Pd/TiO2光催化苯甲酸水溶液产氢性能研究

为了探讨在光催化分解水(下称光解水)制氢反应中含苯有机废水作为牺牲剂的可行性,以光沉积法制备了Pd/TiO₂〔w(Pd)为0.5%〕模型催化剂,并且通过XRD(X射线衍射)、BET(N₂物理吸附)、TEM(透射电镜)、XPS(X射线光电子能谱)和UV-vis DRS(紫外-可见漫反射吸收光谱)等表征手段考察了催化剂的微观结构及性质, 使用泊菲莱Labsolar-Ⅲ AG系统评价了苯甲酸、邻苯二甲酸、间苯三甲酸作为牺牲剂的光催化性能. 结果表明:引入的Pd以Pb0和Pb2+高度分散在TiO₂基底表面,未改变TiO₂的晶体结构；与TiO₂相比,Pd/TiO₂具有更大的比表面积、更小的孔径和更强的光吸收性能. 苯甲酸、邻苯二甲酸、间苯三甲酸光解水产氢速率分别为4.264、6.429和5.400 mmol/(g·h),分别为空白处理〔无牺牲剂,0.733 mmol/(g·h)〕的5.8、8.8、7.4倍. 依据乙酸和三氟乙酸的光解水产氢速率数据及结构特征,初步探讨了苯甲酸参与价带空穴氧化反应的机理,发现光解水产氢速率的大小与苯甲酸牺牲剂的还原性强弱、羧基个数以及空间位阻有关,表现为牺牲剂发生photo-Kolbe脱羧反应越容易、羰基数目越多、空间位阻越小,其光解水产氢速率越高. 未来应进一步探寻高效、稳定的模型牺牲剂,以应用于氢能源生产研究. 

Photocatalytic Hydrogen Evolution from Water over Pd/TiO2 with Benzoic Acid Compounds as Sacrificial Agents

In recent decades, photocatalytic decomposition of water to hydrogen has attracted much interest. In order to explore the feasibility of wastewater containing benzene as the sacrificial agents, the photocatalytic activity of Pd/TiO₂ for water-splitting to hydrogen with benzoic acid solution was investigated. A Perfectlight Labsolar-Ⅲ AG reaction system equipped with a double seven-valve system and a 300 W Xenon lamp as the light source was used for the photocatalytic activity experiment. The used model photocatalyst Pd/TiO₂ (w(Pd)=0.5 %) was prepared by photo-deposition. The structure and properties of a series of Pd/TiO₂ samples were characterized by X-ray powder diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflection spectrum (DRS). The results indicated that introduction of Pd did not change the TiO₂ anatase structure, but led to higher specific surface area and smaller pore size than TiO₂. Moreover, the photoabsorption edge of Pd/TiO₂ was unchanged after adding Pd, but the absorption range increased slightly. The introduced Pd was primarily presented as Pd0 and Pd2+ and highly dispersed as nanoparticles on the surface of TiO₂. When benzoic acid, phthalic acid, and trimesic acid solution were used as the sacrificial agents, the rates of hydrogen production on the photocatalyst were 4.264,6.429 and 5.400 mmol/(g·h), respectively. The rates were 5.8,8.8 and 7.4 times higher than those without the sacrificial agents 0.733 mmol/(g·h), respectively. Acetic acid and trifluoroacetic acid as the sacrificial agents were also studied for insight into the effect of structure of the sacrificial agents. The rate of hydrogen production was closely related to the difficulty of decarboxylation reaction and the amount and spatial arrangement of the carboxyl groups present on the sacrificial agents (the easier the photo-Kolbe decarboxylation reaction reacted, more amount of carbonyl and smaller spatial arrangement of the sacrificial agents, which will led to the higher rate of hydrogen production). The results provide important guidance for the selection of sacrificial agents in photocatalytic water-splitting reactions. There is still a long way to go in exploring efficient and stable sacrificial agents for further exploration of the photocatalytic water-splitting into hydrogen.