Visual detection method for simply, rapidly and quantitatively detecting hexavalent chromium in water

Abstract

The invention discloses a visual detection method for simply and rapidly quantifying hexavalent chromium in water, the method realizes etching reaction of Au-core Ag-shell nanoparticles (Au-coated Ag NPs) and hexavalent chromium by adding a hydrogen bromide solution and strictly controlling the dosage of the hydrogen bromide solution, and the method comprises the following steps: (1) preparing an Au-coated Ag NPs nano colorimetric probe solution, (2) preparing standard solutions of hexavalent chromium with different concentrations, and (3) measuring the concentration of hexavalent chromium in the standard solutions. The method comprises the following steps: (1) adding a standard solution of hexavalent chromium into a detection solution containing an Au (at) Ag NPs nano colorimetric probe solution and a hydrogen bromide solution, and determining a standard curve and a detection limit of the hexavalent chromium according to a blue channel intensity value IB, and (3) carrying out visual detection on an actual water sample of the hexavalent chromium. The detection conditions are mild, matrix interference can be well eliminated, stability and sensitivity are high, the whole recognition and detection process has the advantages of being easy and convenient to operate, rapid, real-time, quantitative and low in cost, and the method has very wide application prospects.

Description

Technical Field

[0001] The invention relates to a visual detection method for simply and quickly quantifying hexavalent chromium in water, belonging to the technical field of analytical chemistry. Background Art

[0002] Hexavalent chromium (Cr(VI)) is a chemical element with high oxidizing power, commonly used in industrial applications such as metal electroplating, dye manufacturing, and pigment production. It is strictly regulated due to its toxicity and carcinogenicity. Hexavalent chromium can enter the human body through inhalation, ingestion, or skin contact, which may cause respiratory problems, skin allergies, and other health problems, and is listed as a Class 1 carcinogen. With the continuous development of industry, the emission of hexavalent chromium in water is also increasing, which may cause certain harm to the growth of crops and other plants in the soil. If the water quality is not properly treated and ingested by the human body, it will continue to accumulate in the human body, causing great harm to the human respiratory system, nervous immune system, and gastrointestinal tract, and it also has a strong irritating effect on the skin and mucous membranes. Therefore, it is crucial to develop a simple, sensitive, and rapid method for detecting hexavalent chromium.

[0003] There are many traditional methods for detecting Cr(VI), including atomic absorption spectroscopy, chromatography, electrochemical method, colorimetry, chemiluminescence and fluorescence spectroscopy. These methods require the use of specialized equipment, and the operation process is time-consuming, complicated and expensive. Therefore, developing a method that can detect hexavalent chromium ions in real time and quantitatively in ordinary laboratories or even in the field is of great significance for environmental monitoring of hexavalent chromium ions. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a visual detection method for real-time quantitative hexavalent chromium in water in an ordinary laboratory or even in the field, which can overcome the problem that the existing image colorimetry method based on color recognition is cumbersome and time-consuming when detecting hexavalent chromium ions.

[0005] Technical solution: The present invention discloses a simple and rapid quantitative visual detection method for hexavalent chromium in water, which comprises using gold core silver shell nanoparticles (Au@Ag NPs) as a colorimetric probe to react with hexavalent chromium in the presence of a hydrobromic acid (HBr) solution, photographing the solution after the reaction by a photographing device, performing RGB recognition on each color image, and obtaining a blue channel intensity value I B , using the linear relationship with the hexavalent chromium concentration to quantify hexavalent chromium.

[0006] The simple and rapid quantitative visual detection method of hexavalent chromium in water of the present invention comprises the following steps:

[0007] (1) Preparation of Au@Ag NPs nanocolorimetric probe solution;

[0008] (2) Prepare hexavalent chromium standard solutions of different concentrations, mix the Au@Ag NPs nanocolorimetric probe solution with a hydrobromic acid solution to obtain a detection solution, add hexavalent chromium standard solutions of different concentrations to the detection solution for reaction, take color images of the reaction solution, perform RGB recognition on each color image, and obtain the blue channel intensity value I corresponding to the different concentrations of hexavalent chromium B， Using the blue channel intensity value I B A standard curve was constructed with different hexavalent chromium concentrations;

[0009] (3) Mix the Au@Ag NPs nanocolorimetric probe solution with the hydrobromic acid solution to obtain a detection solution, add the water to be tested into the detection solution to react, and obtain the blue channel intensity value I B , the concentration of hexavalent chromium in the water to be tested is obtained using the standard curve obtained in step (2).

[0010] Furthermore, in step (1), the method for preparing the Au@Ag NPs nanocolorimetric probe comprises the following steps:

[0011] Trisodium citrate was quickly added to the HAuCl4 solution, and the boiling reaction was continued under rapid stirring. After the solution was cooled to room temperature, ascorbic acid and AgNO3 were added to the solution in sequence. Stirring was continued, and the color of the solution gradually changed from wine red to orange, thus obtaining the Au@Ag NPs nanocolorimetric probe solution.

[0012] Further, in step (2), the concentration of the Au@Ag NPs nanocolorimetric probe solution is 0.2-0.5 mmol / L, the concentration of the hydrobromic acid solution is 0.05-0.15 mol / L, and the volume ratio of the Au@Ag NPs nanocolorimetric probe solution to the hydrobromic acid solution in the mixed solution is (500-1000):(10-50). Most preferably, the concentration of the Au@Ag NPs nanocolorimetric probe solution is 0.2 mmol / L, the concentration of the hydrobromic acid solution is 0.15 mol / L, and the volume ratio of the Au@Ag NPs nanocolorimetric probe solution to the hydrobromic acid solution in the mixed solution is 700:30.

[0013] Furthermore, in step (2), the concentrations of different hexavalent chromium standard solutions are 2.5 μmol / L, 5 μmol / L, 8 μmol / L, 10 μmol / L, 12 μmol / L, 15 μmol / L, 20 μmol / L, 25 μmol / L, 30 μmol / L, and 35 μmol / L, respectively.

[0014] Further, in step (2), the standard curve is y=4.209x+108.049, wherein x is the hexavalent chromium ion concentration (μM), and Y is the blue channel intensity value I B .

[0015] Furthermore, in step (2), the linear range of the standard curve is 2.5-35 μmol / L.

[0016] Furthermore, when the reaction liquid is photographed as a color image, the distance between the camera of the photographing device and the reaction liquid is 5-10 cm.

[0017] Furthermore, the color picking function in the smartphone camera is used to perform RGB recognition on each color image.

[0018] Furthermore, in step (2) and step (3), the reaction time is within 12 minutes.

[0019] Construction mechanism: Au@Ag NPs undergo a redox reaction with hexavalent chromium in the presence of hydrobromic acid (HBr) solution, resulting in the etching of Au@Ag NPs. Chromium changes from hexavalent to trivalent, and the silver shell of the core-shell Au@Ag NPs gradually thins until it is completely etched into gold nanospheres. During this process, the color of the Au@AgNPs solution changes vividly from orange to pink to lavender. The color change can be converted into RGB values ​​through the color block capture function in the smartphone camera, and a linear relationship is established with the hexavalent chromium concentration to achieve the quantification of hexavalent chromium.

[0020] The hexavalent chromium ions of the present invention can oxidatively etch Au@Ag NPs in the presence of HBr solution, causing the solution color to change from orange to light, then to pink and finally to lavender. The change in solution color is closely related to the concentration of hexavalent chromium ions. A smartphone is used to take a photo, identify and read the color of the solution, and finally convert it into the concentration of hexavalent chromium ions. The image obtained is represented by the blue channel intensity value I B A standard curve was constructed for the hexavalent chromium ion concentration, and the fitting correlation coefficient was very high. This detection method can effectively eliminate matrix interference and has good stability and precision.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0022] (1) The present invention is simple and convenient to implement visual detection of hexavalent chromium ions by mobile phone photography, and has low detection cost, and does not require professional and expensive detection equipment and well-trained operators.

[0023] (2) The present invention uses Au@Ag NPs as a colorimetric probe, which has a simple preparation process. Unlike most colorimetric sensors based on metal nanoparticles, which only show a single color change when responding to a target, its different color changes correspond to different target concentrations, so that the naked eye can easily determine the approximate concentration of the detection target, and it is regarded as an efficient colorimetric sensor in actual detection.

[0024] (3) The colorimetric probe provided by the present invention exhibits good selectivity and sensitivity for the detection of hexavalent chromium, is hardly interfered by other ions, and has a linear relationship with the hexavalent chromium concentration within a certain range. Therefore, the hexavalent chromium content can be detected in an aqueous environment, and has a very broad application prospect.

[0025] (4) The colorimetric probe provided by the present invention has a short detection time, the reaction can be completed quickly within 12 minutes, the operation is simple, and it can be operated at room temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of detection of hexavalent chromium ion standard solution in Example 14;

[0027] Figure 2 It is a line graph of the three sets of RGB values ​​and the hexavalent chromium concentration, and a constructed standard curve graph. The large graph is a line graph of the three sets of RGB values ​​and the hexavalent chromium concentration, and the small graph is a constructed standard curve. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0029] The following components of the detection solution include: Au@Ag NPs in an amount of 0.5-1.0 mL, HBr in an amount of 10-50 μL. The implementation conditions not specified are usually the conditions in routine experiments. In addition, it should be noted that the numerical values ​​given in the following examples are as accurate as possible, but due to the inevitable measurement errors and experimental operation problems of those skilled in the art, each number should be understood as an approximate number rather than an absolutely accurate value.

[0030] Example 1 Preparation of Au@Ag NPs as a colorimetric probe:

[0031] 1.5 mL of trisodium citrate was quickly added to 100 mL of HAuCl4 solution, and the boiling reaction was continued for 15 minutes under rapid stirring. After the solution was cooled to room temperature, 3 mL of 0.1 mol / L ascorbic acid solution and 3 mL of 1 mmol / L AgNO3 solution were added to the solution in sequence, and stirring was continued for 30 minutes. The color of the solution gradually changed from wine red to orange, and the Au@AgNPs colorimetric probe solution was obtained; the concentration of Au@Ag NPs was measured by UV-Vis spectroscopy, that is, UV-Vis absorbance combined with Beer-Lambert law to obtain the concentration of Au@Ag NPs colorimetric probe solution of 0.2 mmol / L.

[0032] Example 2

[0033] (1) Mix 0.5 mL of 0.2 mmol / L Au@Ag NPs colorimetric probe solution with 10 μL of 0.15 mol / L HBr solution, and add ultrapure water to obtain 1.1 mL of detection solution.

[0034] (2) Take 0.4 mL of the 20 μmol / L hexavalent chromium solution to be tested and mix it with the test solution, shake it well and let it stand for 10 minutes; a blank experiment is performed using ultrapure water instead of the hexavalent chromium solution;

[0035] Rough judgment: Visually, if the solution changes from orange to pink or purple, it indicates the presence of hexavalent chromium;

[0036] Accurate identification: Use the smartphone camera to take an image of the solution and then perform RGB identification to obtain the blue channel intensity value I B , compared with the blue channel intensity value I obtained in the blank experiment B0 By comparison, if the two values ​​change significantly, it indicates the presence of hexavalent chromium.

[0037] Embodiment 3-8

[0038] The detection process is the same as in Example 2, and the components of the detection solution are shown in Table 1.

[0039] Table 1 Components of the test solution of Examples 3-8

[0040] Components Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Au@Ag NPs 0.5mL 0.6mL 0.7mL 0.8mL 0.9mL 1.0mL HBr 20μL 20μL 20μL 20μL 20μL 20μL Ultrapure water margin margin margin margin margin margin

[0041] For the detection solution for hexavalent chromium of Examples 3-8, color change, I B The determination was made by means of intensity value change degree, color change time, etc. The determination results are shown in Table 2.

[0042] Table 2 Judgment results of Examples 3-8

[0043]

[0044] As can be seen from Table 2, in Examples 3-8, the solution color changes from orange to pink. B The intensity value changes are obvious, which can be used to determine the presence of hexavalent chromium. B The intensity value changes the most, the color change time is the shortest, and the effect is the best. It also shows that the amount of Au@Ag NPs has an impact on the detection effect.

[0045] Examples 9-13

[0046] The detection process is the same as in Example 2, and the components of the detection solution are shown in Table 3.

[0047] Table 3 Components of the test solution of Examples 9-13

[0048] Components Example 9 Example 10 Embodiment 11 Example 12 Example 13 Au@Ag NPs 0.7mL 0.7mL 0.7mL 0.7mL 0.7mL HBr 10μL 20μL 30μL 40μL 50μL Ultrapure water margin margin margin margin margin

[0049] For the detection solution for hexavalent chromium of Examples 9-13, color change, I B The intensity value change degree, color change time, etc. are used for judgment, and the judgment results are shown in Table 4.

[0050] Table 4 Judgment results of Examples 9-13

[0051]

[0052] As can be seen from Table 4, in Examples 9-13, the solution color changes from orange to pink. B The intensity value changes are obvious, which can be used to determine the presence of hexavalent chromium. B The intensity value changes the most and the color change time is the shortest, so it is judged to be the best effect. This also shows that the amount of HBr is crucial in the simple and rapid visual detection method of hexavalent chromium.

[0053] Comparative Examples 1-6

[0054] The detection process is the same as in Example 6, and the components of the detection solution are shown in Table 5.

[0055] Table 5 Detection liquid composition table of comparative examples 1-6

[0056] Components Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Au@Ag NPs 0.7mL 0 0.3mL 0.4mL 0.7mL 0.7mL HBr 0 20μL 20μL 20μL 60μL 70μL Ultrapure water margin margin margin margin margin margin

[0057] For the detection liquid for hexavalent chromium of Comparative Examples 1-6, the color change, I B The determination results are shown in Table 6.

[0058] Table 6 Determination results of comparative examples 1-6

[0059]

[0060] Combining Examples 2-13 and Comparative Example 1, it can be shown that the presence of HBr is crucial in the simple and rapid visual detection method of hexavalent chromium. Combining Examples 2-13 and Comparative Example 2, it can be shown that Au@Ag NPs plays a key role in the simple and rapid visual detection method of hexavalent chromium. Combining Example 2 and the above two comparative examples, it can be seen that Au@Ag NPs and HBr are indispensable in the simple and rapid visual detection method of hexavalent chromium.

[0061] Comparative Examples 5-8, before adding the hexavalent chromium solution, the detection solutions of Comparative Examples 3 and 4 were pink and light orange, respectively, indicating that the amount of HBr relative to Au@Ag NPs was excessive, making the system unstable. These two cases will affect the quantitative detection results of hexavalent chromium, and it is determined that the detection solution is invalid.

[0062] Compared with Examples 9-13, the colors of the detection solutions of Comparative Examples 5 and 6 were light orange and pink, respectively, at the beginning, indicating that excessive use of HBr would affect the stability of Au@Ag NPs, causing the detection solution to change color when the hexavalent chromium solution was not added, and it was judged that the detection solution was ineffective.

[0063] Based on Examples 3-13, from the color change time of the above examples, it can be considered that the detection solution of the present invention can quickly and accurately determine the presence of hexavalent chromium. The effective volume ratio of the detection solution components is (500-1000): (10-50), and the most preferred volume ratio is 700:30.

[0064] Example 14 Construction and detection limit of hexavalent chromium ion standard curve

[0065] (1) Prepare a 100 μM stock solution of hexavalent chromium ion standard substance with pure water. Take 1.25 mL, 2.5 mL, 4 mL, 5 mL, 6 mL, 7.5 mL, 10 mL, 12.5 mL, 15 mL, and 17.5 mL of the stock solution in a 50 mL volumetric flask, dilute to the mark with pure water, and prepare 2.5 μM, 5 μM, 8 μM, 10 μM, 12 μM, 15 μM, 20 μM, 25 μM, 30 μM, and 35 μM hexavalent chromium ion standard solutions, respectively.

[0066] (2) Mix 0.7 mL of 0.2 mmol / L Au@Ag NPs colorimetric probe solution with 30 μL of 0.15 mol / L HBr solution, and add ultrapure water to obtain 1.1 mL of detection solution.

[0067] (3) Take 0.4 mL of the hexavalent chromium ion standard solution of different concentrations to be tested and mix it with the test solution, shake it well and let it stand for 10 minutes; the blank experiment is carried out using ultrapure water instead of the hexavalent chromium solution; the test schematic diagram is shown in the figure below. Figure 1 shown.

[0068] (4) Use the smartphone camera to perform RGB recognition on the standard solutions of different colors and obtain the blue channel intensity value I B , I B0 and I B’ are the blue channel color intensity values ​​of the blank sample and the hexavalent chromium ion standard solutions with different concentrations, and the obtained blue channel intensity value I B The standard curve was constructed with the concentration of hexavalent chromium ions (μM) as the ordinate and the linear range, regression equation, correlation coefficient, detection limit and relative standard deviation as shown in Table 7. Figure 2 shown.

[0069] Table 7 Regression equation, linear range, correlation coefficient, detection limit and relative standard deviation for constructing standard curve

[0070] Detection target Regression equation Linear range Correlation coefficient Detection limit Relative standard deviation Hexavalent chromium ion y=4.209x+108.049 2.5-35μM 0.991 1.57μM 5.47％

[0071] In Table 7, x is the hexavalent chromium ion concentration, μM; Y is the blue channel intensity value, I B ; b: S / N ratio = 3;

[0072] From Table 7 and Figure 2 It can be seen from the results that the linear correlation coefficient of the standard curve constructed by the method provided by the present invention is very high.

[0073] Example 15 Experiment on the influence of interference of single metal ions

[0074] (1) Preparation of hexavalent chromium solutions with single metal ion interference: pipette 1 mL of each of a 1000 mg / L trivalent chromium standard solution, a total nickel standard solution, a total cadmium standard solution, a total lead standard solution, a total copper standard solution, a total zinc standard solution, a trivalent iron standard solution, and a total aluminum standard solution into a single 500 mL volumetric flask; dilute to the mark with the prepared 20 μM (1.04 mg / L) hexavalent chromium standard solution; thus, 8 groups of 20 μM hexavalent chromium solutions with single metal interference ions, each containing 2 mg / L trivalent chromium ions, total arsenic ions, total nickel ions, total cadmium ions, total lead ions, total copper ions, total zinc ions, and total aluminum ions, were obtained;

[0075] (2) Mix 0.7 mL of 0.2 mmol / L Au@Ag NPs colorimetric probe solution with 30 μL of 0.15 mol / L HBr solution, and add ultrapure water to obtain 1.1 mL of detection solution.

[0076] (3) Take 0.4 mL of 20 μM hexavalent chromium solution of 8 groups of single metal interfering ions to be tested and mix with the detection solution, shake well and let it stand for 10 minutes.

[0077] (4) Use a camera to take an image of the solution after the reaction, and use the color picking function of the smartphone camera to perform RGB recognition on each color image to obtain the blue channel intensity value I B According to the blue channel intensity value I B The content of hexavalent chromium ions in each group of samples was calculated using the standard curve established in Example 14. The results are shown in Table 8.

[0078] Table 8 8 groups of single metal ions interfere with the detection results of hexavalent chromium ion content in hexavalent chromium solution

[0079] Single metal ion interference sample Hexavalent chromium concentration (μM) Ion interference Trivalent chromium ion 19.534 2.33％ Arsenic ion 19.378 3.11％ Cadmium ions 18.733 6.34％ Lead ions 18.962 5.19％ Copper ions 19.293 3.54％ Zinc ion 19.267 3.67％ Nickel Ion 18.569 7.16％ Aluminum ion 19.479 2.61％

[0080] It can be seen from Table 8 above that the calculated interference ion impact meets the national requirement that the ion interference index requirement is ≤±15%, so the presence of the above-mentioned interfering ions will basically not interfere with the quantitative detection of hexavalent chromium.

[0081] Example 16 Interference Effect of Mixed Metal Ions

[0082] (1) Preparation of hexavalent chromium solution with mixed metal ion interference: pipette 100 μL of each of trivalent chromium standard solution, total nickel standard solution, total cadmium standard solution, total lead standard solution, total copper standard solution, total zinc standard solution, trivalent iron standard solution, and total aluminum standard solution, all with a concentration of 1000 mg / L, into a 50 mL volumetric flask; use the prepared 20 μM (1.04 mg / L) hexavalent chromium standard solution to make the volume constant to the mark; thus, a group of 20 μM hexavalent chromium solutions with mixed metal interfering ions, including trivalent chromium ions, total arsenic ions, total nickel ions, total cadmium ions, total lead ions, total copper ions, total zinc ions, and total aluminum ions, with a concentration of 2 mg / L, are obtained;

[0083] (2) Mix 0.7 mL of 0.2 mmol / L Au@Ag NPs colorimetric probe solution with 30 μL of 0.15 mol / L HBr solution, and add ultrapure water to obtain 1.1 mL of detection solution.

[0084] (3) Take 0.4 mL of the 20 μM hexavalent chromium solution of the mixed metal interfering ion to be tested and mix it with the test solution, shake it well and let it stand for 10 minutes. Repeat three times.

[0085] (4) Use a smartphone camera to take an image of the solution after the reaction, and use the color picking function of the smartphone camera to perform RGB recognition on each color image to obtain the blue channel intensity value I B According to the blue channel intensity value I B The content of hexavalent chromium ions in the sample was calculated using the standard curve. The results are shown in Table 9.

[0086] Table 9 Detection results of hexavalent chromium ion content in hexavalent chromium solution with interference from mixed metal ions

[0087] Mixed metal ion interference samples Hexavalent chromium concentration (μM) Ion interference 1 19.628 1.86％ 2 19.597 2.02％ 3 19.466 2.67％

[0088] The results in Table 9 further verify that the method of the present invention is suitable for detecting hexavalent chromium in water under the condition of coexistence of multiple mixed ions.

[0089] Example 17 Detection of hexavalent chromium content in environmental water samples and recovery rate experiment

[0090] (1) Collect water samples from a freshwater lake in Nanjing, Jiangsu Province, and filter them through a 0.22 μm aqueous filter membrane to remove particulate matter. Measure the samples as soon as possible after collection, but not more than 24 hours.

[0091] (2) Mix 7 mL of 0.2 mmol / L Au@Ag NPs colorimetric probe solution with 300 μL of 0.15 mol / L HBr solution, and add ultrapure water to obtain 1.1 mL of detection solution.

[0092] (3) Take 4 mL of the three groups of lake water samples to be tested and mix them with the test solution. Shake well and let it stand for 10 minutes.

[0093] (4) Use a smartphone camera to take an image of the water sample solution; perform RGB recognition on the lake water sample image to obtain the blue channel intensity value I B According to the blue channel intensity value I B The standard curve obtained in Example 14 was used to calculate the content of hexavalent chromium ions in the lake water sample, as shown in the initial detection values ​​in Table 10.

[0094] (5) 1 mL, 2 mL, and 2.5 mL of the 100 μM hexavalent chromium stock solution in Example 14 were added to three groups of 9 mL, 8 mL, and 7.5 mL of lake water samples after filtration to prepare spiked water samples, and the content of hexavalent chromium ions in the spiked water samples was re-determined. The matrix spiked recovery experiment was performed, and the results are shown in Table 8. Wherein, recovery rate = spiked detection value / (initial detection value+added value).

[0095] Table 10 Spiked test results

[0096] sample Initial detection value (μM) Addition value (μM) Spiked detection value (μM) Recovery rate (%) 1 7.96 10 17.35 96.60 2 7.07 20 27.14 100.26 3 7.98 25 32.16 97.51

[0097] The detection limit of hexavalent chromium in the method of the present invention can reach 1.57 μM, which meets the limit standard of drinking water, and has good linear correlation within the detection range of 2.5-35 μM.

[0098] The above embodiments are only optimized implementation methods of the present invention, which are used to illustrate the principles and effects of the present invention, but not to limit the present invention. It should be pointed out that, for those of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application.

Claims

1. A simple and rapid visual detection method for quantitative hexavalent chromium in water, characterized in that: The method comprises using gold core silver shell nanoparticles (Au@Ag NPs) as a colorimetric probe, reacting with hexavalent chromium in the presence of a hydrobromic acid (HBr) solution, photographing a color image of the solution after the reaction by a photographing device, performing RGB recognition on each color image, and obtaining a blue channel intensity value I B , using the linear relationship with the hexavalent chromium concentration to quantify hexavalent chromium.

2. The visual detection method for simple and rapid quantitative hexavalent chromium in water according to claim 1, characterized in that: The following steps are involved: (1) Preparation of Au@Ag NPs nanocolorimetric probe solution; (2) Prepare hexavalent chromium standard solutions of different concentrations, mix the Au@Ag NPs nanocolorimetric probe solution with a hydrobromic acid solution to obtain a detection solution, add hexavalent chromium standard solutions of different concentrations to the detection solution for reaction, take color images of the reaction solution, perform RGB recognition on each color image, and obtain the blue channel intensity value I corresponding to the different concentrations of hexavalent chromium B， Using the blue channel intensity value I B A standard curve was constructed with different hexavalent chromium concentrations; (3) Mix the Au@Ag NPs nanocolorimetric probe solution with the hydrobromic acid solution to obtain a detection solution, add the water to be tested into the detection solution to react, and obtain the blue channel intensity value I B , the concentration of hexavalent chromium in the water to be tested is obtained using the standard curve obtained in step (2).

3. The visual detection method for simple and rapid quantitative hexavalent chromium in water according to claim 2, characterized in that: The preparation method of Au@Ag NPs nanocolorimetric probe includes the following steps: Trisodium citrate was quickly added to the HAuCl4 solution, and the boiling reaction was continued under rapid stirring. After the solution was cooled to room temperature, ascorbic acid and AgNO3 were added to the solution in sequence. Stirring was continued, and the color of the solution gradually changed from wine red to orange, thus obtaining the Au@Ag NPs nanocolorimetric probe solution.

4. The visual detection method for simple and rapid quantitative hexavalent chromium in water according to claim 2, characterized in that: In step (2), the concentration of the Au@Ag NPs nanocolorimetric probe solution is 0.2-0.5 mmol / L, the concentration of the hydrobromic acid solution is 0.05-0.15 mol / L, and the volume ratio of the Au@Ag NPs nanocolorimetric probe solution to the hydrobromic acid solution in the mixed solution is (500-1000):(10-50).

5. The visual detection method for simple and rapid quantitative hexavalent chromium in water according to claim 2, characterized in that: In step (2), the concentrations of different hexavalent chromium standard solutions are 2.5 μmol / L, 5 μmol / L, 8 μmol / L, 10 μmol / L, 12 μmol / L, 15 μmol / L, 20 μmol / L, 25 μmol / L, 30 μmol / L, and 35 μmol / L, respectively.

6. The visual detection method for simple and rapid quantitative hexavalent chromium in water according to claim 2, characterized in that: In step (2), the standard curve is y=4.209x+108.049, where x is the hexavalent chromium ion concentration (μM) and Y is the blue channel intensity value I B .

7. The visual detection method for simple and rapid quantitative hexavalent chromium in water according to claim 2, characterized in that: The linear range of the standard curve was 2.5-35 μmol / L.

8. The method for simple and rapid quantitative visualization of hexavalent chromium in water according to claim 2, characterized in that: When the reaction solution is photographed for color development, the distance between the camera of the photographing device and the reaction solution is 5-10 cm.

9. The visual detection method for simple and rapid quantitative hexavalent chromium in water according to claim 2, characterized in that: The color extraction function in the smartphone camera is used to perform RGB recognition on each color image.

10. The method for simple and rapid quantitative visualization of hexavalent chromium in water according to claim 2, characterized in that: In step (2) and step (3), the reaction time is within 12 minutes.

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