Hydrogen-terminated silicon nanowires for biocatalyzed artificial photosynthesis

Abstract

Silicon nanowires have been widely used in many nanoscale devices, including solar cells, photoelectrochemical cells, transistors, and battery electrodes. In this thesis study, highly efficient biocatalyzed artificial photosynthetic system is developed by employing hydrogen-terminated silicon nanowires (H-SiNWs) that exhibit good photocatalytic property with large surface area and strong light absorption across visible-light range. H-SiNWs, fabricated by metal-assisted chemical etching process, possessed enlarged band gap from the effect of quantum confinement and enabled cascade electron transfer from electron donor to NAD+ via an Rh-based electron mediator. Approximately 80% of NADH was photo-regenerated from NAD+ by H-SiNWs within 2 hrs of light irradiation ( $lambda$> 420 nm), which was successfully coupled with photoenzymatic synthesis of L-glutamate. In addition, H-SiNWs can act as a rechargeable hydride source for cofactor-dependent enzymatic reactions. During the regeneration of NADH, the Si-Hx bonds on H-SiNWs were oxidized to form Si-OH and Si-O-Si bonds on the nanowire surface and evolve hydrogen. The oxidized H-SiNWs were readily recharged by treatment in a diluted HF solution for the repeated generation of NADH and continuous enzymatic reactions for the synthesis of D-lactate from pyruvate catalyzed by lactate dehydrogenase.