Kinetics of PMS activation by graphene oxide and biochar.

Carbon-based materials have been studied as metal-free catalyst for persulfate activation. At present, the activation performance of carbon materials for persulfate is usually characterized by the removal efficiency of organic pollutants. However, the kinetics of persulfate activation by carbon materials has not been investigated. In this study, the kinetics of peroxymonosulfate (PMS) activation by reduced graphene oxide (RGO) and sludge-derived biochar (BC) were investigated. The experimental results showed that the kinetics of PMS activation followed the two-phase kinetic model (fast phase (a1) and slow phase (a2)). In the absence of organic pollutants, the a1 and a2 were calculated to be 0.320 and 0.0471 min-1 for BC, respectively, and 0.322 and 0.0850 min-1 for RGO, respectively. Based on the characterization of BC and RGO, it can be concluded that the fast phase was mainly due to the formation of surface-bound active species. Competitive adsorption between PMS and targeted pollutants decreased the kinetic constant for the first phase (a1) and the kinetic constant for the second phase (a2) for both BC and RGO. The value of a1 and a2 increased for BC after the addition of phenol, due to the enhanced PMS activation by surface adsorbed phenol. The increase of phenol concentration decreased slightly the value of a1 and a2. The increase of PMS concentration increased significantly the value of a1 and a2. The decrease of a1 and a2 in repeated use of carbon materials could be due to the decrease of oxygen-containing functional groups and defect intensity.