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±0.1μM of SO4- was generated from PMS during the BF-nP/PMS process (0.1gL-1, 0.40mM PMS, natural pH). The Bi2Fe4O9 nanoplates has a remarkable potential for use as a reusable, nontoxic, highly-efficient and stable PMS activator.