A porous aluminum-based metal-organic framework (MOF) comprises inorganic aluminum chains linked via carboxylate groups of 1H-pyrazole-3,5-dicarboxylate (HPDC) linkers, and of formula: [Al(OH)(C5H2O4N2)(H2O)].

INTRODUCTION

Water adsorption by porous solids is important for many industrial applications, such as the dehumidification,1adsorption-driven heat pump for air-conditioning,2and more recently, direct water harvesting from atmosphere for clean water generation.3Criteria for porous solids that can be applied in these applications are (1) high capacity for maximum water or heat delivery; (2) steep uptake at low relative partial pressure (P/P0, 0.1-0.3) (3) high stability and cycling performance (4) easy regeneration.4Traditional materials such as zeolites suffer from low capacity and high regeneration energy, while silica gels suffer from a gradual uptake and only reach high uptake at high relative pressures (close to saturation). Metal-organic frameworks (MOFs) have been recently proposed to this field, which show great potential.2-5For examples, MOF-801 (zirconium fumarate) has a steep water uptake at P/P0=0.05 to 0.1 and the maximum uptake is 28 wt % (P/P0=0.9), MOF-841 (zirconium methanetetrayltetrabenzoate) has a steep uptake at P/P0=0.2 and the maximum uptake is 48 wt %,4MIL-160 (aluminum furandicarboxylate) has a steep uptake at P/P0=0.05 to 0.2 and the maximum uptake is 37 wt %.5All those materials show good cycling performance. A device based on MOF-801 for water harvesting have been demonstrated recently, being capable of harvesting 28 wt % water per MOF mass at low relative humidity (20%) and requires no additional input of energy.1

We demonstrated here the use of MOF-303 and MOF-573 for water harvesting. MOF-303 has a steep uptake at P/P0=0.15 and the maximum uptake is 48 wt %. The material can be easily fully regenerated at room temperature, with no decrease in performance in 5 cycles. Further kinetic cycling test shows that the materials shows no decrement in performance for up to 150 cycles (34 wt % delivery capacity under following condition: adsorption in 40% R.H. N2flow, desorption in dry N2flow at 85° C. for 30 mins), demonstrating high capacity and high stability of this material (FIG. 3).

MOF-303 can be used to capture other oxide based gases similar to CO2, such as SO2, NOx, which can be applied to remove these pollutants from air and post-combustion flue gases.

We further demonstrated the use of MOF-303 for high-pressure methane storage. It is shown that MOF-303 can hold 190 cm3cm−3of methane at 35 bar, 298 K, which is in line with the best performing materials ever reported (HKUST-1, 190-227 cm3cm−3, Ni-MOF-74, 208-230 cm3cm−3),7the delivery capacity is 106 cm3cm−3, indicating the application for storage and delivery of energy gases.

SUMMARY OF THE INVENTION

This disclosure provides two porous metal-organic frameworks (MOFs), MOF-303, [Al(OH)(C5H2O4N2)(H2O)] and MOF-573 [Al(OH)(C5H2O4N2) (H2O)] constructed by linking aluminum (III) ions and 3,5-pyrazoledicarboxylic acid. These MOFs show permanent porosity and have Brunauer-Emmett-Teller (BET) surface areas of 1380 and 980 m2g−1, respectively. MOF-303 and MOF-573 can be easily synthesized in hot water with only aluminum chloride or sulfate salt, 3,5-pyrazoledicarboxylic acid, and a base (e.g. NaOH) in short period (12-72 h). We demonstrated the use of MOF-303 for water harvesting from humid air. The material can take 500 cm3g−1(40 wt %) water at low relative humidity (P/P0=0.2), and can be easily fully regenerated at room temperature, with no decrease in performance after 5 cycles. Further kinetic cycling test shows that the material at least shows no decrement in performance for up to 150 cycles (34 wt % working capacity under following condition: adsorption in 40% R.H. N2flow, desorption in dry N2flow at 85° C. for 30 mins), demonstrating use for water harvesting from humid air.

The easy synthesis and scalibilty allows a variety of applications, including water harvesting from humid air. The material (MOF-303) provides high capacity compared to other known materials at low relative humidity, which provides a key component of portable and clean water generating devices.

In an aspect the invention provides a porous aluminum-based metal-organic framework (MOF) comprising inorganic aluminum chains linked via carboxylate groups of 1H-pyrazole-3,5-dicarboxylate (HPDC) linkers, and of formula: [Al(OH)(C5H2O4N2)(H2O)], wherein: each Al (III) ion is capped by four O atoms from four different carboxylate groups and two O atoms from two hydroxyl groups forming AlO6octahedra, and the AlO6octahedra form corner-sharing chains, depending on the cis- and trans-position of the two adjacent bridging hydroxyl groups, helical chains in MOF-303 (cis-) and MOF-573 (trans-) form respectively.

In embodiments the MOF is MOF-303, wherein:

the linkers further bridge two of the chains together, leading to the formation of a 3D framework delimiting square-shaped one dimensional channels with diameter of 6 Å in diameter (measured by the largest fitting sphere);

the MOF-303 has a topology of xhh; and/or

the MOF has permanent porosity and a Brunauer-Emmett-Teller (BET) surface area of 1380 and pore volume of 0.55 cm3g−1.

In embodiments the MOF is MOF-573, wherein:

the linkers further bridge two of the chains together, leading to the formation of a 3D framework delimiting square-shaped one dimensional channels with diameter of 5 Å in diameter (measured by the largest fitting sphere);

the MOF has a topology of upt; and/or

the MOF has permanent porosity and a Brunauer-Emmett-Teller (BET) surface area of 980 m2g−1and pore volume of 0.56 cm3g−1.

In embodiments, the MOF further comprises an adsorbed material such as water, or a gas such carbon dioxide, or other oxide such as SO2or NOx (NO, NO2, etc.) or a fuel or flue gas, such as a hydrocarbon gas like methane, propane, etc.

In further aspects the invention provides a method of making the MOF comprising the step of linking aluminum (III) ions and 3,5-pyrazoledicarboxylic acid.

In further aspects the invention provides a method of using the MOF for water harvesting from humid air, comprising the steps of: contacting the MOF with humid air to absorb water from the air, and desorbing the water.

In further aspects the invention also provides methods of using the disclosed MOFs, such as for gas adsorption, comprising the steps of: contacting the MOF with a gas wherein the gas adsorbs into the MOF, such as wherein the gas is carbon dioxide, or other oxide such as SO2or NOx (NO, NO2, etc.) or a fuel or flue gas, such as a hydrocarbon gas like methane, propane, etc.

The invention encompasses all combination of the particular embodiments recited herein, as if each combination had been laboriously recited.

DESCRIPTION OF PARTICULAR EMBODIMENTS OF THE INVENTION

Unless contraindicated or noted otherwise, in these descriptions and throughout this specification, the terms “a” and “an” mean one or more, the term “or” means and/or.

The present invention relates to the preparation of two porous aluminum-based MOFs and the examination of their properties in water harvesting, as well as gas adsorption such as methane, carbon dioxide, etc. Specifically, MOF-303, [Al(OH)(C5H2O4N2)(H2O)] and MOF-573 [Al(OH)(C5H2O4N2)(H2O)] constructed by linking aluminum (III) ions and 3,5-pyrazoledicarboxylic acid. MOF-303 and MOF-573 can be synthesized in hot water with low-cost starting materials, aluminum chloride hexahydrate or aluminum sulfate octacahydrate, 3,5-pyrazoledicarboxylic acid, and a base (e.g. NaOH) in short period (24 h or 72 h) at 100° C.

Single crystal X-ray diffraction studies show that both MOF-303 and MOF-573 contains inorganic aluminum chains linked via the carboxylate groups of the linkers and the hydroxyl groups. Each Al (III) ion is capped by four O atoms from four different carboxylate groups and two O atoms from two hydroxyl groups forming AlO6octahedra, and AlO6octahedra form corner-sharing chains, depending on the cis- and trans-position of the two adjacent bridging hydroxyl groups, helical chains in MOF-303 (cis-) and MOF-573 (trans-) form respectively. The ditopic linker further bridged two of the chains together, leading to the formation of a 3D framework delimiting square-shaped one dimensional channels with diameter of 6 Å and 5 Å in diameter, respectively (measured by the largest fitting sphere). MOF-303 has a topology of xhh, and MOF-573 has a topology of upt (FIG. 1).

These two MOFs show permanent porosity and have Brunauer-Emmett-Teller (BET) surface areas of 1380 and 980 m2g−1and pore volume of 0.55 and 0.56 cm3g−1, respectively (FIG. 2). Interestingly, MOF-303 represents a rigid framework while MOF-573 represents a flexible structure, evidenced by the change of pxrd patterns upon activation and the huge hysteresis in nitrogen sorption isotherms, indicating structural transformation upon activation and gas adsorption.

We demonstrated here the use of MOF-303 and MOF-573 for water harvesting. MOF-303 has a steep uptake at P/P0=0.15 and the maximum uptake is 48 wt %. The material can be easily fully regenerated at room temperature, with no decrease in performance in 5 cycles. Further kinetic cycling test shows that the materials shows no decrement in performance for up to 150 cycles (34 wt % delivery capacity under following condition: adsorption in 40% R.H. N2flow, desorption in dry N2flow at 85° C. for 30 mins), demonstrating high capacity and high stability of this material (FIG. 3).

MOF-303 can also capture other oxide based gases similar to CO2, such as SO2, NOx, which can be applied to remove these pollutants from air and post-combustion flue gases.

We further demonstrated the use of MOF-303 for high-pressure methane storage. It is shown that MOF-303 can hold 190 cm3cm−3of methane at 35 bar, 298 K, which is in line with the best performing materials ever reported (HKUST-1, 190-227 cm3cm−3, Ni-MOF-74, 208-230 cm3cm−3),7the delivery capacity is 106 cm3cm−3, indicating the application for storage and delivery of energy gases.

REFERENCES

Aluminum chloride hexahydrate (AlCl3.6H2O), aluminum sulfate octadecahydrate [Al2(SO4)3.18H2O], 3,5-pyrazoledicarboxylic acid monohydrate (H3PDC.H2O), Sodium hydroxide (NaOH), anhydrous methanol were purchased from commercial source and were used directly without further purification.

All the synthetic procedures were conducted in open air. The MOFs were activated by the following procedure: Firstly, the as-synthesized crystalline material was exchanged with fresh DI water for one day, six times per day; then exchanged with anhydrous methanol for one day, six times per day. After that, the solvent-exchanged MOFs were filtered, dried in air before fully evacuated to remove guest molecules under dynamic vacuum (Masterprep, 0.01 Torr) at ambient temperature for 4 h, then at elaborated temperature of 50° C. for 2 h, 100° C. for 2 h, 150° C. for 2 h and finally 180° C. for 2 h to give the activated sample. Additionally, the sample can also be directly activated under flow hot air (above 100° C.) after washing with water. The following measurements were all conducted using the activated samples unless otherwise noted.

Elemental analyses (EA) were performed using a Perkin Elmer 2400 Series II CHNS elemental analyzer; attenuated-total-reflectance Fourier-transform infrared (ATR-FTIR) spectra were recorded on a Bruker ALPHA Platinum ATR-FTIR Spectrometer.

Single crystal X-ray diffraction (SXRD) data was collected for both MOFs using as-synthesized crystals. Data for MOF-303 was collected at beamline 11.3.1 of the ALS at LBNL, equipped with a Bruker Photon 100 CMOS area detector using synchrotron radiation (10-17 KeV), at 0.7749(1) Å. Data for MOF-573 was collected on a Bruker D8 Venture diffractometer equipped with a CMOS area detector using micro-focus Cu Kα radiation (λ=1.54184 Å). Samples were mounted on MiTeGen® kapton loops and placed in a 100(2) K nitrogen cold stream.

Data were processed with the Bruker APEX2 software package,1,2integrated using SAINT v8.34A and corrected for the absorption by SADABS routines (no correction was made for extinction or decay). The structures were solved by intrinsic phasing (SHELXT) and refined by full-matrix least squares on F2(SHELXL-2014). Atomic positions of MOF-303 can be obtain from the single crystal data, but the anisotropic refinement remains unstable due to the poor diffraction of the crystals, thus the structure model was further refined by Pawley refinement using Material Studio 7.0.3All non-hydrogen atoms in MOF-573 were refined anisotropically. Hydrogen atoms were geometrically calculated and refined as riding atoms, highly disordered guest molecules occupying the cavities of the structure, which could not be modeled and so were accounted for using solvent masking using the Olex2 software package.4,5See the CIFs for further details.

A colorless plate-shaped (20 μm×20 μm×10 μm) crystal of as-synthesized MOF-303 was quickly picked up from the mother liquor, and placed in paratone oil, and mounted at beamline 11.3.1 at the ALS using radiation at λ=0.7749(1) Å at 100 K.

A colorless plate-shaped (50 μm×50 μm×20 μm) crystal of as-synthesized MOF-573 was quickly picked up from the mother liquor and mounted at Bruker D8 Venture diffractometer equipped with a CMOS area detector using micro-focus Cu Kα radiation (λ=1.54184 Å).

Low Pressure Gas Adsorption Measurements

Ultrahigh-grade gases (99.999% for N2, CO2, CH4, and He) and activated samples of MOFs were used for measurements. The N2(77 K) isotherms were measured on a Quadrasorb-SI. Apparent surface area of ZIFs were estimated by BET methods. The CO2, CH4, and N2adsorption isotherms were measured at 273 K, 283 K and 298 K and at pressures up to 1.0 bar using Autosorb-1 (Quantachrome) volumetric gas adsorption analyzer. High-pressure methane adsorption isotherms were measured using the static volumetric method on an HPVA-100 from the VTI Corporation (currently Particulate Systems). A liquid nitrogen bath was used for adsorption measurements at 77 K. A water circulator was used for measurements at 273, 283, and 298 K. The framework density was measured using a pycnometer (Ultrapyc 1200e, Quantachrome).

Water vapor isotherms at 298 K were measured in-house on a BEL Japan BELSORP-aqua3. Prior to measurements, the analyte water was flash frozen in liquid nitrogen and then evacuated under dynamic vacuum at least twice to remove any gases in the reservoir. The measurement temperature was controlled and monitored with a water bath held at 298 K. Helium was used to estimate dead space for vapor adsorption measurements.

SUPPLEMENTAL REFERENCES