Photocatalytic reduction of CO2 over exposed-crystal-face-controlled TiO2 nanorod having a brookite phase with co-catalyst loading

Abstract

Photocatalytic reduction of carbon dioxide (CO2) was carried out using exposed-crystal- face-controlled titanium(IV) oxide (TiO2) having a brookite phase. Methanol (CH3OH) was detected as the main product, and trace amounts of formic acid, carbon monoxide, methane, and hydrogen were also detected in some cases. The prepared nanorod-shaped brookite TiO2 with large {210} and small {212} exposed crystal faces showed larger CH3OH generation than that of commercial brookite TiO2 powder (Kojundo Chemical Laboratory Co., Ltd.). The activity of a brookite TiO2 nanorod for CO2 reduction depended on its aspect ratio because the {210} crystal faced worked as a reduction site, whereas an oxidation site was assigned to {212} crystal faces. Photodeposition of gold (Au) or silver (Ag) nanoparticles on the nanorod-shaped brookite TiO2 induced a dramatic increase in CH3OH production because the deposited metal particles work as reductive sites for multi-electron reduction of CO2. Among the co-catalyst-loaded brookite TiO2 nanorods, nanorod-shaped brookite TiO2 loaded with Ag showed higher activity. The source of carbon of CH3OH obtained by CO2 reduction is discussed on the basis of results of a labeling experiment using 13CO2.