Activation of sulfite via zero-valent iron-manganese bimetallic nanomaterials for enhanced sulfamethazine removal in aqueous solution:Key roles of Fe/Mn molar ratio and solution pH

Abstract

In this study, the nano zero-valent iron-manganese (NZVIM) bimetallic materials with different Fe/Mn molar ratios were synthesized by one-step liquid-phase reduction method and utilized to activate sulfite for the elimination of sulfamethazine (SMT) at different pH (3.0, 6.0, and 8.0). It was found the optimum Fe/Mn molar ratio was different under different solution pH conditions. The sulfite could be efficiently activated by nano zero-valent iron (NZVI) and NZVIM with Fe/Mn = 2:1 and 1:1 to remove SMT with a high removal efficiency at pH 3.0. While the NZVIM/sulfite system corresponding to Fe/Mn ratios of 1:1 and 2:1, respectively, could degrade SMT more efficiently than the NZVI/sulfite system at neutral and alkaline conditions. The improvement of degradation efficiency of SMT may result from the addition of Mn element. On the one hand, the ability of direct electron transfer inside the NZVIM particles might be enhanced, and on the other hand, Mn(II) promoted the conversion of Fe(III) to Fe(II), thereby enhancing the ability of free radical generation. Besides, electron spin resonance (ESR) analysis and the radical quenching experiments confirmed that •OH was the primary radicals that responsible for SMT elimination. Then the intermediates of SMT were identified by high-performance liquid chromatography mass spectrometry (LC-MS) and possible degradation pathways were proposed. Additionally, the developmental toxicity and bioaccumulation factors of SMT and its possible intermediates were predicted by quantitative structure–activity relationship (QSAR) analysis. In addition, the effect of some typical coexisting components (Cl−, HCO3−, HA) in water was examined. The effectiveness of NZVIM/sulfite system for SMT removal in two actual water matrices (i.e., tap water and river water) was investigated. These results indicated that the NZVIM/sulfite system is viable and effective for the elimination of SMT in water, and the Fe/Mn molar ratio and solution pH are two critical factors influencing the performance of the NZVIM/sulfite system.