Biogenic Photoactive Chalcogenide ZnS and Copper‐Doped ZnS Using Sulfate‐Reducing Desulfococcus biacutus Strain AU08 for Methylene Blue Dye Degradation

ABSTRACT In this study, a sulfate‐reducing bacterium, which is later identified as Desulfococcus biacutus (PQ449043), was isolated from coal mine drainage sample. A cell‐free extract (CFE) of the isolate was used for preparation of photoactive nano‐sized ZnS and copper‐doped Cu@ZnS. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) revealed polydispersed nanoparticles of the size (4–20 nm). Energy dispersive x‐ray spectroscopy (EDAX) and XPS analysis confirmed the presence of element, for example, Cu, Zn, and S, whereas x‐ray diffraction (XRD) analysis confirmed polycrystalline structures with (1 1 1), (2 2 0), and (3 1 1) crystallographic planes. Fourier transform infrared spectroscopy (FTIR) revealed characteristic molecular vibrations. Optical bandgaps were determined as 3.62 eV (ZnS) and 2.96 eV (Cu@ZnS) using the Tauc relation. Photoluminescence spectra showed excitation/emission peaks at 398/614 nm for ZnS and 384/535 nm for Cu@ZnS. The Q max for ZnS and Cu@ZnS was found to be 72.55 and 83.43 mg/g and followed Freundlich model as R 2 value of 0.963 was found to be greater than Langmuir isotherm model. The most widely used dye, methylene blue, degradation was carried out using a white light‐activated chamber with ZnS and Cu@ZnS nanoparticles, generating reactive species for dye decomposition. It is for first time where sulfur metabolizing anaerobic bacterium CFE is used for degradation of the dye. Findings of the study suggest that biofunctionalized nanoparticle particles sorbed dye first, and upon photooxidation, dye was degraded, highlighting prepared chalcogenide potential in textile effluent treatment.