Site Sensitivity of Interfacial Charge Transfer and Photocatalytic Efficiency in Photocatalysis: Methanol Oxidation on Anatase TiO₂ Nanocrystals

Abstract

Photocatalytic oxidation of methanol on various anatase TiO2 nanocrystals was studied by in situ and time‐resolved characterizations and DFT calculations. Surface site and resulting surface adsorbates affect the surface band bending/bulk‐to‐surface charge migration processes and interfacial electronic structure/interfacial charge transfer processes. TiO2 nanocrystals predominantly enclosed by the {001} facets expose a high density of reactive fourfold‐coordinated Ti sites (Ti4c) at which CH3OH molecules dissociate to form the CH3O adsorbate (CH3O(a)Ti4c). CH3O(a)Ti4c localized density of states are almost at the valence band maximum of TiO2 surface, facilitating the interfacial hole transfer process; CH3O(a)Ti4c with a high coverage promotes upward surface band bending, facilitating bulk‐to‐surface hole migration. CH3O(a)Ti4c exhibits the highest photocatalytic oxidation rate constant. TiO2 nanocrystals enclosed by the {001} facets are most active in photocatalytic methanol oxidation.

Surface-Terminated Hydroxyl Groups for Deciphering the Facet-Dependent Photocatalysis of Anatase TiO2

“…Since the discovery that TiO 2 can photocatalyze the splitting of water, intense interest has been shown on photocatalytic H 2 O cleavage using TiO 2 . − The TiO 2 surface is decisive for its catalytic performance because the critical processes (substrate adsorption, interfacial charge transfer, and redox reaction) readily take place on the surface. − Exposure of diversified facets may result in dramatic discrepancies of the surface structures and therefore the performances. For instance, the theoretical calculations have revealed that water molecules can be dissociatively adsorbed on the anatase (001) facet via hydrogen bonding but molecularly on the (101) facet by Ti–O coordination. , In addition to substrate adsorption, several studies have unraveled the facet dependence of charge carrier behaviors.…”

An efficient catalyst of CuPt/TiO2 for photocatalytic direct dehydrogenation of methanol to methyl formate at ambient temperature

“…Scheme 1 shows the possible reaction mechanism of photocatalytic direct dehydrogenation of methanol to methyl formate. At the beginning of the reaction, methanol molecules react with the surface hydroxyls to give rise to methoxy groups and water (steps 1a and b in Scheme 1), [16][17][18]40 but the hydroxyls cannot be recovered after the methoxy groups are consumed during the reaction due to oxygen not being involved. Other studies showed that molecular methanol adsorbed on Ti 4+ is isoenergetic with its dissociated state (CH 3 O + H), suggesting that the exposed Ti 4+ sites on titania, resulting from the consumption of the surface methoxy groups, are prone to adsorbing methanol molecules to give rise to methoxy groups.…”

Preparation of Ag3PO4/TiO2(B) Heterojunction Nanobelt with Extended Light Response and Enhanced Photocatalytic Performance

“…However, TiO 2 has a band gap as large as 3.2 eV and hence is photocatalytically active only under UV light, which accounts for merely approximately 5% of solar radiation energy. Therefore, TiO 2 as a photocatalyst has a low utilization of solar radiation energy and insignificant photocatalytic performance [11][12][13]. However, combining TiO 2 with other narrow-band-gap semiconductor materials to construct heterojunctions can effectively enhance the photocatalytic performance of TiO 2 .…”