Photocatalysis of Cementitious Materials: Clean Buildings and Clean Air
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Photocatalysis of
Cementitious Materials: Clean Buildings and Clean Air Luigi Cassar
Abstract While the primary function of concrete is structural, its pervasiveness in our society lends it to other functions and creates the need for it to maintain its integrity and aesthetic quality. Therefore, concrete with added functionality—for example, self-cleaning characteristics and the ability to remove pollutants—is desirable. Heterogeneous photocatalysis (e.g., gas–solid or liquid–solid catalytic processes caused by light irradiation) by semiconductor particles or coatings has now reached a high level of development and is a promising technology for the reduction of global environmental pollutants. Among the various semiconductor materials, TiO2 in the form of anatase has attracted wide interest, due to its strong oxidizing power under near-UV radiation, its chemical stability when exposed to acidic and basic compounds, its chemical inertness in the absence of UV light, and the absence of toxicity. TiO2 has proved very effective in the reduction of pollutants such as NOx, aromatics, ammonia, and aldehydes. Surprisingly, the use of TiO2 in combination with cementitious materials has shown a favorable synergistic effect in the reduction of pollutants. These new materials have already found relevant applications in self-cleaning building walls and in the reduction of urban pollutants. Keywords: cement, construction materials, photocatalysis, NOx, urban pollutants, self-cleaning concrete.
Introduction Light plays a primary role in biological processes and environmental equilibria, and until the early 1900s, energy and materials production were derived both directly and indirectly from sunlight. In the past century, however, the demographic boom, the creation of new materials, and the increasing use of oil and nuclear power for energy purposes have led to an everincreasing gap between nature and society. In modern times, we rarely think of the role solar energy can play in engineered structures, and instead our infrastructure is built to be resistant to the effects of sunlight.
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The solar energy reaching the earth’s surface is about 5 1024 J per year, more than 104 times the annual worldwide consumption of energy. This plentiful resource, and the need for a cleaner environment, urges architects and designers to think again of using sunlight in combination with specially engineered building materials to lower energy use and reduce pollutants. In this article, we will describe how photochemistry applied to construction materials may be an attractive path to this end. The enormous surface area of cement-based materials used in construction offers a useful
resource to productively harness the energy of light and apply it to societal needs.
Heterogeneous Photocatalysis A photocatalyst is a compound that, with the absorption of light, facilitates a chemical reaction and is regenerated in the process.1,2 It can be a dye, a coordination compound, or a semiconductor material. Heterogeneous photocatalysis is based on the i
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