The Photocatalytic Efficacy of Potassium Hydroxide–Based Modification of Titanium Dioxide in the Oxidative Destruction of Gaseous Formaldehyde

Formaldehyde (FA) is a carcinogenic oxygenated volatile organic compound and a key constituent of indoor air pollution. Photocatalytic oxidation (PCO) is a promising strategy for managing FA in indoor environments. Here, the PCO of FA in indoor air has been investigated by modifying TiO₂ with KOH (KOH/TiO₂: expressed as KT-x, where x = the molar concentration of KOH from 0.1-2 m). The KOH treatment achieves superior FA removal performance of KT-0.1 over TiO₂ (e.g., space-time yield: 1.78E-03 versus 9.91E-04 molecules photon^-1mg^-1 and dynamic clean air delivery rate: 10 versus 5.43 L mg^-1 min^-1). Such differences in photocatalytic activity reflect an enhancement in charge separation, molecular oxygen activation (on the photocatalyst surface), and electron mobility facilitated by the presence of surface hydroxyl groups and potassium on the TiO₂ surface. On the KT-x surface, the PCO of FA proceeds through several reactive intermediates (e.g., formate and dioxymethylene). According to density functional theory, the PCO of FA by KT-x is promoted by the synergistic combination of oxygen vacancies and potassium impurities on the TiO₂ surface. This research offers valuable insights into the development of cost-effective photocatalysts with enhanced PCO performance.