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

Abstract

The composition of SrCu_xO mixed metal oxides (MMOs) was engineered via varying the amount of copper relative to strontium. As-synthesized SrCu_xO were highly active for degrading methyl orange (MO) pollutant at dark ambient conditions without the aid of other reagents. The catalytic activity of SrCu_xO 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 ($\cdots {Cu}^{2+}\overset{+{e}^{-}}{\to }{Cu}^{+}\overset{-{e}^{-}}{\to }{Cu}^{2+}\cdots$) from MO to dissolved O₂, inducing the consecutive generation of reactive oxygen species, which resulted in MO degradation as evidenced by radical trap** 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.