Bromate inhibition by reduced graphene oxide in thermal/PMS process

Bromate (BrO₃^-), as a contaminant producing from bromide (Br^-) oxidation, has been revealed for generation in sulfate radical involved processes. In this work, reduced graphene oxide (rGO) was firstly applied to inhibit the formation of BrO₃^- in thermally activated peroxymonosulfate (thermal/PMS) treatment. In the presence of 5-35 mg/L rGO, the decomposition rate of PMS was slightly increased from 0.0162 ± 0.0013 min^-1 to 0.0200 ± 0.0010 min^-1, corresponding to removal rate of target pollutant increasing from 0.0157 ± 0.0012 min^-1 to 0.0204 ± 0.0022 min^-1. This suggested the decay of PMS, the concentration and distribution of radicals were not influenced dramatically by the addition of rGO, which was partly supported by the almost unchanged HPLC chromatograms as compared with that in the absence of rGO. However, the produced BrO₃^- was significantly lowered by 67%-100% with the addition of rGO in a wide range of pH at 5-9 and activation temperature at 60-80 °C. Moreover, a quick reduction of hypobromous acid (HOBr) to Br^- was achieved with addition of rGO at room temperature, whilst no abatement of BrO₃^- and Br^- was observed in the same conditions. Therefore, masking HOBr was probably the role of rGO on bromate inhibition in thermal/PMS process. Because HOBr is a requisite intermediate for BrO₃^-, the inhibition effect of rGO is likely irrelevant of oxidation processes, which was inevitably showed by the good performance of rGO on BrO₃^- suppress in ozonation. Therefore, the addition of rGO in tens of mg/L is a promising measure to avoid the formation of unwanted bromine species in advanced oxidation processes.