Oxidation and adsorption of antimony(iii) from surface water using novel Al2O3-supported Fe-Mn binary oxide nanoparticles: effectiveness, dynamic quantitative mechanisms, and life cycle analysis

Antimony(iii) or Sb(iii) contamination in surface waters poses a serious threat to the ecological system and human health, and green and cost-effective technologies are urgently needed to mitigate its toxic effects. We green synthesized a novel oxidative sorbent, referred to as Al2O3-supported Fe-Mn binary oxide nanoparticles (Fe-Mn@Al2O3), and investigated its removal effectiveness and dynamic quantitative removal mechanisms of Sb(iii) at environmentally relevant levels from simulated surface water. Fe-Mn binary oxides (Fe-Mn) were successfully attached on the surface of Al2O3 viaintermolecular hydrogen bonding, resulting in the formation of Fe-Mn@Al2O3 with a larger specific surface area, greater oxidizing reactivity, and more sorption sites compared to Fe-Mn. The resulting composite is mainly composed of FeOOH, Fe2O3, MnO2, and Al2O3. Life cycle assessment (LCA) indicated that the Fe-Mn@Al2O3 synthesis met green chemistry principles. Fe-Mn@Al2O3 at a Fe : Al2O3 molar ratio of 1 : 2 displayed an enhanced Sb(iii) sorption capacity of 272.2 mg g(-1) at pH 6.4 within 48 h. Sorption kinetic data were adequately simulated with the pseudo second-order kinetic model and the intraparticle diffusion model, suggesting that the sorption kinetics were a combination of chemisorption and intraparticle diffusion. The Freundlich isotherm model outperformed the Langmuir model in simulating the sorption isotherm data, which aligns with the heterogeneous surface sorption sites of Fe-Mn@Al2O3. MnO2 in Fe-Mn@Al2O3 oxidized Sb(iii) to Sb(v), whereas FeOOH and Al(2)O(3)acted as adsorption sites towards Sb(iii) and Sb(v). Most importantly, Fe-Mn@Al2O3 still maintained high sorption efficiencies towards Sb(iii) after five consecutive regeneration cycles. The dynamic quantitative removal mechanisms were proposed thereafter. Upon equilibrium, 92.8% of Sb(iii) was sorbed by Fe-Mn@Al2O3, and 94.9% of sorbed Sb(iii) was oxidized to produce Sb(v) and Mn(ii). 59.1% of the formed Sb(v) was adsorbed onto Fe-Mn@Al2O3 and 40.9% of Sb(v) was released into the solution. The new quantitative and mechanistic insights contribute to an improved understanding of the uptake of Sb(iii) by Fe-Mn@Al2O3 in natural and engineered systems, and the results may guide further preparation and application of reactive adsorbents for removal of redox-active contaminants from water.