Photocatalytic Conversion of <i>p</i>-Xylene into <i>p</i>-Tolualdehyde with Near 100% Selectivity via a Novel Hydroxyl Radical-Mediated Oxygenation Route

<i>p</i>-Tolualdehyde (<i>p</i>-TALD) is an important chemical intermediate that is widely used in the fragrance and pharmaceutical industries. Photocatalytic upgrading of <i>p</i>-xylene into <i>p</i>-TALD is a promising route but suffers from undesired overoxidation via conventional molecular oxygen-mediated oxygenation due to difficulties associated with desorbing the products from catalyst active sites. In this work, a novel photocatalytic hydroxyl radical (·OH)-mediated oxygenation route is reported for <i>p</i>-xylene to <i>p</i>-TALD conversion, in which the ·OH serves as oxygen donors to generate intermediates containing hydroxyl functional groups that readily form hydrogen bonds with surface hydroxyl groups of the P25 photocatalyst. This hydrogen bonding interaction effectively regulates the adsorption-desorption behavior of intermediates and products, thereby significantly enhancing the selectivity toward <i>p</i>-TALD from 45.25% to nearly 100%, delivering an impressive <i>p</i>-TALD production rate of 3568.8 μmol g^-1 h^-1. This work provides a promising strategy for overcoming the common issue of severe overoxidation encountered during photocatalytic upgrading of organic substrates.