Synergistic effects in ordered Co oxides for boosting catalytic activity in advanced oxidation processes

Synergistic effects are often used in catalyst design for many environmental/energy applications, however, the mechanism and a molecular-level structure to exert maximal synergy effects in catalyzing advanced oxidation processes (AOPs) in wastewater remediation are still unknown. Here, by designing a model perovskite family RBaCo₂O_6-δ (R = lanthanides) with Co⁴⁺ in octahedral coordination (Co4+ oct) and Co³⁺ in pyramidal coordination (Co3+ pyr), we ambitiously confirm the unique synergy of unsaturated (Co3+ pyr) and metallic (Co4+ oct) Co sites for efficient peroxymonosulfate (PMS) activation. Combined X-ray adsorption spectra and theoretical calculations strongly demonstrate that Co3+ pyr and Co4+ oct synergistically contribute to PMS adsorption and O[sbnd]O bond cleavage, and facilitate Co³⁺/Co⁴⁺ redox cycle for radical generation. With appropriate ratio and ordered distribution of Co3+ pyr/Co4+ oct, the Gd_0.5La_0.5BaCo₂O_5.75 exhibits remarkable catalytic activity for pollutant degradation, outperforming all previously reported Co⁴⁺-related oxides. This work may inspire rational design of efficient metal oxide catalysts.