Mechanisms of tetracycline hydrochloride degradation via persulfate activation by mesoporous carbon: the dual function of superoxide radical

Abstract

Carbon-based material is one of crucial activators in advanced oxidation processes (AOPs), however, some mysteries in the activation mechanisms are still awaiting researchers to reveal. In this study, mesoporous carbon (MC) was prepared by manganese oxide template method, which exhibited a satisfied performance for persulfate (PS) activation to degrade tetracycline hydrochloride (TCH). We found that TCH removed in the MC/PS system was primarily via an oxidation degradation pathway (90.4 %) rather than adsorption pathway (9.6 %). However, the excellent adsorption ability (51.4 % by MC alone) is necessary in a heterogeneous activation system, for the reason that TCH absorbed on the MC surface is not only beneficial to electrons transfer from TCH to reactive oxygen species (ROS) generated on the MC surface but enhance the TCH removal via an electron transport pathway (ETP) among TCH, MC, and PS. Therefore, an adsorption catalytic model named Langmuir-Kinetic pseudo second order coupled model was established (R2 = 0.918) to better evaluate the kinetic characteristics of TCH degradation process. Experiment results revealed that TCH degradation in the MC/PS system was dominated by ETP while radical dotO2−, 1O2, radical dotOH, and SO4radical dot− played a second role. Specifically, radical dotO2− played a dual function role: as both 1O2 precursor and essential electron shuttle in TCH degradation through ETP. Furthermore, only some organic functional groups such as –COOH and π–π* of MC were involved in ROS generation. This discovery would provide some new insights in the carbon materials based AOPs in organic wastewater purification.