Pueraria lobata nano-silver composite hydrosol, preparation method and application thereof

Abstract

A preparation method of a Pueraria lobata nano-silver composite hydrosol includes: dispersing Pueraria lobata powder in water, then heating to perform gelatinization, then adjusting a pH value, then sequentially adding an alkyl polyglucoside solution, a silver nitrate solution, and a sodium chloride solution, and performing a reaction by microwave heating to obtain the Pueraria lobata nano-silver composite hydrosol. The Pueraria lobata nano-silver composite hydrosol promotes seed germination of a Polygonatum Mill genus, and is applied in antibiotic detection and agricultural sterilization used as a fungicide. Organic solvents, harmful reducing agents, and dispersing agents are completely avoided to be used, and raw materials for preparing the hydrosol are safe and environment-friendly; the preparation method is simple, no harsh conditions are needed, and reaction conditions are mild; a required time is extremely short, energy is saved, consumption is reduced, and a basic principle of green chemistry is completely met.

Claims

1. A preparation method of a Pueraria lobata nano-silver composite hydrosol, comprising the following steps: dispersing Pueraria lobata powder in water, heating the Pueraria lobata powder and the water to perform gelatinization, thereby obtaining a paste; adjusting a potential of hydrogen (pH) value of the paste, and then sequentially adding an alkyl polyglucoside solution, a silver nitrate solution, and a sodium chloride solution into the paste to obtain a mixture, and performing a reaction on the mixture by microwave heating to obtain the Pueraria lobata nano-silver composite hydrosol; wherein the pH value of the paste is adjusted to 13; wherein a ratio of addition amounts of the Pueraria lobata powder: the water: the alkyl polyglucoside solution: the silver nitrate solution: the sodium chloride solution is in a range of 10 grams (g): 450-550 milliliters (mL): 20 mL: 40-50 mL: 10.sup.15 ml; wherein a concentration of the silver nitrate solution is 40 grams per liter (g/L); wherein a concentration of the sodium chloride solution is 1 g/L; wherein the alkyl polyglucoside solution is obtained by diluting 1 mL of alkyl polyglucoside with a branched chain of 10 carbons in 50 ml of water; wherein the performing a reaction on the mixture by microwave heating comprises: performing the reaction on the mixture for 4 minutes (min) by the microwave heating, taking out the mixture and stirring the mixture for 10 seconds(s), then continuing the microwave heating for 1.1 min, taking out the mixture, and standing the mixture for 1-2 h accompanied with intermittent stirring; and wherein a power of the microwave heating in the performing a reaction on the mixture by microwave heating is 800 watts (W), and a temperature for the microwave heating is 95 degrees Celsius ( C.).

2. The preparation method of the Pueraria lobata nano-silver composite hydrosol according to claim 1, wherein the heating the Pueraria lobata powder and the water to perform gelatinization comprises: performing microwave heating on the Pueraria lobata powder and the water for 3 min to obtain the paste, then taking out the paste and stirring the paste for 10 s, then continuing the microwave heating for 1.2 min to perform the gelatinization until the paste appears transparent; and wherein a power of the microwave heating in the heating the Pueraria lobata powder and the water to perform gelatinization is 800 W, and a temperature for the microwave heating in the heating the Pueraria lobata powder and the water to perform gelatinization is 75 C.

3. A Pueraria lobata nano-silver composite hydrosol, wherein the Pueraria lobata nano-silver composite hydrosol is prepared by the preparation method of the Pueraria lobata nano-silver composite hydrosol according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWING

(1) Attached drawings that form a part of the present disclosure are used to provide a further understanding of the present disclosure. Illustrated embodiments of the present disclosure and descriptions thereof are used to explain the present disclosure and do not constitute an improper limitation of the present disclosure.

(2) FIG. 1 illustrates a photograph of a Pueraria lobata nano-silver composite hydrosol by using transmission electron microscope (TEM) according to an embodiment 1 of the present disclosure.

(3) FIG. 2 illustrates a spectrum of the Pueraria lobata nano-silver composite hydrosol by using energy dispersive spectrometer (EDS) according to the embodiment 1 of the present disclosure.

(4) FIG. 3 illustrates a spectrum of the Pueraria lobata nano-silver composite hydrosol by using X-ray diffraction (XRD) according to the embodiment 1 of the present disclosure.

(5) FIG. 4A illustrates an average particle size of the Pueraria lobata nano-silver composite hydrosol according to the embodiment 1 of the present disclosure.

(6) FIG. 4B illustrates Zeta potential of the Pueraria lobata nano-silver composite hydrosol according to the embodiment 1 of the present disclosure.

(7) FIG. 5 illustrates an ultraviolet-visible (UV-vis) absorption spectrum of the Pueraria lobata nano-silver composite hydrosol according to the embodiment 1 of the present disclosure.

(8) FIG. 6 illustrates a detection of tetracycline by surface-enhanced Raman spectroscopy (SERS) of the Pueraria lobata nano-silver composite hydrosol according to the embodiment 1 of the present disclosure.

(9) FIGS. 7A-7C illustrate effects of the Pueraria lobata nano-silver composite hydrosol according to the embodiment 1 of the present disclosure with different concentrations on seed germination of a Polygonatum Mill genus, where FIG. 7A illustrates processing No. 1, FIG. 7B illustrates processing No. 2, and FIG. 7C illustrates processing No. 3.

DETAILED DESCRIPTION OF EMBODIMENTS

(10) The technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the attached drawings in the embodiments of the present disclosure. Apparently, the described embodiments are only parts, not all, of the embodiments of the present disclosure. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the related art without creative efforts fall within the scope of the protection of the present disclosure.

(11) In order to make the above objectives, features and advantages of the present disclosure more obvious and understandable, the present disclosure will be described in further detail below with reference to the attached drawings and the illustrated embodiments.

(12) Raw materials used in the embodiments of the present disclosure are all purchased from commercial sources.

Embodiment 1

(13) A preparation method of a Pueraria lobata nano-silver composite hydrosol includes the following steps.

(14) 10 g of Pueraria lobata powder is weighed and placed in a 1 liter (L) large beaker, 500 mL of deionized water is added into the beaker and the Pueraria lobata powder is added into the deionized water accompanied with mixing evenly, the Pueraria lobata powder added with the deionized water is placed in a microwave oven, microwave heating is performed for 3 min at 800 W, thereby obtaining a paste, the paste is taken out and is stirred with a glass rod for 10 s, and then the paste is performed gelatinization by the microwave heating for 1.2 min at 800 W until the paste appears transparent. Thereafter, the transparent paste is taken out, and is quickly cooled down to 35 C. with cold water to obtain a cooled paste, and a pH value of the cooled paste is adjusted to 13 by using a potassium hydroxide (KOH) solution or a sodium hydroxide (NaOH) solution. Moreover, 20 mL of an APG0810 solution with a dilution ratio of 1:50 (V: V), 50 mL of AgNO.sub.3 solution with a concentration of 40 g/L, and 15 mL of NaCl solution with a concentration of 1 g/L are added into the cooled paste to obtain a mixture. The mixture is mixed evenly and quickly placed in a microwave oven, first microwave heating is performed on the mixture for 4 min at 800 W, and then is stirred with a glass rod for 10 s, then the microwave heating is performed again for 1.1 min at 800 W, the mixture is taken out and naturally stood for 1-2 h accompanied with intermittently stirring by using the glass rod, and finally the Pueraria lobata nano-silver composite hydrosol is obtained.

(15) Technical effects are as follows.

(16) 1. Structural Characterization

(17) FIG. 1 illustrates morphology of the Pueraria lobata nano-silver composite hydrosol observed with the TEM. It can be seen that the Pueraria lobata nano-silver particles contained in the prepared Pueraria lobata nano-silver composite hydrosol are all quasi spherical and have relatively narrow particle size distribution that is mainly distributed between 24 nm and 25 nm.

(18) FIG. 2 illustrates the spectrum of silver nanoparticles by using the EDS. It can be seen that the obtained Pueraria lobata nano-silver composite hydrosol contains elements, e.g., carbon (C), oxygen (O), and Ag, among which C and O are components of the starch contained in the Pueraria lobata. This result confirms that the silver nanoparticles exist in the nano composite material (i.e., the Pueraria lobata nano-silver composite hydrosol).

(19) FIG. 3 illustrates the spectrum of the Pueraria lobata nano-silver composite hydrosol by using the XRD. It can be seen that four diffraction peaks located at 20=38.4, 44.36, 64.42, and 77.38 can be attributed to crystal planes i.e., (111), (200), (220), and (311) of the nano-silver particles respectively (with reference to joint committee on powder diffraction standards abbreviated as JCPDS No. 04-0783). Therefore, the synthesized Pueraria lobata nano-silver particles have a face-centered cubic (FCC) structure. Specially, the 4 diffraction peaks are sharp, indicating that the synthesized Pueraria lobata nano-silver particles have high crystallinity.

(20) FIG. 4A illustrates the average particle size of the Pueraria lobata nano-silver composite hydrosol and FIG. 4B illustrates the Zeta potential of the Pueraria lobata nano-silver composite hydrosol. It can be seen that the average particle size of the Pueraria lobata nano-silver particles is 24.5 nm and the Zeta potential is .sup.10.2 millivolts (mV), indicating that the substances adsorbed on the surface of the obtained Pueraria lobata nano-silver particles have negative charges. These substances may be alkaloids, flavonoids, polysaccharides, proteins, etc. mixed in the Pueraria lobata nano-silver particles during the preparation process of the starch contained in the Pueraria lobata. It is precisely due to the electrostatic repulsion between the negative charges on the surface of the Pueraria lobata nano-silver particles that the obtained nano-silver material is less prone to agglomeration.

(21) FIG. 5 illustrates the UV-vis absorption spectrum of the Pueraria lobata nano-silver composite hydrosol (i.e., illustrated as absorbance). It can be seen that the Pueraria lobata nano-silver composite hydrosol has a strong absorption peak at 396.7 nm, indicating that the prepared the Pueraria lobata nano-silver composite hydrosol has an obvious quantum size effect, which is due to the absorption caused by surface plasmon resonance effect of the nano-silver particles. According to the Mie theory, a single surface plasmon resonance band shows that the synthesized Pueraria lobata nano-silver particles are mainly spherical. Moreover, a absorption band appearing at UV 396.7 nm of the Pueraria lobata nano-silver particles is in a relatively narrow wavelength range, indicating that the particle size range of the Pueraria lobata nano-silver particles is relatively small, which is consistent with the TEM detection result.

(22) 2. Stability Test

(23) 50 mL of the Pueraria lobata nano-silver composite hydrosol prepared in the embodiment 1 is added into a 150 mL Erlenmeyer flask, and then the Erlenmeyer flask added with the Pueraria lobata nano-silver composite hydrosol is placed in a 30 C. constant-temperature incubator for 10 d, 20 d and 30 d respectively to investigate the stability of the Pueraria lobata nano-silver composite hydrosol in the practical application, results of which are shown in the following Table 1.

(24) TABLE-US-00001 TABLE 1 Stability of the Pueraria lobata nano-silver composite hydrosol under different standing times Optical Wavelength Standing density corresponding to Number time (d) (OD) peak peak () 1 0 1.480 409.8 2 10 1.488 407.8 3 20 1.499 406.4 4 30 1.604 406.8

(25) As can be seen from Table 1, within 30 d, the absorption band of the Pueraria lobata nano-silver composite hydrosol in the UV-vis absorption spectrum has no significant variations, indicating that the Pueraria lobata nano-silver composite hydrosol has good stability. Moreover, when left for 30 d, compared with the newly prepared Pueraria lobata nano-silver composite hydrosol, the absorption peak of the Pueraria lobata nano-silver composite hydrosol left for 30 d is increased, indicating that the amount of Pueraria lobata nano-silver particles is further increased during the placement process.

(26) 3. Bactericidal Property Test

(27) After streaking test strains of Escherichia coli and Staphylococcus aureus on nutrient broth (NB) plates respectively, the NB plates are cultured in a constant temperature incubator at 37 C. until the NB plates clearly appear bacterial plaques. An appropriate amount of mature colonies in the bacterial plaques is selected respectively, and then the mature colonies are added to a 3 mL NB liquid culture medium, followed by mixing well, and the mature colonies are cultured in the constant temperature incubator at 37 C. for 10.sup.15 h until an OD600 value is about 0.5. Thereafter, Escherichia coli bacterial solution cultured by the NB liquid and the Pueraria lobata nano-silver composite hydrosol obtained in the embodiment 1 are used to prepare the Escherichia coli bacterial solutions containing Pueraria lobata nano-silver particles with final concentrations of 5 mg/L, 10 mg/L, and 20 mg/L respectively. Meanwhile, Staphylococcus aureus bacterial solution cultured by the NB liquid and the Pueraria lobata nano-silver composite hydrosol obtained in the embodiment 1 are used to prepare the Staphylococcus aureus bacterial solutions containing Pueraria lobata nano-silver particles with final concentrations of 80 mg/L, 160 mg/L, 320 mg/L, and 640 mg/L. And then, 100 microliters (L) of the Escherichia coli bacterial solutions and the Staphylococcus aureus bacterial solutions are obtained respectively to smear on the NB plates, the NB plates are incubated at 37 C. for 10.sup.15 h, and then the NB plates are taken photos and counted.

(28) TABLE-US-00002 TABLE 2 illustrates the bactericidal properties of the Pueraria lobata nano-silver composite hydrosol. Nano-silver particle Number of Bacteria concentration (mg/L) CFU (count) Escherichia coli 5 1282 Escherichia coli 10 9 Escherichia coli 20 6 Staphylococcus aureus 80 2816 Staphylococcus aureus 160 263 Staphylococcus aureus 320 7 Staphylococcus aureus 640 3

(29) The results in Table 2 show that the Pueraria lobata nano-silver composite hydrosol prepared in the embodiment 1 of the present disclosure has bactericidal ability against the Escherichia coli and the Staphylococcus aureus. The MBC value against the Escherichia coli is 10 mg/L, and the MBC value against the Staphylococcus aureus is 320 mg/L. Among them, the MBC value represents the minimum bactericidal concentration, that is, the minimum concentration of Pueraria lobata nano-silver particles required to kill 99.9% (a reduction of 3 orders of magnitude) of the tested microorganisms.

(30) 4. Tetracycline Detection and Verification

(31) Tetracycline (with a chemical formula of C.sub.22H.sub.24N.sub.2O.sub.8) solutions with different concentrations (i.e., 5106 mole per liter abbreviated as mol/L, 510-5 mol/L, 510-4 mol/L, 2.510-4 mol/L, and 110-4 mol/L) are prepared. Then, 1 mL of the tetracycline solutions with different concentrations is obtained respectively, and then is evenly mixed with the Pueraria lobata nano-silver composite hydrosol prepared in the embodiment of the present disclosure in equal volumes. Thereafter, a Raman spectrometer is used to test, an excitation wavelength is set to 785 nm, an output power is set to 300 megawatts (mW), and test samples at 1002,000 cm.sup.1 of the Raman spectrum are collected.

(32) FIG. 6 illustrates the SERS diagram of the Pueraria lobata nano-silver composite hydrosol. The results show that when the residual concentration of tetracycline in the water ranges from 0.1 mg/L to 22 mg/L, there is a well linear relationship between the residual concentration of tetracycline in the water and the peak intensity at 1590 cm.sup.1. The linear equation is expressed as follows: Y=218015X+32.49; and the coefficient of determination R.sup.2 is 0.99526. Therefore, the Pueraria lobata nano-silver composite hydrosol obtained by the present disclosure can meet the requirements for the detection of tetracycline residues in water, laying a good foundation for on-site rapid detection of tetracycline residues in the water.

(33) 5. Detection on Promotion of Seed Germination of Polygonatum Mill Genus

(34) The MS (containing sucrose and agar) culture medium (also referred to a basal medium) is added with 0.2 mg/L of 6-BA and 0.2 mg/L of NAA, and then the MS culture medium is added with the Pueraria lobata nano-silver composite hydrosol obtained in the embodiment 1. Moreover, seeds of the Polygonatum Mill genus stored by sand storage at 4 C. for 30 d are selected to perform seed germination test to observe and compare the effects of Pueraria lobata nano-silver composite hydrosol on the germination of the seeds of the Polygonatum Mill genus. After inoculation, a time for the seed germination, growth vigor, and a germination rate are observed and compared. Specially, the germination rate (%)=total number of germinations/number of test seeds100%. The details of different treatments are shown in the following Table 3, and the results are shown in Table 4 and FIGS. 7A-7C. Among them, FIG. 7A illustrates processing No. 1, FIG. 7B illustrates processing No. 2, and FIG. 7C illustrates processing No. 3.

(35) TABLE-US-00003 TABLE 3 Composition of culture medium with different concentrations of Pueraria lobata nano-silver particles Pueraria lobata Basal 6-BA NAA nano-silver particles Number medium (mg/L) (mg/L) (mg/L) 0 MS 0.2 0.2 0 1 MS 0.2 0.2 2 2 MS 0.2 0.2 5 3 MS 0.2 0.2 10

(36) TABLE-US-00004 TABLE 4 illustrates the effects of different concentrations of Pueraria lobata nano-silver particles on the germination of the seeds of the Polygonatum Mill genus. Germination Germination Number star-up time (d) Growth vigor percentage (%) 0 28 Few green and major 42.8 2.6a yellowish 1 10 dark green and partial 74.8 4.3bc yellowish 2 6 Dense green 79.6 3.7c 3 12 Yellowish 67.8 2.4d

(37) It is noted that different uppercase and lowercase letters indicate a significant level of 0.05.

(38) It can be seen that after 60 days of culture, most of the seeds germinate into stem and root buds. Among them, the No. 2 MS medium with 6-BA (0.2 mg/L) and NAA (0.2 mg/L) that is added with 5.0 mg/L of the Pueraria lobata nano-silver has the highest germination rate, reaching 79.6%. Moreover, the rhizome buds are dark green, the root system is developed, and small seedlings with 1 to 2 cotyledons are grown. The start-up germination time is also the shortest. Germination can be seen about 6 d after inoculation. The No. 0 MS medium is used as a control group, which has the lowest germination rate and the longest time to start up the germination. Germination in the No. 0 MS medium occurs after 28 d of the inoculation. The rhizome buds are green and some are yellowish.

(39) The above description is only used to describe the illustrated embodiments of the present disclosure, but the scope of the protection of the present disclosure is not limited thereto. Those skilled familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed in the present disclosure. All of the changes or the substitutions are covered by the scope of the protection of the present disclosure. Therefore, the scope of the protection of the present disclosure should be subject to the disclosure.