Experimental and theoretical aspects of biochar-supported nanoscale zero-valent iron activating HO for ciprofloxacin removal from aqueous solution.

Ciprofloxacin has been frequently detected in water environment, and its removal has become a significant public concern. Biochar-supported nanoscale zero-valent iron (BC/nZVI) to activate hydrogen peroxide (HO) has many advantages on promoting the removal of organic contaminants. In this paper, the BC/nZVI activating HO degradation of ciprofloxacin was systematically investigated by experimental and theoretical approaches. The morphologies and property analysis showed that nZVI particles distributed uniformly on the biochar surface, which mainly include OH, >CO and COC and CO groups. Different reaction conditions were compared to define the optimal conditions for ciprofloxacin removal in BC/nZVI/HO system. More than 70% of ciprofloxacin was removed in the optimal conditions: acidic condition (pH 3∼4), low doses of HO (20 mM), and temperature of 298 K. The hydroxyl radical (OH) oxidation was the primary pathway in BC/nZVI/HO degradation of ciprofloxacin process. The theoretical calculation indicated that hydrogen atom abstraction (HAA) pathways were the dominant oxidation pathways contributing 92.3% in overall second‒order rate constants (k) of OH and ciprofloxacin. The current results are valuable to evaluate the application of BC/nZVI activating HO degradation of ciprofloxacin and other fluoroquinolone antibiotics in water treatment plants.