A method for rapid visual screening of perfluoro- and polyfluoroalkyl compound adsorbents based on a liquid crystal platform

Abstract

The present application relates to the field of adsorption separation technology, and particularly relates to a method for quickly visualizing screening of PFAS adsorbents based on a liquid crystal platform. When a PFAS solution with a certain concentration is added dropwise to the surface of the liquid crystal, the PFAS in the solution will gather at the water / liquid crystal interface, the hydrophilic head of the PFAS remains in the aqueous solution, and the hydrophobic tail is inserted into the liquid crystal interface, thereby inducing the ordered arrangement of the liquid crystal, and the liquid crystal molecules present a dark image under a polarized light source; when the adsorbent adsorbs the concentration of the PFAS to a concentration that can make the liquid crystal dark and below, the liquid crystal molecules will be arranged in disorder, and at this time, the optical image is bright. Because the adsorption performance of each adsorbent is different, the concentration of the remaining PFAS solution in the solution is different, thereby leading to the fact that the brightness of the liquid crystal image is also different, wherein the brighter the brightness of the liquid crystal image, the more the adsorbed PFAS, and the stronger the adsorption capacity of the adsorbent, and vice versa, which indicates that the adsorption capacity of the adsorbent is poorer.

Description

Technical Field

[0001] This invention relates to the field of adsorption separation technology, specifically to a method for rapid and visual screening of perfluorinated and polyfluoroalkyl compound adsorbents based on a liquid crystal platform. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Per- and polyfluoroalkyl substances (PFAS) are a collective term for a series of synthetic organofluorine compounds. Originally used to extinguish large oil fires, PFAS are commonly used in the manufacture of everyday consumer goods and fire-fighting products requiring waterproofing, stain resistance, and grease resistance due to their extremely stable chemical structure and oleophobic and hydrophobic properties. PFAS contain high-energy carbon-fluorine bonds, exhibiting poor degradation, high persistence, and high mobility. They are ubiquitous in water, sediments, soil, atmosphere, and organisms, posing potential environmental and health risks.

[0004] To remove PFAS from water resources, various removal methods have been developed, including photocatalytic degradation, biodegradation, and ultrasonic decomposition. However, these technologies have inherent weaknesses, such as low efficiency, high energy consumption, and the need for specialized equipment. Meanwhile, adsorption separation is a simple and efficient method for removing PFAS. PFAS compounds are mostly negatively charged, and strongly positively charged porous adsorbents can be used to adsorb and remove PFAS from water. However, there is currently no rapid and convenient method for evaluating the adsorption capacity of adsorbents. Currently, the evaluation of adsorbents relies solely on high-performance liquid chromatography-mass spectrometry (HPLC-MS) to detect the adsorption amount. This method requires specialized instruments, is time-consuming and expensive, and cannot achieve real-time screening. Therefore, a low-cost and rapid method for screening PFAS adsorbents is urgently needed. Summary of the Invention

[0005] To overcome the above problems, the present invention provides a method for rapid and visual screening of perfluorinated and polyfluoroalkyl compound adsorbents based on a liquid crystal platform.

[0006] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0007] A first aspect of the present invention provides a method for rapidly visually screening perfluorinated and polyfluoroalkyl compound adsorbents based on a liquid crystal platform, comprising:

[0008] (1) After mixing polydimethylsiloxane prepolymer (PDMS) and polydimethylsiloxane curing agent, the mixture is coated onto a clean glass slide and dried to obtain a PDMS-coated glass slide. Then, liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) is dropped onto the PDMS-coated glass slide, heated to an isotropic phase, and then cooled to room temperature to obtain a liquid crystal platform.

[0009] (2) Add PFAS solutions of gradient concentrations to the liquid crystal platform, observe the optical response of the liquid crystal, obtain the standard curve of the bright area coverage (Br) of the liquid crystal platform image and the concentration of PFAS solution, and obtain the concentration value C0 of PFAS solution when Br is 2% to 5%.

[0010] (3) Limit the PFAS solution to CO, add the same mass of different adsorbents to the PFAS solution, remove the adsorbents at the specified time points, and drop the adsorbed PFAS solution onto the liquid crystal platform when Br is 2% to 5%, and observe the optical response of the liquid crystal platform; if the Br change is large under the same adsorption time, the larger the Br, the better the adsorption performance of the adsorbent; if the Br change is small under the same adsorption time, screen the adsorbent by the standard curve of Br and PFAS solution concentration.

[0011] In one or more embodiments, the PFAS is perfluorooctanoic acid (PFOA).

[0012] In one or more embodiments, in step (1), the mass ratio of polydimethylsiloxane prepolymer (PDMS) to polydimethylsiloxane curing agent is 10:1.

[0013] In one or more embodiments, in step (1), after mixing polydimethylsiloxane prepolymer (PDMS) and polydimethylsiloxane curing agent and removing air bubbles, the mixture is coated onto a clean glass sheet.

[0014] In one or more embodiments, in step (1), when the polydimethylsiloxane prepolymer (PDMS) and polydimethylsiloxane curing agent are mixed and coated onto a clean glass slide, the coating method is spin coating, the spin coating speed is 1800-2500 rpm, preferably 2000 rpm, and the spin coating time is 15-25 s, preferably 20 s.

[0015] In one or more embodiments, the cleaning of the glass slide in step (1) includes washing it with deionized water and ethanol 3 to 5 times respectively.

[0016] In one or more embodiments, in step (1), 1 μL of 5CB is used based on a glass slide of 25.4 × 76.2 mm.

[0017] In one or more embodiments, in step (1), the temperature of heating to the isotropic phase is 33-38°C, preferably 35°C.

[0018] In one or more embodiments, in step (2), when the PFAS is perfluorooctanoic acid (PFOA), the gradient concentration is 200-450 mg / L; when obtaining the standard curve of the bright area coverage (Br) of the liquid crystal platform image and the PFAS solution concentration, the PFAS solution concentrations are 310 mg / L, 320 mg / L, 330 mg / L, 340 mg / L and 350 mg / L, respectively.

[0019] In one or more embodiments, in step (2), the optical response of the liquid crystal is observed and photographed, and the bright area coverage (Br) of the liquid crystal platform image is obtained by Adobe Photoshop 2021 software.

[0020] In one or more embodiments, in step (3), if the Br change is small under the same adsorption time, the optical response of the liquid crystal is observed and photographed. The bright area coverage (Br) of the liquid crystal platform image is obtained by Adobe Photoshop 2021 software. The concentration of the PFAS solution after adsorption is obtained by the standard curve of Br and PFAS solution concentration. The lower the concentration, the better the adsorption performance of the adsorbent.

[0021] The beneficial effects of this invention are as follows:

[0022] (1) Figure 1 The principle behind the rapid visual screening of PFAS adsorbents based on a liquid crystal platform in this invention is as follows: Specific surfactant molecules affect the alignment of liquid crystals and cause changes in the orientation of liquid crystal molecules, resulting in alternating dark and bright optical responses. In this invention, because PFAS has hydrophobic tails and hydrophilic heads, it can be considered a surface-active substance. When a PFAS solution of a certain concentration is added to the liquid crystal surface, the PFAS in the solution aggregates at the water / liquid crystal interface. The hydrophilic heads of PFAS remain in the aqueous solution, while the hydrophobic tails insert into the liquid crystal interface, thereby inducing the liquid crystal to align in an orderly manner. Under a polarized light source, the liquid crystal molecules present a dark image. After the adsorbent adsorbs PFAS, the concentration of PFAS in the aqueous solution decreases. When the adsorbent adsorbs the PFAS concentration to a level that darkens the liquid crystal or below, the liquid crystal molecules will align randomly, resulting in a bright optical image. Because the adsorption properties of different adsorbents are different, the concentration of the remaining PFAS solution in the solution is different, which in turn leads to different brightness of the liquid crystal image. The brighter the liquid crystal image, the more PFAS is adsorbed and the stronger the adsorption capacity of the adsorbent. Conversely, the brighter the liquid crystal image, the weaker the adsorption capacity of the adsorbent.

[0023] This invention utilizes the optical response of liquid crystal and PFAS solution concentration for rapid and visual screening of adsorbents. The screened adsorbents maximize PFAS adsorption within the same time frame. The specific method includes: first, determining the PFAS solution concentration C0 when Br is 2-5%, limiting the PFAS solution to C0, adding the same mass of adsorbent to each PFAS solution, removing the adsorbent at defined time points, and then dropping the adsorbed PFAS solution onto a liquid crystal platform with Br of 2%-5%. The optical response of the liquid crystal platform is observed. If there is a large difference in Br change within the same adsorption time, it is clearly visible to the naked eye which liquid crystal platform has the highest Br; a higher Br indicates better adsorption performance of the adsorbent. If there is a small difference in Br change within the same adsorption time, and the brightness cannot be clearly observed to the naked eye, Br is obtained using Adobe Photoshop 2021 software. The concentration of the PFAS solution after adsorption is obtained through a standard curve of Br versus PFAS solution concentration; a lower concentration indicates better adsorption performance of the adsorbent.

[0024] (2) The method for rapid visual screening of PFAS adsorbents based on a liquid crystal platform provided by the present invention enables rapid quantitative and simple instantaneous acquisition of the adsorption amount of PFAS by the adsorbent solely by the brightness of the liquid crystal image without relying on complex instruments, thereby achieving rapid visual screening of PFAS adsorbents. The entire process is simple to operate and low in cost, effectively solving the problems of complexity and high cost of existing screening methods, and providing a new approach for adsorbent screening. Attached Figure Description

[0025] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0026] Figure 1 This invention illustrates the principle of rapid and visual screening of PFAS adsorbents based on a liquid crystal platform. a represents the adsorption process before adsorption, and b represents the adsorption process after adsorption.

[0027] Figure 2 This study explores the response between PFOA concentration and liquid crystal brightness in Example 1, and establishes a standard curve for Br and PFOA solution concentration.

[0028] Figure 3 Images showing Br brightness at 2% and 3% respectively;

[0029] Figure 4In Figure a, after different adsorbents adsorbed for the same amount of time, the solution was dropped onto a liquid crystal platform with Br content of 2%–3%, and the bright area coverage of the liquid crystal platform was displayed. In Figure b, the solution after adsorption by different adsorbents was dropped onto the liquid crystal platform, and the change of Br content over time was displayed.

[0030] Figure 5 The experimental results were verified, among which... a The adsorption amount was determined by high-performance liquid chromatography-mass spectrometry (HPLC-MS). b The adsorption amount is the average value calculated by the liquid crystal platform (n≥3). Detailed Implementation

[0031] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0034] In the following examples, PFOA was available from Shanghai Aladdin Biochemical Technology Co., Ltd., activated carbon powder was available from Shanghai McLean Biochemical Technology Co., Ltd., zeolite was available from Nantong Feiyu Biotechnology Co., Ltd., NU-1000 was synthesized in-house, and MIL-101-Fe, UIO-66, and ZIF-8 were available from Jilin Zhongke Science & Technology Co., Ltd. The liquid crystal images were captured by a digital camera (TK-9301EC, JVC, Japan) connected to a transmission polarization microscope (POM, XPF-800C, Tianxing, China) with a 2.5× objective lens.

[0035] Example 1

[0036] (1) Fabrication of the liquid crystal platform:

[0037] Glass slides were washed 3–5 times with deionized water and ethanol, respectively, and dried under nitrogen atmosphere. Polydimethylsiloxane prepolymer (PDMS) and PDMS curing agent were mixed at a weight ratio of 10:1. The mixture was evacuated for 20 min to remove air bubbles, and then spin-coated onto a clean glass slide (25.4 × 76.2 mm) at 2000 rpm for 20 s. The coated glass was then placed in an 80°C oven for 4 h to dry, resulting in a PDMS-coated glass slide. A 75-mesh copper grid was placed on the PDMS-coated glass slide, and 1 μL of 5CB was dropped onto each grid. The slide was then heated to 35°C to achieve an isotropic liquid crystal phase. After cooling to room temperature, excess 5CB was removed from the grid using a capillary tube to obtain a uniform vertical array of 5CB, thus preparing a liquid crystal platform.

[0038] (2) Dissolve and disperse PFOA in an aqueous solution, mix thoroughly to obtain a PFOA solution, and dilute the solution to a concentration gradient of 200–450 mg / L (specifically 200 mg / L, 250 mg / L, 300 mg / L, 350 mg / L, 400 mg / L, and 450 mg / L). Then, transfer the PFOA solutions of the concentration gradient to a liquid crystal platform to observe the optical response of the liquid crystal and take pictures. Obtain the bright area coverage (Br) of the liquid crystal image using Adobe Photoshop 2021 software and create a bar chart as shown below. Figure 2 As shown in Figure a. From Figure 2 As can be seen from Figure a, Br varies significantly within the range of 300–350 mg / L. Therefore, a standard curve was established for Br versus PFOA solution concentration within this range, and the results are shown below. Figure 2 As shown in b.

[0039] pass Figure 3 It can be seen that when the Br brightness is at its minimum (2% to 3%), the liquid crystal platform still has some brightness and cannot reach 0%. Therefore, in the experiment, it was determined that a Br brightness of less than 5% is a completely dark environment.

[0040] Experimental Example 2

[0041] Depend on Figure 2As shown in b, when the Br brightness is at its minimum (2%–3%), the PFOA solution concentration C0 is 350 mg / L. Six PFOA solutions with a concentration of 350 mg / L were taken, and the same mass of NU-1000, MIL-101-Fe, UIO-66, ZIF-8, activated carbon powder, and zeolite were added to each solution. The mixture was then transferred to a shaker at 200 rpm. Using a syringe and a 0.22 μm filter, the mixture was extracted at 1, 3, 5, 10, 20, and 40 rpm to remove the adsorbent. The adsorbed PFOA solution was then added dropwise to a liquid crystal platform where the Br concentration was 2%–3%, and the optical response of the liquid crystal platform was observed. The results are as follows: Figure 4 As shown in Figure a, from Figure 4 As shown in section a, at 1 minute, the Br content on the liquid crystal platform is the highest when the solution after adsorption by NU-1000 is added to the liquid crystal platform. Meanwhile, section b reflects the change in Br content over time when solutions after adsorption by different adsorbents are added to the liquid crystal platform. Figure 4 The results show that NU-1000 is the optimal adsorbent.

[0042] To further confirm the accuracy of the experimental results, liquid chromatography-mass spectrometry (LC-MS) and a surface area and porosity analyzer (BET) were used to verify the results. The results are as follows: Figure 5 As shown in the figure. This confirms that NU-1000 is the optimal adsorbent.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for rapid visual screening of perfluoro- and polyfluoroalkyl compound adsorbents based on a liquid crystal platform, characterized in that, The method comprises the following steps: (1) mixing a polydimethylsiloxane prepolymer and a polydimethylsiloxane curing agent, coating the mixture on a clean glass sheet, drying to obtain a polydimethylsiloxane prepolymer coated glass sheet, dropping liquid crystal 4-cyano-4'-pentyl biphenyl on the polydimethylsiloxane prepolymer coated glass sheet, heating to isotropic phase, cooling to room temperature, and obtaining a liquid crystal platform; (2) dropping a gradient concentration perfluoro and polyfluoro alkyl compound solution on the liquid crystal platform, observing the optical response of the liquid crystal, obtaining a standard curve of bright area coverage of the liquid crystal platform image and the concentration of the perfluoro and polyfluoro alkyl compound solution, and obtaining the concentration value C0 of the perfluoro and polyfluoro alkyl compound solution when the bright area coverage is 2%-5%; (3) limiting the perfluoro and polyfluoro alkyl compound solution to C0, adding the same mass of different adsorbents to the perfluoro and polyfluoro alkyl compound solution respectively, removing the adsorbents at a limited time point, dropping the adsorbed perfluoro and polyfluoro alkyl compound solution on the liquid crystal platform with a bright area coverage of 2%-5%, and observing the optical response of the liquid crystal platform; if the bright area coverage changes greatly at the same adsorption time, the greater the bright area coverage indicates that the adsorption performance of the adsorbent is better; if the bright area coverage changes little at the same adsorption time, the adsorbent is screened through the standard curve of the bright area coverage and the concentration of the perfluoro and polyfluoro alkyl compound solution.

2. The method of claim 1, wherein, The perfluoro and polyfluoro alkyl compound is perfluorooctanoic acid.

3. The method of claim 1, wherein, In step (1), the mass ratio of the polydimethylsiloxane prepolymer and the polydimethylsiloxane curing agent is 10:

1.

4. The method of claim 1, wherein, In step (1), when the polydimethylsiloxane prepolymer and the polydimethylsiloxane curing agent are mixed and coated on the clean glass sheet, the coating method is spin coating, the spin coating speed is 1800-2500 rpm, and the spin coating time is 15-25 s.

5. The method of claim 1, wherein, In step (1), the glass sheet cleaning method comprises washing with deionized water and ethanol for 3-5 times, respectively.

6. The method of claim 1, wherein, In step (1), based on a glass sheet with a size of 25.4*76.2 mm, 1 μL of liquid crystal 4-cyano-4'-pentyl biphenyl is used.

7. The method of claim 1, wherein, In step (1), the heating temperature to isotropic phase is 33-38℃.

8. The method of claim 1, wherein, In step (2), when the PFAS is perfluorooctanoic acid, the gradient concentration is 200-450 mg / L; when the standard curve of the bright area coverage of the liquid crystal platform image and the concentration of the perfluorooctanoic acid solution is obtained, the perfluorooctanoic acid solution concentrations are 310 mg / L, 320 mg / L, 330 mg / L, 340 mg / L and 350 mg / L, respectively.

9. The method of claim 1, wherein, In step (2), the optical response of the liquid crystal is observed and photographed, and the bright area coverage of the liquid crystal platform image is obtained by Adobe Photoshop 2021 software.

10. The method of claim 1, wherein, In step (3), if the difference in bright area coverage is small under the same adsorption time, observe the optical response of the liquid crystal and take a picture to record it. Obtain the bright area coverage of the liquid crystal platform image using Adobe Photoshop 2021 software. Obtain the concentration of perfluorinated and polyfluoroalkyl compounds after adsorption by the standard curve of bright area coverage versus concentration of perfluorinated and polyfluoroalkyl compounds solution. The lower the concentration, the better the adsorption performance of the adsorbent.

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