Tetraphenylporphine-polymer composite films for optochemical HCl gas sensors. Effects of polymer matrix on sensing characteristics

Changes in the UV-Visible spectra of HCl-sorbed tetraphenylporphine (TPPH42+)-polymer composite films were examined for detection of ppm levels of HCl gas. On exposing the films to HCl gas, the following reversible reaction takes place; TPPH2+2HCl(film) reversible arrow TPPH42+. 2Cl(-). Due to the formation of the dicationic form, the concentration of HCl gas was considered to be determined by the measurement of the absorbance changes. The sensitivity to HCl was discussed on the bases of the sorption models of Freundlich / Langmuir-type, clustering type and Henry's type. Freundlich / Langmuir-type sorption model was applied for the polymer with a higher glass transition temperature. Changes from Freundlich / Langmuir type sorption to clustering type sorption and then Henry's type sorption was observed with a decrease in the glass transition temperature.