Kinetics and mechanism of organic pollutants degradation with cobalt–bicarbonate–hydrogen peroxide system: Investigation of the role of substrates

The kinetics and mechanism of a simple system, Co2+–HCO3−–H2O2 for degrading highly stable organic pollutants have been reported. Fast and versatile decolorization of organic dyes was observed in an aqueous solution containing 10 mM NaHCO3, 10 μM Co2+ ions and 10 mM H2O2, while the degradation rate of p-nitrophenol and 2,4-dinitrophenol was very slow. From cyclic voltammetry and UV–vis spectra, it was found that different complexes between Co2+ ions and methylene blue (MB) were formed in HCO3− solution, and being confirmed by photoluminescence probing and electron spin resonance spin-trapping technologies, the 1:1 complex [CoII(HCO3−)(MB)]+ was more efficient in catalyzing decomposition of H2O2 into OH radicals. The other tested pollutants also played an important role in the rate of OH radicals production in the system. Based on the kinetic observations of MB decolorization, a possible mechanism was proposed.

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► Co2+–HCO3−–H2O2 system efficiently catalyzes degradation of highly stable organic dyes.
► The rate of OH radicals production increases after Co2+–methylene blue complexes formation.
► The tested other pollutants play an important role in OH radicals production in the system.