Tag Archives: metal-organic framework (MOF)

Capturing neon in an organic environment

Neon observed experimentally within the pores of NiMOF-74 at 100 K and 100 bar of neon gas pressure Courtesy: Cambridge Crystallographic Data Centre (CCDC)

Neon observed experimentally within the pores of NiMOF-74 at 100 K and 100 bar of neon gas pressure Courtesy: Cambridge Crystallographic Data Centre (CCDC)

An Aug. 10, 2016 news item on Nanowerk announces the breakthrough (Note: A link has been removed),

In a new study, researchers from the Cambridge Crystallographic Data Centre (CCDC) and the U.S. Department of Energy’s (DOE’s) Argonne National Laboratory have teamed up to capture neon within a porous crystalline framework. Neon is well known for being the most unreactive element and is a key component in semiconductor manufacturing, but neon has never been studied within an organic or metal-organic framework until now.

The results (Chemical Communications, “Capturing neon – the first experimental structure of neon trapped within a metal–organic environment”), which include the critical studies carried out at the Advanced Photon Source (APS), a DOE Office of Science user facility at Argonne, also point the way towards a more economical and greener industrial process for neon production.

An Aug. 10, 2016 Cambridge Crystallographic Data Centre (CCDC) press release, which originated the news item, explains more about neon and about the new process,

Neon is an element that is well-known to the general public due to its iconic use in neon signs, especially in city centres in the United States from the 1920s to the 1960s. In recent years, the industrial use of neon has become dominated by use in excimer lasers to produce semiconductors. Despite being the fifth most abundant element in the atmosphere, the cost of pure neon gas has risen significantly over the years, increasing the demand for better ways to separate and isolate the gas.

During 2015, CCDC scientists presented a talk at the annual American Crystallographic Association (ACA) meeting on the array of elements that have been studied within an organic or metal-organic environment, challenging the crystallographic community to find the next and possibly last element to be added to the Cambridge Structural Database (CSD). A chance encounter at that meeting with Andrey Yakovenko, a beamline scientist at the Advanced Photon Source, resulted in a collaborative project to capture neon – the 95th element to be observed in the CSD.

Neon’s low reactivity, along with the weak scattering of X-rays due to its relatively low number of electrons, means that conclusive experimental observation of neon captured within a crystalline framework is very challenging. In situ high pressure gas flow experiments performed at X-Ray Science Division beamline 17-BM at the APS using the X-ray powder diffraction technique at low temperatures managed to elucidate the structure of two different metal-organic frameworks with neon gas captured within the materials.

“This is a really exciting moment representing the latest new element to be added to the CSD and quite possibly the last given the experimental and safety challenges associated with the other elements yet to be studied” said Peter Wood, Senior Research Scientist at CCDC and lead author on the paper published in Chemical Communications. “More importantly, the structures reported here show the first observation of a genuine interaction between neon and a transition metal, suggesting the potential for future design of selective neon capture frameworks”.

The structure of neon captured within the framework known as NiMOF-74, a porous framework built from nickel metal centres and organic linkers, shows clear nickel to neon interactions forming at low temperatures significantly shorter than would be expected from a typical weak contact.

Andrey Yakovenko said “These fascinating results show the great capabilities of the scientific program at 17-BM and the Advanced Photon Source. Previously we have been doing experiments at our beamline using other much heavier, and therefore easily detectable, noble gases such as xenon and krypton. However, after meeting co-authors Pete, Colin, Amy and Suzanna at the ACA meeting, we decided to perform these much more complicated experiments using the very light and inert gas – neon. In fact, only by using a combination of in situ X-ray powder diffraction measurements, low temperature and high pressure have we been able to conclusively identify the neon atom positions beyond reasonable doubt”.

Summarising the findings, Chris Cahill, Past President of the ACA and Professor of Chemistry, George Washington University said “This is a really elegant piece of in situ crystallography research and it is particularly pleasing to see the collaboration coming about through discussions at an annual ACA meeting”.

The paper describing this study is published in the journal Chemical Communications, http://dx.doi.org/10.1039/C6CC04808K. All of the crystal structures reported in the paper are available from the CCDC website: http://www.ccdc.cam.ac.uk/structures?doi=10.1039/C6CC04808K.

Here’s another link to the paper but this time with a citation for the paper,

Capturing neon – the first experimental structure of neon trapped within a metal–organic environment by
Peter A. Wood, Amy A. Sarjeant, Andrey A. Yakovenko, Suzanna C. Ward, and Colin R. Groom. Chem. Commun., 2016,52, 10048-10051 DOI: 10.1039/C6CC04808K First published online 19 Jul 2016

The paper is open access but you need a free Royal Society of Chemistry publishing personal account to access it.

Solar cells and ‘tinkertoys’

A Nov. 3, 2014 news item on Nanowerk features a project researchers hope will improve photovoltaic efficiency and make solar cells competitive with other sources of energy,

 Researchers at Sandia National Laboratories have received a $1.2 million award from the U.S. Department of Energy’s SunShot Initiative to develop a technique that they believe will significantly improve the efficiencies of photovoltaic materials and help make solar electricity cost-competitive with other sources of energy.

The work builds on Sandia’s recent successes with metal-organic framework (MOF) materials by combining them with dye-sensitized solar cells (DSSC).

“A lot of people are working with DSSCs, but we think our expertise with MOFs gives us a tool that others don’t have,” said Sandia’s Erik Spoerke, a materials scientist with a long history of solar cell exploration at the labs.

A Nov. 3, 2014 Sandia National Laboratories news release, which originated the news item, describes the project and the technology in more detail,

Sandia’s project is funded through SunShot’s Next Generation Photovoltaic Technologies III program, which sponsors projects that apply promising basic materials science that has been proven at the materials properties level to demonstrate photovoltaic conversion improvements to address or exceed SunShot goals.

The SunShot Initiative is a collaborative national effort that aggressively drives innovation with the aim of making solar energy fully cost-competitive with traditional energy sources before the end of the decade. Through SunShot, the Energy Department supports efforts by private companies, universities and national laboratories to drive down the cost of solar electricity to 6 cents per kilowatt-hour.

DSSCs provide basis for future advancements in solar electricity production

Dye-sensitized solar cells, invented in the 1980s, use dyes designed to efficiently absorb light in the solar spectrum. The dye is mated with a semiconductor, typically titanium dioxide, that facilitates conversion of the energy in the optically excited dye into usable electrical current.

DSSCs are considered a significant advancement in photovoltaic technology since they separate the various processes of generating current from a solar cell. Michael Grätzel, a professor at the École Polytechnique Fédérale de Lausanne in Switzerland, was awarded the 2010 Millennium Technology Prize for inventing the first high-efficiency DSSC.

“If you don’t have everything in the DSSC dependent on everything else, it’s a lot easier to optimize your photovoltaic device in the most flexible and effective way,” explained Sandia senior scientist Mark Allendorf. DSSCs, for example, can capture more of the sun’s energy than silicon-based solar cells by using varied or multiple dyes and also can use different molecular systems, Allendorf said.

“It becomes almost modular in terms of the cell’s components, all of which contribute to making electricity out of sunlight more efficiently,” said Spoerke.

MOFs’ structure, versatility and porosity help overcome DSSC limitations

Though a source of optimism for the solar research community, DSSCs possess certain challenges that the Sandia research team thinks can be overcome by combining them with MOFs.

Allendorf said researchers hope to use the ordered structure and versatile chemistry of MOFs to help the dyes in DSSCs absorb more solar light, which he says is a fundamental limit on their efficiency.

“Our hypothesis is that we can put a thin layer of MOF on top of the titanium dioxide, thus enabling us to order the dye in exactly the way we want it,” Allendorf explained. That, he said, should avoid the efficiency-decreasing problem of dye aggregation, since the dye would then be locked into the MOF’s crystalline structure.

MOFs are highly-ordered materials that also offer high levels of porosity, said Allendorf, a MOF expert and 29-year veteran of Sandia. He calls the materials “Tinkertoys for chemists” because of the ease with which new structures can be envisioned and assembled. [emphasis mine]

Allendorf said the unique porosity of MOFs will allow researchers to add a second dye, placed into the pores of the MOF, that will cover additional parts of the solar spectrum that weren’t covered with the initial dye. Finally, he and Spoerke are convinced that MOFs can help improve the overall electron charge and flow of the solar cell, which currently faces instability issues.

“Essentially, we believe MOFs can help to more effectively organize the electronic and nano-structure of the molecules in the solar cell,” said Spoerke. “This can go a long way toward improving the efficiency and stability of these assembled devices.”

In addition to the Sandia team, the project includes researchers at the University of Colorado-Boulder, particularly Steve George, an expert in a thin film technology known as atomic layer deposition.

The technique, said Spoerke, is important in that it offers a pathway for highly controlled materials chemistry with potentially low-cost manufacturing of the DSSC/MOF process.

“With the combination of MOFs, dye-sensitized solar cells and atomic layer deposition, we think we can figure out how to control all of the key cell interfaces and material elements in a way that’s never been done before,” said Spoerke. “That’s what makes this project exciting.”

Here’s a picture showing an early Tinkertoy set,

Original Tinkertoy, Giant Engineer #155. Questor Education Products Co., c.1950 [downloaded from http://en.wikipedia.org/wiki/Tinkertoy#mediaviewer/File:Tinkertoy_300126232168.JPG]

Original Tinkertoy, Giant Engineer #155. Questor Education Products Co., c.1950 [downloaded from http://en.wikipedia.org/wiki/Tinkertoy#mediaviewer/File:Tinkertoy_300126232168.JPG]

The Tinkertoy entry on Wikipedia has this,

The Tinkertoy Construction Set is a toy construction set for children. It was created in 1914—six years after the Frank Hornby’s Meccano sets—by Charles H. Pajeau and Robert Pettit and Gordon Tinker in Evanston, Illinois. Pajeau, a stonemason, designed the toy after seeing children play with sticks and empty spools of thread. He and Pettit set out to market a toy that would allow and inspire children to use their imaginations. At first, this did not go well, but after a year or two over a million were sold.

Shrinky Dinks, tinkertoys, Lego have all been mentioned here in conjunction with lab work. I’m always delighted to see scientists working with or using children’s toys as inspiration of one type or another.