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-crystalface-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 13 CO2.

Brookite: Nothing New under the Sun?

“…(by oxidation of Pb 2+ nitrate) on rutile, anatase [69], and brookite [68,70]. On brookite TiO 2 nanorods, reduction and oxidation reactions were observed to proceed predominantly on {210} and {212} exposed crystal faces, respectively [68,70].…”

“…On brookite TiO 2 nanorods, reduction and oxidation reactions were observed to proceed predominantly on {210} and {212} exposed crystal faces, respectively [68,70]. In brookite nanosheets, {201} facets acted as oxidation sites, while {210} and {101} facets acted as reduction sites [64].…”

“…All polymorphs show pronounced structure/activity relations, with distinct crystal faces showing dramatically different reactivity and specifically promoting reduction or oxidation [64]. Ohno et al reported clear evidence of such facedependent reactivity by studying the photodeposition of Pt (by reduction of PtCl6 − ) and of PbO2 (by oxidation of Pb 2+ nitrate) on rutile, anatase [69], and brookite [68,70]. On brookite TiO2 nanorods, reduction and oxidation reactions were observed to proceed predominantly on {210} and {212} The EPR results further indicated that electrons in longer nanorods transfer to Pt faster than electrons in shorter nanorods.…”

In situ synthesis of ordered mesoporous Co-doped TiO2 and its enhanced photocatalytic activity and selectivity for the reduction of CO2

“…It is noteworthy that the photocatalytic performance shown in this study under visible light is significantly higher or comparable in comparison with the previously reported photocatalytic systems under visible light, even under UV-vis light (Table S2). 21,27,43,[62][63][64][65][66][67][68][69][70] However, due to the different experimental conditions (such as light intensity, illumination area, photocatalysts dosage) in these photocatalytic systems, the direct comparison is not appropriate. Therefore, we also compared our materials with some typical semiconductors or composites (including N-doped TiO 2 , Au/TiO 2 , C 3 N 4 , WO 3 , P25) measured in the same reactor system.…”

Nature of Reduced States in Titanium Dioxide as Monitored by Electron Paramagnetic Resonance. II: Rutile and Brookite Cases

“…We are thus facing the paradox of a great deal of basic research available on rutile and a parallel intense activity in applied research on anatase and P25. As far as the brookite polymorph is concerned, a relatively smaller number of studies is available even though, in the last years, the number of papers related to this material has rapidly grown [20,21,22].…”