg/L) was degraded after 480 min under solar light - 32% of bromocresol green (10 mg/L) was degraded after 480 min under solar light

(47)

Hydrothermal method - Particles 50 - 70 nm

2.35 - 70% of methylene blue (0.1 g/L) was degraded after 60 min under solar light

(10)

Hydrothermal method - Particles 20–50 nm

- - 23% of rhodamine-b (1×10−5 M) was degraded after 30 min

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CHAPTER 3 RESEARCH METHODOLOGY

In this work, copper sulfide catalysts were synthesized by hydrothermal method, character ized by several techniques and appl ied to use in photodegradation. In this part, deal with the catalyst preparation, characterization and photodegradation. Moreover, the kinetic of copper sulfide catalysts in the photodegradation were developed by Langmuir–Hinshelwood (L–H) model. 3.1 Materials and apparatus 3.1.1 Materials

1. Copper chloride dihydrate (CuCl2·2H2O, 98%, Carlo Erba, France)

2. Sodium sulfide nonahydrate (Na2S·9H2O, 99.9%, Carlo Erba, France)

3. Hexadecyl trimethyl ammonium bromide (CTAB,

CH3(CH2)15N(Br)(CH3)3, 99%, Acros Organics, U.S.A.) 4. Methyl viologen dichloride hydrate (Paraquat, C12H14Cl2N2 ·xH2O,

98%, Acros Organics, U.S.A.) 5. Hydrogen peroxide (H2O2, 30% w/w in water, Carlo Erba, France) 6. Ethanol (C2H5OH, 95%, Sigma-Aldrich, Germany) 7. Titanium dioxide P25 (TiO2 P25, >99.5% Aeroxide, China)

3.1.2 Instrument and Apparatus

1. Teflon-lined stainless steel autoclave (external diameter = 7.5 cm, height = 16.5 cm)

2. Oven (ED240, Binder, Germany) 3. Compact centrifuge (Z206, Hermle Labortechnik, Germany) 4. Pyrex glass photoreactor (250 mL)

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5. Refrigerated water bath circulator (RTE-111, Neslab, U.S.A.) 6. LED visible light bulb (6W, Philips, China) 7. Magnetic stirrer (C-MAG HS 7, IKA, Germany) 8. Solarimeter (SL100, from Kimo, France) 9. UV meter (UV-meter 5.0, Solartech, USA) 10. UV-Visible spectrophotometer (V-630, Jasco, Japan) 11. Laboratory glasswares

3.2 Synthesis of CuS Copper sulfide (CuS) catalysts were synthesized from copper chloride dehydrate (CuCl2·2H2O) as copper source and sodium sulfide nonahydrate (Na2S·9H2O) as sulfur source. The hydrothermal method was used to synthesize copper sulfide (CuS) catalysts which modified from literature(31). The preparation of copper sulfide (CuS) catalysts was varied with different molar ratios of copper to sulfur (1:6, 1:8 and 1:10) and hydrothermal times (24, 48 and 72 h) at 130°C. The procedures are listed as describe below and as shown in Figure 3.1: 1) 3 mmol of copper chloride dehydrate (CuCl2·2H2O) was mixed with 1 mmol of hexadecyl trimethyl ammonium bromide (CTABl) in 60 ml of distilled water by stirred for 10 min that was poured into buret. CTAB was used to increase the link between copper (Cu) and sulfur (S) which provide as a surfactant. 2) 30 mmol of sodium sulfide nonahydrate (Na2S·9H2O) solution was prepared in 60 ml of distilled water. 3) Then dropwise copper solution added into sodium solution. The molar ratios of copper to sulfur in 120 ml of solutions were 1:6, 1:8 and 1:10. After stirring 30 min, the mixture was transferred into a Teflon-lined stainless steel autoclave for further hydrothermal treatment. 4) The autoclave was kept for 24, 48, and 72 h at 130°C in an oven. After the hydrothermal treatment, the autoclave was cooled down to room temperature before collecting the sample.

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5) The as-synthesized materials were washed by distilled water and ethanol for several times until the solution became transparent before centrifuged at 5000 rpm for 5 min and dried in vacuum oven at 60°C for overnight.

Figure 3.1 Copper sulfide (CuS) nanocrystal preparations. 3.3 Material Characterizations The physical structure and chemical properties of synthesized CuS photocatalysts at various conditions were examined by many techniques such as X-Ray diffraction (XRD) was used to determine the crystal structure, the images of CuS nanostructure was provided by scanning electron microscope (SEM) and the energy band gap of CuS nanocrystals were estimated from the adsorption spectra that determined by UV-Vis diffuse reflectance spectroscopy (UV-DRs).

130

CuCl2 · 2H2O & Cetyl Trimethyl Ammonium Bromide (CTAB) mixture

Na2S · 9H2O solution

The mixture was transferred into a Teflon-lined stainless steel autoclave

CuCl2 · 2H2O & Cetyl Trimethyl Ammonium Bromide (CTAB) mixture

130

Na2S · 9H2O solution

The mixture was transferred into a teflon-

lined stainless steel autoclave.

In oven for 24,

48, 72 hrs. at 130 C

Stired 10 min

after dropping

5000

Washed and

centrifuged at

5000rpm

60

Dried at 60 C

60

Dried at 60 ºC For 24, 48 and 72 hoursat 60 ºC

Washed and centrifuged at 5000 rpm

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3.3.1 X-Ray Diffraction (XRD) The X-ray diffraction (XRD) of CuS nanocrystals was recorded on

Bruker AXS (Model D8 Discover, Germany) diffractometer with CuKα radiation. The X-ray was generated with a current of 40 mA and a potential of 40 kV. In addition, the

CuS samples were scanned from 20 to 80 degrees (2θ) in steps of 0.02 degrees per second. The average crystallite size (D) of CuS nanocrystals was estimated with the assist of Scherrer equation using the XRD data:

θcosβ

kλD (3.1)

Where, D = crystallite size (nm) k = crystallite shape factor (0.94)

λ = X-ray wavelength for CuKα (0.15406 nm)

β = the full-width-half-maximum (FWHM) of the peak

θ = Bragg angle 3.3.2 Scanning Electron Microscope (SEM) The morphology of each CuS sample was analyzed by a scanning electron microscope (JEOL JSM-6610LV, Japan) that operates at 1 kV to 30 kV with an ultimate resolution of 3 nm to 1.2 nm in high vacuum mode with secondary electron image conditions and the electron micrograph technique. The accelerating voltage ranges from 0.3 kV to 30 kV, and the magnification range runs from 5X to 300,000X 3.3.3 UV-Vis Diffuse Reflectance Spectroscopy (UV-DRs) The diffusion reflectance of CuS nanocrystals were measured by UV-diffuse reflectance absorption spectrometer (Hitachi model U-3501, Japan) equipped with integrating sphere. The reflectance of samples was detected in the 400-800 nm wavelength range. The pure power of BaSO4 was used as a reference. The band gap energies of the CuS nanocrystals can be estimated from the equation of the Tauc’s law (1968):

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)Eh(A)h( g2 (3.2)

Where,

α = the optical absorption coefficient

hν = the photon energy (eV) Eg = the energy band-gap (eV) A = an energy-independent constant

3.4 Photocatalytic Degradation Studies There are two parts in photodegradation studies. The first part was comparison of photocatalytic activities between 9 CuS samples that synthesized with different molar ratios of copper to sulfur (1:6, 1:8 and 1:10) and hydrothermal times (24, 48 and 72 hours) were evaluated by the paraquat degradation efficiency. The second part was selecting the CuS which one has the best photocatalytic performance to estimate the efficiency of catalyst with different concentration of paraquat solution and the kinetic of photodegradation will be investigated. The experimental set up are shown in Figure 3.2 that photocatalyst (1.0 g/L) and hydrogen peroxide (0.22 M) were added into 40 ml of paraquat solution in a 250 ml Pyrex glass reactor, and maintain at 25 °C by refrigerated water bath circulator. The reactor was placed at the fixed distance of 20 cm away from a 6W LED bulb where the irradiance is equal to 6 W/m2 and was stirred at constant speed during the photoreaction process. The reactor and LED bulb were insulated by 1.0 m2 opaque cabinet.

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Figure 3.2 The experimental set up for photocatalytic degradation under visible light. 3.4.1 Photodegradation of Paraquat over CuS The CuS samples were compared by photocatalytic performances which were synthesized with different molar ratios of copper to sulfur (1:6, 1:8 and 1:10) and hydrothermal times (24, 48 and 72 h) at 130°C. The paraquat degradation efficiencies were estimated by following the procedures as follows: 1) The initial concentration of paraquat solution was 40 ppm all over the photocatalytic reaction. 2) The photocatalyst (1.0 g/L) was added into 40 ml of 40 ppm paraquat solution. 3) The mixture solution was magnetically stirred in the dark for 1 hr to confirm adsorption equilibrium.

25 oCCooling water in

Visible light

ParaquatSolution(40 ppm)

CuS

Cooling water out

6 w/m2

A catalyst dosagewas 1 g/L.

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4) 1.0 mL of hydrogen peroxide (H2O2, 30% w/w in water) was added into the mixture. The first sample was taken out at the 10th minute after H2O2 was added. 5) The light was turned on immediately, and sampling every 20 minutes.

6) The samples were filtered with PTFE-Millipore disk (0.45 μm) to remove the photocatalysts. 7) The filtrates were analyzed by the Jasco V630 UV-Visible spectrophotometer at the characteristic band of 257 nm to determine the paraquat concentration.

3.4.2 Effect of Initial Paraquat Concentrations The CuS was chosen which one has the best photocatalytic performance from previous part. The photocatalytic activities of CuS were evaluated by degradation efficiency of different concentration paraquat (20, 40, 60, 80, 100 mg/L). The procedures are listed consequently as follow: 1) The photocatalyst (1.0 g/L) was added into 40 ml of paraquat solution with various concentrations such as 20, 40, 60, 80 and 100 mg/L, respectively. 2) The reaction mixture was magnetically stirred in the dark for 1 hr to confirm adsorption equilibrium. 3) 1.0 mL of hydrogen peroxide (H2O2, 30% w/w in water) was added into the mixture. The first sample was taken out at the 10th minute after H2O2 was added. 4) The light was turned on immediately, and sampling every 10 minutes.

5) The samples were filtered with PTFE-Millipore disk (0.45 μm) to remove all photocatalysts.

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6) The filtrates were analyzed by the Jasco V630 UV-Visible spectrophotometer at the characteristic band of 257 nm to determine the paraquat concentration. 3.4.3 Kinetic study of photodegradation The Langmuir–Hinshelwood–Hougen–Watson (LHHW) model was the most commonly applicable for photoreaction of water dissolved organic compounds(51). In this study, can be applied the kinetic model to the photocatalytic reaction. The rate of photodegradation was estimated by pseudo-first order (Eq. 3.3) in LHHW kinetic model as following equation:

)CK1(

CKk

dt

dCr

a

ar

(3.3)

Where, kr = the surface reaction rate constant Ka = the Langmuir–Hinshelwood adsorption equilibrium constant C = the concentration of paraquat (mM) at a given time

To evaluate those parameters, an initial rate method(52) was applied. L–H rate expression (Eq. 3.3) could be written and linearized as follows;

)CK1(

CKk

dt

dCr

0a

0ar0

(3.4)

r0ar0 k

1

CKk

1

r

1 (3.5)

Hence, the values of kr and Ka can be estimated by plotting the reciprocal of degradation rate as a function of the reciprocal of initial parauat concentration.

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CHAPTER 4 RESULTS AND DISCUSSION

The synthesized copper sulfide (CuS) photocatalysts were characterized by several techniques including X-Ray diffraction (XRD), Scanning electron microscope (SEM) and UV-Vis Diffuse Reflectance Spectroscopy (UV-DRs). The kinetic of paraquat degradation under visible light were reported.

4.1 Characterization of photocatalyst 4.1.1 X-Ray Diffraction (XRD) Figure 4.1 shows X-Ray diffraction patterns of 9 synthesized CuS samples with different molar ratios of copper to sulfur (1:6, 1:8 and 1:10) and

hydrothermal times (24, 48 and 72 hours) at 130°C and the cell parameters are ɑ =

3.796 Å and с = 16.38 Å. All XRD patterns of obtained CuS present the characteristic

peaks at 2θ = 27.9, 29.4, 32.4, 46.4and 54.8corresponding to the (101), (102), (103), (110) and (108) in JCPDS card number 06-0464. The results indicated that obtained CuS existed as covellite phase. Copper oxide or other impurity phases were not observed in these XRD pattern, suggesting that the product was pure copper sulfide. The intensity of (110) standard diffraction peak was particularly strong which indicates the preferential orientation growth along (110) plane of the sample. This may have some effects with the morphology of the products(7).

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2 Theta (degree)20 30 40 50 60 70 80

Inte

nsity

(a.u

.) 72 h

48 h

24 h

(a)

(101

)(1

02)

(103

) (110

)

(108

)

2 Theta (degree)

20 30 40 50 60 70 80

Inte

nsity

(a.u

.)

72 h

48 h

24 h

(b)

(101

)(1

02)

(103

) (110

)

(108

)

2 Theta (degree)

20 30 40 50 60 70 80

Inte

nsity

(a.u

.) 72 h

48 h

24 h

(c)

(101

)(1

02)

(103

) (110

)

(108

)

Figure 4.1 XRD patterns of the synthesized CuS at 130 °C. (a) Cu:S = 1:6 (b) Cu:S = 1:8 (c) Cu:S = 1:10

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Table 4.1 Average crystallite size (D) of synthesized CuS obtained at 130°C.

Cu:S Hydrothermal time (hours)

(110) Peak intensity

β

(radian) θ

(degree) Crystallite size (nm)

1:6

24 245 0.004720 23.19 33.39

48 262 0.004103 23.16 38.40 72 226 0.005173 23.19 30.47

1:8

24 250 0.004700 23.23 33.54

48 201 0.005068 23.19 31.10 72 252 0.004254 23.23 37.06

1:10

24 216 0.004913 23.19 32.08

48 201 0.006091 23.27 25.89 72 162 0.005120 23.19 30.78

Table 4.1 shows the average crystallite size of the catalysts determined by using Scherrer equation (Eq. 3-1) where the full width at half maximum (FWHM) of the prominent X-Ray diffraction is employed at (110) broadening peak. The crystallite sizes of Cu:S = 1:6 with hydrothermal time 24, 48 and 72 hours were found to be 33.39, 38.40 and 30.47 nm, respectively. Moreover, the crystallite sizes were reported at 33.54, 31.10 and 37.06 over Cu:S = 1:8 with hydrothermal time 24, 48 and 72 hours, respectively. Regarding to higher Cu:S ratio (1:10) with hydrothermal time 24, 48 and 72 hours, the crystallite sizes were 32.08, 25.89 and 30.78 nm, respectively. Considering the effect of Cu:S ratio and hydrothermal duration, the results investigated that the crystallite sizewas not significantly different among all conditions and the average crystallite size of catalyst was approximately 32.52 nm.

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4.1.2 Scanning Electron Microscope (SEM) SEM images of 9 synthesized copper sulfide (CuS) catalysts were shown in Figure 4.2. The images of Cu:S 1:6 samples displayed uniform distribution in size and plate shape. The results demonstrated that the range of particle size were around 160 - 660 nm, 200-300 nm (ca. 30 nm thickness) and 200-330 nm at 24, 48 and 72 hours of hydrothermal time, respectively (Fig. 4.2a-c). However, some morphology of plate structure was found to become hierarchical structure, displayed in Figure 4.2c. At higher Cu:S ratio (Cu:S = 1:8) with hydrothermal time 24 hours, the morphology exhibited that there was approximately 80 % of a particle structure with 170 - 650 nm and 20 % of a rope-like structure with 500 - 1100 nm length and 170 - 650 nm width (Fig. 4.2d). Regarding to Cu:S = 1:8 with hydrothermal time 48 hours, the morphology revealed about 50 % of a particle structure with sizing 130 - 330 nm, 30 % of a plate uniform with 250 -350 nm diameter and 30 nm thickness and 20 % of a hierarchical structure with sizing 300 - 400 nm (Fig. 4.2e). Over Cu:S = 1:8 with hydrothermal time 72 hours, 20 % of a particle structure was shown in sizing 180 - 350 nm, 50 % of a plate structure with 250 - 350 nm diameter and 30 nm thickness and 30 % of a hierarchical structure with sizing 300 - 400 nm (Fig. 4.2f). In case of Cu:S = 1:10 ratio, the results demonstrated that the structure of all hydrothermal condition became not uniform and bigger in size comparing with other Cu:S ratio. The condition of 24 hours hydrothermal, shown in Figure 4.2g, the morphology presented around 50 % of a particle structure with sizing 300 - 500 nm and 50 % of a rope-like structure with 500 - 1100 nm length and 160 nm width. Over Cu:S = 1:10 with hydrothermal time 48 hours, the image exhibited 45 % of a rope-like structure with 500 - 1100 nm length and 160 nm width, 10 % of a plate structure with 500 - 750 nm diameter and 30 nm thickness and 45 % of a hierarchical structure with sizing 300 -400 nm (Fig. 4.2h). In case of Cu:S = 1:10 with hydrothermal time 72 hours, the morphology was a plate-like hierarchical structure with 300 - 500 nm diameter and 30 nm thickness (Fig. 4.2i).

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SEM results revealed that the plate particle structure of CuS became a rope-like structure by increasing the molar ratio of sulfur, on the other hand it became a hierarchical structure with increasing hydrothermal times.

Figure 4.2 SEM images of the prepared CuS obtained at 130°C. (a) Cu:S = 1:6 obtained for 24 h (b) Cu:S = 1:6 obtained for 48 h (c) Cu:S = 1:6 obtained for 72 h (d) Cu:S = 1:8 obtained for 24 h (e) Cu:S = 1:8 obtained for 48 h (f) Cu:S = 1:8 obtained for 72 h (g) Cu:S = 1:10 obtained for 24 h (h) Cu:S = 1:10 obtained for 48 h (i) Cu:S = 1:10 obtained for 72 h

(i)

(f)

(c)

(h)

(e)

(b)

(g)

(d)

(a)

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4.1.3 UV-Vis Diffuse Reflectance Spectroscopy (UV-DRs) The UV-Vis Diffuse Reflectance spectra of 9 synthesized copper sulfide (CuS) catalysts are shown in Fig. 4.3. The band gap energy of samples was

estimated from Tauc plot (αhν)2 as a function of photon energy (hν)(8) , where α is

the absorption coefficient, h is the Planck constant, ν is the light frequency, as shown in Figure 4.4. The linear extrapolation was estimated by drawing a tangent line through the maximum slope and taking the intersection with x axis. It was found that the average band gap energy of catalysts were in the range 1.88 - 2.04 eV, as tabulated in Table 4.2. Table 4.2 Band gap energy (Eg) of synthesized CuS obtained at 130°C.

Hydrothermal times (hours)

Eg (eV) Cu:S = 1:6 Cu:S = 1:8 Cu:S = 1:10

24 1.91 2.04 1.94

48 1.88 1.93 1.98 72 1.98 1.98 1.99

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Wavelength (nm)

400 450 500 550 600 650 700 750 800

Refle

ctan

ce

.81.01.21.41.61.82.02.22.42.6

72 h

48 h

24 h

(a)

Wavelength (nm)

400 450 500 550 600 650 700 750 800

Refle

ctan

ce

1.0

1.5

2.0

2.5

3.0

3.5(b)

Wavelength (nm)

400 450 500 550 600 650 700 750 800

Refle

ctan

ce

1.0

1.5

2.0

2.5

3.0

3.5

4.0(c)

72 h48 h24 h

72 h48 h24 h

Figure 4.3 UV-Vis Diffuse Reflectance spectra of the synthesized CuS obtained at 130°C (a) Cu:S = 1:6 (b) Cu:S = 1:8 (c) Cu:S = 1:10

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1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

5

10

15

20

25

30

35

40

24h

48h

72h

(a)

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

( h

)2 (eV2 /c

m2 )

5

10

15

20

25

30

35

40

24h

48h

72h

(b)

1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0

5

10

15

20

25

30

24h

48h

72h

(c)

h (eV)

( h

)2 (eV2 /c

m2 )

h (eV)

( h

)2 (eV2 /c

m2 )

h (eV)

Figure 4.4 Band gap energy spectra of the synthesized CuS obtained at 130 °C (a) Cu:S = 1:6 (b) Cu:S = 1:8 (c) Cu:S = 1:10

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4.2 Photocatalytic Activities of Paraquat Degradation The efficiency of synthesized CuS catalysts in the photodegradation of paraquat was investigated under visible light irradiation (6 W/m2) with catalyst dosage 1.0 g/L. The photodegradation of paraquat solution was carried out in the dark for 1 hour to study the adsorption effect. Concentration of paraquat was analyzed by the

UV-vis spectrophotometer with a detector setting at λ = 257 nm. 4.2.1 Photocatalytic Degradation of Paraquat by using various CuS The photodegradation of 40 ppm paraquat solution over 9 synthesized copper sulfide (CuS) catalysts under visible light with catalyst dosage 1.0 g/L and additional hydrogen peroxide dosage 0.22 M while irradiance equal to 6 W/m2 were shown in Fig. 4.5. Considering the effect of adsorption onto the catalyst, the concentration of paraquat decreased around 10% of initial paraquat concentration for all 9 types of catalysts. The disappearance of paraquat should be due to the adsorption over available surface of CuS catalysts. Under visible irradiation as the photo activity, 40 ppm paraquat can be 100 % degraded within 240 minutes for all 9 synthesized copper sulfide (CuS) catalysts. The fastest degradation of paraquat was observed over Cu:S = 1:8 with 72 hydrothermal times which paraquat was completely degraded by 100 min, following by Cu:S = 1:8 with 48 hours and Cu:S = 1:6 with 48 hours hydrothermal reaction. However, at Cu:S = 1:8 with 72 hours hydrothermal reaction was selected to photocatalytic degradation of paraquat by comparison with TiO2.

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Irradiation time (min)0 60 120 180 240

C/C 0

0.0

.2

.4

.6

.8

1.0

1:6 24 h

1:6 48 h

1:6 72 h

Irradiation time (min)0 60 120 180 240

C/C 0

0.0

.2

.4

.6

.8

1.0

1:8 24 h

1:8 48 h

1:8 72 h

Irradiation time (min)

0 60 120 180 240

C/C 0

0.0

.2

.4

.6

.8

1.0

1:10 24 h

1:10 48 h

1:10 72 h

(a)

(b)

(c)

Figure 4.5 Photocatalytic degradations of 40 ppm paraquat solution over 9 synthesized copper sulfide (CuS) catalysts under visible light. (a) Cu:S = 1:6 (b) Cu:S = 1:8 (c) Cu:S = 1:10

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4.2.2 Photocatalytic Degradation of Paraquat by comparison between CuS and TiO2 Figure 4.6 shows the photodegradation of 40 ppm paraquat solution over a synthesized CuS catalyst (Cu:S = 1:8, hydrothermal time 72 hours) and TiO2 P25 with catalyst dosage 1.0 g/L and additional of hydrogen peroxide dosage 0.22 M under visible light irradiation (6 W/m2). The concentration of paraquat was only completely degraded over CuS in the presence of H2O2 under visible irradiation (Fig. 4.6). As observed in other catalysts, paraquat could be degraded less than 10%. CuS with additional H2O2 exhibited obviously higher efficiency compared to TiO2 with H2O2, and only H2O2. This can be described that the presence of H2O2 can enhance the photodegradation of paraquat solution. H2O2 is an electron acceptor that can overcome the drawback of charge recombination(26). For using TiO2 catalyst with H2O2, it was removed few contaminant of paraquat by surface adsorption instead of photocatalysis, owing to

the absorption of photon energy (hν) from visible light irradiation was not higher than or equal to band gap energy of TiO2 (3.2eV)(1).

Irradiation time (min)

0 60 120 180

C/C 0

0.0

.2

.4

.6

.8

1.0

Only H2O2

TiO2 with H2O2

CuS with H2O2

Only paraquat

Figure 4.6 Photocatalytic degradations of 40 ppm paraquat solution over a Cu:S = 1:8 with hydrothermal time 72 hours and TiO2 P25 with catalyst dosage 1.0 g/L and hydrogen peroxide dosage 0.22 M under visible light.

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4.3 Kinetic study The kinetic study of photocatalytic reaction of CuS was evaluated. In this study, CuS (Cu:S = 1:8, hydrothermal time 72 hours) and various concentration of paraquat solution (20, 40, 60, 80, 100 mg/L) is selected to express the kinetic investigation. The Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model was applied to the photodegradation of paraquat solution. The LHHW adsorption equilibrium constant and the surface reaction rate constant can be estimate from the intercept and slope of Eq. 3-5 that plotted of 1/r0 versus 1/C0, shown in Figure 4.7. Moreover, the LHHW adsorption equilibrium constant (Ka) and the surface reaction rate constant (kr) of paraquat degradation were 10.34 mM-1 and 2.5×10-3 min-

1, respectively. It can be confirmed that the CuS can reveal photodegradation of paraquat solution and follow the as-estimated equation (Eq. 4.1).

747.395259.381

00

Cr

(4.1)

C0 (mM)

0.0 .1 .2 .3 .4

r 0 (

x10-2

mM

min

-1)

0.00

.05

.10

.15

.20

.25

1/C0 (mM-1)

2 4 6 8 10 12 14 16

1/r 0

(min

กEm

M-1

)

400

500

600

700

800

900

10001/r0 = 38.259/C0 + 395.747

R2 = 0.9584

Figure 4.7 Plot of initial rate method for Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model.

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CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions 1. The copper sulfide (CuS) photocatalysts were successfully prepared by hydrothermal method from the solution of CuCl2·2H2O and Na2S·9H2O with various sulfur molar ratios by employing CTAB as a reducing agent at 130°C. 2. All of synthesized copper sulfide (CuS) photocatalysts were in hexagonal phase and the crystallite sizes were in range of 25.89 - 38.40 nm. The more complex structures such as plate, rope-like and hierarchical structure were obtained with increasing molar ratio of sulfur content and reaction times. The particle sizes of synthesized CuS were ranged from 250 to 500 nm and the band gap energies were in range of 1.88–2.04 eV. 3. The photocatalytic degradation of 40 ppm paraquat solution in the presence of H2O2 using all synthesized copper sulfide (CuS) as photocatalysts were investigated under visible light with the catalyst loading of 1 g/L. From the results, the copper sulfide (Cu:S = 1:8 for 72 hours) photocatalyst revealed the best photocatalytic performance. 4. The synthesized copper sulfide (Cu:S = 1:8, hydrothermal time 72 hours) photocatalyst enhanced the photocatalytic performance better than the commercial TiO2 P25 photocatalyst for degrading 40 ppm paraquat solution under visible light in the presence of H2O2. 5. The kinetic of paraquat photocatalytic degradation was revealed by the Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model of LHHW adsorption equilibrium constant (Ka) = 10.34 mM-1 and the surface reaction rate constant (kr) = 2.5×10-3 min-1.

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5.2 Recommendations 1. In this work, the compositions of prepared CuS should be analyzed by X-ray fluorescence spectroscopy (XRF) and the size distribution of prepared CuS should be measured by zetasizer. 2. Mechanism pathway (intermediates) of paraquat photodegradation over CuS with H2O2 under visible irradiation should be characterized by HPLC. 3. The effect of various dosages of H2O2 and CuS in heterogeneous photo-Fenton-like oxidation system should be investigated.

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APPENDICES

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APPENDIX A

Raw data of the experiments and Calculations

Figure A.1 Calibration Curve of Paraquat Solution.

Abs

0.0 .2 .4 .6

Conc

entra

tion

(ppm

)

0

2

4

6

8

10

y = 15.02x + 0.246

R2 = 0.999

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Table A.1 Photocatalytic Degradation of 40 ppm Paraquat Solution over Cu:S = 1:6 obtained for 24 h.

Time Abs ppm C/C0 -60 0.2504 40.0701 -

-40 0.2369 38.0499 - -20 0.2348 37.7195 -

0 0.2288 36.8183 1

20 0.2036 33.0332 0.8972 40 0.1719 28.2719 0.7679

60 0.1369 23.0149 0.6251

80 0.1029 17.9156 0.4866 100 0.0743 13.6199 0.3699

120 0.0454 9.2716 0.2518

180 -0.0545 0 0 240 -0.1561 0 0

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Table A.2 Photocatalytic Degradation of 40 ppm Paraquat Solution over CuS = 1:6 obtained for 48 h.

Time Abs ppm C/C0 -60 0.2187 35.3087 -

-40 0.2019 33.2285 - -20 0.2008 32.6277 -

0 0.1954 31.8166 1

20 0.1913 31.1933 0.9804 40 0.1466 24.4718 0.7692

60 0.0854 15.2946 0.4807

80 0.0465 9.4368 0.2966 100 0.0015 2.6778 0.0842

120 -0.0374 0 0

180 -0.1500 0 0 240 -0.2124 0 0

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Time Abs ppm C/C0 -60 0.2509 40.1527 -

-40 0.2379 38.2001 - -20 0.2283 36.7507 -

0 0.2279 36.6906 1

20 0.2159 34.8957 0.9511 40 0.1854 30.3146 0.8262

60 0.1462 24.4192 0.6655

80 0.1016 17.7203 0.4830 100 0.0679 12.6661 0.3452

120 0.0321 7.2739 0.1983

180 -0.0412 0 0 240 -0.1192 0 0

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Time Abs ppm C/C0 -60 0.2540 40.6108 -

-40 0.2464 39.4618 - -20 0.2401 38.5155 -

0 0.2350 37.7570 1

20 0.2111 34.1597 0.9047 40 0.1880 30.6976 0.8130

60 0.1456 24.3291 0.6444

80 0.1008 17.6002 0.4661 100 0.0558 10.8337 0.2869

120 0.0219 5.7419 0.1512

180 -0.0786 0 0 240 -0.1511 0 0

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Time Abs ppm C/C0 -60 0.2212 35.6842 -

-40 0.2126 34.3925 - -20 0.2081 33.7099 -

0 0.2014 32.7028 1

20 0.1639 27.0778 0.8280 40 0.1227 20.8820 0.6385

60 0.0866 15.4598 0.4727

80 0.0462 9.3917 0.2872 100 0.0179 5.1486 0.1574

120 -0.0156 0 0.0036

180 -0.0942 0 0 240 -0.1756 0 0

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Time Abs ppm C/C0 -60 0.2116 34.2348 -

-40 0.2102 34.0320 - -20 0.2063 33.4463 -

0 0.1989 32.3273 1

20 0.1546 25.6734 0.7942 40 0.1112 19.1622 0.5928

60 0.0713 13.1693 0.4074

80 0.0244 6.1174 0.1892 100 -0.0190 0 0

120 -0.0471 0 0

180 -0.1325 0 0 240 -0.2085 0 0

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Time Abs ppm C/C0 -60 0.2297 36.9534 -

-40 0.2173 35.0910 - -20 0.2152 34.7755 -

0 0.2063 33.4463 1

20 0.2007 32.5976 0.9746 40 0.1937 31.5462 0.9432

60 0.1737 28.5422 0.8534

80 0.1583 26.2367 0.7844 100 0.1299 21.9635 0.6567

120 0.0913 16.1733 0.4836

180 0.0119 4.2399 0.1268 240 -0.0694 0 0

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Time Abs ppm C/C0 -60 0.2626 41.9025 -

-40 0.2583 41.2492 - -20 0.2628 41.9251 -

0 0.2551 40.7760 1

20 0.2441 39.1238 0.9595 40 0.2313 37.1938 0.9121

60 0.2177 35.1510 0.8621

80 0.1916 31.2383 0.7661 100 0.1667 27.4983 0.6744

120 0.1480 24.6896 0.6055

180 0.0861 15.3922 0.3775 240 0.0050 3.2035 0.0000

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Time Abs ppm C/C0 -60 0.2347 37.7119 -

-40 0.2205 35.5716 - -20 0.2116 34.2423 -

0 0.2048 33.2210 1

20 0.1972 32.0794 0.9656 40 0.1715 28.2193 0.8494

60 0.1431 23.9536 0.7210

80 0.1061 18.3887 0.5535 100 0.0707 13.0716 0.3935

120 0.0365 7.9423 0.2391

180 -0.0535 0 0 240 -0.1201 0 0

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Figure A.2 XRD data of Copper Sulfide (Cu:S = 1:6 obtained for 24 h).

2 (o)

40 42 44 46 48 50

Inte

nsity

0

50

100

150

200

250

Half Maximum

46.29o 46.56o

= 23.19

The average crystallite size (D) of Copper Sulfide was estimated by Scherrer equation using the XRD data:

θcosβ

kλD

Where; D = crystallite size (nm) k = crystallite shape factor (0.94)

λ = X-ray wavelength, for CuKα (0.15406 nm)

β = the full-width-half-maximum (FWHM) of the peak (radian)

θ = Bragg angle (o)

k = 0.94 λ= 0.15406 0.00472180

46.29)(46.56

β θ = 23.19o

23.19 cos 0.00472

0.15406)(0.94D = 33.39 nm

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APPENDIX B Conference

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BIOGRAPHY

Name Ms.Laddawan Boonglomglin Date of Birth June 4, 1992 Educational Attainment Publications

Academic Year 2014: Bachelor of Engineering (Chemical Engineering), Srinakharinwirot University, Thailand

1. L. Boonglomglin, R. Khunphonoi, W. Den, & N. Grisdanurak. Photocatalytic application of copper sulfide: Effect of copper to sulfur ratio. Oral Presentation at The Pure and Applied Chemistry International Conference (PACCON 2017), Centra Government Complex Hotel & Convention centre, Chaeng Wattana, Bangkok, Thailand, February 2-3, (2017).

photocatalytic application of copper sulfide: effect of...

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