Jiangfeng Yang

Ionothermal synthesis and structure analysis of an open-framework zirconium phosphate with a high CO2/CH4 adsorption ratio.

Less is more: an open-framework zirconium phosphate with unusual 7-ring channels was synthesized ionothermally from a deep-eutectic solvent. This small-pore material displays a CO(2)/CH(4) adsorption ratio (17.3 at 1 bar) that is significantly higher than that of typical 8-ring materials, making it highly attractive for CO(2)/CH(4) separations.

Exploiting the gate opening effect in a flexible MOF for selective adsorption of propyne from C1/C2/C3 hydrocarbons

The separation of propyne from light hydrocarbon mixtures is of technological importance but poses considerable technical challenges. This article reports on the potential of a flexible metal–organic framework [Cu(dhbc)2(4,4′-bipy)], with gate-opening characteristics, that exhibits adsorption selectivity in favor of propyne in a C1/C2/C3 mixture of hydrocarbons. The separation potential of the flexible MOF is established using a judicious combination of measurements of unary isotherms, IAST calculations of mixture adsorption equilibrium, transient breakthrough simulations, along with transient breakthrough experiments. Our multi-tier investigation strategy confirms that propyne can be selectively adsorbed from C1/C2/C3 hydrocarbons in fixed bed adsorbers that are commonly employed in the process industries.

Hydroquinone and Quinone-Grafted Porous Carbons for Highly Selective CO2 Capture from Flue Gases and Natural Gas Upgrading.

Hydroquinone and quinone functional groups were grafted onto a hierarchical porous carbon framework via the Friedel-Crafts reaction to develop more efficient adsorbents for the selective capture and removal of carbon dioxide from flue gases and natural gas. The oxygen-doped porous carbons were characterized with scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier transform infrared spectroscopy, and Raman spectroscopy. CO2, CH4, and N2 adsorption isotherms were measured and correlated with the Langmuir model. An ideal adsorbed solution theory (IAST) selectivity for the CO2/N2 separation of 26.5 (298 K, 1 atm) was obtained on the hydroquinone-grafted carbon, which is 58.7% higher than that of the pristine porous carbon, and a CO2/CH4 selectivity value of 4.6 (298 K, 1 atm) was obtained on the quinone-grafted carbon (OAC-2), which represents a 28.4% improvement over the pristine porous carbon. The highest CO2 adsorption capacity on the oxygen-doped carbon adsorbents is 3.46 mmol g(-1) at 298 K and 1 atm. In addition, transient breakthrough simulations for CO2/CH4/N2 mixture separation were conducted to demonstrate the good separation performance of the oxygen-doped carbons in fixed bed adsorbers. Combining excellent adsorption separation properties and low heats of adsorption, the oxygen-doped carbons developed in this work appear to be very promising for flue gas treatment and natural gas upgrading.

Targeted capture and pressure/temperature-responsive separation in flexible metal–organic frameworks

Based on an in-house-constructed separation apparatus, controlled and targeted CO2 and CH4 capture, respectively, from binary mixtures (CO2/CH4 or CH4/N2) has been realized on two flexible MOFs, [Cu(dhbc)2(4,4′-bipy)] and [Cu(4,4′-bipy)2(BF4)2], in the form of a packed bed of particles. These gas mixtures were effectively separated on the flexible MOFs by using a unique two-stage separation technique. Molecular dynamic simulations have been performed to assess the atomistic interactions of small molecules in flexible MOFs that directly influence the dynamic gas separation. Furthermore, the structural stability and the effect of H2O on these gas separations have been investigated, and the results suggest that the flexible MOFs show significantly improved gas separation performances.

A versatile synthesis of metal–organic framework-derived porous carbons for CO2 capture and gas separation

We report a versatile fabrication method, detailed material characterization, pore architecture formation patterns, and surface functionality of MIL-100Al-derived porous carbons. Oxygen-doped porous carbons were prepared via carbonization of MIL-100Al, MIL-100Al/F127 composite, and MIL-100Al/KOH mixture. Microscopy tools showed different Al2O3 composite patterns and morphologies in the carbon particles, and a coherent discussion of versatile fabrication methods on carbon textural properties is demonstrated. The obtained porous carbons have a large specific surface area (up to 1097 m2 g−1), well-developed narrow microporosity (up to 92% of the pore volume arises from micropores), and excellent CO2 adsorption capacities of 6.5 mmol g−1 at 273 K and 4.8 mmol g−1 at 298 K at an ambient pressure, which is among the highest reported so far for the MOF-derived carbons. Furthermore, excellent CO2/N2 selectivity of 45, CO2/CH4 selectivity of 14.5, and CH4/N2 selectivity of 5.1 were achieved at 298 K and 1 bar. Kinetic selectivity was also calculated, in which high CH4/N2 selectivity (up to 11) was reached at 273 K and 1 bar. Potent gas separation performance and outstanding regenerability, demonstrated by breakthrough simulation and adsorption–desorption cycling tests, enable these MOF derived porous carbons to function as suitable solid adsorbents for CO2 capture from flue gas and bio-gas upgradation.

Computational study of oxygen adsorption in metal–organic frameworks with exposed cation sites: effect of framework metal ions

The current inefficient separation of O2 from air is an important industrial problem. Metal–organic frameworks containing coordinatively unsaturated metal sites (CUS) have emerged as competitive new adsorbents for such targets. In this study, dispersion-corrected density functional theory calculations were performed to investigate the influence of framework metal ions on the adsorption behavior of O2 in M3(BTC)2-type materials (M = Cr, Mn, Fe, Co, Ni and Cu; BTC = 1,3,5-benzenetricarboxylate acid). The results show that Ni3(BTC)2 can be potentially considered as promising oxygen adsorbent with relatively easier deoxygenation than Cr3(BTC)2. The magnitude of charge transfer from the CUS to O2 molecule was found to have a significant impact on the interaction energies of O2 with M3(BTC)2 except for the Cu version. Furthermore, it was revealed that the origin of the difference in the charge transfer can be attributed to the different electronegativity of the metals.

Protection of open-metal V(III) sites and their associated CO2/CH4/N2/O2/H2O adsorption properties in mesoporous V-MOFs

Metal-organic frameworks with open metal site are potential sorbents for the separation of gas mixtures; however, low valence metal will bind to oxygen in the open air causing a decrease in adsorption ability. We now report open-metal sites V(III) on both MIL-100V(III/IV) and MIL-101V(III/IV) that can be protected with water molecules, and which associated CO2/CH4/N2/O2 adsorption properties on these two mesoporous V-MOFs were investigated. The protective properties of water were investigated and evaluated using density functional theory simulations. The binding energy of single O2 on open-metal V(III) site was 93.278 kJ/mol, which decreased to 26.5 kJ/mol when H2O occupies the site. When the water coating is removed, the X-ray photoelectron spectroscopy pattern of V2p showed that the V-MOF changes to MIL-100V(IV) and MIL-101V(IV) at 298 K because of the action of O2. Under these conditions, O2 binds strongly on the open V site significantly reducing the BET (Brunauer-Emmett-Teller) surface and CH4 adsorption volume of the V-MOFs. From the ideal adsorbed solution theory calculated, the adsorption selectivity of CH4/N2 is higher before than after binding of O2 (with V(III) site). In contrast, the adsorption selectivity of CO2/CH4 is higher after than before O2 binding (with no more V(III) sites).

Separation of CO2/CH4 and CH4/N2 mixtures using MOF-5 and Cu3(BTC)2

In this paper we used MOF-5 and Cu3(BTC)2 to separate CO2/CH4 and CH4/N2 mixtures under dynamic conditions. Both materials were synthesized and pelletized, thus allowing for a meaningful characterization in view of process scale-up. The materials were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). By performing breakthrough experiments, we found that Cu3(BTC)2 separated CO2/CH4 slightly better than MOF-5. Because the crystal structure of Cu3(BTC)2 includes unsaturated accessible metal sites formed via dehydration, it predominantly interacted with CO2 molecules and more easily captured them. Conversely, MOF-5 with a suitable pore size separated CH4/N2 more efficiently in our breakthrough test.

Ammonia capture and flexible transformation of M-2(INA) (M=Cu, Co, Ni, Cd) series materials.

With the conflicting problems of pollution due to ammonia emissions and the demand for ammonia, we propose M-2(INA) (M=Cu, Co, Ni, Cd) (INA=isonicotinic acid), a series of materials that exhibit flexible conversion in ammonia adsorption. They can capture both wet and dry ammonia for recycling. The materials were obtained by dehydration of coordination materials M(INA)2(H2O)4 (M=Cu, Co, Ni, Cd) (150°C) at atmospheric pressure for 2h. M-2(INA) could reversibly transform to the stable coordination compounds M(INA)2(H2O)2(NH3)2 by adsorbing ammonia in the presence of moisture. The capacity for pure ammonia could reach 12-13mmol/g. Importantly, these materials could stably retain NH3 at a maximum temperature of 80°C and could regenerate below 150°C with no performance loss.

Kinetically controlled ammonia vapor diffusion synthesis of a Zn(II) MOF and its H2O/NH3 adsorption properties

A unique method for synthesizing a Zn(II) complex Zn(INA)2(H2O)4 (INA = isonicotinate) has been developed by kinetically controlled ammonia (NH3) vapor diffusion at low temperatures without any external energy input. The pH gradient caused by ammonia diffusion from the gas phase to the liquid phase affords an appropriate environment for the rapid, catalytic-like growth of single crystals. This provides a novel method for the synthesis of complex crystal films by an interface reaction. It was found that the three-dimensional MOF Zn(INA)2 obtained by dehydration of Zn(INA)2(H2O)4 could capture ammonia under dry conditions, without any influence on the structure, over several cycles. Interestingly, Zn(INA)2 can co-adsorb H2O and NH3 to form a new material, Zn(INA)2(H2O)2(NH3)2, in moist ammonia. In addition, the amount of NH3 adsorbed by Zn(INA)2 was 6 mmol g−1 whether under dry or moist conditions, and the adsorbent could only be regenerated without performance loss by heating. This particular ammonia adsorption property of Zn(INA)2 has advantages in ammonia capture over other MOFs, which show structural instability.