Schottky junction-engineered titanium dioxide/microporous carbon composites for visible light-driven mineralization of formaldehyde under mild conditions.

A series of multifunctional composite catalysts, ATx-K, are synthesized by combining activated carbon (AC: A) and titanium dioxide (TiO2: T), followed by a potassium hydroxide (KOH: K) treatment, where the subscript x denotes the T/A mass ratio. These catalysts are then used for the photocatalytic oxidation (PCO) of formaldehyde (FA) in air. The best performing catalyst, AT9-K, achieves complete mineralization of FA into carbon dioxide with a maximum reaction rate (rmax) of 3272 μmol g-1 h-1 and an apparent quantum yield (AQY) of 6.14 % at a gas hourly space velocity (GHSV) of 400 L g-1 h-1. This enhanced activity is attributed to a dual mechanism. Firstly, the KOH treatment creates abundant surface hydroxyl (-OH) groups on AC and reduces the TiO2 bandgap from 3.21 to 2.96 eV, promoting visible-light absorption. Secondly, the formation of a Schottky junction between AC and TiO2 facilitates the separation and transfer of photogenerated electron-hole pairs. In-situ diffuse reflectance infrared Fourier transform spectroscopy confirms that the PCO of FA proceeds through dioxymethylene and formate intermediates. These findings collectively demonstrate that AT9-K is a promising and scalable photocatalyst for indoor air purification applications.