Nitrogen dioxide sensing characteristics at elevated temperature of sol-gel glass thin films containing substituted porphyrin dyes

An optical gas sensor device based on tetra-substituted porphyrin dye entrapped in sol-gel glass displays greatly improved signal strength (1400% at 295 K) on exposure to 4.4 ppm nitrogen dioxide (in N-2) gas compared to a multilayer Langmuir-Blodgett film fabricated from the same porphyrin. Temporal response was found to be similar, but differences in the two deposition methods were observed in terms of signal strength and response/recovery times. This behaviour is explained in terms of the differing nature of the two film types. A room temperature sensitivity of 176 ppb was measured and the response obeyed Langmuir adsorption kinetics.