Shaddock peels derived multilayer biochar with embedded CoO@Co nanoparticles for peroxymonosulfate based wastewater treatment.

The utilization of bio-wastes, such as shaddock peels, is of great significance for sustainable development. Combined with the potential of peroxymonosulfate (PMS) based advanced oxidation process (AOP) in wastewater treatment, a highly efficient functional catalyst, derived from shaddock peels biochar (SPC) and embedded with CoO@Co nanoparticles, i.e. Co-SPC-x(y), was prepared using a facile impregnation-calcination method and used for refractory organics degradation with PMS. The decoration amount of Co and annealing temperature were optimized, and the effects of various reaction factors were investigated. The results indicated that the optimized sample of Co-SPC-10 (900) consisted of multilayer biochar with curly edges and highly dispersed CoO@Co nanoparticles in the range of 20-200 nm, which is in cubic metallic Co and CoO. Moreover, it also possessed a specific surface area of 248.6 m2/g, and exhibited excellent PMS activation ability with ∼100% chlortetracycline hydrochloride (CTC) removal ratio within only 12 min of operation. The Co-SPC-10 (900)/PMS system showed relatively high tolerance for HPO42-, NO3- and SO42-, while the Cl- and HA had considerable effects on it. Mechanism exploration results revealed that both radical and non-radical pathways existed in the Co-SPC-10 (900)/PMS system, in which the multilayered biochar functioned as an electron transfer carrier to facilitate the continuous cycle of Co2+/Co3+ in the CoO@Co nanoparticles by reacting with the absorbed CTC and PMS, resulting in the production of •OH, SO4•-, O2•- and 1O2. Additionally, the Co-SPC-10 (900) also showed good stability and catalytic oxidation performance for various refractory organics.