The pH-depending enhancement of electron transfer by {001} facet-dominating TiO2 nanoparticles for photocatalytic H2 evolution under visible irradiation

Abstract

TiO₂ nanoparticles with an exposed reactive {001} facet have exhibited more favourable properties in photocatalysts, batteries and photoelectrochemical cells owing to their superiority of association properties with adsorbents, electron transfer, ion insertion capacity, etc. to the conventional TiO₂. We recently revealed the effects of {001} facet-dominating TiO₂ on the electron injection from photo-excited dye-sensitizers exhibiting an order of magnitude increase in the rate constant. We herein report that {001} facet-dominating TiO₂ enhances the efficiency of photocatalytic H₂ evolution with the porphyrine dye-sensitized TiO₂ nanoparticles in an aqueous suspension especially with the specific pH region above 8 (in alkaline solution) under visible irradiation as compared with conventional P25. The analysis of fluorescence quenching in a TiO₂ colloidal suspension based on the Stern–Volmer relationship is employed to estimate the electron injection efficiency of photo-excited electrons in dye-sensitizers. The results imply that the enhancement of H₂ evolution by {001} facet-dominating TiO₂ is attributed to its efficient photo-excited electron injection process from dye-sensitizers to TiO₂ as compared with conventional P25.