Beta-cyclodextrin-modified polyvinyl alcohol-sodium alginate aerogel, method of making and use thereof

Abstract

The application discloses a beta-CD modified polyvinyl alcohol-sodium alginate aerogel, a preparation method and application thereof, the specific surface area of the aerogel is 2.29 m 2 / g, and the average pore size is 13.4 nm; when the aerogel is enlarged to 300 mu m, the aerogel shows an uneven porous reticular structure, the thickness of the reticular structure wall is fine and adjacent holes are blocked. The oxygen content of the aerogel is close to 70%, the aerogel has good selectivity to rare earth elements europium (Eu), gadolinium (Gd) and dysprosium (Dy), and the maximum adsorption capacities are 222.22 mg / g, 217.39 mg / g and 204.08 mg / g respectively. The cyclic regeneration experiment shows that after 6 times of adsorption-desorption, the adsorption efficiency of the aerogel to Eu, Dy and Gd still remains at 96%, and the desorption efficiency remains at 94%. The aerogel is used for recovery of rare earth elements in simulated acid mine water, and in the case that the concentration of competitive ions is 3 orders of magnitude higher than that of rare earth ions, the adsorption rate of the aerogel to rare earth elements is more than 99%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aerogel production, in particular to a β-CD modified polyvinyl alcohol-sodium alginate aerogel, a preparation method and application thereof. BACKGROUND

[0002] Rare earth elements are a total of 17 elements including 15 lanthanide series elements and yttrium and scandium. Due to the unique electronic layer structure, rare earth elements have excellent magnetic, optical, electrical and other physical and chemical properties, and play an important role in emerging industries such as new energy vehicles, electronic information, aerospace and high-end equipment manufacturing. It is an indispensable core basic material.

[0003] Rare earth elements are prone to environmental pollution during development and use. For example, strong acid or strong alkali solution is often used in rare earth mining, and the direct discharge of the generated acid mine wastewater will pollute the environment, which also contains heavy metals, flotation reagents and the like, resulting in that rare earth ions cannot be effectively recycled and reused. Rare earth resources are limited and cannot be quickly regenerated after mining.

[0004] Existing recycling of substances contained in rare earth wastewater mainly adopts adsorption, precipitation, extraction, ion exchange, membrane dialysis and the like. Compared with other technologies, the adsorption technology has the advantages of high efficiency, simple operation and reusability, and is a widely used rare earth recycling technology.

[0005] Gel is an important adsorbent material, which is easy to recover and simple to synthesize with abundant raw materials. Natural polymer materials are prone to degradation in complex solution systems, which seriously affects the service life of the adsorbent. Existing studies have shown that materials formed by combining natural polymers with synthetic polymers have the advantages of both, and have good biocompatibility and mechanical strength.

[0006] Sodium alginate (SA) is a natural polymer material mainly derived from linear anionic polysaccharides in marine brown algae, which is rich in hydroxyl and carboxyl groups and can be complexed with metal ions. It has become one of the most commonly used materials for preparing adsorption gels.

[0007] Polyvinyl alcohol (PVA) is a synthetic polymer material rich in active hydroxyl groups, which has excellent chemical resistance, biodegradability and biocompatibility, and is often used to enhance the mechanical strength of materials.

[0008] The aerogel made of polyvinyl alcohol (PVA) and sodium alginate (SA) has the advantages of both, but the adsorption equilibrium and adsorption performance of the composite gel made by the existing method are not ideal, and it is usually not used as an adsorbent. To solve this problem, existing methods mainly add substances with adsorption function to increase active adsorption sites in order to improve the defects of PVA-SA adsorbents.

[0009] Among various modification reagents, β-cyclodextrin (β-CD) is a natural cyclic oligosaccharide with a large number of oxygen-containing functional groups on the outer surface and can bond a variety of organic / inorganic ions and molecules. For example, an elastic aerogel and a preparation method thereof disclosed in CN 202210082200.0, wherein only cyclodextrin is used as a pore-forming agent, and the aerogel with strong adsorption capacity for rare earth elements prepared by simultaneously using cyclodextrin, polyvinyl alcohol and sodium alginate is not disclosed. The prior art mainly discloses that the aerogel obtained by using a water-based pore-forming agent has high elasticity, fatigue resistance, and a multi-level structure with a porous shape and thin-layer porous fibrous pore walls in the interior.

[0010] The prior art does not disclose an aerogel adsorbent capable of effectively recovering rare earth ions in a complex solution system.

[0011] The existing common adsorbent for rare earth elements can only be in the form of small particles to ensure the contact area or be loaded on a porous small particle carrier for adsorption. Due to the small particle size, it is difficult to recover after use, which easily causes secondary pollution. The adsorption capacity of the existing common adsorbent for rare earth elements is usually not high, the recyclability is insufficient, the preparation steps are complex, and the cost is high.

[0012] The information disclosed in the background section is only intended to increase the understanding of the overall background of the present application and should not be considered as acknowledging or implying in any form that the information constitutes prior art known to those of ordinary skill in the art. SUMMARY

[0013] The present application provides a β-CD modified polyvinyl alcohol-sodium alginate aerogel, a preparation method and applications thereof, which has a three-dimensional network porous structure, a clear thickness of the hole side wall, an average pore size of 13.4 nm, a specific surface area of 2.29 m 2 / g, and an oxygen content of nearly 70%. The aerogel has good selectivity for rare earth elements europium (Eu), gadolinium (Gd) and dysprosium (Dy), and the adsorption capacities are 222.22, 217.39 and 204.08 mg / g, respectively.

[0014] The present application provides a β-CD modified polyvinyl alcohol-sodium alginate aerogel, which has a specific surface area of 2.29 m 2 / g and an average pore size of 13.4 nm. When the aerogel is enlarged to 300 μm, a three-dimensional network porous structure is shown, and the wall thickness of the network structure is clear and separates adjacent pores.

[0015] Aerogels have higher specific surface area and porosity, and therefore have broad application prospects in the field of metal ion removal. The synthesized β-CD@PVA-SA aerogel has a large number of oxygen-containing functional groups on the outer surface, and therefore can be an attractive and potentially feasible option for removing pollutants in water.

[0016] Another aspect of the present application provides a rare earth element adsorbent comprising: the β-CD modified PVA-SA aerogel as described above.

[0017] Preferably, the rare earth element adsorbent is used by mixing the rare earth element adsorbent with a rare earth element-containing solution for 4-12 hours, filtering, and obtaining the rare earth element-adsorbed particles. The rare earth element-containing solution treated by the adsorbent can be pure water containing only rare earth elements, or a solution containing various impurities. When the impurities contained are solids, the rare earth element-containing solution can be subjected to conventional pretreatment operations such as filtration.

[0018] Preferably, the rare earth element is at least one of Eu, Dy, and / or Gd.

[0019] Preferably, the rare earth element-containing solution comprises at least one of alkali, alkaline earth, or heavy metal ions. The adsorbent can also be used to treat a solution containing at least one of alkali, alkaline earth, or heavy metal ions, and good adsorption efficiency can also be obtained when the solution contains multiple ions.

[0020] Preferably, the rare earth element-containing solution comprises at least one ion of K, Na, Mg, Ni, Zn, Ce, La, Nd, Pr, Sm, Tb, Ho, Er, Al, Mn, Ca, Mg, and Fe.

[0021] Preferably, the content of the β-CD modified PVA-SA aerogel in the rare earth adsorbent is greater than 50 mg / L; more preferably, the content of the β-CD modified PVA-SA aerogel in the rare earth adsorbent is 50-225 mg / L.

[0022] Preferably, the content of the β-CD modified PVA-SA aerogel in the rare earth adsorbent is 50, 75, 100, 125, 150, 175, 200, or 225 mg / L.

[0023] Another aspect of the present application also provides a preparation method of the β-CD modified PVA-SA aerogel, comprising the following steps:

[0024] 1) adding β-CD to a PVA solution and stirring to react at 60°C for 3 hours to obtain a grafted cyclodextrin PVA solution;

[0025] 2) adding glutaraldehyde to the grafted cyclodextrin PVA solution, crosslinking at 80°C for 3 hours, then adding a SA solution, and stirring at room temperature for 1-2 hours to obtain the β-CD modified PVA-SA aerogel.

[0026] Preferably, the method further comprises: preparing the β-CD modified PVA-SA aerogel into an aerogel bead.

[0027] Preferably, step 1) further comprises: adding β-CD into the PVA solution to obtain a reactant, dissolving epichlorohydrin in dimethyl sulfoxide, adding sodium hydroxide, mixing the obtained mixture with the reactant, and reacting at 60℃ for 3 hours to obtain a grafted β-CD polyvinyl alcohol solution.

[0028] Preferably, the mass concentration of the SA solution used is 3.85%; the mass concentration of the PVA solution used is 10.71%; and the mass concentration of the β-cyclodextrin added in the PVA solution is 7.41%.

[0029] The application can produce beneficial effects, including:

[0030] 1) The β-cyclodextrin modified polyvinyl alcohol-sodium alginate aerogel (β-CD@PVA-SA) provided by the application has a three-dimensional network porous structure, an average pore size of 13.4 nm, a specific surface area of 2.29 m 2 / g, and an oxygen content of nearly 70%. The adsorption capacity of the β-CD@PVA-SA for rare earth elements europium (Eu), gadolinium (Gd) and dysprosium (Dy) is 222.22 mg / g, 217.39 mg / g and 204.08 mg / g, respectively. In the presence of various competitive ions (alkali, alkaline earth and heavy metal ions), the removal rates of Eu, Dy and Gd are 84%, 88% and 84%, respectively, showing that the β-CD@PVA-SA has high adsorption performance and good element selectivity. In 6 adsorption-desorption cycles, the adsorption rate of the aerogel is maintained at more than 98%, showing excellent recycling ability.

[0031] 2) The β-cyclodextrin modified polyvinyl alcohol-sodium alginate aerogel provided by the application has a recovery rate of more than 99% for rare earth elements in nearly acidic mine water. The aerogel has the advantages of simple preparation process, high adsorption capacity, long service life, easy separation, and can be used as a regenerated rare earth adsorbent.

[0032] 3) The β-cyclodextrin modified polyvinyl alcohol-sodium alginate aerogel provided by the application uses inexpensive and green polyvinyl alcohol, sodium alginate and β-cyclodextrin as raw materials, and obtains the β-CD@PVA-SA aerogel through a simple reaction. After the aerogel is adsorbed in the solution to be treated, the separation of the adsorbent and the solution can be realized by only filtering, the adsorption material can be recycled, and secondary pollution can be avoided. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The FT-IR test results of the SA, PVA-SA and β-CD@PVA-SA obtained in Example 1 are provided for the application;

[0034] Figure 2XRD test results of SA, PVA-SA and β-CD@PVA-SA obtained in Example 1 are provided for the present application;

[0035] Figure 3 Constant temperature nitrogen adsorption-desorption test results of β-CD@PVA-SA obtained in Example 1 are provided for the present application;

[0036] Figure 4 SEM test results of β-CD@PVA-SA obtained in Example 1 are provided for the present application;

[0037] Figure 5 EDS results of β-CD@PVA-SA obtained in Example 1 are provided for the present application;

[0038] Figure 6 Experimental results of β-CD@PVA-SA obtained in Example 1 are provided for the present application, wherein (a) is Eu;

[0039] (b) is Dy; (c) is Gd;

[0040] Figure 7 Columnar analysis results of β-CD@PVA-SA obtained in Example 1 are provided for the present application, wherein (a) is Eu;

[0041] Figure 8 Columnar analysis results of β-CD@PVA-SA obtained in Example 1 are provided for the present application, wherein (a) is Eu;

[0042] Figure 9 Adsorption results of β-CD@PVA-SA obtained in Example 1 are provided for the present application, wherein (a) is Eu;

[0043] Figure 10 Desorption results of β-CD@PVA-SA obtained in Example 1 are provided for the present application, wherein (a) is Eu. DETAILED DESCRIPTION

[0044] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the accompanying drawings herein can be arranged and designed in various different configurations.

[0045] The following detailed description of embodiments of the application in the drawings provided is not intended to limit the scope of the application as claimed, but merely represents selected embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the application.

[0046] The technical means not described in detail in the present application and not used to solve the technical problems of the present application are set according to the common knowledge in the art, and various common knowledge setting methods can be implemented.

[0047] Embodiments

[0048] The materials and instruments used in the following examples are obtained from commercial channels unless otherwise specified; the detection methods used are existing methods unless otherwise specified.

[0049] Example 1 Preparation of β-CD@PVA-SA aerogel

[0050] 1) Preparation of sodium alginate (SA) solution: a suitable amount of SA was dissolved in deionized water under ultrasonic oscillation for 2 hours to obtain a 3.85% SA solution;

[0051] 2) Preparation of polyvinyl alcohol (PVA) solution: a suitable amount of PVA was dissolved in deionized water at 90°C to obtain PVA solutions with concentrations of 3.85%, 7.41%, and 10.71%.

[0052] 3) Grafting β-cyclodextrin (β-CD): after adding β-CD (mass concentration of added β-cyclodextrin 7.41%) to the PVA solution, continue stirring until the solution is clear again to obtain a reactant. After dissolving epichlorohydrin in dimethyl sulfoxide and adding sodium hydroxide, the obtained mixture is mixed with the reactant, and the mixture is reacted at 60°C for 3 hours to obtain a grafting β-CD polyvinyl alcohol solution.

[0053] 4) Crosslinking: add glutaraldehyde (mass concentration of added glutaraldehyde 13.64%) to the grafting cyclodextrin polyvinyl alcohol solution, and perform crosslinking reaction at 80°C for 3 hours to obtain a crosslinked PVA solution.

[0054] 5) Formation of double network structure: mix the SA solution with the crosslinked PVA solution, and stir at room temperature for 1-2 hours to obtain a mixed solution.

[0055] 6) Preparation of gel beads: drop the mixed solution into a calcium chloride (5%, w / v) solution at a rate of 1 drop per second, and soak in the calcium chloride solution overnight to obtain gel beads.

[0056] 7) Preparation of aerogel beads: The gel beads were frozen at -18 °C for 16-24 h and then freeze-dried to obtain β-CD@PVA-SA aerogel beads.

[0057] Example 2 Structural characterization of β-CD@PVA-SA aerogel

[0058] 1) FT-IR

[0059] The transmittance of SA, PVA-SA and β-CD@PVA-SA obtained in Example 1 was tested using FT-IR, and the results are shown in Figure 1 .

[0060] As shown in Figure 1 , SA showed strong characteristic absorption peaks at 3278.29 cm -1 (-OH stretching vibration), 2932.56 cm -1 (-C-H asymmetric stretching vibration), 1592.25 cm -1 and 1417.83 cm -1 (-COO- asymmetric and symmetric stretching vibration) and 1019.38 cm -1 (-C-O stretching vibration).

[0061] As shown in Figure 1 , PVA-SA showed an increased absorption peak intensity at 2926.26 cm -1 , which may be due to the increase in the content of -C-H caused by the addition of PVA. The peak of -C-O moved to 1085.27 cm -1 and 1025.58 cm -1 , which may be due to the formation of crosslinking points.

[0062] Compared with PVA-SA, β-CD@PVA-SA showed an increased intensity at 1589.15 cm -1 and a decreased intensity at 3278.29 cm -1 , which may be due to the successful grafting of β-cyclodextrin, which consumed the hydroxyl groups of polyvinyl alcohol and introduced carboxyl groups. These all prove the successful synthesis of β-CD@PVA-SA aerogel.

[0063] 2) XRD

[0064] The crystal structure of SA, PVA-SA and β-CD@PVA-SA obtained in Example 1 was studied using XRD, and the results are shown in Figure 2 .

[0065] As can be seen from Figure 2 , the characteristic peaks of SA appeared at 12.46 ° , indicating that SA has a crystal structure.

[0066] PVA incorporation PVA-SA resulting 19.6 ° The intensity of PVA diffraction peak in the results of β-CD@PVA-SA obtained after adding CD is significantly weakened, indicating that the functionalization process of the material destroys the original crystal properties of PVA.

[0067] The above results show that the successful synthesis of β-CD@PVA-SA aerogel.

[0068] 3) N2 adsorption-desorption

[0069] The specific surface area and pore size of the aerogel were studied by constant temperature nitrogen adsorption-desorption, and the results are shown in Figure 3 According to the BJH algorithm and pore size distribution curve, the specific surface area of β-CD@PVA-SA is 2.29 m 2 / g, and the average pore size is 13.4 nm.

[0070] 4) SEM

[0071] The morphology of the aerogel material β-CD@PVA-SA obtained in Example 1 was studied by scanning electron microscopy. As can be seen from Figure 4 , the material presents a three-dimensional network porous structure, the porous structure has high density, the network structure is dense, and can provide a large specific surface area.

[0072] 5) EDS

[0073] The elemental analysis of the aerogel material β-CD@PVA-SA obtained in Example 1 was carried out by energy dispersive spectrometer, and the results are shown in Figure 5 The distribution and percentage of C and O elements in the sample were determined. The oxygen content is close to 70%, mainly from hydroxyl, carboxyl, ester, ether bond and other oxygen-containing functional groups.

[0074] Example 3: Detection of the adsorption performance of rare earth ions of the aerogel material β-CD@PVA-SA

[0075] 1. The maximum adsorption capacity and selective adsorption performance of β-CD@PVA-SA for Eu, Dy and Gd:

[0076] 1) Dissolve europium nitrate hexahydrate, dysprosium nitrate hexahydrate and gadolinium nitrate hexahydrate in distilled water respectively to prepare 1000 mg / L stock solution. Dilute the stock solution to obtain standard solutions of different concentrations. The specific rare earth concentrations are 1, 5, 10 and 20 mg / L.

[0077] 2) The aerogel material β-CD@PVA-SA was mixed with rare earth ion solutions of different concentrations (50-225 mg / L, specifically 50, 75, 100, 125, 150, 175, 200, 225 mg / L), and placed in a shaker for adsorption at 25°C and 120 r / min for 4-12 hours. After separating the adsorbent from the solution, the concentration of each rare earth ion in the solution was tested by ICP-OES.

[0078] 3) The adsorption capacity and recovery rate in the equilibrium state were calculated according to the test results and formulas (1) and (2).

[0079]

[0080]

[0081] wherein Co represents the initial concentration of the rare earth ion, Ce represents the equilibrium concentration, and V and m respectively represent the solution volume and the adsorbent mass;

[0082] The adsorption capacity test results for Eu, Dy and Gd are shown in Figs. (a), (b) and (c), respectively. The test results show that the adsorption capacity of β-CD@PVA-SA for Eu, Dy and Gd is 222.22, 217.39 and 204.08 mg / g, respectively. Figure 6

[0083] 2. Detection of the adsorption performance of the aerogel for rare earth elements in the presence of various competitive ions (alkali, alkaline earth and heavy metal ions)

[0084] Fifteen mg of the β-CD@PVA-SA aerogel was added to a mixed solution of rare earth ions (Eu, Dy and Gd) and competitive ions (K, Na, Mg, Ni, Zn) with a concentration of 50 mg / L, and placed in a shaker for adsorption for 4 hours. After filtration, the concentration of each ion in the solution was tested by ICP-OES. According to the test results, the removal rate of the aerogel for Eu, Dy and Gd was 84%, 88% and 84%, respectively, while the removal rate of the competitive ions was not more than 14%. The obtained results are shown in the columnar analysis diagram of Figure 7 .

[0085] 3. Performance test of β-CD@PVA-SA for the recovery of rare earth elements in simulated acid mine water

[0086] The composition of the experimental solution is shown in the following table.

[0087] Table 1. Composition and concentration of the simulated acid mine water (solution pH = 3.1)

[0088]

[0089] ​

[0090] 15 mg of the β-CD@PVA-SA aerogel material was mixed with 25 mL of acid mine water at 25°C and 120 r / min for 4 hours, and the concentration of each ion in the solution was tested by ICP-OES after filtration.

[0091] The results are shown in Table 1. Figure 8 As shown in Table 1, the adsorption rate of the β-CD@PVA-SA aerogel material for rare earth elements was more than 99% when the concentration of the competitive ions was 3 orders of magnitude higher than that of the rare earth ions. The aerogel material still showed excellent selectivity for rare earth elements in the presence of various competitive ions (alkali, alkaline earth and heavy metal ions).

[0092] Example 4: Recycling experiment of the aerogel material β-CD@PVA-SA

[0093] In order to study the reusability of the β-CD@PVA-SA aerogel, 25 mg of the β-CD@PVA-SA aerogel was put into 10 mL of a 50 mg / L europium nitrate hexahydrate, dysprosium nitrate hexahydrate or gadolinium nitrate hexahydrate aqueous solution, and adsorbed at 25°C and 120 r / min for 5 hours.

[0094] The aerogel after adsorbing the rare earth elements was placed in an eluent of a mixture of 0.5 mol / L HCl and 0.1 mol / L CaCl2, and desorbed at 25°C and 120 r / min for 5 hours.

[0095] The adsorption-desorption operation was repeated 6 times.

[0096] The concentration of the rare earth ions in the adsorption solution and the elution solution was determined by ICP-OES, and the removal rate was calculated according to formula (3). The adsorption efficiency and the desorption efficiency were calculated according to the test results and formula (2) and (3).

[0097]

[0098] In formula (3), Co is the initial concentration of the rare earth ions, Ct is the concentration of the rare earth ions at a certain time, and Cde is the concentration of the rare earth ions in the elution solution after desorption.

[0099] The column chart of the recycling results of the aerogel material β-CD@PVA-SA is shown in Table 2. Figures 9-10 As shown in Table 2, the adsorption efficiency of the aerogel for Eu, Dy and Gd remained at 96% and the desorption efficiency remained at 94% after 6 times of adsorption-desorption.

[0100] As can be seen from Examples 2-4, the aerogel material provided by the present application can effectively adsorb rare earth elements in various solutions, and has high adsorption efficiency.

[0101] Although the present application has been described in detail with reference to the foregoing embodiments, the technical solutions recorded in the foregoing embodiments can be modified, or some of the technical features can be replaced by equivalent features, by those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. The application of β-CD modified polyvinyl alcohol-sodium alginate aerogel beads in the selective adsorption of rare earth elements, characterized in that, The preparation method of β-CD modified polyvinyl alcohol-sodium alginate aerogel beads includes the following steps: 1) Add β-CD to PVA solution and stir to obtain reactants. Dissolve epichlorohydrin in dimethyl sulfoxide and add sodium hydroxide. Mix the resulting mixture with the reactants and react at 60°C for 3 hours to obtain a polyvinyl alcohol solution grafted with cyclodextrin. 2) Glutaraldehyde was added to the polyvinyl alcohol solution grafted with cyclodextrin, and after crosslinking reaction at 80°C for 3 hours, SA solution was added, and after stirring at room temperature for 1-2 hours, a mixed solution was obtained. The mixed solution was added dropwise to a calcium chloride solution with a mass-volume concentration of 5% at a rate of 1 drop per second, and the solution was soaked in the calcium chloride solution overnight to obtain gel beads. 3) Freeze the gel beads at -18℃ for 16 to 24 hours, and then freeze-dry them to obtain β-CD modified polyvinyl alcohol-sodium alginate aerogel beads; The obtained β-CD modified polyvinyl alcohol-sodium alginate aerogel beads exhibit a three-dimensional network porous structure with an average pore size of 13.4 nm and a specific surface area of ​​2.29 m². 2 / g; In a solution containing rare earth elements, β-CD modified polyvinyl alcohol-sodium alginate aerogel beads achieved removal rates of 84%, 88%, and 84% for Eu, Dy, and Gd, respectively. The solution containing rare earth elements also includes K, Na, Mg, Ni and Zn ions; the rare earth elements in the solution are europium (Eu), gadolinium (Gd) and dysprosium (Dy).

2. The application according to claim 1, characterized in that, The concentration of rare earth ions in the solution containing rare earth elements is 50–225 mg / L.

3. The application according to claim 1, characterized in that, The concentration of rare earth ions in the solution containing rare earth elements is 50, 75, 100, 125, 150, 175, 200 or 225 mg / L.

4. The application according to claim 1, characterized in that, In the preparation method of β-CD modified polyvinyl alcohol-sodium alginate aerogel beads, the mass concentration of SA solution used was 3.85%; the mass concentration of PVA solution used was 10.71%; and the mass concentration of β-cyclodextrin added to the PVA solution was 7.41%.

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