Preparation method and application of iron-zirconium bimetal MOF (Metal Organic Framework) adsorbent

Abstract

The invention discloses a preparation method and application of an iron-zirconium bimetal MOF adsorbent, and belongs to the technical field of adsorbents and wastewater treatment. According to the invention, Zr is doped on the basis of Fe to form a bimetallic-center MOF material, and the formed iron-zirconium bimetallic MOF adsorbent has a larger specific surface area and more active sites, so that the arsenic capturing capability of the adsorbent is remarkably improved. Meanwhile, the bimetal center provides multiple types of adsorption sites, and arsenic (such as As (III) and As (V)) with different valence states can be effectively combined, so that the adsorption efficiency is improved. Due to the design of the double metal centers, the selectivity of the adsorbent to arsenic is remarkably improved, and the adsorbent can preferentially adsorb arsenic in the presence of other metal ions, so that the arsenic removal efficiency is improved, and the wastewater treatment effect is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of adsorbents and wastewater treatment, and in particular relates to a preparation method and application of an iron-zirconium bimetallic MOF adsorbent. Background Art

[0002] Arsenic is a non-metallic toxic element widely distributed in nature. Arsenic and its compounds are toxic and hazardous substances, highly toxic to living organisms. With the advancement of modern industrialization, arsenic levels in natural water bodies have gradually increased. Long-term consumption of water containing excessive arsenic can cause arsenic to accumulate in the human body, leading to a range of health problems, including cancer, cardiovascular disease, neurotoxicity, and immune system suppression.

[0003] Currently, the main methods for arsenic removal include coagulation and sedimentation, ion exchange, membrane separation, biological methods, and adsorption. Traditional coagulation and sedimentation, while simple to operate and low in raw material costs, are ineffective in treating low-concentration arsenic water and may even cause secondary pollution. In contrast, membrane separation and ion exchange, while more efficient, are technically expensive, have strict water quality requirements, require resin replacement, and suffer from slower processing speeds.

[0004] While adsorption is highly effective for arsenic removal, the adsorption capacity of the adsorbent is a key limitation. Existing high-efficiency adsorbents are costly and economical, and other ions compete with arsenic for adsorption sites, affecting arsenic removal efficiency. Therefore, there is an urgent need for an adsorbent with high arsenic selectivity, high arsenic removal efficiency, and low cost to address these challenges. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention proposes a preparation method and application of an iron-zirconium bimetallic MOF adsorbent.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing an iron-zirconium bimetallic MOF adsorbent, comprising the following steps:

[0008] Terephthalic acid, iron salt and zirconium salt are added to an organic solvent and subjected to hydrothermal synthesis to obtain the iron-zirconium bimetallic MOF adsorbent;

[0009] The molar ratio of the iron salt to the zirconium salt is 3:1.

[0010] Technical principle: The present invention forms a MOF material with a bimetallic center by doping Zr on the basis of Fe. The formed iron-zirconium bimetallic MOF adsorbent has a larger specific surface area and more active sites, which significantly improves the adsorbent's ability to capture arsenic. At the same time, the bimetallic center provides a variety of adsorption sites that can effectively bind arsenic of different valence states (such as As(III) and As(V)), thereby improving the adsorption efficiency. The design of the bimetallic center also significantly improves the selectivity of the adsorbent for arsenic, and can preferentially adsorb arsenic in the presence of other metal ions, thereby improving the arsenic removal efficiency and ensuring the wastewater treatment effect.

[0011] Furthermore, the hydrothermal synthesis temperature is 150° C. and the time is 15 h.

[0012] Furthermore, the hydrothermal synthesis further includes the steps of centrifugation, washing and drying.

[0013] Furthermore, the centrifugal speed is 8000 rpm; and / or the drying temperature is 60° C. and the drying time is 12 h.

[0014] The present invention also provides the use of the iron-zirconium bimetallic MOF adsorbent prepared by the preparation method described in the above technical solution in removing arsenic.

[0015] Furthermore, the application of the iron-zirconium bimetallic MOF adsorbent in removing arsenic comprises the following steps: adding the iron-zirconium bimetallic MOF adsorbent to arsenic-containing wastewater for reaction, and removing the arsenic through solid-liquid separation.

[0016] Furthermore, the liquid-solid ratio of the arsenic-containing wastewater to the iron-zirconium bimetallic MOF adsorbent is 1:(0.1-0.2) (L / g).

[0017] Furthermore, when the arsenic-containing wastewater contains trivalent arsenic, the method further comprises the step of adding H2O2; the amount of H2O2 added is 1.6-2.1% of the volume of the arsenic-containing wastewater.

[0018] Furthermore, the concentration of arsenic in the arsenic-containing wastewater is 1-100 mg / L.

[0019] Furthermore, the method further includes the step of adjusting the pH of the arsenic-containing wastewater to 3-11.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects:

[0021] In the bimetallic MOF structure designed in this invention, Fe and Zr provide multiple types of adsorption sites with varying affinities for arsenic, effectively adsorbing arsenic ions of varying valences. In practical applications, since wastewater typically contains multiple metal ions, these ions may compete with arsenic for adsorption sites. The design of the bimetallic center significantly improves the adsorbent's selectivity for arsenic, enabling preferential adsorption of arsenic in the presence of other metal ions, thereby enhancing arsenic removal efficiency and ensuring effective wastewater treatment.

[0022] When using the iron-zirconium bimetallic MOF adsorbent for the removal of trivalent arsenic, the present invention adds H2O2 to the reaction system. This improves the adsorption efficiency through oxidation and surface complexation. Combined with the various adsorption sites provided by the bimetallic center, the adsorption efficiency of arsenic is further improved. Experimental results show that the arsenic removal rate is as high as 98.22%. The addition of H2O2 eliminates the need for a separate pre-oxidation treatment of the arsenic-containing reaction aqueous solution, and can simultaneously improve the oxidation and adsorption performance of the entire reaction system during the adsorption process, making MIL-101 (Fe, Zr) more feasible in practical applications. The overall reaction requires low material costs, low solid waste volume, and a wide applicable pH range. The adsorption process itself does not produce a large amount of secondary pollutants such as arsenic-containing sludge, reducing the difficulty and cost of subsequent solid waste treatment. Compared with existing technologies, the composite system of MIL-101 (Fe, Zr) and H2O2 can improve adsorption kinetics, accelerate the rate of arsenic adsorption, and simultaneously carry out arsenic oxidation and adsorption reactions, thereby improving treatment efficiency. The addition of iron can change the electronic structure of MOF and enhance its interaction with arsenic, thereby improving adsorption selectivity and capacity. The addition of H2O2 helps to quickly oxidize the difficult-to-bind trivalent arsenic during the adsorption process and form a surface complex with arsenic, thereby improving adsorption efficiency, reducing costs, and improving economic benefits.

[0023] The present invention uses adsorption instead of traditional chemical precipitation to remove arsenic. Chemical precipitation typically produces large amounts of waste residue when treating arsenic in wastewater. This waste residue requires further processing and disposal, increasing treatment costs and resource consumption while also posing a potential risk of environmental pollution. In contrast, the present invention utilizes MIL-101 (Fe, Zr) adsorbent to efficiently remove arsenic from wastewater without generating large amounts of solid waste, thereby reducing the difficulty and cost of waste treatment.

[0024] The MIL-101(Fe,Zr) adsorbent prepared by the present invention exhibits excellent stability and adsorption performance under various pH conditions. Its excellent chemical stability and structural diversity make it stable in both acidic and alkaline environments and resistant to decomposition. Experimental results show that the MIL-101(Fe,Zr) adsorbent prepared by the present invention can effectively remove arsenic from arsenic-containing wastewater within the pH range of 5-11. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 This is the SEM image of MIL-101 (Fe, Zr) prepared in Example 1;

[0027] Figure 2 XRD pattern of MIL-101 (Fe, Zr) prepared in Example 1;

[0028] Figure 3 This is the XPS pattern of MIL-101 (Fe, Zr) prepared in Example 1;

[0029] Figure 4 This is the O orbital XPS peak diagram of MIL-101 (Fe, Zr) prepared in Example 1, where the left figure is before the reaction and the right figure is after the reaction;

[0030] Figure 5 This is the Zr orbital XPS peak diagram of MIL-101 (Fe, Zr) prepared in Example 1, where the left figure is before the reaction and the right figure is after the reaction;

[0031] Figure 6 This is the Fe orbital XPS peak diagram of MIL-101 (Fe, Zr) prepared in Example 1, where the left figure is before the reaction and the right figure is after the reaction;

[0032] Figure 7 Nitrogen adsorption-desorption isotherm of MIL-101 (Fe, Zr) prepared in Example 1;

[0033] Figure 8 This is the pore size distribution diagram of MIL-101 (Fe, Zr) prepared in Example 1. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] The present invention provides a method for preparing an iron-zirconium bimetallic MOF adsorbent, comprising the following steps:

[0037] Terephthalic acid, iron salt and zirconium salt are added to an organic solvent and hydrothermally synthesized to obtain the iron-zirconium bimetallic MOF adsorbent. The core mechanism of the present invention using Fe and Zr to synergistically improve the adsorption performance of the adsorbent for arsenic includes: (1) Structural advantage: the high specific surface area dominated by mesopores in the iron-zirconium bimetallic MOF accelerates mass transfer, and the bimetallic nodes provide high-density active sites; (2) Chemical synergy: Fe 3+ With Zr 4+ The complementary hydroxylated surface of Fe, Zr broadens pH adaptability, and the high oxygen affinity of Zr enhances the strength of coordination bonds; (3) Dynamic balance: Fe and Zr charges synergistically optimize surface electrical properties, inhibit competitive adsorption, and enhance anti-interference ability. The above mechanisms together give MIL-101 (Fe, Zr) efficient, wide pH applicability, and regenerative arsenic adsorption performance.

[0038] In a preferred embodiment, the molar ratio of the iron salt to the zirconium salt is 3:1; the molar ratio of the terephthalic acid to the iron salt is 4:3; the iron salt is selected from ferric chloride hexahydrate; and the zirconium salt is selected from zirconium tetrachloride. The reason why the molar ratio of the iron salt to the zirconium salt is controlled within the above range in the present invention is that when the iron salt and the zirconium salt are combined in a ratio of 3:1: 1) the adsorption sites synergistically formed by iron and zirconium have a significantly improved ability to capture arsenic compared to using iron or zirconium alone; 2) regular pores of about 3.823 nm are formed inside the material (observation results of electron microscopy), allowing arsenate ions to quickly enter the pores; 3) the specific surface area of ​​the material can reach 125.65 m 2 / g (nitrogen adsorption test), providing a large number of adsorption sites. If the ratio of iron salt and zirconium salt deviates from this range, the material structure will become unstable and the adsorption capacity will drop by 30%-50%. The present invention uses terephthalic acid as an organic ligand. 1) Its rigid structure makes the material resistant to high temperature and acid and alkali; 2) The carboxylic acid group can enhance the binding force between the metal site and arsenic, so that the arsenic removal efficiency reaches more than 95%; 3) The hydrophobic property of the benzene ring can reduce the interference of common ions in water (such as phosphate), and still maintain high adsorption performance in complex water quality. Practical application tests show that the material can be reused more than 3 times with a performance degradation of less than 20%.

[0039] In a preferred embodiment, the hydrothermal synthesis temperature is 150°C and the time is 15 hours. The temperature and time of the hydrothermal synthesis affect the crystal structure of the iron-zirconium bimetallic MOF adsorbent. Controlling the temperature and time of the hydrothermal synthesis within the above range is conducive to obtaining an iron-zirconium bimetallic MOF adsorbent with excellent adsorption performance.

[0040] In a preferred embodiment, the hydrothermal synthesis further includes the steps of centrifugation, washing and drying.

[0041] In a preferred embodiment, the centrifugal speed is 8000 rpm.

[0042] In a preferred embodiment, the drying temperature is 60° C. and the drying time is 12 hours.

[0043] The present invention also provides the use of the iron-zirconium bimetallic MOF adsorbent prepared by the preparation method described in the above technical solution in removing arsenic.

[0044] In a preferred embodiment, the use of the iron-zirconium bimetallic MOF adsorbent in removing arsenic includes the following steps: adding the iron-zirconium bimetallic MOF adsorbent to arsenic-containing wastewater for reaction, and removing the arsenic through solid-liquid separation.

[0045] In a preferred embodiment, the liquid-to-solid ratio of the arsenic-containing wastewater to the iron-zirconium bimetallic MOF adsorbent is 1:(0.1-0.2) (L / g).

[0046] In a preferred embodiment, when the arsenic-containing wastewater contains trivalent arsenic, the process further includes adding H2O2; the H2O2 is a 30% by mass H2O2 aqueous solution, and the amount of H2O2 added is 1.6-2.1% of the volume of the arsenic-containing wastewater, so that the final concentration of H2O2 in the reaction system reaches 0.15-0.20 mol / L.

[0047] In a preferred embodiment, the concentration of arsenic in the arsenic-containing wastewater is 1-100 mg / L.

[0048] In a preferred embodiment, the method further comprises adjusting the pH of the arsenic-containing wastewater to 3-11; the reagent for adjusting the pH of the arsenic-containing wastewater comprises 0.1M HCl solution or 0.1M NaOH solution.

[0049] The room temperature in the embodiments of the present invention refers to "25±2°C".

[0050] Unless otherwise specified, the raw materials in the examples of the present invention were purchased from commercial sources.

[0051] Example 1

[0052] A method for preparing an iron-zirconium bimetallic MOF adsorbent comprises the following steps: adding ferric chloride hexahydrate, zirconium tetrachloride, and terephthalic acid in a molar ratio of 3:1:4 to 80 mL of DMF, subjecting the mixture to ultrasonic vibration for 5 minutes until completely dissolved, and heating the mixture at 150°C for 15 hours using a hydrothermal synthesis method. The resulting solution is allowed to cool to room temperature, centrifuged at 8000 rpm for 8 minutes, and then washed three times with anhydrous ethanol and deionized water, respectively. The mixture is then dried in a 60°C drying oven for 12 hours to obtain powdered MIL-101 (Fe, Zr).

[0053] Figure 1 This is the SEM image of MIL-101 (Fe, Zr) prepared in Example 1. Figure 1 It can be seen that the morphology of MIL-101 (Fe, Zr) presents a multi-faceted three-dimensional structure, the crystal surface is smooth and angular, and nanoparticles attached to the crystal surface, as well as structural defects and roughness are observed. These characteristics are Zr 4+ Local lattice defects caused by doping and chemical modification of surface active sites.

[0054] Figure 2 This is the XRD pattern of MIL-101 (Fe, Zr) prepared in Example 1. Figure 2 It can be seen that the characteristic peak of MIL-101(Fe) is retained near 2θ=7.3°, indicating that Zr 4+ The doping of Zr did not cause significant lattice distortion, and the material still maintained the topological network structure of MIL-101. 4+ The ionic radius of Fe 3+ There are differences, but they are embedded in the framework through local substitution rather than overall reconstruction, so the material still maintains a topological network structure, proving the formation of metal-doped MIL-101 (Fe, Zr).

[0055] Figure 3 This is the XPS graph of MIL-101 (Fe, Zr) prepared in Example 1. Figure 3It can be seen that the main element peaks of the material before the reaction include C1s (284.8eV), O 1s (531.5eV), Fe 2p (710.5eV) and Zr 3d (182.1eV). These elements have obvious peaks before and after the reaction. The element peaks of MIL-101 (Fe, Zr) before the reaction are consistent with the expected composition of the material, confirming that Fe 3+ and Zr 4+ The material was successfully embedded into the MOF framework, resulting in a successful synthesis and structural integrity. Furthermore, no significant peaks characteristic of other free metal oxides or uncoordinated ligands were detected in the sample, indicating a high degree of material purity. After As(V) adsorption onto MIL-101(Fe,Zr) (i.e., post-reaction), a new, distinct As 3d peak appeared in the material's energy spectrum, located in the 44.5-45.5 eV range. This indicates that As(V) was chemically fixed to the material surface, confirming the successful bonding of As with the adsorbent and, therefore, the successful adsorption of As on the material surface.

[0056] Figure 4 The O orbital XPS peak diagram of MIL-101 (Fe, Zr) prepared in Example 1, where the left diagram is before the reaction and the right diagram is after the reaction. Figure 4 As can be seen in the O 1s spectrum, the peaks at 530.08 eV and 531.78 eV are attributed to Fe-O-Fe and Fe-OH, respectively. After As(V) adsorption onto MIL-101(Fe,Zr), the intensity and peak area of ​​the peak at 530.51 eV change significantly, indicating that some Fe-O-Fe is converted to Fe-O-As, reflecting the formation of Fe-O-As. The peak intensity of oxygen decreases after adsorption, with the peak at 531 eV decreasing from 65.2% to 57.6%. This is due to the reduction of the Fe-OH / Fe-OC bond during the adsorption process, indicating that the Fe-OH / Fe-OC groups are involved in the adsorption process. The Fe-O-Fe peak at 530.08 eV disappears, indicating that the Fe-O-Fe group is also involved in the adsorption process.

[0057] Figure 5 This is the Zr orbital XPS peak diagram of MIL-101 (Fe, Zr) prepared in Example 1, where the left picture is before the reaction and the right picture is after the reaction. Figure 5 It can be seen that one typical peak of Zr 3d shows a small shift to higher binding energy, while the other peak remains almost at the same position. The position of Zr 3d peak remains basically unchanged, indicating that Zr 4+ In the reaction, it mainly participates in the adsorption process through electrostatic attraction and coordination.

[0058] Figure 6 The Fe orbital XPS peak diagram of MIL-101 (Fe, Zr) prepared in Example 1, where the left diagram is before the reaction and the right diagram is after the reaction. Figure 6 It can be seen that the Fe orbital exhibits a typical double peak feature at the binding energy of 713.5eV and 726.3eV, corresponding to Fe 3+ 2p 3 / 2 With 2p 1 / 2 orbital, confirming that the Fe element in the material exists stably in the +3 valence state. After As(V) adsorption, Fe 2p 3 / 2 The peak shifts to higher binding energy and the intensity of the companion peak weakens, indicating that Fe 3+ Coordination bonds were formed with the oxygen atoms of As(V), confirming that the adsorption process was related to the chemical interaction between Fe and As.

[0059] Figure 7 The nitrogen adsorption-desorption isotherm of MIL-101 (Fe, Zr) prepared in Example 1. Figure 7 It can be seen that the isotherm of MIL-101 (Fe, Zr) belongs to a typical type II adsorption isotherm with an H3 hysteresis loop, which means that the structure of MIL-101 (Fe, Zr) has mesoporous characteristics. This porous structure is conducive to the diffusion of pollutants in the pores and the effective combination of adsorption sites. The specific surface area of ​​MIL-101 (Fe, Zr) is 125.65 m 2 / g.

[0060] Figure 8 This is the pore size distribution of MIL-101(Fe,Zr) prepared in Example 1. According to the Barrett-Joyner-Halenda (BJH) model (based on desorption branch data), the average pore diameter and pore volume of MIL-101(Fe,Zr) are 3.823 nm and 0.1201 cc / g, respectively. The synergistic effect of the mesopore-dominated pore size distribution and the high specific surface area provides a structural foundation for rapid mass transfer of arsenic species and efficient utilization of surface active sites.

[0061] Application Example 1 (Effect of Initial pH Value on Arsenic Removal)

[0062] 4 mg of MIL-101 (Fe, Zr) prepared in Example 1 was accurately weighed, and 20 mL of a 10 mg / L As(V) solution was measured and placed in a conical flask. The pH of the As(V) solution was then adjusted to 1, 3, 5, 7, 9, and 11, respectively, using 0.1 M HCl solution or NaOH solution. The conical flask was placed in a constant temperature oscillator at 180 r / min. After oscillation for 48 hours, the MIL-101 (Fe, Zr) was removed using a 0.22 μm filter membrane to obtain a clear solution to be tested. The residual concentration of As(V) in the clear solution to be tested was measured, and the adsorption amount and removal rate were calculated. The results are shown in Table 1.

[0063] Table 1

[0064] pH <![CDATA[C0(mg / L)]]> <![CDATA[C e (mg / L)]]> <![CDATA[q e (mg / g)]]> Removal rate (%) 1 10 3.15 34.22 68.45 3 10 1.61 41.93 83.86 5 10 0.67 46.63 93.26 7 10 0.19 49.07 98.15 9 10 0.27 48.63 97.25 11 10 4.41 27.93 55.87

[0065] In Table 1, C0 represents the initial concentration of As(V), C e Indicates the residual concentration of As(V) in the test solution, q e Indicates the adsorption amount.

[0066] As can be seen from Table 1, the MIL-101 (Fe, Zr) prepared in Example 1 exhibits excellent wide pH adaptability. In the pH range of 3-9, the As(V) removal rate is higher than 80%; in the pH range of 5-9, the As(V) removal rate is higher than 90%, with a peak at pH = 7, where the removal rate reaches 98.15%. At pH = 1 and pH = 11, the As(V) removal rates are still 68.45% and 55.87%. This is due to the synergistic effect of Fe and Zr bimetallic: Fe 3+ and Zr 4+ The hydroxylated surface (≡Fe-OH and ≡Zr-OH) forms a stable coordination bond with As(V) under neutral conditions, and the high oxygen affinity of Zr enhances the adsorption strength. In weak acid systems, MIL-101 (Fe, Zr) is not significantly affected by the competition of protons. However, the adsorption efficiency is significantly reduced in alkaline systems (pH>9), which may be due to the large amount of OH - This leads to the degradation of some MIL-101(Fe,Zr), which in turn leads to the reduction of active centers. In general, MIL-101(Fe,Zr) exhibits excellent As(V) removal performance in acidic and neutral solutions, while the removal performance is slightly reduced in weak alkaline solutions.

[0067] Application Example 2 (Effect of Initial Arsenic Concentration on Arsenic Removal)

[0068] 4 mg of MIL-101 (Fe, Zr) prepared in Example 1 was accurately weighed and placed in 20 50 mL centrifuge tubes, and 20 mL of As (V) solution and As (III) solution with concentrations of 2, 4, 6, 8, 10, 20, 40, 60, 80 and 100 mg / L were measured and placed in centrifuge tubes, totaling 20 groups, wherein the As (III) solution group was further added with 15% of the volume of the As (III) solution H2O2. The centrifuge tube was placed in a constant temperature oscillator at 25 ° C. and oscillated at a speed of 180 r / min. After oscillation for 48 hours, MIL-101 (Fe, Zr) was removed with a 0.22 μm filter membrane to obtain a clear solution to be tested. The residual concentration of As (V) and the residual concentration of As (III) in the clear solution to be tested were tested, and the corresponding adsorption amount and removal rate were calculated. The results are shown in Tables 2 and 3. Table 2 shows the test results of pentavalent arsenic, and Table 3 shows the test results of trivalent arsenic.

[0069] Table 2

[0070] <![CDATA[C0(mg / L)]]> <![CDATA[C e (mg / L)]]> <![CDATA[q e (mg / g)]]> Removal rate (%) 2 0.05 9.75 97.44 4 0.15 19.25 96.28 6 0.35 28.25 94.14 8 0.60 37.00 92.53 10 0.90 45.50 90.99 20 3.50 82.50 82.49 40 17.00 145.00 57.50 60 26.00 170.00 56.66 80 35.00 180.00 56.25 100 46.00 184.50 53.00

[0071] Table 3

[0072] <![CDATA[C0(mg / L)]]> <![CDATA[C e (mg / L)]]> <![CDATA[q e (mg / g)]]> Removal rate (%) 2 0.35 8.24 82.40 4 0.85 15.74 78.69 6 1.60 21.99 73.31 8 2.50 27.51 68.78 10 3.60 32.00 64.02 20 14.89 48.54 25.54 40 27.88 61.81 30.31 60 42.89 69.54 28.51 80 60.75 76.53 24.06 100 79.50 78.50 20.50

[0073] In Tables 2 and 3, C0 represents the initial concentration of As(V) or As(III), C e Indicates the residual concentration of As(V) or As(III) in the test solution, q e Indicates the adsorption amount.

[0074] It can be seen from Table 2 and Table 3 that when the initial concentration of As(III) is in the range of 2-10 mg / L, the removal rate of As(III) by MIL-101(Fe,Zr) prepared in Example 1 is higher than 60%, and when the initial concentration of As(III) is further increased to above 20 mg / L, the removal rate of As(III) by MIL-101(Fe,Zr) is still above 20%. When the initial concentration of As(V) is in the range of 2-10 mg / L, the removal rate of As(V) by MIL-101(Fe,Zr) prepared in Example 1 is higher than 90%, and when the initial concentration of As(V) is further increased to above 40 mg / L, the removal rate of As(V) by MIL-101(Fe,Zr) is still above 50%. The process of arsenic adsorption by MIL-101(Fe,Zr) conforms to the Langmuir monolayer adsorption model, and its theoretical maximum adsorption capacity (Q m ) is 192.42 mg / g. The adsorption of As(V) on MIL-101(Fe,Zr) may involve two steps of binding: the first step is monolayer adsorption, in which As(V) is directly bound to the metal node after being adsorbed by MIL-101(Fe,Zr); the second step is the interaction between free As(V) and adsorbed As(V) to form an As-O-As oligomer structure on the node, which significantly improves the actual adsorption capacity of the material.

[0075] Application Example 3 (Effect of Time on Arsenic Removal)

[0076] 40 mg of MIL-101(Fe,Zr) prepared in Example 1 was accurately weighed, and 200 mL of a 10 mg / L As(V) solution was placed in a 500 mL conical flask. The flask was then placed in a constant temperature oscillating oven at 25°C at 180 rpm. Samples were taken at 0, 0.08, 0.25, 0.5, 1, 2, 4, 8, 12, and 24 h, and the MIL-101(Fe,Zr) was removed using a 0.22 μm filter to obtain a clear solution. The residual As(V) concentration in the clear solution was measured, and the adsorption capacity and removal rate were calculated. The results are shown in Table 4.

[0077] Table 4

[0078] T / h <![CDATA[C0(mg / L)]]> <![CDATA[C e (mg / L)]]> <![CDATA[q t (mg / g)]]> Removal rate (%) 0.08 10 7.49 12.54 25.07 0.25 10 5.38 23.10 46.21 0.5 10 4.10 29.50 59.00 1 10 2.84 35.81 71.62 2 10 1.76 41.19 82.38 4 10 1.26 43.72 87.45 8 10 1.008 44.96 89.93 12 10 0.59 47.03 94.07 24 10 0.10 49.50 99.00 48 10 0.02 49.92 99.84

[0079] In Table 4, C0 represents the initial concentration of As(V), C e Indicates the residual concentration of As(V) in the test solution, q t Indicates the adsorption amount.

[0080] It can be seen from Table 4 that the As removal rate of MIL-101 (Fe, Zr) gradually increases with time, and after 24 hours, the As removal rate reaches more than 99%.

[0081] The adsorption kinetics experimental data (i.e., C in Table 4) were analyzed using pseudo-first-order kinetics and pseudo-second-order kinetics models. e ) was fitted, and the R 2 Greater than the R of the pseudo-first-order kinetic model 2 This indicates that the quasi-second-order kinetic model is more suitable for the adsorption of As(V) and As(III) by MIL-101(Fe,Zr). The quasi-second-order adsorption kinetic model includes the entire adsorption process including liquid film diffusion, surface adsorption, and internal diffusion. The results show that the adsorption process is dominated by chemical adsorption.

[0082] Application Example 4 (Adsorption Regeneration Experiment)

[0083] 4 mg of MIL-101(Fe,Zr) prepared in Example 1 was accurately weighed, and 20 mL of an As(V) solution with an initial mass concentration of 10 mg / L was added. The mixture was placed in an Erlenmeyer flask, and the pH was adjusted to 7 using 0.1 mol / L HCl or NaOH solution. The flask was transferred to a thermostatic oscillator (25°C) and continuously shaken at 180 rpm for 48 hours. After the reaction was completed, the solid and liquid phases of the reaction system were separated by a 0.22 μm filter membrane. The supernatant was obtained, and the As(V) concentration was measured and the removal rate was calculated. The adsorbed MIL-101(Fe,Zr) was collected, gently washed with deionized water, dispersed in a 1.0 M NaOH solution, shaken at room temperature for 6 hours, and then washed to a pH of 7.0 to complete desorption. The adsorption-desorption process was repeated three times, with each cycle repeated three times. The arsenic removal rate of MIL-101(Fe,Zr) was recorded. The results are shown in Table 5.

[0084] Table 5

[0085] Number of cycles Removal rate (%) 1 98.47 2 94.40 3 89.57

[0086] As can be seen from Table 5, the removal efficiency of MIL-101 (Fe, Zr) decreased from 98.5% to 89.6% after three cycles of adsorption of As(V). The key factor for the attenuation of adsorption performance includes the irreversible loss of active sites. - Alkaline desorption in an environment may cause some ≡Fe-OH groups to be converted into irreversible ≡Fe-O - , thus reducing the subsequent coordination ability. In summary, although the removal rate of MIL-101(Fe,Zr) decreases to a certain extent at the beginning of each cycle, it still has good regeneration stability.

[0087] Application Example 5 (Effect of Interfering Substances on Arsenic Removal)

[0088] Accurately weigh 4 mg of MIL-101 (Fe, Zr) prepared in Example 1, measure 20 mL of 10 mg / L As(V) solution and place it in a conical flask, then add HA and NO3 according to the molar ratio of As to interfering substances of 1:75. - 、Cl - 、SO4 2- 、CO3 2- PO4 3- (The concentration of interfering substances was 1 mmol / L) and the pH of the As(V) solution was adjusted to 7 with 0.1 M NaOH solution. The conical flask was placed in a thermostatic oscillator at 180 r / min. After oscillation for 48 hours, MIL-101(Fe,Zr) was removed with a 0.22 μm filter membrane to obtain a clear solution to be tested. The residual As(V) concentration in the clear solution to be tested was measured, and the removal rate was calculated. Each experiment was repeated three times. The results are shown in Table 6.

[0089] Table 6

[0090] Interfering substances Removal rate (%) blank 98.50 HA 75.10 <![CDATA[NO3 - ]]> 83.60 <![CDATA[Cl - ]]> 80.41 <![CDATA[SO4 2- ]]> 85.37 <![CDATA[CO3 2- ]]> 78.20 <![CDATA[PO4 3- ]]> 23.22

[0091] As can be seen from Table 6, PO4 3- The most significant interference effect is caused by the fact that phosphorus and arsenic both belong to the VA group elements. Ka The highly similar atomic structures and chemical properties of arsenate and phosphate make them easy to form inner sphere complexes with the same adsorbent active sites. Other anions such as SO4 2- 、NO3 - 、CO3 2- 、Cl - The interference effect is relatively weak, and the removal rate remains between 74.8-83.5%.

[0092] In addition to the above-mentioned coexisting anions, dissolved organic matter (DOM) is ubiquitous in nature and has a high activity towards metals. Studies have found that when DOM is incubated with arsenic and hematite, it reduces the adsorption of arsenic on hematite, indicating that there is also competitive adsorption between DOM and arsenic. Therefore, HA was selected to evaluate the effect of DOM on arsenic removal. It can be seen from Table 6 that in the presence of HA, the removal rate of As(V) by MIL-101(Fe,Zr) prepared by the present invention is slightly reduced. This may be because the organic matter HA covers some of the adsorption sites, resulting in a slight decrease in the removal rate of MIL-101(Fe,Zr) for As(V).

[0093] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing an iron-zirconium bimetallic MOF adsorbent, characterized in that: The following steps are involved: Terephthalic acid, iron salt and zirconium salt are added to an organic solvent and subjected to hydrothermal synthesis to obtain the iron-zirconium bimetallic MOF adsorbent; The molar ratio of the iron salt to the zirconium salt is 3:

1.

2. The preparation method of the iron-zirconium bimetallic MOF adsorbent according to claim 1, characterized in that: The hydrothermal synthesis was carried out at a temperature of 150° C. and for 15 hours.

3. The preparation method of the iron-zirconium bimetallic MOF adsorbent according to claim 1, characterized in that: The method further comprises the steps of centrifugation, washing and drying after the hydrothermal synthesis.

4. The method for preparing the iron-zirconium bimetallic MOF adsorbent according to claim 3, characterized in that: The centrifugal speed is 8000 rpm; and / or the drying temperature is 60° C. and the drying time is 12 h.

5. Use of an iron-zirconium bimetallic MOF adsorbent prepared by the preparation method according to any one of claims 1 to 4 in removing arsenic.

6. The use of the iron-zirconium bimetallic MOF adsorbent according to claim 5 in removing arsenic, characterized in that: The method comprises the following steps: adding the iron-zirconium bimetallic MOF adsorbent into arsenic-containing wastewater for reaction, and removing arsenic through solid-liquid separation.

7. The use of the iron-zirconium bimetallic MOF adsorbent according to claim 6 in removing arsenic, characterized in that: The liquid-solid ratio of the arsenic-containing wastewater to the iron-zirconium bimetallic MOF adsorbent is 1:(0.1-0.2) (L / g).

8. The use of the iron-zirconium bimetallic MOF adsorbent in removing arsenic according to claim 6, characterized in that: When the arsenic-containing wastewater contains trivalent arsenic, the method further comprises the step of adding H2O2; the amount of H2O2 added is 1.6-2.1% of the volume of the arsenic-containing wastewater.

9. The use of the iron-zirconium bimetallic MOF adsorbent according to claim 6 in removing arsenic, characterized in that: The concentration of arsenic in the arsenic-containing wastewater is 1-100 mg / L.

10. The use of the iron-zirconium bimetallic MOF adsorbent according to claim 6 in removing arsenic, characterized in that: The method also includes the step of adjusting the pH of the arsenic-containing wastewater to 3-11.

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