a DoE Energy Frontier Research Center

A Spin Transition Mechanism for Cooperative Adsorption in Metal–Organic Frameworks

Designing new adsorbents for industrial gas separations requires maximizing both selectivity for the gas of interest and the recyclability of the material, where the selective adsorbent can be easily regenerated under mild conditions. We have made significant progress in designing selective adsorbents known as metal–organic frameworks (MOFs) that exhibit cooperative carbon monoxide adsorption for highly energy-efficient separations. Specifically, these materials contain interacting iron(II) sites where binding carbon monoxide at one iron site assists the binding of CO at neighboring metal sites, much like biological systems such as hemoglobin. This occurs through a spin transition mechanism where during this binding process neighboring iron sites undergo a simultaneous transition from high-spin to low-spin. Due to this adsorption mechanism, these materials can exhibit large working capacities utilizing small temperature swings, making them highly energy efficient in terms of regeneration while also remaining selective for CO adsorption. Importantly, this spin transition was shown to be highly tunable through variation of the organic linkers of the framework. As a similar response can be achieved through adsorption of a variety of different industrially relevant gases, further modification of this system can result in next generation materials for several different separation processes.
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The Chemistry of CO2 Capture in an Amine-Functionalized Metal–Organic Framework under Dry and Humid Conditions

New products resulting from CO2 capture in porous materials can lead to enhanced efficiency of the solid sorbents. The use of two primary alkylamine functionalities covalently tethered to the linkers of IRMOF-74-III results in a material that can uptake CO2 at low pressures through a chemisorption mechanism. In contrast to other primary amine-functionalized solid adsorbents that uptake CO2 primarily as ammonium carbamates, we observe using solid state NMR that the major chemisorption product for this material is carbamic acid. The equilibrium of reaction products also shifts to ammonium carbamate when water vapor is present; a new finding that has impact on control of the chemistry of CO2 capture in MOF materials. This finding also highlights the importance of geometric constraints within the pores of MOFs as the amines in IRMOF-74-III are positioned such that formation of carbamic acid is favored under dry conditions. The understanding of this chemistry gleaned here can be applied to the synthesis of next-generation solid CO2 sorbents.
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Controlling Cooperative CO2 Adsorption in Diamine-Appended Metal–Organic Frameworks

In the transition to a clean-energy future, CO2 separations will play a critical role in mitigating current greenhouse gas emissions and facilitating conversion to cleaner-burning and renewable fuels. Diamine-appended variants of the metal–organic framework Mg2(dobpdc) (dobpdc4- = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) are a particularly promising materials for CO2 separations owing to their high selectivities for CO2 adsorption, large CO2 removal capacities, and low regeneration energies. These frameworks feature step-shaped CO2 adsorption isotherms resulting from cooperative and reversible insertion of CO2 into metal–amine bonds to form ammonium carbamate chains. A detailed structure–activity study revealed that small modifications to the diamine structure can shift the threshold pressure for cooperative CO2 adsorption by over 4 orders of magnitude at a given temperature, and the observed trends were rationalized on the basis of crystal structures of the isostructural zinc frameworks. These results can be leveraged to precisely tailor adsorbents to the conditions of a given CO2 separation process, highlighting the potential of diamine-appended frameworks as next-generation adsorbents for a wide array of CO2 separations.
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Structural Characterization of Framework–Gas Interactions by in Situ Single-Crystal X-ray Diffraction

The crystallographic characterization of framework-guest interactions provides unparalleled insight on the nature and location of guest binding sites within metal-organic frameworks. In collaboration with Beamline 11.3.1 at the Advanced Light Source, experimental apparatus and techniques have been developed for in situ single-crystal X-ray diffraction experiments on porous crystals. These methods have enabled the direct observation of the adsorption of small molecules (CO, N2, O2, CH4, Ar, and P4) in Co2(dobdc) (dobdc4- = 2,5-dioxido-1,4-benzene-dicarboxylate), a metal-organic framework with coordinatively unsaturated cobalt(II) sites. The resulting structures reveal the location of the primary, secondary (for N2, O2, and Ar) and tertiary (for O2) adsorption sites for these gases within the framework. Remarkably, these gases interact with the framework cobalt(II) centers through distinctly weak interactions compared to those found in molecular complexes. As a consequence, this work represents the first report of the characterization of such species by single-crystal X-ray diffraction. Furthermore, these results are correlated with low- and high-pressure gas adsorption isotherms to establish the relationship between structure and adsorption behavior.
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The Influence of Intrinsic Framework Flexibility on Adsorption in Nanoporous Materials

For applications of metal-organic frameworks (MOFs) such as gas storage and separation, flexibility is often seen as a parameter that can tune material performance. In this work we aim to determine the optimal flexibility for the shape selective separation of similarly sized molecules (e.g., Xe/Kr mixtures). To obtain systematic insight into how the flexibility impacts this type of separation, we develop a simple analytical model that predicts a material’s Henry regime adsorption and selectivity as a function of flexibility. Selectivity performance is either improved or reduced with increasing flexibility, depending on the material’s pore size characteristics. However, the selectivity of a material with the pore size and chemistry that already maximizes selectivity in the rigid approximation is continuously diminished with increasing flexibility, demonstrating that the globally optimal separation exists within an entirely rigid pore. Molecular simulations show that our simple model predicts performance trends that are observed when screening the adsorption behavior of flexible MOFs. Thus, for shape selective adsorption applications, the globally optimal material will have the optimal pore size/chemistry and minimal intrinsic flexibility even though other nonoptimal materials' selectivity can actually be improved by flexibility. Equally important, we find that flexible simulations can be critical for correctly modeling adsorption in these types of systems.
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Ultra-Selective High-Flux Membranes from Directly Synthesized Zeolite Nanosheets

Porous crystalline materials with uniform pore sizes and high pore densities are promising for membrane separation applications, which are energy-efficient alternative to the conventional separation processes. However, the fabrication cost of such material is relatively high, and cost reduction or performance improvement is required for industrial applications. One promising approach is to fabricate a thin and intergrown membrane based on 2-dimensional crystals (nanosheets). In this work, we have, for the first time, developed a direct synthesis method of single MFI nanosheets and demonstrated their high separation performances. Previously, zeolite MFI nanosheets were prepared by exfoliation of multi-lamella MFI materials. This exfoliation process is costly and time-consuming and suffers from fracture of the nanosheets (<300 nm). In comparison, our direct synthesis method can yield larger (~2 µm) nanosheets with an improved production yield. This was enabled by seeded growth based on twining, which triggers the emergence of nanosheet from the seed crystal. These nanosheets with high aspect ratios can form high-density coating on porous supports, which are further intergrown into continuous membranes. These thin membranes exhibit superior separation performances, as established for xylene isomer mixtures, alcohol/water mixture, and linear/branched hydrocarbon mixtures.
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Continuous Flow Processing of ZIF-8 Membranes on Polymeric Porous Hollow Fiber Supports for CO2 Capture

Inorganic membranes can have very high gas permeability and selectivity compared to conventional polymeric membranes. But the fabrication of inorganic membranes is costly, time consuming and needs aggressive synthesis conditions. Also, scale-up and reproducibility are big problems, in part due to the use of expensive ceramic supports. In this work, we have successfully fabricated defect-free ZIF-8 membranes on polymeric hollow fiber supports using a continuous flow processing method that is simple, scalable, reduces manufacturing costs, and is environmentally friendly. The formation of a continuous ZIF-8 membrane that is ~8 µm thick was controlled by flowing an aqueous metal solution on the shell side of a polymer hollow fiber while flowing the 2-methylimidazole linker through the bore. The formation of ZIF-8 was confirmed using XRD and EDX. The ZIF-8 membrane was grown and anchored to the microporous region of the outer surface of supports for better mechanical properties and to avoid the delamination of membrane. These membranes demonstrated CO2 permeance of 22 GPU and CO2/N2 selectivity of 52. This method is very useful to scale up the fabrication of inorganic membranes for industrial applications, as the membrane can be formed in situ in a pre-assembled hollow fiber module.
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Chemical Conversion of Linkages in Covalent Organic Framework

Covalent organic frameworks (COFs) are ordered, porous polymers formed from the assembly of small molecular building blocks. The typical linking reactions employed are reversible so that any defects arising during COF synthesis can be dissolved and subsequently reformed. The inherent linkage reversibility leaves the frameworks subject to chemical degradation through this reverse reaction. This report describes a chemical modification of the framework from easily hydrolyzed imine linkages to more chemically stable amide functionalities. This reaction can be performed under mild oxidative conditions at room temperature, and leaves the underlying structure of the starting materials unchanged. The conversion of these materials can be confirmed can both infrared and solid state nuclear magnetic resonance (NMR) spectroscopy. In addition, the products maintain the crystallinity of the parent compounds, as measured by powder X-ray diffraction. While the amide-linked materials are permanently porous, their surface area is lowered by this transformation, probably due to included oligomeric species, whose existence is supported by preliminary NMR experiments. The improved chemical stability of these new materials was assessed by measurement of diffraction before and after treatment with strong aqueous acid and base.
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About the CGS


Who We Are

The Center for Gas Separations is one of 32 Energy Frontier Research Centers funded by the Department of Energy to conduct fundamental research that addresses the five Basic Energy Sciences Grand Challenges:

  1. How do we control material processes at the level of electrons?
  2. How do we design and perfect atom- and energy-efficient synthesis of revolutionary new forms of matter with tailored properties?
  3. How do remarkable properties of matter emerge from complex correlations of the atomic or electronic constituents and how can we control these properties?
  4. How can we master energy and information on the nanoscale to create new technologies with capabilities rivaling those of living things?
  5. How do we characterize and control matter away -especially very far away- from equilibrium?

The Center is made up of researchers across the US, at the University of California, Berkeley (lead institution), Lawrence Berkeley National Lab, Texas A&M University, University of Minnesota, the National Energy Technology Laboratory, and the National Institute of Standards and Technology.


What We Do

Although it is challenging to calculate the energy used by all chemical separation processes, the best estimates indicate that they account for 10-15% of the energy consumed globally. Some of the largest offenders are the purification of oxygen (O2, 91% of energy input is for separating N2), petroleum refining (>50% energy expended is for separations), and the separation of carbon dioxide (CO2) from H2 necessary for ammonia production (25% of energy consumed). In the US alone, separations account for an even greater ~22% of the total national energy input. Furthermore, when faced with climate change resulting from continually-increasing anthropogenic CO2 emissions and the corresponding necessity of large-scale carbon capture and storage, the cost of separations is expected to increase significantly. Reducing the total energy costs of separations would therefore contribute substantially to minimizing wasteful energy consumption globally.

To address this need, the primary goal within the Center for Gas Separations (CGS) is to tailor-make novel materials for highly efficient gas separations, with an emphasis on adsorbents that are highly selective for CO2 capture. This strategy addresses the 2nd Grand Challenge and requires a fundamental understanding of materials properties, molecular interactions, and the design of adsorbents tuned precisely for interactions with specific gases.

Announcements


Date  
September
2017
Hints from hemoglobin lead to better carbon monoxide storage: Scientists at Berkeley and University of Turin designed a MOF for cooperative CO adsorption.
Read a paper: [PDF] [Nature website]
Learn more: Berkeley NEWS [PDF], APS Science Highlights [PDF]
July
2017
EFRC newsletter: The latest issue of Frontiers in Energy Research is now available, and Stephen Meckler provided a comprehensive and thoughtful article. [PDF]
July
2017
2017 All-Hands Meeting
Date: December 4-5, 2017
Location: DoubleTree Hilton at the Berkeley Marina
June
2017
Efrem Braun (Smit group) has won the 2017 AIChE Separations Division Graduate Student Award in the Adsorption and Ion Exchange Area. [AIChE website]
March
2017
The CGS team participated in the College & Career Day at Berkeley Arts Magnet elementary school on March 10.
November
2016
Carbon Capture and Storage: Carbon Capture and Storage themed issue, Faraday Discussions. [RSC website]
September
2016
Evok Innovations Announces First Round of Investments: Mosaic Materials, which is working to commercialize materials initially discovered in the CGS, is selected as one of five cleantech companies. [PDF]
September
2016
EFRC Program Booklet: BES has recently published a booklet that summarizes the history and mission of the EFRC program and highlights the accomplishments since 2009. [PDF]
June
2016
2016 All-Hands Meeting
Date: November 8-9, 2016
Location: DoubleTree Hilton at the Berkeley Marina
April
2015
Materials Science: The Hole Story (Nature: News Feature, 520, 148-150, April 8, 2015)
March
2015
Materials Chemistry: Cooperative Carbon Capture (Nature News & Views, 519, 294-295, March 19, 2015)
March
2015
Porous Crystal Supersuckers Capture Carbon (IEEE Spectrum, March 18, 2015)
March
2015
New Material Captures Carbon at Half the Energy Cost (Phys.org, March 11, 2015)
March
2015
New Material Captures Carbon at Half the Energy Cost (Science Daily, March 11, 2015)
March
2015
New Material Captures Carbon at Half the Energy Cost (Scicasts, March 11, 2015)
March
2015
A Better Way To Scrub CO2 (Science 2.0, March 19, 2015)
March
2015
A Better Way of Scrubbing CO2 (Newswise, March 17, 2015)
March
2015
A Better Way of Scrubbing CO2 (Lab Manager, March 19, 2015)
March
2015
Researchers Triple CO2-Scrubbing Capacity of MOFs by Appending a Diamine Molecule (Azonano, March 18, 2015)
March
2015
A Better Way of Scrubbing CO2 (Nanowerk, March 17, 2015)
March
2015
A Better Way of Scrubbing CO2 (EurekAlert! March 17, 2015)
March
2015
A Better Way of Scrubbing Carbon Dioxide (R&D Mag, March 17, 2015)
March
2015
Cooperative Insertion of CO2 in Diamine-appended Metal-organic Frameworks (Bioportfolio, March 11, 2015)
March
2015
A Better Way of Scrubbing CO2 (Innovations Report, March 18, 2015)
March
2015
New Material Captures Carbon at Half the Energy Cost (Health Medicinet, March 2015)
March
2015
Material Captures Carbon at Half the Energy Cost (Product Design & Development, March 13, 2015)
March
2015
Cooperative Capture (Nature podcast interview of Jeff Long on work reported in 3/12/15 Nature article)
March
2015
The Proof Is in the Pores (EFRC Newsletter, March 2015)
March
2015
Predicting Cheaper Routes for Carbon Capture (EFRC Newsletter, March 2015)
December
2014
Cover of Chemical Science (Chem. Sci., Dec. 2014)
November
2014
Playing Catch and Release with Molecules (Frontiers in Energy Research, Nov. 2014)
October
2014
New Carbon Capture Method is the Best of Both Worlds (Nature World News, Oct. 2014)
October
2014
Un captage de carbone (encore) plus rentable et plus efficace ? (Enerzine, Oct. 2014)
October
2014
MOF Slurry-Based Process May Revolutionize Carbon Capture (Azonano, Oct. 2014)
October
2014
A Cost-effective and Energy-efficient Approach to Carbon Capture (Science Newsline, Oct. 2014)
October
2014
A Cost-effective and Energy-efficient Approach to Carbon Capture (Phys.org, Oct. 2014)
October
2014
New 'Slurry' Could Make Carbon Capture More Efficient (Climate Central, Oct. 2014)
October
2014
A Cost-effective and Energy-efficient Approach to Carbon Capture (e! Science News, Oct. 2014)
October
2014
A Cost-effective and Energy-efficient Approach to Carbon Capture (Science Daily, Oct. 2014)
October
2014
A Cost-effective and Energy-efficient Approach to Carbon Capture (USA News, Oct. 2014)
October
2014
A Cost-effective and Energy-efficient Approach to Carbon Capture with MOFs (Nanowerk, Oct. 2014)
September
2014
New Sorbents for Greener Cooling (C&EN, Sept. 2014)
June
2014
An Inside Look at a MOF in Action (ALS Highlight, June 2014)
April
2014
MOFs (MRS-TV video, April 2014)
December
2013
Research Highlight: Cage Calculations (Nature Chemistry, Dec. 2013)
August
2013
New method predicts adsorption in carbon dioxide-scrubbing materials (R&D Magazine, Aug. 2013)
August
2013
Cover of Advanced Materials (Adv. Mat., Aug. 2013)
June
2013
Cover of the Journal of Physical Chemistry C (J. Phys. Chem. C, June 2013)
May
2013
Material That Sorts Molecules by Shape Could Lower the Price of Gas (MIT Technology Review, May 2013)
April
2013
Researchers discover materials to transform methane into fuel (The Daily Californian, April 2013)
April
2013
Methane-gobbling material found, scientists say (NBC News, April 2013)
April
2013
Inside back cover of Angewandte Chemie (Angewandte Chemie, April 2013)
December
2012
MOFiosos: Berkeley scientists make carbon a structure it cannot refuse (Berkeley Science Review, Dec. 2012)
November
2012
Cover of ChemPhysChem (ChemPhysChem, Nov. 2012)
October
2012
Nanosolutions for Grand Challenges (EFRC Newsletter, Oct. 2012)
October
2012
News and Views in Nature Chemistry: Force fields for carbon capture (Nature Chemistry, Oct. 2012)
October
2012
Cover picture on Angewandte Chemie (Angewandte Chemie, Oct. 2012)
September
2012
Biomimetic And Extreme Surface-Area Frameworks (C&EN, Sept. 2012)
August
2012
Cover of PCCP (PCCP, Aug. 2012)
May
2012
Computer Model Pinpoints Prime Materials for Efficient Carbon Capture (Science Daily, May 2012)
May
2012
New Materials could Reduce Parasitic Load of CO2 Capture by up to 40%, Researchers Say (GHG Monitor, May 2012)
May
2012
New Materials Could Cut Parasitic Energy Costs for CO2 Capture by up to 30-40% (Green Car Congress, May 2012)
April
2012
A Step Up for Separating Hydrocarbons (C&EN, April 2012)
March
2012
New Material Cuts Energy Costs of Separating Gas for Plastics and Fuels (e! Science News, March 2012)
March
2012
Cutting the Cost for Commercial Gas Purification -Theory Leads the Way for a Materials Solution (DOE-BES highlight, March 2012)
March
2012
Carbon Dioxide Catchers (Nanowerk, March 2012)
August
2011
Inside front cover of Advanced Materials (Advanced Materialds, Aug. 2011)
October
2010
Structure of the Week - # 10 October 25, 2010 (ACS, Oct. 2010)
September
2011
Metal Organic Frameworks (CEN Online video, Sept. 2011)
July
2010
Carbon Smackdown: Carbon Capture (Berkeley Lab video, July 2010)
May
2010
Hunt for Improved Carbon Capture Picks up Speed (Berkeley Lab video, May 2010)
February
2010
Carbon Cycle 2.0: Carbon Capture (Berkeley Lab video, Feb. 2010)