Mediating the Oxidizing Capability of Surface-Bound Hydroxyl Radicals Produced by Photoelectrochemical Water Oxidation to Convert Glycerol into Dihydroxyacetone

Highly selective oxidation of a single specific hydroxyl group in glycerol is attractive but challenging because glycerol contains three similar hydroxyl groups. In this work, we developed a ternary photoanode comprising Ag nanoparticle-supported layered double hydroxide (LDH) nanosheets on TiO2 (denoted Ag@LDH@TiO2) for the glycerol selective oxidation to 1,3-dihydroxyacetone via photoelectrochemical water oxidation under neutral conditions. It was proved that hydroxyl radicals generated by water oxidation were the dominating active oxygen species and oxygen atoms in the main oxidation product came from water. The LDHs and Ag nanoparticles enhanced the selectivity of secondary hydroxyl oxidation, and the Ag nanoparticles further accelerated the corresponding kinetics. The Ag@LDH@TiO2 photoanode exhibited a 1,3-dihydroxyacetone selectivity of 72% at 1.2 V vs reversible hydrogen electrode, which is obviously higher than that of pure TiO2 (23.5%) and surpasses most materials reported thus far. The role of LDHs and Ag nanoparticles in selective oxidation of glycerol was revealed through detailed spectroscopic and computational studies. Specifically, Fourier transform infrared spectroscopy analysis revealed that the middle hydroxyl group is preferentially adsorbed to LDH surfaces, while density function theory calculations verified that the surface-bound hydroxyl radicals mediated dehydrogenation barriers of middle carbon of adsorbed glycerol; the Ag nanoparticles promoted the selective adsorption of middle hydroxyl of glycerol, which further induced its selective oxidation.