Engineering SrCuxO composition to tailor the degradation activity toward organic pollutant under dark ambient conditions.

The composition of SrCuxO mixed metal oxides (MMOs) was engineered via varying the amount of copper relative to strontium. As-synthesized SrCuxO were highly active for degrading methyl orange (MO) pollutant at dark ambient conditions without the aid of other reagents. The catalytic activity of SrCuxO demonstrated a reverse-volcano relationship with copper content. Copper-rich MMOs (SrCu2O) exhibited the highest degradation activity for MO by far and degraded ca. 96% MO within 25 min. MO degradation over SrCu2O was a surface-catalytic reaction and fitted pseudo-first-order reaction kinetics. The contact between MO molecules and catalyst surface initiated the reaction via the catalytic-active phase (Cu+/Cu2+ redox pair), which serves as an electron-transfer shuttle ([Formula: see text]) from MO to dissolved O2, inducing the consecutive generation of reactive oxygen species, which resulted in MO degradation as evidenced by radical trapping experiment. XPS and XRD analysis revealed that active phases in SrCu2O materials underwent irreversible transformation after reaction, contributing to the observed deactivation in the cycling experiment. The observations in this study demonstrate the significance of chemical composition tailoring in catalyst synthesis for environmental remediation under dark ambient conditions. Graphical abstract.