Guest-induced breathing mediated selective alcohol recovery from water by MIL-88A(Fe)

Abstract

The recovery of alcohols from low-concentration aqueous solutions is of great interest due to the wide use of alcohols in industrial processes. In this regard, adsorption-based separation is considered a green and cost-effective alternative towards high-energy demanding processes, which have been traditionally used in the separation of alcohol/water mixtures. Therefore, in this work, the recovery of different alcohols (methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, isobutyl alcohol, and tert-butyl alcohol) from water has been studied based on the adsorptive separation properties of a very flexible metal–organic framework (MOF): MIL-88A(Fe). The adsorption capacity of the material has been studied for different alcohols by the magnetic sustentation technique taking advantage of the paramagnetic iron(III) metal centers in the structure. Interestingly, the competitive adsorption studies between different alcohols aqueous mixtures (methanol/tert-butyl alcohol, methanol/isopropyl alcohol and n-butyl alco-hol/tert-butyl alcohol) revealed the dominance of hydrophobicity of the alcohol over the size and shape factor, resulting in higher preference toward the alcohols with higher number of carbons. In addition, theoretical studies were carried out in order to have a deeper understanding of the adsorptive performance of MIL-88A(Fe), which demonstrated that framework flexibility and diffusion play a key role in alcohol adsorption. PVDF@MIL-88A(Fe) membranes with different MOF loadings were prepared to address the processability aspect of MOF powder. The synergetic contributions from PVDF and MIL-88A(Fe) resulted in a higher adsorption capacity of the composite material compared to the performance of each component, independently. Such systematic and strategic utilization of flexible MOFs can provide a promising platform for challenging alcohol separation from water and environmental remediation technologies.