Magnetic carbon-supported cobalt derived from a Prussian blue analogue as a heterogeneous catalyst to activate peroxymonosulfate for efficient degradation of caffeine in water.

Extensive usage of caffeine (CAF) as a medicine and additives in beverages has led to increasing presence of CAF in wastewater and even drinking water. To remove CAF, peroxymonosulfate (PMS), is adopted to generate sulfate radical to degrade CAF in water. To facilitate PMS activation, a magnetic carbon-supported cobalt (MC/Co) hybrid material is prepared via carbonization of a cobalt-containing Prussian blue analogue framework (Co3[Co(CN)6]2). The resultant MC/Co contains Co and Co3O4 nanoparticles supported on a carbon matrix, making it an attractive magnetic catalyst to activate PMS for degrading CAF. MC/Co-activated PMS was shown to degrade CAF much more effectively than PMS and Co3O4-activated PMS. Parameters affecting CAF degradation by MC/Co-activated PMS were also examined, including MC/Co and PMS concentrations, temperature, pH, and salt. Effects of radical quenchers were also examined to provide insights into the CAF degradation mechanism. MC/Co-activated PMS was much more favorable at higher temperatures than ambient temperature, and under neutral conditions. Nevertheless, the presence of concentrated NaCl noticeably hindered CAF degradation. Through examining effects of radical quenchers, the mechanism of CAF degradation by MC/Co-activated PMS was attributed primarily to sulfate radicals and hydroxyl radicals to a lesser extent. The degradation products of CAF by MC/Co-activated PMS were also identified and a possible degradation pathway is proposed. MC/Co can activate PMS over multiple cycles without loss of catalytic activity. These findings demonstrate that MC/Co, simply prepared from simple carbonization of Co3[Co(CN)6]2 can be a promising heterogeneous catalyst for activating PMS to degrade CAF.