Three-dimensional calcium alginate hydrogel beads-entrapped g-C3N4/Ag composites for enhanced photocatalysis under LED irradiation

Herein, g-C3N4/Ag composites entrapped in three-dimensional (3D) reticulated calcium alginate hydrogel beads (g-C3N4/Ag/CAHBs) were prepared by a simple self-polymerization method. Under light-emitting diode (LED) irradiation, the g-C3N4/Ag/CAHBs could efficiently activate peroxymonosulfate (PMS) through the coupled effect of g-C3N4 and the abundant C=O groups in the CAHBs to degrade rhodamine B (RhB). The system of g-C3N4/Ag/CAHBs and PMS showed excellent photocatalytic efficiency for RhB degradation, and could remove 99.2 % of RhB within 60 min. Moreover, its photocatalytic performance was almost unaffected by the initial solution pH and the presence of various anions (Cl−, SO42−, SO32−, HPO42−, HCO3−, NO3−). In addition, the g-C3N4/Ag/CAHBs could be easily recovered from an aqueous solution and recycled, and presented high stability after five cycles. The results of active species scavenging experiments and electron spin resonance spectroscopy indicated that the active species, including 1O2, •O2−, SO4•−, and •OH, played an important role in degrading RhB. Furthermore, g-C3N4/Ag/CAHBs removed ciprofloxacin in the presence of PMS and LED irradiation over a wide pH range. Moreover, g-C3N4/Ag/CAHBs exhibited satisfactory antibacterial properties against Staphylococcus aureus and Escherichia coli under LED irradiation. Investigations into the antibacterial mechanism revealed that the treatment with g-C3N4/Ag/CAHBs could damage the cell membrane and enhance the levels of intracellular reactive oxygen species, resulting in a reduced survival rate. In summary, this work provides a simple strategy to prepare green 3D hydrogel beads for removing organic contaminants.