Photoelectron-Promoted\nSulfate Reduction for Heavy\nMetal Removal without Organic Carbon Addition

Sulfate-reducing microorganisms (SRMs) show promise for\nheavy metal\nremoval from contaminated environments, but their scalability is limited\nby reliance on organic carbon, sludge formation, and CO<sub>2</sub> emissions. This study investigates using photoelectrons from biogenic\n(Bio-ZnS) and abiogenic (Abio-ZnS) sphalerite nanoparticles to enhance\nthe activity of Desulfovibrio desulfuricans G20 (G20) for sulfate reduction and lead removal without organic\nsubstrates. Both Abio-ZnS and Bio-ZnS NPs promote sulfate reduction\nand energy production in G20 cells under illumination without the\naddition of organic substrates, with Bio-ZnS achieving 1.6 times greater\nsulfate reduction and 3.1 times higher ATP production compared to\nAbio-ZnS. This superior performance of Bio-ZnS NPs is due to their\nwider band gap, higher photoconversion efficiency, lower charge-transfer\nresistance, and closer proximity to cells, which enable more efficient\nphotoelectron uptake, enhanced intracellular electron transfer, and\nreduced energy consumption for motion and filamentation. The uptake\nof photoelectrons also promotes G20s resistance to high Pb<sup>2+</sup> concentrations through enhanced PbS precipitation, biofilm formation,\nenzymatic detoxification, and Pb<sup>2+</sup> efflux, thus improving\nlong-term and cyclic lead removal by G20 under substrate-depleted\nconditions. This approach harnesses solar energy, reduces reliance\non organic substrates, and lowers costs and CO<sub>2</sub> emissions,\noffering a sustainable solution for utilizing SRMs in bioremediation.