“Sonochemically synthesized Ag(I) and Ni(II) schiff base complexes as efficient visible-light photocatalysts for dye degradation with DFT insights.”

Water pollution caused by synthetic dyes is a pressing environmental concern, necessitating the development of highly efficient and reusable photocatalysts. Herein, we report the sonochemical synthesis and comprehensive characterization of nanoscale Ag(I) and Ni(II) Schiff base complexes derived from an isatin–sulfathiazole ligand (H₂L). The complexes were characterized by elemental analysis, molar conductance, magnetic susceptibility, FT-IR spectroscopy, ¹H NMR spectroscopy, UV–visible spectroscopy, XRD, TGA, and mass spectrometry. The obtained results confirmed their nanoscale dimensions, non-electrolytic behavior, and proposed tetrahedral geometries. TGA further assessed thermal stability and the presence of coordinated and lattice water molecules, with thermodynamic parameters calculated via the Coats–Redfern method. Complementary density functional theory (DFT) calculations provided detailed electronic and structural insights, supporting the proposed geometries and revealing reduced HOMO–LUMO energy gaps, distinct charge distribution patterns that highlight electron-rich and electron-deficient regions, and enhanced thermodynamic stability. Optical studies further confirmed the semiconducting nature of the synthesized compounds, consistent with their observed photocatalytic behavior. Both complexes exhibited remarkable photocatalytic performance under visible light, achieving Methylene Blue (MB) degradation efficiencies of 95.3% for the Ag(I) complex and 91.7% for the Ni(II) complex under optimized conditions (pH 11, 30 mg catalyst per 100 mL, and 10 ppm MB). Kinetic studies confirmed pseudo-first-order behavior, while recyclability tests demonstrated excellent stability and reusability over four consecutive cycles. These results highlight the potential of sonochemically synthesized Schiff base complexes as efficient, durable, and eco-friendly photocatalysts for wastewater treatment applications.