Metal-organic frameworks for alcohol gas sensor

Metal-organic frameworks (MOFs) containing unsaturated coordination metal(II) sites (or open metal sites) have shown high selectivity for gas adsorption, separation and chemical sensor applications. The compound Zn-3(btc)(2)center dot 12H(2)O (Zn-btc), a coordination polymer with specific binding sites for guest molecules consist of Zn(II) ions and benzene tricarboxylic acid (btc) as anionic organic linkers, stabilized by numerous hydrogen bonds from crystal water molecules was synthesized. For the first time alcohol gas sensing interaction with Zn-btc framework was studied by using work function change methods. The as prepared Zn-btc thin layers show good response with reference to the alcohol concentration, chain length and a pronounced influence of humidity. The results are interpreted starting from the known crystal structure of Zn-btc. It is argued that the sensing mechanism is based on the exchange of Zn-coordinated water against alcohol molecules. The unfavourable loss of hydrogen bonds when replacing water against alcohol in the structure can be partially balanced by van der Waals interactions between alcohols alkyl chains and the aromatic rings of the btc linker molecules. These non-polar interactions should also be responsible for the work function change induced by alcohol adsorption in the framework. (C) 2015 Elsevier B.V. All rights reserved.