Titanium Based Oxides For Photocatalysis:Effect Of Plasmonics,Electron Sink,and High Crystallinity

Titanium dioxide(TiO2),strontium titanate(SrTiO3),and cadmium titanate(CdTiO3)are three of the important titanium based oxides.They are semiconductors with wide band gap so they can absorb only UV light which constitutes about 5%of the solar radiations.These semiconductors also suffer from a fast charge recombination during photocatalytic reactions,which greatly reduces their photocatalytic efficiency.We aim to develop strategies for visible light activation and suppression of charge recombination for enhanced photocatalysis over Ti02,SrTiO3,and CdTiO3.Ag,Au,and CuO were loaded separately onto TiO2 via a reverse microemulsion synthesis method.UV-vis spectra of Ag/TiO2,Au/TiO2,and CuO/TiO2 showed absorbance in the visible region.The visible light absorption was attributed to the surface plasmon resonance(SPR)of Ag and Au,while to interfacial charge transfer(IFCT)in the case of CuO.The as prepared materials did not show any degradation of methyl orange(MO)under visible light.Ag/AgCl/TiO2 was synthesized and then CuO was introduced into it via a reverse microemulsion.CuO/Ag/AgCl/TiO2 composite was characterized and evaluated for the visible light photocatalysis.Degradation of about 42%MO and 53%phenol was achieved over Ag/AgCl/TiO2 under our experimental conditions.The visible light photocatalytic performance of Ag/AgCl/TiO2 was greatly enhanced by introducing a small amount of CuO into Ag/AgCl/TiO2.The MO and phenol degradation was increased up to 93%and 71%,respectively,when CuO/Ag/AgCl/TiO2 was used as photocatalyst under the same experimental conditions.Copper oxide is suggested to act as sink for photogenerated electrons,which resulted in better charge separation and hence enhanced photocatalysis.Ag/AgX(X=Cl,Br)was loaded onto ATiO3(A=Cd,Sr)to fabricate a new series of plasmonic photocatalysts.Pristine ATiO3 did not show activity for visible light photodegradation of MO or RhB.Ag/AgBr/SrTiO3 was found to be the best photocatalyst resulting in 93%MO degradation in 15 min and 96%RhB degradation for 25 min under visible light illumination.The enhanced activity is attributed to Ag SPR,visible light absorption by AgBr,and a more negative conduction band position of AgBr.Chloride as a capping agent during the microemulsion-based synthesis was found to significantly improve the crystallinity of CdTi03 which was found to greatly enhance the photodegradation of MO under solar light.About 27%degradation of MO was achieved from CdTi03 synthesized in the absence of chloride.In contrast,about 98%degradation of MO was achieved from CdTiO3 synthesized in the presence of optimum amount of chloride.Better charge separation due to the high crystallinity resulted in improved photocatalytic activity.