Surface design of g-CN quantum dot-decorated TiO(001) to enhance the photodegradation of indoor formaldehyde by experimental and theoretical investigation.

Formaldehyde (CHOH), a common volatile organic compound, causes many adverse effects on human health. The highly exposed TiO(001) facet possesses a high photodegradation efficiency of CHOH due to its excellent ability to trap photogenerated holes and high density of surface unsaturated Ti atoms (Ti5c) to bind CHOH. However, the rapid recombination of photoinduced electron-hole pairs of TiO(001) limits the photodegradation efficiency. We adopted a strategy of decorating TiO(001) with g-CN quantum dots (QDs), exploiting the quantum effect of g-CNQDs and their combined staggered band structure. This decoration improves the photocatalytic activity of TiO(001). Moreover, the chemical configuration of g-CNQDs/TiO(001) and the combination mode between the g-CNQDs and TiO(001) support were explored in detail using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Following the physiochemical characteristic results, the transport mechanism of photoinduced carriers was further analyzed by ultraviolet photoelectron spectroscopy (UPS), electron paramagnetic resonance (EPR), and Heyd-Scuseria-Ernzerh (HSE) exchange-correlation functional calculations. Finally, the performance and reaction mechanism of the photodegradation of CHOH by TiO(001) and g-CNQDs/TiO(001) were thoroughly investigated. The results show that the g-CNQDs were composed of an N-defect tri-s-triazine supported by TiO(001) via a strong C-O-Ti chemical bond, which accelerated the separation of photoinduced carriers through a Z-scheme route. The photodegradation and mineralization efficiencies of CHOH were significantly promoted by 30% and 60% for g-CNQDs/TiO(001) compared with those of TiO(001). The photodegradation mechanism proceeded as CHOH - dioxymethylene - formate - carbonate - CO. This study provides a surface engineering means to design highly active modified TiO for CHOH photodegradation.