Phthalocyanine photoregeneration for low power consumption chemiresistors.

It is well known that the applicability of phthalocyanine chemiresistors suffers from long recovery times after NO2 exposures. This circumstance enforces the necessity to operate the sensors at elevated temperatures (150-200 °C), which shortens the sensor lifetime and increases its power consumption (anyway, a typical measurement period is longer than 15 min). In this paper, we propose a new method for a fast and effective recovery by the UV-VIS illumination at a low temperature (55 °C). The method is based on a short illumination following a short NO2 exposure. To support and optimize the method, we investigated the effects of light in the wavelength and intensity ranges of 375-850 nm and 0.2-0.8 mW/mm2 on the rate of NO2 desorption from the phthalocyanine sensitive layer during the recovery period. This investigation was carried out for a set of phthalocyanine materials (ZnPc, CuPc, H2Pc, PbPc and FePc) operating at slightly elevated temperatures (55-100 °C) and was further supported by the analysis of UV-VIS and FTIR spectral changes. We found out that the light with the wavelength shorter than 550 nm significantly accelerates the NO2 desorption from ZnPc, CuPc and FePc, and allows to bring the measurement period under 2 min and to decrease the sensor power consumption by 75 %. Possible mechanisms of the light-stimulated desorption were discussed.