A method for oxidatively degrading pollutants using a chromium-periodate system

Abstract

The application discloses a method for degrading pollutants by using a chromium-potassium periodate system, and comprises the following steps: adding chromium sulfate into ultrapure water while stirring, and adjusting the pH of the solution to 8-11; under the stirring state, adding potassium periodate into the solution to form a chromium-potassium periodate system solution; and adding the chromium-potassium periodate system solution into a solution of pollutants to be degraded to perform reaction and degrade the pollutants. The method can realize efficient oxidation and degradation of organic pollutants in water under the conditions of low catalyst consumption and proper pH. The application breaks through the pH condition of chromium, and makes the application of chromium not limited to the low pH field, avoids the generation of toxic by-product Cr(VI), and realizes the cleanness and environmental protection of the process.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of water pollution control advanced oxidation, and particularly relates to a method for oxidizing and degrading pollutants by using a chromium-persulfate system. BACKGROUND

[0002] As a technology for activating / catalyzing a parent chemical oxidant to produce highly active oxidizing species to oxidize pollutants by using energy or chemical reagents, the advanced oxidation technology has been studied by people due to its excellent catalytic oxidation degradation effect and wide application range. The advanced oxidation process (AOPS) based on the persulfate salt has attracted more and more scientific research attention due to its good oxidation ability (1.60 V) and satisfactory decontamination performance. However, the application of the persulfate salt system (PI) is limited due to the lack of high-performance activation methods.

[0003] At present, the activation methods of the persulfate salt system include ultraviolet irradiation, alkali activation and metal / metal oxide catalytic activation. Compared with other methods, the metal ion activation has the advantages of good performance, low cost and easy availability of metal ions. Many reports show that transition metal ions of different valence states all exhibit relatively good activation effect, but the effect is still not ideal at neutral pH, and the metal ion dosage is usually high (mM level). The use of excessive metal ions may increase the treatment cost, and there is also the problem of secondary pollution. Therefore, it is necessary to develop a catalyst with higher catalytic activation performance for the persulfate salt system, and to seek efficient oxidation and degradation of organic pollutants in water under the condition of low catalyst dosage (μM level) and appropriate pH. SUMMARY

[0004] To solve the above technical problems, the present application provides a method for oxidizing and degrading pollutants by using a chromium-persulfate system, which can realize effective degradation of pollutants under the condition of low catalyst dosage and neutral pH, and does not generate toxic by-products such as Cr(Ⅵ), which is more conducive to realizing green and clean production.

[0005] To achieve the above purpose, the technical scheme of the present application is as follows:

[0006] A method for oxidizing and degrading pollutants by using a chromium-persulfate system, comprising the following steps:

[0007] Step 1: adding chromium sulfate into ultrapure water while stirring, and adjusting the pH of the solution to 8-11;

[0008] Step 2: adding potassium periodate into the solution under stirring to form a chromium-persulfate system solution;

[0009] Step 3: adding the chromium-persulfate system solution into a solution to be degraded to react and degrade the pollutants.

[0010] In the above scheme, in step 1, the pH of the solution is 10.

[0011] In the above scheme, the molar concentration ratio of chromium sulfate to potassium periodate is 1:2-1:7.

[0012] Preferably, the molar concentration ratio of chromium sulfate to potassium periodate is 1:6.

[0013] In the above scheme, in step 1, sodium hydroxide solution is used to adjust the pH of the solution.

[0014] In the above scheme, in step 1 and step 2, the stirring speed is 500 rpm.

[0015] Through the above technical solution, the method of oxidative degradation of pollutants using a chromium-periodate system provided by the present invention has the following beneficial effects:

[0016] (1) Compared with the common advanced oxidation methods for water pollution control, the present invention provides a new method for activating periodate systems using transition metals, which can significantly improve the degradation rate of pollutants.

[0017] (2) Compared with other activation methods of periodate systems, the present invention can achieve efficient oxidative degradation of organic pollutants in water at low catalyst dosage (μM level) and appropriate pH conditions.

[0018] (3) The present invention can achieve a breakthrough in the pH conditions applicable to chromium, so that it is not limited to the low pH field, while avoiding the formation of toxic byproduct Cr(VI), thus achieving the cleanliness and environmental protection of the process.

[0019] (4) The present invention adopts heterogeneous Fenton-like technology to produce ·OH, ·O2 - The strong oxidizing property of free radicals is used to catalyze the degradation of target pollutants, thereby improving the oxidative degradation effect while avoiding the formation of toxic by-products such as Cr(VI), providing a new idea for periodate activation in the field of advanced oxidation for water pollution control. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0021] Figure 1 The present invention is a flow chart of a method for oxidative degradation of pollutants using a chromium-periodate system.

[0022] Figure 2 Free superoxide radical·O2 - EPR spectrum.

[0023] Figure 3 Singlet oxygen radical1 EPR spectrum of O2.

[0024] Figure 4 Pollutant degradation curve for Example 1.

[0025] Figure 5 Cr(Ⅵ) generation curve for Example 1.

[0026] Figure 6 Pollutant degradation curves for different concentration ratios of Cr(Ⅲ) and periodate ions.

[0027] Figure 7 Degradation rate comparison chart for different concentration ratios of Cr(Ⅲ) and periodate ions.

[0028] Figure 8 Pollutant degradation curves under different pH conditions.

[0029] Figure 9 Degradation rate comparison chart under different pH conditions. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application.

[0031] The present application provides a method for oxidatively degrading pollutants by using a chromium-periodate system, which generates free radicals such as ·OH and ·O2- to degrade target pollutants.

[0032] Example 1

[0033] Step 1: Preparation of target pollutant solution

[0034] 20 mg of methylene blue was added to 1000 mL of ultrapure water to form a 20 mg / L solution as the pollutant to be degraded;

[0035] Step 2: Preparation of Cr(Ⅲ)-periodate system and pollutant degradation, as shown in Figure 1

[0036] (1) 0.0272 g of chromium sulfate was added to 50 mL of ultrapure water while stirring, and the pH of the solution was adjusted to 10 with NaOH;

[0037] (2) 0.0720 g of potassium periodate was added to the solution under stirring to form a Cr(Ⅲ)-periodate system solution;

[0038] (3) 50 mL of the pollutant to be degraded was mixed with the Cr(Ⅲ)-periodate system solution, and the reaction immediately occurred.

[0039] Step 3: Sample detection system degradation effect​

[0040] Magnetic stirring was performed throughout the reaction at 500 rpm. 5 mL of sample was taken every 5 minutes and the absorbance was recorded using visible UV light at 664 nm. A degradation curve was then plotted.

[0041] 1. Research on degradation mechanism:

[0042] The O2 produced in Example 1 - and 1 O2 was subjected to electron paramagnetic resonance analysis.

[0043] Take 200 μl of chromium sulfate solution (10 mg / L) and mix it with 200 μl of capture agent solution DMPO (methanol as solvent, 100 mM) and TEMP (water as solvent, 50 mM). Then, add potassium periodate (60 mg / L), mix well and use capillary tube to load the sample for testing. EPR spectrum is shown in Figure 2 、 Figure 3 .

[0044] DMPO and TEMP are used to capture free superoxide radicals and O2 - and singlet oxygen 1 When methanol replaces water as the dispersant of DMPO, DMPO is more likely to react with superoxide radicals and O2 - The reaction produces 6 peaks, such as Figure 2 As shown, it means O2 - The generation of TEMP; similarly, 1 O2 capture such as Figure 3 This proves the generation of the free radical in the system. This proves that O2 is generated in the system. - and 1 O2.

[0045] 2. System degradation process

[0046] In order to better understand the degradation ability of the system and the generation of related by-products, the present invention sets Example 1 to demonstrate the degradation effect of the system by means of the degradation of methylene blue solution. Figure 4 As shown in the figure, during the reaction process, the concentration of the pollutants to be degraded steadily decreased, and the degradation was basically completed in 20 minutes, achieving basic removal of the pollutants.

[0047] Meanwhile, considering the particularity of the toxicity of Cr(Ⅵ), the application specifically draws the generation curve of the byproduct. First, the standard concentration curve of hexavalent chromium is drawn by using potassium dichromate, then the color reaction is carried out according to the DPC coloration method, 1 mL of the solution is taken in a 1.5 mL centrifuge tube every 5 min in the pollutant degradation process in Example 1, 10 μL of 6M hydrochloric acid is added to adjust the pH of the solution, then 40 μL of DPC solution (0.0250g DPC is dissolved in 10 mL of acetone) is added for coloration, after standing for 5 min, the ultraviolet test solution absorbance is carried out at a wavelength of 540 nm.

[0048] As shown in Figure 5 , the sharp increase of the concentration at the beginning of the reaction is related to the generation of intermediate complexes in the system, and during the reaction process, the Cr(Ⅵ) concentration is always controlled below 0.2 mg / L, which is relatively low compared with the total chromium reaction input of 10 mg / l, and is in a controllable range, and has a smaller degree of harm to the environment.

[0049] 3, Effect of different concentration ratios of the system on the oxidative degradation

[0050] The application sets a comparative example 1, the concentration ratio of Cr(Ⅲ) to periodate ion 1:6 in Example 1 is replaced by other concentration ratios, and the other conditions are the same as those in Example 1. The degradation effects of comparative example 1 and Example 1 are compared, and the results are shown in Figure 6 , Figure 7 .

[0051] As shown in Figure 6 , all the concentration conditions are basically degraded within 25 min. The concentration ratio of Cr(Ⅲ) to periodate ion shows obvious and similar degradation curves after 1:2.

[0052] As shown in Figure 7 , with the increase of the concentration ratio of periodate ion in the system, the degradation rate generally shows an upward trend, until the concentration ratio of Cr(Ⅲ) to periodate ion 1:6 is used in Example 1 of the application, the oxidative degradation rate of the system is 94.6%, which is the highest value, and if the concentration ratio continues to increase, the degradation rate will decrease. If 80% is taken as the target degradation rate, the concentration ratio of Cr(Ⅲ) to periodate ion from 1:2 to 1:7 can meet the degradation effect, especially when the concentration ratio of Cr(Ⅲ) to periodate ion is 1:6, the degradation effect is the best.

[0053] This is because the appropriate concentration ratio makes the system more likely to form appropriate intermediate complexes, accelerating the formation of active free radicals to facilitate the degradation of organic matter. This also proves that the system relies on free radicals generated by Fenton-like reactions to degrade pollutants. At the same time, the appropriate concentration prevents excessive Cr(III) from forming high-valent toxic byproducts, reducing environmental harm. However, while excessive periodate accelerates the reaction process, it is not conducive to the formation of intermediate complexes and, to a certain extent, inhibits the generation of various active free radicals, thereby reducing the degradation effect. To ensure the pollutant degradation effect and reaction speed, the optimal reactant concentration ratio was set at 1:6 for Cr(III) to periodate.

[0054] 4. Effect of different pH conditions on oxidative degradation

[0055] The present invention sets up comparative example 2, and replaces the pH condition in embodiment 1 with other pH conditions, and other conditions are the same as embodiment 1. Comparative example 2 is compared with the pollutant oxidation degradation effect in embodiment 1, and the results are shown in FIG. Figure 8 、 Figure 9 .

[0056] like Figure 8 As shown, at pH 2 and 4, the pollutant concentration in the system increased instead of decreased, failing to achieve a good degradation effect and therefore lacking reference value. At pH 6, the degradation rate was relatively slow. At pH 8-11, the degradation effect was good and the degradation curves were similar. In particular, at pH 9-11, the pollutant concentration in the system became negative. This is because the methylene blue in the system has been largely degraded, leaving the system with primarily yellow-green free radicals, which have a weaker absorption capacity for 665nm wavelength light, resulting in a negative value.

[0057] like Figure 9 As shown, starting from pH 6, the degradation rate of the system increases with the increase of pH conditions. When the pH condition is 10 in Example 1 of the present invention, the system oxidative degradation rate reaches 103.8% (the abnormal reason is the same as above), which is the highest value. If the proportional concentration continues to increase, the degradation rate will decrease. If 80% is the target degradation rate, the target degradation effect can be achieved at pH conditions of 8-11. In particular, the degradation effect is best when the pH condition is 10.

[0058] This is because under low pH conditions, Cr ions are easy to form high valence Cr(Ⅵ) ions, which are not easy to combine with PI ions in the system to generate active free radicals; under high pH conditions, Cr ions will form a precipitate and lose the degradation effect. In particular, Cr(Ⅲ) ions will form a gray-green precipitate at a conventional pH of 4.5-4.8, but will not produce a precipitate in a system containing high-valence iodine ions and can continue to react. This also proves that the Cr(Ⅲ)-periodate system has a mutual activation effect, making the oxidative degradation effect of the system superior to that of the same transition metal activation.

[0059] The above description of disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those of ordinary skill in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Therefore, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for oxidative degradation of pollutants using a chromium-periodate system, characterized in that: The steps include: Step 1: adding chromium sulfate to ultrapure water while stirring to adjust the pH of the solution to 8-11; Step 2: adding potassium periodate to the solution under stirring to form a chromium-periodate system solution; Step 3, adding the chromium-periodate system solution to the pollutant solution to be degraded to react and degrade the pollutant; The molar concentration ratio of chromium sulfate to potassium periodate is 1:2-1:

7.

2. The method for oxidative degradation of pollutants using a chromium-periodate system according to claim 1, characterized in that: In step 1, the pH of the solution is 10.

3. The method for oxidative degradation of pollutants using a chromium-periodate system according to claim 1, characterized in that: The molar concentration ratio of chromium sulfate to potassium periodate is 1:

6.

4. The method for oxidative degradation of pollutants using a chromium-periodate system according to claim 1, characterized in that: In step 1, the pH of the solution is adjusted using sodium hydroxide solution.

5. The method for oxidative degradation of pollutants using a chromium-periodate system according to claim 1, characterized in that: In step 1 and step 2, the stirring speed is 500 rpm.

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