Porous Liquids Open New Horizons: Synthesis, Applications, and Prospects

Conspectus Though the idea of liquids with accessible porosity seems counterintuitive, porous liquids (PLs) have indeed demonstrated themselves to hold great promise in versatile fields, thus arousing great attention and interests from both academic and industrial communities since the concept of PLs was first proposed in 2007. PLs are a novel class of a flowing liquid system that possesses accessible permanent porosity, and they integrate the processable advantages of liquids with superior accommodative capacities of porous solids. By and large, the development of PLs went through the starting stage of the concept proposal and the arrival stage of various synthesized examples to the period of application-specific extensions. From the point of view of producing functions, PLs consist of two parts: sterically hindered solvents and pore generators. Correspondingly, pore generators provide accessible cavities for the resultant PLs, while sterically hindered solvents endow pore generators with a flowing behavior. Undoubtedly, engineering permanent porosity with shape-persistent cavities into a liquid is leading to an inherent change that porosity can not only be created in conventional solids, thus providing new opportunities by utilizing the processability of PLs. Therefore, the field of PLs has seen considerable progress in the design, synthesis, and emerging applications since the example of hollow silica based PLs was demonstrated by Dai et al. in 2015 ( Zhang, J. S.; Chai, S. H.; Qiao, Z. A.; Mahurin, S. M.; Chen, J. H.; Fang, Y. X.; Wan, S.; Nelson, K.; Zhang, P. F.; Dai, S. Porous Liquids: A Promising Class of Media for Gas Separation. Angew. Chem., Int. Ed. Engl. 2015, 54, 932−936.), especially during the past four years. Until now, PLs have emerged as promising platforms for a variety of applications, including but not limited to gas capture, molecule separation, catalytic conversion, biomedicine, and beyond. Anyhow, the further development toward practical applications of PLs depends heavily on the universal synthesis method and the process optimization, where the former is undoubtedly the core. This Account mainly showcases the evolution of our recent progress in the design and synthesis of PLs. Importantly, we tell the story of how we apply the synthesis idea of another similar liquidlike material (i.e., solvent-free nanofluids, SFNs) that has been investigated for more than 20 years in our laboratory in the preparation of PLs. Emphasis is put on the construction of PLs from the perspective of interface interactions (e.g., the electrostatic interaction, the acid–base interaction, and the dipole–dipole/quadrupole interaction, etc.) between sterically hindered solvents and pore generators. Then, we present and summarize related applications in the field of environmental remediation including gas sorption, membrane separation, metal ion selective sorption, and extractive desulfurization, etc. Finally, the challenges, opportunities, and future directions in developing novel PLs are provided and outlined. It is expected that this Account will stimulate the interest of researchers working in broadly diverse fields to fully unleash the potential of porous liquids for versatile application scenarios.