Efficient activation of peroxymonosulfate for catalytic degradation of organic pollutants by simultaneously using low-level cobalt ions and calcium carbonate micro-particles

An efficient catalytic system was developed to remove various organic pollutants by simultaneously using low-level cobalt ions, calcium carbonate micro-particles and peroxymonosulfate (PMS). A simple base-induced precipitation was used to successfully loaded Co-centered reactive sites onto the surface of CaCO3 microparticles. Under optimal conditions at 25 °C, 10 mg/L methylene blue (MB) could be completely degraded within 10 min with 480 µg/L Co2+, 0.4 g/L CaCO3 microparticles (or 0.4 g/L Co@CaCO3) and 0.1 g/L PMS. The MB degradation followed the pseudo first order kinetics with a rate constant of 0.583 min−1, being 8.3, 11.5 and 53.0 times that by using Co-OH (0.07 min−1), Co2+ (0.044 min−1) and CaCO3 (0.011 min−1) as the catalyst, respectively. It was confirmed that there was a synergistic effect in the catalytic activity between Co species and the CaCO3 particles but the major contributor was the highly dispersed Co species. When Co2+-containing simulated electroplating wastewater was used as the Co2+ source, not only the added MB was also completely degraded within 5 min in this catalytic system, but also the coexisting heavy metal ions were substantially removed. The presently developed method was applied to simultaneously treat organic wastewater and heavy metals wastewater. The present method was also successfully used to efficiently degrade other organic pollutants including bisphenol A, sulfamethoxazole, rhodamine B, tetrabromobisphenol A, ofloxacin and benzoic acid. A catalytic mechanism was proposed for the PMS activation by Co@CaCO3. The surface of CaCO3 particles favors the adsorption of Co2+. More importantly, the surface of CaCO3 particles provides plentiful surface -OH and -CO32+, and these surface groups complex with Co2+ to produce more catalytically active species such as surface [CoOH]−, resulting in rapid Co2+/Co3+ cycling and electron transfer. These interactions cause the observed synergistic effect between Co species and CaCO3 particles in PMS activation. Due to good cycle stability, strong anti-interference ability and wide universality, the new method will have broad application prospects.