A continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles

Abstract

The present invention relates to the technical field of nano-material preparation, and particularly relates to a continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles, which includes a reduction mixing step, a thiol mixing step, a carbon powder dispersion step, and a carbon powder loading step. It also includes a backmixing step and a monitoring step. The backmixing step is arranged between the thiol mixing step and the carbon powder dispersion step, and the monitoring step is arranged after the carbon powder loading step. Through the above process, continuous production of products above hundreds of grams can be achieved, reducing redundant intermediate steps, precisely controlling the particle size and distribution of gold nanoparticles while ensuring a good yield. Compared with the prior art, it solves the problems that the steps of carbon-supported gold nanoparticles in large-scale production are complex and difficult to repeat, the obtained product has too large particle size, uneven distribution, and is prone to agglomeration, resulting in poor dispersion and stability of the product and low yield.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterial preparation, and particularly to a continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles. Background Art

[0002] Carbon-supported gold nanoparticle (AuNPs) catalysts exhibit excellent catalytic performance in many chemical reactions and are widely used in fields such as organic synthesis, environmental governance, and fuel cells. Their excellent catalytic performance is attributed to the high surface energy and highly active surface of gold nanoparticles. Generally, loading gold nanoparticles on carbon materials can further improve their catalytic performance and stability.

[0003] Currently, the methods for preparing carbon-supported gold nanoparticle catalysts are mainly divided into traditional batch methods and innovative continuous flow methods. Traditional batch methods generally include solution methods, chemical reduction methods, precipitation methods, etc. Although these methods are relatively mature, they usually have complex steps and poor repeatability, making it difficult to carry out large-scale production and limiting their wide industrial application.

[0004] Patent CN116672984A discloses a continuous and controllable synthesis method of carbon nanotube nanocomposites loaded with nano metal particles and a microfluidic synthesis platform. By precisely controlling reaction conditions at the microscale and achieving uniform mixing of reaction reagents within milliseconds, rapid and efficient mixing can reduce the difference in residence time between reaction reagents, thereby effectively improving the dispersibility and repeatability of synthesized nanoparticles. However, the reaction flow rate is too small, making it suitable for small-scale reactions.

[0005] Moreover, various organic stabilizing ligands, including phosphines, amines, and thiols, are often used to synthesize gold nanoparticles and regulate their surface properties. Among them, thiols strongly adsorb on the surface of gold nanoparticles during the synthesis process, minimizing the van der Waals interaction between adjacent grains and having extensive applications in regulating the particle size, distribution, and shape of monodisperse gold nanoparticles.

[0006] Patent CN116801978A discloses a gold-loaded carbon catalyst and its manufacturing method, including a gold particle generation step, a treatment step, and a loading step. Although the size and distribution of gold particles can be precisely controlled by adjusting parameters such as the coverage rate of alkylthiol coordination agents and reaction conditions, this preparation method requires multiple steps with cumbersome conversions between steps, a long reaction time, which is not conducive to large-scale production. Moreover, the synthesis of the gold-carbon catalyst requires the prior synthesis of gold nanoparticles in solution and then the separation and washing of gold nanoparticles, which not only results in the loss of gold elements but also inevitably leads to the aggregation of gold nanoparticles, and the operation is complex and not conducive to industrial scale-up.

[0007] At present, the selection of reducing agents and the control of reaction conditions during the process of loading continuous flow reaction onto carbon materials can affect the size and morphology of the finally formed nanoparticles, and will also inevitably lead to the aggregation of gold nanoparticles. There is a need for a method that can be precisely regulated to improve the particle size and distribution in the industrial scale-up production of continuous flow reactions, so as to improve the dispersibility and stability of the obtained gold nanocatalysts. Summary of the Invention

[0008] In order to solve the above problems, the present invention provides a continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles. By increasing the ligand, the size and distribution of gold nanoparticles can be effectively regulated, the preservation time of the catalyst can be further extended, and at the same time, the continuous flow method is improved, which can realize the continuous production of products above 100 grams, reduce intermediate redundant steps, precisely regulate the particle size and distribution of gold nanoparticles while ensuring good yield, and has good potential for industrial scale-up.

[0009] A continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles includes a reduction mixing → thiol mixing → carbon powder dispersion → carbon powder loading stage, and also includes a backmixing stage and a monitoring stage. The backmixing stage is set between the thiol mixing stage and the carbon powder dispersion stage, and the monitoring stage is set after the carbon powder loading stage; wherein, the backmixing stage is a process in which the initial mixed solution flowing out of the thiol mixing stage is sent back to the thiol mixing stage through a backmixing pipeline and remixed to obtain a remixed solution; the monitoring stage includes a process of filtering the catalyst solution obtained in the carbon powder loading stage and monitoring the color change of the filtrate.

[0010] Further, the volume of the initial mixed solution sent back to the thiol mixing stage through the backmixing pipeline for remixing is not less than one-fifth of the total volume of the initial mixed solution flowing out of the thiol mixing stage.

[0011] Further, the flow rate of the solution in the reduction mixing stage, the thiol mixing stage and the carbon powder dispersion stage is 6-12 L / h.

[0012] Further, the reduction mixing stage is a process in which a gold salt solution and a reducing agent solution are mixed to obtain gold nanoparticles. The concentration of the gold salt solution is 18.00-22.75 mmol / L, and the concentration of the reducing agent solution is 23.40-27.90 mmol / L.

[0013] Further, the thiol mixing stage is a process in which a thiol solution and the gold nanoparticles obtained in the reduction mixing stage are mixed to obtain an initial mixed solution. The concentration of the thiol solution is 18.00-22.75 mmol / L.

[0014] Further, the toner dispersion stage is a process in which the primary mixture obtained from the thiol mixing stage and the remixing liquid obtained from the backmixing stage are respectively added to the toner dispersion liquid for mixing to obtain a toner dispersion mixture. The concentration of the toner dispersion liquid is 13.40 - 17.20 g / L.

[0015] Further, the toner loading stage is a process in which the toner dispersion mixture obtained from the toner dispersion stage is added with a precipitant to load gold nanoparticles on the toner. The flow rate of the precipitant is 1 - 7 L / h, and the residence time is 2 - 5 min.

[0016] Further, it is judged whether the toner loading is complete according to the filtrate color in the monitoring stage, and then the flow rate of the precipitant is adjusted.

[0017] Further, the gold salts in the reduction mixing stage include chloroauric acid tetrahydrate and chloroauric acid trihydrate, and the reducing agents include any one of borane tert-butylamine, dimethylamine borane, and morpholine borane.

[0018] Further, the thiol in the thiol mixing stage includes any one of n-dodecyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, and n-hexadecyl mercaptan.

[0019] Further, the precipitant in the toner loading stage is anhydrous ethanol or methanol.

[0020] Further, the solvents used in the reduction mixing stage and the thiol mixing stage are a mixed solution of n-hexane and oleylamine, and the volume ratio of n-hexane to oleylamine is 1.5 - 1:1.

[0021] Further, the temperature in the reduction mixing stage and the thiol mixing stage is 25 - 40 °C.

[0022] Further, the solvent used in the toner dispersion stage is anhydrous ethanol or methanol.

[0023] Further, the toner dispersion liquid to be added in the toner dispersion stage needs to be continuously stirred.

[0024] The advantages of the present invention are as follows:

[0025] 1. By using the continuous flow method, the present invention can improve production efficiency. By continuously flowing the reactants into the reaction system and performing rapid reaction and product separation, continuous production can be achieved, reducing intermediate redundant steps, and having good industrial scale-up potential. Continuous production of products above 100 grams can be realized, while ensuring a good yield. Compared with the prior art, it can solve the technical problems of complex steps, difficulty in repetition, and low product yield in large-scale production.

[0026] 2. By setting a thiol mixing stage and a backmixing stage in the continuous flow production process, the present invention enables the addition of thiol to precisely control the particle size and distribution of gold nanoparticles. The backmixing stage allows the thiol and the gold nanoparticle solution to be fully mixed and aged, achieving a narrow size distribution of gold nanoparticles, thereby improving the dispersibility and stability of the catalyst and solving the problem in the prior art that the particle size of carbon-supported gold nanoparticles is too large and the distribution is uneven during scale-up production, resulting in poor dispersibility.

[0027] 3. By setting a monitoring stage in the continuous flow production process, the present invention determines whether the carbon powder loading is complete by filtering the color of the gold-carbon catalyst solution, and then precisely controls the dosage of the sedimentation agent. Compared with the existing scale-up production process of carbon-supported gold nanoparticles, it can avoid the problems of aggregation of gold nanoparticles and an increase in production particle size caused by excessive dosage of the sedimentation agent. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a process flow chart of a continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles according to the present invention;

[0029] Figure 2 is a schematic diagram of the pipeline connection of the continuous flow platform built according to the present invention;

[0030] Figure 3 is an X-ray diffraction pattern of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 1 of the present invention;

[0031] Figure 4 is a transmission electron microscope image of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 1 of the present invention;

[0032] Figure 5 is an X-ray diffraction pattern of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 2 of the present invention;

[0033] Figure 6 is a transmission electron microscope image of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 2 of the present invention;

[0034] Figure 7 is an X-ray diffraction pattern of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 3 of the present invention;

[0035] Figure 8 is a transmission electron microscope image of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 3 of the present invention;

[0036] Figure 9 is an X-ray diffraction pattern of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 4 of the present invention;

[0037] Figure 10It is the transmission electron microscope image of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 4 of the present invention;

[0038] Figure 11 It is the X-ray diffraction pattern of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 5 of the present invention;

[0039] Figure 12 It is the transmission electron microscope image of the thiol-modified carbon-supported gold nanoparticle catalyst obtained in Example 5 of the present invention;

[0040] Figure 13 It is the X-ray diffraction pattern of the carbon-supported gold nanoparticle catalyst obtained in Comparative Example 1 of the present invention;

[0041] Figure 14 It is the transmission electron microscope image of the carbon-supported gold nanoparticle catalyst obtained in Comparative Example 1 of the present invention;

[0042] Figure 15 It is the X-ray diffraction pattern of the carbon-supported gold nanoparticle catalyst obtained in Comparative Example 2 of the present invention;

[0043] Figure 16 It is the transmission electron microscope image of the carbon-supported gold nanoparticle catalyst obtained in Comparative Example 2 of the present invention;

[0044] Figure 17 It is the X-ray diffraction pattern of the carbon-supported gold nanoparticle catalyst obtained in Comparative Example 3 of the present invention;

[0045] Figure 18 It is the transmission electron microscope image of the carbon-supported gold nanoparticle catalyst obtained in Comparative Example 3 of the present invention;

[0046] Figure 19 It is the X-ray diffraction pattern of the carbon-supported gold nanoparticle catalyst obtained in Comparative Example 4 of the present invention;

[0047] Figure 20 It is the transmission electron microscope image of the carbon-supported gold nanoparticle catalyst obtained in Comparative Example 4 of the present invention. Detailed implementation manners

[0048] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0049] It should be noted that the installation methods and technical terms mentioned in the present invention are all well-known technical terms in the technical field, so no further explanation will be given.

[0050] Example 1 This example provides a method for continuously preparing thiol-modified carbon-supported gold nanoparticles. First, prepare the raw material solutions:

[0051] Prepare a mixed solution as the solvent in a ratio of n-hexane: oleylamine = 1:1 (volume ratio); prepare a chloroauric acid solution, a reducing agent solution, and a thiol solution for standby, using chloroauric acid trihydrate, borane tert-butylamine, and n-dodecanethiol as solutes respectively; prepare a carbon powder dispersion using absolute ethanol as the solvent for standby; prepare absolute ethanol as the precipitant for standby;

[0052] Then, feed the prepared raw material solutions into a continuous flow platform for the preparation of thiol-modified carbon-supported gold nanoparticles. The preparation process is as Figure 1 shown, including reduction mixing → thiol mixing → backmixing → carbon powder dispersion → carbon powder loading → monitoring stage. The specific steps are as follows:

[0053] Reduction mixing stage: Drive the gold salt solution and the reducing agent solution to flow out of the raw material container through a peristaltic pump and feed them into the first mixing tube through a connecting tube for mixing. The concentration of the gold salt solution is 18 mmol / L, the flow rate is 6 L / h, the concentration of the reducing agent solution is 23.4 mmol / L, the flow rate is 6 L / h, and the temperature is 25°C. Start the reduction reaction. The reducing agent in the reducing agent solution reduces the Au 3+ ions in the gold salt solution to zero-valent gold to obtain gold nanoparticles;

[0054] Thiol mixing stage: Drive the thiol solution to flow out of the raw material container through a peristaltic pump and feed it into the second mixing tube through a connecting tube together with the gold nanoparticles flowing out of the reduction mixing stage in step (1) to obtain a preliminary mixed solution. The mixing temperature is 25°C, and the concentration of the thiol solution is 18 mmol / L, and the flow rate is 6 L / h.

[0055] (3) Backmixing stage: A backmixing tube is connected to the outlet of the second mixing tube. 1 / 5 (volume) of the preliminary mixed solution flowing out of the outlet of the second mixing tube flows into the next stage, and 4 / 5 (volume) of the preliminary mixed solution flowing out of the outlet of the second mixing tube flows back to the inlet of the second mixing tube through the backmixing tube and flows into the second mixing tube again with the continuously flowing thiol solution for mixing to obtain a re-mixed solution. After a period of time, a narrow size distribution of gold nanoparticles is achieved through Ostwald ripening;

[0056] (4) Carbon powder dispersion stage: The carbon powder dispersion liquid driven by a peristaltic pump flows out from the raw material container, passes through the connecting pipe, and flows into the third mixing pipe together with 1 / 5 of the preliminary mixed liquid and 4 / 5 of the remixing liquid to obtain a carbon powder dispersion mixed liquid. The concentration of the carbon powder dispersion liquid is 17.20 g / L, and the flow rate is 12 L / h.

[0057] (5) Carbon powder loading stage: The precipitant driven by a peristaltic pump flows out from the raw material container, passes through the connecting pipe, and flows into the fourth mixing pipe together with the carbon powder dispersion mixed liquid to obtain a thiol-modified carbon-supported gold nanoparticle catalyst solution. The flow rate of the precipitant is controlled between 1 - 7 L / h, and the residence time is 5 min;

[0058] (6) Monitoring stage: The obtained thiol-modified carbon-supported gold nanoparticle catalyst solution is filtered through a needle filter, and it is monitored whether the color of the obtained filtrate is significantly red. If so, it indicates that the gold nanoparticles are not fully loaded. Then, the flow rate of the precipitant is appropriately adjusted, and the samples in the first 5 minutes of the reaction are additionally processed. The catalyst solution after 5 minutes of the reaction basically meets the requirements of particle size distribution.

[0059] The production scale of this example is 250 g / day, and the yield is 87%.

[0060] The schematic diagram of the pipeline connection of the continuous flow platform built in this example is as Figure 2 shown, successively including five raw material containers, peristaltic pumps, a first mixing pipe, a second mixing pipe, a third mixing pipe, a fourth mixing pipe, a backmixing pipe, a needle filter, and a product container. Among them, the raw material containers of the gold salt solution, reducing agent solution, thiol solution, and carbon powder dispersion liquid are all connected to the inlet of the first peristaltic pump. Because of the inconsistent flow rates, the raw material container of the precipitant is connected to the inlet of the second peristaltic pump. The outlets of the first peristaltic pump and the second peristaltic pump are connected to a flow meter. The first mixing pipe, the second mixing pipe, the third mixing pipe, and the fourth mixing pipe are located between the flow meter and the product container. Connecting pipes are provided between each mixing pipe, and the flow meter, mixing pipes, and product container are all connected through the connecting pipes. The mixing pipes and the connecting pipes are connected through three-way joints. Among them, the outlet of the fourth mixing pipe and two pipelines are connected to both ends of the three-way joint. One of them is connected to one end of the upper valve, and the other end is connected to the first pipeline. Then the first pipeline is connected to the needle filter, and a transparent reagent bottle is placed at the outlet of the filter to observe the color of the filtrate. The other of the two pipelines is connected to one end of the lower valve, and the other end is connected to the second pipeline. Then the second pipeline is connected to the product container. The raw material solutions for preparing the carbon-supported gold nanoparticle catalyst flow out continuously from the five raw material solution containers under the pressure of the peristaltic pump, and after being regulated by the flow meter, the reduction mixing → thiol mixing → backmixing → carbon powder dispersion → carbon powder loading → monitoring stage are successively completed through the first mixing pipe, the second mixing pipe, the third mixing pipe, and the fourth mixing pipe to complete the mixing reaction.

[0061] The connecting pipe in this embodiment is made of PTFE pipe.

[0062] The mixing pipe in this embodiment adopts a static mixer, which is internally designed with structures such as spiral blades and corrugated plates, and can effectively disrupt the laminar flow of the fluid, promote mixing, accelerate the reaction process, and improve the reaction efficiency.

[0063] A stirrer is arranged in the raw material container of the toner dispersion liquid in this embodiment. The stirrer is vertically erected at the top outlet of the raw material container of the toner dispersion liquid, and the stirring end of the stirrer extends into the raw material container of the toner dispersion liquid to stir the toner dispersion liquid, so as to prevent the toner dispersion liquid from settling under static conditions, resulting in inconsistent toner concentrations at the top and bottom of the dispersion liquid.

[0064] In this embodiment, small temperature sensors are respectively installed on the side walls of the first mixing pipe, the second mixing pipe, the third mixing pipe and the fourth mixing pipe to monitor the temperature change in real time, and measures are taken to maintain the temperature to ensure that the reaction proceeds at the optimal temperature, improving the reaction selectivity and the product quality.

[0065] Characterization and analysis: The product obtained in this embodiment is subjected to XRD test, and the test spectrum is as Figure 3 shown. It is confirmed by XRD that the crystal structure of the product is Au / C, and the catalyst particle size is 1.7 nm.

[0066] Among them, the calculation formula for the catalyst grain size is:

[0067]

[0068] In the formula, d is the grain size (nm), representing the average thickness of the grain in the direction perpendicular to the (hkl) crystal plane. λ is the wavelength of the incident X-ray (here taken as 1.54056 Å), and θ is the incident angle of the X-ray to the crystal plane. B is the half-height width of the measured sample diffraction peak. After double-line correction and instrument factor correction, it needs to be converted to radians (rad) during the calculation process.

[0069] The product obtained in this embodiment is subjected to TEM test, and the TEM image is as Figure 4 shown. It can be seen that the obtained thiol-modified carbon-supported gold nanoparticles have a narrow size distribution at 200 nm, the particle sizes are the same, the distribution is uniform, there is no obvious agglomeration phenomenon, and they have high dispersibility.

[0070] Example 2 The preparation method of this example is the same as that of Example 1, except that the parameter conditions in the process are different, specifically as follows:

[0071] In this example, a mixed solution is prepared as the solvent at a ratio of n-hexane: oleylamine = 1.5:1 (volume ratio); chloroauric acid solution, reducing agent solution, and thiol solution are prepared separately with chloroauric acid tetrahydrate, dimethylamine borane, and n-hexadecanethiol as solutes for standby; a carbon powder dispersion is prepared with methanol as the solvent for standby; methanol is used as the precipitant for standby.

[0072] In the reduction mixing stage of this example, the temperature is 40°C, the concentration of the gold salt solution is 22.75 mmol / L, the flow rate is 12 L / h, the concentration of the reducing agent solution is 27.90 mmol / L, and the flow rate is 12 L / h.

[0073] In the thiol mixing stage of this example, the temperature is 40°C, the concentration of the thiol solution is 22.75 mmol / L, and the flow rate is 12 L / h.

[0074] In the carbon powder dispersion stage of this example, the concentration of the carbon powder dispersion is 17.20 g / L, and the flow rate is 12 L / h.

[0075] In this example, the flow rate of the precipitant is controlled between 1 - 7 L / h, and the residence time is 2 min.

[0076] The production scale of this example is 350 g / day, and the yield is 83%.

[0077] Characterization and analysis:

[0078] The product obtained in this example is also subjected to XRD test and TEM test. The test methods and the calculation method of particle size are the same as those in Example 1. It is confirmed by XRD that the crystal structure of the catalyst product obtained in this example is Au / C, and the catalyst particle size is 2.3 nm (the test spectrum is as Figure 5 shown). It is obtained by TEM that the catalyst product particles are evenly distributed, without obvious agglomeration phenomenon, and have high dispersibility (the TEM image is as Figure 6 shown).

[0079] Example 3 The preparation method of this example is the same as that of Example 1, except that the parameter conditions in the process are different. In this example, the flow rates of the solutions in the reduction mixing stage, thiol mixing stage, and carbon powder dispersion stage are all 15 L / h.

[0080] Characterization and analysis:

[0081] The product obtained in this example is also subjected to XRD test and TEM test. The test methods and the calculation method of particle size are the same as those in Example 1. It is confirmed by XRD that the crystal structure of the catalyst product obtained in this example is Au / C, and the catalyst particle size is 4.6 nm (the test spectrum is as Figure 7As shown), through TEM testing, it is found that the obtained catalyst particles are unevenly distributed and there is partial agglomeration. This is because the flow rate is too fast, resulting in unstable flow rate of the peristaltic pump, and partial mixing is uneven and insufficient (TEM images are as Figure 8 shown).

[0082] The production scale of this example is 200 g / day, and the yield is 85%.

[0083] Example 4 The preparation method of this example is the same as that of Example 1, except that the parameter conditions in the process are different. In this example, the flow rate of the solution in the reduction mixing stage, thiol mixing stage, and carbon powder dispersion stage is 4 L / h.

[0084] Characterization analysis:

[0085] The product obtained in this example is also subjected to XRD testing and TEM testing. The testing method and the calculation method of particle size are the same as those in Example 1. After XRD confirmation, the crystal structure of the catalyst product obtained in this example is Au / C, and the catalyst particle size is 3.4 nm (the test spectrum is as Figure 9 shown). Through TEM testing, it is found that the obtained catalyst product particles are unevenly distributed and there is partial agglomeration. This is because the flow rate is too slow, resulting in unstable flow rate of the peristaltic pump and partial uneven mixing (TEM images are as Figure 10 shown).

[0086] The production scale of this example is 250 g / day, and the yield is 83%.

[0087] Example 5 The preparation method of this example is the same as that of Example 1, except that the parameter conditions in the process are different, specifically as follows:

[0088] In this example, the concentration of the gold salt solution is 30 mmol / L, the concentration of the reducing agent solution is 15 mmol / L, the concentration of the thiol solution is 10 mmol / L, and the concentration of the carbon powder dispersion is 20 g / L.

[0089] Characterization analysis:

[0090] The product obtained in this example is also subjected to XRD testing and TEM testing. The testing method and the calculation method of particle size are the same as those in Example 1. After XRD confirmation, the crystal structure of the catalyst product obtained in this example is Au / C, and the catalyst particle size is 3.9 nm (the test spectrum is as Figure 11 shown). Through TEM testing, it is found that the obtained catalyst product particles are very unevenly distributed, the particle size is relatively large, and there is partial obvious agglomeration (TEM images are as Figure 12 shown).

[0091] The production scale of this example is 300 g / day, and the yield is 80%.

[0092] Comparative Example 1

[0093] In this comparative example, carbon-supported gold nanoparticles were prepared by a traditional batch method. The preparation process is as follows:

[0094] (1) Prepare solution A (6.176 g chloroauric acid + 450 mL oleylamine + 450 mL n-hexane, stirred and mixed in argon for 20 min) and solution B (1304.4 mg TBAB (borane-tert-butylamine) + 50 mL oleylamine + 50 mL n-hexane, ultrasonically mixed evenly) separately for standby;

[0095] (2) Reduction: Under stirring conditions, quickly add solution B to solution A, react at room temperature for 1 h under argon protection, add a small amount of cyclohexane to the product (to clean the inner wall of the flask), transfer it to a centrifuge tube, add absolute ethanol (cyclohexane:absolute ethanol = 1:4), and directly centrifuge and wash three times to obtain solid gold nanoparticles;

[0096] (3) Disperse carbon powder and load: Weigh a certain amount of carbon powder according to the required loading amount. Prepare the amount of cyclohexane according to the ratio of 2 mL cyclohexane for every 6 mg carbon powder. First, mix half of the cyclohexane with the carbon powder and ultrasonically mix for 10 min. Then dissolve the gold nanoparticles with the remaining cyclohexane and transfer it to a round-bottom flask. Add the carbon powder dispersion while stirring and stir overnight at room temperature for 12 h;

[0097] (4) Separation and washing: After stirring, let it stand for half an hour. Wait for the product to completely settle. Use a pipette to transfer the supernatant, pour the lower-layer product into a centrifuge tube, centrifuge and wash three times, and vacuum dry at 60 °C. Collect the sample and grind it to obtain solid powder.

[0098] Characterization and analysis:

[0099] The product obtained in this comparative example was also subjected to XRD test and TEM test. The test methods and the calculation method of particle size are the same as those in Example 1. It was confirmed by XRD that the crystal structure of the catalyst product obtained in this comparative example is Au / C (the XRD test spectrum is as shown in Figure 13 ), and the catalyst particle size is 6.7 nm. The TEM image is as shown in Figure 14 . It can be seen that the carbon-supported gold nanoparticles prepared by the traditional batch method have larger particle sizes at 200 nm, uneven particle size distribution, and obvious agglomeration in some parts.

[0100] The maximum reaction scale of this comparative example is 20 g, and the yield is 70%.

[0101] Comparative Example 2

[0102] The preparation method of this comparative example is the same as that of Example 1, except that in this comparative example, there is no backmixing stage. After the thiol and gold nanoparticles flow through the thiol mixing stage and are mixed, the resulting mixed solution directly flows into the carbon powder dispersion stage and is mixed with the carbon powder dispersion liquid.

[0103] The product obtained in this comparative example was also subjected to XRD testing and TEM testing. The testing methods and the calculation method of particle size are the same as those in Example 1. It was confirmed by XRD that the crystal structure of the catalyst product obtained in this comparative example is Au / C, and the average size of the catalyst particles is 3.5 nm (the test spectrum is as Figure 15 shown). It was found by TEM that the size of the gold nanoparticles in the obtained catalyst is relatively large, the particle size distribution is uneven, and there is a phenomenon of agglomeration of a small amount of gold nanoparticles (the TEM image is as Figure 16 shown).

[0104] The production scale of this comparative example is 200 g / day, and the yield is 75%.

[0105] Comparative Example 3

[0106] The preparation method of this comparative example is the same as that of Example 1, except that in this comparative example, there is no thiol modification stage and backmixing stage. The gold nanoparticles obtained after the reduction stage directly flow into the carbon powder dispersion stage and are mixed with the carbon powder dispersion liquid.

[0107] The product obtained in this comparative example was also subjected to XRD testing and TEM testing. The testing methods and the calculation method of particle size are the same as those in Example 1. It was confirmed by XRD that the crystal structure of the catalyst product obtained in this comparative example is Au / C, and the average size of the catalyst particles is 4.5 nm (the test spectrum is as Figure 17 shown). It was found by TEM that the particle distribution range of the obtained catalyst product is relatively wide, the distribution is uneven, the particle diameters are different, and there is an obvious agglomeration phenomenon in part (the TEM image is as Figure 18 shown).

[0108] The production scale of this comparative example is 200 g / day, and the yield is 80%.

[0109] Comparative Example 4

[0110] The preparation method of this comparative example is the same as that of Example 1, except that in this comparative example, there is no monitoring stage. The dispersion liquid flowing out of the carbon powder dispersion stage and the sedimentation agent flow into the carbon powder loading stage together, and the carbon-supported gold nanoparticle catalyst solution obtained after staying for 5 minutes directly flows into the product solvent for collection.

[0111] The product obtained in this comparative example was also subjected to XRD testing and TEM testing. The testing methods and the calculation method of particle size are the same as those in Example 1. It was confirmed by XRD that the crystal structure of the catalyst product obtained in this comparative example is Au / C, and the average size of the catalyst particles is 4.0 nm (the test spectrum is as Figure 19as shown), obvious agglomeration phenomenon occurred in the obtained catalyst product particles as revealed by TEM (TEM images are as Figure 20 shown).

[0112] The production scale of this example is 200 g / day, and the yield is 77%.

[0113] The results of Example 1 and Comparative Example 1 show that the method of this application has simple steps and is applicable to the continuous production of products above 100 grams. At the same time, a good yield of up to 87% can be guaranteed. The maximum reaction scale of the method in Comparative Example 1 is only 20 g, and the yield is 70%. From the catalyst particle size and dispersion results of Examples 1-5 and Comparative Examples 2-4, it can be seen that in the present invention, by setting a thiol mixing stage and a backmixing stage in the continuous flow production process, the addition of thiol can accurately control the particle size and distribution of gold nanoparticles. The backmixing stage can make the thiol and the gold nanoparticle solution fully mixed and aged, realizing a narrow size distribution of gold nanoparticles, thereby improving the dispersion and stability of the catalyst. The regulation of the precipitant in the monitoring stage can improve the agglomeration phenomenon.

[0114] For those skilled in the art, the present invention is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0115] The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any minor modifications, equivalent substitutions, and improvements made to the above embodiments based on the technical essence of the present invention should be included in the protection scope of the technical solution of the present invention.

Claims

1. A continuous flow preparation method for thiol-modified carbon-supported gold nanoparticles, comprising reduction mixing → thiol mixing → carbon powder dispersion → carbon powder loading stages, characterized in that: It also includes a back-mixing stage and a monitoring stage, wherein the back-mixing stage is arranged between the mercaptan mixing stage and the carbon powder dispersion stage, and the monitoring stage is arranged after the carbon powder loading stage; wherein the back-mixing stage is a process in which the primary mixed liquid flowing out of the mercaptan mixing stage is sent back to the mercaptan mixing stage through a back-mixing pipeline to be mixed again to obtain a remixed liquid; and the monitoring stage includes a process of filtering the catalyst solution obtained in the carbon powder loading stage and monitoring the color change of the filtrate; The reduction and mixing stage is a process of mixing a gold salt solution with a reducing agent solution to obtain gold nanoparticles, wherein the concentration of the gold salt solution is 18.00-22.75 mmol / L, and the concentration of the reducing agent solution is 23.40-27.90 mmol / L; The thiol mixing stage is a process of mixing the thiol solution with the gold nanoparticles obtained in the reduction mixing stage to obtain a primary mixed solution, and the concentration of the thiol solution is 18.00-22.75 mmol / L; The carbon powder dispersion stage is a process in which the primary mixed liquid obtained in the thiol mixing stage and the remixed liquid obtained in the back-mixing stage are added to the carbon powder dispersion liquid to mix to obtain a carbon powder dispersion mixed liquid, wherein the concentration of the carbon powder dispersion liquid is 13.40-17.20 g / L; The carbon powder loading stage is a process in which a precipitant is added to the carbon powder dispersion mixture obtained in the carbon powder dispersion stage to load the gold nanoparticles with carbon powder. The flow rate of the precipitant is 1-7 L / h and the residence time is 2-5 min. The flow rate of the precipitant is regulated according to the color of the filtrate in the monitoring stage.

2. The continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles according to claim 1, characterized in that: The flow rate of the solution in the reduction mixing stage, the thiol mixing stage and the carbon powder dispersion stage is 6-12 L / h.

3. The continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles according to claim 1, characterized in that: The volume of the initially mixed liquid sent back to the mercaptan mixing stage through the back-mixing pipeline for remixing is not less than one fifth of the total volume of the initially mixed liquid flowing out of the mercaptan mixing stage.

4. The continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles according to claim 1 or 2, characterized in that: The gold salt in the reduction mixing stage includes tetrahydrate chloroauric acid and trihydrate chloroauric acid, and the reducing agent includes any one of tert-butylamine borane, dimethylamine borane, and morpholine borane; the thiol in the thiol mixing stage includes any one of n-dodecyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, n-decyl mercaptan, and n-hexadecyl mercaptan, and the precipitant in the carbon powder loading stage is anhydrous ethanol or methanol.

5. The continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles according to claim 4, characterized in that: The solvent used in the reduction mixing stage and the mercaptan mixing stage is a mixed solution of n-hexane and oleylamine, the volume ratio of n-hexane to oleylamine is 1.5-1:1, and the temperature of the system is 25-40°C.

6. The continuous flow preparation method of thiol-modified carbon-supported gold nanoparticles according to claim 1, characterized in that: The toner dispersion to be added in the toner dispersion stage needs to be continuously stirred, and the solvent of the toner dispersion is anhydrous ethanol or methanol.

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