Preparation method and application of a hollow nano-adsorbent with both uranium extraction and heat storage functions

Abstract

The present invention belongs to the technical field of adsorption and separation functional materials, and discloses a preparation method and application of a hollow nano-adsorbent with both uranium extraction and heat storage functions. Ethylene phosphoric acid is added to an aqueous dispersion of carbon nitride as the aqueous phase, and a trace amount of sodium dodecyl sulfate is added; paraffin is dissolved in styrene as the oil phase, and an emulsion is formed using a high-speed stirrer. Interfacial polymerization is carried out under light conditions, and three polymers with hollow structures of different morphologies are constructed by soap-free emulsion polymerization according to the ratio of ethylene phosphoric acid and styrene, as well as the content of sodium dodecyl sulfate. These three polymers with different morphologies can meet different requirements for heat storage and uranium extraction performance. At the same time, the use of light-initiated emulsion photopolymerization has the advantages of being environmentally friendly, low cost, and high production efficiency. The internally encapsulated phase change material also provides a new idea for extracting uranium from nuclear wastewater while storing nuclear waste heat.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of functional materials for adsorption and separation, and relates to a method for preparing a hollow nano-adsorbent suitable for enriching uranyl ions in nuclear wastewater and storing nuclear waste heat at the same time, and in particular to a method for preparing and applying a hollow nano-adsorbent having both uranium extraction and heat storage functions. Background Art

[0002] The development of nuclear energy produces a large amount of wastewater and waste heat. The direct discharge of wastewater and waste heat not only brings environmental pollution, but also causes waste of resources. The efficient recovery of uranium and heat in wastewater is in line with the concept of green and sustainable development. Therefore, recovering waste heat while extracting uranium has important environmental, economic and social significance.

[0003] However, extracting uranium from nuclear wastewater faces challenges such as numerous interfering ions and high industrial costs. Adsorption separation, however, has become one of the most effective methods for extracting uranium from nuclear wastewater due to its advantages, including high separation efficiency, ease of continuous operation, excellent stability, and low cost. Commonly used adsorbents for uranium extraction include carbon materials, silicon materials, and polymer resins, which exhibit excellent adsorption properties for uranium ions. However, current adsorbents for uranium extraction still face two major challenges: complex preparation processes and poor adsorption selectivity. Furthermore, the associated large amounts of nuclear waste heat can easily cause thermal pollution, and traditional phase change materials face the difficulty of being easily utilized and recycled. Therefore, there is an urgent need to develop a high-performance adsorbent with a simple preparation process that can achieve the selective enrichment of uranyl ions from nuclear wastewater while simultaneously storing the waste heat.

[0004] Traditional phase change materials have shortcomings such as phase leakage, supercooling and phase separation, which are the key reasons why they are difficult to use and recycle. The use of polymer materials to encapsulate solid or liquid core phase change materials in microparticles with hollow structures can effectively overcome this shortcoming and broaden the application areas of phase change energy storage materials. It is well known that the traditional emulsion template method can construct hollow structures, but there are problems such as easy emulsifier residue and complex preparation process. The soap-free emulsion polymerization method has the advantages of simplified process, green environmental protection and mild polymerization process. It is the preferred option for preparing high-performance adsorbents with hollow structures. Therefore, this work intends to prepare a hollow nano-adsorbent with both uranium extraction and heat storage functions based on the soap-free emulsion polymerization method. By encapsulating the phase change material inside, it can achieve the extraction of uranyl ions from nuclear wastewater while storing nuclear waste heat. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to achieve the selective extraction of uranyl ions from nuclear wastewater while simultaneously recovering and storing the accompanying nuclear waste heat. This method provides a method for preparing a hollow nano-adsorbent that combines uranium extraction and heat storage capabilities. Using ethylene phosphonic acid and styrene as comonomers and paraffin as a phase change material, a hollow nano-adsorbent with both uranium extraction and heat storage capabilities was prepared.

[0006] In order to achieve the above technical purpose, the technical solution adopted by the present invention is as follows:

[0007] (1) uniformly dispersing a certain amount of carbon nitride in a certain amount of deionized water by ultrasonication, adding a certain amount of ethylene phosphate monomer, ultrasonicating the mixture again to uniformly disperse the mixture, and adding a certain amount of sodium lauryl sulfate to obtain an aqueous phase;

[0008] (2) dissolving a certain amount of styrene monomer in paraffin to obtain an oil phase;

[0009] (3) The aqueous phase and the oil phase are mixed and stirred at a high speed at a certain speed. After the solution changes from clear color to milky white, it is immediately placed in a constant temperature and humidity chamber and illuminated with LED light for a period of time. When white polymer appears on the upper layer, the illumination is stopped and the product is collected by centrifugation, washed with ethanol, and vacuum dried to obtain the hollow nano-adsorbent P(St-VA).

[0010] Furthermore, in step (1) and step (2), the ratio of carbon nitride, deionized water, sodium lauryl sulfate, ethylene phosphate monomer, styrene monomer and paraffin is 0.75-1.25 mg:1.0 mL:0.25-0.75 mg:1.0 mL:0.11-9.0 mL:0.0625-0.1875 mL.

[0011] Furthermore, in step (3), the speed of the high-speed stirring is 20,000 to 25,000 rpm.

[0012] Furthermore, in step (3), the temperature in the constant temperature and humidity chamber is 25° C. and the humidity is 60%.

[0013] Furthermore, in step (3), the power of the LED is 50W, and the irradiation time is 2.0 to 12 hours.

[0014] Furthermore, in step (3), the temperature in the vacuum drying oven is 45° C. and the time is 24 h.

[0015] The hollow nano-adsorbent prepared in the present invention, which has both uranium extraction and heat storage functions, is used for enriching uranyl ions in nuclear wastewater and storing nuclear waste heat.

[0016] Compared with the prior art, the beneficial effects of the present invention are embodied in the following aspects:

[0017] This invention uses a photoinitiated soap-free emulsion polymerization method, using styrene and vinyl phosphate as comonomers, utilizing phosphate groups as functional groups for uranium extraction, and paraffin as a phase change material for waste heat storage. Through interfacial polymerization, a novel hollow nanoadsorbent (P(St-VA)) with both heat storage and uranium extraction functions is prepared. This adsorbent is then used for the selective extraction of uranyl ions from nuclear wastewater. When the P(St-VA) material is used to adsorb uranyl ions in 10 mL of a 10 ppm solution, it reaches adsorption equilibrium within 4 hours. Calculations using a pseudo-second-order model show that the adsorption equilibrium capacity of P(St-VA)-1 is 35.84 mg / g, that of P(St-VA)-2 is 35.76 mg / g, and that of P(St-VA)-3 is 51.96 mg / g. The material undergoes a phase transition process that repeatedly absorbs and releases heat between 25°C and 70°C. Thermogravimetric data show that paraffin wax degrades between 170°C and 350°C, indicating that the paraffin wax is successfully encapsulated and has a good heat storage effect. Furthermore, the nano-adsorbent prepared by the present invention has the following advantages:

[0018] (1) The present invention adopts soap-free emulsion to prepare hollow nano-adsorbents, which provides a new method for the preparation of hollow nano-adsorbents and solves the problems of easy residue of surfactants, difficulty in cleaning, easy to cause serious environmental pollution, cumbersome operation process and easy to affect the adsorption effect in traditional water-in-oil and oil-in-water systems.

[0019] (2) The present invention adopts photoinitiator to induce emulsion polymerization, and uses carbon nitride, which is non-toxic, abundant, easy to synthesize, and has good chemical and thermal stability, as a photoinitiator, providing a mild and simple method for emulsion polymerization.

[0020] (3) Phosphate-functionalized adsorbents achieve adsorption of uranyl ions through the coordination of phosphoric acid and uranyl ions. They have strong affinity for uranyl ions, a wide range of applications, and better adsorption selectivity, and have practical application potential.

[0021] (4) Paraffin wax, as a latent heat storage material, has the advantages of large latent heat of phase change, small volume change during solid / liquid phase change, good thermal stability, no supercooling phenomenon, and low price. By encapsulating paraffin wax in an adsorbent, a new approach is provided for storing waste heat during uranium extraction.

[0022] (5) Based on the abundant grafting sites provided by the hollow structure, ethylene phosphate and styrene were selected as comonomers to encapsulate the phase change material in the adsorbent, thereby achieving fast mass transfer rate, high adsorption capacity, and good adsorption selectivity of the adsorbent while realizing the recovery and release of thermal energy.

[0023] In summary, the use of photoinitiated soap-free emulsion polymerization to construct hollow nano-adsorbents with both uranium extraction and heat storage functions is not only green and environmentally friendly, with a simple preparation process, but also improves the selectivity of the adsorbent; the use of hollow structures to encapsulate phase change materials enables the adsorbent to have the dual functions of efficiently extracting uranium while recovering waste heat, providing a new method for the preparation of multifunctional adsorbents. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 These are SEM images of P(St-VA) prepared at different ratios of ethylene phosphonic acid and styrene in Example 1.

[0025] Figure 2 SEM images of P(St-VA)-1 prepared in Examples 1-3, in which the amount ratio of water to sodium lauryl sulfate is 1.0 mL:0.25 mg, P(St-VA)-2 prepared in which the amount ratio of water to sodium lauryl sulfate is 1.0 mL:0.5 mg, and P(St-VA)-3 prepared in which the amount ratio of water to sodium lauryl sulfate is 1.0 mL:0.75 mg.

[0026] Figure 3 These are SEM images of P(St-VA)-1 prepared in Example 1 at different polymerization times.

[0027] Figure 4 TEM images of P(St-VA)-1 prepared in Example 1 before and after washing out the paraffin.

[0028] Figure 5 The effect of pH value on the adsorption capacity of uranyl ions by P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3 prepared in Examples 1-3 is shown.

[0029] Figure 6 These are the DSC curves of P(St-VA)-1, P(St-VA)-2, and P(St-VA)-3 prepared in Examples 1-3.

[0030] Figure 7 These are the thermogravimetric curves of P(St-VA)-1, P(St-VA)-2, and P(St-VA)-3 prepared in Examples 1-3.

[0031] Figure 8 Zeta potential of P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3 at different pH values ​​in Examples 1-3.

[0032] Figure 9The adsorption kinetics of uranyl ions by P(St-VA)-1, P(St-VA)-2, and P(St-VA)-3 prepared in Examples 1-3 and their model fitting curves are shown.

[0033] Figure 10 It is the adsorption selectivity of P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3 prepared in Examples 1-3. DETAILED DESCRIPTION

[0034] The present invention will be further described below with reference to specific implementation examples.

[0035] Example 1:

[0036] (1) 3.0 mg of carbon nitride was uniformly dispersed in 4.0 mL of deionized water by ultrasonication, 4.0 mL of ethylene phosphoric acid was added, and ultrasonication was repeated to uniformly disperse the carbon nitride. 1.0 mg of sodium lauryl sulfate was added to obtain an aqueous phase.

[0037] (2) Dissolve 0.44 mL of styrene in 0.25 mL of paraffin to obtain an oil phase;

[0038] (3) The aqueous phase and the oil phase were mixed and stirred at a high speed of 20,000 rpm for 30 seconds. After the solution changed from clear to milky white, it was immediately placed in a constant temperature and humidity chamber at a temperature of 25°C and a humidity of 60% and illuminated with a 50W LED light for 2.0 hours. When a white polymer appeared on the upper layer, the illumination was stopped and the product was collected by centrifugation at a speed of 10,000 rpm for 3.0 minutes. After washing with 99% ethanol three times, it was placed in a vacuum drying oven at a temperature of 45°C and dried for 24 hours to obtain the hollow nano-adsorbent P(St-VA)-1.

[0039] Other conditions remain unchanged, and only the ratio of ethylene phosphate and styrene is adjusted to 1:9, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1. Figure 1 Figure 3 is the SEM image of the two monomers, ethylene phosphate and styrene, in P(St-VA)-1 at different ratios. When the ratio of ethylene phosphate to styrene is 1:9, most of the monomers are large fragments. It is not until the ratio is 5:5 that a hemispherical structure slowly appears. The optimal structural morphology is reached at 7:3. Subsequently, when the ratio of ethylene phosphate to styrene is increased to 9:1, almost no morphology is formed, indicating that the optimal ratio of ethylene phosphate to styrene for obtaining P(St-VA)-1 is 7:3.

[0040] Other conditions remain unchanged, only the LED lighting duration is adjusted to 2.0h, 4.0h, 6.0h, 8.0h, 10h, 12h. Figure 3The SEM images of the prepared P(St-VA)-1 under different illumination times show that when the light-initiated emulsion polymerization time is 2.0 h, P(St-VA)-1 is almost not formed. When the illumination time is 8.0 h, P(St-VA)-1 begins to gradually form. When the illumination time is 12 h, P(St-VA)-1 is completely formed, which proves the key role of photoinitiation in emulsion polymerization.

[0041] Example 2:

[0042] (1) 4.0 mg of carbon nitride was uniformly dispersed in 4.0 mL of deionized water by ultrasonication, 4.0 mL of ethylene phosphoric acid was added, and ultrasonication was repeated to uniformly disperse the carbon nitride. 2.0 mg of sodium lauryl sulfate was added to obtain an aqueous phase.

[0043] (2) Dissolve 4.0 mL of styrene in 0.5 mL of paraffin to obtain an oil phase;

[0044] (3) The aqueous phase and the oil phase were mixed and stirred at a high speed of 22500 rpm for 30 seconds. After the solution changed from clear to milky white, it was immediately placed in a constant temperature and humidity chamber at a temperature of 25°C and a humidity of 60% and illuminated with a 50W LED light for 8.0 hours. When a white polymer appeared on the upper layer, the illumination was stopped and the product was collected by centrifugation at a speed of 10000 rpm for 3.0 minutes. After washing with 99% ethanol three times, it was placed in a vacuum drying oven at a temperature of 45°C and dried for 24 hours to obtain the hollow nano-adsorbent P(St-VA)-2.

[0045] Example 3:

[0046] (1) 6.0 mg of carbon nitride was uniformly dispersed in 4.0 mL of deionized water by ultrasonication, 4.0 mL of ethylene phosphoric acid was added, and ultrasonication was repeated to uniformly disperse the carbon nitride. 3.0 mg of sodium lauryl sulfate was added to obtain an aqueous phase.

[0047] (2) Dissolve 36 mL of styrene in 0.75 mL of paraffin to obtain an oil phase;

[0048] (3) The aqueous phase and the oil phase were mixed and stirred at a high speed of 25,000 rpm for 30 seconds. After the solution changed from clear to milky white, it was immediately placed in a constant temperature and humidity chamber at a temperature of 25°C and a humidity of 60% and illuminated with a 50W LED light for 12.0 hours. When a white polymer appeared on the upper layer, the illumination was stopped and the product was collected by centrifugation at a speed of 10,000 rpm for 3.0 minutes. After washing with 99% ethanol three times, it was placed in a vacuum drying oven at a temperature of 45°C and dried for 24 hours to obtain the hollow nano-adsorbent P(St-VA)-3.

[0049] Figure 2The SEM images of prepared P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3 are shown in Figure 2. Figure 2 As shown in the figure, depending on the usage ratio of water and sodium dodecyl sulfate, the polymer showed three different morphologies: P(St-VA)-1 showed a hollow hemisphere, P(St-VA)-2 showed small spheres with mesopores, and P(St-VA)-3 showed adhered nanospheres, which proved the important role of sodium dodecyl sulfate in the emulsion polymerization process.

[0050] Figure 4 TEM images of the prepared P(St-VA)-1 before and after the paraffin is removed. As shown in the images (a1 and a2), the P(St-VA)-1 is encapsulated with paraffin before the paraffin is removed. However, after the paraffin is removed, the P(St-VA)-1 structures (b1 and b2) are hollow, indicating that the paraffin acts as a phase change material within the P(St-VA)-1.

[0051] In a specific embodiment of the present invention, the recognition performance is evaluated using a static adsorption experiment: first, 10 mg of P(St-VA)-1, P(St-VA)-2, and P(St-VA)-3 are subjected to an adsorption experiment on uranyl ions in the pH range of 3.0-9.0. The content of uranyl ions after adsorption is measured by inductively coupled plasma emission spectrometry, and the optimal adsorption pH is determined based on the results; then, to study the time it takes for P(St-VA)-1, P(St-VA)-2, and P(St-VA)-3 to reach adsorption equilibrium, an adsorption equilibrium test is performed at a uranyl ion concentration of 10 mg / L for up to 6.0 hours. The adsorption data are fitted using a pseudo-first-order kinetic model and a pseudo-second-order kinetic model, and the time to reach adsorption equilibrium is calculated based on the results; finally, the adsorption selectivity of P(St-VA)-1, P(St-VA)-2, and P(St-VA)-3 for uranyl ions is studied in a simulated seawater environment.

[0052] Performance testing:

[0053] The environmental pH value has a great influence on the adsorption behavior of metal ions; therefore, the adsorption capacity of P(St-VA)-1, P(St-VA)-2, and P(St-VA)-3 for uranyl ions in the pH range of 3.0 to 9.0 was studied. Figure 5Figure 2 shows the effect of pH on the adsorption capacity of the prepared P(St-VA)-1, P(St-VA)-2, and P(St-VA)-3. As can be seen from the figure, the adsorption capacity of P(St-VA)-1 and P(St-VA)-2 reaches its maximum at pH 7.0, indicating that the optimal pH for P(St-VA)-1 and P(St-VA)-2 is 7.0. The adsorption capacity of P(St-VA)-3 reaches its maximum at pH 8.0, indicating that the optimal pH for P(St-VA)-3 is 8.0.

[0054] Figure 8 The Zeta potential of P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3 at different pH values ​​is shown in the figure. As can be seen from the figure, when the pH value is 7.0, the surface charge of P(St-VA)-1 and P(St-VA)-2 is negative. At the same time, when the pH value is 8.0, the surface charge of P(St-VA)-3 is also negative, and the negative value is the largest. This is because the phosphate group is negatively charged. The more phosphate groups there are, the higher the negative value of the Zeta potential is. Figure 5 The adsorption capacity is also larger.

[0055] The adsorption kinetics of P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3 are shown in Figure 2. Figure 9 As shown in the figure, the adsorption capacity of P(St-VA)-1 and P(St-VA)-2 increased rapidly within the first 2.0 hours. The adsorption rates of P(St-VA)-1 and P(St-VA)-2 slowed significantly over the next 2.0 to 3.0 hours, ultimately reaching equilibrium at 4.0 hours. At this time, the adsorption equilibrium capacity of P(St-VA)-1 was 35.84 mg / g, and that of P(St-VA)-2 was 35.76 mg / g. The adsorption capacity of P(St-VA)-3 increased rapidly within the first 3.0 hours, then grew more slowly after 3.0 hours, ultimately reaching equilibrium within 4.0 hours. At this time, the adsorption equilibrium capacity of P(St-VA)-3 was 51.96 mg / g.

[0056] In order to measure the possible effects of other interfering ions in nuclear wastewater on the adsorption capacity of P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3, we selected VO3 - ,Ni 2+ ,Fe 3+ ,Co 2+ ,Zn 2+ ,Pb 2+ ,Cu 2+ ,Na + ,Mg 2+ ,K + and Ca2+ As a competitor of uranyl ions, the adsorbent was studied in the presence of UO2 2+ ,VO3 - ,Ni 2+ ,Fe 3+ ,Co 2+ ,Zn 2+ ,Pb 2+ ,Cu 2+ ,Na + ,Mg 2+ ,K + and Ca 2+ Adsorption behavior in mixed solutions. Figure 10 As shown in the figure, in the presence of numerous interfering ions, P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3 still have the highest adsorption capacity for uranyl ions, reaching 0.61 mg / g, 0.62 mg / g and 1.65 mg / g respectively, which is much greater than VO3 - ,Ni 2+ ,Fe 3+ ,Co 2+ ,Zn 2+ ,Pb 2+ ,Cu 2+ ,Na + ,Mg 2+ ,K + and Ca 2+ The corresponding adsorption capacity.

[0057] In order to study the heat storage effect of P(St-VA)-1, P(St-VA)-2 and (St-VA)-3, we conducted thermal analysis of the materials, including measuring their DSC curves and TGA curves, such as Figure 6 As shown in the figure, P(St-VA)-1, P(St-VA)-2 and P(St-VA)-3 all have multiple endothermic and exothermic processes in the temperature range of 25-70℃, which proves that all three materials have good heat storage performance. Among them, P(St-VA)-2 has poorer heat storage performance than P(St-VA)-1 and P(St-VA)-3 due to the presence of mesopores in its morphology, which leads to the leakage of paraffin. The best heat storage effect is P(St-VA)-1, which can store the most paraffin due to its large hollow structure. In addition, Figure 7 As shown in the figure, these three materials also experience weight loss in the range of 100-600℃. The heat loss in the range of 170-350℃ is due to the decomposition of paraffin, the heat loss in the range of 350-450℃ is caused by the thermal degradation of carbon nitride, the heat loss within 100℃ can be attributed to the evaporation weight loss of adsorbed water, and the weight loss after 500℃ may be caused by the thermal degradation of the polymer.

[0058] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although this specification has described the present invention in detail with reference to the above embodiments, it should be understood by those skilled in the art that the present invention may still be modified or replaced by equivalents. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A method for preparing a hollow nano-adsorbent with both uranium extraction and heat storage functions, characterized in that: The following steps are involved: (1) uniformly dispersing a certain amount of carbon nitride in a certain amount of deionized water by ultrasonication, adding a certain amount of ethylene phosphate monomer, ultrasonicating the mixture again to uniformly disperse the carbon nitride, and adding a certain amount of sodium lauryl sulfate to obtain an aqueous phase; (2) Dissolving a certain amount of styrene monomer in paraffin to obtain an oil phase; (3) The aqueous phase and the oil phase are mixed and stirred at a high speed at a certain speed. When the solution changes from clear to milky white, it is immediately placed in a constant temperature and humidity chamber and illuminated with LED light for a period of time. When white polymer appears on the upper layer, the illumination is stopped and the product is collected by centrifugation, washed with ethanol, and vacuum dried to obtain the hollow nano-adsorbent P(St-VA); In step (1) and step (2), the ratio of carbon nitride, deionized water, sodium lauryl sulfate, ethylene phosphate monomer, styrene monomer and paraffin wax is 0.75-1.25 mg:1.0 mL:0.25-0.75 mg:1 mL:0.11~1 mL:0.0625~0.1875 mL; The power of the LED is 50W, and the irradiation time is 8.0~12 h.

2. The preparation method according to claim 1, characterized in that In step (3), the speed of the high-speed stirring is 20,000-25,000 rpm.

3. The preparation method according to claim 1, characterized in that In step (3), the temperature in the constant temperature and humidity chamber is 25°C and the humidity is 60%.

4. The method for preparing a hollow nano-adsorbent having both uranium extraction and heat storage functions according to claim 1, characterized in that: In step (3), the temperature in the vacuum drying oven is 45°C and the time is 24 hours.

5. A hollow nano-adsorbent with both uranium extraction and heat storage functions, characterized in that: It is prepared by the method according to any one of claims 1 to 4.

6. The hollow nano-adsorbent having both uranium extraction and heat storage functions according to claim 5 is used for enriching uranyl ions in nuclear wastewater and storing nuclear waste heat.

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