CN113842889A

CN113842889A - Microwave synthesis metal organic framework material DUT-5(Al) and synthesis method and application thereof

Info

Publication number: CN113842889A
Application number: CN202111230978.3A
Authority: CN
Inventors: 张双灵; 郭萌萌; 胡月; 戴振建; 姜文利; 薛长晖; 杜德红; 王丽; 东野子璇
Original assignee: Qingdao Agricultural University
Current assignee: Qingdao Agricultural University
Priority date: 2021-10-22
Filing date: 2021-10-22
Publication date: 2021-12-28
Anticipated expiration: 2041-10-22
Also published as: CN113842889B

Abstract

The invention discloses a microwave synthesized metal organic framework material DUT-5(Al) and a synthesis method and application thereof. The method comprises the following steps: dissolving biphenyldicarboxylic acid in N, N-dimethylformamide, and adding Al (NO)₃)₃•9H₂And O, uniformly stirring, carrying out microwave reaction on the mixed solution, cooling the reaction solution after the reaction is finished, centrifugally collecting precipitate, washing and drying to obtain the metal organic framework material DUT-5 (Al). The microwave synthesis DUT-5(Al) not only greatly shortens the synthesis time and improves the synthesis efficiency, but also obviously improves the adsorption efficiency of the DUT-5(Al) to PFOS and PFOA, can be recycled for more than 4 times and can be used for PFOS and PFOA in a water environmentThe adsorption regeneration rate reaches more than 90 percent, so the method has wide application prospect.

Description

Microwave synthesis metal organic framework material DUT-5(Al) and synthesis method and application thereof

Technical Field

The invention belongs to the field of adsorbent materials, and particularly relates to a microwave synthesized metal organic framework material DUT-5(Al) and a synthesis method and application thereof.

Background

Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are generally considered to be the most representative perfluoro and polyfluoroalkyl species (PFAS). Due to their unique hydrophobic and lipophobic physicochemical properties, they have been widely used in surfactants, insecticides, fire fighting foams and industrial production. PFOS and PFOA are persistent, bioaccumulating, toxic, and even potentially carcinogenic. PFOS and PFOA pose potential threats to the ecological environment and human health. PFOS and its salts, PFOA and its salts, and PFOA-related compounds have been listed in the St.Google's convention. According to the requirements of the ecological environment department of China, the production, circulation, use and import and export of perfluorooctane sulfonate, salts thereof and perfluorooctanoic acid except acceptable use are forbidden. PFOS and PFOA are widely present in drinking water, groundwater, rainwater, lake water and wastewater. Therefore, the development of a treatment technology for PFOS and PFOA in an aqueous environment is urgent.

Many techniques for removing PFOS and PFOA, such as adsorption, membrane treatment, biotechnology, and the like, are currently studied. Adsorption technology is widely recognized as the most effective and feasible method for treating PFOS and PFOA. So far, activated carbon, molecularly imprinted polymer, anion exchange resin, etc. have been used as adsorbents for removing PFOS and PFOA in water. However, these materials and methods suffer from drawbacks such as higher cost, limited availability, recycling problems, and potential environmental unfriendliness.

Metal-organic frameworks (MOFs) are distinguished among many materials due to their characteristics of porosity, large specific surface area, structural and functional diversity, and are widely used in the fields of gas separation and the like. The traditional synthesis method of MOFs is a hydrothermal/solvothermal method, but the method is long in time consumption and low in efficiency, so that an efficient and controllable method is needed for synthesizing MOFs, and at present, there are few published reports that MOFs are used for removing PFOS and PFOA in water.

Disclosure of Invention

The invention aims to provide a microwave synthesized metal organic framework material DUT-5(Al) and a synthesis method and application thereof. The invention verifies that the microwave synthesis of the DUT-5(Al) not only has high efficiency, but also can improve the removal efficiency of the PFOS and PFOA of the DUT-5 (Al).

In order to realize the purpose of the invention, the invention adopts the following technical scheme to realize:

the invention provides a method for microwave synthesis of a metal organic framework material DUT-5(Al), which comprises the following steps: dissolving biphenyldicarboxylic acid in N, N-dimethylformamide, and adding Al (NO)₃)₃•9H₂And (3) after the O is uniformly stirred, carrying out microwave reaction on the mixed solution, heating to 120-140 ℃ at a heating rate of 10-20 ℃/min in the reaction process, continuing to react for 1-2 h, cooling and centrifuging the reaction solution after the reaction is finished, collecting the precipitate, washing and drying to obtain the metal organic framework material DUT-5 (Al).

Further, the biphenyldicarboxylic acid and Al (NO)₃)₃•9H₂The mass ratio of O is 1: 1-2.

Further, the microwave power in the microwave reaction process is controlled at 200W.

Preferably, the method comprises the steps of: 0.484g of biphenyldicarboxylic acid was dissolved in 60mL of N, N-Dimethylformamide (DMF), and 0.968 g of Al (NO) was added₃)₃•9H₂O, magnetically stirring for 30min, transferring the mixed solution into a polytetrafluoroethylene microwave reaction tube, performing microwave reaction by using a microwave synthesizer, controlling the microwave power to be 200W, and controlling the microwave power to be 2And heating to 120 ℃ at the heating rate of 0 ℃/min, continuing to react for 1h, cooling the reaction solution to room temperature after the reaction is finished, centrifuging for 15min at 4000 r/min, collecting the precipitate, washing the precipitate for 2-3 times by using DMF (dimethyl formamide) and methanol, and drying in a vacuum drying oven at 80 ℃ to obtain the metal organic framework material DUT-5 (Al).

The invention also provides the DUT-5(Al) prepared by the method for microwave synthesis of the metal organic framework material DUT-5 (Al).

The invention also provides application of the DUT-5(Al) in preparing an adsorbent for removing perfluor and polyfluoroalkyl substances in water environment.

Further, the metal organic framework material DUT-5(Al) can be used as an adsorbent alone or prepared into an adsorbent together with an anion remover and a carrier for use.

Further, the use method of the adsorbent comprises the following steps: the use method of the adsorbent comprises the following steps: taking a solution containing perfluoro and polyfluoroalkyl substances in a water environment, adjusting the pH value of the solution to 3-4.83, adding an adsorbent, and oscillating at a constant temperature of 25-30 ℃ for 5-24 h.

Further, the mass volume ratio of the adsorbent to the solution is 1: 4-6.

Further, the use method of the adsorbent comprises the following steps: taking 25mL of water environment solution containing PFOS or PFOA with the concentration of 30mg/L, adjusting the pH value of the water environment solution to 3 by using 0.1 mol/L HCl or NaOH solution, adding 5mg of adsorbent, keeping the temperature at 25 ℃, and oscillating for 10 hours at 150 r/min.

Further, the adsorbent also comprises an anion remover; the anion remover comprises Cl⁻Removing agent, SO₄ ²⁻Remover and CO₃ ^2-At least one of the removers.

Further, the adsorbent can be recycled at least 4 times.

Further, the perfluoro and polyfluoroalkyl materials are perfluorooctanesulfonic acid and perfluorooctanoic acid.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. according to the invention, a metal organic framework material DUT-5(Al) is synthesized by using a microwave-assisted method, and the DUT-5-2 is numbered, so that compared with the DUT-5-1 synthesized by a hydrothermal/solvothermal method, the DUT-5-2 is optimized, the synthesis time is greatly shortened, the synthesis efficiency is improved, and the PFOS and PFOA adsorption efficiency of the DUT-5-2 is also obviously improved. This is the first disclosure of using microwave-assisted methods to synthesize DUT-5(Al) and to adsorb PFOS and PFOA in aqueous environments.

2. The invention is also verified by experiments that when the pH is =3, the removal rate of the PFOS and the PFOA by the DUT-5-2 is the highest, the PFOS and the PFOA are removed by physical adsorption and monolayer adsorption, the DUT-5-2 synthesized by the microwave-assisted method is used as an adsorbent, and after the circulation use for 4 times, the adsorption regeneration efficiency of the DUT-5-2 on the PFOS (92.5%) and the PFOA (93.0%) is still over 90 percent, so the DUT-5-2 can become a promising adsorbent. Besides, the invention also proves that anions in the water environment have more or less negative influence on the removal rate of PFOS and PFOA, so the DUT-5-2 and an anion remover can be used together for preparing an adsorbent for removing PFOS and PFOA in the water environment. Therefore, the invention provides a new idea for removing pollutants in water environment by microwave synthesis of metal organic framework materials.

Drawings

FIG. 1 is a flow chart of the synthesis of MOFs.

FIG. 2 shows the results (a) of the amounts of PFOS and PFOA adsorbed in an aqueous solution and the appearance (b) of 7 MOFs.

FIG. 3 is a graph of the results of the topographical and structural characterization of DUT-5-2; (a) DUT-5-2 SEM diagram of x 20000, (b) DUT-5-2 SEM diagram of x 30000, (c) Zeta potential diagram of DUT-5-2, (d) x-ray polycrystal diffraction XRD diagram of DUT-5-2, (e) DUT-5-2 and Al (NO) raw material thereof₃)₃·9H₂O, BPDC FT-IR spectrum, (f) N of DUT-5-2₂Adsorption-desorption isotherms.

FIG. 4 is a quasi-first and quasi-second order adsorption kinetics fit curve of DUT-5-2 to PFOS and PFOA.

FIG. 5 is a Langmuir and Freundlich sorption isotherm fit curve of DUT-5-2 to PFOS (a) and PFOA (b).

FIG. 6 shows the results of the effect of pH (a) and ions (b) on the removal rate of PFOS and PFOA at DUT-5-2.

FIG. 7 is a graph showing the results of the adsorption capacity and regeneration efficiency of DUT-5-2 for PFOS and PFOA.

Detailed Description

The technical solution of the present invention will be further described in detail with reference to the following specific examples. In the following examples, unless otherwise specified, the experimental methods used were all conventional methods, and materials, reagents and the like used were all available from biological or chemical reagents companies.

Example 1: synthesis of MOFs

The MOFs are synthesized by a hydrothermal/solvothermal method or microwave assistance, and a material synthesis schematic diagram is shown in figure 1.

1. Synthesis of UIO-66

The traditional solvent thermal synthesis method is adopted. According to n (ZrCl)₄): n (terephthalic acid) = 1:1, 2.33g of zirconium tetrachloride (Zrcl)₄) And 1.66g of terephthalic acid (H)₂BDC) was dissolved in 200mL of N, N-Dimethylformamide (DMF), stirred until dissolved and charged into a polytetrafluoroethylene reaction vessel (15.5 × 7.70 cm, mallotus japonicus experimental apparatus ltd), and reacted at 120 ℃ for 24 hours. The product was washed 3 times with DMF and methanol respectively and collected by centrifugation. And finally, placing the product in a vacuum oven at 120 ℃ for drying for 8h to obtain a metal organic framework material UIO-66 crystal, and sealing and storing the UIO-66 crystal powder for later use.

2. Synthesis of UIO-67

According to n (ZrCl)₄): n (bpdc) = 1:1, 0.466g of ZrCl₄Dissolving in 30 mL of DMF to give solution A, and dissolving 0.484g of biphenyldicarboxylic acid (BPDC) in 30 mL of DMF to give solution B; adding the solution B into the solution A under the stirring state, and magnetically stirring for 30-60 min. The solution was mixed well and transferred to a 100 mL reactor. The reaction kettle was placed in an oven and heated at 120 ℃ for 24 h. Cooling to room temperature, centrifugally separating (4000 r, 15 min), and washing the precipitate with DMF and methanol for 2-3 times. Drying in a vacuum drying oven at 80 deg.C for a certain time to obtain final product UIO-67.

3. Synthesis of MOF-801

According to n (ZrCl)₄): n (fumaric acid) = 1: 3 ratio of ZrCl₄(0.2411 g), fumaric acid (0.3598 g), formic acid (3.90 mL), and ultrapure water (20 mL) were sonicated for 30 minutes and then transferred to a 30 mL polytetrafluoroethylene-lined stainless steel autoclave. And sealing the autoclave, placing the autoclave in a furnace at 120 ℃ for 24h, cooling to room temperature, then carrying out centrifugal separation (4000 r, 15 min), thoroughly and fully washing with ultrapure water and absolute ethyl alcohol, and drying at 80 ℃ for 24h to obtain a final product MOF-801.

4、NH₂Synthesis of-MIL-101 (Fe)

According to n (FeCl)₃·6H₂0): n (2-aminoterephthalic acid) = 2: 1 proportion of FeCl₃·6H₂0 (0.675 g), 2-aminoterephthalic acid (0.225 g) and 7.5 mL of DMF were reacted in a hydrothermal synthesis reactor at 110 ℃ for 24 hours. After 3 washes in ethanol and DMF, the precipitate was solidified in vacuo at 60 ℃ for 8 hours to give the final product, dark red NH₂MIL-101(Fe) samples.

5. Synthesis of Co-MOF

According to n (Co (NO)₃)₃·6H₂O): n (trimesic acid) = 1:1 weighing 25mL deionized water at a ratio of 1, adding 1.45g Co (NO)₃)₃·6H₂O, 1.05g of trimesic acid and 2mL of triethylamine, placing the beaker on a magnetic stirrer, stirring for l 5min, transferring the solution into a polytetrafluoroethylene reaction kettle, and sealing and placing the kettle in an electrothermal blowing dry box at 190 ℃ for 24 h. Centrifuging (6000 r, 2 min) obtained after the reaction to obtain precipitate, repeatedly washing with ethanol and deionized water for 3 times respectively, and drying at 60 ℃ in vacuum to obtain the final product Co-MOF.

6. Synthesis of DUT-5-1

According to n (Al (NO)₃)₃·9H₂O): n (bpdc) = 1.3: 1, 0.968 g of Al (NO)₃)₃·9H₂Dissolving O in 30 mL of DMF to obtain a solution A; 0.484g of BPDC was dissolved in 30 mL of DMF to give solution B; adding the solution B into the solution A under the stirring state, and magnetically stirring for 30-60 min. The solution is mixed uniformlyAfter homogenizing, the mixture was transferred to a 100 mL reactor. The reaction kettle was placed in an oven and heated at 120 ℃ for 24 h. Cooling to room temperature, centrifugally separating (4000 r, 15 min), and washing the precipitate with DMF and methanol for 2-3 times. And (5) drying the mixture in a vacuum drying oven at 80 ℃ for a certain time to obtain a final product DUT-5-1.

7. Synthesis of DUT-5-2

0.484g of BPDC was dissolved in 60mL of DMF, and 0.968 g of Al (NO) was added₃)₃•9H₂O, magnetically stirring for 30min, transferring the mixed solution into a polytetrafluoroethylene microwave reaction tube, performing microwave reaction by using a microwave synthesizer (Flexiwave, Milestone company), controlling the microwave power to be 200W, heating to 120 ℃ at the heating rate of 20 ℃/min, and continuing to react for 1 h. After the reaction is finished, cooling the reaction liquid to room temperature, performing centrifugal separation (4000 r, 15 min), and washing and precipitating for 2-3 times by using DMF and methanol; and (5) drying the mixture in a vacuum drying oven at 80 ℃ for a certain time to obtain a final product DUT-5-2.

Example 2: screening of adsorbents

For evaluation of the synthesized MOFs (DUT-5-1, DUT-5-2, UIO-66, UIO-67, MOF-801, NH)₂MIL-101 and Co-MOF) for PFOS and PFOA, performing static adsorption experiments. The method specifically comprises the following steps: 5mg of the adsorbent was added to a 50 mL polypropylene centrifuge tube containing 25mL of a 30mg/L PFOS or PFOA solution, and the pH of the PFOS or PFOA solution was adjusted to 3.0. + -. 0.1 with 0.1 mol/L HCl or NaOH solution before the adsorbent was added. The mixture was shaken in a constant temperature shaker (25 ℃) at 150 r/min for 24 h. Samples were taken and filtered through a 0.22 μm filter and the concentration of PFOS and PFOA in the solution was determined after filtration. And the adsorption amount is calculated according to the formula (1).

Formula (1);

wherein: c₀-initial concentration of PFOS or PFOA (mg/L);

C_t-residual concentration of PFOS or PFOA (mg/L);

m-mass of adsorbent (mg);

v-volume of PFOS or PFOA solution (mL).

The detection method of the PFOS and the PFOA comprises the following steps: the concentration of PFOS or PFOA is determined by ultra fast liquid chromatography/tandem mass spectrometry (UFLC-MS/MS). Ultra-fast liquid chromatography, model LC-20 from Shimadzu, Japan, was combined with a quadrupole-linear ion trap complex mass spectrometry system, model 5500 QTRAP from AB SCIEX, with an electrospray ionization source (ESI). Kinetex XB-C₁₈The column was used at 40 ℃. The binary mobile phase consisted of solvent A (5 mmol/L ammonium acetate solution) and solvent B (pure methanol). Elution gradient: 0-0.5 min, 10% -40% B; 0.6-8.0 min, 40% -95% B; 8.1-10.0 min, 95% B; 0.1-12.0 min, 10% B, flow rate of 0.3 mL/min, and sample size of 5 μ L.

The results are shown in FIG. 2a, with other adsorbents (UIO-66, UIO-67, MOF-801, NH)₂MIL-101, Co-MOF) has better adsorption capacity of PFOS and PFOA of DUT-5-1, respectively 136.8 mg/g and 91.0 mg/g. DUT-5-2, as the optimized material of DUT-5-1, has the adsorption capacity of 145.4 mg/g and 98.2 mg/g for PFOS and PFOA, respectively, and the adsorption capacity is significantly higher than DUT-5-1. In addition, the time for synthesizing the DUT-5-2 by microwave is 1h, while the time for synthesizing the DUT-5-1 is 24h, so that the synthesis time of the DUT-5-2 is obviously shortened, and the microwave-assisted method can obviously improve the adsorption efficiency of the DUT-5(Al) on PFOS and PFOA. FIG. 2b is an appearance diagram of 7 MOFs, and DUT-5-2 is a white powder with small particles (500-700 nm).

Example 3: study on adsorption behavior of DUT-5-2 to PFOS and PFOA

1. Morphology and structural characterization of DUT-5-2

(1) Scanning Electron Microscope (SEM) and Zeta potential analysis

The surface morphology of the metal organic framework was observed with a JEOL 7500F Scanning Electron Microscope (SEM). Fixing the obtained sample powder on a stainless steel sample table through conductive adhesive, and spraying a layer of gold on the surface to avoid electron beam charging. And (3) placing the sample subjected to gold spraying under a scanning electron microscope at 2.00 KV to observe the surface microstructure of the metal organic framework.

Zeta potentiostat, model Nano-ZS, from Marvin instruments, Inc., UK was used. The specific test method comprises the following steps: dispersing 10 mg of sample in a conical flask filled with 100 mL of glutaraldehyde solution to obtain 100 mg/L solution, fully and uniformly stirring, adjusting the pH value to 2-10, and finally pouring into a potential dish for Zeta potential measurement.

SEM results As shown in FIGS. 3a and 3b, the synthesized DUT-5-2 has an irregular spherical shape and relatively uniform particles (500-700 nm).

The pH has a significant effect on the performance of the adsorbent. FIG. 3c shows that the surface charge of DUT-5-2 decreases with increasing pH and the isoelectric point (pI) of DUT-5-2 is 4.83. As the pH value was increased from 2 to 10, the surface charge of DUT-5-2 decreased from 22.9 mV to-19.9 mV.

(2) X-ray diffraction (XRD)

The sample was ground to a fine powder using a D8 ADVANCE X-ray polycrystalline diffractometer from Bruker, Germany. The X-ray light pipe is a ceramic X-ray pipe and a Cu target, the X-ray of Cu Ka1 is lambda =0.15045nm, the power of the light pipe is 2.2 kw, the voltage of the tube is 60 kV, the current of the tube is 60 mA, the background of the whole detector is 0.1 cps, and the energy resolution is 20%. The 2 theta range in the experiment was 5-30 deg..

The XRD pattern is shown in fig. 3d, and it can be seen that characteristic diffraction peaks appear at 6.1 °, 12.0 ° and 18.2 ° (2 θ), respectively, corresponding to the (010), (020) and (030) crystal planes identified by Jade 6. The characteristic diffraction peaks and intensities of the peaks for the synthesized powder are essentially consistent with those reported previously for DUT-5(Al), indicating the successful synthesis of DUT-5-2. The relative crystallinity of the obtained DUT-5-2 was 74%, indicating that the crystallinity was high.

(3) Fourier Infrared Spectroscopy (FT-IR) analysis

FT-IR of Thermo Fisher Scientific company, Nicolet Nexus IS10, USA, IS used to analyze the spectrum change before and after the ligand and metal ion coordinate, and to judge whether complex IS formed and possible coordination mode. The specific method comprises the following steps: and grinding the ligand material uniformly, tabletting the ground ligand material and the synthesized sample powder respectively, and then placing the tablets under an infrared spectrometer for determination. The measurement temperature of the infrared spectrometer is 25 ℃, and the wavelength scanning range is 4000-^-1Resolution of 4 cm^-1Wavelength precision of 0.01 cm^-1The number of scans was 64. The air background was subtracted when scanning the samples.

FIG. 3e shows DUT-5-2 and its raw material Al (NO)₃)₃·9H₂FT-IR spectra of O and BPDC. At DUT-5-2 and Al (NO)₃)₃·9H ₂3420 cm were observed in O^-1Nearby peaks (O — H tensile vibration); the DUT-5-2 and the BPDC are arranged at 1430-1600 cm^-1Has similar vibration absorption peak of benzene ring skeleton. These two phenomena indicate Al (NO)₃)₃·9H₂O and BPDC were successfully synthesized into DUT-5-2. In the FT-IR spectrum of DUT-5-2, at 1603 cm respectively^-1(asymmetric vibration, v_as) And 1427 cm^-1(symmetric vibration, v_s) In the presence of a relatively strong carboxylic acid group (-COO)^-) Absorption peak. The difference between the two peaks ([ delta ] v = 176 cm)^-1) Higher than free carboxylic acid group ([ delta ] v = 170 cm)^-1) Description of-COO^-The coordination mode with Al metal ions is monodentate coordination.

(4) Determination of Specific Surface Area (SSA), pore volume and pore diameter

BET characterization data was obtained using an American Micromeritics Instrument model ASAP 2460 adsorber. Putting a sample to be detected into a sample tube in advance, degassing at 110 ℃ for 12h, transferring the degassed sample to an analysis port, and adding liquid nitrogen into a Dewar flask of the analysis port to analyze the sample. The total pressure of the nitrogen and helium gas cylinders is more than 3 MPa, and the partial pressure is set to be 0.14 MPa.

Pore volume from relative pressure (P/P)₀) N of 0.99 hours₂The condensation value of the adsorption capacity was estimated, and the pore diameter was obtained by the Horvath-Kawazoe method using the ASAP 2460 system, SSA being a single layer of N per mL₂The product of the occupied area and Vm, Vm is based on the Brunauer-Emmett-Teller (BET) model formula (2) in P/P₀Calculated in the range of 0.05-0.30.

Formula (2)

Wherein: P-N₂Absolute pressure (mmHg);

P₀—N₂saturated pressure (mmHg);

v-weight of sample to N₂Adsorption amount (cm)³/g）

Vm-sample surface pair N₂Saturated adsorption capacity (cm) of the monomolecular layer of (A)³/g）；

C is a constant related to the adsorption performance of the material.

N of DUT-5-2₂The adsorption-desorption isotherm is shown in FIG. 3f, from which it can be seen that the amount of adsorption (cm) is observed in the low-pressure zone³Rapid increase in (P/P) (/ g)₀= 0.0-0.1). DUT-5-2 exhibits a type I isotherm, according to the International Union of pure and applied chemistry classification, which is characteristic of microporous materials.

The micropore performance of DUT-5-2 is shown in Table 1. DUT-5-2 has a BET SSA of 1840 m²Per g, pore volume 0.93 cm³(ii)/g, pore diameter of 0.85 nm. The DUT-5 synthesized by the invention has higher specific surface area than the DUT-5 reported in the past, which shows that the microwave-assisted synthesis of DUT-5(Al) is a better method.

Table 1: microporous Properties of DUT-5

2. Adsorption characteristics of DUT-5-2 to PFOS and PFOA

10 mg of PFOS and PFOA standard are dissolved in a beaker with a certain amount of methanol and transferred to a 10mL brown volumetric flask to bring to volume 10 mL. Obtaining 1000 mg/L standard stock solution, and refrigerating for storage. During the experiment, the ultra-pure water can be diluted into different concentrations according to different experiment requirements. All experiments were performed in 3 replicates (n = 3) with pH adjusted to 3.0 ± 0.1. Meanwhile, a blank experiment is also carried out to eliminate errors caused by other factors in the experiment.

(1) Adsorption kinetics experiment

25mL of PFOS or PFOA solution with the initial mass concentration of 30mg/L is taken to be put into a 50 mL polypropylene (PP) centrifuge tube, 5mg of adsorbent DUT-5-2 is added, shaking is carried out at the constant temperature of 150 r/min at 25 ℃, samples are respectively taken at 30, 60, 180, 300, 480, 600, 780, 900, 1440, 1500, 1560, 1680 and 1800 min, filtration is carried out by using a 0.22 mu m filter membrane, and the mass concentration of the PFOS is measured after filtration. And (4) calculating the adsorption quantity according to the formula (1) and making an adsorption kinetic curve.

In order to study the adsorption type (physisorption or chemisorption) of PFOS and PFOA by DUT-5-2, two kinetic models (quasi-primary and quasi-secondary) were used to describe the adsorption kinetics, which are expressed as equation (3) and equation (4), respectively.

Formula (3);

formula (4);

wherein:

-amount of PFOS or PFOA adsorbed by the adsorbent (mg/g) at adsorption equilibrium;

-the amount of PFOS or PFOA adsorbed by the adsorbent at time t (mg/g);

t-time (min);

k₁quasi-first order kinetic adsorption rate constant (mg/g min);

k₂quasi-second order kinetic adsorption rate constant (g/mg. min).

Fitting curve of adsorption kinetics of the DUT-5-2 to the PFOS and the PFOA is shown in FIG. 4, and the result shows that the adsorption amount of the DUT-5-2 to the PFOS and the PFOA is increased rapidly in the first 300 min and then increased slowly to 600 min, and the equilibrium is reached around 600 min.

Adsorption kinetics of PFOS and PFOA on DUT-5-2 fitting parameters are shown in Table 2, and qe (mg/g) fitting values of the quasi-primary model to PFOS and PFOA are found to be 148.2 mg/g and 91.8 mg/g, respectively, which are closer to the experimental values (qt, t = 10 h, 147.5 and 90.4mg/g) than the quasi-secondary model (164.0 and 105.9 mg/g). Correlation coefficient (R) of quasi-first order model² _PFOS = 0.9835；R² _PFOA= 0.9708) is higher than the correlation coefficient (R) of the quasi-second order model² _PFOS = 0.9447；R² _PFOA= 0.9382). These phenomena indicate that the quasi-first-level model fits better than the quasi-second-level model, and better meets the experimental values of PFOS and PFOA, and further indicate that the adsorption of the DUT-5-2 to PFOS and PFOA is mainly physical adsorption.

Table 2: dynamic parameters of adsorption of PFOS and PFOA by DUT-5-2

(2) Adsorption isotherm experiment

PFOS and PFOA solution with the concentration of 10-140 mg/L is prepared, 25mL of PFOS and PFOA solution and 5mg of adsorbent DUT-5-2 are added into a 50 mL polypropylene centrifuge tube, the temperature is kept at 25 ℃ in a constant temperature shaking table at the rotation speed of 150 r/min, sampling is carried out after 24h, a 0.22 mu m filter membrane is used, and then the concentration of PFOS and PFOA in the solution is measured. The adsorption amount is calculated according to the formula (1), and an adsorption isotherm is drawn.

To study the maximum adsorption capacity and adsorption pattern (single-layer or multi-layer adsorption) of DUT-5-2 for PFOS and PFOA, the data obtained were fitted with nonlinear isotherm models Langmuir and Freundlich, respectively. Equations (5) and (6) give Langmuir and Freundlich isotherm models, and the maximum adsorption amount q is calculated from equation (5)_m (mg/g)。

Formula (5);

formula (6);

wherein:

-concentration of PFOS or PFOA at adsorption equilibrium (mg/L);

-amount of PFOS or PFOA adsorbed by the adsorbent at equilibrium (mg/g);

maximum adsorption capacity (mg/g) of the adsorbent for PFOS or PFOA;

b-Langmuir model constant (mg/L);

freundlich model constants.

Langmuir and Freundlich adsorption isotherms for adsorption of PFOS and PFOA by DUT-5-2 referring to FIG. 5, it can be seen that the equilibrium adsorption amount of PFOS by DUT-5-2 increases rapidly and then the growth trend becomes slower, indicating that at lower PFOS concentrations, DUT-5-2 adsorption is in an unsaturated state. The equilibrium adsorption amount of PFOA by DUT-5-2 increases more slowly than PFOS, resulting in a lower adsorption amount of PFOA by DUT-5-2. Both Langmuir and Freundlich isothermal models fit the experimental values of PFOS and PFOA well.

Model parameters for Langmuir and Freundlich see Table 3, correlation coefficient for Langmuir model (R)² _PFOS = 0.9825；R² _PFOA= 0.9921) is higher than the correlation coefficient (R) of the Freundlich model² _PFOS = 0.9797；R² _PFOA= 0.9872) indicating that the adsorption process is monolayer adsorption. As can be seen from Table 3, the maximum adsorption amount (1015 mg/g) of PFOS by DUT-5-2 is much higher than the maximum adsorption amount (473.7 mg/g) of PFOA by DUT-5-2, and it can be seen that the adsorption amount of PFOS by DUT-5-2 is much larger. The tails of PFAS compounds are generally hydrophobic in aqueous solution, PFOS molecules are more hydrophobic than PFOA molecules because of an additional C-F chain in the perfluoroalkyl chain of the former. Thus, DUT-5-2 adsorbs more PFOS than PFOA by hydrophobic interaction, which is consistent with the results of PFOS and PFOA adsorption kinetics of DUT-5-2 (FIG. 4).

Table 3: isothermal line parameters of DUT-5-2 for adsorbing PFOS and PFOA

The invention also compares the maximum adsorption capacity of PFOS and PFOA by different MOFs disclosed in recent years. The results are shown in Table 4, the maximum adsorption capacity of the DUT-5-2 to PFOS (1015 mg/g) and PFOA (473.7 mg/g) is higher than that of other MOFs, such as the adsorption capacity of the NanoZIF-67 to PFOS is 846.0 mg/g, and the adsorption capacity of UIO-66- (F4) to PFOA is 467.0 mg/g. Thus, it was shown that microwave-assisted synthesis of DUT-5-2 is a promising adsorbent for removing PFOS and PFOA in aqueous solution.

Table 4: maximum adsorption capacity of PFOS and PFOA of different MOFs

3. Effect of pH and ions on the removal Rate of PFOS and PFOA at DUT-5-2

(1) Influence of the pH value

In 25mL of a PFOS or PFOA solution having a concentration of 30mg/L, the pH was adjusted to 3-10 with 0.1 mol/L HCl or NaOH solution, 5mg of an adsorbent DUT-5-2 was added, and the influence of the pH on the removal rates of PFOS and PFOA by DUT-5-2 was measured.

Results referring to FIG. 6a, PFOS and PFOA removal rates by DUT-5-2 gradually decreased with increasing pH. The pKa's of PFOS and PFOA are around-3.27 and-0.1, respectively. Thus, PFOS and PFOA exist in anionic form in pH range (3-10), as shown in FIG. 3c, at pH 3-4.83 (pI), DUT-5-2 surface is positively charged, at which time, DUT-5-2 can effectively adsorb PFOS and PFOA molecules by electrostatic action. The removal rate of PFOS (96.6%) and PFOA (60.9%) by DUT-5-2 was the highest at pH = 3. And when the pH value is greater than 4.83, the surface of DUT-5-2 becomes negative, resulting in electrostatic repulsion between DUT-5-2 and PFOS, PFOA, and thus the removal rate of PFOS and PFOA is reduced. When pH = 10, DUT-5-2 had the lowest removal rate of PFOS (46.9%) and PFOA (19.6%).

(2) Influence of anions

PFOS and PFOA are often detected in real aquatic environments. Unlike ultrapure water, the water environment may contain inorganic ions, which compete for adsorption sites and affect the adsorption performance of DUT-5-2. Therefore, it is necessary to study the influence of the coexisting ions on the adsorption of PFOS and PFOA.

To examine the effect of different ions on the removal rate, 5mg of DUT-5-2 was placed in a solution containing 25 mg/L or 100 mg/L of Cl⁻、SO₄ ²⁻And CO₃ ^2-PFOS or PFOA solution (25 mL, 30 mg/L). The mixture was kept in a constant temperature shaker at 25 ℃ and at a rotation speed of 150 r/min, and after 10 hours, a sample was taken and passed through a 0.22 μm filter, and the removal rate of PFOS or PFOA was calculated from the formula (7).

Formula (7);

wherein: c₀-initial concentration of PFOS or PFOA (mg/L);

C_e-concentration of PFOS or PFOA at equilibrium (mg/L).

The results of the effect of the three coexisting anions on the PFOS and PFOA removal rates of DUT-5-2 are shown in FIG. 6b, and the anion functions in the order of Cl⁻ < SO₄ ²⁻ < CO₃ ^2-. In Cl^–(PFOS: 95.6%, 93.6%; PFOA: 60.6%, 58.9%) and SO₄ ²⁻(PFOS: 90.9%, 88.9%; PFOA: 58.0%, 56.9%) had a slight negative effect on PFOS and PFOA removal rates. SO (SO)₄ ²⁻Effect on adsorption Performance of DUT-5-2 over Cl⁻Slightly more pronounced, this may be due to SO₄ ²⁻BiCl⁻Has a lower surface charge, SO₄ ²⁻Has stronger affinity with DUT-5-2. In CO₃ ^2-The most significant negative effects were found when present. When CO is present₃ ^2-When the concentration is increased from 25 mg/L to 100 mg/L, the removal rates of PFOS and PFOA are reduced to 49.8% and 19.9%, respectively. This may be due to CO₃ ^2-Readily react with H in solution⁺Combine to produce more OH ^-25 mg/L and 100 mg/L CO₃ ^2-The pH of the solution was 10.3 and 10.6, respectively. Such thatThe alkaline environment caused the decrease of PFOS and PFOA removal rate of DUT-5-25, which is consistent with the results of pH effect in the experiment.

4. Reproducibility test

An effective adsorbent should have good adsorption capacity and regeneration performance. In the regenerative experiments, PFOS and PFOA adsorbed by DUT-5-2 were desorbed with methanol. The DUT-5-2 was subjected to 4 regeneration-type experiments. Specifically, 5mg of the adsorbent DUT-5-2 is put into 25mL of PFOS or PFOA solution with the concentration of 30mg/L and is shaken on a constant temperature shaking table (150 r/min) at 25 ℃ for 10 h. After filtration of the adsorbent, the filtrate was eluted with 30 mL of methanol, washed with 25mL of ultrapure water several times, and dried in vacuo. And (3) performing cycle experiments on the adsorbent for multiple times, and respectively calculating the adsorption amount and the regeneration efficiency of the adsorbent on PFOS or PFOA according to the formula (1) and the formula (8).

Formula (8);

wherein: q. q.s₀Initial PFOS or PFOA adsorption by DUT-5-2 (mg/g);

q_iregeneration of the PFOS or PFOA adsorption quantity (mg/g) of DUT-5-2 i times.

PFOS and PFOA adsorption Capacity and regeneration efficiency results of DUT-5-2 are shown in FIG. 7, and when DUT-5-2 was used for the first time, PFOS and PFOA adsorption amounts were 148.3 mg/g and 98.2 mg/g, respectively. After the fourth cycle, the adsorption amounts of PFOS and PFOA slightly decreased to 137.1 mg/g and 91.3mg/g, respectively. The reason for this may be the loss of DUT-5-2 material and the presence of small amounts of undesorbed PFOS and PFOA at the surface, possibly resulting in a reduced number of adsorption sites. After 4 cycles, the regeneration efficiency of the DUT-5-2 to PFOS (92.5%) and PFOA (93.0%) is more than 90%, which shows that the DUT-5-2 still has good adsorption capacity to PFOS and PFOA in the solution. The results show that DUT-5-2 has good regeneration performance.

In conclusion, the MOF material DUT-5-2 prepared by the microwave-assisted method has high PFOS and PFOA adsorption capacity (PFOS: 145.4 mg/g; PFOA: 98.2 mg/g), and the DUT-5-2 is verified to have micropore characteristics (the pore diameter is 0.85 nm) and monodentate coordination mode (-COO)^-And Al: Δ ν = 176 cm^-1) The adsorption kinetics and the adsorption isotherm of the compound accord with a quasi-first order kinetic model (R)²: quasi-first level 0.9835>Quasi-second order 0.9447) and Langmuir model (R)²：Langmuir 0.9825 >Freundlich 0.9797), thereby indicating that there is physisorption and monolayer sorption of DUT-5-2 during the sorption process.

In addition, the maximum adsorption amounts of the DUT-5-2 to PFOS (1015 mg/g) and PFOA (473.7 mg/g) are higher than those reported for other MOFs. The removal rate of PFOS (96.6%) and PFOA (60.9%) by DUT-5-2 was highest when pH = 3. The main mechanism of action of DUT-5-2 for adsorbing PFOS and PFOA is through electrostatic and hydrophobic interactions during adsorption. The anion having the sequence Cl⁻ < SO₄ ²⁻ < CO₃ ^2-。Cl^-And SO₄ ²⁻Has slight adverse effect on the removal rate of PFOS and PFOA, while CO₃ ^2-Inhibiting the adsorption of PFOS and PFOA. After 4 cycles, DUT-5-2 still showed higher adsorption and regeneration efficiency for PFOS (131.1 mg/g, 92.5%) and PFOA (91.3mg/g, 93.0%), indicating that DUT-5-2 has good regeneration performance. The results show that the synthesis of DUT-5-2 by the microwave-assisted method is a method which not only greatly shortens the synthesis time, but also can effectively improve the PFOS and PFOA adsorption efficiency of the synthesized product, and the obtained DUT-5-2 can be a promising adsorbent for effectively removing PFOS and PFOA in an aqueous solution.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions.

Claims

1. A method for microwave synthesis of a metal organic framework material DUT-5(Al), the method comprises the following steps: will be provided withDissolving biphenyldicarboxylic acid in N, N-dimethylformamide, and adding Al (NO)₃)₃•9H₂And (3) after the O is uniformly stirred, carrying out microwave reaction on the mixed solution, heating to 120-140 ℃ at a heating rate of 10-20 ℃/min in the reaction process, continuing to react for 1-2 h, cooling and centrifuging the reaction solution after the reaction is finished, collecting the precipitate, washing and drying to obtain the metal organic framework material DUT-5 (Al).

2. The microwave synthesis method of metal-organic framework material DUT-5(Al) according to claim 1, wherein Biphenyldicarboxylic acid and Al (NO) are used₃)₃•9H₂The mass ratio of O is 1: 1-2.

3. The microwave synthesis method of metal-organic framework material DUT-5(Al) according to claim 1, wherein the microwave power during the microwave reaction is controlled at 200W.

4. The metal-organic framework material DUT-5(Al) prepared by the method for microwave synthesis of metal-organic framework material DUT-5(Al) as claimed in claim 1.

5. Use of the metal organic framework material DUT-5(Al) according to claim 4 for the preparation of an adsorbent for the removal of perfluorinated and polyfluoroalkyl species in an aqueous environment.

6. The use according to claim 5, wherein the adsorbent is used by: taking a solution containing perfluoro and polyfluoroalkyl substances in a water environment, adjusting the pH value of the solution to 3-4.83, adding an adsorbent, and oscillating at a constant temperature of 25-30 ℃ for 5-24 h.

7. The use according to claim 6, wherein the mass to volume ratio of the adsorbent to the solution is 1:4 to 6.

8. Use according to claim 6, characterised in thatThe adsorbent also comprises an anion remover; the anion remover comprises Cl⁻Removing agent, SO₄ ²⁻Remover and CO₃ ^2-At least one of the removers.

9. Use according to claim 5, wherein the adsorbent can be recycled at least 4 times.

10. Use according to claim 5, wherein the perfluoro and polyfluoroalkyl materials are perfluorooctanesulfonic acid and perfluorooctanoic acid.