Preparation method of imprinted functionalized straw adsorbent

Abstract

The present invention belongs to the technical field of material preparation and adsorption separation, and particularly relates to a preparation method of an imprinted functionalized straw adsorbent. The preparation method of the imprinted functionalized straw adsorbent described in the present invention comprises the following steps: (1) preparing pretreated straw powder; (2) preparing amino-functionalized straw powder; (3) dissolving the amino-functionalized straw powder in a first methanol-deionized water mixed solution, dissolving ethylenediaminetetraacetic anhydride in a second methanol, then placing the above two in a reaction vessel and mixing evenly, subsequently adding carboxylated carbon nanotubes and stirring evenly, and finally adding gadolinium trichloride hexahydrate and continuing to stir. After the reaction is completed, post-treatment is carried out to prepare the imprinted functionalized straw adsorbent. The preparation method described in the present invention adopts the ion imprinting technology to endow it with a memory function for gadolinium ions, so as to achieve the purpose of selectively removing gadolinium ions in a complex water environment.

Description

Technical Field

[0001] The present invention belongs to the technical fields of material preparation and adsorption separation, and specifically relates to a preparation method of an imprint-functionalized straw adsorbent. Background Art

[0002] Rare earth metal gadolinium has excellent optical and magnetic properties and is crucial in production fields such as medical imaging, magnetic refrigeration, nuclear reactions, and optical isolators. The rapid development of technology has forced the excessive growth of the demand for gadolinium. The active mining of rare earth ores and the improper treatment of gadolinium-containing waste have caused pollution to the surrounding water environment. Free gadolinium ions in water bodies are toxic, which will seriously threaten the health and safety of living organisms in the long run. Therefore, the efficient and selective removal of gadolinium ions from water bodies has important practical significance for maintaining ecological safety and improving the level of water purification technology.

[0003] Currently, the methods for treating gadolinium pollution in water bodies mainly include chemical precipitation method, solvent extraction method, ion exchange method, etc. However, they also face many problems in practical applications, such as unpredictable secondary pollution to the environment, complex large-scale production procedures, and relatively high costs. In recent years, straw adsorbents have gradually come into the public eye, and there have been more and more studies on their removal of dyes and heavy metal ions from water bodies, but there has been no report on the remediation of rare earth metal gadolinium ions in water bodies. A problem worthy of attention is that when using adsorbents to treat water environment problems, other metal ions coexisting in the water body often compete with gadolinium ions to attach to the same active sites on the surface of the adsorbent, resulting in a decrease in the removal ability of the adsorbent for gadolinium ions. Therefore, it is urgent to develop an adsorbent with selective adsorption function, economic efficiency, and convenience.

[0004] In addition, since the straw adsorbent mainly undergoes chemical adsorption for metal ions, the functional groups carried by the adsorbent play a key role in the adsorption ability for gadolinium ions. Therefore, how to enable the straw adsorbent to more strongly and specifically remove gadolinium ions from water bodies is the key technical problem to be solved in the present invention. Summary of the Invention

[0005] The purpose of the present invention is to provide a preparation method of an imprint-functionalized straw adsorbent. This preparation method adopts ion imprinting technology to endow it with a memory function for gadolinium ions, thereby achieving the purpose of selectively removing gadolinium ions in a complex water environment.

[0006] The preparation method of the imprint-functionalized straw adsorbent described in the present invention comprises the following steps:

[0007] (1) Grind rice straw into powder, soak it in sodium hydroxide solution for a period of time, then carry out suction filtration, washing with water, and drying to obtain pretreated straw powder;

[0008] (2) Add the pretreated straw powder, potassium persulfate, and water prepared in step (1) into a reaction vessel and mix well. Then, add acrylamide solution dropwise for an oil bath reaction. Finally, perform suction filtration, wash with water, and dry to obtain amino-functionalized straw powder.

[0009] (3) Dissolve the amino-functionalized straw powder prepared in step (2) in the first methanol-deionized water mixed solution, dissolve ethylenediaminetetraacetic anhydride in the second methanol, then place the above two in a reaction vessel and mix well. Subsequently, add carboxylated carbon nanotubes and stir to mix well. Finally, add gadolinium(III) chloride hexahydrate and continue stirring. After the reaction is completed, perform post-treatment to obtain the imprint-functionalized straw adsorbent.

[0010] Wherein:

[0011] In step (1), the rice straw is ground into powder, and the powder is sieved through a 60-mesh sieve.

[0012] In step (1), the concentration of the sodium hydroxide solution is 0.5 mol / L, the soaking temperature is 65 °C, and the soaking time is 1 h.

[0013] In step (1), the drying temperature is 40 °C, and the drying time is 12 h.

[0014] In step (2), add the pretreated straw powder, potassium persulfate, and water prepared in step (1) into a reaction vessel and mix well. The mixing temperature is 80 °C, and the mixing time is 30 min.

[0015] During the reaction process in step (2), control the stirring speed at 1700 r / min.

[0016] In step (2), the temperature of the oil bath reaction is 80 °C, and the time of the oil bath reaction is 3 h.

[0017] In step (2), the mass ratio of the pretreated straw powder, potassium persulfate, and water is 1:0.27:150.

[0018] In step (2), the mass ratio of potassium persulfate to acrylamide in the acrylamide solution is 0.27:7.1 - 21.3.

[0019] In step (2), the acrylamide solution uses water as the solvent, and the mass concentration is 12.43% - 29.87%.

[0020] In step (2), the water washing time is 15 min, the drying temperature is 40 °C, and the drying time is 8 h.

[0021] In step (3), the mass ratio of the amino-functionalized straw powder, ethylenediaminetetraacetic anhydride, carboxylated carbon nanotubes, and gadolinium(III) chloride hexahydrate is 1:3 - 9:0.1:0.125 - 0.5.

[0022] In step (3), the volume ratio of the first methanol to deionized water in the first methanol-deionized water mixed solution is 1:1.

[0023] In step (3), the mass-volume ratio of the amino-functionalized straw powder to the first methanol-deionized water mixed solution is 1:20, with the unit of g / mL.

[0024] In step (3), ethylenediaminetetraacetic anhydride is dissolved in the second methanol, and the mass-volume ratio of ethylenediaminetetraacetic anhydride to the second methanol is 3 - 9:100, with the unit of g / mL.

[0025] In step (3), the stirring speed during the reaction process is controlled at 1700 r / min, and gadolinium(III) chloride hexahydrate is finally added and stirring continues for 24 h.

[0026] The post-treatment in step (3) is to filter the product by suction, add ethanol and continue stirring for 16 h with a stirring speed of 1500 r / min, then filter by suction again, immerse in 1 mol / L HCl solution for 12 h, then filter the product by suction again, wash with deionized water, wash with 0.1 mol / L NaOH solution, wash with deionized water, and dry to obtain the imprinted functionalized straw adsorbent; wherein, the volume ratio of ethanol to the sum of the volumes of the first methanol and the second methanol is 15:11.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) In the preparation method of the imprinted functionalized straw adsorbent described in the present invention, the rice straw used is a natural and high-yield biomass, and it is used as the substrate material of the adsorbent, which has the advantages of green economy and sustainable development. When preparing, the pretreated straw is first amino-functionalized, aiming to provide binding sites that can interact with ethylenediaminetetraacetic anhydride, laying a foundation for the ion imprinting process. Ethylenediaminetetraacetic anhydride not only serves as a functional monomer for adsorbing gadolinium ions but also serves as a cross-linking agent to polymerize the ion imprinted polymer in one step, greatly simplifying the ion imprinting process. Ethylenediaminetetraacetic anhydride undergoes an amidation reaction with amino groups to form an EDTA structure with six-coordination ability. Using gadolinium(III) chloride hexahydrate as a template ion, after elution with hydrochloric acid, a pore cavity matching the size of gadolinium ions is formed. The specific pores formed by the imprinting technique improve the selectivity for gadolinium ions, and carboxylated carbon nanotubes provide rich oxygen-containing functional groups (-COOH), enhancing the coordination with gadolinium ions. The two work together to ensure that the prepared imprinted functionalized straw adsorbent has excellent adsorption selectivity and adsorption capacity.

[0029] (2) The preparation method of the imprinted functionalized straw adsorbent described in the present invention not only simplifies the ion imprinting procedure, provides more gadolinium ion adsorption sites, but also can specifically and effectively solve the problem of removing gadolinium ions from water in one step. Description of the Drawings

[0030] Figure 1 It is a scanning electron microscope comparison diagram of the pretreated straw powder prepared in Example 2, the amino-functionalized straw prepared in Example 2, the imprint-functionalized straw adsorbent prepared in Example 2, the non-imprint-functionalized straw adsorbent prepared in Comparative Example 3, and the imprint-functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4;

[0031] Figure 1 In the figure: Figure a is the scanning electron microscope image of the pretreated straw powder prepared in Example 2 at a magnification of 2000, Figure b is the scanning electron microscope image of the amino-functionalized straw prepared in Example 2 at a magnification of 2000, Figure c is the scanning electron microscope image of the imprint-functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4 at a magnification of 2000, Figure d is the scanning electron microscope image of the imprint-functionalized straw adsorbent prepared in Example 2 at a magnification of 2000, Figure e is the scanning electron microscope image of the non-imprint-functionalized straw adsorbent prepared in Comparative Example 3 at a magnification of 2000, and Figure f is the scanning electron microscope image of the non-imprint-functionalized straw adsorbent prepared in Comparative Example 3 at a magnification of 5000;

[0032] Figure 2 It is the infrared spectrum diagram of the pretreated straw powder prepared in Example 2, the amino-functionalized straw prepared in Example 2, the imprint-functionalized straw adsorbent prepared in Example 2, the non-imprint-functionalized straw adsorbent prepared in Comparative Example 3, and the imprint-functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4;

[0033] Figure 2 In the figure: P-S represents the pretreated straw powder in Example 2, AMS represents the amino-functionalized straw in Example 2, CEAMS-IIM represents the imprint-functionalized straw adsorbent prepared in Example 2, CEAMS-NIIM represents the non-imprint-functionalized straw adsorbent prepared in Comparative Example 3, and EAMS-IIM represents the imprint-functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4;

[0034] Figure 3 It is the nitrogen adsorption / desorption isotherm diagram of the pretreated straw powder prepared in step (1) of Example 2, the imprint-functionalized straw adsorbent prepared in step (3) of Example 2, the non-imprint-functionalized straw adsorbent prepared in Comparative Example 3, and the imprint-functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4;

[0035] Figure 3In the figure: P-S represents the pretreated straw powder in Example 2, CEAMS-IIM represents the imprinted functionalized straw adsorbent prepared in Example 2, CEAMS-NIIM represents the non-imprinted functionalized straw adsorbent prepared in Comparative Example 3, and EAMS-IIM represents the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4;

[0036] Figure 4 It is the adsorption isotherm data and model diagram of gadolinium ions by the imprinted functionalized straw adsorbent prepared in step (3) of Example 2, the non-imprinted functionalized straw adsorbent prepared in Comparative Example 3, and the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4;

[0037] Figure 4 In the figure: CEAMS-IIM represents the imprinted functionalized straw adsorbent prepared in Example 2, CEAMS-NIIM represents the non-imprinted functionalized straw adsorbent prepared in Comparative Example 3, and EAMS-IIM represents the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4; LangmuirFit is the Langmuir fitting model; FreundlichFit is the Freundlich fitting model;

[0038] Figure 5 It is the adsorption kinetic data and model diagram of gadolinium ions by the imprinted functionalized straw adsorbent prepared in step (3) of Example 2, the non-imprinted functionalized straw adsorbent prepared in Comparative Example 3, and the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4;

[0039] Figure 5 In the figure: CEAMS-IIM represents the imprinted functionalized straw adsorbent prepared in Example 2, CEAMS-NIIM represents the non-imprinted functionalized straw adsorbent prepared in Comparative Example 3, and EAMS-IIM represents the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4; PFOKMFit is the fitting curve of the adsorption kinetic data with the pseudo-first-order kinetic model; PSOKMFit is the fitting curve of the adsorption kinetic data with the pseudo-second-order kinetic model. Detailed implementation mode

[0040] The present invention will be further described below in conjunction with the embodiments.

[0041] The manufacturer of the carboxylated carbon nanotubes is Macklin Chemical Reagent Co., Ltd., with a purity > 95%, an inner diameter of about 2 - 5 nm, an outer diameter < 8 nm, a length of about 10 - 30 μm, and a carboxyl functional group content of about 3.9 wt%.

[0042] Example 1

[0043] The preparation method of the imprinted functionalized straw adsorbent described in Example 1 consists of the following steps:

[0044] (1) Cut the washed and dried rice straw into small segments with a length of 5 cm, then put it into a grinding machine to grind it into powder, and sieve the powder through a 60-mesh sieve. Immerse the powder in a NaOH solution with a temperature of 65 °C and a concentration of 0.5 mol / L for 1 h, and finally carry out suction filtration, water washing, and drying (the drying temperature is 40 °C and the drying time is 12 h) to prepare the pretreated straw powder.

[0045] (2) Put 1 g of the pretreated straw powder prepared in step (1), 0.27 g of potassium persulfate, and 150 mL of deionized water into a round-bottom flask, and carry out an oil bath at 80 °C for 30 min. Subsequently, dissolve 7.1 g of acrylamide in 50 mL of deionized water to prepare an acrylamide solution, and dropwise add the acrylamide solution to the above round-bottom flask, and continue to react in an oil bath at 80 °C for 3 h. During the reaction process, control the stirring speed at 1700 r / min. Filter the product by suction, soak it in deionized water for 15 min, and then dry it at 40 °C for 8 h to obtain the amino-functionalized straw.

[0046] (3) Disperse 1 g of the amino-functionalized straw powder obtained in step (2) in a mixed solution of the first methanol and deionized water (the volume ratio of the first methanol to deionized water is 10 mL:10 mL), and disperse 3 g of ethylenediaminetetraacetic anhydride in 100 mL of the second methanol. Put the two into a round-bottom flask and stir to mix evenly, and then add 0.1 g of carboxylated carbon nanotubes and continue to stir until uniform. Add 0.125 g of gadolinium(III) chloride hexahydrate to the round-bottom flask and continue to stir for 24 h. Control the stirring speed at 1700 r / min during the reaction process. Filter the product by suction, add 150 mL of ethanol and continue to stir for 16 h, then filter the product by suction again, immerse it in a 1 mol / L HCl solution for 12 h, then filter the product by suction again, wash it with deionized water, wash it with a 0.1 mol / L NaOH solution, wash it with deionized water, and dry it to obtain the imprinted functionalized straw adsorbent.

[0047] Comparative Example 1

[0048] The preparation method of the straw adsorbent described in this Comparative Example 1 is the same as that in Example 1. The only difference is that gadolinium(III) chloride hexahydrate is not added in step (3), and a non-imprinted functionalized straw adsorbent is prepared.

[0049] Comparative Example 2

[0050] The preparation method of the straw adsorbent described in this Comparative Example 2 is the same as that in Example 1. The only difference is that carboxylated carbon nanotubes are not added in step (3), and an imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes is prepared.

[0051] Example 2

[0052] The preparation method of the imprinted functionalized straw adsorbent described in this Example 2 consists of the following steps:

[0053] (1) Cut the washed and dried rice straw into small sections with a length of 5 cm, then put it into a grinding machine to grind into powder, and the powder is sieved through a 60-mesh sieve. Immerse the powder in a NaOH solution with a temperature of 65 °C and a concentration of 0.5 mol / L for 1 h, and finally carry out suction filtration, water washing, and drying (the drying temperature is 40 °C and the drying time is 12 h) to prepare the pretreated straw powder (named P-S).

[0054] (2) Put 1 g of the pretreated straw powder prepared in step (1), 0.27 g of potassium persulfate, and 150 mL of deionized water into a round-bottom flask, and carry out an oil bath at 80 °C for 30 min. Subsequently, dissolve 14.2 g of acrylamide in 50 mL of deionized water to prepare an acrylamide solution, and dropwise add the acrylamide solution to the above round-bottom flask, and continue to react in an oil bath at 80 °C for 3 h. During the reaction process, control the stirring speed at 1700 r / min. Filter the product by suction, soak it in deionized water for 15 min, and then dry it at 40 °C for 8 h to obtain amino-functionalized straw (named AMS).

[0055] (3) Disperse 1 g of the amino-functionalized straw powder obtained in step (2) in a mixed solution of the first methanol and deionized water (the volume ratio of the first methanol to deionized water is 10 mL:10 mL), and disperse 6 g of ethylenediaminetetraacetic anhydride in 100 mL of the second methanol. Put the two into a round-bottom flask and stir to mix evenly, and then add 0.1 g of carboxylated carbon nanotubes and continue to stir until evenly mixed. Add 0.25 g of gadolinium(III) chloride hexahydrate to the round-bottom flask and continue to stir for 24 h. Control the stirring speed at 1700 r / min during the reaction process. Filter the product by suction, add 150 mL of ethanol and continue to stir for 16 h, then filter the product by suction again, immerse it in a 1 mol / L HCl solution for 12 h, then filter the product by suction, wash it with deionized water, wash it with a 0.1 mol / L NaOH solution, wash it with deionized water, and dry it to obtain the imprinted functionalized straw adsorbent (named CEAMS-IIM).

[0056] Comparative Example 3

[0057] The preparation method of the straw adsorbent described in this Comparative Example 3 is the same as that of Example 2. The only difference is that gadolinium(III) chloride hexahydrate is not added in step (3), and a non-imprinted functionalized straw adsorbent (named CEAMS-NIIM) is prepared.

[0058] Comparative Example 4

[0059] The preparation method of the straw adsorbent described in Comparative Example 4 is the same as that in Example 2. The only difference is that in step (3), carboxylated carbon nanotubes are not added, and an imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes is prepared (named EAMS-IIM).

[0060] Example 3

[0061] The preparation method of the imprinted functionalized straw adsorbent described in this Example 3 consists of the following steps:

[0062] (1) Cut the washed and dried rice straw into small segments with a length of 5 cm, then put them into a grinder to grind into powder, and pass the powder through a 60-mesh sieve. Immerse the powder in a NaOH solution with a temperature of 65 °C and a concentration of 0.5 mol / L for 1 h, and finally carry out suction filtration, water washing, and drying (the drying temperature is 40 °C and the drying time is 12 h) to prepare the pretreated straw powder.

[0063] (2) Put 1 g of the pretreated straw powder prepared in step (1), 0.27 g of potassium persulfate, and 150 mL of deionized water into a round-bottom flask, carry out an oil bath at 80 °C for 30 min, and then dissolve 21.3 g of acrylamide in 50 mL of deionized water to prepare an acrylamide solution, and dropwise add the acrylamide solution to the above round-bottom flask, and continue to react in an oil bath at 80 °C for 3 h, and control the stirring speed during the reaction to be 1700 r / min. Filter the product by suction, soak it in deionized water for 15 min, and then dry it at 40 °C for 8 h to obtain amino-functionalized straw.

[0064] (3) Disperse 1 g of the amino-functionalized straw powder obtained in step (2) in a mixed solution of the first methanol and deionized water (the volume ratio of the first methanol to deionized water is 10 mL:10 mL), and disperse 9 g of ethylenediaminetetraacetic anhydride in 100 mL of the second methanol. Put the two into a round-bottom flask and stir to mix evenly, and then add 0.1 g of carboxylated carbon nanotubes and continue to stir until uniform. Add 0.5 g of gadolinium(III) chloride hexahydrate to the round-bottom flask and continue to stir for 24 h, control the stirring speed during the reaction to be 1700 r / min, filter the product by suction, add 150 mL of ethanol and continue to stir for 16 h, then filter the product by suction, immerse it in a 1 mol / L HCl solution for 12 h, then filter the product by suction, wash it with deionized water, wash it with a 0.1 mol / L NaOH solution, wash it with deionized water, and dry it to obtain the imprinted functionalized straw adsorbent.

[0065] Comparative Example 5

[0066] The preparation method of the straw adsorbent described in this Comparative Example 5 is the same as that in Example 3. The only difference is that in step (3), gadolinium(III) chloride hexahydrate is not added, and a non-imprinted functionalized straw adsorbent is prepared.

[0067] Comparative Example 6

[0068] The preparation method of the straw adsorbent described in this Comparative Example 6 is the same as that of Example 3. The only difference is that in step (3), carboxylated carbon nanotubes are not added, and an imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes is prepared.

[0069] Scanning electron microscopy tests were performed on the pretreated straw powder (named P-S) prepared in step (1) of Example 2, the amino-functionalized straw (named AMS) prepared in step (2) of Example 2, the imprinted functionalized straw adsorbent (named CEAMS-IIM) prepared in step (3) of Example 2, the non-imprinted functionalized straw adsorbent (named CEAMS-NIIM) prepared in Comparative Example 3, and the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes (named EAMS-IIM) prepared in Comparative Example 4, and the attached Figure 1 is shown as a comparison diagram of scanning electron micrographs. From the attached Figure 1 , it can be seen that the surface morphologies of P-S and AMS are similar. Compared with AMS, EAMS-IIM has a shrunk surface structure, indicating that the introduction of EDTA will change the surface morphology of AMS. Compared with EAMS-IIM, several protrusions are dispersed on the surface of the layered structure of CEAMS-IIM, which may be caused by the aggregation of COOH-CNTs. The surface morphology of CEAMS-NIIM is similar to that of CEAMS-IIM, but the surface of CEAMS-NIIM is smoother, which may be due to the presence of imprinted cavities on the surface of CEAMS-IIM. In summary, the grafting effect of functional groups and the imprinting effect on the surface morphologies of different materials are helpful for evaluating whether the materials are successfully prepared and whether the imprinting sites are successfully constructed.

[0070] Infrared spectroscopy tests were performed on the pretreated straw powder (named P-S) prepared in step (1) of Example 2, the amino-functionalized straw (named AMS) prepared in step (2) of Example 2, the imprinted functionalized straw adsorbent (named CEAMS-IIM) prepared in step (3) of Example 2, the non-imprinted functionalized straw adsorbent (named CEAMS-NIIM) prepared in Comparative Example 3, and the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes (named EAMS-IIM) prepared in Comparative Example 4, and the attached Figure 2 is shown as the infrared spectrogram.

[0071] Figure 2 are the infrared spectrograms of P-S, AMS, EAMS-IIM, CEAMS-IIM, and CEAMS-NIIM. From Figure 2 , it can be seen that all materials have a wavelength of 3434 cm -1There is a relatively wide adsorption peak at this position, which corresponds to the stretching vibrations of O-H and N-H, and there is a stretching vibration of C-H at the wavelengths of 2933 and 2852 cm -1 Compared with P-S, several characteristic adsorption peaks appear at the wavelengths of 891, 1388 and 1626 cm -1 These are the bending vibration of N-H and the stretching vibration of C-N in AM, indicating that AM has been successfully grafted onto the P-S skeleton. For EAMS-IIM, CEAMS-IIM and CEAMS-NIIM, after grafting EDTA onto AMS, the peak intensities at 891, 1388 and 3434 cm -1 decrease, and a new characteristic absorption peak appears at 1741 cm -1 This is the C=O stretching vibration peak of the free carboxyl group, indicating that they have successfully grafted EDTA. There is no significant difference between CEAMS-IIM and CEAMS-NIM, indicating that the imprinting effect has little effect on the change of functional groups.

[0072] Perform adsorption-desorption tests on the pretreated straw powder prepared in step (1) of Example 2 (named P-S), the imprinted functionalized straw adsorbent prepared in step (3) of Example 2 (named CEAMS-IIM), the non-imprinted functionalized straw adsorbent prepared in Comparative Example 3 (named CEAMS-NIIM), and the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes prepared in Comparative Example 4 (named EAMS-IIM) to obtain the Figure 3 nitrogen adsorption / desorption isotherm diagram shown.

[0073] From Figure 3It can be seen that the adsorption isotherm models of P-S and EAMS-IIM are similar, characterized by a significant increase in adsorption capacity near a relatively high relative pressure (P / P0 > 0.8). In contrast, the adsorption of CEAMS-IIM and CEAMS-NIIM starts to increase at a relative pressure of about 0.4, and an obvious H3-type isotherm hysteresis loop appears, indicating that both have abundant slit-shaped mesopores. While the hysteresis loops of P-S and EAMS-IIM are smaller or there is no hysteresis loop, suggesting that their pores are mainly macropores or non-rigid pores (such as interparticle packing gaps). The BET surface area and pore volume of CEAMS-IIM and CEAMS-NIIM are much larger than those of P-S and EAMS-IIM, and the pore diameter is much smaller, which is due to the introduction of COOH-CNTs. After testing, the BET surface area and pore diameter of CEAMS-IIM are 56.24 m² / g and 7.256 nm respectively, the BET surface area and pore diameter of CEAMS-NIIM are 43.45 m² / g and 8.070 nm respectively, the BET surface area and pore diameter of P-S are 7.379 m² / g and 21.50 nm respectively, and the BET surface area and pore diameter of EAMS-IIM are 7.725 m² / g and 28.30 nm respectively. These results indicate that there are imprinting sites in CEAMS-IIM, which is beneficial to the adsorption of gadolinium ions in water.

[0074] Figure 4 Adsorption isotherm data and model diagrams of gadolinium ions for the imprinted functionalized straw adsorbent (named CEAMS-IIM) prepared in step (3) of Example 2, the non-imprinted functionalized straw adsorbent (named CEAMS-NIIM) prepared in Comparative Example 3, and the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes (named EAMS-IIM) prepared in Comparative Example 4.

[0075] From Figure 4 it can be seen that the equilibrium adsorption capacity of CEAMS-IIM ( q e ) is the highest, significantly superior to EAMS-IIM and CEAMS-NIM, indicating that the introduction of carboxylated carbon nanotubes and imprinting technology synergistically improve the adsorption capacity for gadolinium ions. The Langmuir model has a better fitting effect ( R 2 close to 1), indicating that the adsorption behavior of the three materials is more in line with monolayer chemisorption, and the surface adsorption sites are evenly distributed. The fitting degree of the Freundlich model is relatively low, indicating that the adsorption process is less affected by surface heterogeneity and multilayer adsorption, further supporting the monolayer-dominated adsorption mechanism.

[0076] The adsorption capacities of the imprinted functionalized straw adsorbent in Example 2, the non-imprinted functionalized straw adsorbent in Comparative Example 3, and the imprinted functionalized straw adsorbent without doped carboxylated carbon nanotubes in Comparative Example 4 for gadolinium ions are 59.82 mg / g, 45.02 mg / g, and 39.54 mg / g, respectively. Among them, the imprinted functionalized straw adsorbent in Example 2 has the best adsorption performance for gadolinium ions, mainly due to the chemical complexation of carboxyl functional groups in the imprinting sites with gadolinium ions and the specific selectivity effect of steric hindrance, indicating that abundant imprinting active sites can enhance the adsorption performance of the adsorbent for gadolinium ions.

[0077] Meanwhile, the adsorption capacities of the materials prepared in Example 1, Example 3, Comparative Examples 1-2, and Comparative Examples 5-6 were tested, and the results are as follows: The adsorption capacities of the imprinted functionalized straw adsorbent in Example 1, the non-imprinted functionalized straw adsorbent in Comparative Example 1, and the imprinted functionalized straw adsorbent without doped carboxylated carbon nanotubes in Comparative Example 2 for gadolinium ions are 50.66 mg / g, 41.88 mg / g, and 30.65 mg / g in sequence. The adsorption capacities of the imprinted functionalized straw adsorbent in Example 3, the non-imprinted functionalized straw adsorbent in Comparative Example 5, and the imprinted functionalized straw adsorbent without doped carboxylated carbon nanotubes in Comparative Example 6 for gadolinium ions are 51.07 mg / g, 42.94 mg / g, and 31.32 mg / g in sequence.

[0078] Figure 5 The adsorption kinetic data and model diagrams of the imprinted functionalized straw adsorbent (named CEAMS-IIM) prepared in step (3) of Example 2, the non-imprinted functionalized straw adsorbent (named CEAMS-NIIM) prepared in Comparative Example 3, and the imprinted functionalized straw adsorbent lacking carboxylated carbon nanotubes (named EAMS-IIM) prepared in Comparative Example 4 for gadolinium ions. PSOKMFit is the pseudo-second-order kinetic model, and PFOKMFit is the pseudo-first-order kinetic model.

[0079] From Figure 5 it can be seen that CEAMS-IIM has the fastest adsorption rate and reaches the adsorption equilibrium within a short time (about 300 minutes), while EAMS-IIM and CEAMS-NIM require a longer time (about 600 minutes), indicating that the carboxylated carbon nanotubes and the imprinting technology cooperate to improve the mass transfer efficiency. The pseudo-second-order kinetic model has a better fit (R² is close to 1), indicating that the adsorption process is mainly chemical adsorption, involving ion exchange, coordination, or covalent bond interactions; the fitting degree of the pseudo-first-order kinetic model is lower, indicating that the contribution of physical adsorption is smaller.

[0080] It can be seen from the comparison between Example 2 and Comparative Examples 3-4 that the specific cavities formed by the imprinting technique improve the selectivity for gadolinium ions; the carboxylated carbon nanotubes provide abundant oxygen-containing functional groups (-COOH), enhancing the coordination with gadolinium ions; the synergistic effect of the two ensures that the prepared imprinted functionalized straw adsorbent has excellent adsorption selectivity and adsorption capacity.

Claims

1. A method for preparing an imprinted functionalized straw adsorbent, characterized in that: It consists of the following steps: (1) grinding rice straw into powder, soaking it in a sodium hydroxide solution for a period of time, and then filtering, washing, and drying to prepare pretreated straw powder; (2) adding the pretreated straw powder prepared in step (1), potassium persulfate and water into a reaction container and mixing them evenly, then dropping an acrylamide solution to carry out an oil bath reaction, and finally filtering, washing with water and drying to prepare amino-functionalized straw powder; (3) The amino-functionalized straw powder prepared in step (2) is dissolved in a first methanol-deionized water mixed solution, ethylenediaminetetraacetic anhydride is dissolved in a second methanol, and then the two are placed in a reaction container and mixed, followed by adding carboxylated carbon nanotubes and stirring, and finally adding gadolinium trichloride hexahydrate and continuing to stir. After the reaction is completed, post-treatment is performed to prepare an imprinted functionalized straw adsorbent.

2. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: In step (1), the rice straw is ground into powder, and the powder is controlled to pass through a 60-mesh sieve; In step (1), the concentration of the sodium hydroxide solution is 0.5 mol / L, the immersion temperature is 65° C., and the immersion time is 1 h; In step (1), the drying temperature is 40° C. and the drying time is 12 h.

3. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: In step (2), the pretreated straw powder, potassium persulfate and water prepared in step (1) are added into a reaction container and mixed evenly at a mixing temperature of 80° C. for 30 min. During the reaction of step (2), the stirring speed is controlled to be 1700 r / min; The temperature of the oil bath reaction in step (2) is 80° C., and the time of the oil bath reaction is 3 h.

4. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: The mass ratio of the pretreated straw powder, potassium persulfate and water in step (2) is 1:0.27:150; In step (2), the mass ratio of potassium persulfate to acrylamide in the acrylamide solution is 0.27:7.1-21.

3.

5. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: In step (2), the acrylamide solution uses water as solvent and has a mass concentration of 12.43%-29.87%; In step (2), the washing time is 15 minutes, the drying temperature is 40°C, and the drying time is 8 hours.

6. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: In step (3), the mass ratio of amino-functionalized straw powder, ethylenediaminetetraacetic anhydride, carboxylated carbon nanotubes, and gadolinium trichloride hexahydrate is 1:3-9:0.1:0.125-0.5; In step (3), the volume ratio of the first methanol to the deionized water in the first methanol-deionized water mixed solution is 1:

1.

7. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: In step (3), the mass volume ratio of the amino-functionalized straw powder to the first methanol-deionized water mixed solution is 1:20, expressed in g / mL.

8. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: In step (3), ethylenediaminetetraacetic anhydride is dissolved in the second methanol, and the mass volume ratio of ethylenediaminetetraacetic anhydride to the second methanol is 3-9:100, and the unit is g / mL.

9. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: In step (3), the stirring speed is controlled at 1700 r / min during the reaction, and finally gadolinium trichloride hexahydrate is added and stirring is continued for 24 hours.

10. The method for preparing the imprinted functionalized straw adsorbent according to claim 1, characterized in that: The post-treatment in step (3) is to filter the product, add ethanol and continue stirring for 16 hours at a stirring speed of 1500 r / min, filter again, immerse in 1 mol / L HCl solution for 12 hours, filter the product again, wash with deionized water, wash with 0.1 mol / L NaOH solution, wash with deionized water, and dry to obtain an imprinted functionalized straw adsorbent; wherein the ratio of the volume of ethanol to the sum of the volumes of the first methanol and the second methanol is 15:11.

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