不同pH值制备的TiO2和TiO2/SiO2催化剂结构、表面性质及光催化活性

以TiOSO₄和SiO₂溶胶为原料, 采用沉淀法用氨水调节pH值制备TiO₂和TiO₂/SiO₂催化剂. 制备的催化剂用X射线衍射(XRD), 扫描电镜(SEM), N₂吸附(BET), 紫外-可见(UV-Vis)漫反射光谱, 程序升温脱附(NH₃-TPD), 傅里叶变换红外(FT-IR)光谱技术分析. XRD谱图显示纯TiO₂中锐钛型和金红石相共存, 且金红石相含量随pH值升高而增加. 但是, TiO₂/SiO₂催化剂只有锐钛型. 扫描电镜发现制备的催化剂呈类球形, 颗粒间相互交叠, 粒径在10-25 nm之间. TiO₂和TiO₂/SiO₂光催化剂的比表面积随pH值升高略有增大. SiO₂的添加会增大催化剂的比表面积. 程序升温脱附实验结果说明催化剂的表面酸量随pH值升高而增加. TiO₂/SiO₂的表面酸量比相同pH值制备的TiO₂大. 红外光谱分析说明Si掺杂和高pH值有利于催化剂表面生成更多的羟基. TiO₂和TiO₂/SiO₂光催化剂的催化活性随pH值升高而明显增强. TiO₂/SiO₂的光催化活性优于TiO₂. TiO₂/SiO₂催化剂具有较好的耐久性.

Structure,Surface Properties and Photocatalytic Activity of TiO2 and TiO2/SiO2 Catalysts Prepared at Different pH Values

TiO2 and SiO2-doped TiO2 (TiO2/SiO2) catalysts were prepared using aqueous solutions containing a TiOSO4 and/or SiO2 sol in which NH3·H2O was used to adjust the pH value by a precipitation method. The as-synthesized photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption (BET), UV-Vis diffuse reflectance spectroscopy, NH3 temperature programmed desorption (NH3-TPD), and Fourier transform infrared (FT-IR) spectroscopy. The XRD patterns showed that anatase and rutile coexisted in the as-prepared TiO2 and the rutile phase content increased with the increase in pH value. However, only anatase-TiO2 was observed in the TiO2/SiO2 catalysts. SEM revealed that the surface morphology of the particles was a sub-spherical shape and some agglomeration occurred on the surface while the particle size was mostly between 10 and 25 nm. Surface area measurements showed that the surface areas of the catalysts increased slightly with the increase in pH value. The incorporation of SiO2 increased the surface area. NH3-TPD analysis indicated that the amount of surface acid increased as the pH increased. The amount of surface acid on SiO2-doped TiO2 was higher than that on TiO2 when they were prepared at identical pH values. The addition of silica and the high pH value environment led to more surface hydroxyl groups on the catalysts as determined by FT-IR spectroscopy. The photocatalytic activity of the catalysts improved remarkably with the increase in pH value. The photocatalytic activity of SiO2-doped TiO2 is better than that of TiO2. The TiO2/SiO2 catalyst has better durability.