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

[Display omitted] • Synergistic effects of Co3+ pyr and Co4+ oct were studied for PMS activation. • A model oxide system LnBaCo 2 O 6- δ with tunable Co3+ pyr and Co4+ oct were prepared. • Ordered distribution of active sites in catalyst exerted maximal synergistic effects. • XAS spectrum and DFT calculation were performed to demonstrate the reaction mechanism. • Co3+ pyr contributes to PMS adsorption and Co4+ oct facilitates charge exchange. 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 R BaCo 2 O 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 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 0.5 La 0.5 BaCo 2 O 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. [ABSTRACT FROM AUTHOR]