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

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 {2 1 0} and small {2 1 2} 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 {2 1 0} crystal faced worked as a reduction site, whereas an oxidation site was assigned to {2 1 2} 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

Dependence of photocatalytic activity on aspect ratio of a brookite TiO2 nanorod and drastic improvement in visible light responsibility of a brookite TiO2 nanorod by site-selective modification of Fe3+ on exposed faces

Exposed crystal face-controlled brookite titanium(IV) oxide (TiO2) nanorods with various aspect ratios were prepared by a hydrothermal process with or without PVA or PVP as an aspect reagent. The nanorod-shaped brookite TiO2 had larger {2 1 0} and smaller {2 1 2} exposed crystal faces, which were assigned by TEM with the SAED technique. Their aspect ratios were greatly influenced by the addition of PVA or PVP as an aspect ratio control reagent to the reaction solution used in the hydrothermal treatment. The photocatalytic activity for decomposition of acetaldehyde increased with increase in the aspect ratio because the surface area ratio of {2 1 0} to {2 1 2} exposed crystal faces, which are attributed to reduction and oxidation sites, respectively, became more optimal. The {2 1 2} exposed crystal faces of surface-controlled brookite TiO2 were site-selectively modified with trivalent iron(III) (Fe3+) ions by utilizing the adsorption property of iron(III)/iron(II) (Fe3+/Fe2+) ions. The brookite TiO2 nanorod with site-selective modification of Fe3+ ions showed much higher photocatalytic activity than that of commercial brookite TiO2 loaded with Fe ions under visible-light irradiation because of the separation of redox sites. In other words, oxidation and reduction proceed over Fe3+ ion-modified {2 1 2} faces of the TiO2 surface and on {2 1 0} faces of the TiO2 surface without modification of Fe3+, respectively

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

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 {2 1 0} and small {2 1 2} 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 {2 1 0} crystal faced worked as a reduction site, whereas an oxidation site was assigned to {2 1 2} 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