Ultrathin gold nanosheet with high thickness-diameter ratio and synthesis method thereof

Abstract

The invention discloses a high-thickness-diameter-ratio ultrathin gold nanosheet and a synthesis method thereof, and belongs to the technical field of micro-nano materials. According to the invention, a phytic acid reagent aqueous solution and a humic acid reagent aqueous solution are added into a chloroauric acid aqueous solution, wherein the phytic acid reagent and the humic acid reagent play roles of a reducing agent and a protective agent. Nucleation and growth of the ultrathin gold nanosheet with the high thickness-diameter ratio are achieved by regulating and controlling the reaction temperature, the pH value of the chloroauric acid water solution, the concentration of the phytic acid reagent water solution, the concentration of the humic acid reagent water solution and the like. The diameter of the synthesized ultrathin gold nanosheet with the high thickness-diameter ratio is 10-50 microns, the thickness of the nanosheet is 5-10 nm, and the slicing rate is larger than 90%; wherein a small amount of spherical gold particles exist, and the particle size of the spherical gold particles is 0.1-0.5 mu m. According to the method, phytic acid and humic acid biomass reagents are used for synthesizing the ultrathin gold nanosheets with the high thickness-diameter ratio, pollution of toxic reducing agents or surfactants to the environment is reduced, multi-valued utilization of the phytic acid and humic acid biomass reagents is effectively improved, the whole process is simple and easy to operate, large-scale production can be achieved, and the method is suitable for industrial production. The material is expected to be applied to the fields of catalysis and high-reliability electronic devices.

Description

Technical Field

[0001] This invention relates to an ultrathin gold nanosheet with a high aspect ratio and its synthesis method, belonging to the field of micro and nanomaterials technology. Background Technology

[0002] Noble metal micro / nanomaterials possess excellent physicochemical properties due to their unique structure and characteristics. They are widely used in catalysis, nanodevices, drug delivery, electronic pastes, and other fields. Especially in today's rapidly developing high-tech era, the demand for gold micro / nanomaterials is constantly increasing, particularly in flexible electronic devices, catalysis, electrochemical biosensors, and electrodes. Firstly, gold micro / nanomaterials exhibit superior performance compared to most other metal nanomaterials due to their excellent conductivity, excellent chemical stability, corrosion resistance, stable contact resistance, and precision machinability. Although the cost is higher, the value brought by their superior performance and long lifespan in critical applications far exceeds the material cost. Secondly, the morphology and size of gold micro / nanomaterials directly determine their performance in catalysis and high-reliability electronic nanodevice applications. Traditional spherical gold nanoparticles have a lower specific surface area compared to sheet-like gold micro / nanomaterials, resulting in a relatively lower surface atomic ratio during catalysis and a greater number of hidden atoms in the bulk phase (i.e., lower atomic utilization rate than sheet-like gold micro / nanomaterials). On the other hand, when applied in fields such as flexible electronics and sensors, point contact results in a low contact area, low thixotropy, and is unsuitable for demanding applications such as sensors and electronics. Therefore, in electronic nanodevices for catalysis and high reliability, sheet-like gold micro / nanomaterials are often preferred, thus attracting widespread attention and research.

[0003] The preparation of noble metal micro / nanomaterials typically employs bottom-up chemical methods, such as liquid-phase reduction, seed-mediated growth, template methods, and vapor deposition. Among these, liquid-phase reduction is the preferred method due to its advantages, including relatively simple reaction conditions, mass production capability, and low product performance variability. However, traditional liquid-phase reduction methods often use toxic reducing agents, surfactants, or dispersants, posing certain risks to the environment and human health. Therefore, environmentally friendly, inexpensive, and functionally rich biomass materials are increasingly being used in the synthesis of noble metal micro / nanomaterials.

[0004] In recent years, research on the synthesis of noble metal nanomaterials using biomass materials has gradually increased, such as cellulose, bovine serum albumin, soluble starch, and plant polyphenols (catechins, gallic acid). However, the micro- and nanomaterials synthesized using these reagents in published patents and literature generally suffer from high levels of reducing agent residue, complex post-processing, or excessively small nanomaterial sizes, making them difficult to apply in fields such as high-reliability electronic nanodevices and catalysis. Currently, the synthesis of micro- and nanomaterials using phytic acid and humic acid biomass reagents mostly produces particulate products, and the preparation process only plays a role in complexing or chelating metal ions, still requiring the addition of additional reducing agents such as ascorbic acid or sodium borohydride. Furthermore, the reducing and protective effects of phytic acid and humic acid biomass materials on metal ions have not been revealed. In addition, a survey of existing gold micro- and nanosheet research has found that some existing preparation processes still have limitations, such as the use of toxic reagents (e.g., toluene, hexadecyltrimethylammonium bromide), the need for high-temperature hydrothermal reactions, or the use of templates that are difficult to prepare in large quantities. For example, patent CN 115464132 B discloses a controllable preparation method for phytic acid-coated silver nanoparticles. This method uses silver nitrate as the silver source, phytic acid as a dispersant and stabilizer, and ascorbic acid as a reducing agent. The pH value is adjusted using NaOH to prepare the silver nanoparticles, resulting in an average particle size of 8.36 nm and a spherical shape. Patent CN 115229177 B discloses a preparation method and application of sodium humate-copper nanoclusters. This method uses copper salt as the copper source, sodium humate as a protective agent, and ascorbic acid as a reducing agent. The components are mixed in a certain proportion and reacted at a constant temperature in a magnetic stirrer for a period of time. After the reaction, the mixture is allowed to stand, cooled, and centrifuged to obtain a light yellow sodium humate-copper nanocluster solution.

[0005] In summary, current reports on the preparation of metal micro / nanomaterials using phytic acid and humic acid biomass reagents only demonstrate the adsorption and protection effects of phosphate and hydroxyl groups on metal ions through complexation and chelation. However, the reducing effects of these phosphate and hydroxyl groups on metal ions remain largely unexplored. Therefore, in-depth research on the reduction of metal ions using phytic acid and humic acid biomass reagents to prepare metal micro / nanomaterials is of great significance. Secondly, current metal nanomaterials prepared using phytic acid and humic acid biomass reagents in combination with other reducing agents are often too small in size, with a predominantly spherical particle morphology, making them difficult to apply practically in catalysis and high-reliability electronic nanodevices. Fully exploring the use of phytic acid and humic acid biomass reagents in the preparation of metal micro / nanomaterials not only improves their high-value utilization rate but also has significant practical implications. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention proposes a high aspect ratio ultrathin gold nanosheet and its synthesis method.

[0007] A method for synthesizing ultrathin gold nanosheets with high aspect ratio includes the following steps: (1) Adjust the pH of the chloroauric acid aqueous solution to prepare solution a, and set aside; (2) Prepare solution b by adding phytic acid and / or humic acid reagents to water for later use; (3) Mix and stir solutions a and b at a certain temperature, then heat and react for a period of time to obtain a high aspect ratio ultrathin gold nanosheet stock solution; (4) The high aspect ratio ultrathin gold nanosheet stock solution obtained in step (3) is subjected to ultrasonic washing, centrifugation and water dispersion treatment with anhydrous ethanol and deionized water in sequence to obtain an aqueous suspension of high aspect ratio ultrathin gold nanosheets.

[0008] In a preferred embodiment of the present invention, the molar concentration of chloroauric acid in the chloroauric acid aqueous solution is 0.01~0.1 mol / L, and the pH value is 1.0~3.0; the pH value of the chloroauric acid aqueous solution is adjusted by hydrochloric acid or sodium hydroxide aqueous solution, wherein the volume concentration of hydrochloric acid is 36~38%, and the molar concentration of sodium hydroxide aqueous solution is 0.1~0.5 mol / L.

[0009] In a preferred embodiment of the present invention, the phytic acid reagent is one or more of phytic acid, zinc phytate, potassium phytate, sodium phytate, calcium phytate, dipotassium phytate, calcium magnesium phytate, and sodium dodecanoate phytate; the humic acid reagent is one or more of humic acid, sodium humate, and potassium humate.

[0010] In a preferred embodiment of the present invention, the mass concentration of phytic acid and / or humic acid reagents in solution b is 1~30 g / L.

[0011] In a preferred embodiment of the present invention, in step (3), the volume ratio of solution a to solution b is 1:5 to 1:10.

[0012] As a preferred embodiment of the present invention, in step (3), the mixing and stirring temperature of solution a and solution b is 20~40 ℃, and the mixing and stirring time is 5-20 min; the reaction temperature is 50~80 ℃, and the reaction time is 2-10 h.

[0013] The present invention also claims protection for the high aspect ratio ultrathin gold nanosheets prepared by the synthesis method of the high aspect ratio ultrathin gold nanosheets, wherein the microstructure of the high aspect ratio ultrathin gold nanosheets includes nanosheets and gold particles, wherein the diameter of the nanosheets is 10~50 μm, the flake ratio is higher than 90%, the flake thickness is 5~10 nm, and the gold particle size is 0.1~0.5 μm.

[0014] The mechanism involved in this invention: Firstly, phytic acid-based biomass reagents mainly include phytic acid, zinc phytate, potassium phytate, sodium phytate, calcium phytate, dipotassium phytate, calcium magnesium phytate, and dodecanoic acid phytate. Phytic acid and its salts are primarily derived from plant seeds, especially the outer shells of cereals and oilseed crops. Humic acid and its salts, on the other hand, are primarily derived from plant residues, formed through coalification and biochemical processes into natural mineralized organic carboxylic acid polymers, which lack definite molecular formulas and molecular weights. Research on the preparation of gold micro / nanomaterials using these phytic acid and humic acid-based biomass reagents revealed that these reagents typically complex and chelate Au at room temperature. 3+ The adsorption effect is mainly due to the weak reduction of the phosphate groups and hydroxyl groups on the inositol ring in phytic acid reagents at room temperature, which primarily react with Au. 3+ Strong chelation, strong complexation, and electrostatic interactions occur between them, making it difficult to prepare gold micro / nanosheets at room temperature.

[0015] However, experimental investigations have revealed that under appropriate reaction temperatures, the oxidation or degradation of phosphate groups in phytic acid and humic acid reagents can be promoted, thereby providing Au. 3+ Electrons are required for reduction. Phytic acid and humic acid reagents have relatively mild and controllable reducing power; they are weaker than strong reducing agents (such as sodium borohydride), but stronger than some weak reducing agents (such as trisodium citrate). This mildness is precisely their advantage, which is beneficial for controlling the nucleation and growth rate of Au and reducing excessive aggregation, resulting in structures with uniform size and specific morphology. Furthermore, the phosphate groups in phytic acid and humic acid reagents are effective against Au nucleation. 3+ It has strong coordination effect, when Au 3+ When reduced to gold atoms, the phosphate groups and hydroxyl groups on the inositol rings exhibit the strongest adsorption on the Au(111) crystal plane. As gold atoms are continuously reduced and gradually deposited on the Au(110) crystal plane, they eventually grow into ultrathin gold nanosheets with a high aspect ratio based on the (111) plane.

[0016] The beneficial effects of this invention are as follows: This invention adds aqueous solutions of phytic acid and humic acid biomass reagents, which act as both reducing and protecting agents, to a chloroauric acid solution. By controlling the temperature gradient, reactant concentration, and pH value of the chloroauric acid aqueous solution, the invention achieves the efficient synthesis of ultrathin gold nanosheets with high aspect ratios. This realizes the multi-value utilization of phytic acid and humic acid reagents, providing a new approach for the green synthesis of metal micro / nanomaterials. The method of this invention can effectively adjust the size and proportion of gold nanosheets, showing excellent application prospects in catalysis and high-reliability electronic devices. Attached Figure Description

[0017] Figure 1 This is a flowchart of the green synthesis process of the high aspect ratio ultrathin gold nanosheets of the present invention.

[0018] Figure 2 This is a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Example 1 of this invention, with a scale bar of 5 μm.

[0019] Figure 3 This is a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Example 2 of this invention. The scale bar in the image is 50 μm.

[0020] Figure 4 This is a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Example 3 of this invention. The scale bar in the image is 10 μm.

[0021] Figure 5 This is a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Example 5 of this invention. The scale bar in the image is 20 μm.

[0022] Figure 6 This is a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Comparative Example 1 of this invention. The scale bar in the image is 20 μm.

[0023] Figure 7 This is a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Comparative Example 2 of this invention. The scale bar in the image is 20 μm.

[0024] Figure 8 This is a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Comparative Example 3 of this invention. The scale bar in the image is 50 μm.

[0025] Figure 9 This is a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Comparative Example 4 of this invention. The scale bar in the image is 20 μm.

[0026] Figure 10 Figure 1 shows a scanning electron microscope (SEM) image of the gold nanosheets synthesized in Comparative Example 7 of this invention. The scale bar in Figure 1(a) is 20 μm, and the scale bar in Figure 1(b) is 500 nm. Figure 1(b) is a magnified view of the area within the red box in Figure 1(a). Detailed Implementation

[0027] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0028] Example 1 The green synthesis method of high aspect ratio ultrathin gold nanosheets according to the present invention includes the following steps: (1) Add 1 ml of 0.1 mol / L chloroauric acid aqueous solution to 10 mL of deionized water to dilute to 0.01 mol / L chloroauric acid solution. Use hydrochloric acid (36-38%, volume concentration) to adjust the pH of the chloroauric acid solution to 0.5 to obtain solution a, which is ready for use.

[0029] (2) Dissolve 0.1 g of potassium humate in 100 mL of deionized water to prepare solution b for later use.

[0030] (3) Mix solutions a and b at a volume ratio of 1:10 under magnetic stirring at a certain temperature of 20 ℃, a stirring speed of 100 rpm, and a stirring time of 5 min to obtain mixed solution c.

[0031] (4) Increase the reaction temperature of the mixed solution c to 50 °C, stir at 100 rpm for 10 h to obtain the high aspect ratio ultrathin gold nanosheet stock solution.

[0032] (5) The high aspect ratio ultrathin gold nanosheet stock solution obtained in step (4) is first washed once with an equal volume of anhydrous ethanol, and then washed twice with an equal volume of deionized water; the ultrasonic time is 5 min; the centrifugation speed is 4000 rpm and the centrifugation time is 10 min; finally, the high aspect ratio ultrathin gold nanosheets are dispersed in 5 mL of water to obtain a high aspect ratio ultrathin gold nanosheet suspension.

[0033] Depend on Figure 2 It is known that using potassium humate as a reducing agent and protective agent can prepare ultrathin gold nanosheets with high aspect ratio. The proportion of ultrathin gold nanosheets in the product is greater than 90%, with an average size of 10-20 μm and a thickness of 5-10 nm; a small number of spherical particles exist, with a particle size of 0.3-0.5 μm.

[0034] Example 2 The method for synthesizing high aspect ratio ultrathin gold nanosheets according to the present invention specifically includes the following steps: (1) Take 1 ml of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0035] (2) Dissolve 15 g of potassium humate in 500 mL of deionized water to prepare solution b, and set aside.

[0036] (3) Mix solutions a and b at a volume ratio of 1:5 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0037] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 h to obtain the high aspect ratio ultrathin gold nanosheet stock solution.

[0038] (5) The high aspect ratio ultrathin gold nanosheet stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the high aspect ratio ultrathin gold nanosheets are dispersed in 30 mL of water to obtain a high aspect ratio ultrathin gold nanosheet suspension.

[0039] Depend on Figure 3 It can be seen that under the experimental parameters, potassium humate can be used to prepare ultrathin gold nanosheets with high aspect ratio. The proportion of ultrathin gold nanosheets in the product is greater than 90%, with an average size of 10~15 μm and a thickness of 5~10 nm; a small number of spherical particles with a particle size of 0.1~0.3 μm are also present.

[0040] Example 3 The method for synthesizing high aspect ratio ultrathin gold nanosheets according to the present invention specifically includes the following steps: (1) Add 1 ml of 0.1 mol / L chloroauric acid aqueous solution to 2 mL of deionized water to dilute to 0.05 mol / L chloroauric acid solution. Use hydrochloric acid (36-38%, volume concentration) to adjust the pH of the chloroauric acid solution to 2.0 as solution a for later use.

[0041] (2) Dissolve 7.5 g of potassium humate in 500 mL of deionized water to prepare solution b, and set aside.

[0042] (3) Mix solutions a and b at a volume ratio of 1:8 under magnetic stirring at a certain temperature. The stirring temperature is 30 ℃, the stirring speed is 200 rpm, and the stirring time is 12 min to obtain mixed solution c.

[0043] (4) Increase the reaction temperature of the mixed solution c to 65 °C, stir at 200 rpm for 6 h to obtain the high aspect ratio ultrathin gold nanosheet stock solution.

[0044] (5) The high aspect ratio ultrathin gold nanosheet stock solution obtained in step (4) is first washed twice with an equal volume of anhydrous ethanol, and then washed three times with an equal volume of deionized water. The ultrasonic time is 12 min. The centrifugation speed is 4400 rpm and the centrifugation time is 20 min. Finally, the high aspect ratio ultrathin gold nanosheets are dispersed in 17 mL of water to obtain a high aspect ratio ultrathin gold nanosheet suspension.

[0045] Depend on Figure 4It can be seen that under these experimental parameters, high aspect ratio ultrathin gold nanosheets can also be prepared. Under these experimental parameters, the proportion of high aspect ratio ultrathin gold nanosheets prepared is greater than 90%, with an average size of 10-15 μm and a thickness of 5-10 nm; a small number of particles exist, with a size of 0.1-0.3 μm.

[0046] Example 4 The method for synthesizing high aspect ratio ultrathin gold nanosheets according to the present invention specifically includes the following steps: (1) Take 1 ml of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH value of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0047] (2) Dissolve 15 g of sodium humate in 500 mL of deionized water to prepare solution b, and set aside.

[0048] (3) Mix solutions a and b at a volume ratio of 1:10 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0049] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 h to obtain the high aspect ratio ultrathin gold nanosheet stock solution.

[0050] (5) The high aspect ratio ultrathin gold nanosheet stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the high aspect ratio ultrathin gold nanosheets are dispersed in 30 mL of water to obtain a high aspect ratio ultrathin gold nanosheet suspension.

[0051] As shown in Table 1, high aspect ratio ultrathin gold nanosheets can also be prepared using sodium humate reagent. The average size of the prepared ultrathin gold nanosheets is 10-15 μm and the thickness is 5-10 nm. The sheet formation rate is greater than 90%, and some spherical nanoparticles with a particle size of 0.1-0.5 μm are present in the product.

[0052] Example 5 The method for synthesizing high aspect ratio ultrathin gold nanosheets according to the present invention specifically includes the following steps: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and use 0.5 mol / L sodium hydroxide aqueous solution to adjust the pH value of the chloroauric acid aqueous solution to 3.0 as solution a for later use.

[0053] (2) Dissolve 15 g of humic acid in 500 mL of deionized water to prepare solution b, and set aside.

[0054] (3) Mix solutions a and b at a volume ratio of 1:10 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0055] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 h to obtain the high aspect ratio ultrathin gold nanosheet stock solution.

[0056] (5) The high aspect ratio ultrathin gold nanosheet stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the high aspect ratio ultrathin gold nanosheets are dispersed in 30 mL of water to obtain a high aspect ratio ultrathin gold nanosheet suspension.

[0057] Depend on Figure 5 It can be seen that humic acid reagent can also effectively prepare ultrathin gold nanosheets with high aspect ratios, and the morphology of the ultrathin gold nanosheets is relatively regular. The average size of the ultrathin gold nanosheets is 10~12 μm, and the thickness is 5~10 nm; the shape is triangular and hexagonal, and a small number of nanoparticles are present in the product, with a nanoparticle diameter of 0.1~0.3 μm and a sheet formation rate of more than 90%.

[0058] Comparative Example 1 Comparative Example 1 and Example 2 are the same in all other steps, except that the mass of potassium humate in step (2) is 20 g. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and use 0.5 mol / L sodium hydroxide aqueous solution to adjust the pH value of the chloroauric acid aqueous solution to 3.0 as solution a for later use.

[0059] (2) Dissolve 15 g of potassium humate in 500 mL of deionized water to prepare solution b, and set aside.

[0060] (3) Mix solutions a and b at a volume ratio of 1:5 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0061] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 hours to obtain the gold nanomaterial stock solution.

[0062] (5) The gold nanomaterial stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold nanomaterial is dispersed in 30 mL of water to obtain the gold nanomaterial suspension.

[0063] Depend on Figure 6 It can be seen that when the mass concentration of potassium humate is too high, there is a large amount of agglomeration in the prepared gold nanomaterials and no obvious plate-like morphology appears. In the end, a large number of nanoparticles and irregular morphological gold nanomaterials are formed, with an average particle size of 0.5~1.0 μm.

[0064] Comparative Example 2 The steps in Comparative Example 2 and Example 4 are the same except that the mass of sodium humate in step (2) is 0.1 g. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0065] (2) Dissolve 0.4 g of sodium humate in 500 mL of deionized water to prepare solution b, and set aside.

[0066] (3) Mix solutions a and b at a volume ratio of 1:10 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0067] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 hours to obtain the gold nanomaterial stock solution.

[0068] (5) The original solution of gold nanomaterials obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold nanomaterials are dispersed in 30 mL of water to obtain a gold nanomaterial suspension.

[0069] Depend on Figure 7 It can be seen that when the mass concentration of potassium humate is too low, high aspect ratio ultrathin gold nanosheets cannot be obtained, but a large number of nanoparticles are formed, with an average particle size of 0.3~0.5 μm.

[0070] Comparative Example 3 The steps in Comparative Example 3 and Example 4 are the same except that the pH of solution a is 0.5 in step (1). The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and use hydrochloric acid (36-38%, volume concentration) to adjust the pH value of the chloroauric acid aqueous solution to 0.5 as solution a for later use.

[0071] (2) Dissolve 15 g of sodium humate in 500 mL of deionized water to prepare solution b, and set aside.

[0072] (3) Mix solutions a and b at a volume ratio of 1:10 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0073] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 hours to obtain the gold nanomaterial stock solution.

[0074] (5) The gold nanomaterial stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold nanomaterial is dispersed in 30 mL of water to obtain the gold nanomaterial suspension.

[0075] Depend on Figure 8 It is known that at a low pH value (pH=0.5) of chloroauric acid, abnormal growth will occur when gold nanomaterials are prepared using sodium humate. The gold nanomaterials in the product have a severely irregular sheet-like morphology, producing large-sized micron-sized irregular particles with an average particle size of 0.5~2.0 μm.

[0076] Comparative Example 4 Comparative Example 4 and Example 5 follow the same steps, except that in step (1), the pH of solution a is 4.0. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 4.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0077] (2) Dissolve 15 g of sodium humate reducing agent in 500 mL of deionized water to prepare solution b, and set aside.

[0078] (3) Mix solutions a and b at a volume ratio of 1:10 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0079] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 hours to obtain the gold nanomaterial stock solution.

[0080] (5) The gold nanomaterial stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold nanomaterial is dispersed in 30 mL of water to obtain the gold nanomaterial suspension.

[0081] Depend on Figure 9 It is observed that under high pH conditions of chloroauric acid (pH=4.0), gold nanomaterials prepared using sodium humate tend to form a large number of gold particles. This is because as the pH of the chloroauric acid aqueous solution gradually increases, phytic acid and humic acid reagents are largely deprotonated, making it difficult for them to effectively exert their own reducing and protective effects. The resulting gold nanomaterials are predominantly (~80%) irregular micron-sized particles with an average particle size of 1.0~3.0 μm.

[0082] Comparative Example 5 Comparative Example 5 and Example 2 are the same in all other steps, except that the reaction temperature in step (4) is 40 °C. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0083] (2) Dissolve 15 g of potassium humate in 500 mL of deionized water to prepare solution b, and set aside.

[0084] (3) Mix solutions a and b at a volume ratio of 1:5 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0085] (4) The reaction temperature of the mixed solution c was kept at 40 °C, the stirring speed was 300 rpm, and the stirring reaction time was 10 h to obtain the gold nanomaterial stock solution.

[0086] (5) The gold nanomaterial stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold nanomaterial is dispersed in 30 mL of water to obtain the gold nanomaterial suspension.

[0087] Table 1 shows that when the reaction temperature is too low (40 °C), the prepared gold nanomaterials contain a small amount (~30%) of ultrathin gold nanosheets with an average size of 1~5 μm. This is because the growth of the gold nanosheets is slow due to the low reaction temperature; the remaining majority (~70%) is Au. 3+ Nanoparticles are generated by reduction, with a particle size of 0.2~0.5 μm.

[0088] Comparative Example 6 Comparative Example 6 and Example 2 are the same in all other steps, except that the reaction temperature in step (4) is 90 °C. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0089] (2) Dissolve 15 g of potassium humate in 500 mL of deionized water to prepare solution b, and set aside.

[0090] (3) Mix solutions a and b at a volume ratio of 1:5 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0091] (4) The reaction temperature of the mixed solution c was kept at 90 °C, the stirring speed was 300 rpm, and the stirring reaction time was 2 h to obtain the gold nanomaterial stock solution.

[0092] (5) The original solution of gold nanomaterials obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold nanomaterials are dispersed in 30 mL of water to obtain a gold nanomaterial suspension.

[0093] Table 1 shows that when the reaction temperature is too high (90 ℃), the proportion of gold nanosheets in the prepared gold nanomaterial is extremely low (~10%), and the product contains a large number (~90%) of micron-sized particles with an average particle size of 1.0~5.0 μm. Excessive reaction temperature leads to a decrease in the proportion of gold nanosheets in the prepared gold nanomaterial. 3+ The rapid reduction and explosive nucleation process leads to the formation of micron-sized large particles, which severely restricts their anisotropic growth and is not conducive to the synthesis of ultrathin gold nanosheets with high aspect ratio.

[0094] Comparative Example 7 Comparative Example 7 and Example 2 are the same in all other steps, except that potassium humate in step (2) is replaced with xylan. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0095] (2) Dissolve 15 g of xylan in 500 mL of deionized water to prepare solution b, and set aside.

[0096] (3) Mix solutions a and b at a volume ratio of 1:5 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0097] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 hours to obtain the gold micron sheet stock solution.

[0098] (5) The gold micron sheet stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold micron sheet is dispersed in 30 mL of water to obtain the gold micron sheet suspension.

[0099] Depend on Figure 10 It can be seen that when xylan is used as the reagent, the prepared product is gold microsheets with an average size of 3-5 μm and an average thickness of approximately 90-100 nm; the sheet formation rate is greater than 60%, the particle ratio is less than 40%, and the average particle size is 0.5-1.0 μm. Obviously, it is impossible to prepare high aspect ratio ultrathin gold nanosheets when the reducing agent is changed.

[0100] Comparative Example 8 Comparative Example 8 and Example 2 are the same in all other steps, except that potassium humate in step (2) is replaced with glycine. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0101] (2) Dissolve 15 g of glycine in 500 mL of deionized water to prepare solution b, and set aside.

[0102] (3) Mix solutions a and b at a volume ratio of 1:5 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0103] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 hours to obtain the gold micron sheet stock solution.

[0104] (5) The gold micron sheet stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold micron sheet is dispersed in 30 mL of water to obtain the gold micron sheet suspension.

[0105] Comparative Example 9 Comparative Example 9 and Example 2 are the same in all other steps, except that potassium humate in step (2) is replaced with corn steep liquor powder. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0106] (2) Dissolve 15 g of corn steep liquor powder in 500 mL of deionized water to prepare solution b, and set aside.

[0107] (3) Mix solutions a and b at a volume ratio of 1:5 under magnetic stirring at a certain temperature of 35 ℃, a stirring speed of 300 rpm, and a stirring time of 20 min to obtain mixed solution c.

[0108] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 2 hours to obtain the gold micron sheet stock solution.

[0109] (5) The gold micron sheet stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold micron sheet is dispersed in 30 mL of water to obtain the gold micron sheet suspension.

[0110] Comparative Example 10 Comparative Example 10 and Example 2 are the same in all other steps, except that potassium humate in step (2) is replaced with sodium lignosulfonate. The specific steps are as follows: (1) Take 1 mL of 0.1 mol / L chloroauric acid aqueous solution and adjust the pH of the chloroauric acid aqueous solution to 3.0 using 0.5 mol / L sodium hydroxide aqueous solution as solution a for later use.

[0111] (2) Dissolve 15 g of sodium lignosulfonate in 500 mL of deionized water to prepare solution b for later use.

[0112] (3) Mix solutions a and b at a volume ratio of 1:5 under magnetic stirring at a certain temperature. The stirring temperature is 40 ℃, the stirring speed is 300 rpm, and the stirring time is 20 min to obtain mixed solution c.

[0113] (4) Increase the reaction temperature of the mixed solution c to 80 °C, stir at 300 rpm for 10 h to obtain the gold nanosheet stock solution.

[0114] (5) The gold nanosheet stock solution obtained in step (4) is first washed three times with an equal volume of anhydrous ethanol, and then washed five times with an equal volume of deionized water. The ultrasonic time is 20 min. The centrifugation speed is 4800 rpm and the centrifugation time is 30 min. Finally, the gold nanosheets are dispersed in 30 mL of water to obtain the gold nanosheet suspension.

[0115] The specific performance parameters of the gold micro / nanomaterials synthesized in Examples 1-5 and Comparative Examples 1-10 are shown in Table 1 below.

[0116] Table 1 In summary, the reaction temperature, the mass concentration of the reducing agent, and the pH value of the chloroauric acid aqueous solution play a major role in the preparation of high aspect ratio ultrathin gold nanosheets using phytic acid and humic acid reagents. If the reaction temperature is too low (<40 ℃), the reaction is slow and incomplete; if the reaction temperature is too high (>90 ℃), Au atoms undergo explosive nucleation, resulting in a significant increase in the proportion of particles in the product system and an increase in the thickness of the sheets. Similarly, the mass concentration of the reducing agent should not be too low or too high. If the mass concentration is too low, Au atoms cannot continue to grow to form high aspect ratio ultrathin gold nanosheets, and incomplete reaction and inhibited growth of gold nanosheets occur. Conversely, if the mass concentration of the reducing agent is too high, it excessively promotes the nucleation and growth of Au atoms, ultimately forming a large number of spherical gold micro / nanoparticles, making it difficult to anisotropically grow into high aspect ratio ultrathin gold nanosheets. The pH value of the chloroauric acid aqueous solution also significantly affects the morphology, size, and sheet formation rate of the product; both excessively low and excessively high pH values ​​inhibit the growth of gold nanosheets. Therefore, only under suitable conditions of reaction temperature, reducing agent concentration, and precursor pH can high aspect ratio ultrathin gold nanosheets with good morphology, size, and flake formation rate be synthesized.

[0117] Furthermore, the type of biomass reagent is also crucial for controlling the morphology and size of gold nanosheets. Comparative Examples 7-10 of this invention used xylan, glycine, corn steep liquor powder, and sodium lignin sulfonate, respectively, corresponding to four different types of biomass reagents: polysaccharides, amino acids, soluble starches, and lignins. The results showed that the gold nanosheets synthesized using these four common biomass reagents generally had a larger thickness. This is mainly attributed to the weaker interaction between the functional groups in the above reagent structures and Au atoms, while the interactions between the polyphosphate groups and hydroxyl groups in phytic acid reagents, and the various groups (carboxyl groups, phenolic hydroxyl groups, carbonyl groups, etc.) in humic acid reagents and Au atoms are stronger (strong complexation and strong chelate adsorption). This leads to effective control over the nucleation and growth of Au atoms, ultimately resulting in the Au(111) crystal plane being complexed and chelated by polyphosphate groups and various groups such as carboxyl groups, while also experiencing steric hindrance. Therefore, the growth of the Au(111) crystal plane is strongly suppressed, and Au atoms are selectively and directionally deposited on the Au(110) crystal plane and other crystal planes, ultimately growing into ultrathin gold nanosheets with high aspect ratio. The synthesis of ultrathin gold nanosheets with high aspect ratio using phytic acid / humic acid biomass reagents is green and environmentally friendly, and the operation process is simple, showing great application potential in the fields of catalysis and high-reliability nanodevices.

[0118] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for synthesizing ultrathin gold nanosheets with high aspect ratio, characterized in that: Includes the following steps: (1) Adjust the pH of the chloroauric acid aqueous solution to prepare solution a, and set aside; (2) Prepare solution b by adding phytic acid and / or humic acid reagents to water for later use; (3) Mix and stir solutions a and b at a certain temperature, then heat and react for a period of time to obtain a high aspect ratio ultrathin gold nanosheet stock solution; (4) The high aspect ratio ultrathin gold nanosheet stock solution obtained in step (3) is subjected to ultrasonic washing, centrifugation and water dispersion treatment with anhydrous ethanol and deionized water in sequence to obtain an aqueous suspension of high aspect ratio ultrathin gold nanosheets.

2. The method for synthesizing high aspect ratio ultrathin gold nanosheets according to claim 1, characterized in that: The chloroauric acid aqueous solution has a molar concentration of 0.01~0.1 mol / L and a pH value of 1.0~3.

0.

3. The method for synthesizing high aspect ratio ultrathin gold nanosheets according to claim 1, characterized in that: The phytic acid reagent is one or more of phytic acid, zinc phytate, potassium phytate, sodium phytate, calcium phytate, dipotassium phytate, calcium magnesium phytate, and sodium dodecanoate phytate; the humic acid reagent is one or more of humic acid, sodium humate, and potassium humate.

4. The method for synthesizing high aspect ratio ultrathin gold nanosheets according to claim 1, characterized in that: The mass concentration of phytic acid and / or humic acid reagents in solution b is 1~30 g / L.

5. The method for synthesizing high aspect ratio ultrathin gold nanosheets according to claim 1, characterized in that: In step (3), the volume ratio of solution a to solution b is 1:5 to 1:

10.

6. The method for synthesizing high aspect ratio ultrathin gold nanosheets according to claim 1, characterized in that: In step (3), the mixing and stirring temperature of solution a and solution b is 20~40 ℃, and the mixing and stirring time is 5~20 min; the reaction temperature is 50~80 ℃, and the reaction time is 2~10 h.

7. The high aspect ratio ultrathin gold nanosheets prepared by the synthesis method of any one of claims 1-6, wherein the microstructure of the high aspect ratio ultrathin gold nanosheets includes nanosheets and gold particles, wherein the diameter of the nanosheets is 10-50 μm, the flake ratio is higher than 90%, the flake thickness is 5-10 nm, and the spherical gold particles have a particle size of 0.1-0.5 μm.

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