Breaking the pH limitation by Mo modulated amorphous medium-entropy alloys as efficient advanced oxidation catalysts

Abstract

The inherent limitations of conventional metallic glass (MG) catalysts in adapting to complex water environments over a wide pH range stem from their monotonic active site, which is incapable of simultaneously fulfilling multiple functional purposes. Herein, we overcome the narrow range of pH adaptability of existing advanced oxidation catalysts by designing a series of quinary FeCoNiMoB medium-entropy alloys in amorphous structure (referred to as A-MEAs). In particular, the slight modulation of Mo to obtain Fe₂₅Co₂₅Ni₂₅Mo_0.5B_24.5 A-MEA with highest Gibbs free energy achieves a complete degradation of pollutants both at acidic and alkaline conditions in 10 min. This performance surpasses that of most traditional MGs and high-entropy alloys (HEAs) constrained by the composition limits for entropy maximization. Further insights reveal that in both cases, the multi-site synergistic effects of Mo-driven fast electron transfer of M (M = Fe, Co, and Ni) as active sites and surface-mediated reaction cycles of M^2 +/M³⁺ contribute to the accelerated transformation of reactive oxygen species (ROS) from peroxydisulfate (PDS) and the remarkable catalytic performance of A-MEAs. The radical evolution demonstrates that SO₄·‾ plays a major role under acidic conditions while O₂·‾ dominates the catalytic reactions under alkaline conditions. Accordingly, this work aims to fill the gap of A-MEAs for catalytic oxidation of organic pollutants and provide the design strategy of novel MEA catalysts.