US20220323642A1

US20220323642A1 - Photocatalytic ceramic

Info

Publication number: US20220323642A1
Application number: US17/639,807
Authority: US
Inventors: Isidoro Giorgio Lesci
Original assignee: Italcer SpA
Current assignee: Italcer SpA Benefit Soc; Lungenclinic Grosshandsdorf
Priority date: 2019-09-05
Filing date: 2020-08-12
Publication date: 2022-10-13
Also published as: IT201900015677A1; BR112022003640A2; EP3789368A1; WO2021044237A1; MA54199A; MX2022002604A; CN114423523A; EP4025547A1; US11446644B2; CA3152495A1; CN112441744A; US20210069681A1

Abstract

The present invention relates to a method for producing an antibacterial photocatalytic ceramic that comprises: —making available at least one amorphous metal; —making available a biomimetic material or a biomaterial based on calcium phosphate; —functionalizing said biomimetic material or said biomaterial based on calcium phosphate, with said at least one amorphous metal, obtaining a functionalized and oriented composite; —adding said functionalized composite to a ceramic mixture, and/or applying said functionalized composite on a ceramic semi-finished product, where ceramic semi-finished product means the ceramic material before baking; —applying said functionalized composite on a ceramic semi-finished product; —baking at a temperature between 600 and 1400° C., preferably between 900 and 1300° C., for a time that varies from 20 to 500 minutes, obtaining an antibacterial photocatalytic ceramic. The present invention further relates to a photocatalytic ceramic material that comprises a biomimetic material having a nanostructured hierarchical structure with macro and micro cavities, within which at least one photocatalytic material selected from metal oxides and/or sulphides in the crystalline form with a rutile-like structure is included, and tiles, sanitary ware and tableware comprising the same.

Description

PRIOR ART

Ceramics are among the most used materials in buildings and, with ever increasing interest, are encountered in the field of fittings, used as coverings and/or as constructional elements for making hard parts in the kitchen and bath fittings sector (for example counter top and/or backsplash). Uses range from the residential sector to hospitality, and research laboratories.
The use of ceramic materials having antimicrobial properties has obvious advantages. Photocatalysis is the natural phenomenon by which a photocatalyst produces a strong oxidation process that decomposes organic and inorganic contaminants, transforming them into harmless substances. Titanium dioxide TiO₂stands out among the materials most studied in photocatalysis. TiO₂combines long-term stability and low toxicity for the biosphere with good photocatalytic activity. The photocatalytic properties of TiO₂have been investigated in recent years on a wide range of pollutants, both of the atmosphere and of water: alcohols, halides, aromatic hydrocarbons. The studies conducted have given promising results for organic acids, dyes, NO_xand others. For these reasons TiO₂is already widely used in surface treatment.
These properties of TiO₂have been applied in the removal of bacteria and harmful organic materials in water and in the air, as well as on surfaces, particularly in medical/hospital settings. The activity of TiO₂is influenced by a variety of factors, such as crystalline structure, the surface, the size distribution of the nanoparticles, porosity, number and density of hydroxyl groups on the surface of the TiO₂.
TiO₂in fact occurs in amorphous form or in crystalline forms, and the amorphous form is photocatalytically inactive. Three natural crystalline forms of TiO₂are known, called anatase, rutile and brookite. Anatase and rutile have a tetragonal structure, while the structure of brookite is orthorhombic. Brookite is the less common form. Anatase and rutile are photocatalytically active, while brookite has never been tested for photocatalytic activity. Pure anatase is more active as a photocatalyst compared to rutile, probably because it has a higher negative potential at the edge of the conduction band, which means higher potential energy of photogeneration of electrons, and a higher number of hydroxyl groups on its surface.
Luttrell T. et al., Scientific Reports 4, Article number 4043, 2014, describe that the higher or lower photocatalytic activity of rutile and anatase might depend on the properties of the surface on which they are deposited and on the thickness of the coating deposited on the surface. For example, with identical surface conditions, anatase reaches its maximum activity if the coating is thicker than 5 nm, while for rutile a coating of 2.5 nm is sufficient. This activity can be increased by doping TiO₂appropriately. In recent years the scientific literature has been enriched with detailed studies on the doping of TiO₂with metal oxides.
On calcining in the range 300-500° C., formation of pure anatase is observed. With increasing temperature, an increase in the size of the crystals is observed. On calcining between 500-700° C., a mixed anatase-rutile is obtained.
Some research groups (Jung W. Y. et al., Synthesis of Ti-containing SBA-15 materials and studies on their photocatalytic decomposition of orange II. Catal. Today, 131:437-443, 2008. Lihitkar N. B. et al., Titania nanoparticles synthesis in mesoporous molecular sieve MCM-41. J. Colloid Interface Sci., 314: 310-316, 2007. Ikeda S. et al., Structural effects of titanium (IV) oxide encapsulated in a hollow silica shell on photocatalytic activity for gas-phase decomposition of organics. Appl. Cat. A: General, 369: 113-118, 2009) focused their attention on the possibility of increasing the photoactivity of TiO₂by increasing its surface area, thereby increasing the number of molecules adsorbed on its surface and promoting the charge transfer process.
The introduction of the photocatalyst on another material leads to an advantage of a practical nature. In fact, immobilization on a support inhibits or slows sintering of the particles, which is the cause of a decrease in surface area.
A further methodology used for increasing the activity of TiO₂relates to the possibility of acting upon the electronic levels of the semiconductor, decreasing the energy of the band-gap so as to be able to use light at a lower frequency than the visible, to promote the electrons from the valence band (VB) to the conduction band (CB) (Parida K. M., Naik B. Synthesis of mesoporous TiO2−xNx spheres by template free homogeneous co-precipitation method and their photo-catalytic activity under visible light illumination. J. Colloid Interface Sci., 333: 269-276, 2009. Irie H. et al., Nitrogen-Concentration Dependence on Photocatalytic Activity of TiO2−xNx Powders. J. Phys. Chem. B, 107: 5483-5486, 2003. Asahi R. et al., Visible-light photocatalysis in nitrogen-doped titanium oxides. Science, 293. 269-271, 2001). This methodology envisages modification of the material by doping and consists of introducing, in the synthesis step, suitable precursors of elements capable of modulating its electronic properties.
From the electronic viewpoint, TiO₂is an n-type semiconductor; the value of Eg of anatase is equal to 3.2 eV, that of rutile 3.0 eV. From these values, we find, from equation (1):
Eg=h v=hc/λ=1240/λ (1)
that anatase is “activated” by light having a wavelength λ≤388 nm, i.e. from the UVA portion of the electromagnetic spectrum, while rutile has λ=413 nm, therefore light in the visible region (PAR, 400-700 nm). In equation (1), h represents Planck's constant, v is the frequency of the incident radiation and c is the speed of light in a vacuum; the product hc, a constant, is expressed in [eV×nm] and the wavelength λ in nm.
WO2010146410A1 describes baking of the ceramic base at a temperature between 900 and 1250° C. and then using micrometric, crystalline TiO₂dispersed in water in post-baking, to obtain a surface layer, under which a layer of adhesive is deposited. A subsequent heat treatment at 600° C. allows softening of the adhesive but not conversion of anatase to rutile, considered insufficiently photoactive.
EP1304366B2 describes the deposition of a layer of amorphous titanium on surfaces, generally vitreous. Subsequent baking of the material at a maximum temperature of 525° C. transforms the amorphous titanium to anatase.
SnO2 played a marginal role in photocatalysis, having a band gap, i.e. an energy gap between the valence and conduction band, which requires an energy (3.8 eV) corresponding to wavelengths (326 nm) poorly represented in the solar radiation, which makes the photocatalytic process with solar radiation or artificial white light ineffective.
Biomimetics is a multidisciplinary science in which biological processes are utilized for designing new “smart” materials or structures. For example, nature supplies soft and hard materials whose peculiar functional properties depend on the hierarchical organization of the fundamental molecular units constituting them at the level of the macro- and nano-scale.
There is a strongly perceived need for a ceramic material with high antibacterial activity, obtainable using an economically sustainable production process.

DESCRIPTION OF THE INVENTION

In the present invention, a “bio-inspired” ceramic surface is produced, formed from a new material with a hierarchical structure that is modelled on the structure of bone, with micro and macro cavities, and with micrometric dimensions, nano-structured and biocompatible, where oxides or sulphides of at least one metal with rutile type structure crystallize at high temperatures on an inorganic support suitable for producing crystals with dimensions, morphology, structure and orientation such as to make the photocatalytic properties thereof particularly advantageous.

Definitions

Here, the terms “ceramic” or “ceramic material” or “ceramic product” mean the material and the finished product consisting thereof. Among the finished products, coating and covering materials, such as tiles and roofing-tiles, sanitary ware, and tableware, are highlighted here, as being of particular interest for the aims of the present invention.
Here, the term “oriented functionalized composite”, or “composite”, means a biomimetic material that comprises a metal in a crystalline rutile like form arranged in an orderly manner, i.e. with a regular crystallographic arrangement relative to the substrate, where substrate means said biomimetic material (Brinker C. J. 1998 Current Opinion in Colloid & Interface Science. 3: 166-173).
Here, the term “ceramic semifinished product” means the ceramic material after the steps of moulding and, optionally, drying, which typically precede the baking process.
The term “coated ceramic semi-finished product” means the ceramic material as mentioned above, on which a mixture has been applied that comprises the oriented functionalized composite according to the present invention.
Here, the term “ceramic mixture” means the mixture of raw materials which, on moulding, will constitute the ceramic semi-finished product and hence the ceramic article.
The term “enriched ceramic mixture” means a ceramic mixture that comprises the oriented functionalized composite according to the present invention.

DESCRIPTION OF THE FIGURES

FIG. 1: X-ray diffraction spectrum of nHA.

FIG. 2: schematic diagram of an embodiment of the surface functionalization process according to the present invention. The dots indicate at least one amorphous metal, and the diamonds indicate oxides and/or sulphides of said at least one metal in the rutile like crystalline form. The black strip is the ceramic substrate, and the line represents the biomaterial or the biomimetic material.

FIG. 3: (A) X-ray diffraction spectrum of the photocatalytic, active ceramic surface according to a first embodiment of the present invention, Ti form. (B) example images obtained with EDS spectroscopy (Energy Dispersive X-ray Spectrometry) of the photocatalytic, active ceramic surface according to the present invention, Ti form. The photographs show the surface localization of the P, Ca and Ti atoms, respectively.

FIG. 4: X-ray diffraction spectrum of the photocatalytic and active ceramic surface according to a second embodiment according to the present invention, Sn form. The typical peaks of casserite (A) and anorthite (B) are highlighted.

FIG. 5: examination by scanning electron microscope (SEM) of the photocatalytic active ceramic surface according to the Ti form embodiment. (A) hydroxyapatite microcrystals; (B) photograph highlighting the nanostructured hierarchical structure; (C) EDS microanalysis spectrum.

FIG. 6: Scanning Electron Microscope (SEM) analysis of the photocatalytic and active ceramic surface according to the Sn embodiment. (A) hydroxyapatite microcrystals; (B) EDS microanalysis spectrum.

FIG. 7: comparative test of photocatalytic activity at 12 hours (panel A) and at 48 hours (panel B) of a photocatalytic ceramic material according to the Ti embodiment (a) or of a commercial photocatalytic material that comprises anatase (b). Curve (c) relates to the result obtained on a non-photocatalytic surface.

FIG. 8: (A) emission spectrum of the Philips PL-S 9 W/2P BLB lamp used for the irradiation of the samples in experiment 7; (B) emission spectrum of the 6500 K LED lighting system used for irradiation of the samples in experiment 7; concentration profiles for NO, NO₂and NOx with UV irradiation during the photocatalytic test on ceramic tile (C) including SnO₂; (D) comprising SnO₂and TiO₂in rutile form 1:1; (E) comprising TiO₂; concentration profiles for NO, NO₂and NOx with visible irradiation during the photocatalytic test on a ceramic tile (F) including SnO₂; (G) comprising SnO₂and TiO₂in rutile form 1:1; (H) comprising TiO₂.

FIG. 9: photocatalytic activity, rhodamine test (A) absorbance curves; (B) absorbance over time.

The present invention relates firstly to a method for producing an antibacterial photocatalytic ceramic that comprises:

- making available at least one amorphous metal;
- making available a biomimetic material and/or a biomaterial based on calcium phosphate;
- functionalizing said biomimetic material and/or said biomaterial based on calcium phosphate with said at least one amorphous metal, obtaining a functionalized and oriented composite;
- adding said functionalized composite to a ceramic mixture, and/or applying said functionalized composite on a ceramic semi-finished product, where ceramic semi-finished product means the ceramic material before baking;
- baking at a temperature between 600 and 1400° C., preferably between 900 and 1300° for a time that varies from 20 to 500 minutes, obtaining an antibacterial photocatalytic ceramic.

In one embodiment, said at least one metal in amorphous form is selected from transition metals (elements of group d) and post-transition metals (elements of group p).
In one embodiment, said at least one metal is selected from the group that comprises Titanium, Tin, Zinc, Zirconium, Cadmium, Tungsten.
In one embodiment, said at least one metal is selected from the group that comprises titanium(IV) oxysulphate, titanium tetrachloride, titanium tetraisopropoxide, titanium isopropoxide, titanium oxychloride, SnCl₂, SnCl₄, Sn(NO₃)₂, SnSO₄, Sn(CH₃SO₃)₂, WO₃.
In one embodiment, Ti form, said method comprises making amorphous Titanium available, obtaining an antibacterial photocatalytic ceramic which comprises TiO₂in rutile form.
In an embodiment, Sn form, said method comprises making amorphous Tin available, obtaining an antibacterial photocatalytic ceramic comprising SnO₂in a rutile-like crystalline form.
In an embodiment, Sn/Ti form, said method comprises making available Tin and amorphous Titanium, obtaining an antibacterial photocatalytic ceramic which comprises SnO₂in rutile-like crystalline form and TiO₂in rutile form.
In further embodiments, said photocatalytic ceramic comprises ZnO, ZnS, ZrO₂, CdS, and/or WO₃.
Said material, synthetic (biomimetic) or of natural origin (biomaterial), is preferably selected from the group that comprises brushite, monetite, hydroxyapatite (HA), (β/α) tricalcium phosphate (TCP). Said material is calcium-deficient on the surface.
In a preferred embodiment, said material is nanocrystalline hydroxyapatite (nHA). Said hydroxyapatite is advantageously obtained at a pH between 7 and 14, preferably at pH 11, by neutralizing a suspension of calcium hydroxide or calcium acetate or calcium chloride or calcium nitrate drop by drop with phosphoric acid under vigorous stirring for 2-12 hours. The synthesis envisages a molar ratio between surface Ca/P of between 1.55 and 1.70, preferably 1.64.
FIG. 1 shows the diffraction spectrum of nHA thus obtained, showing that it is a crystalline material that has the diffraction maxima characteristic of hydroxyapatite. Said nHA exposes both positive and negative charges at the surface, which make it particularly reactive. This indicates that said nHA is able to bind quantities of the at least one amorphous metal and to bond to the components of the ceramic semi-finished product.
After said functionalization, the resulting composite is a functionalized and oriented composite, that is a material characterized by a regular crystallographic arrangement. Said biomimetic materials or biomaterials, in fact, are made up of a structure of PO₄ ³⁻ tetrahedra which includes two oxygen atoms on the horizontal plane. The authors of the present invention have surprisingly shown that said at least one amorphous metal binds the oxygens arranged on said horizontal plane and, following exposure to temperatures higher than 600° C., preferably higher than 900° C., rutile-like crystals are formed that grow in an ordered direction, determined by said deposit of said at least one amorphous metal on said plane.
In one embodiment, Ti form, said functionalization is effected by adding said amorphous Ti dropwise to a solution of calcium phosphate in the form of brushite and/or monetite, in the case of acid hydrolysis (pH 1-6), or in the form of nHA or (β/α) TCP, in the case of basic hydrolysis (pH 7-14). Preferably, said amorphous Ti is added dropwise in an amount of 10-30 wt % relative to the volume of the hydrolysis solution, preferably of 15%, and said dropwise addition takes place under vigorous stirring for 2-12 hours.
In one embodiment, said functionalization is effected with doped titanium and said amorphous Ti is added dropwise in suspension with one or more metal ions selected from Cu, Zn, Ag, Sr, Al, Sb, W, Mn, Sn, V, Cr, Zr, Mo, Pd, preferably solvated. In one embodiment, said metal ions are solvated with 10-30% of isopropyl alcohol or, alternatively, ethyl alcohol.
In one embodiment, at least two metal ions are present. Preferably, said two metal ions are in 1/1 ratio to one another.
In one embodiment, said suspension comprises 10-30% (w/v) of said amorphous Ti and 0.1-0.5% (w/v) of said one or more solvated metal ions.
In an embodiment, Sn form, said functionalization with amorphous Tin occurs first by obtaining a basic aqueous suspension of said amorphous Tin which is mixed with a suspension comprising nHA.
In one embodiment, said functionalization occurs with doped Tin and said amorphous Tin is dripped in suspension with one or more metal ions selected from Cu, Zn, Ag, Sr, Al, Sb, W, Mn, V, Cr, Zr, Mo, Pd. In one embodiment, said metal ions are solvated. In one embodiment, said metal ions are solvated with 10-30% of isopropyl alcohol or, alternatively, ethyl alcohol.
In one embodiment, at least three metal ions are present. Preferably, said three metal ions are in a 1/1 ratio to each other.
Preferably, said metal ions are Cu, Zn and Ag.
In one embodiment, said suspension comprises 10-30% (w/v) of said amorphous Tin and 0.1-0.5% (w/v) of said one or more metal ions, optionally solvated.
In one embodiment, said functionalization with doped Tin occurs first by obtaining an aqueous suspension of said amorphous Tin and Zn ions, a solution which is brought to basic pH, preferably with KOH, and then mixed with a solution comprising nHA and Cu ions and, optionally, with a basic solution comprising Ag ions.
In one embodiment, Sn/Ti form, said functionalized and oriented composite Ti is mixed with said functionalized and oriented Sn composite, obtaining a functionalized and oriented Ti/Sn composite. In one embodiment, said functionalized and oriented composite is exposed at a temperature of 100°-150° C.
In one embodiment, said functionalized composite, optionally after said heating to 100°-150° C., is applied on a ceramic semi-finished product to give a coated ceramic semi-finished product. As an example, said oriented functionalized composite is applied simultaneously with one or more glazing applications, or mixed with engobe applied after the forming step, or between one or more glazing applications. Moreover, said composite is applied during the process of screen printing, or of salt glazing, where present. By way of example, said composite is mixed with engobe, preferably in a ratio of 10-50% w/v, and then applied on the ceramic semi-finished product. Said engobe is selected from the engobes known in the ceramic sector, it is preferably a mixture that comprises kaolin, crystalline silica, and zirconium. Said engobe is typically applied on the ceramic semi-finished product in an amount between 460 and 880 g/m²at a density between 1200 and 1500 g/litre (dry equivalent: from 210 to 440 g/m²). Alternatively, or in addition, said composite is applied during the glazing step, for example in amounts between 100-300 g/m².
Alternatively, said functionalized and oriented composite is added to the ceramic mixture, obtaining an enriched ceramic mixture. When said functionalized composite is mixed with a ceramic mixture, said functionalized composite is added in a percentage of 10-50% w/v, preferably 20%. After moulding, said enriched ceramic mixture gives rise to a ceramic semi-finished product that comprises the oriented functionalized composite.
The ceramic semi-finished product that comprises the oriented functionalized composite is then submitted to a baking cycle at temperatures between 600 and 1400° C., preferably between 900 and 1300° C.
The duration of said baking cycle is closely linked to the thickness of the ceramic semi-finished product, where the baking times get longer with increase in thickness. Merely as an example, 60×60 tiles with a thickness of 10 mm require a baking cycle of about 40 minutes. Keeping the same surface area but increasing the thickness to 20 mm, the baking times required increase to about 90 minutes.
The authors of the present invention have surprisingly demonstrated that after said baking, said biomimetic material and/or biomaterial passes from a nanometric state to a nanostructured micrometric state.
The ceramic material thus obtained advantageously comprises a crystalline material that has the diffraction maxima characteristic of rutile. In the Ti form embodiment, X-ray diffraction, spectrum in FIG. 3A, shows the principal phases present: rutile (R), quartz (Q), mullite (M), anorthite (A), wollastonite (W). In the Sn embodiment, the X-ray diffraction spectrum in FIG. 4 shows the main phases present: Cassiterite (lines in panel A), and Anorthite (lines in panel B).
Examination with the scanning electron microscope (SEM) shows, as shown in FIG. 5 for the Ti embodiment, that hydroxyapatite microcrystals were obtained with a nanostructured hierarchical structure, constituted of rutile at the surface (FIG. 5B), indicating that baking has modified the hydroxyapatite from nanometric to nanostructured micrometric. The particles all have a micrometric size; the distribution ranges from about 1 to 100 micrometres. The spectrum obtained in EDS microanalysis (5C) shows that the elemental composition of the particles consists of calcium and phosphorus in a ratio compatible with that of hydroxyapatite. Moreover, the signal of titanium and that of oxygen are noted. The particles analysed at different points give the same composition, supporting the fact that a hydroxyapatite-rutile aggregate has formed.
For the Sn embodiment, scanning electron microscope (SEM) analysis shows, as highlighted in FIG. 6A, that microcrystals of hydroxyapatite with nano-structured hierarchical structure have been obtained, indicating that firing has modified the nano-sized hydroxyapatite to micrometric nanostructured. The particles all have a micrometric size; the distribution ranges from about 1 to 100 micrometers. The spectrum obtained with the EDS microanalysis (FIG. 6B) shows that the elemental composition of the particles is made up of calcium and phosphorus in a compatible ratio with that of hydroxyapatite. Tin and Oxygen signals are also noted. The particles analyzed at different points give the same composition, supporting the fact that a hydroxyapatite-casserite aggregate is formed.
In a further embodiment, the present invention relates to a photocatalytic ceramic material endowed with antibacterial activity, where said ceramic material is characterized in that it comprises hydroxyapatite microcrystals with a nanostructured hierarchical structure with macro and micro cavities. Within said microcavities, is comprised at least one photocatalyst selected from the metal oxides and/or sulphides in the crystalline form with a rutile-like structure.
In the Ti embodiment, said ceramic material is characterized by the X-ray diffraction spectrum as in FIG. 3A and by surface mapping of the atoms present in the ceramic material, obtained by means of “mapper EDS” or EDS spectroscopy (Energy Dispersive X-ray Spectrometry) that utilizes the emission of X-rays generated by an accelerated electron beam when it hits the ceramic sample, as in FIG. 3B. The images highlight that the localization of the titanium atoms is substantially superimposable on that of the phosphorus and calcium atoms, where said phosphorus and calcium atoms belong to the hydroxyapatite, which is in fact functionalized with titanium.
For comparative purposes, the photocatalytic activity of a photocatalytic ceramic material according to the present invention (Ti embodiment, sample (a) curve in FIG. 7) was compared with that of a commercial photocatalytic ceramic material that comprises anatase, sample (b) curve in FIG. 7.
The test involved measuring the amount of methylene blue before and after irradiating the material with a mercury vapour lamp.
Surfaces samples (a) and (b) were covered with an equal volume of a 1 ppm solution of methylene blue and they were irradiated for 12 hours. The diagram in FIG. 7A shows, curve (a), the extraordinary photocatalytic activity of the ceramic material according to the present invention. On prolonging the irradiation to 48 hours, the difference is still significant (FIG. 7B, curve a). Curve (c) shows, in both diagrams, a non-photocatalytic surface covered with the same volume of a 1 ppm solution of methylene blue.
The photocatalytic activity of a photocatalytic ceramic material according to the Sn embodiment was evaluated by covering the material with a stable and coloured pollutant, specifically rhodamine B was used, and by measuring the amount of rhodamine B before and after irradiation of the material with a mercury vapour lamp. The reduction in the amount of rhodamine on the photocatalytic ceramic material according to the present invention after irradiation is indicative of the extraordinary photocatalytic activity of the ceramic material according to the present invention.
Surprisingly, the present inventors have developed an innovative “bio-inspired” ceramic material and a method for producing it efficiently.
The innovative technique according to the present invention in fact envisages a single baking step, i.e. baking once in a first firing.
With the technique according to the present invention, biomimetic microcrystals are obtained that have a hierarchical macro and microporous structure after baking, said microcrystals having a morphology and dimensions that make them extremely reactive and available for binding with rutile, which is crystallized starting from amorphous Ti inside and outside said microporous structure. The experimental data obtained, and reported here, show the high photocatalytic, antibacterial and anti-contamination activity of the ceramic material according to the present invention. The macro and micro cavities present in the hierarchical structure characterizing the ceramic material according to the present invention function as reaction chambers or centres. Contaminating organic substances are trapped and then degraded therein, when the surface is exposed to wavelengths in the visible.
Among the known crystalline forms of TiO₂, rutile is the thermodynamically most stable natural form, as well as being the only form that is activated at wavelengths in the visible. Addition of metal during preparation permits doping of the titanium, which mainly activates it at wavelengths in the visible region.
Surprisingly, the authors of the present invention have shown how other metal oxides and/or sulphides, such as SnO₂, are able to crystallize in the biomimetic material, giving rise to a rutile-like structure.
Advantageously, the ceramic according to the present invention does not lose the antibacterial and anti-contamination activity over time, since nHA/amorphous metal, deposited on the ceramic semi-finished product or added to the ceramic mixture, undergoes a heat treatment at high temperatures, i.e. above 600° C., sufficient to “weld” it to the ceramic, making it resistant to abrasion. The examples that follow are purely for the purpose of better illustrating the invention and are not to be understood as limiting it, its scope being defined by the claims.

Example 1: Synthesis of HA+Ti (Basic Hydrolysis)

Preparation of hydroxyapatite nHA: 16 ml of 1.35 M calcium hydroxide is added to 70 ml of water and is neutralized with 10 ml of 1.26 M phosphoric acid. The pH is adjusted to 11 with about 4 ml of 1 M sodium hydroxide. A hydrolysis suspension based on nanocrystalline hydroxyapatite is obtained.
Suspension of amorphous Ti: 0.1-0.5% w/v of one or more metal ions selected from Cu, Zn, Ag, Sr, Al, solvated with 10-30% of isopropyl alcohol or alternatively ethyl alcohol and 10-30% w/v of amorphous Ti.
nHA functionalized with amorphous Ti is obtained by adding, slowly and while stirring vigorously, said suspension of amorphous Ti, in an amount between 20-60% w/v, to said hydrolysis suspension.

Example 2: Synthesis of TCP+Ti (Basic Hydrolysis)

Preparation of hydroxyapatite β-TCP, Ca/P ratio 1.30-1.55 preferably 1.51:14 ml of 1.35 M calcium hydroxide is added to 70 ml of water and is neutralized with 10 ml of 1.26 M phosphoric acid. The final pH should be between 7 and 11, preferably 8. A hydrolysis suspension is obtained.
Suspension of amorphous Ti: 0.1-0.5% w/v of one or more metal ions selected from Cu, Zn, Ag, Sr, Al, solvated with 10-30% of isopropyl alcohol or alternatively ethyl alcohol and 10-30% w/v of amorphous Ti.
Said suspension of amorphous Ti is added, slowly and while stirring vigorously, to said hydrolysis suspension, obtaining hydroxyapatite functionalized with amorphous Ti.

Example 3: Brushite Synthesis (Acid Hydrolysis)

To prepare 100 ml of a suspension of brushite and/or monetite (CaHPO₄*2H₂O (brushite) and CaHPO₄(monetite)), 16 ml of 1.35 M calcium hydroxide is added to 70 ml of water and is neutralized with 10 ml of 1.26 M phosphoric acid. The final pH should be between 4 and 7, preferably 6. A suspension of amorphous Ti constituted as follows: 0.1-0.5% w/v of one metal ion, or mixture thereof in 1/1 ratio, of Cu, Zn, Ag, Sr, Al and solvated with 10-30% of isopropyl alcohol or alternatively ethyl alcohol and 10-30% w/v of amorphous Ti, are added, slowly and while stirring vigorously, to said hydrolysis suspension.
nHA functionalized with amorphous Ti is thus obtained.

Example 4: Synthesis HA+Doped Sn (Basic Hydrolysis)

Preparation of nHA hydroxyapatite: 16 ml of 1.35 M calcium hydroxide are added to 70 ml of water and neutralized with 10 ml of 1.26 M phosphoric acid. The pH is brought to 11 with about 4 ml of sodium hydroxide 1 M. What is obtained is a hydrolysis suspension based on nanocrystalline hydroxyapatite.
Suspension of amorphous Sn: 0.1-0.5% w/v of one or more metal ions selected from Cu, Zn, Ag and 10-30% w/v of amorphous Sn.
nHA functionalized with amorphous Sn is obtained by adding said suspension of amorphous Sn to said hydrolysis suspension, slowly and with vigorous stirring, in an amount comprised between 20-60% w/v.

Example 5: HA+Doped Sn+Ti Synthesis (Basic Hydrolysis)

In a mixer, are added in a 1:1 ratio nHA functionalized with amorphous Sn obtained from example 4 and nHA functionalized with amorphous Ti obtained from example 1.

Example 6: Mixture with Engobe

Functionalized nHA as from examples 1-5, which is the functionalized and oriented composite, is added to the engobe mixture in percentages of 10-50% w/v and applied on a ceramic semi-finished product in an amount between 460 and 880 g/m²at a density between 1200 and 1500 g/litre (dry equivalent: from 210 to 440 g/m²). Said engobe comprises kaolin, crystalline silica, zirconium. Said coated ceramic semi-finished product is then exposed to baking in a first firing, at temperatures between 900 and 1300° C.
Where said nHA is nHA functionalized with amorphous Sn as in example 4, and said ceramic semi-finished product is of the rough type, the ceramic defined AR is obtained.
Where said nHA is nHA functionalized with amorphous Ti as in example 1, and said ceramic semi-finished product is of the rough type, the CR ceramic is obtained.
Where said nHA is nHA functionalized with amorphous Sn and amorphous Ti as in example 5, and said ceramic semi-finished product is of the rough type, BR ceramic is obtained.

Example 7: Mixture with Salt Glazing

Functionalized nHA as from examples 1-5, which is the functionalized and oriented composite, is added to the mixture of salt glazing in percentages of 10-50% w/v and applied on the ceramic product that has not yet undergone the baking process in amounts: from 260 to 360 g/m²at a density from 1100 to 1500 g/litre (dry equivalent: from 110 to 170 g/m²). Said salt glazing mixture comprises ceramic frits, crystalline silica, kaolin. Said coated ceramic semi-finished product is then exposed to baking in a first firing, at temperatures between 900 and 1300° C.
Where said nHA is nHA functionalized with amorphous Sn as in example 4, and said ceramic semi-finished product is of the rough type, AR ceramic is obtained.
Where said nHA is nHA functionalized with amorphous Ti as in example 1, and said ceramic semi-finished product is of the rough type, the CR ceramic is obtained.
Where said nHA is nHA functionalized with amorphous Sn and amorphous Ti as in example 5, and said ceramic semi-finished product is of the rough type, BR ceramic is obtained.

Example 8: Antibacterial Activity

The AR ceramic material obtained as per example 6 or 7 was tested for antibacterial activity. The same ceramic material fired without adding functionalized nHA to the engobe was used for comparative purposes. The method for measuring the antibacterial activity of photocatalytic semiconductor materials ISO 27447:2019 was followed, using a polypropylene film. The antibacterial activity is given by the difference between the logarithm of the total number of live bacteria that are found on the material being analyzed after UV irradiation and the logarithm of the total number of live bacteria on the same material kept in the dark. The irradiation was provided by an 18 W mercury vapour UV lamp for an exposure time of 8 hours. Escherichia coli was used, inoculating 8.8×10e5 CFU/ml
The results obtained are shown in table 1 and show, for the material according to the present invention, a reduction of the bacterial activity with irradiation compared to the untreated material equal to 99.4%.

TABLE 1

	Irradiation	CFU/ml

Untreated material	NO	16,400
(comparative)
Untreated material	YES	1,700
(comparative)
AR material	NO	15,900
AR material	YES		10

Example 9: Photocatalytic Activity, Nitric Oxide Reduction

The NO reduction tests were performed with the tangential flow method, in accordance with the UNI 11484-2013 standard. The tests were carried out with a simplified procedure, i.e. once the stability condition of the concentrations measured under irradiation was reached or the maximum irradiation time of 180 minutes was reached, the flow velocity inside the reactor was not changed, ending hence the test under these conditions. The samples were studied under both UV and visible irradiation.
The determination of the NO/NO₂content in the measurement streams was made by means of an APNA 370 chemiluminescence meter. The measurement reactor had an internal volume of 3.6 dm³. The mixing inside the reactor was ensured by a compact axial fan EBMPAPST 612 JH (dimensions 60×60×32 mm) which provides a nominal flow of 70 m³h⁻¹.
The UV irradiation took place using a set of two Philips PL-S 9 W/2P BLB fluorescent lamps with a significant emission in the UV whose emission spectrum is shown in FIG. 8A. The intensity of the radiation incident on the sample was 10 W m⁻²between 290 and 400 nm.
In the case of visible radiation, notwithstanding the UNI 11484 standard, a LED illuminator (6500 K) with no UV emission was used. The spectrum of this source is shown in FIG. 8B. The irradiance on the sample surface was 250 W m⁻²between 400 and 800 nm.
The light intensity was evaluated by spectroradiometry using an Ocean Optics USB2000+UV-VIS spectrophotometer equipped with an optical fiber having a diameter of 400 μm and a length of 30 cm equipped with a cosine corrector (Ocean Optics CC-3-UV-T, PTFE optical diffuser, spectral range 200-2500 nm, outer diameter 6.35 mm, field of view 180°). The spectroradiometer was calibrated with an Ocean Optics DH-2000-CAL Deuterium-Halogen Light Sources lamp for UV-Vis-NIR measurements which was itself calibrated in absolute irradiance by the vendor (Radiometric Calibration Standard UV-NIR, calibration certificate #2162).
The tested samples were three ceramic tiles (respectively called AR, BR, CR) with dimensions of 9.9 cm×9.9 cm×10 mm. The three samples consisted of AR, BR, CR ceramics, obtained as in example 6 or 7.
The tests in accordance with the UNI 11484 standard but with visible irradiation took place on the samples used for the similar test under UV irradiation, but after washing with demineralization water and drying at 90° C.
The list of samples analyzed with the respective irradiated areas is shown in Table 2.

TABLE 2

	Sample		Reduction	Area
Sample	description	Irradiation	test	cm²	Pre-treatment

AR(UV)	Ceramic tiles	UV	NO/NOx UNI	98.0	NO
			11484: 2013
BR(UV)	Ceramic tiles	UV	NO/NOx UNI	98.0	NO
			11484: 2013
CR(UV)	Ceramic tiles	UV	NO/NOx UNI	98.0	NO
			11484: 2013
AR(Vis)	Ceramic tiles	Visible	NO/NOx UNI	98.0	H₂O washing
			11484: 2013		after UV test
			(visible)
BR(Vis)	Ceramic tiles	Visible	NO/NOx UNI	98.0	H₂O washing
			11484: 2013		after UV test
			(visible)
CR(Vis)	Ceramic tiles	Visible	NO/NOx UNI	98.0	H₂O washing
			11484: 2013		after UV test
			(visible)

The evolution of NO and NO₂concentrations during the test is shown in FIG. 8, where panels C, D, E show data with UV light exposure, panels F, G and H show data with light exposure visible.
The three samples tested showed a measurable reduction of NO both under UV and visible radiation.

Example 10: Photocatalytic Activity, Rhodamine B Test

The photocatalytic activity of a photocatalytic ceramic material according to the present invention was measured by dirtying the tiles with a stable collared pollutant, rhodamine B. The tiles were then exposed to a light source for a period of up to 20 hours. From the very first hours the results of the photocatalytic action appeared to be considerable. The measurement of the amount of rhodamine B before and at different times after irradiation of the material with a mercury vapour lamp is shown in FIG. 9, where the curves of panel A show the extraordinary photocatalytic activity of the AR ceramic material according to the present invention, the graph of panel B shows how the decrease in the pollutant is linear over time.

Claims

1. A method for producing an antibacterial photocatalytic ceramic, the method comprising:

making available at least one amorphous metal-containing material;

making available a biomimetic material or a biomaterial based on calcium phosphate;

functionalizing the biomimetic material or biomaterial based on calcium phosphate with the at least one amorphous metal-containing material, thereby obtaining a functionalized oriented composite, where oriented refers to having a regular crystallographic arrangement;

adding the functionalized oriented composite to a ceramic mixture, and/or applying the functionalized oriented composite on a ceramic semi-finished product, where the ceramic semi-finished product refers to a ceramic material before baking; and

baking at a temperature between 600 and 1400° C., for 20 to 500 minutes, thereby forming the antibacterial photocatalytic ceramic.

2. The method of claim 1, wherein the at least one amorphous metal-containing material comprises a metal which is at least one selected from the group consisting of a transition metal and a post-transition metal.

3. The method of claim 1, wherein the at least one amorphous metal-containing material comprises a metal which is at least one selected from the group consisting of Titanium, Tin, Zinc, Zirconium, Cadmium, and Tungsten.

4. The method of claim 1, wherein the amorphous metal-containing material is at least one selected from the group consisting of titanium(IV) oxysulphate, titanium tetrachloride, titanium tetraisopropoxide, titanium isopropoxide, titanium oxychloride, SnCl₂, SnCl₄, Sn(NO₃)₂, SnSO₄, Sn(CH₃SO₃)₂.

5. The method of claim 1, wherein the biomimetic material or biomaterial based on calcium phosphate is at least one selected from the group consisting of brushite, monetite, hydroxyapatite (nHA), and (β/α) tricalcium phosphate (TCP); and the biomimetic material or biomaterial based on calcium phosphate is calcium-deficient on the surface.

6. The method of claim 1, wherein the biomimetic material or biomaterial based on calcium phosphate is a biomimetic material which is nanocrystalline hydroxyapatite (nHA) obtained at a pH between 7 and 14 by neutralizing a suspension of a calcium source which is at least one selected from the group consisting of calcium hydroxide, calcium acetate, calcium chloride, and calcium nitrate drop by drop with phosphoric acid under vigorous stirring for 2-12 hours.

7. The method of claim 6, wherein the nHA has a molar ratio of surface Ca/P in a range of 155 to 1.70.

8. The method of claim 1, wherein the functionalizing is performed by adding the at least one amorphous metal-containing material dropwise to a solution of calcium phosphate in the form of brushite and/or monetite in a case of acid hydrolysis (pH 1-6), or in the form of nHA or (β/α) TCP in a case of basic hydrolysis (pH 7-14).

9. The method of claim 1, wherein the functionalizing is performed with a doped titanium and/or a doped tin and the doped titanium and/or the doped tin is added dropwise in suspension with one or more dopant metal ions selected from the group consisting of Cu, Zn, Ag, Sr Al, Sb, W, Mn, Sn, V, Cr, Zr, Mo, and Pd.

10. The method of claim 9, wherein said dopant metal ions are solvated.

11. The method of claim 1, wherein the functionalized oriented composite is applied on a ceramic semi-finished product simultaneously with one or more glazing applications, or is mixed with engobe applied after the forming step, or is applied between one or more glazing applications and/or during a process of screen printing, and/or of salt glazing.

12. An antibacterial photocatalytic ceramic material, comprising a ceramic material based on calcium phosphate which is at least one selected from the group consisting of a microcrystalline biomimetic material and a biomaterial, the ceramic material having a nanostructured hierarchical structure with macro and micro cavities within which is disposed a photocatalyst which is at least one selected from the group consisting of a metal oxide and a metal sulphide, the photocatalyst being in crystalline form with rutile-like structure, the rutile-like structure being arranged in a regular crystallographic arrangement.

13. The antibacterial photocatalytic ceramic material of claim 12, wherein photocatalyst is at least one selected from the group consisting of TiO₂, SnO₂, ZnO, ZrO₂, CdS and WO₃.

14. The antibacterial photocatalytic ceramic material of claim 12, wherein said at least one photocatalyst in crystalline form with rutile-like structure is TiO₂, SnO₂or mixtures thereof.

15. (canceled)

16. A ceramic article, comprising the photocatalytic ceramic material of claim 12, wherein the ceramic article is at least one selected from the group consisting of a tile, a sanitary ware, and a tableware.