Preparation method of Schiff base covalent organic polymer and application of Schiff base covalent organic polymer in gallium adsorption

Abstract

The invention belongs to the technical field of preparation of effective recycling materials of gallium ions, and particularly relates to a preparation method of a Schiff base covalent organic polymer and application of the Schiff base covalent organic polymer to gallium adsorption. According to the technical scheme, the Schiff base covalent organic polymer takes tris (2-aminoethyl) amine and terephthalaldehyde as reactants, water is taken as a solvent, a solvent evaporation induced self-assembly (EISA) method is adopted for reaction, and an adsorption material capable of efficiently adsorbing gallium ions in a solution is obtained. The method has the biggest advantages that the traditional covalent organic polymer which takes an organic solvent as a reaction medium is broken through, a green and environment-friendly aqueous solution system is adopted for reaction, and the preparation method is mild in reaction condition, rapid, simple, convenient and short in consumed time. The Schiff base has dynamic chemical reversibility, so that a space structure with strong affinity to gallium ions is easy to construct, and the Schiff base has high-recognition adsorption performance and certain practical application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing effective recovery materials for gallium ions, and particularly relates to a preparation method of a Schiff base covalent organic polymer and its application in adsorbing gallium. Background Art

[0002] Gallium (Ga) is a rare element located in the third main group of the fourth period. Its concentration in the earth's crust is low, and most of it exists in the form of associated minerals, making it very difficult to obtain gallium. With the rapid development of technology, gallium has become an indispensable element in the fields of medicine, catalysis, semiconductors, batteries, etc. due to its unique physical and chemical properties. It is a non-renewable resource. Continuous intensive mining and the lack of effective resource recovery strategies will lead to a sharp reduction in resources and also cause a large amount of gallium to be lost with sewage. Therefore, it is crucial to develop a green process for recovering the rare element gallium from mining wastewater.

[0003] Currently, the methods for separating and pre-concentrating gallium mainly include extraction, adsorption, precipitation, bioleaching, neutralization, complexation, ion exchange, etc. Adsorption technology is widely regarded as the most suitable method for recovering metal ions, and it has relatively low large-scale costs. However, the results of literature research show that the adsorption method has disadvantages such as small adsorption capacity, poor selectivity, and low adsorption rate. Therefore, there is still a large research space in the preparation of adsorption materials for efficient recovery of gallium.

[0004] Schiff base covalent organic polymers have high recognition adsorption properties because the Schiff base bond has the reversibility of dynamic chemistry and is easy to construct a spatial structure with strong affinity for gallium ions. While using the solvent evaporation-induced self-assembly method (EISA) to overcome the disadvantage of the long preparation time of adsorption materials, the preparation method of the present invention uses water as the reaction solvent instead of organic solvents such as DMF, greatly reducing toxicity, making the preparation more environmentally friendly and reducing environmental pollution. Summary of the Invention

[0005] To solve the above problems, the present invention provides a preparation method of a Schiff base covalent organic polymer and its application in adsorbing gallium.

[0006] The present invention is achieved by the following technical solutions:

[0007] A Schiff base covalent organic polymer uses tris(2-aminoethyl)amine (TREN) and terephthalaldehyde (TPAL) as reactants, selects water as the solvent, and uses the solvent evaporation-induced self-assembly method (EISA) for reaction to obtain an adsorption material (TREN-TPAL) that can efficiently adsorb gallium ions in aqueous solution.

[0008] The above preparation method of a Schiff base covalent organic polymer includes the following steps:

[0009] 1) Add an aqueous solution and terephthalaldehyde to a beaker, sonicate until terephthalaldehyde is uniformly dispersed to form a stable suspension, drop in tris(2-aminoethyl)amine, and after heating, obtain a yellow solid product;

[0010] 2) Take the solid product obtained in step 1), add anhydrous methanol for washing, centrifuge until the solution is no longer yellow, and place it in an oven for drying to obtain a Schiff base covalent organic polymer.

[0011] Further, in the above preparation method, in step 1), the acidity of the aqueous solution is pH = 4.

[0012] Further, in the above preparation method, in step 1), by molar ratio, tris(2-aminoethyl)amine: terephthalaldehyde = 1:0.5 - 2.

[0013] Further, in the above preparation method, in step 1), the heating time is 2 - 48 h.

[0014] Further, in the above preparation method, in step 1), the heating temperature is 100 °C.

[0015] The application of the above Schiff base covalent organic polymer in adsorbing gallium ions.

[0016] Further, in the above application, the method is as follows: Take a solution containing gallium ions, add the Schiff base covalent organic polymer, shake and adsorb at 30 °C and 180 r / min for 8 h, filter, and use an atomic absorption spectrophotometer to detect the concentration of gallium ions in the filtrate.

[0017] Even further, in the above application, the solution containing gallium ions is a solution with pH = 3 and a concentration of 20 - 200 ppm.

[0018] Even further, in the above application, the solid-liquid ratio of the Schiff base covalent organic polymer to the solution containing gallium ions is 1 mg:(1 - 5) mL.

[0019] The beneficial effects of the present invention are:

[0020] 1. The Schiff base covalent organic polymer prepared by the present invention, due to the reversibility of dynamic chemistry of Schiff base bonds, is easy to construct a spatial structure with strong affinity for gallium ions, making it have high recognition adsorption performance for gallium ions, with relatively fast adsorption kinetics, and can be applied to the adsorption and recovery of rare metal gallium in aqueous solutions.

[0021] 2. The present invention uses the solvent evaporation-induced self-assembly method for preparation, with mild reaction conditions, fast and efficient, and can omit the precipitation separation of precursors and structure guiding agents in the solvent, overcoming the disadvantages of complex operation and long reaction time in the preparation of adsorption materials.

[0022] 3. The present invention uses water as a solvent for the reaction without using organic solvents such as DMF, etc., that is, the synthesis is carried out in the aqueous phase rather than the organic phase, and the preparation conditions are green, environmentally friendly, and have little pollution.

[0023] 4. For the Schiff base covalent organic polymer prepared by the present invention, the adsorption of Ga(III) can reach equilibrium at 8 h, and the adsorption kinetics is relatively fast.

[0024] 5. For the Schiff base covalent organic polymer prepared by the present invention, when pH = 3 and the adsorption time is 24 h, the adsorption rate of the Schiff base covalent organic polymer for Ga(III) with a concentration of 20 ppm can reach 100%, and the maximum saturated adsorption capacity is 105.78 mg·g -1 .

[0027] In summary, the Schiff base covalent organic polymer prepared by the present invention can effectively adsorb gallium ions, and the preparation reaction conditions are mild, fast, efficient, green and environmentally friendly. The adsorbent has a high adsorption rate and has practical applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic diagram of the synthesis of Schiff base covalent organic polymer (1TREN-1.5TPAL-2).

[0029] Figure 2 is a scanning electron micrograph of Schiff base covalent organic polymer (1TREN-1.5TPAL-2).

[0030] Figure 3 is an infrared spectrum of Schiff base covalent organic polymer (1TREN-1.5TPAL-2).

[0031] Figure 4 is a comparison chart of the gallium adsorption performance of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) at different acidities.

[0032] Figure 5 is a comparison chart of the gallium adsorption performance of Schiff base covalent organic polymers prepared at different heating times.

[0033] Figure 6 is an adsorption isotherm fitting chart of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) for gallium at pH = 3.

[0034] Figure 7 is an adsorption kinetics fitting chart of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) for gallium at pH = 3. DETAILED DESCRIPTION OF THE INVENTION

[0035] To enable those of ordinary skill in the art to more comprehensively understand the present invention, the present invention will be further elaborated through the following specific embodiments, but the embodiments do not limit the present invention in any way.

[0036] Example 1 Schiff base covalent organic polymers prepared from reactants with different molar ratios (I) Schiff base covalent organic polymer (1TREN - 0.5TPAL - 2)

[0037] Add 12 mL of an aqueous solution with pH = 4 and 0.134 g (1 mmol) of terephthalaldehyde to a beaker, and ultrasonically treat until the terephthalaldehyde is uniformly dispersed to form a stable suspension. Then, drop in 0.292 g (2 mmol) of tris(2 - aminoethyl)amine, and heat at 100 °C for 2 h to completely evaporate the water in the beaker to obtain a solid product; then add anhydrous methanol for washing, and centrifuge until the solution is no longer yellow, and place it in an oven for drying to obtain the Schiff base covalent organic polymer, named 1TREN - 0.5TPAL - 2.

[0038] (II) Schiff base covalent organic polymer (1TREN - 1TPAL - 2)

[0039] Prepared according to the method described in (I), the only difference is that the amount of terephthalaldehyde added is 0.268 g (2 mmol). In the same way, 1TREN - 1TPAL - 2 was synthesized.

[0040] (III) Schiff base covalent organic polymer (1TREN - 1.5TPAL - 2)

[0041] Prepared according to the method described in (I), the only difference is that the amount of terephthalaldehyde added is 0.402 g (3 mmol). In the same way, 1TREN - 1.5TPAL - 2 was synthesized.

[0042] (IV) Schiff base covalent organic polymer (1TREN - 2TPAL - 2)

[0043] Prepared according to the method described in (I), the only difference is that the amount of terephthalaldehyde added is 0.526 g (4 mmol). In the same way, 1TREN - 2TPAL - 2 was synthesized.

[0044] (V) Characterization

[0045] 1. Figure 2 is the scanning electron micrograph of the Schiff base covalent organic polymer (1TREN - 1.5TPAL - 2). From Figure 2It can be seen that 1TREN-1.5TPAL-2 has a centrally closely stacked lamellar structure, demonstrating that tris(2-aminoethyl)amine and terephthalaldehyde can also yield a two-dimensional lamellar structure in aqueous solution. Moreover, from the local enlarged view, thin and upturned edges can be observed, which can provide more adsorption sites for gallium. At the same time, it also indicates that the Schiff base covalent organic polymer has been successfully prepared.

[0046] 2. Figure 3 This is the infrared spectrum of the Schiff base covalent organic polymer (1TREN-1.5TPAL-2). As can be seen from Figure 3 it, the characteristic absorption peak of the amino group still exists at 3424 cm -1 for the Schiff base covalent organic polymer, and the characteristic absorption peak of -C=N- exists at 1638 cm -1 . This indicates that 1TREN-1.5TPAL-2 is formed by Schiff base bonds through the aminolysis reaction of the amino group and the aldehyde group, and some amino groups have not reacted. However, compared with the raw material tris(2-aminoethyl)amine, the intensity of the characteristic absorption peak of the amino group in 1TREN-1.5TPAL-2 becomes lower and shifts towards a higher wavenumber direction, proving that the amino group has reacted and the lone pair electrons on N may form a p-π conjugation effect with the generated imine bond. The change in the displacement of the amino characteristic peak also confirms that terephthalaldehyde and tris(2-aminoethyl)amine have reacted to form the framework structure of the Schiff base covalent organic polymer.

[0047] Example 2 Schiff base covalent organic polymers prepared with different heating times (I) Schiff base covalent organic polymer (1TREN-1.5TPAL-12)

[0048] Prepared according to the method described in Example 1 (III), with the only difference being that the heating time is 12 h. Using the same method, 1TREN-1.5TPAL-12 was synthesized.

[0049] (II) Schiff base covalent organic polymer (1TREN-1.5TPAL-24)

[0050] Prepared according to the method described in Example 1 (III), with the only difference being that the heating time is 24 h. Using the same method, 1TREN-1.5TPAL-24 was synthesized.

[0051] (III) Schiff base covalent organic polymer (1TREN-1.5TPAL-48)

[0052] Prepared according to the method described in Example 1 (III), with the only difference being that the heating time is 48 h. Using the same method, 1TREN-1.5TPAL-48 was synthesized.

[0053] Application of Schiff base covalent organic polymer in highly efficient adsorption of gallium ions (I) Adsorption performance of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) for gallium at different acidities

[0054] Method: Weigh 10 mg of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) and add it to 10 mL of Ga(III) solution with a concentration of 20 ppm. Adjust the pH of the solution to 1, 2, 3, and 10 respectively, and shake and adsorb at 30 °C and 180 r / min for 24 h. Then filter the mixture and use an atomic absorption spectrophotometer to detect the concentration of Ga(III) in the filtrate.

[0055] It can be seen that Figure 4 when the pH of the solution is 1, 2, 3, and 10 respectively, the adsorption performance of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) for Ga(III) shows a trend of first increasing and then decreasing. The adsorption rate of Ga(III) can reach 100% at pH = 3. The experimental results show that 1TREN-1.5TPAL-2 has a good adsorption effect on low-concentration gallium and can be further applied to the recovery of gallium in actual mining wastewater.

[0056] (II) Adsorption performance of Schiff base covalent organic polymers prepared with different heating times for gallium

[0057] Method: Weigh 10 mg of 1TREN-1.5TPAL-2, 1TREN-1.5TPAL-12, 1TREN-1.5TPAL-24, and 1TREN-1.5TPAL-48 respectively, and add them to 10 mL of Ga(III) solution with a concentration of 50 ppm and pH = 3. Shake and adsorb at 30 °C and 180 r / min for 24 h. Then filter the mixture and use an atomic absorption spectrophotometer to detect the concentration of Ga(III) in the filtrate.

[0058] It can be seen that Figure 5 as the reaction time increases, the adsorption rate of Schiff base covalent organic polymer for Ga(III) shows a downward trend, which may be related to the reduction of gallium adsorption sites due to the change of the framework structure caused by long heating time. This proves that Schiff base covalent organic polymer with good adsorption effect for gallium can be prepared in a short time by the solvent-induced evaporation self-assembly method (EISA).

[0059] (III) Adsorption isotherm of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) for Ga(III)

[0060] Method: Weigh 10 ± 0.5 mg of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) separately and place it in Ga(III) solutions with different volumes of 50, 100, and 200 ppm and a pH of 3. Then, shake and adsorb at 30 °C and 180 r / min for 8 h. After completion, filter the mixture and use an atomic absorption spectrophotometer to detect the concentration of Ga(III) in the filtrate.

[0061] According to the acidity experiment results, 1TREN-1.5TPAL-2 has a better adsorption effect at a pH value of 3. Therefore, under the condition of pH = 3, we tested the saturated adsorption capacity of this adsorbent and fitted the experimental data with four adsorption isotherm models. The fitting results are as Figure 6 shown. The correlation coefficients R 2 of Langmuir, Freundlich, and Temkin are 0.988, 0.949, and 0.985 respectively. The fitting results show that the Langmuir model has a higher fitting degree for the adsorption isotherm of 1TREN-1.5TPAL-2 adsorbing Ga(III), indicating that 1TREN-1.5TPAL-2 adopts a monolayer adsorption method for Ga(III) and the adsorption sites are evenly distributed. At this time, the maximum adsorption capacity can reach 105.78 mg·g -1 .

[0062] (IV) Adsorption Kinetics of Schiff Base Covalent Organic Polymer (1TREN-1.5TPAL-2) Adsorbing Ga(III)

[0063] Method: Weigh 10 mg of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) and add it to 10 mL of Ga(III) solution with a concentration of 50 ppm. Shake and adsorb at 30 °C and 180 r / min for 5, 10, 30 min and 1, 2, 4, 6, 8, 12, 24 h respectively. Then filter the mixture and use an atomic absorption spectrophotometer to detect the concentration of Ga(III) in the filtrate. The results are as Figure 7 .

[0064] It can be seen from Figure 7 that the adsorbent can reach adsorption equilibrium completely at 8 h and the adsorption rate is relatively fast. When fitting the kinetic experimental data of Schiff base covalent organic polymer (1TREN-1.5TPAL-2) adsorbing Ga(III) with the pseudo-first-order and pseudo-second-order kinetic models, the values of the correlation coefficient R 2 are 0.662 and 0.955 respectively, indicating that the adsorption kinetic data is more in line with the pseudo-second-order kinetic model, that is, chemical adsorption is the main rate-controlling step.

Claims

1. A Schiff base covalent organic polymer, characterized in that, The Schiff base covalent organic polymer is an adsorption material TREN-TPAL prepared by reacting tris(2-aminoethyl)amine and terephthalaldehyde as reactants in water as a solvent using a solvent evaporation-induced self-assembly method.

2. The preparation method of a Schiff base covalent organic polymer according to claim 1, characterized in that, It includes the following steps: 1) Add an aqueous solution and terephthalaldehyde to a beaker, ultrasonically disperse until terephthalaldehyde is uniformly dispersed to form a stable suspension, and drop in tris(2-aminoethyl)amine. After heating, a yellow solid product is obtained; 2) Take the solid product obtained in step 1), wash it with anhydrous methanol, centrifuge until the solution is no longer yellow, and dry it in an oven to obtain the Schiff base covalent organic polymer.

3. The preparation method according to claim 2, characterized in that, In step 1), the acidity of the aqueous solution is pH = 4.

4. The preparation method according to claim 2, characterized in that, In step 1), by molar ratio, tris(2-aminoethyl)amine:terephthalaldehyde = 1:0.5 - 2.

5. The preparation method according to claim 2, wherein In step 1), the heating time is 2 - 48 h.

6. The preparation method according to claim 2, characterized in that, In step 1), the heating temperature is 100 °C.

7. Application of the Schiff base covalent organic polymer according to claim 1 in adsorbing gallium ions.

8. The application according to claim 7, characterized in that, The method is as follows: Take a solution containing gallium ions, add the Schiff base covalent organic polymer, shake and adsorb at 30 °C and 180 r / min for 8 h, filter, and use an atomic absorption spectrophotometer to detect the concentration of gallium ions in the filtrate.

9. The application according to claim 8, wherein The solution containing gallium ions is a solution with pH = 3 and a concentration of 20 - 200 ppm.

10. The application according to claim 8, characterized in that, The solid-liquid ratio of the Schiff base covalent organic polymer to the solution containing gallium ions is 1 mg:(1 - 5) mL.

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