WO2018134334A1

WO2018134334A1 - Process for obtaining a porous material from powder materials, a porous material and use thereof for the capture of atmospheric particulate matter and organic contaminants

Info

Publication number: WO2018134334A1
Application number: PCT/EP2018/051263
Authority: WO
Inventors: Elza Bontempi; Laura Eleonora DEPERO; Laura Treccani; Alessandra ZANOLETTI
Original assignee: Consorzio Interuniversitario Nazionale Per La Scienza E Tecnologia Dei Materiali; Università degli Studi di Brescia
Priority date: 2017-01-20
Filing date: 2018-01-19
Publication date: 2018-07-26
Also published as: IT201700006271A1

Abstract

The present invention relates to a process for the production of a porous, ceramic or vitreous material, from powder materials, preferably waste materials. According to a different embodiment, the present invention relates to a process for applying a coating of a porous material obtained from powder materials, preferably waste materials, to a pre-existing solid surface. The alternative processes according to the present invention provide for the steps of mixing under stirring a solvent, a binder, and a cross-linking agent until a gelling solution is obtained, and adding to said solution a powder material, and a chemical leavening agent to obtain a homogeneous mixture, which is heated at low temperature until a porous solid material is obtained. The present invention also relates to a porous, ceramic or vitreous material, comprising a generally amorphous phase, in turn comprising inorganic oxides, and a binder, obtainable by a process according to the invention, suitable for the capture of atmospheric particulate matter and organic contaminants.

Description

Title: Process for obtaining a porous material from powder materials, a porous material and use thereof for the capture of atmospheric particulate matter and organic contaminants

DESCRIPTION Technical Field

In its most general aspect, the present invention relates to a process for the production of a porous, ceramic or vitreous material, from powder materials, comprising inorganic oxides, preferably waste powder material such as ashes or derivatives thereof. More specifically, the present invention relates to a process of the aforementioned type carried out by heating.

The present invention also relates to a porous, ceramic or vitreous material, obtainable by means of the aforementioned process according to the present invention, and uses thereof. Background Art

Improving air quality is a goal of increasing importance at global, European and national level. Parallel to policies that promote a lifestyle with a diminished carbon footprint, we are continually looking for new processes for the production of materials with low environmental impact.

In particular, especially in the urban environment and in reference to those polluting emissions attributable to car-vehicular traffic and obsolete civil heating systems, the problem of pollution caused by atmospheric particulate matter and high molecular weight organic substances, such as polycyclic aromatic hydrocarbons (PAH), is particularly felt. The overrun of the daily fine dust limit imposed by the law (50 μg/m³ for PMio) is now a fairly common occurrence that also occurs tens of times per year in the main European urbanized areas, especially those located in low-lying areas and in the inland, such as the Po Valley, the Parisian region and the Polish Silesia, to name a few, as well as in mountainous areas, or areas located in the valley floor, characterized by intense anthropic activity. The production of materials for use in building as adsorbents of polluting substances such as cements able of oxidizing the adsorbed organic and inorganic polluting substances, due to photo-catalysts duly introduced into the mixture at the time of formulation or deposited on the surface of the material after its formation is known in the art. See, for example, the patent application WO 2004074202.

However, such materials have a rather limited application, since they are often overly expensive materials. Therefore, such materials can not represent a solution to the problem of air pollution in urban centres, especially in historic city centres or in the proximity of high-traffic arteries such as ring roads and access roads to cities, as well as in mountain areas, or areas located in the valley floor, characterized by intense anthropic activity.

The need is therefore felt to provide a material able of adsorbing pollutants, particularly suitable for use in construction, having a low cost and which can be applied not only to new structures, but also to already existing buildings and infrastructures.

Among the possible alternatives, activated carbon exists that can be used as a filter for aqueous solutions, as well as a filter inside air filtering equipment.

However, this kind of material, besides not being particularly suitable for a large-scale use for building-type applications, especially for cost issues, also presents considerable desorption problems.

Therefore, it is necessary to develop materials that are not only inexpensive, but also have a high adsorbent capacity and a faster desorption kinetics with the possibility of being easily regenerated.

In this sense, a possible alternative to activated carbon can be provided by porous ceramic materials, which are rather known and widespread for various kinds of applications, for example as filters for aqueous solutions, but also as exhaust gas filters for chimney pots and flue gas ducts.

For both the above-mentioned applications, materials as porous ceramic foams, for example alumina, titanium oxide or zirconia ceramic foams are known.

In this sense, processes for obtaining porous ceramic materials obtained by using an inorganic starting material, first of all alumina, and alginates, for example sodium alginate, are known. Commonly, such materials are also obtained by means of processes which provide for a high temperature sintering step, typically higher than 1000°C.

A process for the production of such materials is disclosed in the publication "Formation of porous articles with ordered capillary structure by alginate sol-gel technique" of B. Liebig et al., wherein it is contemplated to start from ceramic powder (alumina and titanium oxide) and an alginate, performing a gelling step induced by using a copper ions source, followed by leaching of the ions themselves. Such process then ends with a sintering step at a temperature of 1200 °C or 1500 °C thus obtaining a ceramic foam.

In conclusion, the known processes for the production of porous ceramic materials which use inorganic powders as starting material and a polysaccharide as gelling agent during the formulation process necessarily require a sintering step with heating at temperatures above 1000°C.

Therefore, such processes require adequate equipment to withstand high temperatures and, above all, determine a large consumption of energy, making the finished product not only not ecologically sustainable, but also significantly expensive.

Another aspect of interest in the field of porous material for trapping molecules is the control of pores sizes, which can be achieved through various method known in the art, for example using specific precursors for nano-casting or using variable size surfactant templates for template growth.

In the publication "A Review of recent developments of mesoporous materials", Steven L. Suib, Chem. Rec, 2017, 17, 1- 16, is described a sol- gel method using triblock copolymer pluronic surfactant PI 23 which is used in acidic medium by following an evaporation-induced self-assembly (EISA) method; thus, obtained ordered mesoporous silica (OMS) with incorporated magnesium and calcium oxides are used for acidic greenhouse gases sorption at ambient and elevated temperature, such as CO2.

However, these materials are used to obtain only selected ranges of pores dimensions and their structures do not have pores connected to one another. In addition, after synthesis the template agent must be removed, for example by thermal or chemical treatments. Then, these methods are expensive and time consuming.

Therefore, exists the need to develop a process for the production of a low- cost and environmentally sustainable porous adsorbent material, as well as the provision of a material having similar advantages.

The main object of the present invention is therefore to provide a process for the production of a porous material, which does not require steps at high temperatures and at the same time is simple and economical to implement for an industrial application, in order to overcome the limitations of the aforementioned known technologies for obtaining porous ceramic materials.

Accordingly, another object of the present invention is to provide a porous material, having a wide variability in pores size, suitable for use as an adsorbent substrate for polluting substances, specifically for polluting species included in air as atmospheric particulate matter or high molecular weight organic substances.

Summary of the invention

In an embodiment, such technical problem is solved by a process for obtaining a porous, ceramic or vitreous material starting from powder materials comprising inorganic oxides, wherein said process comprises the following steps: a) mixing under stirring a solvent, preferably water, a polysaccharide binder and a cross-linking agent, until a gelling solution is obtained; b) adding under stirring a powder material, comprising inorganic oxides, and a chemical leavening agent to said gelling solution, until a homogeneous mixture is obtained; c) heating the homogeneous mixture to a predetermined temperature and to a predetermined time so to obtain a solid porous material, wherein said temperature is between 35 °C- 1 10 °C, and the time is longer than 45 minutes; d) cooling to room temperature said solid porous material.

Preferably, said step c) is carried out by putting said homogeneous mixture into a mould. This way the operator can pre-set the dimensions and the shape of the material which is going to be produced by means of the following step of the present process. According to an alternative embodiment, such technical problem is solved by a process for applying a coating of a porous, ceramic or vitreous material, obtained from powder materials comprising inorganic oxides, to a preexisting solid surface, wherein such process can include the following steps: a') mixing under stirring a solvent, preferably water, a polysaccharide binder and a cross-linking agent, until a gelling solution is obtained; b') adding under stirring a powder material comprising inorganic oxides and a chemical leavening agent to said gelling solution, until a homogeneous mixture is obtained; c') adding under stirring a further portion of such solvent to said homogeneous mixture until a diluted homogeneous mixture is obtained; d') applying said diluted homogeneous mixture to a hard surface to form a coating of said diluted homogeneous mixture on said pre-existing solid surface, wherein said coating can preferably have a thickness ranging from 0.1 mm to 5 mm; e') heating the diluted homogeneous mixture coating at a temperature between 35 °C and 1 10 °C and for a time longer than 45 minutes; f) cooling to room temperature said coating of porous solid material.

Preferably, according to this alternative embodiment, the step of applying the diluted homogeneous mixture to a hard surface according to the last described embodiment of the process of the invention can be carried out by spraying.

The latter embodiment of the present invention allows to apply the above mentioned diluted homogeneous mixture to simply and quickly cover wide hard surfaces, for example inside or outside walls of industrial buildings and warehouses, roofs, or elements of road infrastructures.

More generally, according to a generic process of the present invention, the aforementioned powder material, comprising inorganic oxides, can be a waste material, deriving from industrial, civil or agricultural processes.

Preferably such powder waste material, deriving from industrial, civil or agricultural processes, comprising inorganic oxides, can be selected from the group consisting of silica fume, wood ash, coal ash, desulfurization ash, ash deriving from combustion sewage sludges and any combination of the previous elements.

In accordance with the present invention, with the expression "polysaccharide binder" is intended a polysaccharide or a mixture of different polysaccharides which can be dissolved in the aforementioned solvent, together with the aforementioned cross-linking agent, in order to form the aforementioned gelling solution.

In particular, when mixed with said solvent and with said cross-linking agent during above step a), such polysaccharide binder can be dissolved in the solvent at room temperature just by mechanically stirring, allowing the gelation process to take place immediately, i.e. by ion chelation mechanism which involves the interaction between some polysaccharide chains and divalent ions (the latter being released in the solution by dissolving the aforementioned cross-linking agent).

Preferably, the aforementioned polysaccharide binder can be an alginate, more preferably said alginate is sodium alginate.

Preferably, during said step a) or a') of a process according to the present invention, the aforementioned solvent is present in said gelling solution in an amount equal to 35-60 parts by weight and the aforementioned binder is present in said gelling solution in an amount equal to 1- 10 parts by weight. Preferably, during said step a) or a') of a process according to the present invention, the aforementioned cross-linking agent is a calcium salt or a barium salt soluble in an aqueous medium. More preferably, said cross- linking agent is selected from an element of the group consisting of calcium iodate, calcium chloride, barium chloride and any combination thereof. Even more preferably, said cross-linking agent is calcium iodate and is present in said gelling solution in an amount equal to 1- 10 parts by weight.

Preferably, during said step b) or b') of a process according to the present invention, in said homogeneous mixture the aforementioned powder material is present in an amount equal to 25-55 parts by weight.

In accordance with the present invention, with the expression "chemical leavening agent" it is intended a chemical composition comprising a chemical specie which decomposes to give CO₂, for example under specific environmental conditions such as under a specific temperature or at a specific pH.

When such chemical leavening agent is mixed in said step b) or b') of a process according to the present invention, it is in the condition of generating CO₂ bubbles which get trapped in said gel-like homogeneous mixture, thus determining the formation of a nano-porous material after following steps of the process.

In particular, due to the choice of the compounds and material used, i.e. the use of said chemical leavening agent, and thanks to the specific sequence of the steps of the processes of the present invention, it is determined the formation of a nano-porous material having a wide variability in the pores size and in which said pores are connected to one another, so that to create a porous ceramic foam material.

Preferably, during said step b) or b') of a process according to the present invention, the aforementioned chemical leavening agent is an element of the group consisting of sodium hydrogen carbonate, ammonium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, an alkali metal salt of tartaric acid and any combination thereof.

More preferably, said chemical leavening agent is sodium hydrogen carbonate and is present in said homogeneous mixture in an amount equal to 1- 15 parts by weight.

Preferably, during said c) or e') of heating the homogeneous mixture of a process according to the present invention, said temperature is comprised between 55°C and 90°C, preferably said temperature is equal to 80°C. According to another embodiment, the process according to the present invention can comprise a further step of aging, during which said porous solid material or said coating of porous solid material is kept at room temperature for a predetermined time, preferably for a time longer than two weeks, more preferably longer than three weeks. Preferably, according to another embodiment, before said step of aging of the process according to the present invention a step of rinsing is carried out, wherein during said rinsing said porous solid material thus obtained is washed to remove unreacted components.

The aforementioned technical problem can also be solved by a porous, ceramic or vitreous material, obtainable by a process according to the present invention, wherein said porous material comprises an amorphous phase and it is obtained from powder materials, comprising inorganic oxides, preferably a waste material and deriving from industrial, civil or agricultural processes, and wherein said material has a density between 150 kg/m³ and 300 kg/m³, preferably between 180 kg/m³ and 220 kg/m³ and has nano-pores with an average size less than or equal to 200 nm, preferably equal to or less than 150 nm.

The amorphous phase comprised in the aforementioned material comprises in turn inorganic oxides in an amount by weight equal to or greater than 10% with respect to the weight of such amorphous phase, preferably it can comprise organic oxides in an amount by weight greater than or equal to 30% with respect to weight of such amorphous phase.

Specifically, the amorphous phase can comprise any one of the elements selected from the group consisting of silica, aluminium oxide, ferric oxide, ferrous oxide and any combination thereof. Preferably, the amorphous phase comprises silica.

Similarly, such amorphous phase comprises a polysaccharide binder, preferably an alginate.

In view of the solution of the aforementioned technical problem, the present invention provides that the aforementioned porous ceramic or vitreous material can be used as a filter for the adsorption of fine atmospheric particulate matter and/ or organic contaminants, preferably in the facing of buildings, roofs or in the covering of road structural elements

In particular, the present invention also provides a manufactured product made with the aforementioned porous material according, wherein said manufactured product is suitable for the use as a filter for a fluid comprising polluting.

Detailed description

After extensive research, the inventors have developed a new process for the production of a porous, ceramic or vitreous material from powder materials, including inorganic oxides, which allows to brilliantly achieve the aforementioned purposes.

In a preferred manner, adding under stirring a powder material, comprising inorganic oxides, during the aforementioned step b) or b'), the process in object allowed to develop a porous, ceramic or vitreous material from powder waste materials, deriving from industrial, civil or agricultural processes comprising inorganic oxides.

According to the present invention, the term "powder waste materials, deriving from industrial, civil or agricultural processes, including inorganic oxides" means a solid mixture comprising mostly inorganic substances obtained as by-products in industrial processes, including oxides, hydroxides or metallic salts and/ or metalloid salts with an average particle size between 0.2 μηι and 50 μιη.

According to the present invention, the term "silica fume" means a byproduct obtained in melting plants in the production industry of elementary silicon and of iron-silicon alloys. Specifically, the reduction reaction of the silica to elementary silicon, which occurs at temperatures above 2000°C, causes the formation of SiO₂ vapours, which in turn condense in the coldest areas of the reactor as fine particulate comprising mainly non-crystalline silica. Generally, silica fume can contain an amount of silica between 85% and 95% by weight.

According to the present invention, the aforementioned silica fume has particles with an average particle size between 0.6 μηι and 20 μιη. According to the present invention, the term "wood ash" means a by-product obtained by combustion and/ or fractionation of plant material from forest plant sources (wood, wood derivatives, branches) or from waste from the agricultural industry such as walnut shells, hazelnut shells, rice husks, fruit pits, olive pomace, corn cobs, wheat straw, discarded pieces of grain kernels, sugar cane stalks, marc and grape seed. The wood ash can include inorganic oxides in amorphous form, such as silica, for example, and may include inorganic oxides in crystalline form such as calcium oxides and fairchildite.

According to the present invention, the term "coal ash" means a by-product obtained during the combustion of coal. The coal ash can be of coarser grain, being identified as "bottom ash", i.e. fine particles that precipitate directly into the combustion chamber, or it can be made up of even finer particles that remain suspended in the gas flow and are transported by the flow of combustion gases outside the furnace, being identified with the expression "fly ash". The carbon ash can include inorganic oxides in amorphous form, such as silica, for example, and can include inorganic oxides in crystalline form such as quartz, hematite and mullite.

According to the present invention, the term "desulfurization ash" means a by-product obtained from the cycle of thermoelectric combustion of coal, more specifically desulfurization gypsums obtained by desulfurization of the combustion gases generated by the combustion of coal by reaction between sulphurous anhydride, calcium carbonate and water.

As briefly summarized in the summary, a process according to the invention can comprise different steps which will be reported below. According to a first step a) of such process, a solvent, preferably water, a polysaccharide binder, and a cross-linking agent are mixed under stirring, until a gelling solution is obtained. According to a second step b), a powder material comprising inorganic oxides and a chemical leavening agent are added to said gelling solution, under stirring, until a homogeneous mixture is obtained.

Then, according to said step c), said homogeneous mixture is heated at a temperature between 35°C- 1 10°C and for a time longer than 45 minutes.

Finally, according to said step d), such porous solid material is cooled at room temperature.

As anticipated in the summary, according to a particular embodiment, the above-described process according to the present invention provides for the further step of placing the aforementioned homogeneous mixture in a mould, while carrying out said heating step c).

In this way, therefore, in an absolutely advantageous manner, the above- described process according to the present invention allows to obtain manufactured products made of porous, ceramic or vitreous material with a predetermined shape and thickness, wherein such shapes and thicknesses can be completely improved as a function of the final use.

According to an alternative embodiment, the present invention provides for a process for applying a coating of a porous, ceramic or vitreous material obtained from powder materials, comprising inorganic oxides, to a pre- existing solid surface, wherein such process comprises the following steps: a') mixing under stirring a solvent, preferably water, a polysaccharide binder agent and a cross-linking agent, until a gelling solution is obtained; b') adding under stirring a powder material, comprising inorganic oxides, and a chemical leavening agent, to such gelling solution, until a homogeneous mixture is obtained; c') adding under stirring a further portion of such solvent to such homogeneous mixture until a diluted homogeneous mixture is obtained; d') applying such diluted homogeneous mixture to a hard surface to form a coating of such diluted homogeneous mixture on said pre-existing solid surface, wherein such coating can preferably have a thickness ranging from 0.1 mm to 5 mm; e') heating the diluted homogeneous mixture coating at a predetermined temperature and time to obtain a coating of porous solid material, wherein the temperature is between 35°C and 1 10°C and the time is longer than 45 minutes; f) cooling to room temperature said coating of porous solid material.

Preferably, in the step of adding under stirring a further portion of solvent to the homogeneous mixture until a diluted homogeneous mixture is obtained, the further portion of solvent is equal to 1-5 parts by weight with respect to the weight of the other components of the diluted homogeneous mixture.

In a more preferable way, the step of applying such diluted homogeneous mixture to a hard surface according to the just-described process of the invention can be carried out by spraying.

The process of applying a coating of a porous ceramic or vitreous material to a pre-existing solid surface actually contemplates an in situ application of a homogeneous mixture comprising a solvent, a polysaccharide binder, a cross-linking agent, a chemical leavening agent and a powder material, comprising inorganic oxides. More precisely, rather than producing a manufactured product having a predetermined size, such alternative method contemplates the coating of existing solid surfaces with a thin coating of fluid and viscous material to be subsequently heated to obtain a solid surface covered with a thin coating of porous, ceramic or vitreous material.

In detail, once the thin coating layer has been deposited, the heating (and drying) step of the previously deposited homogeneous mixture follows, which can easily take place by means of a hot air flow.

For example, such heating and drying step can be carried out simply exposing the so coated surface to the atmosphere.

In fact, the in situ application of the process according to the present invention is particularly suitable for covering newly constructed or undergoing maintenance architectural elements, such as wall internal surfaces, for example inside or outside industrial buildings and warehouses, roofs, facades of buildings, or elements of road infrastructures, as elements at the edge of the roadway: retaining walls, concrete bridges and overpasses, safety barriers and sound-absorbing barriers, for example.

Going more specific and referring in general terms to a generic process according to the present invention, the polysaccharide binder can be any suitable polysaccharide, i.e. any completely soluble polysaccharide, compatible with the other elements of the mixture and able to guarantee an increase of the viscosity in the solvent medium. Preferably, the polysaccharide binder can be an alginate, more preferably sodium alginate. In particular, the binder, for example sodium alginate, can be dissolved in water at room temperature by mechanically stirring. At the addition of the cross-linking agent, i.e. a divalent metallic salt, during said step a) of the process, the gelation of the sodium alginate takes place immediately.

Then, when powder material comprising metallic oxides, i.e. silica fume, is added to said gelling solution obtained during step a), on the surface of the silica fume particles, a large number of silanol groups are deprotonated; thus, the bivalent cations dissolved in the mixture and coming from the cross-linking agent can react with the deprotonated silanoic groups of the silica fume, forming ionic bonds with the silanol groups thereof. Then, the so-modified surface of the silica fume particles can interact with the negatively charged alginate groups in order to promote the formation of new bonds and to obtain a stable material.

As anticipated in the summary, in an advantageous manner, such powder material can be a powder waste material deriving from industrial, civil or agricultural processes. According to this preferred embodiment, it is therefore possible to further enhance the entire production process, using materials otherwise destined for potentially non-remunerative uses and/ or to be discarded.

Next, it should be specified that such powder waste material, deriving from industrial, civil or agricultural processes, comprising inorganic oxides, is preferably silica fume and/ or wood ash and/ or coal ash and/ or desulfurization ash and/ or ash resulting from the combustion of sewage sludges, for example sludges obtained during a sewage treatment process. The above-mentioned waste materials have the best cost/ benefit ratio among the similar ones on the market. In fact, they are waste materials which have a low cost, mainly due to the easy availability and the simple preliminary treatments that they undergo before going on the market. At the same time, they are particularly suitable for use during the process according to the invention and for obtaining a product according to the invention with optimal characteristics, which will be described further on.

Preferably, the solvent is present in the gelling solution in an amount equal to 35-60 parts by weight and the polysaccharide binder is present in the gelling solution in an amount equal to 1- 10 parts by weight.

Preferably, the cross-linking agent is a water-soluble calcium or barium salt, more preferably it is selected from one of the elements of the group consisting of calcium iodate, calcium chloride, barium chloride and any combination of these elements. Even more preferably, the cross-linking agent is calcium iodate. Specifically, when the cross-linking agent is calcium iodate, it is mixed in such first step with the other elements of the mixture to be present in said gelling solution in an amount equal to 1- 10 parts by weight.

More preferably, in said homogeneous mixture said powder material is present in amounts equal to 25-55 parts by weight with respect to the parts by weight of the other components of said homogeneous mixture.

Furthermore, the chemical leavening agent is preferably an element of the group consisting of sodium hydrogen carbonate, ammonium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, an alkali metal salt of tartaric acid and any combination thereof.

More preferably, the chemical leavening agent is sodium hydrogen carbonate. When the chemical leavening agent is sodium hydrogen carbonate, it is mixed in the second step b) according to the present process to be present in said homogeneous mixture in an amount equal to 1- 15 parts by weight on the total weight of said mixture.

According to a preferred embodiment, during the step of adding under stirring a powder material to the gelling solution, it is possible to add titanium oxide and/ or zinc oxide and/ or any suitable catalyst with photo- catalytic properties and/or any mixture thereof. Specifically, when titanium oxide and/ or zinc oxide and/ or a mixture thereof is added, the titanium oxide and/ or zinc oxide and/ or a mixture thereof is present in the aforementioned homogeneous mixture in an amount between 1 and 10 parts by weight.

In a completely preferable manner, such predetermined temperature in a generic heating step of the homogeneous mixture or of the diluted homogeneous mixture is between 55°C and 90°C, even more preferably it is equal to about 80°C.

Indeed, the heat allows the hydrogen carbonate ion, or the carbonate ion present in the chemical leavening agent to release gaseous carbon dioxide: the progressive accumulation of this gas gives rise to the formation of bubbles in the highly viscous mixture in the process of solidification, which remain trapped therein.

In this way, the highly viscous material, drying out, necessarily becomes porous.

The choice of the type of chemical leavening agent is determined by the dispersibility of the same in the mixture, the temperature at which it decomposes to give CO₂, as well as the cost of the same.

On an equally preferable basis, this predetermined time in a generic heating step of a homogeneous mixture or of the diluted homogeneous mixture is comprised between 30 minutes and 3 hours, more preferably is about 60 minutes. Preferably, the porous solid material obtained by means of a generic process according to the invention can be subjected to a further step of aging. During this further step, the material is stored for a predetermined time at room temperature. More preferably, this predetermined time is greater than two weeks, even more preferably it is greater than three weeks. The present invention also refers to a porous, ceramic or vitreous material, obtainable by any process according to the present invention, generally comprising an amorphous phase, said porous material being obtained from powder materials, comprising inorganic oxides, preferably waste materials and deriving from industrial, civil or agricultural processes, wherein said porous material has a density between 150 kg/m³ and 300 kg/m³, preferably between 180 kg/m³ and 220 kg/m³ and has nano-pores with an average size less than or equal to 200 nm, preferably equal to or less than 150 nm.

In particular, the porous material according to the present invention has pores with a wide range of dimensions which are connected to one another. The pores are present in form of two different kind of pores, macropores, i.e. pores with the diameter between the 5 μπι and 50 μπι, and nanopores, i.e. pores with a diameter less than 1 μπι, in particular less or equal to 200 nm, preferably less than or equal to 150 nm.

The aforementioned nanopores can in their turn be present on the surface of the material according to the present invention as ink-bottle shaped pores, as better explained in the following experimental part.

Advantageously, said ink-bottle pores are the most suitable pores to act as particulate matter trap for ultrafine and fine particles, i.e. particles having a diameter less than 100 nm, which are the most harmful for the human body. More in detail, when particulate matter particles enter in such ink- bottle shaped pores, it results hard to exit, typically because of pore size and dimensions.

According to the present invention, with the expression "porous, ceramic or vitreous material, generally comprising an amorphous phase", it is meant that the material according to the present invention, when of the ceramic type, can often also comprise a crystalline phase, in addition to the amorphous phase.

The amorphous phase generally included in the material according to the invention can comprise inorganic oxides in an amount by weight equal to or greater than 10% with respect to the weight of said amorphous phase, more preferably greater than or equal to 30% with respect to the weight of said amorphous phase. The amount by weight of inorganic oxides included in the amorphous phase of the material in object depends on the type of material used in the process according to the invention.

For example, in the case of using a high silica content material, such as silica fume, the inorganic oxides included in the amorphous phase can be present in an amount by weight equal to or greater than 40%, preferably equal to or greater than 50% , more preferably equal to or greater than 60% , even more preferably equal to or greater than 70%.

Moreover, the specific weight of the porous material according to the invention can preferably be between 1600-2300, preferably between 1764- 2156 kg-rn V².

In particular, the amorphous phase of the material in object is substantially consisting of microscopic granules of inorganic material, deriving from powder materials, and comprising inorganic oxides, used in the production process, and a polymeric network of organic binder, deriving from the polysaccharide binder used in the production process.

Similarly, the polysaccharide binder included in the aforementioned amorphous phase can be an alginate.

Specifically, as already mentioned above, the individual chains of the polysaccharide network, especially when the used polysaccharide binder is an alginate, are linked to each other by "metal bridges" consisting of positive metal ions. More in detail, the metal bridges are consisting of calcium ions or barium ions deriving from a cross-linking agent used during the process for obtaining the porous material in object. Furthermore, the porous, ceramic or vitreous material, according to the invention can comprise from 70% to 100% by weight of the amorphous phase on the total weight of the material.

In fact, according to a particular embodiment of the present invention, the material according to the present invention can also comprise a crystalline phase from 0 to 30% by weight based on the total weight of the material.

The crystalline phase possibly included in the material according to the invention can in turn comprise calcium carbonate (CaCO₃), nahcolite (NaHCO₃) and calcium iodate monohydrate (Ca(IO₃)₂-H₂O), when calcium iodate is used as cross-linking agent, or it can comprise other salts, when other cross-linking agents are used.

Specifically, such crystalline phase can be present on the surface of the porous, ceramic or vitreous material, according to the invention as isolated and physically distinct crystalline formations.

Within the amorphous phase the material according to the present invention can further comprise a coloured pigment. Due to the presence of a coloured pigment, the material according to the present invention is more pleasing to the eye. In fact, in the absence of pigments, the material according to the invention may have a colour that ranges from white to dark grey.

More generally, the material according to the invention, due to its high porosity, is able of adsorbing polluting solid particles and organic macromolecules present in the atmosphere with which it comes into contact.

In particular, the material according to the invention is able of adsorbing heavy metals, removing them from the fluids with which the surface thereof is brought into contact. The material according to the invention is particularly suitable for adsorbing atmospheric particulate matter deriving from the combustion of fossil fuels or waste fuels and in adsorbing poly cyclic aromatic hydrocarbons.

In particular, the above-mentioned crystalline surface formations do not in any way negatively affect the properties associated with the material according to the invention.

Another aspect of the material according to the present invention is the fact of being able to be "regenerated" by simple washing with water.

Specifically, after exposure to polluted and charged with atmospheric particulate matter and/ or polluting organic macromolecules air, the material according to the invention can be effectively washed by simple application of a water jet on the surface of the same. As a result of the force exerted on the surface of the material by the applied water flow, the particulate matter and the organic substances adsorbed on the surface of the material according to the invention are removed and transported by the flow itself, sensibly cleaning the surface of the material so that it can adsorb further particulate matter and polluting molecules.

Among various characteristics and advantages, it has been observed that, in a material according to the present invention when first polluting organic substances, such as polycyclic aromatic hydrocarbons, are adsorbed on its surface and then it is hit by a light beam comprising ultraviolet radiation, such adsorbed organic pollutants undergo progressive degradation. At least, 20% by weight of the total adsorbed organic polluting compounds can be decomposed after few hours of exposition to a light beam comprising ultraviolet radiation.

Therefore, the material according to the invention is not only able of adsorbing possible polluting organic substances, removing them from the environment and purifying the air which contacts the surface thereof, but it can also catalyse the decomposition of such compounds to less polluting chemical species and, above all, less harmful to human health.

According to another embodiment, the porous material according to the present invention can comprise titanium oxide and/ or zinc oxide and/ or any catalyst with photo-catalytic properties and/ or any combination thereof.

A porous material comprising a catalyst with photo-catalytic properties shows an even higher capability to decompose organic polluting compounds adsorbed on its surface, when the latter is hit by a light beam (comprising UV radiation). According to the present embodiment, when porous material comprising titanium oxide is hit by a light beam (comprising UV radiation) more than 50% of the pollution substances can be decomposed.

With reference to what has been described in the previous paragraphs, the present invention also provides that the aforementioned porous, ceramic or vitreous material can be used as a filter for the adsorption of fine atmospheric particulate matter and/or organic contaminants, possibly present in the atmosphere. Specifically, as previously mentioned in relation to the process according to the invention, the material in object can be used as a coating for new or already existing buildings, for example during renovation, for example for coating roofs or walls/facades, or in the covering of road structural elements, newly built or already existing, for example during maintenance.

Particularly suitable is the use of the material according to the present invention as a facing for buildings or in the covering of road structural elements in urban centres, especially in historic city centres or near major communication arteries such as ring roads and access roads to cities, as well as in mountain areas, or areas located in the valley bottom, characterized by intense anthropic activity.

Having the a structure comprising pores with a wide range of dimensions connected with one another, macropores and nanopores, as already disclosed before, the use of the just-mentioned material according to the present invention is particularly effective as it allows to purify the polluted air directly in the proximity of the pollution source, such as particulate matter with particle of a large variety of dimensions, in particular particulate matter having particles with a diameter less than 100 nm ( PM 0.1 μπι) and polluting organic substances formed by combustion of fossil fuels in internal combustion engines or in boilers for houses/offices, particulate matter formed due to wear of the components constituting the braking systems of vehicles (cars and motor vehicles, rail transport vehicles), particulate matter formed by rubbing of tires on the roadway or particulate matter from industrial sources, such as incinerators, often located not far from residential areas.

In particular, when the material according to the present invention is used for the facing by means of an external surface coating of buildings or architectural elements exposed to weather, the material according to the present invention can be advantageously regenerated by rainwater action; the rainwater removes by washing the atmospheric particulate matter and the organic molecules adsorbed on the surface and in the micro surface cavities of the material according to the invention. The flow of formed water, wherein the particulate matter and the polluting organic molecules are dispersed, is naturally conveyed into the sewer due to gravity. Furthermore, the porous material according to the present invention can be produced as a manufactured product. Such manufactured product can be used as a filter for a polluted fluid, more precisely as a filter intended as a replaceable element, wherein such replaceable element is part of a more complex apparatus or system, able to remove impurities from a flow of a polluted fluid.

Moreover, always due to the high porosity, the material according to the present invention is able to effectively absorb sound waves. Consequently, when applied to walls of buildings or on the external surface of sound- absorbing barriers, for example, it may not only be useful in blowing down pollutants in the air, but it can also be very effective in reducing noise pollution which is often a non-secondary problem for the inhabitants of buildings located close to major road arteries or busy roads in urban centres. In conclusion, the process for obtaining a porous, ceramic or vitreous material from powder materials, comprising inorganic oxides, the process for applying a thin coating of a porous, ceramic or vitreous material, obtained from a powder material, comprising inorganic oxides, to a preexisting solid surface and the above-described porous, ceramic or vitreous material according to the present invention allow to obtain numerous advantages: the main one is to provide a ceramic-like or vitreous porous solid low-cost material with high capacity to adsorb on its surface atmospheric particulate matter and polluting organic macromolecules, such as poly cyclic aromatic hydrocarbons. A further advantage is certainly the provision of a material with a high added value due to the simple production process through which it is obtained and the optional re-use of a waste material such as coal and wood ashes, silica fume, desulphurisation ashes and ashes deriving from sewage sludges. In fact, some solid by-products deriving from combustion, such as those exemplified in the present disclosure, are commonly disposed in large amounts in conventional landfills, representing a cost at economic and environmental level.

Then, there are further advantages among which are listed: - the provision of an economic and ecological production process, with particular reference to the low temperatures required during the heating step;

- the possibility of obtaining and applying the material according to the present invention directly to the place of use, for example by means of a spray application technique with subsequent heating and cooling in situ;

- the provision of an easily washable material, whose adsorbing properties can be periodically regenerated by simple wash with water of the surface thereof; - the provision of a material with photo-catalytic properties which allows the gradual destruction of the polluting organic substances adsorbed on the surface thereof;

- the possibility of incorporating into the material according to the present invention a coloured pigment to make it more pleasing to the eye. Further characteristics and advantages of the invention will be shown from the following examples, given by way of non-limiting example with reference to the accompanying figures, wherein:

- Figure 1 shows a manufactured product obtained based on a process according to the invention (on the right), and a manufactured product based on a process according to the invention followed by a sintering step (on the left);

- Figure 2 shows the cross-section of a detail of the manufactured product obtained based on a process according to the invention, shown in Figure 1 ;

- Figure 3 shows a photography of the material obtained by a process not according to the invention;

- Figure 4 shows an image taken by scanning electron microscope representing the surface of a sample of the material according to the invention, obtained with the process according to the invention;

- Figure 5 shows an enlargement of a detail of the image shown in Figure 3; - Figure 6 shows an enlargement of a different detail of the image shown in Figure 3;

- Figure 7 shows an enlargement of a different detail of the image shown in Figure 3;

- Figure 8 shows an X-ray diffractogram of a sample of material according to the invention, obtained based on a process according to the invention;

-Figure 9 shows N2 physisorption isotherms and pore size distributions for a sample of the porous material according to the invention;

- in Figure 10 two different images taken with a light microscope are shown, on the left a sample of material according to the invention and, on the right, a sample of material according to the invention subjected to an adsorption test;

- in Figure 1 1 an image taken with a conventional camera is shown, representing on the right a sample of material according to the invention after being subjected to an adsorption test and, on the left, a sample of material according to the invention subjected first to a test of adsorption and then to a washing test.

Example 1 : obtaining of a ceramic porous material obtained from silica fume

A sample of ceramic porous material was prepared from grey silica fume.

First, to 50 ml of demineralized water (milli-Q® ultrapure water) 1.2 g of sodium alginate and 2 g of calcium iodate were added under vigorous stirring. The mixture was left under stirring for a few minutes until a very viscous transparent solution was obtained. To the thus obtained viscous solution, first 35 g of grey silica fume were added under vigorous stirring, from companies processing iron-silicon alloys, then 10 g of sodium bicarbonate. The thus obtained mixture was left under stirring for a few minutes until a homogeneous mixture with a uniform anthracite grey colour was obtained.

Subsequently, 30 ml of the thus obtained homogeneous mixture were arranged into an aluminium mould. The thus filled mould was then placed on a heating plate of the Arex type of Velp Scientifica, set at a temperature of 80 °C.

After 60 minutes, the mould containing the mixture was taken off the plate; the homogeneous mixture laid in the mould showed the consistency of a very rough solid disk which was visibly porous on the surface. The mould containing the solid disk was then placed in a dry environment at a temperature of about 20°C for four weeks.

The thus obtained solid disk had a grey colour, slightly less intense than the disk immediately after picking up the mould from the heating plate. By exerting a modest pressure, the thus obtained solid disk was broken into two parts. The inner surface at the sectional fracture of the thus obtained parts showed a porous structure also inside the solid disk.

Example 2: comparative test between a ceramic porous material obtained from silica fume at a low temperature and a similar material obtained by sintering According to the process already described in Example 1 , a homogeneous mixture comprising grey coloured silica fume was obtained.

Subsequently, 60 ml of the thus obtained homogeneous mixture were extruded directly onto an Arex type heating plate by Velp Scientifica, using a totally conventional 20 ml polypropylene syringe, obtaining two different mixtures with a "waffle" shape.

The thus obtained mixtures were heated for 60 minutes at a temperature of 80°C.

Subsequently, the solidified mixtures were picked up from the plate, obtaining two manufactured products. A first thus obtained manufactured product was then placed in a dry environment at a temperature of about 20°C for four weeks.

At the same time, a second manufactured product was subjected to a sintering treatment in a tubular oven at a temperature of 500°C, for a total time of 2 hours. The thus obtained first mixture and the second mixture are shown in Figure 1.

The consistency of the first mixture and the consistency of the second manufactured product were totally comparable.

In Figure 2 a cross-section of the first manufactured product obtained according to the present example is shown: the internal macroporous structure of the thus obtained manufactured product is evident.

Example 3: material obtained by a process not according to the invention not involving the formation of a gelling solution

A process not according to the present invention is carried out with the aim to obtain a porous material with the same reagents and material used in the process according to the present invention.

Firstly, 50 ml of demineralized water (milli-Q ultrapure water) were mixed with 35 g of silica fume. Under stirring, 1.2 g of sodium alginate are added.

The formation of a gelling solution is not observed. Then, under vigorous stirring 2 g of calcium iodate are added to the mixture thus obtained. At the end, 10 g of sodium bicarbonate are added.

Subsequently, 30 ml of the thus obtained mixture were arranged into an aluminium mould.

The mould, thus filled with the above mixture was then placed on a heating plate of the Arex type of Velp Scientifica, set at a temperature of 80 °C.

After 60 minutes, the mould containing the mixture was taken off the plate; the mixture laid in the mould was not homogeneous and very brittle.

The homogeneous mixture disk obtained in Example 1 was compared with the material obtained with a process not according to the present invention (Figure 3).

The latter lacked consistency and showed several cracks running from its upper surface to its lower surface, rather showing the aspect of a single- piece solid material, having a specific and characteristic porous structure, of the former (as showed in detail in the following examples). Example 4: characterization of the ceramic porous material obtained from grey silica fume

The mixture of Example 1 obtained by a process according to the invention with a final "aging" at room temperature for four weeks was characterized by a scanning electron microscope (SEM), by X-ray diffraction spectroscopy (XRD) and by N2 physisorption.

In Figure 4, in Figure 5, in Figure 6, and in Figure 7, SEM images of the surface of the solid mixture of the Example 1 are shown, obtained with grey silica fume and with a process according to the invention. In Figure 4 it is clearly noted that on the surface of the material widespread needle-like crystalline formations are present, in sharp contrast with a prevalent and darker amorphous phase.

In Figure 5 an enlargement of such needle-like crystalline formations present on the surface of the sample shown in Figure 4 is shown. In Figure 6 an enlargement of the sample surface shown in Figure 4 in an area without such crystalline formations is shown. It evident that two different kind of pores macropores are present, i.e. pores with a diameter around 10 μπι, indicated in upper image c with dashed arrows, and nanopores, i.e. pores with a diameter less than 1 μπι, indicated in upper image d with dashed arrows.

In Figure 7 a further enlargement of the sample surface of Figure 5 is shown. It evident that pores with a diameter less than 200 nm are present.

In Figure 8 a diffractogram of a sample of material taken from the surface of the mixture according to Example 1 is shown, obtained with grey silica fume and with a process according to the invention.

The presence of the characteristic peaks of calcium carbonate salts, nahcolite and calcium iodate monohydrate are observed; this analysis confirms the chemical nature of the crystals observed during the scanning microscope analysis. In Figure 9 N2 physisorption isotherms and pore size distributions for a sample of the porous material according to the present invention are shown. Measures are made in adsorption (ADS) and desorption (DES) to evaluate the pore dimensions.

Nitrogen (N2) physisorption measurements at the liquid nitrogen temperature was been employed to investigate the textural properties of the materials. Prior measurements 500 mg of each sample were degassed at 100°C overnight.

N2 physisorption measurements, realized with a Micromeritics ASAP 2020 analyzer, have been made in order to investigate the morphologic structure of the material and the dimensions of the pores having a diameter equal to or less than 200 nm.

Following IUPAC recommendations, the isotherms shown in Figure 9 are IV isotherms, typical of mesoporous materials. The cumulative pore volume is low (10- 12 m² g ¹). Notably, pore size distributions calculated from the desorption branch of the isotherms show relative maxima (at 15 and 30 nm) at lower values with respect to those calculated from the correspondent adsorption branch (1 10 nm). This behaviour indicates that ink-bottle pores are present on the surface of the material, as also suggested by the hysteresis loops observed in the N2 physisorption isotherms.

The biaxal mechanical strength of the porous material described in Example 1 was also tested using a ball on three ball test according to ASTM F 394. The mechanical strength resulted in the range of 1-2 Mpa.

Such result was extremely good, considering that mechanical strength in porous material results affected by porosity.

Considering its considerable high mechanical strength and its low density (about 180-220 kg/m³), the material according to the present invention can be definitely used as a lightweight plaster.

Example 5: ceramic porous material obtained from white silica fume and adsorption test

By the same process already described in Example 1 , a homogeneous mixture comprising white silica fume was obtained.

Subsequently, 30 ml of the thus obtained homogeneous mixture were placed in an aluminium mould.

The thus filled mould was then placed on a heating plate of the Arex type of Velp Scientiflca, set at a temperature of 80°C.

After 60 minutes, the mould containing the mixture has been picked up from the plate; the homogeneous mixture laid in the mould showed the consistency of a very rough white solid disk on the surface.

The mould containing the solid disk was then placed in a dry environment at a temperature of about 20°C for four weeks.

The thus obtained manufactured product was broken in several parts to first visually verify the internal structure: the material proved to be visibly porous both externally and internally.

Subsequently, a portion of the manufactured product was subjected to an adsorption test for the verification of the particulate matter trapping properties of the material. The material was placed in contact with a flow of exhaust gas from the exhaust pipe of a diesel engine car for 15 minutes, at a pressure of 1 atm and at a temperature of about 22°C.

In Figure 10 two different images taken with an optical microscope are shown; on the left an image taken on the sample before being subjected to the adsorption test, on the right an image of the sample after being subjected to the adsorption test.

From Figure 10 it is evident that the tested material according to the invention is particularly suitable, in general, for the adsorption of pollutants (presumably largely solid particulate matter) on its porous surface.

The samples of Figure 10 before and after the adsorption test was analysed by EDS (Energy Dispersive X-ray Spectroscopy). The sample (sample b) analysed after the exposition to diesel emissions contains a large amount, more than 23% in weight on its total weight of carbon on its surface. A comparative table, comprising the results of EDX analysis made on the two samples follows: Element C O Na Si Ca Ti I

(% w/w)

Sample / 39.44 1.44 51.27 1.01 4.98 1.87 before

exposition

(a)

Sample 23.35 39.69 22.97 1 1.63 / 0.76 1.60 after

exposition

(b)

Example 6: ceramic porous material obtained from white silica fume and washing test

The sample of manufactured product subjected to a capture test of the particulate matter according to the previous example and shown in Figure 10 was then subjected to a washing test.

The said sample was placed in a beaker and was washed with 20 ml of demineralized water (milli-Q® ultrapure water) with the help of a syringe.

Figure 1 1 shows the comparison between a sample of porous material according to the invention after exposure to a flow of exhaust gas coming from an exhaust pipe of a diesel engine according to the method of the previous example (on the left) and a sample of the same type subsequently subjected to a washing operation.

From the comparison between the two different samples shown in Figure 1 1 , it is evident how the material according to the invention is easily washable with a modest flow of water, which can easily remove the dark polluting solid material adsorbed on the surface of the porous material.

Example 7: ceramic porous material obtained from grey silica fume and adsorption test of polycyclic aromatic hydrocarbons

A portion of the manufactured product of Example 1 weighting 0.66 g and obtained by a process according to the invention, with a final "aging" at room temperature for four weeks, was tested for the adsorption of polycyclic aromatic hydrocarbons. The sample was placed in a beaker containing a standard solution of polycyclic aromatic hydrocarbons (PAH) containing acenaphthylene with a concentration of 20 g/L and acenaphthene with a concentration of 20

The sample was left soaking for 60 minutes.

Subsequently, the adsorption capacity in reference to the PAHs present in the standard solution by mass spectroscopy was evaluated, comparing the intensity of the characteristic peaks of the above-mentioned PAHs in the standard solution with that of the same peaks in the solution after the soaking of the sample for 60 minutes.

The outcome of the test was particularly successful as it was estimated that more than two fifths of acenaphthylene and about one third of the acenaphthene present in the standard solution were adsorbed from the sample under examination. Example 8: ceramic porous material obtained from grey silica fume and decomposition test of polycyclic aromatic hydrocarbons

A sample of ceramic porous material was prepared from grey silica fume.

First, to 50 ml of demineralized water (milli-Q® ultrapure water) 1.2 g of sodium alginate and 2 g of calcium iodate were added under vigorous stirring. The mixture was left under stirring for a few minutes until a very viscous transparent solution was obtained. To the thus obtained viscous solution, first 35 g of grey silica fume were added under vigorous stirring, from companies processing iron-silicon alloys, then 2 g of titania, and finally 10 g of sodium bicarbonate. The thus obtained mixture was left under stirring for a few minutes until a homogeneous mixture with a uniform anthracite grey colour was obtained.

Subsequently, 30 ml of the thus obtained homogeneous mixture were arranged into an aluminium mould.

The thus filled mould was then placed on a heating plate of the Arex type of Velp Scientifica, set at a temperature of 80°C.

After 60 minutes, the mould containing the mixture has been picked up from the plate; the homogeneous mixture laid in the mould showed the consistency of a very rough solid disk which was visibly porous on the surface.

The thus obtained solid disk had a grey colour, slightly less intense than the disk immediately after picking up the mould from the heating plate.

A portion weighting 0.66 g of the thus obtained disk has been tested for the adsorption of poly cyclic aromatic hydrocarbons, exactly following the process described in Example 7.

Following the soaking in the PAH-containing solution, the sample was stored overnight in a dry environment at a temperature of 20°C.

The following morning, the sample was subjected to a decomposition test by subjecting it to a beam of UV light generated by a Philips UV lamp, emission in the range 340-410 nm with a maximum of 365 nm, for 12 hours.

Then, the amount of PAH adsorbed on the sample surface following the decomposition test and subsequently the decomposition capacity with reference to the PAHs present in the standard solution by mass spectroscopy were measured.

The amount of PAHs adsorbed on the surface of the sample measured in Example 7 was compared with the amount of PAHs measured on the sample of this example after being subjected to the decomposition test.

The outcome of this comparison showed that about 90% of the acenaphthene and 90% of the acenaphthylene adsorbed on the sample was decomposed following the decomposition test. The material according to the invention has therefore shown an excellent ability to decompose the polycyclic aromatic hydrocarbons adsorbed on its surface when subjected to UV radiation. Example 9: ceramic porous material obtained from grey silica fume and adsorption test ultrafine air particulate matter ( PM 0.1 mm) A portion of the manufactured product of Example 1 weighting 0.843 g and having a surface area of 4.15 (±0.01 ) cm², obtained by a process according to the invention, with a final "aging" at room temperature for four weeks, was tested for the adsorption of poly cyclic aromatic hydrocarbons. Firstly, the sample was conditioned at about 105°C for 6 hours before its use, according to ASTM D6552 - 06 technique.

Mettler Toledo XS3DU model balance operating at 12 V and 150 mA was employed for samples weight.

Then, a burning incense stick was put on a working bench. The adsorbing material was placed on a support at a distance of about 30 cm from the particle source (burning incense emits particles with a relatively close size distribution: the average particle diameter is close to 100 nm; Indoor Air, 2010, 20, 147- 158, "Characterization of particles emitted by incense burning in an experimental house"). When the first incense stick finished to burn, the weight of the sample was evaluated. Then, an additional incense stick was burned, and so on.

In order to evaluate the maximum amount of ultra-fine particulate that can be trapped by the porous material according to the present invention, the experiment proceeded with the same procedure till a stable porous material mass was obtained (6 incense sticks were burnt in total).

In the following table, the so obtained results are reported.

Therefore, it results from this example that the sample of the material according to the present invention is able to adsorb at least 2.4 mg/cm² of particulate matter having an average particle dimension lower than 1 μιη. Example 10: obtaining a ceramic porous material obtained from coal ash

A sample of ceramic porous material was prepared from coal ash.

First, 1.2 g of sodium alginate and 2 g of calcium iodate were added under vigorous stirring to 50 ml of demineralized water (milli-Q® ultrapure water). The mixture was left under stirring for a few minutes until a very viscous transparent solution was obtained.

To the thus obtained viscous solution, first 37 g of coal ashes, from coal- fired thermal power plants, were added with vigorous stirring, then 7 g of sodium bicarbonate. The thus obtained mixture was left under stirring for a few minutes until a homogeneous mixture with a dark grey, almost black, uniform colour was obtained.

After 60 minutes, the mould containing the mixture has been picked up from the plate; the homogeneous mixture laid in the mould showed the consistency of a very rough solid disk which was visibly porous on the surface. The mould containing the solid disk was then placed in a dry environment at a temperature of about 20°C for four weeks.

The thus obtained solid disk had a dark grey colour, slightly less intense than the disk immediately after being picked up from the mould from the heating plate. By exerting a modest pressure, the thus obtained solid disk was broken into two parts. The inner surface at the sectional fracture of the thus obtained parts showed a porous structure even inside the solid disk.

Example 1 1 : obtaining a ceramic porous material obtained from wood ash

A sample of ceramic porous material was prepared from wood ash.

Firstly, 1.2 g of sodium alginate and 2 g of calcium iodate were added under vigorous stirring to 45 ml of demineralized water (milli-Q® ultrapure water). The mixture was left under stirring for a few minutes until a very viscous transparent solution was obtained.

To the thus obtained viscous solution, firstly 45 g of wood ash (beech) were added under vigorous stirring, then 12 g of sodium bicarbonate. The thus obtained mixture was left under stirring for a few minutes until a homogeneous mixture of uniform graphite grey colour was obtained.

Subsequently, 25 ml of the thus obtained homogeneous mixture were arranged into an aluminium mould.

The thus obtained solid disk had a markedly grey colour, slightly less intense than the disk immediately after being picked up from the mould from the heating plate. By exerting a modest pressure, the thus obtained solid disk was broken into two parts. The inner surface at the sectional fracture of the thus obtained parts showed a porous structure even inside the solid disk.

Claims

1. A process for obtaining a porous, ceramic or vitreous, material from powder materials comprising inorganic oxides, said process comprising the following steps: a) mixing under stirring a solvent, preferably water, a polysaccharide binder and a cross-linking agent, until a gelling solution is obtained; b) adding under stirring a powder material, comprising inorganic oxides, and a chemical leavening agent to said gelling solution, until a homogeneous mixture is obtained; c) heating said homogeneous mixture to a predetermined temperature and to a predetermined time to obtain a solid porous material, wherein said predetermined temperature is between 35°C and 1 10°C, and said time is longer than 45 minutes; d) cooling to room temperature said solid porous material.

2. Process according to claim 1 , said step c) of heating said homogeneous mixture is carried out by putting said homogeneous mixture into a mould.

3. A process for the application of a coating of a porous, ceramic or vitreous material, obtained from powder materials comprising inorganic oxides, to a pre-existing solid surface, said process comprising the following steps: a') mixing under stirring a solvent, preferably water, a polysaccharide binder and a cross-linking agent, until a gelling solution is obtained; b') adding under stirring a powder material, comprising inorganic oxides, and a chemical leavening agent, to said gelling solution, until a homogeneous mixture is obtained; c') adding under stirring a further portion of said solvent to said homogeneous mixture until a diluted homogeneous mixture is obtained; d') applying said diluted homogeneous mixture to a pre-existing solid surface to form a coating of said diluted homogeneous mixture on said hard surface, preferably wherein said coating has a thickness ranging from 0.1 mm to 5 mm; e') heating said diluted homogeneous mixture coating at a predetermined temperature and to a predetermined time to obtain a coating of porous solid material, wherein said temperature is between 35°C and 1 10°C and said time is longer than 45 minutes; f) cooling to room temperature said coating of porous solid material.

4. Process according to claim 3, wherein said step d) of applying the diluted homogeneous mixture to said pre-existing solid surface is carried out by spraying.

5. Process according to any one of the preceding claims, wherein said powder material is a waste material, coming from industrial, civil or agricultural processes.

6. Process according to claim 5, wherein said powder material is selected from the group consisting of silica fume, wood ash, coal ash, desulphurization ash, ash coming from the combustion of sewage sludges and any combination thereof.

7. Process according to any one of the preceding claims, wherein said polysaccharide binder is an alginate.

8. Process according to any one of the preceding claims, wherein said solvent is present in said gelling solution in an amount equal to 35-60 parts by weight and said polysaccharide binder is present in said gelling solution in an amount equal to 1- 10 parts by weight.

9. Process according to any one of the preceding claims, wherein said cross- linking agent is a calcium salt or a barium salt soluble in an aqueous medium, being said cross-linking agent preferably selected from any of the elements of the group consisting of calcium iodate, calcium chloride, barium chloride and any combination of these elements, more preferably being said cross-linking agent calcium iodate and being said cross-linking agent present in said gelling solution in an amount equal to 1- 10 parts by weight.

10. Process according to any one of the preceding claims 8 or 9, wherein in said homogeneous mixture said powder material is present in an amount equal to 25-55 parts by weight.

1 1. Process according to any one of the preceding claims, wherein said chemical leavening agent is an element of the group consisting of sodium hydrogen carbonate, ammonium hydrogen carbonate, potassium hydrogen carbonate, sodium carbonate, an alkali metal salt of tartaric acid and any combination of these elements, preferably being said chemical leavening agent sodium hydrogen carbonate and being said chemical leavening agent present in said homogeneous mixture in an amount equal to 1- 15 parts by weight.

12. Process according to any one of the preceding claims, wherein said predetermined temperature is comprised between 55°C and 90°C, preferably being said predetermined temperature equal to 80°C.

13. Process according to any one of the preceding claims, said process comprising a further step of aging, being said porous solid material or said coating of porous solid material kept at room temperature for a predetermined time, preferably being said predetermined time longer than two weeks, more preferably longer than three weeks.

14. A porous, ceramic or vitreous material, obtainable from a process according to any one of the preceding claims, wherein said material is obtained from powder materials, preferably waste materials and coming from industrial, civil or agricultural processes, comprises an amorphous phase, has a density comprised between 150 kg/m³ and 300 kg/m³, preferably between 180 kg/m³ and 220 kg/m³, and shows nano-pores with an average size less than or equal to 200 nm, preferably less than or equal to 150 nm, said amorphous phase comprising inorganic oxides in an amount by weight higher than or equal to 10% compared to the weight of said amorphous phase, preferably said amorphous phase comprising inorganic oxides in an amount by weight higher than or equal to 30% compared to the weight of said amorphous phase.

15. Porous material according to claim 14, wherein said amorphous phase comprises a polysaccharide organic binder, preferably being said organic binder an alginate.

16. Use of a material according to claims 14 or 15 as a filter for the adsorption of fine atmospheric particulate matter and/ or organic contaminants, preferably for the facing of buildings, roofs or for the covering of road structural elements.

17. Manufactured product made with a porous material according to claims 14 to 15, being said manufactured product suitable for the use as a filter for a fluid comprising polluting substances.