Iron-ortho phenol-boric acid ternary composite adsorbent and preparation method and application thereof

Abstract

This invention discloses a ternary composite adsorbent based on iron-catechol-boric acid, its preparation method, and its application, belonging to the field of dyeing and printing wastewater treatment. The adsorbent of this invention uses tannic acid with a surface rich in catechol groups as a substrate. A stable metal-phenolic network is formed through the coordination of trivalent iron with catechol groups, efficiently capturing anions using metal bridging and electrostatic attraction to form the adsorption core. Boric acid groups are further introduced as specific recognition units, forming specific dynamic covalent bonds with the catechol groups of anionic dyes. Compared with traditional adsorbents, the adsorbent of this invention provides ultra-high adsorption capacity and selectivity through the synergistic effect of multiple mechanisms, including electrostatic adsorption, coordination complexation, hydrogen bonding, and reversible covalent bonding of borate ester bonds. It can achieve efficient desorption of dyes and recycling of materials, and efficiently and rapidly remove anionic dyes from water.

Description

Technical Field

[0001] This invention belongs to the field of dyeing and printing wastewater treatment, specifically relating to a ternary composite adsorbent based on iron-catechol-boric acid, its preparation method, and its application. Background Technology

[0002] As one of the earliest countries to develop textiles and dyeing technology, my country has witnessed rapid industrialization and economic growth in recent years. The textile industry has undergone a leap from manual to mechanized and automated processes, resulting in a sharp increase in production efficiency and a wide variety of products. However, the dyeing process requires anionic dyes, which have low utilization rates and consume large amounts of water and salt compounds. This has led to the generation of dyeing wastewater with high salt content, significant water quality variations, high color intensity, and poor biodegradability. Consequently, the content and types of pollutants in the aquatic environment are gradually increasing, making the pollution problem increasingly serious. This type of wastewater is among the most difficult to treat and accounts for a large proportion of industrial wastewater discharge. Anionic dyes, such as methyl orange and alizarin red S, are physically and chemically stable and difficult to degrade. Their intermediate products are also highly toxic, affecting the normal growth of various aquatic organisms. Improper disposal can easily cause secondary pollution to groundwater and soil, seriously threatening the ecological environment and human health. Therefore, there is a need to develop a treatment method that is highly efficient in removing anionic dyes from dyeing wastewater, is easy to operate, has low cost, and facilitates resource recycling.

[0003] In the traditional field of dyeing and printing wastewater treatment, various technologies are commonly used, including biological methods, coagulation, chemical precipitation, and advanced oxidation. Chemical precipitation is simple, inexpensive, and efficient, but it carries the risk of secondary pollution and high costs, and the sludge settles slowly. Coagulation is simple to operate and efficient, but it is currently only at the laboratory stage and requires further exploration and research in practical applications. Fenton's advanced oxidation process can degrade various organic pollutants in wastewater and has low requirements for reaction conditions, but it is too costly and has a long reaction time.

[0004] Currently, physical adsorption, as a highly efficient, rapid, and widely used technology, plays a crucial role in treating various anionic pollutants. This method primarily utilizes porous adsorption materials with well-developed pore structures and high specific surface areas to enrich and immobilize pollutants on the material surface, thereby achieving efficient removal. In the treatment of anionic dyes in dyeing and printing wastewater, such as methyl orange and alizarin red S, some adsorbents have already been applied.

[0005] Traditional adsorbent systems rely excessively on the high specific surface area of ​​activated carbon, sacrificing adsorption selectivity; while resins offer high selectivity, they are complex to synthesize and costly. For example, patent CN102921378A uses natural zeolite as its raw material, which is widely available and inexpensive, has strong adsorption capacity for pollutants such as anionic dyes, is easily biodegradable, and has good ecological performance, but its adsorption cycle is long (requiring 24-48 hours) and difficult to recycle. Patent CN119746827A contains both phenolic hydroxyl groups and quaternary ammonium salt groups, possessing dual adsorption capabilities and a large adsorption capacity, but it uses chloromethyl polystyrene resin, which is costly and has a complex synthesis process. Summary of the Invention

[0006] This invention proposes a ternary composite adsorbent based on iron-catechol-boric acid, its preparation method, and its application. Through simple coordination chemistry, the advantages of natural molecules are combined with the characteristics of metal ions to achieve broad-spectrum adsorption of anionic dyes. Furthermore, the adsorbent is loaded with boric acid groups, enabling specific adsorption of anionic dyes containing catechol, forming reversible borate ester bonds. This provides the possibility for intelligent regeneration of the adsorbent and resource utilization of dyes.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A ternary composite adsorbent based on iron-catechol-boric acid, wherein trivalent iron coordinates with the catechol groups of tannic acid to form a network of metal-phenolic coordination compounds, and the remaining phenolic hydroxyl groups on the tannic acid form hydrogen bonds with the amino groups; the structural formula is: .

[0009] A method for preparing an iron-catechol-boric acid ternary composite adsorbent includes the following steps:

[0010] S1: Dissolve tannic acid in PBS (phosphate buffer solution) to form a clear tannic acid solution;

[0011] S2: Under acidic to neutral conditions, the tannic acid solution is slowly added dropwise to the ferric salt solution and stirred. The color changes from pale yellow to blue-black, indicating the formation of an iron-tannic acid coordination complex, forming a stable ferric-tannic acid coordinated metal-organic network (Fe-TA).

[0012] S3: Centrifuge the mixture obtained in S2, discard the supernatant, and wash the precipitate repeatedly;

[0013] S4: The wet solid obtained in S3 is ultrasonically dispersed in deionized water, a reagent containing boric acid groups is added, ultrasonically dispersed again to obtain a suspension, and the pH is adjusted.

[0014] S5: The product obtained in S4 was centrifuged, washed, and then freeze-dried to obtain the final iron-tannic acid-boric acid composite adsorbent material (Fe-TA@BA).

[0015] In the steps described above, the concentration of the tannic acid solution in S1 is 10 mg / mL, the dispersion method is magnetic stirring at a speed of 400 rpm, and the stirring time is 15 minutes;

[0016] The pH of S2 under acidic to neutral conditions is 4.0 to 6.0. The molar ratio of ferric ions to phenolic hydroxyl groups of tannic acid in the ferric salt solution is 1:20 to 1:10. The preferred ferric salt is ferric nitrate nonahydrate. The stirring speed is 400 rpm, the reaction temperature is 25°C, and the reaction time is 3 to 4 hours.

[0017] In S3, the centrifugation parameters are 8000 rpm and 10 minutes. Rinse repeatedly with deionized water or PBS buffer solution. No drying is required.

[0018] The boric acid-containing reagent mentioned in S4 is 3-aminophenylboronic acid, with a molar ratio of 4:1 to 1:1 with iron; the reaction time is 8 to 12 hours, the reaction temperature is 35 to 50°C, and the pH value is adjusted to 8.0 ± 0.1.

[0019] The aforementioned ternary composite adsorbent based on iron-catechol-boric acid can be used for the removal of anionic dyes.

[0020] Beneficial effects: This invention provides a ternary composite adsorbent based on iron-catechol-boric acid, its preparation method, and its application. Compared with the prior art, this invention has the following advantages:

[0021] 1) Multiple synergistic mechanisms

[0022] The composite adsorbent prepared in this invention uses a ferric solution as a substrate, coordinating with the catechol groups of tannic acid to form a stable, network-like metal-phenolic coordination compound. This not only introduces a large number of positive charges onto the material surface but also enhances the material's stability and porosity. Furthermore, the amino group of 3-aminophenylboronic acid forms hydrogen bonds with the remaining phenolic hydroxyl groups on the tannic acid, thereby enhancing the overall stability and affinity of the bond, making the three-dimensional network structure more compact, increasing the specific surface area, and the phenylboronic acid group itself is also a functional group, exhibiting better adsorption effects on molecules containing catechol structures. The composite adsorbent possesses multiple adsorption mechanisms (electrostatic, coordination, hydrogen bonding, π-π effect) working synergistically, exhibiting a large adsorption capacity and fast adsorption speed for anionic dyes, through Fe... 3+ The numerous positively charged sites introduced by coordination generate strong electrostatic attraction with anionic dyes; electron-rich groups such as sulfonic acid groups and azo groups in the dye molecule can act as electron donors, interacting with Fe in the adsorbent. 3+Further coordination occurs, forming a stable complex; the hydroxyl groups on the adsorbent can form a hydrogen bond network with oxygen, nitrogen and other atoms in the dye molecule, increasing the adsorption capacity; the benzene ring in the adsorbent and the aromatic ring structure of the dye molecule can produce a π-π stacking effect, which enhances the adsorption selectivity, especially for dyes containing a large conjugated system (such as methyl orange).

[0023] 2) Reversible covalent bonding between boric acid groups and catechol

[0024] The phenylboronic acid group can specifically covalently bind with the catechol structure present in the dye molecule to form a five-membered borate ester bond, which increases the cross-linking degree of the material, giving the adsorbent molecular recognition ability and high selectivity. This binding has a strong specific recognition ability and is pH-controlled. When the adsorbent is saturated, it can be rinsed with an acidic solution, which will break the borate ester bond and release the dye molecules, thereby achieving efficient regeneration of the adsorbent and enabling multiple cycles of use.

[0025] 3) Resistance to ion interference

[0026] The dyeing and printing wastewater contains a large amount of inorganic salt ions (Cl). - SO4 2- Na + Ca 2+ These ions compete with dyes for electrostatic adsorption sites on the material, severely interfering with the effectiveness of pure electrostatic adsorption. In this invention, the π-π stacking of the adsorbent is not directly affected by competing ions in the water. The π-π stacking interaction between tannic acid and the aromatic ring of the dye molecule remains unchanged. These inorganic ions do not have large aromatic rings and cannot participate in π-π stacking, which allows the π-π stacking sites to efficiently capture the target dye molecules.

[0027] 4) Green recycling and dye resource recovery

[0028] Dye desorption and green regeneration can be achieved through simple pH adjustment. Under acidic conditions, the borate ester bonds are hydrolyzed, completely destroying the electrostatic adsorption and allowing the dye to be released rapidly, thus achieving acidic desorption. The collected desorption solution can be directly reused in the printing and dyeing process after neutralization and concentration, thereby constructing an integrated closed-loop recycling system of "adsorption-desorption-reuse". The entire regeneration process only requires dilute acid, without the need for organic solvents or high temperature and high pressure conditions, and the raw materials used are inexpensive and have low toxicity, which is in line with the concept of environmental friendliness. Attached Figure Description

[0029] Figure 1 This is a reaction mechanism diagram of the preparation method in a specific embodiment of the present invention;

[0030] Figure 2 This is a diagram illustrating the adsorption effect of anionic dyes in a specific embodiment of the present invention;

[0031] Figure 3 This is a graph showing the adsorbent's performance in MO cycle regeneration in a specific embodiment of the present invention;

[0032] Figure 4 This is a graph showing the performance of the adsorbent for ARS cycle regeneration in a specific embodiment of the present invention. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0034] Example 1

[0035] like Figure 1 As shown, a method for preparing an iron-catechol-boric acid ternary composite adsorbent includes the following steps:

[0036] Weigh 10 g of tannic acid and dissolve it in 1 L of pH 5.5 PBS. Stir magnetically for 30 min until completely dissolved to form a tannic acid solution with a concentration of 10 mg / mL. Then weigh 3 g of ferric nitrate nonahydrate and dissolve it in 1 L of deionized water to prepare an iron salt solution. Under room temperature and magnetic stirring conditions, adjust the pH to 4-6. Slowly add the ferric nitrate nonahydrate solution to the tannic acid solution. The mixture will immediately darken in color and gradually form a blue-black coordination complex Fe-TA. Continue stirring for 4 h to ensure complete reaction and network structure stability. Centrifuge the resulting mixture, discard the supernatant, and repeatedly wash the precipitate. Weigh 1 g of wet solid and sonicate it in deionized water to obtain a suspension. Add 4 g of 3-aminophenylboronic acid. While stirring slowly, add 0.1 M sodium hydroxide solution dropwise to precisely adjust the pH of the system to 8.0 ± 0.1. Then transfer the system to a water bath at 35-50°C and continue the reaction for 8-12 hours. After the reaction was completed, the product was centrifuged, washed, and freeze-dried at -50°C for 24 hours to obtain the final product, namely the iron-tannic acid-boric acid composite adsorbent material Fe-TA@BA.

[0037] Example 2

[0038] like Figure 1 As shown, a method for preparing an iron-catechol-boric acid ternary composite adsorbent includes the following steps:

[0039] Weigh 10 g of tannic acid and dissolve it in 1 L of pH 5.5 PBS. Stir magnetically for 30 min until completely dissolved to form a tannic acid solution with a concentration of 10 mg / mL. Then weigh 4 g of ferric nitrate nonahydrate and dissolve it in 1 L of deionized water to prepare an iron salt solution. Under room temperature and magnetic stirring conditions, adjust the pH to 4-6. Slowly add the ferric nitrate nonahydrate solution to the tannic acid solution. The mixture will immediately darken in color and gradually form a blue-black coordination complex Fe-TA. Continue stirring for 4 h to ensure complete reaction and network structure stability. Centrifuge the resulting mixture, discard the supernatant, and repeatedly wash the precipitate. Weigh 1g of wet solid and ultrasonically disperse it in deionized water to obtain a suspension. Add 2.7g of 3-aminophenylboronic acid, and while stirring slowly, add 0.1M sodium hydroxide solution dropwise to precisely adjust the pH of the system to 8.0±0.1. Then transfer the system to a water bath at 35~50℃ and continue the reaction for 8~12 hours. After the reaction is complete, centrifuge and wash the product, and freeze-dry it at -50°C for 24 hours to obtain the final product, namely the iron-tannic acid-boric acid composite adsorbent material Fe-TA@BA.

[0040] Example 3

[0041] like Figure 1 As shown, a method for preparing an iron-catechol-boric acid ternary composite adsorbent includes the following steps:

[0042] Weigh 10g of tannic acid and dissolve it in 1L of pH 5.5 PBS. Stir magnetically for 30min until completely dissolved to form a 10mg / mL tannic acid solution. Weigh 6g of ferric nitrate nonahydrate and dissolve it in 1L of deionized water to prepare an iron salt solution. Under room temperature and magnetic stirring conditions, adjust the pH to 4-6. Slowly add the ferric nitrate nonahydrate solution to the tannic acid solution. The mixture will immediately darken in color and gradually form a blue-black coordination complex Fe-TA. Continue stirring for 4h to ensure complete reaction and network stability. Centrifuge the resulting mixture, discard the supernatant, and repeatedly wash the precipitate. Weigh 1g of wet solid and sonicate it in deionized water to obtain a suspension. Add 2g of 3-aminophenylboronic acid. While stirring slowly, add 0.1M sodium hydroxide solution dropwise to precisely adjust the pH of the system to 8.0±0.1. Then transfer the system to a water bath at 35-50℃ and continue the reaction for 8-12 hours. After the reaction was completed, the product was centrifuged, washed, and freeze-dried at -50°C for 24 hours to obtain the final product, namely the iron-tannic acid-boric acid composite adsorbent material Fe-TA@BA.

[0043] Example 4

[0044] The iron-catechol-boric acid ternary composite adsorbents prepared in Examples 1-3 were applied to the treatment of anionic dye wastewater, including the following steps:

[0045] First, a series of methyl orange and alizarin red S standard solutions with different concentrations (20, 40, 60, 80, 100 mg / L) were prepared. The absorbance was measured at their maximum absorption wavelengths (464 nm for methyl orange and 422 nm for alizarin red S) using a UV-Vis spectrophotometer, and concentration-absorbance standard curves were plotted.

[0046] Prepare 200 mL of 40 mg / L methyl orange solution and place it in different Erlenmeyer flasks. Add 20 mg of each of the four adsorbents (Fe-TA, Example 1, Example 2, Example 3). Shake the flasks in a shaker for 150 min at 25°C and 150 rpm. After shaking, measure the absorbance of the supernatant to obtain the residual concentration. Similarly, prepare 200 mL of 45 mg / L alizarin red S solution, add 25 mg of each of the different adsorbents, shake, and then measure the residual concentration of the anionic dye. The results are shown in Tables 1 and 2. Figure 2 As shown:

[0047] Table 1. Comparison of adsorption effects of Fe-TA@BA and Fe-TA on methyl orange

[0048] Adsorbent Fe-TA Example 1 Example 2 Example 3 Remaining concentration (mg / L) 10.02 7.88 3.79 6.71 Adsorption capacity (mg / g) 299.8 321.2 362.1 332.9 Removal rate (%) 74.95 80.3 90.53 83.23

[0049] Table 2 Comparison of adsorption effects of Fe-TA@BA and Fe-TA on Alizarin Red S

[0050] Adsorbent Fe-TA Example 1 Example 2 Example 3 Remaining concentration (mg / L) 9.52 4.88 2.99 7.64 Adsorption capacity (mg / g) 283.84 320.96 336.08 298.88 Removal rate (%) 78.84 89.16 93.36 83.02

[0051] Fe-TA achieves a removal rate of less than 80% for methyl orange and alizarin red S, while Fe-TA@BA achieves a removal rate of over 80% for anionic dyes, with an adsorption capacity exceeding 300 mg / g. This is because loading boric acid groups increases the cross-linking degree of the material, enhancing its adsorption capacity through coordination, hydrogen bonding, and π-π effects in addition to electrostatic interactions. Furthermore, the covalent bonding of boric acid groups with the dyes significantly improves the removal capacity for anionic dyes containing catechol. In summary, the above adsorbents possess highly efficient adsorption capabilities, are suitable for the removal of anionic dyes, and utilize low-cost raw materials and are easy to prepare, demonstrating excellent application prospects.

[0052] Among them, the adsorbent prepared in Example 2 showed the best effect, with adsorption capacities reaching 362.1 mg / g and 336.08 mg / g, respectively. This is because it was prepared according to the combination ratio of iron, catechol, and boric acid groups. If the content of the latter two is too high, it may lead to pore blockage; if it is too low, the number of sites will be insufficient, and the adsorption capacity will decrease significantly.

[0053] Based on this, the optimal adsorbent (Example 2) was selected and mixed with methyl orange and alizarin red S solutions respectively. The mixtures were then shaken in a water bath constant-temperature shaker under the same conditions as described above. The supernatant was taken to determine the remaining concentration. Desorption was performed using 0.1 M HCl, followed by filtration and drying. The above operation was repeated to test its adsorption performance and cycling stability, as shown in Tables 3 and 4. After 5 cycles, the removal rate of alizarin red S by this adsorbent material remained above 82%, indicating good cycling adsorption performance. However, for anionic dyes without catechol, it lacks the advantages of specific recognition and efficient recycling, resulting in a significant decrease in adsorption capacity. Figure 3 , 4 As shown.

[0054] Table 3. Cyclic adsorption performance of Fe-TA@BA for methyl orange

[0055] Loop count 1 2 3 4 5 Remaining concentration (mg / L) 3.7 7.21 10.73 15.82 20.11 Adsorption capacity (mg / g) 363 327.9 292.7 241.8 198.9 Removal rate (%) 90.75 81.98 73.18 60.45 49.73

[0056] Table 4 Performance of Fe-TA@BA cyclic adsorption of alizarin red S

[0057] Loop count 1 2 3 4 5 Remaining concentration (mg / L) 3.08 5.27 6.88 6.92 8.01 Adsorption capacity (mg / g) 335.36 317.84 304.96 304.64 295.92 Removal rate (%) 93.16 88.29 84.71 84.62 82.2

[0058] The above are merely preferred embodiments of the present invention, which will help those skilled in the art to further understand the present invention. However, the implementation of the present invention is not limited to the above embodiments. It should be noted that for those skilled in the art, any modifications and improvements made without departing from the principle of the present invention are protected by the present invention.

Claims

1. A ternary composite adsorbent based on iron-catechol-boric acid, characterized in that, In the composite adsorbent, ferric iron coordinates with the catechol groups of tannic acid to form a network of metal-phenolic coordination compounds, and the remaining phenolic hydroxyl groups on the tannic acid form hydrogen bonds with the amino groups.

2. The ternary composite adsorbent based on iron-catechol-boric acid according to claim 1, characterized in that, The composite adsorbent has the following structural formula: 。 3. A method for preparing an iron-catechol-boric acid ternary composite adsorbent, characterized in that, Includes the following steps: S1: Dissolve tannic acid in a phosphate buffer solution to form a clear tannic acid solution; S2: Under acidic to neutral conditions, the tannic acid solution is slowly added dropwise to the ferric salt solution and stirred to form a stable ferric-tannic acid coordinated metal-organic network; S3: Centrifuge the mixture obtained in S2, discard the supernatant, and wash the precipitate repeatedly; S4: The wet solid obtained in S3 is ultrasonically dispersed in deionized water, a reagent containing boric acid groups is added, and the suspension is obtained by dispersion and pH adjustment. S5: The product obtained in S4 is centrifuged, washed, and then freeze-dried to obtain the final iron-tannic acid-boric acid composite adsorbent material.

4. The preparation method of the iron-catechol-boric acid ternary composite adsorbent according to claim 3, characterized in that, The dispersion method in S1 is magnetic stirring at a speed of 400 rpm for 15 minutes.

5. The preparation method of the iron-catechol-boric acid ternary composite adsorbent according to claim 3 or 4, characterized in that, The concentration of the tannic acid solution formed in S1 is 10 mg / mL.

6. The preparation method of the ternary composite adsorbent based on iron-catechol-boric acid according to claim 3, characterized in that, In the ferric salt solution described in S2, the molar ratio of ferric ions to the phenolic hydroxyl groups of tannic acid is 1:20 to 1:

10.

7. The preparation method of the iron-catechol-boric acid ternary composite adsorbent according to claim 3 or 6, characterized in that, The pH of S2 under acidic to neutral conditions is 4.0~6.0, the stirring speed is 400 rpm, the reaction temperature is 25℃, and the reaction time is 3~4 hours.

8. The preparation method of the ternary composite adsorbent based on iron-catechol-boric acid according to claim 3, characterized in that, The boric acid-containing reagent mentioned in S4 is 3-aminophenylboronic acid, with a molar ratio of 4:1 to 1:1 with iron.

9. The preparation method of the ternary composite adsorbent based on iron-catechol-boric acid according to claim 3 or 8, characterized in that, The reaction time in S4 is 8~12 hours, the reaction temperature is 35~50℃, and the pH value is adjusted to 8.0±0.

1.

10. The application of the ternary composite adsorbent based on iron-catechol-boric acid as described in any one of claims 1-2, characterized in that, The composite adsorbent is used for the removal of anionic dyes.

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