"MICROPARTICLES WITH PHOTOCATALYTIC ACTIVITY AND PROCESS

FOR THE PREPARATION THEREOF"

Cross-Reference to Related Applications

This Patent Appl ication claims priority from Italian Patent Application No . 102022000006182 filed on March 29 , 2022 the entire disclosure of which is incorporated herein by reference .

Technical Sector

The present invention relates to composite microparticles , to a process for their manufacture and their uses .

The present invention further relates to a method for the surface treatment of a substrate and to a treated article .

Background of the Invention

In the field of ceramic materials it is known to coat obj ects with TiC>2 so that such obj ects can express photocatalytic properties . Usually the coating is made using nanosi zed particles of titanium dioxide in order to obtain easily cleanable materials and able to partially puri fy the air from organic pollutants (VOCs - volatile organic compounds ) and inorganic pollutants ( such as NOx and SOx - nitrogen oxides and, respectively, sulphur oxides ) . Often, organic polymers are used to obtain good adhesion of TiO2 on the surface of the obj ects .

The known methods for coating ceramic obj ects with titanium dioxide and the articles thus obtained have several drawbacks , among which we mention the following .

• The use of nanometric nanoparticles is harmful to health .

• The use of titanium dioxide particles with dimension smaller than 0 , 1 pm is considered harmful . • The catalytic effects are not always sufficiently high, especially in the absence of UV-A rays.

• The solidity of the adhesion of the TiC ₂ layer to the objects is not always stable over time.

International patent application having publication number W02010146410 (filed by the same Applicant) proposes the use of micrometric TiC ₂ particles for the surface treatment of tiles. Laboratory tests have confirmed that the tiles obtained in this way have a photocatalytic efficiency such that under UV-A irradiation they are: photocatalytic by degradation of methylene blue in the aqueous step (ISO 10678:2010) ; antibacterial also for MRSA (Antibiotic-resistant) bacteria (ISO 27447:2009) ; capable of degrading NOx (ISO 22197-1:2007) ; capable of degrading VOC (ethanol, toluene, acetone, acetaldehyde) ; self-cleaning according to ISO 27448-1:2009 standard; have photodegrading activity that also takes place in the aqueous step. Tests carried out on both powders and on tiles have demonstrated the efficiency in the degradation of organic dyes, acetylsalicylic acid (aspirin) and paracetamol.

It should be noted, however, that TiO2 is photoexcited between 315 and 400 nm (with maximum at 380 nm) in the full UV-A field (the theoretical data of 380 nm is typical of the single crystals) .

The tiles treated with TiC ₂ are therefore not able to act in the absence of UV-A light and are completely ineffective if they are installed in closed environments illuminated by normal LED lights (which typically emit with wavelengths over 400 nm and therefore only in the visible and not in the ultraviolet) .

In addition, in order to be produced, the tiles with TiO2 must be fired twice. They are subjected to a first firing at temperatures higher than 700 ° C, then treated with TiO2 and subj ected to a second firing at lower temperatures . This is because i f TiC ₂ were subj ected to higher temperatures it would be deactivated passing from anatase to rutile .

Note that having to treat TiC ₂ at relatively low temperatures , it is di f ficult to obtain a strong bond with the substrate .

Aim of the present invention is to provide composite microparticles , a process for their manufacture , their uses , a method for the surface treatment of a substrate and a treated article , which allow to overcome , at least partially, the drawbacks of the prior art and are, at the same time , of easy and economical implementation and/or use .

Summary

According to the present invention there are provided composite microparticles , a process for their manufacture , their uses and a method for the surface treatment of a substrate according to what is recited in the following independent Claims and, preferably, in any one of the Claims directly or indirectly dependent on the independent Claims .

Brief Description of the Drawings

The invention is described below with reference to the accompanying figures , which show non-limiting embodiments thereof , wherein :

- Figures 1 and 2 show photographs taken by means of TEM microscopy o f composite microparticles in accordance with the present invention;

- Figures 3 to 6 are photographs showing di f ferent steps for the preparation of composite microparticles in accordance with the present invention .

Detailed Description

In accordance with a first aspect of the present invention, there are provided composite microparticles , each of which comprises ( in particular consists of ) a respective titanate microparticle ( in particular perovskite , i . e . having a crystal structure ABX3 , wherein A denotes an alkaline or an earth alkaline - in this case strontium, B denotes another cation - in this case titanium - and X is an anion - in this case oxygen) and a further component selected from the group consisting of: Ag, Cu, SnC ₂ , ZnO, W, WO3, Au and a combination thereof. Advantageously but not necessarily, the further component is selected in the group consisting of: Ag, SnC ₂ , ZnO, W, WO ₃ and a combination thereof. In particular, the further component is Ag.

The titanate is selected from the group consisting of BaTiO ₃ , SrTiO ₃ and a combination thereof. Advantageously, the titanate comprises (in particular, is) SrTiO ₃ . In these cases, in other words, the titanate microparticle is a microparticle of SrTiO ₃ .

Note that, according to embodiments alternative to each other, the titanate microparticle (which may also be called base microparticle) consists of only titanate or consists of titanate and of the further component.

Advantageously, the titanate microparticle consists of only titanate. In this case, the preparation procedure provides for a reduced emission of carbon dioxide.

In some non-limiting cases, the titanate microparticle (which may also be called the base microparticle) consists of titanate and of the further component. In these cases, the composite microparticles have experimentally demonstrated to be particularly active.

Advantageously but not necessarily, each microparticle comprises a plurality of respective nanoparticles, which comprise (are of) the further component.

Note that (in accordance with what indicated by IUPAC) microparticle means a particle with dimensions (diameter) between 1×10 ^-7 m and 1×10 ^-4 m (i.e. between 0.1 pm and 100 pm) .

Nanoparticle means a particle with dimensions (diameter) between 1 nm and 100 nm.

In particular, the dimensions (diameter) of the particles can be measured by means of TEM microscopy. Advantageously but not necessarily, the nanoparticles are supported by the relative titanate microparticle. In particular, each titanate microparticle has a respective outer surface; the nanoparticles are linked to the outer surface and exposed to the outside.

According to some non-limiting embodiments, each composite microparticle consists of a titanate microparticle and a plurality of said nanoparticles linked to the respective titanate microparticle (in particular to the outer surface thereof) .

In some non-limiting cases, the titanate microparticles have an average diameter ranging from about 0.05 pm (in particular, about 0.1 pm; more in particular, from about 0.2 pm) to about 1 pm (more precisely, to about 0.5 pm) (in particular, measured by means of XRD) .

Advantageously but not necessarily, the nanoparticles have an average diameter up to about 30 nm (in particular, to about 20 nm; in some cases, to about 10 nm) (in particular, measured by means of TEM microscopy) .

Additionally or alternatively, the nanoparticles have an average diameter of at least about 1 nm (in particular, of at least about 8 nm) (in particular, measured by means of TEM microscopy) .

More precisely but not necessarily, each titanate microparticle has a diameter up to about 0.5 pm (in particular, measured by means of XRD) .

In particular, the composite microparticles have an average diameter ranging from about 0.05 pm (in particular, about 0.1 pm; more in particular, from about 0.2 pm) to about 1 pm (more precisely, to about 0.5 pm) . According to some embodiments, the composite microparticles have an average diameter up to about 0.2 pm (more precisely, up to about 0.13 pm ) .

More precisely but not necessarily, each composite microparticle has an average diameter up to about 0.5 pm (in particular, measured by means of XRD) . Additionally or alternatively, each composite microparticle has an average diameter of at least about 0.1 pm (in particular, measured by means of XRD) .

Unless explicitly stated otherwise, in the present text, the average diameter of the titanate microparticles and of the composite microparticles is measured by means of X-ray diffraction (XRD) . More precisely, the calculation of the average diameter of the titanate microparticles and of the composite microparticles is carried out using the Scherrer equation: t= 0.9λ/ ( β _hkl x cosQhkl) , wherein t is the crystallite dimension (corresponding to the particle) , λ is the X-ray radiation wavelength for CuKβ, β _hkl is the halfmaximum amplitude (FWHM) at (hkl) peak, and Qhki is the diffraction angle. In particular, the measurements are carried out using a diffractometer PW3050/60 X'Pert PRO MPD from PAN analytical working Bragg-Brentano, and using as a source the high-power ceramic tube PW3373/10 LFF with a Cu anode equipped with a Ni filter to attenuate Kβ . The scattered photons were collected by a X ' accelerator-detector RTMS (Real Time Multiple Strip) . Verifications of the correctness of the measurement can be made by means of TEM microscopy (as indicated below relatively to the silver nanoparticles) .

Unless explicitly stated otherwise, in the present text, the average diameter of the nanoparticles (of the further component) is measured by means of TEM microscopy. More precisely, the calculation of the average diameter is carried out by measuring the dimension greater than one hundred particles (taken randomly) and averaging. In particular, a JEOL 3010-UHR instrument is used (acceleration potential: 300 kV; filament LaB ₆ ) .

Advantageously but not necessarily, the composite microparticles comprise first particles, whose titanate comprises (in particular, is) SrTiO ₃ , and second particles, whose titanate comprises (in particular, is) SrTiO ₃ .

Alternatively or additionally, the composite microparticles comprise particles, whose titanate comprises (in particular, is) a combination of BaTiO ₃ and SrTiO ₃ .

According to some non-limiting embodiments, the weight ratio BaTiO ₃ /SrTiO ₃ ranges from about 20/1 to about 1/20, in particular from about 10/1 to about 1/10, more in particular from about 10/1 to about 7/1.

Advantageously but not necessarily, the further component comprises (in particular, is) Ag, Au and/or Pt. In particular, the further component is selected from the group consisting of: Ag, Au, Pt and a combination thereof.

According to specific embodiments, the further component comprises (in particular, is) Ag.

Alternatively or additionally, the further component comprises (in particular, is) Au. These embodiments demonstrated to be experimentally particularly active in the degradation of NO _X .

Alternatively or additionally, the further component comprises (in particular, is) Pt. These embodiments demonstrated to be experimentally particularly active in the degradation of NO _X .

Alternatively or additionally, the further component comprises (in particular, is) a combination of Au and Pt. These embodiments demonstrated to be experimentally particularly active in the degradation of NO _X .

Advantageously but not necessarily, each composite microparticle comprises about 0.1% (in particular, about 1%; more in particular, about 3%) to about 12% (in particular, to about 10%; more in particular, to about 7%; even more in particular, to about 5%) by weight, relative to the overall weight of the composite microparticle, of the further component .

According to some non-limiting embodiments, the microparticles comprise about 0.1% to about 3% (in particular, about 0.1 to about 1%) by weight, relative to the overall weight of the microparticles, of Au.

Alternatively or additionally, each microparticle comprises about 0.1% to about 3% (in particular, about 0.1 to about 1%) by weight, relative to the overall weight of the composite microparticle, of Pt.

Alternatively or additionally, each microparticle comprises about 3% (in particular, about 4%; more in particular, from about 5%) to 12% (in particular, to about 10%; more in particular, to about 7%; even more in particular, to about 5%) by weight, relative to the overall weight of the microparticles, of Ag.

Advantageously but not necessarily, alternatively or additionally, each composite microparticle comprises about 0.1% to about 6% (in particular, to about 5%; more in particular, to about 3%) by weight, relative to the overall weight of the microparticle, of the further component, when the further component is selected from Au, Pt and a combination thereof.

Additionally or alternatively, each composite microparticle comprises about 3% (in particular, about 4%; more in particular, from about 5%) to 12% (in particular, to about 10%; more in particular, to about 7%; even more in particular, to about 5%) by weight, relative to the overall weight of the microparticle, of the further component, when the further component is Ag.

In accordance with a second aspect of the present invention, there is provided a process to manufacture composite microparticles as defined above (in particular, in accordance with the first aspect of the present invention) .

The process comprises a loading step, during which nanoparticles of the further component are linked to outer surfaces of titanate microparticles so as to obtain said composite microparticles and which comprises, in turn, a mixing sub-step, a drying sub-step and a heating sub-step, which is at least partially subsequent to the drying substep .

In particular, during the mixing sub-step, a solution containing water, ions of the further component and the titanate microparticles is agitated so as to obtain an intermediate mixture . Additionally or alternatively, during the drying sub-step, the water content of the intermediate mixture is reduced ( in particular, the intermediate mixture is dried) by supplying heat to the intermediate mixture . Additionally or alternatively, during the heating sub-step, the intermediate mixture is kept at a temperature higher than about 300 ° C for at least about 30 minutes ( in particular, so that the nanoparticles of the further component are linked to outer surfaces of titanate microparticles ; more in particular so as to obtain the composite microparticles ) . More precisely but not necessarily, during said heating sub-step, the intermediate mixture is kept at a temperature higher than about 650 ° C ( in particular of at least about 700 ° C ) .

In particular, during said heating sub-step, the intermediate mixture is kept at a temperature up to about 950 ° C .

Advantageously but not necessarily, the heating substep has a duration of at least about 30 minutes ( in particular, at least about 1 hour ; more in particular, at least about 1 hour and 30 minutes ; in particular up to about 3 hours ) . In other words , the intermediate mixture is kept at the temperatures indicated above (higher than about 300 ° C ; higher than about 650 ° C ; at least about 700 ° C; up to about 950 ° C ) for at least about 30 minutes ( in particular, for at least about 1 hour ; more in particular, for at least about 1 hour and 30 minutes ; in particular up to about 3 hours ) .

In particular, during the loading step, the titanate microparticles comprise (more in particular, are of ) SrTiO ₃ .

According to some non-limiting embodiments , during the loading step, SrTiO ₃ is used as titanate .

Advantageously but not necessarily, the process comprises a further loading step, during which nanoparticles of the further component are linked to outer surfaces of microparticles of SrTiO ₃ so as to obtain said composite microparticles and which in turn comprises a further mixing sub-step, a further drying sub-step and a further heating sub-step, at least partially subsequent to the further drying sub-step .

In particular, during the further mixing sub-step, a solution containing water, ions of the further component and microparticles of SrTiO ₃ is agitated so as to obtain a further intermediate mixture . Additionally or alternatively, during the further drying sub-step, the water content of the further intermediate mixture is reduced ( in particular, the intermediate mixture is dried) by supplying heat to the further intermediate mixture itsel f . Additionally or alternatively, during the further heating sub-step, said further intermediate mixture is kept at a temperature higher than about 300 ° C for at least about 30 minutes ( in particular, so that the nanoparticles of the further component are linked to outer surfaces of titanate microparticles ; more in particular so as to obtain the composite microparticles ) .

Advantageously but not necessarily, the process further comprises a mixing step, during which the composite microparticles obtained from the loading step and the further loading step are mixed together . In particular, during the mixing step, the composite microparticles obtained from the loading step and the further loading step are mixed together by means of sonication and/or a submicron mills .

Advantageously but not necessarily, the process further comprises a disaggregation step, during which the titanate microparticles are disaggregated in a liquid, in particular by means of sonication or submicron mills .

According to some non-limiting embodiments , the process comprises a wetting step, which is ( at least partially) prior to the loading step and during which the titanate microparticles are wetted with an organic solvent .

In particular, during the heating sub-step, the intermediate mixture is kept at a temperature higher than at least about 400 ° C for at least about 1 hour .

Additionally or alternatively, during the further heating sub-step, the further intermediate mixture is kept at a temperature of at least about 400 ° C for at least about 1 hour .

In accordance with a third aspect of the present invention there is also provided a method for the surface treatment of a substrate . The method comprises an application step, during which composite microparticles as defined above ( in particular, in accordance with the first aspect of the present invention) are laid on at least one surface of the substrate so as to obtain an intermediate product ; and a thermal treatment step, during which the intermediate product is treated at a temperature of at least about 120 ° C ( in particular up to about 950 ° C ) .

In particular, by means of the method described above it is possible to obtain a treated article ( described in more detail below) .

Alternatively or additionally, during the application step, titanate microparticles and ions of a further component ( in particular in the form of salts ) are laid on at least one surface of the substrate so as to obtain the intermediate product .

In particular, the titanate microparticles are defined as described above relatively to the first aspect of the present invention .

Additionally or alternatively, the further component is defined as described above relatively to the first aspect of the present invention .

Advantageously but not necessarily, during the thermal treatment step, the intermediate product is treated at a temperature of at least about 400 ° C ( in particular, of at least about 780 ° C ; more in particular, at least about 850 ° C ) .

According to some non-limiting embodiments , during the thermal treatment step, the intermediate product is treated at a temperature of at least about 650 ° C ( in particular, of at least about 700 ° C ) .

In particular, during the thermal treatment step, the intermediate product is treated at a temperature up to about 950 ° C (more in particular, up to about 900 ° C ) .

Advantageously but not necessarily, during the thermal treatment step, the intermediate product is treated for a time from about 10 minutes to about 60 minutes ( in particular, to about 30 minutes ) .

In accordance with a further aspect of the present invention, there is provided a treated article obtainable ( in particular, obtained) by means of the method as referred to in the third aspect of the present invention . In particular, the article has a base product ( substrate ) . More in particular, the base product ( substrate ) comprises ceramic (more precisely, consisting of ceramic ) .

In particular, the article comprises ( a plurality of ) composite particles on (more precisely, linked to ) the surface of the article . More precisely, the composite particles are linked to the surface ( of the base product ) .

According to some embodiments , the article has at least 0 . 1 g (more precisely, from 0 . 6 g) of composite particles per square metre of said surface . In particular, the article has up to 5 g (more precisely, up to 3 g; even more precisely, up to 1 . 3 g) of composite particles per square metre of said surface ( of the base product ) .

More precisely, the composite particles are defined as indicated in accordance with the first aspect of the present invention .

According to a further aspect of the present invention, there is provided a use of composite microparticles as described above ( in accordance with the first aspect of the present invention) for air puri fication .

Alternatively or additionally, there is provided a use of composite microparticles as described above ( in accordance with the first aspect of the present invention) for the degradation of volatile organic compounds (VOCs - in particular, present in the air ) .

Alternatively or additionally, there is provided a use of composite microparticles as described above ( in accordance with the first aspect of the present invention) for reducing the concentration of N0 _x ( in particular, in the air ) .

Alternatively or additionally, there is provided a use of composite microparticles as described above ( in accordance with the first aspect of the present invention) for reducing the concentration of SOx ( in particular, in the air ) .

Alternatively or additionally, there is provided a use of composite microparticles as described above ( in accordance with the first aspect of the present invention) for reducing odours .

Alternatively or additionally, there is provided a use of composite microparticles as described above ( in accordance with the first aspect of the present invention) for sel f-cleaning .

Note that composite particles in accordance with the present invention have several advantages over the state of the art . These include the fact that they have a surprisingly high degradation activity ( even in the visible ) of VOCs and NOx even when thermally treated at relatively high temperatures .

These characteristics are particularly interesting when, for example , the particles are laid on a substrate ( e . g . of ceramic material ) which must then be treated at high temperature .

Further characteristics of the present invention will become apparent from the following description of some merely illustrative and non-limiting examples .

Example 1

This example reports the process for the production of Barium Titanate microparticles supporting silver nanoparticles ( treated particles ) . 3 grams of powder of BaTiO ₃ (Nantong Titanates) were wetted with 10 ml acetone to remove surface dirt and release the pores of the oxide.

0.42 g of AgNO ₃ (Fluka® with 99% purity) were dissolved in 5 ml of water. The solution thus obtained was added to the powder of BaTiO ₃ and was placed in a flask connected to a rotary evaporator. In the rotary evaporator the mixture of the powder and of the solution was agitated gently for about 24 hours at about 40°C. Subsequently, the obtained wet powder was dried in a stove at about 90 °C for about 24 hours and then calcined for about 2 hours at temperatures between 400°C and 700 °C.

Microparticles (shown in Figures 1 and 2) with about 5% Silver and about 95% BaTiO ₃ are obtained.

Example 2

This example reports the process for the production of Strontium Titanate microparticles supporting silver nanoparticles (treated particles) .

The procedure described in Example 1 above was followed by replacing BaTiO ₃ with SrTiO ₃ (Nantong® Titanates) . In particular, 3 grams of powder SrTiO ₃ and 0.42 g of AgNC ₃ were used .

Microparticles with about 5% Silver and about 95% SrTiO ₃ are obtained.

Example 3

This example describes the process for the preparation of mixed microparticles of Strontium Titanate and of Barium Titanate supporting silver nanoparticles (treated particles) .

The procedure of the Example 1 was followed by replacing the 3 grams of BaTiO ₃ (Nantong Titanates) with 1.5 grams of BaTiO ₃ and 1.5 grams of SrTiO ₃ (Nantong Titanates) previously mixed together.

Microparticles with about 5% Silver, about 47.5% of BaTiO ₃ and about 47.5% of SrTiO ₃ are obtained.

The process was repeated using a BaTiO ₃ /SrTiO ₃ weight ratio of 9/1, 8/2 and 1/9.

Example 4

This example describes a first procedure to obtain a formulation suitable to be applied, by means of spray, onto a substrate.

The microparticles obtained according to Example 3 were mixed with water and a commercial dispersant with the following composition: high molecular weight polysaccharide 11.55 %

(xanthan gum) quartz 11.55 % sodium ion 30.50 % chloride ion 46.40 %

100 litres of the formulation were obtained by mixing 85 1 of water, 15 1 of the dispersant and 2 kg of microparticles of the Example 3.

Example 5

This example describes a procedure to obtain a suitable formulation to be applied, by means of a digital printer (inkjet printer) , on a substrate.

The following components were used: Printojet W 012 (Lambert!®) 60%; Fluijet 13940 (Lambert!®) 10%; Viscojet W 26770 (Lambert!®) 20%; and titanates (microparticles obtained according to one of the Examples 1, 2 and 3) 10%. Printojet is a solvent and gives a low viscosity to the final ink; Fluijet is a dispersing agent and avoids aggregations among particles; Viscojet acts as a suspending agent (deflocculant) .

For a 300 kg load, all the components are introduced into a micrometre rotary ink mill and ground at 36°C, with cooling set to avoid temperature rises, up to a maximum absorption of 180 kW of power for about 6 hours.

Example 6

This example describes a second procedure to obtain a formulation to be applied, by means of a digital printer ( inkj et printer ) , on a substrate .

The microparticles obtained according to Example 1 were mixed in equal parts with the microparticles obtained according to Example 2 and subsequently used as described in Example 5 so as to obtain the formulation .

Example 7

This example describes a third procedure to obtain a formulation to be applied to a substrate .

The microparticles obtained according to Example 1 were used as described in Example 5 so as to obtain a first component of the formulation .

The microparticles obtained according to Example 2 were used as described in Example 5 so as to obtain a second component of the formulation .

The first and second components were mixed in equal parts .

Example 8

This example reports the procedure to manufacture tiles using the formulations of the examples 5 , 6 and 7 .

The preparation of the tiles was carried out as follows :

Dry brushing of the tiles ( 6 to 20 mm thick) with finished surface to remove surface dirt

Application with digital inkj et printer (more precisely, the printer used was a Creadigit model from System SpA equipped with DIMATIX Starfire Model M Heads ) with titanate-based inks in order to apply about 10 g ( can vary indicatively between 5 and 22 g) o f ink on square metres of tile . The tiles thus obtained were subj ected to the following subsequent treatments .

Kiln firing at 950 ° C with a cycle (which depends on the thickness of the tiles ) of about 45 min cold-cold ( in particular, the cycle involves bringing the tiles from room temperature to 950 ° C over a period of 20 minutes , once this temperature is reached the tiles are cooled so as to reach room temperature again over a further 25 minutes ) ; Washing with water and mechanically brushed to remove the photocatalyst (titanates possibly with silver) not tenaciously adhered to the surface of the tiles;

Drying under compressed air;

Quality control;

Storage.

The tiles were characterized by means of high- resolution "SEM-field emission".

Example 9

This example reports experimental tests relative to the activity on NOx of the treated particles obtained according to one of the Examples 1, 2 and 3 and with particles obtained as per Example 2, also adding HAuC14*3H2O (tetrachloroauric acid) (E2Au) and H ₂ PtCl ₆ (hexachloroplatinic acid) (E2Pt) .

The experimental procedure followed is reported in: C.L Bianchi, C. Pirola, F. Galli, G. Cerrato, S. Morandi, V. Capucci, "Pigmentary Ti02: a challenge for its use as photocatalyst in NOx air purification", Chemical Eng J, 261, (2015) 76-82. The experimental parameters used were:

500 ppb of pure pollutant mixed in synthetic air

Flat LED lamp at 4000K (UV-A at 0W/m2)

Controlled humidity

Testing time: 3 hours

The results obtained (% degradation values) are reported in the following Tables 1-6, wherein El (BaTiO ₃ with 5% Ag) , E2 (SrTiO ₃ with 5% Ag) and E3 (BaTiO ₃ and SrTiO ₃ with 5% Ag) indicate the microparticles obtained according to Example 1, 2 and 3, respectively. In addition, E2Au and E2Pt indicate the microparticles obtained following the procedure of the Example 2 by also adding HAuC14*3H2 0 (150 pl - Fluka® purity 99.99%) and H ₂ PtCl ₆ (150 pl - Fluka® purity 99.99%) , respectively. The temperatures reported are the calcination temperatures (with duration of 2 hours) . With regard to the particles E3 and the mixtures of El and E2 (denoted as E1+E2) , the weight ratio of BaTiO ₃ to SrTiO ₃ is 9/1 in Table 2, 1/9 in Table 3, 8/2 in Table 4 and 1/1 in Table 5. Table 1

Table 2 (BaTiO ₃ /SrTiO ₃ 9/1)

The microparticles E1A and E2A were obtained according to the processes of the Examples 1 and 2 without however the final calcination. In this case, the calcination was done only after E1A and E2A were mixed and treated with ultrasounds (ultrasonic bath for 30 minutes at room temperature in distilled water and subsequent drying and calcination at 400°C for 2 hours) . In the last row of Table 2, the microparticles El and

E2 were produced separately (with calcination at 400°C for 2 hours) , then mixed and finally recalcined at 700°C for 2 hours .

Table 3 (BaTiO ₃ /SrTiO ₃ 1/9) Also with regard to Table 3, the microparticles E1A and E2A were obtained according to the processes of the Examples 1 and 2 without however the final calcination. In this case, the calcination was done only after E1A and E2A were mixed and treated with ultrasounds (ultrasonic bath for 30 minutes at room temperature in distilled water and subsequent drying and calcination at 400 ° C for 2 hours ) .

This example reports experimental tests relative to the antibacterial activity of the particles obtained according to Examples 1-4 .

In accordance with the procedure referred to in ISO 27447 : 2009 standard, the antibacterial activity is tested both with UV-A and (modi fying the procedure by replacing only the type of lamp ) LED lamp .

In accordance with the procedure referred to in ISO 22196 : 2009 standard, the anti-bacterial activity is tested in the dark .

Even in these cases ( antibacterial activity in the presence of UV-A, with LED and in the dark) , the results are positive .

Example 11

This example describes the process for the preparation of microparticles of Strontium Titanate , Barium Titanate and mixtures of Strontium Titanate and Barium Titanate supporting silver nanoparticles ( treated particles ) by means of one-pot procedure .

The following materials were used .

Test 1

20 cm ³ of titanate-iso-propoxide in 200 cm ³ of distilled water

1.5 g of AgNO ₃

10 g of citric acid

10 g of a salt of Sr ²⁺

Test 2

20 cm ³ of titanate-iso-propoxide in 200 cm ³ of distilled water

1.5 g of AgNO ₃

10 g of citric acid

10 g of a salt of Ba ²⁺

Test 3

20 cm ³ of titanate-iso-propoxide in 200 cm ³ of distilled water

1.5 g of AgNO ₃

10 g of citric acid

3) 5 g of a salt of Ba ²⁺ + 5 g of a salt of Sr ²⁺ .

The procedure followed was as follows

Solution A titanate-iso-propoxide was poured dropwise into a 2/1 molar solution of distilled water and citric acids.

Solution B

AgNC ₃ and Sr(CH3COO)2 (and/or Ba(CH3COO)2) were dissolved in the least amount of water by adding a few drops of citric acid.

The solutions A and B were mixed and then rotavaporized (Figure 3) at 60-70°C and 40 rpm.

Before complete evaporation (Figure 4) , the gel is placed in a capsule and brought to 100°C for 24 hours. The orange powder (Figure 5) obtained is calcined at 800-950°C for 60 min (the powder obtained is shown in Figure 6) .

Example 12

This example reports experimental tests relative to the activity on NOx of the particles obtained according to Example 11 - test 1.

The experimental procedure followed is reported in: C.L Bianchi, C. Pirola, F. Galli, G. Cerrato, S. Morandi, V. Capucci, "Pigmentary TiCt: a challenge for its use as photocatalyst in NOx air purification", Chemical Eng J, 261,

(2015) 76-82. The experimental parameters used were:

500 ppb of pure pollutant mixed in synthetic air

Flat LED lamp at 4000K (UV-A at 0W/m2)

Controlled humidity (50%, ± 5%)

Testing time: 3 hours

The results obtained (degradation values NO%) , after 30 minutes, 60 minutes and 180 minutes are reported in the following Table 7.

Table 7

Example 13

This example reports experimental tests relative to the activity on NOx and VOC (in particular propionic acid and ethanol) of the particles obtained according to the example 11 - tests 1 and 2 - and carrying out the calcination at 850°C for 2 hours.

The experimental procedure followed is reported in: C.L Bianchi, C. Pirola, F. Galli, G. Cerrato, S. Morandi, V. Capucci, "Pigmentary TiO2: a challenge for its use as photocatalyst in NOx air purification", Chemical Eng J, 261, (2015) 76-82. The experimental parameters used were:

500 ppb of pure pollutant mixed in synthetic air

Flat LED lamp at 4000K (UV-A at 0W/m2)

Controlled humidity (50%, ± 5%)

Testing time: 3 hours

The results obtained (degradation values %) , after 180 minutes are reported below.

Test 1 (microparticles of SrTiO ₃ with Silver on the surface) .

Table 8 Test 2 (microparticles of BaTiO ₃ with Silver on the surface ) .

Table 9