Digital Printing: a new tool to activate Ceramic Surfaces using Micro- TiO2 as Photocatalyst

Nowadays pollution is one of the biggest concerns of both the public and different governments, considering its crucial impact on human health and every habitat. Photocatalysis is one of the most promising advanced oxidation process and TiO2 is the best semiconductor able to oxidize pollutants; especially, it can be applied on materials, which are capable of reacting with the most common air pollutant molecules (NOx or VOCs), degrading them, and therefore carrying out an effective anti-pollution action. Some of good features required of porcelain tiles are hardness, lack of porosity, vitrified surface, and durability; however, the innovative ceramic materials present features such as light weight, flexibility and ductility. One particularly interesting product of technological progress is a maxi floor and wall tile system, which combines the traditional qualities of porcelain with the new features of ultra-high performance. Concerning this, the digital printing was exploited as a new tool to manufacture photocatalytic tiles even of very large size (150x300 cm). In the present work, traditional porcelain grés tiles have been transformed into an eco-active material, digitally printing the ceramic surface with a TiO2-based ink creating a stable photocatalytic film with all the properties of a photocatalytic material. An important and key factor in the photocatalytic active tiles preparation is the use of micro-TiO2 instead of nano: in fact, nanoparticles exhibit potential risks in terms of dispersibility, ecotoxicity, persistency, and bioaccumulation. In literature, there are a lot of references that describe and present information on titanium dioxide health risks, as the International Agency for Research on Cancer (IARC) classified ultrafine TiO2 as possible carcinogenic to humans. Thus, despite the good properties and the high efficiency of nano-sized TiO2, these concerns over safety may limit its applications, and it is very important to find a replacement. We present the results obtained for different pollutants degradation in gas phase, in particular nitrogen oxides, which are the main responsible for outdoor pollution, and some of the most widespread volatile organic compounds, which are the main cause of indoor pollution and the so-called sick building syndrome. Among all the pollutants, nitrogen oxides (NOx) are continuously monitored all over the world and guidelines on the alarm levels of these molecules in air were published by WHO (World Health Organization). The photoefficiency of the material in the NOx degradation was measured on tiles of 600x600 mm. Concerning VOCs, photocatalytic performances of active tiles were exploited in particular against formaldehyde, very dangerous for human health and ubiquitous, as well as very difficult to monitor at low concentration. The results confirm the good performances of the tiles to tackle the environment pollution, and the surface of the photoactive slabs was analyzed by HR-SEM showing an excellent uniformity.