WO2013086596A1

WO2013086596A1 - Process for producing a silica nanoparticle hydrogel, silica nanoparticles and silica nanoparticles with adsorbed ions; products produced and the corresponding uses thereof

Info

Publication number: WO2013086596A1
Application number: PCT/BR2012/000508
Authority: WO
Inventors: Fernando APARECIDO SIGOLI; Tábita Cristina BELINI; Ítalo ODONE MAZALI
Original assignee: Universidade Estadual De Campinas - Unicamp; Iharabrás S/A Indústrias Químicas
Priority date: 2011-12-13
Filing date: 2012-12-07
Publication date: 2013-06-20
Also published as: BRPI1105171A2; BRPI1105171B1

Abstract

The present invention relates to a process for producing silica-based nanoproducts, using sodium silicate as the source of silicon and organic acid as a catalyst for the hydrolysis and condensation reactions. The final products are described as being a silica nanoparticle hydrogel and silica nanoparticles, which can have ions adsorbed to the silica surface thereof. One of the numerous uses for said particles is as an adsorbent material, mainly for metal ions, some of which have fungicidal/bactericidal properties. With the adsorption of specific metal ions to the silica nanoparticles, products that have bactericidal and fungicidal activity can be produced, which can be used in various agricultural sectors.

Description

PROCEDURE FOR OBTAINING HYDROGEL FROM NANO SILICA PARTICULATES, SILICA NANOParticles AND NANO SILICA PARTICULATES WITH ADSORTED IONS; PRODUCTS OBTAINED AND THEIR USES

Field of the invention

The present invention relates to a process for obtaining silica-based nanoproducts from sodium silicate. More specifically, the present invention relates to a process for obtaining hydrogel from silica nanoparticles and silica nanoparticles that may be used for adsorption of ions on their surface.

Silica nanoparticle hydrogel and silica nanoparticle can be used for agrochemical, home and personal care applications in the rubber industry as an additive to formulations and carrier systems. In addition, they may contain ions adsorbed on their surface and are mainly used as bactericidal and / or fungicidal materials, depending on the ion used.

Fundamentals of the invention

Interest in nanotechnology and therefore nanoscience is growing. These interests have enabled major advances in various areas of industry, such as microelectronics and telecommunications. Nanomaterials are also present in nonlinear optics, luminescence, catalysis, solar energy conversion, biological detection, lasers, optical fibers, sensors, drugs and cosmetics, as well as in other areas (P. 0 ^' Brien, NL Pickett. Nanocrystalline Semiconductors: Syntheses, Properties and Perspectives, Chemistry of Materials, 2001, Vol. 13, pp. 3843-385). The physicochemical properties of materials can be related to particle size, shape and composition. The size and shape of a particle can be manipulated by adjusting experimental conditions such as temperature, reagent concentration ratio, reaction time, pH and solution dielectric constant, solvent type, reagent concentration, among others (LM Liz-Marzán, Nanometals: Formation and Color, Materials Today, 2004, pp. 26-31). Silicon oxide, called silica (Si0 ₂ ) is one of the most abundant components in the earth's crust and widely used in the glass, ceramics, polymers, paints, toothpastes and other industries. More specifically it is used and marketed as insulating glazing material, used as a support for heterogeneous catalysts, as adsorbent, as stationary phase for gas and liquid chromatographs, rubber reinforcing agent, elastomers, texturizing agent, filler, abrasives, polishing material, For many of these applications, silicon oxide must be presented as small aggregates or small particles in order to obtain stable suspensions.

Silica gel is a non - crystalline inorganic polymer with high porosity, consisting of SI0 ₄ tetrahedral units randomly distributed and connected by siloxane bonds (Si-O-Si) , and silanol groups (Si - OH) on the particle surface.

Chemical reactivity is mainly determined by silanol groups on the silica surface. Hydroxyls present on the silica surface can be chemically modified, resulting in the functionalization of the silanol groups. Such a reaction makes it possible to obtain a more selective and versatile silica matrix, as it incorporates the characteristics of the modifying agent. Therefore, a silica matrix can be used to anchor other substances - such as metal ions or organic molecules - either by direct bonding to the silanol groups or by modifying such groups and chemical interaction with the modified terminals.

The classic method for obtaining silica nanoparticles is sol-gel, which consists of obtaining solid particles through liquid precursors through hydrolysis and condensation reactions. The main precursors of this reaction are silicon alkoxides.

In the case of silica synthesis from silicates, the process is started by hydrolysis of this precursor by acid catalysis, resulting in a colloidal silicon oxide / hydroxide system - the sun. Later reactions of Condensation leads to gel formation which, when dried, results in a structure called xerogel (CJ Brinker, GW Sherer. Sol-Gel Science. 1990, Academic Press: New York).

Such method has numerous advantages, such as purity and homogeneity, and is easily transposed to industrial scale. The precipitation of silica through this process is widely presented in the literature, and the main methods use the acidification of a sodium silicate solution or precipitation through tetraethylorthosilicate - TEOS (RK Iler. The Chemistry of Silica. 1979, John Wiley & Sons : New York).

The most common process for colloidal silica synthesis is called Stöber process and makes use of TEOS as a source of silicon. The method was developed by Werner Stöber in 1968 and consists of hydrolyzing / condensing tetraethylorthosilicate in an alcoholic solution in the presence of ammonium hydroxide (catalyst). The size of the synthesized particles can be controlled by varying the TEOS and alcohol concentrations as well as the nature of the alcohol. It is a widespread method and several works are still developed on the basis of it (I. A. M. Ibrahim et al., J Am Sei, 2010, 11, 985-989).

However, nanoparticle synthesis parameters from TEOS such as volume, reactor shape, temperature, reaction time, agitation and atmosphere should be controlled within a narrow window of parameter variations to obtain nanoparticles of size and controlled. Thus, large-scale production of silica nanoparticles by hydrolysis and condensation reactions of TEOS requires strict control of these parameters, making it difficult to obtain them on a large scale. It is also worth mentioning the small number of suppliers of this precursor worldwide, being zero or very small in Brazil, which depends on the importation of this input. In addition to the difficulties encountered in production, TEOS is an unstable reagent against moisture. When exposed to water (either direct source or moisture), it may hydrolyze to release ethanol and therefore requires care with regard to handling and storage. Thus, knowing all the industrial difficulties for obtaining silica nanoparticles from TEOS and knowing the high availability of sodium silicate, the present invention proposes a viable alternative for the industrial production of silica nanoparticles using sodium silicate.

It is a "one pot" method in which the nanoparticles obtained are stable even under adverse storage conditions and have a narrow size distribution, with the average diameter being around 10 nm. Sodium silicate is non-flammable, is widely available on the market, is much lower in cost than TEOS and does not require special stock and synthesis conditions for nanoparticles.

Several methods of silica synthesis using sodium silicate are found in the literature. US2483868 of 10/04/1949 discloses a method for producing silica gel which consists of nebulizing a sodium silicate solution in a sulfuric acid solution by stirring it for a certain time. It is a simple process to be applied on an industrial scale for the production of silica micrometer particles, but it does not allow the obtaining of nanoparticles and does not present data on the control of the shape and size of the silica particles. US2935482 of 05/03/1960, which also produces silica from sodium silicate and chlorine gas, making use of a specific apparatus. The use of specific apparatus was employed to interrupt the condensation reaction of the sol-gel process, preventing gel formation. Besides disadvantageously having to employ an apparatus for production, the document also does not describe the formation and control of size and shape of silica nanoparticles.

The sodium silicate solution is alkaline (approximately pH 12) and for the hydrolysis reaction to take place a catalyst is required, but the addition of acid neutralizes the medium which induces the condensation reaction. It quickly acidified to ^pH's acid, is achieved circumvent this condition. However, the low pH makes it impossible to use silica in some applications and, moreover, pHs below 5 do not lead to the formation of isolated nanoparticles.

In this context, several works were developed to stabilize the synthesized product at pH close to neutrality. EP0537375 of 10/15/1991, EP0557740 of 02/01/1993 and EP0996 588 of 06/30/1998 describe methods for producing colloidal silica suspensions of up to 50% (w / w) from sodium silicate and strong inorganic acids (such as sulfuric acid, hydrochloric acid, nitric), however the process presented is not simple. The main step is to pass the sodium silicate solution through ion exchange columns (cationic and anionic), thus altering the electric double layer of the formed silica particles, allowing the solution to be concentrated without gelling it. If this ion exchange is not promoted, the addition of acids triggers the gelation process of the solution, leading to the formation of xerogel, as published by Witoon et al. (T. Witoon J et al. Ceram Inter, 2011, 37, 2297-2303 ). In this case, the authors started the precipitation process by the addition of acetic acid, which induced the formation of colloidal silica and then added hydrochloric acid to pH 2, which triggered the condensation reactions between the silica particles, producing the xerogel. Unlike the present invention, the final product obtained has highly aggregated silica particles which hinders their redispersion and, consequently, hinders some of their applications, especially in the field of agriculture.

The present invention has dispersed and water dispersible silica nanoparticles, which already guarantees unique advantages regarding its use in various areas, especially the agricultural field, due to the ease of preparation and application of the syrup. EP0537375 of 10/15/1991, EP0557740 of 02/01/1993 and EP0996 588 of 06/30/1998 use various unit operations, increasing the length and decreasing process productivity, as well as requiring the installation of specific equipment. in the manufacturing plant, such as ion exchange columns. The present invention makes use of weak acids and eliminates some unit operations making the manufacturing process simpler and still preparing highly stable solution-stable silica nanoparticles hydrogel.

Therefore, in view of the described technologies, the great advantage of the present invention is that it is capable of forming and stabilizing silica nanoparticles from sodium silicate, making use of a weak acid as catalyst in the absence of other surface modifiers. The process control occurs by the sodium silicate / acid ratio, acid strength and time and system heating, and therefore can be accomplished by reducing the number of unit operations.

Silica applications are numerous, standing out as adsorbent material. Silanol groups present on the surface of the particle are able to interact with various compounds such as metal ions, gases, organic molecules and so on. Godói and collaborators (RHM Godói, L. Fernandes, M. Jafelicci Jr., RC Marques, LC Veranda, MR Davolos. Investigation of the silica and silica systems containing chromium in alcohol medium. Journal of Non-Crystalline Solids. 1999, Vol. 47, pp. 141-145) describe a method for synthesizing chromium-containing silica particles from sodium silicate in alcoholic medium. This is a process adapted from Stober's method in which a salt of the metal of interest is inserted during the precipitation of the silica so that such an ion is trapped in the formed structure. The limitation of this method is that the final product is in gel form.

Some metals are known to have bactericidal / fungicidal activities (such as silver and copper), so when incorporated into the silica matrix, a compound with characteristics is obtained that can be employed as additives in the home and personal care industry, for disease control in agriculture, among others.

WO2007 / 122651 of 24/04/2006 describes a process for producing particles with activity against viruses and bacteria. These are particles of a metal oxide (such as silica, zinc oxide, titanium dioxide, among others) whose surface has been chemically modified. to bind to ions that exhibit the desired activity. The advantage associated with this method is that it can be used for several oxides, however the associated problem is that the functionalization of silica requires the use of organic solvents, making the process less sustainable - which is not in accordance with the principles of "chemistry". green "- and presents greater risk to handlers, compromising their health. In addition, surface functionalization requires new unit operations which are eliminated in the present invention, where the adsorption of ions occurs only by weak chemical interaction. This weak chemical interaction between the ions and the silica surface makes these ions more bioavailable compared to coordinating and organometallic compounds and thus the bactericidal and / or fungicidal action is achieved by using a lower concentration of metal ions.

In WO2008 / 017176 of 7/23/2007 the inventor proposes a method using TEOS to produce silica nanoparticles containing copper and silver ions as well as other compounds which exhibit bactericidal / fungicidal activity. The process involves preparing a solution of a silicon precursor in organic solvent, together with the component having the desired activity, and subjecting such solution to pyrolysis. The final product obtained is solid phase silica nanoparticles with an average diameter between 30 and 100 nm. The process involves the burning of organic solvents by pyrolysis spray, a process that demands high temperatures, releasing toxic gases and making use of unitary operations that are not necessary in the present invention. In the present invention the solvent used is water which can be recovered and reused in the process. Nanoparticle synthesis parameters from TEOS, such as volume, reactor shape, temperature, reaction time, agitation and atmosphere should be controlled within a narrow range window to obtain controlled size and shape nanoparticles. Thus, large-scale production of silica nanoparticles by hydrolysis and condensation reactions of TEOS requires strict control of production parameters, making it difficult to obtain them on a large scale. It is also worth mentioning the small number of worldwide suppliers of this precursor, being zero or very small in Brazil that depends on the importation of this input. In addition to the difficulties encountered in production, TEOS is an unstable reagent against moisture. When exposed to water (either direct source or moisture), it may hydrolyze to release ethanol and therefore requires some care with regard to handling and storage.

And WO2010 / 068275 of 10/12/2009 deals with a bactericidal and fungicidal copper-based formulation using a silica matrix. However, the author synthesized the matrix from TEOS - an adapted Stober's method - and evaluates the differences between the effectiveness of nanoparticles called "nanogel", which consists of polymerized silica nanoparticles. However, it is unlikely to be used in industry - especially in the agrochemical industry, which is a commodity industry - due to the limitations already discussed previously regarding tetraethylorthosilicate.

In view of the foregoing, the present invention has advantages in several respects. Firstly, it proposes a new process for the synthesis of silica nanoparticles from sodium silicate, employing an acid catalyst and limiting the kinetics of condensation reactions at pH10, which lead to efficient gelation of the solution. In addition, such a process can easily be transposed to industrial scale and the reagents used are not impediments to large scale production. The present invention advantageously employs a weak organic acid, thereby achieving better control of pH adjustment, which is critical for precipitating colloidal silica and keeping it in the form of individual particles by controlling the size of nanoparticles. Another crucial point for the process is heating, combined with the time the sodium silicate solution undergoes, which enables the formation of individual particles and promotes their stabilization over a long period of storage.

Thus, with the process described herein it is possible to synthesize stable silica nanoparticles in aqueous solution from a source of silicon other than tetraethylorthosilicate (TEOS), non-flammable sodium silicate is widely available at a lower cost than TEOS and does not require special stock and synthesis conditions for nanoparticles without the use of specific apparatus as mentioned in US2935482. Another advantage of the presented process is in relation to the reagents used, which do not require any extra purification process and do not present great danger to man and the environment, as well as do not require special handling conditions, complicated synthesis and storage protocols.

Highlighting the products obtained in the present invention, such nanoparticles do not have surface modifiers, such as surfactants, and yet are re-dispersible in water, that is, the use of adjuvants is not necessary to maintain the dispersion of the particles. Nanoparticles are stable even under adverse storage conditions and have a narrow size distribution, with an average diameter around 10 nm.

Among the various applications that these nanoparticles present, one of them is related to the adsorption of metal ions, such as copper (ll), which guarantees this oxide fungicidal / bactericidal action. The agrochemical industry, for example, has been continually seeking alternatives to survive consolidated active ingredients and aims to reduce the dosage used while maintaining effectiveness. Therefore, the present invention offers an alternative to this need by reducing the amount of copper (11) used for application in the agricultural sector, highlighting an important new route for obtaining differentiated products with less impact on the environment.

Brief Description of the Invention

The present invention relates to a process for obtaining silica based nanoproducts. Additional objects are the products obtained by the described process, comprising silica nanoparticles hydrogel, silica nanoparticles and silicon nanoparticles of interest. adsorbed to its surface. Furthermore, the present invention also relates to the use of said nanoproducts.

The invention describes a process comprising the steps of preparing sodium silicate solutions and a weak organic acid, adding one solution to another, refluxing, filtration, concentration, drying, adsorption and drying.

Brief Description of the Figures

The structure and operation of the present invention, together with further advantages thereof may be better understood by reference to the accompanying figures and the following description:

- Figure 1 shows the size distribution of silica nanoparticles.

Figure 2 shows an X-ray diffractogram of solid phase silica nanoparticles.

- Figure 3 shows the size distribution of silica nanoparticles after spray dryer processing and redispersion of the particles in water.

- Figure 4 shows the scanning electron microscopy of the silica nanoparticle hydrogel.

- Figure 5 shows the scanning electron microscopy of the redispersed silica nanoparticles in water.

Detailed Description of the Invention

The present invention describes a process for obtaining silica nanoproducts employing sodium silicate and a weak organic acid catalyst which can be applied as a hydrogel or a powder, such as silica nanoparticles, and also with ions adsorbed to nanoparticle surface

Silica nanoproducts obtained by the process described in this invention comprise silica nanoparticle hydrogel, silica nanoparticle and silica nanoparticle with adsorbed ions. An object of the present invention is a process for obtaining the products described above comprising the following steps:

a) Preparation of solutions

a1) Silicate solution

a2) Solution of a weak organic acid b) Addition of the solution of (a2) to (a1)

c) Reflux

d) Filtration

e) Concentration

f) Drying

g) Adsorption

h) Drying

The first solution preparation step (a) is initiated by step (a1), in which an alkaline sodium silicate solution is prepared in distilled water of between 0.1 and 10%, preferably 1% (w / v). Then, in step (a2), a weak organic acid solution selected from picric acid, squaric acid, oxalic acid, citric acid, formic acid, ascorbic acid, benzoic acid, acetic acid, p-nitrophenol, peracetic acid, propionic, butyric acid, valyric acid, caproic acid, caprylic acid, capric acid, succinic acid, glutaric acid, adipic acid, D-tartaric acid, L-tartaric acid, lactic acid, uric acid, maleic acid, fumaric acid, isovaliric acid , furic acid, sorbic acid, salicylic acid, trans-cinnamic acid, acetylsalicylic acid, myristic acid) being preferably citric acid at a concentration of 0.5 to 5 mol L ^"1 , preferably 1 mol L ^{" 1} , is also ready.

In the next step (b) the weak organic acid solution obtained in step (a2) is added to the solution prepared in step (a1), so that the pH decreases to a range of 12 to 9.0, preferably 10.5. The definition of a suitable pH, which in the present invention is easily achieved, especially for industrial scale application, by the use of a weak organic acid, is essential to promote the hydrolysis reactions of the product. silicate, limiting condensation reactions, which lead to efficient hydrogel formation in subsequent steps.

The final solution is refluxed (c), at which time nanoparticles form. At this stage the solution is heated to 50 to 100 ° C, preferably to 90 ° C for a period of 4 to 48 hours, preferably 24 hours. Reflux is critical for obtaining stable and individual nanoparticles.

The suspension is then cooled to room temperature until complete cooling. The material obtained in step (c) is subjected to filtration step (d) in a simple filtration system, thus obtaining the so-called silica nanoparticle hydrogel. This hydrogel obtained in step (d) is colorless, with medium diameter silica nanoparticles ranging from 1 to 100 nm, preferably 10 nm, zeta potential ranging from -100 to +100 mV, preferably -35 mV.

The hydrogel obtained in step (d) may or may not be concentrated by removing water from the system (step e), preferably by distillation. The obtained compound - concentrated or diluted - can be applied as metal ion adsorbent materials, stationary phase for gas and liquid phase chromatography, rubber reinforcing agent, elastomers, texturizing agent, filler, abrasives, polishing material, carrier systems and inert / additives for the agrochemical industry, home and personal care, ceramics, polymers and paints.

The next process step consists of drying (f) the hydrogel obtained in step (d) or (e). At this stage the material is spray dried at a temperature of 100 to 200 ° C, preferably 150 ° C, with a flow rate of 1 to 20 mL / min, preferably 5 mL / min, and with a nozzle of 0.7 to 2.0 mm, preferably 1.5 mm, for removal of all residual water to give the solid phase silica nanoparticles, a water redispersible powder.

The silica nanoparticles obtained in step (f) have a mean diameter ranging from 5 to 200 nm, preferably 20 nm, zeta potential ranging from -150 to +150 mV, preferably -80 mV. And they can be applied as support for catalysts, adsorbent materials, stationary phase for gas and liquid phase chromatography, rubber reinforcing agent, elastomers, texturizing agent, filler, abrasives, polishing material, filler and additive systems for the agrochemical industry, home and personal care, ceramics, polymers and paints.

Silica nanoparticles obtained in step (f) and hydrogel obtained in steps (d) and (e) can be used for adsorption (g) of ions on their surface. For this purpose a suspension of the nanoparticles at a pH ranging from 1 to 11, preferably 8, is prepared using a weak organic acid solution selected from picric acid, squaric acid, oxalic acid, citric acid, formic acid, ascorbic acid, benzoic acid, acetic acid, p-nitrophenol, peracetic acid, propionic acid, butyric acid, valyric acid, caproic acid, caprylic acid, capric acid, succinic acid, adipic acid, D-tartaric acid, L-tartaric acid, lactic acid, uric acid, maleic acid, fumaric acid, isovalyric acid, furic acid, sorbic acid, salicylic acid, trans-cinnamic acid, acetylsalicylic acid, myristic acid), being preferably citric acid at a concentration ranging from 0.5 to 5 mol L ^" \ preferably at 1 mol L ^{" 1} . After adjustment, a soluble salt of the ion of interest may be added, which may be copper (1), copper (11), mercury (11), silver (1), zinc (11), iron (11), iron (11). ), lead (11), lead (11) and bismuth (11), with copper (11) being preferably chloride, nitrate or sulfate, and the solution is stirred briefly.

After the addition of the salt of interest, the solution obtained in step (g), which can be used as a hydrogel with bactericidal and fungicidal properties, is submitted to a drying step (h), processed in a spray dryer at 100 to 200 ° C, preferably 150 ° C, with a flow rate of 1 to 20 mL / min, preferably 5 mUmin, and nozzle of 0.7 to 2.0 mm, preferably 1.5 mm, for removal of all wastewater.

Silica nanoparticles obtained in steps (g) and (h) may have bactericidal and fungicidal action or act as a catalyst, depending on the metal ions adsorbed to their surface, and may be applied in various branches of industry, such as the sectors: agricultural, electronic, home and personal care, pharmaceutical, polymers, rubbers, among others.

The chemical reactions that represent the formation of silica nanoparticles from the process described in the present invention are as follows:

N SI0 _z ₃ + H ₂ 0 + "5f (0TF) 2JVa ^÷ ₄ + (1)

≡ Si - OH + ≡ St - → ≡ Si - O - S7≡ + + ( ³ )

The first step is the proton catalyzed hydrolysis of sodium silicate to generate silicic acid. Protonation of such acid leads to condensation of such molecules, forming polysilicic acid. If such a reaction is not controlled, the chains continue to undergo condensation and crosslinking, leading to hydrogel formation.

The obtained silica nanoparticles were characterized by several techniques, such as dynamic light scattering (DLS), X-ray diffraction (XRD) and particle morphology were evaluated by scanning electron microscopy.

Example 1: Silica Nanoparticle Hydrogel Preparation Process

A 1% (w / v) alkaline sodium silicate solution is prepared and 1 mol L ^" citric acid is added such that the pH reaches a value close to 10.5. refluxing solution for 4 to 24 hours After this time the final suspension is filtered on a qualitative filter paper and finally the silica nanoparticle hydrogel is obtained.

This hydrogel is colorless and the nanoparticles obtained have an average diameter of 10 nm (Figure 1), zeta potential of - 32.1 mV and are quite dispersed as shown by electron microscopy (Figure 4). As mentioned the hydrogel is completely colorless and translucent and the only visual means to check if precipitation has occurred is by light scattering.

The Tyndall effect predicts that suspended particles are capable of scattering light, regardless of their size or medium in which they are scattered. Thus, by pointing a laser at a solution, if there are suspended particles, it will be possible to observe the path of light through the liquid medium, which does not occur in the case of water or a true solution, for example.

Example 2: Silica Nanoparticle Preparation Process

To obtain the solid phase silica nanoparticles, the refluxed solution is processed after filtration in a spray dryer.

Samples were processed at 150, 180 and 200 ° C with 1.5 mm nozzle. These conditions were changed to see if they would influence the morphology and size of the dried particles. As other parameters, aspiration was standardized at 85%, the pump at 15% (which is approximately 5 mL / min) and nozzle cleanerem 5 (arbitrary units).

He observed that the best condition for obtaining solid phase silica nanoparticles occurs at 150 ° C. Silica nanoparticles (Figure 5) were characterized as non-crystalline

(Figure 2) and a bimodal size distribution via DLS was observed (Figure 2).

3) with a significant population at 20 nm and another population with a lower count at 200 nm.

Example 3: Process of preparing adsorbed copper (ll) ions silica nanoparticles

Adsorption of copper ions on the surface of silica nanoparticles occurs through chemical interactions. The metal cation interacts with the dissociated hydroxyls of the silanol groups, since the solution is kept at slightly basic pH. However, the pH should be adjusted so that precipitation of copper ions in the form of hydroxide does not occur. Therefore, pH 8 was established as optimal, based on data published in the literature (CJ Brinker et al. Sol-Gel Science, 1990)

The silica suspension prepared as described in Example 1 is adjusted to pH with a 1 mol L ^"1 citric acid solution to pH 8. Then a soluble copper salt (11) may be added, which may be chloride , nitrate, sulfate, among others, and the solution is briefly stirred, and the copper salt will solubilize in the solution, providing the copper ions which in turn will interact with the silica surface.

To obtain the compound in solid phase, the spray dryer solution is processed under the same conditions as described in Example 2. A water-redispersible blue solid is obtained at the end of the process.

Example 4: Bactericidal Applications

Copper-containing silica nanoparticles were obtained and the in vitro efficacy tests were conducted and the bactericidal action was verified with Xanthomonas axonopodis and Ralstonia solanacearum strains.

The test consists of spreading a certain volume of a bacterial solution on a specific culture medium (in this case, BDA - potato, dextrose and agar was used) and in the center of the petri dish a filter paper disc is placed. moistened in a solution of the formula to be tested with known concentration. At concentrations where the formula has activity, a halo will be formed around the filter disc, indicating that in this region the bacteria did not develop, and the larger this halo, the greater the activity of the tested formulation.

Thus, the spray-dried formulation was tested at dosages of 1; 5; 10; 25; 50 and 100 ppm of copper ions adsorbed on silica nanoparticles and, as a commercial reference, a formula based on copper hydroxide was used at the recommended concentration of 300g / 100L of water, which is equivalent to 1050 ppm copper (ll). .

Example 4.1: Evaluation with Xanthomonas axonopodis pv. phaseoli

Xanthomonas axonopodis pv. phaseoli is the etiological agent of bean bacterial growth. It is a bacteriosis largely mainly in hot and humid climates (such as the states of São Paulo, Rio de Janeiro, Minas Gerais, Paraná, Santa Catarina, Espirito Santo, Rio Grande do Sul and the Midwest) harvesting 10 to 70% under natural attack conditions and the difficulties of disease control.

The copper ion-containing silica nanoparticle proposed in the present invention has been effective in controlling this bacterium from 25 ppm copper (11) when metal ions are adsorbed to the surface while the commercial reference concentration is 1050 ppm copper (11). - concentration at which control was observed in the in vitro test.

Example 4.2: Evaluation with Ralstonia solanacearum

Ralstonia solanacearum causes bacterial wilt in numerous hosts, including tomato and potato crops. Initially the disease affects only the fruit, but with the development of the bacteria, it eventually spreads to the plant, causing its death. Therefore, if not controlled at the beginning of the infestation, it causes great damage to the farmer.

In conditions of high soil infestation, control necessarily involves the use of resistant cultivars, given the difficulty of controlling this disease. Therefore, a contact formulation that is capable of controlling the infestation of this bacterium will be very well accepted by the agrochemical market.

The developed silicon nanoparticle containing copper (ll) ions was effective in controlling Ralstonia solanacearum at 50 ppm, while the commercial reference at 1050 ppm copper (ll).

Therefore, for both bacteria, the silica-based nanoparticle showed good efficacy compared to the commercial reference. Accordingly, the efficacy of this copper (11) -containing silica-based formulation as a bactericide is proven and offers an option to the market for the control of these diseases.

Claims

Process for obtaining nanoproducts characterized by comprising the following steps:

a) Preparation of solutions:

a1 ) Silicate solution;

a2) Solution of a weak organic acid;

b) Addition of the solution of (a2) to (a1);

c) Reflux;

d) Filtration;

e) Concentration;

f) Drying;

g) Adsorption, and

h) Drying.

Process, according to claim 1, characterized by step (a) comprising the preparation of a solution of alkaline sodium silicate (a1) in distilled water between 0.1 and 10%, preferably 1% (m/v).

Process, according to claim 1, characterized by step (a) comprising the preparation of a solution of weak organic acid (a2) selected from picric acid, squaric acid, oxalic acid, citric acid, formic acid, ascorbic acid, benzoic acid , acetic acid, p-nitrophenol, peracetic acid, propionic acid, butyric acid, valyric acid, caproic acid, caprylic acid, capric acid, succinic acid, glutaric acid, adipic acid, D-tartaric acid, L-tartaric acid, lactic acid , uric acid, maleic acid, fumaric acid, isovalyric acid, furoic acid, sorbic acid, salicylic acid, trans-cinnamic acid, acetylsalicylic acid, myristic acid. Process according to claim 3, characterized by the fact that the organic acid is preferably citric acid.

5. Process, according to claim 4, characterized by comprising a concentration of citric acid varying between 0.5 and 5 mol L ^" \ preferably 1 mol L ^"1 .

6. Process, according to claim 1, characterized by step (b) comprising adding the weak organic acid solution obtained in step (a2) to the solution prepared in step (a1), until reaching a pH between 12.0 to 9.0, preferably 10.5.

7. Process, according to claim 1, characterized by the reflux step (c) of the solution obtained in step (b) between 50 and 100°C, preferably at 90°C, for a period between 4 and 48 hours, preferably 24 hours.

8. Process, according to claim 1, characterized in that the filtration step (d) is carried out in a simple filtration system at room temperature.

9. Process, according to claim 1, characterized in that the concentration step (e) is carried out in a water removal system, preferably distillation.

10. Process, according to claim 1, characterized in that step (e) is performed optionally.

1 1. Silica nanoparticle hydrogel characterized by being obtained according to the steps described in claims 1 to 10.

12. Silica nanoparticle hydrogel as claimed

1 1 , characterized by the fact that it comprises nanoparticles with an average diameter varying between 1 and 100 nm, preferably 10 nm.

13. Silica nanoparticle hydrogel as claimed

1 1 , characterized by the fact that it comprises a zeta potential variable between -100 to +100 mV, preferably -35 mV.

14. Use of the silica nanoparticle hydrogel, according to claim 11, characterized in that it is used as a support for catalysts, stationary phase adsorbent materials for gas and liquid phase chromatography, rubber, elastomers, texturizing agent, filler material, abrasives, polishing material, carrier systems and fillers/additives for the agrochemical industry, home and personal care, ceramics, polymers and paints.

15. Process, according to claim 1, characterized by the drying step (f) of the hydrogel obtained in steps (e) or (f) preferably in a spray dryer at a temperature of 100 to 200 °C, preferably at 150 °C, with a flow rate of 1 to 20 mL/min, preferably 5 mL/min, and with a nozzle of 0.7 to 2.0 mm, preferably 1.5 mm.

16. Silica nanoparticles characterized by being obtained according to the steps described in claims 1 to 10 and 15

17. Silica nanoparticles, according to claim 16, characterized by the fact that it comprises an average diameter ranging between 5 and 200 nm, preferably 20 nm.

18. Use of silica nanoparticles, according to claim 16, characterized by being used as a support for catalysts, stationary phase adsorbent materials for gas and liquid phase chromatography, rubber reinforcing agent, elastomers, texturizing agent, filler material , abrasives, polishing material, carrier systems and inerts/additives for the agrochemical industry, home and personal care, ceramics, polymers and paints.

19. Process, according to claim 1, characterized by the adsorption step (g) comprising adding a soluble salt of the ion of interest to a suspension of silica nanoparticles obtained in steps (d), (e) or (f) .

20. Process, according to claim 19, characterized by comprising a soluble salt of the ion of interest selected from chloride, nitrate or sulfate salts.

21. Process, according to claim 20, characterized by comprising an ion selected from the group copper(l), copper(ll), mercury(ll), silver(l), zinc(ll), iron(ll), iron(lll), lead(ll), lead(lll) and bismuth(ll), preferably copper(ll).

22. Process, according to claim 19, characterized by comprising a suspension of nanoparticles at a pH between 1.0 and 11.0, preferably 8.0.

23. Process according to claim 19, characterized by adding a weak organic acid solution selected from picric acid, squaric acid, oxalic acid, citric acid, formic acid, ascorbic acid, benzoic acid, acetic acid, p. -nitrophenol, peracetic acid, propionic acid, butyric acid, valyric acid, caproic acid, caprylic acid, capric acid, succinic acid, glutaric acid, adipic acid, D-tartaric acid, L-tartaric acid, lactic acid, uric acid, acid maleic acid, fumaric acid, isovalyric acid, furoic acid, sorbic acid, salicylic acid, trans-cinnamic acid, acetylsalicylic acid, myristic acid).

24. Process according to claim 23, characterized in that the organic acid is preferably citric acid.

25. Process, according to claim 23, characterized by comprising a concentration of citric acid varying between 0.5 and 5 mol L ^"1 , preferably 1 mol L ^"1 .

26. Process, according to claim 1, characterized in that the drying step (h) comprises the processing of the solution obtained in step (g), preferably in a spray dryer at a temperature of 100 to 200 °C, preferably at 150 °C, with a flow rate of 1 to 20 mL/min, preferably 5 mL/min, and with a nozzle of 0.7 to 2.0 mm, preferably 1.5 mm.

27. Silica nanoparticle with adsorbed ions characterized by being obtained according to the steps described in claims 1 to 10, 15 and 19 to 26.

28. Silica nanoparticle with adsorbed ions, according to claim 27, characterized by the fact that it comprises an average diameter ranging between 5 and 200 nm, preferably 20 nm.

29. Silica nanoparticle with adsorbed ions, according to claim 27, characterized by the fact that it comprises a zeta potential between -150 and +150 mV, preferably at -80 mV.

30. Use of the silica nanoparticle with adsorbed ions, according to claim 27, characterized by being used as a fungicidal and/or bactericidal agent in the agrochemical, pharmaceutical, home and personal care industries.