A self-supporting nickel-iron tungstate electrode, its preparation method, and its application in the oxidation reaction of luteolin.

Abstract

This invention relates to a method for preparing nickel iron tungstate and its application in the electrochemical detection of luteolin, belonging to the field of electrolytic catalytic materials technology. This invention prepares a FeNiWO4 / SS self-supporting electrode on a stainless steel wire mesh (SS) using a continuous ion-layer adsorption reaction method, simplifying the traditional continuous ion-layer adsorption reaction method. This not only reduces the operational difficulty of preparing the FeNiWO4 / SS self-supporting electrode but also ensures its catalytic performance.

Description

Technical Field

[0001] This invention relates to a self-supporting nickel-iron-tungstate electrode, its preparation method, and its application in the oxidation reaction of luteolin, belonging to the field of electrolytic catalytic materials technology. Background Technology

[0002] In modern food industry and medicine, the demand for the detection and analysis of natural compounds is increasing. Luteolin (3,4,5,7-tetrahydroxy-ketone) is a natural flavonoid compound widely distributed in plants and fruits such as celery, oranges, and apples. Luteolin is a natural drug with various pharmacological activities, including uric acid-lowering, antibacterial, antitumor, and anti-inflammatory effects. In the food industry, it is considered an important food additive due to its excellent antioxidant and anti-inflammatory properties, used to improve the nutritional value and extend the shelf life of food. Developing a rapid, accurate, and convenient detection method is crucial for detecting luteolin levels in food. Currently, the main methods for detecting luteolin include high-performance liquid chromatography (HPLC), ultraviolet-visible spectrophotometry (UV-Vis), and capillary electrophoresis. Although these methods have high accuracy, the high cost of equipment, complex operation, and long detection time make luteolin detection costly. In recent years, electrochemistry has come into focus due to its advantages such as simple equipment, easy operation, low cost, high reliability, and fast response speed, and is considered an ideal alternative method. High-efficiency electrocatalysts, such as precious metal electrocatalysts, are difficult to produce on a large scale due to their high cost and low reserves. Summary of the Invention

[0003] This invention relates to a method for preparing nickel iron tungstate and its application in the electrochemical detection of luteolin. A FeNiWO4 / SS self-supporting electrode was prepared on a stainless steel wire mesh (SS) using a continuous ion layer adsorption reaction method. This method simplifies the traditional continuous ion layer adsorption reaction method, which not only reduces the operational difficulty of preparing the FeNiWO4 / SS self-supporting electrode, but also ensures the catalytic performance of the FeNiWO4 / SS self-supporting electrode.

[0004] A self-supporting nickel iron tungstate electrode includes a stainless steel wire mesh carrier and a nickel iron tungstate active material loaded on the surface of the carrier. The nickel iron tungstate active material is composed of nickel, iron and tungsten elements, and the active material is directly bonded to the surface of the carrier without adhesive.

[0005] The molar ratio of nickel to iron in the nickel tungstate active material is 1:9-4:6, preferably 2:(7-9).

[0006] The stainless steel wire mesh is selected from a conductive porous metal carrier, which includes nickel mesh, titanium mesh, or nickel foam; the nickel iron tungstate active material is in nanoparticle form.

[0007] The method for preparing the self-supporting nickel-iron-tungstate electrode employs a continuous ion layer adsorption reaction method, and includes the following steps:

[0008] (1) The stainless steel wire mesh is alternately immersed in a first aqueous solution containing nickel salt and iron salt and a second aqueous solution containing tungstate in a cyclic operation, so that nickel iron tungstate is deposited on the surface of the stainless steel wire mesh.

[0009] (2) The material obtained in step (1) is dried to obtain the self-supporting nickel tungstate electrode.

[0010] The nickel salt is selected from water-soluble nickel salts, preferably nickel chloride, nickel nitrate, or nickel sulfate; the iron salt is selected from water-soluble iron salts, preferably ferric chloride, ferric nitrate, or ferric sulfate; the tungstate is selected from water-soluble tungstates, preferably sodium tungstate, potassium tungstate, or ammonium tungstate.

[0011] The concentration of nickel salt in the first aqueous solution is 0.01-0.05M, and the concentration of iron salt is 0.05-0.15M; the concentration of tungstate in the second aqueous solution is 0.05-0.2M.

[0012] The number of cycles is 10-50 times, preferably 20-40 times; the immersion time in the first or second aqueous solution is 10-60 seconds each time; the drying temperature is 30-80℃ and the time is 0.5-4 hours.

[0013] The application of the self-supporting nickel tungstate electrode in the electrochemical detection of luteolin.

[0014] The electrochemical detection employs a three-electrode system, with the self-supporting nickel-iron-tungstate electrode serving as the working electrode, and the electrolyte being a 0.1-1M NaOH solution.

[0015] The linear range of the electrochemical detection is 100-2900 μM, the detection limit is 24 μM, and the sensitivity is 10 μAmM⁻¹cm⁻²; the electrochemical detection is performed at a potential of 0.35 V vs. RHE.

[0016] The beneficial effects of this invention are as follows: Continuous Ion Adsorption Reaction (SILAR) has the advantages of simple operation and low cost. Compared with the traditional hydrothermal method, the SILAR preparation method is more suitable for large-scale mechanized preparation. Compared with other FeNiWO4 / SS electrodes with different nickel-iron ratios, FeNiWO4 / SS with a nickel-iron ratio of 2:8 is more conducive to the catalytic performance of luteolin oxidation. FeNiWO4 / SS (2:8) has an ultra-low detection limit and high detection accuracy when measuring actual luteolin-containing samples, which helps to improve selectivity in complex real-world environments. The adsorption and synthesis of FeNiWO4 on the surface of stainless steel wire mesh (SS) to form an independent electrode (FeNiWO4 / SS) is a simple, economical, and efficient method for the sensing and detection of highly non-enzymatic luteolin, meeting the needs of industrial development. Attached Figure Description

[0017] Figure 1 SEM characterization of FeNiWO4 / SS: (a) 30 cycles, nickel-iron ratio 2:8, 400 µm; (b) 30 cycles, nickel-iron ratio 5:5, 400 µm; (c) 50 cycles, nickel-iron ratio 2:8, 400 µm; (d) 30 cycles, nickel-iron ratio 2:8, 5 µm; (e) 30 cycles, nickel-iron ratio 5:5, 5 µm; (f) 50 cycles, nickel-iron ratio 2:8, 5 µm.

[0018] Figure 2 XRD characterization of FeNiWO4 / SS;

[0019] Figure 3 Comparison of cyclic voltammetry (CV) curves of electrodes in 1 M NaOH solution with and without 10 mM luteolin solution, scan rate 5 mV s⁻¹;

[0020] Figure 4 Comparison of electrode performance. (a) Comparison of cyclic voltammetry (CV) curves of electrodes prepared with different cycle numbers in 1 M NaOH + 10 mM luteolin solution. (b) Comparison of cyclic voltammetry (CV) curves of electrodes prepared with different nickel-iron ratios in 1 M NaOH + 10 mM luteolin solution;

[0021] Figure 5 Electrocatalytic performance of luteolin sensing. (a) Timing current response (It) of FeNiWO4 / SS when luteolin is continuously injected into 0.1 M NaOH solution. (b) Linear fitting results of the corresponding current concentration (Ic).

[0022] Figure 6 Performance curves of current density prediction methods. Detailed Implementation

[0023] In some specific embodiments of this patent, the following technical solutions are included:

[0024] A bimetallic oxide is used as a support for a stainless steel wire mesh (SS), on which a nickel iron tungstate catalyst is adsorbed and synthesized.

[0025] A catalyst for the oxidation reaction of luteolin includes a support and an active material on the support, wherein the active material is the aforementioned nickel iron tungstate metal oxide, and the support is a stainless steel wire mesh.

[0026] The above-mentioned catalyst preparation method includes the following steps:

[0027] Step 1: Immerse the stainless steel wire mesh in an aqueous solution containing nickel salts and iron salts for adsorption, so that the surface of the stainless steel wire mesh adsorbs nickel ions and iron ions. Then immerse it in an aqueous solution containing tungstate to react and generate nickel iron tungstate on the surface of the stainless steel wire mesh.

[0028] Step 2: Place the material obtained in Step 1 in an oven for drying to obtain the catalyst.

[0029] In step 1, the nickel salt, iron salt, and tungstate are nickel chloride, ferric chloride, and sodium tungstate, respectively; their concentrations in the aqueous solution are 0.02 M, 0.08 M, and 0.1 M, respectively.

[0030] The dimensions of the stainless steel wire mesh are: 300 mesh, 0.045 mm aperture, 0.04 mm wire diameter, and 0.15 x 2 x 5 cm. 3 Stainless steel wire mesh.

[0031] The drying conditions were 40 °C for 1 h.

[0032] The above-mentioned catalysts are used in the oxidation reaction of luteolin.

[0033] The above-mentioned catalysts are used in luteolin detection sensors.

[0034] In the aforementioned applications, the catalyst is used to improve the sensor's resistance to interference from exogenous substances, increase detection accuracy, and reduce the detection limit.

[0035] Example 1: Sample Synthesis Steps

[0036] Before synthesizing the sample, a stainless steel wire mesh was made with dimensions of 2*5*0.15 cm. 3Stainless steel wire mesh (SS) was prepared, then sanded to smooth its surface, and ultrasonically cleaned with ethanol to remove surface oxides and organic impurities. FeNiWO4 composite materials were obtained through continuous ion adsorption synthesis. SS was immersed in 100 mL of an aqueous solution containing 0.02 M NiCl2•6H2O and 0.08 M FeCl3•6H2O (solution 1) for 30 s. Then, SS was immersed in 100 mL of an aqueous solution containing 0.1 M NaWO4 (solution 2) for 30 s. SS was then immersed in solution 1 again, and this cycle was repeated 30 times. Afterward, the synthesized sample was dried in an oven to obtain the final sample (labeled FeNiWO4 / SS (2:8)). For comparison, FeNiWO4 / SS (10:0, 8:2, 5:5, 0:10) samples were synthesized using the same preparation route, with a total metal cation and tungstate ion concentration of 0.1 M. Finally, FeNiWO4 / SS (2:8) was obtained, and other electrode materials with different ratios were obtained in the same way.

[0037] The characterization results are as follows:

[0038] FeNiWO4 / SS (2:8) is prepared through a two-step process, in which Fe... 3+ Ni 2+ Adsorbed onto the surface of stainless steel wire mesh. After wetting for 30 seconds, the adsorbed stainless steel wire mesh is immersed in an aqueous solution of sodium tungstate, causing a synthesis reaction to occur on the surface of the stainless steel wire mesh to generate FeNiWO4. FeNiWO4 / SS (XRD). Figure 1 In Figures a through b, the number of cycles is 30, and the nickel-iron ratios are 2:8 and 5:5, respectively. With the increase of the ferric chloride ratio, the nickel-iron tungstate nanomaterials are more prone to aggregation. Figure 1 The c represents the number of cycles (50), and the nickel-iron ratio is 2:8. It can be seen that due to the excessive number of cycles, the nickel-iron-tungstate nanomaterials are severely stacked, and some active sites are covered. Figure 1 The SEM images in d~f range at higher magnifications further demonstrate that a 5:5 nickel-iron ratio is more prone to agglomeration than a 2:8 ratio, and that 50 cycles result in greater agglomeration and stacking than 30 cycles. Figure 2 As shown in the figure, the XRD pattern of FeNiWO4 / SS shows that FeNiWO4 was successfully prepared and successfully adsorbed onto the stainless steel wire mesh electrode.

[0039] Electrochemical testing:

[0040] Electrochemical data were obtained using a three-electrode system. FeNiWO4 / SS, a smooth carbon rod, and an Ag / AgCl electrode were used as the working electrode, counter electrode, and reference electrode, respectively. Electrochemical measurements of luteolin sensing were performed in 0.1 M NaOH. The catalytic performance of the samples was studied by cyclic voltammetry (CV), and the stability of the samples was studied by chronopotentiometrics (IT).

[0041] Using a three-electrode system, in 1 M (mol / L) solutions containing (10 mM) or without luteolin. -1 Luteolin was detected in NaOH solution. The oxidation reaction of luteolin was performed on the test electrode using cyclic voltammetry (CV). Figure 3 As shown, NiFeWO 4 / SS exhibits 0.5 mA cm⁻¹ at a potential of 0.35 V (vs. RHE). -2 The highest oxidation peak current (Iox) was significantly higher than that of the solution without luteolin. This verifies that NiFeWO4 / SS (nickel-iron ratio 2:8) has a highly sensitive response to luteolin.

[0042] The number of cycles in SILAR was explored, such as Figure 4 As shown in Figure a, in the comparative experiments of 10, 30, 50, and 100 cycles (nickel-iron ratio 5:5), it is evident that the nickel-iron-tungstate nanomaterial prepared with 30 cycles exhibits superior detection performance. The results are shown in the table below:

[0043] Loop count <![CDATA[Current density at 0.4 V (mA cm -2 ).]]> 1 10 0.052 2 30 0.489 3 50 0.167 4 100 0.097

[0044] Next, ensuring the cycle count was consistently 30 times, different nickel-iron ratios were adjusted. Figure 4 As can be seen from b, under different nickel-iron ratio synthesis conditions, a nickel-iron ratio of 2:8 is the optimal nickel-iron ratio (under 30 cycles), which is found in 1 mL of [material name missing]. -1 The highest sensitivity to luteolin is found in NaOH.

[0045] Nickel-iron ratio <![CDATA[Current density at 0.4 V (mA cm -2 ).]]> 1 0:1 0.344 2 0.2:0.8 0.489 3 0.5:0.5 0.127 4 0.8:0.2 0.083 5 1:0 -0.044

[0046] At a fixed potential of 0.35 V (vs. RHE), the performance of a motor fabricated with a nickel-iron ratio of 0.2:0.8 and 30 cycles was tested using chronoamperometry. The current density response to the concentration (C) of luteolin was recorded after continuous addition of luteolin. These time-varying data were converted into calibration curves of current density (j) versus luteolin concentration (electrodes obtained under the 0.2:0.8, 30-cycle conditions). Therefore, as... Figure 5 As shown, the linear response equation for NiFeWO4 / SS is y(mA cm -2)=0.0101•C(mM)+0.0248(R 2 =0.99). The limit of detection (LOD) NiFeWO4 / SS is calculated using the formula: LOD = 3σ / S, where σ is the standard deviation of the blank current (n = 10), and S is the sensitivity (the slope of the calibration curve). The final conclusion is that the detection linear range is 100–2900 μM, and the sensitivity is 10 μA mM. -1 cm -2 The detection limit is 24 μM.

[0047] Construction of a model relating electrode fabrication conditions to electrode performance

[0048] Considering that Ni plays a promoting role, and that excessive Ni would weaken the continuity of active sites in the Fe-enriched phase or reduce the density of surface charge transfer and effective oxidation sites, Ni is considered a low-content promoting component, and the F-enriched phase is considered the main oxidation channel. Under the conditions of fixed operating potential and fixed luteolin concentration, the current density is mainly determined by interfacial reaction kinetics, thus yielding:

[0049]

[0050] In the formula, j refers to the net current density at 0.4V; n refers to the number of electrons transferred during the apparent oxidation of luteolin; F refers to the Faraday constant; and r refers to the apparent Faraday reaction rate per unit geometric area.

[0051] The reaction rate is calculated using the following formula:

[0052] In the formula It is the apparent electron transfer rate constant related to the Ni / Fe ratio; This refers to the effective active site density per unit area; in the formula... This refers to the concentration of luteolin. The effect of sodium tungstate treatment is included in the constant term in this model.

[0053] Let x represent the mole fraction of Ni in the precursor solution:

[0054] (1)

[0055] n Ni This refers to the amount of nickel salt; n in the formula Fe This refers to the amount of iron salts.

[0056] The Fe-rich phase surface provides the main oxidation channels. A small amount of Ni activates neighboring Fe sites by modulating the local electronic structure, adsorption configuration, or deprotonation environment. However, excessive Ni dilutes the continuous network of the Fe-rich phase. Therefore, it is assumed that the truly effective locally active microregions are approximately considered as 1 Ni promoting site + m Fe supporting sites. If the surface is considered as randomly mixed, the areal density of such microregions can be written as... In the formula is the maximum scaling factor that allows for the formation of active microregions per unit area; m is the effective Fe support site order required around a Ni promoting site. Substituting the above equation into the preceding kinetic expression, and combining the constants resulting from the fixed potential, fixed concentration, fixed temperature, and constant W treatment, we obtain the synergistic catalytic current term as follows:

[0057] (2)

[0058] This is the additional catalytic current density contributed by the Ni-Fe synergistic microregion; A is a parameter. Further considering the baseline contributions from the pure Fe and pure Ni ends themselves, the total current density can be written as...

[0059] (3)

[0060] In the formula This refers to the current density of the pure Ni-terminal sample when x=1; in the formula... This refers to the current density of the pure Fe end sample when x=0.

[0061] Differentiating equation (3), we get

[0062]

[0063] In the formula This refers to the rate of change of current density with respect to the mole fraction of Ni. Considering that the current density is affected by the Ni content, the peak position can be considered to be mainly determined by the synergistic term. Therefore, the peak condition can be approximated as follows: In the formula This refers to the mole fraction of Ni that maximizes the current density. Based on experimental results, the optimal value under a 2:8 ratio is assumed to be... Considering that the NiFe content on the electrode surface is obtained through adsorption and is not entirely consistent with that in the solution, a further conversion of the effective surface stoichiometry is introduced, assuming: (4);

[0064] This refers to the effective Ni fraction in the surface active layer; K in the formula refers to the surface introduction / retention selectivity coefficient of Ni relative to Fe. The final model is written as:

[0065] (5)

[0066] In the model, A and K are the parameters to be fitted. After fitting, the following results were obtained: A = 3.400355 ± 1.016516; K = 1.607762 ± 0.457322; R0 2 = 0.967184. Comparison between model predictions and actual experimental values. Figure 6 As shown in the figure, the model's predicted values ​​fit the actual values ​​well.

Claims

1. A self-supporting iron nickel tungstate electrode, characterized in that, The device includes a stainless steel wire mesh carrier and a nickel-iron tungstate active material loaded on the surface of the carrier. The nickel-iron tungstate active material is composed of nickel, iron and tungsten elements, and the active material is directly bonded to the surface of the carrier without adhesive.

2. The self-supporting nickel-iron tungstate electrode according to claim 1, characterized in that, The molar ratio of nickel to iron in the nickel tungstate active material is 1:9-4:6, preferably 2:(7-9).

3. The self-supporting nickel-iron tungstate electrode according to claim 1, wherein, The stainless steel wire mesh is selected from a conductive porous metal carrier, which includes nickel mesh, titanium mesh, or nickel foam; the nickel iron tungstate active material is in nanoparticle form.

4. A process for the preparation of a self-supporting iron nickel tungstate electrode according to any one of claims 1 to 3, characterized in that, The continuous ion layer adsorption reaction method includes the following steps: (1) The stainless steel wire mesh is alternately immersed in a first aqueous solution containing nickel salt and iron salt and a second aqueous solution containing tungstate in a cyclic operation, so that nickel iron tungstate is deposited on the surface of the stainless steel wire mesh. (2) The material obtained in step (1) is dried to obtain the self-supporting nickel tungstate electrode.

5. The preparation method according to claim 4, characterized in that, The nickel salt is selected from water-soluble nickel salts, preferably nickel chloride, nickel nitrate, or nickel sulfate; the iron salt is selected from water-soluble iron salts, preferably ferric chloride, ferric nitrate, or ferric sulfate; the tungstate is selected from water-soluble tungstates, preferably sodium tungstate, potassium tungstate, or ammonium tungstate.

6. The production method according to claim 5, wherein The concentration of nickel salt in the first aqueous solution is 0.01-0.05M, and the concentration of iron salt is 0.05-0.15M; the concentration of tungstate in the second aqueous solution is 0.05-0.2M.

7. The production method according to claim 6, wherein The number of cycles is 10-50 times, preferably 20-40 times; the immersion time in the first or second aqueous solution is 10-60 seconds each time; the drying temperature is 30-80℃ and the time is 0.5-4 hours.

8. The preparation method according to claim 6, characterized in that, By varying the concentrations of nickel and iron salts in the first aqueous solution, the current density of the prepared self-supporting nickel-iron tungstate electrode in the electrochemical detection of luteolin is kept within a set range. The relationship between the controlled concentrations of nickel and iron salts and the predicted current density is calculated using the following formula: ； where x refers to the molar fraction of Ni in the precursor solution, ; n Ni refers to the amount of substance of the nickel salt; n Fe refers to the amount of substance of the iron salt; j(x) is the current density; j Ni refers to the current density of the pure Ni end-member sample, i.e. the end-member current density for x = 1; j Fe refers to the current density of the pure Fe end-member sample, i.e. the end-member current density for x = 0; effective Ni fraction in the surface active layer; ; A and K are coefficients to be fitted.

9. The use of the self-supporting nickel tungstate electrode as described in any one of claims 1-3 in the electrochemical detection of luteolin.

10. Use according to claim 9, characterized in that, The electrochemical detection employs a three-electrode system, with the self-supporting nickel-iron-tungstate electrode serving as the working electrode, and the electrolyte being a 0.1-1M NaOH solution. The linear range of the electrochemical detection is 100-2900 μM, the detection limit is 24 μM, and the sensitivity is 10 μAmM⁻¹cm⁻². The electrochemical detection is performed at a potential of 0.35V vs. RHE.

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