A bio-based hierarchical porous adsorbent, its preparation method and application

Abstract

The present invention discloses a bio-based hierarchical porous adsorbent and its preparation method and application, belonging to the technical fields of materials science and environmental engineering. The preparation method includes: S1. Dissolve a metal salt in a CaCl2 solution and perform ultrasonic treatment to obtain a metal salt solution I; S2. Add terephthalic acid to deionized water, then add NaOH, perform ultrasonic treatment, and after complete dissolution, add a bio-based natural polymer and continuously stir for 2 h to obtain a ligand solution II; S3. Slowly drop the ligand solution II obtained in step S2 into the metal salt solution I, let it stand for aging, centrifuge to collect the precipitate, wash, freeze-dry, and grind to obtain the bio-based hierarchical porous adsorbent. The bio-based hierarchical porous adsorbent prepared by the present invention exhibits excellent adsorption performance towards various organic dye molecules and has important application potential in the treatment of industrial wastewater and printing and dyeing wastewater.

Description

Technical Field

[0001] The present invention belongs to the technical fields of materials science and environmental engineering, and particularly relates to a bio-based hierarchically porous adsorbent, a preparation method thereof, and an application thereof. Background Art

[0002] In current industrial production, wastewater discharge, especially the discharge of organic pollutants, has caused serious damage to the ecological environment. Particularly in industries such as printing and dyeing, textile, and pigment manufacturing, the problem of dye wastewater discharge is particularly prominent. According to statistics, the global annual output of dyes exceeds 700,000 tons. Untreated dye wastewater is highly toxic and difficult to degrade, posing a major threat to the ecological environment and human health. Traditional sewage treatment technologies, such as filtration, coagulation, and sedimentation, often cannot efficiently remove dye pollutants, and there are problems such as low treatment efficiency and long treatment cycles. Therefore, it has become particularly important to develop rapid, efficient, and low-cost printing and dyeing wastewater treatment technologies. The adsorption method has become one of the widely used printing and dyeing wastewater treatment technologies due to its advantages of economic efficiency, simple operation, and no secondary pollution. Activated carbon, polymer materials, and metal-organic frameworks are common adsorption materials, but they have problems such as low adsorption efficiency, high cost, and complex synthesis.

[0003] Metal-organic framework materials (MOFs) have shown potential in the field of water treatment due to their large specific surface area and adjustable pore size. However, MOFs in powder form are prone to agglomeration, resulting in a decrease in adsorption efficiency. For this reason, researchers have begun to focus on natural renewable resources, such as chitosan, cellulose, cyclodextrin, and sodium alginate, etc. These materials show application potential in the field of water treatment. Sodium alginate (SA), as a polysaccharide derived from natural brown algae, has the advantages of wide source, simple extraction process, and low cost. It contains a large number of carboxyl (-COOH) and hydroxyl (-OH) groups, and can form chelates with polyvalent metal ions to prepare a bio-polymer-based hydrogel-type adsorbent. However, the dye adsorption capacity of sodium alginate is relatively low, and its structural stability needs to be improved.

[0004] Therefore, developing low-cost, green, and efficient adsorbents and applying them to the treatment of printing and dyeing wastewater has become an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a bio-based hierarchically porous adsorbent, a preparation method thereof, and an application thereof. The bio-based hierarchically porous adsorbent exhibits excellent adsorption performance towards various organic dye molecules.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A preparation method of a bio-based hierarchically porous adsorbent, comprising the following steps:

[0008] S1. Dissolve the metal salt in a 1 - 1.5 wt% CaCl 2 solution, and perform ultrasonic treatment to obtain metal salt solution I;

[0009] S2. Add terephthalic acid to deionized water, then add solid NaOH until the final concentration is 0.5 - 1 wt%, perform ultrasonic treatment, and after complete dissolution, add a bio - based natural polymer until the final concentration is 1 - 1.5 wt%, and continuously stir for 2 h to obtain ligand solution II;

[0010] S3. Slowly drip the ligand solution II obtained in step S2 into the metal salt solution I obtained in S1, let it stand and age, centrifuge to collect the precipitate, wash it, freeze - dry it, and grind it to obtain a bio - based hierarchical porous adsorbent.

[0011] Preferably, in step S1, the metal salt is selected from one of metal salts of Al, Fe, Zr, Ce, Co, Mn or a mixture of metal salts of Al - Fe, Fe - Zr, Zr - Ce, Fe - Co.

[0012] Preferably, in step S1, the ultrasonic process parameters are: ultrasonic frequency is 40 kHz, ultrasonic power is 100 W, ultrasonic time is 5 - 10 min, and ultrasonic temperature is 25 °C.

[0013] Preferably, in step S2, the ultrasonic process parameters are: ultrasonic frequency is 40 kHz, ultrasonic power is 100 W, ultrasonic time is 5 - 10 min, and ultrasonic temperature is 25 °C.

[0014] Preferably, in step S2, the bio - based natural polymer is selected from one of sodium alginate, chitin, chitosan, and cellulose.

[0015] Preferably, in step S3, when slowly dripping the ligand solution II obtained in step S2 into the metal salt solution I, let it stand and age for 15 - 20 h, and centrifuge at 10000 rpm for 5 - 10 min.

[0016] Preferably, in step S3, wash the precipitate collected by centrifugation 3 times with deionized water, and freeze - dry it at - 50 °C for 12 - 24 h.

[0017] The present invention also provides a bio - based hierarchical porous adsorbent prepared by the preparation method as described above.

[0018] The present invention also provides an application of the bio - based hierarchical porous adsorbent prepared by the preparation method as described above or the bio - based hierarchical porous adsorbent in wastewater purification.

[0019] Compared with the prior art, the present invention has the following advantages and technical effects:

[0020] The present invention provides a bio-based hierarchically porous adsorbent and a preparation method thereof. By using natural bio-based renewable polymer materials, under room-temperature aqueous conditions, the present invention can construct a novel green and environmentally friendly adsorbent with a hierarchically porous structure in one step. This preparation process simplifies the traditional multi-step synthesis method, avoids the use of harmful chemicals and high-temperature conditions, and reduces energy consumption and environmental impact.

[0021] The bio-based hierarchically porous adsorbent prepared by the present invention exhibits excellent adsorption performance towards various organic dye molecules. Especially in removing organic dyes such as Congo red, its performance far exceeds that of the prior art. Under neutral conditions, the saturated adsorption capacity of this adsorbent reaches 1980 mg / g, while under acidic conditions, its adsorption capacity is significantly increased to 4128 mg / g, showing sensitivity and adaptability to pH conditions. The adsorbent of the present invention has important application potential in treating industrial wastewater and dye wastewater.

[0022] The raw materials used in the present invention, such as sodium alginate and metal salts, etc., are not only low in price and easy to obtain, but also all environmentally friendly materials, enhancing the environmental protection characteristics of the present invention. The green environmental protection of the synthesis conditions and the simplicity and high efficiency of the synthesis process provide a solid foundation for the industrial production and commercial application of the present invention.

[0023] The technical solutions of the present invention will be further described in detail below through the accompanying drawings and examples. Description of the Drawings

[0024] Figure 1 It is the preparation flow chart of the bio-based hierarchically porous adsorbent of the present invention;

[0025] Figure 2 It is the SEM images of the adsorbents provided in Example 1 and Comparative Example 1 of the present invention. Among them, Figure 2 (a) is the SA morphology structure of Comparative Example 1 with a scale of 100 μm, Figure 2 (b) is the SA morphology structure of Comparative Example 1 with a scale of 10 μm, Figure 2 (c) is the SA@MIL-53(Al) morphology structure of Example 1 with a scale of 400 nm, Figure 2 (d) is the SA@MIL-53(Al) morphology structure of Example 1 with a scale of 200 nm, Figure 2 (e) is the SA@MIL-53(Al) morphology structure of Example 1 with a scale of 1 μm, Figure 2 (f) is the C element distribution map of SA@MIL-53(Al) of Example 1, Figure 2 (g) is the O element distribution map of SA@MIL-53(Al) of Example 1, Figure 2In (h), it is the elemental distribution map of Al in SA@MIL-53(Al) of Example 1, Figure 2 In (i), it is the elemental distribution map of Ca in SA@MIL-53(Al) of Example 1;

[0026] Figure 3 XRD, FTIR, BET and BJH characterization results of SA@MIL-53(Al), SA, and MIL-53(Al) adsorbents provided in Example 1, Comparative Example 1, and Comparative Example 2 are shown. Among them, Figure 3 In (a), it is the XRD pattern, Figure 3 In (b), it is the FTIR pattern, Figure 3 In (c), it is the BET pattern, Figure 3 In (d), it is the BJH pattern;

[0027] Figure 4 The performance test results of the SA@MIL-53(Al) adsorbent provided in Example 1 of the present invention are shown. Among them Figure 4 In (a), it is the adsorption result diagram of SA@MIL-53(Al) for 5 dye molecules, Figure 4 In (b), it is the change trend of the adsorption amount of SA@MIL-53(Al) for CR with contact time; Figure 4 In (c), it is the influence of the dosage of SA@MIL-53(Al) on the CR removal efficiency; Figure 4 In (d), it is the change of the adsorption effect of SA@MIL-53(Al) on CR in the pH range of 3 - 11; Figure 4 In (e), it is the pHpzc test result of SA@MIL-53(Al), Figure 4 In (f), it is the change of the relationship between the adsorption capacity of SA@MIL-53(Al) and the initial dye concentration;

[0028] Figure 5 The adsorption isotherm fitting diagram of the SA@MIL-53(Al) adsorbent for CR provided in Example 1 of the present invention is shown. Among them Figure 5 In (a), it is the non-linear adsorption isotherm of the Langmuir model for SA@MIL-53(Al), Figure 5 In (b), it is the non-linear adsorption isotherm of the Freundlich model for SA@MIL-53(Al); Figure 5 In (c), it is the non-linear adsorption isotherm of the Temkin model for SA@MIL-53(Al); Figure 5 In (d), it is the non-linear adsorption isotherm of the Redlich-Peterson model for SA@MIL-53(Al). Detailed implementation manners

[0029] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0030] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention pertains.

[0031] In the present invention, unless otherwise specified, other test materials and instrument devices are all conventional test materials in the art and can be obtained through commercial channels.

[0032] Example 1

[0033] This example provides a bio-based hierarchical porous adsorbent, and the preparation method includes the following steps:

[0034] S1. Dissolve 50 mmol of AlCl 3 in 50 mL of 1 wt% CaCl 2 solution, and perform ultrasonic treatment for 5 min at a frequency of 40 kHz, a power of 100 W, and 25 °C to obtain metal salt solution I;

[0035] S2. Add 50 mmol of terephthalic acid to 50 mL of deionized water, and then add solid NaOH until the final concentration is 0.5 wt%. Perform ultrasonic treatment for 5 min at a frequency of 40 kHz, a power of 100 W, and 25 °C. After complete dissolution, add solid sodium alginate until the final concentration is 1 wt%, and continuously stir for 2 h to obtain ligand solution II;

[0036] S3. Slowly drop the ligand solution II obtained in step S2 into the metal salt solution I, stand for aging for 15 h, centrifuge at 10000 rpm for 5 min to collect the precipitate, wash it 3 times with deionized water, freeze-dry it at -50 °C for 12 h, and grind it to obtain the bio-based hierarchical porous adsorbent SA@MIL-53(Al).

[0037] Example 2

[0038] This example provides a bio-based hierarchical porous adsorbent, and the preparation method includes the following steps:

[0039] S1. Dissolve 100 mmol of AlCl 3 in 100 mL of 1.5 wt% CaCl 2 solution, and perform ultrasonic treatment for 10 min at a frequency of 40 kHz, a power of 100 W, and 25 °C to obtain metal salt solution I;

[0040] S2. Add 100 mmol of terephthalic acid to 100 mL of deionized water, then add solid NaOH to a final concentration of 1 wt%, and under the conditions of a frequency of 40 kHz, a power of 100 W, and a temperature of 25 °C, perform ultrasonic treatment for 10 min. After complete dissolution, add chitin to a final concentration of 1.5 wt%, and continuously stir for 2 h to obtain ligand solution II;

[0041] S3. Slowly drop the ligand solution II obtained in step S2 into metal salt solution I, let it stand and age for 20 h, centrifuge at 10000 rpm for 10 min to collect the precipitate, wash it 3 times with deionized water, freeze-dry it at -50 °C for 24 h, and grind it to obtain the bio-based hierarchical porous adsorbent.

[0042] Comparative Example 1 This comparative example provides an alginate adsorbent SA, and the preparation method is as follows:

[0043] At room temperature, slowly drop 50 mL of 1 wt% sodium alginate into 50 mL of 1 wt% CaCl 2 and let it stand and age for 18 hours to obtain white spherical objects. Perform vacuum filtration, wash the obtained solid several times with deionized water, and freeze-dry it to obtain the alginate adsorbent SA.

[0044] Comparative Example 2 This comparative example provides an MIL-53(Al) adsorbent, and the preparation method is as follows: Dissolve 50 mmol of AlCl 3 ·6H 2 O) in 50 mL of deionized water, and under the conditions of a frequency of 40 kHz, a power of 100 W, and a temperature of 25 °C, perform ultrasonic treatment for 5 min to obtain a uniform metal salt solution. Add 50 mmol of H 2 BDC to 50 mL of deionized water, add 100 mmol of NaOH, and under the conditions of a frequency of 40 kHz, a power of 100 W, and a temperature of 25 °C, perform ultrasonic treatment for 5 min to fully dissolve it and obtain a uniform ligand solution. Slowly drop the above ligand solution into the metal salt solution, stir for 12 hours, centrifuge at 10000 rpm for 5 minutes, then wash the obtained solid several times with deionized water, freeze-dry it, and grind it to obtain MIL-53(Al).

[0045] The adsorbents provided in Example 1 and Comparative Examples 1-2 above were verified for their effects through the following tests:

[0046] Physicochemical characterization: 1. The micro-morphologies of the alginate adsorbent provided in Comparative Example 1 and the bio-based hierarchical porous adsorbent SA@MIL-53(Al) provided in Example 1 were characterized by SEM, and the results are as Figure 2 .

[0047] As can be seen from Figure 2 , Figure 2In (a) and (b) are the morphological structures of the sodium alginate adsorbent. Similar to the literature reports, a sponge-like structure is formed due to the sublimation of ice during the freeze-drying process. From Figure 2 in (c)- Figure 2 in (e), it can be seen that the microscopic morphology of the bio-based hierarchically porous adsorbent SA@MIL-53(Al) provided in Example 1 exhibits obvious hierarchically porous characteristics. MIL-53(Al) uses SA as an attachment skeleton and grows into a "coral"-like structure. The entire adsorbent contains both the microporous channels of the MOF and has more macroporous / mesoporous parts. From Figure 2 the element distribution results in (f)-(i), it can be seen that C, O, Al, and Ca elements are relatively evenly distributed in the SA@MIL-53(Al) structure, and the content of Al element is more abundant than that of Ca element.

[0048] 2. The adsorbents provided in Example 1 and Comparative Examples 1-2 were characterized by XRD, FTIR, and BET, and the results are as Figure 3 .

[0049] The XRD patterns of SA, MIL-53(Al), and SA@MIL-53(Al) are as shown in Figure 3 (a). The XRD spectrum of SA shows an obvious broad peak at 2θ = 22°, revealing the amorphous structure of SA. The XRD pattern of MIL-53(Al) has characteristic diffraction peaks at 2θ = 17.36°, 25.11°, 27.89°, and 31.70° for the MIL-53(Al) structure. The XRD pattern of SA@MIL-53(Al) shows the characteristic spectral band of SA around 2θ = 22°. At the same time, the characteristic peaks of MIL-53(Al) appear at 2θ = 17.34°, 25.14°, 27.87°, and 31.63°, indicating that Al-MOF was successfully loaded on the surface of the SA matrix.

[0050] Fourier transform infrared spectroscopy (FTIR) analysis was performed on different samples, and the results are as shown in Figure 3 (b). The peaks at 1600 cm -1 and 1510 cm -1 , 1410 cm -1 correspond to the asymmetric and symmetric stretching vibrations of the carboxyl group respectively. The peak around 1700 cm -1 corresponds to the uncoordinated carboxylate salt, indicating that there are free carboxyl groups in the structure, which can produce more hydrogen bond interactions. The characteristic absorption peaks at 1020 cm -1 and 1130 cm -1 are for the formation of Al 3+ -O bonds with the ligand, indicating that the metal ion is connected to terephthalic acid through Al-O coordination bonds. At 3420 cm -1The absorption peak nearby corresponds to the absorption peak of water molecules on the adsorbent surface.

[0051] Figure 3 As can be seen from (c) in, the N of SA@MIL-53(Al) 2 The adsorption / desorption isotherm is of type IV, and the hysteresis loop is of type H3. After measurement, the BET specific surface area of this adsorbent is 22.797 m 2 / g. Figure 3 As can be seen from (d) in, the total pore volume is 0.089 cm 3 / g, the most accessible pore diameter is 11.479 nm, and the larger pore diameter is beneficial to reducing the mass transfer resistance and providing more effective adsorption sites.

[0052] 3. Performance tests were carried out on the SA@MIL-53(Al) adsorbent provided in Example 1, and the test method is as follows: Prepare undiluted stock solution (2500 mg L -1 ). Dissolve a certain amount of IC, MO, CR, RhB, and CV dyes in different glass jars with distilled water respectively. Then dilute the stock solution to the required concentration with a beaker for further research. After adsorption, the adsorbent was separated from the reaction solution by centrifugation. Then, the supernatant was detected with a UV-visible spectrophotometer at the maximum absorption wavelength (λ max ) of the dye solution determined previously. The effects of contact time (0 - 120 min), adsorbent dosage (0.1 - 1 mg / ml), pH (3 - 11), temperature (25 - 45 °C), and initial pollutant concentration (100 - 2500 mg / L) on the adsorption capacity of SA@MIL-53(Al) were studied. After treatment, the maximum absorption wavelength of each analyte was determined by UV-visible spectrophotometry, and the concentration of the pollutant was calculated. All experiments were repeated 2 times, and the average value was taken for data analysis. The adsorption capacity of SA@MIL-53(Al) for pollutants and the percentage of pollutant removal were calculated using Equations (1) and (2). The calculation formulas are as follows:

[0053]

[0054] Where C 0 and C e (mg L -1 ) are the initial concentration and final concentration of the dye solution respectively; q e (mg g -1 ) is the absorption capacity of the adsorbent at equilibrium; m (g) is the mass of the adsorbent SA@MIL-53(Al); V (L) is the solution volume. The results are as Figure 4 .

[0055] From Figure 4As can be seen from (a) in [reference], the adsorbent SA@MIL-53(Al) has different adsorption effects on five dye molecules, namely indigo carmine (IC), crystal violet (CV), congo red (CR), methyl orange (MO), and rhodamine B (RhB). In different dye wastewaters, SA@MIL-53(Al) has the highest adsorption removal rate for congo red.

[0056] Figure 4 (b) in [reference] shows the variation trend of the adsorption capacity of SA@MIL-53(Al) for CR with contact time. When the CR concentration is 600 mg / L, more than 70% of the CR adsorbate is adsorbed within the first 20 minutes of the adsorption process, and the q t value reaches 860 mg / g, and then it rises slowly until it reaches a plateau at 80 minutes. The above results indicate that SA@MIL-53(Al) has the fastest adsorption rate for CR and has better affinity. As the contact time between the adsorbent / adsorbate increases, the adsorption sites on the surface of SA@MIL-53(Al) are gradually occupied, and the dye molecules begin to diffuse into the internal pores, resulting in a slowdown in the adsorption rate until it enters the equilibrium stage.

[0057] In Figure 4 As can be seen from (c) in [reference], the dosage of SA@MIL-53(Al) (2 - 20 mg) has different effects on the removal efficiency of CR. In a 600 mg / L CR solution, when only 2 mg of the adsorbent is added, the removal rate can reach 80.7%, which indicates that SA@MIL-53(Al) is an extremely efficient adsorption material. As the dosage of SA@MIL-53(Al) gradually increases, the removal rate of CR also gradually increases to 93.4%. This is because a higher dosage of the adsorbent provides sufficient active sites for the removal of CR. When the dosage of SA@MIL-53(Al) increases to 10 mg, the removal rate of CR is close to the maximum value.

[0058] Figure 4 (d) in [reference] shows the change in the adsorption effect of the adsorbent SA@MIL-53(Al) on CR in the pH range of 3 - 11. The results show that when the CR concentration is 600 mg / L and pH = 3, SA@MIL-53(Al) can completely remove CR in only 20 minutes. At pH = 5, 7, and 9, SA@MIL-53(Al) can still maintain good adsorption performance and adsorption rate, and has good pH tolerance. However, when pH = 11, the adsorption performance of the adsorbent begins to decline. The reason may be that CR is an azo anionic dye containing a negatively charged sulfonic acid group (SO 3 - 3

[0059] From Figure 4As can be seen from (e) in [reference], the isoelectric point of SA@MIL-53(Al) is 3.5. Therefore, at pH = 3, an electrostatic attraction can be generated between the positively charged adsorbent and CR. As the pH increases, the charge of SA@MIL-53(Al) changes from positive to negative, and the electrostatic attraction between it and CR turns into electrostatic repulsion, resulting in a decrease in the adsorption performance due to the electrostatic repulsion. On the other hand, under strongly alkaline conditions, there will be many OH- molecules in the solution competing with CR for adsorption sites, leading to a decrease in the adsorption performance of the adsorbent.

[0060] Figure 4 (f) in [reference] shows the relationship change between the adsorption capacity of the adsorbent and the initial dye concentration. Under neutral conditions, when the initial concentration of CR is between 100 mg / L and 2000 mg / L, the equilibrium adsorption capacity increases significantly. When the CR concentration is 1500 mg / L, the upward trend begins to slow down, and the maximum adsorption amount is about 1980 mg / g. At pH = 3, the maximum adsorption amount of SA@MIL-53(Al) can reach 4128 mg / g, about twice that under neutral conditions, indicating that the adsorbent has better adsorption performance at a lower pH. Under neutral conditions, due to the presence of a large number of unoccupied adsorption sites on the surface of the adsorbent, CR molecules can easily interact on the surface of the adsorbent and quickly reach the adsorption equilibrium. A higher dye concentration will bring a greater mass transfer driving force, resulting in an increase in the maximum adsorption capacity. Therefore, as the initial dye concentration increases, the adsorption capacity of the adsorbent shows an upward trend. Thereafter, as the initial concentration of the adsorbate CR further increases, the adsorption sites of SA@MIL-53(Al) gradually become saturated, reaching a relatively stable adsorption plateau region.

[0061] 4. The SA@MIL-53(Al) provided in Example 1 was used for the adsorption isotherm fitting of CR, and the test scheme is as follows: Adsorption isotherms are often used to describe the relationship between the adsorbent and the adsorbate under equilibrium conditions.

[0062] The Langmuir, Freundlich, Temkin, and Redlich–Peterson models were used to simulate the CR adsorption process. The Langmuir model used to explain monolayer adsorption is represented by Equation (3); the Freundlich model characterizes multilayer adsorption in a non-uniform environment and is represented by Equation (4); the Temkin model explains the behavior of the solute at the diffusion interface as shown in Equation (5); the Redlich–Peterson model was used to explain the mixed adsorption behavior as shown in Equation (6). This mixed isotherm model has the characteristics of both the Langmuir model and the Freundlich model, and the calculation formula is as follows:

[0063] C e / q e =1 / KL q m + C e / q m

[0064] Equation (3)

[0065] log q e = log K F + 1 / n log C e

[0066] Equation (4)

[0067] q e = B T ln K L + B T ln C e

[0068] Equation (5)

[0069]

[0070] Where C e (mg / L) is the equilibrium concentration of the dye in the solution, q m (mg / g) is the maximum adsorption capacity. K L (L / mg) and K F (mg 1-(1 / n) L 1 / n g -1 ) are the Langmuir and Freundlich model constants, respectively. K T (L / mg) and B T (J·mol -1 ) are the Temkin constants representing the maximum equilibrium binding energy and the adsorption heat, respectively. K RP is the Redlich-Peterson constant related to the adsorption capacity (L·g -1 ), α RP is the binding site affinity (mg -1 ), and β is the isotherm index. The non-linear adsorption isotherms of the four models are as Figure 5 shown, and the adsorption parameters are listed in Table 1.

[0071] Table 1 Adsorption parameters

[0072]

[0073]

[0074] It can be seen from Figure 5 that the correlation coefficient (R 2)Between 0.92 and 0.96. Compared with other adsorption models, the correlation coefficient (R 2 = 0.96) of the Freundlich model is higher than that of other model equations, indicating that the adsorption of CR by SA@MIL-53(Al) may be multilayer adsorption. In addition, the n value in the Freundlich model represents the ease of adsorption. Generally, an n value less than 0.5 is considered difficult to adsorb, while 2 - 10 is considered easy to adsorb.

[0075] In Table 1, the n value of SA@MIL-53(Al) is 2.66, indicating that the adsorption process is easy to carry out. In addition, the Redlich-Peterson model also has a high correlation (R 2 = 0.944), indicating that there are both physical adsorption and chemical adsorption of CR on the non-uniform surface. In the calculation results of the Temkin model, the adsorption heat b T is 4.938 J / mol, indicating that the adsorption process is an endothermic reaction. The Langmuir fitting results show that the maximum theoretical adsorption capacity of SA@MIL-53(Al) for CR is 2032 mg / g, which is relatively close to the q e value (1980 mg / g) of the actual test results.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements cannot make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a bio-based hierarchical porous adsorbent, characterized in that: The steps include: S1, dissolving a metal salt in a 1-1.5 wt% CaCl2 solution, and ultrasonically treating the solution to obtain a metal salt solution I; S2, adding terephthalic acid to deionized water, then adding solid NaOH to a final concentration of 0.5-1 wt%, ultrasonic treatment, and adding bio-based natural polymer to a final concentration of 1-1.5 wt% after complete dissolution, and stirring for 2 hours to obtain ligand solution II; S3, slowly dripping the ligand solution II obtained in step S2 into the metal salt solution I in step S1, allowing to stand for aging, collecting the precipitate by centrifugation, washing, freeze-drying, and grinding to obtain a bio-based hierarchical porous adsorbent; In step S2, the bio-based natural polymer is selected from one of sodium alginate, chitin, chitosan, and cellulose; In step S3, the ligand solution II obtained in step S2 is slowly dripped into the metal salt solution I, and the mixture is allowed to stand for aging for 15-20 hours, and centrifuged at 10,000 rpm for 5-10 minutes.

2. The preparation method according to claim 1, characterized in that: In step S1, the metal salt is selected from one of Al, Fe, Zr, Ce, Co, Mn metal salts or a mixture of Al-Fe, Fe-Zr, Zr-Ce, Fe-Co metal salts.

3. The preparation method according to claim 1, characterized in that: The ultrasonic process parameters in step S1 are: ultrasonic frequency of 40 kHz, ultrasonic power of 100 W, ultrasonic time of 5-10 min, and ultrasonic temperature of 25°C.

4. The preparation method according to claim 1, characterized in that: The ultrasonic process parameters in step S2 are: ultrasonic frequency of 40 kHz, ultrasonic power of 100 W, ultrasonic time of 5-10 min, and ultrasonic temperature of 25°C.

5. The preparation method according to claim 1, characterized in that: In step S3, the precipitate collected by centrifugation is washed three times with deionized water and freeze-dried at -50°C for 12-24 h.

6. The bio-based hierarchical porous adsorbent prepared by the preparation method according to any one of claims 1 to 5.

7. Use of the bio-based hierarchical porous adsorbent as claimed in claim 6 in wastewater purification.

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