A method for the preparation of trivalent cobalt and the determination of the second-order reaction rate constant of reactants

Abstract

The present invention discloses a method for preparing trivalent cobalt. The method comprises the following steps: Prepare a 10 mL solution containing 0.1 - 0.15 M CoSO4 and 5 M H2SO4, and place it in a glass bottle; Add a stirring rotor, place it on a magnetic stirrer under a constant temperature ice bath at 0 °C and mix for 10 minutes, and then start electrolysis for 10 minutes; After the electrolysis is completed, a dark blue-green Co(III) stock solution is obtained, and then it is immediately stored in a refrigerator at -20 °C. The beneficial effects achieved by the present invention are that the preparation of trivalent cobalt and the reaction system with reactants are simple, the interference of generating other secondary active substances can be effectively excluded, the detection process is simple, the detection result is accurate, at the same time, the detection cost is low and the precision is high, which has important value for the research of high-valence transition metals.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of trivalent cobalt, and specifically provides a method for the preparation of trivalent cobalt and the determination of the second-order reaction rate constant of reactants. Background Art

[0002] In recent years, persulfate has become an emerging water treatment agent and is currently a research hotspot. Persulfates include: peroxymonosulfate (PMS) and persulfate (PDS). PMS and PDS belong to inorganic peroxides. The structures of PMS and PDS are similar to that of H2O2. Compared with PDS and H2O2, PMS has an asymmetric structure. Therefore, its stability is less than the former two, and it shows good effects in the catalytic process. Therefore, due to its special properties, PMS has become the most studied peroxide in the current water treatment field.

[0003] Transition metal ions can activate PMS at room temperature to generate sulfate radicals (SO4 ·- ) and trivalent cobalt (Co(III)). Among the commonly used transition metals, Co 2+ has the highest efficiency in catalyzing and activating PMS compared with other transition metal ions. The main reaction formulas for the activation of persulfate by transition metals are as follows:

[0004] Co 2+ +HSO5 - →Co 3+ +SO4 ·- +OH - (1)

[0005] Co 3+ +HSO5 - →Co 2+ +SO5 ·- +H + (2)

[0006] Co 2+ +SO4 ·- →Co 3+ +SO4 2 (3). Summary of the Invention

[0007] The purpose of the present invention is to provide a method for the preparation of trivalent cobalt and the determination of the second-order reaction rate constant of reactants.

[0008] To solve the above technical problems, the present invention provides the following technical solutions:

[0009] A method for the preparation of trivalent cobalt, the method comprising the following steps:

[0010] S1 Prepare a 10 mL solution containing 0.1 - 0.15 M CoSO4 and 5 M H2SO4, and place it in a glass bottle;

[0011] S2 Add a magnetic stirring rotor, place it on a magnetic stirrer in a constant temperature ice bath at 0 °C and mix for 10 minutes, then start electrolysis for 10 minutes;

[0012] S3 After the electrolysis is completed, a dark blue - green Co(III) stock solution is obtained, and then it is immediately placed in a refrigerator at -20 °C for storage.

[0013] It should be noted that during electrolysis, both the anode and the cathode are platinum plates with dimensions of 10 × 10 × 0.2 mm, which are fixed in parallel on the reactor cover with a 1 cm interval in the middle; the electric field is provided by a DC power supply with a voltage of 5.0 V.

[0014] Based on the trivalent cobalt obtained by the present invention, the present invention also provides a method for measuring the second - order reaction rate constant between trivalent cobalt and reactants. The measurement method includes calibrating the concentration of the Co(III) stock solution by the traditional iodide ion colorimetric method, setting different dosages of Co(III) such that it is more than 25 times the concentration of the reactant to ensure that the pseudo - first - order reaction rate constant of the reactant degradation can be fitted, adjusting the pH to 2 with sulfuric acid; finally, calculating the second - order reaction rate constant through the second - order reaction rate constant between the reactant and Co(III).

[0015] It should be noted that the formula for the second - order reaction rate constant is:

[0016] - ln ([P] / [P]0) = k obs t (I)

[0017] k obs = k Co (III)-P [Co(III)] (2)

[0018] Through formula (1), plot -ln([P] / [P]0) as the ordinate and t as the abscissa, and the slope obtained is k obs , and then through formula (2), plot k obs as the ordinate and [Co(III)]0 as the abscissa, and the slope obtained is k Co(III)-P , which is the second - order reaction rate constant between the reactant and Co(III).

[0019] The beneficial effects achieved by the present invention are as follows: the preparation of trivalent cobalt and the reaction system with reactants are simple, which can effectively exclude the interference of the formation of other secondary active substances, the detection process is simple, the detection results are accurate, and at the same time, the detection cost is low and the precision is high, which has important value for the research of high - valence transition metals. Description of the Drawings

[0020] Figure 1 Absorption spectrum of prepared trivalent cobalt at a wavelength of 300 - 800 nm under ultraviolet light

[0021] Figure 2 Degradation kinetics of carbamazepine by trivalent cobalt, where CBZ represents carbamazepine

[0022] Figure 3 Fitting of the second - order reaction rate constant between trivalent cobalt and carbamazepine

[0023] Figure 4 Degradation kinetics of chloramphenicol by trivalent cobalt, where CAP represents chloramphenicol

[0024] Figure 5 Fitting of the second - order reaction rate constant between trivalent cobalt and chloramphenicol Detailed implementation manners

[0025] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0026] The present invention relates to a preparation method of trivalent cobalt, and the method includes the following steps:

[0027] S1: Prepare a 10 - mL solution containing 0.1 - 0.15 M CoSO4 and 5 M H2SO4 and place it in a glass bottle

[0028] S2: Add a stirring rotor, place it on a magnetic stirrer, mix for 10 minutes in a constant - temperature ice bath at 0 °C, and then start electrolysis for 10 minutes

[0029] S3: After electrolysis is completed, obtain a dark blue - green Co(III) stock solution, and then immediately store it in a refrigerator at - 20 °C

[0030] It should be noted that during electrolysis, both the anode and the cathode are platinum plates with dimensions of 10 × 10 × 0.2 mm, which are fixed in parallel on the reactor cover with a 1 - cm interval in the middle; the electric field is provided by a DC power supply with a voltage of 5.0 V

[0031] Based on the trivalent cobalt obtained by the preparation of the present invention, the present invention also provides a method for determining the second-order reaction rate constant between trivalent cobalt and reactants. The determination method includes calibrating the concentration of the Co(III) stock solution by the traditional iodide colorimetric method, setting different dosages of Co(III), making it more than 25 times the concentration of the reactants to ensure that the pseudo-first-order reaction rate constant of the degradation of the reactants can be fitted, and adjusting the pH to 2 with sulfuric acid; finally, calculating the second-order reaction rate constant through the second-order reaction rate constant between the reactants and Co(III).

[0032] It should be noted that the formula for the second-order reaction rate constant is:

[0033] - ln ([P] / [P]0) = k obs t (I)

[0034] k obs = k Co (III)-P [Co(III)] (2)

[0035] Through formula (1), with -ln([P] / [P]0) as the ordinate and t as the abscissa to plot a graph, the slope obtained is k obs , and then through formula (2), with k obs as the ordinate and [Co(III)]0 as the abscissa, the slope k Co(III)-P is obtained, which is the second-order reaction rate constant between the reactants and Co(III).

[0036] Example 1

[0037] Prepare a trivalent cobalt solution. The specific preparation process is as follows: The ambient temperature is 25°C. Prepare 10 mL of a solution containing 0.12 M CoSO4, add a certain amount of concentrated sulfuric acid to make the concentration of H2SO4 in the solution 5 M, place it in a 20 mL glass bottle, put the glass bottle in an ice bath of a mixture of ice and water, add a stirring rotor, mix well for 10 minutes, and then use platinum sheets as the anode and cathode, fix them in parallel on the reactor cover with a 1 cm interval in the middle. The electric field is provided by a DC power supply with a voltage of 5.0 V, and electrolyze for 10 minutes to obtain a dark blue-green trivalent cobalt solution. Trivalent cobalt has absorption peaks at 403 nm and 613 nm. Take 3 mmol / L trivalent cobalt for a full UV spectrum scan at pH 2.

[0038] Example 2:

[0039] Determination of the second-order reaction rate constant of trivalent cobalt with carbamazepine. The ambient temperature was 25 °C, the pH of the solution was 2. The dosages of trivalent cobalt were set at 25, 50, and 100 μmol / L, the concentration of carbamazepine was 1 μmol / L, and the quenching agent was sodium thiosulfate (the ratio to the concentration of trivalent cobalt was 4:1). Samples were taken at specific time points to determine the degradation kinetics changes of carbamazepine at different dosages of trivalent cobalt.

[0040] From Figure 1 and formula (1), the k obs (s -1 ) for the degradation of carbamazepine at the three dosages of trivalent cobalt were calculated to be 0.0232 s -1 , 0.0423 s -1 , and 0.0841 s -1 , respectively. Then, a graph was plotted with k obs (s -1 ) on the vertical axis and the concentration of trivalent cobalt (mol / L) on the horizontal axis. The result is as Figure 2 shown. According to formula (2), the second-order reaction rate constant of trivalent cobalt with carbamazepine was obtained as 846.1 M -1 s -1 .

[0041] -ln([P] / [P]0) = k obs t (1)

[0042] k obs = k Co(III)-P [Co(III)] (2)

[0043] Example 3

[0044] Determination of the second-order reaction rate constant of trivalent cobalt with metronidazole. The ambient temperature was 25 °C, the pH of the solution was 2. The dosages of trivalent cobalt were set at 25, 50, 100, and 200 μmol / L, the concentration of metronidazole was 1 μmol / L, and the quenching agent was sodium thiosulfate (the ratio to the concentration of trivalent cobalt was 4:1). Samples were taken at specific time points to determine the degradation kinetics changes of metronidazole at different dosages of trivalent cobalt.

[0045] Calculations were carried out in the same steps as in Example 2. From Figure 4 and Figure 5 , the second-order reaction rate constant of trivalent cobalt with metronidazole was obtained by fitting as 127.7 M -1 s -1 .

[0046] For those skilled in the art, various corresponding changes can be made based on the above technical solutions and concepts, and all such changes should be included within the protection scope of the claims of the present invention.

Claims

1. A method for determining the second-order reaction rate constant of trivalent cobalt with reactants, characterized in that, The described determination method includes calibrating the concentration of the Co(III) stock solution using the traditional iodide ion colorimetric method, setting different dosages of Co(III), with each dosage being greater than 25 times the concentration of the reactant to ensure that the first-order reaction rate constant of the reactant degradation can be fitted, adjusting the pH of the reaction solution to 2 with sulfuric acid; finally, calculating and obtaining the second-order reaction rate constant through the second-order reaction rate constant formula of the reactant and Co(III), where the reactant is carbamazepine or metronidazole; The preparation method of the trivalent cobalt includes the following steps: S1 Prepare a 10 mL solution containing 0.1 - 0.15 M CoSO4 and 5 M H2SO4 and place it in a glass bottle; S2 Add a magnetic stirring rotor, place it on a magnetic stirrer and mix for 10 minutes in an ice bath at 0 °C, and then start electrolysis for 10 minutes; S3 After the electrolysis is completed, a dark blue-green Co(III) stock solution is obtained, and then it is immediately stored in a refrigerator at -20 °C.

2. The method for determining the second-order reaction rate constant of trivalent cobalt and reactants according to claim 1, wherein During the electrolysis, platinum plates with dimensions of 10×10×0.2 mm for both the anode and the cathode are used, fixed in parallel on the reactor cover with a 1 cm interval in the middle; the electric field is provided by a DC power supply with a voltage of 5.0 V.

3. A method for determining the second-order reaction rate constant of trivalent cobalt and a reactant according to claim 1, characterized in that, The formula for the second-order reaction rate constant is: -ln([P] / [P]0) = K obs t (1) k obs = k Co(III)-P [Co(III)] (2) By Equation (1), plot -ln([P] / [P]0) on the vertical axis and t on the horizontal axis to obtain a slope of k obs , and then by Equation (2), plot k obs on the vertical axis and [Co(III)] on the horizontal axis to obtain a slope of k Co(III)-P , which is the second-order reaction rate constant of the reactant with Co(III).

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