Copper-iron bimetallic oxide, preparation method and application in hexavalent chromium detection

Abstract

The present invention discloses the use of a copper-iron bimetallic oxide in the colorimetric detection of hexavalent chromium. The present invention utilizes a coprecipitation method to synthesize the copper-iron bimetallic oxide in a single step. This inexpensive and readily available copper-iron bimetallic oxide can highly selectively catalyze the Cr(VI) and 3,3',5,5'-tetramethylbenzidine (TMB) system to produce a visual blue color. Within a certain concentration range, the depth of the blue color is proportional to the Cr(VI) concentration, thus establishing a new colorimetric method for the detection of Cr(VI). In this system, the linear range for Cr(VI) detection is 0.3 μmol / L to 26 μmol / L, with a detection limit of 0.17 μmol / L. The system can be used for the detection and analysis of Cr(VI) in the environment and food.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical analysis and detection, and particularly relates to a copper-iron bimetallic oxide, a preparation method and application of the copper-iron bimetallic oxide in colorimetric detection of hexavalent chromium. Background Art

[0002] Hexavalent chromium is a highly oxidizing, mutagenic, and carcinogenic heavy metal that poses a persistent environmental hazard. It is generally believed to be 100 times more toxic than trivalent chromium. Regulations stipulate that the maximum permissible discharge of hexavalent chromium in industrial wastewater is 0.5 mg / L, and the maximum level of hexavalent chromium in drinking water cannot exceed 0.05 mg / L. Excessive discharge of hexavalent chromium inevitably causes serious chromium pollution in the environment, endangering human and biological health. Therefore, convenient and rapid detection of hexavalent chromium in water is not only an urgent requirement in the public safety sector, but also crucial for environmental protection. Compared with conventional detection methods, colorimetric detection of hexavalent chromium offers advantages such as intuitiveness, rapid identification speed, and low cost. Therefore, designing a colorimetric system for rapid detection of the heavy metal hexavalent chromium is of great significance.

[0003] Copper oxide-based nanomaterials have advantages such as easy synthesis, low cost, and good biocompatibility. Therefore, they have a wide range of applications in catalysis, adsorption, and enzyme mimicry. As an enzyme mimic, they can be used for the detection of H2O2, glucose, and other substances. However, the catalytic activity of copper oxide is relatively low, so improving its catalytic activity has become an important research topic, and metal doping is one method to enhance its catalytic activity. Summary of the Invention

[0004] The present invention aims to overcome the shortcomings of the prior art by providing a copper-iron bimetallic oxide that is inexpensive, readily available, and suitable for large-scale production. The present invention uses the inexpensive and readily available copper-iron bimetallic oxide as a catalyst and TMB as a probe. In the presence of Cr(VI), TMB is oxidized to a blue oxidation product, TMBox, with the intensity of the blue color proportional to the Cr(VI) concentration. Based on this, a colorimetric method for the detection of hexavalent chromium (Cr(VI)) has been established. The copper-iron bimetallic oxide is used for the colorimetric detection of Cr(VI), with a linear range of 0.3 to 26 μmol / L and a detection limit of 0.17 μmol / L.

[0005] The present invention also provides a preparation method of the copper-iron bimetallic oxide and application of the copper-iron bimetallic oxide in colorimetric detection of hexavalent chromium (Cr(VI)).

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a copper-iron bimetallic oxide comprises synthesizing a copper bimetallic oxide in one step by coprecipitation of a certain proportion of a divalent copper salt and a trivalent iron salt. Specifically, the method comprises preparing a mixed aqueous solution containing a soluble divalent copper salt and a soluble trivalent iron salt, adjusting the pH to 8-10 (weakly alkaline), stirring the solution for reaction for 15-50 minutes, then placing the solution in a water bath at 75-95°C for reaction for 15-24 hours, cooling the solution to room temperature, and subjecting the solution to solid-liquid separation, washing, and drying.

[0008] Furthermore, the soluble copper salt may be one or more of copper chloride, copper sulfate and copper nitrate; the soluble iron salt may be one or more of iron chloride, iron sulfate and iron nitrate.

[0009] Furthermore, in the mixed aqueous solution, Cu 2+ and Fe 3+ The molar ratio is preferably 8 to 1:1.

[0010] Furthermore, a 0.4-0.6 mol / L sodium hydroxide aqueous solution may be used to adjust the pH to 8-10.

[0011] The present invention provides a copper-iron bimetallic oxide prepared by the above-mentioned preparation method.

[0012] The present invention also provides the use of the copper-iron bimetallic oxide in detecting hexavalent chromium Cr(VI) by colorimetry.

[0013] An application of the copper-iron bimetallic oxide in the colorimetric detection of hexavalent chromium Cr(VI) comprises the following specific steps:

[0014] 1) In a buffer solution of pH 3 to 4, copper-iron bimetallic oxide, 3,3',5,5'-tetramethylbenzidine (TMB) and a series of different concentrations of Cr 6+ , incubate at room temperature for 5-20 min, and measure the absorbance of the system;

[0015] 2) Cr 6+ The concentration is the horizontal axis and the absorbance is the vertical axis. The standard curve is drawn and the linear equation is calculated.

[0016] 3) Determine the Cr content using the same method as step 1) 6+ The absorbance of the sample system is substituted into the linear equation to calculate the Cr content in the sample. 6+ content.

[0017] Furthermore, the buffer solution may be an acetic acid-sodium acetate buffer solution, or a phosphate buffer solution.

[0018] Furthermore, the concentration of the copper-iron bimetallic oxide added is preferably 10-35 mg / L, and the concentration of 3,3',5,5'-tetramethylbenzidine (TMB) added is preferably 0.4-1.0 mmol / L.

[0019] Furthermore, Cr 6+ The linear detection range was 0.3-26 μmol / L, and the detection limit was 0.17 μmol / L.

[0020] This invention uses a coprecipitation method to synthesize iron-doped copper-iron oxide. Under its catalysis, dichromate oxidizes TMB to produce TMBox, a blue oxide visible to the naked eye. The absorbance of the system is proportional to the hexavalent chromium content, thus establishing a new colorimetric method for the detection of hexavalent chromium. This system has a wide linear range for Cr(VI) detection, reaching 0.3 μmol / L to 26 μmol / L, and a detection limit of 0.17 μmol / L for Cr(VI). Compared with existing technologies, this invention has the following advantages:

[0021] 1) The copper iron oxide catalyst used in the colorimetric detection of Cr(VI) by the present invention is cheap, readily available, easy to synthesize on a large scale, and environmentally friendly;

[0022] 2) The Cr(VI) detection system designed in the present invention can detect the Cr(VI) content in the environment and food with high selectivity, high sensitivity, wide range and visualization. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the EDS layered diagram of the copper-iron bimetallic oxide prepared in Example 1;

[0024] Figure 2 The XRD pattern of the copper-iron bimetallic oxide prepared in Example 1 is given;

[0025] Figure 3 The graph shows the trend of absorbance variation with Cr(VI) concentration in the detection system composed of Cr(VI), copper iron oxide and TMB, and the standard working curve.

[0026] Figure 4 is the effect of other coexisting ions on the absorbance of the system. DETAILED DESCRIPTION

[0027] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0028] In the following examples, unless otherwise specified, all raw materials used are common commercial products that can be directly purchased in the art. Room temperature refers to 25±5°C.

[0029] Example 1

[0030] A method for preparing a copper-iron bimetallic oxide catalyst is disclosed, wherein the catalyst is synthesized in one step by coprecipitation of a certain proportion of a divalent copper salt and a trivalent iron salt; the details are as follows:

[0031] Weigh 0.96 g of CuCl₂·2H₂O and 0.76 g of FeCl₃·6H₂O in a molar ratio of 2:1 and dissolve them in 75 mL of ultrapure water. After thorough dissolution and mixing, adjust the pH to a weakly alkaline range (pH = 9) with 0.5 mol / L aqueous NaOH. Stir the mixture at room temperature for 30 min. Then, crystallize the mixture in an 85°C water bath for 18 h. Cool to room temperature. Centrifuge, rinse with ultrapure water until neutral, dry overnight at approximately 90°C, and grind to obtain the copper-iron bimetallic oxide catalyst for later use.

[0032] Figure 1 The EDS layer diagram of the copper-iron bimetallic oxide prepared in this example is given; Figure 2 The XRD pattern of the copper-iron bimetallic oxide prepared in this example is given; Figure 1 and Figure 2 It can be confirmed that the prepared material is a copper-iron bimetallic oxide in which copper and iron elements are evenly distributed.

[0033] Example 2

[0034] The specific steps of the method for determining the application of the copper-iron bimetallic oxide in the colorimetric detection of hexavalent chromium Cr(VI) are as follows:

[0035] 1) In an acetic acid-sodium acetate buffer solution at pH 3 to 4, add copper-iron bimetallic oxide, 3,3',5,5'-tetramethylbenzidine (TMB) and Cr 6+ , Cr in the system 6+ The concentrations of the solution were 0.05, 0.1, 0.5, 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, and 28 μmol / L, respectively. The mixture was shaken evenly and incubated at room temperature for 10 min. The absorbance of the system was measured (the absorbance values at 652 nm and 750 nm of the system were measured respectively, and the absorbance at 750 nm was subtracted from the absorbance at 652 nm, i.e., A 652 nm -A 750 nm ∆A was calculated); the concentration of copper-iron bimetallic oxide added was 20 mg / L, and the concentration of TMB added was 0.5 mmol / L;

[0036] 2) Draw the working curve: Cr 6+ With concentration as the horizontal axis and absorbance ∆A as the vertical axis, draw a standard curve and obtain a linear equation. Figure 3 ;

[0037] 3) Detection of Cr(VI) content in the sample: Use the same method as step 1) to determine the Cr content. 6+ The absorbance of the sample system is substituted into the linear equation to calculate the Cr content in the sample. 6+ content.

[0038] Figure 3 The following is a graph and standard curve showing the change trend of absorbance with Cr(VI) concentration in the detection system composed of Cr(VI), copper iron oxide and TMB. Figure 3 It can be seen that the absorbance of the system increases with Cr 6+ The detection range of this method is relatively wide, ranging from 0.3 to 26 μmol / L. The detection limit of this method is calculated to be 0.17 μmol / L using LOD = 3σ / slope.

[0039] Selective testing

[0040] Figure 4 For other coexisting ions (Fe 3+ 、Cu 2+ 、Co 2+ 、Hg 2+ , Pb 2+ 、Zn 2+ 、Mn 2+ Mg 2+ 、Ba 2+ 、Al 3+ 、Ni 2+ 、Na + , K + 、Ag + , Ca 2+ 、Cd 2+ NH4 + , I - 、SO3 2- Br - 、NO3 - 、SO4 2- 、HCO3 - PO4 3- 、H2PO4 - The absorbance of each system when the molar concentration of the coexisting ions is 40 μM and the molar concentration of the coexisting ions is four times that of Cr(VI).

[0041] Depend on Figure 4 It can be seen that only Cr(VI) greatly enhances the absorbance of the system, while other ions have no enhancing effect on the absorbance of the system. Therefore, the system has high selectivity for the detection of Cr(VI).

[0042] Accuracy test

[0043] A sample with a known hexavalent chromium concentration of 20.00 μmol / L was tested using the national standard GB 7467-87 (Water quality - Determination of hexavalent chromium - Diphenylcarbazide spectrophotometric method) and the method described in Example 2 of the present invention. The hexavalent chromium concentration results are shown in the following table.

[0044]

[0045] The results in the table above demonstrate that the measurement error of the present method (2.30%) is smaller than the 7.65% error of the GB 7467-87 method. Compared to the hexavalent chromium concentration of 18.47 μmol / L determined by the GB 7467-87 method, the hexavalent chromium concentration of 19.54 μmol / L measured by the present method is more accurate and closer to the true concentration of 20.00 μmol / L.

[0046] Repeatability test

[0047] The method described in Example 2 of this method was used to detect samples with hexavalent chromium concentrations of 12.00 μmol / L and 4.00 μmol / L, respectively. The measurements were repeated three times and the average value was taken. The measurement results are shown in the table below.

[0048] From the results in the above table, it can be seen that the measurement error of the method of the present invention is between 2% and 3%. The hexavalent chromium concentration measured by the measurement method is accurate, close to the actual concentration, and has good repeatability.

Claims

1. An application of a copper-iron bimetallic oxide in detecting hexavalent chromium, characterized in that: Under the catalysis of the copper-iron bimetallic oxide, dichromate oxidizes TMB to produce a blue oxide TMBox visible to the naked eye, and the absorbance of the system is proportional to the content of hexavalent chromium; The copper-iron bimetallic oxide is prepared by the following steps: Prepare a mixed aqueous solution containing soluble copper salt and soluble iron salt, then adjust the pH to 8-10, stir and react for 15-50 minutes, then place in a 75-95°C water bath to react for 15-24 hours, cool to room temperature, separate the solid and liquid, wash, and dry to obtain the product.

2. The use of the copper-iron bimetallic oxide in detecting hexavalent chromium according to claim 1, characterized in that: The soluble copper salt is one or more of copper chloride, copper sulfate and copper nitrate; the soluble iron salt is one or more of iron chloride, iron sulfate and iron nitrate.

3. The use of the copper-iron bimetallic oxide in detecting hexavalent chromium according to claim 2, characterized in that: In the mixed aqueous solution, Cu 2+ and Fe 3+ The molar ratio is 8~1:

1.

4. The use of the copper-iron bimetallic oxide in detecting hexavalent chromium according to claim 1, characterized in that: A 0.4-0.6 mol / L sodium hydroxide aqueous solution is used to adjust the pH to 8-10.

5. The use of the copper-iron bimetallic oxide in detecting hexavalent chromium according to claim 1, characterized in that: Here are the steps: 1) In a buffer solution of pH 3 to 4, copper-iron bimetallic oxide, 3,3',5,5'-tetramethylbenzidine and a series of different concentrations of Cr 6+ , incubate at room temperature for 5-20 min, and measure the absorbance of the system; 2) Cr 6+ The concentration is the horizontal axis and the absorbance is the vertical axis. The standard curve is drawn and the linear equation is calculated. 3) Determine the Cr content using the same method as step 1) 6+ The absorbance of the sample system is substituted into the linear equation to calculate the Cr content in the sample. 6+ content.

6. The use of the copper-iron bimetallic oxide in detecting hexavalent chromium according to claim 5, characterized in that: The buffer solution is an acetic acid-sodium acetate buffer solution or a phosphate buffer solution.

7. The use of the copper-iron bimetallic oxide in detecting hexavalent chromium according to claim 5, characterized in that: The concentration of copper-iron bimetallic oxide added is 10-35 mg / L, and the concentration of 3,3',5,5'-tetramethylbenzidine added is 0.4-1.0 mmol / L.

8. The use of the copper-iron bimetallic oxide in detecting hexavalent chromium according to claim 5, characterized in that: Cr 6+ The linear detection range was 0.3-26 μmol / L.

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