Preparation method and application of polyphenol modified alginate aerogel

Abstract

The invention relates to a preparation method and application of polyphenol modified alginate aerogel. The method comprises the following steps: adding sodium alginate into pure water, stirring at a low speed, adding polyphenol and a cross-linking agent, stirring and homogenizing for 2 minutes; and adding glucolactone, stirring, homogenizing for 1 minute, standing for 12 hours, and drying with supercritical carbon dioxide to obtain the aerogel.

Description

Technical Field

[0001] The invention relates to a method for preparing a gel, and in particular to a method for preparing a polyphenol-modified alginate aerogel and application thereof. Background Art

[0002] Depleted uranium (DU) is a byproduct produced during the uranium enrichment process of nuclear fuel. It contains a lower concentration of uranium-235 isotopes, but its uranium-238 isotope ratio is higher than that of uranium ore in nature, so it is both chemically toxic and radioactively toxic. There are many sources of uranium in water bodies. The use of depleted uranium weapons, the testing of nuclear weapons, and the discharge of radioactive waste from nuclear power plants may cause uranium pollution in water bodies. When depleted uranium enters the human body through food or water, it can be retained in the kidneys, bones and other tissues for a long time, causing "internal irradiation". Not only will its radioactivity directly damage cells, leading to DNA damage, cell mutations and even cancer, but it may also cause local tissue inflammation, fibrosis and other serious health problems due to the chemical toxicity of depleted uranium. At present, the treatment methods for uranium-containing wastewater are usually: coagulation and precipitation method, adsorption method, evaporation concentration method, extraction method, etc. Adsorption method, extraction method, and evaporation concentration method are effective, with high uranium removal rate, but they are expensive and not conducive to large-scale use. The coagulation and precipitation method is simple and low-cost, but the uranium removal rate is not up to standard and needs further treatment, and the precipitation product also needs secondary treatment. Therefore, it is an urgent problem to seek a method with simple preparation process, low price and high removal efficiency to treat depleted uranium in radioactive decontamination wastewater.

[0003] Sodium alginate is a long-chain polysaccharide compound derived from nature. Its unique molecular structure is mainly composed of alternating or random arrangements of guluronic acid and mannuronic acid. Under suitable and stable conditions, when divalent cations (such as calcium ions, copper ions, etc.) are added to the sodium alginate solution, these ions can cross-link with the carboxyl groups in the sodium alginate molecules to quickly form a stable hydrogel. Sodium alginate hydrogel is widely used in many fields such as biomedicine, food industry, environmental protection and agriculture due to its many unique physical and chemical properties. These properties include biocompatibility, low toxicity, low price, high adsorption capacity and mild gelation conditions. Sodium alginate shows broad application prospects in many fields.

[0004] Tannic acid is a polyphenol compound derived from plants. Its molecular structure is rich in polyphenolic hydroxyl groups, which can electrostatically attract and complex with a variety of metal ions. Heavy metal pollution is a major challenge facing the current environmental field, and the strong complexing ability of tannic acid with metal ions provides the possibility for the development of efficient heavy metal adsorption materials. The experimental results show that the gelatin composite material containing tannic acid exhibits excellent adsorption performance for a variety of heavy metal ions (such as lead, cadmium, copper, etc.), which is mainly due to the strong interaction between polyphenolic hydroxyl groups in tannic acid molecules and heavy metal ions. The composite of tannic acid and gelatin not only improves the physical properties of gelatin materials, but also gives it new environmental application functions, especially in the treatment of heavy metal pollution, showing good prospects. This research result provides new ideas and methods for developing new environmentally friendly materials and addressing environmental pollution problems. Summary of the invention

[0005] The invention provides a preparation method and application of a polyphenol-modified alginate aerogel, and provides a new method for adsorbing depleted uranium in radioactive decontamination waste liquid.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is as follows: The preparation method of polyphenol-modified alginate aerogel comprises the following steps: adding sodium alginate into pure water, stirring at a low speed, adding polyphenol and a cross-linking agent, stirring, and homogenizing for 2 minutes; adding gluconolactone, stirring, and homogenizing for 1 minute, letting stand for 12 hours, and drying with supercritical carbon dioxide to obtain the aerogel.

[0007] The mass ratio of the sodium alginate to pure water is 1:50.

[0008] The mass ratio of the polyphenol to sodium alginate is 2:1.

[0009] The mass ratio of gluconolactone to sodium alginate is 1:2.

[0010] The mass percentage concentration of the cross-linking agent is 0.5%.

[0011] The polyphenols are one or more of tannic acid and gallic acid.

[0012] The cross-linking agent is selected from any one of calcium carbonate and calcium chloride.

[0013] The stirring was performed mechanically at a rate of 500 rpm for 2 hours.

[0014] The homogenization adopts a high-speed homogenizing emulsifier, and the rotation speed is 10000 rpm.

[0015] The polyphenol-modified alginate aerogel prepared by the above method is used for adsorbing depleted uranium in radioactive decontaminated waste liquid.

[0016] Beneficial effects of the present invention: The polyphenol-modified alginate aerogel prepared by the method of the present invention forms a stable gel through the cross-linking of sodium alginate with calcium ions and tannic acid. The cross-linking between tannic acid and sodium alginate can improve the thermal stability of the aerogel and increase the swelling rate of the aerogel. Gluconolactone plays a positive role in the stability of the aerogel as a stabilizer and coagulant. The swelling characteristics of the polyphenol-modified alginate aerogel and the strong complexing ability of tannic acid with metal ions make it have a significant effect in adsorbing depleted uranium in radioactive decontamination waste liquid. The good adsorption performance of the material provides a new way to solve the problem of purifying radioactive decontamination waste liquid, and has certain practical application value in treating radionuclides in radioactive decontamination waste liquid. The method of the present invention is prepared at normal temperature and pressure, the raw materials are economical and easy to obtain, the finished product is non-toxic and harmless and environmentally friendly, and is convenient for large-scale application.

[0017] The applicant has experimentally verified that tannic acid, sodium alginate and gluconolactone can be 2+ A cross-linking reaction occurred, and the removal rate of DU(VI) in radioactive decontamination waste liquid by polyphenol-modified alginate aerogel was 82.63%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is the scanning electron microscope image of aerogel; Figure 2 This is the Fourier infrared spectrum of aerogel; Figure 3 Thermogravimetric diagram of aerogel; Figure 4 Figure 2 shows the efficiency of aerogel in adsorbing depleted uranium from radioactive decontamination wastewater. DETAILED DESCRIPTION

[0019] The reagents used in this implementation were all commercially available analytically pure products.

[0020] Example 1 Preparation of polyphenol-modified alginate aerogel Sodium alginate was added to pure water and stirred to completely dissolve, followed by the addition of tannic acid and calcium carbonate, and homogenization was performed for 2 minutes at 10,000 rpm using an IKA T25 high-speed homogenizer under mechanical stirring at 500 rpm to fully mix; gluconolactone was added, and homogenization was performed for 1 minute at 10,000 rpm under mechanical stirring at 500 rpm to fully mix, and the mixture was allowed to stand for 12 hours and dried with supercritical carbon dioxide to obtain polyphenol-modified alginate aerogel. Aerogel scanning electron microscopy see Figure 1 .

[0021] Example 2 Preparation of radioactive decontaminated waste liquid Prepare 210 mg / L Na with ultrapure water +, 145 mg / LK + , 90 mg / L Ca 2+ 、87 mg / L Mg 2+ , 20 mg / LUO2 2+ and a mixed solution of 40 mg / L DTPA to simulate radioactive decontamination waste liquid.

[0022] Example 3 FTIR spectroscopy detection of polyphenol-modified alginate aerogel CaCO3 at 1428 cm -1 The CO asymmetric stretching vibration appears; tannic acid at 1620 cm -1 The characteristic peak of ester bond appears at 1450 cm -1 It is the C=C stretching vibration of the benzene ring. Sodium alginate has a wavelength of 1610 cm -1 and 1420 cm -1 They are the asymmetric vibration and symmetric stretching vibration of the carboxylic acid group (-COOH) at 1029 cm -1 The stretching vibration of C-OH appears. Gluconolactone at 1727 cm -1 The stretching vibration absorption peak of the ester carbonyl (-C=O) appears. The infrared spectrum of polyphenol-modified alginate aerogel shows that the absorption characteristic peaks of tannic acid and sodium alginate are retained, but the position is shifted to a certain extent, which indicates that tannic acid, sodium alginate and gluconolactone are absorbed by Ca 2+ A cross-linking reaction occurs.

[0023] Example 4 Thermogravimetric analysis curve of polyphenol modified alginate aerogel The weight change of polyphenol-modified alginate aerogel was tested under the condition of temperature change. Figure 3 At about 145.89℃, the mass fraction decreased by 11.37%; at about 180.09℃, the polyphenol-modified alginate aerogel began to decompose; the most significant mass loss occurred at 240.99℃, where the thermal degradation rate reached the maximum. Therefore, the polyphenol-modified alginate aerogel is in a stable state at room temperature.

[0024] Example 5 Evaluation of adsorption performance of polyphenol-modified alginate aerogel Take 1 g of the polyphenol-modified alginate aerogel obtained in Example 1, add it to 200 mL of the radioactive decontamination waste liquid obtained in Example 2 (the pH value was adjusted to 6 in advance with 0.1 M NaOH or 0.1 M HCl), place it in a constant temperature oscillating box, oscillate for 24 hours (100 rpm, 25 degrees), centrifuge it at 3000 rpm for 10 minutes, take the supernatant and use an inductively coupled plasma mass spectrometer (ICP-MS) to measure the residual radioactive nuclide concentration in the radioactive decontamination waste liquid after adsorption, and calculate the removal rate of DU (VI) in the radioactive decontamination waste liquid by the aerogel material. The removal rate (%) of DU (VI) by aerogel is calculated as follows: R=1-(Ct × V / m)× 100% In the formula, Ct is the uranium concentration in the solution after adsorption for t time (mg / L), V is the volume of the radioactive decontamination waste liquid after adsorption (L), and m is the total amount of DU in the radioactive decontamination waste liquid (g) The removal efficiency of DU(VI) in radioactive decontamination waste liquid by polyphenol-modified alginate aerogel was 82.63%.

Claims

1. A method for preparing polyphenol-modified alginate aerogel, characterized in that: Sodium alginate was added into pure water, stirred at a low speed, polyphenol and cross-linking agent were added, stirred, and homogenized for 2 minutes; gluconolactone was added, stirred, and homogenized for 1 minute, allowed to stand for 12 hours, and dried with supercritical carbon dioxide to obtain aerogel.

2. The method according to claim 1, characterized in that: The mass ratio of the sodium alginate to pure water is 1:

50.

3. The method according to claim 1, characterized in that: The mass ratio of polyphenols to sodium alginate is 2:

1.

4. The method according to claim 1, characterized in that: The mass ratio of gluconolactone to sodium alginate is 1:

2.

5. The method according to claim 1, characterized in that: The mass percentage concentration of the cross-linking agent is 0.5%.

6. The method according to claim 1, characterized in that: The polyphenols are one or more of tannic acid and gallic acid.

7. The method according to claim 1, characterized in that: The cross-linking agent is selected from calcium carbonate and calcium chloride.

8. The method according to claim 1, characterized in that: The stirring was performed mechanically at a rate of 500 rpm for 2 hours.

9. The method according to claim 1, characterized in that: The homogenization adopts a high-speed homogenizing emulsifier, and the rotation speed is 10000 rpm.

10. Use of polyphenol-modified alginate aerogel prepared according to any one of claims 1 to 9 in preparing an adsorbent for adsorbing depleted uranium in radioactive decontaminated waste liquid.

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