Polyimide/Cu-doped TiO2 Janus membranes for direct capture and photocatalytic reduction of carbon dioxide from air

The direct conversion of carbon dioxide in atmosphere into valuable compounds or fuels is the most effective way to fundamentally solve the problem of the greenhouse effect. In this study, a Janus membrane with different layers and structures was designed to demonstrate the idea of simultaneously capturing and converting carbon dioxide directly from air. The selective layer was prepared through a dry-casting process to form a dense layer with appropriate CO2 permeance and selectivity to efficiently generate CO2-enriched air. The reactive layer was prepared through non-solvent induced phase separation (NIPS) method to create a continuous porous structure that houses the photocatalyst. This membrane morphology enhanced the contact efficiency between CO2 and the photocatalyst. The photocatalyst was synthesized from titanium tetrachloride (TiCl4) and copper chloride dihydrate (CuCl2·2H2O) through hydrothermal method and activated in the membrane using UV-light. The copper doping amount on TiO2 was investigated to obtain the optimal photocatalytic activity in converting or regenerating CO2 to CO. The synthesized Cu-doped TiO2 particles were characterized through X-ray diffraction, X-ray photoelectron, and photoluminescence spectroscopies. While the membrane morphology was observed using scanning electron microscopy. Then the gas separation performance of the Janus membranes was analyzed. The CO2 was able to be concentrated in the selective layer and resides in the reactive layer with the photocatalyst with good efficiency. It was found that at 20 wt% loading of Cu-TiO2 yielded 2.21 μmol g−1 hr-1 of CO. This research provides an avenue for potential simultaneous capture and conversion of CO2 from air using Janus membranes.