Designing an eco-friendly Co/MnS/S-g-C₃N₄ nanocomposites: revolutionizing photocatalytic dye degradation and antibacterial efficiency

This study utilized an eco-friendly, simple, and cost-effective co-precipitation method to synthesize pure MnS and a series of Co/MnS nanoparticles (NPs) with varying cobalt contents (2%, 4%, 6%, 8%, and 10%). Thiourea was calcined at 552 °C to prepare S-g-C₃N₄ (SCN) nanosheets. The optimal doped NPs were combined with S-g-C₃N₄ to create a series of nanocomposites (10%, 30%, 50%, 70%, and 90%). The materials band gap (Eg) values were determined using Tauc plots. Photodegradation of MB dye was conducted with a UV-Vis spectrophotometer. According to the best of our knowledge, Sulfur-doped graphitic carbon nitride (S-g-C₃N₄) has been used for the first time in combination with cobalt and manganese sulfide nanoparticles to synergistically enhance visible-light photocatalytic activity, enabling efficient degradation of a toxic organic dye methylene blue. Besides photocatalytic treatment, the antibacterial results reveal that (Co /MnS/ S-g-C₃N₄) effectively destroyed bacteria with a synergy effect among cobalt elements, MnS and S-g-C₃N₄. Results indicated that doping 6% cobalt into the MnS lattice enhanced photocatalytic oxidation/reduction. The highest photodegradation performance was observed in 6% Co/MnS@10% SCN nanocomposites, attributed to improved charge separation and reduced charge recombination. The synthesized nano-catalysts maintained significant degradation percentages even after three cycles. The structural morphologies of pure MnS, 6% Co/MnS, S-g-C₃N₄, and 6% Co/MnS@ 10% SCN nanocomposites were analyzed using XRD and FTIR. Kinetic studies of the prepared nanomaterials were conducted to determine their rate constants. The antibacterial performance of the best photocatalysts was tested against Bacillus subtilis and Escherichia coli. The results suggest that composite synthesis and doping enhanced the antibacterial activity of MnS, with the trend for antimicrobial activity being MnS < 6% Co/MnS < 6% Co/MnS@10% SCN. Graphical Abstract: (Figure presented.)