Water-alcohol adsorptive separations using metal-organic frameworks and their composites as adsorbents

This review gives an overview of the synthetic strategies used for designing metal-organic frameworks (MOFs) and MOFs-based composites studied for water-alcohol separation applications. It shows that various organic linkers, including flexible, hydrophobic and zwitterionic ligands have been used for the synthesis of MOFs with flexible frameworks, highly hydrophobic MOFs as well as MOFs with unique electronic distribution in the pores. Due to their specific structural properties, all these materials show different adsorption behavior in the presence of water and alcohols, being able to separate water-alcohol mixtures. Several studies focused on using microporous MOFs to separate water-alcohol mixtures based on the difference in the molecular size of water and alcohols. Combining MOFs with organic polymers into composites is viewed as a viable alternative to tackle some problems that powdered MOFs may cause in industrial applications. The research so far shows that MOFs embedded in polymer matrixes have led to improved efficiency and mixture permeability when comparing with the performance of pristine polymer membranes. Nevertheless, the design of membranes with high permeability, selectivity and stability is difficult due to the swelling of the polymer matrix as well as the difficulties in retaining the matrix integrity while increasing the MOF loading.