Type II porous ionic liquid based on metal-organic cages that enables L-tryptophan identification

Improving Light-Responsive Efficiency of Type II Porous Liquid by Tailoring the Functionality of Host

Light-responsive porous liquids (LPLs) attract significant attention for their controllable gas uptake under light irradiation, while their preparation has remained a great challenge. Here we report the fabrication of type II LPLs with enhanced light-responsive efficiency by tailoring the host's functionality for the first time. The functionality of light-responsive metal-organic cage (MOC-RL, constructed from dicopper and responsive ligands) is modified by introducing the second long-chain alkyl ligand, producing MOC-RL-AL as a new host. A spatially hindered solvent based on polyethylene glycol, IL-NTf2, is designed and can dissolve MOC-RL-AL due to the suitable interaction, creating a type II LPL (PL-RL-AL). Under light irradiation, the variation in propylene adsorption for PL-RL-AL increases by 58.0 % compared to PL-RL. The enhanced light-responsive efficiency is caused by easier control in accessibility of internal cavities within MOCs and increased number of external cavities between MOCs and IL-NTf2. This makes PL-RL-AL the first LPL with the probability for propylene/propane separation.

Construction of an organic cage-based porous ionic liquid using an aminal tying strategy

An aminal tying method was applied to post-synthetically modify a flexible organic cage, RCC1, to construct a porous ionic liquid (PIL). The resulting PIL, [RCC1-IM][NTf2]6, displayed melting behaviour below 100 °C, a transition to a glass phase on melt-quenching, CO2 uptake, and its permanent porosity was confirmed using molecular dynamic simulations.

Sub-5 Ångstrom Porosity Tuning in Calixarene-Derived Porous Liquids via Supramolecular Complexation Construction

Sub-Ångstrom-level porosity engineering, which is appealing in gas separations, has been demonstrated in solid carbon, polymer, and framework materials but rarely achieved in the liquid phase. In this work, a gas molecular sieving effect in the liquid phase at sub-5 Ångstrom scale is created via sophisticated porosity tuning in calixarene-derived porous liquids (PLs). Type II PLs are constructed via supramolecular complexation between the sodium salts of calixarene derivatives and crown ether solvents. The chemical structure variation and assembly behavior of the porous host upon PL construction are monitored by spectroscopy-, X-ray-, and neutron-scattering techniques. The presence of permanent porosity in calixarene-derived PLs is verified by pressure swing gas uptake, altered CO2 physisorption behavior, and molecular simulations. Sub-5 Ångstrom porosity tuning within the PL phase is achieved by introducing bulky substituted groups on the benzene ring of the calixarene host, which then greatly affects the dynamic motion and transport behavior of CO2 molecules and the Xe uptake performance. The approach being demonstrated in this work represents a promising pathway to tune and leverage the porosity effect for enhanced gas uptake capacity and selectivity in liquid sorbents.

Type I Porous Liquids with Super-Low Viscosities: the Construction through a Rather Simple One-Step Covalent Linkage Strategy and Its Facile Regulation by a Mixed-Ligand Strategy

Porous liquids (PLs) are a novel class of flowing liquid systems that possess accessible permanent porosity, exhibiting great prospects in gas capture and separation. Nevertheless, the further development of PLs lies in the facile synthesis and regulation of PLs with low viscosities. Herein, a novel strategy of preparing type I PLs with super-low viscosity is proposed through a simple one-step covalent linkage reaction using UiO-66-NH2 as the pore generator and monoglycidyl ether terminated polydimethylsiloxane (E-PDMS) as the sterically hindered solvent, respectively. More importantly, the idea that PLs can be regulated like advanced porous materials (APMs) is proposed and demonstrated, that is, PLs can be regulated by modulating pore generators with the mixed-ligands method. As expected, the resultant PLs not only demonstrate a promising potential in CO2 sorption as a flowing sorbent but also exhibit a superior CO2/N2 selective separation. Meanwhile, positron annihilation lifetime spectrum (PALS) and molecular dynamics (MD) simulations further verify the accessible permanent porosity and the favorable CO2 selective sorption. This work provides a simple and facile method to prepare type I PLs with super-low viscosities, shedding light on the precise regulation of PLs toward task-specific applications.

Porous liquids: an integrated platform for gas storage and catalysis

Porous liquids (PLs) represent a new frontier in materials design, combining the unique features of fluidity in liquids and permanent porosity in solids. By engineering well-defined pores into liquids via designed structure modification techniques, the greatly improved free volume significantly enhances the gas transport and storage capability of PL sorbents. Triggered by the promising applications of PLs in gas separation, PLs are further explored in catalysis particularly to integrate the gas storage and catalytic transformation procedure. This emerging field has demonstrated promising progress to advance catalytic procedures using PLs as catalysts, with performance surpassing that of the pure liquid and porous host counterparts. In this perspective article, the recent discoveries and progress in the field of integrated gas storage and catalysis by leveraging the PL platforms will be summarized, particularly compared with the traditional homogeneous or heterogeneous catalytic procedures. The unique features of PLs endow them with combined merits from liquid and solid catalysts and beyond which will be illustrated first. This will be followed by the unique techniques being utilized to probe the porosity and active sites in PLs and the structural evolution during the catalytic procedures. The catalytic application of PLs will be divided by the reaction categories, including CO2-involving transformation, O2-involving reaction, H2S conversion, hydrogenation reaction, and non-gas involving cascade reactions. In each reaction type, the synthesis approaches and structure engineering techniques of PLs, structure characterization, catalytic performance evaluation, and reaction mechanism exploration will be discussed, highlighting the structure-performance relationship and the advancement benefiting from the unique features of PLs.

What Matters to Fabrication of Type II Porous Liquids: A Case Study on Metallocages and Bulky Ionic Liquid?

Porosity in bulky solvents can be created by the methods of dispersing and dissolving porous hosts or by their chemical adornment. And the ensuing liquids with cavities offer requisite high gas uptakes. Intriguingly, metal-organic cages (MOCs) as discrete nanoporous hosts have been utilized recently as soluble entities to obtain a series of interesting type II porous liquids (PLs). Yet, factors affecting the fabrication of type II PLs have not been disclosed. Herein, three metallocages (NUT-101, ZrT-1-NH2, and ZrT-1) with the same zirconocene nodes but different organic ligands are chosen as porous hosts and a polyethylene-glycol (PEG) linked bis-imidazolium based IL, IL(NTf2), is used as a bulky solvent. It is revealed for the first time that the generation of type II PL depends upon the flexibility of MOCs and the interaction between MOCs and solvent molecules. The maximum solubility is observed with NUT-101 (5%) in IL(NTf2) while ZrT-1-NH2 and ZrT-1 remain least soluble (0.5% and 0.2%). As a result, PL-NUT-101-5% with most intrinsic cavities shows higher CO2 uptake (0.576 mmol g-1) than PL-ZrT-1-NH2-0.5% and PL-ZrT-1-0.2% as well as those reported type II PLs.

Advanced Materials for NH3 Capture: Interaction Sites and Transport Pathways

Ammonia (NH3) is a carbon-free, hydrogen-rich chemical related to global food safety, clean energy, and environmental protection. As an essential technology for meeting the requirements raised by such issues, NH3 capture has been intensively explored by researchers in both fundamental and applied fields. The four typical methods used are (1) solvent absorption by ionic liquids and their derivatives, (2) adsorption by porous solids, (3) ab-adsorption by porous liquids, and (4) membrane separation. Rooted in the development of advanced materials for NH3 capture, we conducted a coherent review of the design of different materials, mainly in the past 5 years, their interactions with NH3 molecules and construction of transport pathways, as well as the structure-property relationship, with specific examples discussed. Finally, the challenges in current research and future worthwhile directions for NH3 capture materials are proposed.

Porous ionic liquids for oxidative desulfurization influenced by electrostatic solvent effect

Developing a highly efficient strategy for the stabilization of the solid-liquid interface is a persistent pursuit for researchers. Herein, porous ionic liquids based on UiO-66 (Zr) porous materials were synthesized and applied to the selective desulfurization catalysis, which integrates the permanent pores of porous solids with the exceptional properties of ionic liquids. Results show that porous ionic liquids possess high activity and selectivity for dibenzothiophene. Experimental analysis and density functional theory calculations revealed that the ionic liquids moiety served as an extractant to enrich dibenzothiophene into the porous ionic liquids phase through the π···π and CH···π interactions. Additionally, the electrostatic solvent effect in the porous ionic liquids contributes to the stabilization solid-liquid interface, which was favorable for UiO-66 moiety to catalytically activate hydrogen peroxide (H2O2) to generate ·OH radicals, and subsequently oxidized dibenzothiophene to the corresponding sulfone. It is hoped that the development of porous ionic liquids could pave a new route to the stabilization of the solid-liquid interface for catalytic oxidation.

Accelerating Metal-Organic Framework Selection for Type III Porous Liquids by Synergizing Machine Learning and Molecular Simulation

MOF-based type III porous liquids, comprising porous MOFs dissolved in a liquid solvent, have attracted increasing attention in carbon capture. However, discovering appropriate MOFs to prepare porous liquids was still limited in experiments, wasting time and energy. In this study, we have used the density functional theory and molecular dynamics simulation methods to identify 4530 MOF candidates as the core database based on the idea of prohibiting the pore occupancy of porous liquids by the solvent, [DBU-PEG][NTf2] ionic liquid. Based on high-throughput molecular simulation, random forest machine learning models were first trained to predict the CO2 sorption and the CO2/N2 sorption selectivity of MOFs to screen the MOFs to prepare porous liquids. The feature importance was inferred based on Shapley Additive Explanations (SHAP) interpretation, and the ranking of the top 5 descriptors for sorption/selectivity trade-off (TSN) was gravimetric surface area (GSA) > porosity > density > metal fraction > pore size distribution (PSD, 3.5-4 Å). RICBEM was predicted to be one candidate for preparing porous liquid with CO2 sorption capacity of 20.87 mmol/g and CO2/N2 sorption selectivity of 16.75. The experimental results showed that the RICBEM-based porous liquid was successfully synthesized with CO2 sorption capacity of 2.21 mmol/g and CO2/N2 sorption selectivity of 63.2, the best carbon capture performance known to date. Such a screening method would advance the screening of cores and solvents for preparing type III porous liquids with different applications by addressing corresponding factors.

Desulfurization of diesel via joint adsorption and extraction using a porous liquid derived from ZIF-8 and a phosphonium-type ionic liquid

A type-III porous liquid based on zeolitic imidazolate framework-8 (ZIF-8) and an ionic liquid trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([THTDP][BTI]) was synthesized and used for the desulfurization of model diesel. The desulfurization effect by ZIF-8/[THTDP][BTI] combined both the adsorptive desulfurization by ZIF-8 and the extraction desulfurization by [THTDP][BTI]. The removal of the three chosen aromatic organic sulfides by the ZIF-8/[THTDP][BTI] porous liquid followed the order of dibenzothiophene (73.1%) > benzothiophene (70.0%) > thiophene (61.5%). It was further found that deep desulfurization could be realized by ZIF-8/[THTDP][BTI] through triple desulfurization cycles and ZIF-8/[THTDP][BTI] can be regenerated readily. The desulfurization mechanism was explored further in detail by conformation search and density functional theory calculations. Calculations supported that the large molecular volume of [THTDP][BTI] excluded itself from the cavities of ZIF-8, making the pores of ZIF-8 in the porous liquid unoccupied and accessible by other guest species, here the studied organic sulfides. These calculations indicate that the van der Waals interactions were the main interactions between ZIF-8/[THTDP][BTI] and specifically benzothiophene. This work supports that the porous liquid ZIF-8/[THTDP][BTI] could potentially be used for desulfurization of diesel in industry.

Rational Design of Porous Ionic Liquids for Coupling Natural Gas Purification with Waste Gas Conversion

Removal of trace impurities for natural gas purification coupled with waste gas conversion is highly desired in industry. We here report a type of porous ionic liquids (PILs) that can realize the continuous flow separation of CH4 /CO2 /H2 S and the conversion of the captured H2 S to useful products. The PILs are synthesized through a step-by-step surface modification of ionic liquids (ILs) onto UiO-66-OH nanocrystals. The introduction of free tertiary amine groups on the nanocrystal surface endows these PILs with an exceptional ability to enrich H2 S from CO2 and CH4 with impressive selectivity, while the permanent pores of UiO-66-OH act as containers to store an exceptionally higher amount of the selectively captured H2 S than the corresponding nonporous ILs. Simultaneously, the tertiary amines as dual functional moieties offer effective catalytic sites for the conversion of the H2 S stored in PILs into 3-mercaptoisobutyric acid, a key intermediate required for the synthesis of Captopril (an antihypertensive drug). Molecular dynamics, density functional theory calculations and Grand Canonical Monte Carlo simulations help understand both the mechanisms of separation and catalysis performance, confirming that the tertiary amines as well as the permanent pores in UiO-66-OH play vital roles in the whole procedure.

Interfacial Self-assembly of Chiral Selenide Nanomembrane for Enantiospecific Recognition

Here, we report the synthesis of chiral selenium nanoparticles (NPs) using cysteine and the interfacial assembly strategy to generate a self-assembled nanomembrane on a large-scale with controllable morphology and handedness. The selenide (Se) NPs exhibited circular dichroism (CD) bands in the ultraviolet and visible region with a maximum intensity of 39.96 mdeg at 388 nm and optical anisotropy factors (g-factors) of up to 0.0013 while a self-assembled monolayer nanomembrane exhibited symmetrical CD approaching 72.8 mdeg at 391 nm and g-factors up to 0.0034. Analysis showed that a photocurrent of 20.97±1.55 nA was generated by the D-nanomembrane when irradiated under light while the L-nanomembrane generated a photocurrent of 20.58±1.36 nA. Owing to the asymmetric intensity of the photocurrent with respect to the handedness of the nanomembrane, an ultrasensitive recognition of enantioselective kynurenine (Kyn) was achieved by the ten-layer (10L) D-nanomembrane exhibiting a photocurrent for L-kynurenine (L-Kyn) that was 8.64-fold lower than that of D-Kyn, with a limit of detection (LOD) of 0.0074 nM for the L-Kyn, which was attributed to stronger affinity between L-Kyn and D-Se NPs. Noticeably, the chiral Se nanomembrane precisely distinguished L-Kyn in serum and cerebrospinal fluid samples from Alzheimer's disease patients and healthy subjects.

Interfacial engineered superelastic metal-organic framework aerogels with van-der-Waals barrier channels for nerve agents decomposition

Chemical warfare agents (CWAs) significantly threaten human peace and global security. Most personal protective equipment (PPE) deployed to prevent exposure to CWAs is generally devoid of self-detoxifying activity. Here we report the spatial rearrangement of metal-organic frameworks (MOFs) into superelastic lamellar-structured aerogels based on a ceramic network-assisted interfacial engineering protocol. The optimized aerogels exhibit efficient adsorption and decomposition performance against CWAs either in liquid or aerosol forms (half-life of 5.29 min, dynamic breakthrough extent of 400 L g^-1) due to the preserved MOF structure, van-der-Waals barrier channels, minimized diffusion resistance (~41% reduction), and stability over a thousand compressions. The successful construction of the attractive materials offers fascinating perspectives on the development of field-deployable, real-time detoxifying, and structurally adaptable PPE that could be served as outdoor emergency life-saving devices against CWAs threats. This work also provides a guiding toolbox for incorporating other critical adsorbents into the accessible 3D matrix with enhanced gas transport properties.

Solvent Induced Conversion of a Self-Assembled Gyrobifastigium to a Barrel and Encapsulation of Zinc-Phthalocyanine within the Barrel for Enhanced Photodynamic Therapy

A rare gyrobifastigium architecture (GB) was constructed by self-assembly of a tetradentate donor (L) with Pd^II acceptor in DMSO. The GB was converted to its isomeric tetragonal barrel (MB) upon treatment with water. The hydrophobic cavity of MB has been explored for the encapsulation of zinc-phthalocyanine (ZnPc), which is an excellent photosensitizer for photodynamic therapy (PDT). However, the poor water-solubility and aggregation tendency are the main reasons for the suboptimal PDT performance of free ZnPc in the aqueous medium. Effective solubilization of ZnPc in an aqueous medium was achieved by encapsulating it in the cavity of MB. The inclusion complex (ZnPc⊂MB) showed enhanced singlet oxygen generation in water. Higher cellular uptake and anticancer activity of the ZnPc⊂MB compared to free ZnPc on HeLa cells indicate that encapsulation of ZnPc in an aqueous host is a potential strategy for enhancement of its PDT activity in water.