TiO2-loaded Cr-modified molecular sieves for 4-chlorophenol photodegradation under visible light

Here we report the aqueous photodegradation of 4-chlorophenol under visible light (wavelength >400 nm>400 nm) with three kinds of mesoporous molecular sieves (MCM-41, MCM-48, and SBA-15) incorporated with Cr and TiO2 (TiO2/Cr-MS). The Si/Cr atomic ratios in the synthesized materials are 80, 40, and 20, respectively. These materials are characterized with BET surface area, pore size distribution, X-ray diffraction (XRD), ultraviolet–visible light (UV–vis) spectra, and temperature-programmed reduction (TPR). UV–vis and TPR results indicate that the Cr is present as Cr6+ in all Cr-MS and TiO2/Cr-MS samples. The TPR results further indicate that an SiOCrOSi bond structure is formed in the MCM-41 matrix, bulk Cr oxide exists outside the MCM-48 matrix, and Cr interacts mainly with silica on the surface of SBA-15. The incorporation of Cr extends the light absorption edge of TiO2/Cr-MS to 550 nm. The activities of TiO2/Cr-MS with different molecular sieves are compared for aqueous photodegradation of 4-chlorophenol under visible light. It is found that the molecular sieve plays an important role in photocatalyst activity and that MCM-41 is the support producing the best photocatalyst. The interaction of Cr6+ and TiO2 allows for a special transition under visible light, Cr6+O2− → Cr5+O1−, and is essential for the activity of a photocatalyst under visible light.