FIELD OF THE INVENTION

The present invention concerns the sector of devices for reducing polluting agents in a gaseous mixture.

In particular, the present invention concerns a nano-functionalized support which is particularly suitable for installation in an air filter.

BACKGROUND OF THE INVENTION

The development and spread of human activities over the years has led to an increasingly significant increase in polluting substances present in the air that we breathe.

In particular, attention is increasingly focused on the effects that the emission of the pollutants produced—for example by production systems and means of transport—has on the environment and ecosystems.

However, many studies have demonstrated that the level of pollutants that accumulate in a closed area can be equal to, or even greater than, the level present in the outside environment.

The substances present at the highest levels are generally nitrogen oxides (NOx) and volatile organic compounds (VOCs), which can also originate from commonly used domestic objects, including: cleaning products, deodorants, air conditioning systems and interior furnishings.

The need to ensure the livability of indoor, domestic or work environments, without the health of the occupants being jeopardized, has led to the study of filtering systems that are capable of removing all substances that could be harmful to human health, or at least capable of making these substances innocuous.

In particular, it is known that in the presence of oxygen and water, photocatalytic compounds such as titanium dioxide are capable of efficiently breaking down and oxidizing and above-mentioned pollutant compounds present in the air.

This characteristic is what has led to titanium dioxide becoming a compound that is used particularly in the air filter production sector, since it is capable of markedly improving the quality of the air breathed in domestic and work environments.

In particular, the anatase form of titanium dioxide remains the most promising photocatalytically active semiconductor in this sector and numerous efforts have been made to attempt to optimize the processes for the production and application of this particular crystalline form.

For example, excellent results for this sector have been obtained using a method for the production of an aqueous dispersion of nanoparticles of titanium dioxide in accordance with that which is disclosed in document WO2007088151 by the same applicant.

In further detail, titanium dioxide has photocatalytic properties that can be activated when the compound is illuminated with ultraviolet light, for example with a wavelength ranging between 300 and 390 nm, and therefore only 5% of the visible light radiation is able to activate it.

The incident photons are absorbed by the titanium dioxide, giving rise to the formation of radicals that are capable of oxidizing many environmental contaminants, thus making them innocuous.

It follows that this type of device has a very low level of efficiency unless it is used in combination with ultraviolet lamps specially designed and produced to carry out the function of activating the titanium dioxide.

Over the course of the last decades, the problem of the lack of absorption of visible radiation has been solved by using doping agents that are capable of improving the photocatalytic efficiency of TiO2in the visible region. Some doping agents that have been studied are for example the noble metals, the rare-earth elements, several transition metals (Cu, Ni, Co, Mn, Fe, Cr etc.) and non-metals (such as C, S, F and N). In particular, interesting results have been obtained by using TiO2doped with nitrogen, which modifies the band gap energy of titanium dioxide, increasing its photocatalytic efficiency in the visible region.

An example concerning photocatalytic application of nitrogen-doped titanium dioxide in the visible region appears in the article by M. Tahir et. al. (M. Tahir, B. Tahir, Applied Surface Science 377 (2016) 244-252), in which a ceramic support with a honeycomb structure and that is coated with nitrogen-doped TiO2is described. However, this coated support was used exclusively to study the efficiency of photocatalytic reduction of CO2to CO and CH4, under visible light irradiation, in the presence of molecular hydrogen, while applications concerning oxidation (also carried out in the visible region) of polluting agents such as nitrogen oxides (NO, NOx, NO2) and volatile organic compounds (VOCs) are not described.

Moreover, the process for preparing the coated support described in the article by M. Tahir et al. does not make it possible to obtain a product that can be used on an industrial scale. In fact, by applying the process described in this article, one obtains a support coated with a considerable amount of loose, doped TiO2powder not adhering to the surface. This limits the possibility of its incorporation in a device for water and air treatment and thus its use on a large scale. In fact, as highlighted in the comparative experiment described in the section of examples, the support coated according to the process described by M. Tahir et al. requires a washing step prior to its use in order to eliminate the doped titanium dioxide powder not adhering to the surface, resulting in considerable losses and waste of the product. Furthermore, the washed support reveals reduced photocatalytic efficiency in terms of oxidation of polluting agents (particularly nitrogen oxides) in the visible region.

In this context, the technical task underlying the present invention is to propose a nano-functionalized support that can be subsequently installed inside an air filter and that overcomes at least some of the drawbacks of the prior art cited herein above.

SUMMARY OF THE INVENTION

The defined technical task and the specified aims are substantially achieved by a nano-functionalized support comprising the technical characteristics set forth in one or more of the appended claims.

In accordance with the present invention, a nano-functionalized support is shown which comprises an application surface configured to receive nanoparticles and a photocatalytic nanoparticle coating deposited on the application surface.

The photocatalytic nanoparticle coating comprises titanium dioxide doped with a nitrogen-containing doping agent.

