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) similar to Bi2O3 similar to Bi3+ similar to Fe3+. The empirical relationship of the apparent rate constant (k(app)), BF-nP loading and PMS dosage can be described as follows: k(app) = 0.69[BF-nP](0-6)[PMS](0.4) (R-2 = 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 center dot- is the dominant reactive radical (>92% of the total SMX degradation). A method to quantify SO4 center dot- in the heterogeneous Bi2Fe4O9/PMS systems based on the quantitation of benzoquinone, which is the degradation byproduct of p-hydroxybenzoic acid and SO4 center dot-, is proposed.