An optochemical HCl gas sensor using 5,10,15,20-tetrakis (3′,5′-di-tert-butyl,4′-hydroxyphenyl) porphin-ethylcellulose composite films

The absorbance of the Soret and Q-bands of free-base tetraphenylporphins is reversibly sensitive to ppm levels of HCl. The replacement of the hydrogen para to the phenyl group with an -OH group enhances the sensitivity of the Soret and the Q-band region. While both response and recovery times of tetra 4′-OH substituted tetraphenylporphins is considerably longer than that of tetraphenylporphin, the replacing the hydrogen meta to the phenyl group with tert-butyl group is effective to improve both response and recovery times. The HCl gas sensor based on substituted-tetraphenylporphin with 4′-OH and 3′,5′-di-C(CH3)3 to the phenyl group shows superior performance for detection of emissions of ppm levels of HCl gas.