Insight into the molecular interaction of trace As (III) and As(V) onto the hybrid anion exchanger impregnated with Fe/Mn nanoparticles (HA502P-Fe/Mn)

In this study, a hybrid anion exchanger impregnated with Fe/Mn nanoparticles (HA502P-Fe/Mn) was synthesized via two-step mixed metal oxide precipitation using 50:50 % DI: ethanol as solvent. Trace As(III) and As(V) removal efficiency was comprehensively validated in both equilibrium adsorption isotherms and kinetics. The maximum adsorption capacities of HA502P-Fe/Mn toward As(III) and As(V) were 21,590 and 18,930 mu g/g, respectively. The kinetics of As(III) removal were best predicted (R-2 = 0.986) using a pseudo-second order model (k(2) = 0.001 g/mu g As(III)center dot min). Adsorption mechanisms were further characterized using X-ray absorption spectroscopy (XANES and EXAFS), including a comparison with the density functional theory (DFT) data. The XANES results showed complex redox transformation of the adsorbed As(V) on HA502P-Fe/Mn. The EXAFS spectra indicate predominant inner-sphere complex formation of bidentate mononuclear edge-sharing (E-2) complexes for Mn-As (bond distance 2.94 angstrom), and bidentate binuclear corner-sharing (C-2) complexes for Fe-As (bond distance 3.34 angstrom) on HA502P-Fe/Mn surfaces. Based on the DFT simulation, the obtained 3D structures were optimized, and the bond lengths between Fe-As and Mn-As were comparable with the EXAFS. For practical purposes, the fixed-bed column experiments were fully investigated for both As(III) and As(V) removal using NSF standard 53 test water (As(III) 300 ppb, pH 6.5), including the regeneration. The HA502P-Fe/Mn demonstrated 2X treatable bed volumes (4,300 vs 2,000 BVs) more than the commercially available As selective adsorbent. The experiments demonstrated that HA502P-Fe/Mn is a promising novel adsorbent for As(III) removal owing to its relatively high As adsorption capacity and regenerating ability.

Automated summary

A hybrid anion exchanger impregnated with Fe/Mn nanoparticles (HA502P-Fe/Mn) was synthesized and its efficacy in removing trace As(III) and As(V) was evaluated through isotherms, kinetics, and characterization techniques. The adsorption capacities of HA502P-Fe/Mn for As(III) and As(V) were found to be 21,590 and 18,930 µg/g, respectively. X-ray absorption spectroscopy and density functional theory were used for characterizing the adsorption mechanisms. Fixed-bed column experiments showed that HA502P-Fe/Mn has a higher treatable bed volume compared to commercial adsorbents. Overall, HA502P-Fe/Mn is a promising adsorbent for As(III) removal due to its high adsorption capacity and regenerating ability.