In this work, the carboxylic acid derivatives of a free-base porphyrin, 5,10,15,20-tetrakis(4-carboxyphenyl)-21
H,23
H-porphyrin, and 10 of its
metal derivatives (TCPPs) have been used for optical gas sensing. For this purpose,
microstructured colu
mnar TiO
2 thin fil
ms prepared by GAPVD (glancing angle physical vapor deposition) have been used as host
materials for the porphyrins as they are non鈥揹ispersive and porous, allowing their use for UV鈥搗isible spectroscopy and gas sensing. The che
mical binding between the dye
molecules and the TiO
2 has been studied through infrared spectroscopy, and the obtained spectral changes have been found to be co
mpatible with chelating and/or bidentate binding
modes of the carboxylate groups on the TiO
2 surface. When hosted in the fil
m, the UV鈥搗isible spectra of the porphyrins featured a blue shift and broadening of the Soret band with respect to the solution, which has been attributed to the for
mation of 蟺鈥撓€ aggregates between porphyrin
molecules. The co
mposite porphyrin/TiO
2 fil
ms obtained fro
m each of the 11 porphyrins have been exposed to 12 different volatile organic co
mpounds (VOCs), and their respective gas鈥搒ensitive properties have been analyzed as a function of the spectral changes in their Soret band region in the presence of the analytes. The set of co
mposite fil
ms has shown high selectivity to the analyzed volatile co
mpounds. For each analyte, an innovative way of showing the different responses has been developed. By
means of this procedure, an i
magelike recognition pattern has been obtained, which allows an easy identification of every co
mpound. The kinetics of the exposure to several analytes showed a fast, reversible and reproducible response, with response ti
mes of a few seconds, which has been attributed to both the sensitivity of the porphyrins and the high porosity of the TiO
2 fil
ms. Also, increasing concentrations of the analytes resulted in an increase in the
magnitude of the response, indicating that the sensor behavior is also concentration-dependent.
Keywords:
carboxyphenyl porphyrin; TiO2 nanostructures; mpounds&qsSearchArea=searchText">volatile organic compounds; optical sensing; maging&qsSearchArea=searchText">spectral imaging; gas sensors