As sunscreens, benzophenones (BPs), are regarded as emerging contaminants, most of studies are focused on removal of 2-hydroxy-4-methoxybenzophenone (BP-3), which, however, has been employed for protecting skin. Another major class of BPs, which is used to prevent UV-induce degradation in various products, is completely neglected. Thus, this present study aims to develop a useful advanced oxidation process (AOP) for the first time to eliminate such a class of BP sunscreens from contaminated water. Specifically, 2,2',4,4'-Tetrahydroxybenzophenone (BP-2) would be focused here as BP-2 is intensively used in perfumes, lipsticks, and plastics for preventing the UV-induced degradation. As monopersulfate (MPS)-based AOP is practical for degrading emerging contaminants, a facile nanostructured cobalt-based material is then developed for maximizing catalytic activities of MPS activation by immobilizing Co nanoparticles onto carbon substrates. In particular, ZIF-67 is employed as a template, followed by the etching and carbonization treatments to afford the thorny nanobox of Co@C (TNBCC) with the hollow-nanostructure. In comparison to the solid (non-hollow) nanocube of Co@C (NCCC) from the direct carbonization of ZIF-67, TNBCC possesses not only the excellent textural features, but also superior electrochemical properties and highly reactive surfaces, making TNBCC exhibit the significantly higher catalytic activity than NCCC as well as Co3O4 in activating MPS to degrade BP-2. Mechanisms of BP-2 degradation are also elucidated and ascribed to both radical and non-radical routes. These advantageous features make TNBCC a useful catalyst of activating MPS in BP-2 degradation.
Keywords: BP-2; Cobalt; Etching; Hollow; MPS activation; Nitrogen-doped carbon.
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