Flame aerosol synthesized Cr incorporated TiO2 for visible light photodegradation of gas phase acetonitrile

Abstract

A series of Cr-TiO2 nanoparticles with different atomic ratios of Ti to Cr have been synthesized by adopting a one-step flame aerosol synthesis technique. The photocatalytic activity of flame aerosol made TiO2 loaded with various amounts of Cr was studied as a catalyst for gas phase photodegradation of acetonitrile (ACN) under visible light (400-800 nm). It was found that the optimal concentrations of Cr and TiO2 exist (Ti/Cr atomic ratio = 40) for the efficient oxidation of ACN in the gas phase. XRD patterns showed a decrease in the anatase phase with increase in the amount of Cr loading. Our H2-temperature programmed reduction (TPR) results indicate a strong interaction (Cr-O-Ti) between support and dopant in the Cr modified TiO2 as-synthesized catalysts. Our XPS results illustrated that the relative atomic percentage value of Ti3+/Ti4+ characterized by XPS was significantly high for the Cr/TiO2 nanoparticles with Ti/Cr = 40 atomic ratio (Ti3+/Ti4+ = 1.14, 42.1%), whereas other samples demonstrated low atomic percentage value of Ti3+/Ti4+ (Ti3+/Ti4+ = 0.18-1.05). Moreover, Cr interacts with the TiO2 nanostructure in the interface of flame-made nanoparticles, bulk Cr oxide exists over the surface of TiO 2 nanostructure. The photodegradation ability of TiO2/Cr catalyst with Ti/Cr atomic ratio of 40 was highly related to the existence of Cr6+ species which strongly interacted with TiO2. The reduction peaks in Cr-doped TiO2 shifted to much lower temperatures, due to the increase in the reduction potential of titania and chromium species. The strong interaction (formation of Cr-O-Ti bonds) is the main reason that Cr/TiO2 is an active photocatalyst in visible light. Among all of the catalysts tested, the system with Ti/Cr atomic ratio 40 demonstrated a superior catalytic performance with the rate constant of 0.812 m3 g -1 mol-1 under visible light irradiation. The proposed route of the catalytic activity of the above material in visible light involves the reaction of dopant level electrons with surface Cr, which makes available valence band holes to perform oxidation reactions. © 2013 American Chemical Society.