Electrochemical sensor for detecting perfluorooctanoic acid and method for manufacturing the same

Abstract

The present invention relates to an electrochemical sensor, and more specifically, to a technology for a method of manufacturing the same, comprising a tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes for detecting perfluorooctanoic acid (PFOA). The present invention provides a mechanism for detecting perfluorooctanoic acid through deprotonation of the carboxyl group of a perfluorooctanoic acid molecule, formation of a free radical intermediate by electron removal, formation of a secondary free radical through a Kolbe electrolytic decarboxylation reaction, and a reduction reaction. The sensor of the present invention, based on such electrochemical oxidation-reduction reactions, can be effectively utilized for real-time field monitoring of perfluorooctanoic acid.

Description

Technology Field

[0001] The present invention relates to an electrochemical sensor for detecting perfluorooctanoic acid, and more specifically, to an electrochemical sensor for detecting perfluorooctanoic acid (PFOA), an environmentally hazardous substance, based on an electrode modified by coating a tin dioxide-tungsten trioxide nanocomposite immobilized on carbon nanotubes, and a method for manufacturing the same.

[0002] Specifically, the present invention relates to a technology for a high-sensitivity electrochemical sensor capable of selectively detecting perfluorooctanoic acid through an electrode material manufactured by synthesizing a tin dioxide-tungsten trioxide nanocomposite using a hydrophilic thermal method and immobilizing it on a carbon nanotube. Background Technology

[0003] Environmental pollution presents significant challenges to human health and well-being in modern society. Rapid industrialization and urbanization are intensifying the depletion of water resources, leading to reduced availability of freshwater and an increase in waterborne diseases.

[0004] Perfluorinated compounds (PFAS), synthetic chemicals that have been widely used in industry since the 1950s, are emerging as a major public health problem.

[0005] Perfluorinated compounds are called "forever chemicals" due to their tendency to accumulate in plants, animals, and the human body, and among them, perfluorooctanoic acid (PFOA) can cause various health risks, including nerve damage, immune system disruption, hormonal imbalance, liver toxicity, and cancer.

[0006] PFOA is frequently detected in wastewater, drinking water, groundwater, and food samples, and is used in various applications such as food packaging materials, textiles, electronic products, and flame retardants.

[0007] Existing methods for detecting PFOA include chromatography and mass spectrometry, but these methods have the disadvantage of being costly and time-consuming. To effectively address environmental pollution issues, it is essential to develop economical and efficient technologies capable of early detection of PFAS contamination.

[0008] Electrochemical sensing is attracting attention as a sustainable solution for rapid pollutant detection. Electrochemical sensors exhibit superior characteristics compared to existing analytical methods due to advantages such as portability, excellent selectivity and sensitivity, rapid response time, real-time monitoring capabilities, and low energy consumption.

[0009] However, detecting analytes that exhibit low reactivity under electrochemical conditions, such as PFAS molecules, remains a major challenge in the field of electrochemistry.

[0010] To address these challenges, research on the development of new materials is actively underway, and in particular, metal oxide semiconductor (MOS) nanostructures are attracting attention as important sensing materials due to their simple synthesis, cost-effectiveness, versatility, large specific surface area, and excellent charge transport properties.

[0011] However, existing metal oxide-based sensors still have room for improvement in terms of sensitivity, selectivity, and stability, so the development of new composite materials to enhance them is required. Prior art literature

[0012] Chinese Patent Publication No. 117538394, "Perfluorooctane sulfonic acid sensor as well as preparation method and application thereof" The problem to be solved

[0013] The present invention aims to provide enhanced electrochemical performance through the synergistic effect of a tin dioxide-tungsten trioxide nanocomposite and carbon nanotubes in an electrochemical sensor for detecting perfluorooctanoic acid.

[0014] The present invention aims to provide an electrochemical sensor for detecting perfluorooctanoic acid having a low detection limit at the ppb level and excellent sensitivity.

[0015] The present invention aims to provide an electrochemical sensor for detecting perfluorooctanoic acid that is stable against changes in pH and capable of selective detection even under conditions where interfering substances, such as metal ions, are present.

[0016] The present invention aims to provide a practical electrochemical sensor for detecting perfluorooctanoic acid that exhibits a high recovery rate even in actual samples such as tap water, vegetable and fruit samples.

[0017] The present invention aims to provide a method for manufacturing an economical electrochemical sensor for detecting perfluorooctanoic acid that can be mass-produced through a simple hydrophilic thermal method.

[0018] The present invention aims to provide an electrochemical sensor for detecting perfluorooctanoic acid that has excellent long-term storage stability and is reusable.

[0019] The present invention aims to provide a portable electrochemical sensor system capable of real-time field monitoring. means of solving the problem

[0020] An electrochemical sensor for detecting perfluorooctanoic acid according to an embodiment of the present invention comprises an electrode modified with a tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on a carbon nanotube, wherein the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotube comprises single-crystal tin dioxide-tungsten trioxide nanoparticles dispersed and immobilized on the surface of the carbon nanotube, wherein the tin dioxide-tungsten trioxide nanocomposite immobilized on the carbon nanotube forms an anion through the deprotonation of the carboxyl group (-COOH) of a perfluorooctanoic acid (PFOA) molecule, forms a free radical intermediate by the detachment of an electron from the formed anion, and forms a secondary free radical through a Kolbe electrolytic decarboxylation reaction of the free radical intermediate, and wherein It is characterized by performing an electrochemical oxidation-reduction reaction to produce reduced perfluorooctanoic acid through the reduction reaction of the carbonyl group (-C=O) of the perfluorooctanoic acid molecule.

[0021] The tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on the carbon nanotubes above are 1.78 x 10 -4 mA / nM mm 2 It can have the sensitivity of.

[0022] In addition, the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotubes can have a detection limit of 2.434 nM (1.0079 ppb).

[0023] In addition, the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotubes may have a linear detection range of 10 nM to 120 nM.

[0024] In addition, the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotubes can exhibit a stable electrochemical response in the pH range of 4 to 9.

[0025] In addition, the tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on the carbon nanotubes can exhibit a recovery rate of 93.83% to 97.37% in tap water, vegetable, and fruit samples.

[0026] In addition, the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotubes can exhibit a signal change of 5% or less under conditions where a metal ion interfering agent is present.

[0027] An electrochemical sensor for detecting perfluorooctanoic acid according to an embodiment of the present invention comprises the steps of: preparing a homogeneous aqueous solution by sequentially adding sodium tungsten dihydrate (Na2WO4·2H2O), tin(IV) chloride pentahydrate (SnCl4·5H2O), and glucose to deionized water; a first hydrothermal reaction step in which the homogeneous aqueous solution is placed in a stainless steel high-pressure reactor with a Teflon inner wall and subjected to a hydrothermal reaction at 180°C for 48 hours; preparing a tin dioxide-tungsten trioxide (SnO2-WO3) nanocomposite by centrifuging, washing, and drying the solid product generated from the first hydrothermal reaction, and then heat-treating it at 400°C for 6 hours; and dispersing carbon nanotubes and the tin dioxide-tungsten trioxide (SnO2-WO3) nanocomposite in deionized water and subjecting them to ultrasonic treatment. The method comprises the steps of: preparing a tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes by carrying out a second hydrothermal reaction of the dispersion at 180°C for 48 hours; and applying the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes onto an electrode.

[0028] The sodium tungsten dihydrate (Na2WO4·2H2O) and tin chloride (IV) pentahydrate (SnCl4·5H2O) are each 1 mmol, and the glucose may be 1 g.

[0029] In addition, the carbon nanotubes are dispersed in deionized water at a concentration of 2 mg / mL, and 0.5 g of the tin dioxide-tungsten trioxide (SnO2-WO3) nanocomposite may be added.

[0030] In addition, the above ultrasonic treatment can be performed for 1 hour.

[0031] In addition, the dispersion may be washed three times with ethanol and deionized water after the second hydrothermal reaction and dried at 60°C. Effects of the invention

[0033] According to one embodiment, the electrochemical sensor for detecting perfluorooctanoic acid of the present invention has 1.78 x 10 -4 mA / nM mm 2 Excellent sensitivity and a low detection limit of 2.434 nM (1.0079 ppb) can be achieved.

[0034] According to one embodiment, the electrochemical sensor for detecting perfluorooctanoic acid of the present invention provides a wide linear detection range of 10 nM to 120 nM, which enables the detection of perfluorooctanoic acid at various concentrations.

[0035] According to one embodiment, the electrochemical sensor for detecting perfluorooctanoic acid of the present invention exhibits a stable electrochemical response over a wide pH range of pH 4 to 9, so it can be utilized in various environments.

[0036] According to one embodiment, the electrochemical sensor for detecting perfluorooctanoic acid of the present invention can provide excellent selectivity by exhibiting only a signal change of 5% or less even under conditions where a metal ion interfering substance is present.

[0037] According to one embodiment, the electrochemical sensor for detecting perfluorooctanoic acid of the present invention exhibits a high recovery rate of 93.83% to 97.37% in tap water, vegetable and fruit samples, and can be effectively utilized for the analysis of actual environmental samples.

[0038] According to one embodiment, the method for manufacturing an electrochemical sensor for detecting perfluorooctanoic acid according to the present invention enables mass production using a simple hydrophilic thermal method, and since the process is simple, it is possible to manufacture an economical sensor.

[0039] According to one embodiment, the electrochemical sensor for detecting perfluorooctanoic acid of the present invention can provide excellent stability by maintaining 93.83% to 97.37% of the initial response even after long-term storage of 6 to 10 days.

[0040] According to one embodiment, the electrochemical sensor for detecting perfluorooctanoic acid of the present invention can provide excellent reproducibility by exhibiting a low relative standard deviation of 1.27%. Brief explanation of the drawing

[0042] Figure 1 illustrates the manufacturing process and characteristics of an electrochemical sensor for detecting perfluorooctanoic acid according to the present invention. Figure 2 illustrates the morphological characteristics and elemental distribution of an electrochemical sensor for detecting perfluorooctanoic acid according to an embodiment of the present invention. Figure 3 illustrates the electrochemical detection characteristics of an electrochemical sensor for detecting perfluorooctanoic acid using a tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes according to the present invention. Figure 4 is a schematic diagram showing the detection mechanism of a chemical sensor for detecting perfluorooctanoic acid using tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes. Specific details for implementing the invention

[0043] Embodiments of the present invention will be described in detail below with reference to the attached drawings and the contents described therein, but the present invention is not limited or restricted by the embodiments.

[0044] The terms used herein are for describing the embodiments and are not intended to limit the invention. In this specification, the singular form includes the plural form unless specifically stated otherwise in the text. As used herein, “comprises” and / or “comprising” do not exclude the presence or addition of one or more other components or steps mentioned in the description.

[0045] As used herein, terms such as “examples,” “examples,” “aspects,” “examples,” etc., are not to be interpreted as implying that any described aspect or design is superior or advantageous to other aspects or designs.

[0046] Furthermore, the term 'or' refers to an inclusive or rather an exclusive or. That is, unless otherwise noted or is clear from the context, the expression 'x uses a or b' refers to any one of the natural inclusive permutations.

[0047] Additionally, singular expressions (“a” or “an”) used in this specification and claims should generally be interpreted to mean “one or more” unless otherwise stated or it is clear from the context that they relate to the singular form.

[0048] The terms used in the following description have been selected as common and universal in the relevant technical field, but other terms may exist depending on technological development and / or changes, conventions, preferences of the skilled technician, etc. Therefore, the terms used in the following description should not be understood as limiting the technical concept, but as illustrative terms to explain the embodiments.

[0049] In addition, in specific cases, there are terms arbitrarily selected by the applicant, and in such cases, their detailed meanings will be described in the relevant explanatory section. Therefore, the terms used in the description below must be understood not merely as their names, but based on their meanings and the content throughout the specification.

[0050] Unless otherwise defined, all terms used in this specification (including technical and scientific terms) may be used in a meaning that is commonly understood by those skilled in the art to which the present invention pertains. Additionally, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0051] Meanwhile, in describing the present invention, if it is determined that a detailed description of related known functions or configurations could unnecessarily obscure the essence of the invention, such detailed description will be omitted. Furthermore, the terminology used in this specification is used to appropriately express embodiments of the present invention, and such terminology may vary depending on the intent of the user or operator, or the conventions of the field to which the invention belongs. Accordingly, the definitions of these terms should be based on the content throughout this specification.

[0053] Figure 1 illustrates the manufacturing process and characteristics of an electrochemical sensor for detecting perfluorooctanoic acid according to the present invention.

[0054] More specifically, FIG. 1 (A) is a schematic diagram of the synthesis of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, FIG. 1 (B) is the X-ray diffraction (XRD) pattern of tin dioxide-tungsten trioxide nanocomposites (SnW NCs) and tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, FIG. 1 (C) is the X-ray photoelectron spectroscopy (XPS) survey spectrum of tin dioxide-tungsten trioxide nanocomposites (SnW NCs) and tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, and FIG. 1 (D) and (G) are, respectively W 4f XPS spectra of tin dioxide-tungsten trioxide nanocomposites and tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, (E) and (H) of FIG. 1 are Sn 3d XPS spectra of tin dioxide-tungsten trioxide nanocomposites and tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, respectively, and O 1s XPS spectra of tin dioxide-tungsten trioxide nanocomposites and tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, respectively. Figure 1 (J) shows the C 1s XPS spectrum of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0055] Figure 1 (A) illustrates the synthesis process of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0056] Referring to (A) of FIG. 1, a homogeneous aqueous solution is prepared by sequentially adding sodium tungsten dihydrate (Na2WO4·2H2O, 1 mmol), tin chloride (IV) pentahydrate (SnCl4·5H2O, 1 mmol), and glucose (1 g) to 100 mL of deionized water. This aqueous solution is hydrothermally reacted in a stainless steel high-pressure reactor with a Teflon inner wall at 180°C for 48 hours.

[0057] The reactants, naturally cooled to room temperature, are centrifuged, washed with deionized water and ethanol, and dried at 60°C. The dried product is heat-treated in air at 400°C for 6 hours to prepare a tin dioxide-tungsten trioxide (SnW) nanocomposite.

[0058] The interaction between tin dioxide and tungsten trioxide is primarily controlled by the formation of a heterojunction due to their different work functions and electron affinities. Since the conduction band edge of tin dioxide is higher than that of tungsten trioxide, electron transfer occurs from tin dioxide to tungsten trioxide, resulting in charge redistribution and the formation of an internal electric field.

[0059] This enhances electron mobility while reducing charge recombination. Additionally, oxygen vacancies present in both tin dioxide and tungsten trioxide provide active sites for electronic interactions and defect-mediated charge transfer, further stabilizing the hybrid structure.

[0060] Next, carbon nanotubes (2 mg / mL) and the SnW nanocomposite prepared above (0.5 g) are dispersed in 100 mL of deionized water and sonicated for 1 hour under magnetic stirring. During this process, the carbon nanotubes introduce strong π-π interactions and electrostatic forces with the metal oxide, thereby promoting efficient charge transfer and improving the electronic properties of the composite.

[0061] Oxygen-containing functional groups such as -OH, -COOH, and C=O on carbon nanotubes enable hydrogen bonding and electrostatic attachment with tin dioxide and tungsten trioxide, thereby enhancing the dispersibility and integration of metal oxides within the carbon nanotube network.

[0062] This dispersion is again hydrothermally reacted in a high-pressure reactor with a Teflon inner wall at 180°C for 48 hours. After natural cooling to room temperature, it is centrifuged, washed three times with ethanol and deionized water, and dried at 60°C to finally obtain tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0064] Figure 1 (B) shows the X-ray diffraction (XRD) patterns of tin dioxide-tungsten trioxide nanocomposites (SnW NCs) and tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0065] Referring to (B) of Fig. 1, all diffraction peaks of monoclinic tungsten trioxide (WO3) and tetragonal tin dioxide (SnO2) were observed in the XRD pattern of the tin dioxide-tungsten trioxide nanocomposite, which correspond well with JCPDS card numbers 01-083-0950 and 01-072-1147, respectively.

[0066] As shown in Fig. 1 (B), in the XRD pattern of the tin dioxide-tungsten trioxide nanocomposite, diffraction peaks corresponding to the (002), (020), (200), (120), (211), (202), (222), (004), (114), (303), and (-402) planes of monoclinic tungsten trioxide were observed at 2θ = 23.23°, 23.56°, 24.19°, 26.83°, 29.49°, 34.23°, 41.78°, 47.37°, 50.69°, 52.24°, and 55.17° were observed. In particular, the strong diffraction peak of the (002) plane observed at 23.23° indicates that the tungsten trioxide crystals grew preferentially in the (002) direction.

[0067] In addition, as shown in (B) of Fig. 1, diffraction peaks corresponding to the (110), (101), (111), (211), (221), (301) and (321) planes of tetragonal tin dioxide were observed at 26.6°, 33.92°, 38.07°, 52.22°, 62.28°, 66.17° and 79.16°. This shows a tetragonal structure with lattice constants a = b = 4.7370 Å and c = 3.1850 Å. This is in exact agreement with the data of JCPDS card number 01-072-1147.

[0068] In addition, as shown in (B) of Fig. 1, strong diffraction peaks at 26.6°, 33.92°, and 52.22° indicate characteristic peaks of tin dioxide. The separation of several peaks observed in the XRD pattern of the tin dioxide-tungsten trioxide nanocomposite indicates that tin dioxide has been successfully incorporated into the tungsten trioxide matrix.

[0069] Meanwhile, XRD results of tin dioxide-tungsten trioxide nanocomposites immobilized on carbon nanotubes (SnW-CNT NCs) show that the presence of carbon nanotubes did not alter the crystal structure of the tin dioxide-tungsten trioxide nanocomposites.

[0070] However, compared to the tin dioxide-tungsten trioxide nanocomposite sample, it was observed that the peak intensity weakened, shifted slightly to a lower angle, and the diffraction peak broadened; this indicates the presence of carbon nanotubes in the tin dioxide-tungsten trioxide nanocomposite and a reduction in particle size. The reduction in particle size exposes more edges and active sites, which may be advantageous for electrochemical sensing applications.

[0072] Figure 1 (C) shows the X-ray photoelectron spectroscopy (XPS) survey spectrum of tin dioxide-tungsten trioxide nanocomposites (SnW NCs) and tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0073] Referring to (C) of Fig. 1, the XPS survey spectrum of the tin dioxide-tungsten trioxide nanocomposite detected tungsten (W), tin (Sn), and oxygen (O) elements, and also detected a small amount of carbon (C) due to contamination of the sample.

[0074] In contrast, the XPS survey spectrum of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes confirmed the presence of all constituent elements, and a high-intensity carbon peak was observed due to the introduction of carbon nanotubes.

[0075] As shown in (C) of Fig. 1, the results of the atomic percentage analysis showed that the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) sample immobilized on carbon nanotubes exhibited a high carbon (C1s) content of 42.3% due to the introduction of carbon nanotubes, which reduced the relative atomic percentages of tin (Sn), tungsten (W), and oxygen (O).

[0076] However, the ratio of tin to tungsten in the two samples remained constant, which suggests that the elemental distribution is maintained despite the presence of carbon nanotubes.

[0078] Figure 1 (D) shows the W 4f XPS spectrum of the tin dioxide-tungsten trioxide nanocomposite. Referring to Figure 1 (D), W 4f at binding energies of 35.83 eV and 37.97 eV, respectively 7 / 2 W 4f 5 / 2 A spin-orbit doublet corresponding to was observed. The spin-orbit separation energy of 2.14 eV is W of WO3 6+ Indicates the oxidation state.

[0080] In addition, (E) of Fig. 1 shows the Sn 3d XPS spectrum of the tin dioxide-tungsten trioxide nanocomposite, with Sn 3d at 486.94 eV and 495.38 eV, respectively. 5 / 2 and Sn 3d 3 / 2 A doublet peak corresponding to was observed. A binding energy difference of 8.44 eV indicates the +4 valence state of tin ions in the sample.

[0082] Figure 1 (F) shows the O 1s XPS spectrum of the tin dioxide-tungsten trioxide nanocomposite, where three distinct bands were observed at 530.69 eV, 530.93 eV, and 532.07 eV. The strong peak at 530.69 eV is associated with lattice oxygen in WO3 and SnO2, while the peak at 530.93 eV is associated with oxygen vacancies and O2- ions in oxygen defect regions. The peak at 532.07 eV is associated with physically adsorbed and chemisorbed water on or near the surface.

[0084] In addition, Fig. 1 (G) shows the W 4f XPS spectrum of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes. Referring to Fig. 1 (G), the W 4f peak is at 35.93 eV (W 4f 7 / 2 ) and 38.09 eV(W 4f 5 / 2 It was observed that it had shifted slightly to ), which is attributed to the insertion of carbon nanotubes.

[0086] In addition, Figure 1 (H) shows the Sn 3d XPS spectrum of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes. Referring to Figure 1 (H), the peak intensity continuously decreased compared to the tin dioxide-tungsten trioxide nanocomposites, and Sn 3d 5 / 2 and Sn 3d 3 / 2The peaks shifted to higher binding energies at 487.21 eV and 495.65 eV, respectively. This suggests an interaction between tin dioxide-tungsten trioxide and carbon nanotubes.

[0087] In addition, Figure 1 (I) shows the O 1s high-resolution spectrum of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes. Referring to Figure 1 (I), a shift in binding energy along with a change in peak intensity was observed due to the introduction of carbon nanotubes, which indicates that the chemical environment of oxygen within the composite has changed.

[0089] Figure 1 (J) illustrates the C 1s region of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes. Referring to Figure 1 (J), the strong and high-intensity peaks at 284.52 eV and 284.97 eV are attributed to sp2 hybrid graphite carbon (CC / C=C), while the peaks at 286.61 eV and 288.92 eV correspond to CO and C=O bonds, respectively. In the context of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, these peaks appear to represent carbon atoms interacting with tin / tungsten atoms.

[0091] Figure 2 illustrates the morphological characteristics and elemental distribution of an electrochemical sensor for detecting perfluorooctanoic acid according to an embodiment of the present invention.

[0092] Figure 2 (A) shows a scanning electron microscope (SEM) image of tin dioxide-tungsten trioxide nanocomposites (SnW NCs) at a magnification of 5 μm.

[0093] Referring to Figure 2 (A), the tin dioxide-tungsten trioxide nanocomposite exhibits microstructural features of an irregular mixture, specifically, it can be seen that small, non-uniform aggregated particles are deposited on a lamellar structure similar to coral plates or irregularly shaped stones.

[0094] The heterogeneity shown in (A) of Fig. 2 highlights the inherent complexity of the tin dioxide-tungsten trioxide nanocomposite and suggests the presence of a high surface area and various active sites that play an important role in the electrochemical sensing process.

[0095] In addition, the morphology illustrated in (A) of Fig. 2 can provide structural features that can significantly improve the electronic properties and reactivity of the nanocomposite, and consequently contribute to the improvement of performance as an electrochemical sensor.

[0097] Figures 2 (B) and (C) show scanning electron microscope (SEM) images of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes at magnifications of 2 μm and 1 μm, respectively.

[0098] Referring to Figures 2 (B) and (C), a tin dioxide-tungsten trioxide nanocomposite is grown on a carbon nanotube in the form of a thread or tube, showing the complex interaction between the carbon nanotube and the tin dioxide-tungsten trioxide structure.

[0099] Specifically, it shows a structure in which carbon nanotubes penetrate and intertwine with a tin dioxide-tungsten trioxide nanocomposite.

[0100] The structural integration illustrated in (B) and (C) of Fig. 2 exhibits a form similar to the natural conductive pathways of plant tissues, which is optimized for efficient electron and ion transport. The close coupling between tin dioxide-tungsten trioxide and carbon nanotubes enhances structural stability and promotes improved electron transport, which can significantly improve the electrical conductivity of the composite and its sensitivity in electrochemical applications.

[0101] According to an embodiment of the present invention, it can be confirmed that carbon nanotubes not only serve as a support for the tin dioxide-tungsten trioxide nanocomposite but also act as an active component that improves electrochemical performance.

[0103] Figures 2 (D) and (E) show high-resolution transmission electron microscope (HRTEM) images of tin dioxide-tungsten trioxide nanocomposites.

[0104] Referring to FIG. 2, (D) and (E) of FIG. 2 are high-resolution transmission electron microscope (HRTEM) images of tin dioxide-tungsten trioxide nanocomposites (SnW NCs) at magnifications of 10 nm and 2 nm, respectively.

[0105] In Figures 2 (D) and (E), HRTEM images show a morphology with diffused bright and dark contrasts, representing moderately dispersed nanoscale spherical or sheet-shaped irregular aggregates. These morphological features highlight the complex microstructure of the tin dioxide-tungsten trioxide nanocomposite.

[0106] In particular, the interplanar distance was measured using the Fast Fourier Transform (FFT) and the corresponding line histogram obtained from the HRTEM image of the selected area in image (E) of Fig. 2, and the lattice plane spacing was observed to be approximately 0.315 nm and 0.357 nm. These were confirmed to be the lattice spacings corresponding to tin dioxide and tungsten trioxide, respectively.

[0107] In addition, the parts labeled i and ii in (E) of Fig. 2 represent the inverse FFT images of the selected regions, and the lattice spacing measured in each region clearly shows the crystal structures of tin dioxide and tungsten trioxide. This confirms that the tin dioxide-tungsten trioxide nanocomposite was successfully synthesized.

[0109] Figures 2 (F) to (H) show HRTEM images of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0110] More specifically, (F) to (H) of FIG. 2 show HRTEM images of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes at magnifications of 20 nm, 10 nm, and 2 nm, respectively.

[0111] The images shown in (F) through (H) of FIG. 2 show different phases within the nanocomposite and exhibit morphological features such as nanosheets or irregularly shaped nanoparticles. Specifically, it can be seen that tin dioxide-tungsten trioxide nanocomposites with diffused bright and dark contrasts are immobilized and dispersed on the tubular structures of carbon nanotubes.

[0112] Images shown in (F) through (H) of Fig. 2 clearly show that tin dioxide-tungsten trioxide nanocrystals were synthesized on the surface of carbon nanotubes and exhibited strong bonding at the interface.

[0113] In particular, (H) of Fig. 2 is an HRTEM image at 2 nm magnification, showing the results of measuring the lattice spacing through the inverse FFT image obtained from selected regions labeled i, ii, and iii and the corresponding line histogram, and the measured lattice spacings were found to be 0.313 nm, 0.352 nm, and 0.329 nm for tin dioxide, tungsten trioxide, and carbon nanotubes, respectively.

[0114] The decrease in lattice distance in tin dioxide-tungsten trioxide nanocomposites immobilized on carbon nanotubes (SnW-CNT NCs) compared to the tin dioxide-tungsten trioxide nanocomposites is attributed to the introduction of carbon nanotubes, suggesting that good contact was formed between the carbon nanotubes and the tin dioxide-tungsten trioxide nanocomposites.

[0115] Furthermore, according to embodiments of the present invention, strong interfacial interactions are important for promoting efficient charge transfer, which is a key requirement for enhanced electrochemical sensing performance. The observed interconnected assemblies and rough surface textures indicate a high degree of structural integration among components within tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, which generates abundant active sites and pathways for electron transport, essential for effective electrochemical sensing.

[0117] Figure 2 (I) shows the energy dispersive X-ray spectroscopy (EDS) spectrum and selected region electron diffraction (SAED) pattern of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0118] Referring to (I) of Figure 2, the energy dispersive X-ray spectroscopy (EDS) spectrum of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes is shown, and the inset image shows the selected region electron diffraction (SAED) pattern.

[0119] The EDS spectrum analysis results shown in (I) of Fig. 2 confirm the presence of tin (Sn), tungsten (W), oxygen (O), and carbon (C), which are the major elements constituting the nanocomposite. This supports the successful synthesis of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0120] In addition, according to an embodiment of the present invention, the SAED pattern shown in (I) of FIG. 2 demonstrates the crystallinity of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, and the concentric diffraction pattern indicates the polycrystalline characteristics of the sample. This is consistent with the lattice spacing measurement results from the HRTEM images observed earlier, and the crystal structure of the nanocomposite can be further confirmed.

[0121] These analysis results demonstrate the successful composite formation of tin dioxide-tungsten trioxide nanocomposites with carbon nanotubes, providing important structural features that support their potential for application as electrochemical sensors.

[0123] Figure 2 (J) shows an elemental mapping image of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0124] Referring to (J) in Fig. 2, in the results of the High-angle annular dark-field (HAADF) color mapping analysis to confirm the elemental distribution of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes, the color mapping for the selected area shows the distribution of tin (Sn, red), tungsten (W, green), oxygen (O, blue), and carbon (C, cyan), which is consistent with the results of the EDS spectrum described earlier.

[0125] In addition, as shown in (J) of Fig. 2, a detailed examination of the color mapping confirms that all elements are uniformly distributed throughout the nanocomposite. The mapping images for each element sequentially show the individual distributions of tin, tungsten, oxygen, and carbon, starting with an integrated mapping that includes all elements.

[0126] The uniform elemental distribution shown in (J) of Fig. 2 demonstrates the effective combination of tin dioxide-tungsten trioxide nanocomposites and carbon nanotubes, which provides structural features supporting excellent performance as an electrochemical sensor.

[0128] Figure 3 illustrates the electrochemical detection characteristics of an electrochemical sensor for detecting perfluorooctanoic acid using a tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes according to the present invention.

[0129] More specifically, FIG. 3 illustrates the electrochemical detection characteristics of an electrochemical sensor comprising a modified electrode based on a tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on a carbon nanotube according to an embodiment of the present invention.

[0130] According to the example, tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes can be applied to a glass carbon electrode (GCE).

[0131] That is, the electrochemical detection characteristics shown in Fig. 3 are data for an electrochemical sensor on an electrode (glass carbon electrode, GCE) modified from SnW-CNT NCs, not the SnW-CNT NCs themselves, and the PFOS / PFOA detection performance of SnW-CNT NCs was evaluated through electrochemical measurements after electrode modification.

[0132] Accordingly, instead of referring to it as an electrochemical sensor based on a modified electrode based on tin dioxide-tungsten trioxide nanocomposites immobilized on carbon nanotubes (SnW-CNT NCs), it will be named as tin dioxide-tungsten trioxide nanocomposites immobilized on carbon nanotubes (SnW-CNT NCs).

[0133] Figure 3 (A) shows the cyclic voltammetry (CV) response of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes in the presence or absence of perfluorooctanoic acid (PFOA).

[0134] Referring to Fig. 3 (A), for the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention, the CV profile was measured in a PBS solution at a scan rate of 50 mV / s and in a potential range of 1 V to -0.5 V.

[0135] As shown in Fig. 3 (A), the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention exhibits notable oxidation and reduction peaks at 0.17 V and 0.0012 V, respectively, which is attributed to the synergistic effect of the composite components and the unique structural characteristics of the nanocomposite.

[0136] In addition, the introduction of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention significantly enhances electrical conductivity, thereby providing an efficient electron transport pathway, and the tin dioxide and tungsten trioxide components provide multiple active sites with catalytic properties essential for oxidation-reduction reactions.

[0137] In addition, the high surface area and porous structure of the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention can further enhance electrochemical activity by increasing interaction with the analyte and promoting efficient diffusion.

[0138] In addition, according to the example, when 10 nM of PFOA was added to the PBS solution, it was observed that these oxidation and reduction peaks became more distinct and shifted to potential values ​​of 0.1905 V and -0.061 V, respectively. This increased current response to PFOA can be attributed to electrocatalytic properties and enhanced electronic conductivity resulting from deformation of the electrode surface.

[0139] Figure 3 (B) shows the cyclic voltammetry (CV) voltammetry of perfluorooctanoic acid at different concentrations using tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0140] Referring to Figure 3 (B), experiments were conducted in a perfluorooctanoic acid concentration range from 10 nM to 120 nM to evaluate the performance of the electrode, and the presence of perfluorooctanoic acid was detected through changes in current intensity, and it was confirmed that the peak current consistently increased as the concentration of perfluorooctanoic acid increased.

[0142] Figure 3 (C) shows a calibration curve of peak current according to the concentration of perfluorooctanoic acid using tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0143] Referring to Fig. 3 (C), the linear regression equation is Ip = 3.48 x 10 -3 PFOA + 0.614, and R 2 = 0.9908 correlation coefficient was shown.

[0144] Based on the results shown in Figure 3 (C), the detection limit (DL) and quantification limit (QL) of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes were calculated. The detection limit is D L = 3σ b / m (where σ b The result calculated using the formula (where is the standard deviation of the blank sample measured three times individually and m is the slope of the calibration curve) is 2.434 nM (1.0079 ppb), and the limit of quantification is Q L The result calculated using the formula = 10σ / m is 8.114 nM (3.36 ppb). In addition, the sensitivity to perfluorooctanoic acid is 1.78 x 10⁻⁶ -4 mA / nM mm 2 It was decided as.

[0145] Figure 3 (C) shows that tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes have excellent linearity suitable for the quantitative detection of perfluorooctanoic acid. Through this calibration curve, the concentration of perfluorooctanoic acid in actual samples can be accurately determined.

[0146] Tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention demonstrate that they can be utilized as effective electrochemical sensor materials for the quantitative detection of perfluorooctanoic acid.

[0148] Figures 3 (D) to (F) illustrate voltage-current showing the effect of pH in the detection of perfluorooctanoic acid using tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0149] Figure 3 (D) shows the cyclic voltammetry response over a wide pH range from pH 2 to pH 12. Referring to Figure 3 (D), a significant change in the CV shape was observed under strong basic conditions (pH 10-11), which is attributed to the high concentration of hydroxide ions (OH-).

[0150] Such high OH- ion concentrations cause competitive side reactions that hinder the electrochemical reduction of perfluorooctanoic acid, thereby reducing the reduction efficiency of perfluorooctanoic acid and increasing decarboxylation activity.

[0152] Figure 3 (E) shows the voltammetry behavior of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention under acidic pH conditions, and the inset graph is an enlarged view thereof. Referring to Figure 3 (E), the reduction rate of perfluorooctanoic acid was significantly reduced under strong acidic conditions.

[0153] This is attributed to insufficient electrophoretic mass transfer caused by the presence of undissociated perfluorooctanoic acid molecules at low pH. According to the examples, at low pH, most perfluorooctanoic acid exists in an undissociated form, which restricts its movement to the electrode surface and may result in a decrease in the electrochemical reduction rate.

[0155] Figure 3 (F) shows the voltammetry behavior of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention under basic pH conditions, and the inset graph is an enlarged view thereof. Referring to Figure 3 (F), the reduction response of perfluorooctanoic acid was stable in the pH range between 4 and 9, and no significant change was observed in the shape of the CV peak.

[0156] This suggests that the electrochemical environment within this pH range is optimized for the consistent redox activity of perfluorooctanoic acid. The absence of significant changes in peak shape within this range implies that the electron transfer process is not significantly affected by pH changes.

[0158] Figure 3 (G) illustrates the change in peak current (Ip) according to various pH values ​​in the detection of perfluorooctanoic acid using tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0159] Referring to Figure 3 (G), the maximum peak current was recorded at pH 7, and the oxidation peak current (Ipa) showed a positive value and maintained a relatively stable value between pH 4 and 8, then showed a tendency to decrease sharply above pH 9. On the other hand, the reduction peak current (Ipc) showed a negative value and maintained a constant value between pH 4 and 8, then showed a tendency to gradually increase above pH 9.

[0160] As shown in Fig. 3 (G), it was confirmed that pH 7 is the condition for obtaining the highest electrochemical response. Furthermore, as shown in Fig. 3 (G), the peak potential of perfluorooctanoic acid showed only minimal change depending on the pH level of the electrolyte, demonstrating stable pH-independent electrochemical behavior in which the oxidation-reduction process of perfluorooctanoic acid is not significantly affected by the pH of the supporting electrolyte.

[0162] Figure 3 (H) shows the voltage-current diagram according to various scan rates from 10 mV / s to 100 mV / s in cyclic voltammetry of perfluorooctanoic acid using tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0163] Referring to (H) in Fig. 3, a linear relationship is shown in which the peak current increases as the scanning rate increases, suggesting that the electrode response is controlled by a surface-mediated mechanism.

[0164] However, as shown in (H) of Figure 3, a slight shift in peak potential and a change in the separation between peaks were observed with increasing scanning speed, which indicates a quasi-reversible electrochemical response of perfluorooctanoic acid in a modified electrode based on a tin dioxide-tungsten trioxide nanocomposite immobilized on carbon nanotubes.

[0165] Figure 3 (I) illustrates the change in peak current according to the scanning rate for tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0166] Referring to (I) of Figure 3, the oxidation and reduction peak currents show a linear relationship with the scan rate, which suggests that the reaction at the electrode surface is a surface control process.

[0167] Figure 3 (J) illustrates the relationship between the square root of the oxidation and reduction currents and the scan rate for tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0168] Referring to (J) in Fig. 3, both the oxidation and reduction peak currents are the square root of the scan rate (ν). 1 / 2 It exhibited excellent linearity with correlation coefficients of 0.9995 and 0.9989 for ). These results indicate that mass transfer on the electrode surface based on tin dioxide-tungsten trioxide nanocomposites immobilized on carbon nanotubes is a diffusion-controlled process.

[0169] (K) of FIG. 3 shows the relationship between log(Ip) and log(ν) for tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0170] Referring to (K) in Fig. 3, the regression equations are expressed as log(Ipa) = 0.58347 log(ν) + 2.488 (R² = 0.9998) and log(Ipc) = 0.6234 log(ν) + 2.887 (R² = 0.9999), and the slope value being close to 0.5 shows that this process is controlled by diffusion.

[0172] Figure 3 (L) illustrates the effect of various interfering ions on the detection of perfluorooctanoic acid by tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) electrodes immobilized on carbon nanotubes.

[0173] Referring to Figure 3 (L), the detection performance of perfluorooctanoic acid was evaluated in the presence of surfactants and various metal salts. Even when the concentration of interfering ions increased up to four times, the electrochemical characteristics of perfluorooctanoic acid remained stable and did not have a significant effect on the voltage-current response. The peak potential or signal change was minimal, and it was confirmed that in all cases, it was within the acceptable error range (≤5%).

[0174] An electrochemical sensor comprising an electrode based on a tin dioxide-tungsten trioxide nanocomposite immobilized on carbon nanotubes according to an embodiment of the present invention demonstrates that it maintains selectivity and accuracy for perfluorooctanoic acid even under conditions where high concentrations of interfering substances are present. This demonstrates the specificity and robustness of the electrode material, which enables the selective detection of perfluorooctanoic acid even in complex sample matrices.

[0176] [Table 1] shows perfluorooctanoic acid (PFOA) spiked sample experiments on various actual samples to evaluate the practical applicability of tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0177] Referring to Table 1, recovery rates were measured by adding 15 μM, 25 μM, and 35 μM of perfluorooctanoic acid to ground water, tap water, tomato, potato, apple, kiwi, and banana samples, respectively.

[0178] As a result of the experiment, groundwater samples showed a recovery rate of 95.15% to 98.80% and a relative standard deviation (RSD) of 3.37% to 5.43%, with an average RSD of 4.19%. Tap water samples showed a recovery rate of 94.51% to 97.91% and a relative standard deviation of 3.18% to 5.18%, with an average RSD of 3.90%.

[0179] Tomato and potato samples, which are vegetables, showed recovery rates of 90.73% to 95.40% (average relative standard deviation 5.64%) and 95.07% to 97.69% (average relative standard deviation 5.01%), respectively. Apple, kiwi, and banana samples, which are fruits, showed recovery rates of 94.82% to 96.31% (average relative standard deviation 4.75%), 95.13% to 96.59% (average relative standard deviation 3.98%), and 95.67% to 96.69% (average relative standard deviation 4.48%), respectively.

[0180] These results demonstrate that tin dioxide-tungsten trioxide nanocomposite electrodes immobilized on carbon nanotubes exhibit excellent recovery rates and reproducibility in actual samples, proving that they can be effectively utilized for the actual detection of perfluorooctanoic acid.

[0181] [Table 1]

[0182]

[0184] A modified electrode based on a tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention was stored in a dry, airtight container for 6 to 10 days and then used for perfluorooctanoic acid analysis. This pre-storage treatment was performed to ensure the repeatability and reliability of the analysis data.

[0185] As a result of the test, the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs)-based modified electrode according to an embodiment of the present invention showed excellent stability, maintaining 93.83% to 97.37% of the initial electrochemical response when exposed to a 10 nM perfluorooctanoic acid solution.

[0186] This consistent response demonstrates the robustness and durability of the matrix modified with tin dioxide-tungsten trioxide nanocomposites immobilized on carbon nanotubes, indicating that the material's performance does not significantly degrade during storage and functionality is effectively maintained.

[0187] In addition, to evaluate the reproducibility in electrochemical detection, the response to a 10 nM perfluorooctanoic acid solution was measured within 24 hours, and in three repeated measurements, the peak current showed a relative standard deviation (RSD) of 1.27%, indicating high reproducibility.

[0188] These low relative standard deviation values ​​demonstrate that tin dioxide-tungsten trioxide nanocomposites immobilized on carbon nanotubes provide a reliable and consistent electrochemical response, proving their suitability for the accurate measurement of perfluorooctanoic acid.

[0189] Consequently, the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs)-based modified electrode according to an embodiment of the present invention exhibits both excellent long-term stability and high reproducibility in electrochemical measurements, proving to be a reliable and effective system for perfluorooctanoic acid detection in various applications.

[0191] Figure 4 is a schematic diagram showing the detection mechanism of a chemical sensor for detecting perfluorooctanoic acid using tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes.

[0192] Referring to Fig. 4, the detection mechanism of perfluorooctanoic acid includes the following steps.

[0193] Carboxylate ions ((b) carboxylate ions) are formed through the deprotonation of the carboxyl group (-COOH) of perfluorooctanoic acid (PFOA, (a) PFOA). At this time, reversible addition and removal of hydrogen ions (H+) occur.

[0194] Electrons are removed from the formed carboxylate ions to generate a free radical intermediate in the oxidized form ((c) Oxidized form).

[0195] This oxidized form forms a secondary free radical in the radical form ((d) Radical form) as carbon dioxide (CO2) is removed through the Kolbe electrolytic decarboxylation reaction.

[0196] In addition, the perfluorooctanoic acid molecule can be converted into a reduced form ((e) Reduced form) through the introduction of electrons and hydrogen ions (H+).

[0197] Intermediates such as anionic species, free radicals, and carboxylate ions generated in this series of electrochemical processes can be interconverted, and perfluorooctanoic acid can be detected through these electrochemical oxidation-reduction reactions.

[0198] The electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention exhibited a limit of detection (LOD) of 1.0079 ppb, showing a significantly lower value than many previously reported electrochemical sensors. In addition, 1.78 × 10 -4 mA / nM mm 2 Its high sensitivity proves that it is highly competitive in ultra-high sensitivity detection.

[0199] Although conventional Cu2O@C@NiCo2O4-based sensors have reported a lower detection limit of 0.016 ppb, the dynamic range of 0.207 - 4.14 nM (207 - 4140 ng / L) of conventional sensors is narrower than the detection range of 10-120 nM of the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs)-based electrochemical sensor according to an embodiment of the present invention.

[0200] In addition, the wider detection range of the electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to the embodiment of the present invention is advantageous for monitoring perfluorooctanoic acid at various concentrations in real-world environmental samples, thereby ensuring greater applicability.

[0201] Furthermore, while conventional Cu2O@C@NiCo2O4 sensors are not suitable for large-scale implementation due to the high cost and the need for a complex multi-step synthesis process, the electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention provides a simple and efficient detection method with a wider and more practical detection range.

[0202] Stability is another important factor in sensor performance, especially in real-time applications. The electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention demonstrated superior performance compared to several reported sensors by maintaining 93.83% to 97.37% of the initial response for 10 days.

[0203] Conventional graphene-based sensors showed a retention rate of 89.9–94.3% for 30 days, and Hf-WO₃ / carbon matrix sensors showed a retention rate of 86.9–94.6% for 10–15 days. In contrast, conventional Cu2O@C@NiCo2O4 sensors showed stability for only 8 days and exhibited a significantly low signal retention rate of 76%, showing rapid signal degradation.

[0204] In addition, the electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention exhibits minimal signal change (≤5%) under conditions where interfering ions are present, thereby providing an important factor in ensuring selectivity and reliable detection in samples from complex environments.

[0205] Beyond excellent detection limits and stability, cost-effectiveness is another major advantage of the electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention.

[0206] The simple hydrophilic thermal synthesis method used in fabrication is economical and scalable, unlike other sensors that require complex and costly processes.

[0207] For example, conventional graphene-based sensors require multi-step synthesis and moderate material costs, while Hf-WO3 / carbon matrix sensors require expensive materials and complex fabrication techniques.

[0208] In contrast, the electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention is composed of tin dioxide and tungsten trioxide, which are readily available at low cost, making it a highly suitable option for large-scale environmental monitoring. On the other hand, conventional Cu2O@C@NiCo2O4 sensors are significantly expensive due to multi-step doping and modification, further limiting their feasibility for widespread use.

[0209] The electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention provides a unique combination of high sensitivity, excellent stability, and cost-effective fabrication, making it an ideal candidate for real-time in-situ perfluorooctanoic acid detection.

[0210] From low detection limits, strong selectivity, extended operational stability, and economical synthesis, the electrochemical sensor based on tin dioxide-tungsten trioxide nanocomposites (SnW-CNT NCs) immobilized on carbon nanotubes according to an embodiment of the present invention outperforms many existing electrochemical sensors in key performance indicators. The aforementioned results strongly demonstrate the importance of the approach of the present invention and enhance the practical advantages of the proposed sensor for environmental applications.

[0212] As described above, although the present invention has been explained by limited embodiments and drawings, the present invention is not limited to the above embodiments, and various modifications and variations are possible from this description by those skilled in the art to which the present invention belongs. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims set forth below as well as equivalents thereof.

Claims

Claim 1 The electrode comprises a modified tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes, wherein the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes comprises single-crystal tin dioxide-tungsten trioxide nanoparticles dispersed and immobilized on the surface of the carbon nanotubes, wherein the tin dioxide-tungsten trioxide nanocomposite immobilized on carbon nanotubes forms an anion through the deprotonation of the carboxyl group (-COOH) of a perfluorooctanoic acid (PFOA) molecule, forms a free radical intermediate by the detachment of electrons from the formed anion, forms a secondary free radical through the Kolbe electrolytic decarboxylation reaction of the free radical intermediate, and reduces the carbonyl group (-C=O) of the perfluorooctanoic acid molecule An electrochemical sensor for detecting perfluorooctanoic acid characterized by performing an electrochemical oxidation-reduction reaction that generates reduced perfluorooctanoic acid through the reaction. Claim 2 In claim 1, the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotube is 1.78 x 10 -4 mA / nM mm 2 Electrochemical sensor for detecting perfluorooctanoic acid, characterized by having sensitivity. Claim 3 The electrochemical sensor for detecting perfluorooctanoic acid according to claim 1, characterized in that the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotube has a detection limit of 2.434 nM (1.0079 ppb). Claim 4 The electrochemical sensor for detecting perfluorooctanoic acid according to claim 1, wherein the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotube has a linear detection range of 10 nM to 120 nM. Claim 5 An electrochemical sensor for detecting perfluorooctanoic acid according to claim 1, wherein the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotube exhibits a stable electrochemical response in the pH range of 4 to 9. Claim 6 An electrochemical sensor for detecting perfluorooctanoic acid according to claim 1, wherein the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotube exhibits a recovery rate of 93.83% to 97.37% in tap water, vegetable and fruit samples. Claim 7 The electrochemical sensor for detecting perfluorooctanoic acid according to claim 1, wherein the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on the carbon nanotube exhibits a signal change of 5% or less under conditions in which a metal ion interfering substance is present. Claim 8 A method for manufacturing an electrochemical sensor for detecting perfluorooctanoic acid comprises: a step of preparing a homogeneous aqueous solution by sequentially adding sodium tungsten dihydrate (Na2WO4·2H2O), tin(IV) chloride pentahydrate (SnCl4·5H2O), and glucose to deionized water; a first hydrothermal reaction step of placing the homogeneous aqueous solution into a stainless steel high-pressure reactor with a Teflon inner wall and performing a hydrothermal reaction at 180°C for 48 hours; a step of preparing a tin dioxide-tungsten trioxide (SnO2-WO3) nanocomposite by centrifuging, washing, and drying the solid product generated from the first hydrothermal reaction, and then heat-treating it at 400°C for 6 hours; a step of dispersing carbon nanotubes and the tin dioxide-tungsten trioxide (SnO2-WO3) nanocomposite in deionized water and ultrasonically treating the dispersion; and a second hydrothermal reaction step of the dispersion at 180°C for 48 hours. A method for manufacturing an electrochemical sensor for detecting perfluorooctanoic acid, comprising the steps of: manufacturing a tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes; and applying the tin dioxide-tungsten trioxide nanocomposite (SnW-CNT NCs) immobilized on carbon nanotubes onto an electrode. Claim 9 A method for manufacturing an electrochemical sensor for detecting perfluorooctanoic acid according to claim 8, characterized in that the sodium tungsten dihydrate (Na2WO4·2H2O) and tin chloride (IV) pentahydrate (SnCl4·5H2O) are each 1 mmol, and the glucose is 1 g. Claim 10 A method for manufacturing an electrochemical sensor for detecting perfluorooctanoic acid according to claim 8, characterized in that the carbon nanotubes are dispersed in deionized water at a concentration of 2 mg / mL, and 0.5 g of the tin dioxide-tungsten trioxide (SnO2-WO3) nanocomposite is added. Claim 11 A method for manufacturing an electrochemical sensor for detecting perfluorooctanoic acid according to claim 8, characterized in that the ultrasonic treatment is performed for 1 hour. Claim 12 A method for manufacturing an electrochemical sensor for detecting perfluorooctanoic acid according to claim 8, characterized in that the dispersion is washed three times with ethanol and deionized water after a second hydrothermal reaction and dried at 60°C.

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