Evaluation of the photocatalytic performance of construction materials for urban air depollution

Abstract

The photocatalytic degradation of trichloroethylene and nitric oxide (model volatile organochloride and inorganic compounds)

by two commercial TiO2-

based cementitious materials at the laboratory scale was studied. TiO2

P25 was selected

as the benchmark photocatalyst. The materials were characterized by N2

adsorption–desorption, TGA, SEM–EDX, and

XRD, and the hydrophobic/hydrophilic nature of the cement surface was determined through contact angle measurements.

Preliminary photoactivity tests in which a glass plate was covered with photocatalytic material were performed. Moreover,

the photocatalytic activities of asphalt plates (approximately 1 cm thick) covered with either of the photoactive cementitious

materials were also evaluated. A notable improvement in the photocatalytic activity from the first to the second photocatalytic

run was observed because sample conditioning with airflow and UV-A irradiation led to the elimination of species

(carbonates) that were adsorbed at active TiO2

sites, ensuring stability under operating conditions. The cementitious samples

completely photooxidized the organochloride compound but presented reduced photoefficiency for nitric oxide oxidation. The

results obtained when the materials were deposited on glass and asphalt showed the crucial influences of the sample loading

and the nature of the substrate on nitric oxide photooxidation. Using TiO2

P25 led to the complete conversion of nitric oxide

but also to the formation of a large amount of nitrogen dioxide. On the other hand, one of the photoactive asphalts exhibited

a nitric oxide conversion rate of 32%, which was lower than that achieved with pure TiO2-

P25, but using this material did not

lead to the release of nitrogen dioxide. When tested according to the ISO 22197-1:2007 standard, the selected photocatalytic

asphalt removed 29% of the NO and 22% of the NOx

under more demanding operating conditions.