Toxic gas detection using porphyrin dispersed polymer composites

The optochemical sensing performances of the porphyrin dyes dispersed in ethylcellulose (EC) matrix to toxic gases such as HCl, NO2 and SO2 were examined using a photo-reflection spectrum technique. The intensity of the characteristic Soret- and Q-bands of the porphyrins sensitively changed with the concentration of the gasses. Introducing electron-donating OCH3 and OH groups to the phenyl-group in the tetraphenylporphyrin (TPPH2) molecule enhanced the sensitivity and that was in the order of TP(4-OH)4PH2 > TP(3,5-OCH3)4PH2 > TPPH2 to HCl. In contrast, electron-withdrawing COOH group decreased in the sensitivity. It was interpreted that the electron density at the pyrrole nitrogen increased with the electron-donationing groups. Doping of dioctylphthalate (DOP) as a plasticizer to the porphyrin–EC composites remarkably modified their sensitivity and response behavior. The sensitivity to NO2 was extremely high and sub-ppm level of detection was possible for all the composites. In the case of SO2, the sensitivity was lower than NO2, but the composite of TP(4-OH)4PH2 exhibited enough sensitivity to detect the concentration of 0.5 ppm. The sensing performance was strongly dependent on the humidity.