Synthesis And Performance Of Supported Visible-Light-Driven Potocatalyst

A common approach to enhance the photocatalytic activity of potocatalyst is to reduce the particle size. These small particles tend to agglomerate by strong interparticle forces when the nanometric size region is reached. In order to avoid the aggregation of these small subnanometric clusters, one methodology that has been developed consists in incorporating these clusters inside the rigid framework of microporous hosts. In this thesis, supported visible-light-driven potocatalyst were synthesised and the performance was further investigated. The details are listed as follows:1.Cr-MCM-48 was synthesized under acid condition and alkali condition and then 25 wt.% TiO2 were loaded by a post-impregnation method. XRD analysis showed that the MCM-48 structure was formed in all the samples synthesized under acid condition but only in the samples synthesized under alkali condition with Si/Cr ratio larger than 20. The BET surface area of TiO2/Cr-MCM-48 decreased with much more metals incorporated. DRS results indicated that Cr6+ was present in all samples. It was found that the photodegradation ability of 25% TiO2/Cr-MCM-48 synthesized under acid condition was higher than 25% TiO2/Cr-MCM-48 synthesized under alkali condition with the same Si/Cr ratio. This could be attributed to the presence of the high amount of Cr6+ in 25% TiO2/Cr-MCM-48 synthesized under acid condition. The sample aci-20-7-25 (Si/Cr=20, pH=7) showed the best visible-light photoactivity.2. MCM-48 modified by Bi2WO6 with a high photocatalytic activity in the visible-light range was synthesized for the first time using a facile one-step process. The XRD patterns and Nitrogen adsorption isotherms of the prapared materials exhibited the characteristic of MCM-48. The XRD and TEM showed that the small subnanometric Bi2WO6 clusters began to aggregate into bigger Bi2WO6 particles when much more metal precursors were introduced. A blue shift in the band gap transition could be seen for Bi2WO6/MCM-48 in diffuse reflectance UV-vis spectra. Raman spectra illustrated the crystal structure of Bi2WO6 on MCM-48. In comparison to Bi2WO6 synthesised via traditional solid-state reactions and hydrothermal processes, the Bi2WO6/MCM-48 with small crystal size and appropriate metal oxide loading amount offers highly enhanced photocatalytic activity under visible light irradiation.