Preparation And Photocatalytic Activity Of Tantalic Oxide-based Nanomaterials

Tantalic oxide(Ta2O5)is a typical wide bandgap semiconductor with a bandgap of ~4.0 e V.It is of great importance for wide bandgap Ta2O5 to response to wide spectral range and enhance the charge separation of photo-induced electrons and holes by the chemical technologies.In this work,we successfully synthesized the Ta2O5 photocatalysts and its composites with different morphologies,and investigated the different influences on photocatalytic performances in detail.Besides,some different chemical technologies,shch as the fabrication of heterojunction photocatalyst,the construction of defect-rich semiconductor and mesocrystal photocatalysts,and bimetallic Pd-Pt co-catalysts modified mesocrystal photocatalysts,were used to promote the charge separation and improve the photocatalytic performance of Ta2O5-based photocatalysts.Ta2O5 quantum dots with Ta4+ self-doping and g-C3N4 modified Ta2O5 quantum dots photocatalyst were successfully synthesized by the vapor hydrolysis and calcination method.The as-prepared Ta4+ self-doped Ta2O5 quantum dots in this work showed the obvious visible light absorption,mainly because of the formation of oxygen vacancy defects.The as-prepared Ta2O5 quantum dots also showed the obvious visible light absorption,mainly because of the formation of the oxygen vacancy defects,and the Ta2O5 quantum dots showed the visible light photocatalytic activity.The as-prepared g-C3N4/Ta2O5 composite photocatalyst showed highly enhanced visible light absorption and photocatalytic activity,and the photocatalytic hydrogen production rate and Rh B degradation constant were 624.99 μmol g-1 h-1 and 0.1512 min-1,mainly because of the formation of Ta-O-C chemical bonds,which improve the separation of photo-induced electrons and holes of g-C3N4/Ta2O5 photocatalyst.Besides,the g-C3N4/Ta2O5 photocatalyst also showed good photocatalytic stability.Oxygen vacancy defect-rich Ta2O5 nanorods were successfully prepared by the vapor hydrolysis method with tantalum ethoxide and ammonium fluoride as the raw materials.The results showed that the vapor hydrolysis temperatures had important influences on the as-prepared Ta2O5 nanorod photocatalyst.The higher the reaction temperature was,the higher content of oxygen vacancy was,the deeper the color of Ta2O5 nanorods were,and the stronger UV-vis absorption was,which resulted in the effciently decreasing of the optical band gaps of the Ta2O5 nanorods,and showed obvious advantages in comparison with that of commercial Ta2O5.The specific surface area of the as-prepared Ta2O5 nanorods was as high as 237.9 m2 g-1,which was much higher than that of commercial Ta2O5 photocatalyst.The photocatalytic hydrogen production rates of Ta2O5 nanorods under the UV light,simulated sunlight and visible light were 10.167 mmol g-1 h-1、356.689 μmol g-1 h-1 and 23.351 μmol g-1 h-1,respectively.And the photocatalytic activity under the simulated sunlight was increased by 6.39 times in comparison to that of commercial Ta2O5.Besides,this work also provided a new method for the preparation of defect-rich semiconductor photocatalysts and its composite materials under the mild conditions.Mesocrystalline(NH4)2Ta2O3F6 nanorods with oxygen vacancy defects were successfully prepared by the vapor hydrolysis method through increasing the dosage of ammonium fluoride.The as-prepared(NH4)2Ta2O3F6 photocatalyst was the rod-like shapes,and the UV light absorption was weaker than that of commercial Ta2O5 photocatalyst.Defect-rich mesocrystalline Ta2O5 nanosheets were also successfully fabricated by the topotactic transformation method with mesocrystalline(NH4)2Ta2O3F6 nanorods as as the raw materials.The as-prepared mesocrystalline Ta2O5 nanosheets showed obvious visible light absorption,which was mainly due to the formation of oxygen vacancy defects.The photocatalytic hydrogen production activity of mesocrystalline Ta2O5 nanosheets was as high as 11268.241 μmol g-1 h-1,which was much higher than that of commercial Ta2O5 and mesocrystalline(NH4)2Ta2O3F6 nanorods.In addition,the potential of the valence band of mesocrystalline Ta2O5 photocatalyst was higher than that of commercial Ta2O5.The specific surface area of mesocrystalline Ta2O5 nanosheets was much higher than that of commercial Ta2O5 photocatalyst,which was also contributing to improve the photocatalytic activity of mesocrystalline Ta2O5 nanosheets.The co-catalysts played important influences on the photocatalytic performances of the semiconductor photocatalyst.Based on the successful preparation of mesocrystalline Ta2O5 nanosheets,the bimetallic Pd-Pt/mesocrystalline Ta2O5 nanosheet photocatalyst was successfully synthesized by the ultrasonication-assisted photo-reduction method.The as-prepared Pd-Pt/mesocrystalline Ta2O5 nanosheet photocatalyst showed the enhanced UV-Vis light absorption in comparison to that of commercial Ta2O5,mesocrystalline(NH4)2Ta2O3F6 nanorods,mesocrystalline Ta2O5 nanosheets and Pt/mesocrystalline Ta2O5 nanosheets and Pd/mesocrystalline Ta2O5 nanosheets,and the photocatalytic activity of Pd-Pt/mesocrystalline Ta2O5 nanosheets was also highly enhanced.The photocatalytic hydrogen production rate was as high as 21529.521 μmol g-1 h-1,which was about 20 times higher than that of commercial Ta2O5,fully demonstrating the synergistic effects of bimetallic Pd-Pt nanoparticles in enhancing the UV-Vis light absorption property and promoting the separation of photo-induced electrons and holes.