Mesoporous nanocomposites tio2 MCM 41 synthesized from fly ash for photo catalysis degradation of reverse osmosis concentrate

MESOPOROUS NANOCOMPOSITES TIO2/MCM-41 SYNTHESIZED FROM FLY ASH FOR PHOTO-CATALYSIS DEGRADATION OF REVERSE OSMOSIS CONCENTRATE WU YE National University of Singapore 2014 MESOPOROUS NANOCOMPOSITES TIO2/MCM-41 SYNTHESIZED FROM FLY ASH FOR PHOTO-CATALYSIS DEGRADATION OF REVERSE OSMOSIS CONCENTRATE WU YE (M.Sc., Peking University) A THESIS SUBMITTED FOR THE MASTER DEGREE OF SCIENCE DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2014 I Declaration I hereby declare that this thesis is my original work and it has been written by me in its entirety, under the supervision of Professor Li Fong Yau, Sam, Department of Chemistry, National University of Singapore, between 05/08/2013 and 04/08/2014 I have duty acknowledged all the sources of information which have been used in the thesis This thesis has also not been submitted for any degree in any university previously WU 2014-12-12 YE Name Signature I Date ACKNOWLEGEMENTS Acknowledgements I would like to extend my appreciation to all the people who help me and always stand by my side when I am in need Thank you all, without your help, I certainly cannot achieve this I would especially want to thank PUB (Public Utilities Board) for providing the SPORE scholarship to afford my master studies in Singapore First I would like to thank my supervisor Prof Li Fong Yau, Sam Prof Li is a kind man with a thoughtful heart He always encourages us to pursue our interests and tries his best to inspire us Thank you for the great help and support throughout my master studies Your profound knowledge and rigorous attitude benefit me a lot Secondly I would like to express my gratitude to my mentor Mr Lin Xuanhao Thank you for training me TOC, ICP-MS, BET and FTIR Thank you for guiding me my project step by step and sharing your life experience with me Thirdly I would also want to thank all the members in our group Thank you for the unhesitatingly help and companion through the whole years’ study I regard this group as a big family, and I really appreciate the time we spent together I would want to thank all my twenty-one classmates in SPORE program Especially my roommates for the one year companion in Singapore, we lived like a family here and your companion brought me a lot joy I also want to thank the examiners for all the energy and time you Thank you for your kindly advice also Last but not least, I want to thank my parents and younger sister Thank you for all the supports, both materially and spiritually, thank you for all the love and understanding You are the reason and motivation of my struggle II ACKNOWLEGEMENTS I know commencement not just means ending, it also has a meaning of starting With all these years’ learning and training, I am now finally free to pursue my dreams I will always bear in mind that: “do not hesitate to what you like and not be afraid to step outside your comfort zone Be sure to keep struggling and try to make a difference.” Wu Ye 2014-08-20 National University of Singapore III CONTENTS Contents Declaration I Acknowledgements II Contents IV Summary VI List of Tables VII List of Figures VIII List of Abbreviations IX Introduction 1.1 MCM-41 synthesized from fly ash 1.1.1 General remarks of fly ash 1.1.2 Properties of MCM-41 1.2 Properties of TiO2 1.2.1 Photo-catalysis mechanism of TiO2 1.2.2 Synthesis method of TiO2 Materials and Methods 11 2.1 Materials 11 2.2 Characterization of fly ash 11 2.3 Preparation of MCM-41 and TiO2/MCM-41 14 2.3.1 Synthesis methods of F-MCM-41 14 2.3.2 Synthesis method of P-MCM-41 15 2.3.3 Synthesis method of TiO2/MCM-41 16 2.4 ROC reaction under UV light 17 2.5 Characterization 18 2.5.1 ICP-MS analysis 18 IV CONTENTS 2.5.2 XRD analysis 21 2.5.3 BET analysis 21 2.5.4 FESEM analysis 22 2.5.5 TOC analysis 22 Synthesis of F-MCM-41 from Fly Ash 23 3.1 Comparison of F-MCM-41 synthesis method 23 3.1.1 Ionic strengths of Si4+ solution and Al3+ solution 23 3.1.2 XRD results of fly ash after silica extraction 24 3.3 Characterization of F-MCM-41 25 3.3.1 Crystalline characterization of F-MCM-41 25 3.3.2 Pore architecture of the F-MCM-41 materials 27 3.4 Summary 30 Photo-catalysis Reaction to Degrade Reverse Osmosis Concentrate 31 4.1 Characterization of TiO2/MCM-41 31 4.2 Degradation efficiency of reverse osmosis concentrate 33 4.2.1 Reverse osmosis concentrate 33 4.2.2 Reverse osmosis concentration treatment technology 35 4.2.3 Reverse osmosis concentrate degradation efficiency 36 4.3 Summary 37 Conclusions and Future Work 38 References 39 V SUMMARY Summary Due to its wide band gap, TiO2 is widely used in environmental decontamination field Most contaminants like organics and heavy metals can be mineralized to harmless compounds through TiO2 photo-catalysis process However, the high cost of catalyst may hinder its application In the meanwhile, as the coal thermal power generation industry is widely applied around the world, it is urgent to find an economical and environmental friendly way to dispose the main coal industry by-product, namely fly ash In this study, mesoporous F-MCM-41 (Fly ash Al-MCM-41) materials synthesized from fly ash was used as the carrier of TiO2 to reduce the cost F-MCM-41 with good mesoporous structure and high surface area (952 SBET, m2g-1) was synthesized successfully from fly ash Compared with alkali fusion method, NaOH solution method was proved to be a greener and more efficient way to extract Si from fly ash In this study, different types of TiO2/MCM-41catalysts were synthesized through hydrothermal method TiO2/F-MCM-41 synthesized from inorganic silica source (fly ash) tended to have more mesoporous crystalline structure than TiO2/P-MCM-41 synthesized from organic silica sources However catalyst consisting of mixed TiO2 with MCM-41 directly achieved better ROC removal efficiency than synthesized TiO2/MCM-41 regardless of the purity and silica sources Our results show that reusing waste (fly ash) as resource to facilitate ROC degradation is environmental friendly and quite promising However, more research needs to be done to improve the efficiency VI LIST OF TABLES List of Tables Table 1-1 Chemical composition of fly ash Table 1-2 Major processes and their characteristic times for TiO2 photo-catalysis degradation Table 2-1 Standard curve for Si ICP-MS analysis 20 Table 2-2 Standard curve for Al ICP-MS analysis 21 Table 3-1 Ionic strengths in the extraction solution 24 Table 3-2 Desorption surface area for different pore sizes 29 Table 3-3 Specific surface and pore architecture of F-MCM-41 30 Table 4-1 Characteristics of the reverse osmosis concentrate 35 Table 4-2 ROC degradation efficiency under UV light 36 VII LIST OF FIGURES List of Figures Figure 1-1 Synthesize procedure of MCM-41 Figure 1-2 Semiconductor cell of photo-catalysis reaction Figure 1-3 Photooxidative mineralization of organic compounds with activated oxygen Figure 2-1 SEM images of fly ash 11 Figure 2-2 Constitutes of fly ash characterized by EDS 12 Figure 2-3 X-ray diffraction pattern of coal fly ash 13 Figure 2-4 Nitrogen adsorption-desorption isotherms for fly ash 13 Figure 2-5 Reactor vessel for TiO2/MCM-41 synthesis 17 Figure 2-6 Reaction vessel for ROC reaction 18 Figure 2-7 Calibration curve of Si4+ ions detected by ICP-MS 19 Figure 2-8 Standard curve of Al3+ calculation 20 Figure 3-1 XRD results for fly ash and fly ash residuum after Si extraction 25 Figure 3-2 X-ray diffraction characterization of F-MCM-41 26 Figure 3-3 Nitrogen adsorption-desorption isotherms of F-MCM-41 27 Figure 3-4 Pore size distribution of F-MCM-41 28 Figure 4-1 Comparison of XRD results of F-MCM-41 and TiO2/F-MCM-41 32 Figure 4-2 Comparison of XRD results of P-MCM-41 and TiO2/P-MCM-41 32 VIII CHAPTER THREE SYNTHESIS OF F-MCM-41 FROM FLY ASH Different pore size distribution of F-MCM-41 was compared in Fig 3-4 From the figure, we can see that pore size of these four materials all range from 2-4 nm, which indicated that the pores are mainly mesoporous The results further confirm the mesoporous structure conclusion drew from XRD characterization Figure 3-4 Pore size distribution of F-MCM-41 A1 (pH=4) and A2 (pH=11) were synthesized by NaOH solution method; B1 (pH=4) and B2 (pH=11) were synthesized by alkali fusion method As for F-MCM-41 A1, the size distribution is narrower and a high peak appeared at nm However, to F-MCM-41 B1, the size distribution is also narrow but there are two peaks appearing at 2.3 nm and nm separately F-MCM-41 A2 and F-MCM-41 B2 appeared to have much wider size distributions and less sharp peaks, which are located around 2.4 nm From that we can deduce that materials F-MCM-41 A1 tends to have better regulated mesoporous structure compared with other three materials, these results can also be confirmed by XRD and nitrogen adsorption and desorption isotherm 28 CHAPTER THREE SYNTHESIS OF F-MCM-41 FROM FLY ASH Table 3-2 lists desorption pore area for materials with different pore sizes Mesopores and macropores can be directly calculated from the BJH desorption pore distribution report While pore area of micropores can be calculated according to the equation: micropores’ pore area = t-Plot external surface area - BET surface area We can see that all the three kinds of pore areas were quite small in fly ash, which indicates that fly ash is a non-porous material According to Table 3-2, mesopores are the main composition in all the four F-MCM-41 samples, which is 2-7 times larger than the sum of the area of the other two type pores Thus we can conclude that all the F-MCM-41 synthesized from fly ash is mesoporous material FMCM-41 synthesized from NaOH solution method exhibited larger desorption pore area in mesopores distribution, and F-MCM-41 A1 had the largest pore area As to pH, acidic condition is better than basic condition for the synthesis reaction Table 3-2 Desorption surface area for different pore sizes Desorption Pore Area (m2g-1) Sample Micropores ([...]... suppose Al -MCM- 41 synthesized from fly ash can be used as the supporters of TiO2 and will improve the photo- catalysis ability of TiO2 In this research, we first synthesized Al -MCM- 41 from fly ash; then TiO2 was doped onto the supporter Al -MCM- 41 using the hydrothermal method; finally catalysts synthesized through this method were used to degrade reverse osmosis wastewater to test its photo- catalysis. .. considered MCM- 41 synthesized from fly ash as the carrier Thus, in this research we use MCM- 41 synthesized from the fly ash as the carrier of TiO2, and try to investigate the photo- catalytic efficiency of TiO2/ MCM- 41 1.2 Properties of TiO2 TiO2 is a wide-band gap semiconductor Due to its chemical stability, non-toxicity, low cost and other advantages, TiO2 has gained a good deal of attention nowadays 1.2.1 Photo- catalysis. .. m2g-1) Hence the fly ash was grinded to smaller particles to improve its adsorption property (Janos, Buchtova et al 2003) MCM- 41 has hundreds time higher surface area than fly ash and make it a more suitable adsorbent 2.3 Preparation methods of MCM- 41 and TiO2/ MCM- 41 2.3.1 Synthesis methods of F -MCM- 41 Three methods were used to synthesize F -MCM- 41 (i.e MCM- 41 synthesized from fly ash) The differences... 1.1 MCM- 41 synthesized from fly ash 1.1.1 General remarks of fly ash Fly ash is a by-product generated during the combustion of coal for energy production Among developing countries like India and China where coal is the main source of energy, large amount of fly ash is produced every year (Ahmaruzzaman 2010, Zhang, Kang et al 2013) The disposal of fly ash is becoming a more and more urgent problem for. .. level, thus is suitable for reverse osmosis concentrate detection 22 CHAPTER THREE 3 SYNTHESIS OF F -MCM- 41 FROM FLY ASH Synthesis of F -MCM- 41 from Fly Ash As the by-product of coal energy industry, ten thousand tons of fly ash are produced every year around the word, especially in countries like India and China where coal is the main energy sources (Ahmaruzzaman 2010) Most of them are either dumped... residuum of fly ash was collected and characterized by X-ray diffraction method Fig 3-1 compared the crystalline structure of fly ash and fly ash residuum to compare the extraction method of silica From Fig 3-1 we can see that after the extraction from NaOH solution method, the crystalline 24 CHAPTER THREE SYNTHESIS OF F -MCM- 41 FROM FLY ASH structure of fly ash residuum didn’t show much difference from. .. compared MCM- 41 synthesized from 10 kinds of polish fly ash, and in their study the ionic strength of supernatants of fly ash alkali fusion method extraction were from 726.87 mg/L to 3038 mg/L for Si4+ and from 237.88 mg/L to 964.76 mg/L for Al3+ From these results we can conclude that the Si4+ extraction in our research is quite efficient, especially by NaOH solution method 3.1.2 XRD results of fly ash. .. composition of fly ashes would affect the solubility of Si and Al, thus affecting the extraction efficiency Fly ash which contained more aluminosilicate glasses tended to generate more Si4+ during the extraction process Majchrzaka-Kuceba and Nowak (2011) compared MCM- 41 synthesized from 10 different polish fly ash sources, and found that content of Al and Si varied from the type and origin of fly ash The... acidity of MCM- 41 (Kosslick, Lischke et al 1999) This property can be beneficial to some acid-catalyzed processes Thus transforming fly ash to MCM- 41 is a feasible way to reuse fly ash waste, which is also an economical and environmental friendly process 1.1.2 Properties of MCM- 41 Since its first discover by Mobil Research and Development Corporation in 1992, MCM- 41 has become an important member of mesoporous. .. to the mouth of the RBF Heat was then applied to the an oil bath and the solution was heated under 90 ± 2 for six hours The RBF was lifted up from the oil bath and removed from heat to allow the oil on the top to drop and was left overnight to cool To determine whether MCM- 41 could improve TiO2 photo- catalysis performance, pure TiO2 was synthesized by the same way just as from TiO2/ MCM- 41 0.5 g TiOSO4 .. .MESOPOROUS NANOCOMPOSITES TIO2/ MCM- 41 SYNTHESIZED FROM FLY ASH FOR PHOTO- CATALYSIS DEGRADATION OF REVERSE OSMOSIS CONCENTRATE WU YE (M.Sc., Peking University) A THESIS SUBMITTED FOR THE... by-product, namely fly ash In this study, mesoporous F -MCM- 41 (Fly ash Al -MCM- 41) materials synthesized from fly ash was used as the carrier of TiO2 to reduce the cost F -MCM- 41 with good mesoporous structure... for reverse osmosis concentrate detection 22 CHAPTER THREE SYNTHESIS OF F -MCM- 41 FROM FLY ASH Synthesis of F -MCM- 41 from Fly Ash As the by-product of coal energy industry, ten thousand tons of