Schottky junction-engineered titanium dioxide/microporous carbon composites for visible light-driven mineralization...

A series of multifunctional composite catalysts, AT_x-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 (r_max) 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.