Toxic gas detection using porphyrin dispersed polymer composites

Abstract

The optochemical sensing performances of the porphyrin dyes dispersed in ethylcellulose (EC) matrix to toxic gases such as HCl, NO 2 and SO 2 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 OCH 3 and OH groups to the phenyl-group in the tetraphenylporphyrin (TPPH 2) molecule enhanced the sensitivity and that was in the order of TP(4-OH) 4PH 2 > TP(3,5-OCH 3) 4PH 2 > TPPH 2 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 NO 2 was extremely high and sub-ppm level of detection was possible for all the composites. In the case of SO 2, the sensitivity was lower than NO 2, but the composite of TP(4-OH) 4PH 2 exhibited enough sensitivity to detect the concentration of 0.5 ppm. The sensing performance was strongly dependent on the humidity.