Preparation of nanometer cuprous oxide by microwave assisted reduction under atmospheric pressure

Cuprous oxide is higher than the value A copper sulfate-based salts, widely used in the coatings industry, glass industry, agriculture and the like. In recent years, with the ultra-fine and high purity of cuprous oxide, its application value has been greatly improved. The Cu ₂ O particle diameter obtained by the preparation method of several kinds of Cu ₂ O particles in the country is usually in the range of several micrometers to several tens of micrometers, and the dispersibility is poor. In this study, nano-sized cuprous oxide was prepared by microwave-assisted sodium sulfite reduction under normal pressure. Several factors affecting the yield of cuprous oxide were investigated. The surface morphology and particle size distribution of Cu ₂ O were characterized.

First, reagents and instruments

Reagents: self-produced copper sulfate, sodium sulfite, self-dispensing agent.

Instrument: NN-S3440WF household modified microwave oven, electronic constant speed mixer, electric thermostatic water bath, XL30W scanning electron microscope, LS800 laser particle size tester.

Second, the principle of testing

Copper sulfate and sodium sulfite were separately prepared into a solution of a certain concentration, and mechanical impurities in the solution were removed by filtration. The copper sulfate and sodium sulfite solutions to which the dispersing agent was added and adjusted in pH were separately charged into the dosing bottle. After the reaction was started, the two solutions were cocurrently added to the Erlenmeyer flask in the microwave oven through a Y-shaped tube. After the reaction was completed, the conical flask was taken out, clarified, filtered, and repeatedly washed with alcohol until the sulfate was qualified. The product is kept in an anhydrous alcohol medium to prevent oxidation. Its reaction formula is issued:

2CuSO ₄ +3Na ₂ SO ₃ →Cu ₂ O+3Na ₂ SO ₄ +2SO ₂ (g)

Third, the results and discussion

(1) Single factor test

1. Effect of microwave power on the yield of cuprous oxide

Sodium sulfite excess coefficient The system pH was adjusted to 3, microwave heating for 40 min, and the effect of microwave power on the yield of cuprous oxide was shown in Table 1.

Table 1 Effect of microwave power on reduction of cuprous oxide

It can be seen from Table 1 that when the microwave power is 140W, the color of the solution after the reaction is light green, indicating that there is still a part of unreacted copper ions in the solution after the reaction, and the yield of copper is low; when the microwave power is 530 W, the reaction process A large amount of SO ₂ gas is generated, the operating environment is deteriorated, and a large amount of green-white powder is present in the cup wall and U-shaped tube, indicating that high-power microwave radiation causes the solution to reach a boiling state, and the solution is largely volatilized, which not only causes large copper loss, but also produces The equipment is seriously corroded; when the microwave power is 320W, the solution is colorless after the reaction, and the product is mud red. Therefore, the microwave radiation power is preferably 320W.

2. Effect of solution pH on the yield of cuprous oxide

The microwave radiation power was 320 W, the amount of sodium sulfite was 1.3 times of the theoretical amount, and the reduction time was 40 min. The effect of the solution pH on the yield of cuprous oxide is shown in Fig. 1.

It can be seen from Fig. 1 that as the pH of the solution increases, the recovery rate of cuprous oxide increases gradually; when the pH is less than 2.0, the yield of cuprous oxide is lower than that of the water bath in the same period, indicating that the moisture in the system is easily volatilized under microwave irradiation. The acidity of the solution is increased, so that sodium sulfite is easily decomposed to produce sulfur dioxide gas; the pH is between 1 and 2, and the yield of cuprous oxide is very slow; when the pH is between 2 and 3, the recovery rate of cuprous oxide is greatly increased; When the pH is too high, the divalent copper ions will be hydrolyzed, and white copper hydroxide precipitates, which not only affects the yield of cuprous oxide, but also affects the purity of cuprous oxide.

Therefore, when reducing, the pH of the solution should be maintained at 3.0, and the pH of the solution after the reaction is maintained between 3.5 and 5.5.

3. Effect of excess sodium sulfite on the yield of cuprous oxide

Microwave radiation power 320W, solution pH=3, microwave irradiation for 40min, the effect of sodium sulfite excess coefficient on the recovery of cuprous oxide is shown in Fig. 2. It can be seen that as the amount of sodium sulfite increases, the yield of cuprous oxide gradually increases. From the viewpoint of reaction kinetics, the more the reducing agent is used, the better the reduction effect, and the formed cuprous oxide is immersed in the reducing solution to reduce the oxidation of cuprous oxide. However, on the other hand, the amount of reducing agent is too much, and sodium sulfite is easily precipitated in the product, and it is easily oxidized to sodium sulfate, resulting in excessive sodium sulfate in the product. Therefore, the actual amount of sodium sulfite is 1.3 times the theoretical amount.

4. Effect of reduction time on the yield of cuprous oxide

Microwave radiation power 320W, solution pH=3, the amount of sodium sulfite is 1.3 times of the theoretical amount, and the effect of reaction time on the yield of cuprous oxide is shown in Fig. 3.

As can be seen from Fig. 3, as the reduction reaction proceeds, the yield of cuprous oxide gradually increases. Under sufficient reaction time, sodium sulfite and copper sulfate can be fully contacted, and the reduction reaction proceeds relatively completely. After a certain period of reaction, the solution system tends to balance, and prolonging the reaction time does not increase the yield of cuprous oxide. Considering comprehensively, the reaction time is best at 40 min.

(2) Product characterization

The cuprous oxide prepared under the optimum conditions of 1.3 times the theoretical amount of sodium sulfite, microwave irradiation power 320 W, system pH=3, reaction time 40 min, adding a certain amount of dispersant and co-current addition, using scanning electron microscopy and The morphology and particle size were characterized by a laser particle size analyzer. The results are shown in Fig. 4 and Fig. 5. The chemical composition analysis results are shown in Table 2.

Table 2 Chemical composition analysis data of products

It can be seen that the morphology of cuprous oxide prepared by reduction under microwave conditions is relatively regular and uniform, and the particle size is between 0.4 and 0.9 μm, which is relatively small and the distribution is relatively narrow. The product quality basically meets the industrial copper oxide first grade standard.

Fourth, the conclusion

(1) Under normal pressure, the nanometer cuprous oxide was prepared by microwave assisted reduction method. The optimum test conditions were determined by single factor test method: the excess coefficient of sodium sulfite was 1.3, the microwave radiation power was 320 W, the system pH was 3, and the reduction time was 40 min.

(B) Under the optimal conditions, the yield of cuprous oxide is 95.3%, the purity can reach 97.2%, and the product quality meets the industrial product quality standards.

(3) The microwave-specific heating method makes the prepared cuprous oxide particles finer, more uniform, and more dispersible, and the morphology is nearly spherical, and the particle size is between 400 and 900 nm.

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