5 - Nano-tailored TiO2-based photocatalytic cementitious systems for NOx reduction and air cleaning

Abstract

Air quality is one of the main factors having incontestable effect on the quality of life of every being on earth. In addition to its effect on the public health, low air quality also has an indispensable negative effect on the society, environment, and economy as it requires rigorous efforts to be made for proper reduction and/or elimination. Because of the rapidly increasing urban population and industrial activities, the incremental trend in the air pollution, which is one of the world’s major problems nowadays, will most likely continue in the future since the release of greenhouse gases into the atmosphere is also expected to continue at an increasing pace as a consequence of the progressive man-made activities. Among various air pollutants, toxic nitrogen oxide (NOx) is of special interest recently as the release of NOx from the industrial organizations and vehicles has reached serious levels, especially in crowded cities. In an effort to adequately tackle the increased levels of NOx, researchers have looked into several solutions and realized that light irradiated from different types of sources [ultraviolet (UV), visible, solar light, etc.] activates the photocatalytic reactions reducing the pollutiveness of NOx and large surface areas of building members in contact with different light sources offer a unique opportunity for the elimination of detrimental effects of NOx through stimulation of photocatalytic reactions. Given the widespread utilization of cementitious systems in the construction industry, numerous ongoing and completed studies focusing on the use of various photocatalytic materials (photocatalysts) within the cementitious systems can be found. The main focus of these studies is to develop new-generation multi-functional cementitious composites with air cleaning feature without compromising the mechanical features and cost of production. In order to equip cementitious systems with the air cleaning feature, titanium dioxide (TiO2) is a very commonly used semiconductor photocatalyst. The commonness of utilization of TiO2 in cementitious systems is originated from the material’s high efficiency in oxidization of NOx, chemical/photochemical stability, chemical inertness in the absence of irradiation, safety, comparative cost-effectiveness, and nontoxicity. In this chapter, a comprehensive review about the mechanism/properties/advantages of TiO2-based photocatalytic multi-functional cementitious composites with air purification capability is presented.