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 O2 evolution from an aqueous silver nitrate solution under visible light ( > 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 O2 evolution among the three polymorphs, and also served as an O2 evolution photocatalyst in Z-scheme overall water splitting in combination with Rh-doped strontium titanate (SrTiO3:Rh) and an Fe3+/ Fe2+ redox-shuttle mediator.
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