a DoE Energy Frontier Research Center

Redox-Switchable Breathing Behavior in Metal–Organic Frameworks

Metal-organic frameworks (MOFs) that respond to external stimuli such as guest molecules, temperature, or redox conditions are highly desirable for their potential applications as smart absorbents for gas separation and storage. A representative example of framework flexibility is the breathing effect in which the framework experiences a reversible unit-cell dimensional change resulting from guest adsorption or desorption. We demonstrated that the flexibility and the associated breathing behavior of MOFs can be controlled by redox chemistry. Guided by topology, two flexible isomeric MOFs with a formula of In(Me2NH2)(TTFTB) were constructed via a combination of [In(COO)4]- metal nodes and tetratopic tetrathiafulvalene-based linkers (TTFTB). The breathing behaviors of two compounds upon N2 sorption were studied by single-crystal X-ray diffractions and molecular simulations. More importantly, the rigidity of TTF-based linkers can be switched by reversible redox reaction, which in turn controls the flexibility of MOFs. The redox-controlled dynamic behavior of MOFs is reminiscent of sophisticated biological behavior such as redox regulation of enzymes. We believe that the redox-switchable flexible MOFs can potentially be applied to the design of smart absorbents with higher storage capacities and efficient gas release.
READ MORE

Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks

The separation of alkylaromatics o-xylene, m-xylene, p-xylene, and ethylbenzene is of enormous importance industrially, but very technically challenging due to the different isomers' similar physical properties. Metal–organic frameworks are promising as potential selective adsorbents, but separation of larger hydrocarbon mixtures remains a challenge. Here, we demonstrate the ability of Co2(dobdc) (dobdc4– = 2,5-dioxide-1,4-benzenedicarboxylate) and Co2(m-dobdc) (m-dobdc4– = 4,6-dioxido-1,3-benzenedicarboxylate) to differentiate these different isomers, with Co2(dobdc) preferentially binding o-xylene > ethylebenzene > m-xylene > p-xylene. This was shown through single component vapor adsorption isotherms, multi-component vapor breakthrough measurements, and multi-component solution phase adsorption measurements. Structural analysis through single crystal and powder X-ray diffraction showed that these materials perform these separations through multiple metal site interactions, in which adjacent Co(II) centers bind to the same xylene molecule. Due to the different shapes of these isomers, the degree to which each xylene molecule can effectively bind to both Co(II) sites dictates the strength of interaction, providing an effective basis for separation. Finally, previously unobserved pore flexing in the hexagonal channels of Co2(dobdc) allows for greater xylene uptake capacities.
READ MORE

Unexpected Diffusion Anisotropy of Carbon Dioxide in the Metal−Organic Framework Zn2(dobpdc)

Metal–organic frameworks are promising materials for energy-efficient gas separations, but little is known about the diffusion of adsorbates in materials featuring one-dimensional porosity at the nanoscale. An understanding of the interplay between framework structure and gas diffusion is important for the practical application of these materials as adsorbents or in mixed-matrix membranes. Here, we investigated the diffusion of CO2 within the pores of Zn2(dobpdc) (dobpdc4– = 4,4′-dioxidobiphenyl-3,3′-dicarboxylate) using pulsed field gradient (PFG) nuclear magnetic resonance (NMR) spectroscopy and molecular dynamics (MD) simulations. Importantly, our PFG NMR method allowed measurement of self-diffusion in different crystallographic directions. In addition to observing CO2 diffusion through the channels parallel to the crystallographic c axis we unexpectedly found that CO2 is also able to diffuse between the hexagonal channels in the crystallographic ab plane, despite the walls of these channels appearing impermeable by single-crystal X-ray crystallography and flexible lattice MD simulations. Observation of such unexpected diffusion in the ab plane suggests the presence of defects that enable effective multidimensional CO2 transport in a metal–organic framework with nominally one-dimensional porosity.
READ MORE

On the Direct Synthesis of Cu(BDC) MOF Nanosheets and their Performance in Mixed Matrix Membranes

Metal-organic framework (MOF)-based membranes have gained increasing attention for their potential utility in the separation of CO2 from natural gas and flue gas streams. Mixed matrix membranes (MMMs), which consist of MOF particles imbedded in a polymer matrix, are particularly appealing from a manufacturing standpoint. Compared to isotropic MOF crystals, the use of high aspect-ratio MOF nanosheets may enhance the separation performance of MMMs, although it has been a challenge to develop simple and scalable methods for nanosheet synthesis. In this work, we describe the facile preparation of Cu(BDC) (BDC2– = 1,4-benzenedicarboxylate) nanosheets with aspect ratios as high as 100 via direct synthesis from a well-mixed solution of metal and ligand precursors. Notably, incorporation of the Cu(BDC) nanosheets into a Matrimid polymer matrix results in a MMM with a 70% increase in CO2/CH4 selectivity compared to neat Matrimid. Our approach is suitable for large-scale synthesis and can also be extended to the preparation of other varieties of MOF nanosheets. Analysis of gas permeation data for Cu(BDC) MMMs using a mathematical model also indicates that additional membrane performance improvements may be achieved by varying the choice of polymer used in the continuous phase.
READ MORE

Relaxometry and Diffusometry of Small Molecules in MOFs

How do molecules move when confined within small spaces? We placed three molecules (ortho-, meta-, and para-xylene) inside of a special material (metal-organic framework IRMOF-1) that has small pores, about the twice the size of these molecules. NMR spectroscopy revealed differences in how fast the molecules diffuse, as well as how the molecules rotate when confined to the MOF. Diffusion measurements come from a method known as NMR pulsed-field gradient diffusion and compare quite well with computer simulations of diffusion using sophisticated force fields created by quantum chemistry. The most cylindrically-shaped molecule, para-xylene, diffuses the fastest of the three because it has the weakest interactions with the MOF walls, as revealed by computer simulations. The rotation of these molecules was discerned via NMR relaxation times and, when combined with computer simulated probability maps, show that these molecules rotate like a Frisbee, and not like a flipping pancake, while in the MOF. Interestingly, the para-xylene molecules diffuse the fastest, yet have the highest energy barrier to rotate because these molecules don’t fit well in the MOF pores.
READ MORE

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.
READ MORE

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.
READ MORE

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.
READ MORE

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.
READ MORE

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  
July
2018
MOFs separate chemicals of similar size: CGS research was featured in the latest issue of Frontiers in Energy Research.
Read a web article: [PDF] [EFRC website]
November
2017
A Molecular Zipper for Efficient Gas Separation: The DOE Office of Science recently published a highlight about the CGS research in cooperative CO capture materials.
Read a web article: [PDF] [DOE BES website], [PDF] [Newswise website]
November
2017
Helping Membranes Perform Under Pressure: CGS research was featured in the latest issue of Frontiers in Energy Research.
Read a web article: [PDF] [EFRC website]
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)