New TiO₂-Ag/BEA composites with dual Ag-functionalization for specific adsorption and catalytic sites. Synergism between phases in the ethylene removal for climateric fruit conservation

Abstract

A new series of TiO2-Ag/BEA composites was specifically designed for use in filter/photo-reactors intercalated in air recirculation circuits in storage facilities for climacteric fruits. The sol-gel procedure for TiO2 deposition was combined with ionic exchange (IE) or incipient wet impregnation (IWI) techniques for Ag doping, with the proportions of both fractions also varying. The prepared materials were thoroughly characterized in terms of their porous texture, chemical composition, crystalline structure, and Ag dispersion, among other properties. Dynamic ethylene adsorption was recorded in the dark. After saturation, ethylene photooxidation was analyzed under UV or UVA-visible light, with varying contact times, flow rates, and concentrations, and with or without humidity present. The maximum ethylene adsorption capacity (361 μmol g− 1 ) corresponds to the sample with the highest Ag content (5 wt%), added by IE, while the best photocatalytic performance is obtained for samples doped by IWI. The performance of the samples was found to be correlated with their physicochemical properties and was specifically determined by the nature and dispersion of the silver species in the composites. Total ethylene photooxidation is achieved even under UV–Vis radiation; the reaction develops selectively to CO2 in all cases, despite the strong negative effect of humidity on the formation of more active HO• radicals. The high adsorption capacity and effective photooxidation of ethylene enable control of this maturation hormone below the established limits.