Excitonic Interfacial Proton-Coupled Electron Transfer Mechanism in the Photocatalytic Oxidation of Methanol to Formaldehyde on TiO₂(110)

Abstract

CHOH on a single-crystal rutile TiO(110) surface is a widely studied model system for heterogeneous photocatalysis. Using spin-polarized density functional theory with a hybrid functional (HSE06), we study the photocatalytic oxidation of CHOH adsorbed at a coordinately unsaturated Ti site as an excited-state process with triplet spin multiplicity. The oxidation to CHO is stepwise and involves a CHO intermediate. The first O-H dissociation step follows an excitonic interfacial proton-coupled electron transfer mechanism where the hole-electron (h-e) pair generated during the excitation is bound, and the h is transferred to the adsorbate. The O-H dissociation paths associated with other h-e pairs are unreactive, and the moderate experimental efficiency is due to the different reactivity of the h-e pairs. The excited-state CHO intermediate further deactivates through a seam of intersection between the ground and excited states. It can follow three different paths, regeneration of adsorbed CHOH or formation of the ground-state CHO anion or an adsorbed CHO radical anion. The third channel corresponds to photochemical CHO formation from CHOH, where a single photon induces one electron oxidation and transfer of two protons. These results expand the current view on the photocatalysis of CHOH on TiO(110) by highlighting the role of excitons and showing that adsorbed CHOH may also be an active species in the photocatalytic oxidation to CHO.

One dimensional hierarchical nanostructures composed of CdS nanosheets/nanoparticles and Ag nanowires with promoted photocatalytic performance

“…The smaller semicircle in the EIS Nyquist plot suggests a fast interfacial charge transfer in the semiconductor. 58,59 This result also demonstrates that the 1D Ag@CdS hierarchical nanowires display superior efficiency compared to that of the CdS nanoflower in separating the electron-hole pairs, which is consistent with the results of PL spectroscopy.…”

Same titanium glycolate precursor but different products: successful synthesis of twinned anatase TiO2 nanocrystals with excellent solar photocatalytic hydrogen evolution capability

“…As a matter of fact, in the EIS Nyquist plot, the smaller semicircle size indicates fast interfacial charge transfer in the semiconductor. 47,48 The above result suggests that more effective interfacial charge transfer occurs on the twinned anatase TiO 2 photocatalyst rather than anatase and brookite TiO 2 under these conditions. Based on these results, it was concluded that the enhancement of the photocatalytic hydrogen evolution activity of the twinned anatase TiO 2 nanocrystals was attributed to the faster separation of photogenerated carriers and lower recombination of photoinduced electron-hole pairs.…”

Fundamentals of TiO2 Photocatalysis: Concepts, Mechanisms, and Challenges

“…For example, the mechanisms of CH 3 OH photolysis on R‐TiO 2 (110) proposed by Henderson's group and Wang's group mainly consider the role of holes. However, Migani and Blancafort predicted that the photooxidation of CH 3 OH on R‐TiO 2 (110) is initiated by interfacial excitons rather than separated holes using DFT calculations. The O–H dissociation step occurs through an excitonic interfacial PCET mechanism with hole transferring to the CH 3 O Ti groups, forming excited‐state CH 3 O Ti • intermediates ( Figure ).…”