Photocatalytic degradation of gaseous toluene using self-assembled air filter based on chitosan/activated carbon/TiO<inf>2</inf>

Photocatalytic filters are integrated with air purifiers and ventilation systems to remove volatile organic compounds (VOCs) from indoor air. However, the filters, generally prepared by dip or spray coating, are less stable as the deposited TiO2 NPs are prone to be blown off by treated air. In the present study, we propose a novel filter preparation method based on self-assembly of activated carbon (AC) and TiO2 on non-woven polyethylene terephthalate (PET) fabric using chitosan (CS). The prepared filter (CSAT-PET) was characterized for morphological and chemical properties which revealed the homogeneity and chemical bonding of deposited TiO2. Photocatalytic activity of the prepared filter was evaluated for toluene degradation (200-600 ppb) under dark and UV illumination. Toluene removal efficiency reached 91% over CSAT-PET, while it was only 62% over pure TiO2 filter. About 40% of toluene removal was achieved by adsorption on CSAT-PET. Furthermore, CSAT-PET showed robust performance for selected face velocity ranging from 0.5 to 1.5 m/s and, the reaction rate followed Langmuir-Hinshelwood model. FTIR study identified benzaldehyde and benzoic acid as adsorbed intermediates. A UV-induced filter regeneration partially released the adsorbed species. CSAT-PET showed consistent toluene removal and intact morphology over five degradation cycles. The Box-Behnken design (BBD) in RSM was applied to optimize the filter preparation method. The optimum values of TiO2, AC and CS loading were 38.3 g/m2, 52.6 g/m2 and 2.06% (w/v), respectively which exhibited highest removal efficiency for toluene (93%). The proposed methodology can be adapted to fabricate low-cost, stable, and reusable photocatalytic filter for air purification applications.