Bioderived sludge/biochar (BS/BSC) coupled with TiO2 to construct BS/BSC/TiO2 composite for stimulating photocatalytic CO2 reduction

In this work, low-cost bio-sludge (BS) and bio-sludge-derived biochar (BSC) were employed as co-catalysts to fabricate BS/TiO 2 and BSC/TiO 2 composites for photocatalytic CO 2 reduction. The incorporation of BS and BSC enhanced CO 2 utilization, and promoted the separation of photogenerated charge carriers. Photocatalytic CO 2 reduction experiments were performed in a continuous-flow photoreactor under UV-visible light irradiation. Among the BSC/TiO 2 photocatalysts, the 3% BSC5/TiO 2 synthesized at 500 °C exhibited the highest activity, producing 9.175 μmol g −1 of CO and 5.56 μmol g −1 of CH 4 under lower light intensity, corresponding to 4.23- and 2.63-fold enhancements over pristine TiO 2 , respectively. The improved photocatalytic performance was attributed to the conductive carbon matrix and metallic constituents of BSC, which facilitated charge separation and suppressed electron–hole recombination. A comparative evaluation of BS and BSC-based composites revealed that BS/TiO 2 favored CO production, whereas BSC/TiO 2 promoted the formation of both CO and CH 4 . The effect of different sacrificial agents, including H 2 , and methanol, were also investigated. Under CO 2 hydrogenation conditions, the BS/TiO 2 composite achieved a CO yield of 14.15 μmol g −1 , which was 10.26 times higher than that of the BSC5/TiO 2 composite. Furthermore, feed mixtures containing H 2 or methanol significantly enhanced CO production by serving as proton sources and effective hole scavengers. Both composites also exhibited excellent stability during prolonged continuous-flow operation, maintaining consistent CO and CH 4 production over multiple reaction cycles. Overall, these findings demonstrate that bio-sludge and its derived biochar are sustainable, low-cost, and efficient co-catalysts for enhancing solar-driven photocatalytic CO 2 conversion into value-added fuels.