Ultra sensitive ammonia sensors based on microwave synthesized nanofibrillar polyanilines

Abstract

Ultra sensitive ammonia sensors based on microwave (MW) nanofrillar polyaniline (PANI) with ppb sensing range were developed. First PANIs synthesized by classical (CS) and MW assisted methods using different dopants (HCl, H2SO4) and oxidants – (ammonium persulfate (APS) and potassium iodate (KIO3)) were exposed to 1ppm (700μgm−3) of ammonia to select the more sensitive. The couple dopant/oxidant (H2SO4/KIO3) leads to PANIs presenting the best responses whatever the method of synthesis used. These selected samples have been further investigated and characterized from a metrological point of view in terms of response, sensitivity, quantification limit, repeatability and reversibility. Compared to CS method, the MW synthesized PANI gives rise to sensor presenting better metrological performances which can be correlated with the physical properties of the samples obtained by using FTIR (Fourier Transform Infrared) and EPR (Electron Paramagnetic Resonance) spectroscopies. In order to further improve the sensitivity of MW PANI at low concentrations of ammonia, conductive composite materials were synthesized using a polyurethane (PU) matrix. The influence of PANI content in the blend on the response to 1ppm of ammonia was studied and the composite with 38% (in weight) of doped PANI in the matrix presents the largest response. MW PANI composite with 38% (in weight), MW PANI and CS PANI were submitted to a large panel of ammonia concentrations. The composite showed better sensitivity at low concentration of ammonia with a calculated quantification limit of 0.3ppb while MW PANI provided better responses to high concentrations of ammonia (>5ppm (3500μgm−3)). MW PANI in composite provides a way to improve the quantification limit leading to ultra sensitive sensors.