Synergistic catalysis of ozonation and photooxidation by sandwich structured MnO2-NH2/GO/p-C3N4 on cephalexin degradation

Antibiotics such as cephalexin (CLX) are often detected in water and sewage, and advanced oxidation processes (AOPs) are usually the most effective method to degrade them. Currently, the synergy of AOPs has raised lively interest in water and wastewater treatment. Here the sandwiched catalyst of MnO2-NH2/GO/p-C3N4 (MN/GO/CN) is synthesized, in which graphene oxide (GO) acts as "core layer" connecting aminated MnO2 (MnO2-NH2) for catalytic ozonation and proton-functionalized g-C3N4 (p-C3N4) for photocatalysis. The MN/GO/CN combines the AOPs of catalytic ozonation and photocatalysis, initiates hydroxyl radicals 4.2 times the sum of catalytic ozonation and photocatalysis, and achieves the first order kinetics constant of 2.4 × 10-2/s, which is 2.7, 8.1 and 20.1 times that of catalytic ozonation, photo ozonation, and photocatalysis, respectively, and consequently reduces CLX from 1.0 mg/L to below the detection limit within 2.5 min, demonstrating the strong synergism between the AOPs. The sandwich structure enables GO to mediate the electron transfer between p-C3N4 and MnO2-NH2, which not only hinders electron-hole recombination on p-C3N4, but also speeds redox electron cycle on MnO2 to promote the catalytic activity. The simultaneous catalytic ozonation and photocatalysis by sandwiched bifunctional catalyst to obtain synergistic effect will find its broad prospect in water and wastewater treatment.