Influence of MnO2 on the photocatalytic activity of P-25 TiO2 in the degradation of methyl orange

摘要

Influences of alpha-MnO2,beta-MnO2,and delta-MnO2 on the photocatalytic activity of Degussa P-25 TiO2 have been investigated through the photocatalytic degradation of methyl orange.The TiO2 photocatalyst,before and after being contaminated by MnO2,was characterized by UV-visible diffuse reflectance spectroscopy (UV-vis DRS),photoluminescence (PL),and X-ray photoelectron spectroscopy (XPS).The results showed that photocatalytic activity of TiO2 could be inhibited significantly or completely deactivated due to the presence of even a small amount of MnO2 particles.It was found that the poisoning effect varied with the crystal phases of MnO2 and the effect was in the order delta-MnO2>alpha-MnO2 >beta-MnO2.The poisoning effect was attributed to the formation of heterojunctions between MnO2 and TiO2 particles.The heterojunctions changed the chemical state of Ti~(4+) and O~(2-) sites in the crystalline phase of TiO2.MnO2 in contact with TiO2 particles also broadens the band-gap of TiO2,which decreases UV absorption of TiO2.It can also create some deep impurity energy levels serving as photoelec-tron-photohole recombination center,which accelerates the electron-hole recombination.