Preparation and characterization of cobalt porphyrin modified tin dioxide films for sensor applications

Herein we report the preparation of hybrid Co porphyrin-SnO2 thin films by sol-gel technique and a study of their sensing properties. The porphyrin structure bears a carboxylic group to improve its stabilization into the oxide matrix. SEM characterization of the spin-coated thin films deposited onto alumina substrates showed a homogeneously morphology. These CoTCPP-SnO2 sensors showed fast and reversible responses towards the detection of methanol vapors and highest responses were obtained at the working temperature of 250 degreesC. Optical characterization of the heated CoTCPP-SnO2 thin films indicated that the metalloporphyrin is still present after heating up to 320 degreesC, while it was completely decomposed after thermal treatment at 400 degreesC. These results support the presence of a catalytic effect of the CoTCPP at lower temperature, which induces a significant increase in the sensor responses at 250 degreesC, while at higher temperature, where the porphyrin is thermally decomposed, the hybrid CoTCPP-SnO2 sensors behave similarly to pure SnO2 devices. On the contrary, no significant differences in the sensor responses where observed in the case of CO detection, showing that metalloporphyrins can be used to modify the selectivity of SnO2 sensors. (C) 2004 Elsevier B.V. All rights reserved.