CN108115150B - Preparation method of nano silver with adjustable size - Google Patents
Preparation method of nano silver with adjustable size Download PDFInfo
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- CN108115150B CN108115150B CN201711381953.7A CN201711381953A CN108115150B CN 108115150 B CN108115150 B CN 108115150B CN 201711381953 A CN201711381953 A CN 201711381953A CN 108115150 B CN108115150 B CN 108115150B
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- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/16—Making metallic powder or suspensions thereof using chemical processes
- B22F9/18—Making metallic powder or suspensions thereof using chemical processes with reduction of metal compounds
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- B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
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- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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Abstract
The invention discloses a preparation method of nano silver with adjustable size, which comprises the following steps: step 10) adding deionized water into a container and heating to a boiling state; adding sodium citrate solution into deionized water in a boiling state to form stabilizer solution; step 20) adding silver "seed" solution to the stabilizer solution prepared in step 10), adding AgNO during stirring 3 The solution and hydroquinone solution are stirred and kept in boiling state; step 30) cooling the solution prepared in the step 20) at room temperature to prepare the spherical nano silver. The preparation method can conveniently obtain the spherical nano silver with good monodispersity, and the size of the spherical nano silver is widely adjustable.
Description
Technical Field
The invention relates to a preparation method of nano silver, in particular to a preparation method of nano silver with adjustable size.
Background
The nano silver has excellent physical and chemical properties different from macroscopic blocks, and has wide application prospects in various fields of catalysis, biological and chemical sensors, optical imaging, nonlinear optics, surface-enhanced Raman scattering, electronics and the like. Currently, nanosilver has become the most used material in consumer products of the nanotechnology class. Numerous studies have shown that the performance of nanosilver is strongly dependent on its shape and size. Thus, the controllable preparation of nano-silver is a prerequisite for achieving its performance regulation and subsequent application. From the practical application, the spherical nano silver is the most stable and easy to prepare. For the adjustable size preparation of spherical nano silver, the preparation is carried out under an organic solvent system, such as ethanol, glycol, oleylamine/toluene and 4-tert-butylAnd toluene. However, silver nanoparticles prepared in an organic solvent system are generally not easy to perform water phase conversion, and are difficult to perform subsequent hydrophilic surface functionalization modification, so that the application of nano silver is severely limited. And meanwhile, the use of organic solvents is easy to cause environmental pollution. In contrast, aqueous phase synthesis of spherical nanosilver has greater potential advantages. The sodium citrate reduction method is the most common and simple method for synthesizing nano gold and silver by water phase, namely, under the boiling state, a metal precursor (chloroauric acid or silver nitrate) solution reacts with a sodium citrate solution to obtain nano gold or silver. Wherein, the sodium citrate plays a plurality of roles of reducing agent, stabilizing agent and pH regulator. Particularly, sodium citrate not only has excellent biocompatibility, but also is easier to replace with other ligands or biomolecules because citrate is a weaker ligand, so that the multifunctional surface modification is realized, and the application of nano silver in a biological system is facilitated. However, as silver precursors such as silver nitrate have high reactivity under the water phase and the non-single action mode of citrate in the reaction, the nucleation and growth of nano silver cannot be controlled, and a mixture with various sizes and shapes is extremely easy to form. One of the methods to deal with the above problems is to separate the nucleation and growth of nano silver, i.e. using a "seed" growth method: first, a strong reducing agent such as sodium borohydride (NaBH) 4 ) The small-size nano silver is synthesized to serve as a seed, and the seed is taken as a growth center for continuous growth, so that the nucleation process and the growth process are effectively separated, and the size-adjustable preparation of the spherical nano silver is hopefully realized. Although the above method is effective in growing spherical nano-silver of small size (within 20 nm), when growing nano-silver of larger size, a secondary nucleation phenomenon occurs remarkably, that is, the original "seed" is not taken as a growth center any more, but a large amount of nano-silver is spontaneously generated, which results in that the finally obtained spherical nano-silver is not uniform in size and is accompanied by a large amount of non-spherical structures such as rod-shaped and plate-shaped nano-silver, etc. Therefore, in order to reduce the occurrence of secondary nucleation, when growing spherical nano silver with larger size, links such as stepwise growth and multi-parameter modulation are generally inevitably required.
Hydroquinone is an organic compound formed by substituting two para-hydrogen atoms of benzene with hydroxyl groups, is easily soluble in water, and is mainly used as a photographic developer: in the case that silver 'seeds' are present in the solution, hydroquinone only reduces the precursor of silver in the solution on the surface of the silver 'seeds' to form a silver simple substance film. Since hydroquinone has a moderate redox potential (e° = -0.699v vs nhe, ag + /Ag 0 E degree= +0.799V), the above process can be performed rapidly (1) at normal temperature. Similarly, the above strategy is also applicable to the preparation of gold films at room temperature (AuCl 4 - /Au 0 ,E°＝+1.002V)(2)。
Particularly, hydroquinone and an oxidation product benzoquinone thereof have only very weak adsorption effect on the metal surface, and if a stabilizer with strong adsorption effect (such as citrate) exists in a reaction system, the adsorption effect of the hydroquinone and the benzoquinone can be replaced by adsorption competition effect, so that the citrate-stable nano material is formed. Based on the two characteristics of hydroquinone, in recent years, attempts have been made to prepare sodium citrate-stable nano gold and silver by a "seed" method under normal temperature conditions by using hydroquinone as a selective reducing agent and sodium citrate as a stabilizer. However, although the above-mentioned hydroquinone- "seed" method strategy realizes the large-scale adjustable preparation of spherical nano gold with stable sodium citrate, the obtained product has serious problems of very limited adjustable range of size and a large amount of flaky nano silver during the preparation of spherical nano silver.
Disclosure of Invention
Technical problems: the technical problems to be solved by the invention are as follows: the preparation method of the nano silver with adjustable size can conveniently prepare the spherical nano silver with good monodispersity, and the size of the spherical nano silver is widely adjustable.
In order to solve the technical problems, the technical scheme adopted by the embodiment of the invention is as follows:
a method for preparing nano silver with adjustable size, which comprises the following steps:
step 10) adding deionized water into a container and heating to a boiling state; adding sodium citrate solution into deionized water in a boiling state to form stabilizer solution;
step 20) adding silver "seed" solution to the stabilizer solution prepared in step 10), adding AgNO during stirring 3 The solution and hydroquinone solution are stirred and kept in boiling state;
step 30) cooling the solution prepared in the step 20) at room temperature to prepare the spherical nano silver.
As a preferred example, the container has a reflux effect.
As a preferred example, in the step 20), agNO is contained in the final reaction solution 3 And hydroquinone in a molar ratio of 1:2.
As a preferred example, in the step 20), the molar ratio of sodium citrate to silver nitrate in the final reaction solution is 0.2 to 0.3:1.
As a preferred example, the silver "seed" solution is prepared as follows: mixing deionized water with a sodium citrate solution, and stirring to form a stabilizer solution; the stabilizer solution was heated to the temperature of the water bath and then AgNO was added 3 Adding NaBH into the solution 4 A solution; and cooling at room temperature, and then, fixing the volume by deionized water to prepare the silver 'seed' solution.
As a preferred example, in the step 20), agNO is added first 3 The solution was immediately followed by the hydroquinone solution.
The beneficial effects are that: compared with the prior art, the invention has the following beneficial effects:
the preparation method of the embodiment of the invention can conveniently prepare the spherical nano silver with good monodispersity, and the size of the spherical nano silver is widely adjustable. According to the method, silver nitrate is used as a silver precursor, sodium citrate is used as a stabilizer, hydroquinone is used as a selective reducing agent, and the nucleation and growth processes of nano silver are effectively separated by a seed growth method under thermal reflux, so that the occurrence of secondary nucleation is avoided, and nano silver with good monodispersity is successfully prepared. According to the preparation method disclosed by the invention, by only changing the dosage of the silver seeds in the step 20), under the condition that the ratio of silver nitrate to sodium citrate in the growth solution is not required to be changed, a series of spherical nano silver with adjustable size and good monodispersity is prepared through a one-step seed growth process, and the steps of multiple growth and multi-parameter adjustment which are generally necessary are not required.
Drawings
FIG. 1 (a) is a transmission electron microscope characterization photograph of nano-silver prepared in example 1;
FIG. 1 (b) is a transmission electron microscope characterization photograph of the nano-silver prepared in example 2;
FIG. 1 (c) is a transmission electron microscope characterization photograph of the nano-silver prepared in example 3;
FIG. 1 (d) is a transmission electron microscope characterization photograph of the nano-silver prepared in example 4;
FIG. 2 (a) is a transmission electron microscope characterization photograph of nano-silver prepared in comparative example 1;
FIG. 2 (b) is a transmission electron microscope characterization photograph of the nano-silver prepared in comparative example 2;
FIG. 2 (c) is a transmission electron microscope characterization photograph of the nano-silver prepared in comparative example 3;
FIG. 2 (d) is a transmission electron microscope characterization photograph of the nano-silver prepared in comparative example 4;
FIG. 2 (d) is a transmission electron microscope characterization photograph of the nano-silver prepared in comparative example 4;
FIG. 3 is an ultraviolet-visible spectrum of the nano silver prepared in example 1-example 4;
FIG. 4 is an ultraviolet-visible spectrum of the nano silver prepared in comparative example 1-comparative example 4;
FIG. 5 (a) is a transmission electron microscope characterization photograph of the nano-silver prepared in example 5;
FIG. 5 (b) is a transmission electron microscope characterization photograph of the nano-silver prepared in example 6;
FIG. 5 (c) is a transmission electron microscope characterization photograph of the nano-silver prepared in example 7;
FIG. 5 (d) is a transmission electron microscope characterization photograph of the nano-silver prepared in example 8;
FIG. 6 is a transmission electron microscope characterization photograph of the nano silver prepared in comparative example 5;
fig. 7 is a transmission electron microscope characterization photograph of the nano silver prepared in comparative example 6.
Detailed Description
The following describes the technical scheme of the invention in detail.
The preparation method of the nano silver with adjustable size comprises the following steps:
step 10) adding deionized water into a container and heating to a boiling state; adding sodium citrate solution into deionized water in a boiling state to form stabilizer solution;
step 20) adding silver "seed" solution to the stabilizer solution prepared in step 10), adding AgNO during stirring 3 The solution and hydroquinone solution are stirred and kept in boiling state;
step 30) cooling the solution prepared in the step 20) at room temperature to prepare the spherical nano silver.
In the preparation method, hydroquinone is used for preparing AgNO in the presence of silver seeds 3 Is much more reductive than sodium citrate. After the hydroquinone solution is added into the reaction solution, the hydroquinone only reduces AgNO on the surface of silver seeds 3 As silver atoms, the generated silver atoms are continuously deposited by taking silver 'seeds' as cores, so that the silver 'seeds' grow gradually. The above reaction characteristics effectively separate the nucleation and growth processes of nano silver and avoid the occurrence of secondary nucleation. Hydroquinone still maintains the ability to selectively reduce in the boiling state (i.e. AgNO is reduced on its surface only in the presence of silver "seeds") 3 ). According to the Van der Waals rule, the reaction is usually accelerated 2 to 4 times per 10 degree increase in temperature. As a result of simple calculation, the reaction rate at boiling (100 ℃ C.) was 128 times that at normal temperature (30 ℃ C.). Under high reaction rate, silver atoms are deposited on the surface of silver seeds in a centrosymmetric way without differentiating crystal faces and without selectivity, so that spherical nano silver with stable thermodynamics is formed, and the formation of non-spherical structures such as silver nano sheets or silver nano rods is eliminated. On the other hand, toThe adsorption capacity of the benzenediol and the oxidation product benzoquinone thereof on the metal surface is far weaker than that of sodium citrate, so that the sodium citrate only plays a role of a stabilizer. Thus, spherical nano silver with stable sodium citrate is finally formed.
According to the embodiment, silver nitrate is used as a silver precursor, sodium citrate is used as a stabilizer, hydroquinone is used as a selective reducing agent, and the nucleation and growth processes of nano silver are effectively separated by a seed growth method under thermal reflux, so that the occurrence of secondary nucleation is avoided, and nano silver with good monodispersity is prepared. The spherical nano silver with good monodispersity fully ensures the reliability of various physicochemical properties, such as but not limited to optical, electrical, catalytic, surface enhanced Raman scattering, antibacterial/bacteriostatic properties and the like, due to uniform individual shape and size, and is particularly beneficial to practical application. The nano silver prepared in the example is spherical nano silver with thermodynamic stability.
The preparation method of the embodiment can prepare the spherical nano silver with widely adjustable size. Under the condition of not changing other reaction parameters, the size of the spherical nano silver can be widely adjusted by only changing the amount of silver seeds.
In the above embodiment, the container has a reflux effect. For example, the container is a container with a condenser tube. During the preparation of this example, the solution was in a boiling state. The vapor from boiling and evaporating solution encounters the condenser tube and becomes liquid and returns to the container, so that the volume of the solution is kept unchanged before and after the reaction.
In the above example, in step 20), agNO was present in the final reaction solution 3 And hydroquinone in a molar ratio of 1:2. This ensures that the reaction proceeds adequately. In the final reaction solution, the molar ratio of the sodium citrate to the silver nitrate is 0.2-0.3:1. This ensures the stabilization of sodium citrate to nano silver and prevents sodium citrate from reacting with silver nitrate during the addition process.
There are various methods for preparing silver "seed" solutions. The following preparation methods are preferred in this example: mixing deionized water with a sodium citrate solution, and stirring to form a stabilizer solution; stabilizer solutionHeating to water bath temperature, adding AgNO 3 Adding NaBH into the solution 4 A solution; and cooling at room temperature, and then, fixing the volume by deionized water to obtain the silver seed solution.
For example: preparing silver seed solution: mixing 60-80 mL of deionized water with 20mL of sodium citrate solution with the mass volume ratio of 1%, and uniformly stirring to form a stabilizer solution; heating the stabilizer solution to the temperature of the water bath at 70-80 ℃ in the water bath, and then adding 1.7mL of AgNO with the mass-volume ratio of 1% into the stabilizer solution 3 A solution; adding NaBH with mass volume ratio of 0.1% of 1.5-2.5 mL into the stabilizer solution under the stirring of a mechanical stirring rod 4 Stirring the solution for 60-120 min; finally, cooling the solution at room temperature, and then, using deionized water to fix the volume to 100mL, thereby preparing the silver 'seed' solution.
The method can prepare stable silver seeds with narrow size distribution. In the method, a reaction mode of combining rapid reaction with heating curing in the presence of sodium citrate is adopted, and the presence of a large amount of sodium citrate can effectively prevent the generated silver seeds from being oversized. By NaBH 4 To make AgNO 3 Is quickly reduced to nucleate and grow into nano particles. The silver seeds are further cured under heating, which is equivalent to the ablation of laser external field, so that the final product has good monodispersity. The method can obtain silver seeds with good stability and narrow size distribution, and the average size of the silver seeds can be ensured to be 4nm. The preparation method is the prior art, and can be seen in Chinese patent of patent number ZL 201210183257.6. The silver "seed" preparation method described in this patent can be applied to the present invention.
In step 20) of the above example, agNO is added first 3 And (3) adding a hydroquinone solution. Because AgNO is added first 3 The solution is fully and uniformly dispersed around the silver seeds added in the reaction solution, so that the hydroquinone solution added later is convenient for uniformly reducing the hydroquinone solution on the surfaces of the silver seeds.
The preparation method of the above embodiment can prepare a stableHigh quality silver "seeds" with narrow size distribution. In the preparation method, a reaction mode of combining rapid reaction with heating curing in the presence of a large amount of sodium citrate is adopted, and the excessive sodium citrate can effectively prevent the generated silver seeds from being oversized. Preferably, the method of this example uses sodium citrate at a mass concentration 10 to 15 times that required for the conventional sodium citrate method (procedure of comparative example 5 below) to prepare nano-silver. By NaBH 4 To make AgNO 3 Is quickly reduced to nucleate and grow into nano silver. The silver seeds are further cured under proper heating conditions, which is equivalent to the ablation of laser external fields, so that the final product has good monodispersity. The preparation method of the invention can obtain silver seeds with good stability and narrow size distribution, and the average size of the silver seeds can be controlled to be about 4nm.
The preparation method of the embodiment is environment-friendly and efficient. According to the preparation method of the spherical nano silver with adjustable size, in the growth process of the nano silver, only silver nitrate is needed as an oxidant, sodium citrate is needed as a stabilizer and hydroquinone is needed as a selective reducing agent, a special reaction device (an electric heating sleeve or an electric furnace is not needed during heating), external field assistance such as laser ablation and the like are not needed in the whole process, an additional auxiliary agent (such as polyvinylpyrrolidone, a macromolecular surfactant such as polyethylene glycol or other micromolecules or ions such as NaCl, naBr and the like are not needed to control the shape of the nano silver), and pH value of a system is not needed to be adjusted through acid and alkali solutions, so that the preparation method is environment-friendly, efficient and expandable.
The preparation method of the embodiment can prepare spherical silver nano particles with good monodispersity under the condition that the addition amount of seeds is only required to be changed, and the size of the spherical nano silver is widely adjustable, so that the steps of multiple growth and multi-parameter adjustment which are generally necessary are not required.
The following experiments were conducted to verify the good effects of the examples of the present invention.
Example 1
Preparation of spherical nanoparticlesSilver: adding 60-80 mL of deionized water into a container, and heating to a boiling state; adding 0.25mL of sodium citrate solution with the molar concentration of 0.1M into deionized water in a boiling state to form a stabilizer solution; 1.0mL of silver "seed" solution was added to the stabilizer solution, and 1.0mL of AgNO at a molar concentration of 0.1M was added during stirring 3 The solution and 1.0mL of hydroquinone solution with a molar concentration of 0.05M are stirred and kept boiling for 60min; cooling the solution at room temperature to obtain spherical nano silver.
Example 2
Preparing spherical nano silver: adding 60-80 mL of deionized water into a container, and heating to a boiling state; adding 0.25mL of sodium citrate solution with the molar concentration of 0.1M into deionized water in a boiling state to form a stabilizer solution; 2.5mL of silver "seed" solution was added to the stabilizer solution, and 1.0mL of AgNO at a molar concentration of 0.1M was added during stirring 3 The solution and 1.0mL of hydroquinone solution with a molar concentration of 0.05M are stirred and kept boiling for 60min; cooling the solution at room temperature to obtain spherical nano silver.
Example 3
Preparing spherical nano silver: adding 60-80 mL of deionized water into a container, and heating to a boiling state; adding 0.25mL of sodium citrate solution with the molar concentration of 0.1M into deionized water in a boiling state to form a stabilizer solution; 5mL of silver "seed" solution was added to the stabilizer solution, and 1.0mL of AgNO at 0.1M molar concentration was added during stirring 3 The solution and 1.0mL of hydroquinone solution with a molar concentration of 0.05M are stirred and kept boiling for 60min; cooling the solution at room temperature to obtain spherical nano silver.
Example 4
Preparing spherical nano silver: adding 60-80 mL of deionized water into a container, and heating to a boiling state; adding 0.25mL of sodium citrate solution with the molar concentration of 0.1M into deionized water in a boiling state to form a stabilizer solution; 10mL of silver "seed" solution was added to the stabilizer solution, and 1.0mL of AgNO at 0.1M molar concentration was added during stirring 3 Solution and 1.0mL of hydroquinone solution with molar concentration of 0.05M, and keepingStirring and boiling for 60min; cooling the solution at room temperature to obtain spherical nano silver.
Example 5
Preparing spherical nano silver: adding 60-80 mL of deionized water into a container, and heating to a boiling state; adding 0.25mL of sodium citrate solution with the molar concentration of 0.1M into deionized water in a boiling state to form a stabilizer solution; 30mL of silver "seed" solution was added to the stabilizer solution, and 1.0mL of AgNO at 0.1M molar concentration was added during stirring 3 The solution and 1.0mL of hydroquinone solution with a molar concentration of 0.05M are stirred and kept boiling for 60min; cooling the solution at room temperature to obtain spherical nano silver.
Example 6
Preparing spherical nano silver: adding 60-80 mL of deionized water into a container, and heating to a boiling state; adding 0.25mL of sodium citrate solution with the molar concentration of 0.1M into deionized water in a boiling state to form a stabilizer solution; 0.5mL of silver seed solution was added to the stabilizer solution, and 1.0mL of AgNO having a molar concentration of 0.1M was added during stirring 3 The solution and 1.0mL of hydroquinone solution with a molar concentration of 0.05M are stirred and kept boiling for 60min; cooling the solution at room temperature to obtain spherical nano silver.
Example 7
Preparing spherical nano silver: adding 60-80 mL of deionized water into a container, and heating to a boiling state; adding 0.25mL of sodium citrate solution with the molar concentration of 0.1M into deionized water in a boiling state to form a stabilizer solution; 0.1mL of silver "seed" solution was added to the stabilizer solution, and 1.0mL of AgNO at a molar concentration of 0.1M was added during stirring 3 The solution and 1.0mL of hydroquinone solution with a molar concentration of 0.05M are stirred and kept boiling for 60min; cooling the solution at room temperature to obtain spherical nano silver.
Example 8
Preparing spherical nano silver: adding 60-80 mL of deionized water into a container, and heating to a boiling state; adding 0.25mL of sodium citrate solution with the molar concentration of 0.1M into deionized water in a boiling state to form a stabilizer solution; dissolving into stabilizer0.015mL of silver "seed" solution was added to the solution, and 1.0mL of AgNO at a molar concentration of 0.1M was added during stirring 3 The solution and 1.0mL of hydroquinone solution with a molar concentration of 0.05M are stirred and kept boiling for 60min; cooling the solution at room temperature to obtain spherical nano silver.
Comparative example 1
In the traditional method, hydroquinone is used as a reducing agent, sodium citrate is used as a stabilizing agent, and silver nitrate is used as nano silver prepared by an oxidizing agent at normal temperature: the procedure was the same as in the above examples, but at normal temperature (30 ℃). Wherein, the silver "seed" is added to 1mL.
Comparative example 2
The same as in comparative example 1, except that 2.5mL of silver "seed" solution was added.
Comparative example 3
The same as in comparative example 1, except that 5mL of silver "seed" solution was added.
Comparative example 4
The same as in comparative example 1, except that 10mL of silver "seed" solution was added.
Comparative example 5
The traditional sodium citrate method is used for preparing nano silver: 18 mg AgNO 3 Dissolving in 100mL of deionized water, heating to boiling, adding 2mL of sodium citrate solution with mass-volume ratio of 1%, reacting for 60min under boiling and continuous stirring, and cooling the solution at room temperature to obtain sodium citrate stable nano silver. Reference is made to: P.C.Lee, D.Meisel, adsorption and surface-enhanced Raman of dyes on silver and gold sols, J.Phys.chem.86 (1982) 3391-3395.
Comparative example 6
Sodium citrate stable nano silver is prepared by a conventional silver 'seed' growth method: adding 60-80 mL of deionized water into a container, then adding 2mL of sodium citrate solution with mass volume ratio of 1% into the deionized water to form a reducer solution, and heating the reducer solution to a boiling state; adding 1mL of silver seed solution into the reducer solution, and adding 1.7mL of AgNO with mass-volume ratio of 1% in the stirring process 3 The solution was kept stirred and boiled for 60min. Cooling the solution at room temperatureAnd obtaining the nano silver with stable sodium citrate.
Reference is made to: Y.Wan, Z.Guo, X.Jiang, K.Fang, X.Lu, Y.Zhang, N.Gu, quasi-spherical silvernanoparticles: aqueous synthesis and size control by theseed-mediated Lee-Meisel method, J.Colid Interface Sci.394 (2013) 263-268.
The nano silver prepared in examples 1 to 4 was subjected to transmission electron microscope characterization photographing. The transmission electron microscope characterization photographs are shown in fig. 1 (a) - (d). The transmission electron microscope characterization photo of the nano silver prepared in example 1 is shown in fig. 1 (a), the transmission electron microscope characterization photo of the nano silver prepared in example 2 is shown in fig. 1 (b), the transmission electron microscope characterization photo of the nano silver prepared in example 3 is shown in fig. 1 (c), and the transmission electron microscope characterization photo of the nano silver prepared in example 4 is shown in fig. 1 (d).
The nano silver prepared in comparative examples 1 to 4 was subjected to transmission electron microscope characterization photographing. The transmission electron microscope characterization photographs are shown in fig. 2 (a) - (d). The transmission electron microscope characterization photo of the nano silver prepared in comparative example 1 is shown in fig. 2 (a), the transmission electron microscope characterization photo of the nano silver prepared in comparative example 1 is shown in fig. 2 (b), the transmission electron microscope characterization photo of the nano silver prepared in comparative example 3 is shown in fig. 2 (c), and the transmission electron microscope characterization photo of the nano silver prepared in comparative example 4 is shown in fig. 2 (d).
As can be seen from fig. 1 (a) - (d), the nano-silver prepared in examples 1-4 each exhibited a spherical shape and the size distribution was uniform. As can be seen from fig. 2 (a) - (d), the nano-silver prepared in comparative examples 1 to 4 contained a large amount of non-spherical silver nano-sheet structures.
For further comparison, we have performed spectroscopic characterization of the nano-silver solutions prepared in examples 1 to 4 and the nano-silver solutions prepared in comparative examples 1 to 4, respectively. Fig. 3 shows uv-vis spectra of nano-silver prepared in examples 1 to 4. Fig. 4 shows uv-visible spectrum diagrams of nano-silver prepared in comparative examples 1 to 4.
As can be seen from fig. 3, the uv-vis spectra of the nano-silver prepared in examples 1 to 4 all show sharp, symmetrical peak patterns. This demonstrates that the prepared nanosilver has good monodispersity. This is consistent with the transmission electron microscope result characterization of fig. 1. As can be seen from fig. 4, the ultraviolet-visible spectrum patterns of the nano-silver prepared in comparative examples 1 to 4 are remarkably widened and accompanied by the occurrence of shoulder peaks. This suggests that the nano-silver prepared is poorly monodisperse and contains non-spherical structures. This verifies the transmission electron microscope characterization results of fig. 2.
The nano silver prepared in examples 5 to 8 was subjected to transmission electron microscope characterization photographing. The transmission electron microscope characterization photographs are shown in fig. 5 (a) - (d). The transmission electron microscope characterization photo of the nano silver prepared in example 5 is shown in fig. 5 (a), the transmission electron microscope characterization photo of the nano silver prepared in example 6 is shown in fig. 5 (b), the transmission electron microscope characterization photo of the nano silver prepared in example 7 is shown in fig. 5 (c), and the transmission electron microscope characterization photo of the nano silver prepared in example 8 is shown in fig. 5 (d). As can be seen from fig. 5 (a) - (d): under the condition that the adding amount of the seeds is only changed, spherical nano silver with good monodispersity can be prepared, and the size of the spherical nano silver is widely adjustable within the range of 15nm-150 nm.
The nano silver prepared in comparative example 5 and comparative example 6 was subjected to transmission electron microscope characterization photographing. A transmission electron microscope characterization photograph of the nano silver prepared in comparative example 5 is shown in fig. 6. A transmission electron microscope characterization photograph of the nano silver prepared in comparative example 6 is shown in fig. 7. As can be seen from fig. 6: the conventional sodium citrate method for preparing nano silver is difficult to control in shape and size. As can be seen from fig. 7: the conventional silver seed growth method for preparing sodium citrate-stable nano silver is easy to generate secondary nucleation in the preparation process, so that a large amount of non-spherical structures such as silver nano rods are generated.
The foregoing has shown and described the basic principles, principal features and advantages of the invention. It will be understood by those skilled in the art that the present invention is not limited to the specific embodiments described above, and that the above specific embodiments and descriptions are provided for further illustration of the principles of the present invention, and that various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined in the appended claims. The scope of the invention is defined by the claims and their equivalents.
Claims (4)
1. The preparation method of the nano silver with adjustable size is characterized by comprising the following steps of:
step 10) adding deionized water into a container and heating to a boiling state; adding sodium citrate solution into deionized water in a boiling state to form stabilizer solution;
step 20) adding silver "seed" solution to the stabilizer solution prepared in step 10), adding AgNO during stirring 3 The solution and hydroquinone solution are stirred and kept in boiling state; wherein AgNO is added first 3 Immediately adding hydroquinone solution;
step 30) cooling the solution prepared in the step 20) at room temperature to prepare spherical nano silver;
hydroquinone vs AgNO in the presence of silver "seeds 3 Is much more reductive than sodium citrate; after the hydroquinone solution is added into the reaction solution, the hydroquinone only reduces AgNO on the surface of silver seeds 3 As silver atoms, the generated silver atoms are continuously deposited by taking silver seeds as cores, so that the silver seeds grow gradually; according to the preparation method, silver nitrate is used as a silver precursor, sodium citrate is used as a stabilizer, hydroquinone is used as a selective reducing agent, and the nucleation and growth processes of nano silver are effectively separated by a seed growth method under thermal reflux, so that the occurrence of secondary nucleation is avoided, and nano silver with good monodispersity is prepared; the nano silver is spherical nano silver; under the condition that the addition amount of silver seeds is only required to be changed, spherical silver nano particles with good monodispersity can be prepared by the preparation method;
the silver "seed" solution was prepared as follows: mixing deionized water with a sodium citrate solution, and stirring to form a stabilizer solution; the stabilizer solution was heated to the water bath temperature and AgNO was then added 3 Adding NaBH into the solution 4 A solution; and cooling at room temperature, and then, fixing the volume by deionized water to prepare the silver 'seed' solution.
2. The method of preparing adjustable size nanosilver according to claim 1, wherein the container has a reflow effect.
3. The method for preparing nano-silver with adjustable size according to claim 1, wherein in the step 20), agNO is contained in the final reaction solution 3 And hydroquinone in a molar ratio of 1:2.
4. The method for preparing nano-silver with adjustable size according to claim 1, wherein in the step 20), the molar ratio of sodium citrate to silver nitrate in the final reaction solution is 0.2-0.3:1.
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