John J. Perry

Direct Air Capture of CO2 by Physisorbent Materials

Sequestration of CO2, either from gas mixtures or directly from air (direct air capture, DAC), could mitigate carbon emissions. Here five materials are investigated for their ability to adsorb CO2 directly from air and other gas mixtures. The sorbents studied are benchmark materials that encompass four types of porous material, one chemisorbent, TEPA-SBA-15 (amine-modified mesoporous silica) and four physisorbents: Zeolite 13X (inorganic); HKUST-1 and Mg-MOF-74/Mg-dobdc (metal-organic frameworks, MOFs); SIFSIX-3-Ni, (hybrid ultramicroporous material). Temperature-programmed desorption (TPD) experiments afforded information about the contents of each sorbent under equilibrium conditions and their ease of recycling. Accelerated stability tests addressed projected shelf-life of the five sorbents. The four physisorbents were found to be capable of carbon capture from CO2-rich gas mixtures, but competition and reaction with atmospheric moisture significantly reduced their DAC performance.

Assessing the Purity of Metal−Organic Frameworks Using Photoluminescence: MOF-5, ZnO Quantum Dots, and Framework Decomposition

Photoluminescence (PL) spectroscopy was used to characterize nanoscale ZnO impurities, amine-donor charge-transfer exciplexes, and framework decomposition in samples of MOF-5 prepared by various methods. The combined results cast doubt on previous reports describing MOF-5 as a semiconductor and demonstrate that PL as a tool for characterizing MOF purity possesses advantages such as simplicity, speed, and sensitivity over currently employed powder XRD MOF characterization methods.

Sextuplet phenyl embrace in a metal-organic Kagome lattice

A novel Kagomé lattice that demonstrates the modular nature of metal-organic networks has been prepared and is to our knowledge the first example of a metal-organic coordination polymer that incorporates the sextuplet phenyl embrace as a supramolecular synthon.

Connecting structure with function in metal–organic frameworks to design novel photo- and radioluminescent materials

The exemplary structural versatility and permanent porosity of Metal–Organic Frameworks (MOFs) and their consequent potential for breakthroughs in diverse applications have caused these hybrid materials to become the focus of vigorous investigation. These properties also hold significance for applications beyond those traditionally envisioned for microporous materials, such as radiation detection and other luminescence-based sensing applications. In this contribution we demonstrate that luminescence induced by ionizing radiation (also known as scintillation) is common in appropriately designed MOFs and describe how this property can be harnessed to generate novel materials useful for detecting radiation. Through a diverse selection of MOFs, we explore the structural properties of MOFs that give rise to scintillation and photoluminescence in these materials. These results enable us to define a new structure-based hierarchical system for understanding luminescent properties in MOFs. Finally, we describe some performance metrics for MOF-based scintillation counters, such as luminosity and resistance to radiation damage, and discuss how these materials relate to the current state of the art in scintillation counters.

Tuning Pore Size in Square‐Lattice Coordination Networks for Size‐Selective Sieving of CO2

Porous materials capable of selectively capturing CO2 from flue-gases or natural gas are of interest in terms of rising atmospheric CO2 levels and methane purification. Size-exclusive sieving of CO2 over CH4 and N2 has rarely been achieved. Herein we show that a crystal engineering approach to tuning of pore-size in a coordination network, [Cu(quinoline-5-carboxyate)2 ]n (Qc-5-Cu) ena+bles ultra-high selectivity for CO2 over N2 (SCN ≈40 000) and CH4 (SCM ≈3300). Qc-5-Cu-sql-β, a narrow pore polymorph of the square lattice (sql) coordination network Qc-5-Cu-sql-α, adsorbs CO2 while excluding both CH4 and N2 . Experimental measurements and molecular modeling validate and explain the performance. Qc-5-Cu-sql-β is stable to moisture and its separation performance is unaffected by humidity.

Flue-gas and direct-air capture of CO2 by porous metal-organic materials.

Sequestration of CO2, either from gas mixtures or directly from air (direct air capture), is a technological goal important to large-scale industrial processes such as gas purification and the mitigation of carbon emissions. Previously, we investigated five porous materials, three porous metal–organic materials (MOMs), a benchmark inorganic material, Zeolite 13X and a chemisorbent, TEPA-SBA-15, for their ability to adsorb CO2 directly from air and from simulated flue-gas. In this contribution, a further 10 physisorbent materials that exhibit strong interactions with CO2 have been evaluated by temperature-programmed desorption for their potential utility in carbon capture applications: four hybrid ultramicroporous materials, SIFSIX-3-Cu, DICRO-3-Ni-i, SIFSIX-2-Cu-i and MOOFOUR-1-Ni; five microporous MOMs, DMOF-1, ZIF-8, MIL-101, UiO-66 and UiO-66-NH2; an ultramicroporous MOM, Ni-4-PyC. The performance of these MOMs was found to be negatively impacted by moisture. Overall, we demonstrate that the incorporation of strong electrostatics from inorganic moieties combined with ultramicropores offers improved CO2 capture performance from even moist gas mixtures but not enough to compete with chemisorbents. This article is part of the themed issue ‘Coordination polymers and metal–organic frameworks: materials by design’.

Highly Selective Separation of C2H2 from CO2 by a New Dichromate-Based Hybrid Ultramicroporous Material

A new hybrid ultramicroporous material, [Ni(1,4-di(pyridine-2-yl)benzene)2(Cr2O7)]n (DICRO-4-Ni-i), has been prepared and structurally characterized. Pure gas sorption isotherms and molecular modeling of sorbate-sorbent interactions imply strong selectivity for C2H2 over CO2 (SAC). Dynamic gas breakthrough coupled with temperature-programmed desorption experiments were conducted on DICRO-4-Ni-i and two other porous materials reported to exhibit high SAC, TIFSIX-2-Cu-i and MIL-100(Fe), using a C2H2/CO2/He (10:5:85) gas mixture. Whereas CO2/C2H2 coadsorption by MIL-100(Fe) mitigated the purity of trapped C2H2, negligible coadsorption and high SAC were observed for DICRO-4-Ni-i and TIFSIX-2-Cu-i.

DFT-based force field development for noble gas adsorption in metal organic frameworks

Density Functional Theory (DFT) based force fields (FFs) for Ar and Xe adsorption in six metal–organic frameworks were developed using three DFT functionals (PBE-D2, vdW-DF, vdW-DF2) in periodic systems. These force fields include van der Waals (vdW) and polarization terms, and the effect of the latter was shown to be small. Using our DFT-derived and standard (UFF) FFs in grand canonical Monte Carlo simulations, adsorption isotherms and heats of adsorption were calculated and compared with experiment. In most of the cases, it was possible to accurately predict adsorption isotherms using one of the DFT-derived FFs. Still, among the DFT functionals investigated, no single DFT functional could accurately describe all of the adsorbate-framework interactions. On average, performance of UFF and PBE-D2 based FFs to predict experimental isotherms were at a similar quality, still, UFF was slightly superior. Although vdW-DF2 based FFs predicted experimental isotherms almost perfectly for ZIF-8 and HKUST-1 up to 20 bar, their average performance was less than that of PBE-D2 based FFs. Nevertheless, the overall performance of UFF, PBE-D2 and vDW-DF2 FFs was similar. Lastly, vdW-DF based FFs always over-predicted experiments.

Reversible Switching between Highly Porous and Nonporous Phases of an Interpenetrated Diamondoid Coordination Network that Exhibits Gate‐Opening at Methane Storage Pressures

Herein, we report that a new flexible coordination network, NiL2 (L=4-(4-pyridyl)-biphenyl-4-carboxylic acid), with diamondoid topology switches between non-porous (closed) and several porous (open) phases at specific CO2 and CH4 pressures. These phases are manifested by multi-step low-pressure isotherms for CO2 or a single-step high-pressure isotherm for CH4 . The potential methane working capacity of NiL2 approaches that of compressed natural gas but at much lower pressures. The guest-induced phase transitions of NiL2 were studied by single-crystal XRD, in situ variable pressure powder XRD, synchrotron powder XRD, pressure-gradient differential scanning calorimetry (P-DSC), and molecular modeling. The detailed structural information provides insight into the extreme flexibility of NiL2 . Specifically, the extended linker ligand, L, undergoes ligand contortion and interactions between interpenetrated networks or sorbate-sorbent interactions enable the observed switching.

Network diversity through two-step crystal engineering of a decorated 6-connected primary molecular building block

[Cr3O(nicotinate)6]+ was isolated and then utilised as a new primary molecular building block, PMBB, linked by 2-, 3- and 4-connected metal centres. Five novel metal–organic materials (MOMs) with acs, stp, rtl, fsc and pcu topologies were thereby isolated and characterised.