Photo-electro-Fenton-like process for rapid ciprofloxacin removal: The indispensable role of polyvalent manganese in Fe-free system

Abstract

The residual ciprofloxacin (CIP) in water seriously menaces the ecological safety and public health. Here, a Fe-free photo-electro-Fenton-like (PEF) system was designed for efficient degradation of CIP in water. A Z-scheme MnO_x/g-C₃N₄ (MCN) nanocomposite with low-cost, large specific surface area and abundant active sites was successfully synthesized as a photoelectric catalyst. The XPS analysis indicated the presence of Mn²⁺, Mn³⁺ and Mn⁴⁺ in the MCN (1:6) composite, and the conversion among polyvalent manganese made the decomposition of H₂O₂ more efficient. Therefore, the manganese ions replaced the Fe element in traditional Fenton system. With the MCN (1:6), the PEF system could also produce O₂^-, OH and h⁺ under the visible light irradiation. The synergetic excitation of multiple active species promoted the rapid decomposition of CIP. Besides, the polyvalent property of manganese oxide resulted in the presence of oxygen vacancies which could improve the electrocatalytic reactivity of the catalyst. Finally, the degradation efficiency of CIP was 96.23% in 120 min and the mineralization efficiency was 80.02% in 240 min.

Keywords: Ciprofloxacin; MnO(x)/g-C(3)N(4); Photo-electro-Fenton-like; Polyvalent manganese; Z-scheme heterojunction.