Mechanism insights into visible light-induced crystalline carbon nitride activating periodate for highly efficient ciprofloxacin removal

The development of suitable and efficient periodate activation methods is currently a hot research topic. In this study, a novel efficient photocatalytic activation strategy using crystalline carbon nitride (CCN) and visible light (Vis) to activate PI for pollutant degradation was proposed. In the CCN/PI/Vis system, 100% ciprofloxacin hydrochloride (CIP) degradation was achieved within 10 min which was much higher than polymerized carbon nitride (PCN)/PI/Vis system. Besides, CCN/PI/Vis system demonstrated outstanding CIP removal activity in a wide range of pH, anions and organic matter, and natural water environments. Mechanistic studies demonstrated that the CCN/PI/Vis system decomposed CIP via nonradical/radical mixing processes dominated by 1O2 and electron transfer. The excellent degradation ability depends on the establishment of an electron cycle among CCN, PI, and CIP. In which, CCN generated photogenerated electrons, CIP acted as an electron donor, and PI served as an electron acceptor. Due to the extended in-plane periodicity and reduced interlayer distance and the formation of ordered electron transport channels caused by the increase of crystallinity, CCN had stronger light absorption and more efficient charge carriers separation and mobility than PCN, resulting in more durable and efficient photogenerated electron and thus much enhanced synergetic photocatalytic and PI activation ability of CCN.