FCDI system based on modified MOFs material derived carbon and its application in heavy metal ion removal

Abstract

The application discloses a FCDI system based on modified MOFs material derived carbon and application thereof in heavy metal ion removal, and relates to the field of environmental engineering and sewage treatment. Through modification operation on the MOFs derived carbon material in a liquid phase, a MOFs derived carbon material with a larger specific surface area than traditional carbon materials is obtained, and the MOFs derived carbon material has a stronger heavy metal ion adsorption capacity. Compared with a traditional FCDI system, the FCDI system based on the modified MOFs material derived carbon has the advantage of wide application range.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of environmental engineering and sewage treatment, and particularly relates to a FCDI system based on modified MOFs material derived carbon and application thereof in heavy metal ion removal. BACKGROUND

[0002] With the rapid development of global society, water resource shortage and water pollution problems are imminent. Under this premise, a kind of capacitive deionization technology (CDI) for low concentration wastewater is born. The basic principle of capacitive deionization technology is that under the condition of applying external voltage, the wastewater is introduced into the CDI device, and the ions in the wastewater will migrate to both sides of the electrode under the action of electric field force, and finally be bound in the double electric layer on the surface of the electrode material, so as to remove the ions in the solution. When the electrodes on both sides reach saturation, they can be regenerated by reversing the electrodes or applying a short-circuit potential. Capacitive deionization technology has the advantages of low cost, low energy consumption, easy regeneration of electrode, no secondary pollution to environment, etc., and is considered as a good alternative to traditional desalination technology, so it has attracted widespread attention.

[0003] The traditional CDI device uses fixed electrodes, which is not conducive to continuous operation. On this basis, a kind of flow electrode capacitive deionization technology (FCDI) which can be continuously operated is proposed. FCDI technology uses flow electrode slurry, which is obtained by uniformly mixing electrode material, conductive agent and electrolyte solution, to achieve good desalination capacity and continuous operation. At the same time, the slurry electrode can be continuously mixed and regenerated outside the device. FCDI technology realizes the desalination capacity of the original CDI technology, and has the advantages of low cost, low energy consumption, easy regeneration of electrode, no secondary pollution to environment, etc., and makes the device continuously operated.

[0004] The electrode material applied to FCDI technology includes pseudo-capacitive material and carbon-based material. The pseudo-capacitive material has the disadvantage of only having adsorption effect on single ion, which has great limitation. The traditional carbon-based material such as activated carbon, carbon black and carbon nanotube is more limited by specific surface area. In order to achieve high treatment effect, the mass fraction of carbon material needs to be increased, which will bring high energy consumption and the risk of flow electrode blockage. Metal organic framework (MOFs) is a material with high specific surface area. The derived carbon material of MOFs is commonly used in capacitors and batteries. Since its adsorption mainly relies on the formation of double electric layer on the surface of electrode material, it will not be limited to a certain ion, and can realize the adsorption of multiple heavy metal ions. However, the activation and modification of MOFs material derived carbon mostly use urea or KOH solid grinding, which has the disadvantages of low modification efficiency and small specific surface area improvement. SUMMARY

[0005] Based on the shortcomings in the background art, the application discloses a FCDI system based on modified MOFs material derived carbon and application of the system. By using liquid phase KOH modified MOFs material ZIF-8 derived carbon, the surface area is increased to 2458 m 2 / g, with rich small pores, promoting ion transmission, and the structure of the internal pores of the material also provides rich diffusion paths for ions, exhibiting excellent electrochemical properties and achieving good adsorption effect; the FCDI system is optimized for the deionization effect of low-concentration heavy metal ion wastewater, and the electric adsorption removal efficiency is improved.

[0006] A FCDI system based on modified MOFs material derived carbon comprises the following components:

[0007] A FCDI system based on modified MOFs material derived carbon comprises the following components:

[0008] The anion exchange membrane and the cation exchange membrane are both homogeneous.

[0009] The power supply is a direct current power supply, and the constant voltage is 1.2V.

[0010] The flow electrode is MOFs material derived carbon.

[0011] The FCDI system based on modified MOFs material derived carbon, wherein the preparation process of the modified MOFs material derived carbon is as follows:

[0012] (1) Synthesis of precursor substance: 2-methyl imidazole and zinc nitrate hexahydrate are reacted in a methanol solution to prepare a precursor substance ZIF-8;

[0013] (2) Centrifugation and drying: the ZIF-8 obtained in step (1) is centrifuged and dried;

[0014] (3) First calcination: the product of step (2) is calcined under a nitrogen atmosphere to obtain MOFs derived carbon;

[0015] (4) Activation: the MOFs derived carbon and KOH are put into deionized water, stirred, and vacuum dried to obtain modified MOFs derived carbon;

[0016] (5) Second calcination: the modified MOFs derived carbon obtained in step (4) is put into a tube furnace and calcined, and after cooling, the KOH activated modified MOFs derived carbon is obtained.

[0017] The reaction temperature in step (1) is 20-25℃.

[0018] The centrifugal speed in the step (2) is 8000 rpm, the temperature of the vacuum drying box is 60℃, and the drying time is 12 h.

[0019] The calcination temperature in the step (3) is 800℃, and the heating rate is 5℃ / min,

[0020] The mass ratio of the MOFs-derived carbon to KOH in the step (4) is 1:3, and the mass ratio of the MOFs-derived carbon to deionized water is 1:50; the stirring temperature is 85℃, the stirring speed is 300 rpm, and the drying temperature is 110℃;

[0021] The calcination temperature in the step (5) is 800℃, and the heating rate is 5℃ / min.

[0022] The principle of the FCDI system based on the modified MOFs material-derived carbon for adsorbing heavy metal ions is as shown in Figure 1 The wastewater containing heavy metal ions is passed into the FCDI system at a certain flow rate, and under the condition of external voltage, the heavy metal ions in the solution are bound to the double electric layer formed on the surface of the electrode material.

[0023] The application of the FCDI system based on the modified MOFs material-derived carbon in the removal of heavy metal ions includes the following steps:

[0024] 1) Prepare the flow electrode slurry, and perform ultrasonic oscillation on the prepared electrode slurry;

[0025] 2) Add the flow electrode slurry into the electrode storage tank and stir;

[0026] 3) Add the wastewater into the wastewater storage tank and stir;

[0027] 4) Turn on the switch to make the wastewater and the flow electrode enter the device;

[0028] 5) Use the conductivity meter and the pH meter to measure the conductivity and the pH value of the wastewater and the flow electrode every 5 min, and use the inductively coupled plasma (ICP) to measure the concentration of the heavy metal ions in the wastewater every 20 min.

[0029] In the application of the FCDI system based on the modified MOFs material-derived carbon in the removal of heavy metal ions, a single-channel peristaltic pump is used for the wastewater entering the device, and a double-channel peristaltic pump is used for the flow electrode entering the device.

[0030] In the application of the FCDI system based on the modified MOFs material-derived carbon in the removal of heavy metal ions, the wastewater and the flow electrode are subjected to magnetic stirring at a speed of 500 rpm throughout the treatment process.

[0031] The application of the FCDI system based on the modified MOFs material derived carbon in the removal of heavy metal ions, wherein the modified MOFs material derived carbon is used as a flow electrode, the material is ground to a particle size of 100 meshes, then filtered and cleaned three times, and finally dried in a vacuum oven at 60 DEG C for 12 hours.

[0032] The application of the FCDI system based on the modified MOFs material derived carbon in the removal of heavy metal ions, wherein the flow electrode slurry is a mixture of the modified MOFs material derived carbon and a 500 mg / L NaCl solution, and the slurry is ultrasonically oscillated for 1.5 hours before use to ensure uniform mixing.

[0033] The application of the FCDI system based on the modified MOFs material derived carbon in the removal of heavy metal ions, wherein the wastewater is wastewater containing low-concentration heavy metal ions.

[0034] The FCDI system based on the modified MOFs material derived carbon, wherein the volume of the wastewater treated at one time is 100 ml, the volume of the flow electrode is 80 ml, the mass fraction of the modified MOFs material derived carbon is 3%, and the concentration of NaCl as the electrolyte solution is 500 mg / L.

[0035] The FCDI system based on the modified MOFs material derived carbon, wherein the volume of the wastewater treated at one time is 100 ml, the volume of the flow electrode is 80 ml, the mass fraction of the modified MOFs material derived carbon is 3%, and the concentration of NaCl as the electrolyte solution is 500 mg / L.

[0036] 1. The application discloses a carbon material of MOFs modified by liquid-phase KOH for a FCDI system, which has a larger specific surface area than traditional activated carbon materials, can promote ion migration, and can provide a shorter diffusion path for ions.

[0037] 2. The larger specific surface area also endows the carbon material disclosed by the application with stronger heavy metal adsorption capacity.

[0038] 3. Compared with activated carbon materials, which also rely on double electric layers but have a relatively small specific surface area and are prone to double electric layer overlap, increasing the resistance and reducing the adsorption effect; and compared with pseudo-capacitive materials, which have good adsorption effect but can only adsorb a specific ion due to the adsorption mechanism relying on pseudo-capacitive reaction, the MOFs material derived carbon modified by KOH has a high specific surface area, can provide abundant active sites for heavy metal ions, is not prone to double electric layer overlap, and has good adsorption effect on multiple metal ions.

[0039] 4. Compared with traditional FCDI systems that are mainly used for treating wastewater containing sodium chloride, the FCDI system based on the modified MOFs material derived carbon disclosed by the application has a wider range of applicable ions and can be applied to wastewater containing heavy metals. Attached Figure Description

[0040] Figure 1 A schematic diagram illustrating the adsorption principle of a carbon-derived FCDI system based on modified MOFs materials for heavy metal ion adsorption.

[0041] Figure 2 This is a schematic diagram of the FCDI unit structure;

[0042] Figure 3 This is a diagram showing the operation of FCDI equipment. Detailed Implementation

[0043] The parameters of the FCDI system selected in this embodiment are as follows: the dimensions of the two outer plates are 110×120 mm, the dimensions of the two graphite current collectors are 110×135×55 mm, the dimensions of the two ion exchange membranes are 110×120 mm, the input voltage is 1.2V, the wastewater flow rate is 5 ml / min, the flow electrode flow rate is 40 ml / min, and the electroadsorption time is 80 min.

[0044] Example 1

[0045] Preparation of modified MOFs materials and derived carbon materials

[0046] 23.6 g of 2-methylimidazole and 10.7 g of zinc nitrate hexahydrate were mixed in methanol and stirred at 25 °C to prepare the precursor ZIF-8. The mixture was centrifuged at 8000 rpm and dried in a vacuum drying oven at 60 °C for 12 h. Then, it was calcined in a tube furnace at 800 °C under a nitrogen atmosphere for 2 h with a heating rate of 5 °C / min. The obtained product was added to deionized water at a mass ratio of 1:3 with KOH (the ratio of MOFs-derived carbon to deionized water was 1:50). The mixture was stirred at 85 °C and 300 rpm for 3 h and then dried under vacuum at 110 °C for 24 h. Finally, it was calcined again in a tube furnace at 800 °C under a nitrogen atmosphere for 2 h with a heating rate of 5 °C / min to obtain KOH-activated MOFs-derived carbon.

[0047] Example 2

[0048] like Figures 2-3 As shown, an FCDI system based on modified MOF-derived carbon is assembled, consisting of two outer plates, two graphite current collectors, one cation and anion exchange membrane, three gaskets, a DC power supply, a flow electrode made of modified MOF-derived carbon, two peristaltic pumps, and a flow electrode storage tank. The two outer plates, two graphite current collectors, three gaskets, and two homogeneous cation and anion exchange membranes all require thorough cleaning with deionized water before use. The pump tubing is first cleaned with an ultrasonic cleaner for 10 minutes, and then thoroughly cleaned with deionized water.

[0049] The liquid phase modified MOFs material derived carbon was filtered with deionized water for more than three times before use, then dried in a vacuum oven at 60°C for 12h, finally mixed with 500mg / L NaCl solution and ultrasonic oscillation for 1.5h.

[0050] The application of the FCDI system based on modified MOFs material derived carbon in heavy metal ion removal was carried out according to the following steps:

[0051] 1) 100ml deionized water containing 3mg / L Pb 2+ ion was prepared, NaCl was added as electrolyte at a concentration of 500mg / L to improve conductivity, and magnetic stirring at a speed of 500rpm was maintained during use;

[0052] 2) 80ml NaCl solution with a concentration of 500mg / L was used to prepare a flow electrode with a mass fraction of 3%, the mixed flow electrode slurry was ultrasonic oscillated for 1.5h before use, and magnetic stirring at a speed of 500rpm was maintained during use;

[0053] 3) The flow electrode was connected to the same end of the two pump tubes of the double-channel peristaltic pump, the other end of the two pump tubes was connected to the lower end inlet of the cathode chamber and the anode chamber of the FCDI unit respectively, and the upper end outlet of the cathode chamber and the anode chamber was connected to the electrode storage tank respectively, and finally the two-chamber electrode was regenerated by mixing in the electrode storage tank. During this cycle, the flow rate of the flow electrode was maintained at 40ml / min;

[0054] 4) The wastewater obtained in step 1) was connected to one end of the pump tube of the single-channel peristaltic pump, the other end of the pump tube was connected to the lower end inlet of the water chamber of the FCDI unit, and the upper end outlet of the water chamber was connected to the wastewater, forming a cycle. During this cycle, the flow rate of the wastewater was maintained at 5ml / min;

[0055] 5) A direct current power supply of 1.2V was connected to continuously input voltage;

[0056] 6) The conductivity and pH value of the wastewater and the flow electrode were measured every 5min using a conductivity meter and a pH meter, and the concentration of heavy metal ions in the wastewater was measured every 20min using ICP;

[0057] 7) After 80min of adsorption, the conductivity and ion concentration of the wastewater remained stable and did not change, indicating that the ion adsorption equilibrium was reached and the electrosorption process was completed;

[0058] 8) The removal rate of Pb 2+ was calculated, and the results are shown in Table 1.

[0059] Example 3

[0060] On the basis of Example 1, Pb2+ions were replaced by Cu2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Cu2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Cu2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Cu2+ions

[0061] Example 4

[0062] On the basis of Example 1, Pb2+ions were replaced by Cd2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Cd2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Cd2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Cd2+ions

[0063] Example 5

[0064] On the basis of Example 1, Pb2+ions were replaced by Zn2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Zn2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Zn2+ions 2+ On the basis of Example 1, Pb2+ions were replaced by Zn2+ions

[0065] Table 1 Removal efficiency of low concentration Pb2+, Cu2+, Cd2+, Zn2+ions by FCDI device based on modified MOF material derived carbon. 2+ 2+ 2+ 2+

[0066] ​​​​

Claims

1. An FCDI system based on carbon derived from modified MOF materials, characterized in that, It consists of two outer plates, two graphite current collectors, anion and cation exchange membranes, gaskets, a DC power supply, a flow electrode based on modified MOFs-derived carbon, a peristaltic pump, and a flow electrode storage tank; the flow electrode based on modified MOFs-derived carbon is a mixture of modified MOFs-derived carbon and 500 mg / L NaCl solution. The preparation process of the modified MOF material-derived carbon is as follows: (1) Synthesis of precursor material: 2-methylimidazole and zinc nitrate hexahydrate were reacted in methanol solution to prepare precursor material ZIF-8; (2) Centrifugation and drying: Centrifuge and dry the ZIF-8 obtained in step (1); (3) First calcination: The product of step (2) is calcined under a nitrogen atmosphere to obtain MOFs-derived carbon; (4) Activation: MOF-derived carbon and KOH are placed in deionized water, stirred, and then vacuum dried; (5) Secondary calcination: The product obtained in step (4) is placed in a tube furnace for calcination. After cooling, it is taken out to obtain KOH-activated modified MOFs-derived carbon. In step (1), the reaction temperature is 20-25℃; in step (2), the centrifugation speed is 8000 rpm, and the drying is carried out in a vacuum drying oven at a temperature of 60℃; in step (3), the calcination temperature is 800℃, and the heating rate is 5℃ / min; in step (4), the mass ratio of MOFs-derived carbon to KOH is 1:3, and the mass ratio of MOFs-derived carbon to deionized water is 1:50; the stirring temperature is 85℃, the stirring speed is 300 rpm, and the drying temperature is 110℃; in step (5), the calcination temperature is 800℃, and the heating rate is 5℃ / min.

2. The FCDI system based on modified MOFs-derived carbon according to claim 1, characterized in that, The anion and cation exchange membrane is homogeneous.

3. The FCDI system based on modified MOFs-derived carbon according to claim 1, characterized in that, The voltage of the DC power supply is a constant 1.2 V.

4. The application of the FCDI system based on modified MOFs-derived carbon as described in any one of claims 1-3 in the removal of heavy metal ions, characterized in that, The application method includes the following steps: (1) Prepare a flowable electrode slurry, and then subject the prepared electrode slurry to ultrasonic oscillation; (2) Add the flowing electrode to the electrode storage tank and stir; (3) Add the wastewater to the wastewater storage tank and stir; (4) Turn on the switch to allow wastewater and the moving electrode to enter the device; (5) The conductivity and pH of the wastewater and the flow electrode were measured every 5 minutes using a conductivity meter and a pH meter, and the concentration of heavy metal ions in the wastewater was measured every 20 minutes using inductively coupled plasma.

5. The application according to claim 4, characterized in that, When using modified MOFs-derived carbon as a flow electrode, the material is first ground to a particle size of 100 mesh, filtered and washed, and then dried at 60°C.

6. The application according to claim 4, characterized in that... The wastewater inlet device uses a single-channel peristaltic pump, while the flow electrode inlet device uses a dual-channel peristaltic pump.

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