Optochemical sensor for HC1 gas based on tetraphenylporphyrin dispersed in styrene-acrylate copolymers - Effects of glass transition temperature of matrix on HCl detection

The spectral changes of tetraphenylporphyrin (TPPH2)-polymer composites in the visible region were examined in order to detect HCl gas. For TPPH2, the absorbance of the Soret and Q bands were sensitive to ppm levels of HCl. The sensing mechanism were characterized basing the protonation reaction and sorption isotherm: TPPH2 + 2HCl(film) reversible arrow TPPH42+ . 2Cl(-) and [HClfilm] = a[HClgas]". The equilibrium constant of the former was decreased with increase in the working temperature and in glass transition temperature (T-g) of polymer matrix. The number of active sites (a) for HCl sorption decreased with a decrease in the T-g. The response behavior was improved by using polymer with lower T-g. (C) 2002 Elsevier Science B.V. All rights reserved.