ZrP-C preparation method based on MOF-808 and application of ZrP-C in removal of fluorine ions

Abstract

The invention provides a preparation method of ZrP-C based on MOF-808 and application of ZrP-C in removal of fluorine ions, and relates to the technical field of chemical adsorption, the preparation method comprises the following steps: preparing MOF-808; placing MOF-808 in a phosphate solution, stirring at room temperature for 4-6 hours until an adsorption equilibrium point is reached, collecting a product, and drying for 10-15 hours; and heating the product to 400-450 DEG C at the speed of 10 DEG C / min in an inert gas environment, and preserving heat for 1-3 hours. According to the preparation method, the amorphous zirconium phosphate carbon-based nano material is prepared through monopotassium phosphate modification and subsequent one-step high-temperature carbonization by taking MOF-808 as a template, the nano material has good adsorption performance, stability and renewability, and a very potential solution is provided for efficient and economical water defluorination.

Description

Technical Field

[0001] This invention relates to the field of chemisorption technology, and in particular to a method for preparing ZrP-C based on MOF-808 and its application in the removal of fluoride ions. Background Technology

[0002] Trace amounts of fluoride are crucial for human health. However, industrial wastewater contains high levels of fluoride ions, severely impacting the ecological environment. More seriously, excessive fluoride intake can cause severe damage to the nervous, cardiovascular, reproductive, liver, and kidney systems, leading to diseases such as pulmonary edema, dental fluorosis, skeletal fluorosis, and kidney damage. Globally, over 200 million people are at risk from drinking water with excessively high fluoride concentrations, and the incidence of fluorosis is increasing annually in various countries and regions. The World Health Organization (WHO) lists fluoride as a contaminant in drinking water and sets a limit of 1.5 mg / L for fluoride ions in drinking water. Some countries, such as China, have already stipulated that the fluoride content in drinking water must not exceed 1.0 mg / L. Therefore, effectively removing low concentrations of fluoride ions from water bodies is essential.

[0003] Currently, common methods for removing fluoride ions from water include adsorption, membrane separation, coagulation and sedimentation, and ion exchange. Among these, adsorption is particularly popular due to its simplicity and relatively low cost. However, existing adsorbents generally have some inherent drawbacks. For example, many traditional adsorbents, such as activated alumina and bone char, have limited adsorption capacity and, in complex aquatic environments, generally exhibit low selectivity for fluoride ions. Coexisting anions such as chloride, sulfate, and carbonate, especially phosphate, can severely interfere with their adsorption effect on fluoride ions. Furthermore, these materials often have poor regeneration performance, with a significant decrease in adsorption capacity after repeated use.

[0004] Therefore, this invention is proposed. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing ZrP-C based on MOF-808 and its application in fluoride ion removal. This method simplifies the preparation process by preparing amorphous zirconium phosphate carbon-based nanomaterials through a one-step high-temperature carbonization following phosphate modification. The material prepared by this process exhibits high adsorption capacity, rapid kinetics, easy regeneration, and strong stability, providing a highly promising solution for efficient and economical water fluoride removal.

[0006] In order to achieve the objective of this invention, the following technical solution is adopted: This invention provides a method for preparing ZrP-C based on MOF-808, comprising the following steps: S1. Preparation of MOF-808; S2. Place the MOF-808 in a phosphate solution and stir at room temperature for 4-6 hours until the adsorption equilibrium point is reached. Collect the product and dry it for 10-15 hours. S3. The product is heated to 400°C-450°C at a rate of 10°C / min in an inert gas environment and kept at that temperature for 1-3 hours to obtain the product.

[0007] Furthermore, the phosphate solution is a potassium dihydrogen phosphate solution.

[0008] Furthermore, the concentration of the potassium dihydrogen phosphate solution is 50 mg / mL to 200 mg / mL.

[0009] Furthermore, the concentration of the potassium dihydrogen phosphate solution is 150 mg / mL.

[0010] Furthermore, the preparation of MOF-808 in S1 specifically includes the following steps: S101. H3BTC is placed in a mixture of hydrochloric acid and acetic acid and dissolved at 35°C to obtain the ligand; S102. Add ZrOCl2·8H2O to the ligand, reflux and stir in an oil bath at 110 °C for 10-15 h, wash, and dry to obtain the final product.

[0011] Furthermore, the volume ratio of hydrochloric acid to acetic acid is 1:100; The concentration of the hydrochloric acid is 36%-38%. The concentration of the acetic acid is 36%.

[0012] The present invention also provides amorphous zirconium phosphate carbon-based nanomaterials prepared by the above preparation method.

[0013] The present invention also provides the application of the aforementioned amorphous zirconium phosphate carbon-based nanomaterials in the adsorption and removal of fluoride ions in water.

[0014] Furthermore, the pH of the water body is 3-6; the temperature of the water body is 20°C-50°C.

[0015] Furthermore, the pH of the water body is 6, and the temperature of the water body is 50°C.

[0016] The present invention also provides a water treatment device or system comprising the above-mentioned amorphous zirconium phosphate carbon-based nanomaterial.

[0017] The present invention has the following technical effects: The preparation method of this invention uses MOF-808 as a template to prepare amorphous zirconium phosphate carbon-based nanomaterials through potassium dihydrogen phosphate modification and subsequent one-step high-temperature carbonization. This preparation process enables the prepared adsorbent material to have good adsorption performance, complete the initial rapid adsorption within 10 minutes, and reach equilibrium within 200 minutes. At the same time, the prepared material has excellent stability and renewability, providing a highly promising solution for efficient and economical defluoridation of water bodies. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 The images show the morphology of ZrP-C-3, where (a)-(d) are SEM images of ZrP-C-3; (e)-(g) are high-resolution transmission electron microscope images of ZrP-C-3; and (h)-(l) are EDS images of ZrP-C-3. Figure 2 : ZrP-C structure analysis diagram, where (a) is the XRD spectrum of phosphate adsorbed by MOF-808; (b) is the XRD spectrum of ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4 after carbonization; Figure 3 The results of the spectral analysis are as follows: (a) Fourier transform infrared spectra of ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4; (b) X-ray photoelectron spectrum of ZrP-C-3 nanomaterial; (c) High-resolution O 1s spectrum; (d) High-resolution C 1s spectrum; (e) High-resolution P 2p spectrum; and (f) High-resolution Zr 3d spectrum. Figure 4 Nitrogen adsorption-desorption isotherms and BJH pore size distribution analysis results, where (a) is the specific surface area and pore size distribution characteristics of ZrP-C-1; (b) is the specific surface area and pore size distribution characteristics of ZrP-C-2; (c) is the specific surface area and pore size distribution characteristics of ZrP-C-3; and (d) is the specific surface area and pore size distribution characteristics of ZrP-C-4. Figure 5The adsorption thermodynamic results are shown in the following figures: (a) is the residual fluoride ion rate diagram after adsorption of ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4; (b) is the equilibrium adsorption capacity diagram of ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4; (c) is the adsorption kinetic diagram of ZrP-C-3; (d) is the adsorption isotherm diagram of ZrP-C-3; (e) is the thermodynamic adsorption curve diagram of ZrP-C-3; and (f) is the thermodynamic spectrum of ZrP-C-3. Figure 6 The experimental results of Examples 6-9 are shown below. (a) is a species distribution diagram of fluoride at different pH values; (b) is a zeta potential diagram of ZrP-C-3; (c) is a diagram showing the effect of pH value of ZrP-C-3 solution on the adsorption capacity of ZrP-C-3; (d) is a diagram showing the effect of coexisting anions on the fluoride ion removal rate; (e) is a diagram showing the effect of ZrP-C-3 recycling; and (f) is a diagram showing the effect of ZrP-C-3 adsorbent dosage after treating raw water with Y1 and Y2 representing the original water concentration, and subsequent dosages of 0.5 g / L, 1.0 g / L, 1.5 g / L, and 2 g / L. Figure 7 Characterization images of ZrP-C-3 before and after fluoride ion adsorption, where (a)-(b) are SEM images of ZrP-C-3 with fluoride adsorption; (c) is a high-resolution transmission electron microscope image of ZrP-C-3 with fluoride adsorption; (d) is an EDS image of ZrP-C-3 with fluoride adsorption; (d1) is an EDS image of C; (d2) is an EDS image of O; (d3) is an EDS image of Zr; (d4) is an EDS image of P; and (d5) is an EDS image of F. Figure 8 The results for Experiment 10 are as follows: (a) is the FTIR spectrum of ZrP-C-3 before and after adsorption; (b) is the photoelectron spectrum of ZrP-C-3 before and after adsorption; (c) is the spectrum of high-resolution F 1s adsorption; (d) is the spectrum of high-resolution C 1s adsorption; (e) is the spectrum of high-resolution O 1s adsorption; and (f) is the spectrum of high-resolution P 2p adsorption. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] In a first aspect, the present invention provides a method for preparing ZrP-C based on MOF-808, comprising the following steps: S1. Preparation of MOF-808; S2. Place the MOF-808 in a phosphate solution and stir at room temperature for 4-6 hours until the adsorption equilibrium point is reached. Collect the product and dry it for 10-15 hours. S3. The product is heated to 400°C-450°C at a rate of 10°C / min in an inert gas environment and kept at that temperature for 1-3 hours to obtain the product.

[0022] In some embodiments, the phosphate solution is a potassium dihydrogen phosphate solution.

[0023] In some embodiments, the concentration of the potassium dihydrogen phosphate solution is 50 mg / mL to 200 mg / mL.

[0024] In some embodiments, the concentration of the potassium dihydrogen phosphate solution is 150 mg / mL.

[0025] In some embodiments, the preparation of MOF-808 in S1 specifically includes the following steps: S101. H3BTC is placed in a mixture of hydrochloric acid and acetic acid and dissolved at 35°C to obtain the ligand; S102. Add ZrOCl2·8H2O to the ligand, reflux and stir in an oil bath at 110 °C for 10-15 h, wash, and dry to obtain the final product.

[0026] In some embodiments, the volume ratio of hydrochloric acid to acetic acid is 1:100; The concentration of the hydrochloric acid is 36%-38%. The concentration of the acetic acid is 36%.

[0027] Secondly, the present invention also provides amorphous zirconium phosphate carbon-based nanomaterials prepared by the above preparation method.

[0028] Thirdly, the present invention also provides the application of the aforementioned amorphous zirconium phosphate carbon-based nanomaterials in the adsorption and removal of fluoride ions in water.

[0029] In some embodiments, the pH of the water body is 3-6; the temperature of the water body is 20°C-50°C.

[0030] In some embodiments, the pH of the water body is 6, and the temperature of the water body is 50°C.

[0031] Fourthly, the present invention also provides a water treatment device or system comprising the above-mentioned amorphous zirconium phosphate carbon-based nanomaterial.

[0032] The following is a detailed explanation using specific embodiments: Example 1 Experimental materials and instruments Reagents: Zirconium oxychloride octahydrate (ZrOCl2·8H2O), Shanghai Haohong Biomedical Technology Co., Ltd.; Potassium dihydrogen phosphate (KH2PO4), analytical grade, Sinopharm Chemical Reagent Co., Ltd.; H3BTC (C6H3(CO2H)3, mass fraction ≥98%, Aladdin), Shanghai Aladdin Biochemical Technology Co., Ltd.; Sodium fluoride (NaF), ≥99%, Nanjing Chemical Reagent Co., Ltd.; Hydrochloric acid (HCl, analytical grade, Sinopharm Chemical Reagent Co., Ltd.); Acetic acid (C2H4O2, 36%, Sinopharm Chemical Reagent Co., Ltd.); Ethanol (C2H6O), analytical grade, Sinopharm Chemical Reagent Co., Ltd. All actual solutions were prepared using deionized water (DI water) prepared by reverse osmosis.

[0033] Instruments: X-ray powder diffractometer (Bruker D8 Advance, Bruker GmbH, Germany), scanning electron microscope (JSM-7800F PRIME, NEC Japan), X-ray photoelectron spectroscopy (PHI QUANTERA II, Vacuum Instruments, Japan), surface area and pore size analyzer (BELSORP-MAX, Bell Japan), Fourier transform infrared spectrometer, anion chromatograph (AQUION, Thermo Fisher Scientific, USA), benchtop high-speed centrifuge (CenLee16K, Hunan Xiangli Technology Instrument Co., Ltd.), vacuum drying oven (DZF-6020AB, Shanghai Lichen Instrument Technology Co., Ltd.), forced-air drying oven (DHG-9070J, Hunan Chuangweilai Electromechanical Equipment Manufacturing Co., Ltd.), thermostatic magnetic stirrer (85-2, Jiangsu Jinyi Instrument Technology Co., Ltd.), tube furnace (7L1200, Nanjing Boyuntong Instrument Technology Co., Ltd.), water bath thermostatic shaker (THZ-82, Hangzhou Jingfei Instrument Technology Co., Ltd.), ultrasonic cleaner (KQ3200DE, Kunshan Ultrasonic Instrument Co., Ltd.).

[0034] A. Preparation of MOF-808 H3BTC (0.63 g, 3.0 mmol) was added to a mixed solution of 300 μL hydrochloric acid and 30 mL acetic acid and dissolved completely at 35 °C to obtain the ligand precursor. Then, 2.98 g ZrOCl2·8H2O was added to the ligand precursor solution, and the mixture was refluxed and stirred in an oil bath at 110 °C for 12 hours. The synthesized white powder was washed three times with ethanol. The product was dried overnight in an oven at 80 °C.

[0035] B. 250 mg of MOF-808 was added to 100 mL of potassium dihydrogen phosphate solutions of different concentrations: 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L. The mixture was stirred at room temperature for 5 hours. After adsorption equilibrium was reached, the product was collected by filtration and dried overnight. The collected product was heated to 400 °C at a rate of 10 °C / min for 2 hours under nitrogen atmosphere to obtain materials ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4, respectively. The experimental procedure is as follows. Figure 1 As shown.

[0036] Note: In all experiments of this invention, anion chromatography was used to test the concentration of fluoride ions in the water sample after ZrP-C adsorption. The concentration of fluoride ions in the water sample after ZrP-C adsorption was calculated. - Adsorption amount q e (mg / g) and removal rate E (%) are calculated using formulas (1) and (2): In the formula: q e The adsorption amount at adsorption equilibrium is (mg / g); E is the removal rate (%); c0 and c e The initial and equilibrium adsorption concentrations are respectively (mg / L); V is the solution volume (mL); and m is the adsorbent mass (g).

[0037] Experimental Example 1: Characterization of Adsorbents The crystal structure and composition of the material were analyzed using X-ray powder diffraction (XRD, tube voltage 40 kV, tube current 40 mA, 2θ = 5°–70°). The surface morphology of ZrP-C was characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FT-IR, detection range 400–4000 cm⁻¹) was used. -1 The resolution is 1 cm. -1 Surface functional groups were evaluated. The pore structure and specific surface area of ​​ZrP-C were determined using a BELSORP-MAX specific surface area and pore size analyzer. The valence state and composition of the samples were obtained by X-ray photoelectron spectroscopy (XPS).

[0038] The microstructure of the material was observed using scanning electron microscopy (SEM). The ZrP-C-3 material exhibited octahedral collapse due to phosphate adsorption and subsequent high-temperature carbonization; the irregular particles displayed a layered microstructure of zirconium phosphate. Figure 1 As shown in (ad), there are numerous adsorption active sites within the particles. The particle size is between 500-600 nm, and the distribution is relatively uniform. Figure 1(e.g.) Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) images show that ZrP-C-3 has a porous, folded nanosheet structure, filled with irregular black nanoparticles of zirconium oxide (ZrO2) and zirconium phosphate (ZrP). The microstructural changes of ZrP-C were observed. Furthermore, lattice calculations indicate that ZrP-C-3 comprises two crystals, confirming the presence of ZrO2 and ZrP. Figure 1 (hl)EDS energy dispersive spectroscopy analysis results show that the material surface mainly contains C, O, Zr and P elements, which are basically consistent with the elements in zirconium oxide and zirconium phosphate, further confirming the composition of the material.

[0039] The ZrP-C structure was analyzed using X-ray diffraction (XRD) technology. Figure 2 (a, b) show the XRD spectra of the four materials before and after carbonization. It can be clearly seen that the material structure was not destroyed after phosphate adsorption, retaining the original characteristic peaks of MOF-808. The diffraction peaks observed at 2θ of 8.32°, 8.69°, 10.03°, and 10.90° correspond to the (311), (222), (400), and (331) crystal planes, respectively. The spectrum after carbonization shows the formation of a characteristic peak of ZrO2 at 2θ = 30.26°, while ZrP-C contains ZrO2 and a portion of amorphous ZrP. Therefore, the characteristic peaks of zirconium phosphate are not observed.

[0040] Fourier transform infrared spectroscopy (FT-IR) is used to characterize the functional groups in ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4. The spectra of these materials are as follows: Figure 3 As shown in (a). Between 3284 and 3450 cm. -1 The peaks in the range correspond to the stretching vibrations of -OH groups, primarily originating from the physisorption of water molecules on the adsorbent surface. Furthermore, the peak intensity of the hydroxyl groups in ZrP-C-3 is significantly higher than that of ZrP-C-1, ZrP-C-2, and ZrP-C-4, indicating that the synthesized ZrP-C-3 adsorbent has significantly more hydroxyl groups on its surface than the other three adsorbents. (1613 cm⁻¹) -1 The peak at 1544 cm⁻¹ represents the trans vibration of the carboxylate. -1 C-C bond vibrations of the benzene ring were observed at 1380 and 1443 cm⁻¹. -1 Corresponding to the symmetric vibrations of carboxylates, and 1000-1115 cm -1 The characteristic bands within this range represent the deformation vibrations of the -OH groups on Zr6 clusters (Zr-OH). Furthermore, with P doping, PO symmetric vibration peaks also become clearly apparent. This is mainly due to PO42-. 3- Vibrations and deformations of functional groups. 758 cm -1This corresponds to the deformation vibration of CH on the aromatic ring.

[0041] Furthermore, X-ray photoelectron spectroscopy (XPS) analysis of ZrP-C-3 nanomaterials was also presented. We can see the total [value missing] after phosphate adsorption. Figure 3 In (b), a binding energy peak for phosphorus (P) appears. The small peak value indicates a low amount of P adsorbed on the surface. It does not significantly affect the peak values ​​of other elements, suggesting that ZrP-C-3 contains four different elements. For example... Figure 3 The spectral analysis shown in (cf) indicates that the elements are carbon (C), oxygen (O), phosphorus (P), and zirconium (Zr). The O 1s spectrum shows the presence of PO bonds in ZrP-C-3, indicating that phosphorus doping occurs in the form of zirconium phosphate. In the P 2p spectrum, the peaks at 134.03 eV and 135.19 eV correspond to PO and P-O bonds, respectively. The Zr 3d spectrum shows that zirconium in ZrP-C-3 exists mainly as ZrO2, with a small amount existing as ZrP. Based on the above FT-IR and XPS results, it can be inferred that the ZrP-C-3 nanomaterial contains a carbon framework, ZrO2, zirconium phosphate (ZrP), and some -OH and -COOH groups. The remaining edge carbons are saturated with hydrogen atoms. Previous studies have shown that biochar materials have high electron density localization. However, the introduction of phosphorus can reduce the electron density and increase the surface potential difference of the original carbon layer. Furthermore, due to the negative electronegativity of the electron cloud surrounding P, the derived carbon structure can accelerate the adsorption process, thereby leading to the adsorption and immobilization of positively charged metallic substances.

[0042] like Figure 4 As shown in (ad), the specific surface area and pore size distribution characteristics of ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4 were analyzed using nitrogen adsorption-desorption isotherms and BJH pore size distribution. The MOF-derived carbon, after P doping, all exhibited typical Type IV isotherms. The curves in the low p / p0 region are convex upwards, similar to Type II isotherms. In the higher p / p0 region, the isotherm rises rapidly due to capillary condensation of the adsorbate. Due to capillary condensation, a hysteresis phenomenon can be observed in this region. The pore size distribution confirms that the material is mainly mesoporous; key data are summarized in Table 1. The BET specific surface area of ​​ZrP-C-3 is 52.28 m². 2 The average pore size and pore volume are significantly increased by 1 g. This is attributed to its relatively small particle size and good dispersibility, which provide favorable conditions for fluoride ion adsorption.

[0043] Table 1: Specific surface area, average pore size, and pore volume of ZrP-C Experimental Example 2: Adsorption Effect of ZrP-C with Different P Contents The adsorption effects of ZrP-C with different P contents are as follows: Figure 5 As shown in (a, b), the adsorption efficiency of the carbonized adsorbent for phosphate materials at concentrations of 50 mg / L, 100 mg / L, 150 mg / L, and 200 mg / L on a 100 mg / L fluoride ion solution is demonstrated. The adsorbent ZrP-C-3, which adsorbs 150 mg / L phosphate, exhibits the best adsorption performance. This corresponds to the large number of hydroxyl groups on the surface of the ZrP-C-3 adsorbent as evaluated by Fourier transform infrared spectroscopy. ZrP-C-3 achieves a maximum adsorption capacity of 37.2 mg / g for fluoride ions, demonstrating excellent fluoride ion removal efficiency.

[0044] Experimental Example 3: Adsorption Kinetics of ZrP-C-3 In the adsorption kinetics experiment, 100 mL of a 20 mg / L fluoride ion solution was prepared, and different proportions of adsorbent were added, with an adsorbent concentration of 1 g / L. Samples were taken at intervals ranging from 1 min to 400 min.

[0045] The fitting curve of the kinetic equation of ZrP-C is as follows: Figure 5 As shown in (c), rapid adsorption of fluoride ions was observed in the first 10 minutes, mainly due to the abundant active sites on the adsorbent. Between 10 and 200 min, the adsorption rate of fluoride ions by ZrP-C slowed down as the available adsorption sites on the adsorbent surface gradually decreased, reaching adsorption equilibrium around 200 min. During this process, fluoride ions gradually transferred to the interior of the adsorbent, thereby achieving the removal of fluoride ions from the solution.

[0046] The adsorption mechanism was analyzed using pseudo-first-order and pseudo-second-order reaction kinetic equations, and the calculation formulas are shown in equations (3) and (4): In the formula: q e and q t These represent the adsorption equilibrium and the effect of time t on the substrate (F). - The adsorption amount (mg / g); t is the reaction time (min); k1 and k2 are the rate constants of the first-order and second-order kinetic models, respectively, in units of (min). -1 ), (g / mg / min).

[0047] Table 2: Correlation coefficients of pseudo-first-order and pseudo-second-order kinetic models of ZrP-C Pseudo-first-order kinetics indicates that the reaction rate is directly proportional to the concentration of the reactant, while pseudo-second-order kinetics indicates that the reaction rate is directly proportional to the square of the concentration of the reactant. According to Table 2 of the model fitting results, ZrP-C-3 exhibits good adsorption performance for fluoride ions. The equilibrium adsorption capacity is 16.20 mg / g. Furthermore, the pseudo-second-order kinetic correlation coefficient R0 for ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4 is shown. 2 The correlation coefficients are all greater than those of the pseudo-first-order kinetics and closer to 1. The pseudo-second-order kinetic model assumes that the adsorption rate is controlled by the chemisorption mechanism, involving electron sharing or transfer between the adsorbent and adsorbate. The adsorption behavior of ZrP-C agrees well with the pseudo-second-order kinetic model; however, it deviates somewhat from the pseudo-first-order kinetic model, indicating lower reliability. Therefore, the pseudo-second-order kinetic model is more suitable for describing the adsorption process, and the adsorption of fluoride ions by ZrP-C is mainly chemisorption.

[0048] Experiment Example 4: Adsorption Isotherm Prepare 20 mL of fluoride ion solution. The solution concentration ranges from 10 mg / L to 100 mg / L, with different proportions of adsorbent added, and the adsorbent dosage is 1 g / L. After running the solution in a water bath at 160 rpm for 12 hours, samples are taken.

[0049] Isothermal adsorption experiments compare different initial F - The F- adsorption capacity of ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4 at different concentrations was measured. Experimental results show that as the initial F- concentration in the solution increases... - With increasing content, the F of each adsorbent - The adsorption capacity increases rapidly until it reaches equilibrium. The Langmuir and Freundlich models were used to analyze the relationship between the adsorption amount and F at adsorption equilibrium. - The relationship between mass concentration and adsorption concentration was analyzed by linear fitting. The expressions for the Langmuir and Freundlich adsorption isotherm models are shown in equations (5) and (6), respectively.

[0050] In the formula: c e q represents the mass concentration of fluoride ions in the water at adsorption equilibrium (mg / L); e q represents the adsorption capacity for fluoride ions (mg / g); m K represents the adsorption capacity of fluoride ions at adsorption saturation (mg / g). L K is the Langmuir adsorption constant (L / mg). F and n are Freundlich's characteristic adsorption constants. They are related to the adsorption capacity.

[0051] Table 3: Isothermal adsorption fitting data for fluoride ions of ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4. The Langmuir adsorption isotherm and Freundlich adsorption isotherm of ZrP-C are as follows: Figure 5 As shown in (d), the fitted data are shown in Table 3. In the Freundlich model, the Freundlich model is used to describe multilayer adsorption at non-uniform phase points. When the value of 1 / n is between 0.1 and 0.5, it indicates that the material has a good adsorption effect on fluoride ions. Table 3 shows that ZrP-C-1, ZrP-C-2, ZrP-C-3, and ZrP-C-4 have good adsorption effects on fluoride ions. - The equilibrium adsorption capacities were 35.72, 33.68, 37, and 14.02 mg / g, respectively, all demonstrating good fluoride ion adsorption performance.

[0052] In addition, the R-values ​​of the Langmuir model for the four materials are... 2 All values ​​are greater than the Freundlich model, indicating a high degree of agreement between the Langmuir model and the ZrP-C adsorption model. However, the adsorption behavior of ZrP-C differs somewhat from the Freundlich model, indicating lower reliability. Therefore, the Langmuir model has higher reliability, suggesting that the adsorption of fluoride ions by ZrP-C is primarily monolayer adsorption. The adsorption sites are uniform and have the same energy. Based on the fitting results, ZrP-C-3 exhibits the best adsorption performance, with a saturation adsorption capacity qs. m The concentration was 54.38 mg / g. This indicates that ZrP-C-3 has a high fluoride ion adsorption capacity, and also reflects the strong affinity between the adsorbent and the adsorbate.

[0053] Experimental Example 5: Adsorption Thermodynamics ZrP-C-3 was selected as the adsorbent, and 20 mL of fluoride ion solution was prepared. Solution concentrations ranged from 10 mg / L to 100 mg / L, and the adsorbent concentration was 1 g / L. Thermodynamic adsorption experiments were conducted at 25℃, 35℃, 45℃, and 55℃. Figure 5 (e) It was found that the adsorption capacity of ZrP-C-3 for fluoride ions increased with increasing solution temperature, with maximum adsorption capacities of 35.78 mg / g, 36.89 mg / g, 38.02 mg / g, and 40.13 mg / g at 25℃, 35℃, 45℃, and 55℃, respectively. Thermodynamic parameters were calculated using thermodynamic equations (7), (8), and (9), and the results are shown in Table 4.

[0054] In the formula: K eq is the adsorption equilibrium constant, L / g; e The adsorption capacity of the adsorbent at equilibrium is expressed in mg / g; C e This represents the concentration of elemental iodine in the solution at equilibrium, in mg / L. H represents enthalpy change, kJ / mol; S represents entropy change, J / mol·K; G is the Gibbs free energy change, kJ / mol; R is the gas molar constant, 8.314 J / mol·K; T is the thermodynamic temperature, K.

[0055] With 1 / T as the x-axis, lnK e For the ordinate Figure 5 (f). By Figure 5 (f) and the change in Gibbs free energy of the parameter calculated by the thermodynamic equation. G, Entropy change S and enthalpy change H is shown in Table 4.

[0056] S and The values ​​of H are respectively determined by 1 / T and lnK. e The intercept and slope were calculated. At 25℃, 35℃, and 45℃, The negative values ​​of G indicate that the adsorption process of fluoride ions by ZrP-C-3 is spontaneous. H > 0 indicates that heat is absorbed during the reaction. The adsorption capacity increases as the reaction temperature rises from 25℃ to 45℃, and increasing the temperature favors the reaction. Furthermore, the increased disorder of the reaction system during adsorption further contributes to the reaction. S > 0.

[0057] Table 4: Thermodynamic parameters of ZrP-C-3 Experiment Example 6: The Effect of Solution pH on Adsorption Experiments ZrP-C-3 was selected as the adsorbent, and its adsorption performance at different pH solutions was studied. Several portions of 20 mg adsorbent were added to 20 mL of solution with an initial fluoride ion concentration of 100 mg / L. -1 In the solution, before adding the adsorbent, the pH of the solution was adjusted to 3, 5, 7, 9, and 11 using 1 mol / L dilute hydrochloric acid and sodium hydroxide, respectively. 2 mL of the solution was taken with a syringe and filtered through a 0.22 μm filter membrane. The fluoride ion concentration in the solution was then detected using an anion chromatography instrument.

[0058] The pH value of the solution plays a crucial role in the adsorption of fluoride ions. This influence mainly stems from the changes in the ionic species and ζ potential of the adsorbent when the initial pH value of the solution varies. The distribution of fluoride ion species at different pH values was evaluated using Visual MINTEQ ver. 3.1, as shown in the figure Figure 6 (a) In an aqueous solution, fluoride ions exist in three forms: HF, F - and HF2 - , but the main forms are HF and F - . The isoelectric point (pHpzc) of ZrP-C-3 (pH at the zero charge point) is 5.57 Figure 6 (b).

[0059] As Figure 6 (c) shown, when 3 < pH < 6. The adsorption performance of ZrP-C-3 for fluoride ions gradually increases. The main reasons are the gradual decrease in the content of HF and the gradual increase in the content of F - in the aqueous solution, as well as the positively charged protonated adsorbent surface capturing negatively charged F - through enhanced electrostatic interaction. When pH > 6, the adsorbent shows electronegativity in the aqueous solution. As the pH increases, the enhanced electronegativity on the adsorbent surface further strengthens the electrostatic repulsion between the adsorbent and fluoride ions, resulting in a decrease in adsorption performance. Even so, at alkaline pH, the decrease in the adsorption capacity of the adsorbent for fluoride ions is not obvious. This indicates that the adsorbent achieves the capture effect of fluoride ions through other mechanisms such as ligand exchange mechanism, rather than just electrostatic interaction. The Zr metal active sites in the adsorbent first bind with -OH as ligands. Since the affinity between Zr and fluoride ions is greater than the affinity between Zr and hydroxyl groups, fluoride ions are captured by exchanging -OH ligands

[0060] Experimental Example 7: Influence of coexisting ions on the experiment ZrP-C-3 was selected as the adsorbent, and a 20 mL fluoride ion solution with a concentration of 20 mg / L was prepared, with the adsorbent dosage being 1 g / L. NaCl, NaNO3, Na2SO4, NaHCO3, Na2CO3, and Na3PO4 were added to study the influence of the corresponding anions on the adsorption of fluoride ions. Since the concentration of the 20 mg / L fluoride ion solution is approximately 1.053 mmol / L, at the same time, to explore the competitive effect of different concentrations of anions; the concentrations of coexisting anions were set to 0.1, 0.5, 1.5, and 2 mmol / L. The differences in the adsorption capacities of each group were compared. If the adsorption amount decreased significantly, it indicated that the coexisting ion had competitive inhibition

[0061] The presence of competing anions in wastewater can interfere with the adsorption of fluoride ions. Therefore, adsorbents used in practical water treatment must possess good anti-interference performance and excellent fluoride ion selectivity. Most research on adsorbent anti-interference focuses on binary systems, where fluoride ions coexist with other ions. However, in real wastewater, multiple ions coexist. In multi-ion systems, these ions can form various complexes and compete with fluoride ions for active sites on the adsorbent.

[0062] By studying Cl - NO3 - SO4 2- HCO3 - CO3 2- and PO4 3- The effects of these six typical anions on fluoride ion adsorption experiments: Previous experiments showed that ZrP-C-3 can adsorb up to 16.2 mg / g of a 20 mg / L fluoride ion solution. For example... Figure 6 As shown in (d), the highest fluoride ion removal rate in the experimental group was less than 70%, meaning the adsorption capacity was less than 14.0 mg / g, which is lower than the 16.2 mg / g of the blank group. This indicates that the six anions have an inhibitory effect on fluoride ion adsorption. With increasing concentrations of these six anions, the fluoride ion removal rate gradually decreased. Furthermore, the figure shows that the effects of the six anions on fluoride ion adsorption are different. The inhibitory effect, from largest to smallest, is PO42-. 3- CO3 2- HCO3 - SO4 2- NO3 - and Cl - .

[0063] The effect of anions on fluoride ion adsorption mainly depends on their charge density, hydrated ionic radius, and affinity for the adsorbent surface. The analytical mechanism is as follows: PO4 3- High charge (3-), forms a strong inner-layer complex with the adsorbent surface (such as metal oxides), and with F - Competition for the same adsorption sites results in the greatest interference. CO3 2- As a divalent anion, it readily reacts with hydroxyl groups (-OH) on the adsorbent surface, altering the surface charge or occupying active sites, thus significantly inhibiting F. - Adsorption of HCO3. - As a weak acid anion, it can indirectly affect F by increasing pH or competing for adsorption sites. - Adsorption, but weaker than CO3. 2- SO4 2- It is a divalent anion, but with a relatively large hydration radius (approximately 4.0 Å), and its surface affinity is weaker than that of higher-valent ions (such as PO4). 3- ), for F- The effect of adsorption is moderate. NO3 - As monovalent ions with low charge density, they primarily compete with F through electrostatic interactions. - The adsorption interference is relatively small. (Cl) - It is a monovalent ion with a small hydration radius (approximately 3.3 Å), but its extremely weak hydrolysis ability means that it hardly competes for specific adsorption sites, thus having the least impact.

[0064] In summary, high-valence anions such as PO4 3- and CO3 2- Strong electrostatic attraction makes it easier to occupy adsorption sites. It forms inner-layer complexes with metal oxides, directly competing with F. - Adsorption sites. And NO3... - and Cl - It has low affinity for F through ion exchange alone. - Adsorption causes relatively little interference. Therefore, in actual defluoridation, pretreatment to remove high-valence anions (such as chemical precipitation for phosphorus removal) can improve the efficiency of subsequent defluoridation. In addition, actual water quality testing is necessary, as the order of coexisting ions may change depending on their concentration ratio.

[0065] Experiment Example 8: Desorption and Regeneration Experiment ZrP-C-3 was selected as the adsorbent. 100 mg of the adsorbent was added to 100 mL of a 20 mg / L fluoride solution, and the contact time was 5 h, followed by sampling. Subsequently, the fluoride-loaded adsorbent was immersed in a 0.1 M sodium hydroxide solution and stirred for 5 h to regenerate the adsorbent. The recovered adsorbent was washed with deionized water and dried overnight in a vacuum drying oven at 80 °C for subsequent adsorption. The above procedure was repeated 4-5 times to explore the reusability of the adsorbent.

[0066] Using a 0.1 mol / L NaOH solution as the desorbent in the desorption experiment, the desorption effect was very significant, with a desorption rate exceeding 85%. This may be because OH... - With F - The ion exchange between them is strong, which can effectively convert F - Displaced from the ZrP-C-3 surface.

[0067] The desorbed ZrP-C-3 was regenerated and reused for fluoride ion adsorption. The results are as follows: Figure 6(e) shows that after four regeneration experiments, the adsorption capacity of ZrP-C-3 can reach 12.99 mg / g, still reaching 80% of the initial adsorption capacity. This indicates that ZrP-C-3 has good regeneration performance. After each desorption, the adsorption performance of ZrP-C-3 decreases slightly, which may be due to the difficulty in completely removing the adsorbate, resulting in undisturbed fluoride ions occupying a small portion of the adsorption sites. In practical defluorination applications, desorption regeneration can achieve material reuse, reduce costs, and improve economic efficiency.

[0068] Analysis of the desorption and regeneration experiments leads to the conclusion that NaOH solution is an effective desorbent, enabling efficient desorption of fluoride ions from ZrP-C-3; ZrP-C-3 exhibits good regeneration performance and can be reused multiple times, showing great promise in practical defluorination applications.

[0069] Experiment Example 9: Actual Wastewater Treatment Effect To investigate the actual defluorination effect of ZrP-C-3, samples of fluoride-containing wastewater from the Donghai quartz pickling processing base were collected. The samples were primary defluorination wastewater that had undergone lime coagulation sedimentation and pH adjustment treatment. First, the pH of the water samples was measured, finding it to be between 6 and 7. Subsequently, the initial concentration was measured, and multiple measurements were taken, with the average value recorded. Figure 6 As shown in (f), Y1 and Y2 represent the raw water concentrations, which are 18.2 and 18.41 mg / L respectively, meaning the initial concentration of the water sample was approximately 18.3 mg / L. During the test, the Cl- concentration in the raw water was found to be... - The concentration of Cl is very high, while the concentrations of other ions have dropped to very low levels. We know from previous coexisting ion experiments that Cl... - For F - The adsorption process minimizes interference. However, excessively high concentrations can still negatively impact fluoride removal, making real-time water quality monitoring essential, which will not be elaborated upon here. We subsequently conducted adsorption experiments, adding 0.5, 1.0, 1.5, and 2 g / L of ZrP-C-3 adsorbent. After adsorption equilibrium was reached, samples were taken for testing, yielding final concentrations of 5.84, 3.23, 1.89, and 0.86 mg / L, respectively. It can be seen that the fluoride ion removal effect becomes more significant with increasing adsorbent dosage.

[0070] Experimental Example 10: Adsorption Mechanism SEM, HRTEM, FT-IR, and XPS characterization techniques were used to characterize ZrP-C materials before and after fluoride ion adsorption. Figure 7 (ac) shows the SEM and HRTEM images of the material after adsorption. The surface of the material before and after adsorption still maintains the octahedral collapse morphology and does not change much. EDS Figure 7 (d) and element mapping Figure 7(d1-d5) shows that the element F appears in addition to C, Zr, O, and P, indicating that ZrP-C-3 is associated with F. - Adsorption was performed. The atomic percentages were C: 41.64%, O: 41.05%, F: 0.45%, Zr: 15.21%, and P: 1.65%.

[0071] Figure 8 (a) shows the FT-IR characterization results of the adsorbent before and after adsorption. The characteristic adsorption bands range from 1000 to 1115 cm⁻¹. -1 The -OH stretching vibration peak is between 3284 and 3450 cm⁻¹. -1 Within the specified range, the adsorption capacity is significantly reduced after fluoride ion adsorption. This can be attributed to the interaction between ion exchange and surface complexation, specifically the ion exchange of H+ in ZrP-C-3. + With F - The exchange reaction. Surface complexation: ZrP-C-3 adsorbs fluoride ions through the exchange of -OH ligands. The Zr-OH group reacts with F... - An inner-layer complex is formed. The formula is as follows: In addition, the adsorption process may also involve electrostatic interactions (H). + This leads to physical adsorption.

[0072] XPS spectroscopy can further elucidate the mechanism of fluoride ion removal by ZrP-C-3. Compared with the original broad-scan XPS spectrum of unadsorbed fluoride ions, a new F1s peak appears in the spectrum after fluoride ion adsorption. Figure 8 (b) indicates that fluoride ions were successfully captured on the ZrP-C-3 surface. High-resolution spectra are shown below. Figure 8 As shown in (c), a characteristic peak appears with a binding energy of 685.20 eV. This corresponds to the Zr-F bond formed between the adsorbent and fluoride ions. This indicates a strong affinity between Zr and F. Furthermore, Figure 8 (e) shows that after fluoride ion adsorption, the Zr 3d peak shifts to a higher binding energy, indicating the formation of a new chemical bond (Zr-F bond) due to the strong affinity between Zr and F. Because of the high electronegativity of fluorine, the electron cloud density around Zr adsorbed on ZrP-C-3 decreases, thus increasing the binding energy. Figure 8 As shown in (f), the O 1s spectra before and after adsorption can be divided into three regions: Zr-OH, OCO, and Zr-O-Zr. However, the O 1s spectra after adsorption show a significant reduction in the area of ​​the Zr-OH region. This further indicates that the Zr active sites achieve adsorption and removal of fluoride ions from aqueous solutions by exchanging hydroxyl ligands.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing ZrP-C based on MOF-808, characterized in that, Includes the following steps: S1. Preparation of MOF-808; S2. Place the MOF-808 in a phosphate solution and stir at room temperature for 4-6 hours until the adsorption equilibrium point is reached. Collect the product and dry it for 10-15 hours. S3. The product is heated to 400°C-450°C at a rate of 10°C / min in an inert gas environment and kept at that temperature for 1-3 hours to obtain the product.

2. The method for preparing ZrP-C based on MOF-808 according to claim 1, characterized in that, The phosphate solution is a potassium dihydrogen phosphate solution.

3. The method for preparing ZrP-C based on MOF-808 according to claim 2, characterized in that, The concentration of the potassium dihydrogen phosphate solution is 50 mg / mL to 200 mg / mL.

4. The method for preparing ZrP-C based on MOF-808 according to claim 3, characterized in that, The concentration of the potassium dihydrogen phosphate solution is 150 mg / mL.

5. The method for preparing ZrP-C based on MOF-808 according to claim 1, characterized in that, The preparation of MOF-808 in S1 specifically includes the following steps: S101. H3BTC is placed in a mixture of hydrochloric acid and acetic acid and dissolved at 35°C to obtain the ligand; S102. Add ZrOCl2·8H2O to the ligand, reflux and stir in an oil bath at 110 °C for 10-15 h, wash, and dry to obtain the final product.

6. The method for preparing ZrP-C based on MOF-808 according to claim 5, characterized in that, The volume ratio of hydrochloric acid to acetic acid is 1:100; The concentration of the hydrochloric acid is 36%-38%. The concentration of the acetic acid is 36%.

7. An amorphous zirconium phosphate carbon-based nanomaterial prepared by the ZrP-C preparation method based on MOF-808 as described in any one of claims 1-6.

8. The application of the amorphous zirconium phosphate carbon-based nanomaterial as described in claim 7 in the adsorption and removal of fluoride ions in water.

9. The application of the amorphous zirconium phosphate carbon-based nanomaterial according to claim 8 in the adsorption and removal of fluoride ions in water, characterized in that, The pH of the water is 3-6; the temperature of the water is 20°C-50°C.

10. A water treatment apparatus or system, characterized in that, The system or device includes the amorphous zirconium phosphate carbon-based nanomaterial as described in claim 7.

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