Designing of Nonmetal-Doped ZnSb₂O₄-Based Composites Toward Enhanced Photocatalytic, Catalytic Performance and Antibacterial Studies

S@ZnSb2O4 and C@ZnSb2O4 composites have been developed by the introduction of nonmetals, that is, C and S as dopants, and they emerge as potential photocatalysts toward photocatalytic dye degradation and catalytic C–C bond formation in solvent-free Knoevenagel condensation reaction and also act as antibacterial disinfectants. Table sugar was utilized to prepare C@ZnSb2O4 composite, while carbon disulfide was used as the S-source to prepare S@ZnSb2O4. SCXRD analysis reveals that ZnSb2O4 crystallizes in tetragonal symmetry (SG: P42/mbc) and is composed of [ZnO6] octahedra and [SbO3E] tetrahedra, where E represents a stereochemically active lone pair. A significant lowering of the band gap energy to 2.75 eV in C@ZnSb2O4 and 2.55 eV in S@ZnSb2O4, respectively, than the band gap of ZnSb2O4 (3.48 eV) has been demonstrated, resulting in enhanced light absorption efficiency and higher ROS generation in composites. Microscopic inspection reveals a change of color to black in the case of C@ZnSb2O4 and to a reddish-brown for S@ZnSb2O4 compared to colorless ZnSb2O4 crystallites. FESEM analysis also confirms a deformed quasi-cubic morphology upon composite formation compared to that of pure ZnSb2O4. Enhanced photocatalytic methylene blue degradation was observed while using S@ZnSb2O4 and C@ZnSb2O4 as photocatalysts compared to the parent compound. A similar trend of enhanced catalytic activity for the Knoevenagel condensation reaction was also observed, where all compounds achieve high yields even at 80 °C under solvent-free conditions. Antibacterial activity against eight pathogenic bacteria, for example, Klebsiella sp., Enterobacter sp., Escherichia coli, Pseudomonas sp., Salmonella sp., Proteus sp., Staphylococcus sp., and Bacillus sp. was investigated by a “disk diffusion method.” The result demonstrated enhanced antibacterial activity of C@ZnSb2O4 against all pathogens, while S@ZnSb2O4 exhibits superior efficiency against E. coli, Klebsiella sp., Proteus sp., and Salmonella sp. compared to pure ZnSb2O4.