CARTRIDGE

Field of the invention

The object of the present invention is a non-woven filtering material for purification fluids, a method for manufacturing of the filtering material and the filtering cartridge comprising such non-woven filtering material, in particular, the invention is directed to filtering elements for cleaning the air, also in septic areas and for purification of a fuel and oil, for example, in motor vehicles.

Background of the invention

Advanced technologies in which nanoparticles are formed, that is, nanometric sized particles, and also natural nanoobjects present in the environment result in the need to apply modern separation methods for recovery of such particles through their separation from fluids, a gas or a liquid, in such a manner to simultaneously obtain their appropriate purity.

The most effective method of separation of nanoparticles from the continuous phase (liquid, gas) is its filtration through non-woven materials, in particular materials containing polymer fibres. Since the main mechanism for the deposition of nanoparticles on fibres is diffusion, a high efficiency of separation is achieved by means of a large development of the surface of the filtering material in the filter volume. In the case of non-woven filters, this leads to the production of nanofibres, from which a filtering material is manufactured.

From Polish patent application No P.388235 composite filtering structures are known and the method of their obtaining. The filtering structure is made of a fibrous composite comprising nano-size fibres (nanofibres) spatially distributed among the fibres of micrometer sizes. It is preferred in the filtering structures, if the nanometric fibres have a diameter in the range from 100 to 400 nanometres, and microfibers have the diameter ranging from 5 to 10 micrometers.

The nanoparticles of impurities present in the gas or liquid may have abiotic nature (solid particles or liquid droplets) , or they may be biologically active (bacteria, viruses, fungi, moulds), i.e. having the biotic nature. During filtration of biotic or abiotic particles or liquid droplets, in addition to the high filtration efficiency the further effects associated with the disposal of the material accumulated on the surface of the fibre should be taken into account. During filtration of an oil mist the collected droplets degrade the filter and make worse its further operation. In this case it is necessary to improve drainage, i.e. fibres dripping. This can be achieved e.g. by forming nanoprotrusions on the surface of the fibre of the non-woven filtering structure, in a form of "nano-hair" palisade oriented substantially as perpendicular as possible to the surface of the fibre in accordance with the teachings of WO/2009/144647. As a result of a surface interaction between the droplets and such structure, the droplet is "pushed away" and as a consequence it easy drips over the surface of the fibre. WO/2009/144647 discloses a composite filtering structure formed of a polymeric non-woven fabric comprising microfibers and nanofibres, in which low surface affinity of the liquid to the fibre is provided by forming a palisade of nano-sized lips in a form of polymeric nano-protrusions on the fibres of a composite comprising nanofibre spatially arranged between microfibers. When microorganisms e.g. bacteria, are accumulated on the fibres, their natural multiplication and reproduction occurs in the filter, especially in the conditions of a high humidity and temperature. We are dealing with such problematic cases in air condition systems of buildings, hospitals and vehicles including cars. In the case of significant accumulation of microorganisms on the filter they are re-emitted to the airflow. Microorganisms, getting into the room or space, cause strong infections (nosocomial infections, sick building syndrome) .

Among many inorganic compounds having bacteriostatic effect the zinc oxide ZnO is known. There is known in literature information concerning the preparation of ZnO nanorods primarily on flat glass surfaces, ceramic and polymer surfaces, but also on the textile surfaces, including textile materials containing polymeric fibres. There are also known results of tests relating to the potential use of ZnO nanorods in the solar systems, on self-cleaning surfaces, in an electronic engineering, in medical materials and on surface of textile materials.

Among others, from the publication of the article "Growth of ZnO nanowires on non-woven polyethylene fibres" published on 13.06.2008 in Science and Technology of Advanced Materials 9 (2008) . 025009 (on line at: stacks. iop . org/STAM/9/025009) it is known a method for conducting growth of ZnO nanorods and nanowires having diameters ranging from 50 nm to 1 pm on the fibres of a non- woven net of polyethylene fibres using of the hydrothermal method at a temperature about 95°C i.e. below the boiling point of water, in a bath of chemical reagents containing zinc nitrate with hexamine (HMTA) for up to 20 hours, wherein said polyethylene fibres were previously subjected to nucleation by way of synthesis in a solution of isopropanol by reduction of zinc acetate hydrate with sodium hydroxide, wherein the nuclei of ZnO nanoparticles having diameters of approximately 6-7 nm were subjected to bonding treatment to fibres using thiol. The non-woven fabric obtained of polyethylene fibres coated with ZnO nanorods. has been subseguently used in the water purification treatment from impurities by photo- catalysis method.

From WO2006026385 (A2) an apparatus and a method for removal of contaminants and other harmful substances from a stream of gas or liguid by the filtering structure in a form of microfiber matrix with particles/fibres of reactive materials embedded in it are known, wherein both material of microfibers and the reactive material may be selected within a wide range depending on the particular application for removal of specific, type of pollutants, wherein one of the reactive materials may be ZnO.

U.S. 2007/0284303 discloses a nanostructural polymer membrane comprising randomly arranged, bonded together fibres of a water-insoluble polymer, wherein the fibres are subjected to a suitable chemical treatment to form functional groups thereon, in particular including carboxyl or acid groups, and then the functional membrane is immersed in a solution containing zinc fluoride and in this way the covering layer of ZnO is formed on the fibres. The functional structure formed in this way may have various applications, for example, it can be used in the water purification process.

From U.S. 2007/0151921 it is also known a self-cleaning fibrous membrane for filtration applications, formed of micro- and nanofibres of inorganic material, wherein nanoparticles of metal or metal oxide having photo catalytic properties, such as titanium, are deposited on the surface of the fibres.

Additionally, methods of deposition of ZnO nanorods on a surface of textile materials are known to impart for them special properties, including fabrics containing polymeric fibres, for example PA, PET and PP fibres, wherein ZnO nanostructures are grown from a solution of zinc nitrate and hexamethylenetetramine (HMT) at a temperature of 95°C within the time of 9h.

It is also known a method for preparation of polymeric fibres for growth process of ZnO microstructures , in which the surface of polymer fibres of PET, PA and/or PP is modified using low-temperature plasma treatment in a corona discharge generating device. Then, the ZnO nanostructure is deposited on the modified fibres by . CBD method, i.e. by chemical bath deposition, in an aqueous solution containing an equimolar amount of Zn (N0 ₃ ) ₂ and hexamethylenetetramine (HTM) with a concentration lOOmM within the time of 9 hours, (conference papers of the IV National Conference on Nanotechnology Nano 2010, Poznan 2010, art. No. P-Te-18, p. 177 and art. No. P-Tue-64 p. 223).

An essence of the invention However, it remains the problem of forming such filtering structures, by means of which it would be possible to eliminate all the adverse effects occurring in the prior art filtering structures, in particular consisting in a large pressure drop across the filter, damaging it after a relatively short period of use, i.e. it is desirable to develop a filtering material which would allow to extend the lifetime of the filter without damaging pressure drop across the filter while simultaneously providing excellent filtration and bacteriostatic properties and excellent coalescence of moisture from the filtered medium.

This task is solved according to the invention by forming a non-woven filtering material in the form of a polymeric, non-woven filtering structure in which the surface of the fibres is provided with a biologically active nanometric sized nanopalisade of protrusions.

This object is solved according to the invention in particular by providing a polymeric non-woven filtering structure comprising nanoprotrusions in the form of nanorods deposited on the surface of the polymer fibres, which nanorods are distributed uniformly over the whole volume of the structure, and a method for its manufacture.

The object of the present invention is a non-woven filtering material of high filtering efficiency, modified by ZnO nanorods, for use in filtering systems and devices for purifying liquids and/or gases, in particular in air and water filters and in coalescers.

In the present invention, a new solution consists in that on the surface of the fibres of the filtering material of a thermoplastic polymer produced by the melt blowing technique (melt-blown fibres), having controlled fibre diameter, preferably in the range 0.1 - 10 μιτι, forming a non- woven, polymer structure of the filtering material, it is developed a palisade of ZnO nanoprotrusions in the form of nanorods having diameters, preferably in the range 10-100 nanometres, the heights, preferably, in the range 50-1000 nanometres and the distance between the adjacent rods on the surface of the fibre preferably 30-300 nanometres, as measured by SEM observation of cross-sections of fibres with ZnO nanorods deposited thereon, which measuring method is also used for determining the other parameters and values relating to a fibre and nanorods morphology described according to the invention in the following text. According to the invention there is provided a non-woven filtering material in the form of a non-woven polymeric filtering structure, comprising a set of polymer fibres with micrometric and nanometric diameters in the range from 0.1 pm to 10 μη, packed into the structure of a packing density in the range 0.1 - 0.2, wherein the volume fraction of fibres having nanometric diameters between 100 to 500 nm in the filtering structure is substantially in the range of about 0-30%, preferably 0-20%, and particularly 5-20% of the total volume of the filtering structure, characterising in that on the surface of the fibres, both of micrometric and nanometric diameters, in the whole and entire volume of the filtering structure, ZnO nanorods are arranged in the form of ZnO protrusions, manufactured in a process comprising the step of growing of ZnO nanorods on the polymeric fibres, under conditions of a flow of the mixture of reactants, comprising at least one zinc compound, right through the whole volume of said non-woven polymeric filtering structure, wherein the nanorods form a ZnO nanorods palisade developed on individual fibres throughout the whole volume of the filtering structure and are arranged on the surface of the each fibre at an angle in the range 70 - 120°, and preferably substantially perpendicular to the surface of the each fibre and which ZnO nanorods are permanently secured to them.

In one embodiment of the invention, nanorods having diameters in the range, preferably, 5-100 nanometres, having the height, preferably, in the range 50-500 nanometres and the distance between nanorods on the surface of the fibres in the range, preferably, from 30 nanometres to 1 μτη, are arranged on the surface of the fibres throughout the whole volume of the filtering structure. In the variant of the invention, the filtering structure comprises nanofibres having diameter sizes ranging from 300 to 400 nm, and microfibers having diameters in the range 5. to 10 μπι, which are arranged so that nanofibres of the larger diameters from the range diameters given above are arranged among the microfibers of the larger diameters, and nanofibres of the smaller diameters are arranged among microfibers of the smaller diameters. According to another embodiment, the filtering structure comprises fibres with micrometric diameters in the range from 1 to 10 micrometers, wherein the volume fraction of those fibres in the total volume of the structure is substantially 100%.

In the further embodiment of the invention, depending on the predicted application of the filtering material according to the invention and the surface tension of the droplets of the filtered medium, the diameter of ZnO nanorods is in the range between 30 - 60 nm, the height in the range 70 - 100 nm, and the distance between the nanorods on the surface of the fibre is about from 100 nm to 1 pm, in another embodiment, depending on the application of the filtering material and the surface tension of the droplets of the filtered medium, the diameter of ZnO nanorods is in the range between 20 - 50 nm, the height in the range 50 - 70 nm, and the distance between the nanorods on the surface of the each fibre is from 80 nm to 300 nm, in yet another embodiment, depending on the predicted application of the filtering material and the surface tension of the droplets of the filtered medium, the diameter of ZnO nanorods is in the range from 10 nm to 30 nm, the height in the range 50-70 nm, and the distance between the adjacent nanorods on the surface -of the ^' each fibre is from 50 nm to 100 nm. According to the invention it is also provided a method for manufacturing a polymer non-woven filtering material according to the invention, wherein ZnO nanorods are formed on the surface of the polymer fibres in the whole volume of the filtering structure by means of a process comprising one or more of the following steps: step "a" - modification of fibres by a low-temperature plasma treatment in a corona discharge, step "b" - nucleation and fusion of a nucleus into a fibre material of a nonwoven structure, or modification of the surface of the fibres by means of compounds being activators of nanorods growth and step "c" - controlled growth of nanorods, substantially in the direction of the main axis of the rod, wherein ZnO nanorods palisade that is developed on individual fibres throughout the whole volume of the filtering structure is produced under conditions of a flow of the mixture of reacting substances, comprising at least one zinc compound, through the whole volume of said non-woven polymeric filtering structure, which ZnO nanorods are arranged on the surface of the fibres at an angle in the range between 70 - 120°, and preferably substantially perpendicular to the surface of the each fibre and permanently fixed on and associated with them, and wherein at least one of the following steps of the said process, namely step "b" and/or step "c", is carried out under conditions of a forced flow of said reaction mixture i.e. the mixture of reacting substances right through the non-woven fabric at a flow rate in the range from 1 cm/s to 40 cm/s, preferably from 2 cm/s to 20 cm/s, and most preferably from 2 cm/s to 10 cm/s.

In the one embodiment of the invention, nanorods having diameters in the range, preferably, from 5 to 100 nanometres, with the height, preferably, in the range from 50 rati to 500 nanometres and the distance between nanorods on the surface of each of the fibres in the range, preferably, from 30 nanometres to 1 μπι arranged on the surface of the fibres throughout the whole volume of the filtering structure are produced.

In an embodiment of the method according to the invention, in the step "a" - modification of fibres in the process of forming ZnO nanorods - functional groups, for example: carboxyl, hydroxyl and carbonyl groups, are incorporated into the surface of the fibres by means of treatment of the non-woven fabric in a low temperature plasma or by means of a corona discharge during forming the fibres in an atmosphere of a gas, preferably the air and/or the argon.

According to the further embodiment of the invention the step "b" - nucleation and fusion of the nucleus into the material of the non-woven fabric for the growth of ZnO nanorods is performed by depositing of the ZnO nanoparticles on the surface of the fibres functionalised in the step "a" during a forced flow of the ZnO particles suspension through the non-woven fabric, wherein said particles having diameter preferably in the range 10 - 30 nm, . and particle concentration of 10 ⁴ l/cm ³ , at a linear speed preferably in the range 2-3 cm/s, and the deposited nuclei are immobilized and permanently fixed on the surface of the fibre by heating of the polymer non-woven fabric to the temperature of the softening point of the polymer, and after the step "b", in the step "c" the resulted non-woven structure is subjected to a process of a growth of nanorods to achieve the desired morphology thereof by means of a hydrothermal method from a reactive mixture in the form of an aqueous solution of zinc compounds, such as, for example, zinc nitrate, or zinc sulphate or zinc chloride, with hexamine (urotropin, HMTA) and optionally with additives changing surface charge of ZnO and/or additives in the form of surface-active agents controlling the slenderness of the resulting nanorods, wherein step "c" - of nanorods growth is carried out in the flow process during the forced flow of the reactive mixture through the non-woven fabric structure containing nuclei deposited and immobilized on the surface of fibres, at a speed preferably in the range 2 - 5 cm/s for a period of time in the range 4 - 6 hours, at a temperature ranging between 70 - 90°C, wherein the operation time affects the final shape of the each ZnO nanorod.

In a further, alternative embodiment of the invention the surface of the fibres of the non-woven polymer filtering structure is subjected to modification in the step "b" by means of activation with an aqueous KMn0 ₄ solution to form the layer being the zinc ions attractor, wherein the modification comprises contacting the non-woven fabric with an aqueous KMn0 ₄ solution under the forced flow conditions for a period from 5 to 120 minutes, preferably from 10 to 80 minutes, most preferably from 15 to 60 minutes, and then in the following step "c" the growth of ZnO nanorods is carried out in aqueous solution of a zinc salt in the presence of ethanolamine under conditions of the forced flow of the reactant mixture through the whole volume of the non-woven fabric structure for a period of time ranging from 30 to 120 minutes, at a temperature from 60 to 95°C, preferably from 75 to 85°C.

According to the invention, durability of the connection of ZnO nanorods to each fibre, created during its manufacturing is accomplished by heating the resulting filtering polymer structure to the softening temperature of the polymer, from which the fibre is formed, through a time period from 20 s - 40 s, preferably 28 s - 35 s, and most preferably about 30 s, and then subsequently rapidly cooling of the structure.

According to further one embodiment of the method of the invention, the filtering polymer structure comprises nanofibres with diameter sizes ranging from 300 to 400 nm, and the microfibers having diameters in the range from 5 to 10 pm, which are arranged so that the nanofibres having larger diameters from the range diameters given above are arranged spaced apart among the microfibers having larger diameters, and the nanofibres of smaller diameters . are arranged spaced apart among the microfibers of the smaller diameters, in yet another embodiment, the filtering structure comprises fibres having micrometric diameters in the range from 1 to 10 micrometers, wherein the volume fraction of those fibres in the total volume of the structure is substantially 100%.

According to the invention, a polymer non-woven filtering cartridge is further provided comprising at least one or more filtering layers arranged successively, one after another, as viewed from the side of inflowing filtered medium, and at least a support element, wherein at least one filtering layer or more filtering layers comprise a filtering material according to the invention.

The non-woven filtering cartridge according to one embodiment of the invention comprises at least three filtering layers, arranged in succession one after another, as viewed from the side of the inflowing filtered medium, namely: an outer, a middle and an inner layer, wherein at least the first i.e. the outer filtering layer, as viewed from the side of the inflowing filtered medium, representing 10% to 60% of the total thickness of the filtering cartridge, comprises polymer fibres, on the surface of which, in the whole and entire volume of . the layer, ZnO nanorods are arranged at a distance of 50-80 nm each other on the surface of the each fibre.

In the further one embodiment of the filtering cartridge, it comprises at least three filtering layers arranged in a succession, one after another from the side of the inflowing filtered medium, namely: the outer, the middle and the inner layer, wherein at least the second middle filtering layer, as viewed from the side of the inflowing filtered medium, representing from 10% to 60% of the total thickness of the filtering cartridge comprises polymer fibres having diameters from 0.1 to 10 pm, on the surface of which, in the whole volume of the layer, ZnO nanorods are arranged having diameters in a range from 5 to 60 nm, at a distance from 40 nm to 1 μτα from each other, on the surface of the each fibre.

According to another further embodiment, the filtering cartridge comprises at least three filtering layers arranged in succession, one after another, as seen from the side of the inflowing filtered medium, namely: the outer, the middle and the inner layer, wherein at least the third i.e. the inner filtering layer, as viewed from the side of the inflowing filtered medium, representing from 20% to 40% of the total thickness of the filtering cartridge comprises polymer fibres having diameters from 100 to 5 μηα, on the surface of which, in and thorough the whole volume of the layer, ZnO nanorods are arranged, which are arranged spaced apart one another by a distance from 50 nm to 200 μηα on the surface of the each fibre.

In the further embodiment of the invention the cartridge comprises at least three filtering layers, arranged in succession, one following another, as seen from the side of the inflowing filtered medium, namely: the outer, the middle and the inner layer, wherein at least the first i.e. the outer filtering layer and/or the second i.e. the. middle filtering layer and/or the third i.e. the inner filtering layer, as viewed from the side of the inflowing filtered medium, comprises polymer fibres, on the surface of which, in and thorough the whole volume of the layer, ZnO nanorods are arranged having diameters from 5 to 100 nm, at a distance from 30 nm to 1 μηα one from each other on the surface of the fibre .

Short description of drawings

Application example of the non-woven filtering material of the invention in the filtering cartridge for fuel purification is shown in fig. 1, while figs. 2-4 show, for example, enlarged photos of the non-woven, polymer structure of the invention with ZnO nanorods formed on the surface of the fibres.

Detailed description of the invention embodiments

The non-woven filtering material in the embodiment of the invention comprises a non-woven polymeric filtering structure composed of a mixture of polymer fibres having micrometric and nanometric diameters in the range from 0.1 μπι to 10 μηα, packed into the structure of a packing density in the range 0.1 - 0.2 , wherein the volume fraction of fibres having nanometric diameters between 100 to 500 nm in the filtering structure is substantially in the range from about 0 to 30% of the total volume of the filtering structure, while on the surface of the fibres, having both micrometric and nanometric diameters, in the whole volume of the filtering structure, ZnO nanorods are arranged forming ZnO nanorods palisade in the form of ZnO protrusions. ZnO nanorods are formed on the surface of the fibres by a process comprising the step of growing ZnO nanorods on the polymeric fibres, under conditions of a forced flow of the mixture of reactants, comprising at least one zinc compound, such as, for example, zinc nitrate, zinc chloride and/or zinc sulphate, right through the whole volume of said non-woven polymeric filtering structure, which process is described in details hereinafter. The nanorods form ZnO nanorods palisade developed on the individual fibres in the whole volume of the non-woven filtering structure, which ZnO nanorods are arranged on the surface of the fibres at an angle in the range 70 - 120° to the longitudinal dimension of the fibre, and particularly preferably substantially perpendicular to the surface of each fibre and which ZnO nanorods are permanently bonded to the fibres. ZnO nanorods arranged on the surface of the fibres in the whole volume of the filtering structure have diameters in the range, preferably, 5-100 nanometres, the height, preferably, in the range 50-500 nanometres and the distance between adjacent nanorods spaced apart on the surface of each fibre of the fibres in the range from 30 nanometres to 1 μπκ

In one of preferred embodiments of the invention a non- woven filtering material in the form of a polymer non-woven filtering structure comprises a non-woven fabric comprising fibres which, depending on the intended use, may be made of thermoplastic plastic material, with a predetermined set chemical resistance.

According to a further variant of the embodiment of the non-woven filtering material of the invention, the non-woven filtering structure can comprise nanofibres having diameter sizes ranging from 100 to 400 nm, preferably, from 300 to 400 nm and microfibers having diameters in the range from 5 to 10 μπ\, which are arranged so that the nanofibres having larger diameters in the range diameters given above, are arranged among the microfibers having larger diameters, and the nanofibres having smaller diameters are arranged among the microfibers having smaller diameters. In a preferred embodiment, a mixture of nanofibres of larger diameters and microfibers of larger diameters, preferably, is arranged in the outer part of the composite filtering structure, and a mixture of nanofibres of smaller diameters and microfibers of smaller diameters is located in the inner part of the composite filtering structure, as viewed in the flow direction of the filtered medium. Furthermore, in further preferred variant of the embodiment of the invention, the nanofibres are distributed in the filtering structure uniformly spaced among the microfibers, wherein it is particularly recommended that the nanofibres would occupy volumetrically 10% -50% of the total volume of the structure, preferably 20% -40%, for example up to 30%. According to the invention preferred filtering structures have an average porosity of more, than 70%. The invention is not limited to the non-woven fabric of the above-described type and it is possible to use other types of polymeric filtering non-woven materials comprising fibres having micrometer diameters, optionally with or without admixture of fibres having nanometric diameters. According to the further variant of another embodiment of the invention, the non-woven filtering material comprises non-woven filtering structure consisting of fibres having micrometric diameters in the range from 1 to 10 micrometers, wherein the volume fraction of those fibres in the total volume of the structure is substantially 100%.

Because the filtering material comprising ZnO nanorods is an effective filter for removing in addition to particulate matter also liquid droplets, from the filtered medium, the configuration of the nanorods in the case of liquid droplets will depend on the surface tension of the liquid forming the droplets. It is the reason for the distinction of the morphology of ZnO nanorods for use in such application.

According to further embodiment of the invention, in the polymer non-woven filtering material, depending on the prospective application of the filtering material and on said surface tension (as described above) , the diameter of ZnO nanorods is in the range about 30 - 60 nm, the height in the range about 70 - 100 nm, and the distance between the ZnO nanorods spaced on the surface of the fibre is from about 100 nm to 1 μπι. In the further embodiment of the invention, depending on the application of the filtering material and on the above mentioned surface tension, the diameter of ZnO 14 000007 nanorods is in the range between about 20 - 50 nm, the height in the range between 50 - 70 nm, and the distance between the ZnO nanorods spaced on the surface of the fibre is from about 80nm to 300nm. In yet another embodiment of the invention, depending on the expected application of the filtering material and the above mentioned surface tension of the filtered medium droplets, the diameter of ZnO nanorods is in the range between about 10 - 30 nm, the height in the range between about 50 - 70 nm, and the distance between the ZnO nanorods spaced on the surface of the individual fibre is from about 50 nm to 100 nm.

The filtering material in the form of a polymeric, non- woven filtering structure according to the invention comprising and/or constituting the above-described fibrous filtering layer, the fibres of which are provided with the ZnO nanorods palisade on their outer surface, is manufactured in an embodiment of the invention by means of the hydrothermal process from solutions of the zinc salts. The process is at least three-step process and it comprises following steps "a"-"c", wherein:

1. Step "a" - the process of modification of the filtering fabrics by low-temperature plasma treatment of the polymer non-woven material comprising polybutylene terephthalate (PBT) , polyamide (PA) or polycarbonate (PC) and polypropylene (PP) in order to functionalise the surface of the fibres in order to change their properties in such a manner to allow carrying out the nucleation process with ZnO nanoparticles; 2. Step "b" - nucleation of the polymeric non-woven material through persistent and uniform deposition of ZnO nanoparticles onto the surface of the fibres from an aqueous or alcohol dispersion, depending on the 2014/000007 used substrate material i.e. the fibre material;

3. Step "c" - growing of ZnO nanorods forming the nanoprotrusions palisade on the surface of the nucleated fibres. The Step "a" i.e. the first step of the process according to the invention, i.e.. the modification of the non- woven filtering fabrics may be carried out, for example, in two ways depending on the type of material being modified.

In the case of modification of the finished filtering non-woven fabrics, available on the market, the process is carried out in a plasma reactor under vacuum conditions, using different gases and using radio frequency discharge. Characteristics of the power supply system and a geometry of the electrodes in a plasma reactor, which determine the type of electrical discharge during which the plasma is generated, as well as the type of the gas used and the treatment time can be selected depending on the material of filtering non- woven fabric, its structure and the expected characteristics after the modification. It is preferable that the power supply system can allow to use of sinusoidal voltage frequencies from 1 kHz to 1 GHz, wherein the supply voltage is in the range between 100-1000 V, which, allows to obtain ionized gas particles having energies not causing degradation of the structure of the filtering polymer fibres. In the further embodiment of the filtering structure of the invention using a non-woven material comprising polypropylene fibres, in the case of modification of polypropylene filtering non-woven fabrics comprising fibres having an average fibre diameter in the range from 1 to 100 m produced by a melt-blown method, i.e. by the technique of blowing a molten polymer, the best results of the modification of such filtering non-woven material were obtained by using, preferably, a frequency of 13.56 MHz, AC voltage within the range from about 100V to 1000V, power 50W, time 5 min. and an oxygen atmosphere. In the case of non- woven fabrics comprising nanometric fibres having an average diameter of fibres ranging from .0.1 to 1 μηα, most preferred results. were obtained by using an argon or nitrogen atmosphere, allowing prevention of fibres degradation during the modification process. In all cases the process parameters used allow modification of the fibre surface with functional OH- and COOH- groups, which modification results in a homogeneous, uniform covering of non-woven material fibres with ZnO nanonuclei.

In the case where, in the further one of a preferred embodiment, a filtering non-woven fabric is subjected to the modification process during the production step of the non- woven filtering fabric by a melt-blown method, a corona discharge is used in the modification process obtained in an electrode system installed under the nozzles of the melt- blown system. Under the fibrillization die for a molten polymer, in a distance from the die head in the range from 20 to 50 mm, in parallel to the stream of the out-flowing polymer fibres, which are still in a plastic state, the electrodes, namely: the emitting electrode (needle electrode) and the cylindrical collecting electrode, that are both connected to a high voltage power supply, are provided. The voltage on the electrodes in the range from 5 to 30 kV and the distance between the electrodes in the range from 10 to 40 mm are selected, such that the corona discharge occurs under conditions of the flowing gas stream and fibres flowing out and discharged from a nozzle in a molten state.. The resulting ions are adsorbed onto the surface of the fibres and firmly "frozen" on their surface after solidification of the fibres , i . e .. they are fixedly deposited on the surface of the produced fibres. In this way, on the surface of the fibres functional groups are produced and formed, which are the active sites for nucleation and growth of ZnO nanorods, in the course of the further process steps for manufacturing ZnO nanorods, forming a palisade of protrusions on the surface of the fibres. The packing density of functional groups on the surface of the fibre depends on the linear velocity of the fibre in the corona discharge zone, and therefore on the conditions of the production of non-woven fabrics, which may be chosen depending on the . expected purpose. Such obtainable fibres with the functional groups on their surface are collected on a core member to form a filtering layer having an expected thickness, depending on the requirements relating to the use of a produced filtering structure. The modified filtering structure which has been produced in the above described manner in a first step "a" is then subjected to further treatment (in the steps "b" nucleation and "c" - nanorods growth, i.e. in the second and third steps as described above) to obtain . the desired nanorods palisade on the surface of the fibres. According to an embodiment of the present invention, the process step "b", i.e. nucleation of non-woven fabric is carried out in an alcoholic dispersion of ZnO nanoparticles /ZnO (nuclei) obtained by means of a synthesis or by milling, wherein it is preferable that the nuclei have a size of from 5 to 50 ran. The non-woven fabric, produced by blowing the molten polymer, which is intended for nucleation, for example such as described in the cited in the present application by reference Polish patent application P.388235, but it is also possible to use other polymeric non-woven fabrics, for example comprising microfibers constituting up to 100% by volume of the non-woven fabrics, is impregnated by ZnO nuclei dispersion in alcohol. Nucleation step in the process according to the invention is preferably carried out in one of the embodiments as follows: 1. According to a first variant of the solution according to the invention the modified non-woven structure (e.g. fabric) obtained in the first step (step "a") is arranged and shaped in the form of a finished filtering cartridge (cartridge) of the desired geometry, depending on particular application of the filter (e.g., in the form of a flat or cylindrical structure) , then it is dipped in the nano-nuclei dispersion, and finally the entire structure is placed in a vacuum chamber. The under-pressure occurring therein, in relation to atmospheric pressure, allows removing from the solution air bubbles, retained between the fibres during immersion of the cartridge in the dispersion (slurry) . This operation allows obtaining uniform distribution of the ZnO nanonuclei on the surface of the fibres . Or alternatively:

2. In a second variant of the invention, the ZnO nanonuclei slurry is passed through a formed cartridge consisting of the filtering material (i.e., in the form of the non-woven structure superimposed on the perforated core) at a linear velocity between 2 cm/s to 10 cm/sec, preferably 2-3 cm/s, wherein it is preferable that the direction of the slurry flow through the filter cartridge could be performed interchangeably, i.e. in the direction from the outer surface side of the filter towards the core, or vice versa. 3. In a third variant of the invention, the nucleation takes place _, directly on the surface of the fibres after plasma modification. The non-woven fabrics, obtained in the first step (step "a") of the process, after modification with plasma and afterwards being wound on a perforated core, is subsequently immersed in a solution of zinc nitrate in isopropanol (isopropyl alcohol) and then it is placed in a vacuum chamber, in which the _. air that remains in the spaces between the fibres is removed. Then sodium hydroxide is added and the whole mixture is heated to a temperature of 60 °C and maintained in this temperature for two hours. The ZnO nano ^¬ nuclei formed as a result of the reaction occurring, due to their higher surface energy, crystallize at the surface of the fibres rather than in a volume of solution.

4. In a further alternative variant of an embodiment of the method according to the invention, in a modified embodiment of the second step (step "b") and the third step i.e. step "c", in the step "b" the surface of the polymer fibres in the non-woven structure is activated and modified by means of an aqueous solution of KMn0 ₄ to form the layer which is an attractor of zinc ions. The modification consists of contacting the non-woven fabric with an aqueous solution of K n04 preferably of the concentration of 0.1-5.0 mM in the forced flow conditions for a time period ranging from 5 to 120 minutes, preferably 10-80 minutes, in particular preferably 15-60 minutes, at a temperature in the range 70- 90°C, preferably 75-85°C, in particular 80°C. The growth of ZnO nanorods takes place in an aqueous solution of zinc salt preferably of the concentration 0.01-0.1M such as: zinc sulphate, zinc nitrate and/or zinc chloride, in the presence of ethanolamine having concentration preferably 1-5M and takes place under conditions of a forced flow of the mixture of the reactants throughout the whole volume of the non-woven fabric for a time period of 30-120 minutes, at a temperature in the range 75-85°C, in particular preferably about 80°C.

According to this last variant (the 4 ^th one) of the method for forming ZnO nanorods, it is possible to avoid a step "b" for preparing nanonuclei and their deposition on the surface of the fibres of the non-woven fabric, described above in variants 1-3. According to this alternative embodiment of the method, the surface of the non-woven fabric is subjected only to activation (in the step "a") and then the growth of ZnO nanorods is carried out in the presence of ethanolamine - "step c" of the process.

In the next operation of the step "b" of nucleation, the non-woven fabric impregnated and soak with one of the above described methods is subjected to a heat treatment - hold at higher temperature - aiming to produce a permanent connection between the substrate material (i.e. the fibre), and the nuclei deposited. The temperature of the process, which is generally in the range from 120°C to 250°C, and particularly preferably from 130 to 240°C, depends on the properties of the substrate material used and should be hold within limits of softening temperature of the material of the fibres. For example, in the case of non-woven fabrics made of polypropylene fibres (PP) the temperatures from 140 to 165°C ^■ are used. In the case of polybutylterephtalate (PBT) fibres, the temperatures from 200 to 230°C are used, for fibres made of polyamide (PA) from 190 to 220°C, while for polycarbonate fibres (PC) from 210 to 230°C. Proper selection of the temperature depends on the type of used plastic material, mainly on its molecular weight and on the fibres' thickness. In accordance with the invention the heating is carried out for a time period in the range 20-40 s, preferably for 28-35 s, and particularly preferably for about 30 s.

The temperatures lower by a few degrees in relation to the above mentioned are preferably used for the thinner fibres and for PP of a lower molecular weight, while higher ones are used for thicker fibres and for PP of a higher molecular weight.

For obtaining adequate morphology . of the ZnO nanorods and their arrangement on the fibres in an entire volume of the non-woven filtering structure of the invention it is essential that the heat treatment in each process step starting from the nucleation step "a", through step "b", to the growth of nanorods step "c" according to the invention is characterized by different parameters than in the solutions known in the art, wherein the difference lies in the fact that, according to the present invention, the heat treatment is carried out for a short time, using a pulse heating, because the main idea is merely to begin to melt (i.e. partial melting) only the surface of the fibre but simultaneously to avoid melting it in whole its volume.

The suitable concentration of the ZnO nanoparticles in the suspension, i.e. in the dispersion for nucleation, preferably in the range about lOVcm ³ and their size in the range from 5 to 50 nm, is chosen depending on the specific surface of the modified non-woven fabric and on the diameter distribution of its fibres in such a manner that the uniform mono-layer of the nuclei is deposited on the surface of the fibres. Preferably, it is used a nuclei' diameter in the range 5 - 50 nm, and the distance between the adjacent nuclei in the range 30 - 300 nm.

In the here described step of the process according _. , to the invention, the nucleation process (step "b") and heating operation i.e. holding in a high, temperature can be repeated several times depending on the material of the substrate, i.e. the fibre, used and the required distribution density of the ZnO nanorods on the surface of the fibre after the growing process.

The third step of the process according to the invention

- i.e. the step "c" - comprises carrying out of the growing process of the ZnO nanorods forming the palisade of nanoprotrusions on the surface of the fibres, in particular the nucleated fibres of the polymer filtering structure, preferably of the polymeric non-woven structure (fabric) of the aforementioned kind, which step "c" is carried out by hydrothermal method from aqueous solution of zinc compounds, such as for example, zinc nitrate, zinc sulphate and/or zinc chloride, with urotropin (i.e. hexamethylenetetramine) and other additives which, for example, change the surface charge of ZnO, mainly with surfactants, such as, for example, dodecanethiol, DPPC (dipalmitoylphosphatidylcholine) or polyethyleneimine, designed to control the thickness of the grown nanorods. In the step "c" of growth of the nanorods on the surface of the nucleated fibres, the treated non-woven fabric is subjected to an influence of the said aqueous solution of a zinc salt, for example zinc nitrate and urotropin (HMTA) with additives, wherein the solution is forced to flow through the treated non-woven fabric.

The growth process of nanorods is carried out at a temperature between 40 and 90°C, preferably 70-80°C. The duration of the process depends on the height of grown rods forming nano-protrusions that is assumed to be reached.

The agents and compounds used, for example dodecanethiol and DPPC, are designed to block the growth of produced nanorods in any directions other than along the main axis, whereby it is possible to stop the growth of their thickness. The selection of the duration time of the process between 4 and 6 hours depends on the desired height of the grown rods in the range from 30 nanometres to 100 nanometers. In the case of longer times, which should be selected according to the size of the modified non-woven fabric, its specific surface, etc. the replacement of the reactant solution is necessary during the process, the purpose of which replacement is to complement reacting substances. After completion of the growth, the resulting material with the nanorods palisade formed on the surface of fibres is subjected to washing in alcohol, and then it is subjected to a thermal treatment for the fixation of the connection between nanorods and the fibres.

The detailed exemplary embodiment of the process Preparation of nuclei in the second step "b" of the process according to the invention i.e. in the step "b" - nucleation.

Synthesis of the ZnO nanonuclei is conducted in isopropanol environment. For this purpose, 40 ml of the 2 mM zinc acetate solution in isopropanol and 40 ml of the 40 mM sodium hydroxide solution in isopropanol are prepared. The solutions are heated to 45°C with vigorous stirring to dissolve the reacting substances and then they are cooled to 25°C. The zinc acetate solution is diluted with isopropanol to a volume of 460 ml, and then the solution of sodium hydroxide with vigorous stirring is added to it drop by drop. The mixture of the above-mentioned reacting substances is heated in an oil bath to the temperature of 60 °C and hold at this temperature for 120 _. minutes. After this time the nuclei slurry of zinc oxide ZnO is cooled to the temperature of 25°C and diluted with isopropanol to a volume of 1000 ml.

Modification of non-woven fabrics with ZnO nanonuclei (step "b" - nucleation of non-woven fabric)

In the slurry prepared as described above, the non-woven fabric, previously modified by means of _. low-temperature plasma treatment according to one of the variants described earlier in the first step of the process (step "a") according to the invention, is wound on a perforated core while giving it the form of the filtering cartridge and the whole such formed cartridge is placed for 15 minutes in a vacuum drier where the cartridge is evacuated to 20 mbar pressure in order to remove air from inside of the non-woven fabric. Afterwards the reacting substance mixture (solution) is forced to flow through the non-woven fabric with a linear velocity, preferably, of 3 cm/s. The process is carried out for 5 hours. Then the non-woven fabric is dried at a temperature 35°C, and after complete drying it is hold for 5 seconds at a temperature 145°C. The use of the forced flow through the non-woven filtering structures in both steps "b" and "c", i.e. during nucleation of ZnO nanoparticles on the surface of the fibres of the filtering non-woven structure and during the growth of the nanorods allows to control the distribution of the nuclei on the surface of the fibres in a filter, and to control their growth, i.e. to obtain the desired diameter and a height of the ZnO nanorods.

The growth of ZnO nanorods in the third step of the process (step "c") according to the invention

In the further step (step ^w c") of the process an aqueous, equimolar solution of zinc nitrate and urotropin HMTA of a concentration 1 mM is prepared. The solution is subjected to ultrasonic action for 15 minutes for degassing. The solution together with the filtering cartridge is then placed in a flow chamber after the step of nucleation and the whole system is placed for 15 minutes in a vacuum drier, wherein the system is pumped out to a pressure of 20 mbar. Then the non-woven fabric is removed from the flow chamber, dried and subjected to a heat treatment by placing it for 5 seconds at a temperature 145°C.

The most important difference in comparison to the solutions known from the prior art is the method of carrying out the ZnO nanorods growing process in the conditions of forced flow, which is used according to the present invention in the third step of the manufacturing process i.e. in the step "c". Only the method provided by the invention in which the step of growing ZnO nanorods is carried out in forced flow conditions allows to growth of ZnO nanorods on the surface of the polymer fibres thorough the whole volume of the filtering non-woven fabric i.e. right through whole thickness of the non-woven fabric. The inventive method allows for modification of finished, known non-woven filters available on the market, by forming the ZnO nanorods palisade according to the invention on the surface of fibres which they include, and thus giving them excellent filtering, and also coalescence and bacteriostatic, properties. Commonly used methods for the preparation of ZnO nanoparticles on polymeric fibres, consisting in immersing the textile material in the solution for growing i.e. solution of reactants allow only modification of fibres on the external surfaces of the material. In contrast to that, the non-woven filtering fabric made by the method according to the invention comprises in its entire volume i.e. right through its entire thickness fibres modified by creating on their surface the ZnO nanorods palisade, forming nanoprotrusions , distributed substantially perpendicular to the surface of the fibre having the desired packing density and specific dimensions, as required for specific applications.

The above-described technique for manufacturing composite non-woven structures of polymeric fibres comprising micro- and/or nanofibres with deposited on their surfaces ZnO nanoprotrusions forming ZnO nanorods palisade in the form of needles - nanorods - with predetermined morphology and an arrangement over the surface of each fibre of the fibres, and fixedly bounded to the fibre, is used to create filtering materials, the construction of which depends on the particular application of the filter.

Simultaneously, the surface modification of the fibres in the filtering material with ZnO nanorods, due to specific morphology and the highly developed specific surface of the fibres, allows manufacturing high filtering performance filters with respect to nanoparticles of the solid phase from gases including air, significantly better in comparison to the unmodified filters. Another parameter that characterizes the work of the filter is its life-time. This life-time is determined by the operation period of the filter in which the pressure drop across the filter reaches a threshold limit value because of building up with the filtered particles. In the case of, for example, water filtration, the permissible pressure drop in conventional non-woven filters is 1.5 bars.

The experimental data obtained from tests of non-woven filters indicate that the same non-woven filter, after modification of its component fibres according to the present invention, i.e. by means of covering the surface of the fibres in the entire volume of the filtering layer with ZnO nanoprotrusions, having above described parameters according to the invention, has its life-time increased by 30% comparing to the life-time of the same filter without modification, and it has the filtration efficiency of 99.98% as compared to the performance of the same but unmodified filter which, under the same filtration conditions, amounts to 95%. Improvement in the performance of the filtering cartridge according to the invention results from the uniform distribution of deposits in the whole space of the filter comprising filtering material according to the invention, caused by interactions between the surfaces of the fibres modified with ZnO nanorods and nanoparticles of impurities.

The non-woven filtering material according to the present invention finds a wide application in non-woven filtering cartridges, e.g., as a solid-particle filter for filtering variety of fluid media, including liquid fuels, gaseous fuels and other gaseous media, in many applications, wherein the non-woven filtering cartridge may have construction consisting of a single-layer or multi-layered construction, for example a three-layer structure, wherein it may comprise layers, having fibrous structure different from each other. At least one filtering layer or more layers of the filtering cartridge comprises a non-woven filtering material according to the invention, wherein it may be only one filtering layer, for example, the outer one, the middle one and/or the internal layer with respect to the direction of the flow of the filtered medium, from plurality of layers forming a filtering cartridge. It is also possible to have two or more filtering layers that can be adjacent or spaced apart from each other in a volume of the filter structure, and preferably all of the filtering layers of the filtering cartridge made of non-woven filtering material according to the present invention.

In one embodiment of the invention, the non-woven filtering cartridge comprises a plurality of filtering layers, each having different structure, preferably at least three filtering layers, each of which is made of a non-woven filtering material according to the invention, wherein the cartridge has the following structure: the first filtering layer of the filtering cartridge, the outer one as seen in the direction of the flow of filtered medium comprises polymeric fibres with diameters ranging from 0.1 to 10 μπι and which layer constitutes from about 10 to 50%, preferably about 20% of the total thickness of the filtering cartridge and on the surface of the fibres the ZnO nanorods are arranged spaced apart by the distance 50 - 80 nm from each other, wherein the same distance is between nanorods arranged on the surface of the fibre, the next middle layer of the filtering cartridge comprises fibres with diameters in the range 10 - 2 pm, wherein the middle layer constitutes from 35-60%, preferably 50% of the total thickness of the filtering cartridge, wherein the ZnO nanorods are arranged on the surface of the fibres spaced apart by the distance 60-90 nm from each other, the following next layer i.e. the third filtering layer comprises nanofibres of _. diameters in. the range 100 - 400 nm, on the surface of which the nuclei of ZnO nanorods for ZnO nanorods growth or ZnO nanorods are arranged spaced apart at the distance of 70 - 100 nm from each other, wherein the thickness of this layer is between 20-40%, preferably 25-35%, and particularly 30% of the total thickness of the filtering cartridge.

In this case the morphology of ZnO nanorods is according to the invention and in-line with specified and previously described values and embodiments according to the invention.

For example, according to another embodiment of the invention, the non-woven filtering cartridge comprises number of filtering layers, wherein there are the first filtering layers of the non-woven filtering cartridge, as seen from the side of flowing-in medium, comprising liquid droplets as a dispersed phase, which layers comprise from 5% to 40%, and preferably up to 30% of the entire thickness of the whole filtering cartridge, comprise polymeric fibres having a thickness/diameter preferably in the range 0.1 pm - 10 pm, with a packing density of 0.15, at least one middle filtering layer having a thickness of up to 50%, preferably up to 40% of the entire thickness of the whole filtering cartridge and consisting of a mixture of fibres with diameters in the range 0.1 - 5 pm and a packing density preferably of 0.2, wherein ZnO nanorods are arranged on the surface of the fibres in this at least one middle layer, which ZnO nanorods having diameters values in the range of 30-60 nm, preferably 35-50 nm, the height preferably in the range 70-100 nm and the distance between adjacent ZnO nanorods on the each fibre surface preferably in the range 100 nm - 1 pm, and at least one third layer, constituting up to 20%, and preferably up to 15% of the entire volume of the whole filtering cartridge, comprising fibres having diameters, preferably, in the range 0.1 pm - 1 pm, preferably from 0.4 pm - 1 pm and having a packing density of 0.10. In further another embodiment of the invention in the non-woven filtering cartridge, comprising at least three filtering layers the first filtering layer, as seen from the side of inflowing medium to be filtered, constituting 5-15%, and preferably at least 10% of the entire thickness of the whole filtering cartridge, comprises a mixture of polymer fibres having diameters preferably in the range 1 - 10 μηα with a packing density of 0.15, a following layer constituting 40-70%, preferably 50-60%, in particular 60% of the total thickness of the filtering cartridge, comprises a mixture of fibres having diameters in the range 0.1 - 5 μπ\, preferably 0.3 - 4 μιη and a packing density of 0.2, wherein on the surface of the fibres in this layer are arranged ZnO nanorods according to the invention, whose diameter is preferably 20 - 5 nm, the height is preferably 50 - 70 nm, and the distance between adjacent nanorods is preferably 80 - 300 nm, the third layer constituting 5-30%, preferably 5-20%, especially 20% of the entire thickness of the filtering cartridge, comprises a mixture of fibres having diameters in the range 0.1 - 1 μπι, preferably 0.3 - 1 μπι and packing density of 0.2, and on the surface of the fibres in this layer are arranged ZnO nanorods, wherein the nanorods diameter is preferably 10 - 30 nm, the height is 50 - 70 nm, and the distance between nanorods is preferably 50 - 100 nm, According to further another embodiment of the invention, in the filtering cartridge according to the invention, which is applicable especially as a coalescing filter or a coalescer, a first layer of the non-woven filtering cartridge, as seen from the side of inflowing filtered medium, having a thickness constituting 45-70%, preferably 55-60%, _. and especially about 60% of the entire thickness of the filtering cartridge, is made of fibres with diameters preferably in the range 1 - 3 μιη and with a packing density in the range 0.1 - 0.15, and the next following layer with a thickness constituting 5-20%, preferably 10% of the entire thickness of the filtering cartridge is made of fibres, preferably of a diameter of 1-5 pm, preferably 3 pm and a packing density of 0.15, wherein the fibres in this layer are covered with ZnO nanorods according to the invention which nanorods having diameters preferably in the range 10 nm to 15 nm, the height ranging from 50 to 300 nm and the distance between the adjacent nanorods on the surface of a fibre preferably in the range 40 - 60 nm, and the third layer having a thickness constituting 20-40% and preferably about 30% of the entire thickness of the whole filtering cartridge, comprises the fibres having a thickness preferably in the range 0.3 - 5 μπ microns and packing density of 0.2, wherein between said first and second layers a spacer is provided in the form of a perforated corrugated barrier retaining the distance between the layers, preferably in the range 2 - 3 nm.

The intended morphology of the ZnO nanorods, adapted to the specific needs and requirements concerning the designed filter, permitting antibacterial functioning of the filters and the increase in the filtering efficiency of the nanoparticles from filtered media, including gases, is obtained by selection of the operating parameters of the process for their manufacturing, in particular in the second step of the process, i.e. in the step "b" of nucleation of the non-woven fabric.

The preferred morphology of the ZnO nanorods palisade according to the invention on the surface of the fibres for the application of the filtering non-woven fabric according to the invention in filtering coalescing systems, depending on the surface tension of the liquid drop (droplet) of the filtered medium, . is as follows: nanorods diameter in the range 30 - 60 nm, height in the range 70 - 100 nm, the distance between adjacent nanorods spaced over the fibre surface from in the range 100 nm to 1 μπι. In the applications of the non-woven filtering fabric according to the invention in septic filters, i.e. for filtration of bacteria and/or viruses, the following morphology of the ZnO nanorods palisade deposited on the surface of fibres is preferable: for bacteria filtration: nanorods diameter in the range 20 - 50 nm, a height in the range 50 - 70 nm and the distance between adjacent nanorods 80 - 300 nm spaced on the surface of each fiber, while for viruses filtration: diameter of ZnO nanorods in the range 10 - 30 nm, the height in the range 50 - 70 nm, and the distance adjacent between nanorods in the range 50-100 nm on the surface of the fibre.

In the case of application of the non-woven filtering material according to the invention in the fuel filters, in particular in terms of a fuel for diesel engines, i.e. diesel oil, in which filters both filtration and coalescence of liquid droplets (drops) is carried out simultaneously, a multilayer structure of a filter is provided which is shown schematically, for example, in fig. 1, while figs. 2 - 4 show photos of the non-woven structure according to the invention with an developed ZnO nanoprotrusions palisade on the surface of the polymer fibres, taken with a scanning electron microscope (SEM) , Hitachi SU 8000. The first layers, as seen from the side of inflowing filtered medium, in this case a fuel, are intended to droplets coalescence and are constructed of traditional, known non-woven structures, further following them the free space is arranged, in which there are no any fibres, and then there is/there are one or more hydrophobic layers disposed, which is (are) made of the filtering material according to the invention and comprise fibres whose surface is covered with ZnO nanoprotrusions (nanorods) in the form of the nanopalisade according to the invention distributed over the fibre surface.

The filter operates in such a way that after coalescence on the first layers the large droplets firstly pass into the hydrophobic layer (s) through which the fuel (oil) flows freely, and the formed droplets as a result of the hydrophobicity flow down the hydrophobic layer and flow into the free space between the layers and are collected in the reservoir provided below the filter. The free space between the coalescing and hydrophobic layers facilitates and makes easier the flow of droplets and their removal from the filter area. The structure of the fuel filter using a filtering material according to the invention is similar to the above described structure of the coalescing filter, except of that the outer layers, one or more, as viewed in the direction of the filtered medium flow, i.e. from the side of inflowing medium for purification, which are designed to remove solid particulates from the fuel and to simultaneous coalescence of the water droplets, are composed of fibres having diameters preferably in the range 1-3 μπι and the packing density, preferably in the range 0.1 - 0.15, and the following layers have hydrophobic properties, wherein the fibres are monodisperse, preferably with a diameter of 3 μπι and a packing density of 0.15. The hydrophobicity is achieved by incorporating into the surface of the fibres of ZnO nanoprotrusions , distributed over the surface of each fibre through the whole volume of the layer,, which ZnO nanorods having diameters preferably in the range from 10 nm to 50 nm, the height ranging from 50 to 300 nm and the distance between the adjacent nanorods on the surface of the fibres preferably in the range of 40-60 nm, according to the mechanisms for forming of the ZnO nanoprotrusions on the surfaces of the fibres, i.e. the above described method according to the invention.