Degradation of antibiotic amoxicillin using 1×1 molecular sieve-structured manganese oxide

The kinetics and mechanism of amoxicillin (AMO) degradation using a 1×1 molecular sieve-structured manganese oxide (MnO₂) was studied. The presence of the buffer solution (i.e., NaHCO₃, NaH ₂PO₄ and KH₂PO₄) diminished AMO binding to MnO₂, thus reducing AMO degradation in the pretest; therefore, all other experiments in this study were conducted without the addition of a buffer. Third-order rate constants, second-order on AMO and first-order on MnO₂ increased with elevating pH level (2.81-7.23) from 0.54 to 9.17 M^-2 s^-1, and it decreased to 4.27 M ^-2 s^-1 at pH 8.53 beyond the pka₂ of AMO (7.3). The dissolution of the MnO₂ suspension with and without AMO exhibited a similar trend; that is, Mn²⁺ concentration increased with decreasing pH. However, the dissolution of MnO₂ with AMO was greater than that without AMO, except for the reaction occurring at pH 8.53, partially indicating that MnO₂ acts as an oxidant in AMO degradation. The preliminary chromatogram data display different products with varying pH reaction s, implying that AMO elimination using this 1×1 molecular sieve-structured MnO₂ is by adsorption as well as oxidative degradation. A complementary experiment indicates that the amount of oxidatively degraded AMO increases substantially from 65.5% at 4 h to 95% at 48 h, whereas the AMO adsorbed onto MnO₂ decreases slightly from 4.5% at 4 h to 2.4% at 48 h. The oxidative degradation accounted for more AMO removal than adsorption over the whole reaction course, indicating that the oxidative reaction of AMO on MnO₂ dominated the AMO removal.