Ni–O–Ca Interfacial Electron Transfer Channels Engineered From Electroplating Sludge for Ultrafast 4-Nitrophenol Reduction

Abstract

The catalytic reduction of 4-nitrophenol (4-NP), a persistent environmental pollutant faces dual challenges reliance on noble metals and inefficient utilization of hydrogen radicals (H*). Meanwhile, nickel-containing sludge generated by the electroplating industry, classified as hazardous waste has long posed significant disposal conundrums. Herein, we developed a noble metal-free pyroxene-type CaNi(Si₂O₆) catalyst, synthesized from electroplating sludge, that simultaneously addresses these challenges through dynamically reconstructed Ni–O–Ca interface with oxygen vacancies and interfacial electron transfer channels. Ni@Ca-195/20 establishes a self-sustaining catalytic system, achieving a remarkable conversion of 96.8% with 0.1 mM NaBH₄ and 0.05 mg catalyst, while maintaining stability over 31 cycles in low concentration regimes. Integrated characterization combined with catalytic performance evaluation reveals an interfacial electron transfer mechanism: the engineered interface enables in situ reduction of Ni²⁺ generates metallic electron-deficient Ni^δ+ species, enhancing 4-NP⁻ and BH₄⁻ adsorption through dual-site coordination. Oxygen vacancies accelerate BH₄⁻ hydrolysis, while electron transfer channels sustain H* flux via Ca²⁺ modulated charge equilibration. This work establishes a waste-to-functionality paradigm for designing defect-engineered catalysts while advancing sustainable remediation of nitroaromatic pollutants.