An adsorbate biased dynamic 3D porous framework for inverse CO2 sieving over C2H2.

Separating carbon dioxide (CO2) from acetylene (C2H2) is one of the most critical and complex industrial separations due to similarities in physicochemical properties and molecular dimensions. Herein, we report a novel Ni-based three-dimensional framework {[Ni4(µ3-OH)2(µ2-OH2)2(1,4-ndc)3](3H2O)}n (1,4-ndc = 1,4-naphthalenedicarboxylate) with a one-dimensional pore channel (3.05 × 3.57 Å2), that perfectly matches with the molecular size of CO2 and C2H2. The dehydrated framework shows structural transformation, decorated with an unsaturated Ni(ii) centre and pendant oxygen atoms. The dynamic nature of the framework is evident by displaying a multistep gate opening type CO2 adsorption at 195, 273, and 298 K, but not for C2H2. The real time breakthrough gas separation experiments reveal a rarely attempted inverse CO2 selectivity over C2H2, attributed to open metal sites with a perfect pore aperture. This is supported by crystallographic analysis, in situ spectroscopic inspection, and selectivity approximations. In situ DRIFTS measurements and DFT-based theoretical calculations confirm CO2 binding sites are coordinatively unsaturated Ni(ii) and carboxylate oxygen atoms, and highlight the influence of multiple adsorption sites.

Noncovalent interaction guided selectivity of haloaromatic isomers in a flexible porous coordination polymer.

Porous, supramolecular structures exhibit preferential encapsulation of guest molecules, primarily by means of differences in the order of (noncovalent) interactions. The encapsulation preferences can be for geometry (dimension and shape) and the chemical nature of the guest. While geometry-based sorting is relatively straightforward using advanced porous materials, designing a "chemical nature" specific host is not. To introduce "chemical specificity", the host must retain an accessible and complementary recognition site. In the case of a supramolecular, porous coordination polymer (PCP) [Zn(o-phen)(ndc)] (o-phen: 1,10-phenanthroline, ndc: 2,6-naphthalenedicarboxylate) host, equipped with an adaptable recognition pocket, we have discovered that the preferential encapsulation of a haloaromatic isomer is not only for dimension and shape, but also for the "chemical nature" of the guest. This selectivity, i.e., preference for the dimension, shape and chemical nature, is not guided by any complementary recognition site, which is commonly required for "chemical specificity". Insights from crystal structures and computational studies unveil that the differences in the different types of noncovalent host-guest interaction strengths, acting in a concerted fashion, yield the unique selectivity.

Tailoring a robust Al-MOF for trapping C2H6 and C2H2 towards efficient C2H4 purification from quaternary mixtures.

Light hydrocarbon separation is considered one of the most industrially challenging and desired chemical separation processes and is highly essential in polymer and chemical industries. Among them, separating ethylene (C2H4) from C2 hydrocarbon mixtures such as ethane (C2H6), acetylene (C2H2), and other natural gas elements (CO2, CH4) is of paramount importance and poses significant difficulty. We demonstrate such separations using an Al-MOF synthesised earlier as a non-porous material, but herein endowed with hierarchical porosity created under microwave conditions in an equimolar water/ethanol solution. The material possessing a large surface area (793 m2 g-1) exhibits an excellent uptake capacity for major industrial hydrocarbons in the order of C2H2 > C2H6 > CO2 > C2H4 > CH4 under ambient conditions. It shows an outstanding dynamic breakthrough separation of ethylene (C2H4) not only for a binary mixture (C2H6/C2H4) but also for a quaternary combination (C2H4/C2H6/C2H2/CO2 and C2H4/C2H6/C2H2/CH4) of varying concentrations. The detailed separation/purification mechanism was unveiled by gas adsorption isotherms, mixed-gas adsorption calculations, selectivity estimations, advanced computer simulations such as density functional theory (DFT), grand canonical Monte Carlo (GCMC) and ab initio molecular dynamics (AIMD), and stepwise multicomponent dynamic breakthrough experiments.

A Dynamic Chemical Clip in Supramolecular Framework for Sorting Alkylaromatic Isomers using Thermodynamic and Kinetic Preferences.

Adsorptive chemical separation is at the forefront of future technologies, for use in chemical and petrochemical industries. In this process, a porous adsorbent selectively allows a single component from a mixture of three or more chemical components to be adsorbed or permeate. To separate the unsorted chemicals, a different adsorbent is needed. A unique adsorbent which can recognize and separate each of the chemicals from a mixture of three or more components is the necessity for the next generation porous materials. In this regard, we demonstrate a "dynamic chemical clip" in a supramolecular framework capable of thermodynamic and kinetics-based chemical separation. The dynamic space, featuring a strong preference for aromatic guests through π-π and C-H⋅⋅⋅π interactions and adaptability, can recognize the individual chemical isomers from mixtures and separate those based on thermodynamic and kinetic factors. The liquid-phase selectivity and separation of the aromatic isomers are possible by the adaptability of the "chemical clip" and here we elucidate the prime factors in a combinatorial approach involving crystallographic evidence and detailed computational studies.

Nanocomposite Hydrogel of Pd@ZIF-8 and Laponite® : Size-Selective Hydrogenation Catalyst under Mild Conditions.

The composite hydrogel of a nanoscale metal-organic framework (NMOF) and nanoclay has emerged as a new soft-material with advanced properties and applications. Herein, we report a facile synthesis of a hydrogel nanocomposite by charge-assisted self-assembly of Pd@ZIF-8 nanoparticles with Laponite® nanoclay which coat the surface of Pd@ZIF-8 nanoparticles. Such surface coating significantly enhanced the thermal stability of the ZIF-8 compared to the pristine framework. Further, the Pd@ZIF-8+LP hydrogel nanocomposite shows better size-selective catalytic hydrogenation of olefins than Pd@ZIF-8 nanoparticles based on selective diffusion of the substrate.

Modulating Hierarchical Micro/Mesoporosity by a Mixed Solvent Approach in Al-MOF: Stabilization of MAPbBr3 Quantum Dots.

Various hierarchical micro/mesoporous MOFs based on {[Al(µ-OH)(1,4-NDC)]⋅H2 O} (MOF1) with tunable porosities (pore volume and surface area) have been synthesized by assembling AlIII and 1,4-NDC (1,4-naphthalenedicarboxylate) under microwave irradiation by varying water/ethanol solvent ratio. Water/ethanol mixture has played a crucial role in the mesopore generation in MOF1M25 , MOF1M50 , and MOF1M75 , which is achieved by in situ formation of water/ethanol clusters. By adjusting the ratio of water/ethanol, the particle size, surface area and micro/mesopore volume fraction of the MOFs are controlled. Furthermore, reaction time plays a critical role in mesopore formation as realized by varying reaction time for the MOF with 50 % ethanol (MOF1M50 ). Additionally, hierarchical MOF (MOF1M50 ) has been used as a template for the stabilization of MAPbBr3 (MA=methylammonium) perovskite quantum dots (PQDs). MAPbBr3 PQDs are grown inside MOF1M50 , where mesopores control the size of PQDs which leads to quantum confinement.

Photochromic Conjugated Microporous Polymer Manifesting Bio-Inspired pcFRET and Logic Gate Functioning.

Design and synthesis of solid-state photochromic materials remain a challenge because of high structural constrain. However, this can be mitigated in attaining structural flexibility by introducing permanent porosity into the system. Here, we report for the first time the design and synthesis of a photochromic conjugated microporous polymer (pcCMP) by assembling photochromic dithienylethene aldehyde and benzene-1,3,5-tricarbohydrazide. The yellow photo-isomer pcCMP-O gets converted to a deep-green photo-isomer pcCMP-C by UV-light irradiation, which can be reverted to pcCMP-O by visible light or thermal treatment. Owing to the thermo-irreversible nature, the pcCMP is found to be suitable for designing an INH functioning logic gate. pcCMP-C shows highly enhanced conductivity (92 times) because of enhanced conjugation compared to pcCMP-O. Furthermore, we demonstrate the bio-inspired photo-switchable pcFRET process by encapsulation of a red-emissive green fluorescent protein (gfp) chromophore analogue into the pcCMP. This material shows high processibility and has been exploited further for secret writing.

Synergistic Role of Microwave and Perturbation toward Synthesis of Hierarchical Porous MOFs with Tunable Porosity.

Creating hierarchical porosity in MOFs has attracted significant interest due to their immense potential in a wide range of applications from materials to life science. Herein, we report a unique methodology of combining perturbation assisted nanofusion (PNF) with microwave (MW) stimuli to generate wide additional pores from (5-18) nm in the prototype MOF, Ni-MOF-74. An optimized combination of microwave exposure, perturbation in form of stirring, and solvent effect induces additional mesoscale porosity by fusion of MOF nanoparticles. The effect of microwave is realized by varying reaction time and medium using a range of solvents having different dielectric constant (DMSO, DMF, DMA, acetone, EA, and THF). Introducing this method, for the first time, we are able to generate a wide scale mesopore by fusion of nanoscale microporous MOF within a short reaction time by vigorous stirring, without using any template. This additional mesopore, thus generated, has been exploited by encapsulating 4.6 µmol·g-1 of large biomolecule Vitamin B12 (VB12).

Solvent-Modulated Emission Properties in a Superhydrophobic Oligo( p-phenyleneethynylene)-Based 3D Porous Supramolecular Framework.

A chromophoric oligo( p-phenyleneethynylene) (OPE) bola-amphiphile with dioxyoctyl side chains (H2OPE-C8) has been self-assembled with CdII to form a 1D coordination polymer, {Cd(OPE-C8)(DMF)2(H2O)} (1), which is further interdigitated to form a 2D network. Such 2D networks are further interwoven to form a 3D supramolecular framework with surface-projected alkyl chains. The desolvated framework showed permanent porosity, as realized from the CO2 adsorption profile. 1 showed high water contact angles, portraying its superhydrophobic nature. 1 also showed a linker-based cyan luminescence. Solvent removal led to a bathochromic shift in emission into the green region. Resolvation with N, N-dimethylformamide brought back the original cyan emission, whereas for tetrahydrofuran, ethanol, and methanol, it persisted at an intermediate state. Density functional theory calculations unraveled that, twisting of the OPE phenyl rings generated the red shift in emission.

In Situ Growth of Self-Assembled ZIF-8-Aminoclay Nanocomposites with Enhanced Surface Area and CO2 Uptake.

Self-assembly of metal-organic framework (MOF) nanoparticles (NPs) with a functional material can result in MOF nanocomposites having new and advanced properties along with the fabrication of new nanoscopic structures. However, such assembly of MOFs has not been realized to date. Here we report self-assembled nanocomposites of the zeolitic imidazolate framework (ZIF-8) and layered aminoclay (AC) for the first time, and the ZIF-8@AC composites exhibit significantly enhanced adsorption properties in comparison to those of pristine ZIF-8 nanoparticles. Four different composites denoted as ZIF-8@AC-1, ZIF-8@AC-2, ZIF-8@AC-3, and ZIF-8@AC-4 were synthesized by varying the clay content, and their AC contents were found to be 12.1, 18.3, 22.2, and 27.2 wt %, respectively. The composites were thoroughly characterized by PXRD, FTIR, Raman, and various microscopic techniques (FESEM, TEM, and STEM). The formation of the composites is driven by the specific interaction between unsaturated Zn(II) sites of ZIF-8 nanoparticles and NH2 groups of the aminoclay, which was validated from ζ potential and Raman spectroscopic measurements. The adsorption studies of the desolvated composites were also carried out in detail. The best performance is achieved with one of the composites, which exhibits a 42% increase in BET surface area while CO2 uptake at 298 K is doubled in comparison to the ZIF-8 nanoparticles.