Enhancing photocatalytic performance of bismuth oxybromide via algae-derived hydrochar

Paraben pollutants are frequently detected in aquatic environments and pose potential risks to ecosystems and human health, particularly benzyl paraben (BzP), highlighting the development of green and efficient removal technologies. Algae-derived hydrochar (HC) possesses the merits such as abundant biomass availability, intrinsic carbon fixation, and facile synthesis, and shows considerable potential for catalyst modification. Herein, HC produced from microalgae Chlorella was composited with bismuth oxybromide (BiOBr, BOB) to form HC/BOB material with a hierarchical flower-like nanosheet architecture and an intimate interface between HC and BOB. Compared with BOB, HC/BOB composites displayed broadened light absorption and improved charge separation, leading to enhanced photocatalytic degradation of BzP, with 5%HC/BOB exhibiting the highest performance (>94% removal within 40 min). Although water matrix factors (pH, co-existing of different ions or HA) affected the photocatalytic performance of HC/BOB composite, the removal efficiencies of BzP remained above 69.4%. Radical-trapping and EPR results identified superoxide radicals (•O2-) as the dominant reactive species, followed by singlet oxygen (1O2) and photogenerated holes (h⁺); HC modification facilitated the generation of •O2- and 1O2, thereby accelerating BzP degradation. This work provides a promising strategy for the valorization of algae-derived HC and enhancement of BOB-based photocatalytic systems.