Preparation Of Transitionmetal Doped NaTaO₃ By Hydrothermal Process And Studies Of Structural Performance

Recently, perovskite NaTaO3 has become one of the popular research subjects in the field of photocatalysis for its unique structure. It is demonstrated that NaTaO3 has a more attractive prospect than any other semiconductor photocatalytic material in the photocatalytic process including photocatalytic water-splitting to producing hydrogen, degradation of organic dyestuffs, photocatalytic reduction of CO2. However, the large band gap of NaTaO3 greatly reduces the utilization of solar energy. An effective approach to expand the scope of the optical response of NaTaO3 could be obtained by doping metal ions in NaTaO3. In this work,Cr3+,Mn2+,Fe3+,Co2+,Cu2+,Zn2+-doped NaTaO3 has been successfully synthesized by a hydrothermal process. The structure of Cr3+, Mn2+, Fe3+, Co2+, Cu2+, Zn2+-doped NaTaO3 was characterized by XRD,XPS,FT-IR,UV-VIS.Meanwhile,the Cr3+, Mn2+, Fe3+, Co2+, Cu2+, Zn2+-doped NaTaO3 were studied depending on computational simulation in order to deeply understanding of the mechanism.The powder X-ray diffraction patterns show that the NaTaO3 powders are slightly shifted to higher angles with the increase in the amounts of doped chromium and manganese.And the NaTaO3 powders are slightly shifted to lower angles with the increase in the amounts of doped iron,cobalt,copper,zincum.The shift indicates that a part of chromium, manganese, iron, cobalt, copper, zincum at least is homogeneously doped into the NaTaO3 lattice. The XPS spectrums of Cr3d, Mn3d and Cu3d show that typical peaks of 2P1/2,2P3/2 assigned to trivalent chromium,bivalent manganese and bivalent copper.The typical peaks indicate that a part of chromium, manganese and copper is doped into the NaTaO3 lattice. FT-IR spectras of samples show that the bands around 1636 and 3436 cm-1 corresponded to the bending and stretching modes of the-OH groups on catalyst surface and surface-adsorbed water. And the band around 500-700 cm-1 in all figures are attributed to Ta-O stretching vibration.The optical properties of transitionmetal-doped NaTaO3 were determined by UV-vis diffuse reflection spectroscopy (DRS). The result revealed that the absorption onsets of the doped samples have the slight red shift with the increased trans itionmetal ions content. And the band gap was gradually decreased with the increased trans itionmetal ions content. The photocatalytic activity of MB solution degraded by NaTaO3 sample under ultraviolet (UV) light irradiation was determined. It showed that the photocatalyst activity was best by the 5 percent content of chromium and manganese ions in NaTaO3, the photocatalyst activity was worst by copper and zincum ions in NaTaO3 and the photocatalyst activity was medium by iron and cobalt ions in NaTaO3.The band structure and density of states for Cr3+, Mn2+, Fe3+, Co2+, Cu2+, Zn+-doped NaTaO3 were calculated with Mn+ ion was located in the site of Ta5+ using the first principles. The results indicate that the band gap was narrowed after Cr3+,Mn2+,Cu2+,Zn2+-doped NaTaO3 The conduction band across the fermi level and overlap with valence band after Fe3+,Co2+-doped NaTaO3 which makes the band near the fermi level disappeared and the NaTaO3 with metallicity and not conducive to photocatalysis. Integrated band structure and density of states analysis, we speculated that Cr3+,Mn2+, Fe3+,Co2+ doping would cause red shift of light absorption, but Fe3+,Co2+ doping would make NaTaO3 unfavorable for photocatalytic activity due to the metal nature; Cu2+,Zn2+ doping would cause red shift of light absorption changed little or no red shift phenomenon and the lower photocatalytic activity.