Sustainable photocatalytic porcelain grés slabs active under LED light for indoor depollution and bacteria reduction

In order to face the increasing environmental concerns related to compelling to reduce the risks in cities, houses, and workplaces due to either scarce air quality and/or polluted water, the employment of more and more TiO2-based products has been observed in the last decade [1]. This is easy to understand, as new photocatalytic building materials have been developed so far, starting from the earlier studies carried out dating to the 90s of the last century [2]. As recently reported [3], the global market based on photocatalysts will reach $2.9 billion by 2020 due to the huge request for self-cleaning coatings in the building sector. Ceramic tile is one of the most widely used materials in construction, and in the last years, the demand for environmentally responsible construction and the ever more restrictive environmental requirements derived from the legislation are increased in the functional tiles [4]. Substituting antimicrobial tiles for other surfaces support is important to have a healthier environment, and in this, it is essential to improve ability to control and destroy microorganisms in many organizations and industries such as health care, food and drink, water treatment, and military industries [5]. There are several approaches that have been studied to obtain a multifunctional surface for ceramic tiles using both soluble salt solutions and solgel technology. In particular, TiO2 improves the surface cleanability properties, and it is widely utilized as a self-cleaning and self-disinfecting material for surface coating in many applications [6]. These properties have been applied in removing bacteria and harmful organic materials from water and air, as well as in self-cleaning or self-sterilizing surfaces for places such as medical centers [7]. As well known, TiO2 activity is influenced by a variety of factors such as crystal structure, surface area, nanoparticles size distribution, porosity, and a number and density of hydroxyl groups on the TiO2 surface [8]. Thus, starting from the point that TiO2 deposition on ceramic tiles is a key factor in the industrial production, their preparation and characterization are at the base of a new kind of fired tiles able to reduce polluting molecules present in air thanks to new photocatalytic properties. However, if until today almost all the techniques and procedures involve the use of the classical nanometric TiO2, a novel approach is the surface deposition of micro-sized TiO2 instead of nano. Indeed, the nanoparticles exhibit potential risks, in particular in terms of dispersibility, ecotoxicity, and bioaccumulation. Human health danger related to nanopowders of TiO2 includes both inhalation and exposure [9], because they lead to various toxic effects, from genotoxicity to diseases such as inflammations or lung diseases, although TiO2 is chemically inert [1013]. The possibility to use micro-sized TiO2 in a commercially manufactured product, such as tiles, opens a new generation of building materials intrinsically safer than the traditional photocatalytic products for both workers in the factories and public safety [14].