Preparation method and application of zirconium-based metal organic gel material

Abstract

The invention discloses a preparation method and application of a zirconium-based metal organic gel material, and the preparation method comprises the following steps: (1) adding zirconium oxychloride into distilled water, stirring and dissolving at room temperature to obtain a zirconium oxychloride solution; (2) adding trimesic acid into absolute ethyl alcohol, and stirring and dissolving at room temperature to obtain a trimesic acid solution; (3) mixing the zirconium oxychloride solution and the trimesic acid solution at room temperature, and continuously stirring to obtain a mixed solution; and (4) carrying out hydrothermal reaction on the mixed solution, naturally cooling to room temperature after the reaction is finished, and carrying out freeze drying to obtain the zirconium-based metal organic gel material. The prepared zirconium-based metal organic gel material is used for treating pulp wastewater with the pH value of 2-12 and containing lignin and / or humic acid organic matters, and the problem that when an existing metal organic gel material is used for treating the pulp wastewater, the pH application range is narrow can be solved.

Description

Technical Field

[0001] This invention relates to the field of pulp wastewater treatment technology. Specifically, it relates to a method for preparing and applying a zirconium-based organometallic gel material. Background Technology

[0002] Pulping wastewater is industrial wastewater generated by the cotton textile industry. Currently, pulping wastewater is mainly treated using physical, chemical, biological, membrane separation, and advanced oxidation technologies. Chemical coagulation is one of the main processes for pulping wastewater treatment; however, this technology suffers from high energy consumption, high operating costs, and limited efficiency in removing complex pollutants, making it difficult to meet the requirements for advanced treatment and water reuse of pulping wastewater. Therefore, developing efficient, low-cost, and environmentally adaptable flocculants has become a key research objective in this field to reduce pollutants and achieve wastewater resource recovery.

[0003] In recent years, metal-organic gels (MOGs) have emerged as a new type of material, possessing diverse and tunable porosity, large specific surface area, and abundant surface functional groups. They are widely used in adsorption separation, catalysis, and other fields, making them promising materials for wastewater treatment. Current research utilizes the amide-containing organic ligand H6TPBTM with Zr... 4+ A structurally stable zirconium-based metal-organic gel material (HNU-G6) was successfully synthesized through assembly. The abundant amide and carboxyl functional groups in this gel material exhibit excellent adsorption properties for U(VI) and Pb(II), with adsorption capacities reaching 604.3 mg·g⁻¹ at pH 5. -1 and 453.2 mg·g -1 Furthermore, it maintains excellent adsorption performance and cycling stability even in complex high-salinity water bodies. A study reported a Cu(II) metal-organic gel (Cu-MOG) with an adsorption capacity of up to 650.32 mg·g for cationic dyes. -1 Furthermore, it exhibits good recyclability. Additionally, an Al / Fe bimetallic-organic gel (JLUE-MOG-4) was successfully synthesized, demonstrating excellent adsorption performance for tetracycline chlorocycline, with an adsorption capacity of 1600 mg / g. -1 In conclusion, organometallic gel materials exhibit good treatment effects on wastewater containing metal ions, dyes, and organic matter, and have broad application prospects.

[0004] However, existing organometallic gel materials, such as HNU-G6 and MOG-Al / Fe, have the drawback of a narrow pH range when used for pulp wastewater treatment. When the pH range of pulp wastewater varies greatly, especially for pulp wastewater with extreme pH values, the treatment effect using organometallic gel materials cannot achieve the expected results. Therefore, it is necessary to further improve existing organometallic gel materials to meet the application requirements of pulp wastewater treatment with a wider pH range. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a method for preparing and applying a zirconium-based organometallic gel material, so as to solve the problem that the existing organometallic gel materials have a narrow pH range when treating pulp wastewater.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A method for preparing a zirconium-based metal-organic gel material includes the following steps:

[0008] Step (1): Add zirconium oxychloride to distilled water and stir to dissolve at room temperature to obtain zirconium oxychloride solution; Compared with polar solvents such as anhydrous ethanol and DMF, zirconium oxychloride solution prepared with distilled water as solvent is more likely to form zirconium-based metal organic gel with stable pulp wastewater treatment effect at a wide pH range in subsequent hydrothermal reaction with a specific proportion of pyromellitic acid solution.

[0009] Step (2): Add pyromellitic acid to anhydrous ethanol and stir to dissolve at room temperature to obtain a pyromellitic acid solution. Compared with distilled water, using anhydrous ethanol as the solvent for pyromellitic acid can ensure that the pyromellitic acid at the concentration required by this invention is uniformly and stably dispersed and dissolved in the solvent at room temperature. On the other hand, the pyromellitic acid solution prepared with anhydrous ethanol as the solvent can more easily form a zirconium-based metal organogel with a wider pH range in the hydrothermal reaction with the zirconium oxychloride solution prepared with distilled water as the solvent.

[0010] Step (3): Mix the zirconium oxychloride solution and the trimesic acid solution at room temperature and stir continuously to obtain a mixed solution;

[0011] Step (4): The mixed solution is subjected to a hydrothermal reaction. After the reaction is completed, it is naturally cooled to room temperature and then freeze-dried to obtain a zirconium-based metal organogel material.

[0012] During the experiments of this invention, it was found that if anhydrous ethanol or DMF is used as the solvent for zirconium oxychloride, or distilled water is used as the solvent for trimellitic acid, even with simultaneous adjustments and optimization of the concentrations of the zirconium oxychloride solution, the trimellitic acid solution, the volume ratio of the two solutions, and the hydrothermal reaction conditions, the zirconium oxychloride solution and trimellitic acid solution either fail to form a gel after the hydrothermal reaction, or the resulting gel exhibits unstable performance under a wide pH range and has poor treatment effect on pulp wastewater; while zirconium oxychloride solutions prepared with distilled water within a specific concentration range and using distilled water... A zirconium-based organometallic gel with stable pulp wastewater treatment effects over a wide pH range can be formed by mixing and stirring a pyromellitic acid solution of a specific concentration range prepared with anhydrous ethanol at a certain volume ratio and then carrying out a hydrothermal reaction. This may be because zirconium oxychloride is more conducive to the formation of a controllable hydrolysis / coordination precursor state in an aqueous system, while pyromellitic acid can maintain uniform dispersion in anhydrous ethanol, avoiding premature local complexation. The two states work synergistically in the subsequent mixing and hydrothermal reaction process to construct a gel network structure evolution path that is different from that of conventional co-solution systems.

[0013] In the preparation method of the above zirconium-based metal organogel material, in step (1), the stirring time is 10-20 min; the molar concentration of the zirconium oxychloride solution is 0.3-0.8 mol / L.

[0014] In the preparation method of the above zirconium-based metal organogel material, in step (2), the stirring time is 15-25 min; the molar concentration of the trimesic acid solution is 0.1-0.2 mol / L.

[0015] In the preparation method of the above zirconium-based metal organogel material, in step (3), the stirring time is 15-30 min; the volume ratio of pyromellitic acid solution to zirconium oxychloride solution is 1:(0.5-1.0).

[0016] In the preparation method of the above zirconium-based metal organogel material, in step (3), the stirring time is 20 min; the volume ratio of pyromellitic acid solution to zirconium oxychloride solution is 1:0.75.

[0017] In the preparation method of the above zirconium-based metal organogel material, in step (4), the hydrothermal reaction conditions are: reaction temperature 130-150℃, reaction time 1-3h; during freeze drying, the freeze dryer is set to freeze temperature -50℃ to -40℃, and the material is freeze-dried for 20-28h before being taken out.

[0018] In the preparation method of the above zirconium-based metal organogel material, the hydrothermal reaction conditions in step (4) are: reaction temperature 140℃, reaction time 2h; during freeze drying, the freeze dryer is set to freeze temperature -50℃, and the material is taken out after freeze drying for 24h.

[0019] In the preparation method of the above zirconium-based metal organogel material, in step (1), the stirring time is 15 min; the molar concentration of zirconium oxychloride solution is 0.6 mol / L; in step (2), the stirring time is 20 min; the molar concentration of trimesic acid solution is 0.1665 mol / L; in step (3), the stirring time is 20 min; the volume ratio of trimesic acid solution to zirconium oxychloride solution is 1:0.75; in step (4), the hydrothermal reaction conditions are: reaction temperature 140℃, reaction time 2 h; during freeze drying, the freeze dryer is set to freeze temperature -50℃, and the material is taken out after freeze drying for 24 h.

[0020] The method for preparing zirconium-based organometallic gels according to the present invention can produce zirconium-based organometallic gels with a wide pH application range. However, if zirconium oxychloride and trimellitic acid are directly added to a solvent formed by mixing anhydrous ethanol and distilled water in different proportions and stirred to dissolve before hydrothermal reaction, the stability of the treatment effect of the prepared zirconium-based organometallic gel on pulp wastewater at different pH values ​​decreases significantly. This may be because the preparation method of zirconium-based organometallic gels of the present invention first prepares zirconium oxychloride solutions and trimellitic acid solutions of specific concentrations using distilled water and anhydrous ethanol as solvents, then mixes and stirs them in a specific volume ratio, and finally controls the hydrothermal reaction conditions to enable Zr(IV) to strongly coordinate with carboxylates to form a highly hydrochemically stable framework, thereby ensuring that the active sites of the prepared zirconium-based organometallic gel material persist in acid / alkali environments (pH 2-12). At the same time, under the preparation conditions of the present invention, Zr-OH / carboxyl groups capable of reversible protonation-deprotonation are formed on the surface of the zirconium-based organometallic gel material, so that the surface charge of the zirconium-based organometallic gel material varies with pH. The material is adaptive; and the open Zr(IV) sites provide a pH-insensitive "chemical grabbing" channel for the inner-layer complexation / coordination exchange of oxygen-containing functional groups. Combined with multi-level pore diffusion and non-electrostatic interactions such as π–π / hydrogen bonding, the zirconium-based metal-organic gel material can stably remove lignin and humic acid organic matter from pulp wastewater under a wide pH range.

[0021] An application of a zirconium-based organometallic gel material: The zirconium-based organometallic gel material prepared by the above-mentioned preparation method is used for the treatment of pulp wastewater with a pH of 2-12 and containing lignin and / or humic acid organic matter.

[0022] In the application of the above-mentioned zirconium-based organometallic gel material, when treating pulp wastewater, the dilution ratio of the pulp wastewater is 15-25 times, the dosage of the zirconium-based organometallic gel material is 0.8-1.3 wt% of the mass of the diluted pulp wastewater, the treatment temperature is 20-35℃, and the settling time is 10-15h.

[0023] The technical solution of the present invention achieves the following beneficial technical effects:

[0024] This invention discloses a method for preparing zirconium-based organometallic gel materials. Distilled water and anhydrous ethanol are selected as solvents for zirconium oxychloride and trimellitic acid, respectively. By controlling the concentration and volume ratio of the zirconium oxychloride solution and the trimellitic acid solution, the mixture is first stirred continuously at room temperature for a specific time. Then, by controlling the hydrothermal reaction temperature and time, a zirconium-based organometallic gel material with a wide pH range can be prepared. This zirconium-based organometallic gel material has an amorphous and highly disordered structure, and a three-dimensional network structure with both macroporous and mesoporous components, which is beneficial for improving the treatment effect of zirconium-based organometallic gel materials on organic matter in pulp wastewater. The zirconium-based organometallic gel material prepared by the method of this invention can achieve a turbidity removal rate of up to 97% in pulp wastewater within a pH range of 2-12, exhibiting good acid-base adaptability. The zirconium-based organometallic gel material prepared by this invention mainly relies on the gel network structure and charge neutralization to achieve flocculation of lignin-like organic matter in pulp wastewater; and mainly relies on coordination and electrostatic attraction to achieve flocculation of humic acid pollutants in pulp wastewater. In actual pulp wastewater treatment, the zirconium-based metal-organic gel material prepared by this invention can synergistically remove a variety of organic substances through multiple functions such as flocculation, coordination and adsorption, thereby improving the purification effect of pulp wastewater. Attached Figure Description

[0025] Figure 1 XRD patterns of MOG-Zr materials prepared in embodiments of the present invention;

[0026] Figure 2a SEM image of the MOG-Zr material prepared in this embodiment of the invention at 3333x magnification;

[0027] Figure 2b and Figure 2c All images are SEM images of MOG-Zr materials prepared in the embodiments of the present invention at 5000x magnification;

[0028] Figure 2d , Figure 2e and Figure 2f All images are SEM images of MOG-Zr materials prepared in the embodiments of the present invention at 25,000x magnification.

[0029] Figure 3a , Figure 3b , Figure 3c , Figure 3d , Figure 3e and Figure 3f The XPS full spectrum, C 1s spectrum, Cl 2p spectrum, N 1s spectrum, O 1s spectrum and Zr 3d spectrum of the MOG-Zr material prepared in the embodiments of the present invention are shown respectively.

[0030] Figure 4 Thermogravimetric analysis of MOG-Zr materials prepared in the embodiments of the present invention;

[0031] Figure 5a and Figure 5b The images show the adsorption-desorption curves and pore size distribution of the MOG-Zr materials prepared in the embodiments of the present invention, respectively.

[0032] Figure 6a and Figure 6b The figures show the treatment effect of MOG-Zr material prepared in the embodiments of the present invention on pulp wastewater under different dosages and the Zeta potential diagrams, respectively.

[0033] Figure 7a and Figure 7b The figures show the treatment effect of the MOG-Zr material prepared in the embodiments of the present invention on pulp wastewater of different concentrations and the zeta potential diagram, respectively.

[0034] Figure 8a and Figure 8b The figures show the treatment effect of the MOG-Zr material prepared in the embodiments of the present invention on pulp wastewater at different temperatures and the zeta potential diagram, respectively.

[0035] Figure 9 Flocculation effect of MOG-Zr material prepared in this embodiment of the invention at different standing times;

[0036] Figure 10 The treatment effect of the MOG-Zr material prepared in this embodiment of the invention on pulp wastewater at different pH values ​​is shown in the figure.

[0037] Figure 11a and Figure 11b The figures show the treatment effect of the MOG-Zr material prepared in the embodiments of the present invention on lignin-based simulated wastewater and the zeta potential diagram, respectively.

[0038] Figure 12a and Figure 12b The figures shown are the treatment effect diagram and Zeta potential diagram of the MOG-Zr material prepared in the embodiments of the present invention on humic acid-based simulated wastewater. Detailed Implementation

[0039] 1. Preparation of Zirconium-based Metal Organogel Materials

[0040] Preparation of zirconium-based organometallic gel material (MOG-Zr material): 3.2225 g of anhydrous zirconium oxychloride was weighed and placed in a 500 mL beaker, and 30 mL of distilled water was added. The mixture was stirred for 15 min at room temperature to dissolve. 1.40 g of trimellitic acid was weighed and placed in a 500 mL beaker, and 40 mL of anhydrous ethanol was added. The mixture was stirred for 20 min at room temperature to dissolve. The prepared zirconium oxychloride solution and trimellitic acid solution were mixed and stirred for 20 min at room temperature to obtain a homogeneous solution. The homogeneous solution was then poured into a PTFE-lined hydrothermal synthesis reactor and reacted in an oven at 140 °C for 2 h. After cooling to room temperature, the sample was removed and then dried in a freeze dryer for 24 h to obtain the MOG-Zr material.

[0041] 2. Preparation of simulated waste liquid

[0042] Preparation of humic acid-based simulated waste liquid: Weigh 0.8 g of humic acid and 0.4 g of fulvic acid into an empty beaker, add 100 mL of deionized water to dissolve them, and after complete dissolution, stir magnetically for 1 h. Add 0.08 g of NaOH solid, continue stirring for 1 h, and bring the volume to 1000 mL. Name it simulated waste liquid 1 and store it in a refrigerator at 4 ℃ for later use.

[0043] Preparation of lignin-based simulated waste liquid: Weigh 1.6 g of lignin and place it in an empty beaker. Add 100 mL of deionized water to dissolve it. After complete dissolution, stir magnetically for 1 h. Add 0.15 g of NaOH solid and continue stirring for 1 h. Make up the volume to 1000 mL and name it simulated waste liquid 2. Store it in a refrigerator at 4 ℃ for later use.

[0044] 3. Evaluation of flocculation experiment

[0045] Preparation of pulp wastewater: Take an appropriate amount of pulp wastewater stock solution and place it in a 500 mL beaker. Add distilled water to the beaker to dilute it to a fixed ratio. Adjust the initial pH and temperature. Let the diluted pulp wastewater stand for 10 min before proceeding with subsequent experiments.

[0046] Experimental procedure: Weigh a certain amount of MOG-Zr material sample and add it to 100 mL of experimental pulp waste liquid. Stir for 15 min and let stand for a certain period of time. Measure the turbidity of the supernatant after flocculation and calculate the turbidity removal rate using the following formula to evaluate the flocculation effect.

[0047] Turbidity removal rate = (turbidity value before flocculation - turbidity value after flocculation) / turbidity value before flocculation × 100%.

[0048] 4 Results Analysis

[0049] 4.1 Characterization of MOG-Zr materials

[0050] XRD patterns of MOG-Zr materials, such as Figure 1 As shown, the XRD pattern of the MOG-Zr material exhibits a broad "bun peak" in the 20°-35° range, with low intensity and a wide peak shape. This broad peak morphology is typical of X-ray diffraction characteristics of amorphous or highly disordered materials. This indicates that the MOG-Zr material sample lacks a periodic ordered structure and has low crystallinity. Sharp and high-intensity diffraction peaks are observed at 8.5° and 17.1° in the XRD pattern, typical of zirconium cluster-based metal-organic framework materials. A new, relatively distinct and sharp diffraction peak appears near 33°, its position closely matching the strongest diffraction peak (111) of zirconium oxide (c-ZrO2) (PDF#20-0684, ZrO-Cubic zirconia). The unique amorphous and highly disordered structural state of the MOG-Zr material is consistent with the typical characteristics of metal-organic gel (MOG) materials. This structural characteristic is formed by zirconium ions and trimesic acid ligands under specific synthetic conditions.

[0051] Figures 2a to 2f These are SEM images of MOG-Zr material at different magnifications. Figure 2c , Figure 2d , Figure 2e and Figure 2f The basic building blocks constituting the three-dimensional network of MOG-Zr materials can be clearly observed. These units mainly exhibit interconnected nanosheet or thin-layer structures. These nanosheets are relatively thin, with smooth surfaces and clearly visible edges, and form open structures through connections between them. Figure 2a and Figure 2b This indicates the presence of numerous irregular macropores ranging in size from hundreds of nanometers to several micrometers in MOG-Zr materials. These macropores are separated by a nanosheet network framework, providing rapid channels for mass transport. At higher magnification ( Figures 2d to 2f In the SEM images, the stacking and intersecting of nanosheets form small pores. These pores are mostly in the range of a few nanometers to tens of nanometers in size, falling into the mesoporous category. They mainly originate from the incomplete stacking of nanosheets, the gaps between layers, and the voids within the network framework. The open network structure observed in the SEM images shows good connectivity between channels of different sizes. This morphology, which simultaneously contains macropores and mesopores, is a significant advantage of MOG-Zr materials.

[0052] from Figure 3aThe binding energy (BEs) peaks are 183.68, 198.46, 284.8, 400.52, and 532.04 eV, indicating the presence of Zr, Cl, C, N, and O elements on the sample surface. All peaks show chemical bonding between oxygen and zirconium atoms in the MOG-Zr material. XPS narrow energy spectrum deconvolution analysis revealed two peaks at 182 eV and 185 eV, corresponding to Zr3d3 / 2 and Zr3d5 / 2 orbitals, respectively. These Zr3d peaks originate from the Zr-O cluster structure coordinated to the carboxylic acid group of the BDC ligand in the MOG-Zr material. The BEs peaks of Cl2p are 192.93 eV and 198.07 eV, corresponding to Cl2p and Zr-Cl, respectively. Fitting the C1s peaks shows that the peaks at 284.80 eV and 288.61 eV correspond to the C—C / C=C and -COOH bonds of the carboxyl group, respectively. Figure 3b The BEs peaks of N1s are 389.68 eV and 399.97 eV, corresponding to Zr-N and -NH2, respectively. Figure 3d After deconvolution processing of the O1s spectrum, three characteristic peaks appeared in the range of 525 to 535 electron volts. Figure 3e The three peaks at 530.56 eV, 531.61 eV, and 533.01 eV correspond to zirconium-oxygen-zirconium bonds, zirconium-oxygen-carbon bonds, and carbon-oxygen-carbon bonds, respectively. The presence of zirconium-oxygen-carbon bonds indicates that the metal and organic groups in the MOG-Zr material have been successfully bonded. The observed zirconium-oxygen-carbon peaks suggest that the amorphous gel network structure is relatively stable. The O1s peak indicates that the oxygen atoms in the MOG-Zr material may originate from non-coordinated and coordinated carboxylate groups in trimesic acid.

[0053] from Figure 4 As can be seen, a significant mass loss (15%) was observed in the MOG-Zr material samples between 0 and 200 °C. This is generally related to the desorption of physically adsorbed water and the volatilization of a small amount of residual solvent. Although freeze-drying can effectively remove most of the solvent and maintain the porous structure of the material, moisture from the environment will inevitably be adsorbed on the material surface and within the pores, and trace amounts of synthetic solvent may remain. Due to dehydration, the weight decreased slightly below 300 °C, indicating good thermal stability. When the temperature rises to 456 °C, the MOG-Zr material undergoes structural collapse (rapid weight loss), and the weight loss range corresponds to the collapse and oxidative decomposition process of the three-dimensional structure. This is because the decomposition of the MOF organic linker results in zirconium dioxide as the residual oxide. When the temperature rises to 607 °C, the material finally collapses and degrades into a mixture of carbon dioxide, CO, and zirconium oxide (ZrO2).

[0054] To determine the pore size distribution and specific surface area of ​​the MOG-Zr material, N2 adsorption-desorption tests were performed (see...). Figure 5a The MOG-Zr material exhibits a Type III adsorption isotherm, indicating weak interaction between its surface and nitrogen gas, and a limited number of micropores and mesopores. Its primary adsorption mechanism is weak surface multilayer adsorption. The Type III isotherm arises because the affinity between the adsorbate molecules and the solid adsorbent surface is very weak; this interaction energy is less than or close to the heat of liquefaction of the adsorbate molecules themselves. The BET specific surface area of ​​the MOG-Zr material is 2.132 m². 2 / g, this is a very low specific surface area value, classifying it as a non-porous / macroporous material. The low specific surface area limits its adsorption performance, potentially making it suitable for macromolecular loading or low surface reaction scenarios. The extremely low P / P0 adsorption capacity in the low-pressure region directly explains the low specific surface area—almost no contribution from micropores (micropores are the main contributor to high specific surface area), with the surface area of ​​the mesopore walls being the primary source. The sharp increase in adsorption capacity in the high-pressure region (P / P0>0.8) indicates the presence of macropores or interparticle packing pores in the material. Pore size distribution Figure 5b The curve shows a sharp and high-intensity main peak, located at a pore size of approximately 3-4 nm. This sharp main peak indicates the presence of numerous uniformly sized pores in the MOG-Zr material. Following the main peak, the pore size distribution curve exhibits a broad peak or plateau extending to 20 nm or even larger, suggesting the presence of large mesopores with a wider size distribution in the MOG-Zr material. The MOG-Zr material exhibits a bimodal mesopore distribution, with its pore structure dominated by highly uniform mesopores (approximately 3-4 nm) accompanied by large mesopores with a wider size distribution (approximately 5-30 nm or larger).

[0055] 4.2 Performance Study of MOG-Zr Material in Treating Pulp Wastewater

[0056] 4.2.1 Treatment effect of pulp wastewater with different MOG-Zr material dosages

[0057] At room temperature, 6 mL of black liquor (i.e., raw pulp wastewater) was drawn into a beaker, and distilled water was added to 100 mL to dilute the black liquor by 16.67 times. Different weights of MOG-Zr material (0.7 g to 1.3 g) were added to the beaker as flocculants. The mixture was stirred at room temperature for 10 min to allow it to react fully. After settling for 12 h, the supernatant was drawn and the removal rate was calculated to evaluate the flocculation effect of different MOG-Zr material dosages.

[0058] As shown in Figure 6, when the dosage of MOG-Zr material ranges from 0.7 g to 1.1 g, the zeta potential of the colloid increases from -9.75 mV to -5.07 mV with the increase of flocculant. This indicates that the positive charge carried by the MOG-Zr material effectively neutralizes the negative charge on the surface of the colloidal particles, weakening the electrostatic repulsion between particles and thus promoting flocculation. When the dosage of MOG-Zr material is 1.1 g, the turbidity removal rate reaches a maximum of 97%. With further increases in the dosage of MOG-Zr material, excessive positive charges of MOG-Zr material adsorb onto the colloidal surface, which may induce charge reversal. Although the zeta potential does not turn positive, its significant positive shift foreshadows this trend, leading to the restabilization of the colloid and a subsequent decrease in the turbidity removal rate. This phenomenon conforms to the basic laws of electrostatic interaction in colloids, further illustrating that electrostatic interaction plays a key role in the flocculation process of MOG-Zr material.

[0059] 4.2.2 Treatment effect of MOG-Zr material on pulp wastewater of different concentrations

[0060] At room temperature, 3-9 mL of black liquor was drawn and added to a beaker. Distilled water was added to 100 mL to dilute the black liquor to 11.1-33.33 times. 1.1 g of MOG-Zr material was added to the beaker as a flocculant. The mixture was stirred at room temperature for 10 min to allow it to react fully. After settling for 12 h, the supernatant was drawn and the removal rate was calculated to evaluate the flocculation effect of different dilution ratios at the same MOG-Zr material dosage.

[0061] The flocculation effect of MOG-Zr material on black liquor with different dilution ratios is shown in Figure 7. When the amount of diluted black liquor added is 3 mL and 1.1 g of flocculant is added, the removal rate is 66%. At this point, the flocculant is relatively excessive, and the surface charge of colloidal particles may be excessively neutralized or even reversed, resulting in increased electrostatic repulsion between particles, enhanced dispersibility, difficulty in forming effective flocs, and insufficient sedimentation of pollutants. When the amount of diluted black liquor added is between 4 mL and 6 mL, the turbidity removal rate reaches the optimal value of 93.8% to 96.5%. The amount of flocculant added and the pollutant concentration reach the optimal ratio. MOG-Zr material effectively neutralizes the negative charge of colloidal and dissolved pollutants (such as lignin and hemicellulose) through its positive surface charge, weakens electrostatic repulsion, and promotes floc formation and sedimentation. When the dosage of diluted black liquor is between 7 mL and 9 mL, the turbidity removal rate decreases significantly with increasing black liquor concentration. At this point, the pollutant concentration is high, and the flocculant is relatively insufficient. Although the Zeta potential shifts slightly negatively, the overall change is weak, indicating that the charge neutralization capacity has reached saturation and cannot further effectively compress the electric double layer. Excessive pollutants may cover the floc surface, hindering its continued growth, leading to poor floc structure and reduced settling efficiency. Throughout this process, the Zeta potential remains negative with minimal fluctuations, further illustrating that while charge neutralization participates in the flocculation process, it is not the sole dominant mechanism. Adsorption bridging and net-trapping sweeping effects may play a synergistic role at higher pollutant concentrations. In conclusion, the optimal dilution ratio for treating pulp waste liquor is 20 times.

[0062] 4.2.3 Treatment effect of MOG-Zr material on pulp wastewater at different temperatures

[0063] At room temperature, 6 mL of black liquor was drawn into a beaker, and distilled water was added to 100 mL to dilute the black liquor 16.67 times. 1.1 g of MOG-Zr material was added to the beaker as a flocculant. After stirring for 10 min at different temperatures, the mixture was allowed to stand for 12 h, and the turbidity of the supernatant was measured. The black liquor treatment effect of MOG-Zr material at different temperatures is shown in Figure 8. Figure 8 shows that when the temperature increased from 20 ℃ to 30 ℃, the turbidity removal rate increased from 92.8% to 97.12%. During this stage, the Zeta potential increased from -3.94 mV to -3.22 mV, indicating that the positive charge of MOG-Zr material enhanced the neutralization effect on the negative charge on the surface of colloidal particles in the black liquor, further reducing electrostatic repulsion and promoting particle aggregation. Although no floc formation was observed, the stability of the colloidal system decreased, and particle aggregation became more likely, thus improving the sedimentation turbidity removal efficiency. When the temperature exceeds 30 °C, the turbidity removal rate decreases from 93.6% to 88.9%. Excessively high temperatures intensify molecular thermal motion, potentially disrupting the existing structure and causing colloid redispersibility. Simultaneously, some bound contaminants may desorb, thus reducing overall turbidity removal performance. In conclusion, the system exhibits optimal turbidity removal at 30 °C, indicating that this temperature represents the best operating condition for MOG-Zr materials in treating black liquor.

[0064] 4.2.4 Treatment effect of MOG-Zr material with different settling times on pulp wastewater

[0065] At room temperature, 6 mL of black liquor was drawn into a beaker, and distilled water was added to a final volume of 100 mL to dilute the black liquor 16.67 times. 1.1 g of MOG-Zr material was then added to the beaker as a flocculant. After stirring at 30 °C for 10 min, the supernatant was collected, and its turbidity was measured at different times. The flocculation effect of MOG-Zr material at different settling times is shown below. Figure 9 As shown, the removal rate of wastewater by MOG-Zr gel continuously increases with increasing settling time, indicating that the longer the settling time, the better the flocculation effect. With longer settling time, smaller pollutants with slower settling rates settle to the bottom, and the turbidity removal rate of the supernatant gradually increases. However, in actual operation, factory conditions need to be considered to determine the optimal settling time; 12 hours was selected as the optimal treatment time.

[0066] 4.2.5 Treatment effect of MOG-Zr material on pulp wastewater with different pH values

[0067] Six mL of black liquor was drawn into a beaker, and distilled water was added to a final volume of 100 mL to dilute the black liquor 16.67 times. Dilute sulfuric acid and sodium hydroxide were added to adjust the pH, and the pH was measured. 1.1 g of MOG-Zr material was added to the beaker as a flocculant, and the mixture was stirred at room temperature for 10 min. The supernatant was collected, and the turbidity values ​​at different pH levels were measured, and the removal rate was calculated. The flocculation effect of MOG-Zr material on wastewater at different pH levels is as follows: Figure 10 As shown, MOG-Zr material exhibits the best turbidity removal effect in black liquor under extremely acidic and strongly alkaline conditions, achieving a maximum turbidity removal rate of 97.0% at pH 10. Under strongly acidic conditions, the surface of MOG-Zr material becomes protonated and carries a strong positive charge. Most of the acidic groups (-COOH, -OH) in the black liquor are also protonated, resulting in a relatively weak overall charge on the colloidal particles, which may lead to Zr... 4+ The binding of hydroxyzirconium ions with protonated organic matter is also observed. Furthermore, strongly acidic conditions may cause the precipitation of certain components in black liquor. In strongly alkaline environments, negatively charged hydroxyzirconium complexes possess abundant coordination sites, forming stable metal-organic complexes with negatively charged black liquor organic matter. This complexation overcomes electrostatic repulsion, forming insoluble macromolecular complex precipitates. These surface MOG-Zr materials maintain good performance even under extreme pH conditions, demonstrating that pH 10 is the optimal operating condition.

[0068] 4.3 Performance Study of MOG-Zr Material in Treating Simulated Wastewater

[0069] Cotton pulp wastewater contains a complex mixture of substances, including various organic pollutants, inorganic ions, and suspended solids. This makes it difficult to directly study the interaction mechanism between MOG-Zr materials and cotton pulp wastewater. However, by using simulated wastewater and controlling experimental conditions, the reaction effect of MOG-Zr materials on specific substances in pulp wastewater can be accurately investigated, thus clearly identifying which target pollutant is responsible for the removal effect. In this embodiment, the most abundant and difficult-to-treat organic pollutants in actual pulp wastewater, such as lignin, humic acid, and fulvic acid, were selected as model substances, and two simulated wastewater solutions were prepared. Lignin is one of the main sources of COD and color in papermaking wastewater, while humic acid and fulvic acid are major components of natural organic matter, widely present in various water bodies, and are also key substances causing color and disinfection byproduct precursors. If the flocculant exhibits a high removal effect in the simulated wastewater, it indicates that the flocculant also has good treatment potential in actual pulp wastewater.

[0070] 4.3.1 Treatment effect of MOG-Zr material on pulp wastewater with different pH values

[0071] At room temperature, 100 mL of lignin-simulated wastewater was placed in a beaker, and MOG-Zr material of different weights (0.7 g to 1.2 g) was added. The mixture was stirred for 10 min at room temperature to allow for complete reaction. After settling for 12 h, the supernatant was collected, and the removal rate was calculated to evaluate the wastewater treatment effect of different dosages of MOG-Zr material. As shown in Figure 11, when the dosage increased from 0.7 g to 0.9 g, the removal rate gradually increased with the increase of MOG-Zr material dosage. Zr on the MOG-Zr material... 4+ Electrostatic interaction occurs between the MOG-Zr and the negatively charged lignin colloids in the simulated wastewater, causing the Zeta potential to approach neutral (-1.85 mV). This trapping effect leads to floc formation and sedimentation. Therefore, increasing the amount of flocculant results in a better turbidity removal effect. When the MOG-Zr dosage exceeds 0.9 g, the removal rate decreases to 65.14% with further increases in dosage. The increase in MOG-Zr causes a reversal of the surface charge of the colloids, changing from negative to positive. The Zeta value increases from -3.41 mV to -1.68 mV, generating repulsive forces between particles in the solution, making floc formation difficult and thus reducing the removal rate.

[0072] 4.3.2 Treatment effect of MOG-Zr material on simulated wastewater containing sodium humate and fulvic acid

[0073] At room temperature, 100 mL of simulated wastewater containing sodium humate and fulvic acid was measured, and MOG-Zr material of different weights (0.7 g to 1.2 g) was added to the beaker as a flocculant. The mixture was stirred for 10 min at room temperature to allow for complete reaction. After settling for 12 h, the supernatant was collected, and the removal rate was calculated to evaluate the treatment effect of different dosages of MOG-Zr material. As shown in Figure 12, the surface of MOG-Zr material carries a positive charge, while the humic / fulvic acid colloids in the simulated wastewater carry a negative charge. The added MOG-Zr material adheres to the negatively charged colloid surface through electrostatic attraction. With the increase of MOG-Zr material dosage, the positive charge increases, neutralizing the negative charge on the colloid surface. Charge neutralization weakens the electrostatic repulsion between colloids, allowing particles to collide and flocculate to form larger flocs, which then settle, thus improving the turbidity removal rate. When the MOG-Zr material dosage was 0.9 g, the turbidity removal rate increased from 34.9% to 80.6%, due to charge neutralization. When the MOG-Zr material dosage was 1.4 g, the Zeta potential reversed, dropping to -1.076 mV. Excess charge adsorbed by the flocculant on the colloidal surface reversed, and the colloid became positively charged. Electrostatic repulsion began to inhibit flocculation, and the turbidity removal rate decreased to 26.26%.

[0074] 4.3.3 Possible Mechanism of MOG-Zr Material in Treating Simulated Wastewater

[0075] The removal of organic pollutants such as lignin, humic acid, and fulvic acid from simulated wastewater by MOG-Zr materials mainly relies on the positively charged Zr on their surface. 4+ The electrostatic attraction between MOG-Zr and negatively charged colloidal pollutants is crucial. At appropriate dosages, MOG-Zr neutralizes the zeta potential of colloidal particles, weakening the electrostatic repulsion between particles and promoting collisional aggregation to form larger flocs, which then achieve effective separation through sedimentation. Furthermore, the porous structure and large specific surface area of ​​MOG-Zr enhance its adsorption and trapping capacity for organic molecules, further improving the turbidity removal rate. However, when excessive amounts of MOG-Zr are added, the colloidal surface undergoes charge reversal due to excessive adsorption of positive charges, reforming into stable positively charged colloids. This increases electrostatic repulsion, leading to a decrease in flocculation efficiency.

[0076] In actual pulp wastewater, the removal mechanism of MOG-Zr materials for typical organic matter (such as lignin, humic acid, and fulvic acid) is consistent with that of the simulated wastewater system. Lignin is mainly removed through flocculation, while humic acid and fulvic acid are removed through coordination and electrostatic attraction. Furthermore, due to the complex composition of pollutants in actual pulp wastewater, MOG-Zr materials may also achieve co-precipitation and net-sweeping of various pollutants (such as suspended solids, colloidal organic matter, and some inorganic ions) through their three-dimensional network structure. Competitive adsorption or synergistic removal effects may exist between different pollutants, thereby enhancing the overall pollutant removal efficiency to some extent. Therefore, when treating actual cotton pulp wastewater, MOG-Zr materials not only possess highly efficient removal capabilities for specific model pollutants but may also exhibit broader adaptability and treatment potential in practical applications due to their structural characteristics and multiple mechanisms of action.

[0077] 5. Conclusion

[0078] This embodiment successfully prepared a zirconium-based organometallic gel material—MOG-Zr material. The structural properties of MOG-Zr material were characterized, and its treatment effects on pulp wastewater and simulated wastewater containing lignin, sodium humate, and fulvic acid were evaluated. Characterization results showed that the MOG-Zr material exhibits a porous morphology with a three-dimensional network as its basic building block. The excellent wastewater treatment performance of MOG-Zr material stems from its unique pore size distribution, abundant channel structure, and the inherent physicochemical properties of zirconium-based gels. Under optimal conditions—MOG-Zr material dosage of 1.1 g, black liquor dilution ratio of 20 times, pH=10, flocculation temperature of 30 ℃, and flocculation time of 12 h—the turbidity removal rate of pulp wastewater reached as high as 97.0%, and its applicable pH range is wider than that of the existing organogel material MOG-Al / Fe. Simulated wastewater treatment results confirm that MOG-Zr materials possess highly efficient removal capabilities for key organic compounds in pulp wastewater—lignin, sodium humate, and fulvic acid. The mechanism of action is consistent with that in actual pulp wastewater systems: lignin is removed through flocculation, and sodium humate and fulvic acid are removed through coordination and electrostatic attraction. This is primarily due to the electrostatic attraction and charge neutralization between the positively charged zirconium sites on its surface and pollutants, as well as the entrapment effect of its three-dimensional network. In the complex actual pulp wastewater system, MOG-Zr materials exhibit a synergistic effect of multiple mechanisms: in addition to targeted removal of specific organic compounds, its three-dimensional network structure can simultaneously remove suspended solids, colloids, and other dissolved organic matter through co-precipitation and entrapment sweeping, thereby significantly improving the overall treatment effect. The outstanding performance of MOG-Zr materials in pulp wastewater treatment further demonstrates the application potential of metal-organic gel materials in cotton pulp wastewater treatment. The MOG-Zr material prepared by this invention not only provides a highly efficient treatment agent for the treatment of pulp wastewater from the cotton textile industry in southern Xinjiang, but also has significant implications for water resource protection and recycling in southern Xinjiang.

Claims

1. A method for preparing a zirconium-based metal-organic gel material, characterized in that, Includes the following steps: Step (1): Dissolve zirconium oxychloride in distilled water at room temperature by stirring. Step (2): Add pyromellitic acid to anhydrous ethanol and stir to dissolve at room temperature to obtain a pyromellitic acid solution; Step (3): Mix the zirconium oxychloride solution and the trimesic acid solution at room temperature and stir continuously to obtain a mixed solution; Step (4): The mixed solution is subjected to a hydrothermal reaction. After the reaction is completed, it is naturally cooled to room temperature and then freeze-dried to obtain a zirconium-based metal organogel material.

2. The method for preparing the zirconium-based metal-organic gel material according to claim 1, characterized in that, In step (1), the stirring time is 10-20 min; the molar concentration of the zirconium oxychloride solution is 0.3-0.8 mol / L.

3. The method for preparing the zirconium-based metal-organic gel material according to claim 1, characterized in that, In step (2), the stirring time is 15-25 min; the molar concentration of the pyromellitic acid solution is 0.1-0.2 mol / L.

4. The method for preparing the zirconium-based metal-organic gel material according to claim 1, characterized in that, In step (3), the stirring time is 15-30 min; the volume ratio of pyromellitic acid solution to zirconium oxychloride solution is 1:(0.5-1.0).

5. The method for preparing the zirconium-based metal-organic gel material according to claim 4, characterized in that, In step (3), the stirring time is 20 min; the volume ratio of pyromellitic acid solution to zirconium oxychloride solution is 1:0.

75.

6. The method for preparing the zirconium-based metal-organic gel material according to claim 1, characterized in that, In step (4), the hydrothermal reaction conditions are: reaction temperature 130-150℃, reaction time 1-3h; during freeze drying, the freeze dryer is set to freeze temperature -50℃ to -40℃, and the freeze dryer is taken out after 20-28h.

7. The method for preparing the zirconium-based metal-organic gel material according to claim 6, characterized in that, In step (4), the hydrothermal reaction conditions are: reaction temperature 140℃, reaction time 2h; during freeze drying, the freeze dryer is set to freeze temperature -50℃, and the product is taken out after freeze drying for 24h.

8. The method for preparing the zirconium-based metal-organic gel material according to claim 1, characterized in that, In step (1), the stirring time is 15 min; the molar concentration of zirconium oxychloride solution is 0.6 mol / L; in step (2), the stirring time is 20 min; the molar concentration of trimesic acid solution is 0.1665 mol / L; in step (3), the stirring time is 20 min; the volume ratio of trimesic acid solution to zirconium oxychloride solution is 1:0.75; in step (4), the hydrothermal reaction conditions are: reaction temperature 140℃, reaction time 2 h; during freeze drying, the freeze dryer is set to freeze temperature -50℃, and the freeze dryer is taken out after 24 h of freeze drying.

9. An application of a zirconium-based metal-organic gel material, characterized in that, The zirconium-based organometallic gel material prepared by the preparation method of zirconium-based organometallic gel material as described in any one of claims 1-8 is used for the treatment of pulp wastewater with a pH of 2-12 and containing lignin and / or humic acid organic matter.

10. The application of the zirconium-based metal-organic gel material according to claim 9, characterized in that, When using zirconium-based organometallic gel materials to treat pulp wastewater, the pulp wastewater is diluted 15-25 times, the dosage of zirconium-based organometallic gel materials is 0.8-1.3 wt% of the diluted pulp wastewater, the treatment temperature is 20-35℃, and the settling time is 10-15 h.

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