WO2025219582A1 - Improved filter - Google Patents

Abstract

The invention relates to a nanofibre composition comprising mesoporous hydroxyapatite particles distributed in an array formed by the nanofibres, wherein the nanofibres are selected from the group consisting of polymer nanofibres, ceramic nanofibres, metal nanofibres, carbon nanofibres and mixtures thereof, and wherein the proportion of the weight content of nanofibres relative to the weight content of hydroxyapatite particles is between 0.5 and 2. The invention also relates to the filtering material comprising this composition and to the method for producing the filtering material.

Description

IMPROVED FILTER

Technical field

The present invention relates to the use of a hydroxyapatite of specific porosity in filtration. This is done in association with nanofibers, chosen from the group consisting of polymer nanofibers, metal nanofibers, ceramic nanofibers, carbon nanofibers and their mixtures, and, advantageously in the presence of mineral or organic compounds, so as to allow decontamination of aqueous media.

Prior art

The decontamination of an aqueous environment is traditionally carried out by biological, chemical and physical methods.

Physical methods involve sedimentation and filtration.

Biological methods are used on a large scale, for example for wastewater treatment. They involve causing the consumption of organic matter, denitrification, or the degradation of compounds derived from organic chemistry (e.g. hydrocarbons, halogenated compounds, paints, etc.). These methods are effective for a given site, but not very flexible.

Chemical methods include precipitation, coagulation, ion exchange, absorption, neutralization, and solvent extraction. Chemical approaches are therefore more targeted. However, these approaches are sometimes expensive and difficult to implement in practice when it comes to remediating complex environments. Some chemical agents are also harmful or dangerous.

There is therefore a need for the development of hybrid methods that combine the advantages of several of the above methods.

The use of mineral and/or organic compounds in pollution control is known, and such compounds have been advantageously associated with filtration systems. For example, patent application CN105935455 describes a nanocomposite material formed by bringing microcrystalline cellulose into contact with hydroxyurea, then adding a soluble calcium salt and a soluble phosphate salt to obtain a colloidal suspension, which will then be treated with ultrasound before separation and drying.

The stability of this compound was tested in the presence of a solution mimicking biological fluids, and this compound is capable of binding bovine hemoglobin.

Patent applications WO2019/106176 and WO2019/106178 describe the use of hydroxyapatite, for example calcium-deficient and/or supplemented with an additive during its synthesis, for the adsorption of contaminating metals present in an aqueous effluent. The hydroxyapatite may have a size of at least 20 pm, a specific surface area of at least 120 m ² /g and a porosity of at least 0.3 cm ³ /g. The additive may be activated carbon, chitosan, hopcalite, clays, sulfur, an elemental metal, a salt thereof, an oxide or a hydroxide thereof.

On the other hand, patent CN113318603 describes a hybrid separation membrane having a polymeric structure and inorganic particles being crosslinked by silane compounds.

However, none of the solutions described allow effective filtration, which also allows the trapping of contaminating metals.

Brief summary of the invention

The object of the invention is to provide such a solution.

To solve this problem, the invention provides a composition comprising a weight content of nanofibers and a weight content of hydroxyapatite particles distributed in a network formed by said nanofibers, in which said nanofibers are chosen from the group consisting of polymer nanofibers, metal nanofibers, ceramic nanofibers, carbon nanofibers and mixtures thereof, and in which the proportion of the weight content of nanofibers relative to the weight content of hydroxyapatite particles is between 0.5 and 2. In other words, the invention provides a composition comprising nanofibers and hydroxyapatite particles distributed in a network formed by said nanofibers, in which said nanofibers are chosen from the group consisting of polymer nanofibers, ceramic nanofibers, metal nanofibers, carbon nanofibers and mixtures thereof, and in which the mass ratio between the nanofibers and the hydroxyapatite particles is between 0.5 and 2, preferably between 1 and 1.5.

In the context of the present invention, the expression "metal nanofibers" may include metal nanofibers, metal oxide nanofibers and mixtures thereof. The term "metal nanofibers" means, for example, nanofibers of Si, Ba, Ti, Mn, Cu, Fe, Sn, Sb, Ni, Mo, Co. The term "metal oxide nanofibers" means, for example, nanofibers of NiC, CO3O4, CoMn2O4 CeO2, TiC, CuO, Fe2O3, MnC, Mn2O3, SnO2, NiCo2O4, ZnO, ZnS, NiO, ZnO/TiO2, ZnO/SnO2, Ag LaFeOs, CuO-ZnO, CuO/TiC, CuO/CeO2, SnO2/MoO3, ZnO CoNiO2, Ni WO4, BaTiOs.

The term “ceramic nanofibers” means, for example, glass nanofibers, AI2O3, ZrO2, SisN4, SiC.

Preferably, according to the present invention, the "polymer nanofibers" are selected from the group consisting of cellulose nanofibers, poly(s-caprolactone) (PCL), poly(acrylonitrile/dimethyl formamide), poly(vinyl alcohol) (PVA), poly(vinyl chloride) (PVC), poly(vinylidene fluoride) (PVF), poly(L-lactic acid) (PLLA), poly(lactic-co-glycolic acid), ethyl-cyanoethyl-cellulose [(E-CE)C], poly(acrylonitrile) (PAN), poly(ethylene) (PE), poly(ethylene oxide) (PEO), collagen polyethylene oxide, Polyethylene terephthalate (PET), poly(propylene) (PP), poly(2-hydroxyethyl methacrylate) (HEMA), poly(styrene) (PS), poly(ether imide) (PEI), poly(methyl methacrylate) (PMMA), polyurethane (PU), poly(3-hydroxybutyrate co-3-hydroxyvalerate) (PHBV), polyamide (PA), poly(m-phenylene isophthalamide) (PMIA), polysulfone (PSU), polyacrylamide and polyester. In a particular embodiment according to the present invention, the "polymer nanofibers" are selected from the group consisting of nanofibers of poly(s-caprolactone) (PCL), poly(acrylonitrile/dimethyl formamide), poly(vinyl alcohol) (PVA), poly(vinyl chloride) (PVC), poly(vinylidene fluoride) (PVF), poly(L-lactic acid) (PLLA), poly(lactic-co-glycolic acid), ethyl-cyanoethyl-cellulose [(E-CE)C], poly(acrylonitrile) (PAN), poly(ethylene) (PE), poly(ethylene oxide) (PEO), collagen polyethylene oxide, Polyethylene terephthalate (PET), poly(propylene) (PP), poly(2-hydroxyethyl methacrylate) (HEMA), poly(styrene) (PS), poly(ether imide) (PEI), poly(methyl methacrylate) (PMMA), polyurethane (PU), poly(3-hydroxybutyrate co-3-hydroxyvalerate) (PHBV), polyamide (PA), poly(m-phenylene isophthalamide) (PMIA), polysulfone (PSU), polyacrylamide and polyester. It is understood that in this embodiment, the polymer nanofibers do not include cellulose nanofibers.

In another embodiment according to the present invention, the "polymer nanofibers" are cellulose nanofibers, also referred to as nanocellulose fibers.

Preferably, according to the present invention, said nanofibers are polymer nanofibers, as described above.

In a particular embodiment of the invention, the polymer nanofibers are preferably cellulose nanofibers.

Preferably, said hydroxyapatite particles have an average pore diameter measured by nitrogen sorption manometry, also called nitrogen adsorption, at 77K and calculated according to the BJH method applied to the desorption curve between 2 and 50 nm, preferably between 10 and 40 nm, preferably between 15 and 30 nm, and/or, preferably, said hydroxyapatite particles are characterized by the fact that at least 50%, preferably at least 60%, preferably at least 70%, preferably at least 80% of the pore volume is in pores having a diameter of between 3.5 and 50 nm measured by nitrogen sorption manometry at 77K and calculated according to the BJH method applied to the desorption curve. By the terms "an average pore diameter measured by nitrogen sorption manometry at 77K and calculated according to the BJH method" is meant, within the meaning of the present invention, the pore diameter measured by nitrogen sorption manometry at 77K and calculated according to the BJH method applied to the desorption curve using the assumption of a cylindrical pore shape.

The device used is, for example, a 3Flex from Micromeritics where a degassing step prior to adsorption is carried out at 50°C for 10 hours.

In the context of the present invention, mesoporous hydroxyapatite preferably means a structure comprising mainly mesopores, i.e. pores whose diameter is between 2 and 50 nm, preferably between 10 and 40 nm, preferably between 15 and 30 nm (mesopore volume: total porosity).

The measurement is preferably carried out by nitrogen sorption manometry at 77K and is calculated according to the BJH method applied to the desorption curve mentioned above.

The porosity of hydroxyapatite, which refers to the empty spaces within its structure, further enhances the adsorption of metals and pigments, such as Congo Red (CR dye). This porosity results in an internal volume called pore volume (or pore volume) and channels of different sizes, called pores. Porosity is defined as the ratio of the volume of voids (pores and channels) to the total volume of the materials.

Advantageously, the mesoporous hydroxyapatite as described above is obtained via a mixture of two streams, one stream comprising a calcium source and one stream comprising a phosphate source.

Advantageously, the mesoporous hydroxyapatite as described above is obtained via a continuous and simultaneous mixing of two streams, one stream comprising a source of calcium, for example CaO, CaCOs, hydrated lime, and one stream comprising a source of phosphate, for example phosphoric acid. Advantageously, the mesoporous hydroxyapatite as described above is obtained via a continuous and simultaneous mixing of two streams, one stream comprising a soluble calcium salt and one stream comprising a soluble phosphate salt.

Preferably, the hydroxyapatite particles have a specific surface area, measured by nitrogen sorption manometry at 77K and calculated according to the BET method applied to the adsorption curve in the relative pressure range: P/P° between 0.05 and 0.25, of between 60 and 170 m ² /g, preferably between 80 and 140 m ² /g, preferably between 100 and 120 m ² /g.

This has the advantage of allowing greater responsiveness.

The device used is, for example, a 3Flex from Micromeritics where a degassing step prior to adsorption is carried out at 50°C for 10 hours.

Preferably, the hydroxyapatite particles have a particle size distribution characterized by a volume-based dio of between 0.4 and 10 pm, preferably between 0.4 and 4 pm, preferably between 1 and 2 pm, preferably between 4.5 and 10 pm.

Preferably, the hydroxyapatite particles have a particle size distribution characterized by a volume-based dso of between 4 and 40 pm, preferably between 5 and 35 pm, preferably between 10 and 25 pm.

Preferably, the hydroxyapatite particles have a particle size distribution characterized by a volume-based dgo of between 12 and 250 pm, preferably between 50 and 100 pm.

In the context of the present invention, preferably, the expression "dx of y pm" means that a percentage (x%) by volume of particles has a particle size equal to or less than y pm.

A dw is defined as a diameter for which 10% by volume of particles, relative to the total particle volume, have a diameter equal to or less than the dio value. Thus, for example, a composition having a dio of 30 pm means that 10% by volume of particles, relative to the total particle volume, have a particle diameter equal to or less than 30 pm. A dso is defined as a diameter for which 50% by volume of particles, relative to the total particle volume, have a diameter equal to or less than the dso value. Thus, for example, a composition having a dso of 30 pm means that 50% by volume of particles, relative to the total particle volume, have a particle diameter equal to or less than 30 pm.

A dæ is defined as a diameter for which 90% by volume of particles, relative to the total particle volume, have a diameter equal to or less than the dæ value. Thus, for example, a composition having a dæ of 30 pm means that 90% by volume of particles, relative to the total particle volume, have a particle diameter equal to or less than 30 pm.

According to the present invention, the particle size distribution measurements were carried out by laser granulometry.

This particle size distribution, particularly a narrow monomodal distribution, has the advantage of ensuring excellent reproducibility. Indeed, a narrow monomodal distribution means that the particles have very similar sizes, which limits variations in the filter material. Consequently, this significantly reduces the risk of creating heterogeneities within the filter. In other words, a narrow monomodal distribution promotes increased homogeneity of the filter material, thus ensuring uniform and consistent filtration paths.

The hydroxyapatite particles preferably have a pore volume measured by nitrogen sorption manometry at 77K and calculated according to the BJH method applied to the desorption curve of at least 0.2 cm ³ /g, preferably at least 0.3 cm ³ /g, preferably at least 0.4 cm ³ /g of particles.

By the terms "an average pore volume measured by nitrogen sorption manometry at 77K and calculated according to the BJH method applied to the desorption curve", or by the terms "pore volume measured by nitrogen sorption manometry at 77K and calculated according to the BJH method applied to the desorption curve", is meant, within the meaning of the present invention, the volume of pores whose size is between 4 and 230 nm, measured by sorption manometry of nitrogen at 77K and calculated according to the BJH method using the assumption of a cylindrical pore shape on the desorption curve.

Preferably, the hydroxyapatite particles have a pore volume measured by nitrogen sorption manometry at 77K and calculated according to the BJH method described above of between 0.35 and 0.65 cm ³ /g of particles.

The inventors have noted that high porosity, advantageously coupled with a high specific surface area and/or a high mesopore content, allows better fixation of contaminant and/or allows better permeability of the medium to be filtered.

This composition is advantageously combined with a water-permeable support, or arranged to form a filter.

The combination of mesoporous hydroxyapatite in a filtration system has the advantage of combining chemical and physical purification means, in particular of being able to specifically fix chemical compounds, such as metals, heavy metals, pigments (CR dye), fluorine, while retaining contaminating particles.

This composition further comprises, preferably, one or more additives chosen from the group comprising: activated carbon, chitosan, a clay or their mixture.

These additives allow better sequestration of pollutants and/or the neutralization of certain microorganisms.

These additives, when present, are preferably in a weight content relative to the weight of nanofibers, for example in a weight content of the additives of between 0.1 and 0.5 relative to the weight of nanofibers, preferably of between 0.15 and 0.25 (weight of the additive, for example chitosan: weight of nanofibers).

When the nanofibers are nanofibers are polymer nanofibers, in particular cellulose nanofibers, these additives, when present, are preferably in a weight content relative to the weight of polymer nanofibers, in particular cellulose nanofibers, for example in a content weight of the additives between 0.1 and 0.5 relative to the weight of polymer nanofibers, in particular cellulose nanofibers, preferably between 0.15 and 0.25 (weight of the additive, for example chitosan: weight of nanofibers).

For example, chitosan can be added. This has the advantage of binding certain contaminant molecules and providing an antibiotic effect to the filter. In addition, the inventors have noticed that chitosan improves the structural properties of the filter.

Preferably, the composition comprises a weight content of nanofibers and a weight content of hydroxyapatite particles distributed in a network formed by said nanofibers, in which the proportion of the weight content of nanofibers relative to the weight content of hydroxyapatite particles is between 0.5 and 2.

When the nanofibers are polymer nanofibers, in particular cellulose nanofibers, preferably the composition comprises a weight content of polymer nanofibers, in particular cellulose nanofibers and a weight content of hydroxyapatite particles distributed in a network formed by said polymer nanofibers, in particular said cellulose nanofibers, wherein the proportion of the weight content of polymer nanofibers, in particular cellulose nanofibers, relative to the weight content of hydroxyapatite particles is between 0.5 and 2.

Preferably, alternatively or additionally, the proportion of the weight content of chitosan relative to the weight content of nanofibers is between 0.1 and 0.5.

When the nanofibers are polymer nanofibers, in particular cellulose nanofibers, preferably, alternatively or additionally, the proportion of the weight content of chitosan relative to the weight content of polymer nanofibers, in particular cellulose nanofibers, is between 0.1 and 0.5. In the context of the present invention, the terminology "cellulose nanofibers" also called "nanocellulose" refers to any repeating structure of glucoses, linked by (3(1-4) links.

In the context of the present invention, furthermore, the terminology "nanofibers" relates to fibers having a diameter of between 1 and 50 nanometers, preferably between 2 and 30 nanometers, preferably between 5 and 20 nanometers and a length of at least 200 nanometers, preferably at least 1 micrometer.

When the nanofibers are cellulose nanofibers, also referred to as nanocellulose, the terminology “cellulose nanofibers” refers to cellulose fibers having a diameter of between 1 and 50 nanometers, preferably between 2 and 30 nanometers, preferably between 5 and 20 nanometers and a length of at least 200 nanometers, preferably at least 1 micrometer.

Preferably, the nanofibers represent at least 30% of the total weight of the active constituents of the composition (nanofibers, hydroxyapatite, additive possibly present), preferably at least 33%, for example the nanofibers represent between 35 and 40% by weight of the composition, while the hydroxyapatite and the possible additives together represent between 60 and 65% by weight of the composition.

Advantageously, when the nanofibers are polymer nanofibers, in particular cellulose nanofibers, preferably the polymer nanofibers, in particular the cellulose nanofibers, represent at least 30% of the total weight of the active constituents of the composition (nanofibers, hydroxyapatite, additive possibly present), preferably at least 33%, for example the polymer nanofibers, in particular the cellulose nanofibers, represent between 35 and 40% by weight of the composition, while the hydroxyapatite and the possible additives together represent between 60 and 65% by weight of the composition. A related aspect of the present invention relates to a filter, also referred to as a filter material, comprising (or consisting essentially of) the composition comprising nanofibers, as described above, selected from the group consisting of polymer nanofibers, ceramic nanofibers, metal nanofibers, carbon nanofibers and mixtures thereof, and mesoporous hydroxyapatite particles and an optional additive as described above and in the contents described above.

It is understood that the examples and embodiments cited above for polymer nanofibers, ceramic nanofibers, carbon nanofibers and metal nanofibers also apply to the filter.

A not too high hydroxyapatite content (nanofiber weight: hydroxyapatite weight greater than 0.5) ensures a certain flexibility of the filter material.

This filter material may advantageously further comprise additives chosen from chitosan, activated carbon, a clay and mixtures thereof, preferably in the contents described above.

In particular, the inventors noticed that the formulation of nanofibers and mesoporous hydroxyapatite with chitosan increases the mechanical resistance of the filter material, in particular for ratios where the weight content of chitosan is lower than that of nanofibers and lower than that of mesoporous hydroxyapatite.

Advantageously, this filter material has a tensile strength of at least 10 N/mm ² , preferably at least 20 N/mm ² , or even at least 30 N/mm ² .

The filter material can be used in a (filtration) device that separates solid particles or unwanted substances from a fluid by passing it through the filter material, for example a filter.

The filter material may also be incorporated into a filtration device comprising a support, a filter wall, a reservoir, such as a device comprising hollow fiber membranes. Hollow fiber membranes are used to separate particles and contaminants from liquids or gases. These membranes are commonly used in various areas, such as water treatment, pharmaceutical purification, and food production.

Another related aspect of the present invention relates to a method of manufacturing a filter material as described above comprising the following steps:

- suspension in an aqueous solution of nanofibers and mesoporous hydroxyapatite particles making it possible to obtain an aqueous suspension, said nanofibers being chosen from the group consisting of polymer nanofibers, ceramic nanofibers, metal nanofibers, carbon nanofibers and their mixtures,

- filtration of said aqueous suspension to obtain a filtrate and a nanocomposite,

- drying of the nanocomposite, preferably under vacuum.

Preferably, in this method, the nanofibers are as described above and/or the hydroxyapaty particles are as described above (for the composition).

It is understood that the examples and embodiments cited above for polymer nanofibers, ceramic nanofibers, carbon nanofibers and metal nanofibers also apply to the process.

One or more additives as described above, chitosan, clay, activated carbon, and mixtures thereof, is (are) preferably added to the aqueous suspension of this process.

This process is easily applicable on an industrial scale.

Brief description of the drawings

Other characteristics, details and advantages of the invention will emerge from the description given below, without limitation and with reference to the drawings and examples.

Figure 1 shows the Ni capture efficiency (wt.%) depending on the type of hydroxyapatite present in the filter material (Table 2). Figure 2 shows the 77K nitrogen adsorption and desorption isotherm for a hydroxyapatite powder used in a composition according to the invention. This isotherm represents the absorbed quantity (Q) as a function of the relative pressure (p).

Detailed description of one embodiment of the invention

The inventors have succeeded in developing a wastewater treatment approach that is simple, versatile, and does not require modifications or the use of hazardous compounds. Furthermore, it can easily be used on a large scale and requires little energy.

Other features and advantages of the present invention will be drawn from the following non-limiting description, and with reference to the drawings and examples.

Methodology of flexibility and tensile strength tests.

Cutting a rectangular sample of 40 x 10 mm.

Flexibility test: The samples were flexed 100 times with a gap of 20 mm. After the 100 bending cycles, the samples were subjected to a tensile test.

Tensile test: The samples were used directly for tensile fracture test where a preload of 2kN was applied to the sample at a strain rate of 5mm/min.

Tensile strength o max = Pmax /A0, (1 ) where tensile strength (kN/cm ² ), Pmax = maximum load (kN), A0 = original cross-sectional area (cm ² ). The tensile strength values of the samples after and without bending (same sample source) were compared to assess flexibility.

Example 1.-

The inventors selected different types of fibers, including different types of cellulose, such as nanocellulose, cellulose nanocrystals, and bacterial cellulose. Then the fibers were formulated. with hydroxyapatite (mass ratio 1:1.5) then assembled to form a filter material, the mechanical properties of which were measured (tensile strength after one cycle and after 100 cycles and flexibility).

In this situation, the inventors noticed that only nanocellulose allowed sufficient mechanical resistance, namely tensile strength values greater than 50 N/mm ² and sometimes even greater than 60 N/mm ² . After 100 cycles, these values advantageously remain greater than 40 N/mm ² and sometimes even greater than 50 N/mm ² .

Example 2.-

The inventors tested different concentration ratios between nanocellulose and hydroxyapatite. Relative hydroxyapatite contents (nanocellulose:hydroxyapatite) that were too low (less than 1:0.5) or too high (more than 1:2) reduced the mechanical properties of the filter material.

Example 3.-

The inventors tested the addition of an additive (chitosan) at different concentrations in combination with a composition of nanocellulose:hydroxyapatite of 1:1.5.

In this context, contents (nanocellulose: chitosan) between 0.1 and 0.25, for example 0.15, have given very good results with tensile strength values greater than 40 N/mm ² and sometimes even greater than 50 N/mm ² . After 100 cycles, these values remain advantageously greater than 40 N/mm ² . The results are shown in Table 1 .

Table 1.- Mechanical resistance and flexibility tests NC represents nanocellulose, Dis-CH represents dissolved chitosan, CaP represents hydroxyapatite, Po-CH represents chitosan in powder form.

Example 4.-

The inventors then tested the capacity of different mesoporous hydroxyapatite particles to fix metals in an aqueous medium (Figure 1). The properties of these particles are shown in Table 2 above.

Table 2.-

Specific surface area _ . _ _ d50

Diameters

Particle sample

SBET m ² /g Vp _Ore ciïi'/g of pores

(Um) average (nm)

A 80.76 0.43 22.66 4.78

B 97.78 0.34 21.29 6.24

C 74.55 0.32 24.01 6.17

D 1 19.02 0.36 17.1 1 39.30

E 135.78 0.54 17.70 8.09

The methods for measuring average pore diameter, pore volume and specific surface area have been described above, as well as the apparatus used for nitrogen sorption manometry.

Figure 1 represents in particular the quantity of Ni ion captured in relation to the volume filtered by different hydroxyapatite particles, as described in Table 2.

The different hydroxyapatite particles provide good filtration capabilities. However, small particles with a large specific surface area and a large proportion of pores provide greater fixation.

These results were reproduced for other metals, in particular, Cd, Pb, Cr, Mn, V, Sr, Hg, Mo, Ba, ... with each time a strong fixation. Example 5.-

The inventors then tested the capacity of pigment fixation, in particular Congo Red (CR dye), in aqueous medium, by different filter materials: NC: CaP 1:1.5, NC: Po-CH: CaP 1:0.25:1.5, NC: Dis-CH: CaP 1:0.15:1.5 and NC: Dis-CH: CaP 1:0.1:1.5.

The different filter materials ensure good filtration and pigment retention capacities (CR dye) with a quantity of pigment retained (wt.%) close to 98.84 wt.% and 100 wt.% for initial pigment contents in the aqueous medium of 150 ppm, 100 ppm, 50 ppm and 10 ppm respectively.

Example 6-9.-

Nanofibers, particularly polymer nanofibers that do not include cellulose nanofibers, are used in Examples 6-9.

Example 6.-

Nanofibers are formulated with hydroxyapatite (mass ratio 1:1.5) then assembled to form a filter material, the mechanical properties of which are measured (tensile strength after one cycle and after 100 cycles and flexibility).

In this situation, sufficient mechanical strength is expected, namely tensile strength values greater than 50 N/mm ² and sometimes even greater than 60 N/mm, or even after 100 cycles, values advantageously greater than 40 N/mm ² and sometimes even greater than 50 N/mm ² .

Example 7.-

By varying the concentration ratios between nanofibers and hydroxyapatite, it is expected to observe that relative hydroxyapatite contents (nanofibers:hydroxyapatite) that are too low (less than 1:0.5) or too high (greater than 1:2) reduce the mechanical properties of the filter material.

By testing the addition of an additive (chitosan) at different concentrations in combination with a composition of nanofibers:hydroxyapatite of 1:1.5, we expect to observe that contents (nanofibers:chitosan) between 0.1 and 0.25, for example 0.15 give very good results with tensile strength values greater than 40 N/mm ² and sometimes even greater than 50 N/mm, or even after 100 cycles advantageously greater than 40 N/mm ² . Example 9.-

The inventors tested the ability of different hydroxyapatite particles to bind metals in an aqueous medium.

The method of measuring specific surface area has been described above.

The different hydroxyapatite particles have a specific surface area of 80.8 m ² /g, 119.0 m ² /g and 135.8 m ² /g and a dso of 4.8 pm, 39.3 pm and 8.1 pm respectively.

The different hydroxyapatite particles ensure good filtration capacities. However, small particles with a large specific surface area ensure greater fixation.

These results were reproduced for other metals, in particular, Cd, Pb, Cr, Mn, V, Sr, Hg, Mo, Ba, ... with each time a strong fixation.

Finally, it goes without saying that the present invention is not limited to the embodiments described; on the contrary, it encompasses all variants of embodiment and application respecting the same principle.

Claims

1. A composition comprising a weight content of nanofibers and a weight content of hydroxyapatite particles distributed in a network formed by said nanofibers, wherein said nanofibers are selected from the group consisting of polymer nanofibers, ceramic nanofibers, metal nanofibers, carbon nanofibers and mixtures thereof, and wherein the proportion of the weight content of nanofibers relative to the weight content of hydroxyapatite particles is between 0.5 and 2, preferably between 1 and 1.5. 2. The composition according to claim 1, wherein said hydroxyapatite particles have an average pore diameter measured by nitrogen desorption and calculated according to the BJH method between 2 and 50 nm, preferably between 10 and 40 nm, preferably between 15 and 30 nm, and/or wherein said hydroxyapatite particles are characterized by the fact that at least 50% of the pore volume is in pores having a diameter between 3.5 and 50 nm measured by nitrogen sorption manometry at 77K and calculated according to the BJH method applied to the desorption curve. 3. The composition, according to any one of the preceding claims, further comprising one or more additives selected from the group consisting of activated carbon, chitosan, a clay and mixtures thereof, preferably being chitosan. 4. The composition according to claim 3, having a weight content of additives of between 0.1 and 0.5 relative to the weight of nanofibers, preferably of between 0.15 and 0.25. 5. The composition according to any one of the preceding claims, wherein said hydroxyapatite particles have a specific surface area measured by nitrogen sorption manometry at 77K and calculated according to the BET method applied to the adsorption stroke between 60 and 170 m ² /g. 6. The composition according to any one of the preceding claims, wherein said hydroxyapatite particles have a pore volume measured by nitrogen sorption manometry at 77K and calculated according to the BJH method applied to the desorption curve of at least 0.2 cm ³ /g, preferably at least 0.3 cm ³ /g, preferably at least 0.4 cm ³ /g of particles. 7. The composition according to any one of the preceding claims, wherein said hydroxyapatite particles have a particle size distribution characterized by a volume-based d50 of between 4 and 40 pm. 8. The composition according to any one of the preceding claims, wherein said hydroxyapatite particles have a particle size distribution characterized by a volume-based d10 of between 0.4 and 10 µm. 9. The composition according to any one of claims 3 to 8 in which the proportion of the weight content of nanofibers relative to the weight content of hydroxyapatite particles is between 0.5 and 2 and/or the proportion of the weight content of chitosan relative to the weight content of nanofibers is between 0.1 and 0.5. 10. A filter material consisting essentially of the composition according to any one of the preceding claims. 11. The filter material according to claim 10 having a tensile strength of at least 10 N/mm ² , preferably at least 20 N/mm ² . 12. A method of manufacturing a filter material according to claim 10 or 11 comprising the following steps: - suspending in an aqueous solution said nanofibers and said hydroxyapatite particles and, optionally, additives, making it possible to obtain an aqueous suspension, - filtration of said aqueous suspension to obtain a filtrate and a retentate, - drying said retentate so as to form said filter material. 13. The method of claim 12 wherein the filtration is under vacuum. 14. Use of a composition according to any one of claims 1 to 9, in a filtration device.