Improved hydrogen evolution activities under visible light irradiation over NaTaO3 codoped with lanthanum and chromium

Na1−xLaxTa1−xCrxO3 and NaTa1−xCrxO3 (x = 0.01, 0.03, 0.05 and 0.10) have been synthesized by a solid state reaction method. These photocatalysts can produce H2 in the presence of methanol under visible light irradiation (λ > 420 nm). The photocatalytic activities of Na1−xLaxTa1−xCrxO3 are much higher than those of NaTa1−xCrxO3, respectively. Especially, the H2 evolution rate of Na0.9La0.1Ta0.9Cr0.1O3 is 2.2 μmol h−1, which is nearly 4 times higher than that of NaTa0.9Cr0.1O3 (0.6 μmol h−1). The improved activities of Na1−xLaxTa1−xCrxO3 compared with NaTa1−xCrxO3 can be ascribed to two factors: one is smaller particle size and higher specific surface area which is caused by the doping of lanthanum; the other is that Na1−xLaxTa1−xCrxO3 has less Cr6+, which is induced by codoping of lanthanum and chromium.