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 N2) 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.