Nghiên cứu tổng hợp tio2 và khả năng ứng dụng để xử lý cr6+ trong nước thải = reseach on synthesis of tio2 and application for cr6+ treatment in wastewater

BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC BÁCH KHOA HÀ NỘI NGUYỄN VĂN CHÚC NGHIÊN CỨU TỔNG HỢP TIO2 VÀ KHẢ NĂNG ỨNG DỤNG ĐỂ XỬ LÝ SR6+ TRONG NƯỚC THẢI LUẬN VĂN THẠC SĨ KHOA HỌC NGƯỜI HƯỚNG DẪN : TS NGUYỄN HỒNG LIÊN HÀ NỘI – 2010 Research on synthesis of TiO2 and application for Cr6+treatment in wastewater ACKNOWLEDGEMENT I would like to express my gratitude to the people that support me in the completion of my thesis In the first place, I owe a special thank to my dear teachers at the Department of organic and petrochemical technology for their passionate teaching, generosity in dealing with students and also enthusiastic inspiration during the past four years Their devotion to petrochemical technology study and teaching has highly motivated me to pursue my future career as an expert in petrochemical by all my efforts and brain power To my supervisors, I would like to acknowledge and extend my heartfelt gratitude to Doctor Nguyen Hong Lien and Associated Professor, Doctor Le Minh Thang, lecturers of the Department of organic and petrochemical technology Within their petrochemical course, I luckily found my interest in petrochemical technology, and then under their guidance I continued my study in petrochemical technology in my thesis Indeed, I am deeply in debt of their endless patience for their correcting tiny mistakes in my thesis and priceless encouragement that enables me to complete my thesis in due time Last but not less, from deep inside, it is hard to find a suitable word to send my deep thank and express my strong love for my family, my mother, my brothers, my sisters and my girl friend for both their physical and spiritual support Although I have to live far from them, I always feel fully their images and eternal love by my side It is the time I realize that the family is the most wonderful thing I luckily possess To all, I wish you the best Hanoi, October 2010 Student Nguyen Van Chuc Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater TABLE OF CONTENTS ACKNOWLEDGEMENT TABLES IN THE THESIS FIGURES IN THE THESIS INTRODUCTION CHAPTER I: LITERATURE REVIEW I.1 General of wastewater I.1.1 Water pollution I.1.2 Water pollution categories I.1.3 Causes of polluted water 10 I.1.4 Effects of polluted water 10 I.1.5 Control of water pollution 10 I.2 Cr(VI) treatment methods in wastewater 12 I.2.1 Ion exchange method 12 I.2.2 Electrochemistry method 13 I.2.3 Reduction-oxidation method and deposition method 13 I.3 TiO2 review 14 I.3.1 Occurrence 14 I.3.2 Physical and mechanical properties 14 I.3.3 Chemical properties 16 I.3.4 Applications 16 I.4 Mechanism of titanium oxide photocatalytic reactions 17 I.4.1 Band structure of semiconductors and band gap energy 17 I.4.2 Energy structure of titanium oxide and photoeffect 18 I.4.3 Effect of ultraviolet rays in activating titanium oxide 20 I.4.4 Decomposing power of titanium oxide photocatalyst 21 1.4.5 The mechanism of photo-reduction of Cr(VI) 23 I.5 Review of the used precursors in this thesis 24 I.5.1 TiCl4 24 I.5.2 Titanium isopropoxide (TTIP) 28 I Literature review about using TiO2 as a photocatalyst for wastewater treatment 29 I.6.1 In Vietnam 29 I.6.2 In the world 30 I.7 The importance and direction of thesis 36 I.7.1 The importance of the thesis 36 I.7.2 The direction of thesis 36 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater CHAPTER II EXPERIMENTAL 37 II.1 Reagents and materials 37 II.2 Preparation of photocatalysts 37 II.2.1 Sol-gel method 37 II.2.2 Hydrolysis method 38 II.2.3 Impregnating method 39 II.3 The methods to determine the composition of chromium plating wastewater 40 II.3.1 pH meter 40 II.3.2 Atomic Absorption Spectroscopy (AAS) 41 II.4 Physico-Chemical experimental techniques 44 II.4.1 X-ray diffraction (XRD) 44 II.4.2 Scanning electron microscopy (SEM) 46 II.4.3 BET method for the determination of surface area 47 II.5 Catalytic activity test 49 II.5.1 Equipment description 49 II.5.2 The analysis of the composition of reaction solution 50 CHAPTER III RESULTS AND DISCUSSION 63 III.1 Composition of plating chromium wastewater 63 III.2 Physico chemical properties of synthesized catalysts 65 III.2.1 The specific surface areas (SSA) of synthesized catalysts 65 III.2.2 The phase composition of synthesized catalysts 66 III.3 Catalyst activity of synthesized catalysts 70 III.3.1 The influence solar illumination and the suport to the catalytic activity 70 III.3.2 The influence of pH of reaction solution to the catalytic activity 71 III.3.3 The influence of catalytic synthesis methods to the catalytic activity 72 III.3.4 The influence calcination temperature of catalyst to the atalytic activity 73 III.3.5 The influence of amount of TiO2 doped onto Al2O3 to the catalytic activity 74 III.3.5 The influence of concentration of ethanol to the catalytic activity 74 CONCLUSIONS 76 References 77 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater TABLES IN THE THESIS No Name Page Typical physical and mechanical properties of titania 15 Optical properties of titania 15 Ultraviolet rays in ordinary surroundings 22 The physical properties of TiCl4 24 The physical properties of TTIP 29 Properties Computed from Structure 38 The amount of TiO2 loading onto Al2O3 of synthesized catalysts 40 The concentration of the metallic ions in wastewater 64 SSA of synthesized catalysts 66 10 Compositions of catalysts prepared by sol-gel, hydrolysis and Impregnating method 69 11 The changes of concentration of Cr(VI) and COD 71 12 The effects of UV and catalyst to conversion of Cr(VI) and COD 72 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater FIGURES IN THE THESIS No 10 Name 20 Titanium-oxide band structure 21 Crystal structures of titanium oxide 21 Electron structure of titanium oxide 22 Oxidation mechanism 22 Reduction mechanism 39 The Sol-gel method 40 Hydroysis method 41 Impregnating method 42 pH meter Atomic absorption spectrometer block diagram 11 Illustrates how diffraction of X-rays by crystal planes allows one to derive lattice by using Bragg relation 12 The interaction between the primary electron beam and the sample in an electron microscope leads to a number of detectable signals 13 14 15 16 17 Page 43 46 48 49 The BET plot 50 The reactor system The calibration graph of Cr(VI) with 1,5 – diphenylcarbazide solution Concentration of Cr(VI) in three reaction solutions Concentration of Cr(VI) in reaction solution with and without Flocculation 56 57 58 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater 18 19 The XRD patterns of the TiO2/Al2O3 samples SEM images of the synthesized catalysts 56 68 20 The conversion of Cr(VI) deppended on pH of reaction solution 73 21 The conversion of Cr(VI) deppended on the catalytic synthesis methods 74 22 23 24 The conversion of Cr(VI) deppended on calcination temperature of catalyst The conversion of Cr(VI) deppended on amount of TiO2 doped onto Al2O3 The influence of concentration of ethanol to the catalytic activity 74 75 76 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater INTRODUCTION Water pollution has always been a major problem to the environment in the global context It has been supposed the leading worldwide cause of deaths and diseases of human beings, organism in daily life With the increasing growth of the industrialization in major areas and urban cities, the water source just keeps getting more polluted In Vietnam, the water pollution is of the most serious problems which draw the attention of all levels of society, especially, governmental authorities, researchers, and scholars The main reason which caused the water pollution is suggested to originate from non-treated waterwaste discharged from factories, and industrial plants Therefore, wastewater treatment, especially wastewater from coating companies containing a large amout of heavy metal, is important task in Viet Nam in particular and in the world in general In this paper, the research topic focuses on the reduction of heavy metal concentrations by using TiO2 as a photocatalyst Cr(VI) is choosen as a poluted agent and ethanol as a hole scavenger The TiO2/Al2O3 system is synthesized by variety methods and many effect agents are tested The properties of the sythesized catalysts are investigated by the physico-chemical method The catalytic activities of the sythesized catalysts are determined by the conversion of Cr(VI) in water with the presence of ethanol The main content of the paper is divided into three parts Part I discusses the remark of water pollution and its impact to the human life, the wastewater treatment methods, review of TiO2 and precursors, the researches about TiO2 as a photocatalyst for wastewater treatment in the world and Viet Nam Part II introduces the synthesized catalytic methods, the methods to determine the composition of plating chromium wastewater, the methods to investigate the properties of the synthesized catalysts, the methods to calculate the reaction results Part III mentions the results and discussions of the experiments and the research process Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater CHAPTER I: LITERATURE REVIEW I.1 General of wastewater I.1.1 Water pollution Water pollution is currently one of the serious types of pollution facing human beings all over the world The issue has drawn different scales of involvement and cooperation A case in point is that in European Union, a high level of environmental protection and the improvement of the quality of the water environment must be integrated into the policies of the Union and ensured in accordance with the principle of sustainable development The paper will go into depth of the problem in the perspectives of definition and causes of water pollution, and measurement of pollution and control of water pollution In European Charter for sustainable tourism in protected area published in 2000, pollution of water is defined as `the discharge by man, directly or indirectly, of substances or energy into the aquatic environment, the results of which are such as to cause hazards to human health, harm to living resources and to aquatic eco-systems, damage to amenities or interference with other legitimate uses of water There are also a variety of determinations of water pollution by different organizations However, they share together some common points as follows: (i) water pollution is the contamination of water bodies such as lakes, rivers, oceans, and groundwater; (ii) all water Photo I.1: Water polluted by garbage Pollution affects organisms and plants that live in these water bodies and in almost all cases the effect is damaging either to individual species and populations but also to the Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater natural biological communities; (iii) it occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful constituents [46] I.1.2 Water pollution categories Surface water and groundwater have often been studied and managed as separate resources, although they are interrelated [40] Sources of surface water pollution are generally grouped into two categories based on their origin a Point source pollution Point source pollution refers to contaminants that enter a waterway through a discrete conveyance, such as a pipe or ditch Examples of sources in this category include discharges from a sewage treatment plant, a factory, or a city storm drain b Non-point source pollution Non-point source (NPS) pollution refers to diffuse contamination that does not originate from a single discrete source NPS pollution is often accumulative effect of small amounts of contaminants gathered from a large area A typical example is that the leaching out of nitrogen compounds from agricultural land which has been fertilized Nutrient runoff in storm water from "sheet flow" over an agricultural field or a forest are also cited as examples of NPS pollution c Groundwater pollution Interactions between groundwater and surface water are complex Consequently, groundwater pollution, sometimes referred to as groundwater contamination, is not as easily classified as surface water pollution By its very nature, groundwater aquifers are susceptible to contamination from sources that may not directly affect surface water bodies, and the distinction of point vs nonpoint source may be irrelevant Groundwater accounts for 97% amount of fresh water of the Earth However, the water source is contaminated seriously The pollution may derive from fixing dumping ground unsanitarily, waste water from industrial activities, using a huge amount of fertilizer and pesticide The most popular ground water pollution is caused by As Analysis of groundwater contamination may focus on soil characteristics and hydrology, as well as the nature of the contaminant itself Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater Table III.3 Compositions of catalysts prepared by sol-gel, hydrolysis and Impregnating method Sample % Anatase %Rutile %Al2O3 SG 30 35.23 32.00 32.77 IG 30 35.64 33.54 30.82 HD (200oC) 36.42 34.33 29.25 o 37.23 34.96 28.81 o 40.42 35.10 24.48 o 43.38 35.63 22.99 o HD 36 (200 C) 41.79 36.91 21.31 HD 36 (400oC) 42.42 38.29 19.30 HD 36 (550oC) 43.36 40.83 15.81 43.79 43.15 13.06 HD 12 (200 C) HD 22 (200 C) HD 30 (200 C) o HD 36 (700 C) Fig III.1a showed the XRD patterns of the TiO2/Al2O3 samples which depended on the synthesized method In samples IG 30 and M sol-gel, the strong peaks of Al2O3 and those of TiO2 indicated that the structure of Al2O3 did not much change after during loading TiO2 process The weak peaks of support in sample HD 36 (2000C) shown that the structure of Al2O3 changed during the synthesized process The ratio of anatase/rutile of HD 36 (200oC) is higher than those of IG 30 and M sol-gel Thus, the hydrolysis method was the optimal method to synthesize TiO2/Al2O3 catalyst Fig III.1 b showed the XRD atterns of the samples synthesized by hydrolysis calcined at various temperatures All the photocatalysts exhibited the peaks assigned to anatas TiO2 crystalline and a little rutile The peaks of HD 36 (200oC) were broad indicating a very small size of badly crystallized grains due to the low temperature of preparation of the samples Although the peak intensity due to anatase TiO2 crystalline increased with the calcination temperatures for all samples, the peak belonged to rutile TiO2 crystalline also increased faster than that of anatase Therefore, the best temperature to synthesize is 200oC Fig.III.1c showed the XRD patterns of TiO2/Al2O3 photocatalysts with the different amounts of TiO2 calcined at 200oC The formation of the anatase TiO2 crystalline observed on TiO2/Al2O3 photocatalysts increased from HD (200oC) to HD 30 (200oC), while the anatase TiO2 crystalline was decreased and the rutile TiO2 crystalline increased at HD 36 (200oC) With increase in the amount of TiO2 in TiO2/Al2O3, the ratio of rutile phase against anatase phase increased, that was observed by Hiromi Yamashita and was not explained yet [39] 68 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater III.2.3 The surface properties of synthesized catalysts SEM analyses were employed to study the morphology of the particles and the homogeneity of the TiO2 distribution onto the support In Fig.III.2 the SEM images of the studied samples are reported From the images relative to the samples TiO2/Al2O3 it can be noticed that the Al2O3 particles worked as nucleation centres for the precipitation of TiO2 The morphology of the TiO2/Al2O3 samples was very different from that of the corresponding bare support a HD (200oC) a.Al2O3 b HD 12 (200oC) c HD 22 (200oC) d HD 30 (200oC) e HD 36 (200oC) Fig III.2 SEM images of the synthesized catalysts 69 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater The micrographs of the Al2O3 and of the samples HD (200oC), HD 12 (200oC), HD 22 (200oC), HD 30 (200oC), HD 36 (200oC) are shown in Fig.III.1a, b, c, d, e, f respectively Al2O3 consisted of primary particles whose dimensions were smaller than 1000 nm After the deposition of TiO2, nanostructured agglomerates of irregular shape were obtained The average sizes of the TiO2/Al2O3 primary particles were bigger than those of Al2O3 Pore clogging obstruction by the TiO2 particles justifies the reduction of specific surface area in the TiO2/Al2O3 sample III.3 Catalyst activity of synthesized catalysts III.3.1 The influence solar illumination and the suport to the catalytic activity The changes of concentration of Cr(VI) and COD on the solar illumination and support was shown in table III.5 Table III.5 The effects of solar and support to conversion of Cr(VI) and COD Time, h Sample Al2O3 with solar Al2O3 with UV IG 30 with solar IG 30 with UV COD Conversion, COD Conversion, COD Conversion, COD Conversion, % % % % -0.5 751 751 751 751 0 664 16.16 563 15.52 552 19.39 571 15.03 170 7.68 146 9.76 254 19.18 273 42.00 The conversion of Cr(VI) in both reactions with sample Al2O3 increased at the absoption period (-0.5h÷0h) and decreased at the reaction period (0h÷3h) It indicated that the support had no catalytic activity to convert Cr(VI) to Cr(III), and there was the deabsorption of Cr(VI), which had been absorbed in the absorption period from the Al2O3 support within the reaction period To investigate the effect of UV and TiO2 to photocatalytic activities of samples and COD, two reactions without catalyst and two reactions with IG 100 (the catalyst was synthesized by impregnating method with 100% TiO2) were caried out The table III.6 showed the changes of concentration of Cr(VI) and COD of four reaction 70 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater Table III.6 The effects of UV and catalyst to conversion of Cr(VI) and COD Time, h Sample Solar without catalyst UV without catalyst IG 100 with solar IG 100 with UV COD Conversion, COD Conversion, COD Conversion, COD Conversion, % % % % -0.5 751 751 751 751 0 625 630 46 46 125 0.01 276 8.32 19 13.04 The effect of sollar illumination to the catalytic activity was investigated by reactions of sample IG 30 with solar illumination and with UV illumination The conversion of Cr(VI) in both the reactions were performed in this sample decreased at the absoption period, however, in sample IG 30 with solar, the conversion of Cr(VI) was almost constant during reaction times while that was decreased in sample IG 30 with UV This result combined with the changes of Cr(VI) in table II.6 demonstrated that the catalyst had no activity under sollar illumination, solar had no role to convert Cr(VI) to Cr(III), UV had a little activity in Cr(VI) conversion The change of Cr(VI) during absorption period of reaction with IG 100 with and without UV was insignificant; it was due to the low SSA of IG 100 This result showed that there were a very little amount of Cr(VI) were absorbed onto TiO2, the majority of Cr(VI) was absorbed by support and TiO2/Al2O3 system, which had large SSA The COD decreasings between Al2O3 with solar and Al2O3 with UV, between IG 30 with solar and IG 30 with UV, between solar without catalyst and UV without catalyst were the same Ethanol evaporated during reaction time and did not depend on the conversion of Cr(VI) However, the sudden COD decreasings between IG 100 with solar and IG 100 with UV were observed, maybe, there was the strong conversion of ethanol with IG 100 with and without UV III.3.2 The influence of pH of reaction solution to the catalytic activity The samples, HD 36 (200oC) was tested catalytic activities at three pH (2.5; 4.0; 2.5) and Vethanol/Vsolution =1/100, Ccatalyst=1 (g/l) 71 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater 70 HD 36 (200oC) pH=2.5 HD 36 (200oC) pH=4.0 HD 36 (200oC) pH=5.5 Conversion, % 60 50 40 30 20 10 -0.5 0.0 0.5 1.0 1.5 Time, h 2.0 2.5 3.0 Fig III.5 The conversion of Cr(VI) deppended on pH of reaction solution The effect of catalytic synthesis methods on the removal of Cr(VI) was tested by HD 36 (200oC) at variety pH The absorption of Cr(VI) onto samples was very different among all samples and the highest absortion at pH=5.5 This result was due to Cr(VI) existed as anion form at pH≥5 and TiO2 strongly absorpted at anion As indicated from the Fig.III.5, in all samples, the conversation of Cr(VI) was less than 60% However, there was the different conversion among three samples, the conversions at pH=2.5 is the same that at pH=4 and higher than that at pH=5.5 The results was explained by Cr3+ after reaction existed at Cr(OH)3 and deposited onto catalytic surface to prevent catalyst from UV beam and reactants III.3.3 The influence of catalytic synthesis methods to the catalytic activity Three samples, IG 30, HD 30 (200oC), SG 30, were tested catalytic activities at the same reaction condition: pH=4, Vethanol/Vsolution =1/100, Ccatalyst=1 (g/l) 72 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater 70 HD 30 (200oC) IG 30 SG 30 Conversion, % 60 50 40 30 20 10 -0.5 0.0 0.5 1.0 1.5 Time, h 2.0 2.5 3.0 Fig.III.6 The conversion of Cr(VI) deppended on the catalytic synthesis methods The effect of catalytic synthesis methods on the removal of Cr(VI) was tested by HD 30 (200oC), IG 30, SG 30 The absorption of Cr(VI) onto samples was very different among all samples, and less than 20% As indicated from the Fig.III.6, in all samples, the conversation of Cr(VI) was less than 60%, which was lower in compared with that of P25 (86.23% after 3h) This result was due to the ratio of anatase/rutile of the catalysts less than that of P25 However, there was the different conversion among three samples The highest reduction of Cr(VI) in HD 30 (200oC) was caused by TiO2 covered all the surface of the support III.3.4 The influence calcination temperature of catalyst to the atalytic activity Four samples, HD 36 (200oC), HD 36 (400oC), HD 36 (550oC), HD 36 (700oC) were tested catalytic activities at the same reaction condition: pH=4, Vethanol/Vsolution =1/100, Ccatalyst=1 (g/l) 70 HD 36 (200oC) HD 36 (400oC) HD 36 (550oC) HD 36 (700oC) Conversion, % 60 50 40 30 20 10 -0.5 0.0 0.5 1.0 1.5 Time, h 2.0 2.5 3.0 Fig III.7 The conversion of Cr(VI) deppended on calcination temperature of catalyst 73 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater The effect of calcination temperature of catalyst on the removal of Cr(VI) was tested by the samples of HD 36 (200oC) which were calcinated variaty temperater The absorption of Cr(VI) onto samples was almost the same among all samples, and less than 11% As indicated from the Fig.III.7, in all samples, the conversation of Cr(VI) was less than 60% The highest conversion was obseved at sample calcinated at 200oC This result was caused by the specific surface area of this catalyst higher than othe catalysts and the ratio of anatase/rutile of this catalyst higher than other catalysts III.3.5 The influence of amount of TiO2 doped onto Al2O3 to the catalytic activity Five samples, HD (200oC), HD 12 (200oC), HD 22 (200oC), HD 30 (200oC), HD 36 (200oC) were tested catalytic activities at the same reaction condition: pH=4, Vethanol/Vsolution =1/100, Ccatalyst=1 (g/l) 70 HD (200oC) HD12 (200oC) HD 22 (200oC) HD 30 (200oC) HD 36 (200oC) Conversion, % 60 50 40 30 20 10 -0.5 0.0 0.5 1.0 1.5 Time, h 2.0 2.5 3.0 Fig III.8 The conversion of Cr(VI) deppended on amount of TiO2 doped onto Al2O3 The effect of amount of TiO2 doped onto support on the removal of Cr(VI) was tested by HD (200oC), HD 12 (200oC), HD 22 (200oC), HD 30 (200oC), HD 36 (200oC) The absorption of Cr(VI) onto samples was the same among all samples, and less than 20%; it depended on the same specific surface area all the catalysts As indicated from the Fig.III.8, in all samples, the conversation of Cr(VI) was less than 60% The highest reduction of Cr(VI) in HD 36 (200oC) because of the increasing of amount of TiO2 doped onto support However, the conversation of Cr(VI) in sample HD 36 (200oC) was slightly higher than that in sample HD 30 (200oC) because the ratio of anatase/rutile of HD 30 (200oC) higher than that of HD 36 (200oC) III.3.5 The influence of concentration of ethanol to the catalytic activity Four reactions were caried out with samples HD 30 (200oC) at the condition: pH=4, Ccatalyst=1 (g/l); the concentrations of ethanol were Vethanol/Vsolution =0/100; 0.5/100; 1.0/100; 1.5/100 74 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater 70 0/100 0.5/100 1/100 1.5/100 Conversion, % 60 50 40 30 20 10 -0.5 0.0 0.5 1.0 1.5 Time, h 2.0 2.5 3.0 Fig III.9 The influence of concentration of ethanol to the catalytic activity The influence of concentration of ethanol to the catalytic activity on the removal of Cr(VI) was tested HD 30 (200oC) As indicated from the Fig.III.9, in all reaction, the conversation of Cr(VI) was less than 60% The conversion of Cr(VI) was lowest in the reaction without ethanol, because in the presence of ethanol, the photogenerated holes are rapidly scavenged from the TiO2 particles, suppressing electron–hole recombination on TiO2 and accelerating the reduction of Cr(VI) by photogenerated electron One of the important strategies of promoting the photocatalytic reduction of Cr(VI) is enhancing the charge separation, which can be achieved by introducing scavengers of holes and/or electrons in the solution The highest reduction of Cr(VI) in Vethanol/Vsolution= 1.5/100 However, the conversation of Cr(VI) in reaction with Vethanol/Vsolution= 1.5/100 was slightly higher than that in Vethanol/Vsolution= 0.5./100 Vethanol/Vsolution= 1.0/100 because the concentration of ethanol was Vethanol/Vsolution= 0.5/100 enough for reaction to reduce Cr(VI) in wastewater Thus, the optimal concentration of ethanol was Vethanol/Vsolution= 0.5/100 75 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater CONCLUSIONS All the approaches within the research and conclusion of the thesis include: • Analysis of plating chromium wastewater at KYB Company The results showed that all metallic ions in wastewater were extremely higher than those in the standard of wastewater and pH of wastewater was about 5.0 After initial treatment by flocculation, most of the concentrations of metallic ions were lower those in the standard of wastewater However, the concentration of Cr(VI) was very high, accordingly it requires to seek another method to remove Cr(VI) from wastewater • Testing of used method for measuring Cr(VI) presented that ISO 11083 can be used to determine the concentration of Cr(VI) in the solutions The method of ISO 11083 associated with the appropriate treating method can lead to the acceptable deviation range • The experiment on the effects of solar illumination and the support to the catalytic activity showed that solar illumination and the support had no catalytic activity to convert Cr(VI) to Cr(III) • After determining the influence of pH of reaction solution to the catalytic activity, the result demonstrated that the conversions at pH=2.5 is the same that at pH=4 and higher than that at pH=5.5 because at pH=5.5, Cr3+ after reaction existed at Cr(OH)3 and deposited onto catalytic surface to prevent catalyst from UV beam and reactants • The study of the catalytic activities of three kinds of catalyst led to the outcome that the catalyst synthesized by hydrolysis had the highest catalytic activity because TiO2 covered all the surface of the support in this method • The impact of calcination temperature of catalyst to the catalytic activity under the tests showed that the highest conversion was observed at sample calcinated at 200oC The result was caused by the specific surface area of this catalyst higher than other catalysts and the ratio of anatase/rutile of this catalyst higher than other catalysts • The influence of the TiO2 amount doped onto Al2O3 to the catalytic activity showed that the highest reduction of Cr(VI) in HD 36 (200oC) because of the increase of amount of TiO2 doped onto support However, the conversation of Cr(VI) in sample 76 Nguyen Van Chuc Organic and petrochemical Technology Research on synthesis of TiO2 and application for Cr6+treatment in wastewater HD 36 (200oC) was slightly higher than that in the sample HD 30 (200oC) with the reason that the ratio of anatase/rutile of HD 30 (200oC) higher than that of HD 36 (200oC) References Pham Thanh Huyen, Dao Van Tuong, Hoang Trong Yem, Studying specific properties of some transiton-metal loaded onto titanium oxide systems by XRD and TPR, Ha Noi 8, 2003 Bui Thanh Huong, Nguyen Thanh Hong, Nguyen Thi Dung, Chantal Guillard, JeanMarie Herrmann, The degradation of reactive blue 2(RB2) has been studied using P25 Degussa as catalyst and UV-light Hanoi, Viet Nam, 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Technology Research on synthesis of TiO2 and application for Cr6 +treatment in wastewater Pollution prevention practices include low impact development techniques, installation of green roofs and improved... Technology Research on synthesis of TiO2 and application for Cr6 +treatment in wastewater Then another exchange reaction can take place and so on and so forth One exchange reaction can follow another... synthesis of TiO2 and application for Cr6 +treatment in wastewater primarily van der Waals forces, and these weak interactions result in low melting and boiling points, similar to those of CCl4 Ti4+