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Sensors 2015, 15(5), 11118-11132; doi:10.3390/s150511118

Free-Base Carboxyphenyl Porphyrin Films Using a TiO2 Columnar Matrix: Characterization and Application as NO2 Sensors

1
Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Ctra. Utrera Km. 1, 41013 Sevilla, Spain
2
Instituto de Ciencia de Materiales de Sevilla, Universidad de Sevilla–CSIC, Américo Vespucio 49, 41092 Sevilla, Spain
*
Authors to whom correspondence should be addressed.
Academic Editor: Michael Tiemann
Received: 27 February 2015 / Revised: 2 May 2015 / Accepted: 6 May 2015 / Published: 12 May 2015
(This article belongs to the Special Issue Gas Sensors—Designs and Applications)
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Abstract

The anchoring effect on free-base carboxyphenyl porphyrin films using TiO2 microstructured columns as a host matrix and its influence on NO2 sensing have been studied in this work. Three porphyrins have been used: 5-(4-carboxyphenyl)10,15,20-triphenyl-21H,23H-porphyrin (MCTPP); 5,10,15,20-tetrakis(4-carboxyphenyl)-21H,23H-porphyrin (p-TCPP); and 5,10,15,20-tetrakis(3-carboxyphenyl)-21H,23H-porphyrin (m-TCPP). The analysis of UV-Vis spectra of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 composite films has revealed that m-TCPP/TiO2 films are the most stable, showing less aggregation than the other porphyrins. IR spectroscopy has shown that m-TCPP is bound to TiO2 through its four carboxylic acid groups, while p-TCPP is anchored by only one or two of these groups. MCTPP can only be bound by one carboxylic acid. Consequently, the binding of p-TCPP and MCTPP to the substrate allows them to form aggregates, whereas the more fixed anchoring of m-TCPP reduces this effect. The exposure of MCTPP/TiO2, p-TCPP/TiO2 and m-TCPP/TiO2 films to NO2 has resulted in important changes in their UV-Vis spectra, revealing good sensing capabilities in all cases. The improved stability of films made with m-TCPP suggests this molecule as the best candidate among our set of porphyrins for the fabrication of NO2 sensors. Moreover, their concentration-dependent responses upon exposure to low concentrations of NO2 confirm the potential of m-TCPP as a NO2 sensor. View Full-Text
Keywords: carboxyphenyl porphyrin; microstructured TiO2 film; NO2; optical gas sensor; thin film carboxyphenyl porphyrin; microstructured TiO2 film; NO2; optical gas sensor; thin film
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Roales, J.; Pedrosa, J.M.; Guillén, M.G.; Lopes-Costa, T.; Castillero, P.; Barranco, A.; González-Elipe, A.R. Free-Base Carboxyphenyl Porphyrin Films Using a TiO2 Columnar Matrix: Characterization and Application as NO2 Sensors. Sensors 2015, 15, 11118-11132.

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