Enhanced Photocatalytic Activity of Titania Nanosheets via Morphology Control and Interface Engineering

Abstract

Abstract The photocatalytic oxidation of volatile organic compounds over titania nanosheets represents a promising strategy for efficient pollutant removal; however, the effects of nanosheet morphology and interface engineering on photocatalytic activity and selectivity remain insufficiently understood. In this study, titania nanosheets of a crystallographic thickness of 0.75 nm were assembled into molecularly thin monolayer films, and the photocatalytic oxidation of 2-propanol under UV irradiation was systematically examined using films with controlled nanosheet dimensions, different substrate electrical properties, and sectioned nanosheets. The initial reaction rate increased with increasing nanosheet size, whereas nanosheets with lateral dimensions of 3−6 μm exhibited the highest long-term photocatalytic activity. Increasing substrate resistivity enhanced the reaction rate but simultaneously brought about a shift in the product selectivity toward partially oxidized intermediates such as acetone. Further enhancement of the photocatalytic performance was achieved through nanosheet sectioning, which is attributed to the generation of edges exposing well-defined crystallographic facets. In addition, heterostructured bilayer films were designed by assembling a monolayer film of zeolite nanosheets onto a monolayer film of titania nanosheets, and their photocatalytic properties were examined. Although the intrinsic oxidation reactivity of the monolayer titania nanosheet film followed the order 2-propanol > ethanol > methanol, consistent with the relative stability of the intermediate radicals, deposition of a microporous MFI zeolite nanosheet overlayer decreased the overall conversion because of diffusional limitations, with the extent of conversion suppression depending on the kinetic diameter of the reactant. In particular, the conversion of larger alcohols was substantially suppressed, whereas that of methanol remained essentially unchanged, indicating that the MFI overlayer modulates the accessibility of reactants to the photocatalytically active surface. These findings demonstrate that both the activity and selectivity of titania nanosheet photocatalysts can be rationally tailored through control of the nanosheet morphology, substrate properties, and integration with a microporous overlayer.