Synthesis, characterization and photocatalytic activity of titania loaded Cd-MCM-41

Abstract

Catalysts consisting of cadmium incorporated into MCM-41 mesoporous molecular sieves (Cd-MCM-41) with Si/Cd = 80 have been synthesized by the hydrothermal method using cadmium acetate as the source of cadmium. This was then loaded with titania via the sol-gel method to explore the photoactivity in UV light. These two materials were characterized by various physicochemical techniques such as N2 physisorption, O2 chemisorption, diffuse reflectance UV-vis, X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The pore size of the Cd-MCM-41 was higher and the BET surface area was lower than those commonly found in our siliceous MCM-41. This is due to the partial pore breakage, as recorded by pore size distribution analysis. The oxygen chemisorption results shows that the dispersion of cadmium is quite high, and decreased after loading of titania. The XRD patterns of Cd-MCM-41 and 25%TiO2/Cd-MCM-41 are similar to those of siliceous MCM-41; however, the intensity of the d100 peak is decreased and the unit-cell parameter increased with titania loading. Raman spectra could not detect any peaks, whereas peaks were detected at 144, 397, 518 and 641 cm-1 with loading of titania, these peaks being associated with the anatase phase of titania. The surface composition and binding energy of the Cd 3d5/2 peak for Cd-MCM-41 and 25%TiO2/Cd-MCM-41 was analyzed by XPS and showed considerable infusion of cadmium ions on to the surface upon loading of titania. The Cd/Si surface atomic ratio measured by XPS increases 10 times with loading of titania on Cd-MCM-41, indicating that the two separate surface electronic levels such as Cd-O-Si and Cd-O-Ti were found for 25%TiO2/Cd-MCM-41. The 25%TiO2/Cd-MCM-41 showed higher activity than 25%TiO2/MCM-41 for photocatalytic degradation of formic acid. The activity results are compared with the pure titania based on the transformation per site of Ti.