The outdoor application of photocatalytic materials involves the weathering of the active surface with exposition to rain, solar radiation and environmental contaminants. The impact of medium term (>=3500 h) exposition to UV-A radiation and water washing was studied in laboratory using two photocatalytic cement-based samples. The samples were exposed to medium intensity UV-A radiation (~750 µW cm-2) under untreated laboratory air flow. During the study the samples were treated with deionized water in two washing sessions by immersion for 2 and 5 minutes respectively. The photocatalytic activity evolution during the experiment was assessed measuring the degradation of nitric oxide (NO) in air at typical ambient concentration (75 ppb) using a constant-concentration analytical method. Both samples showed relevant variations in the NO degradation rate and the comparison with two identical samples kept in dark conditions demonstrates the substantial effect of the exposition to water and UV-A radiation. Moreover, the two samples showed also a quite different variation pattern, possibly indicating the presence of several mechanisms operating concurrently. The NO degradation rate of the samples was then measured after 170 days of storing in dark conditions, confirming the permanence of the weathering process effects. These results suggest that the activity of photocatalytic materials with complex matrices can be strongly influenced by the exposition to weathering agents and that the previous exposure record can have a deep effect on the photocatalytic reaction rate. The actual activity of a catalytic surface operating outdoor can therefore be very different from the value measured in the laboratory with a fresh specimen, with possible evolution towards lower or also higher levels.
Impact of laboratory aging with water and UV exposition on the nitric oxide degradation activity of cement-based photocatalytic samples
Alberto Strini;Luca Schiavi;
2014
Abstract
The outdoor application of photocatalytic materials involves the weathering of the active surface with exposition to rain, solar radiation and environmental contaminants. The impact of medium term (>=3500 h) exposition to UV-A radiation and water washing was studied in laboratory using two photocatalytic cement-based samples. The samples were exposed to medium intensity UV-A radiation (~750 µW cm-2) under untreated laboratory air flow. During the study the samples were treated with deionized water in two washing sessions by immersion for 2 and 5 minutes respectively. The photocatalytic activity evolution during the experiment was assessed measuring the degradation of nitric oxide (NO) in air at typical ambient concentration (75 ppb) using a constant-concentration analytical method. Both samples showed relevant variations in the NO degradation rate and the comparison with two identical samples kept in dark conditions demonstrates the substantial effect of the exposition to water and UV-A radiation. Moreover, the two samples showed also a quite different variation pattern, possibly indicating the presence of several mechanisms operating concurrently. The NO degradation rate of the samples was then measured after 170 days of storing in dark conditions, confirming the permanence of the weathering process effects. These results suggest that the activity of photocatalytic materials with complex matrices can be strongly influenced by the exposition to weathering agents and that the previous exposure record can have a deep effect on the photocatalytic reaction rate. The actual activity of a catalytic surface operating outdoor can therefore be very different from the value measured in the laboratory with a fresh specimen, with possible evolution towards lower or also higher levels.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
