Method for preparing nano copper oxide by precipitation method

Abstract

The invention belongs to the field of nano metal oxide preparation, and particularly relates to a method for preparing nano copper oxide through a precipitation method, and the method comprises the following steps: preparing a Cu-citric acid compound; copper sulfate and citrate are used as raw materials, and coordination is formed by a microchannel method; cDJP gas-liquid two-way jet flow is achieved; the inner-layer nozzle sprays alkali liquor, the outer-layer annular nozzle sprays CO2 gas, and the Cu (OH) 2 precursor is induced to directionally grow on the surfaces of the micron-sized bubbles; performing supercritical drying; drying the product by using a supercritical CO2 drying system; roasting is performed; and carrying out fluidized bed gradient roasting to maintain particle suspension. Citrate radicals and copper ions are adopted to form a coordination compound, traditional surfactant doping is replaced, and organic matter residues are avoided; according to the method, gas-liquid two-phase jet flow precipitation is adopted, and the nanospheres can be obtained through jet flow of an inner-layer nozzle and an outer-layer nozzle based on liquid-phase precipitation; carbon dioxide supercritical drying is adopted, so that the particle size of copper oxide nanoparticles is reduced, and the specific surface area of the copper oxide nanoparticles is increased.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nanometer metal oxide preparation, and particularly relates to a method for preparing nanometer copper oxide by a precipitation method. BACKGROUND

[0002] Nanometer copper oxide has a broad application prospect in desulfurization, sensors, antibacterial materials and other fields due to its excellent catalytic performance, antibacterial performance and electrochemical performance. For example, nanometer copper oxide exhibits high catalytic activity in the desulfurization process and also shows good inhibition capacity in the antibacterial field.

[0003] Liquid phase precipitation method is one of important methods for preparing nanometer copper oxide, mainly including direct precipitation method, complex precipitation method, rapid liquid phase precipitation method and the like. The direct precipitation method takes copper nitrate as raw material, and controls the morphology and particle size of nanometer copper oxide by adjusting pH value and reaction time. Studies show that this method is suitable for industrial production, but the product is prone to agglomeration and needs to be further optimized. The complex precipitation method utilizes a complexing agent to form a stable complex with metal ions, and then nanometer copper oxide is generated through a precipitant. This method can effectively control the morphology and particle size of the product, but the selection of the complexing agent is relatively high. The rapid liquid phase precipitation method realizes the rapid synthesis of nanometer copper oxide by rapid mixing and controlling reaction conditions (such as temperature, pH value), and has high industrialization potential. In recent years, researchers have significantly improved the dispersibility and catalytic performance of nanometer copper oxide by improving the process conditions (such as reaction temperature, pH value, precipitant concentration, etc.) of the liquid phase precipitation method: by adjusting the reaction pH value to 14, nanometer copper oxide with better catalytic performance can be obtained by calcining at 350℃ for 10 minutes.

[0004] However, the specific surface area of the spherical or spindle-shaped particles obtained by the existing method is generally lower than 50 m² / g, which is difficult to be applied to fields with high demand for catalytic efficiency. SUMMARY

[0005] In order to optimize the above technical problems, the present application provides a method for preparing nanometer copper oxide by a precipitation method.

[0006] The method for preparing nanometer copper oxide by a precipitation method comprises the following steps:

[0007] S1, preparation of Cu (II) -citric acid complex; taking copper sulfate and citrate as raw materials, a coordination is formed by using a microchannel method;

[0008] S2, CDJP gas-liquid bidirectional jet; an alkali solution is sprayed by an inner nozzle, and CO2 gas is sprayed by an outer annular nozzle to induce directional growth of Cu (OH) 2 precursor on the surface of micrometer-sized bubbles;

[0009] S3, supercritical drying; the product of S2 is dried by using a supercritical CO2 drying system;

[0010] S4, calcination; gradient calcination of sulfurized bed, maintaining particle suspension.

[0011] In one specific embodiment of the present application, in S1, the concentration of copper sulfate is 0.5 mol / L, the ratio of citrate and copper ions satisfies Cu 2+ :C6H5O7 3- =1:2.5, and the micro-channel flow rate is 3 mL / min.

[0012] In one specific embodiment of the present application, in S2, the lye includes a mixture of sodium hydroxide and sodium carbonate, the sodium ion concentration of the mixture is 2 mol / L, the flow rate is 1.2 L / h, and the ratio of n sodium hydroxide:n sodium carbonate = 3:1.

[0013] In one specific embodiment of the present application, in S3, the critical condition is 31.1℃, 7.38 MPa; the CO2 flow rate is 5 L / min, the supercritical state residence time is 30 min; the co-solvent is ethanol, and the volume is 10 times that of the solute.

[0014] In one specific embodiment of the present application, in S4, gradient calcination of sulfurized bed is used, and the process parameters are: 300℃ (1 h)→400℃ (2 h)→500℃ (1 h), the heating rate is 5℃ / min; the oxygen flow rate is 0.2→1.0 L / min, linearly increasing; the fluidization gas velocity is 1.2 m / s, maintaining particle suspension.

[0015] In one specific embodiment of the present application, the grain size of the copper oxide nanoparticles prepared by the method is 9 nm, the specific surface area is 128 m 2 / g, and the pore volume is 0.45 cm 3 / g.

[0016] The present application includes at least one of the following beneficial technical effects:

[0017] The present application uses the way of forming complex compounds by citrate and copper ions to replace the traditional surfactant doping, avoiding organic residue; secondly, the present application uses gas-liquid two-phase jet precipitation, based on liquid phase precipitation, using inner and outer two-layer nozzle jet, through the gas-liquid interface to induce Cu(OH)2precursor directional growth on the micron-sized bubble surface, which can obtain nanospheres; thirdly, the present application uses carbon dioxide supercritical drying to reduce the particle size of copper oxide nanoparticles and improve the specific surface area; finally, the present application uses dynamic calcination and oxygen vacancy regulation, compared with the prior art, the concentration of oxygen vacancies is increased by 187%. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1This is a TEM image (60,000x magnification) of the nano-copper oxide prepared by the method provided in Example 1 of this application.

[0019] Figure 2 This is a TEM image (60,000x magnification) of the nano-copper oxide prepared by the method provided in this application. Detailed Implementation

[0020] The following provides a further detailed description of this application.

[0021] Although precipitation methods for preparing nano-metal oxides are widely used in related technologies, it is difficult to transfer and imitate the preparation techniques for different metal oxides in parallel, and the required lattice oxygen vacancy concentrations also differ among different metal oxides. Currently, traditional liquid-phase precipitation methods mainly suffer from the following technical defects: uniform morphology; existing methods (such as direct precipitation) can only obtain spherical or spindle-shaped particles, and the particles tend to aggregate, with a specific surface area generally below 50 m² / g, resulting in insufficient catalytic active sites; the static calcination process makes it difficult to accurately control the CuO lattice oxygen vacancy concentration, which restricts the improvement of catalytic activity.

[0022] Traditional complexation precipitation methods are highly dependent on complexing agents (such as PVP and CTAB), and residual organic matter needs to be removed at high temperatures, which increases energy consumption and introduces impurities.

[0023] After extensive research and development, the applicant proposes the following technical solution:

[0024] Step 1: Preparation of Cu(II)-citric acid complex

[0025] The copper sulfate concentration is 0.5 mol / L (copper source purity ≥ 99.9%); the preferred molar ratio of sodium citrate is Cu. 2+ :C6H5O7 3- =1:2.5; Microchannel flow rate: 3 mL / min (Reynolds number Re = 1200, turbulent enhanced mass transfer)

[0026] By adopting the above technical solution, the applicant discovered that citric acid reacts with Cu via carboxylate ions. 2+ A six-coordinate stable complex is formed, with a micelle size distribution D50 of 8 ± 1.2 nm. This technique can replace traditional surfactants, avoid organic residues, and improve micelle size uniformity by 60%.

[0027] Step 2: Gas-liquid two-phase jet sedimentation

[0028] Traditional precipitation methods suffer from low pH control precision (±0.5), leading to uneven precursor nucleus growth. CDJP technology is employed to achieve dynamic mixing of the gas and liquid phases. Specific parameters are as follows: an inner nozzle injects an alkaline solution, which is a mixed solution of sodium hydroxide and sodium carbonate (sodium ion concentration 2 mol / L, flow rate 1.2 L / h; preferably n...). 氢氧化钠 :n 碳酸钠 =3:1); the outer annular nozzle injects CO2 gas (99.99% purity, flow rate 0.8m³). 3 / h); Reaction temperature: 45±0.5℃ (achieved using a PID temperature control system)

[0029] By employing the above technical solution, CO2 bubbles are used as dynamic templates to induce the directional growth of Cu(OH)2 precursors on the surface of micron-sized bubbles through the gas-liquid interface. By adjusting the ratio of CO2 flow rate to alkaline solution injection rate (1:1.5~1:3), two morphologies are obtained: nanospheres (porosity ≥75%) or hollow spheres (wall thickness 15nm).

[0030] Experiments show that when the partial pressure of CO2 is 0.15 MPa, the specific surface area reaches 128 m². 2 / g (BET method), which is more than 150% higher than the traditional precipitation method.

[0031] Step 3: Breakthrough in Supercritical Drying Technology

[0032] This application employs a supercritical CO2 drying system, with the following critical conditions controlled: 31.1℃, 7.38 MPa; CO2 flow rate: 5 L / min (supercritical residence time 30 min); and co-solvent: ethanol (volume ratio 1:10).

[0033] Part Four: Dynamic Calcination and Oxygen Vacancy Regulation

[0034] Traditional static calcination results in uneven distribution of oxygen vacancies, with a CuO lattice defect concentration of only 0.8 × 10⁻⁶. 18 cm -3 This scheme adopts fluidized bed gradient calcination, with the following process parameters: heating program: 300℃ (1 h) → 400℃ (2 h) → 500℃ (1 h), heating rate: 5℃ / min; oxygen flow rate: 0.2 → 1.0 L / min (linearly increasing); fluidizing gas velocity: 1.2 m / s (to maintain particle suspension);

[0035] By adopting the above technical solution, dynamic oxygen flow promotes O2 - Oxygen vacancies are formed by embedding into the crystal lattice, with a concentration reaching 2.3 × 10⁻⁶. 18 cm -3 (187% improvement). XPS analysis shows that the surface Cu... + / Cu 2+The ratio increased from 0.15 to 0.48.

[0036] Correspondingly, the innovation of this application lies in the coordination between steps and the creative optimization of process parameters. There is no improvement to the equipment on which it is implemented. The main equipment required by this scheme is recommended to adopt the following equipment parameters: microchannel reactor: 316L stainless steel, channel diameter 500 μm; CDJP reactor: volume 200 L, pressure resistance 1.5 MPa.

[0037] Example 1: Preparation of CuO with Nanosphere Morphology

[0038] S1. Raw material preparation: Dissolve copper sulfate (CuSO4·5H2O, purity ≥99.9%) in deionized water to prepare a solution with a concentration of 0.5 mol / L; dissolve sodium citrate (C6H5Na3O7·2H2O, analytical grade) in deionized water to prepare a solution with a concentration of 1.25 mol / L.

[0039] A microchannel reactor made of 316L stainless steel (channel diameter 500 μm, length 2 m) was used. Copper sulfate solution and sodium citrate solution were simultaneously pumped into the reactor at a volume ratio of 1:1 at a flow rate of 3 mL / min (Reynolds number Re=1200, turbulent state); the reaction temperature was controlled at 25±1℃.

[0040] Dynamic light scattering (DLS) analysis showed that the particle size distribution of the complex micelles was D50 = 8 ± 1.2 nm (polydispersity index PDI = 0.12).

[0041] Step 2: Gas-liquid two-phase jet sedimentation

[0042] A coaxial dual-nozzle CDJP reactor is used (inner nozzle diameter 0.5 mm, outer annular nozzle gap 0.2 mm). The reactor has a volume of 200 L, is made of Hastelloy C276, withstands pressure of 1.5 MPa, and is equipped with a high-precision PID temperature control system (accuracy ±0.1℃).

[0043] The solution after step S1 is introduced into the reactor and the temperature is maintained at 45±0.5℃.

[0044] Inner nozzle: sprays 2 mol / L alkaline solution (flow rate 1.2 L / h, pressure 0.3 MPa).

[0045] Outer nozzle: Injects CO2 gas (99.99% purity, flow rate 0.8 m³ / s). 3 / h, pressure 0.15 MPa).

[0046] The gas-liquid two-phase contact time is ≤0.5s, and the CO2 bubble diameter is controlled between 50-100 μm.

[0047] CO2 bubbles act as a dynamic template, inducing the Cu(OH)2 precursor to grow directionally at the gas-liquid interface, forming a nanosphere structure (SEM shows a diameter of approximately 7-9 nm).

[0048] Step 3: Supercritical drying

[0049] A supercritical CO2 drying system (critical point parameters: 31.1℃, 7.38 MPa) is equipped with a CO2 circulation module (recovery rate ≥90%). The co-solvent is anhydrous ethanol (volume ratio of 1:10 to CO2).

[0050] The precipitate was placed in a drying vessel, heated to 35°C, and pressurized to 8.0 MPa for 30 min.

[0051] CO2 flow rate 5 L / min, supercritical residence time 30 min.

[0052] BET has a specific surface area of ​​128 m². 2 / g (traditional method is 50 mg) 2 / g), pore volume 0.45 cm³ 3 / g.

[0053] TEM analysis showed that the grain size was smaller than that obtained by traditional methods ( Figure 2 The wavelength of 14nm was reduced to approximately ( Figure 1 7-9nm. And it can be seen that... Figure 2 Medium-sized particles aggregated severely, and Figure 1 It exhibits good particle dispersibility.

[0054] Step 4: Dynamic Calcination and Oxygen Vacancy Regulation

[0055] The fluidized bed roasting furnace (made of Inconel 600, with an effective volume of 50 L) is equipped with an oxygen flow gradient controller. The fluidizing gas is high-purity nitrogen (99.999% purity), and the fluidizing gas velocity is 1.2 m / s.

[0056] Heating program: Increase from room temperature to 300℃ at a rate of 5℃ / min (hold for 1 h) → 400℃ (hold for 2 h) → 500℃ (hold for 1 h).

[0057] Oxygen flow rate: linearly increased from 0.2 L / min to 1.0 L / min (gradient rate 0.13 L / min·h).

[0058] EPR testing (Bruker EMXplus, frequency 9.85 GHz) showed an oxygen vacancy concentration of 2.3 × 10⁻⁶. 18 cm -3 (Traditional static roasting is 0.8×10) 18 cm-3 ).

[0059] XPS analysis (Thermo Scientific K-Alpha) showed that the surface Cu + / Cu 2+ The molar ratio is 0.48 (0.15 in the traditional method).

[0060] Example 2: Preparation of Hollow Spherical CuO

[0061] The difference between this embodiment and Embodiment 1 is that:

[0062] In step 2, the CO2 flow rate is increased to 1.2 m³ / s. 3 / h, the alkaline solution flow rate was reduced to 0.8 L / h (gas-liquid ratio 1.5:1).

[0063] SEM observations revealed that the product transformed into a hollow spherical structure (wall thickness 15 nm, cavity diameter 80-120 nm).

[0064] BET has a specific surface area of ​​105m². 2 / g, oxygen vacancy concentration 1.8×10 18 cm -3 .

[0065] Performance testing and data comparison

[0066] Catalytic performance:

[0067] Test method: 100 mg of nano-CuO was added to 50 mL of 10 wt% H2O2 solution (30℃), and the amount of O2 released was measured using a gas measuring tube. The results are shown in Table 1.

[0068] Table 1

[0069] Example 15 min decomposition efficiency Final decomposition rate (30 min) Example 1 95% 99% Example 2 85% 97% Conventional method 60% 88%

[0070] Anti-aggregation properties:

[0071] Test method: Nano-CuO was dispersed in ethanol, sonicated for 10 min, and then allowed to stand for 24 h. The dispersibility was evaluated by the sedimentation volume ratio. The results are shown in Table 2.

[0072] Table 2

[0073] Example Settling volume ratio (24 h) Example 1 ≤5% Conventional method ≥20%

[0074] Comparative Example

[0075] This comparative example uses a direct precipitation method to prepare nano-copper oxide through reaction precipitation, filtration, washing, drying, and calcination.

[0076] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing nano-copper oxide by precipitation, characterized in that, Includes the following steps: Preparation of S1, Cu(II)-citric acid complex: Coordination was formed using copper sulfate and citrate as raw materials via microchannel method; S2, CDJP gas-liquid bidirectional jet: the inner nozzle sprays alkaline solution and the outer annular nozzle sprays CO2 gas, inducing Cu(OH)2 precursor to grow directionally on the surface of micron-sized bubbles; S3, Supercritical Drying; The product of S2 is dried using a supercritical CO2 drying system; S4, roasting; gradient roasting in a sulfurized bed to maintain particle suspension.

2. The method for preparing nano-copper oxide by precipitation according to claim 1, characterized in that, In S1, the concentration of copper sulfate is 0.5 mol / L, and the ratio of citrate to copper ions satisfies Cu 2+ :C6H5O7 3- =1:2.5, and the flow rate of the microchannel is 3 mL / min.

3. The method for preparing nano-copper oxide by precipitation according to claim 1, characterized in that, The alkaline solution in S2 comprises a mixture of sodium hydroxide and sodium carbonate, wherein the sodium ion concentration of the mixture is 2 mol / L, the flow rate is 1.2 L / h, and the ratio of n sodium hydroxide to n sodium carbonate is 3:

1.

4. The method for preparing nano-copper oxide by precipitation according to claim 1, characterized in that, The critical conditions described in S3 are 31.1℃ and 7.38 MPa; the CO2 flow rate is 5 L / min and the supercritical residence time is 30 min; the co-solvent is ethanol, and its volume is 10 times that of the solute.

5. The method for preparing nano-copper oxide by precipitation according to claim 1, characterized in that, In S4, a gradient calcination process using a fluidized bed is employed, with the following process parameters: 300℃ (1 h) → 400℃ (2 h) → 500℃ (1 h), heating rate of 5℃ / min; oxygen flow rate of 0.2 → 1.0 L / min, increasing linearly; fluidizing gas velocity of 1.2 m / s, maintaining particle suspension.

6. The method for preparing nano-copper oxide by precipitation according to claim 1, characterized in that, The copper oxide nanoparticles prepared by this method have a grain size of 9 nm and a specific surface area of ​​128 m². 2 / g, pore volume 0.45 cm³ 3 / g.

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