Preparation and application of an electrochemical sensor for detecting nitrobenzene

Abstract

This invention provides an electrochemical sensor method for detecting nitrobenzene. The modified electrode is prepared by electrochemical copolymerization using 1,3,5-tris(N-carbazolyl)benzene (TCB) and N-(6-hydroxyhexyl)carbazole (CbzC6-OH) as carbazole monomers to construct a CMP thin film modified electrode for detecting nitrobenzene. The morphology of the CMP film is characterized by atomic force microscopy. The electrochemical performance of the modified electrode is studied using differential pulse voltammetry. The results show that the electrochemical sensor prepared based on this electrode exhibits high electrocatalytic activity, good stability and selectivity, and a wide detection range in the detection of nitrobenzene. This indicates that the sensor has good prospects for practical applications.

Description

Technical Field

[0001] This invention belongs to the field of porous functional materials chemistry and electrochemical sensing technology, and relates to a method for preparing a modified electrode for nitrobenzene detection and its application. Background Technology

[0002] With industrialization, population growth, and increased human activities, environmental pollution has become increasingly serious. Nitrobenzene (NB) is a carcinogenic organic compound and an essential raw material and product of the chemical industry, used in the production of explosives, herbicides, pesticides, and dyes. It is a persistent organic pollutant that accumulates and has toxic effects on humans and other organisms, making it a major problem. Furthermore, intermediates produced by the biotransformation of NB, such as m-nitrophenol and p-nitrophenol, are more toxic than NB itself. NB is an electron-deficient entity; the electron affinity of the nitro group reduces the electron density of the benzene ring, making NB highly stable and difficult to biodegrade. As industrial waste, it enters natural water resources, accumulates in the food chain, and causes serious health problems in humans. Aqueous NB is released into the air through diffusion, and inhalation of NB can cause damage to the human nervous system by affecting methemoglobin. The maximum permissible limit for NB in ​​drinking water is 17 μg / L. However, even at low concentrations, NB exhibits stability and bioaccumulation in groundwater, threatening the stability of ecosystems. Nitrobenzene is listed as one of the 129 priority contaminants by the U.S. Public Health Service due to its strong environmental retention capacity. In recent years, rapid and sensitive detection has become crucial because of the extreme threat posed by the toxicity of nitrobenzene to humans.

[0003] The detection of nitrobenzene has always been a major issue in environmental monitoring. To date, various methods for measuring and quantitatively analyzing nitrobenzene have been developed, primarily including high-performance liquid chromatography (HPLC), gas chromatography-mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), fluorescence spectroscopy, spectrophotometry, and capillary electrophoresis. However, most reported techniques are not easily operable under routine conditions, suffer from complex mechanisms and high costs, and typically require significant pre-purification time and sophisticated equipment. Recently, electrochemical methods have gained widespread application in the detection of various natural and anthropogenic pollutants due to their high efficiency, sensitivity, low cost, and ease of miniaturization. Compared with other traditional techniques, they offer significant advantages in detection limits, analyte specificity, and operational simplicity. These advantages enable their widespread application in environmental monitoring, clinical, and healthcare diagnostics. As the most common strategy, polymer-modified electrodes have been developed as sensor platforms, making it possible to improve the sensitivity and selectivity of nitrobenzene detection.

[0004] Conjugated microporous polymers (CMPs) have attracted considerable attention in materials science due to their excellent properties, including high surface area, uniform porosity, chemical resistance, and heat resistance. Therefore, CMPs have high application potential in gas trapping and separation, catalysis, organic electronic devices, and sensors. To obtain high-quality CMP films that can be integrated into devices, one approach to overcome the difficulty of powder processing is to directly electrochemically polymerize multifunctional monomers on a suitable substrate for CMP film preparation. This process simultaneously completes the formation of CMPs and the deposition of the film, avoiding secondary processing of CMPs. The resulting CMP films exhibit significantly optimized morphology and chemical functionality, providing new avenues for CMP applications. Flexible CMP films were constructed by electrochemical copolymerization of the rigid monomer 1,3,5-tris(N-carbazolyl)benzene (TCB) with synthesized CbzC6-OH. The compound structure reveals that the TCB monomer is rigid. Films obtained through electrochemical polymerization using a single TCB monomer are prone to breakage and lack toughness during use. However, the addition of the CbzC6-OH monomer successfully softens the rigid film while maintaining its inherent porosity, achieving a surface roughness as low as 3.963 nm. Simultaneously, the flexible CMP film we prepared has a thickness of approximately 50 nm, exhibiting relatively low molecular ionic resistance and a wider range of applications. Therefore, the novelty of this method lies in combining a flexible, smooth-surfaced, and ultrathin CMP film with the electrochemical detection of nitroaromatic analytes. The results show that the electrochemical sensor prepared based on this electrode exhibits high electrocatalytic activity, good stability, and a wide detection range in the detection of nitrobenzene.

[0005] A search revealed no reports of electrodes modified with CbzC6-OH-containing electrochemically polymerized conjugated microporous polymer films for the electrochemical detection of nitrobenzene. Summary of the Invention

[0006] Combining the advantages of existing technologies and overcoming their problems, this invention provides a highly sensitive modified electrode for nitrobenzene detection and its preparation method. A flexible conjugated microporous polymer film is prepared on the surface of a glassy carbon electrode via electropolymerization, and qualitative and quantitative detection of nitrobenzene is achieved using a traditional three-electrode device. The preparation method is simple, the raw materials are readily available, and when applied to the detection of nitrobenzene in water, it features convenient operation, short analysis time, high sensitivity, low detection limit, good stability, and a wide linear range. It has significant advantages in the detection of nitrobenzene compounds.

[0007] This invention is achieved through the following technical solution: an electrochemical sensor for detecting nitrobenzene and its preparation method, comprising the following steps:

[0008] (1) Prepare or purchase two polymer monomers with nitrobenzene selectivity;

[0009] (2) A conjugated microporous polymer film modified electrode was prepared by electrochemical copolymerization of two polymer monomer materials to obtain a nitrobenzene sensor;

[0010] (3) Electrochemical detection of nitrobenzene in solution.

[0011] According to the present invention, the polymer material in step (1) is responsive to the detection of nitrobenzene. Preferably, the polymer monomer is a conjugated microporous polymer monomer, and its structure is preferably shown in Formulas I and II below:

[0012]

[0013] According to a preferred embodiment of the present invention, the specific preparation method of the polymer monomer shown in Formula II is as follows:

[0014] Potassium hydroxide powder was added to DMF and stirred at room temperature. Then, carbazole was added and stirring continued at room temperature. 6-Bromo-1-hexanol was then slowly added, and the mixture was stirred at room temperature. The mixture was then poured into deionized water and filtered to obtain a white solid. The solid was washed again with water and air-dried, then dissolved in ethanol. The residue insoluble in ethanol was filtered off. Deionized water was added to the filtrate for recrystallization, followed by filtration. The resulting solid was separated by silica gel chromatography to obtain a white solid, N-(6-hydroxyhexyl)carbazole.

[0015] According to a preferred embodiment of the present invention, the potassium hydroxide powder is 12 g, the carbazole is 3.3 g, and the 6-bromo-1-hexanol is 5.432 g.

[0016] According to a preferred embodiment of the present invention, the method for preparing a conjugated microporous polymer film modified electrode by electrochemical copolymerization of the prepared polymer material and the purchased polymer material in step (2) is as follows: 1,3,5-tris(N-carbazolyl)benzene (TCB), N-(6-hydroxyhexyl)carbazole (CbzC6-OH), and tetrabutylammonium hexafluorophosphate (TBAPF6) are dissolved in a mixture of dichloromethane and acetonitrile, and stirred thoroughly to obtain a homogeneous electrolyte solution. The solution is placed in a conventional three-electrode electrolytic cell and connected to an electrochemical workstation. A glassy carbon electrode (GC, for electrochemical sensing of nitrobenzene) or indium tin oxide (ITO, for characterization of CMP films) is used as the working electrode (WE), a platinum sheet as the auxiliary electrode (RE), and Ag / AgNO3 as the reference electrode (CE).

[0017] The GC / ITO working electrode was prepared by electropolymerization on its surface using cyclic voltammetry in the electrolyte solution described above. The electrode was then immersed in dichloromethane / acetonitrile solution overnight to remove excess monomers from the surface of the film, thus completing the electrode modification.

[0018] According to a preferred embodiment of the present invention, TCB:CbzC6-OH = 1:1.

[0019] According to a preferred embodiment of the present invention, the ratio of dichloromethane to acetonitrile is 1:4.

[0020] According to a preferred embodiment of the present invention, the glassy carbon electrode has a diameter of Φ = 3 mm and the ITO size is 1.5 × 2 cm.

[0021] According to a preferred embodiment of the present invention, electropolymerization is prepared by cyclic voltammetry from 0 to 1.2 V at a rate of 100 mV / s for 10 cycles.

[0022] According to a preferred embodiment of the present invention, the electrochemical detection of nitrobenzene in solution in step (3) is performed as follows: the prepared glassy carbon electrode is used as the working electrode, the Ag / AgCl electrode is used as the reference electrode, and the platinum sheet electrode is used as the auxiliary electrode. The electrode is connected to an electrochemical workstation and immersed in a phosphate buffer solution containing potassium chloride. The nitrobenzene is dissolved in acetonitrile to prepare the detection solution. Different amounts of detection solution are added to the phosphate buffer solution according to the required concentration. After stirring and enrichment, the peak current of the sample signal is detected by differential pulse voltammetry.

[0023] According to a preferred embodiment of the present invention, the potassium chloride concentration is 0.2 mol / L, the phosphate buffer concentration is 0.1 mol / L, and the pH is 7.4.

[0024] According to a preferred embodiment of the present invention, the differential pulse voltammetry method detects parameters of 0.05 V amplitude, 0.05 s pulse width, 0.5 s pulse period, 0.0167 s sampling width, and 0.004 V increment, with a scanning range of 0 to -1.1 V.

[0025] Technical features and advantages of the present invention:

[0026] 1. The CMP membrane prepared by electrochemical copolymerization successfully softens the rigid film prepared by TCB monomer without sacrificing the inherent porosity due to the introduction of CbzC6-OH monomer, thus making the application range of the film wider.

[0027] 2. The CMP film prepared by electrochemical copolymerization has an ultra-low surface roughness (3.963 nm) and an ultra-thin profile (50 nm), which further improves the film performance;

[0028] 3. The fabrication process of this conjugated microporous polymer film modified glassy carbon electrode electrochemical sensor is simple, easy to implement, and has low material cost. The detection materials and equipment used are easy to prepare and the process is environmentally friendly, which has important application prospects in the field of nitrobenzene detection.

[0029] 4. By combining the advantages of two monomer materials, 1,3,5-tris(N-carbazolyl)benzene (TCB) and N-(6-hydroxyhexyl)carbazole (CbzC6-OH), it is possible to identify nitrobenzene and generate a sensitive electrochemical response signal, thereby realizing the electrochemical sensing detection of nitrobenzene. Compared with traditional preparation and detection methods, it has the characteristics of convenient detection operation, simple experiment, low cost, short analysis time, low detection limit, high sensitivity and good stability, and has obvious advantages in the detection of aromatic compounds. Attached Figure Description

[0030] Figure 1 is a schematic diagram of the fabrication of the electrochemical sensor in Example 2.

[0031] Figure 2 shows the cyclic voltammetry curves recorded for 10 scan cycles during the electropolymerization process in Example 2.

[0032] Figure 3 shows the AFM morphology of the conjugated microporous polymer film obtained in Example 2.

[0033] Figure 4 shows the N2 adsorption-desorption isotherm of the conjugated microporous polymer film obtained in Example 2.

[0034] Figure 5 is a SEM cross-sectional view of the conjugated microporous polymer film obtained in Example 2.

[0035] Figure 6 shows the differential pulse voltammetric response of the modified electrode in Example 3 at different concentrations of nitrobenzene. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to the accompanying drawings.

[0037] Example 1: Synthesis of N-(6-hydroxyhexyl)carbazole

[0038] Potassium hydroxide powder (12 g) was added to DMF (50 mL) and stirred at room temperature for 15 minutes. Then, carbazole (3.3 g) was added and stirring continued at room temperature for 1 hour. Subsequently, 6-bromo-1-hexanol (5.432 g) was slowly added, and the mixture was stirred at room temperature for 24 hours. The mixture was then poured into 0.6 L of deionized water and filtered to obtain a white solid. The solid was washed again with water and air-dried, then dissolved in 70% ethanol. The residue insoluble in ethanol was filtered off. Deionized water was added to the filtrate for recrystallization, followed by filtration. The resulting solid was separated by silica gel chromatography (eluent: dichloromethane) to obtain a white solid N-(6-hydroxyhexyl)carbazole, with a yield of 80%.

[0039] Example 2: Preparation of thin films by electrochemical polymerization of monomers

[0040] 1,3,5-Tris(N-carbazolyl)benzene (TCB) (23 mg, 0.04 mmol), N-(6-hydroxyhexyl)carbazole (CbzC6-OH) (10.7 mg, 0.04 mmol), and tetrabutylammonium hexafluorophosphate (TBAPF6) (1550 mg, 4.0 mmol) were dissolved in a mixture of 40 mL dichloromethane (32 mL) and acetonitrile (8 mL) and stirred thoroughly for 1 hour to obtain a homogeneous electrolyte solution. The solution was placed in a conventional three-electrode electrolytic cell connected to an electrochemical workstation (CHI 660E). A glassy carbon electrode (GC, for electrochemical sensing of nitrobenzene) or indium tin oxide (ITO, for characterization of CMP membranes) was used as the working electrode (WE), a platinum sheet as the auxiliary electrode (CE), and Ag / AgNO3 (0.1 M AgNO3, non-aqueous reference) as the reference electrode (RE).

[0041] Bare glassy carbon electrode (GC, 3 mm in diameter) was polished on chamois surface with alumina powders of 1 μm, 0.3 μm, and 0.05 μm, respectively, then rinsed with deionized water, followed by ultrasonic cleaning with ethanol and deionized water for 5 minutes. Indium tin oxide (ITO, 1.5 × 2 cm) was ultrasonicated with toluene, acetone, ethanol, and deionized water for 15 minutes each, then rinsed thoroughly with deionized water, dried under nitrogen, and repeated three times. The GC / ITO working electrode was subjected to cyclic voltammetry in the above electrolyte solution, from 0 to 1.2 V, at a scan rate of 100 mV / s for 10 cycles to prepare a conjugated microporous polymer film by surface electropolymerization. The film was then immersed overnight in dichloromethane / acetonitrile solution to remove excess monomers from the film surface, thus completing the electrode modification.

[0042] Example 3: Electrochemical Measurement and Detection of Nitro Aromatic Compounds

[0043] The prepared glassy carbon electrode was used as the working electrode, the Ag / AgCl electrode as the reference electrode, and the platinum sheet electrode as the auxiliary electrode. All electrodes were connected to an electrochemical workstation (CHI 660E). The electrodes were immersed in phosphate buffered saline (PBS) containing 0.2 mol / L potassium chloride (0.1 mol / L, pH 7.4). Nitrobenzene was dissolved in acetonitrile to prepare the detection solution. Different amounts of analyte-containing solutions were added to the PBS according to the required concentrations. After stirring and enrichment for 3 minutes, differential pulse voltammetry was used for detection. The parameters were: amplitude 0.05 V, pulse width 0.05 s, pulse period 0.5 s, sampling width 0.0167 s, and increment 0.004 V. The peak current of the sample signal was obtained, and the results are shown in the figure. The concentration range of nitrobenzene tested was 0.1 to 100 μmol / L.

Claims

1. A method for preparing a modified electrode for detecting nitrobenzene content in solution, characterized in that, The modified electrode was prepared as follows: 1,3,5-tris(N-carbazolyl)benzene, N-(6-hydroxyhexyl)carbazole, and tetrabutylammonium hexafluorophosphate were dissolved in a mixture of dichloromethane and acetonitrile, and stirred thoroughly to obtain a homogeneous electrolyte solution. The solution was placed in a three-electrode electrolytic cell connected to an electrochemical workstation. The electrode substrate was placed in the electrolyte solution, and after energizing, a conjugated microporous polymer film was prepared by electropolymerization on the surface of the electrode substrate. Then, the film was soaked overnight in a mixed solution of dichloromethane and acetonitrile to remove excess monomers from the film surface, thereby completing the electrode modification. The electrode substrate was a glassy carbon electrode or ITO conductive glass.

2. The preparation method according to claim 1, characterized in that, The molar ratio of 1,3,5-tris(N-carbazolyl)benzene to N-(6-hydroxyhexyl)carbazole is 1:(0.01~99).

3. The preparation method according to claim 1, characterized in that, Electropolymerization was performed using cyclic voltammetry from 0 to 1.2 V, with 10 cycles at a scan rate of 100 mV / s.

4. The preparation method according to claim 1, characterized in that, The electrode pretreatment operation is as follows: If the electrode substrate is a glassy carbon electrode, polish the chamois surface with alumina powder of 1 μm, 0.3 μm, and 0.05 μm respectively, then rinse with deionized water, and then ultrasonically clean with ethanol and deionized water; if the electrode substrate is ITO conductive glass, ultrasonically clean it for 15 minutes each with toluene, acetone, ethanol, and deionized water respectively, then rinse it with a large amount of deionized water, blow it dry with nitrogen gas, and repeat 3 times.

5. The modified electrode prepared by the method of claim 1 is used in a method for detecting the content of nitrobenzene in solution, characterized in that, The concentration of nitrobenzene in solution was measured using a three-electrode system and electrochemical differential pulse voltammetry.

6. The detection method according to claim 5, characterized in that, The modified electrode was used as the working electrode, the platinum sheet electrode as the counter electrode, the Ag / AgCl electrode as the reference electrode, and the phosphate buffer solution containing KCl as the electrolyte solution. Differential pulse voltammetry was used for detection.

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