ES2921125A1 - High speed adsorbent material (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

High speed adsorbent material. The present invention refers to an adsorbent material characterized by that it is a solid macroporous foam, which reaches the balance of adsorption and/or absorption in a few seconds, its obtaining procedures, as well as its uses in purifying/decontamination of waters through Adsorption and/or physical and/or chemistry processes of toxic elements such as lead, zinc, cadmium, and other heavy metals on adsorbent materials. This invention is aimed at the environmental sector, especially water and waste management, or in the prevention and correction of water or soil contamination by heavy metal. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

HIGH SPEED ADSORBENT MATERIAL

The present invention refers to an adsorbent material characterized in that it is a rigid material, which reaches adsorption and/or absorption equilibrium in a few seconds, its procedures for obtaining it, as well as its uses in water purification/decontamination treatments by means of processes of adsorption and/or physical and/or chemical absorption of toxic elements such as Lead, Zinc, Cadmium, and other heavy metals, as well as pharmaceutical products on adsorbent materials. This invention is directed to the environmental sector, especially to water and waste management, or to the prevention and correction of water or soil contamination by heavy metals.

BACKGROUND OF THE INVENTION

Heavy metal contamination is a very important environmental problem worldwide, due to its toxicity, cumulative capacity in living tissues and potential capacity to cause cancer [N. K. Srivastava and C. B. Majumder, "Novel biofiltration methods for the treatment of heavy metals from industrial wastewater," J. Hazard. Mater., vol. 151, no. 1, pp. 1-8, 2008]. The Pb ion ( II) is considered one of the most important toxic pollutants due to its high stability.Wastewater from some industrial sectors (painting and printing, car batteries, petrochemical industries, mining, etc.) contains a high concentration of Pb ions (II ) that would need to be reduced, and if possible, eliminated. The water quality standard indicates that the concentration of Pb (II) should be between 0.5-1.0 ppm. On the other hand, the World Organization for Health (WHO) recommends a maximum allowable concentration of lead in drinking water of 0.01 ppm, however, industrial wastewater can contain lead concentrations of up to 200-500 ppm.

For the removal of lead and other heavy metals, as well as organic contaminants, both in drinking water and wastewater, there are different methods such as chemical precipitation, filtration, ion exchange, chemical oxidation or reduction, etc., which will be described. later. However, the applicability of these methods has some disadvantages, such as high cost due to high energy, reagent and operational requirements, low selectivity, generation of toxic sludge or other waste products, which are difficult to dispose of.

Among the most used methods and products for the decontamination of water by heavy metals, the following can be mentioned:

1. Chemical precipitation. It is one of the most used methods. It is based on the precipitation of Pb (II) in a basic medium through the formation of Lead hydroxide. It is an expensive and at the same time polluting method, since sulfides are usually used as precipitating agents.

2. Reverse osmosis. It is a process of permeation through a membrane for separation by controlled diffusion or screening. It has the ability to select elements as small as 0.1 micrometers.

3. Membrane filtration. This technology has high efficiencies, requires little space, is easy to operate, and is not selective, but it does generate a large amount of sludge that contains the polluting metals themselves. It consists of passing the fluid through a membrane with a determined pore size.

4. Ion exchange. A solid substrate with acidic or basic functional groups on its surface is used. These solid substrates are usually synthetic resins placed in a column through which the fluid to be treated is passed. The resin, depending on the surface groups, is more selective towards one type of contaminant or another. This method is particularly suitable for the removal of heavy metals from water, but its high cost and the partial removal of other ions limits its use.

5. Ultrafiltration: It is a selective fractionation process using pressures up to 145 psi (10 bar). Concentrates suspended solids and solutes with a molecular weight greater than 1000 amu.

6. Nanofiltration: It is a relatively recent water treatment technique that uses membranes with very small pores (<1 nm) and operating pressures in the range of 10-50 bar. It is a promising and innovative technology that can be widely applied in drinking water and industrial effluent treatment. 7. Adsorption and/or absorption: Adsorption and/or absorption is a process of extracting a material from a solution by concentrating it on the surface of a phase, generally solid, known as an adsorbent. Among the most used materials as adsorbents we can mention: Active carbon, carbon nanotubes or zeolites.

Of all of them, the method that has been most studied according to the consulted bibliography, is the adsorption and/or absorption of polluting metals on different types of adsorbent materials.

Silvia C.R. Santos et al. [Silvia C. R. Santos et al., "Tannin-Adsorbents for Water Decontamination and for the Recovery of Critical Metals: Current State and Future Perspectives." Biotechnol. J. 2019, 14, 1900060] listed a large number of tannin-based adsorbent products for the removal of various contaminating metals such as Pb (II), Cu(II), Cr(VI), etc., with balance between 1h and 24h.

Zhu et al. [Zhu, W., et al. "Synthesis of spherical mesoporous silica materials by pseudomorphic transformation of silica fume and its Pb2+ removal properties.” Microporous and Mesoporous Materials Volume 222, 1 March 2016, Pages 192-201] developed mesoporous spherical materials based on cetyltrimethylammonium bromide as template and fumed silica as silica source.The maximum adsorption and/or absorption achieved was of the order of 59 mg/g The specific surface of these particles is between 15 and 30 m2/g The equilibrium time is approximately 100 minutes.

Prado et al. [Prado, A., et al. "Thermodynamic aspects of the Pb adsorption using Brazilian sawdust samples: Removal of metal ions from battery industry wastewater” Chemical Engineering Journal Volume 160, Issue 2, 1 June 2010, Pages 549-555] used wood residues for Pb removal (II ).The specific surface area is between 1.5 and 3.5 m2/g, with the maximum adsorption and/or absorption of Pb (II) being 145 mg/g.Equilibrium is obtained after a time of contact between the adsorbent and the higher adsorbate at 60 minutes.

For the removal of the Pb(II) ion from water, other researchers have used different types of carbon (activated carbon, carbon nanotubes and graphene).

Sweetman et al. [Sweetmann, M., et al., "Activated Carbon, Carbon Nanotubes and Graphene: Materials and Composites for Advanced Water Purification”. J. of Carbon Research, C 2017, 3, 18] do a complete literature review on this type of materials for the elimination of polluting elements Carbon-based materials have the fundamental characteristic of presenting high values of specific surface (up to 2,500 m2/g), which provides them with a large number of surface active centers where polluting elements can interact. However, for the original, unmodified carbon, the removal is relatively low, in the order of 3 mg/g. When this original carbon is modified, the removal properties are notably increased. In the case of graphene, the authors indicate values elimination of Pb(II) of the order of 90 mg/g When graphene is doped with other types of products, such as polydopamine, the elimination of Pb(II) increases up to 336mg/g.

Fu et al. [Fu, R., et al. "Adsorptive removal of Pb(II) by magnetic activated carbon incorporated with amino groups from aqueous Solutions”. Journal of the Taiwan Institute of Chemical Engineers Volume 62, May 2016, Pages 247-258] use activated carbon doped with iron oxide particles and SiO2 superficially modified with amino groups.These materials have a specific surface of approximately 49 m2/g.They indicate that the adsorption and/or absorption equilibrium is reached after 20 hours, with the maximum adsorption and/or absorption capacity being 104 .2mg/g.

For their part, and in the case of carbon nanotubes, Kabbashi et al. [Kabbashi, NA et al., "Kinetic adsorption of application of carbon nanotubes for Pb(II) removal from aqueous solution” Journal of Environmental Sciences (China), 01 Jan 2009, 21(4):539-544] indicate that the maximum concentration of Pb(II) removed is 96.03% at pH=5, and a contact time of 80 minutes.

Although the adsorption and/or absorption method for the elimination of organic and inorganic contaminants present in the water is considered satisfactory, especially when working at low concentrations of contaminant, to date, complete adsorption is not achieved, and furthermore, the times of equilibrium achieved up to this moment are relatively high, that is to say, that the maximum adsorption and/or absorption is achieved after one hour or more and in pH conditions for the maximum adsorption and/or absorption that are far from the pH of the drinking water, so it is necessary to add acidifiers or other reagents that are then necessary to eliminate.

DESCRIPTION OF THE INVENTION

In a first aspect, the present invention refers to an adsorbent material characterized in that it is a rigid material of alkoxysilane polycondensated with polyphenols; with a BET surface area measured by N 2 adsorption desorption, between 0.3 m 2 /g and 0.6 m 2 /g in a Micromeritics TRISTAR equipment; where it presents at least the following bands in the infrared spectrum with maxima at the following wave numbers 453±10 cm-1, 1077±10 cm-1 obtained in a Perkin-Elmer Spectrum BX equipment; and where the X-ray diffraction spectrum performed on a Bruker D8 Adavance spectrometer with a Linxeye detector with a Cu wavelength of A=1.5408 Á presents an amorphous type diffraction maximum between 20° and 24°.

With this material, the equilibrium of the maximum adsorption and/or absorption of contaminants is reached in a range between 2 s and 120 s, due to the fact that the active centers of the material in the plurality of alkoxysilanes distributed through the pores of the rigid material are more numerous. and with greater accessibility, since the rigid material presents covalent bonds between Si-O-C distributed heterogeneously throughout the material, as can be seen in the infrared bands where a band at 453 cm-1 is observed, which is due to vibration. bending of the O-Si-O bond, said band appears for the material with low concentrations of the starting equivalent alkoxysilane, and its intensity increases continuously as said concentration increases. The highest intensity is for the highest molar ratio used in this study. In the same way, the tension vibration band of the Si-O-Si bond appears at 1077 cm-1, which also increases as there is more amount of alkoxysilane in the solid material. In addition, another advantage associated with the use of said material is that the water in which it is going to be used to absorb contaminants is at a pH of between 3 and 7, which includes neutral pH, so that prior to its use would not require prior treatment of a stream or a drinking water reservoir.

In the present invention, an "amorphous type diffraction maximum" is understood as that maximum of diffraction intensity that does not correspond to a single displacement value 20, but rather forms an r-x dispersion curve showing one or two maxima with a peak width that can reach up to 10° wide, due to the absence of crystalline periodicity in the material and to the fact that only the short-range order is maintained.

The adsorbent material described above is characterized in that it is obtained by the process described in the second aspect of the present invention.

In a preferred embodiment, the density of the synthesized material obtained by Helium pycnometry is between 1.2 and 2.0 g/cm3.

In another preferred embodiment, the adsorbent material has a molar ratio in terms of starting alkoxysilane and polyphenol equivalents of between 1 and 99.

In a more preferred embodiment, the alkoxysilane is selected from Tetraethyl orthosilicate (TEOS), Triethoxy silane (TREOS), Methyl triethoxy silane (MTREOS), Dimethoxy diethyl silane (DMDES), Tetramethyl orthosilicate (TMOS), Methyl trimethoxysilane (MTMOS), Methyl diethoxy silane (MDES), and any combination of the above . In another more preferred embodiment, the polyphenol is selected from tannic acid and tannins.

In the present invention, "tannins" are understood as a type of polymeric compounds present in plants. They contain phenolic groups that must be mostly free and unsubstituted, with a molecular weight between 500 and 20,000 amu, and are generally soluble. in water.

In another more preferred embodiment, the alkoxysilane is TEOS and the polyphenol is tannic acid.

In an even more preferred embodiment, the molar ratio between TEOS and tannic acid is between 1 and 99, more preferably between 1 and 30, and even more preferably between 1 and 10. The adsorbent material with said molar ratio exhibits adsorption and/or absorption of more than 95% of the Pb(II) present in an aqueous solution. This may be due to a correct distribution of the superficial active centers. For low molar ratios of TEOS and tannic acid, the highest concentrations of surface groups come from tannic acid, which does not present a high adsorption and/or absorption. Similarly, for high concentrations of TEOS, most of the surface groups are OH that can be neutralized by water molecules. However, for intermediate concentrations, the ratio of surface groups from both compounds (TEOS and tannic acid) are not shielded and/or neutralized, which produces a better and higher adsorption and/or absorption.

Another aspect of the invention is the procedure for obtaining the adsorbent material described above, characterized in that it comprises the following steps:

a) hydrolyzing an alkoxysilane;

b) dissolving a polyphenol in an aqueous solution of furfuryl alcohol and formaldehyde, and subsequently adding ethyl ether and p-toluenesulfonic acid to the mixture obtained at a temperature between 15 °C and 35 °C;

c) add the solution obtained in step (a) to the solution obtained in step (b) at a temperature between 10 °C and 80 °C and keep stirring for a time between 1 and 10 minutes and then leave at rest for a time between 30 minutes and 130 hours; Y

d) drying the solid material obtained in step (c) at a temperature between 50 °C and 200 °C for a time between 10 min and 100 h.

The advantage of the method is that the metal atom is linked to different groups that can be hydrolysable and non-hydrolysable, and that being in a liquid state allows the mixture obtained to be practically total, thus facilitating the sol-gel process that occurs. in step (c).

In a preferred embodiment of the process, the hydrolysis in step (a) is carried out in an acidic or basic medium. Acidic or basic catalysts, generally HCI and NH4OH, are used to increase the rate of the sol-gel reaction. When the pH of the medium is less than 2.5, hydrolysis occurs rapidly compared to the polymerization and condensation reaction. When the pH of the medium is greater than 2.5, the hydrolysis reaction is fast, as are the polymerization and condensation reactions, obtaining strongly cross-linked polymers generating three-dimensional structures. The final form of the product is highly dependent on the pH of the reaction. Thus, if the catalyst is NH4OH, the gel obtained is made up of numerous spherical particles, while if the catalyst is HCl, said particles are not obtained. In turn, if the pH is acidic, the gelation rate is ten times lower than if the catalyst is basic, and branched structures are obtained.

In a more preferred embodiment, the alkoxysilane is selected from Tetraethyl orthosilicate (TEOS), Triethoxy silane (TREOS), Methyl triethoxy silane (MTREOS), Dimethoxy diethyl silane (DMDES), Tetramethyl orthosilicate (TMOS), Methyl trimethoxysilane (MTMOS), Methyl diethoxy silane (MDES), and any combination of the above. In an even more preferred embodiment, the alkoxysilane is tetraethyl orthosilicate.

The rate of hydrolysis varies considerably depending on the alkoxide used. Regardless of the reaction conditions (pH, temperature, etc.) the rate of hydrolysis of alkoxides depends on the organic chain they have, the longer said chain, the slower the hydrolysis. Additionally, the reaction conditions also have an influence, with the rate of TEOS with respect to tetramethylorthosilicate being about 350 times lower than that of TMOS in pH conditions below 2 and at a temperature of 35 °C.

In a more preferred embodiment, the hydrolysis of step (a) is carried out in an acid medium.

Materials are obtained in which the polyphenol mixes adequately with the Si-OH groups from the hydrolyzed alkoxide, so that the hydrolysis reaction is rapid to generate Si-OH groups and the polycondensation reaction is slow so that there is time enough for the Si-OH groups to bond to the surface groups of the polyphenol.

In an even more preferred embodiment of the process, the hydrolysis is carried out in an acid medium and comprises mixing TEOS with ethanol in a first solution in a volume ratio of between 1:0.5 and 1:10, respectively, stirring for a time of between 2 min and 10 min; prepare a second solution of the same volume of ethanol as that used in the previous mixture, with water, and with an acid selected from HCl, HNO ³ , H ² SO ⁴ , etc., in a molar ratio TEOS/ethanol/water/acid between 1:0.5:4:0.1 and 1:10:4:0.1 respectively, stirring for between 2 min and 10 min; and adding the second solution to the first at a temperature between 20 °C and 30 °C.

The use of an alcohol in the hydrolysis step is motivated by the fact that the alkoxide and water are not miscible. This influences the porosity of the final sample such that as more alcohol solvent is used, the porosity of the final adsorbent material increases. Furthermore, the amount of water needed to hydrolyze metal alkoxides depends on the number of hydrolyzable bonds. The molar ratio of TEOS to water is between 1:1 and 1:8. Said number of hydrolysable bonds of metal alkoxides is equal to the number of OR radicals present in the molecule. In TEOS, which has the general formula Si-(OR) ⁴ where R=CH ² -CH ³ , since it has 4 OR groups, there are 4 hydrolysable groups, which would require 4 moles of water per mole of alkoxide. 2 moles of water per mole of alkoxide would be sufficient since later, in the consolidation process, water is generated that can be used to hydrolyze other molecules. Using more moles of water ensures complete hydrolysis of the alkoxide. When more water, or more alcohol, is used, the material properties and texture change.

In another preferred embodiment of the process, the polyphenol of step b) is selected from tannic acid and tannins. In a more preferred embodiment, the polyphenol is tannic acid.

In another preferred embodiment of the process, the alkoxysilane is TEOS and the polyphenol is tannic acid. In a more preferred embodiment, the molar ratio in the mixture of step c) between TEOS and tannic acid is between 1 and 99, more preferably between 1 and 30, and even more preferably between 1 and 10.

In another preferred embodiment of the process, the temperature after adding the solution obtained in step a) to the solution obtained in step b) is between 20 °C and 30 °C. Solvents at this temperature such as ethanol, etc., do not evaporate, therefore by minimizing evaporation with respect to stoichiometric amounts they minimize contamination and the generation of unwanted products during the reaction.

In another preferred embodiment of the process, the material obtained in step c) is ground and sieved, collecting the fraction comprised between 100 μm and 200 μm. Below this particle size (100 ^m), said particles of the adsorbent material remain in suspension in the solution and above said value of 200 ^m, the agglomerate prevents the pores of the rigid material from being fully accessible, avoiding the adsorption and/or maximum absorption of the material and the speed of the same.

A third aspect of the present invention is the use of the material of the present invention as an adsorbent for metal cations and/or pharmaceutical organic compounds in an aqueous solution.

In a preferred embodiment of the use, in which the adsorbed metal cations are selected from Pb(II), Hg(II), Cd(II), Cu(II), Mn(II), Zn(II), Co( II), As(V) and any combination of the above.

In a preferred embodiment of the use, in which the pharmaceutical organic compounds are selected from Trimethoprim, Phenol, 2-Naphthol, Sodium Dodecylsulfobenzoate, and Sulfamethoxazole.

In another preferred embodiment of the use, the adsorption and/or absorption temperature at which the solution is found is between 5 °C and 35 °C.

In another preferred embodiment of the use, the pH of the aqueous solution is between 3 and 7 for the adsorption and/or absorption of Pb(II).

In another preferred embodiment of the use of the material, the cation in solution that is adsorbed is Pb(II) at a temperature between 5 and 35 °C and the pH is between 5 and 7. At higher pH, the formation of hydroxide is favored of lead. It is observed that for more acidic pH values the adsorption and/or absorption is practically null, increasing rapidly as the pH increases. The maximum adsorption and/or absorption capacity occurs at approximately a pH of 7, obtaining practically complete elimination of the Pb(II) ion. The fact that the maximum adsorption and/or absorption occurs at pH values between 5 and 7 means that the material can be used as an absorbent for contaminants without the need to add pH modifiers to drinking water samples without subsequently being It is necessary to eliminate these additives that modify the pH. In addition, the adsorption and/or absorption performance of Pb(II) in said waters is more than 99%.

A fourth aspect of the present invention is the adsorption and/or absorption system characterized in that it comprises between 0.2 and 2 kg of adsorbent material described above and a container of porous material, selected from metal mesh, polypropylene mesh, mesh polyethylene, nylon mesh, with a pore size of less than 100 micrometers and where the adsorbent material is inside said bag, which is closed.

A fifth aspect of the present invention is the method of using the adsorbent system described above, characterized in that it comprises the following steps

Yo. depositing the system described according to claim 23 or the material according to any of claims 1 to 7 in a passage of a water current or channel or deposit;

ii. wait a time between 5 and 300 seconds, while the water passes through the system deposited in section i);

iii. remove the system from the position described in i); changing the material inside the system for new material or the set of porous material selected from metal mesh, nylon, polyethylene, polypropylene and adsorbent material, and optionally repeating steps i), ii) and iii) at least once.

In a preferred embodiment of the method, the adsorption and/or absorption temperature at which the water current or pipeline or tank is located is between 5 and 35 °C.

In another preferred embodiment of the method, the pH of the water stream or pipeline or reservoir is between 3 and 7.

In another preferred embodiment of the method, the cation in the water stream or pipeline or tank that is adsorbed is Pb(II) at a temperature between 5 and 35 °C and the pH is between 5 and 7.

Throughout the description and claims the word "comprise" and its variants are not intended to exclude other technical characteristics, additives, components or steps. Other objects, advantages and features of the invention will be apparent to those skilled in the art in part from the description and in part from the practice of the invention. The following examples and figures are provided by way of illustration, and are not intended to be limiting of the present invention.

BRIEF DESCRIPTION OF THE FIGURES

Fig 1 . Infrared spectra of the adsorbent materials of example 1 of the present invention.

Fig 2 . X-Ray Diffraction Spectra of the adsorbent materials of example 1 of the present invention.

Fig 3 . Nitrogen adsorption/desorption isotherms of the adsorbent materials of example 1 of the present invention.

Fig 4 . Absorption and/or adsorption of methylene blue, Pb(II) and Cu(II) on the adsorbent materials of example 1 of the present invention in an aqueous solution.

Fig 5 . Absorption and/or adsorption of inorganic ions and pharmaceutical organic compounds in aqueous solution on adsorbent material called RM4.

Fig 6 . Influence of pH on the adsorption and/or absorption of Pb(II).

Fig 7 . Influence of the amount of adsorbent used on the Pb(II) removal capacity.

Fig 8 . Evolution of the adsorption and/or absorption of Pb(II) with temperature.

Fig 9 . Elimination time for pH=3.1.

Fig 10 . Nonlinear fit to the Langmuir model.

Fig 11 . Nonlinear fits to different isotherms at 90 min.

Fig 12 . Nonlinear fits to different isotherms at 1080 min.

EXAMPLES

Next, the invention will be illustrated by tests carried out by the inventors, which reveal the effectiveness of the product of the invention.

Example 1

Process for obtaining the adsorbent material of the present invention.

The raw materials used have been Tetraethylorthosilicate (TEOS) and tannic acid. TEOS has a molecular weight of 208.33 g/mol and a density of 0.934 g/ml.

For its part, tannic acid has a molecular weight of 1701.20 g/mol.

The concentration ranges for the different samples studied are as follows:

Then, the products or materials studied have the following molar ratios against Tannic Acid

Hydrolyze alkoxysilane (TEOS)

This solution is prepared in two steps:

1) Mix 4 mL TEOS (total volume) and 1.15 mL EtOH (half volume) 2) Mix 1.29 mL deionized water, 1.15 mL EtOH (remaining volume), and 0.07 mL of HCl. Both solutions were stirred independently for 5 minutes at room temperature, with magnetic stirring. After this time, the second solution was added to the first, dropwise, over 15 minutes. This time is enough to produce the total hydrolysis of the TEOS molecule. The molar ratio TEOS:EtOH:H ² O:HCl is 1:4:4:0.1. This hydrolysis was carried out at 25°C.

Prepare the polyphenol solution (tannic acid)

The dissolution of tannic acid is carried out as follows:

4.6 ml of furfuryl alcohol (65% aqueous solution), 3 ml of deionized water and 4.54 ml of formaldehyde are mixed in a glass container. Once the mixture is homogenized, 7.5 g of tannic acid are added, dissolving it with the help of a magnetic stirrer or a paddle stirrer. Next, 2.1 ml of ethyl ether and 7.4 ml of 65% p-toluenesulfonic acid are added. This solution is kept under stirring for 10-15 seconds. This process is carried out at 25°C.

Obtaining the adsorbent.

Both solutions are mixed by adding the hydrolyzed TEOS solution to the tannic acid solution. After 5 days, the adsorbent product is obtained, which must be dried in an oven for 2 days at 50°C and two more days at temperatures between 100 and 150°C, to ensure complete elimination of the solvents used. Once dry, it is ground, collecting the fraction between 100 and 200 micrometers to carry out the elimination tests.

Depending on the volumes of the reagents used, as well as the molar ratio of TEOS/Tannic Acid, the times for obtaining the final adsorbent product can vary. range from a few minutes to the 5 days referred to in the previous paragraph.

Example 2

Characterization of the materials obtained according to example 1.

The IR spectrum of the sample obtained without TEOS (MR = 0) shows different bands all belonging to tannic acid. Two peaks located at 1702 and 1604 cm-1, respectively, correspond to the stretching vibration and the bending vibration of the C = O and O-H groups. The peaks located at 1032 and 1008 cm-1 are due to the O-H and C-O-H and O-H groups outside the bending vibration plane. At a lower wave number, three weak bands can be observed in this first spectrum, located at 814, 684 and 567 cm-1 due to, all of them, an aromatic ring. The 814 cm-1 band is due to respiration vibration, 684 cm-1 due to aromatic ring deformation, and 567 cm-1 due to out-of-plane ring deformation.

When a small concentration of TEOS is incorporated (MR = 1 or 2) not very important changes are observed in these spectra. However, for higher additions of TEOS (MR = 4, 8, 15 and 30) new bands start to appear. First, a shoulder located at approximately 954 cm-1 is observed due to the rocking vibration of the CH3 groups for MR = 4. This vibration belongs to the TEOS molecule and its intensity is low, which means that almost the TEOS molecule is completely hydrolyzed. This band increases in intensity continuously as the molar ratio increases. However, the main change is observed at 453 cm-1. This band starts to appear for MR = 1 increasing its intensity continuously. The highest intensity is for the highest molar ratio used in this study. This band is due to the bending vibration of the O-Si-O bond. In the same way, the tension vibration band of the Si-O-Si bond appears at 1077 cm-1, which also increases as there is more alkoxysilane in the rigid material.

These materials have an amorphous nature. This is what is observed in Figure 2, which shows the XRD pattern of the different samples studied. As can be seen, all samples show the same behavior. They present a broad band located at about 22° due to the amorphous structure of the samples obtained. This indicates that the synthesis method creates an amorphous structural organization without phase separation.

Nitrogen adsorption-desorption isotherms used to determine the surface area or specific surface and the pore size distribution of the TEOS / tannic acid samples are shown in Figure 3. All the samples present type II isotherms, characteristic of non-porous or macroporous materials and where adsorbent-adsorbate interactions they are weak. As can be seen, no hysteresis loops are observed, which means that these samples do not have mesopores.

The textural parameters of the TEOS-tannic acid samples calculated from the adsorption-desorption isotherms are presented in the following Table:

The volume of gold was obtained from the distribution of gold obtained by the method

BJH (Barrett-Joyner-Hallenda). Micropore volume was negligible for all samples studied. The specific surface area (SSA) value is very low, less than 1 m2 / g. It is also observed that, for samples with low silica content, the specific surface area is higher than for samples with high silica content. On the other hand, the total volume of pores also presents very low values.

Example 3

All the synthesized materials (MR=1 to MR=30) were subjected to a preliminary adsorption and/or absorption experiment for the selection of the candidate material to identify the adsorption and/or absorption model and its correlation with the surface properties. of the samples. These experiments were carried out using 25 mg of sample with 25 ppm solutions of Pb(II), Cu(II) and blue of methylene at room temperature. Figure 5 shows the removal capacity of the materials where a maximum adsorption and/or absorption close to 67 and 97% is observed for Pb(II) and methylene blue, respectively. No significant differences were found in the adsorption and/or absorption experiments with the Cu(II) ion. Given that the MR4 sample presents the highest adsorption and/or absorption of the two probes, this sample has been used to evaluate the adsorption and/or absorption capacities of the material prepared against a wide variability of organic and inorganic contaminants.

Said MR4 sample presents a better adsorption and/or absorption for inorganic ions than organic compounds (Figure 5). In the case of organic molecules, the highest adsorption and/or absorption is for methylene blue, while the lowest adsorption and/or absorption measured is for sulfamethoxazole. Methylene blue is a cationic dye and, on the opposite side, the structure of alizarin violet 3R and Karman indigo contains two negatively charged sulfonate groups attached to the aromatic structure. Thus, cationic dyes are absorbed more efficiently than anionic or amphoteric dyes in tannin absorbents.

The lowest adsorption and/or absorption is found in the case of fluorescein, which, in addition to being an anionic dye, contains only one carboxylic group in the structure that reduces the ionic strength of the bond. The adsorption and/or absorption capacity also decreases as the polar character of the different molecules decreases. Sulfamethoxazole has a pH of around 7 when dissolved in water and, on the other hand, trimethoprim is a strongly alkaline molecule whose pKa is around 12. The decrease in basic character of the molecule is reflected in a progressive reduction of the adsorption and/or absorption capacity of the material. Highly acidic molecules are also adsorbed with great efficiency on the synthesized adsorbents.

For inorganic ions, the maximum adsorption and/or absorption capacity at natural pH is obtained for Pb(II), which is the most electronegative element among those selected because the adsorption and/or absorption capacity of the material is related with the chelation capacity of these metals with the hydroxyl groups contained in the surface of the material.

Example 4

Study of the different parameters that influence adsorption and/or absorption (pH, temperature, initial concentration and contact time) of the material obtained according to example 4 and called MR4.

Influence of the pH of the medium

The pH is one of the factors that most affect the phenomenon of adsorption and/or absorption of the Pb(II) ion. Figure 6 shows the influence of this parameter for the molar ratio TEOS/Tannic Acid = 4 (MR4), in the pH range between 2 and 7.5. Since at higher pH the formation of lead hydroxide is favored, pH values above this value were not tested. It is observed that for more acidic pH values the adsorption and/or absorption is practically null, increasing rapidly as the pH increases. The maximum adsorption and/or absorption capacity occurs at approximately a pH of 7, obtaining practically complete elimination of the Pb(II) ion. The fact that the maximum adsorption and/or absorption occurs at pH values between 5 and 7 means that it is not necessary to modify the pH of the liquid waste to be decontaminated.

Mass of adsorbent used

The mass of adsorbent used will provide us with information on the capacity of the adsorbent material to remove the contaminant. Figure 7 represents the adsorption and/or absorption of Pb(II) as a function of the weight of adsorbent used, at pH=3.1, which is the pH at which the aqueous solution of pH 7 remains, once adsorbent material MR4 is introduced. Obviously, the greater the amount of adsorbent material used for Pb(II) removal, the greater the percentage of contaminant removed, regardless of the pH of the reaction, although an increase in adsorption and/or absorption was observed with increasing of the pH. However, adsorption and/or absorption tend to stabilize for high doses of adsorbent, and the use of high amounts of this material is discouraged, since, with this, we would not exceed the maximum level of elimination.

The adsorption and/or absorption capacity, q (mg/g), behaves in the opposite way, that is, the greatest elimination occurs for low amounts of adsorbent. Therefore, it is necessary to establish a compromise relationship between the adsorption and/or absorption capacity and the amount of Pb(II) to be removed.

Influence of Temperature.

Temperature is an important factor since, by influencing the equilibrium of the reactions, it also influences the adsorption and/or absorption capacity. The influence of temperature on the adsorption and/or absorption capacity of the prepared tannic product has been studied for a contact time of 90 minutes. Figure 8 shows the evolution of the adsorption and/or absorption of Pb(II) at temperatures between 25 and 50°C. As can be seen, temperature only influences adsorption and/or absorption at temperatures below 30-35°C, stabilizing at temperatures above 40°C. Therefore, for the Pb(II) ion removal process to be truly effective, it must be carried out at room temperature, which has positive repercussions both at the implementation level and at the economic level. The analysis conditions were: pH=3.1, mass of adsorbent 2g, standard solution of 100 ppm of Pb(II).

contact time.

It is very important that the removal of contaminants occurs quickly and effectively, so that the decontamination process is profitable and allows not only time savings, but also economics. To do this, the contact time between the adsorbent material (tannic) and the contaminant solution must be minimal. This parameter is the most important, and is the object of this patent application.

Figure 9 shows the time required for Pb (II) to be eliminated. A contaminant solution with 100ppm of Pb (II) has been used, setting the adsorbent mass at 2.0 g L-1. The elimination reaction was carried out at pH 3.1 and 600 rpm, with the range 0-90 minutes being represented.

Pb elimination occurs at an unusually fast rate, and is completed in a few seconds, reaching equilibrium immediately. The elimination of Pb(II) is not complete as it has not been carried out at the optimum pH value, which, as indicated above, is between 5-7.

Studies were carried out extending to times greater than 3000 minutes, without observing any change in balance. This rapid adsorption and/or absorption indicates that the surface of the tannic material has a high capacity for attraction and affinity for Pb (II) ions, which means that the surface of the sample is made up of multiple active sites where the Pb (II) ions ) can interact electrostatically and be adsorbed.

In addition, different adsorption and/or absorption models have been applied (Langmuir, Freundlich, Dubinin-Radushkevich, etc.), which allow determining the maximum adsorption and/or absorption capacity of this material. To obtain the maximum capacity for removing the Pb(II) contaminant, the results obtained were fitted to the Langmuir adsorption and/or absorption isotherm model. Said adjustment is shown in Figure 10, and corresponds to the test carried out at room temperature, pH 3.1 and adsorbent mass of 2.0 g L-1.

The different pollutant concentrations tested follow the typical trend of the adsorption and/or absorption isotherm proposed by Langmuir. From said adjustment, the elimination or adsorption and/or absorption capacity of the Pb(II) ion is obtained, this being 61.9 mg of Pb(II) per gram of sample. In addition, figures 11 and 12 show how the adsorption and/or absorption isotherm that best fits a time of 90 min and 1080 min, respectively, is the Temkin isotherm, which means that the adsorption capacity and /o Absorption is driven by thermodynamic aspects. By increasing the exposure time, the best fit is obtained by applying the Freundlich isotherm, which indicates that the adsorption and/or absorption takes place in multilayers that present a heterogeneous surface with different active sites. The adsorption and/or absorption kinetics follow a pseudo second order kinetic model, but, over a longer period, the intraparticle diffusion model can also be applied, since at equilibrium there is no increase or decrease in the amount absorbed. for the sample. Dubinin-Radushkevich analysis indicates a low heat of adsorption and/or absorption suggesting a physical adsorption and/or absorption process. Furthermore, the results revealed an endothermic heat of adsorption and/or absorption and a negative free energy value, indicating that the adsorption and/or absorption process of Pb(II) is favored at room temperature.

Claims (27)

1. An adsorbent material characterized in that it is a solid polyphenol-condensed alkoxysilane material; with a BET specific surface area measured by adsorption desorption of N2, between 0.3 m2/g and 0.6 m2/g in a Micromeritics TRISTAR equipment; where it presents at least the following bands in the infrared spectrum with maxima at the following wave numbers 453±10 cm-1, 1077±10 cm-1 obtained in a Perkin-Elmer Spectrum BX equipment; and where the X-ray diffraction spectrum performed on a Bruker D8 Advance spectrometer with a Lynxeye detector with a Cu wavelength of A=1.5408 Á presents an amorphous type diffraction maximum between 20° and 24°. 2. Material according to claim 1, where the density obtained by helium pycnometry is between 1.2 and 2.0 g/cm3. 3. Material according to any of claims 1 or 2, where it has a molar ratio in terms of starting alkoxysilane and polyphenol equivalents of between 1 and 99. 4. Material according to claim 3, where the alkoxysilane is selected from tetraethyl orthosilicate, triethyl ortho silicate, diethoxy dimethyl silane, tetramethyl orthosilicate, methyl trimethoxysilane, methyl triethoxy silane, and any combination of the above. 5. Material according to any of claims 3 or 4, where the polyphenol is selected from tannic acid and tannins. 6. Material according to any of claims 3 to 5, where the alkoxysilane is TEOS and the polyphenol is tannic acid. 7. Material according to claim 6, wherein the molar ratio between TEOS and tannic acid is between 1 and 99, more preferably between 1 and 30, and even more preferably between 1 and 10. 8. A process for obtaining the material according to any of claims 1 to 7, characterized in that it comprises the following steps: a) hydrolyzing an alkoxysilane; b) dissolving a polyphenol in an aqueous solution of furfuryl alcohol and formaldehyde, and subsequently add ethyl ether and p-toluenesulfonic acid to the mixture obtained at a temperature between 15 °C and 35 °C; and c) add the solution obtained in step a) to the solution obtained in step b) at a temperature between 10 °C and 80 °C and keep stirring for a time between 1 and 10 minutes and then leave it at rest for a time between 30 minutes and 130 hours; Y d) drying the solid material obtained in step c) at a temperature between 50 °C and 200 °C for a time between 10 min and 100 h. 9. Process according to claim 8, wherein the hydrolysis of step a) is carried out in an acidic or basic medium. 10. Process according to any of claims 8 or 9, where the alkoxysilane is selected from tetraethyl orthosilicate, triethyl ortho silicate, diethoxy dimethyl silane, tetramethyl orthosilicate, methyl trimethoxysilane, methyl triethoxy silane, and any combination of the above. 11. Process according to claim 10, wherein the alkoxysilane is tetraethyl orthosilicate. 12. Process according to any of claims 9 to 11, wherein the hydrolysis of step a) is carried out in an acid medium. 13. Process according to claim 12, where the hydrolysis is carried out in an acidic medium and comprises mixing TEOS with ethanol in a first solution in a volume ratio of between 1:0.5 and 1:10, respectively, stirring for a time between 2 min and 10 min; prepare a second solution of the same volume of ethanol used in the previous mixture, with water, and with an acid selected from among HCl, HNO ³ , H ² SO ⁴ in a molar ratio TEOS/ethanol/water/acid of between 1: 0.5:4:0.1 and 1:10:4:0.1 respectively, stirring for 2 min to 10 min; and adding the second solution to the first solution dropwise over 15 minutes at a temperature between 20°C and 30°C. 14. Process according to any of claims 8 to 13, wherein the polyphenol of step b) is tannic acid; where the alkoxysilane is TEOS; and where the molar ratio in the mixture of step c) between TEOS and tannic acid is between 3.5 and 41. 15. Process according to any of claims 8 to 14, wherein the temperature after adding the solution obtained in step a) to the solution obtained in step b) is between 20 °C and 30 °C. 16. Process according to any of claims 8 to 15, wherein the material obtained in step c) is ground and sieved, collecting the fraction between 100 ^m and 200 ^m. 17. Use of the material according to any of claims 1 to 7 as an adsorbent for metal cations and/or pharmaceutical organic compounds in an aqueous solution. 18. Use of the adsorbent material according to claim 17, wherein the adsorbed metal cations are selected from Pb(II), Hg(II), Cd(II), Cu(II), Mn(II), Zn(II), Co(II), As(V), and any combination of the above. 19. Use of the material according to any of claims 17 or 18, where the pharmaceutical organic compounds are selected from Trimethoprim, Phenol, 2-Naphthol, Sodium dodecylsulfobenzoate and Sulfamethoxazole. 20. Use of the adsorbent material according to any of claims 17 to 19, wherein the adsorption and/or absorption temperature of the solution is between 5 and 35 °C. 21. Use of the adsorbent material according to any of claims 17 to 20, wherein the pH of the aqueous solution is between 3 and 7. 22. Use of the adsorbent material according to any of claims 17 to 21, wherein the cation in solution that is adsorbed is Pb(II) at a temperature between 5 and 35 °C and the pH is between 5 and 7. 23. A characterized adsorption and/or absorption system comprising between 0.2 and 2 kg of adsorbent material according to any of claims 1 to 7 and a container of porous material, selected from metal mesh, polypropylene mesh, mesh polyethylene, nylon mesh, with a pore size of less than 100 micrometers and where the adsorbent material is inside said bag, which is closed. 24. A method for the adsorption of metal cations and/or organic compounds characterized in that it comprises the following steps: Yo. depositing the system described according to claim 23 or the material according to any of claims 1 to 7 in a passage of a water current or channel or deposit; ii. wait a time between 5 and 300 seconds, while the water passes through the system deposited in section i); iii. remove the system from the position described in i); changing the material inside the system for new material or the set of porous material selected from metal mesh, nylon, polyethylene, polypropylene and adsorbent material, and optionally repeating steps i), ii) and iii) at least once. 25. Method according to claim 24, wherein the adsorption and/or absorption temperature of the water current or pipeline or deposit is between 5 and 35 °C. 26. Method according to any of claims 24 or 25, wherein the pH of the water current or channel or deposit is between 3 and 7. 27. Method according to any of claims 24 to 26, wherein the cation in the water stream or pipe or tank that is adsorbed is Pb(II) at a temperature between 5 and 35 °C and the pH is between 5 and 7.