TiO2/SiO2复合氧化物对庚烯/二氧化氮体系的复相光催化作用研究/

2019-05-11 06:49:42

TiO2 光催化 SiO2 庚烯 heptheptence





随着现代工业的迅猛发展,环境污染问题日趋严重,特别是氮氧化物(NOx)及挥发性有机物(VOCS)对大气的污染,已成为世界各国亟待解决的环保问题。目前,人们已经开展了光催化法消除空气中微量有害气体的研究,自1972年Fujishima和Honda发现在TiO2电极上可光催化分解水。这一事件标志着复相光催化中一个新领域的开始。近年来,应用复相光催化净化环境已成为最活跃的研究领域之一。应用半导体金属氧化物或硫化物作光催化剂可完全消除大气和废水中的有机污染物。TiO2、ZnO、Fe2O3、WO3、CdS等都是半导体,在受到大于其带隙能的光照射时,价带电子被激发到导带上去,产生高反应活性的电子-空穴对,电子-空穴对迁移到固体表面以后,它们与具有适宜氧化还原潜势的吸附质发生电子转移过程,发生光催化氧化还原反应。现在光催化领域降解挥发性有机物已有一定研究,一般有机物可降解为CO2和H2O。在光催化降解氮氧化物上,一般可以降解为N2或者是硝酸根。但同时对二者进行光催化作用的研究还较少,本论文对庚烯与二氧化氮进行光催化,研究了二者的反应。
本论文中,我们首先采用溶胶-凝胶法制备TiO2-SiO2复合催化剂。对硅的加入量和TiO2-SiO2催化剂的焙烧温度进行研究,发现硅的加入可得到粒子粒径小、分布均匀、分散性好的催化剂,所有这些都能提高催化剂的催化活性。但过多的硅加入后会生成无定型的催化剂,无定型的催化剂是没有催化活性的。最后得到9.1%的硅加入量为最佳。由于SiO2加入之后,催化剂的热稳定性就会明显提高,在高温下焙烧,可以很有效的去除大的体相缺陷同时,抑制TiO2的晶型转变及表面积的明显的下降。所以通过降解实验得到600℃为最佳焙烧温度。
本文第三章中以 TiO2/SiO2为光催化剂,在紫外光作用下,讨论了存在NO2时,庚烯在TiO2/SiO2上的吸附和光催化降解的作用。实验结果表明,TiO2/SiO2对庚烯的最大吸附量Mmax=3.10mg,当存在NO2(44.64 μmol/L)时Mmax=3.80mg。另外通过降解40.76 μmol/L 庚烯和163.04 μmol/L 庚烯,在不同的浓度的二氧化氮条件,研究了庚烯的降解和二氧化碳的生成,最后得到二氧化氮与庚烯的摩尔浓度比约为3:1时,庚烯降解速率达到最大。实验通过GC-MS、FT-IR,分别测定了三种不同体系的反应产物,发现C7H15NO2、C6H13ONO2、1,2-C7H14(OH)2、C7H15ONO2、C9H19ONO2等有机物,通过初步分析,已经推理了可能的反应机理。本论文还讨论了氧气和水蒸气不同含量及其光强等对光催化氧化降解庚烯与二氧化氮的影响。随着氧气含量增加,反应速率不断增大,氧量增至5%时,速率最大并趋于稳定。水分子含量对甲苯反应速率的影响也有最佳值15%(相对湿度)。甲苯反应速率随光强增加而增大。最后研究了光催化剂的失活,得到此种方法合成的催化剂有很好的反应耐受性。




The environmental pollution is getting worse day by day because of the rapid development of modern industry, especially the atmospheric pollution causing by NOx and VOCS, which has become the environmental protection question many countries urgent to solve. At present, people already have done some researches on photocatalysis degradation of micro-noxious gas in the atmosphere. In 1972, Fujishima discovered the photocatalytic splitting of water on TiO2 electrodes. This event marked the beginning of a new era in heterogeneous photocatalysis. In recent years, applications to environmental cleanup have been one of the most active areas in heterogeneous photocatalysis. This is inspired by the potential application of semiconductor metal oxides and sulfides photocatalysts for the entire destruction of organic compounds in polluted air and wastewaters. TiO2, ZnO, Fe2O3, WO3, CdS, etc, are semiconductors, Under illumination by photons of greater than band-gap energies, the valence band electrons can be excited to the conduction band, creating highly reactive electron-hole pairs. After migration to the solid surface, these may undergo electron-transfer processes with adsorbates of suitable redox potentials. At present, there are some researches on photocatalytic degradation of volatility organics, and the products are CO2 and H2O. The organics are transformed to N2 or NO3- when photocatalytic degradation of NOX. But studies involving heptheptence and NO2 photocatalysis are relatively few. In this paper, the reaction between heptheptence and NO2 is studied.
In this paper, firstly we prepare the TiO2-SiO2 catalyst by using a sol-gel method. Firstly we studied the effect of SiO2 concentration and TiO2-SiO2calcination temperature. The results showed that the catalyst with little particle size, uniform distributing, and good dispersing was gained after adding SiO2, all of this advantages will increase the catalyzing activity. But the unformed catalyst that lack of activity will be made if adding too much SiO2. Hence through a series experiments we conclude the highest catalyst activity would be achieved when about 9.1 % SiO2 was added. The heat stability was improved in evidence when SiO2 was added. The defect of body appearance will be eliminated effectively, the transformation of crystal type will be restrained and the surface area will be reduced obviously under the process of calcination. Hence through the degradation experiment we achieved the best calcinations temperature was 600℃.
In this paper, the adsorption and photocatalytic degradation of heptheptence over TiO2/SiO2 photocatalyst with the aid of UV light were investigated carefully in the presence of NO2. The experiment data indicated that Mmax (the maximum adsorption amount of TiO2/SiO2 towards heptheptence) is 3.10 mg, and is increased to 3.80mg in the presence of NO2(44.64 μmol/L). In the photocatalytic reaction process of heptheptence (40.76 μmol/L and 163.04 μmol/L), the degradation of heptheptence and creation of CO2 under different NO2 concentrations, the results indicated that when initial concentration of CO2 was equal to 3 times initial concentration of heptheptence (3:1), the degradation of heptheptence was the best. Through GC-MS and FT-IR we respectively determined the intermediate products of three different reaction systems, such as the organic matters C7H15NO2、C6H13ONO2、1,2-C7H14(OH)2、C7H15ONO2、C9H19ONO2 et al., and accordingly deduced the possible reaction mechanism.
In this paper, we also studied the effects of different oxygen and vapor concentration on photocatalyst degradation heptheptence and NO2. The reaction speed increased along with the increase of oxygen concentration. Especially when the oxygen concentration was 5% the speed was the most and close to steady. The best concentration of vapor was 15% that influenced CH3-C6H6 reaction speed. The reaction speed of CH3-C6H6 was increased along with the increase of light strength. Finally the activity losing and regeneration was investigated, and the results showed the synthetic catalyst possess outstanding reaction enduring characteristic.