Composite metal organic framework material as well as preparation method and application thereof

Abstract

The invention discloses a composite metal organic framework material and a preparation method and application thereof.The composite metal organic framework material is synthesized through a solvothermal method with terephthalic acid and polyethyleneimine as ligands and rare earth metal salt as a metal source, and rare earth metal in the rare earth metal salt is Sc, Y, Sm or Eu. Polyethyleneimine with high coordination capability is introduced into a rare earth-based metal organic framework, a three-dimensional porous MOF structure is constructed through synergistic coordination, As (III) and As (V) in a water body are synergistically and efficiently captured by utilizing strong Lewis acid sites of rare earth ions and rich amino functional groups on PEI, and the composite material has the advantages of high adsorption performance, high selectivity, good stability and reproducibility.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of wastewater treatment, and particularly relates to a rare earth-polyethyleneimine composite metal organic framework material, a preparation method thereof and application of the rare earth-polyethyleneimine composite metal organic framework material in treatment of arsenic-containing wastewater. BACKGROUND

[0002] Arsenic pollutants are generally contained in industrial wastewater such as steel smelting and non-ferrous metal smelting. Industrial arsenic-containing wastewater, especially wastewater discharged by steel plants and smelting plants, has a low arsenic concentration (usually between 0.5-50 mg / L), but arsenic is a highly toxic element. Even if the low concentration exists, its continuous discharge will cause serious harm to the environment and human health. These low-concentration arsenic can erode the ecological balance through water circulation, and can be enriched through the food chain, eventually entering the human body, causing skin lesions, nervous system damage, and even cancer and other serious diseases, posing a long-term and hidden serious threat to public health. Existing arsenic removal technologies include chemical precipitation, oxidation-reduction, ion exchange and the like. Although they have application value under certain conditions, their limitations are increasingly prominent when treating low-concentration (especially less than 5 mg / L) arsenic-containing wastewater. The chemical precipitation method: its core is to add chemical reagents (such as iron salts and calcium salts) to make arsenic form a precipitate. However, the treatment effect of this method is extremely sensitive to the pH value of the wastewater, which needs to be accurately controlled, which is difficult to achieve in actual industrial wastewater with complex composition and pH fluctuation. It will produce a large amount of arsenic-containing sludge. These sludges are themselves hazardous waste, and the subsequent transportation, storage and safe disposal costs are high. If not properly handled, it is easy to cause secondary pollution and transfer the pollution in the water body to the soil pollution. Ion exchange method: high operating cost. The exchange resin material itself is expensive, and in a complex wastewater environment, a large number of other coexisting anions and cations in the wastewater will compete with arsenic ions, seriously affecting the selectivity of the resin to arsenic, causing its "poisoning" failure, and frequent replacement is required, which has low economic benefits. Activated carbon adsorption: limited adsorption capacity, complex regeneration process and high energy consumption are limited. Especially when the target concentration is extremely low, the removal rate of these traditional methods is often difficult to meet the standard. For example, the wastewater generated in the steel smelting process usually contains arsenic at a concentration of 0.5-50 mg / L, and the traditional treatment process (coagulation and sedimentation, ion exchange) has a removal rate of less than 60% for low-concentration arsenic (<1 mg / L), and produces arsenic-containing sludge, which has the risk of secondary pollution.

[0003] In recent years, adsorption method has attracted much attention due to its high efficiency, simple operation and low potential cost. For example, Chinese patent CN103553197B discloses a method for removing arsenic and antimony in industrial wastewater by using smelting slag. The arsenic and antimony in the wastewater are quickly and effectively removed within 1-3 hours, and the removal rate is close to 100%. Chinese patent CN105381780B loads weakly magnetic material iron-based gel with strong adsorption capacity on ferrite material with weak adsorption capacity but strong magnetism through in-situ reaction method, so as to obtain material with strong adsorption capacity and excellent magnetic separation characteristics. After the material adsorbs arsenic and antimony, a continuous superconducting magnetic separation system is used to complete solid-liquid separation. Chinese patent CN201510890730.8 discloses a preparation method of manganese dioxide nanowire@multi-dimensional mesoporous metal organic framework adsorbent and an application method of the adsorbent for removing heavy metals such as arsenic and antimony in drinking water and industrial wastewater. However, the capacity and selectivity of the arsenic removal material in the above method still need to be improved. SUMMARY

[0004] The first object of the present application is to provide a composite metal organic framework material with high adsorption capacity, high selectivity and regeneration for treating low-concentration arsenic-containing wastewater. The second object of the present application is to provide a preparation method of the composite metal organic framework material. The third object of the present application is to provide an application of the composite metal organic framework material in arsenic-containing wastewater treatment.

[0005] Technical scheme: The composite metal organic framework (MOF) material is synthesized by a solvothermal method, using terephthalic acid and polyethyleneimine (PEI) as ligands and rare earth metal salt as metal source. The rare earth metal in the rare earth metal salt is Sc, Y, Sm or Eu.

[0006] Preferably, the specific surface area of the material is 1200-1400 m 2 / g.

[0007] Preferably, the mass ratio of the terephthalic acid, polyethyleneimine and rare earth metal salt is 0.5-1.5:1.0-3.0:0.8-2.5.

[0008] Preferably, the molecular weight of the polyethyleneimine is 10000-80000.

[0009] The preparation method of the composite metal organic framework material comprises the following steps:

[0010] (1) Dissolve terephthalic acid and polyethyleneimine in a solvent to make them completely dissolved, then add rare earth salt and disperse uniformly to obtain a mixed solution;

[0011] (2) Transfer the mixed solution to a reaction kettle and perform solvothermal reaction.

[0012] After the reaction is completed, cooling, washing and drying are performed to obtain the composite metal organic framework material.

[0013] Preferably, in step (1), the solvent is a mixed solvent of N,N-dimethylformamide and ethanol in a volume ratio of 5:1 to 2:1.

[0014] Preferably, in step (1), the complete dissolution is achieved by ultrasonic treatment (100 W-500 W) for 20-40 minutes.

[0015] Preferably, in step (1), the uniform dispersion is achieved by continuing ultrasonic treatment for 10-20 minutes.

[0016] Preferably, in step (2), the temperature of the solvothermal reaction is 120-180 DEG C, and the reaction time is 24-72 hours.

[0017] Preferably, in step (3), the cooling, washing and drying are performed by natural cooling to room temperature, suction filtration to collect the product, washing the obtained solid with DMF and anhydrous ethanol for 3-5 times, and then drying in a vacuum drying oven at 60-80 DEG C for 10-16 hours.

[0018] The composite metal organic framework material can be used in the treatment of arsenic-containing wastewater.

[0019] The application method is as follows: the composite metal organic framework material is added into wastewater containing 0.5-50 mg / L of arsenic at a dosage of 0.2-1.0 g / L, and the wastewater is stirred and adsorbed for 1-3 hours under the conditions of pH 5.0-8.0 and temperature 20-40 DEG C, then the material is separated from the water to remove arsenic in the wastewater.

[0020] The composite metal organic framework material has an adsorption capacity for trivalent arsenic of >150 mg / g and an adsorption capacity for pentavalent arsenic of >200 mg / g.

[0021] Preferably, the composite metal organic framework material has an adsorption capacity for trivalent arsenic of 152-160 mg / g and an adsorption capacity for pentavalent arsenic of 215-238 mg / g.

[0022] In the application of continuous flow treatment, the composite metal organic framework material of the present application is used at a dosage of 0.8-1.2 g / cm 3The packing density of the material is filled in a fixed bed reactor, and the wastewater containing 0.5-50 mg / L of arsenic is controlled to pass through the fixed bed at a flow rate of 2 to 5 BV / h. When the material is saturated, the treated wastewater is analyzed for As(III) / As(V) content by high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), and the adsorption can reduce the total arsenic concentration to below 0.01 mg / L. Elution and regeneration are carried out using 0.5M NaOH solution, and the entire regeneration process needs to ensure that the regeneration efficiency is higher than 95%, so as to realize effective recycling of the material.

[0023] Inventive mechanism: The present application introduces polyethyleneimine (PEI) with high coordination ability into rare earth metal organic frameworks by solvothermal method, and constructs a three-dimensional porous MOF structure by coordination. The strong Lewis acid sites of rare earth ions and the rich amino functional groups on PEI are used to cooperatively and efficiently capture As(III) and As(V) in water, so as to overcome the shortcomings of the prior art.

[0024] Advantages: Compared with the prior art, the present application has the following significant advantages:

[0025] (1) High adsorption performance: The material prepared by the present application has a large specific surface area and rich active sites, and the saturated adsorption capacity for As(III) and As(V) can reach 152-160 mg / g and 215-238 mg / g, respectively, and the removal rate of arsenic As(III) / As(V) is more than 95% (initial concentration 0.5-50 mg / L).

[0026] (2) High selectivity: Under the condition that the concentration of common coexisting anions (such as SO4 2- , Cl - , NO3 - ) in wastewater is 50-100 times higher than that of arsenic, the removal rate of arsenic is less than 5-10%, showing excellent selectivity.

[0027] (3) Regenerable: After adsorption saturation, 0.1-0.5M NaOH solution can be used for elution and regeneration, and the adsorption capacity retention rate is still more than 90% after 10 times of repeated use. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be further described below in conjunction with examples.

[0029] Example 1

[0030] (1) Preparation of scandium-polyethyleneimine composite MOF material (Sc-PEI-MOF)

[0031] In a 250 mL beaker, 1.0 g of terephthalic acid and 2.0 g of polyethyleneimine (PEI, molecular weight 10000) were dissolved in 100 mL of a mixed solvent of N,N-dimethylformamide (DMF) and ethanol (volume ratio 2:1) and completely dissolved by ultrasonic treatment (100 W) at room temperature for 30 minutes. Subsequently, 1.5 g of scandium chloride (ScCl3·6H2O) was added, and ultrasonic treatment (100 W) was continued for 15 minutes to ensure uniform mixing. The mixed solution was transferred to a 200 mL high-pressure reaction kettle lined with polytetrafluoroethylene, and after sealing, it was placed in an oven for reaction at a constant temperature of 160°C for 24 hours. After the reaction was completed, it was naturally cooled to room temperature, and the product was collected by suction filtration. The obtained solid was washed with DMF and anhydrous ethanol for 4 times in turn, and then dried in a vacuum drying oven at 80°C for 12 hours to obtain a white powder of Sc-PEI-MOF material. It was detected that the BET specific surface area thereof was 1350 m 2 / g, and the pore volume was 0.85 cm 3 / g.

[0032] (2) Material arsenic removal performance and selectivity test

[0033] 1 L of simulated wastewater with an initial concentration of 10 mg / L of As(V) was taken, and the pH was adjusted to 7.0. 0.5 g (dosing amount 0.5 g / L) of the Sc-PEI-MOF material prepared above was added, and the adsorption was stirred in a constant temperature water bath at 25°C for 2 hours. After the adsorption was completed, the material was separated by filtration through a 0.22 μm filter membrane. The supernatant was taken and analyzed by HPLC-ICP-MS, and the results showed that the concentration of As(V) in the treated wastewater was less than 0.01 mg / L, and the removal rate reached 99.9%.

[0034] According to the Langmuir model calculation, the saturation adsorption capacity of the material for As(V) was 238 mg / g.

[0035] In the above simulated wastewater of As(V), 100 times of As(V) concentration of coexisting anions (i.e. SO4 2 -1000 mg / L, Cl-1000 mg / L) was additionally added. The above adsorption experiment was repeated, and the removal rate of As(V) still reached 99.2%, and the removal rate decreased by 0.7%, showing excellent selectivity.

[0036] The 0.5 g of adsorbed saturated Sc-PEI-MOF material was placed in 100 mL of 0.2 M NaOH solution, stirred at 25 °C for 2 h for elution, then washed with deionized water to neutral and dried, to complete a regeneration. The regenerated material was used for the next adsorption experiment. This "adsorption-regeneration" process was repeated 10 times. The results showed that the first adsorption removal rate was 99.6%, and after 10 cycles, the removal rate of As(V) still reached 92.5%, and the saturated adsorption capacity of As(V) still reached 225 mg / g.

[0037] Example 2

[0038] (1) Preparation of yttrium-polyethyleneimine composite MOF material (Y-PEI-MOF)

[0039] In a 250 mL beaker, 0.5 g of terephthalic acid and 1 g of polyethyleneimine (PEI, molecular weight 80000) were dissolved in 60 mL of a mixed solvent of N,N-dimethylformamide (DMF) and ethanol (volume ratio 4:1) at room temperature, and ultrasonic treatment (200 W) was performed for 20 min to completely dissolve them. Subsequently, 1.8 g of YCl3-6H2O was added, and ultrasonic treatment (200 W) was continued for 12 min to ensure uniform mixing. The mixed solution was transferred to a 200 mL high-pressure reaction kettle lined with polytetrafluoroethylene, and after sealing, it was placed in an oven at a constant temperature of 120 °C for 24 h. After the reaction was completed, it was naturally cooled to room temperature, and the product was collected by suction filtration. The obtained solid was sequentially washed with DMF and anhydrous ethanol for 3 times, and then dried in a vacuum drying oven at 60 °C for 16 h to obtain a white powder of Y-PEI-MOF material. It was detected that the BET specific surface area was 1280 m 2 / g, and the pore volume was 0.81 cm 3 / g.

[0040] (2) Application of fixed bed continuous flow treatment of actual wastewater of steel plant

[0041] The effluent water from the second-stage biochemical treatment in the steelmaking workshop of He Steel Luting Iron and Steel Co., Ltd. has a water quality of total arsenic = 2.8 mg / L, pH = 7.5, SO4 2 - = 850 mg / L, and temperature 25 °C. The prepared Y-PEI-MOF material was filled in a glass adsorption column with an inner diameter of 5 cm, the filling height was 30 cm, and the packing density was 1.0 g / cm 3 . The arsenic-containing wastewater was controlled to pass through the fixed bed from top to bottom at a flow rate of 3 BV / h. After continuous operation for 200 h, the effluent water samples at different time points were analyzed by HPLC-ICP-MS, the total arsenic concentration of the effluent water was continuously and stably below 0.01 mg / L, the removal rates of As(III) / As(V) were 99.6% and 99.7%, and the saturated adsorption capacity of the material for As(III) / As(V) reached 152 / 215 mg / g.

[0042] When the breakthrough point (0.01 mg / L) was reached, the water feed was stopped. The column was regenerated by back-flushing with 0.5 M NaOH solution at a flow rate of 1 BV / h until the concentration of arsenic in the eluate was below the detection limit. Subsequently, the column was washed with deionized water until the effluent pH was neutral. The regenerated material was used for the next adsorption experiment. This "adsorption-regeneration" process was repeated 10 times. The results showed that the removal rates of As(III) / As(V) were 99.6% and 99.7% for the first adsorption, and the removal rates of As(III) / As(V) were still 95.2% and 95.6% after 10 cycles, and the saturated adsorption capacities of As(III) / As(V) were still 146 / 208 mg / g.

[0043] Example 3

[0044] (1) Preparation of Eu-polyethyleneimine composite MOF material

[0045] In a 250 mL beaker, 1.5 g of terephthalic acid and 3.0 g of polyethyleneimine (PEI, molecular weight 6000) were dissolved in 150 mL of a mixed solvent of N,N-dimethylformamide (DMF) and ethanol (volume ratio 3:1) at room temperature by ultrasonic treatment (200 W) for 40 minutes to ensure complete dissolution. Subsequently, 2.2 g of EuCl3·6H2O was added, and ultrasonic treatment (200 W) was continued for 20 minutes to ensure uniform mixing. The mixed solution was transferred to a 200 mL high-pressure reaction kettle lined with polytetrafluoroethylene, and after sealing, it was placed in an oven for reaction at a constant temperature of 170°C for 72 hours. After the reaction was completed, it was naturally cooled to room temperature, and the product was collected by suction filtration. The obtained solid was sequentially washed with DMF and anhydrous ethanol for 5 times each, and then dried in a vacuum drying oven at 70°C for 14 hours to obtain a white powder of Eu-PEI-MOF material. It was detected that the BET specific surface area of the material was 1410 m 2 / g, and the pore volume was 0.75 cm 3 / g.

[0046] (2) Fixed-bed continuous treatment of arsenic-containing wastewater from non-ferrous metal smelting

[0047] The effluent from the secondary treatment of the smelting plant of Tongling Nonferrous Gold Crown Copper Industry was used as the treatment object. The wastewater was complex in quality, and the specific parameters were: total arsenic concentration = 8.5 mg / L (of which As(III) accounted for 30%, and As(V) accounted for 70%), pH = 6.5, temperature = 30°C, and also contained a high concentration of coexisting ions SO4 2 - = 1200 mg / L. The dry Eu-PEI-MOF material was packed in a glass adsorption column with an inner diameter of 5 cm, with a packing height of 45 cm and a packing density of 1.1 g / cm 3The arsenic containing wastewater was continuously passed through the fixed bed reactor from top to bottom at a flow rate of 4 BV / h (Bed Volume / hour). After 300 bed volumes of continuous operation, the effluent samples were periodically analyzed. The results showed that the total arsenic concentration in the effluent was consistently below 0.01 mg / L, the total arsenic removal efficiency was >99.8%, the removal efficiency for As(III) / As(V) was 99.9% and 99.9%, and the saturated adsorption capacity of the material for As(III) / As(V) was 160 / 225 mg / g.

[0048] When the arsenic concentration at the outlet of the adsorption column reached 0.01 mg / L (breakthrough point), the water feed was stopped. Elution regeneration was performed by passing 0.5 M NaOH solution through the adsorption column at a flow rate of 1 BV / h in a counter-current direction. After regeneration, the column was washed with deionized water until the effluent pH was neutral and ready for the next cycle. After 10 cycles of "adsorption-regeneration", the results showed that the removal efficiency for As(III) / As(V) was 99.6% and 99.7% for the first adsorption, and after 10 cycles, the removal efficiency for As(III) / As(V) was still 96.6% and 98.4%, and the saturated adsorption capacity for As(III) / As(V) was still 149 / 215 mg / g.

Claims

1. A composite metal-organic framework material, characterized in that, The material is synthesized by a solvothermal method using terephthalic acid and polyethyleneimine as ligands and rare earth metal salts as metal sources. The rare earth metals in the rare earth metal salts are Sc, Y, Sm or Eu.

2. The composite metal-organic framework material according to claim 1, characterized in that, The mass ratio of terephthalic acid, polyethyleneimine and rare earth metal salt is 0.5-1.5:1.0-3.0:0.8-2.

5.

3. The composite metal-organic framework material according to claim 1, characterized in that, The molecular weight of the polyethyleneimine is 10,000-80,000.

4. The composite metal-organic framework material according to claim 1, characterized in that, The specific surface area of ​​the material is 1200-1400 m². 2 / g.

5. A method for preparing a composite metal-organic framework material according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Dissolve terephthalic acid and polyethyleneimine in a solvent until they are completely dissolved, then add rare earth salts and disperse them evenly to obtain a mixture; (2) Transfer the mixed solution to a reaction vessel for a solvothermal reaction; (3) After the reaction is complete, the material is cooled, washed and dried to obtain the composite metal-organic framework material.

6. The method for preparing the composite metal-organic framework material according to claim 5, characterized in that, In step (2), the temperature of the solvothermal reaction is 120-180℃ and the reaction time is 24-72 hours.

7. The method for preparing the composite metal-organic framework material according to claim 5, characterized in that, In step (1), the solvent is a mixed solvent of N,N-dimethylformamide and ethanol in a volume ratio of 5:1 to 2:

1.

8. The application of the composite metal-organic framework material according to any one of claims 1 to 4 in the treatment of arsenic-containing wastewater.

9. The application according to claim 8, characterized in that, The application method is as follows: the composite metal-organic framework material is added to wastewater containing 0.5-50 mg / L of arsenic at a dosage of 0.2-1.0 g / L. Under the conditions of pH 5.0-8.0 and temperature 20-40℃, the mixture is stirred and adsorbed for 1-3 hours. After the adsorption is completed, the material is separated from the water to remove arsenic from the wastewater.

10. The application according to claim 8, characterized in that, The composite metal-organic framework material has an adsorption capacity of >150 mg / g for trivalent arsenic and >200 mg / g for pentavalent arsenic.