Method for treating heavy metal wastewater by using bimetal MOFs (Metal-Organic Frameworks) derived carbon-porous carbon composite electrode material

Abstract

The invention discloses a method for treating heavy metal wastewater by using a bimetal MOFs (Metal-Organic Frameworks) derived carbon-porous carbon composite electrode material. The method comprises the following steps: preparing the bimetal MOFs derived carbon-porous carbon into a composite electrode material, and assembling the composite electrode material as a working electrode into a capacitive deionization device; and carrying out electro-adsorption treatment on the heavy metal wastewater by utilizing the capacitive deionization device to finish treatment on the heavy metal wastewater. According to the present invention, the bimetallic MOFs derived carbon-porous carbon assembled capacitive deionization device is utilized to treat the heavy metal wastewater, such that the characteristics of high adsorption capacity and selective adsorption are provided while the heavy metal ions are efficiently and rapidly removed so as to achieve the efficient removal of the heavy metals in the wastewater, and the selective recovery of the toxic and harmful metals can be performed; the method has the advantages of being low in cost, simple in process, convenient to operate, high in treatment efficiency, good in removal effect, environmentally friendly and the like, and has high application value and wide application prospects in the aspect of heavy metal polluted water treatment.

Description

Technical Field

[0001] The present invention belongs to the fields of capacitive deionization and electro-adsorption, and relates to a method for treating heavy metal wastewater, in particular to a method for treating heavy metal wastewater by using a bimetallic MOFs-derived carbon-porous carbon composite electrode material. Background Art

[0002] After heavy metals enter the water environment in the form of simple substances or metal ions with rainwater or surface water, they will cause serious damage to the water environment. Taking lead and manganese as examples, after a large amount of lead and manganese enter the water body, they will not only affect the water ecosystem and the water quality of the water body, but they will also have a toxic effect on human safety and threaten the physiological health of humans. Therefore, how to effectively remove heavy metals from wastewater is of great significance.

[0003] Capacitive deionization (CDI) technology is a water treatment technology developed at the end of the 20th century. It has the characteristics of low energy consumption, no secondary pollution, recyclability, fast treatment rate, etc., and has broad application prospects. In theory, CDI can treat any electron-bearing pollutants, but in most studies, CDI devices are mostly limited to seawater desalination, generally removing alkali metals and valuable metals, and there is less research on the removal of heavy metal ions. The electrode is the most important part of the capacitive deionization technology, which determines the application direction and application effect of the capacitive deionization technology. Currently, the carbon-based materials used to prepare capacitive deionization electrodes mainly include activated carbon, graphene, carbon nanotubes, and biochar, but they still have the following defects: For example, the conductivity of activated carbon is relatively low, which affects its charge transfer speed and deionization efficiency; the cost of graphene is relatively high; the preparation method of carbon nanotubes is relatively complex and the cost is high; the pore structure and regulation performance of biochar are relatively low, and its functional characteristics are relatively disordered, unable to adapt to the complex treatment environment. In view of the above defects, some researchers have proposed to prepare capacitive deionization electrodes using metal-organic framework materials (MOFs), but in order to improve the adsorption capacity of capacitive deionization electrodes, it is necessary to carry out pickling treatment during the preparation process of MOF-derived carbon, which results in the CDI electrode material prepared from MOF-derived carbon only having electroadsorption function and not having redox function, thus unable to achieve the conversion of heavy metal ions and difficult to achieve the selective adsorption of heavy metal ions, which greatly limits the wide application of MOF-derived carbon in capacitive deionization technology. In addition, some researchers have proposed to compound MOF-derived carbon with graphene materials to prepare CDI electrode materials, using the high conductivity of graphene materials to improve the conductivity of CDI electrode materials, but the CDI electrode materials constructed thereby still only have electroadsorption function and do not have redox function, thus unable to achieve the conversion of heavy metal ions. At the same time, the CDI electrode materials still have defects such as small specific surface area, few adsorption sites, and small adsorption capacity, resulting in poor adsorption and removal ability of heavy metals, and ultimately difficult to effectively remove heavy metals in water. Therefore, obtaining a bimetallic MOF-derived carbon-porous carbon composite electrode material with a large specific surface area, many adsorption sites, a large adsorption capacity, good conductivity, strong redox ability, and good chemical stability is of great significance for realizing the effective treatment of heavy metal wastewater by capacitive deionization technology. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for treating heavy metal wastewater using a bimetallic MOF-derived carbon-porous carbon composite electrode material, which has the advantages of simple process, convenient operation, low cost, high treatment efficiency, good removal effect, and environmental friendliness.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions.

[0006] A method for treating heavy metal wastewater by using a bimetallic MOFs-derived carbon-porous carbon composite electrode material, comprising the following steps:

[0007] S1. Prepare a bimetallic MOFs-derived carbon-porous carbon composite electrode material from the bimetallic MOFs-derived carbon-porous carbon; the bimetallic MOFs-derived carbon-porous carbon is prepared by carbonizing a composite material of bimetallic MOFs and porous carbon.

[0008] S2. Assemble a capacitive deionization device with the bimetallic MOFs-derived carbon-porous carbon composite electrode material as the working electrode.

[0009] S3. Perform electro-adsorption treatment on the heavy metal wastewater by using the capacitive deionization device to complete the treatment of the heavy metal wastewater.

[0010] In the above method, further improved, the preparation method of the bimetallic MOFs-derived carbon-porous carbon comprises the following steps: heating the composite material of bimetallic MOFs and porous carbon to 450°C to 600°C for carbonization to obtain the bimetallic MOFs-derived carbon-porous carbon; the carbonization is carried out in an inert atmosphere and / or a nitrogen atmosphere; the inert atmosphere is argon and / or helium; the heating rate during the carbonization process is 5°C / min to 15°C / min; the carbonization time is 30 min to 120 min.

[0011] In the above method, further improved, the preparation method of the composite material of bimetallic MOFs and porous carbon comprises the following steps:

[0012] (a) Mix a zinc salt, a cobalt salt and methanol to obtain a metal template solution; mix an organic ligand and methanol, and add porous carbon to obtain an organic ligand solution containing porous carbon.

[0013] (b) Add the organic ligand solution containing porous carbon to the metal template solution and stir to obtain the composite material of bimetallic MOFs and porous carbon.

[0014] In the above method, which is further improved, in step (a), the molar ratio of the zinc salt to the cobalt salt is 1:1 to 3; in the metal template solution, the total molar amount of the zinc salt and the cobalt salt to methanol is 0.01 mol:100 mL to 200 mL; in the organic ligand solution containing porous carbon, the ratio of the organic ligand to methanol is 3.5 g:50 mL to 100 mL; the mass ratio of the porous carbon to the total mass of the zinc salt and the cobalt salt is 1:1 to 3. The zinc salt is at least one of zinc chloride, zinc nitrate and zinc acetate; the cobalt salt is at least one of cobalt chloride, cobalt nitrate and cobalt acetate; the organic ligand is at least one of 1-methylimidazole, 2-methylimidazole, 4,5-dimethylimidazole, 2-ethylimidazole and 2-isopropylimidazole; the porous carbon is porous biochar and / or activated carbon; the particle size of the porous carbon is less than 30 mesh.

[0015] In the above method, which is further improved, in step (b), the stirring is carried out at a temperature of 25 °C to 40 °C; the stirring time is 1 h to 2 h; after the stirring is completed, it further includes: centrifuging the stirred product at 8000 to 12000 r / min, washing the solid product after centrifugation with a washing solution, and drying at 60 to 90 °C; the washing solution is water, an organic solvent and an acidic solution; the organic solvent is at least one of ether, alcohol and ketone; the acidic solution is hydrochloric acid and / or dilute nitric acid.

[0016] In the above method, which is further improved, in step S1, the preparation method of the bimetallic MOFs-derived carbon-porous carbon composite electrode material includes the following steps:

[0017] (1) Mix the bimetallic MOFs-derived carbon-porous carbon, binder and solvent, stir to make an electrode slurry;

[0018] (2) Mix the electrode slurry with carbon felt, ultrasonicate, dry to obtain a carbon felt electrode loaded with the material;

[0019] (3) Paste the carbon felt electrode loaded with the material on a current collector to obtain the bimetallic MOFs-derived carbon-porous carbon composite electrode material.

[0020] In the above method, which is further improved, in step (1), the mass ratio of the bimetallic MOFs-derived carbon-porous carbon to the binder is 4 to 9:1; the total mass of the bimetallic MOFs-derived carbon-porous carbon and the binder to the volume of the solvent is 1 mg:1 mL to 2 mL; the binder is at least one of polyvinyl alcohol and polyvinylidene fluoride; the solvent is N-methylpyrrolidone; the stirring time is ≥4 h.

[0021] For the above method, in a further improvement, in step (2), before using the carbon felt, the following treatments are further included: cutting the carbon felt into sheet materials with a length and width of 5 cm × 5 cm, ultrasonically cleaning in ethanol for more than 2 h, ultrasonically cleaning in water for more than 2 h, and drying.

[0022] For the above method, in a further improvement, in step (3), the carbon felt electrode is pasted on the current collector with conductive carbon glue; the current collector is one of a titanium plate, copper foil, aluminum foil, graphite paper, and graphite plate; before using the current collector, the following treatments are further included: heating the current collector in an oxalic acid solution to 85°C - 100°C, maintaining for 1.5 h - 3 h, successively cleaning with water and ethanol, and drying; the mass fraction of the oxalic acid solution is 5% - 20%.

[0023] For the above method, in a further improvement, in step S3, during the electro-adsorption treatment, the flow rate of the heavy metal wastewater in the capacitive deionization device is controlled to be 15 mL min -1 ~20 mL min -1 。

[0024] For the above method, in a further improvement, in step S3, the residence time of the heavy metal wastewater in the capacitive deionization device is 1 h - 3 h.

[0025] For the above method, in a further improvement, in step S3, during the electro-adsorption treatment, the voltage of the capacitive deionization device is controlled to be 1 V - 1.2 V.

[0026] For the above method, in a further improvement, in step S3, the heavy metals in the heavy metal wastewater are at least one of lead, cadmium, manganese, and copper; the initial concentration of the heavy metals in the heavy metal wastewater ≤ 100 mg L -1 ;the initial pH value of the heavy metal wastewater is < 7.5.

[0027] Compared with the prior art, the advantages of the present invention are as follows:

[0028] (1) Aiming at the deficiencies in existing MOF-derived carbon-based capacitive deionization electrode materials, such as small specific surface area, few adsorption sites, small adsorption capacity, and poor redox ability, as well as the resulting defects of only having desalination function, being difficult to quickly and thoroughly remove heavy metal ions, and being difficult to selectively adsorb heavy metal ions, the present invention creatively proposes a method for treating heavy metal wastewater using a bimetallic MOF-derived carbon-porous carbon composite electrode material. Using the bimetallic MOF-derived carbon-porous carbon composite electrode material made of bimetallic MOF-derived carbon-porous carbon as the working electrode, a capacitive deionization device is assembled, and the capacitive deionization device is used for electro-adsorption treatment of heavy metal wastewater, where the bimetallic MOF-derived carbon-porous carbon is prepared by carbonization treatment of a composite material of bimetallic MOF and porous carbon as the raw material. In the present invention, the composite material of bimetallic MOF and porous carbon is used as the raw material, which is a porous material with porous carbon as the carrier and bimetallic organic framework material loaded thereon. On the one hand, using porous carbon as the carrier can improve the dispersibility of the bimetallic organic framework material, enabling the bimetallic organic framework material to be evenly dispersed and stably loaded on the biochar, so that during the carbonization process, it is beneficial to form a bimetallic MOF-derived carbon-porous carbon with stable structure, large specific surface area, rich mesopores, many adsorption sites, and excellent conductivity. Therefore, using it to prepare the bimetallic MOF-derived carbon-porous carbon composite electrode material is conducive to the efficient removal of heavy metals in water. On the other hand, during the carbonization process, the organic ligands in the bimetallic organic framework material are carbonized to form a carbon framework material. At the same time, the metal ions in the bimetallic organic framework material are converted into metal oxides and embedded in the carbon framework material. Since the metal oxides have excellent semiconductor properties, electrocatalytic ability, and redox ability, the bimetallic MOF-derived carbon-porous carbon has the ability to change the valence state or form of heavy metals, showing very excellent selective adsorption performance. Moreover, under the promotion of the carbon framework, the conductivity of the bimetallic MOF-derived carbon-porous carbon can also be significantly improved, showing very excellent conductive ability. Thus, a bimetallic MOF-derived carbon-porous carbon with excellent electro-adsorption performance and strong redox ability can be formed. Using it to prepare the bimetallic MOF-derived carbon-porous carbon composite electrode material can not only greatly improve the ability of the bimetallic MOF-derived carbon-porous carbon composite electrode material to remove heavy metals, but also greatly improve the rate of the bimetallic MOF-derived carbon-porous carbon composite electrode material to remove heavy metals, and ultimately can achieve the selective adsorption and recovery of heavy metals in water.Therefore, in the present invention, when treating heavy metal wastewater by using a capacitive deionization device assembled with a bimetallic MOF-derived carbon-porous carbon composite electrode material made of bimetallic MOFs-derived carbon and porous carbon as the working electrode, it not only has the characteristics of high adsorption capacity and selective adsorption while efficiently and rapidly removing heavy metal ions, but also can not only achieve the efficient removal of heavy metals in wastewater, but also selectively recover toxic and harmful metals. It has the advantages of low cost, simple process, convenient operation, high treatment efficiency, good removal effect, environmental friendliness, etc., and has high application value and broad application prospects in the treatment of heavy metal-polluted water bodies.

[0029] (2) In the present invention, the composite material of bimetallic MOFs and porous carbon is prepared by using porous carbon as the raw material, zinc salt and cobalt salt as metal templates, and under the action of organic ligands. Compared with the conventional preparation method, using porous carbon as the raw material and zinc salt and cobalt salt as metal templates in the present invention has the following advantages: (a) Porous carbon has high conductivity and capacitance performance, which can enhance the electrochemical performance, enable the capacitive deionization material to have better energy storage capacity, and thus can further improve the conductivity of the capacitive deionization material. (b) Porous carbon has a porous structure, which can provide more active surface areas for the capacitive deionization material, increase the adsorption and storage capacity during the deionization process, and improve the efficiency of the capacitive deionization material. (c) The organic metal framework and porous carbon can make up for each other's deficiencies. Among them, biochar can provide good conductivity and promote electron conduction, while the organic metal framework provides a porous structure and regulation function. Therefore, combining these two materials can form a composite material with excellent conductivity and high tunability, and then through calcination, zinc-cobalt bimetallic MOF-derived carbon-porous carbon with a large specific surface area, rich mesopores, many adsorption sites, good conductivity, and strong catalytic performance can be formed, which is not only beneficial to improving the adsorption capacity of the bimetallic MOF-derived carbon-porous carbon composite electrode material, but also beneficial to improving the adsorption rate of the bimetallic MOF-derived carbon-porous carbon composite electrode material, making the bimetallic MOF-derived carbon-porous carbon composite electrode material exhibit very excellent electroadsorption performance. In addition, the method for preparing the composite material of bimetallic MOFs and porous carbon in the present invention also has the advantages of simple process, easy operation, wide raw material sources, simple preparation conditions, low production cost, high economic benefits, short production cycle, environmental friendliness, etc., and is suitable for large-scale preparation and industrial application. Brief Description of the Drawings

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0031] Figure 1SEM image of the bimetallic MOF-derived carbon - porous carbon prepared in Example 1 of the present invention.

[0032] Figure 2 XRD full spectrum of the bimetallic MOF-derived carbon - porous carbon prepared in Example 1 of the present invention.

[0033] Figure 3 FTIR full spectrum of the bimetallic MOF-derived carbon - porous carbon prepared in Example 1 of the present invention.

[0034] Figure 4 XPS full spectrum of the bimetallic MOF-derived carbon - porous carbon prepared in Example 1 of the present invention.

[0035] Figure 5 Nitrogen adsorption - desorption isotherm of the bimetallic MOF-derived carbon - porous carbon prepared in Example 1 of the present invention.

[0036] Figure 6 Pore size distribution of the bimetallic MOF-derived carbon - porous carbon prepared in Example 1 of the present invention.

[0037] Figure 7 CV diagram of the bimetallic MOF-derived carbon - porous carbon composite electrode material prepared in Example 1 of the present invention.

[0038] Figure 8 Removal rate diagram of treating lead and manganese wastewater with a concentration of 100 mg / L using the bimetallic MOF-derived carbon - porous carbon composite electrode material in Example 1 of the present invention.

[0039] Figure 9 Selective adsorption effect diagram for different ions when treating lead ions with a concentration of 100 mg / L using the bimetallic MOF-derived carbon - porous carbon composite electrode material in Example 1 of the present invention.

[0040] Figure 10 Selective adsorption effect diagram for different ions when treating manganese ions with a concentration of 100 mg / L using the bimetallic MOF-derived carbon - porous carbon composite electrode material in Example 1 of the present invention.

[0041] Figure 11 Comparison diagram of the maximum adsorption capacity between the bimetallic MOF-derived carbon - porous carbon composite electrode material and the pure biochar electrode in Example 1 of the present invention. Detailed implementation mode

[0042] The present invention will be further described below in conjunction with the accompanying drawings of the specification and specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are all commercially available.

[0043] Example 1:

[0044] A method for treating heavy metal wastewater by using a bimetallic MOFs-derived carbon-porous carbon composite electrode material, specifically using a capacitive deionization device assembled with the bimetallic MOFs-derived carbon-porous carbon composite electrode material to treat heavy metal lead wastewater and heavy metal manganese wastewater, including the following steps:

[0045] S1. Prepare the bimetallic MOFs-derived carbon-porous carbon into a bimetallic MOFs-derived carbon-porous carbon composite electrode material, specifically:

[0046] S1-1. Weigh 25 mg of the bimetallic MOFs-derived carbon-porous carbon and 5 mg of polyvinyl alcohol, mix them evenly, add 30 mL of N-methylpyrrolidone (NMP), and stir for 4 h to form a paste-like slurry to obtain an electrode slurry.

[0047] In this step, the bimetallic MOFs-derived carbon-porous carbon used is prepared by carbonization treatment using a composite material of bimetallic MOFs and porous carbon, including the following steps:

[0048] (1.1) According to the equimolar ratio, add 0.01 mol of zinc salt (3 g of zinc nitrate hexahydrate) and 0.01 mol of cobalt salt (3 g of cobalt nitrate hexahydrate) to methanol, and stir at a temperature of 25 °C for 2 h (stirring at a temperature of 25 - 40 °C for 2 - 4 h is also acceptable) to dissolve the zinc salt and cobalt salt in methanol to obtain a metal template solution. The ratio of the total molar amount of zinc salt and cobalt salt to methanol in this metal template solution is 0.01 mol∶100 mL.

[0049] (1.2) Add 7 g of 2-methylimidazole to 200 mL of methanol, and stir at a temperature of 25 °C for 2 h (stirring at a temperature of 25 - 40 °C for 2 - 4 h is also acceptable) to dissolve 2-methylimidazole in methanol to obtain an organic ligand solution (a solution containing 2-methylimidazole).

[0050] (1.3) According to the mass ratio of the porous carbon to the total mass of the zinc salt and cobalt salt being 1∶3 (the mass ratio should not be too high or too low. If the ratio is too low, it will cause the MOFs material to not be fully loaded on the surface of the biochar, and if the ratio is too high, it will lead to uneven dispersion of the MOFs and unstable material performance), add 2 g of porous biochar to the solution containing 2-methylimidazole, and stir at a temperature of 25 °C for 2 h (stirring at a temperature of 25 - 40 °C for 2 - 4 h is also acceptable) to obtain an organic ligand solution containing porous biochar. In this step, the porous biochar used is a carbon material obtained by pyrolyzing biomass under anoxic conditions, and the sources of the biomass include: plant residues, crop wastes, or animal feces, etc.; the particle size of the porous biochar is less than 30 mesh.

[0051] (1.4) Rapidly add the organic ligand solution containing porous biochar to the metal template solution, stir at 25 °C for 2 h (stirring at 25 - 40 °C for 1 - 2 h is acceptable, but not too short. If the time is too short, the metal template cannot be evenly mixed with the organic ligand, resulting in the inability to form a precursor with a dispersed texture and high purity). Finally, centrifuge at 8000 r / min, collect the solid product, then wash it three times repeatedly with methanol, and dry it in an oven at 60 °C to obtain the composite material of bimetallic MOFs and porous carbon.

[0052] (1.5) Place the composite material of bimetallic MOFs and porous carbon into a tubular furnace, introduce nitrogen, heat it to 600 °C at a heating rate of 10 °C / min for carbonization, and keep the temperature for 30 min to obtain bimetallic MOFs-derived carbon-porous carbon.

[0053] S1-2: Mix the electrode slurry with carbon felt (purchased from Tianjin Carbon Factory, high-purity graphite fiber felt, with a length and width of 20 cm × 30 cm), ultrasonicate for 6 h to fully mix the slurry with the carbon felt, and dry it in an oven at 80 °C for 12 hours to obtain the carbon felt electrode. In this step, before using the carbon felt, the following treatment is also included: Cut the carbon felt into sheet materials with a length and width of 5 cm × 5 cm, place it in ethanol for ultrasonic cleaning for 2 h, then place it in water for ultrasonic cleaning for 2 h, and dry it in an oven at 80 °C.

[0054] S1-3: Use conductive carbon glue (SEM double-sided carbon conductive tape purchased from Shunsheng Electronic Technology Co., Ltd., model 5 mm * 20 m, and other similar conductive double-sided carbon glue for testing SEM and EDS experiments are applicable) to paste the carbon felt electrode on the titanium plate to obtain the composite electrode material of bimetallic MOFs-derived carbon-porous carbon. In this step, before using the titanium plate, the following treatment is also included: Place the titanium plate with a length and width of 5 cm × 5 cm in a 10% mass fraction of oxalic acid solution (using an oxalic acid solution with a mass fraction of 5% - 20% is acceptable, but too high a concentration is likely to produce steam that damages the respiratory tract), heat it to 100 °C, keep it boiling for 2 hours to etch the titanium plate, wash it successively with ultrapure water and ethanol to remove residual impurities, and dry it.

[0055] S2: Use the composite electrode material of bimetallic MOFs-derived carbon-porous carbon as the working electrode to assemble a capacitive deionization device.

[0056] S3: Use the capacitive deionization device to perform electro-adsorption treatment on heavy metal lead wastewater (the pH value of this wastewater is 7, and the concentration is 100 mg / L -1 ) and heavy metal manganese wastewater (the pH value of this wastewater is 7, and the concentration is 100 mg / L -1 ), specifically as follows:

[0057] S3-1. Feed the heavy metal wastewater to be treated into the capacitive deionization device. Before power-on, circulate at a flow rate of 15 mL / min for 60 min first to eliminate the influence of physical adsorption on the capacitive deionization performance. -1 This is used to eliminate the influence of physical adsorption on the performance of capacitive deionization.

[0058] S3-2. Turn on the power supply to provide a constant voltage. Under the condition of a voltage of 1.2 V, use the capacitive deionization device to perform electro-adsorption treatment on the heavy metal wastewater. Metal ions in the solution flowing through the capacitive deionization device are transferred to the electrode with the opposite charge under the action of the electric field force. The treated solution flows back to the water tank and circulates in this way. After 2 h of power-on, turn off the power supply to complete the treatment of the heavy metal wastewater.

[0059] Control group: Use unmodified biochar instead of bimetallic MOFs-biochar to make the electrode material, and treat heavy metal lead wastewater and heavy metal manganese wastewater with a concentration of 100 mg / L under the same other conditions. Among them, the preparation method of unmodified biochar is basically the same as that of bimetallic MOFs-biochar, and the only difference is that in the preparation method of unmodified biochar, the MOFs material is not modified.

[0060] Figure 1 This is the SEM image of the bimetallic MOFs-derived carbon-porous carbon prepared in Example 1 of the present invention. As Figure 1 can be seen, after the bimetallic MOFs-derived carbon-porous carbon is modified, a very regular and smooth surface dodecahedral crystal structure appears on the biochar surface, and many positions conducive to charge transfer and catalytic sites are formed on the biochar surface.

[0061] Figure 2 This is the XRD full spectrum of the bimetallic MOFs-derived carbon-porous carbon prepared in Example 1 of the present invention.

[0062] Figure 3 This is the FTIR full spectrum of the bimetallic MOFs-derived carbon-porous carbon prepared in Example 1 of the present invention.

[0063] As Figure 2 can be seen, in the peak distribution of the bimetallic MOFs-derived carbon-porous carbon prepared in the present invention, the arrangement order of ZIF-8 appears, indicating that through the modification step, the organic metal framework composed of Zn and Co has been successfully loaded in the biochar and simultaneously has the basic structure of MOFs. At the same time, through Figure 3 the FTIR test, it can be found that through the introduction of the ligand, an amino functional group conducive to metal ion adsorption appears in the spectrum of the biochar.

[0064] Figure 4 This is the XPS full spectrum of the bimetallic MOFs-derived carbon-porous carbon prepared in Example 1 of the present invention. AsFigure 4 It can be seen that the peak binding energies of Zn and Co elements present in the bimetallic MOF-derived carbon - porous carbon prepared by the present invention are very obvious, indicating that Zn and Co have been loaded onto the biochar in a very stable state.

[0065] Figure 5 This is the nitrogen adsorption - desorption isotherm diagram of the bimetallic MOF-derived carbon - porous carbon prepared in Example 1 of the present invention. Figure 5 It can be seen that this isotherm belongs to the type-IV adsorption isotherm, that is, the pressure and the adsorption amount are basically linearly and evenly distributed. Further analysis reveals that within the pressure range of 0.2 - 0.8, the adsorption amount will increase steadily, indicating that the bimetallic MOF-derived carbon - porous carbon of the present invention has a mesoporous-dominated structure, and under this state, it is more conducive to ion transport and charge conduction. At the same time, the specific surface area of the sample exceeds 1200 m 2 ·g, indicating that the bimetallic MOF-derived carbon - porous carbon prepared by the present invention has excellent adsorption performance. While the specific surface area of the conventional bimetallic MOF-derived carbon - graphene is only 639.1 m 2 ·g. In contrast, the highest adsorption amount of the bimetallic MOF-derived carbon - porous carbon prepared by the present invention reaches 245.03 mg / g, while the highest adsorption amount of the conventional bimetallic MOF-derived carbon - graphene is only 7.92 mg / g.

[0066] Figure 6 This is the pore size distribution diagram of the bimetallic MOF-derived carbon - porous carbon prepared in Example 1 of the present invention. Figure 6 It can be seen that the maximum pore volume of the bimetallic MOF-derived carbon - porous carbon prepared by the present invention exceeds 0.324 cm 3 ·g, and the pore size distribution range is 0 - 150 nm, indicating that the sample has a relatively dense pore-forming region and a relatively wide pore size distribution range. At the same time, Figure 6 it can be seen that the pore size distribution of the bimetallic MOF-derived carbon - porous carbon prepared by the present invention is relatively uniform, and the curve is relatively symmetric, mainly dominated by mesopores (2 - 50 nm).

[0067] Figure 7 This is the CV diagram of the bimetallic MOF-derived carbon - porous carbon composite electrode material prepared in Example 1 of the present invention. Figure 7 It can be seen that the CV diagram of the bimetallic MOF-derived carbon - porous carbon composite electrode material prepared in the present invention presents a spindle-shaped region, and the formed closed image is not symmetric, indicating that the electrochemical reaction should be mainly adsorption, and the ion diffusion is relatively dense and uniform, indicating that the electrode is in a relatively stable state during the reaction.

[0068] In this embodiment, during the electro-adsorption treatment process, samples were taken under different treatment time conditions, the concentration of heavy metals in the wastewater was detected, and the removal rate of heavy metals by different electrode materials was calculated. The results are as follows: Figures 8 - 10 as shown.

[0069] Figure 8 This is the removal rate diagram of using the bimetallic MOFs-derived carbon-porous carbon composite electrode material to treat lead and manganese wastewater with a concentration of 100 mg / L in Example 1 of the present invention. It can be seen from Figure 8 that the bimetallic MOFs-derived carbon-porous carbon has a very good removal effect on lead and manganese ions in capacitive deionization. After a complete power-on operation, both metal ions reach the adsorption equilibrium at about 120 minutes. From the test results of the metal ion concentration by extracting the sample solution at different time periods, it can be seen that the removal efficiency of lead and manganese ions using the bimetallic MOFs-derived carbon-porous carbon is close to 100%, and the effluent concentration has reached the national discharge standard (National Sewage Discharge Standard (<1 mg / L) (GB8978-1996)).

[0070] Figure 9 This is the selective adsorption effect diagram for different ions when using the bimetallic MOFs-derived carbon-porous carbon composite electrode material to treat lead ions with a concentration of 100 mg / L in Example 1 of the present invention.

[0071] Figure 10 This is the selective adsorption effect diagram for different ions when using the bimetallic MOFs-derived carbon-porous carbon composite electrode material to treat manganese ions with a concentration of 100 mg / L in Example 1 of the present invention.

[0072] It can be seen from Figure 9 Figure 10 that the bimetallic MOFs-derived carbon-porous carbon has achieved a selective removal effect on heavy metal ions in capacitive deionization, thus avoiding the removal of necessary and beneficial elements required in the environment, indicating that this material can bring more innovative solutions to the separation technology and environmental fields.

[0073] Figure 11 This is the comparison diagram of the maximum adsorption capacity between the bimetallic MOFs-derived carbon-porous carbon composite electrode material and the pure biochar electrode in Example 1 of the present invention. It can be seen from Figure 11 that after modifying the MOFs-derived carbon with biochar, the adsorption capacity increases exponentially, and the improvement of its removal effect is not limited to a single metal element, indicating that the method of the present invention has universality and is conducive to promotion. By modifying the MOFs-derived carbon, biochar has high adsorption performance, making it an effective tool for solving ion pollution problems, capable of providing solutions for water purification and resource recovery in various industries, and achieving the recycling and utilization of resources in a sustainable manner.

[0074] Based on the above results, it can be seen that the method for treating heavy metal wastewater using the bimetallic MOFs-derived carbon-porous carbon composite electrode material of the present invention can rapidly and thoroughly adsorb heavy metals in water by using the bimetallic MOFs-derived carbon-porous carbon composite electrode material, thereby effectively removing heavy metals in wastewater. It has the advantages of simple process, convenient operation, low cost, high treatment efficiency, good removal effect, environmental friendliness, etc., and has high application value and broad application prospects in treating heavy metal-polluted water bodies.

[0075] The above is only a preferred embodiment of the present invention and does not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above, or modify it into an equivalent embodiment with equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for treating heavy metal wastewater by using a bimetallic MOFs-derived carbon-porous carbon composite electrode material, characterized in that, It includes the following steps: S1. Prepare a bimetallic MOFs-derived carbon-porous carbon composite electrode material; the bimetallic MOFs-derived carbon-porous carbon is prepared by carbonizing a composite material of bimetallic MOFs and porous carbon; S2. Assemble a capacitive deionization device with the bimetallic MOFs-derived carbon-porous carbon composite electrode material as the working electrode; S3. Use the capacitive deionization device to perform electro-adsorption treatment on heavy metal wastewater to complete the treatment of heavy metal wastewater.

2. The method according to claim 1, wherein The preparation method of the bimetallic MOFs-derived carbon-porous carbon includes the following steps: heat the composite material of bimetallic MOFs and porous carbon to 450°C - 600°C for carbonization to obtain bimetallic MOFs-derived carbon-porous carbon; the carbonization is carried out in an inert atmosphere and / or nitrogen atmosphere; the inert atmosphere is argon and / or helium; the heating rate during the carbonization process is 5°C / min - 15°C / min; the carbonization time is 30 min - 120 min.

3. The method according to claim 2, wherein The preparation method of the composite material of bimetallic MOFs and porous carbon includes the following steps: (a) Mix a zinc salt, a cobalt salt and methanol to obtain a metal template solution; mix an organic ligand and methanol, and add porous carbon to obtain an organic ligand solution containing porous carbon; (b) Add the organic ligand solution containing porous carbon to the metal template solution and stir to obtain a composite material of bimetallic MOFs and porous carbon.

4. The method according to claim 3, characterized in that, In step (a), the molar ratio of the zinc salt to the cobalt salt is 1:1 - 3; in the metal template solution, the total molar amount of the zinc salt and the cobalt salt to methanol is 0.01 mol:100 mL - 200 mL; in the organic ligand solution containing porous carbon, the ratio of the organic ligand to methanol is 3.5 g:50 mL - 100 mL; the mass ratio of the porous carbon to the total mass of the zinc salt and the cobalt salt is 1:1 - 3; the zinc salt is at least one of zinc chloride, zinc nitrate and zinc acetate; the cobalt salt is at least one of cobalt chloride, cobalt nitrate and cobalt acetate; the organic ligand is at least one of 1-methylimidazole, 2-methylimidazole, 4,5-dimethylimidazole, 2-ethylimidazole and 2-isopropylimidazole; the porous carbon is porous biochar and / or activated carbon; the particle size of the porous carbon is less than 30 mesh; In step (b), the stirring is carried out at a temperature of 25°C - 40°C; the stirring time is 1 h - 2 h; After the stirring is completed, it further includes: centrifuging the stirring product at 8000 r / min - 12000 r / min, washing the centrifuged solid product with a washing solution, and drying at 60°C - 90°C; the washing solution is water, an organic solvent and an acidic solution; the organic solvent is at least one of ether, alcohol and ketone; the acidic solution is hydrochloric acid and / or dilute nitric acid.

5. The method according to any one of claims 1 to 4, characterized in that In step S1, the preparation method of the bimetallic MOFs-derived carbon-porous carbon composite electrode material includes the following steps: (1) Mix the bimetallic MOFs-derived carbon-porous carbon, a binder and a solvent, and stir to make an electrode slurry; (2) Mix the electrode slurry with the carbon felt, ultrasonicate, and dry to obtain a carbon felt electrode loaded with the material. (3) Paste the carbon felt electrode loaded with the material onto the current collector to obtain a bimetallic MOFs-derived carbon-porous carbon composite electrode material.

6. The method according to claim 5, wherein In step (1), the mass ratio of the bimetallic MOFs-derived carbon-porous carbon to the binder is 4-9:1; the ratio of the total mass of the bimetallic MOFs-derived carbon-porous carbon and the binder to the volume of the solvent is 1 mg:1 mL-2 mL; the binder is at least one of polyvinyl alcohol and polyvinylidene fluoride; the solvent is N-methylpyrrolidone; the stirring time ≥ 4 h; In step (2), before using the carbon felt, the following treatment is also included: cut the carbon felt into sheet materials with a length and width of 5 cm × 5 cm, place them in ethanol for ultrasonic cleaning for more than 2 h, place them in water for ultrasonic cleaning for more than 2 h, and dry. In step (3), paste the carbon felt electrode onto the current collector using conductive carbon paste; the current collector is one of titanium plate, copper foil, aluminum foil, graphite paper, and graphite plate; before using the current collector, the following treatment is also included: place the current collector in an oxalic acid solution and heat it to 85°C-100°C, keep it for 1.5 hours-3 hours, wash it successively with water and ethanol, and dry; the mass fraction of the oxalic acid solution is 5%-20%.

7. The method according to any one of claims 1 to 4, characterized in that In step S3, during the electro-adsorption treatment process, the flow rate of the heavy metal wastewater in the capacitive deionization device is controlled to be 15 mL / min -1 ~20 mL / min -1 .

8. The method according to claim 7, wherein In step S3, the residence time of the heavy metal wastewater in the capacitive deionization device is 1 hour-3 hours.

9. The method according to claim 7, characterized in that, In step S3, control the voltage of the capacitive deionization device to be 1 V-1.2 V during the electroadsorption treatment.

10. The method according to claim 7, wherein In step S3, the heavy metals in the heavy metal wastewater are at least one of lead, cadmium, manganese and copper; the initial concentration of heavy metals in the heavy metal wastewater ≤ 100 mg / L -1 ; the initial pH value of the heavy metal wastewater is < 7.5.

Images