Preparation and application of magnetic nitrogen-doped rGO for persulfate activation.

A heterogeneous catalyst (M-N-rGO) composed of stability enhanced magnetic iron oxide nanoparticles and nitrogen-doped reduced graphene oxide was synthesized and characterized by SEM, XRD, BET, and XPS. It showed excellent catalytic degradation properties in advanced oxidation technology. In the presence of 200 mg/L catalyst and 135 mg/L persulfate at pH 5, 95% of 10-20 mg/L methylene blue could be degraded in 90 min with the TOC removal efficiency of 50%. The rate constant based on pseudo-first-order kinetics ranged from 0.0227 to 0.0488/min in the temperature range of 15 to 32 °C, and the activation energy was 32.5 kJ/mol. Under the optimal operation conditions, 20 mg/L of 2,4-dichlorophneol (2,4-DCP) could be removed almost completely. EPR analysis showed that sulfate and hydroxyl radicals were responsible for degradation of pollutants, and radical quenching experiments indicated that nonradical pathway also played a role in pollutant removal. And a mechanism for M-N-rGO and persulfate system was elucidated. This catalyst was easy for preparation, low-cost, highly effective, convenient for separation, and could be used effectively for four times through 0.1 mol/L H2SO4 regeneration. It provided a choice for wastewater treatment in practice.