磁性复合体光催化材料制备、表征及对Cr（VI）的光催化还原研究
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摘要
光催化技术在处理废水中重金属离子方面有独特的优势,特别适用于组成复杂和低浓度废水的处理,该技术有广泛的应用前景。
目前对TiO_2光催化剂的研究趋向两种形态,颗粒和固定在载体上的光催化膜。固定化光催化膜材料的比表面积有限,没有颗粒光催化材料的比表面积大,所以光催化膜的光催化效率没有颗粒光催化剂的效率高。但是颗粒光催化剂由于粒径太小,难于从反应混合物中分离回收出来,特别是在工业废水光催化处理过程中,由于分离困难造成颗粒光催化剂的流失率大。为了解决颗粒光催化剂的分离回收这一关键问题,我们制备了磁载光催化剂。
我们的方法是以微米级Fe_3O_4作为载体,用溶胶-凝胶方法在Fe_3O_4表面进行SiO_2和TiO_2的包覆,制得磁载光催化剂TiO_2/Fe_3O_4和TiO_2/SiO_2/Fe_3O_4,研究表明:以甲酸为催化剂经溶胶-凝胶过程在磁核Fe_3O_4表面包覆SiO_2后效果较好;TiO_2/SiO_2/Fe_3O_4的磁性能和光催化活性比TiO_2/Fe_3O_4的磁性能和光催化活性有显著的提高。用光化学还原法在TiO_2/SiO_2/Fe_3O_4表面沉积贵金属Ag和Pt,以提高其光催化活性。研究表明:贵金属的沉积对TiO_2/SiO_2/Fe_3O_4的磁性能有影响;与TiO_2/SiO_2/Fe_3O_4相比,适当掺杂量的Ag/TiO_2/SiO_2/Fe_3O_4的光催化活性有所上升,Pt/TiO_2/SiO_2/Fe_3O_4的光催化活性都有所下降。
以Cr(Ⅵ)水溶液为目标物对各样品的光催化活性进行了评价,并对影响光催化效率的因素,如Cr(Ⅵ)溶液初始浓度,光催化剂的加入量,溶液的pH值,重复使用次数,进行了考察。
Photocatalytic technology has special advantages in the treatment of wastewater with heavy metal ions, especially, the treatment of wastewater which has complicated compositions and low concentration, so this technology has a promising prospect.
At present, the research about TiO_2 form has two tendencies: one is TiO_2 powder, another is TiO_2 membrane. Compared with TiO_2 membrane, TiO_2 powder has the larger surface; therefore, its photocatalytic activity is higher. But TiO_2 powder is difficult to be separated from reactants for its small particle diameter. Especially in the system of industrial wastewater, TiO_2 powder has big lost rate when to be separated. In order to solve the problem of TiO_2 powder’s separation and reuse, we prepared magnetic photocatalyst.
Our methods are as follows: by using micron-sized Fe_3O_4 as support, prepare TiO_2 and SiO_2 coatings on the surface of Fe_3O_4 to get TiO_2/Fe_3O_4 and TiO_2/SiO_2/Fe_3O_4 by sol-gel method. The results indicated that using HCOOH as catalyst to prepare SiO_2 coating had a better effect by sol-gel process; TiO_2/SiO_2/Fe_3O_4 has better magnetic performances and photocatalytic activity than that of TiO_2/Fe_3O_4. Then we deposited noble-metal Ag and Pt on the surface of TiO_2/SiO_2/Fe_3O_4 by the photodeposition method. The results indicated that the deposition of noble metal had effects to the magnetic performances of photocatalyst TiO_2/SiO_2/Fe_3O_4; compared with TiO_2/SiO_2/Fe_3O_4, the photocataltic activity of Ag/TiO_2/SiO_2/Fe_3O_4 could increase with a suitable Ag loading, but the photocataltic activity of Pt/TiO_2/SiO_2/Fe_3O_4 was all reduced with varying Pt loadings.
Finally, using Cr(Ⅵ) aqueous solution as object to evaluate the photocatalytic activity of samples, and we also investigated the effect of the concentration of Cr(Ⅵ) aqueous solution, the amount of catalyst, pH values and reuse times on the photocatalytic efficiency.
目前对TiO_2光催化剂的研究趋向两种形态,颗粒和固定在载体上的光催化膜。固定化光催化膜材料的比表面积有限,没有颗粒光催化材料的比表面积大,所以光催化膜的光催化效率没有颗粒光催化剂的效率高。但是颗粒光催化剂由于粒径太小,难于从反应混合物中分离回收出来,特别是在工业废水光催化处理过程中,由于分离困难造成颗粒光催化剂的流失率大。为了解决颗粒光催化剂的分离回收这一关键问题,我们制备了磁载光催化剂。
我们的方法是以微米级Fe_3O_4作为载体,用溶胶-凝胶方法在Fe_3O_4表面进行SiO_2和TiO_2的包覆,制得磁载光催化剂TiO_2/Fe_3O_4和TiO_2/SiO_2/Fe_3O_4,研究表明:以甲酸为催化剂经溶胶-凝胶过程在磁核Fe_3O_4表面包覆SiO_2后效果较好;TiO_2/SiO_2/Fe_3O_4的磁性能和光催化活性比TiO_2/Fe_3O_4的磁性能和光催化活性有显著的提高。用光化学还原法在TiO_2/SiO_2/Fe_3O_4表面沉积贵金属Ag和Pt,以提高其光催化活性。研究表明:贵金属的沉积对TiO_2/SiO_2/Fe_3O_4的磁性能有影响;与TiO_2/SiO_2/Fe_3O_4相比,适当掺杂量的Ag/TiO_2/SiO_2/Fe_3O_4的光催化活性有所上升,Pt/TiO_2/SiO_2/Fe_3O_4的光催化活性都有所下降。
以Cr(Ⅵ)水溶液为目标物对各样品的光催化活性进行了评价,并对影响光催化效率的因素,如Cr(Ⅵ)溶液初始浓度,光催化剂的加入量,溶液的pH值,重复使用次数,进行了考察。
Photocatalytic technology has special advantages in the treatment of wastewater with heavy metal ions, especially, the treatment of wastewater which has complicated compositions and low concentration, so this technology has a promising prospect.
At present, the research about TiO_2 form has two tendencies: one is TiO_2 powder, another is TiO_2 membrane. Compared with TiO_2 membrane, TiO_2 powder has the larger surface; therefore, its photocatalytic activity is higher. But TiO_2 powder is difficult to be separated from reactants for its small particle diameter. Especially in the system of industrial wastewater, TiO_2 powder has big lost rate when to be separated. In order to solve the problem of TiO_2 powder’s separation and reuse, we prepared magnetic photocatalyst.
Our methods are as follows: by using micron-sized Fe_3O_4 as support, prepare TiO_2 and SiO_2 coatings on the surface of Fe_3O_4 to get TiO_2/Fe_3O_4 and TiO_2/SiO_2/Fe_3O_4 by sol-gel method. The results indicated that using HCOOH as catalyst to prepare SiO_2 coating had a better effect by sol-gel process; TiO_2/SiO_2/Fe_3O_4 has better magnetic performances and photocatalytic activity than that of TiO_2/Fe_3O_4. Then we deposited noble-metal Ag and Pt on the surface of TiO_2/SiO_2/Fe_3O_4 by the photodeposition method. The results indicated that the deposition of noble metal had effects to the magnetic performances of photocatalyst TiO_2/SiO_2/Fe_3O_4; compared with TiO_2/SiO_2/Fe_3O_4, the photocataltic activity of Ag/TiO_2/SiO_2/Fe_3O_4 could increase with a suitable Ag loading, but the photocataltic activity of Pt/TiO_2/SiO_2/Fe_3O_4 was all reduced with varying Pt loadings.
Finally, using Cr(Ⅵ) aqueous solution as object to evaluate the photocatalytic activity of samples, and we also investigated the effect of the concentration of Cr(Ⅵ) aqueous solution, the amount of catalyst, pH values and reuse times on the photocatalytic efficiency.
引文
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[4] 李志军,王红英.纳米二氧化钛的制备方法[J].山西化工,2006,26(6):47-49.
[5] 赵敬哲,王子忱,刘拍华.液相一步合成金红石型超细TiO2[J].高等学校化学学报,1996,20(3):467-496.
[6] 张金龙,陈锋.光催化[M].上海:华东理工大学出版社,2004.30-31.
[7] Degan G. . TiO2 aerogels for photocatalytic decontamination of aquatic environments[J].J Phys Chem, 1993, 97(49):12651-12655.
[8] 陈龙武.气凝胶的制备[J].化学通报,1997,60(8):21.
[9] 施尔畏.水热法的应用与发展[J].无机材料学报,1996,11(2):193-198.
[10] 赵文宽.高热稳定性锐钛矿TiO2纳米粉体的制备[J].无机材料学报,1998,13(4):608-612.
[11] 施利毅,李春忠,房鼎业,等.二氧化钛超细粒子的制备及其光催化降解古酚溶液[J].华东理工大学学报,1998,24(3):291.
[12] Manjail tar, Vishol Chhabin, Pushan Ayynb.Synthesis of Fe/TiO2 photocatalyst with nanometer size by solv othermal method and the effect of H2O addition on structural stability and photodecomposition of methanol[J].J Mater Res, 1998, 13 (5): 1249.
[13] 杨建军,李东旭,张治军,等.Pt/Fe2O3/TiO2的制备、表征及其光催化活性研究[J].真空科学与技术,2001,21(4):277-280.
[14] Chun Hu, Yuchao Tang, Zheng Jiang.Characterization and photocatalytic activity of nobel-metal-supported surface TiO2/SiO2[J].Applied catalysis, 2003, 253: 389-396.
[15] M. D. Driessen, V. H. Grassian.Photooxidation of trichloroethylene on Pt/TiO2[J].J. Phys. Chem. B, 1998, 102:1418-1423.
[16] Jean Disider, Jeam-Marie Herrmann, Pierre Pichat.Platinum/Titanium dioxide catalysts[J].J Chem Soc, 1983, 79:651.
[17] Sanches E, Lopex T.Synthesis and characterization of sol-gel Pt/TiO2 catalyst[J].J of Solid State Chem, 1996, 122: 309-314.
[18] Linsebigler A, Rusu C.Absence of platinum enhancement of a photoreaction on TiO2-CO photooxidation on Pt/TiO2 (110) [J].J Am Chem Soc, 1996, 118: 5284-5289.
[19] Dung Duonghong, Enrico Borgarello, Michael Gratzel . Dynamics of light-induced water cleavage in colloid systems[J].J Am Chem Soc, 1981, 103: 4685.
[20] Sclapani A.Influence of silver deposits on the photocatalytic activity of titania[J].J of catalyst, 1997, 168: 117-120.
[21] 程沧沧,李太友.载银TiO2光催化降解 2,4-二氯苯酚水溶液的研究[J].环境科学研究,1998,11(6):27-29.
[22] 姚晓斌.Ag和Pd及其离子对TiO2光催化分解CH3CHO的影响[J].感光科学与光化学,1999,17(1):12-15.
[23] Choi W..The role of metal ion dopants in quantum-size TiO2:correlation between photoreactivity and charge carrier recombination dynamics[J].J Phys Chem, 1994, 98(51): 13669-13679.
[24] Gratzel M, Russell F H..Electron paramagnetic resonance studies of doped colloids[J].J Phys Chem, 1990, 94 (6): 2566-2572.
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