Low-cost 4-methylpyrazole-based Cu/Ni complexes and their carbon-coated transition metal oxides: Rational synthesis and high-efficiency photocatalytic applications

The development of cost-effective and stable photocatalysts for environmental remediation remains a significant challenge. Herein, we report a one-step strategy to synthesize carbon-coated copper/nickel oxides (Cu-Complex@C and Ni-Complex@C) derived from ligand-engineered transition metal complexes (TMCs). Two novel TMCs, [Cu(4-MPZ)₄]·2Cl (Cu-Complex) and [Ni(4-MPZ)₄Cl₂] (Ni-Complex), were synthesized at room temperature via a one-pot reaction, demonstrating advantages of low cost, mild conditions, and scalability. Controlled pyrolysis of these complexes at 800 °C under N₂ by using γ-polyglutamic acid (γ-PGA) generated carbon-coated transition metal oxides (CTMOs) with well-dispersed Cu₂O/NiO particles embedded in graphitic carbon matrices. Systematic characterization confirmed the derived Ni-Complex@C, which exhibited superior UV-light-driven photocatalytic activity, achieving 99.06 % for gentian violet (GV) degradation within 240 min, respectively, outperforming commercial TiO₂ (68.50 %) due to synergistic effects of narrowed bandgap (1.22 eV) and suppressed electron-hole recombination. Quenching and electron spin resonance (ESR) spin trapping experiments analysis identified superoxide radical (·O₂⁻) as dominant reactive species. This work provides a universal pathway to design high-performance photocatalysts from earth-abundant precursors, bridging molecular-level coordination chemistry with macroscopic catalytic functionality for sustainable pollutant degradation applications.