A highly sensitive photoelectrochemical sensor for detecting hexavalent chromium and a preparation method thereof

Abstract

The present invention discloses a photoelectrochemical sensor for the detection of hexavalent chromium ions. The photoelectrochemical sensor is a modified ITO glass electrode, and the modification material is a photosensitive composite film with high-sensitive optoelectronic activity. Due to the strong absorption effect of the photo electron acceptor on the photo electrons generated by the photosensitive complex, the sensor can generate a strong cathodic photoelectrochemical signal. By utilizing the enrichment performance of the photosensitive composite film for hexavalent chromium ions, and under the conditions of light illumination and an applied bias voltage, weakly conductive reduction products can be generated on the surface of the photosensitive composite film, which effectively reduces the conductivity of the photosensitive composite film, inhibits the optoelectrochemical activity, hinders the transfer of photo electrons to the electron acceptor, quenches the photocurrent, and the quenched photocurrent has a correlation with the content of hexavalent chromium. In the present invention, the preparation of the sensor is simple, the cost is low, the response is fast, the sensitivity is high, the detectable range is wide, and the detection limit is as low as 5 pM. The rapid determination of hexavalent chromium in environmental water bodies, drinking water and food can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of photoelectrochemical sensors, and particularly to a photoelectrochemical sensor for detecting hexavalent chromium ions and a preparation method thereof. Background Art

[0002] With the progress of science and technology and the rapid development of industrialization, a large number of harmful heavy metal ions are discharged into the environment, such as hexavalent chromium ions. Hexavalent chromium ions are inhalation and ingestion toxicants that can enter the human body through the digestive tract, respiratory tract, and skin mucosa and are easily absorbed by the human body. They may cause various harms and reactions to the human body, such as skin irritation, tissue cell damage, digestive system damage, inhibited bone growth, liver and kidney toxicity, etc. Therefore, it is very important to quantify hexavalent chromium ions in environmental samples. To monitor the environment and reduce the risk of environmental pollution by industrial waste, we need highly sensitive and fast-responsive detection methods to quantify the content of hexavalent chromium ions.

[0003] In the past few decades, many analytical techniques such as chromatography, fluorescence spectroscopy, and atomic absorption spectroscopy have been used to determine hexavalent chromium ions in different sample matrices. However, these methods require expensive instrument equipment and can only detect the content level of ng / L at the lowest for sample solutions. Therefore, there is an urgent need for a detection method for hexavalent chromium ions that is simple to operate, highly sensitive, has a low detection limit, and good selectivity. The photoelectrochemical method has simple equipment, high sensitivity, and is easy to operate, making it a good alternative method. Summary of the Invention

[0004] The purpose of the present invention is to provide a photoelectrochemical sensor and a detection method for the content of hexavalent chromium ions, aiming to solve the problems such as expensive equipment required for detecting hexavalent chromium, high detection cost, and narrow detection range.

[0005] To achieve the above purpose, the present invention includes the following technical solutions:

[0006] Provide a photoelectrochemical sensor for hexavalent chromium detection, the photoelectrochemical sensor includes a modified ITO conductive glass as a working electrode, and a photosensitive composite film of polymer-doped BiOI-Bi-multi-walled carbon nanotubes is modified on its surface.

[0007] Using the ITO modified with the photosensitive composite film as the working electrode, a three-electrode system is constructed with an auxiliary electrode and a reference electrode. The auxiliary electrode is a Pt electrode, and the reference electrode is a silver / silver chloride (Ag / AgCl) electrode. The photocurrent response of the photoelectrochemical sensor is detected under light source irradiation and a certain bias voltage.

[0008] The working principle of detecting chromium ions is as follows: The sample solution to be tested containing hexavalent chromium is dropped onto the surface of the working electrode. The photosensitive composite film adsorbs and enriches the hexavalent chromium component. Under specific light intensity and applied bias voltage, hexavalent chromium ions are reduced to trivalent chromium oxide on the composite film. Its weak conductivity greatly reduces the transfer efficiency of photo-generated electrons to the photo-electron acceptor, thus quenching the photocurrent. The magnitude of the photocurrent is correlated with the concentration of hexavalent chromium. By detecting the photocurrent of the sample to be tested, the content of hexavalent chromium in the sample can be calculated.

[0009] The present invention uses a BiOI-Bi-multi-walled carbon nanotube composite as the photosensitive matrix, a polymer as the film-forming curing agent, and the photosensitive composite film as the enricher for hexavalent chromium, greatly improving the detection sensitivity of the sensor to chromium, broadening the detection range, and lowering the detection limit. This method is applicable to the rapid determination of hexavalent chromium in environmental water bodies, drinking water, and different foods.

[0010] The polymer is polypyrrole, polyaniline, chitosan, or polyurethane, preferably polyaniline or chitosan.

[0011] The BiOI-Bi-multi-walled carbon nanotube composite is prepared according to the inventor's own previous method (Sensors and Actuators B: Chemical, 2021, 348: 130691). The length of the carbon nanotubes used is 50 - 200 nm, the diameter is 30 - 50 nm, and the mass percentage content of the carbon tubes in the composite is 1 - 5%.

[0012] Furthermore, the preparation method of the sensor includes: dispersing a certain amount of the photosensitive composite into water, dissolving the polymer in a suitable solvent, and then using the stepwise drop-coating method to drop the photosensitive composite dispersion and the polymer dispersion onto the surface of the ITO glass and drying to form a composite sensitive film.

[0013] Preferably, the solvent for polyaniline is N,N-dimethylformamide or N-methylpyrrolidone, or the solvent for chitosan is an aqueous solution containing 1% acetic acid by volume percentage.

[0014] Preferably, the mass percentage content of the polyaniline solution is 0.05% - 0.5%, or the mass percentage content of the chitosan solution is 0.05% - 0.5%.

[0015] Preferably, the mass concentration of the aqueous dispersion of the photosensitive composite is 2 - 10 mg / mL.

[0016] Furthermore, the present invention also provides the application of the photoelectrochemical sensor in detecting hexavalent chromium. The application includes:

[0017] (1) Preparation of standard solution: Take the hexavalent chromium ion standard solution and prepare a series of chromium ion standard solutions with different concentrations to be measured using water.

[0018] (2) Plotting the calibration curve: Take 4 - 10 μL of chromium standard solutions with different concentrations and drop them on the surface of the ITO electrode, enrich for 3 - 45 min, carefully wash, then transfer the three - electrode system into the working electrolyte solution. Under the "on - off" cycle state of the light source, use the constant - potential amperometry method to record the photocurrent of different ITO electrodes, and plot the calibration curve between the photocurrent and the concentration of hexavalent chromium ions.

[0019] (3) Testing of actual samples: Take the treated sample solution to be measured, drop it on the surface of the ITO working electrode, measure the photocurrent using the same method as in step (2), substitute the photocurrent value into the corresponding calibration curve equation above, and obtain the content of hexavalent chromium ions in the sample to be measured through conversion.

[0020] Preferably, the light source is a white - light LED lamp, the light intensity is 20 mW / cm 2 , and the "on - off" cycle time of the light source is 15 s respectively.

[0021] Preferably, the applied bias voltage is - 0.1 V.

[0022] Preferably, the working electrolyte solution is one of Na2SO4 solution, Na2SO3 solution, KCl solution, and phosphate buffer solution, and the concentration of the working solution is 0.1 mol / L - 2.0 mol / L;

[0023] Preferably, the working electrolyte contains one of K3[Fe(CN)6] and FeCl3 as a photoelectron acceptor, and the concentration of the photoelectron acceptor is 10 - 50 mmol / L.

[0024] Compared with the prior art, the advantages of the present invention are as follows:

[0025] (1) The present invention provides a high - performance photoelectrochemical sensor for the detection of hexavalent chromium ions. It utilizes a polymer - doped BiOI - Bi - multi - walled carbon nanotube photosensitive composite film, which has a large specific surface area, excellent photoelectron transfer rate, and high photoelectrochemical activity. The preparation of the sensor is simple in operation, and the modified sensitive film is stable and not easy to fall off.

[0026] (2) The present invention utilizes the high enrichment effect of the photosensitive composite film on hexavalent chromium ions, the strong absorption ability of the photo - electron acceptor for the photo - electrons generated by the photosensitive complex, and the formation of weakly conductive reduction products of hexavalent chromium on the surface of the photosensitive composite film. This not only effectively reduces the conductivity of the photosensitive composite film, inhibits the optoelectronic activity, but also hinders the transfer of photo - electrons to the electron acceptor, resulting in a quenched photocurrent signal. Therefore, this sensor has a low detection limit (as low as 5 pM), high sensitivity, and a wide detectable linear range. Description of the Drawings

[0027] Figure 1 Scanning electron micrograph of the photosensitive composite film composed of BiOI - Bi - multi - walled carbon nanotubes and chitosan on the surface of the sensor prepared in Example 1.

[0028] Figure 2 Photocurrent responses of the sensor prepared in Example 1 to standard solutions of hexavalent chromium ions with different concentrations. The corresponding hexavalent chromium concentrations are 0, 10 pM, 100 pM, 1 nM, 10 nM, 100 nM, 1 mM, 10 mM.

[0029] Figure 3 Logarithmic calibration curve of the sensor prepared in Example 1 for the hexavalent chromium standard solution. Detailed Description of the Invention

[0030] The following are specific examples for the preparation of the Ag / AgI - multi - walled short carbon nanotube composite of the present invention. The following examples are intended to further illustrate the present invention in detail, rather than limiting the present invention.

[0031] Example 1

[0032] (1) Preparation of the sensor

[0033] The short carbon nanotubes (CNTs) were refluxed and acidified in a 1:3 volume ratio of HNO3 (68 wt%) and H2SO4 (98 wt%) at 60 °C for 6 h. The acidified CNTs were washed with water until neutral, centrifuged, and dried for later use. The BiOI - Bi / CNTs composite was prepared by a solvothermal method. An appropriate amount of CNTs, 0.1 g of polyvinylpyrrolidone (PVP), and 0.2 g of Bi(NO3)3·5H2O were dispersed in 20 mL of ethylene glycol. After continuous stirring for 1 h, 70 mg of KI was added to the above - mentioned mixed solution, and stirring was continued for 1 h. Then, it was heated at 180 °C for 12 h in a stainless - steel autoclave with a polytetrafluoroethylene inner liner. After the product was centrifuged and washed, it was dried at 60 °C for 12 h.

[0034] The BiOI-Bi / CNTs prepared in the above steps was formulated into an aqueous solution with a concentration of 5 mg / mL. 10 mL of the solution was dropped onto the ITO electrode and dried at 60 °C for 30 min. Then, 10 mL of a 0.05% chitosan solution prepared with 1% aqueous acetic acid solution was dropped and dried at 60 °C for 30 min.

[0035] (2)Standard curve plotting

[0036] Take the hexavalent chromium ion standard solution and prepare a series of chromium ion standard solutions with different concentrations using water, including 0, 10 pM, 100 pM, 1 nM, 10 nM, 100 nM, 1 mM, and 10 mM.

[0037] Drop 10 mL of chromium ion standard solutions with different concentrations onto the ITO working electrode prepared in step (1) for enrichment for 10 min, wash it clean with ultrapure water, then transfer the three-electrode system into a 1 mol / L KCl solution, add 25 mmol / L of K3[Fe(CN)6], and under the "on-off" cycle state of the white LED lamp, use the potentiostatic amperometry method to test at a voltage of -0.1 V, record the photocurrent, and plot the logarithmic calibration curve between the photocurrent response and the hexavalent chromium ion concentration. 2 Under the "on-off" cycle state of the white LED lamp, use the potentiostatic amperometry method to test at a voltage of -0.1 V, record the photocurrent, and plot the logarithmic calibration curve between the photocurrent response and the hexavalent chromium ion concentration.

[0038] (3)Detection of actual samples

[0039] Take 10 mL of the treated sample solution to be measured, drop it onto the surface of the ITO working electrode for enrichment for 10 min, wash it clean with ultrapure water, measure it using the photoelectrochemical method in step (2), substitute the photocurrent value into the corresponding calibration curve equation above, and obtain the content of hexavalent chromium ions in the sample to be measured through conversion.

[0040] Example 2

[0041] (1)Preparation of the sensor

[0042] Disperse short carbon nanotubes (CNTs) in a mixture of HNO3 (68 wt%) and H2SO4 (98 wt%) with a volume ratio of 1:3 and reflux and acidify at 60 °C for 6 h. Wash the acidified CNTs with water until neutral, centrifuge, and dry for later use. Prepare the BiOI-Bi / CNTs composite material using the solvothermal method. Disperse an appropriate amount of CNTs, 0.1 g of polyvinylpyrrolidone (PVP), and 0.2 g of Bi(NO3)3·5H2O into 20 mL of ethylene glycol. After continuous stirring for 1 h, add 70 mg of KI to the above mixed solution and continue stirring for 1 h. Then heat it in a stainless steel autoclave with a polytetrafluoroethylene inner lining at 180 °C for 12 h. After centrifuging and washing the product, dry it at 60 °C for 12 h.

[0043] The BiOI-Bi / CNTs prepared in the above steps was formulated into an aqueous solution with a concentration of 5 mg / mL. 10 mL of the solution was dropped onto the surface of the ITO electrode and dried at 60 °C for 30 min. Then, 10 mL of a polyaniline solution with a mass percentage of 0.1% prepared with N,N-dimethylformamide was dropped and dried at 60 °C for 30 min.

[0044] (2) Plotting of the standard curve

[0045] Take the hexavalent chromium ion standard solution and prepare a series of chromium ion standard solutions with different concentrations using water, including 0, 10 pM, 100 pM, 1 nM, 10 nM, 100 nM, 1 mM, and 10 mM.

[0046] Drop 6 mL of the chromium ion standard solutions with different concentrations onto the ITO working electrode prepared in step (1) for enrichment for 20 min, wash it clean with ultrapure water, then transfer the three-electrode system into a 1 mol / L Na2SO4 solution, add 50 mmol / L of FeCl3, and under the "on-off" cycle state of the white light LED lamp, use the potentiostatic amperometry method to test at a voltage of -0.1 V, record the photocurrent, and plot the logarithmic calibration curve between the photocurrent response and the hexavalent chromium ion concentration. 2 Under the "on-off" cycle state of the white light LED lamp, use the potentiostatic amperometry method to test at a voltage of -0.1 V, record the photocurrent, and plot the logarithmic calibration curve between the photocurrent response and the hexavalent chromium ion concentration.

[0047] (3) Detection of actual samples

[0048] Take 6 mL of the treated sample solution to be measured, drop it onto the surface of the ITO working electrode for enrichment for 20 min, wash it clean with ultrapure water, measure it using the photoelectrochemical method in step (2), substitute the photocurrent value into the corresponding calibration curve equation above, and obtain the content of hexavalent chromium ions in the sample to be measured through conversion.

[0049] Example 3

[0050] (1) Preparation of the sensor

[0051] Same as step (1) of Example 1

[0052] (2) Plotting of the standard curve

[0053] Take the hexavalent chromium ion standard solution and prepare a series of chromium ion standard solutions with different concentrations using water, including 0, 10 pM, 100 pM, 1 nM, 10 nM, 100 nM, 1 mM, and 10 mM.

[0054] Drop 8 mL of chromium ion standard solutions with different concentrations onto the working electrode prepared in step (1) for enrichment for 30 min, wash it clean with ultrapure water, then transfer the three-electrode system into a 1 mol / L Na2SO4 solution, add 50 mmol / L K3[Fe(CN)6], and under the "on-off" cycling state of a white light LED lamp, use the potentiostatic current method to test at a voltage of -0.1 V, record the photocurrent, and plot the logarithmic calibration curve between the photocurrent response and the concentration of hexavalent chromium ions. 2 Under the "on-off" cycling state of a white light LED lamp, use the potentiostatic current method to test at a voltage of -0.1 V, record the photocurrent, and plot the logarithmic calibration curve between the photocurrent response and the concentration of hexavalent chromium ions.

[0055] (3) Detection of actual samples

[0056] Take 8 mL of the treated sample solution to be tested, drop it onto the surface of the ITO working electrode for enrichment for 30 min, wash it clean with ultrapure water, measure it using the photoelectrochemical method in step (2), substitute the photocurrent value into the corresponding calibration curve equation above, and obtain the content of hexavalent chromium ions in the sample to be tested through conversion.

Claims

1. An optoelectrochemical sensor for hexavalent chromium detection, characterized in that, Using ITO modified with a photosensitive composite film as the working electrode, a three-electrode system is constructed with an auxiliary electrode and a reference electrode. The auxiliary electrode is a Pt electrode, and the reference electrode is a silver / silver chloride (Ag / AgCl) electrode. The photocurrent response of the photoelectrochemical sensor is detected under light source irradiation and a certain bias voltage; the working electrode is ITO conductive glass, and its surface is modified with a polymer-doped BiOI-Bi-multi-walled carbon nanotube photosensitive composite film; the length of the carbon nanotubes is 50-200 nm, the diameter is 30-50 nm, and the mass percentage content of the carbon nanotubes in the composite is 1-5%; the polymer is polyaniline or chitosan.

2. The preparation method of the photoelectrochemical sensor applied to hexavalent chromium detection according to claim 1, characterized in that, A certain amount of the photosensitive composite is dispersed in water, the polymer is dissolved in a suitable solvent, and then the photosensitive composite dispersion and the polymer dispersion are dropped onto the surface of the ITO glass by a stepwise drop-coating method and dried to form a composite sensitive film.

3. The preparation method of the photoelectrochemical sensor for hexavalent chromium detection according to claim 2, characterized in that, The solvent for polyaniline is N,N-dimethylformamide or N-methylpyrrolidone, or the solvent for chitosan is an aqueous solution containing 1% acetic acid by volume percentage.

4. The preparation method of the photoelectrochemical sensor applied to hexavalent chromium detection according to claim 2, characterized in that, The mass percentage content of the polyaniline solution is 0.05% - 0.5%, or the mass percentage content of the chitosan solution is 0.05% - 0.5%.

5. The preparation method of the photoelectrochemical sensor applied to hexavalent chromium detection according to claim 2, characterized in that, The mass concentration of the photosensitive composite aqueous dispersion is 2-10 mg / mL.

6. Use of the photoelectrochemical sensor for the detection of hexavalent chromium according to claim 1 in the detection of hexavalent chromium.

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