Titania nanotube arrays (TNTAs) are very interesting photocatalysts. Particularly, TNTAs obtained by anodic oxidation of metallic titanium foils allow the direct synthesis of high efficiency supported photocatalytic layers without the drawbacks related to the high temperature sintering of anatase nanopowders. The synthesis of TNTAs is however a critical process with several parameters to be optimized in order to obtain high photocatalytic activities. This work investigates the optimization of titanium supported TNTAs for the photocatalytic degradation of toluene in air at ambient concentration. Metal-supported TNTAs were produced by titanium foils anodization using a solution of 0.5 wt.% NaF/1M Na2SO4. The anodization process (3-6 h) was performed at 20 V. The samples were then thermally annealed in air at different temperatures and duration times in order to achieve the crystallization of the obtained amorphous TiO2. The photocatalytic activity was assessed by measuring the toluene degradation in air using a continuous-flow stirred photoreactor operated at constant toluene concentration (0.75 µmol m-3). The TNTAs photocatalytic activity demonstrates to be strictly dependent on several process parameters (e.g. the anodic oxidation solution, the oxidation time and the post-synthesis thermal annealing). The oxidation time was studied in the 3-6 h range demonstrating the best photocatalytic performance for the longest time. The post-synthesis annealing was studied in the 400-600 °C temperature range for 60 and 120 min duration. For both annealing duration times the highest activities were found at 600 °C process temperature, with >6.5 factor improvement from 400 to 600 °C for 120 min process and >4 factor improvement from 500 to 600 °C for 60 min process. At the highest temperature the curing time is however critical and the best activity was found for 60 min curing, with ?30% activity decrease shown by the 120 min annealed sample. The results demonstrate the severe dependence of the TNTAs gas-phase photocatalytic activity on the synthesis process parameters. Particularly, the final TNTAs crystalline structure is critically dependent on post-synthesis annealing with a very pronounced dependence of the obtained photocatalytic activity on the process temperature and duration. The criticality of the annealing process is due both to the amorphous/crystalline and then the anatase/rutile phase transitions and to the morphological transformations triggered at high temperatures. TNTAs obtained by anodization of titanium foils can thus be very interesting natively-supported photocatalysts after a fine tuning of the anodization and annealing process parameters.
Photocatalytic toluene degradation in air at ambient concentration by titania nanotube array: influence of synthesis process parameters
Strini A;
2016
Abstract
Titania nanotube arrays (TNTAs) are very interesting photocatalysts. Particularly, TNTAs obtained by anodic oxidation of metallic titanium foils allow the direct synthesis of high efficiency supported photocatalytic layers without the drawbacks related to the high temperature sintering of anatase nanopowders. The synthesis of TNTAs is however a critical process with several parameters to be optimized in order to obtain high photocatalytic activities. This work investigates the optimization of titanium supported TNTAs for the photocatalytic degradation of toluene in air at ambient concentration. Metal-supported TNTAs were produced by titanium foils anodization using a solution of 0.5 wt.% NaF/1M Na2SO4. The anodization process (3-6 h) was performed at 20 V. The samples were then thermally annealed in air at different temperatures and duration times in order to achieve the crystallization of the obtained amorphous TiO2. The photocatalytic activity was assessed by measuring the toluene degradation in air using a continuous-flow stirred photoreactor operated at constant toluene concentration (0.75 µmol m-3). The TNTAs photocatalytic activity demonstrates to be strictly dependent on several process parameters (e.g. the anodic oxidation solution, the oxidation time and the post-synthesis thermal annealing). The oxidation time was studied in the 3-6 h range demonstrating the best photocatalytic performance for the longest time. The post-synthesis annealing was studied in the 400-600 °C temperature range for 60 and 120 min duration. For both annealing duration times the highest activities were found at 600 °C process temperature, with >6.5 factor improvement from 400 to 600 °C for 120 min process and >4 factor improvement from 500 to 600 °C for 60 min process. At the highest temperature the curing time is however critical and the best activity was found for 60 min curing, with ?30% activity decrease shown by the 120 min annealed sample. The results demonstrate the severe dependence of the TNTAs gas-phase photocatalytic activity on the synthesis process parameters. Particularly, the final TNTAs crystalline structure is critically dependent on post-synthesis annealing with a very pronounced dependence of the obtained photocatalytic activity on the process temperature and duration. The criticality of the annealing process is due both to the amorphous/crystalline and then the anatase/rutile phase transitions and to the morphological transformations triggered at high temperatures. TNTAs obtained by anodization of titanium foils can thus be very interesting natively-supported photocatalysts after a fine tuning of the anodization and annealing process parameters.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
