基于电子顺磁共振的锌卟啉敏化TiO_2光催化性机理的研究

Study on the photocatalytic mechanism of TiO_2 sensitized by zinc porphyrin

为了研究锌卟啉/TiO2复合光催化剂的光催化效率及电子转移问题,本文采用溶胶凝胶法制备了锌卟啉/TiO2的混合光催化材料,并利用紫外可见光谱、电子顺磁共振谱对锌卟啉/TiO2复合光催化剂进行了表征与分析.采用溶胶凝胶法制备了锌卟啉-TiO2的混合光催化材料,通过比较纯P25型TiO2和掺入质量比分别为0.2%,0.5%,0.9%锌卟啉敏化剂的锌卟啉/TiO2混合光催化材料的紫外可见光谱图可知,加入适量锌卟啉敏化剂可提高TiO2对甲基橙溶液的降解效率,过多的掺入锌卟啉敏化剂会导致TiO2表面被敏化剂覆盖,从而影响了其对光子的吸收,降低TiO2的光催化效率,降低TiO2的光降解率,甚至低于纯TiO2的光降解率.应用电子顺磁共振技术对锌卟啉敏化TiO2光催化剂的光催化机理进行了合理的解释,当使用紫外可见光源对粉末样品进行辐照时,锌卟啉受光辐照产生的激发态电子促进具有强氧化性的Ti3+和超氧根自由基的生成,从而有效的促进了光生空穴-电子对的分离,提高了TiO2的光催化性能.

We have investigated the photocatalysis e？ciency and electron transfer of the znic prophyrin/TiO2 composite photocatalyst, a sensitised hybrid porphyrin material, and prepared it successfully by sol-gel method. The UV-visible spectroscopy and electron paramagnetic resonance spectra are used to analyze and characterize the znic pro-phyrin/TiO2composite photocatalyst. The proportions 0%, 0.2%, 0.5% and 0.9% （mass ratio） of zinc porphyrin, and the photocatalytic mechanism of TiO2 sensitized by zinc porphyrin are reasonably explained by ultraviolet visible spec-troscopy and electron paramagnetic resonance spectroscopy （EPR）. Different samples’ UV-visible spectra show that the degradation e？ciency of methyl orange solution by TiO2 may be improved via adding appropriate amount of zinc por-phyrin sensitizer. Prohibitive incorporation of the sensitizer would cause excess of particles in the mixed catalyst, leading to the TiO2 surface covered by the sensitizer, thus affecting the absorption of photons, and the light degradation rate of TiO2 may be lowered, even lower than the pure TiO2. EPR spectra show the excited state of electrons in zinc pro-phyrin generated by irradiation of light can promote the generation of Ti3＋with strong oxidizing and superoxide radicals when using UV-visible light to irradiate the powder samples, thus effectively enhancing the separation of photogenerated electron-hole pairs, and improving the photocatalytic performance of TiO2.