A Janus-MOF composite material and its preparation method and application

Abstract

This invention discloses a Janus-MOF composite material, its preparation method, and its application. The material is heterogeneously integrated with an adsorption module and a signal module via lattice-oriented growth. The adsorption module uses zirconium oxo clusters and tetrafluoroterephthalate ligands to construct molecularly imprinted channels for the specific capture of PFAS. The signal module comprises spiropyran-modified ligands and an electrochemically deposited gold nanotip array. Through photoresponsive aperture control and trimodal (electromagnetic-chemical-mechanical) synergistic enhancement, the signal module achieves a SERS detection limit of 0.05 ppt. The outer shell is doped with titanium dioxide quantum dots, which can degrade PFAS under ultraviolet light and enable substrate recycling ≥5 times. The invention further proposes a dual-mode coupling of surface-enhanced Raman spectroscopy (SERS) and electrochemical impedance spectroscopy (EIS), achieving a cross-validated detection error of ≤15%. This overcomes the poor selectivity, low sensitivity, and inability to in situ regeneration of traditional methods, making it suitable for the rapid detection of trace PFAS in complex matrices such as food, surface (ground) water, and industrial wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of pollutant detection, and more particularly to a Janus-MOF composite material and a preparation method and application thereof. Background Art

[0002] Per- and polyfluoroalkyl substances (PFAS) are a class of widespread persistent organic pollutants. Their strong carbon-fluorine bonds make them difficult to degrade in the environment and pose risks to human health, such as carcinogenicity and immunosuppression. Current PFAS detection technology faces the following challenges:

[0003] Insufficient selectivity of adsorption materials: Traditional metal organic frameworks (MOFs) such as UiO-66 and MIL-101 rely on electrostatic interactions to adsorb PFAS, but they are not suitable for adsorption in Cl-containing - The efficiency of the adsorption of PFAS in water containing interfering substances such as humic acid is significantly reduced. The prior art discloses amino-modified UiO-66 for PFAS adsorption, but does not involve specific recognition or detection functions. The measured selectivity coefficient α is 1.2-2.5.

[0004] Low detection sensitivity: Surface-enhanced Raman spectroscopy (SERS) substrates (such as Au / Ag nanoparticles) lack pre-enrichment capabilities, and the detection limit for PFAS is usually higher than 1 ppt. Existing technologies use Au NPs@ZIF-8 composite substrates to detect PFAS, but the SERS detection limit is 10 ppt and cannot be recycled.

[0005] The substrate is non-renewable: Molecularly imprinted MOF (MIP-MOF) is prone to template molecule elution or structural collapse in the aqueous phase, and the number of reuses is ≤2 times. The existing technology proposes that MIP-MOF be used for PFAS adsorption, but it has poor water stability and the adsorption capacity decreases by >50% after template elution.

[0006] Therefore, how to provide a detection material and method to overcome the defects of the existing technology is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0007] In view of this, the present invention provides a dynamically responsive Janus-MOF composite material, a preparation method thereof, and its application in dual-mode detection and regeneration of perfluoroalkyl substances (PFAS), to solve the problems of poor selectivity, low sensitivity, and inability to regenerate in situ in traditional methods.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] First, the present invention provides a method for preparing a Janus-MOF composite material, comprising the following steps:

[0010] Step 1: Preparation of adsorption module

[0011] ZrCl4, H2TFBDC and PFOS template molecules were dissolved in a DMF / acetic acid mixed solvent at a molar ratio of 4:4:0.5, reacted at 120±5℃ for 20-28 hours, centrifuged and washed, and then treated with a methanol / acetic acid mixture at 60±5℃ for 10-15 hours to remove PFOS molecules and obtain MI-MOF.

[0012] Step 2: Interface modification

[0013] The MI-MOF was dispersed in a 1-3 wt% polyethyleneimine aqueous solution, ultrasonically treated for 20-40 min, and collected by centrifugation to obtain a surface-aminated MOF.

[0014] Step 3: Signal module growth

[0015] The surface-aminated MOF was immersed in a DMF / methanol mixed solvent containing 0.2-0.5 mmol spiropyran-modified ligand SP-H2BDC and 0.05-0.2 mmol HAuCl4, and reacted at 75-85°C for 10-14 h. 0.05-0.2 M ascorbic acid solution was added dropwise, and reduced at 55-65°C for 1-3 h to generate gold nanoparticles with a particle size of 10-20 nm, which was then washed with NaOH solution to obtain a Janus-MOF composite material.

[0016] Preferably, the volume ratio of DMF and acetic acid in the DMF / acetic acid mixed solvent in step 1 is 9:1; the volume ratio of methanol and acetic acid in the methanol / acetic acid mixture is 9:1.

[0017] Preferably, in step three, the modification rate of the spiropyran-modified ligand SP-H2BDC is 20-40%, and its photoisomerization response time is ≤30 s; the volume ratio of DMF and methanol in the DMF / methanol mixed solvent is 6-8:2-4; and the dropwise addition rate of the ascorbic acid is 0.5-1 mL / min.

[0018] The present invention also provides a Janus-MOF composite material prepared by the above technical solution.

[0019] The Janus-MOF composite material's adsorption module, a fluorinated ligand (H2TFBDC), and molecularly imprinted pores enable targeted capture of PFAS, while the signaling module, a spiropyran-modified ligand (SP-H2BDC) and an electrochemically deposited Au nanotip array, enable photoresponsive pore size control. The adsorption and signaling modules are synthesized in stages through PEI interface modification to form a Janus heterostructure.

[0020] The present invention also provides a Janus-MOF composite material prepared according to the above technical solution or the use of the Janus-MOF composite material in preparing a renewable Janus-MOF-based dual-mode PFAS sensor.

[0021] The present invention also provides a method for preparing the regenerable Janus-MOF-based dual-mode PFAS sensor, comprising the following steps:

[0022] Preparation of nanotip by electrochemical deposition: Using an ITO electrode modified with a Janus-MOF composite as the working electrode, a constant potential of -0.1 to -0.3 V (vs. Ag / AgCl) was applied in an electrolyte containing 1-2 mM HAuCl4 and 0.1-0.5 M H2SO4 for 20-40 s to form a vertically oriented gold nanotip array.

[0023] Titanium dioxide doping: The material obtained in step (1) is immersed in a 0.5-2% by volume tetrabutyl titanate ethanol solution, and ammonia water is added dropwise to a pH of 8-10. The mixture is stirred at 50-70°C for 1-3 h to generate a TiO2 quantum dot-doped Janus-MOF-based dual-mode PFAS sensor.

[0024] Preferably, the tip density of the gold nanotip array in step (1) is 50-200 / μm 2 The distance between adjacent tips is 10-30 nm.

[0025] The present invention also provides a regenerable Janus-MOF-based dual-mode PFAS sensor prepared by the method described in the above technical solution.

[0026] The present invention also provides a renewable Janus-MOF-based dual-mode PFAS sensor prepared by the above method or the use of the renewable Janus-MOF-based dual-mode PFAS sensor in the integrated adsorption-sensing detection of PFAS, comprising the following steps:

[0027] S1. Place the water sample in contact with the sensor for 20-60 minutes;

[0028] S2. Irradiate with ultraviolet light at a wavelength of 365 ± 5 nm for 5-10 min, inducing the MOF pore size to shrink by 0.3-0.7 nm, thereby locking the PFAS molecules.

[0029] S3.SERS mode: using 785 ± 5 nm laser, power ≤ 10 mW, integration time ≤ 10 s, collecting PFAS 730-740 cm -1 CF2 characteristic peak within the range;

[0030] S4.EIS mode: in the frequency range 0.1-10 5 The electrochemical impedance spectroscopy was tested at 100 Hz and an amplitude of 5-15 mV, and the interface capacitance change rate was obtained by equivalent circuit fitting;

[0031] S5. Regeneration: After detection, irradiate with 254±5 nm UV light for 20-40 min to degrade the adsorbed PFAS molecules.

[0032] Preferably, the laser wavelength of the SERS detection is 785 nm, the power is 5±0.5 mW, and the integration time is 5±1 s; the equivalent circuit model of the EIS detection is R(QR)(QR), where Q is a constant phase angle element.

[0033] It can be seen from the above technical solutions that, compared with the prior art, the present invention discloses a Janus-MOF composite material and its preparation method and application, which has the following beneficial effects:

[0034] This invention constructs a Janus heterostructure MOF, integrating separation, adsorption, and signal transduction functions. It achieves size sieving through molecularly imprinted pores (1.2±0.3 nm) and enhances selectivity (α>5) through fluorine-fluorine interactions. The invention also introduces a spiropyran photoresponsive ligand, which induces UV-light-induced pore contraction (Δ=0.5 nm), locking PFAS and reducing signal fluctuations. SERS-EIS dual-mode cross-validation improves reliability, and in situ substrate regeneration (degradation rate >95%) is achieved through TiO2 photocatalytic degradation. This invention significantly outperforms existing solutions in terms of technical effectiveness, reducing the detection limit by 20-fold and increasing the number of cycles by 5-fold, providing a new, efficient and low-cost method for trace PFAS monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0036] Figure 1 Preparation flow chart. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] Example 1

[0039] Synthesis and characterization of Janus-MOF:

[0040] Step 1: 0.4 mmol zirconium chloride (ZrCl4), 0.4 mmol tetrafluoroterephthalic acid (H2TFBDC), and 0.05 mmol perfluorooctane sulfonic acid (PFOS) were dissolved in N,N-dimethylformamide (DMF) / acetic acid (40 mL) and ultrasonically dispersed for 15 min until completely dissolved. The mixture was transferred to a 100 mL polytetrafluoroethylene autoclave and reacted at 120°C for 24 h. After natural cooling, the mixture was centrifuged (8000 rpm, 10 min), washed with DMF and methanol three times in sequence, and dried in vacuo at 80°C for 12 h. The MOF was immersed in a methanol / acetic acid mixture (volume ratio 9:1, 50 mL), stirred at 60°C for 12 h, centrifuged, washed, and dried to obtain molecularly imprinted MOF (MI-MOF).

[0041] Step 2: Disperse MI-MOF in 10 mL of PEI solution, sonicate for 30 min, and collect by centrifugation to obtain surface amino-modified MOF.

[0042] Step 3: The aminated MOF was dispersed in a DMF / methanol solution containing 0.3 mmol spiropyran-modified H2BDC (SP-H2BDC) and 0.1 mmol chloroauric acid (HAuCl4) and reacted at 80°C for 12 h. Ascorbic acid solution (0.1 M, 2 mL) was added dropwise and reduced at 60°C for 2 h to generate Au NPs (particle size 15±3 nm). The resulting material was treated with 0.1 M NaOH solution for 5 min to remove loose surface ligands, centrifuged, washed, and dried to obtain the Janus-MOF material.

[0043] Preparation of the sensor:

[0044] Electrochemical deposition of gold nanotip array: The Janus-MOF / ITO electrode (the working electrode was prepared by immersing the ITO electrode in a Janus-MOF dispersion for 24 h) was immersed in the electrolyte and deoxygenated with nitrogen for 10 min. A constant potential of -0.2 V was applied. After deposition for 30 s, the electrode was taken out, rinsed with ultrapure water, and dried with nitrogen. Scanning electron microscopy showed that the tip length was 50±5 nm and the tip curvature radius was 3±1 nm.

[0045] Example 2

[0046] Dual-mode detection performance test

[0047] PFOS standard solutions (0.01 ppt, 0.1 ppt, 1 ppt, 10 ppt, 100 ppt, 1 ppb, 10 ppb, 100 ppb, 1 ppm) were prepared. 1 mL of each concentration solution was added to a Janus-MOF substrate (1 cm × 1 cm). The solution was allowed to adsorb for 30 minutes and then irradiated with 365 nm UV light for 5 minutes to lock the PFAS.

[0048] SERS detection (laser wavelength 785 nm, power 5 mW, integration time 5 s, objective lens 50×), characteristic peak: 735 cm -1 (CF2 stretching vibration), 1230 cm -1 (COC skeleton vibration), LOD is 0.05 ppt;

[0049] EIS quantitative detection verification: The substrate after adsorption of PFOS was used as the working electrode to test the EIS spectrum. The EIS detection capacitance change rate was linearly correlated with the concentration (1ppt-1ppm, R 2 =0.995).

[0050] Example 3

[0051] Recycling performance test

[0052] 1. The degraded substrate was immersed in 10 mL of methanol and ultrasonicated for 30 min to elute the residual PFAS. HPLC-MS quantitative analysis was performed. After detection, the substrate was irradiated with ultraviolet light (254 nm) for 30 min. HPLC-MS showed that the PFOS degradation rate was >95%.

[0053] 2. Repeat the “adsorption-detection-degradation” cycle 5 times on the same substrate, and measure the SERS signal intensity (735 cm -1 The SERS signal decay rate after the 5th cycle is 92.5% of the initial value, and the EIS linearity R 2 >0.99.

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0055] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a Janus-MOF composite material, characterized in that: The following steps are involved: Step 1: Preparation of adsorption module ZrCl4, H2TFBDC and PFOS template molecules were dissolved in a DMF / acetic acid mixed solvent at a molar ratio of 4:4:0.5, reacted at 120±5℃ for 20-28 h, centrifuged and washed, and then treated with a methanol / acetic acid mixture at 60±5℃ for 10-15 h to remove PFOS molecules and obtain molecularly imprinted MOF. Step 2: Interface modification The molecularly imprinted MOF was dispersed in a 1-3 wt% polyethyleneimine aqueous solution, ultrasonically treated for 20-40 min, and collected by centrifugation to obtain the surface-aminated MOF. Step 3: Signal module growth The surface aminated MOF was immersed in a DMF / methanol mixed solvent containing 0.2-0.5 mmol spiropyran-modified ligand SP-H2BDC and 0.05-0.2 mmol HAuCl4, and reacted at 75-85°C for 10-14 h. 0.05-0.2 M ascorbic acid solution was added dropwise, and reduced at 55-65°C for 1-3 h to generate gold nanoparticles with a particle size of 10-20 nm, which was then washed with NaOH solution to obtain a Janus-MOF composite material.

2. The method for preparing a Janus-MOF composite material according to claim 1, wherein: The volume ratio of DMF and acetic acid in the DMF / acetic acid mixed solvent in step 1 is 9:1; the volume ratio of methanol and acetic acid in the methanol / acetic acid mixture is 9:

1.

3. The method for preparing a Janus-MOF composite material according to claim 1, wherein: In step 3, the modification rate of the spiropyran-modified ligand SP-H2BDC is 20-40%, and its photoisomerization response time is ≤30 s; the volume ratio of DMF and methanol in the DMF / methanol mixed solvent is 6-8:2-4; and the dropping speed of the ascorbic acid is 0.5-1 mL / min.

4. A Janus-MOF composite material prepared by the preparation method according to any one of claims 1 to 3.

5. Use of the Janus-MOF composite material according to claim 4 in preparing a renewable Janus-MOF-based dual-mode PFAS sensor.

6. A method for preparing a regenerable Janus-MOF-based dual-mode PFAS sensor according to claim 5, characterized in that: The following steps are involved: Electrochemical deposition of nanotips: Using a Janus-MOF composite modified ITO electrode as the working electrode, a constant potential of -0.1 to -0.3 V vs. Ag / AgCl was applied in an electrolyte containing 1-2 mM HAuCl4 and 0.1-0.5 M H2SO4 for 20-40 s to form a vertically oriented gold nanotip array. Titanium dioxide doping: The material obtained in step (1) is immersed in a 0.5-2% by volume tetrabutyl titanate ethanol solution, and ammonia water is added dropwise to a pH of 8-10. The mixture is stirred at 50-70°C for 1-3 h to generate a TiO2 quantum dot-doped Janus-MOF-based dual-mode PFAS sensor.

7. The method for preparing a regenerable Janus-MOF-based dual-mode PFAS sensor according to claim 6, characterized in that: The tip density of the gold nanotip array in step (1) is 50-200 / μm 2 The distance between adjacent tips is 10-30nm.

8. A regenerable Janus-MOF-based dual-mode PFAS sensor prepared by the method according to any one of claims 6-7.

9. A use of the regenerable Janus-MOF-based dual-mode PFAS sensor according to claim 8 in the integrated adsorption-sensing detection of PFAS, characterized in that: The following steps are involved: S1. Place the water sample in contact with the sensor for 20-60 minutes; S2. Irradiate with ultraviolet light at a wavelength of 365 ± 5 nm for 5-10 min, inducing the MOF pore size to shrink by 0.3-0.7 nm, thereby locking the PFAS molecules. S3.SERS mode: using 785 ± 5 nm laser, power ≤ 10 mW, integration time ≤ 10 s, collecting PFAS 730-740 cm -1 CF2 characteristic peak within the range; S4.EIS mode: in the frequency range 0.1-10 5 The electrochemical impedance spectroscopy was tested at 100 Hz and an amplitude of 5-15 mV, and the interface capacitance change rate was obtained by equivalent circuit fitting; S5. Regeneration: After detection, irradiate with 254±5 nm UV light for 20-40 min to degrade the adsorbed PFAS molecules.

10. The use according to claim 9, characterized in that The laser wavelength of the SERS detection is 785 nm, the power is 5±0.5 mW, and the integration time is 5±1 s; the equivalent circuit model of the EIS detection is R(QR)(QR), where Q is a constant phase angle element.

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