Sepiolite-based photothermo-catalytic materials for integrated air purification and CO₂ valorization

Efficient photothermo-catalytic materials were developed using sepiolite previously dehydrated at 600 °C, thereby generating an anhydrous fibrous silicate scaffold able to stabilize mixed metal oxides. Single MnOx or CeO₂ and binary MnOx/CeO₂ components were incorporated by chemical precipitation, yielding hybrid structures with strong interfacial interactions within the porous clay network. Under simulated solar irradiation, photothermo-catalytic oxidation of toluene, used here as a model volatile organic compound (VOC), showed markedly enhanced conversion to CO₂ at relatively low temperatures, surpassing both thermocatalytic and photocatalytic pathways. This improvement arises from the synergistic MnOx/CeO₂ redox coupling, which promotes high lattice-oxygen mobility and an efficient photothermal response, further reinforced by the structural stability of the anhydrous sepiolite. The resulting composite facilitates an accelerated Mars-van Krevelen mechanism assisted by solar-induced reactive oxygen species. To extend the applicability of this platform, the catalyst was further modified by introducing Ni and Ce species onto the sepiolite-based structure, enabling its application in solar photothermo-catalytic CO₂ methanation, with a CH₄ production rate of 17.5 μmol g−1cat h−1. Moreover, an integrated solar process was demonstrated, in which the CO₂ generated during toluene oxidation was directly used as feed for methanation, yielding measurable CH₄ formation. These results highlight the potential of sepiolite-based photothermo-catalytic materials as low-cost, multifunctional platforms for VOC oxidation and subsequent CO₂ reduction in a continuous and sustainable solar-driven approach for air purification.