Abstract
Mesoporous tantalum-based semiconductors were fabricated without the utilization of a sacrificial template. Zinc tantalate (ZnTa2O6), acting as a starting material, was synthesized by a sol-gel method. The subsequent removal of zinc under ammonia gas at temperatures higher than 800 oC resulted in the formation of mesopores, and the remaining Ta was nitridized to form tantalum nitride (Ta3N5), or with partial oxygen pressure to form tantalum oxynitride (TaON). The mesoporous structure was examined by SEM, TEM, and BET analyses. The highest surface area was about 25 and 20 m2/g for Ta3N5 and TaON, respectively. The mesoporous Ta3N5 and TaON were employed to conduct methylene blue (MB) degradation and water splitting. The mesoporous Ta3N5 annealed at 800 oC showed better photocatalytic activitiy than the Ta3N5 from commercial tantalum oxide (Ta2O5). This result might be ascribed to smaller particle size and larger surface area. The photocatalytic activity of TaON, on the other hand, largely depended on the ratio of O to N, which made it visible light or UV-prone. Platinum and nickel hydroxide (Ni(OH)2) were loaded as co-catalysts on Ta3N5 and TaON by two different approaches. Pt was deposited by a homemade ALD. The amount of Pt loaded increased with the increase of ALD cycle numbers. However, the photocatalytic efficiency does not increase with the addition of Pt. With the increase of ALD cycle numbers, the amount of H2 production decreases. Ni(OH)2, on the other hand, was loaded by a precipitation method. The phase and the stability of Ni(OH)2 were confirmed by XPS. The photocatalytic efficiency of Ni(OH)2 was better than that of Pt on tantalum (oxy)nitrides. The amount of H2 reached about 20 μmol/g after 6 h of irradiation for the Ta3N5 system, and about 10 μmol/g after 6 h for the TaON system.