Hollow multi-shelled CoO as nanoreactors to activate peroxymonosulfate for highly effective degradation of Carbamazepine: A novel strategy to reduce nano-catalyst agglomeration.

Reducing the agglomeration of nano-catalysts to retain the active catalytic sites is crucial for the advanced oxidation processes (AOPs) of peroxymonosulfate activation in wastewater treatments. Herein, CoO hollow multi-shelled structures (HoMSs) were successfully prepared as the nanoreactors to reduce the agglomeration of nano-catalysts in catalytic reaction. Compared with single-shelled and double-shelled CoO HoMSs, triple-shelled CoO HoMSs (TS-CoO) exhibited best catalytic performance and the carbamazepine (5 mg L) degradation reached 100% within 30 min. The hollow multi-shelled structures showed a significant role in reducing the agglomeration of catalysts. The value of hydrodynamic diameter/true particle size of TS-CoO was 1.58, which meant TS-CoO could be regarded as a single dispersion or two together in aqueous solution. The shells of TS-CoO supported each other and outer shells could protect the inner ones, hence the stability increased. Besides, the hollow cavity between shells reduced the mass diffusion resistance and increased the contact of reactants with active sites. Mechanism studies showed sulfate radicals (SO) played a leading role in the degradation of carbamazepine. This work provided an effective way to reduce the agglomeration and retain the active sites of cobalt-based catalysts in AOPs, so as to balance the conflict between the reactivity and stability of nano-catalysts.