KR101494891B1 - silver nanoparticle-based pH indicators in highly alkaline region and manufacturing method thereof - Google Patents

Abstract

The present invention relates to a pH indicator for a strong alkaline region using silver nanoparticles and a method for producing the same. More particularly, the present invention relates to a method for preparing silver nanoparticles by using silver nanoparticles, which are less expensive than gold nanoparticles, The present invention relates to a pH indicator which can be manufactured in a liquid or solid phase and can be used in various fields, and a method for producing the same.
The pH indicator of the strong alkaline region using the silver nanoparticles of the present invention contains silver nanoparticles reduced in an aqueous solution of silver nitrate, and pH can be measured in a strong alkaline region of pH> 11. And the silver nanoparticles are reduced by citrate or sodium borohydride.

Description

[0001] The present invention relates to a pH indicator for a strong alkaline region using silver nanoparticles and a method for manufacturing the same,

The present invention relates to a pH indicator for a strong alkaline region using silver nanoparticles and a method for producing the same. More particularly, the present invention relates to a method for preparing silver nanoparticles by using silver nanoparticles, which are less expensive than gold nanoparticles, The present invention relates to a pH indicator which can be manufactured in a liquid or solid phase and can be used in various fields, and a method for producing the same.

Silver has been known to the public as a type of precious metal for a long time because it has the property of being easily oxidized in air with gold.

Generally, metal has a specific luster of metal, but it is yellow in case of gold and gray in case of silver. If the size of the metal is large (more than micrometer), each metal will have its own luster, but when the size of the metal becomes smaller, it will turn into a completely different color, from gold to yellow to red, .

The reason why the color of the metal changes as the size decreases is because the surface plasmon of the metal causes resonance by the light corresponding to the visible light region. The energy that the surface plasmon resonates is the degree of aggregation of the metal nanoparticles It changes sensitively.

Generally, as the metal nanoparticles aggregate and become larger in size, the resonance energy is shifted to the lower side. For this reason, in the case of gold nanoparticles, the color change from red to purple occurs as the nanoparticles are stacked, To brown in color. That is, the color represented by metal nanoparticles is a good way to monitor how much metal nanoparticles are aggregated. If the color change is large, the change can be observed with the naked eye. Even if it is difficult to visually recognize the change, the change can be monitored simply with the absorption spectroscope. In addition, since the change in color occurs very sensitively depending on the degree of aggregation of the metal nanoparticles, the use of the characteristics of the metal nanoparticles enables a trace amount of the substance to be easily detected with a high detection limit.

The degree of aggregation of metal nanoparticles changes sensitively according to the characteristics of the surface of the metal nanoparticles. For example, when the pH of a solution containing metal nanoparticles changes, the surface charge of the metal nanoparticles changes, and the thickness of the electric double layer also changes. This eventually changes the interaction energy between the particles and the particles, Changes in the degree of aggregation of nanoparticles.

Recently, based on these properties, liquid type pH indicators based on gold nanoparticles have been reported. ¹ citrate-reduced gold nanoparticles are rapidly aggregated as the pH of the solution increases to more than 12.7 ± 0.3. The gold nanoparticles, which were red due to this aggregation, turn purple. This color change makes it easy to monitor the pH of the solution.

Measuring the pH in the strong alkaline region is required in many fields, and is one of the processes required in a wide range of fields from industry, pharmacology to biotechnology, agriculture and environment. ² Despite these demands, there are not many ways to measure and monitor pH in the strong alkaline range. In the case of an electrochemical method using a glass electrode, which is often used for measuring pH, it can not be an effective method because the glass electrode itself may cause a large error in the strong alkali region. ³ There is also little known indication that changes in the strong alkaline range are present, and even the known indicators are expensive or explosive, and are not useful because they are harmful to the human body.

In this sense, the pH indicator based on gold nanoparticles is a kind of noble metal which can be stably existed at normal temperature and pressure and is not easily oxidized. It is not harmful to the human body. This is an example.

However, since conventional gold nanoparticle-based pH indicators use gold nanoparticles, they are not inexpensive in terms of cost. Therefore, a cheaper pH indicator is required in terms of price, while taking advantage of the advantages of gold.

In addition, since the conventional gold nanoparticle-based pH indicator is in a liquid state, there are many limitations in application to various aspects. In the case of a liquid pH indicator, the solution to be measured should be placed in the pH indicator or, alternatively, the pH indicator should be placed in the solution to be measured and the color change observed. Therefore, there is a disadvantage that only the pH of a substance present in a liquid can be measured, and the inconvenience of mixing the solution is accompanied.

1. Korean Patent No. 10-0850160

2. M. Hecht, W. Kraus, K. Rurack, Analyst 138,325 (2013). 3. J. Li, T. Peng, Analytica Chimica ACTA 478, 337 (2003).

The present invention has been made in order to overcome the above problems, and it is an object of the present invention to provide a silver halide photographic light sensitive silver halide color photographic light sensitive silver halide photographic light sensitive silver halide photographic light sensitive silver halide photographic light sensitive silver halide photographic light sensitive silver halide photographic light sensitive silver halide photographic light emitting diode, And a method for producing the same.

Another object of the present invention is to provide a pH indicator capable of overcoming the limitations of the conventional pH indicator in the form of liquid by preparing a solid pH indicator in which silver nanoparticles are fixed on a support so as to be easy to use, An indicator agent and a method for producing the same.

In order to achieve the above object, the pH indicator of the strong alkaline region using the silver nanoparticles of the present invention is characterized by being able to measure the pH in a strong alkaline region of pH> 11 or higher, containing silver nanoparticles reduced in an aqueous solution of silver nitrate.

The silver nanoparticles are characterized in that they are reduced by citrate or sodium borohydride.

And the pH indicator is characterized in that the silver nanoparticles are fixed on the surface of the support.

In order to achieve the above object, the present invention provides a method for preparing a pH indicator of a strong alkaline region using silver nanoparticles, comprising the steps of: a) dissolving silver nitrate in water to obtain a first solution; b) dissolving the citrate or sodium borohydride in water to obtain a second solution; c) mixing the first solution and the second solution to produce reduced silver nanoparticles.

And the silver nanoparticles are immobilized on the surface of the support by contacting the colloid solution in which the silver nanoparticles are formed after the step c) with the support.

It has been confirmed that the present invention can be used sufficiently as a pH indicator in a strong alkaline region by using silver nanoparticles relatively inexpensive instead of gold nanoparticles. The liquid, solid type pH indicator based on the silver nanoparticles of the present invention can be usefully used for monitoring the pH of a strong base in various fields.

In addition, the present invention succeeds in fixing silver nanoparticles on a dredged paper by using a silver colloid solution having a high viscosity, thereby providing a pH indicator of solid form, which is easy to use and overcomes the limitations of a conventional liquid indicator .

FIG. 1 is an image and absorption spectrum of a pH indicator of a liquid type containing silver nanoparticles reduced to citrate according to an embodiment of the present invention,
2 is an image and absorption spectrum of a pH indicator of a liquid type containing silver nanoparticles reduced to sodium borohydride according to another embodiment of the present invention,
FIG. 3 is a graph showing the image of a solid pH indicator containing silver nanoparticles reduced to citrate according to another embodiment of the present invention and the intensity of light quantitated using a scanner. FIG.

Hereinafter, a pH indicator of a strong alkaline region using silver nanoparticles according to a preferred embodiment of the present invention and a method of manufacturing the same will be described in detail.

The pH indicator of the present invention can accurately indicate pH in a strong alkaline region of pH > 11 or more through color change. The pH indicator of the present invention is based on silver nanoparticles having a low manufacturing cost instead of expensive gold nanoparticles. In the case of silver, it is a precious metal located in the same group as gold on the periodic table and has a property similar to gold. Silver can be stably present at room temperature and atmospheric pressure, and is not harmful to the human body. Since the surface plasmon resonance energy of particles is also in the visible light region as in the case of gold nanoparticles, the degree of bundles of silver nanoparticles can easily be discriminated by color.

In the present invention, a pH indicator is prepared using silver nitrate solution as a starting material. Silver ions in silver nitrate solution are reduced with citrate or sodium borohydride (NaBH ₄ ) to produce silver nanoparticles. Sodium citrate (C ₆ H ₅ Na ₃ O ₇ ) can be used as the citrate.

The pH indicator of the present invention is provided in liquid or solid form. It is preferably provided in solid form. An example of a pH indicator in the form of a solid is silver nanoparticles reduced by citrate or sodium borohydride to be fixed on the surface of the support. As the support, paper, nonwoven fabric, fabric, sponge, stick or bar made of wood, metal or resin can be used. The silver nanoparticles are fixed to the surface of the support described above. Fixation can be carried out either by a physical or chemical method, by an adsorption or fixing method, or by a binder.

As an example for producing the pH indicator of the present invention, there is a step of dissolving silver nitrate in water to obtain a first solution, dissolving citric acid or sodium borohydride in water to obtain a second solution , Mixing the first solution and the second solution to reduce silver ions to produce silver nanoparticles. The pH indicator thus prepared is in a liquid phase and exists in the form of a colloidal solution in which silver nanoparticles are dispersed in a liquid.

Another example for producing a pH indicator comprises dissolving silver nitrate in water to obtain a first solution, and then dissolving citric acid or sodium borohydride in water to obtain a second solution. Then, the first solution and the second solution are mixed and reacted to obtain a colloidal solution. The colloidal solution exists in a form in which the silver nanoparticles produced by reduction are dispersed in the liquid. Once the colloidal solution is ready, the colloidal solution is contacted with a support capable of absorbing the liquid and then dried to immobilize the silver nanoparticles on the surface of the support. For example, as a specific example of the fixing method, when a certain amount of colloidal solution is dropped on a filter paper, the liquid is absorbed by the filter paper, and the silver nanoparticles remain on the filter paper. And then dried to prepare a solid pH indicator fixed to the support. It is important to synthesize a colloidal solution of high viscosity to make a pH indicator of solid form. Colloidal solutions with lower viscosity can not be applied in the form of small spots because the colloid solution spreads on the surface of the filter paper when it is applied on the filter paper and the color change can not be observed clearly even when it comes into contact with the strong base solution . A colloidal solution with a high viscosity should be used to prevent spreading of the filter paper and to observe a distinct color change when contacted with a strong base. The viscosity of the colloidal solution to make the pH indicator of the solid form can be 1.1 to 1.5 mPas at 25 DEG C (viscosity of pure water: 0.894 mPas). If it is less than 1.1 mPas, it is difficult to obtain a distribution of the aggregated particles spreading on the support, and when it exceeds 1.5 mPas, handling is inconvenient and the increase of the effect is insignificant.

Hereinafter, the method for producing the pH indicator of the present invention will be described by way of examples. However, the following examples are intended to illustrate the present invention in detail, and the scope of the present invention is not limited to the following examples.

1. Preparation of liquid pH indicator

Citric acid and sodium borohydride were used to reduce silver nitrate in solution to prepare pH indicator.

Each specific manufacturing method is as follows. Unless otherwise stated, all chemicals were reagent grade and aqueous solutions were prepared using tertiary distilled water with a resistance of at least 18.2 M? Cm.

(1) Preparation of pH indicator using citrate

45 mg of silver nitrate (AgNO ₃ ) was first dissolved in 250 ml of water, and 10 ml of a 1% (mass%) aqueous solution of sodium citrate was added while vigorously stirring the magnetic bar solution, followed by heating for about 10 minutes. The color of the solution changes from colorless to pale yellow. In this state, it is heated for about 10 minutes to make the color of the solution opaque and dark yellow. Dark yellow silver means that silver nanoparticles have been successfully synthesized.

(2) Preparation of pH indicator using sodium borohydride (NaBH ₄ )

3.783 mg of sodium borohydride was dissolved in 50 mL of water to make 2 mM of an aqueous solution. Then, 42 mg of nitric acid was added to 50 mL of water to make a 5 mM aqueous solution of silver nitrate, followed by cooling with ice while stirring vigorously. To 50 mL of the sodium borohydride solution, add 5 mM silver nitrate solution dropwise and add approximately 30 to 40 drops. When the silver nitrate aqueous solution is added rapidly, the nanoparticles are not easily formed, such as easily aggregated. Each time an aqueous silver nitrate solution is added, the color of the solution changes from colorless to increasingly yellow. Adjust the number of drops of silver nitrate put through the color of the changing solution. Add silver nitrate until the color of the solution no longer changes.

2. Manufacture of solid phase pH indicator

Prepare a silver colloidal solution with a high viscosity by the following method, then apply one drop onto the filter paper using a syringe. The process of making a silver colloidal solution with a high viscosity is as follows.

5.63 g of silver nitrate is dissolved in 250 mL of water to make a 132.5 mM silver nitrate aqueous solution. Then, 9.99 g of sodium citrate is dissolved in 10 mL of water to prepare a 3.4 M aqueous citric acid solution, followed by mixing 10 mL of a 3.4 M citrate and 250 mL of an aqueous solution of 132.5 mM silver nitrate. The mixture is heated while stirring vigorously. During the heating process, the color of the solution changes from colorless to opaque white. When heated, it becomes dark brown, and heating is stopped. The total heating time is approximately 20 minutes.

A silver colloid solution prepared by using a syringe was dripped onto a filter paper and dried to prepare a solid pH indicator. Showed that when the colloidal solution was dripped, the nanoparticles did not spread along the filter paper but formed spots in the spot. The color of the silver nanoparticles fixed on the filter paper was gray.

3. Measurement method

Sodium hydroxide was added to the liquid phase pH indicator and the color change of the liquid pH indicator was observed with the naked eye. The absorbance spectra were examined using an absorption spectrometer (Optizen 3220UV, Mecasys) to investigate the color change.

In order to observe the color change of the solid pH indicator applied on the filter paper, the color change was observed with the naked eye after spraying the base solution prepared by pH with sodium hydroxide. In order to quantify the intensity of the spot, the image was converted into an image file using a scanner (CLX-3307W, Samsung), and then the intensity was quantified using image software.

4. Experimental results

(1) liquid phase pH indicator using citrate

Silver nanoparticles were synthesized by the reduction of silver ions using citrate to confirm whether nanoparticles could be used as pH indicators in the strong base region instead of gold nanoparticles. The spectral changes were visually observed using an absorption spectrometer.

When the pH of the solution was 7.1 as shown in FIG. 1 (a), the color of the solution was dark yellow, which is a color indicating that a typical spherical shape is a colloidal solution containing silver nanoparticles having a size of about 20 nm as a color of the nanoparticles.

The pH was measured while adding sodium hydroxide to increase the pH. As the pH of the colloidal solution reached 11, the color of the dark yellow solution gradually changed to brown, indicating that the surface plasmon resonance energy was shifted to the long wavelength due to the aggregation of the nanoparticles together do. When sodium hydroxide was further added to reach a pH of 13.3, the color of the solution became dark brown as shown in FIG. 1 (b), and no further large color change was observed even after the addition of sodium hydroxide.

In order to investigate the change of color depending on the pH, the spectrum of the solution according to the pH was measured using an absorption spectroscope. As expected when visually observed at a pH of 7.1, a dark yellow colloidal solution showed a large absorption at a wavelength of approximately 400 nm (Fig. 1 (c)), which corresponds to silver nanoparticles having a diameter of approximately 20 nm Of the surface plasmon resonance energy. The reason why the color of the colloidal solution, which was yellow when sodium hydroxide is added, changes to dark brown because the nanoparticles are bundled together and the resonance energy of the surface plasmon is shifted to the lower side. This fact is shown in FIG. 1 (c) have. It can be seen that when the pH is 12.6, the spectrum showing a large absorption at 400 nm turns into a spectrum showing a large absorption at about 500 nm, and the wavelength at which the greatest absorption is absorbed reaches 600 nm at pH 13.3 Can be confirmed. In order to confirm the rapid change of the absorption spectrum at a certain pH range, the relative absorbance at a wavelength of about 750 nm is compared and the titration curve shown in FIG. 1 (d) can be obtained by plotting the absorbance at pH. It was found that the absorbance changes rapidly in a specific pH range, indicating that silver nanoparticles reduced with citrate can be used as a pH indicator in the strong base region. Figure 1 (d) shows that the absorbance of silver nanoparticles reduced to citrate rapidly changes near pH 12.5.

(2) liquid pH indicator using sodium borohydride

The experiment was carried out in the same manner as the experiment using silver nanoparticles made of citrate.

The color of the liquid phase pH indicator prepared by reduction with sodium borohydride is yellow, indicating that silver nanoparticles of approximately 20 nm in diameter are contained in the colloidal solution. From pH neutral to pH 9.3, the color of the solution did not change significantly (Fig. 2 (a)). The pH of the solution began to change as the pH began to exceed 12.5 by the addition of sodium hydroxide, and when the pH reached 13.3, the color of the solution became dark brown (Fig. 2 (b)), after which sodium hydroxide Were not added.

The absorption spectrum of the colloidal solution according to the pH was measured using an absorption spectrometer (Fig. 2 (c)) in order to identify the pH region where the color change occurs. As shown in FIG. 2 (a), the absorption spectrum did not show a significant change until the pH was 9.3, and it was confirmed that the shape of the spectrum gradually changed as the pH began to exceed 12.5. It can be seen that the wavelength with the highest absorbance is still near 400 nm, but a new peak near 500 nm appears, indicating that aggregated nanoparticles with surface plasmon resonance energy corresponding to this wavelength band are being formed. As the pH reached 13.3, the size of the peak that began to increase in the long wavelength region was further increased, and the absorbance almost equal to that at 400 nm was observed.

Compared with citrate-reduced pH indicators, it can be seen that nanoparticle aggregation begins at higher pH. The color of the solution observed with the naked eye was changed to brown from the pH of approximately 12 as in the case of silver nanoparticles made of citrate until the color of the yellow solution reached pH 13 (FIGS. 2 (a) and 2 (b) . In the case of silver nanoparticles made of citrate, the peak absorbance shifts to near 500 nm at pH 12.6, but silver nanoparticles reduced to sodium borohydride have a peak near 400 nm You can see that it is the largest. That is, in the case of silver nanoparticles made of citrate, the color change of the silver nanoparticle solution occurs near pH 12.5, but in the case of the silver nanoparticles made of sodium borohydride, the nanoparticle aggregation starts at stronger base conditions have.

In order to confirm this fact, the relative absorbance at a wavelength of 650 nm according to pH was compared and it was confirmed how the change in absorbance according to the change in pH occurred (Fig. 2 (d)). As can be seen in FIG. 2 (c), in the case of silver nanoparticles reduced with sodium borohydride, the absorbance increases sharply in the higher pH region than silver nanoparticles reduced to citrate. In the case of silver nanoparticles reduced to citrate, the nanoparticles are rapidly aggregated at a pH of about 12.5, which causes a change in the color of the colloid solution. In the case of silver nanoparticles reduced with sodium borohydride, As can be seen, it can be seen that the change of the absorbance rapidly occurs near pH 13.

(3) Solid phase pH indicator

In the case of liquid phase pH indicators, there are inconveniences in use and various restrictions apply to various applications. If the silver nanoparticle-based pH indicator can be made in the form of a stick to test pregnancy, the pH range of the nanoparticle-based pH indicator can be extended Will be.

For example, to measure the pH of a solution, a silver nanoparticle-based pH indicator stick should be immersed in a solution to see the change in color, and this type of pH measurement can be applied not only to solutions but also to soil and gases. It will be even more useful because you can measure the pH even with a small amount of sample. In order to make the nanoparticle-based pH indicator in the form of a stick, it is necessary to fix the silver nanoparticles to a solid phase (for example, solids such as filter paper).

When the liquid pH indicator prepared in the above-mentioned embodiment is applied to a solid phase such as filter paper, the silver nanoparticles are scattered on the surface of the filter paper while wetting the filter paper, It can not be observed clearly. Silver nanoparticles should be applied at a high density in the solid phase in order to fix the nanoparticles on a solid phase such as dung paper and to observe a distinct color change when contacted with a strong base solution. For this purpose, a silver colloidal solution with a high viscosity should be prepared and prevented from spreading on the filter paper.

The viscosity of the liquid phase pH indicator reduced to citrate was 1.00 mPas at 25 ° C, while the viscosity of the colloid solution to produce the solid pH indicator was 1.16 mPas at 25 ° C . The viscosity of pure water is typically 0.894 mPas at 25 占 폚.

In the present invention, a silver colloid solution having a high viscosity is fixed on a filter paper in order to prepare a solid pH indicator, and the color of silver nanoparticles immobilized on the filter paper is actually changed according to the pH.

In the case of silver colloid solution with high viscosity, it was confirmed that the spots were well formed as shown in FIG. 3 (a) without spreading on the filter paper when the droplets were applied by using the syringe due to the high viscosity. The color of the silver nanoparticle spot dried on the filter paper was gray. pH 7, 9, 10.2, 11.3, 12.9 An aqueous solution of sodium hydroxide was prepared and dropped on a spot by a dropper.

In the case of spots dropped at pH 7, 9, 10.2, and 11.3 when observed with the naked eye, there was almost no change in color, and all of the spots showed a gray color similar to that before dropping the solution. Only the color of the spots dropping the solution of pH 12.9 was changed from gray to dark brown. These results show that silver nanoparticles with high viscosity can be used as a pH indicator in the strong base region when they are immobilized on a solid phase such as urine paper.

In order to more quantitatively understand the color change of the spot, the filter paper was converted into a picture file using a scanner and the brightness of the spot was quantified (Fig. 3 (b)). The spot images of FIG. 3 (b) are images converted by using a scanner. Unlike spots where sodium hydroxide having a low pH is sprayed, the color of spots is relatively dark when the pH is 12.9.

From the above experimental results, it has been succeeded to apply silver nanoparticles without spreading on the papermaking paper by using a silver colloid solution with a high viscosity, and it has been shown that the silver nanoparticle based pH indicator actually works.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation. Accordingly, the true scope of protection of the present invention should be determined only by the appended claims.

Claims (5)

delete delete A silver colloid solution containing silver nanoparticles reduced in an aqueous solution of silver nitrate is contacted with the surface of the support to fix the silver nanoparticles on the surface of the support,
Wherein the silver nanoparticles are reduced by citrate, the colloidal solution has a viscosity of 1.1 to 1.5 mPas at 25 DEG C,
A pH indicator for a strong alkaline region using silver nanoparticles characterized in that pH can be measured in a strong alkaline region of pH> 11. delete a) dissolving silver nitrate in water to obtain a first solution;
b) dissolving the citrate in water to obtain a second solution;
c) mixing the first solution and the second solution to produce a colloidal solution containing reduced silver nanoparticles and having a viscosity of 1.1 to 1.5 mPas at 25 ° C,
Contacting the colloidal solution with a support to fix the silver nanoparticles on the surface of the support,
A pH indicator of a strong alkaline region using silver nanoparticles characterized in that pH can be measured in a strong alkaline region of pH> 11.

Images