Excess nitrogen in water and greenhouse gases, especially atmospheric carbon dioxide (CO 2) from the rapid development of modern society have become an acute threat to the environment. Herein, novel core/shell structured g-C 3 N 4 @WO 3 memory photocatalyst was fabricated by coating g-C 3 N 4 on the surface of WO 3 nanoparticles and applied in the simultaneous coupling of memory photocatalysts and microbial communities (SCMPMC) for the synergistic removal of microbial nitrate and CO 2 fixation in darkness. The results showed that ∼98.6% of nitrate was removed and ∼17.7% of CO 2 was fixed in darkness by microorganisms in the presence of g-C 3 N 4 @WO 3 memory photocatalyst within 48 h. Besides, the investigation of the mechanism evidenced that g-C 3 N 4 @WO 3 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-C 3 N 4 @WO 3 memory photocatalyst in the dark. Furthermore, microbial community analysis revealed that the g-C 3 N 4 @WO 3 memory photocatalyst increased the relative abundance of denitrifiers (i.e., Acidobacterota , Actinobacteria , Chloroflexi , and Proteobacteria) and CO 2 -assimilating microorganisms (i.e., Pseudomonas), in the treated communities compared with the original community in river sediment, demonstrating the positive effects of g-C 3 N 4 @WO 3 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 CO 2 fixation methods and mechanisms in darkness. [Display omitted] • A novel core/shell structured g-C 3 N 4 @WO 3 memory photocatalyst was fabricated. • Coupled g-C 3 N 4 @WO 3 and microbe for synergistic NO 3 removal and CO 2 fixation in dark. • 98.6% of NO 3 was removed and 17.7% of CO 2 was fixed in dark by the coupling system. • The core/shell memory photocatalyst accelerated electrochemical properties in system. • Enzyme activities and microbial communities were improved by memory photocatalyst. [ABSTRACT FROM AUTHOR]