ZSM-5晶粒度对其负载的TiO_2光催化剂性能的影响

Effect of ZSM-5 Crystal Size on Properties of Supported TiO_2 Photocatalyst

采用透射电子显微镜、扫描电子显微镜、X射线荧光分析、X射线光电子能谱、紫外-可见漫反射光谱和吡啶吸附傅里叶变换红外光谱等表征方法以及偶氮染料甲基橙的吸附和光降解反应,研究了ZSM-5晶粒度对TiO2/ZSM-5光催化剂性能的影响.结果表明,TiO2主要负载于ZSM-5沸石外表面,因而减小载体晶粒度有利于提高TiO2的负载量和分散性.纳米ZSM-5沸石负载的TiO2催化剂具有较高的甲基橙吸附量,且吸附发生在ZSM-5外表面的酸中心上,催化剂良好的吸附能力促进了甲基橙的光降解.

The dispersion of TiO2 on supports has become a hot topic in the photocatalysis field.The adsorption of reactant molecules on supports can concentrate them from either liquid phase or gas phase to the vicinity of supported TiO2 photoactive sites.Zeolites and molecular sieves are quite suitable supports because of their unique pore structure and high surface area.In this paper,TiO2/ZSM-5 composite photocatalysts were prepared by supporting TiO2 on the external surface of a series of ZSM-5 zeolites using a sol-gel process.Various characterization techniques such as transmission electron microscopy,scanning electron microscopy,X-ray fluorescence spectroscopy,X-ray photoelectron spectroscopy,diffuse reflectance ultraviolet-visible spectroscopy,and pyridine adsorption Fourier transform infrared spectroscopy were employed to investigate the physicochemical and photoresponse properties of the samples.The adsorption capacity and photodegradation activity of the samples were measured using methyl orange（MO） aqueous solution.It was found that TiO2 is mainly supported on the external surface of the ZSM-5 supports.The decrease in zeolite crystal size is helpful to increase TiO2 loading and dispersion.Nanosized ZSM-5 is effective as an adsorbent for MO molecules.MO adsorption mainly takes place on the external surface of ZSM-5,and the acid sites of the supports are the adsorption sites.The TiO2/ZSM-5 composites exhibit higher MO photodegradation activity than bare TiO2.Moreover,the crystal size of the supports has a significant influence on the catalytic activity,and the maximum activity can be obtained when the crystal size is less than 100 nm.The high photodegradation activity of TiO2 supported on nanosized HZSM-5 can be attributed to the large amount of acid sites on the large external surface of HZSM-5.