Adsorptive Separation of Benzene, Cyclohexene, and Cyclohexane by Amorphous Nonporous Amide Naphthotube Solids

Complete separation of benzene-cyclohexene-cyclohexane mixtures via temperature-dependent molecular sieving by a flexible chain-like coordination polymer

The separation and purification of C6 cyclic hydrocarbons (benzene, cyclohexene, cyclohexane) represent a critically important but energy intensive process. Developing adsorptive separation technique to replace thermally driven distillation processes holds great promise to significantly reduce energy consumption. Here we report a flexible one-dimensional coordination polymer as an efficient adsorbent to discriminate ternary C6 cyclic hydrocarbons via an ideal molecular sieving mechanism. The compound undergoes fully reversible structural transformation associated with removal/re-coordination of water molecules and between activated and hydrocarbon-loaded forms. It exhibits distinct temperature- and adsorbate-dependent adsorption behavior which facilitates the complete separation of benzene, cyclohexene and cyclohexane from their binary and ternary mixtures, with the record-high uptake ratios for C6H6/C6H12 and C6H10/C6H12 in vapor phase and highest binary and ternary selectivities in liquid phase. In situ infrared spectroscopic analysis and ab initio calculations provide insight into the host-guest interactions and their effect on the preferential adsorption and structural transformation.

Harnessing Shape Complementarity for Upgraded Cyclohexane Purification through Adaptive Bottlenecked Pores in an Imidazole-Containing MOF

Shape complementarity is a biological craft for precisely binding substrates at protein-protein interfaces. An analogy to such a function can be drawn conceptually for crystalline porous solids; yet the manifested entities are rare in reticular chemistry. The bottleneck-shaped pores carved out of a metal-organic framework, Zn(MIBA)₂ (aka. MAF-stu-13), can perfectly accommodate benzene molecules. Remarkably, its framework adapts to the optimal guest binding-the enhanced host-guest interactions in the neck in turn minimize the guest-guest repulsion in the pore to the extent it turns into attraction-as demonstrated by the combined X-ray structural and DFT computational studies. This adaptive material can be used for liquid-phase production of ultrahigh-purity (≥99 %) cyclohexane, achieving a balance between uptake capacity and separation selectivity and surpassing the performances of other porous and nonporous crystals reported recently (e.g. product purity 99.4 % vs. 97.5 % to date).

Effective and Rapid Removal of Polar Organic Micropollutants from Water by Amide Naphthotube-Crosslinked Polymers

It is challenging to remove polar organic micropollutants from water through adsorption-mediated processes. Macrocycle-crosslinked polymers were recently shown to be effective adsorbents for nonpolar or charged organic micropollutants through specific host-guest binding, but are rarely used for the treatment of neutral and polar organic micropollutants. This is due to the challenge of recognizing polar molecules in water by macrocyclic hosts. In this research, we report two amide naphthotube-crosslinked polymers which can effectively and rapidly adsorb a wide scope of polar organic micropollutants from water through biomimetic molecular recognition. Amide naphthotubes possess hydrogen bonding sites in their deep hydrophobic cavities and can effectively bind polar organic micropollutants in water through the hydrophobic effects and shielded hydrogen bonds. The cross-linked polymers containing amide naphthotubes are even able to remove a complex mixture of organic micropollutants from water and the used materials can be easily regenerated through washing with MeOH or EtOH. This research provides a solution for the treatment of polar organic micropollutants by using biomimetic molecular recognition in water.