RU2569546C1 - Photochemical method of producing stabilised silver nanoparticles - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: photochemical method of producing stabilised silver nanoparticles includes reacting silver ions with a stabilising agent in an aqueous solution at room temperature under the effect of visible light. The reducing agent and the stabilising agent used are sodium dodecyl sulphate or a polymer product selected from: polyvinyl pyrrolidone, polyvinyl alcohol, starch. The stabiliser-reducing agent is taken in weight excess. The silver ion source used is silver nitrate. The visible light source used is an artificial light source.

EFFECT: invention cuts the duration and power costs of producing aqueous preparations of stabilised silver nanoparticles, which retain stability and bactericidal activity for at least 6 months without further purification and harmful production and environmental factors.

5 cl, 3 dwg, 2 tbl

Description

The invention relates to the field of nanotechnology, specifically to the preparation and use of preparations based on silver nanoparticles, and can be used for the production of bactericides intended for use in medicine, veterinary medicine, the food industry, for domestic and other purposes.

Colloidal dispersions of silver nanoparticles are used in the electronics industry to produce conductive adhesives and inks, and protective screens for graphic displays. The biocidal properties of silver nanoparticles are well known, and the creation of bactericidal preparations based on them is an important achievement in the field of nanotechnology. Stabilized nanosilver preparations are used to obtain bactericidal coatings, disinfectants, detergents, wounds and other products as prophylactic antimicrobial protective agents in catering establishments, in children’s, sports, medical institutions and other places where the likelihood of developing bacterial, fungal and viral infections .

A wide range of compounds, such as sodium citrate or dodecyl sulfate, polyvinyl alcohol, polyvinylpyrrolidone, starch, gelatin and other low molecular weight and polymeric products of natural and artificial origin, are used as stabilizing agents (stabilizers) that help to preserve the nanoscale structure and high bactericidal activity of reduced silver particles. .

There are a large number of chemical, electrochemical, microbiological, as well as combined, combining various approaches, methods for producing stable preparations of silver nanoparticles that maintain stable bactericidal activity during the periods of their storage and use.

As chemical reducing agents use borohydrides, for example [RU 2367512 C1, publ. September 20, 2009], hydrazine derivatives, for example [US 20130029034 A1, publ. 01/31/2013], tannins [RU 2430169 C2, publ. September 27, 2011], ascorbic acid [US 5389122, publ. 02/14/1995], glucose, for example [CN 101941075 A, publ. 12.01.2011], quercetin [RU 2333773 C1, publ. September 20, 2008] and other compounds. The use of chemical reducing agents leads to contamination of the final products with undesirable, often toxic impurities, and requires additional costs for their cleaning. Electrochemical reduction of silver ions to obtain stabilized nanosilver preparations [RU 2364470 C1, publ. 08/20/2009, RU 2390344 C1, publ. 05.27.2010, RU 2410471 C1, publ. 01/27/2011, RU 2456356 C1, publ. July 20, 2012, etc.] is associated with high energy costs.

The use of reverse micellar technologies is described, which allows to obtain stable preparations of silver nanoparticles [RU 2322327 C2, publ. 04/20/2008, RU 2341291 C1, publ. December 20, 2008, etc.], however, the multi-stage method, the need to use a large number of reagents limit the ability to scale production.

Microbiological methods are gaining widespread acceptance, for example [SA 2656323 A1, publ. 01/10/2008, RU 2460797 C2, publ. 09/10/2012, US 20090239280 A1, publ. September 24, 2009, US 20120108425 A1, publ. 05.03.2012, RU 2477172 C1, publ. 03/10/2013, etc.]. Nanosilver preparations obtained using microorganisms may contain biomass residues and harmful metabolic products, the purification of which additionally increases their cost.

Methods for producing silver and other metal nanostructures based on the reduction of ionic silver under the influence of various types of electromagnetic radiation are described. For example, stable, highly ordered | ligand-coated silver nanoparticles are obtained in a polymer matrix of polyvinyl alcohol or gelatin under the action of laser radiation at a wavelength of 510.6 nm or 578.2 nm in a solution containing sodium citrate, sodium oleate and sodium borohydride [RU 2510210 C1, publ. 03/27/2014]. The use of electromagnetic radiation allows to obtain nanosilver without the use of chemical reducing agents. So, a method for producing a colloidal solution of silver nanoparticles [RU 2474471 C2, publ. 02/10/2013] includes gamma irradiation in an inert atmosphere of an aqueous solution of silver nitrate containing carboxymethylchitin as a stabilizer without additional reducing agents. The process is complicated by the need to use an inert gas and harmful gamma radiation to personnel.

The basis of photochemical methods for producing metal nanoparticles is the generation of strong highly active reducing agents - electrons, radicals, excited particles under the influence of light energy. In the work of R.F. Abbasova et al. “Obtaining silver nanoparticles in aqueous solutions of polyacrylic acid and their aggregation during photochemical reduction”, 2009 [1.pdf] describes the formation of nanostructured silver aggregates upon reduction of silver ions by UV irradiation in the presence of polyacrylic acid. Irradiation is carried out with the full light of a high-pressure mercury lamp in air at room temperature without the introduction of additional reducing agents. In this case, nanoparticles are formed that are not contaminated with impurities associated with processes using chemical reducing agents. Under the action of irradiation as a result of photoreduction, not only the processes of obtaining nanoparticles of a certain size go, but also larger aggregates are formed. The authors note the sedimentation instability of the obtained samples, which increases with increasing UV irradiation time. The disadvantage of this method is the need to use unhealthy UV light.

From a practical point of view, technical solutions that are not related to the use of radiation harmful to human health seem to be more preferable. According to [US 8333822 B2, publ. 10/18/2012], stable silver nanoparticles are formed under natural light when compounds are introduced into the system that combine the properties of a stabilizer and a reducing agent (hereinafter “stabilizer-reducing agent”), in particular polyoxyethyleneamine-based polymers. By varying the composition of the polymer and selecting the quantitative ratios of the reagents, it is possible to obtain systems containing silver nanoparticles of various sizes. However, the synthesis of the described polymers is an independent task, which complicates the scaling and creation of industrial production. The tool with antimicrobial activity according to the patent [RU 2278669 C1, publ. 06/27/2006], obtained in the light by the interaction of a silver salt with the natural polysaccharide arabinogalactan, which also plays the role of a stabilizer and a reducing agent. The disadvantage of this method is the need to use a highly alkaline environment and additional heating.

As a prototype, a method for producing silver nanocomposites based on synthetic water-soluble polymers [RU 2485051 C1, publ. 06/20/2013]. According to the invention, copolymers of 2-dioxo-2-methacrylamido-D-glucose with 2-dimethylaminoethyl methacrylate or 2-diethylaminoethyl methacrylate are used as a stabilizing agent. The method is implemented by the interaction of these copolymers with AgNO ₃ in an aqueous solution at room temperature and natural light at a polymer concentration of 0.010-0.100 g / ml and an AgNO ₃ concentration _of 0.001-0.01 g / ml. Depending on the composition of the copolymer, restoration takes from three hours to several days.

The disadvantage of this method is the need to use as a stabilizer-reducer is not a commercial polymer product, the synthesis of which requires prolonged heating in an inert atmosphere with subsequent purification.

Thus, the analysis of the prior art shows that, despite the large number of known methods for producing nanodispersed silver, almost all of them are characterized by disadvantages that limit their use for the industrial production of bactericidal preparations.

The objective of the present invention is to develop a method for producing stabilized silver nanoparticles, which is carried out using available, commercially available reagents, under conditions that exclude the use of harmful production and environmental factors and allow quickly and with minimal energy consumption to obtain stable, not requiring additional purification, end products with bactericidal activity.

The problem is solved by the proposed photochemical method for producing stabilized silver nanoparticles, including the interaction of silver ions with a stabilizing agent in an aqueous solution at room temperature under the influence of visible light, characterized in that sodium dodecyl sulfate or a polymer product selected from the group polyvinylpyrrolidone is used as a stabilizing agent , polyvinyl alcohol, starch, and an artificial source is used as the visible light source lighting.

The process is carried out in air with a massive excess of stabilizer-reducing agent without additional heating with vigorous stirring and without introducing special reducing agents into the system. The reaction system may include, along with polymer stabilizing agents, surfactants.

The basis of the proposed method is the fact that we discovered that, under the conditions of irradiation of aqueous solutions of silver salts with visible light produced by an artificial light source, in the presence of a number of polymer and low molecular weight compounds traditionally used as stabilizers and surfactants ), the process of reduction of silver ions and the formation of stable colloidal dispersions can proceed with high speed in air at room temperature without introducing he further reducing agents. Thus, we have shown that under the influence of irradiating aqueous solutions of reagents with light from a halogen incandescent lamp, effective reduction occurs in the presence of sodium dodecyl sulfate, polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), and starch. In this case, polymer products can be used in combination with surfactants, for example, sodium dodecyl sulfate, oleic acid, Triton X-100.

The use of these substances as stabilizers of silver nanodisperses is known from the prior art, however, special reducing agents are additionally introduced into the reaction system to carry out the reduction process [see, for example, RU 2445951 C1, publ. 03/27/2012, RU 2012151096 A, publ. 10/06/2014, RU 2011140012 A, publ. 10/04/2013] or affect the system with gamma radiation, under the action of which electrons are generated in the solvent, which restore silver ions [RU 2259871 C2, publ. 09/10/2005]. Thus, the unexpected result is that the production of stabilized silver nanoparticles can be carried out under much milder conditions without the use of special reducing agents and hard energy exposure using available compounds traditionally used as stabilizing agents, which play the role of stabilizing reducing agents in this process . The oxo and hydroxo groups of these compounds (carboxyl, carbonyl, hydroxyl) are able to form complexes with silver cations, providing optimal conditions for their reduction by hydrated electrons or hydrogen atoms [Ershov B.G., Henglein Α. // J. Phys. Chem. In 1998. 102. P. 10663], and also interact with positively charged clusters and atoms of the surface of nanoparticles, ensuring their stabilization and size control [Wang W., Chen X., Efrima S. // J. Phys. Chem. B. 1999. 103. P. 7238].

Apparently, other synthetic or natural stabilizers containing oxo and hydroxo groups capable of forming complexes with silver cations can also be used as stabilizing reducing agents.

For the invention, any water-soluble silver compound, in particular silver nitrate, can be used as the silver compound.

Unlike the prototype, according to which the process is carried out in natural light, the use of artificial light sources has obvious advantages. They allow you to smoothly control the intensity and dose of radiation and, thus, control the recovery process, which is of great importance when implementing the method in an industrial environment. As a source of artificial lighting, you can use any lamp that emits visible light. However, the use of mercury lamps is undesirable, since working with them requires water cooling and is associated with the risk of metallic mercury and its vapors entering the environment if the lamp is damaged, and also requires additional costs for their disposal. Optimal from the point of view of economics, ecology and safety measures is the use of incandescent lamps, in particular halogen lamps that emit visible light in the wavelength range 325-1000 nm.

The speed of the process depends on the specific power of the light flux, which, in particular, depends on the power of the radiation source and its distance relative to the irradiated solution. It is important to ensure intensive mixing of the reaction mixture in order to realize uniform irradiation of the entire volume. Empirically selecting the appropriate parameters, it is possible to ensure fast and efficient reduction of ionic silver to obtain stabilized dispersions of silver nanoparticles.

In FIG. Figure 1 shows UV spectra of colloidal solutions of silver nanoparticles obtained using PVP (7), PVA (2), starch (5), sodium dodecyl sulfate (4), PVA in combination with sodium dodecyl sulfate (5) as stabilizing agents ) The UV spectra were recorded using a HACH DR-4000V device (USA).

In FIG. 2 (a-d), by way of illustration, electron micrographs of stabilized silver nanoparticles obtained using PVP (a), PVA (b), starch (c), and sodium dodecyl sulfate (g) as stabilizers are shown.

In FIG. 3 (a-d) as an illustration, diagrams of the size distribution of stabilized silver nanoparticles obtained using PVA as stabilizers, PVA in combination with sodium dodecyl sulfate (b), PVA in combination with oleic acid (c) are shown , PVA in combination with Triton X-100 (g).

The size and statistical size distribution of stabilized silver nanoparticles is determined by transmission electron microscopy using a Hitachi-11 device (Japan).

The invention is as follows.

A solution of a stabilizer-reducing agent or a binary composition of a stabilizer-reducing agent with a surfactant in water is prepared. In the resulting solution, a silver compound, for example silver nitrate, is additionally dissolved. The resulting solution with vigorous stirring is irradiated with incandescent light without additional heating for a time sufficient to complete the process, as judged by the change in the optical density of the solution at a wavelength near 400 nm (see Fig. 1). Moreover, in the range of 30-120 minutes there is an increase in the color intensity characteristic of colloidal solutions of nanosilver. Further irradiation does not lead to a noticeable increase in the content of nanosilver in the reaction mixture. In the examples below, a visible light source is a 150 W halogen lamp complete with lenses and a condenser. The specific power of the light flux measured by the thermoelectric actinometer AT-50 is 10 mW / cm ² . To implement the method on an industrial scale, a transition to a multi-lamp lighting installation will be required, while the exposure time of the light flux should be optimized taking into account real production conditions.

The quantitative ratio of the stabilizer-reducing agent and silver compounds is chosen so as to obtain the most concentrated, non-sedimenting for a long time, colloidal solutions of stabilized silver nanoparticles. For this purpose, a massive excess of a stabilizer-reducing agent is used, which makes it possible to stabilize the entire amount of nanoparticles formed. The presence of a stabilizer-reducing agent in the final product does not adversely affect the possibility of its use as a bactericidal agent.

To obtain stable protective bactericidal coatings, low molecular weight micelle-forming surfactants, for example sodium dodecyl sulfate, oleic acid, Triton X-100, which do not adversely affect either the recovery rate or the size distribution of the obtained nanoparticles, are added to the stabilizing agent (see Fig. . 3). Examples 5-7 below show the possibility of using PVA as a stabilizer-reducer in combination with various surfactants, however, it is obvious that other polymer stabilizers in combination with other surfactants can be used instead of PVA.

It was found that the preparations obtained in accordance with the invention, when stored under standard conditions (in a closed container without access of light at room temperature) for at least 6 months, are sedimentation stable and retain close to the initial size distribution of stabilized silver nanoparticles and close to the initial level of bactericidal activity.

The following examples illustrate the implementation of the proposed method, but do not exhaust all the possibilities of its implementation.

In a standard experiment, 40 mg of a stabilizer-reducer or 80 mg of a mixture (1: 1) of a stabilizer-reducer with a surfactant is dissolved in 50 ml of distilled water, after which 30 mg of silver nitrate are added to the solution, and the resulting clear solution is irradiated with a 150 W halogen lamp at vigorously stirring the solution on a magnetic stirrer. The distance between the solution and the light source is 30 cm, which corresponds to a specific power of the light flux of 10 mW / cm ² . The minimum exposure time under the described conditions is 30 minutes. In this case, the appearance of a color characteristic of colloidal solutions of nanosilver is observed. Within 120 minutes there is an increase in the color intensity and a corresponding change in the UV spectrum of the reaction mixture, indicating an increase in the content of colloidal nanosilver in the system. Further irradiation does not lead to a change in the concentration of nanosilver.

The resulting colloidal solution can be directly used after necessary dilution as a bactericidal agent or dried by any known method to obtain a dry product suitable for storage and further preparation of liquid preparations for practical use as disinfectants.

According to example 1, polyvinylpyrrolidone (M.v. = 26400) is used as a stabilizer-reducing agent.

According to example 2, polyvinyl alcohol is used as a stabilizer-reducing agent (M.v. = 10000).

According to example 3, starch is used as a stabilizer-reducing agent (M.w. = 50,000).

In Example 4, sodium dodecyl sulfate is used as a stabilizing agent.

According to example 5, PVA is used as a stabilizer-reducer, to which sodium dodecyl sulfate is added (mass ratio 1: 1).

According to example 6, PVA is used as a stabilizer-reducer, to which Triton X-100 is added (mass ratio 1: 1).

According to example 7, PVA, to which oleic acid is added (mass ratio 1: 1), is used as a stabilizer-reducing agent.

As can be seen from FIG. 2 and 3, which illustrate electron micrographs and the size distribution of particles obtained using various stabilizing agents, about 70% of the recovered silver is contained in atomic silver clusters of 20-30 nm in size. The rest of the silver is represented by particles with sizes from 2 to 200 nm. When sodium dodecyl sulfate is used as a stabilizer (Example 4), mainly particles with a size of about 60 nm are formed.

The results of the study of the bactericidal activity of preparations of stabilized silver nanoparticles obtained by the claimed method.

To study the bactericidal activity, the colloidal solution obtained as described above is dried in air, and the dry product is used to prepare exact dilutions.

The method of diffusion in agar determined the bactericidal activity of the preparations obtained in examples 1-4. E. coli, S. aureus, S. enteritidis, S. dublin, S. cholerasuis, S. typhimurium were taken as test cultures. In order to study the spectrum of action, the activity of the preparations was also studied against bacteria of the genera Citrobacter, Providencia, Hafnia, Proteus, Morganella and Listeria.

In the thickness of meat-peptone agar containing a daily culture of microorganisms at a dose of 10 ⁷ m.k./ ml, holes 4 mm in diameter are sterilized. Working dilutions of the preparation (35, 17, 8, and 4 mg / L) are added to the wells and placed in a thermostat at 37 ° C for 18-20 hours. The results are evaluated by the size of the growth inhibition zone of the test cultures around the hole. The results obtained on the example of a sample of silver nanoparticles stabilized by polyvinylpyrrolidone are presented in Table 1.

As can be seen from the table, in a concentration of at least 4 mg / l, the drug exhibits a bactericidal effect in relation to all studied microorganisms, which increases with increasing silver concentration. Similar results were obtained for the preparations obtained in examples 2-4.

A study of the stability of the obtained samples during storage for 6 months in closed containers in the dark at room temperature shows that the number of nanoparticles, measured by the relative method by the optical density, decreases by no more than 10%. The size distribution during storage does not change significantly, and at the same time, the preparations retain a close to the initial level of bactericidal activity in relation to the test cultures of E. coli and Salmonella s.p.p. In areas of growth inhibition of S. aureus, slight turbidity of the agar was noted, which indicates the bacteriostatic effect of the drug.

Table 2 shows the results of testing the bactericidal activity of the preparations obtained according to examples 2, 5-7, containing PVA and a mixture of PVA with sodium dodecyl sulfate, Triton X-100, oleic acid as stabilizers and film-forming components in a mass ratio of 1: 1.

From the data presented it follows that all drugs have bactericidal activity against test cultures at a concentration of up to 4 mg / L.

The disinfecting activity of nanosilver preparations obtained according to examples 5-7 was studied on smooth surfaces (tiled and metlach tiles) contaminated with a suspension of the daily culture of the test microorganism using protein protection. The drugs are applied at a rate of 500 ml / m ² . The neutralization of the action of drugs is carried out by ten-fold dilution of swabs from the treated object. Control are objects treated with water. The disinfecting activity against E. coli and Salmonella spp was established in preparations with a concentration of silver nanoparticles of at least 17 mg / l and an exposure time of 3 hours. In the case of S. aureus, complete disinfection of test objects was achieved when exposed to preparations with a silver concentration of at least 35 mg / l at an exposure time of 3 hours

The drugs obtained in examples 5-7 were tested in model experiments in order to reduce the level of contamination of objects of veterinary supervision in poultry farms (the surface of equipment and tools for cutting poultry carcasses). For this, the listed objects were artificially contaminated with a suspension of daily cultures of E. coli and Salmonella spp. The concentration of silver nanoparticles in the preparations was 35 mg / l. Surfaces are treated at a rate of 500 ml / m ² with an exposure time of 3 hours, tools (scissors, tweezers) are immersed in a solution of the drug for 30 minutes, carcasses of a bird are placed in a container containing a silver preparation for 30 minutes. After this time, wash off with sterile cotton swabs into test tubes with saline and conduct bacteriological studies for the presence of test cultures used in the experiment. The control are test objects treated with water.

While in the crops of washouts from surfaces in the control, a continuous growth of test cultures is found, in washings from surfaces treated with nanosilver preparations, there is no growth of test cultures. The growth of microorganisms in the crops of washes from tools treated with nanosilver preparations is represented by single colonies, while in the control it reached hundreds of colonies in separate samples. In washes from carcasses of birds treated with the preparation of stabilized silver nanoparticles, the growth of enterobacteria was observed in the amount of 20-40 colonies in single samples, while in the control, abundant growth of test cultures in crops was obtained in all samples of washes.

The data show that the inventive method allows to obtain aqueous preparations of stabilized silver nanoparticles with high bactericidal activity in a relatively wide range of microorganisms. The drugs remain stable and bactericidal for at least 6 months (observation period) and can be used to disinfect various objects in industry and at home.

Thus, the inventive photochemical method for producing stabilized silver nanoparticles involves the use of available reagents produced by industry, carried out under conditions that exclude the use of harmful production and environmental factors, and allows to obtain final products with minimal energy consumption that do not require additional purification and are suitable after direct dilution for direct use as a disinfectant or to obtain dry preparations, p ednaznachennyh to obtain the required dilution.

Claims (5)

1. A photochemical method for producing stabilized silver nanoparticles, including the interaction of silver ions with a stabilizing agent in an aqueous solution at room temperature under the influence of visible light, characterized in that sodium dodecyl sulfate or a polymer product selected from the group polyvinylpyrrolidone is used as a reducing agent and a stabilizing agent , polyvinyl alcohol, starch, which are taken in excess, silver nitrate is used as a source of silver ions, and as a source visible range veto use of artificial light source. 2. The method according to p. 1, characterized in that the polymer stabilizing agent is used in composition with a surfactant. 3. The method according to p. 2, characterized in that as the surfactant use sodium dodecyl sulfate, or oleic acid, or Triton X-100. 4. The method according to p. 1, characterized in that as a source of artificial lighting using a halogen incandescent lamp. 5. The method according to p. 1, characterized in that the process is carried out with stirring of the reaction mixture.

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