Preparation method and application of a graphene oxide modified MOF multi-stage confinement adsorbent

Abstract

Preparation method and application of a multi-level confined adsorbent of graphene oxide modified MOF, which relates to a preparation method and application of an adsorbent material. The purpose of the present invention is to solve the problems that the existing metal-based MOF has low adsorption efficiency for phosphate and the treatment process is unstable and easy to lose, which is not convenient for subsequent recovery. Method: First, prepare mixed solution A; second, prepare mixed solution B; third, prepare solid powder C; fourth, carry out pyrolysis reaction to obtain a multi-level confined adsorbent of graphene oxide modified MOF. A multi-level confined adsorbent of graphene oxide modified MOF is used for adsorbing phosphate in wastewater. The multi-level confined adsorbent of graphene oxide modified MOF prepared by the present invention can reach an adsorption capacity of 250.2 mg·g ‑1 , and the adsorption kinetics is 13.092 mg·(g·min 0.5 ) ‑1 . The present invention can obtain a multi-level confined adsorbent of graphene oxide modified MOF.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of an adsorption material. Background Art

[0002] Phosphorus is an essential element for all life and is also an essential and non-renewable non-metallic mineral resource. On the other hand, phosphorus usually enters water bodies through industrial mining and human activities, resulting in it becoming the main pollution source in water bodies, and strict phosphate emission laws have been established in many countries currently. Therefore, it is very urgent to develop efficient phosphorus capture technologies to extract and recover phosphorus in water bodies to meet the huge demand for phosphorus resources. As a low-cost technology, the adsorption method in chemical methods has been quite popular due to the advantages of simple operation, mild conditions, and convenient subsequent recovery. And the adsorbent is the key factor determining the efficient adsorption efficiency.

[0003] The adjustable pore structure inside the metal-organic framework (MOF) and the widely distributed active sites provide sufficient transport channels for substrates and products. Therefore, it is highly feasible to form La-MOF with La as the metal site as an adsorbent. However, the difficulty of charge separation inside the MOF leads to a small interfacial electron cloud density, which is not conducive to the cleavage and recombination of chemical bonds, resulting in slow adsorption kinetics and instability during the treatment process, thus affecting the actual adsorption efficiency. Therefore, it is necessary to modify it to optimize the electron transport ability in the system. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems that the existing metal-based MOF has low adsorption efficiency for phosphates and is unstable and easy to lose during the treatment process, which is not convenient for subsequent recovery, and to provide a preparation method and application of a multi-level confined adsorbent of graphene oxide modified MOF.

[0005] A preparation method of a multi-level confined adsorbent of graphene oxide modified MOF is specifically completed according to the following steps:

[0006] First, lanthanum nitrate hexahydrate and 2-aminoterephthalic acid are uniformly dispersed in N,N-dimethylformamide to obtain a mixed solution; the pH value of the mixed solution is adjusted to 10-12 to obtain a mixed solution A;

[0007] Second, the mixed solution A is mixed with graphene oxide, heated and stirred for a period of time, and then stirred at room temperature for a period of time to obtain a mixed solution B;

[0008] Third, the mixed solution B is transferred to a polytetrafluoroethylene high-pressure reaction kettle for hydrothermal reaction to obtain a reaction product; the reaction product is centrifuged and washed, and then dried to obtain a solid powder C;

[0009] IV. Place solid powder C in a tubular furnace under a nitrogen atmosphere, and then heat the tubular furnace to 300°C - 600°C under the protection of a nitrogen atmosphere. Pyrolyze for a period of time at 300°C - 600°C to obtain a multi-level confined adsorbent of graphene oxide modified MOF.

[0010] A multi-level confined adsorbent of graphene oxide modified MOF is used to adsorb phosphate in wastewater.

[0011] Principle and advantages of the present invention:

[0012] I. The present invention selects La-MOF as the precursor and GO as the substrate, and the two are compounded to form a multi-level confined adsorbent of graphene oxide modified MOF (La-MOF@SGO) and a bulk-phase adsorbent of graphene oxide modified MOF (La-MOF / GO); compared with the bulk-phase structure, the formed confined structure enhances the electron transfer ability inside the material, increases the internal vacancies, and increases the active sites for adsorbing phosphate. It can not only adsorb phosphate ultra-efficiently, but also is almost not interfered by pH and coexisting ions on this basis, showing excellent phosphate adsorption performance;

[0013] II. The multi-level confined adsorbent of graphene oxide modified MOF prepared by the present invention can achieve an adsorption capacity of phosphate of 250.2 mg·g -1 , and the adsorption kinetics is as high as 13.092 mg·(g·min 0.5 ) -1 .

[0014] The present invention can obtain a multi-level confined adsorbent of graphene oxide modified MOF. Description of the drawings

[0015] Figure 1 XRD patterns of GO, La-MOF, La-MOF / GO, La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO;

[0016] Figure 2 SEM image of La-MOF prepared in Comparative Example 1;

[0017] Figure 3 SEM image of La-MOF / GO prepared in Step III of Example 1;

[0018] Figure 4 SEM image of La-MOF@SGO prepared in Example 1;

[0019] Figure 5 EPR patterns of GO, La-MOF, La-MOF / GO, La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO;

[0020] Figure 6 Adsorption isotherms of La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO for phosphate wastewater

[0021] Figure 7 Adsorption kinetic efficiency diagram of La-MOF@SGO prepared in Example 1 for phosphate adsorption at 278.15 K

[0022] Figure 8 Adsorption efficiency and zeta potential diagrams of GO, La-MOF, La-MOF / GO, La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO under different pH conditions

[0023] Figure 9 Adsorption efficiency diagrams of La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO in phosphate wastewater containing different coexisting ions Detailed implementation manners

[0024] Detailed implementation manner 1: A preparation method of a multi-level confined adsorbent of graphene oxide modified MOF in this implementation manner is specifically completed according to the following steps:

[0025] 1. Uniformly disperse lanthanum nitrate hexahydrate and 2-aminoterephthalic acid in N,N-dimethylformamide to obtain a mixed solution; adjust the pH value of the mixed solution to 10-12 to obtain a mixed solution A;

[0026] 2. Mix the mixed solution A with graphene oxide, heat and stir for a period of time, and then stir at room temperature for a period of time to obtain a mixed solution B;

[0027] 3. Transfer the mixed solution B to a polytetrafluoroethylene autoclave for hydrothermal reaction to obtain a reaction product; centrifuge and wash the reaction product, and then dry it to obtain a solid powder C;

[0028] 4. Place the solid powder C in a tube furnace under a nitrogen atmosphere, and then heat the tube furnace to 300°C - 600°C under the protection of a nitrogen atmosphere, and pyrolyze for a period of time at 300°C - 600°C to obtain a multi-level confined adsorbent of graphene oxide modified MOF.

[0029] Detailed implementation manner 2: The difference between this implementation manner and detailed implementation manner 1 is that: the molar ratio of lanthanum nitrate hexahydrate to 2-aminoterephthalic acid described in step 1 is (0.5 - 2):1; the molar amount of lanthanum nitrate hexahydrate described in step 1 to the volume ratio of N,N-dimethylformamide is 1 mol:(50 mL - 70 mL). Other steps are the same as those in detailed implementation manner 1.

[0030] Specific Embodiment 3: The difference between this embodiment and one of Specific Embodiments 1 or 2 is that in Step 1, a NaOH solution with a mass fraction of 20% - 40% is used to adjust the pH value of the mixed solution to 10 - 12, obtaining a mixed solution A. Other steps are the same as those in Specific Embodiment 1 or 2.

[0031] Specific Embodiment 4: The difference between this embodiment and one of Specific Embodiments 1 to 3 is that in Step 2, the temperature for heating and stirring is 40°C - 45°C, and the time for heating and stirring is 2 h - 10 h; the time for stirring at room temperature in Step 2 is 0 h - 2 h. Other steps are the same as those in Specific Embodiments 1 to 3.

[0032] Specific Embodiment 5: The difference between this embodiment and one of Specific Embodiments 1 to 4 is that in Step 2, the volume ratio of the mixed solution A to the mass of graphene oxide is 60 mL : (0.002 g - 0.1 g). Other steps are the same as those in Specific Embodiments 1 to 4.

[0033] Specific Embodiment 6: The difference between this embodiment and one of Specific Embodiments 1 to 5 is that in Step 3, the temperature of the hydrothermal reaction is 120°C - 180°C, and the time of the hydrothermal reaction is 6 h - 12 h. Other steps are the same as those in Specific Embodiments 1 to 5.

[0034] Specific Embodiment 7: The difference between this embodiment and one of Specific Embodiments 1 to 6 is that in Step 3, first, water is used as a cleaning agent to centrifuge and wash the reaction product 3 - 6 times, and then absolute ethanol is used as a cleaning agent to centrifuge and wash the reaction product until the reaction product is neutral; the drying in Step 3 is as follows: rotary evaporation is carried out for 2 h - 3 h under the condition of 40°C - 80°C. Other steps are the same as those in Specific Embodiments 1 to 6.

[0035] Specific Embodiment 8: The difference between this embodiment and one of Specific Embodiments 1 to 7 is that in Step 4, the time of pyrolysis is 2 h - 6 h. Other steps are the same as those in Specific Embodiments 1 to 7.

[0036] Specific Embodiment 9: The difference between this embodiment and one of Specific Embodiments 1 to 8 is that in Step 4, the tubular furnace is heated to 400°C - 500°C under the protection of a nitrogen atmosphere, and pyrolysis is carried out for a period of time at 400°C - 500°C. Other steps are the same as those in Specific Embodiments 1 to 8.

[0037] Specific Embodiment 10: This embodiment is a multi - level confined adsorbent of graphene oxide - modified MOF for adsorbing phosphate in wastewater.

[0038] The following examples are used to verify the beneficial effects of the present invention:

[0039] Example 1: A preparation method of a multi-level confined adsorbent of graphene oxide modified MOF is specifically completed according to the following steps:

[0040] I. Dissolve 1 mol of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) and 1 mol of 2-aminoterephthalic acid (H2ATA) uniformly in 60 mL of N,N-dimethylformamide (DMF) to obtain a mixed solution; adjust the pH value of the mixed solution to 11 using a 30% mass fraction NaOH solution to obtain mixed solution A;

[0041] II. Mix mixed solution A with graphene oxide (GO), first stir at 40 °C for 10 h, and then stir at room temperature for 2 h to obtain mixed solution B;

[0042] In step II, the volume ratio of mixed solution A to the mass of graphene oxide is 60 mL:0.002 g;

[0043] III. Transfer mixed solution B to a polytetrafluoroethylene autoclave, carry out hydrothermal reaction at 160 °C for 8 h to obtain a reaction product; first use water as a cleaning agent to centrifuge and wash the reaction product 4 times, then use absolute ethanol as a cleaning agent to centrifuge and wash the reaction product until the reaction product is neutral, and finally carry out rotary evaporation at 60 °C for 2 h to obtain solid powder C;

[0044] IV. Place solid powder C in a tube furnace under a nitrogen atmosphere, then heat the tube furnace to 350 °C under nitrogen atmosphere protection, and pyrolyze at 350 °C for 2 h to obtain a multi-level confined adsorbent of graphene oxide modified MOF (La-MOF@SGO).

[0045] Example 2: The difference between this example and Example 1 is that: in step II, the volume ratio of mixed solution A to the mass of graphene oxide is 60 mL:0.005 g; the multi-level confined adsorbent of graphene oxide modified MOF obtained in step IV is denoted as La-MOF@MGO. Other steps and parameters are the same as those in Example 1.

[0046] Example 3: The difference between this example and Example 1 is that: in step II, the volume ratio of mixed solution A to the mass of graphene oxide is 60 mL:0.1 g; the multi-level confined adsorbent of graphene oxide modified MOF obtained in step IV is denoted as La-MOF@EGO. Other steps and parameters are the same as those in Example 1.

[0047] Control Example 1: The preparation method of La-MOF is completed according to the following steps:

[0048] 1 mol of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) and 1 mol of 2-aminoterephthalic acid (H2ATA) were uniformly dispersed in 60 mL of N,N-dimethylformamide (DMF) to obtain a mixed solution. The pH value of the mixed solution was adjusted to 11 using a 30% NaOH solution by mass, and then transferred to a polytetrafluoroethylene autoclave. Hydrothermal reaction was carried out at a hydrothermal temperature of 160 °C for 8 h to obtain a reaction product. First, water was used as a cleaning agent to centrifuge and wash the reaction product 4 times, and then anhydrous ethanol was used as a cleaning agent to centrifuge and wash the reaction product until it was neutral. Finally, rotary evaporation was carried out at 60 °C for 2 h to obtain La-MOF.

[0049] Figure 1 XRD patterns of GO, La-MOF, La-MOF / GO, La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO;

[0050] Figure 1 The preparation method of La-MOF / GO in is as follows:

[0051] I. 1 mol of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) and 1 mol of 2-aminoterephthalic acid (H2ATA) were uniformly dispersed in 60 mL of N,N-dimethylformamide (DMF) to obtain a mixed solution. The pH value of the mixed solution was adjusted to 11 using a 30% NaOH solution by mass to obtain a mixed solution A;

[0052] II. 60 mL of the mixed solution A was mixed with 0.002 graphene oxide (GO), stirred at room temperature for 2 h, and then transferred to a polytetrafluoroethylene autoclave. Hydrothermal reaction was carried out at a hydrothermal temperature of 160 °C for 8 h. The reaction product was centrifuged and washed with water and ethanol until it was neutral, and then dried to obtain La-MOF / GO.

[0053] From Figure 1 It can be seen that the diffraction peaks corresponding to the initially synthesized precursor La-MOF completely correspond, indicating that it has been successfully prepared and has good crystallinity. Compared with the bulk La-MOF / GO, some characteristic peaks belonging to La-MOF in the confined structure La-MOF@GO disappear, indicating that La-MOF is uniformly dispersed in GO, preliminarily indicating the success of the confined structure. And with different dosages of GO, the intensities of some diffraction peaks are slightly different, indicating that different proportions of adsorbent materials have been successfully formed by changing variables.

[0054] Figure 2 SEM image of La-MOF prepared in Comparative Example 1;

[0055] Figure 3SEM image of La-MOF / GO prepared in Step 3 of Example 1;

[0056] Figure 4 SEM image of La-MOF@SGO prepared in Example 1;

[0057] From Figure 2 it can be seen that the precursor La-MOF has a flower-like morphology of about 10 μm formed by stacking of flakes. In the simple composite formed bulk structure, La-MOF is randomly stacked on GO to form an irregular blocky morphology, while in the confined structure, it can be clearly seen that La-MOF becomes nanoscale particles dispersed in the layered folds of GO. The reduction in size is also the classical size effect of the confined structure, which will affect the phase behavior of substances in the space and related chemical reaction paths. This indicates that the adsorbent material has been successfully regulated, which is consistent with the XRD results.

[0058] Figure 5 EPR images of GO, La-MOF, La-MOF / GO, La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO;

[0059] From Figure 5 it can be seen that the interior of the precursor La-MOF is in a saturated state without the generation of vacancies, nor is there any in the bulk structure La-MOF / GO. La-MOF@SGO in the confined structure has the largest oxygen vacancies, indicating that its internal structure increases and the movement space of phosphate molecules increases, which may be beneficial to the occurrence of the adsorption reaction.

[0060] Application Example 1: 0.005 g of La-MOF@SGO prepared in Example 1, 0.005 g of La-MOF@MGO prepared in Example 2, and 0.005 g of La-MOF@EGO prepared in Example 3 were respectively added to three groups of 50 mL phosphate wastewater with different concentration gradients and adsorbed for 1440 min at three groups of temperatures to obtain phosphate wastewater removal. The adsorption isotherm performance of La-MOF@GO is as Figure 6 shown;

[0061] In Application Example 1, the concentration gradients of the phosphate wastewater are 5, 15, 25, 35, 45 mg·L -1 , and the temperature gradients are 278.15 K, 288.15 K, 298.15 K;

[0062] Figure 6 Adsorption isotherms of La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO for phosphate wastewater;

[0063] From Figure 6It can be seen that under the condition of 278.15K, the adsorption efficiency of La-MOF@SGO for phosphate is the best, up to 250.2mg·g -1 . As the temperature increases, the adsorption efficiency decreases slightly, indicating that this material can achieve good adsorption effect at low temperature and it is an exothermic reaction that is convenient for spontaneous progress.

[0064] Figure 7 Figure showing the adsorption kinetic efficiency of La-MOF@SGO prepared in Example 1 for adsorbing phosphate at 278.15K;

[0065] From Figure 7 it can be obtained that La-MOF@SGO has relatively excellent adsorption efficiency, and its adsorption kinetics is as high as 13.092mg·(g·min 0.5 ) -1 , far exceeding previous work.

[0066] Application Example 2: 0.005g of GO, 0.005g of La-MOF, 0.005g of La-MOF / GO, 0.005g of La-MOF@SGO, 0.005g of La-MOF@MGO, and 0.005g of La-MOF@EGO were respectively added to six groups of 50mL wastewater containing phosphate under different pH conditions and adsorbed for 1440min to obtain wastewater with removed phosphate. The adsorption efficiency of phosphate is shown in Figure 8 as follows;

[0067] The concentration of phosphate in the wastewater containing phosphate in Application Example 2 is 45mg·L -1 .

[0068] Figure 8 Figure showing the adsorption efficiency and zeta potential of GO, La-MOF, La-MOF / GO, La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO under different pH conditions;

[0069] From Figure 8 it can be seen that it is the best at pH = 3. This is because under acidic conditions, phosphate exists in the form of H2PO4 - , and it is relatively easy to be migrated by electrons. Generally, the adsorbents with confined structures are hardly affected by pH. Especially for the La-MOF@SGO adsorbent material, it indicates that not too much electrons are provided by GO, and mainly the internal mass transfer plays an important role.

[0070] Application Example 3: 0.005 g of La-MOF@SGO, 0.005 g of La-MOF@MGO, and 0.005 g of La-MOF@EGO were respectively added to three groups of 50 mL phosphate wastewater containing different 0.1 M coexisting ions (the concentration of each ion was 0.1 M) for 1440 min of adsorption to obtain the wastewater with phosphate removed. The adsorption efficiency of phosphate is shown in Figure 9 as follows;

[0071] In the phosphate wastewater in Application Example 3, the concentration of phosphate was 45 mg·L -1 .

[0072] Figure 9 is the adsorption efficiency diagram of La-MOF@SGO, La-MOF@MGO, and La-MOF@EGO in phosphate wastewater containing different coexisting ions;

[0073] From Figure 9 it can be seen that, comparatively speaking, only La-MOF@SGO is the most stable and is hardly affected, indicating that the large confinement space formed inside effectively protects the internal phosphate adsorption reaction, and also indicating that it is mainly the internal complexation reaction rather than simple external adsorption. This is consistent with the pH result.

Claims

1. A preparation method of a multi-level confined adsorbent of graphene oxide modified MOF, characterized in that: The preparation method is specifically completed according to the following steps:

1. Uniformly disperse lanthanum nitrate hexahydrate and 2-aminoterephthalic acid in N, N-dimethylformamide to obtain a mixed solution; adjust the pH value of the mixed solution to 10-12 to obtain mixed solution A; In step 1, the molar ratio of lanthanum nitrate hexahydrate to 2-aminoterephthalic acid is (0.5-2):1; In step 1, the molar amount of lanthanum nitrate hexahydrate to the volume of N, N-dimethylformamide is 1 mol:(50 mL-70 mL); In step 1, use a 20%-40% NaOH solution by mass to adjust the pH value of the mixed solution to 10-12 to obtain mixed solution A; 2. Mix mixed solution A with graphene oxide, heat and stir for a period of time, and then stir at room temperature for a period of time to obtain mixed solution B; In step 2, the temperature for heating and stirring is 40°C-45°C, and the time for heating and stirring is 2 h-10 h; In step 2, the volume ratio of mixed solution A to the mass of graphene oxide is 60 mL:(0.002 g-0.1 g); 3. Transfer mixed solution B to a polytetrafluoroethylene high-pressure reaction kettle for hydrothermal reaction to obtain a reaction product; centrifuge and wash the reaction product, and then dry it to obtain solid powder C; In step 3, the temperature for the hydrothermal reaction is 120°C-180°C, and the time for the hydrothermal reaction is 6 h-12 h; 4. Place solid powder C in a tubular furnace under a nitrogen atmosphere, and then heat the tubular furnace to 300°C-350°C under the protection of a nitrogen atmosphere, and pyrolyze for a period of time at 300°C-350°C to obtain a multi-level confined adsorbent of graphene oxide-modified MOF.

2. The preparation method of a multi-level confined adsorbent of graphene oxide modified MOF according to claim 1, characterized in that: In step 2, the stirring time at room temperature is 0 h-2 h.

3. The preparation method of a multi-level confined adsorbent of graphene oxide modified MOF according to claim 1, characterized in that: In step 3, first use water as a cleaning agent to centrifuge and wash the reaction product 3-6 times, and then use absolute ethanol as a cleaning agent to centrifuge and wash the reaction product until the reaction product is neutral; the drying in step 3 is: rotary evaporation for 2 h-3 h under the condition of 40°C-80°C.

4. The preparation method of a multi-level confined adsorbent of graphene oxide modified MOF according to claim 1, characterized in that: In step 4, the pyrolysis time is 2 h-6 h.

5. Application of a multi-level confined adsorbent of graphene oxide modified MOF prepared by the preparation method according to claim 1, characterized in that: A multi-level confined adsorbent of graphene oxide-modified MOF is used to adsorb phosphate in wastewater.

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