Cavity-containing rhenium metallacycle treated evanescent wave infrared chemical sensors for the selective determination of odorous amines in the atmosphere

Abstract

An evanescent wave infrared chemical sensor was developed for the selective detection of odorous amino compounds in the atmosphere. To achieve this goal, cavity-containing rhenium metallacycles with multi-recognition sites were prepared and used as host molecules to modify the surface of an evanescent wave infrared (EWIR) sensing element. The unique cavity structure with hydrophobic properties of the Re metallacycle permits the selective trapping of suitably sized compounds with proper functionalities. To explore the scope of the process, two different Re metallacycles were synthesized and used to trap a series of volatile organic compounds (VOCs) with different functionalities. Based on the results, Re metallacycles are selective to detect amino compounds as evidenced by the peak shifts for C[tbnd]O absorption after the amino compounds had been adsorbed. The hydrophobic pocket and hydroxyl groups in the Re metallacycles were also verified to provide extra forces to stabilize the attraction of amino compounds. The efficiency of the Re metallacycles in detecting amino compounds follows the order of amine with phenyl ring > aliphatic primary amine ∼ cyclo-amine > aliphatic secondary amine > aliphatic tertiary amine. This sensor was applied to detect benzyl amine and a linear range up to 1 mg/L could be obtained with a detection limit close to 4 μg/L.