Abatement of Indoor Formaldehyde Vapor via Sequential Adsorption and Photocatalytic Degradation over HKUST-1@TiO2 Nanocomposites

Volatile organic compounds (VOCs) pose a threat to indoor air quality and human health, often necessitating specialized abatement methods due to their ultralow concentrations. This study investigates the passive abatement and photocatalytic destruction of indoor formaldehyde (HCHO) using dual-function HKUST-1@TiO₂ nanocomposites. Using a novel sol–gel method, TiO₂ micro- and nanoparticles were integrated into the HKUST-1 framework and tested in an indoor chamber with varying HCHO concentrations (50, 100 ppm) and visible-light intensities (600–1600 W). Results revealed that HKUST-1@TiO_2nano composite significantly outperformed its TiO_2micro analogue by achieving an adsorption capacity of 4.89 mmol/g and 100% HCHO conversion with a turnover frequency (TOF) of 3.64 × 10^–3 min^–1 under 600 W light at 25 °C and 40% RH. The enhanced performance of this composite was attributed to its higher surface area, more structural defects, and narrower band gap. Additional analysis revealed that, although a higher HCHO concentration enhanced TOF by 103%, elevated humidity negatively impacted photocatalytic activity, as expected, due to H₂O competing for active sites and shifting the equlibrium of the reaction. Light intensity also influenced degradation, with 1600 W yielding a TOF of 4.79 × 10^–3 min^–1. This study highlights the potential of MOF@TiO₂ nanocomposites for the combined capture and photocatalytic degradation of VOCs in indoor settings.