Titanium dioxide based heterogeneous and heterojunction photocatalysts for pollution control applications in the construction industry

Abstract

With increasing urbanization and industrialization there is an upsurge in air pollution that demands immediate attention. The use of nanomaterials to alleviate air pollution is gaining importance. Certain nanomaterials can photocatalytically act on air pollutants such as oxides of nitrogen (NOx), sulfur (SOx), and carbon (CO2), thereby bringing down their concentration locally. Titanium Dioxide (TiO2), its composites, and TiO2 based Z/S scheme heterojunction photocatalysts are a few such nanomaterials. The band-gap of TiO2 in solid-state (3.2 eV) makes it a good photocatalyst in the ultraviolet region and its composites in the visible light region of the spectrum. Metropolitan cities are densely filled with high-rise buildings and the exteriors of these buildings, which are largely exposed to the atmosphere, can be utilized to coat these nano materials to enable photocatalytic reduction of air pollutants in the surrounding atmosphere. The nano photocatalysts can either be applied as coatings on the existing buildings or incorporated into the construction materials during construction. In this review article, an attempt is made to cover the application of photocatalysts in the construction industry starting from the working principle (mechanism) of heterogeneous and heterojunction photocatalysts, their advantages and disadvantages, methods of synthesis, pollution control applications, with emphasis on the methods of incorporating the photocatalysts into construction materials and also as a coating on existing buildings, the set up required to evaluate NOx reduction and the factors that affect the NOx reduction. The current status of pollution control applications in the construction industry and the authors perspective on the application of heterojunction photocatalysts in construction industry are highlighted.