Carbon-containing materials coupled with sulfidized nanoscale zero-valent iron effective sequestration of U(VI) and their microbial toxicity to bacteria and fungi

This study successfully synthesized g-C 3 N 4 -S-nZVI and rGO-S-nZVI composites for U(VI) sequestration and for the assessment of microbial toxicity to bacteria and fungi. The maximum U(VI) adsorption capacities of g-C 3 N 4 -S-nZVI and rGO-S-nZVI were 662.3   mg/g and 578.0   mg/g at pH = 6.0, respectively. The adsorption kinetics followed the pseudo-second-order model, and the isotherm data were well-described by the Langmuir model. The composites had a good application prospect due to their excellent resistance to ionic interference and favorable recyclability. Analysis via X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS), and extended X-ray absorption fine structure (EXAFS) confirmed that U(VI) removal occurred primarily through chemisorption, with uranyl ions forming a bidentate mononuclear edge-sharing coordination complex on the iron oxide surface. The presence of reactive oxygen species inhibited the reduction of U(VI) to U(IV). Fungal toxicity assays indicated good biocompatibility of g-C 3 N 4 and rGO, while S-nZVI and its composites exhibited significant inactivation of Arthrographis arxii . The inactivation mechanism involves the synergistic effects of physical contact, dissolved Fe 2+ , and ROS generation. Sediment microbial community analysis revealed that S-nZVI caused the greatest disturbance to bacterial communities, while the composites formation mitigated their influence. It is worth noting that g-C 3 N 4 -S-nZVI exhibited the most significant anti-fungal efficacy, whereas rGO-S-nZVI had a relatively small impact on bacterial and fungal communities. This research not only provides an effective method for removing U(VI), but also clarifies the impact of material use on environmental microorganisms.