Journal of Materials Chemistry Blog

Acetylene is widely known for its use as a fuel in welding equipment and it is also a very important building block in industrial chemical synthesis. Unfortunately, obtaining high-purity acetylene is not a trivial matter. Removing methane and carbon dioxide via cryogenic distillation is extremely energy intensive due to the low temperature required and therefore a process that avoids the need for such cooling is extremely attractive.

Hui Xu et al. have recently demonstrated the effective purification of acetylene at room temperature and pressure through the use of a microporous metal-organic framework, Cu₆(PDC)₆ ^. 2.6H₂O (PDC = 3,4-pyridine-dicarboxylate). Known as UTSA-50, the material was designed such that its pores are not only optimally sized for gas storage but that they also contain both exposed metal atoms and pyridyl groups. This enables both electrostatic and hydrogen-bonding interactions with acetylene. The latter are thought to be the key to selectivity given the ability of pyridyl nitrogen atoms to form hydrogen bonds with acetylene but not with CO₂ or CH₄.

At 296 K and 1 atm the UTSA-50 framework can adsorb 91 cm^-1 g^-1 acetylene which is comparable to other materials with similar pore size and surface area. Henry’s law selectivities of 68.0 and 13.3 for acetylene over carbon dioxide and methane, respectively, are extremely promising. In fact, the selectivity for CO₂ is, according to the authors, the highest ever reported.

A microporous metal-organic framework with both open metal and Lewis basic pyridyl sites for highly selective C₂H₂/CH₄ and C₂H₂/CO₂ gas separation at room temperature

J. Mater. Chem. A, 2013, 2, 77.  DOI: 10.1039/c2ta00155a

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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For hundreds of years there have been attempts to use explosives for nefarious purposes. Unfortunately, central government can not always rely on mysterious, anonymous letters to prevent their untimely obliteration. A simple, sensitive and reliable means of detecting explosive compounds would not only have security applications; there is also a need to prevent the accidental release of explosive materials into the environment.

In a recent paper, Yuan et al. describe a three-dimensional pourous aromatic framework (PAF) with high-fluorescence quenching ability for nitro-aromatic compounds. As little as 1.5 ppm of an explosive such as TNT (2,4,6-trinitrotoluene) leads to a significant, observable decrease in luminescence intensity. Common aromatics lacking a nitro group elicit no such decrease.

The highly crystalline PAF was formed by a condensation reaction between a germanium-containing, luminescent monomer and aromatic boronic acids. The resulting polymeric framework gives the material a high fluorescence quantum yield that is easily disrupted by interactions with an analyte. The specificity for nitro-aromatics is thought to come from the attraction of electronegative nitro groups to the electron-donating PAF.

Such a sensitive material has enormous potential for use in explosives detection equipment. However, enemies of Jacobean plotters beware! This strategy might not detect gunpowder.

Sensitive detection of hazardous explosives via highly fluorescent crystalline porous aromatic frameworks

J. Mater. Chem., 2012, 22, 24558.  DOI: 10.1039/c2jm35341e

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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