Comparison of metoprolol degradation by FeIII-NTA modified Fenton-like reaction in the absence and presence of manganese: Efficiency and intermediates

•Metoprolol degradation by FeIII-NTA/H2O2 was enhanced in the presence of MnII.•Rapid degradation of metoprolol was obtained by FeIII-NTA/H2O2-Mn at pH 4.0-8.0.•FeIII-NTA/H2O2-Mn led to more efficient degradation of metoprolol and intermediates.•Degradation pathways of metoprolol were proposed.

The degradation of metoprolol in aqueous solutions by traditional Fenton-like reaction (FeIII/H2O2), and FeIII-NTA modified Fenton-like reaction (FeIII-NTA/H2O2) in the absence and presence of MnII (FeIII-NTA/H2O2-Mn) have been investigated. The results show that FeIII-NTA/H2O2 is able to degrade metoprolol at initial neutral pH. In particular, the presence of MnII greatly improved the degradation rate of metoprolol by FeIII-NTA/H2O2 over a wide pH range of 4.0-8.0. Under the same conditions, the degradation rate constants of metoprolol (k) obtained in FeIII-NTA/H2O2-Mn system were typically 7-9-fold larger than those obtained in FeIII-NTA/H2O2 system. The involved reactions in FeIII-NTA/H2O2-Mn system were proposed on the basis of important parameters analysis including ferrous ion concentration, dissolved oxygen (DO) concentration, and the quenching experiments for hydroxyl radial (HO) and superoxide anion radical (O2−). Several intermediates have been identified by mass spectrometry. Our results suggest that the degradation of metoprolol in both FeIII-NTA/H2O2 and FeIII-NTA/H2O2-Mn systems were caused by HO attack. The degradation pathways of metoprolol were proposed on the basis of the identified intermediates. FeIII-NTA/H2O2-Mn system led to more efficient degradation of metoprolol and its intermediates.

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