title: Free-Base Carboxyphenyl Porphyrin Films Using a TiO₂ Columnar Matrix: Characterization and Application as NO₂ Sensors.
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.
authors.affiliation: Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Ctra. Utrera Km. 1, 41013 Sevilla, Spain. jroabat@upo.es.
authors.forename: Javier
authors.initials: J
authors.lastname: Roales
authors.affiliation: Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Ctra. Utrera Km. 1, 41013 Sevilla, Spain. jmpedpoy@upo.es.
authors.forename: José M
authors.initials: JM
authors.lastname: Pedrosa
authors.affiliation: Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Ctra. Utrera Km. 1, 41013 Sevilla, Spain. mariagonzalez88@gmail.com.
authors.forename: María G
authors.initials: MG
authors.lastname: Guillén
authors.affiliation: Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Ctra. Utrera Km. 1, 41013 Sevilla, Spain.
authors.forename: Tânia
authors.initials: T
authors.lastname: Lopes-Costa
authors.affiliation: Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Ctra. Utrera Km. 1, 41013 Sevilla, Spain. pcasdur@upo.es.|Instituto de Ciencia de Materiales de Sevilla, Universidad de Sevilla-CSIC, Américo Vespucio 49, 41092 Sevilla, Spain. pcasdur@upo.es.
authors.forename: Pedro
authors.initials: P
authors.lastname: Castillero
authors.affiliation: Instituto de Ciencia de Materiales de Sevilla, Universidad de Sevilla-CSIC, Américo Vespucio 49, 41092 Sevilla, Spain. angel.barranco@csic.es.
authors.forename: Angel
authors.initials: A
authors.lastname: Barranco
authors.affiliation: Instituto de Ciencia de Materiales de Sevilla, Universidad de Sevilla-CSIC, Américo Vespucio 49, 41092 Sevilla, Spain. arge@icmse.csic.es.
authors.forename: Agustín R
authors.initials: AR
authors.lastname: González-Elipe
mesh_terms: D007700:Kinetics; D016014:Linear Models; D009585:Nitrogen Dioxide / Q000032:analysis*; D011166:Porphyrins / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D014025:Titanium / Q000737:chemistry*
chemical_list: D011166:Porphyrins; C009495:titanium dioxide; D014025:Titanium; D009585:Nitrogen Dioxide
keywords: NO2; carboxyphenyl porphyrin; microstructured TiO2 film; optical gas sensor; thin film