Promoted microbial denitrification and carbon dioxide fixation via photogenerated electrons stored in novel core/shell memory photocatalysts in darkness.

Abstract

Excess nitrogen in water and greenhouse gases, especially atmospheric carbon dioxide (CO2) from the rapid development of modern society have become an acute threat to the environment. Herein, novel core/shell structured g-C3N4@WO3 memory photocatalyst was fabricated by coating g-C3N4 on the surface of WO3 nanoparticles and applied in the simultaneous coupling of memory photocatalysts and microbial communities (SCMPMC) for the synergistic removal of microbial nitrate and CO2 fixation in darkness. The results showed that ∼98.6% of nitrate was removed and ∼17.7% of CO2 was fixed in darkness by microorganisms in the presence of g-C3N4@WO3 memory photocatalyst within 48h. Besides, the investigation of the mechanism evidenced that g-C3N4@WO3 memory photocatalyst can promote electron transfer in the SCMPMC system. Moreover, key enzyme activities (i.e., NAR, NIR, CAT, and ETSA) were accelerated, indicating that the activities of enzymes within microorganisms could be remarkably enhanced by the continuous release of stored electrons by the g-C3N4@WO3 memory photocatalyst in the dark. Furthermore, microbial community analysis revealed that the g-C3N4@WO3 memory photocatalyst increased the relative abundance of denitrifiers (i.e., Acidobacterota, Actinobacteria, Chloroflexi, and Proteobacteria) and CO2-assimilating microorganisms (i.e., Pseudomonas), in the treated communities compared with the original community in river sediment, demonstrating the positive effects of g-C3N4@WO3 memory photocatalyst on river sediment microbial communities. The results in this study could shed new light on the establishment of promising synergistic microbial nitrate removal and CO2 fixation methods and mechanisms in darkness.