A method for detecting gelatin content in copper electrolyte based on C3N4 fluorescent probe with energy band regulation

Abstract

The present invention belongs to the technical field of copper electrolyte additive detection and discloses a method for detecting gelatin content in copper electrolyte using a C3N4 fluorescent probe based on energy band regulation. Since the fluorescence intensity emitted by C-C3N4 is not quenched by the presence of divalent copper ions, when gelatin is present in a C-C3N4 solution, even a very small amount of gelatin will cause quenching of the fluorescence of the C-C3N4 solution, and the concentration of gelatin is linearly related to the change in the fluorescence intensity of C-C3N4. Using C3N4 (C-C3N4) after energy band regulation as a fluorescent probe and employing a fluorescence analysis method, when the C-C3N4 solution is irradiated with light of a wavelength of 320nm, the emission peak of C-C3N4 can be seen at 433nm, thereby achieving quantitative analysis of gelatin in the copper electrolyte. This detection method is simple and efficient, with high detection sensitivity and a low detection limit, and is of positive significance for effectively regulating the quality of copper foil.

Description

Technical Field

[0001] This invention belongs to the technical field of copper electrolyte additive detection technology. Specifically, it relates to a method for accurately analyzing and measuring gelatin concentration in copper electrolytes using gelatin as a copper electrolyte additive to effectively control the quality of electrolytic copper foil. In particular, it relates to a method for detecting gelatin content in copper electrolytes using band-modulated C3N4 (C-C3N4) as a fluorescent probe. The presence of gelatin quenches the fluorescence of C-C3N4, and the change in C-C3N4 fluorescence intensity is linearly correlated with the change in gelatin concentration. Background Art

[0002] In the manufacturing process of electrolytic copper foil, in order to obtain bright and ductile copper foil, it is necessary to add organic matter containing functional groups such as nitrogen and sulfur as additives to the copper electrodeposition solution. Gelatin not only contains functional groups such as nitrogen and sulfur, but also has carboxyl and hydroxyl groups that complex with copper ions. Therefore, gelatin is widely used as an additive in copper electrodeposition solutions.

[0003] Since gelatin is continuously consumed during the manufacturing process of electrolytic copper foil, the current electrolytic copper foil production process usually controls the gelatin concentration in the copper electrodeposition solution by converting the amount of gelatin added into the amount of electricity consumed. As the quality requirements for electrolytic copper foil continue to increase, the precise control of the gelatin concentration in the copper electrodeposition solution has become increasingly intense. Based on this, a series of analytical detection technologies such as gel chromatography, liquid chromatography, and electrochemical analysis have been established. However, these analytical methods require either sample pretreatment or complicated analytical steps, making it difficult to achieve rapid detection of gelatin in the copper electrodeposition solution and monitoring of the copper electrodeposition tank liquid during continuous production.

[0004] Among various nanomaterials, g-C3N4 is a metal-free polymer semiconductor material. It exhibits properties similar to those of graphene and is easy to prepare, thus attracting widespread attention. In particular, in the development of non-toxic fluorescence detection, it avoids secondary pollution during the preparation process. Many research reports in existing domestic and foreign literature use g-C3N4 as a fluorescent probe to achieve analytical detection. Although g-C3N4 is used as a fluorescent probe, in order to achieve high-sensitivity detection, it needs to be combined with other co-reactants to further increase the fluorescence intensity and achieve high-sensitivity detection. In addition, due to Cu 2+ The redox potential of g-C3N4 nanosheets is between the conduction band (CB) and valence band (VB). 2+ When mixed with g-C3N4 nanosheets, CB from g-C3N4 nanosheets to Cu 2+ The photoinduced electron transfer process leads to the fluorescence quenching of g-C3N4 nanosheets.

[0005] There are reports in the literature that extremely small amounts of Cu 2+ This can lead to the fluorescence quenching of the g-C3N4 nanosheet solution, which is not only due to the low fluorescence intensity of the g-C3N4 nanosheet solution, but also due to the 2+ The redox potential of g-C3N4 is just between the valence band and the conduction band, which causes the fluorescence quenching of g-C3N4. 2+ The presence of will undoubtedly greatly improve the selectivity and speed of gelatin analysis in copper electrolyte. Summary of the Invention

[0006] In view of the problems existing in the existing technology for detecting gelatin in copper electrolyte, the purpose of the present invention is to provide a method for detecting the gelatin content in copper electrolyte based on a C3N4 fluorescent probe with energy band regulation.

[0007] The present inventors surprisingly discovered that band-modulated C3N4 (C-C3N4), unlike conventional g-C3N4, exhibits extremely strong luminescence even in the presence of strong acidity and high copper ion concentrations. This undoubtedly lays the foundation for using C-C3N4 as a fluorescent probe to analyze and detect the presence of gelatin. Furthermore, when gelatin is present in a C-C3N4 solution, its fluorescence is quenched. Therefore, the present inventors successfully achieved rapid quantitative analysis of gelatin in copper electrolytes using C-C3N4 as a fluorescent probe.

[0008] The present invention first provides a preparation method of C3N4 (C-C3N4) based on energy band regulation, which adopts the condensation reaction of melamine and formaldehyde. The amount of formaldehyde used should not be too high. The mass volume ratio of melamine to formaldehyde is about 10g:1-1.5mL. Too much formaldehyde will affect the reaction between melamine and cyanuric acid. The melamine that undergoes condensation reaction is then reacted with cyanuric acid. The mass ratio of melamine to cyanuric acid is generally 1:1-1.2. According to this mass ratio, cyanuric acid is in excess. After the reaction, it can be removed by repeated washing with deionized water. The reaction product is calcined to obtain C-C3N4. Compared with g-C3N4, the prepared C-C3N4 has very strong fluorescence and is not affected by the presence of divalent copper ions. Compared with g-C3N4, C-C3N4 shows extremely strong fluorescence ( Figure 1 ), perhaps because the melamine after the condensation reaction with formaldehyde is combined with cyanuric acid, the calcined C-C3N4 contains a large number of carboxyl and carbonyl groups, which effectively regulates the energy levels of the valence band and conduction band of C3N4. The specific steps include the following:

[0009] (1) Melamine was dispersed in deionized water, and formaldehyde was added under stirring. The condensation reaction was carried out at room temperature for 2 h, which was recorded as solution A.

[0010] (2) Dissolve cyanuric acid in 80°C deionized water, referred to as solution B;

[0011] (3) Solution B was added to solution A, heated to 80 °C, stirred for 2 h, centrifuged, washed with deionized water at 80 °C, and the product was collected and redispersed in deionized water. The product was allowed to stand at room temperature for 12 h, and the supernatant was removed to obtain a flocculent precipitate. The product was freeze-dried for 48 h to obtain the C-C3N4 precursor.

[0012] (4) The C-C3N4 precursor was annealed in a tube furnace at 500℃-600℃ under nitrogen conditions for 2 hours to obtain the product C-C3N4.

[0013] Furthermore, in step (1), the mass volume ratio of melamine to formaldehyde is 10 g:1-1.5 mL; and the mass volume ratio of melamine to deionized water is 1 g:300 mL.

[0014] Furthermore, in step (2), the mass of cyanuric acid is 1-1.2 times the mass of melamine described in step (1); and the mass-to-volume ratio of cyanuric acid to deionized water is 1 g:300 mL.

[0015] The band-regulated C3N4 prepared by the present invention is 2+ In the presence of C3N4, no fluorescence quenching occurs, and the C3N4 can be used as a fluorescent probe for the detection of gelatin in copper electrolytes. The maximum excitation wavelength of the C3N4 regulated by the energy band is 320 nm, and the maximum emission wavelength is 433 nm.

[0016] The present invention also provides a method for detecting gelatin content in a copper electrolyte using the above-mentioned C-C3N4 as a fluorescent probe, comprising the following steps:

[0017] S1. Mix C-C3N4 with copper sulfate-sulfuric acid solution and fully disperse it by ultrasonication to obtain a 0.5 mg / ml C-C3N4 copper sulfate-sulfuric acid solution.

[0018] S2. Mix the C-C3N4 copper sulfate-sulfuric acid solution with the gelatin solution to prepare a series of gelatin standard solutions containing 0.05 mg / ml C-C3N4; detect the fluorescence intensity, plot the change in fluorescence intensity before and after the addition of gelatin versus the gelatin concentration, and obtain the corresponding linear regression equation.

[0019] S3. Mix the C-C3N4 copper sulfate-sulfuric acid solution with the copper electrolyte to be tested, and adjust the volume of the copper sulfate-sulfuric acid solution to obtain a mixed solution containing 0.05 mg / ml C-C3N4.

[0020] S4. Detect the fluorescence intensity of the mixed solution, and substitute the fluorescence intensity value into the linear regression equation obtained in step S2 to calculate the actual gelatin concentration in the copper electrolyte.

[0021] In the above technical solution, the copper sulfate-sulfuric acid solution is a mixed solution containing 150 g / L copper sulfate and 100 g / L sulfuric acid. The copper sulfate-sulfuric acid solution has copper ion and sulfuric acid concentrations similar to those of copper electrolytes used in the electrolytic copper foil industry.

[0022] In the above technical solution, the concentrations of gelatin in the gelatin standard solutions of a series of concentrations are 0, 1, 3, 5, 8 and 10 mg / L respectively.

[0023] In the above technical solution, the fluorescence intensity is measured using a fluorescence spectrophotometer with the excitation wavelength set at 320 nm and detected at 433 nm.

[0024] In the above technical solution, the volume ratio of C-C3N4 copper sulfate-sulfuric acid solution to the copper electrolyte to be tested is 1:2.

[0025] The beneficial effects of the present invention are as follows:

[0026] The fluorescence intensity of the band-regulated C-C3N4 prepared by the present invention is extremely high and is not quenched by the presence of copper ions.

[0027] The present invention uses band-regulated C-C3N4 as a fluorescent probe, and can analyze gelatin in copper electrodeposition solution without pretreatment. Due to the convenience of this analysis method, it is fully applicable to intermediate control analysis in the copper electrodeposition production process.

[0028] The gelatin detection method of the present invention has the advantages of rapid detection and high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The fluorescence emission peak λem = 433 nm and the excitation wavelength λex = 320 nm of 0.05 mg / mL g-C3N4 and 0.05 mg / mL C-C3N4 in 150 g / L copper sulfate and 100 g / L sulfuric acid solution.

[0030] Figure 2 The corresponding fluorescence intensity of the C-C3N4 fluorescent probe in copper sulfate-sulfuric acid solution with a concentration of 0.05 mg / ml and gelatin concentrations of (a) 0, (b) 1, (c) 3, (d) 5, (e) 8, and (f) 10 mg / L, respectively.

[0031] Figure 3 This is the relationship curve between the fluorescence intensity of C-C3N4 and the gelatin concentration. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to the following examples and in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following examples.

[0033] In the following specific examples, the method for detecting gelatin content in copper electrolyte based on band-regulated C3N4 fluorescent probe is as follows:

[0034] In the production process of electrolytic copper foil, the concentration of copper sulfate is generally 150 g / L and the concentration of sulfuric acid is about 100 g / L. Therefore, when preparing the standard solutions of C-C3N4 and gelatin in the present invention, a mixed solution of 150 g / L copper sulfate and 100 g / L sulfuric acid is used as the base solution, which is marked as copper sulfate-sulfuric acid solution.

[0035] (1) Prepare a 1000 mg / L gelatin solution in copper sulfate-sulfuric acid: Weigh 0.10 g of gelatin and dissolve it in a 100 mL volumetric flask with the copper sulfate-sulfuric acid solution. This will yield a gelatin solution with a gelatin concentration of 1000 mg / L. Because gelatin decomposes easily in acidic solutions, this gelatin solution must be prepared before analysis and should not be retained.

[0036] (2) Prepare a 0.5 mg / ml C-C3N4 copper sulfate-sulfuric acid solution of the fluorescent probe.

[0037] Take 5.0 mg of C-C3N4 and add it to a 10 ml volumetric flask, make up to volume with copper sulfate-sulfuric acid solution, and fully disperse it using ultrasound to obtain a 0.5 mg / ml C-C3N4 copper sulfate-sulfuric acid solution.

[0038] (3) Preparation of standard solution

[0039] Take 0, 10, 30, 50, 80 and 100 μl of 1000 mg / L gelatin copper sulfate-sulfuric acid solution respectively and place them in 10 ml volumetric flasks, take 1 ml of C-C3N4 copper sulfate-sulfuric acid solution and add it to the above volumetric flasks, and then adjust the volume with copper sulfate-sulfuric acid solution to obtain copper sulfate-sulfuric acid solutions with a C-C3N4 fluorescent probe concentration of 0.05 mg / ml and gelatin concentrations of 0, 1, 3, 5, 8 and 10 mg / L, respectively. These solutions are recorded as gelatin standard solutions.

[0040] (4) Draw a standard curve

[0041] The fluorescence intensity of the gelatin standard solution prepared in step (3) was measured at 433 nm using a fluorescence spectrophotometer with an excitation wavelength of 320 nm. The corresponding linear regression equation was obtained by plotting the change in fluorescence intensity before and after the addition of gelatin against the gelatin concentration.

[0042] (5) Actual sample testing

[0043] Place 1 ml of the C-C3N4 copper sulfate-sulfuric acid solution in a 10 ml volumetric flask. Add 2 ml of the actual copper electrolyte solution to the 10 ml volumetric flask, and then adjust to volume with the copper sulfate-sulfuric acid solution. Detect the fluorescence intensity according to step (4) above. Substitute the obtained fluorescence intensity value into the linear regression equation obtained in step (4) above to calculate the gelatin concentration in the actual electrolytic copper solution. Example 1

[0044] To prepare C-C3N4, 1g of melamine was weighed and added to 300ml of deionized water. 0.1ml of formaldehyde was added while stirring, and the condensation reaction was carried out at room temperature for 2h. 1g of cyanuric acid was dissolved in 300ml of deionized water at 80°C and added to the completed melamine solution. The temperature was raised to 80°C and stirred for 2h. The product was centrifuged and washed with 80°C deionized water to remove unreacted materials. The product was redispersed in deionized water and allowed to stand at room temperature for 12h. The supernatant was removed to obtain a flocculent precipitate. Finally, the precipitate was freeze-dried for 48h to obtain the C-C3N4 precursor. The product C-C3N4 was then annealed in a tube furnace at 500°C, 550°C, and 600°C under nitrogen for 2h.

[0045] Preparation of g-C3N4. 10 g of melamine was weighed and placed in a sealed porcelain crucible. The crucible was then placed in a high-temperature muffle furnace and heated to 550°C at a rate of 5°C / min and held at this temperature for 2 hours. After the crucible was allowed to cool naturally to ambient temperature, the resulting product was transferred to an agate mortar and finely ground. The resulting pale yellow powder is g-C3N4.

[0046] 5.0 mg of C-C3N4 powder prepared at different calcination temperatures was uniformly dispersed in a copper sulfate-sulfuric acid solution. The copper sulfate-sulfuric acid solution was fixed to volume to prepare a 0.5 mg / ml C-C3N4 copper sulfate-sulfuric acid solution. Using a fluorescence spectrophotometer, the excitation wavelength was set to 320 nm and the fluorescence intensity was detected at 433 nm. The fluorescence curve of C-C3N4 obtained by annealing at 550°C for 2 hours is shown in Figure 2. Figure 1 As a comparison, this example also prepared g-C3N4 and tested its fluorescence intensity. Figure 1 As can be seen from the figure, the C-C3N4 prepared by the present invention is not affected by copper ions and shows extremely strong luminescence intensity in the presence of strong acidity and high concentration of copper ions. Example 2

[0047] The C-C3N4 obtained by annealing at 550°C for 2h in Example 1 was used as a fluorescent probe to analyze and detect the concentration of gelatin in the copper electrolyte. The specific steps are as follows:

[0048] (1) Preparation of copper sulfate and sulfuric acid solutions with different gelatin concentrations

[0049] Weigh 0.10 g of gelatin and dissolve it in a 100 mL volumetric flask with a copper sulfate-sulfuric acid solution to obtain a gelatin solution with a gelatin concentration of 1000 mg / L. Dilute this solution with the copper sulfate and sulfuric acid solutions to obtain solutions with gelatin concentrations ranging from 1 to 10 mg / L.

[0050] (2) Preparation of 0.5 mg / ml fluorescent probe C-C3N4 copper sulfate-sulfuric acid solution

[0051] Take 5.0 mg of C-C3N4 and add it to a 10 ml volumetric flask, make up to volume with copper sulfate-sulfuric acid solution, and fully disperse it using ultrasound to obtain a 0.5 mg / ml C-C3N4 copper sulfate-sulfuric acid solution.

[0052] (3) Preparation of standard solution

[0053] Take 0, 10, 30, 50, 80 and 100 μl of the 1000 mg / L gelatin copper sulfate-sulfuric acid solution in step (1) and place them in 10 ml volumetric flasks, take 1 ml of C-C3N4 copper sulfate-sulfuric acid solution and add it to the above volumetric flasks, and then adjust the volume with copper sulfate-sulfuric acid solution to obtain copper sulfate-sulfuric acid solutions with a C-C3N4 fluorescent probe concentration of 0.05 mg / ml and gelatin concentrations of 0, 1, 3, 5, 8 and 10 mg / L, respectively.

[0054] (4) Drawing of standard curve

[0055] Use a fluorescence spectrophotometer, set the excitation wavelength to 320nm, and detect the fluorescence intensity of the standard curve solution prepared in step (3) at 433nm ( Figure 2 By recording the curve of the fluorescence intensity change before and after adding gelatin and the gelatin concentration, the corresponding linear regression equation was obtained ( Figure 3 ). ΔF = 776.6842 + 520.9474C, R 2 = 0.99599. The linear range of gelatin detection was 1-10 mg / L, and the minimum detection limit was 0.33 mg / L.

[0056] (5) Actual sample testing

[0057] 1 ml of the C-C3N4 copper sulfate-sulfuric acid solution was placed in a 10 ml volumetric flask. 2 ml of the actual copper electrodeposition solution (solutions from five different copper electrolytic cells at Company M) was added to the 10 ml volumetric flask, and the volume was then fixed with the copper sulfate-sulfuric acid solution. Following step (4) above, the obtained fluorescence intensity value was substituted into the linear regression equation in step (4) above to calculate the gelatin concentration in the actual electrolytic copper solution. The gelatin concentrations of the copper electrolytic cell solutions are listed in Table 1.

[0058] Comparative Example 1

[0059] A specific comparative example of the detection of gelatin in a copper electrolyte using the g-C3N4 prepared in Example 1 as a fluorescent probe was performed. The analysis method was the same as in Example 1, using the electrolyte solution #1 from Example 1 as the analysis sample. The results are listed in Table 1.

[0060] Comparative Example 2

[0061] Preparation of melamine g-C3N4 based on condensation reaction with formaldehyde. Weigh 1g of melamine and add it to 300ml of deionized water. Add 0.1ml of formaldehyde under stirring and carry out condensation reaction at room temperature for 2h. Place it in a sealed porcelain crucible. Subsequently, place the crucible in a high-temperature muffle furnace, heat it to 550℃ at a heating rate of 5℃ / min and maintain this temperature for 2h. After the crucible is naturally cooled to ambient temperature, the resulting product is transferred to an agate mortar for fine grinding. The light yellow powder finally obtained is g-C3N4. The analysis method is the same as in Example 1, and the analysis sample used is the electrolytic cell liquid #2 in Example 2. The results are listed in Table 1.

[0062] Table 1 Determination of gelatin in copper electrolytic cell solution (n=3)

[0063]

[0064] As shown in Table 1, samples were tested three times in parallel, with a relative standard deviation of less than 3% and spiked recoveries ranging from 98.2% to 102%. These results demonstrate that the analytical method of the present invention is well suited for rapid detection of gelatin concentration in copper electrolytes, enabling effective quality control of electrolytic copper foil.

[0065] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art may make corresponding changes without departing from the scope of the present invention. Therefore, all technical solutions formed by equivalent replacements or equivalent modifications fall within the scope of protection of the present invention.

Claims

1. A fluorescent probe for detecting gelatin in copper electrolyte, characterized in that: The fluorescent probe is band-regulated C3N4, expressed as C-C3N4; the C-C3N4 is in Cu 2+ No fluorescence quenching occurs in the presence of The method for preparing the fluorescent probe for detecting gelatin in copper electrolyte comprises the following steps: (1) Melamine was dispersed in deionized water, and formaldehyde was added under stirring. The condensation reaction was carried out at room temperature for 2 h, which was recorded as solution A. (2) Dissolve cyanuric acid in 80°C deionized water, referred to as solution B; (3) Solution B was added to solution A, heated to 80 °C, stirred for 2 h, centrifuged, washed with deionized water at 80 °C, and the product was collected and redispersed in deionized water. The product was allowed to stand at room temperature for 12 h, and the supernatant was removed to obtain a flocculent precipitate. The product was freeze-dried for 48 h to obtain the C-C3N4 precursor. (4) The C-C3N4 precursor was annealed in a tube furnace at 500℃-600℃ under nitrogen conditions for 2 hours to obtain the product C-C3N4.

2. The fluorescent probe for detecting gelatin in copper electrolyte according to claim 1, characterized in that The maximum excitation wavelength of the C-C3N4 is 320 nm, and the maximum emission wavelength is 433 nm.

3. The method for preparing a fluorescent probe for detecting gelatin in a copper electrolyte according to claim 1 or 2, characterized in that: The steps include: (1) Melamine was dispersed in deionized water, and formaldehyde was added under stirring. The condensation reaction was carried out at room temperature for 2 h, which was recorded as solution A. (2) Dissolve cyanuric acid in 80°C deionized water, referred to as solution B; (3) Solution B was added to solution A, heated to 80 °C, stirred for 2 h, centrifuged, washed with deionized water at 80 °C, and the product was collected and redispersed in deionized water. The product was allowed to stand at room temperature for 12 h, and the supernatant was removed to obtain a flocculent precipitate. The product was freeze-dried for 48 h to obtain the C-C3N4 precursor. (4) The C-C3N4 precursor was annealed in a tube furnace at 500℃-600℃ under nitrogen conditions for 2 hours to obtain the product C-C3N4.

4. The method for preparing a fluorescent probe for detecting gelatin in a copper electrolyte according to claim 3, wherein: In the step (1), the mass volume ratio of melamine to formaldehyde is 10 g:1-1.5 mL; the mass volume ratio of melamine to deionized water is 1 g:300 mL.

5. The method for preparing a fluorescent probe for detecting gelatin in a copper electrolyte according to claim 3, wherein: In step (2), the mass of cyanuric acid is 1-1.2 times the mass of melamine in step (1); and the mass-to-volume ratio of cyanuric acid to deionized water is 1 g:300 mL.

6. The method for detecting gelatin content in copper electrolyte using the fluorescent probe according to claim 1 or 2, characterized in that: The steps include: S1. Mix C-C3N4 with copper sulfate-sulfuric acid solution and fully disperse it with ultrasonic wave to obtain 0.5 mg / ml C-C3N4 copper sulfate-sulfuric acid solution; S2. Mixing the C-C3N4 copper sulfate-sulfuric acid solution with the gelatin solution to prepare a series of gelatin standard solutions containing 0.05 mg / ml C-C3N4; Detect the fluorescence intensity, plot the change in fluorescence intensity before and after adding gelatin and the gelatin concentration, and obtain the corresponding linear regression equation; S3, mixing the C-C3N4 copper sulfate-sulfuric acid solution with the copper electrolyte to be tested, and adjusting the volume of the copper sulfate-sulfuric acid solution to obtain a mixed solution containing 0.05 mg / ml C-C3N4; S4. Detect the fluorescence intensity of the mixed solution, and substitute the fluorescence intensity value into the linear regression equation obtained in step S2 to calculate the actual gelatin concentration in the copper electrolyte.

7. The method for detecting gelatin content in copper electrolyte using a fluorescent probe according to claim 6, characterized in that: The copper sulfate-sulfuric acid solution is a mixed solution containing 150 g / L copper sulfate and 100 g / L sulfuric acid.

8. The method for detecting gelatin content in copper electrolyte using a fluorescent probe according to claim 6, characterized in that: The concentrations of gelatin in the gelatin standard solutions of the series of concentrations are 0, 1, 3, 5, 8 and 10 mg / L respectively.

9. The method for detecting gelatin content in copper electrolyte using a fluorescent probe according to claim 6, characterized in that: The fluorescence intensity was measured using a fluorescence spectrophotometer with an excitation wavelength set at 320 nm and detected at 433 nm.

10. The method for detecting gelatin content in copper electrolyte using a fluorescent probe according to claim 6, characterized in that: The volume ratio of C-C3N4 copper sulfate-sulfuric acid solution to the copper electrolyte to be tested is 1:2.

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