Fabrication of the hierarchical structure photocathode by structuring the surface nanopores on Si nanowires standing on p-Si wafer for the effective photoelectrochemical reduction of Cr(VI) in the aqueous solution

Herein, we reported a method to inhibit the oxidation passivation of Si nanomaterials (taking Si nanowire array (SiNW, about 100 nm of diameter) as a representative) via structuring nanopores (less than 10 nm) on their surface. SiNW array was prepared through metal-assisted chemical etching. After 30 min of etching, nanopores were formed on the surface of SiNW and the amount of nanopores increased with the prolonging of the etching duration. Due to the generation of the nanopores, the decrease of optical reflection was observed. The photoelectrochemical performance of samples prepared after 30, 60 and 90 min etching were evaluated. The sample etched for 60 min displayed the highest and stable photo-current and was used in the photoelectrocatalytic testing. The SiNW with nanopores exhibited significant photoelectrocatalytic stability than that of SiNW. The kinetic constant of Cr(VI) reduction over SiNW with nanopores was 0.081 min (-1), which was 1.8 times as much as that over SiNW (0.045 cm(-1)) and maintained above 0.080 min(-1) after three repeated experimental runs. These results demonstrate that constructing surface nanopores on the surface of SiNW is an effective approach to realize the use of Si materials as photoelectrodes in the aqueous solution. (C) 2016 Elsevier B.V. All rights reserved.