CoOOH with a highly negative CB band for visible-light-driven photocatalytic degradation of refractory organic pollutants in peroxymonosulfate system: Enhanced performance and multi-path synergetic mechanisms.

To date, cobalt ions/oxides were proven to be the best peroxymonosulfate (PMS) activator in the homogeneous/heterogeneous system. Interestingly, we found out that CoOOH with a narrow band gap (2.18 eV) and highly negative CB band (-1.73 eV) showed a good potential to be a visible-light-driven photocatalyst for PMS activation. The results turned out that the reaction rate constant of typical refractory contaminants in the Vis-CoOOH/PMS system was about 2-5 times higher than that in the Dark-CoOOH/PMS system. The photogenerated electron (e-) and hole (h+) can react with PMS, which significantly facilitates charge separation. Meanwhile, the e- on the highly negative CB band can react with oxygen to generate O2•-, which simultaneously accelerates the cycle Co(III)/Co(II) to generate radicals (O2•-, •OH and SO4•-) and non-radical (1O2). As a result, multiple ROS was involved in the degradation of contaminants. Especially, O2•- with a longer half-life over 1O2 is identified as the dominant ROS, enhancing the utilization of radicals and the effective attack with contaminants. Therefore, this study first reports the great potential of CoOOH as a visible-light photocatalyst and reveals the multi-path mechanism of the synergistic visible-light-driven photocatalysis and PMS activation for removing refractory contaminants in wastewater.