Highly selective and efficient removal of arsenic(V), chromium(VI) and selenium(VI) oxyanions by layered double hydroxide intercalated with zwitterionic glycine

In this study, a new strategy for highly selective and extremely efficient removal of toxic oxyanions (Cr(VI), Se(VI), and As(V)) from aqueous solutions using zwitterionic glycine intercalated layered double hydroxide (Gly-LDH) was reported. Hence, to investigate the effect of zwitterionic glycine on the adsorption capacity, selectivity factor and adsorption mechanism of LDHs, two NiAl LDHs intercalated with different inter-layer anions, including NO3- and glycine, were synthesized. The obtained results show that the adsorption capacity and selectivity factor of oxyanions through ion exchange mechanism in NO3-LDH is lower than Gly-LDH. Gly-LDH displayed a selectivity order of Se(VI)< Cr(VI) As(V) for the oxyanions. The enormous adsorption capacity of 731.6 mg g(-1) for As(V) and very high distribution coefficients (K-d) of 5.98 x 10(7) mLg(-1), using a Vim ratio of 2000 mLg(-1), were observed, which are among the highest values reported for As(V) adsorbents. The adsorption kinetic curves for As(V) fitted well with the pseudo-second order model, suggesting a chemical adsorption mechanism via As(V)-NH3+ bonding. For the As(V) (at 40 mg L-1 concentration), the adsorption is exceptionally rapid, showing a 93.5% removal within 30 min, 98.0% removal within 40 min, and 100% removal within 70 min. (C) 2017 Elsevier B.V. All rights reserved.