A DTPA-modified plant fiber adsorbent, its preparation method, and its application in removing cationic dyes from wastewater.

Abstract

This invention discloses a DTPA-modified plant fiber adsorbent, its preparation method, and its application in removing cationic dyes from wastewater, belonging to the technical field of adsorption-based removal of dye wastewater. On the one hand, this invention utilizes agricultural waste as the raw material for the plant fiber matrix, effectively achieving resource utilization and recycling, thus treating waste with waste. On the other hand, it optimizes the traditional synthesis method of APCAs-modified plant fiber adsorbents, reducing the use of carboxylic acid activators such as EDC and NHS to minimize environmental harm and production costs. The proposed method features a short process flow, simple operation, and is environmentally friendly, demonstrating significant adsorption effects.

Description

Technical Field

[0001] This invention belongs to the field of adsorption technology for removing dye wastewater, specifically relating to a DTPA-modified plant fiber adsorbent, its preparation method, and its application in removing cationic dyes from wastewater. Background Technology

[0002] Cationic dyes, a large class of dyes, are widely used in textiles, leather, papermaking, printing, plastics, rubber, and other industries due to their advantages such as high strength, bright colors, and good light fastness. Methylene blue (MB) is a phenothiazine cationic dye with a complex benzene ring structure, posing risks such as carcinogenicity, teratogenicity, and mutagenicity to humans. Therefore, developing novel adsorbents for the efficient removal of MB from wastewater is particularly important. Currently, methods for MB removal mainly include adsorption, solvent extraction, reverse osmosis, membrane separation, chemical oxidation, and biodegradation. Among these methods, adsorption is considered a highly efficient and feasible method due to its advantages of low cost, simple operation, high efficiency, and reusability.

[0003] Plant fibers, a type of biomass, offer advantages over traditional adsorbents, including lower cost, less pollution, stronger regeneration capabilities, biodegradability, non-toxicity, and ease of modification, making them an excellent matrix for adsorbent preparation. Functionalized adsorbents prepared from corn stalk agricultural waste through modification represent an effective approach to the resource utilization of agricultural waste, achieving the goal of "recycling and treating waste with waste." Aminopolycarboxylic acid ligands (APCAs), containing multiple amino and carboxyl groups, possess multifunctional properties such as metal chelation and ion exchange. APCA-modified plant fiber adsorbents have attracted attention due to their good stability, renewability, and multifunctionality. Existing literature reports that the main APCA-modified ligands for plant fibers are iminodiacetic acid (IDA) and diethylenetriaminepentaacetic acid (DTPA), but these studies primarily focus on metal ions, utilizing only the metal chelation properties of APCAs without fully leveraging their ion exchange capabilities. Compared to IDA, DTPA has more carboxyl groups in its structure, and its pK... an With a smaller charge value, DTPA has a greater advantage in ion exchange properties under the same pH conditions.

[0004] Traditional methods for preparing DTPA-modified plant fiber adsorbents often employ 1-ethyl-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) as carboxyl activators to improve the coupling efficiency of the amide reaction (Li M, Zhang S, Cui S, et al. Pre-grafting effect on improving adsorption efficiency of cellulose based biosorbent for Hg(II) removal from aqueous solution[J]. Separation and Purification Technology, 2021(277-):277.). However, EDC and NHS are environmentally harmful, costly, and the controllability of the reaction cannot be guaranteed. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, the present invention aims to provide a DTPA-modified plant fiber adsorbent and its preparation method and its application in removing cationic dyes from wastewater, so as to solve the technical problems of poor environmental friendliness of the reaction reagents used in the existing preparation methods, weak adsorption and removal capacity of the adsorbent for MB, and high cost of the adsorbent.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] This invention discloses a DTPA-modified plant fiber adsorbent, which is obtained by surface modification of plant fibers with DTPA under alkaline conditions using ECH as a spacer arm, introducing abundant carboxyl groups onto the surface to give it excellent ion exchange properties; its structural formula is as follows:

[0008]

[0009] Where n is the number of monomers contained in the cellulose molecule, and the value is generally between 50,000 and 2,500,000.

[0010] The present invention also discloses the above-mentioned method for preparing DTPA-modified plant fiber adsorbent, which can be prepared by direct or indirect methods.

[0011] Preferably, the preparation is carried out by a direct method, comprising:

[0012] Under alkaline conditions, ECH was added to the plant fiber matrix and the reaction was stirred thoroughly to obtain epoxy-functionalized plant fiber matrix; ammonia water, epoxy-functionalized plant fiber matrix and DTPA were refluxed and reacted, and the product was washed and dried to obtain DTPA-modified plant fiber adsorbent.

[0013] More preferably, the stirring reaction is carried out at 50°C for 24 hours, and the reflux reaction is carried out at 80°C for 3 hours.

[0014] More preferably, the plant fiber matrix undergoes pretreatment before use, including:

[0015] Take the plant fiber matrix, add it to the alkaline solution and stir thoroughly for 2 hours. After filtration, wash with water, then add it to the acid solution and stir for 30 minutes. After filtration, wash with water until neutral and dry at 80℃.

[0016] More preferably, the product is washed sequentially with acetic acid, ethanol and deionized water until neutral, and then dried at 45°C for 12 hours.

[0017] Preferably, the preparation is carried out by an indirect method, comprising:

[0018] DTPA was added to an alkaline solution, followed by ECH. The reaction was carried out at a constant temperature, and the pH was adjusted to 13.0-14.0. Plant fiber matrix was then added, and the mixture was stirred thoroughly. After filtration, the mixture was washed and dried to obtain DTPA-modified plant fiber adsorbent.

[0019] More preferably, the isothermal reaction is carried out at 80°C for 3 hours, and the fully stirred reaction is carried out at 50°C for 24 hours.

[0020] More preferably, the plant fiber matrix undergoes pretreatment before use, including:

[0021] Take the plant fiber matrix, add it to the alkaline solution and stir thoroughly for 2 hours. After filtration, wash with water, then add it to the acid solution and stir for 30 minutes. After filtration, wash with water until neutral and dry at 80℃.

[0022] More preferably, the product is washed sequentially with acetic acid, ethanol and deionized water until neutral, and then dried at 45°C for 12 hours.

[0023] This invention also discloses the application of the above-mentioned DTPA-modified plant fiber adsorbent in removing cationic dyes from wastewater.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] This invention discloses a DTPA-modified plant fiber adsorbent. On one hand, it utilizes agricultural waste as the raw material for the plant fiber matrix, effectively achieving resource utilization and recycling, thus treating waste with waste. On the other hand, it optimizes the synthesis method of traditional APCAs-modified plant fiber adsorbents, reducing the use of carboxylic acid activators such as EDC and NHS to minimize environmental harm and production costs. The proposed method features a short process flow, simple operation, and is environmentally friendly, demonstrating significant adsorption effects.

[0026] The preparation method of the DTPA-modified plant fiber adsorbent of this invention adopts an indirect method. Considering the environmental hazards and production costs of the use of EDC and NHS in existing technologies, and using the safer NaOH to replace ammonia, an indirect method for synthesizing APCAs-modified plant fiber adsorbents is proposed based on the direct method. This method improves the safety and controllability of the synthesis process while enhancing the adsorbent's MB adsorption and removal efficiency. This invention simplifies and further improves the modification method by first reacting DTPA with ECH in an alkaline environment, followed by the addition of pretreated corn stalks. Both reactions are carried out in NaOH solution, greatly enhancing safety and controllability.

[0027] This invention applies DTPA-modified plant fiber adsorbents (HQ-DTPA-D and HQ-DTPA-I) prepared by direct method (under ammonia conditions) and indirect method (under NaOH conditions) to the treatment of cationic dye MB in dye wastewater. Compared with traditional carboxylic acid-modified plant fiber adsorbents (HQ-COOH) and sulfonic acid-modified plant fiber adsorbents (HQ-SO3H), it is demonstrated that the adsorbent has good adsorption and removal capacity in the MB wastewater simulated liquid system. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the direct modification process;

[0029] Figure 2 This is a schematic diagram of the indirect modification process;

[0030] Figure 3 This is a schematic diagram of the HQ-DTPA structure simulation;

[0031] Figure 4 This is a comparison chart of the adsorption results of plant fiber adsorbents with different functional groups on MB in a simulated unary wastewater solution.

[0032] Figure 5 This is a comparison chart of the adsorption results of MB by different ratios of DTPA-modified plant fiber adsorbent and DTPA-modified silica adsorbent. Detailed Implementation

[0033] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0034] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0035] The present invention will now be described in further detail with reference to the accompanying drawings:

[0036] The main raw materials used in this invention, namely HQ-DTPA-D, HQ-DTPA-I, HQ-SO3H, HQ-COOH, and Silica-DTPA adsorbent, were all prepared in the laboratory; the wastewater simulation solution containing the cationic dye MB was prepared in the laboratory; and all chemical reagents used were commercially available analytical grade products.

[0037] Example 1: Adsorption of MB mono-component wastewater simulation solution by plant fiber adsorbent

[0038] 1. Preparation of DTPA-modified plant fiber adsorbent

[0039] 1) Pretreatment of corn stalks

[0040] Take 10g of 80-100 mesh corn stalks, add 200mL of 0.2mol / L NaOH solution (m:v=1∶20), stir for 2h, filter, wash three times with ultrapure water, put the corn stalks into 200ml of 0.2mol / L HCl solution, stir for 30min, filter, wash with ultrapure water until neutral, and dry at 80℃ to obtain pretreated corn stalks.

[0041] 2) Preparation of DTPA-modified plant fiber adsorbent (HQ-DTPA-D) by direct synthesis

[0042] 3g of pretreated corn stalks were placed in a 2mol / L NaOH solution, and 5mL of ECH was added. The mixture was stirred at 50℃ for 24h. The mixture was then filtered, and the residue was washed with ethanol and deionized water until neutral. The mixture was then dried at 45℃ to obtain epoxy-functionalized corn stalks.

[0043] Add 2g DTPA and 2g epoxy-functionalized corn stalks to 50mL of ammonia water and reflux at 80℃ for 3h. After the reaction is complete, wash with acetic acid, ethanol and deionized water sequentially until neutral, and dry at 45℃ for 12h to obtain DTPA-modified plant fiber adsorbent HQ-DTPA-D.

[0044] 3) Preparation of DTPA-modified plant fiber adsorbent (HQ-DTPA-I) by indirect synthesis

[0045] Add 2g of DTPA to 50mL of 2mol / L NaOH solution, then add 5mL of ECH dropwise while stirring. React at 80℃ for 3h. Adjust the pH of the reaction solution to 13.0-14.0 with NaOH solution, add 2g of pretreated corn stalks, and react at 50℃ for 24h with stirring. Filter the mixture, wash the residue sequentially with acetic acid, ethanol, and deionized water until neutral, and dry at 45℃ for 12h to obtain DTPA-modified plant fiber adsorbent HQ-DTPA-I.

[0046] 2. Preparation of the simulated solution

[0047] 1) Preparation of stock solution

[0048] Accurately weigh 0.2500 g of MB, dissolve it, and dilute to 250.0 mL to obtain a 1000 mg / L MB stock solution.

[0049] 2) Preparation of MB mono-component wastewater simulation solution

[0050] Take 50.00 mL of MB stock solution, make up to 250.0 mL, and adjust its pH to 8.0 with NaOH solution to obtain a 200 mg / L MB monoprotic wastewater simulation solution with pH = 8.0.

[0051] 3. Adsorption of MB in monoprotic wastewater simulation solution by plant fiber adsorbent

[0052] HQ-SO3H and HQ-COOH adsorbents were prepared according to existing methods, as disclosed in the following literature:

[0053] [1]Parlak E,Arar Removal of copper (Cu) 2+ )from water bysulfonated cellulose[J].Journal of Dispersion Science&Technology,2017:1-6.DOI:10.1080 / 01932691.2017.1405818.

[0054] [2]Nan Zhang, Yan Gao, Kangjia Sheng, Wanghui Jing, Xianliang Xu, Tao Bao, Sicen Wang. Effective extraction of fluoroquinolones from water using facilemodified plant fibers [J]. Journal of Pharmaceutical Analysis: 2022, 12(5): 791-800.

[0055] Five adsorbents—HQ-DTPA-D, HQ-DTPA-I, HQ-SO3H, HQ-COOH, and pretreated corn stalks—were weighed into 100mL Erlenmeyer flasks. 50.00mL of MB simulation solution was transferred to each flask, and the flasks were sealed and placed on a shaker at 200 rpm and 25℃ for 2 hours. After adsorption, the flasks were filtered, and the adsorption equilibrium concentration of MB in the filtrate was measured.

[0056] The concentration of MB in the solution was determined by ultraviolet-visible spectrophotometry. The standard curve for MB was y = 0.206x - 0.0192. The adsorption amount and removal rate were calculated according to formulas (1) and (2), respectively.

[0057] Adsorption capacity Removal rate

[0058] Where: C0—initial concentration, mg / L; C e —Concentration at adsorption equilibrium, mg / L; V—Solution volume, L; m—Mass of adsorbent, g.

[0059] Figure 4 The adsorption capacity and removal rate of MB in a simulated monoprotic wastewater solution were determined by plant fiber adsorbents with different functional groups. Figure 4 It was found that in the simulated MB wastewater solution with a pH value close to that of actual wastewater (pH = 8.0), the adsorption capacity and removal rate of MB by the DTPA-modified plant fiber adsorbent were higher than those of the unmodified pretreated corn stalks. Furthermore, HQ-DTPA-I exhibited the highest adsorption capacity and removal rate for MB, surpassing not only existing adsorbents HQ-SO3H and HQ-COOH, but also significantly outperforming HQ-DTPA-D adsorbent prepared using different synthesis methods with the same ligand. The MB removal rate of HQ-DTPA-I (72.95%) was higher than that of HQ-DTPA-D (52.73%), fully demonstrating the superiority of the indirect synthesis method for plant fiber adsorbents. Therefore, HQ-DTPA-I is considered the optimal adsorbent for removing monobasic MB wastewater.

[0060] Example 2: Adsorption of MB mono-component wastewater simulation solution by DTPA-modified plant fiber adsorbent and DTPA-modified silica gel adsorbent with different ratios.

[0061] 1. Preparation of DTPA-modified plant fiber adsorbent

[0062] 1) Pretreatment of corn stalks with different mesh sizes

[0063] Take 10g of corn stalks of 80-100 mesh and 150-200 mesh respectively, add 200mL of 0.2mol / L NaOH solution (m:v=1∶20), stir for 2h, filter and wash three times with ultrapure water. Put the corn stalks into 200ml of 0.2mol / L HCl solution, stir for 30min, filter and wash with ultrapure water until neutral, and dry at 80℃ to obtain corn stalks pretreated with different mesh sizes.

[0064] 2. Preparation of DTPA-modified plant fiber adsorbent by indirect synthesis

[0065] 1) Add 1g DTPA and 2g DTPA to 50mL of 2mol / L NaOH solution, respectively. Add 5mL ECH dropwise while stirring, and react at 80℃ for 3h. Adjust the pH of the reaction solution to 13.0-14.0 with NaOH solution and test with precision pH paper. Add 2g of pretreated corn stalks and react at 50℃ for 24h. Then filter the mixture, wash the residue with acetic acid, ethanol, and deionized water sequentially until neutral, and dry at 45℃ for 12h. Label the products as 1g+5mL and 2g+5mL, respectively.

[0066] 2) Add 2g DTPA to 50mL of 2mol / L NaOH solution, then add 3mL ECH and 7mL ECH dropwise while stirring. React at 80℃ for 3h. Adjust the pH of the reaction solution to 13.0-14.0 with NaOH solution and test with precision pH paper. Add 2g of pretreated corn stalks and react at 50℃ for 24h. Filter the mixture, wash the residue sequentially with acetic acid, ethanol, and deionized water until neutral, and dry at 45℃ for 12h. Label the products as 2g+3mL and 2g+7mL, respectively.

[0067] 3) Add 2g DTPA to 50mL of 2mol / L NaOH solution, then add 5mL ECH dropwise while stirring. React at 80℃ for 3h. Adjust the pH of the reaction solution to 13.0-14.0 with NaOH solution and test with precision pH paper. Add 2g of 150-mesh pretreated corn stalks and react at 50℃ for 24h with stirring. Then filter the mixture, wash the residues sequentially with acetic acid, ethanol, and deionized water until neutral, and dry at 45℃ for 12h. Label the product as 2g 150-mesh + 5mL.

[0068] 3. Preparation of simulated solution

[0069] 1) Preparation of stock solution

[0070] Accurately weigh 0.250 g of MB, dissolve it, and dilute to 250 mL to obtain a 1000 mg / L MB stock solution.

[0071] 2) Preparation of MB mono-component wastewater simulation solution

[0072] Take 50.00 mL of MB stock solution, make up to 250 mL, and adjust its pH to 8.0 with NaOH solution to obtain a simulated 200 mg / L MB monoprotic wastewater solution with pH = 8.0.

[0073] 4. Adsorption of MB in monoprotic wastewater simulation solution by plant fiber adsorbent

[0074] Silica-DTPA adsorbent was prepared according to existing methods. It was prepared according to the method reported in the following literature:

[0075] [3] Li R., Chen P., Zhang N., et al. Study on the affinity characteristics of proteins on the immobilized metal affinity chromatography column. Anal. Methods, 11 (2019) 4341-4347.

[0076] Weigh out 0.1000 g each of Silica-DTPA, Silica, 1 g + 5 mL, 2 g + 5 mL, 2 g + 3 mL, 2 g + 7 mL, 2 g 150 mesh + 5 mL, pretreated corn stalks, and pretreated 150 mesh corn stalks into 100 mL Erlenmeyer flasks. Transfer 50.00 mL of MB simulation solution to each flask, seal, and place on a shaker. Adsorb at 200 rpm and 25°C for 2 hours. After adsorption is complete, filter and measure the adsorption equilibrium concentration of MB in the filtrate.

[0077] The concentration of MB in the solution was determined by ultraviolet-visible spectrophotometry. The standard curve for MB was y = 0.206x - 0.0192. The adsorption amount and removal rate were calculated according to formulas (1) and (2), respectively.

[0078] Adsorption capacity Removal rate

[0079] Where: C0—initial concentration, mg / L; C e —Concentration at adsorption equilibrium, mg / L; V—Solution volume, L; m—Mass of adsorbent, g.

[0080] Figure 5 The adsorption capacity and removal rate of MB by DTPA-modified plant fiber adsorbent and DTPA-modified silica gel adsorbent with different ratios were investigated. Figure 5 It can be seen that in the simulated MB wastewater solution with a pH value close to that of actual wastewater (pH = 8.0), the adsorption capacity and removal rate of adsorbents with different ratios at the same mesh size showed little difference. Increasing the mesh size significantly improved both the adsorption capacity and removal rate of MB, with the removal rate increasing from 72.25% to 81.05%, which is superior to the adsorption capacity and removal rate of MB by the indirect modified silica gel adsorbent Silica-DTPA at a similar mesh size. Therefore, it can be demonstrated that for the adsorption of cationic dyes, under the same synthesis method and ligand conditions, modified plant fiber adsorbents are superior to traditional modified silica gel adsorbents, thereby reducing the manufacturing cost of the adsorbent.

[0081] Based on Examples 1 and 2, it can be seen that the DTPA-modified plant fiber adsorbent HQ-DTPA-I synthesized by the indirect method exhibits the best adsorption and removal of MB in wastewater.

[0082] In summary, this invention applies DTPA-modified plant fiber adsorbents (HQ-DTPA-D and HQ-DTPA-I) prepared by direct methods (under ammonia conditions) and indirect methods (under NaOH conditions) to the treatment of cationic dye MB in dye wastewater. Comparison with traditional carboxylic acid-modified plant fiber adsorbents (HQ-COOH) and sulfonic acid-modified plant fiber adsorbents (HQ-SO3H) demonstrates that these adsorbents possess good adsorption and removal capabilities in a simulated MB wastewater system. The method proposed in this invention, based on traditional APCAs-modified plant fiber adsorbent synthesis methods, and taking into account cost, safety, and stability of the synthesis process, proposes an indirect method for synthesizing APCAs-modified plant fiber adsorbents. The results show that in cationic dye wastewater systems, the DTPA-modified plant fiber adsorbent synthesized indirectly exhibits excellent ion exchange characteristics and demonstrates superior removal efficiency for the cationic dye MB, surpassing common carboxyl-modified and sulfonic acid-modified plant fiber adsorbents and silica-based adsorbents with the same ligands. Furthermore, the solid adsorbent material is low-cost and easy to recycle. The proposed method features a short process flow, simple operation, and is environmentally friendly, with significant adsorption effects. In practical applications, the adsorbent dosage can be flexibly selected based on the specific conditions of the industrial wastewater and discharge standards. The proposed method has broad application prospects in the treatment of industrial wastewater from the paint, ink, leather, and textile industries.

[0083] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for preparing a DTPA-modified plant fiber adsorbent, characterized in that, Prepared by an indirect method, including: DTPA was added to an alkaline solution, followed by ECH. The reaction was carried out at a constant temperature, and the pH was adjusted to 13.0-14.

0. Plant fiber matrix was then added, and the reaction was stirred thoroughly. After filtration, the solution was washed and dried to obtain DTPA-modified plant fiber adsorbent. The structural formula of the DTPA-modified plant fiber adsorbent is as follows: Where n ranges from 50,000 to 2,500,000; The isothermal reaction was carried out at 80℃ for 3 hours, and the fully stirred reaction was carried out at 50℃ for 24 hours. The added alkaline solution was a 2 mol / L NaOH solution, and the reaction ratio of NaOH solution, DTPA and ECH was 50 mL: 2 g: 5 mL.

2. The method for preparing DTPA-modified plant fiber adsorbent according to claim 1, characterized in that, The plant fiber matrix undergoes pretreatment before use, including: Take the plant fiber matrix, add it to the alkaline solution and stir thoroughly for 2 hours. After filtration, wash with water, then add it to the acid solution and stir for 30 minutes. After filtration, wash with water until neutral and dry at 80℃.

3. The method for preparing DTPA-modified plant fiber adsorbent according to claim 1, characterized in that, The product was washed sequentially with acetic acid, ethanol and deionized water until neutral, and then dried at 45°C for 12 h.

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