Synergistic photocatalytic reduction of CO2 enabled by MIL-101(Cr)-TiO2-polyimide nanocomposite membranes

Converting CO 2 into valuable chemicals through photocatalytic reduction is a promising method to achieve carbon neutrality. Nonetheless, the insufficient active sites of photocatalysts lead to low CO 2 reduction efficiency and product selectivity. Taking advantage of the synergistic effect of photocatalytic heterostructures is an effective way to overcome this shortcoming. Here, metal-organic frameworks (MIL-101(Cr))-titanium dioxide (TiO 2 ) staggered gap (type II) heterojunctions were deposited on different woven polyimide (PI) substrates (MIL-101-TiO 2 PI hybrid photocatalysts) via atomic layer deposition and hydrothermal reaction for CO 2 photoreduction. The immobilized photocatalysts on the PI substrates resolved the challenge of separating powdered photocatalysts from liquid products or reactants. The prepared MIL-101(Cr)-TiO 2 PI hybrid photocatalysts displayed synergistic photocatalytic reduction performance towards CO 2 by separating the photogenerated charge carriers. The charge transfer between the heterojunctions and the substrates extended the lifetime of the excited electrons and holes, thereby generating synergy effects and promoting the CO 2 reduction yield. The rougher surface and higher specific area of the PI felt enabled higher loadings of heterojunctions compared with other woven structures of the fabric and mat. As a result, MIL-101(Cr)-TiO 2 PI felts showed multiple reduction pathways over the heterostructures and enhanced photocatalytic performance, with the main product yields of 29.6, 9.2, and 0.8 μmol g −1 h −1 for CO, CH 4 and H 2 , respectively. Meanwhile, CO selectivity of the MIL-101(Cr)-TiO 2 PI felt reached as high as 75 %. This study provides significant insights into the role of the substrate in flexible and immobilized hybrid photocatalysts with synergistic performance to achieve enhanced CO 2 reduction yield.