Surface–active bismuth ferrite as superior peroxymonosulfate activator for aqueous sulfamethoxazole removal: Performance, mechanism and quantification of sulfate radical

A surface–active Bi2Fe4O9 nanoplates (BF–nP) was prepared using a facile hydrothermal protocol for sulfamethoxazole (SMX) removal via peroxymonosulfate (PMS). The catalytic activity of BF–nP was superior to other catalysts with the following order of performance: BF–nP > Bi2Fe4O9 (nanocubes) >> Co3O4 > Fe2O3 (low temperature co–precipitation method) > Fe2O3 (hydrothermal method) ∼ Bi2O3 ∼ Bi3+ ∼ Fe3+. The empirical relationship of the apparent rate constant (kapp), BF–nP loading and PMS dosage can be described as follows: kapp = 0.69[BF–nP]0.6[PMS]0.4 (R2 = 0.98). The GC–MS study suggests that the SMX degradation proceed mainly through electron transfer reaction. The XPS study reveals that the interconversion of Fe3+/Fe2+ and Bi3+/Bi5+ couples are responsible for the enhanced PMS activation. The radical scavenging study indicates that SO4− is the dominant reactive radical (>92% of the total SMX degradation). A method to quantify SO4− in the heterogeneous Bi2Fe4O9/PMS systems based on the quantitation of benzoquinone, which is the degradation byproduct of p–hydroxybenzoic acid and SO4−, is proposed. It was found that at least 7.8 ± 0.1 μM of SO4− was generated from PMS during the BF–nP/PMS process (0.1 g L−1, 0.40 mM PMS, natural pH). The Bi2Fe4O9 nanoplates has a remarkable potential for use as a reusable, nontoxic, highly–efficient and stable PMS activator.