Photocatalytic hydrogen production over various sodium tantalates

The present study reports the preparation of a series of NaTaO3, Na2Ta2O6, composite sodium tantalates and their photocatalytic activities for hydrogen production. We demonstrate that the crystal structure, band gap, morphology and textural parameters of sodium tantalates can be controlled via a feasible hydrothermal route by changing the pH and reaction time. The prepared materials are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N-2-sorption and UV-Vis spectroscopy. Na2Ta2O6 with pyrochlore-type structure, that has an average particle size of around 27 nm, is synthesized at low alkali concentration. By slightly increasing the alkali concentration, another Na2Ta2O6 sample with an average particle size of 15 nm and higher surface area is obtained. Further increasing the alkali concentration results in a series of composite materials based on a mixture of Na2Ta2O6 and NaTaO3. In addition, large NaTaO3 cubes are prepared at very high alkali conditions. The catalytic activities of the prepared samples are investigated for photocatalytic hydrogen production and their efficiencies are correlated to the composition, surface area and junction between the two crystal structures of the materials. The highest photocatalytic activity is achieved with Na2Ta2O6 nanoparticles with the highest surface area. It is noticed that the hydrogen production rate is not only correlated to the high surface areas of the materials, an enhanced H-2 production is obtained for composite materials that is attributed to junctions between the pyrochlore and perovskite phases of sodium tantalate. (C) 2013 Elsevier B.V. All rights reserved.