Photocatalytic decomposition of 4-nitrophenol on Ti-containing MCM-41

A series of Ti-containing MCM-41 samples, such as Ti-MCM-41 with variable Si/Ti ratios and Cr–Ti-substituted TiO₂-loaded MCM-41 having different TiO₂ loading, were prepared and studied for the photocatalytic decomposition of 4-nitrophenol in UV and visible light. The samples were characterized using surface area measurement, XRD, FT-IR, and UV–vis DRS techniques. In the case of the Ti-MCM-41 samples with Si/Ti ratios higher than 20 which were found to have typical mesoporous structure, the framework incorporation of Ti into MCM-41 increased with decreasing Si/Ti ratio. On the contrary, the Ti-MCM-41 with lower Si/Ti ratio (Si/Ti = 10) shows low structural integrity and the formation of Ti-oxide species, leading to a considerable decrease in surface area. In the case of Cr–Ti-substituted TiO₂-loaded MCM-41 samples, significant absorption occurs in visible light and the absorption in both UV and visible region increases with increasing TiO₂ loading. However, when the amount of TiO₂ loaded on Cr–Ti-MCM-41 increased above 33 wt.%, the absorption in visible light increased slightly. Thus, it seems that, at higher TiO₂ loading, some TiO₂ particles are not closely bound to the wall of Cr–Ti-MCM-41. The photocatalytic activities of Ti-containing MCM-41 samples were strongly influenced by the amount of Ti. Under UV illumination, the highest photocatalytic activity for photocatalytic decomposition of 4-NP was observed for the Ti-MCM-41 having Si/Ti ratio of 20. Among various Ti-containing MCM-41 materials prepared in this work, only Cr–Ti-substituted TiO₂-loaded MCM-41 catalysts exhibited discernable photocatalytic activities in visible light, and their photocatalytic activities increased considerably with increasing TiO₂ loading up to 33 wt.%. Further increase in TiO₂ loading enhanced photocatalytic activity slightly.