Electronic and structural perturbations of microporous ZIF-67 nanoparticles and Cr(VI) molecule during adsorptive water decontamination unveiled by experimental and quantum computational investigations.

[Display omitted] • Cr 2 O 7 2− adsorbed on hydrothermally-synthesized mesoporous ZIF-67 nanoparticles. • Exothermic spontaneous monolayer chemical 2nd-order-kinetics Langmuir adsorption. • Cr(VI)/ZIF-67 adsorption synergism with Cr(VI)/Co(II) oxidation-reduction. • DFT shows adsorption-based H-bonding, van der Waals, π-bonding, Cr N coordination. • DFT shows post-adsorption internal destabilization inside each of Cr 2 O 7 2− & ZIF-67. Metal organic frameworks (MOFs) have attracted great attention due to their unique characteristics and accordingly found their way to a multitude of applications including water remediation. Co-based zeolite imidazole framework (ZIF-67) has recently shown interesting adsorptive decontamination capabilities towards metallic and organic water pollutants. Yet, ZIF-67 adsorption mechanism and stability have not been studied enough. In this study, ZIF-67 nanocrystals (∼40 nm) were synthesized and applied as an adsorbent for Cr 2 O 7 2− from water. The Cr 2 O 7 2−−ZIF-67 adsorption mechanism and both of Cr 2 O 7 2− and ZIF-67 consequent structural changes were investigated by analyzing the elemental composition and oxidation states, the adsorption isotherms, kinetics and thermodynamics, and the optimized quantum computational models. The experimental results fitted well with pseudo-second order and Langmuir models, and gave ΔH° and ΔG° of −86.4 ± 17.6 and 12.8 ± 2.4 kJ/mol, respectively, suggesting exothermic spontaneous monolayer chemical adsorption, with maximum capacity of 370 mg/g. Kinetics also show concurrence surface adsorption with intra-particle diffusion within the micropores. XPS results reveal that both Cr6+ and the less-toxic Cr3+ co-existed in Cr 2 O 7 2−−ZIF-67, whilst the Co3+/Co2+ ratio increased, referring to an oxidation–reduction reaction between Cr and Co. Computational analysis concede that the Cr 2 O 7 2−−ZIF-67 high affinity is based on H-bonding between the Cr 2 O 7 2− oxygens and the imidazole hydrogens, van der Waals attraction between the Cr 2 O 7 2− lone pairs and the imidazole π cloud, the Cr 2 O 7 2−−ZIF-67 electron transfer, and Cr N coordination interaction. However, these computations show that the Cr 2 O 7 2−−ZIF-67 interaction causes internal destabilization within each of Cr 2 O 7 2− and ZIF-67, as Cr 2 O 7 2− tends to dissociate and ZIF-67 integrity weakens. [ABSTRACT FROM AUTHOR]