Absorption and photocatalytic degradation of VOCs by perfluorinated ionomeric coating with TiO2 nanopowders for air purification

In this work, we propose a transparent multilayered perfluoropolymeric coating as immobilization method for TiO2 nanoparticles, and evaluate its suitability in the gas phase photocatalytic degradation of six different volatile organic compounds. The coating was made of a layer of TiO2-containing perfluorosulfonic acid polymer on a layer of perfluorinated amorphous polymer. The chemical stability of perfluoropolymeric materials to UV radiation and UV-activated TiO2 overcomes the possible degradation of the polymeric immobilization system which is typical of more traditional polymeric coatings. Moreover, the TiO2-containing ionomeric perfluorosulfonic layer worked as selective membrane for pollutants absorption and catalyst preservation, depending on the interactions between the superacidic polar heads of the ionomer and the pollutants, in particular those capable of hydrogen bonding. Gas-phase photocatalytic degradation tests were performed using pentane, methanol, 2-propanol, toluene, dichloromethane and pyridine as reference volatile organic pollutants, thus ranging on different polarity properties. Results indicate performances comparable to other approaches reported in the literature and show a strong influence of both atmospheric conditions (namely, humidity) and pollutant nature - polarity, proticity - on the actual kinetics of photodegradation, also depending on the interactions regulating the affinity between the ionomeric layer of the coating and pollutants. The high potential of the coating in the photodegradation was confirmed by the observed values of the photoabatement rates: all approximatively above 10(-5) s(-1) and maximum for alcohols (1.4x10(-4) and 1.7x10(-4) s(-1) in dry and humid conditions, respectively).