Sensing properties of polyoxomolybdate doped polyaniline nanomaterials for oxidising and reducing volatile organic compounds

The polyoxomolybdates encapsulated PAni hybrid materials are prepared by interfacial polymerisation. In P12MPA, the crystal structure of 12MPA is not modified on doping with PAni. However, P11MPA have the polycrystallinity due to the presence of vanadium in the dopant molecule. Though, the hybrids prepared by interfacial polymerisation are in emaraldine salt form, there is a blue shift in the absorption spectra due to dopant induced decrease in conjugation length and over-oxidation. Interfacially polymerised PAniPOM hybrid materials are exposed with various concentrations of vapours of different volatile organic compounds (VOC) such as acetone, methanol, chloroform and carbon tetrachloride. The oxidising VOCs like acetone and methanol on exposure to PAni decrease the resistivity by hydrogen bonding with the redox cites of the polymer. Among these two, the sensitivity towards acetone is more in PAni and its hybrids which can be linked with the vapour pressure of the analyte. Due to the weak acidic characteristics of chlorinated hydrocarbons which are reducing vapours, the resistivity of PAni and its hybrids increases on exposure to chloroform and CCl4. Here, the chlorinated hydrocarbons interact with the redox sites of PAni and reduce it to base form. Bridging of polymer chains is also proposed for the reduction of conductivity on exposure to the analyte. The sensitivity is higher for the reducing analytes than that of the oxidising one.