Cobalt/calcium bimetallic oxides based on bio-waste eggshells for the efficient degradation of norfloxacin by peroxymonosulfate activation.

Cobalt-calcium bimetallic oxide (ECCO) was successfully prepared using eggshells and cobalt nitrate, which could be used to activate peroxymonosulfate (PMS) to remove norfloxacin (NOR). The compositional structure and surface properties of the catalysts were explored by various characterization analysis. The degradation efficiency of ECCO was 7.86 and 440 times higher than that of cobalt oxide and calcium oxide, respectively. The prepared ECCO (0.1 g/L) had a high degradation efficiency of over 90% against NOR (10 mg/L, 100 mL) by activating the PMS (0.15 g/L) at a wide pH range of 3.0-9.0 in 35 min. With a NOR removal efficiency of 91.4% after five cycles, the catalyst showed good reusability. The high degradation efficiency of NOR was resulted from enhanced electron transfer capability, the low point of zero charge and diversified reactive oxygen species (ROS). The ROS were identified as SO4•-, •OH and 1O2, which were produced by activating PMS on the active sites of Co and oxygen vacancies. It is the first report of the use of eggshells to synthesize cobalt-calcium bimetallic oxides ECCO for the activation of PMS to eliminate NOR, which is important for the development of green and efficient catalysts.