Polymerizable complex synthesis of pure Sr2NbxTa2-xO7 solid solutions with high photocatalytic activities for water decomposition into H2 and O2

Phase-pure solid solutions with the composition of Sr2NbTa2-xO7 (SNT, x = 0-2) were prepared at 900 degreesC for 5 h by the Pechini-type polymerizable complex (PC) technique, based upon polymerization between citric acid and ethylene glycol. The two end compounds, Sr2Ta2O7 (X = 0) and Sr2Nb2O7 (X = 2), produced H-2 and O-2 in a stoichiometric ratio from pure water under UV light irradiation without a NiO cocatalyst. The photocatalytic activity of SNT for the water decomposition was greatly improved by loading NiO as a cocatalyst for a whole range of x. The photocatalytic activity was dramatically decreased approximately by 1 order of magnitude once Ta has been replaced by Nb, even when the amount of Nb was small. For all of the NiO-loaded SNT samples, water was stoichiometrically decomposed into H-2 and O-2. While samples prior to the complete crystallization showed very low activities despite their high surface area, the corresponding photocatalytic activities of well-crystallized samples depended primarily on their surface area. The low photocatalytic activities of such premature samples were interpreted as a consequence of the increased number of lattice defects acting as inactivation centers. The maximum photocatalytic activity was obtained for NiO (0.15 wt %)/Sr2Ta2O7 prepared by the PC method at 800 degreesC for 48 h; the photocatalyst having a specific surface a ' rea of 10.4 m(2.)g(-1) produced H-2 and O-2 from pure water with specific rates of 3517 and 1733 mumol(.)h(-1.)g(-1), respectively, 3.5 times larger than the best result for a sample prepared by the conventional solid-state reaction method.