A system and method for continuous synthesis of silver nanowires in a microwave microreactor

Abstract

The application discloses a system and method for continuously synthesizing silver nanowires in a microwave micro-reactor. The main process of the application is to use microwave as the energy supply form, to fully mix the required reagents in the micro-mixer on the basis of the polyol method, to perform microwave irradiation in the microwave spiral inverse micro-flow reactor for a certain time, and to obtain relatively pure silver nanowires after centrifugal washing of the reaction product with methanol and deionized water. The application takes the synthesis of silver nanowires in the microwave micro-reactor as a model system, and realizes the continuous synthesis of silver nanowires by adjusting the structure, material and microwave irradiation conditions of the reactor. Compared with the existing batch reactor, the time efficiency and space-time yield are greatly improved, and the application prospect is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of nanomaterial preparation, in particular to a system and method for continuous synthesis of silver nanowires in a microwave microreactor. BACKGROUND

[0002] Silver nanowires have great development potential in emerging technology fields due to their unique electrical, optical, magnetic and thermal properties and potential applications in microelectronics, optoelectronic devices and sensors, and have a huge demand market.

[0003] In the traditional preparation method of silver nanowires, the reaction temperature is high (generally 150-170℃), and the reaction time is long (usually 1h), which is not conducive to the synthesis of high-yield silver nanowires. In contrast, microwave heating can quickly raise the temperature and even facilitate local heating of the kinetic non-equilibrium chemical process, reducing the reaction time to 3-4min and greatly improving the time efficiency. At present, some patents in China have proposed the use of microwave-assisted method to prepare silver nanowires, such as patent publication numbers CN102029400A and CN105537613A, but the reactors used are batch reactors. Although the growth process of nanowires is optimized by strictly controlling the reaction parameters in the research, the batch reactors still have the disadvantages of differences between batches and low stability. In order to improve the stability of silver nanowires prepared by microwave-assisted method, a more stable reactor is needed.

[0004] The small size and high surface-to-volume ratio of the microreactor can well meet the needs. Compared with traditional batch reactors, microreactors have higher mixing efficiency, higher mass and heat transfer rates, precise control of reaction conditions, and improved process safety, which are more conducive to the large-scale, continuous and stable preparation of silver nanowires. There are many types of microreactors, but there are few reports on how to design microwave microreactors. SUMMARY

[0005] The present application takes the synthesis of silver nanowires in a microwave microreactor as a model system, and realizes the continuous synthesis of silver nanowires by adjusting the structure, material and microwave radiation conditions of the reactor.

[0006] The purpose of the present application is to provide a system and method for continuous synthesis of silver nanowires in a microwave microreactor to overcome the problems of low stability of kettle-type reaction and low efficiency of traditional heating method.

[0007] The present application provides a method for continuous synthesis of silver nanowires in a microwave microreactor, comprising the following steps:

[0008] 1) Construct a system for synthesizing silver nanowires, the system comprising a raw material pump for pumping a mother liquor, a microwave spiral inverter micro-flow reactor in communication with the raw material pump, a microwave generating device for generating microwaves, a micro-reactor disposed within the microwave generating device, and a product collection device for collecting the product; the microwave generating device comprises a microwave generator for generating microwaves and a microwave controller for controlling the microwave power and microwave generation time generated by the microwave generator; the product collection device is a double-port feed bottle placed in an ice water bath, one side of the double-port feed bottle is used for the product to flow out and be collected in the bottle, and the other side is connected with nitrogen for controlling the reaction pressure;

[0009] 2) Dissolve silver nitrate powder and inorganic additive powder in ethylene glycol respectively, mix the two solutions in proportion to prepare a mother liquor A containing silver ions and inorganic additives; dissolve PVP powder in ethylene glycol to obtain a mother liquor B;

[0010] 3) Mix mother liquor A and mother liquor B through the raw material pump into the micro-mixer for sufficient mixing;

[0011] 4) Pass the mixed solution into the micro-reactor and control the microwave generator to emit microwaves by the microwave controller for microwave irradiation, and then transport the obtained product to the product collection device for collection in the ice water bath, and connect nitrogen to the other end of the collection device to control the reaction pressure;

[0012] 5) Add acetone to the collected product, then perform centrifugation, and then wash, centrifuge and ultrasonic disperse the separated solid to obtain silver nanowires.

[0013] As a preferred scheme of the present application, the raw material pump in step 1) has two, and the two raw material pumps pump mother liquor A and mother liquor B into the micro-mixer respectively; the micro-reactor is a microwave spiral inverter micro-flow reactor, the dielectric constant ε of the material of the micro-reactor is between 1-4, the dielectric loss tangent tanδ of the material of the micro-reactor is between 10 -8 -10 -2 ; the temperature rise of the material of the micro-reactor is 100℃, and the change of the dielectric constant ε is <1%.

[0014] As a preferred scheme of the present application, the micro-mixer in step 1) is made of resin, and the internal channel size is 0.5-1mm; the inner diameter of the pipeline of the microwave micro-reactor is 1-2mm, and the length is 1.5-5m.

[0015] As a preferred scheme of the present application, the concentration of silver nitrate in the mother liquor A in step 2) is 0.25-0.4 M; the inorganic additive is ferric chloride, sodium bromide, sodium chloride, copper chloride; the concentration of the inorganic additive in the mother liquor A is 0.4 mM-0.6 mM; the volume ratio of the silver nitrate solution and the inorganic additive solution used for preparing the mother liquor A is 1.2:1; the concentration of the PVP powder in the mother liquor B is 0.025-0.04 M, the PVP powder includes PVP with a molecular weight of 58000 and PVP with a molecular weight of 1300000, and the ratio of the PVP with a molecular weight of 58000 to the PVP with a molecular weight of 1300000 in the PVP powder is 1:1-1:3.

[0016] As a preferred scheme of the present application, the flow rate ratio of the mother liquor A to the mother liquor B in step 3) is 1:4.

[0017] As a preferred scheme of the present application, the microwave power generated by the microwave generator in step 4) is 200-400 W, and the irradiation time is 3-4 min.

[0018] As a preferred scheme of the present application, the pressure of the nitrogen gas in step 4) is 0.18-0.3 MPa.

[0019] Compared with the prior art, the present application has the following beneficial effects:

[0020] (1) The present application introduces a microwave micro-reactor for preparing silver nanowires, overcomes the problem of low time efficiency in the prior art, and achieves higher experimental efficiency compared with traditional kettle-type reaction and higher space-time yield compared with traditional continuous reaction, with the reaction time reduced by 94% and the yield increased by dozens of times.

[0021] (2) The present application adopts a spiral inverter micro-flow reactor, which has a larger specific surface area and a higher mass and heat transfer rate, thus overcoming the problem of unstable sample quality between batches in kettle-type reaction, so as to obtain more precise control of the reaction and better process safety.

[0022] (3) The present application explores the material quality parameters of the microwave micro-reactor, filling the gap in the design of the microwave spiral inverter micro-flow reactor. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The flow chart of the synthesis method of the silver nanowires in the embodiments of the present application is shown in the figure;

[0024] Figure 2 The scanning electron microscope photo of the product obtained in embodiment 1 of the present application is shown in the figure;

[0025] Figure 3 The XRD characterization chart of the product obtained in embodiment 1 of the present application is shown in the figure;

[0026] Figure 4 Transmission electron microscope image of the product obtained in Example 1 of the present application;

[0027] Figure 5 Scanning electron microscope image of the product obtained in Example 2 of the present application;

[0028] Figure 6 Scanning electron microscope image of the product obtained in Example 3 of the present application.

[0029] Figure 7 Scanning electron microscope image of the product obtained in Example 4 of the present application;

[0030] Figure 8 Scanning electron microscope image of the product obtained in Example 5 of the present application. DETAILED DESCRIPTION

[0031] The present application will be further described and illustrated with reference to the specific embodiments. The embodiments are only exemplary and do not circumscribe the scope of the disclosure. The technical features of each embodiment of the present application can be combined accordingly without conflict.

[0032] The present application takes the synthesis of silver nanowires in a microwave microreactor as a model system, and realizes the continuous synthesis of silver nanowires by adjusting the structure, material and microwave radiation conditions of the reactor.

[0033] The present application provides a system for continuously synthesizing silver nanowires in a microwave microreactor, comprising

[0034] 1) Raw material unit

[0035] The reagents used in the present application will be introduced into the micro-mixer by two raw material pumps, wherein raw material pump 1 is a PVP ethylene glycol solution, and raw material pump 2 is a silver nitrate and inorganic additive ethylene glycol solution, and the flow rates of the two raw material pumps are related to the irradiation time.

[0036] 2) Micro-mixer unit

[0037] The micro-mixer is designed by SOLIDWORKS and obtained by 3D printing through Formlabs 3, which is a resin material, and the internal channel size is sub-millimeter level.

[0038] 3) Microreactor unit

[0039] The selectivity of microwave heating is very strong. For liquid phase, microwave heating is usually based on the ability of polarized molecules, which depends on the dielectric properties of the molecules. The relationship between the material and microwave absorption is usually represented by the dielectric constant ε and the dielectric loss tangent tan δ. The dielectric constant ε determines the amount of electrical energy stored in the dielectric, and the dielectric loss tangent tan δ defines the ability of the material to be heated under the microwave field. According to their interaction with microwaves, different materials can be divided into three groups: (i) reflective type, such as metal; (ii) penetrating type, materials that are basically transparent to radiation, such as fused quartz, ceramic, zirconia, etc.; (iii) absorbing type, substances that can absorb energy from the microwave field and heat rapidly.

[0040] The microreactor is located in the microwave generating cavity, and it is important that the microwaves are effectively absorbed by the reaction solution without being absorbed by the outer tube or frame. The wave-transparent material needs to have a low dielectric constant (ε < 10) and a loss tangent value (tan δ < 10 -2 ), and such material does not change significantly with temperature and frequency (such as temperature rise of 100℃, ε change < 1%). Among them, the excellent wave-transparent material ε is only 1-4, to ensure as little electromagnetic wave penetration as possible.

[0041] Common non-polar or slightly polar plastics, such as polyethylene, polystyrene, polytetrafluoroethylene and other pure carbon-hydrogen plastics, have a relatively small dielectric constant (about 2-3) and a small dielectric loss factor (10 -8 -10 -4 ). The dielectric constant of ordinary glass is 6.8-8, and the dielectric constant of quartz glass is generally between 3.5-3.81.

[0042] Based on the above analysis, the final design of the microreactor is a microwave spiral inverter micro-flow reactor. The inner diameter of the microreactor pipe is 1.5 mm, and the length is 3.3 m.

[0043] 4) Product collection unit

[0044] The product collection device is a double-port feeding bottle placed in an ice water bath. One side of the double-port feeding bottle is used for product outflow and collection in the bottle, and the other side is connected to nitrogen gas for controlling the reaction pressure. The product after irradiation is collected in the ice water bath, and 0.18-0.3 MPa of nitrogen gas is added at the end of the product collection device to control the reaction pressure.

[0045] Example 1

[0046] 0.35M AgNO3 ethylene glycol solution and 600μM FeCl3 ethylene glycol solution were mixed at a volume ratio of 1.2:1 to form mother liquor A; 0.909g PVP (Mw~58000) and 0.909g PVP (Mw~1300000) were mixed and dissolved in 250mL ethylene glycol to form mother liquor B; mother liquor A and mother liquor B were injected into a micro-mixer at a flow rate ratio of 1:4 by a syringe pump, and the mixed fluid entered a micro-reactor composed of a PTFE tube with an inner diameter of 0.15mm and an outer diameter of 0.25mm and a support frame made of quartz with an outer diameter of 25mm. The micro-reactor was irradiated with microwaves at 200W for 3.5min in a microwave oven, and the obtained product was collected in an ice water bath. A 0.2MPa nitrogen gas was introduced into the tail end of the product collection device to control the reaction pressure. Acetone was added to the collected product in an amount of 3-5 times the volume of the product, and then centrifugation was performed to remove ethylene glycol and excess PVP. The separated solid was washed with deionized water for 3-5 times, and the obtained product was stored in 5mL deionized water after centrifugation and ultrasonic dispersion.

[0047] Figure 2 The SEM image of the silver nanowires obtained according to Example 1 is given. As can be seen from Figure 2 , the prepared silver nanowires have complete morphology and uniform size, with a diameter of 50.4±7nm and a length of 28.12±5.4μm. The diameter distribution and length distribution are both less than 20%, and the average aspect ratio is about 555. The single silver nanowire production efficiency can reach 0.65g / h. Figure 3 To implement Figure 1 The XRD characterization results of the silver nanowires prepared in Example 1 show that the silver nanowires have complete crystallization, and the structure is face-centered cubic silver. Figure 4 The TEM characterization results of the silver nanowires prepared in Example 1 show that the prepared silver nanowires have complete morphology and are flexible, and can be bent at acute angles without breaking.

[0048] Example 2

[0049] 0.35M AgNO3 solution in ethylene glycol was mixed with 600 μM FeCl3 solution in ethylene glycol at a volume ratio of 1.2:1 to form mother liquor A; 0.909 g PVP (Mw ~ 58000) and 0.909 g PVP (Mw ~ 1300000) were mixed and dissolved in 250 mL ethylene glycol to form mother liquor B; mother liquor A and mother liquor B were injected into a micromixer at a flow rate ratio of 1:4 by a syringe pump, and the mixed fluid entered a microreactor composed of a PTFE tube with an inner diameter of 0.15 mm and an outer diameter of 0.25 mm and a support frame made of quartz with an outer diameter of 25 mm. The microreactor was irradiated with microwaves at 300 W for 3.5 min in a microwave oven. The obtained product was collected in an ice water bath, and 0.2 MPa nitrogen was introduced into the tail end of the product collection device to control the reaction pressure. Acetone was added to the collected product at a volume of 3-5 times that of the product, followed by centrifugation to remove ethylene glycol and excess PVP. The separated solid was washed with deionized water 3-5 times, and the obtained product was stored in 5 mL deionized water after centrifugation and ultrasonic dispersion. Figure 5 The SEM image of the silver nanowires obtained according to Example 2 is given. As can be seen from Figure 5 , the silver nanowires prepared have a complete morphology and a diameter of 46.1 ± 8 nm.

[0050] Example 3

[0051] 0.1M silver nitrate solution was mixed with 0.05M sodium bromide solution at a volume ratio of 30:1 to form mother liquor A; 0.625 mg PVP (MW ~ 1300000) was dissolved in ethylene glycol and made up to 100 mL in a volumetric flask, and after uniform mixing, mother liquor B was formed; mother liquor A and mother liquor B were injected into a micromixer at a flow rate ratio of 3:8 by a syringe pump, and the mixed fluid entered a microreactor composed of a PTFE tube with an inner diameter of 0.15 mm and an outer diameter of 0.25 mm and a support frame made of quartz with an outer diameter of 25 mm. The microreactor was irradiated with microwaves at 300 W for 3 min in a microwave oven. The obtained product was collected in an ice water bath, and 0.2 MPa nitrogen was introduced into the tail end of the product collection device to control the reaction pressure. Acetone was added to the collected product at a volume of 3-5 times that of the product, followed by centrifugation to remove ethylene glycol and excess PVP. The separated solid was washed with deionized water 3-5 times, and the obtained product was stored in 5 mL deionized water after centrifugation and ultrasonic dispersion. Figure 6 The SEM image of the silver nanowires obtained according to Example 2 is given. As can be seen from Figure 6 , the silver nanowires prepared have a complete morphology and a smaller diameter of 18.7 ± 2 nm.

[0052] Example 4

[0053] A solution of 0.35 M AgNO3in ethylene glycol was mixed with a solution of 600 μM FeCl3in ethylene glycol at a volume ratio of 1.2:1 to form mother liquor A; 0.455 g PVP (Mw~58000) and 1.364 g PVP (Mw~1300000) were mixed and dissolved in 250 mL ethylene glycol to form mother liquor B; mother liquor A and mother liquor B were injected into a micromixer by a syringe pump at a flow rate ratio of 1:4, and the mixed fluid entered a microreactor composed of a PTFE tube with an inner diameter of 0.15 mm and an outer diameter of 0.25 mm and a support frame of quartz material with an outer diameter of 25 mm. The microreactor was irradiated by a microwave oven at 200 W for 3.5 min, and the obtained product was collected in an ice water bath. A 0.2 MPa nitrogen gas was introduced into the tail end of the product collection device to control the reaction pressure. Acetone was added to the collected product at a volume ratio of 3-5 times that of the product, and then centrifugation was performed to remove the ethylene glycol and excess PVP. The separated solid was washed with deionized water for 3-5 times, and the obtained product was stored in 5 mL deionized water after centrifugation and ultrasonic dispersion. Figure 7 The SEM image of the silver nanowires obtained according to Example 4 is shown in FIG. 4. As can be seen from FIG. 4, the silver nanowires prepared have a diameter of 63.8±11.4 nm, and there are many impurities such as silver nanoparticles and silver nanorods. Figure 7

[0054] Example 5

[0055] A solution of 0.25 M AgNO3in ethylene glycol was mixed with a solution of 600 μM FeCl3in ethylene glycol at a volume ratio of 1.2:1 to form mother liquor A; 0.909 g PVP (Mw~58000) and 0.909 g PVP (Mw~1300000) were mixed and dissolved in 250 mL ethylene glycol to form mother liquor B; mother liquor A and mother liquor B were injected into a micromixer by a syringe pump at a flow rate ratio of 1:4, and the mixed fluid entered a microreactor composed of a PTFE tube with an inner diameter of 0.15 mm and an outer diameter of 0.25 mm and a support frame of quartz material with an outer diameter of 25 mm. The microreactor was irradiated by a microwave oven at 200 W for 3.5 min, and the obtained product was collected in an ice water bath. A 0.2 MPa nitrogen gas was introduced into the tail end of the product collection device to control the reaction pressure. Acetone was added to the collected product at a volume ratio of 3-5 times that of the product, and then centrifugation was performed to remove the ethylene glycol and excess PVP. The separated solid was washed with deionized water for 3-5 times, and the obtained product was stored in 5 mL deionized water after centrifugation and ultrasonic dispersion. Figure 8 The SEM image of the silver nanowires obtained according to Example 5 is shown in FIG. 5. As can be seen from FIG. 5, the silver nanowires prepared have a diameter of 60±8.9 nm and a complete morphology. Figure 8

[0056] ​​The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation to the patent scope of the present application. For ordinary skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, which shall all fall into the protection scope of the present application.

Claims

1. A method for continuous synthesis of silver nanowires in a microwave microreactor, characterized in that, The method comprises the following steps: 1) constructing a system for synthesizing silver nanowires, the system comprising a raw material pump for pumping a mother liquor, a micro-mixer in communication with the raw material pump, a microwave generating device for generating microwaves, a micro-reactor disposed in the microwave generating device, and a product collection device for collecting the product; the microwave generating device comprises a microwave generator for generating microwaves and a microwave controller for controlling the microwave power and microwave generating time generated by the microwave generator; the product collection device is a double-port feeding bottle placed in an ice-water bath, one side of the double-port feeding bottle being used for the product to flow out and be collected in the bottle, and the other side being in communication with nitrogen for controlling the reaction pressure; The raw material pump has two, and the two raw material pumps respectively pump mother liquor A and mother liquor B into the micro-mixer; the micro-reactor is a microwave spiral inverse variable micro-flow reactor, which is composed of a PTFE pipe and a support frame of quartz material with an outer diameter of 25 mm; the inner diameter of the pipeline of the microwave micro-reactor is 1.5 mm, and the length is 3.3 m; 2) dissolving silver nitrate powder and inorganic additive powder in ethylene glycol respectively, mixing the two solutions in proportion to prepare mother liquor A containing silver ions and inorganic additives; dissolving PVP powder in ethylene glycol to obtain mother liquor B; 3) mixing mother liquor A and mother liquor B into the micro-mixer through the raw material pump for sufficient mixing; 4) passing the mixed solution into the micro-reactor and controlling the microwave generator to emit microwaves through the microwave controller for microwave irradiation, and then transporting the obtained product to the product collection device for collection in the ice-water bath, and connecting nitrogen to the other end of the collection device to control the reaction pressure; the microwave power emitted by the microwave generator is 200-400 W, and the irradiation time is 3-4 min; 5) adding acetone to the collected product, and then performing centrifugation, washing, centrifugation and ultrasonic dispersion operations on the separated solid to obtain silver nanowires.

2. The method of claim 1, wherein, The micro-mixer in step 1) is made of resin, and the internal channel size is 0.5-1 mm.

3. The method of claim 1, wherein, In step 2), the concentration of silver nitrate in mother liquor A is 0.25-0.4 M; the inorganic additive is iron chloride, sodium bromide, sodium chloride, and copper chloride; the concentration of the inorganic additive in mother liquor A is 0.4 mM-0.6 mM; the concentration of PVP powder in mother liquor B is 0.025-0.04 M.

4. The method of claim 1, wherein, In step 2), the volume ratio of the silver nitrate solution and the inorganic additive solution used to configure mother liquor A is 1.2:1; the PVP powder includes PVP with a molecular weight of 58000 and PVP with a molecular weight of 1300000, and the mass ratio of PVP with a molecular weight of 58000 to PVP with a molecular weight of 1300000 in the PVP powder is 1:1-1:

3.

5. The method of claim 1, wherein, In step 3), mother liquor A and mother liquor B are mixed into the micro-mixer at a flow rate ratio of 1:

4.

6. The method of claim 1, wherein, In step 4), the pressure of nitrogen is 0.18-0.3 MPa.

7. The method of claim 1, wherein, In step 5), the added acetone is 3-5 times the volume of the collected product.

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