A multifunctional supramolecular self-assembly system for colori-metric detection of Hg2+, Fe3+, Cu2+ and continuous sensing of volatile acids and organic amine gases
A novel multifunctional gelator (1) based on azobenzene derivative was designed and characterized. This compound could gelate some solvents including hexane, petroleum ether, DMSO, acetonitrile and ethanol through heating-cooling procedure. The self-assembly process in different solvents was studied by means of UV-vis absorption and FTIR spectra, field emission scanning electron microscopy (FESEM), rheological measurement, X-ray powder diffraction and water contact angle experiments. Interestingly, compound 1 had a high-contrast colorimetric detection ability towards Hg2+, Cu2+, Fe3+ and volatile acids and further organic amine gases in solution through its color change. At the same time, organogel 1 in acetonitrile also exhibited the detection performance through color or gel state change. In the response process, the self-assembly structures were changed from nanofiber into microsphere under the inducing of analytes. More significantly, film 1 could continuously detect volatile acids and organic amine gases. The cycle times of film 1 of detection volatile acids and organic amine gases was at least 7 times. The limit of detection (LOD) of film 1 towards TFA was calculated to be 0.0848 ppb. The sensing mechanisms were studied by 1HNMR, FESEM, UV-vis absorption spectra and HRMS. The intramolecular cyclization was occurred on molecule 1 and a H2S molecule was lost in the detection process of Hg2+. It was proposed that the -N=N- bonding could be coordinated Fe3+ and Cu2+ and further induced its absorption spectra and color change. For volatile acid, it was possible that volatile acid was combined with N, N-dimethyl amine group of molecule 1. This research opens a novel pathway to fabricate supramolecular self-assembly gels to detect polymetallic ion and trace volatile acid in the environment.