Photoreforming driven by indium hydroxide/oxide nano-objects

Abstract In(OH)3/In2O3 nano-objects (plates and tubes) were prepared under controlled mild reaction conditions by simple basic thermal hydrolysis of 1-(2-methoxy-ethyl)-3-methyl imidazolium tetrachloro-indate (BMIOMe·InCl4) ionic liquid (IL). As the reaction temperature increased from 10 °C to 80 °C, there was not only an increase in concentration of In2O3 but the growth of nano-tubes (NTs) also increased. At 10 °C, 30 °C, 50 °C, and 80 °C, 25.2 ± 7 nm sized nanoplates (NPls), small nanotubes (26.6 ± 6 nm in length and 8 ± 2 nm in width), NTs with a length of 25.9 ± 6 nm, and larger nanotubes (49.2 ± 18 nm) were obtained, respectively. The surface concentration of In(OH)3 decreased with the augmentation of the reaction temperature (from 100% at 10 °C to 5.1% at 80 °C). The nano-objects displayed a band gap of 5.4 eV, which is in the range expected for photo-catalytic activity to generate hydrogen from alcoholic solutions. Remarkably, In(OH)3/In2O3 catalyst prepared at 30 °C revealed 3.72 μmol h−1 of rate of hydrogen with apparent quantum yield of 16.3%, yielding a total H2 productivity of 57.6 μmol (5.76 mmol/g) after 32 h. This is the most active semiconductor photocatalysts reported so far of bare indium-based. The presence of In2O3 inside the nano-tubes is also important for the photacatalytic activity of the In(OH)3 based semiconductor. The presence of the IL layer not only acts as a template to control the structure of the nano-objects, but its presence also induces H2 generation.