Preparation method of nano copper powder

Abstract

The invention discloses a preparation method of nano copper powder, and belongs to the technical field of nano copper powder preparation, and the preparation method comprises the following steps: S1, preparing a mercaptopropionic acid-ethanol solution; s2, preparing quantum dots with carboxylated surfaces; s3, preparing an enzyme solution; s4, preparing an enzyme solution of which the surface carboxyl is converted into active ester; s5, preparing a surface carboxylated quantum dot solution; s6, preparing a quantum dot-biomolecule mixture; s7, a copper salt solution is prepared, and the PH is adjusted to 5-6; s8, nano copper powder is prepared; according to the preparation method, the copper ions in the copper salt solution are reduced into the copper atoms through the quantum dot-biomolecule mixture to prepare the nano-copper powder, the nucleation rate and quantity of the nano-copper powder prepared through the preparation method can be accurately controlled, the preparation cost is low, and the preparation efficiency is high.

Description

Technical Field

[0001] The invention belongs to the technical field of nano copper powder preparation, and particularly relates to a method for preparing nano copper powder. Background Art

[0002] Nano copper powder refers to a powder material composed of pure copper elements and with nanometer-level particle size. It has the characteristics of large specific surface area, high surface activity, low melting point, good sintering performance and good conductivity. It is widely used in high-efficiency catalysts, conductive materials, electromagnetic shielding and drug additives.

[0003] Currently, the preparation methods of nano copper powder include physical method and chemical method. Among them, the physical method has the problem of relatively high preparation equipment cost and relatively low preparation efficiency, and the chemical method has the problem of difficult control of the preparation rate and quantity of nano copper powder.

[0004] In view of this, a method for preparing nano copper powder is designed to solve the above problems. Summary of the invention

[0005] In order to solve the problems raised in the above background technology, the present invention provides a method for preparing nano copper powder, which has the characteristics of being able to accurately control the nucleation rate and quantity of nano copper powder, low preparation cost and high preparation efficiency.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for preparing nano copper powder, comprising the following steps: S1: adding mercaptopropionic acid and ethanol into a container, stirring at room temperature to accelerate mixing, and preparing a mercaptopropionic acid-ethanol solution with a concentration of 0.1 mol / L; S2: Add mercaptopropionic acid-ethanol solution and CdSe / ZnS quantum dot solution into a container, stir at room temperature to accelerate the coordination reaction for 2-3 hours, centrifuge and wash after the reaction is completed, and prepare surface carboxyl quantum dots; S3: adding glucose oxidase into phosphate buffer solution, stirring at room temperature to accelerate mixing, and preparing an enzyme solution with a concentration of 0.01 mol / L; S4: adding the enzyme solution and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution into a container, and performing the activation reaction for 30-60 minutes. After the reaction is completed, an enzyme solution in which the surface carboxyl groups are converted into active esters is prepared; S5: adding the surface carboxyl-coated quantum dots and the phosphate buffer solution into a container, stirring and accelerating the mixing at room temperature to prepare a surface carboxyl-coated quantum dot solution; S6: adding the enzyme solution for converting the surface carboxyl groups into active esters and the surface carboxyl-modified quantum dot solution into a container, stirring at room temperature to accelerate the covalent connection reaction for 2-4 hours, and after the reaction is completed, centrifuging, washing, and preparing a quantum dot-biomolecule mixture; S7: Add copper sulfate and deionized water into a container, stir and accelerate mixing at room temperature to prepare a copper salt solution with a concentration of 0.01-0.1 mol / L, and adjust the pH to 5-6; S8: Add the quantum dot-biomolecule mixture and copper salt solution into a container, and add ascorbic acid solution with a concentration of 0.01-0.05 mol / L at the same time. Place the container under light conditions, and the copper salt solution dissociates into freely mobile copper ions, which are adsorbed by glucose oxidase. The quantum dots absorb light energy to generate electron-hole pairs, and the electrons are transferred to glucose oxidase to reduce the copper ions to copper atoms. The copper atoms aggregate to form crystal nuclei, and as the crystal nuclei continue to grow, nano copper powder is formed. Centrifugation, washing, and drying are performed to prepare nano copper powder.

[0007] Furthermore, in step S2, the added amounts of mercaptopropionic acid-ethanol solution and CdSe / ZnS quantum dot solution are 0.8 mL and 10 mL respectively.

[0008] Furthermore, in step S2, the specific steps of centrifugation include: Take a pipette and transfer the surface carboxylation quantum dot solution into a centrifuge tube using the pipette; Take ethanol in a volume ratio of 1:1 to the surface carboxylation quantum dot solution, add it into a centrifuge tube, shake it at a constant speed to accelerate mixing, reduce the solubility of the quantum dots in the solution, and make them precipitate; Place the centrifuge tube in a centrifuge and centrifuge at 8000-1000 rpm for 15-20 minutes; After centrifugation, the centrifuge tube is filled with supernatant containing impurities and precipitated quantum dots. Take a pipette and suck out the supernatant containing impurities through the pipette, and the centrifugation is completed.

[0009] Furthermore, in step S2, the specific steps of washing include: Take out the centrifuge tube containing the precipitated quantum dots, add ethanol into the centrifuge tube, cover the precipitated quantum dots with ethanol, and shake at a constant speed to disperse the precipitated quantum dots in the ethanol; Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm; After centrifugation, the centrifuge tube contains the supernatant containing impurities and the reprecipitated quantum dots. Take a pipette and suck out the supernatant containing impurities through the pipette. One-time washing is completed. Repeat the above washing steps 2-3 times until the impurities on the surface of the precipitated quantum dots are completely removed.

[0010] Furthermore, in step S4, the added amounts of the enzyme solution and the aqueous solution of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride are 10 mg and 0.5 mL, respectively.

[0011] Furthermore, in step S6, the added amounts of the enzyme solution for converting surface carboxyl groups into active esters and the surface carboxyl-treated quantum dot solution are 2 mL and 2 mL, respectively.

[0012] Furthermore, in step S8, the added amounts of the quantum dot-biomolecule mixture, the copper salt solution and the ascorbic acid solution are 2 mL, 2 mL and 1 mL respectively.

[0013] Furthermore, in step S8, the illumination condition is simulated by ultraviolet light irradiation, the illumination wavelength is 365nm, the illumination intensity is 10-20mW / cm², and the illumination temperature is 25-30°C.

[0014] Furthermore, in steps S6 and S8, the centrifugation and washing steps are the same as those in S2.

[0015] Furthermore, in step S8, the drying temperature is 40-45° C., and the drying time is 6-12 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention reduces copper ions in a copper salt solution into copper atoms through a quantum dot-biomolecule mixture to prepare nano copper powder. The nano copper powder prepared by this preparation method can accurately control the nucleation rate and quantity of the nano copper powder, and has low preparation cost and high preparation efficiency.

[0017] 2. The quantum dots of the present invention have good chemical stability, which can ensure the continuous and stable progress of the preparation process and is conducive to the formation of nano copper powder with uniform size and regular morphology.

[0018] 3. The high fluorescence quantum yield of the quantum dots of the present invention can be used as fluorescent markers to realize the preparation and tracking of nano copper powder, so as to timely adjust the illumination conditions, optimize the preparation process, and improve the quality of the finished nano copper powder. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a flow chart of the method of the present invention; Figure 2 It is a centrifugal flow chart of the present invention; Figure 3 It is a washing flow chart of the present invention. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] See attached Figure 1 The present invention provides the following technical solution: a method for preparing nano copper powder, comprising the following steps: S1: adding mercaptopropionic acid and ethanol into a container, stirring at room temperature to accelerate mixing, and preparing a mercaptopropionic acid-ethanol solution with a concentration of 0.1 mol / L; S2: Add mercaptopropionic acid-ethanol solution and CdSe / ZnS quantum dot solution into a container, stir at room temperature to accelerate the coordination reaction for 2-3 hours, centrifuge and wash after the reaction is completed, and prepare surface carboxyl quantum dots; In this embodiment, the above operation was performed with 0 mL, 0.5 mL, 0.8 mL, 1 mL and 1.5 mL of mercaptopropionic acid-ethanol solution and 10 mL of CdSe / ZnS quantum dot solution to prepare surface carboxyl quantum dots; See attached Figure 2 The specific steps of centrifugation include: Take a pipette and transfer the surface carboxylation quantum dot solution into a centrifuge tube using the pipette; Take ethanol in a volume ratio of 1:1 to the surface carboxylation quantum dot solution, add it into a centrifuge tube, shake it at a constant speed to accelerate mixing, reduce the solubility of the quantum dots in the solution, and make them precipitate; Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm; After centrifugation, the centrifuge tube contains the supernatant containing impurities and the precipitated quantum dots. Take a pipette and suck out the supernatant containing impurities through the pipette. Centrifugation is completed. See attached Figure 3 The specific steps of washing include: Take out the centrifuge tube containing the precipitated quantum dots, add ethanol into the centrifuge tube, cover the precipitated quantum dots with ethanol, and shake at a constant speed to disperse the precipitated quantum dots in the ethanol; Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm; After centrifugation, the centrifuge tube contains the supernatant containing impurities and the reprecipitated quantum dots. Take a pipette and suck out the supernatant containing impurities through the pipette. One-time washing is completed. Repeat the above washing steps 2-3 times until the impurities on the surface of the precipitated quantum dots are completely removed; The fluorescence intensity of quantum dots was detected by fluorescence spectrometer. The results showed that the fluorescence intensity of quantum dots surface decreased gradually with the increase of mercaptopropionic acid-ethanol solution. The number of carboxyl groups on the quantum dots was detected by infrared spectroscopy. The results showed that the number of carboxyl groups on the surface of the quantum dots gradually increased with the increase of mercaptopropionic acid-ethanol solution. However, the above operation was performed with 0.8 mL of mercaptopropionic acid-ethanol solution and 10 mL of CdSe / ZnS quantum dot solution to prepare surface carboxyl-grouped quantum dots, which not only better maintained the fluorescence properties of quantum dots, but also better met the covalent connection requirements with biomolecules. S3: adding glucose oxidase into phosphate buffer solution, stirring at room temperature to accelerate mixing, and preparing an enzyme solution with a concentration of 0.01 mol / L; S4: adding the enzyme solution and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution into a container, and performing the activation reaction for 30-60 minutes. After the reaction is completed, an enzyme solution in which the surface carboxyl groups are converted into active esters is prepared; In this example, the above operation was performed with 10 mg of enzyme solution and 0 mL, 0.1 mL, 0.3 mL, 0.5 mL and 1 mL of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride aqueous solution, respectively, to prepare enzyme solutions in which surface carboxyl groups were converted into active esters; The connection of the enzyme solution was analyzed by SDS-PAGE electrophoresis. The results showed that with the increase of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution, the amount of glucose oxidase on the quantum dots increased significantly, but when the concentration of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution was 1mL, the enzyme activity decreased significantly, indicating that the excessive 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution caused some damage to the structure of glucose oxidase and affected the enzyme activity. That is, 10 mg of enzyme solution and 0.5 mL of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride aqueous solution is optimal; S5: adding the surface carboxyl-coated quantum dots and the phosphate buffer solution into a container, stirring and accelerating the mixing at room temperature to prepare a surface carboxyl-coated quantum dot solution; S6: adding the enzyme solution for converting the surface carboxyl groups into active esters and the surface carboxyl-modified quantum dot solution into a container, stirring at room temperature to accelerate the covalent connection reaction for 2-4 hours, and after the reaction is completed, centrifuging, washing, and preparing a quantum dot-biomolecule mixture; In this embodiment, the above operations were performed with 1 mL of enzyme solution and 1 mL of quantum dot solution, 1 mL of enzyme solution and 3 mL of quantum dot solution, 3 mL of enzyme solution and 1 mL of quantum dot solution, and 2 mL of enzyme solution and 2 mL of quantum dot solution, respectively, to prepare a quantum dot-biomolecule mixture; See attached Figure 2 The specific steps of centrifugation include: Take a pipette and transfer the quantum dot-biomolecule mixture solution into a centrifuge tube using the pipette; Take ethanol in a volume ratio of 1:1 to the quantum dot-biomolecule mixture solution, add it into a centrifuge tube, shake it at a constant speed to accelerate mixing, reduce the solubility of the quantum dot-biomolecule mixture in the solution, and cause it to precipitate; Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm; After centrifugation, the centrifuge tube contains the supernatant containing impurities and the precipitated quantum dot-biomolecule mixture. Take a pipette and suck out the supernatant containing impurities through the pipette. Centrifugation is completed; See attached Figure 3 The specific steps of washing include: Take out the centrifuge tube containing the precipitated quantum dot-biomolecule mixture, add ethanol into the centrifuge tube, cover the precipitated quantum dot-biomolecule mixture with ethanol, and shake at a constant speed to disperse the precipitated quantum dot-biomolecule mixture in the ethanol; Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm; After centrifugation, the centrifuge tube contains the supernatant containing impurities and the reprecipitated quantum dot-biomolecule mixture. Take a pipette and suck out the supernatant containing impurities through the pipette. One-time washing is completed; Repeat the above washing steps 2-3 times until the impurities on the surface of the precipitated quantum dot-biomolecule mixture are completely removed; The results of UV-visible and fluorescence spectroscopy analysis showed that the glucose oxidase content of the quantum dot-biomolecule mixture increased with the increase of enzyme solution; Through enzyme activity detection, the results showed that the glucose oxidase activity of the quantum dot-biomolecule mixture increased with the increase of enzyme solution, but there was free glucose oxidase at 3 mL; That is, 2 mL of enzyme solution and 2 mL of quantum dot solution are optimal; S7: Add copper sulfate and deionized water into a container, stir and accelerate mixing at room temperature to prepare a copper salt solution with a concentration of 0.01-0.1 mol / L, and adjust the pH to 5-6; S8: adding the quantum dot-biomolecule mixture and the copper salt solution into a container, and adding an ascorbic acid solution with a concentration of 0.01-0.05 mol / L at the same time, placing the container under light conditions, the copper salt solution dissociates into free-moving copper ions, which are adsorbed by glucose oxidase, and the quantum dots absorb light energy to generate electron-hole pairs, which are transferred to the glucose oxidase to reduce the copper ions to copper atoms, which aggregate to form crystal nuclei, and as the crystal nuclei continue to grow, nano copper powder is formed, centrifuged, washed, and dried to prepare nano copper powder; In this embodiment, 1 mL of quantum dot-biomolecule mixture, 1 mL of copper salt solution and 0.5 mL of ascorbic acid solution, 1 mL of quantum dot-biomolecule mixture, 3 mL of copper salt solution and 1.5 mL of ascorbic acid solution, 3 mL of quantum dot-biomolecule mixture, 1 mL of copper salt solution and 0.5 mL of ascorbic acid solution, 2 mL of quantum dot-biomolecule mixture, 2 mL of copper salt solution and 1 mL of ascorbic acid solution were respectively subjected to the above operations to prepare nano copper powder; The lighting conditions are simulated by ultraviolet light irradiation, with a wavelength of 365nm, a light intensity of 10-20mW / cm², and a light temperature of 25-30℃; See attached Figure 2 The specific steps of centrifugation include: Take a pipette and transfer the solution containing nano copper powder into a centrifuge tube by pipette; Take ethanol in a volume ratio of 1:1 to the solution containing nano-copper powder, add it into a centrifuge tube, shake it at a constant speed to accelerate mixing, reduce the solubility of the nano-copper powder in the solution, and make it precipitate; Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm; After centrifugation, the centrifuge tube contains supernatant containing impurities and precipitated nano copper powder. Take a pipette and suck out the supernatant containing impurities through the pipette. Centrifugation is completed; See attached Figure 3 The specific steps of washing include: Take out the centrifuge tube containing the precipitated nano-copper powder, add ethanol into the centrifuge tube, cover the precipitated nano-copper powder with ethanol, and shake at a constant speed to disperse the precipitated nano-copper powder in the ethanol; Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm; After centrifugation, the centrifuge tube contains the supernatant containing impurities and the reprecipitated nano copper powder. Take a pipette and suck out the supernatant containing impurities through the pipette. One-time washing is completed; Repeat the above washing steps 2-3 times until the impurities on the surface of the precipitated nano copper powder are completely removed; Dry and place in a vacuum drying oven at a temperature of 40-45°C for 6-12 hours; Through transmission electron microscopy observation, the results show that the nano copper powder of 1mL quantum dot-biomolecule mixture, 1mL copper salt solution and 0.5mL ascorbic acid solution has large particle size and uneven distribution, with obvious agglomeration phenomenon, and the yield is about 30%; 1mL quantum dot-biomolecule mixture, 3mL copper salt solution and 1.5mL ascorbic acid solution promote the reduction of copper ions due to the increase of copper salt and ascorbic acid, but the particle size control is not good due to the excessively fast local reaction speed, so that the nanoparticle size is reduced but still unevenly distributed, the dispersibility is improved, and the yield is 50%; 3mL quantum dot-biomolecule mixture, 1mL copper salt solution and 0.5mL ascorbic acid solution can provide more nucleation sites due to the excess of quantum dot-biomolecule mixture, so that copper atoms can nucleate and grow on more sites, resulting in a decrease in particle size. However, due to the relative shortage of copper ions, the total amount of nano-copper powder generated is small, so that the nano-copper powder has a smaller particle size and better dispersibility, and the yield is about 20%; 2mL quantum dot-biomolecule mixture, 2mL copper salt solution and 1mL ascorbic acid solution are well matched, so that the nano-copper powder has a uniform particle size and good dispersibility, and the yield is about 60%; That is, 2 mL of quantum dot-biomolecule mixture, 2 mL of copper salt solution and 1 mL of ascorbic acid solution are the best.

[0022] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing nano copper powder, characterized in that: The following steps are involved: S1: adding mercaptopropionic acid and ethanol into a container, stirring at room temperature to accelerate mixing, and preparing a mercaptopropionic acid-ethanol solution with a concentration of 0.1 mol / L; S2: Add mercaptopropionic acid-ethanol solution and CdSe / ZnS quantum dot solution into a container, stir at room temperature to accelerate the coordination reaction for 2-3 hours, centrifuge and wash after the reaction is completed, and prepare surface carboxyl quantum dots; S3: adding glucose oxidase into phosphate buffer solution, stirring at room temperature to accelerate mixing, and preparing an enzyme solution with a concentration of 0.01 mol / L; S4: adding the enzyme solution and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride aqueous solution into a container, and performing the activation reaction for 30-60 minutes. After the reaction is completed, an enzyme solution in which the surface carboxyl groups are converted into active esters is prepared; S5: adding the surface carboxyl-coated quantum dots and the phosphate buffer solution into a container, stirring and accelerating the mixing at room temperature to prepare a surface carboxyl-coated quantum dot solution; S6: adding the enzyme solution for converting the surface carboxyl groups into active esters and the surface carboxyl-modified quantum dot solution into a container, stirring at room temperature to accelerate the covalent connection reaction for 2-4 hours, and after the reaction is completed, centrifuging, washing, and preparing a quantum dot-biomolecule mixture; S7: Add copper sulfate and deionized water into a container, stir and accelerate mixing at room temperature to prepare a copper salt solution with a concentration of 0.01-0.1 mol / L, and adjust the pH to 5-6; S8: Add the quantum dot-biomolecule mixture and copper salt solution into a container, and add ascorbic acid solution with a concentration of 0.01-0.05 mol / L at the same time. Place the container under light conditions, and the copper salt solution dissociates into freely mobile copper ions, which are adsorbed by glucose oxidase. The quantum dots absorb light energy to generate electron-hole pairs, and the electrons are transferred to glucose oxidase to reduce the copper ions to copper atoms. The copper atoms aggregate to form crystal nuclei, and as the crystal nuclei continue to grow, nano copper powder is formed. Centrifugation, washing, and drying are performed to prepare nano copper powder.

2. The method for preparing nano copper powder according to claim 1, wherein: In the step S2, the added amounts of mercaptopropionic acid-ethanol solution and CdSe / ZnS quantum dot solution are 0.8 mL and 10 mL respectively.

3. The method for preparing nano copper powder according to claim 1, wherein: In step S2, the specific steps of centrifugation include: Take a pipette and transfer the surface carboxylation quantum dot solution into a centrifuge tube using the pipette; Take ethanol in a volume ratio of 1:1 to the surface carboxylation quantum dot solution, add it into a centrifuge tube, shake it at a constant speed to accelerate mixing, reduce the solubility of the quantum dots in the solution, and make them precipitate; Place the centrifuge tube in a centrifuge and centrifuge at 8000-1000 rpm for 15-20 minutes; After centrifugation, the centrifuge tube is filled with supernatant containing impurities and precipitated quantum dots. Take a pipette and suck out the supernatant containing impurities through the pipette, and the centrifugation is completed.

4. The method for preparing nano copper powder according to claim 3, characterized in that: In step S2, the specific steps of washing include: Take out the centrifuge tube containing the precipitated quantum dots, add ethanol into the centrifuge tube, cover the precipitated quantum dots with ethanol, and shake at a constant speed to disperse the precipitated quantum dots in the ethanol; Place the centrifuge tube in a centrifuge and centrifuge at a speed of 8000-1000 rpm; After centrifugation, the centrifuge tube contains the supernatant containing impurities and the reprecipitated quantum dots. Take a pipette and suck out the supernatant containing impurities through the pipette. One-time washing is completed. Repeat the above washing steps 2-3 times until the impurities on the surface of the precipitated quantum dots are completely removed.

5. The method for preparing nano copper powder according to claim 1, characterized in that: In the step S4, the added amounts of the enzyme solution and the aqueous solution of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride are 10 mg and 0.5 mL, respectively.

6. The method for preparing nano copper powder according to claim 1, characterized in that: In the step S6, the added amounts of the enzyme solution for converting surface carboxyl groups into active esters and the surface carboxyl-treated quantum dot solution are 2 mL and 2 mL, respectively.

7. The method for preparing nano copper powder according to claim 1, characterized in that: In step S8, the added amounts of the quantum dot-biomolecule mixture, the copper salt solution and the ascorbic acid solution are 2 mL, 2 mL and 1 mL respectively.

8. The method for preparing nano copper powder according to claim 1, characterized in that: In step S8, the illumination condition is simulated by ultraviolet light irradiation, the illumination wavelength is 365nm, the illumination intensity is 10-20mW / cm², and the illumination temperature is 25-30°C.

9. The method for preparing nano copper powder according to claim 1, characterized in that: In steps S6 and S8, the centrifugation and washing steps are the same as those in S2.

10. The method for preparing nano copper powder according to claim 1, characterized in that: In step S8, the drying temperature is 40-45° C. and the drying time is 6-12 hours.

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