Selective Synthesis and Photocatalytic Oxygen Evolution Activities of Tantalum/Nitrogen-Codoped Anatase, Brookite and Rutile Titanium Dioxide

Tantalum/nitrogen codoped titanium dioxide (TiO2:Ta,N) having a rutile structure has recently been reported to be a good photocatalyst for visible-light water oxidation. In this work, three different polymorphs of TiO2:Ta,N (anatase, brookite and rutile) were synthesized by a hydrothermal method using water-soluble titanium/tantalum complexes as precursors, followed by thermal nitridation with dry ammonia gas. Effects of the physicochemical properties on photocatalytic activity for O-2 evolution from an aqueous silver nitrate solution under visible light (lambda > 400 nm) were investigated. Experimental results indicated that defect formation during the nitridation procedure was the dominant factor for photocatalytic activity. Anatase TiO2:Ta,N was the most active for O-2 evolution among the three polymorphs, and also served as an O-2 evolution photocatalyst in Z-scheme overall water splitting in combination with Rh-doped strontium titanate (SrTiO3:Rh) and an Fe3+/Fe2+ redox-shuttle mediator.