环境湿度对TiO_2/活性炭纤维气-固光催化氧化甲苯的影响

Influence of Environmental Humidity on the Photocatalytic Oxidation of Toluene by TiO_2 Loaded on Activated Carbon Fibers

在恒温控湿的环境舱中,以自制的TiO2/ACF(活性炭纤维)为光催化剂,研究了环境湿度对甲苯光催化降解过程的影响.通过N2吸附和扫描电子显微镜分别对TiO2/ACF光催化剂的孔径结构和形貌特征进行了表征;利用GC-MS和GC-FID对甲苯光催化过程中生成的中间产物进行了定性及定量分析.结果表明,环境舱中相对湿度增大,甲苯光催化转化率提高;不同相对湿度下,积累在光催化剂表面的中间产物种类相同,但支链氧化产物(苯甲醇、苯甲醛和苯甲酸)的积累量远多于苯环氧化产物(甲酚和对甲基苯酚)的积累量;随环境相对湿度的增大,苯甲醛在光催化剂表面的积累量减小,其余中间产物的积累量均有不同程度的增加.这说明水分子在甲苯光催化过程中起重要作用,相对湿度不仅影响甲苯的光催化转化效率,还影响其光催化转化的过程.尽管在各湿度条件下,支链氧化都是甲苯光催化降解的主要途径,但环境湿度增大更有利于苯环氧化途径的进行.讨论了水蒸气在甲苯光催化氧化过程中的作用机理.

Photocatalytic oxidation （PCO） of toluene by TiO2 loaded on activated carbon fibers （ACF） in an en- vironmental conditions-controlled chamber was investigated. The TiO2/ACF catalyst was characterized by N2 adsorption for pore structure and scanning electron microscopy for morphology. The remnant of toluene and the accumulation of intermediates on the TiO2/ACF catalyst under different relative humidity （RH） were determined by GC-MS and GC-FID. The results showed that the PCO conversion rate of toluene increased with the increase of RH in the chamber. The species of intermediates were the same at all RH levels. However, the accumulation amounts of side chain oxidation intermediates （benzyl alcohol, benzaldehyde, and benzoic acid） were much more than that of aromatic ring oxidation intermediates （cresol and p-toluquinone）. Elevated RH increased the accumulation of all intermediates except benzaldehyde. These results suggested that environmental humidity plays an important role in the PCO of toluene, which affects both the PCO rate and the PCO process. Although methyl group oxidation is the major path, aromatic ring oxidation, which is not the expected path for the PCO of toluene, is enhanced when the RH increases. The roles of water in the PCO of toluene were discussed.