Photogeneration of reactive oxygen species from biochar suspension for diethyl phthalate degradation

Abstract

In this study, the photogeneration of reactive oxygen species (ROS) from biochar suspension was investigated. The characterizations of biochar particles before and after photochemical reactions were analyzed by using FTIR, Raman, XPS and electron paramagnetic resonance (EPR) techniques. It was found that the model pollutant diethyl phthalate (DEP) was efficiently degraded and partially mineralized under UV and simulated solar lights in biochar suspension, with hydroxyl radicals (OH) and singlet oxygen (1O2) as the dominant ROS. EPR coupled with chemical probe methods and free radical quenching studies were used to quantify and elucidate the formation mechanism of OH and 1O2. The results indicated that biochar carbon matrix (BCM) accounted for 63.6%–74.6% of OH and 10%–44.7% of 1O2 formation, while dissolved organic matter (DOM) derived from biochar generated 46.7%–86.3% of 1O2 and 3.7%–12.5% of OH. BCM-bound persistent free radicals (BCM-PFRs) and quinone-like structure of BCM (BCM-Q) were the predominant factors affecting OH and 1O2 formation from BCM under light. Detailed ROS generation pathways are proposed as: (i) DOM from biochar particles contributes to OH and 1O2 formation via light-induced energy and electron transfer processes; (ii) BCM-Q forms excited triplet states (3[BCM-Q]*) under light irradiation and induces the formation 1O2; (iii) UV promotes the formation of BCM-PFRs, which transfer electrons to oxygen to form superoxide anion radical (O2−), further yielding H2O2; and (iv) H2O2-dependent pathways including BCM-PFRs activation and photo-Fenton reaction are primarily responsible for OH production. Furthermore, BCM exhibits the excellent reusability towards DEP degradation during the three cycles under light.