A method for removing organic pollutants using a fenton reaction pathway with flocs

Abstract

The application discloses a method for removing organic pollutants by Fenton reaction path of floc, comprising the following steps: adding iron sulfate into an organic pollutant solution, and passing oxygen to keep the reaction system in oxygen saturation state; building a three-electrode system by taking a carbon-based titanium dioxide catalytic electrode as a working electrode, a graphite electrode as a counter electrode, and a standard silver chloride electrode as a reference electrode, applying voltage to the working electrode through an electrochemical workstation to carry out an electro-Fenton-like reaction; after the power is turned off, continuing to react for a period of time, and removing the pollutants through flocculation and sedimentation of the floc by self-catalysis of the floc, and finally filtering to remove the pollutants. The method disclosed by the application realizes activation of Fe floc by electrocatalysis to introduce •OH without adjusting pH value and adding H2O2, realizes efficient removal of organic pollutants by self-catalysis of the floc, provides a method for resource utilization of iron floc, and prolongs the Fenton reaction time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of water pollution control advanced oxidation, and particularly relates to a method for removing organic pollutants by using a Fenton reaction path of flocs. BACKGROUND

[0002] Advanced oxidation processes (AOPs) can generate •OH with strong oxidation ability, which is a method that can effectively remove organic pollutants in wastewater, and •OH can decompose organic pollutants into small molecular substances such as water and carbon dioxide. Among various AOPs, Fenton is the most commonly used wastewater treatment technology, which generates •OH by adding hydrogen peroxide (H2O2) and Fe 2+ However, the high operating cost, narrow working pH range, sludge accumulation and other shortcomings limit the application of Fenton. With the progress of Fenton reaction, the generated OH - leads to the increase of pH, thus inevitably producing Fenton sludge.

[0003] It is worth noting that the formation process of Fenton sludge involves the participation of various active oxygen free radicals (ROS) such as •OH and H2O2, which indicates that it may introduce diversity in the reaction interface and process of Fenton reaction. Therefore, the sludge is often regarded as hazardous waste, and its formation usually marks the end of the AOPs reaction, and the sludge needs to be disposed of. However, traditional methods such as combustion and landfill cannot eliminate the environmental risk of Fenton sludge, and may cause the spread of pollutants. At present, the secondary utilization of Fenton sludge mainly focuses on regeneration. For example, Fenton sludge is used as raw material to manufacture adsorbents, heterogeneous catalysts and coagulants, etc., and these technologies usually need acid dissolution and oxidation treatment steps, which leads to more complexity and cost increase in the treatment process. In addition, in these secondary utilization processes, the focus is usually on heavy metals, and the role of ROS is often ignored. SUMMARY

[0004] To solve the above technical problems, the present application provides a method for removing organic pollutants by using a Fenton reaction path of flocs, which realizes the activation of Fe flocs by introducing •OH by electrocatalysis without adjusting the pH value and adding H2O2, realizes the efficient removal of organic pollutants by the catalytic action of the flocs themselves, provides a method for resource utilization of iron flocs, and prolongs the Fenton reaction time.

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

[0006] A method for removing organic pollutants by using a Fenton reaction path of flocs, comprising the following steps:

[0007] Step 1, adding ferric sulfate to the organic pollutant solution, and configuring the ferric sulfate solution of the organic pollutant;

[0008] Step 2, passing oxygen into the ferric sulfate solution of the organic pollutant for a certain time, so that the reaction system is always in an oxygen-saturated state, and oxygen is continuously passed during the reaction;

[0009] Step 3, constructing a three-electrode system with the prepared carbon-based titanium dioxide catalytic electrode as a working electrode, a graphite electrode as a counter electrode, and a standard silver chloride electrode as a reference electrode, applying voltage to the working electrode through an electrochemical workstation, and performing an electro-Fenton-like reaction;

[0010] Step 4, after the power is turned off, continuing the reaction for a period of time, realizing flocculation and sedimentation of the organic pollutants through the catalytic effect of the flocs, and finally removing them by filtration.

[0011] In the above scheme, the organic pollutant is Direct Yellow 12.

[0012] In the above scheme, the concentration of ferric sulfate in the solution in step 1 is 200 mg / L.

[0013] In the above scheme, in step 2, oxygen is passed into the ferric sulfate solution of the organic pollutant for 30 min.

[0014] In the above scheme, the size of the working electrode and the counter electrode is 4 cm x 4 cm x 0.3 cm.

[0015] In the above scheme, the external voltage of the electrochemical workstation is -0.55 V, and the power-on time lasts for 1 hour.

[0016] In the above scheme, in step 4, after the power is turned off, the reaction continues for 1 hour.

[0017] In the above scheme, the whole reaction process is stirred by a magnetic stirrer at a speed of 500 rpm.

[0018] In the above scheme, the preparation method of the carbon-based titanium dioxide catalytic electrode is as follows:

[0019] (1) Pretreatment of graphite powder: mix 10 g of graphite powder with deionized water, heat in a constant temperature water bath for 1 h, and after cooling, repeatedly rinse the impurities with deionized water; after removing the impurities, filter with a vacuum pump, and then dry in a 105℃ oven for 8 h;

[0020] (2) Preparation of carbon-based TiO2 powder: Take 5g of pretreated graphite powder and mix it with 45mL of anhydrous ethanol and 15mL of tetrabutyl titanate. After mixing, react with a magnetic stirrer for 30min to prepare mixed solution A; then mix 1.2mL of concentrated nitric acid, 45mL of anhydrous ethanol and 6mL of deionized water. After mixing, react with a magnetic stirrer for 30min to prepare mixed solution B; add mixed solution B dropwise to mixed solution A, and then let it stand until a gel is formed; dry it in an oven at 105℃ for 8h to obtain granular material; then grind it into powder and calcine it in a muffle furnace at 500℃ for 2h to obtain carbon-based TiO2 powder;

[0021] (3) Preparation of carbon-based TiO2 electrode: Weigh 20 mg of carbon-based TiO2 powder and mix it with 80 μL of Nafion. After mixing evenly, coat it on the surface of graphite sheet electrode and let it air dry at room temperature to obtain carbon-based TiO2 catalytic electrode.

[0022] The method for removing organic pollutants using the Fenton reaction pathway of flocs provided by the above technical solution has the following beneficial effects:

[0023] (1) Compared to Fe 3+ The self-settling and Fenton technology of adding H2O2 provided by this invention utilizes Fe... 3+ The technology of generating •OH through an electro-Fenton (EF-like) reaction can achieve rapid removal of organic pollutants and significantly improve the pollutant removal rate.

[0024] (2) The present invention uses electrocatalysis to generate •OH to activate Fe-like Fenton flocs. After the EF-like reaction stops, the pollutants can still be removed by the flocs’ own catalytic effect, thus prolonging the Fenton reaction time.

[0025] (3) Compared with traditional Fenton technology, the present invention does not require pH adjustment, thus avoiding the addition of acid and alkali and breaking through the pH value limitation.

[0026] (4) The present invention does not require the addition of hazardous chemicals such as H2O2 in the reaction, and the reaction process is clean, safe and inexpensive. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0028] Figure 1 This is a schematic diagram of the reaction apparatus of the present invention;

[0029] Figure 2This is a comparison graph showing the concentration of pollutants reacting during the degradation process of pollutants in Example 1 of the present invention, compared with Comparative Examples 1 and 2.

[0030] Figure 3 This is a graph showing the effect of pollutant removal rates compared between Example 1 and Comparative Example 2 of the present invention;

[0031] Figure 4 This invention is used to compare the pollutant degradation rates with those of Comparative Examples 1 and 2.

[0032] Figure 5 These are optical microscope images of the reaction between flocs and pollutants in this invention and Comparative Examples 1 and 2.

[0033] Figure 6 The image shows the HPLC-MS chromatograms of the reaction of the present invention and Comparative Example 1.

[0034] Figure 7 The diagram shows the valence state changes of Fe in the present invention and Comparative Examples 1 and 2; (a) is Example 1 of the present invention, (b) is Comparative Example 1, and (c) is Comparative Example 2. Detailed Implementation

[0035] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0036] This invention provides a method for removing organic pollutants using the Fenton reaction pathway of flocs. It generates •OH through an EF-like system to activate Fenon flocs, thereby achieving highly efficient removal of organic pollutants. Specifically, it includes:

[0037] I. Preparation of carbon-based titanium dioxide catalytic electrode

[0038] (1) Pretreatment of graphite powder: Mix 10g of graphite powder with deionized water and heat it in a constant temperature water bath for 1 hour. After cooling, rinse it repeatedly with deionized water to remove impurities. After the impurities are removed, filter it with a vacuum pump and then dry it in an oven at 105℃ for 8 hours.

[0039] (2) Preparation of carbon-based TiO2 powder: Take 5g of pretreated graphite powder and mix it with 45mL of anhydrous ethanol and 15mL of tetrabutyl titanate. After mixing, react with a magnetic stirrer for 30min to prepare mixed solution A; then mix 1.2mL of concentrated nitric acid, 45mL of anhydrous ethanol and 6mL of deionized water. After mixing, react with a magnetic stirrer for 30min to prepare mixed solution B; add mixed solution B dropwise to mixed solution A, and then let it stand until a gel is formed; dry it in an oven at 105℃ for 8h to obtain granular material; then grind it into powder and calcine it in a muffle furnace at 500℃ for 2h to obtain carbon-based TiO2 powder;

[0040] (3) Preparation of carbon-based TiO2 electrode: Weigh 20 mg of carbon-based TiO2 powder and mix it with 80 μL of Nafion. After mixing evenly, coat it on the surface of graphite sheet electrode and let it air dry at room temperature to obtain carbon-based TiO2 catalytic electrode.

[0041] II. Preparation of Organic Pollutant Solution

[0042] Add 10 mg of the organic pollutant Direct Yellow 12 (DY12) to 100 ml of ultrapure water to prepare a pollutant solution with a DY12 concentration of 100 mg / L.

[0043] III. Highly efficient removal of pollutants

[0044] Example 1

[0045] Step 1: Add 71.4 mg of ferric sulfate to the organic pollutant solution to prepare a ferric sulfate solution of organic pollutants with a concentration of 200 mg / L.

[0046] Step 2: Before the reaction begins, oxygen is introduced into the ferric sulfate solution of organic pollutants for 30 minutes to keep the reaction system in an oxygen-saturated state, and oxygen is continuously introduced in the subsequent reaction. At the same time, the magnetic stirrer is turned on to 500 rpm to make the solution stir evenly and react fully. Magnetic stirring is carried out at 500 rpm throughout the reaction process.

[0047] Step 3: Using the prepared carbon-based titanium dioxide catalytic electrode as the working electrode, the graphite electrode as the counter electrode, and the standard silver chloride electrode as the reference electrode, a three-electrode system is constructed. A voltage of -0.55 V is applied to the working electrode via an electrochemical workstation to conduct an electro-Fenton-like reaction. The apparatus is as follows: Figure 1 As shown; the reaction was completed after 1 hour of electrolysis.

[0048] Step 4: After the power is turned on, continue stirring and react for 1 hour. The organic pollutants are flocculated and settled through the catalytic effect of the flocs themselves, and finally removed by filtration.

[0049] Comparative Example 1

[0050] Step 1: Add 71.4 mg of ferric sulfate to the organic pollutant solution to prepare a ferric sulfate solution of organic pollutants with a concentration of 200 mg / L.

[0051] Step 2: Add 30 μL of 30% H2O2 to the ferric sulfate solution of the above organic pollutants and react for 2 hours to construct the Fe-H2O2 control system of Comparative Example 1.

[0052] Comparative Example 2

[0053] Step 1: Add 71.4 mg of ferric sulfate to the organic pollutant solution to prepare a ferric sulfate solution of organic pollutants with a concentration of 200 mg / L. Without adjusting the pH, react for 2 hours to construct the Fe self-precipitation control system of Comparative Example 2.

[0054] Organic pollutant removal efficiency test:

[0055] 1. Changes in pollutant concentrations

[0056] In Examples 1, 1, and 2 of this invention, samples were taken every 20 minutes during the reaction process. The absorbance of pollutant DY12 was measured at a wavelength of 398 nm using spectrophotometry. The concentration of pollutant DY12 was calculated using the standard curve method. The results are shown in […]. Figure 2 As shown. From Figure 2 As can be seen, in Example 1 of the present invention, the concentration of DY12 decreased the fastest within the first 1 hour of the heterogeneous electrocatalytic reaction, and continued to maintain a good removal effect in the following 1 hour, which was significantly better than the removal effects of Comparative Example 1 and Comparative Example 2.

[0057] 2. Pollutant removal rate

[0058] In the reaction process of this invention and Comparative Example 2, samples were taken every 20 minutes, and the absorbance of pollutant DY12 was measured at a wavelength of 398 nm using spectrophotometry. The concentration of pollutant DY12 was calculated using the standard curve method, and the removal rate of DY12 was calculated using equation (1). The results are shown in [Figure 1]. Figure 3 ,from Figure 3 As can be seen, the method disclosed in Example 1 of this invention achieves an organic pollutant removal rate of 42.79% in an EF-like system over 1 hour. Within 1 hour after the electrocatalytic reaction is stopped, the pollutants can be degraded by 25.20% through the self-catalytic action of the •OH flocs, which is higher than the total pollutant removal rate (30.58%) achieved by floc self-sedimentation in Comparative Example 2 over 2 hours. Therefore, Example 1 of this invention can significantly improve the pollutant removal rate and maintains good performance even after the EF-like reaction is stopped.

[0059] Removal rate = (C0 - C) t ) / C0 (1)

[0060] Where C0 represents the initial concentration, C t This represents the reaction concentration.

[0061] 3. Pollutant degradation rate

[0062] In the reaction processes of Examples 1, Comparative Examples 1 and 2 of this invention, during the 1 hour of the EF-like reaction and the 1 hour of floc self-degradation, the absorbance of pollutant DY12 was measured at a wavelength of 398 nm every 20 minutes using spectrophotometry. The concentration was calculated using the standard curve method, and the degradation rate of DY12 was calculated using equation (2). k obs (See results) Figure 4 ,from Figure 4 As can be seen from the above, the DY12 removal rate of Example 1 of the present invention is much higher than that of Comparative Example 1 and Comparative Example 2. Moreover, even after 1 hour of reaction time, when pollutants are removed by the flocs themselves, the reaction rate of Example 1 is still the highest.

[0063] ln(C t / C0) = - k obs t (2)

[0064] Where C0 represents the initial concentration, C t t represents the reaction concentration, and t represents the reaction time.

[0065] 4. Floc particle size test

[0066] The flocs produced after the reaction in Examples 1, 1, and 2 of this invention were immediately removed and observed under a 40x optical microscope. Their particle size and specific surface area were measured using a laser particle size analyzer. The results are shown in Table 1 and... Figure 5 As shown in Table 1 and Figure 5 As can be seen from the data, the flocs in Example 1 (158.86 μm) 2 The area of ​​the flocs in this invention is significantly smaller than that of the other two types of flocs, and the degree of floc aggregation is low. Furthermore, the flocs were characterized by a laser particle size analyzer, and it was found that compared with Comparative Example 1 and Comparative Example 2, the particle size of this invention is smaller and the specific surface area is larger, which can provide more reaction sites for pollutants.

[0067] Table 1 Floc Particle Size Data

[0068]

[0069] 5. HPLC-MS detection of flocs

[0070] The flocculents from Examples 1 and 1 of this invention were immediately removed and analyzed by HPLC-MS. The results are shown in the figure. Figure 6 ,from Figure 6As can be seen, a charge-to-mass ratio of 317 represents undegraded DY12. According to the HPLC-MS chromatogram, a small portion of the pollutant DY12 was decomposed in this invention, with the main removal pathway being adsorption on the floc surface. In Comparative Example 1, the pollutant DY12 was completely decomposed, with the main removal pathway being destruction by •OH.

[0071] 6. Determination of Fe(II) and Fe(III) concentrations

[0072] During the reaction process of Example 1 of this invention, samples were taken every 20 minutes, and the concentrations of Fe(II) and Fe(III) in the solution were determined by spectrophotometry. The results are shown in [Figure Number]. Figure 7 As can be seen, in Example 1 of this invention, Fe(II) showed a trend of first increasing and then decreasing, while the initial reaction solution was Fe(III), indicating that a large amount of Fe(II) was generated during the electro-Fenton-like reaction. After the current was stopped, Fe(II) was continuously consumed as the reaction proceeded. In contrast, almost no Fe(II) was generated in Comparative Examples 1 and 2.

[0073] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not 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 removing organic pollutants using the Fenton reaction pathway of flocs, characterized in that, Includes the following steps: Step 1: Add ferric sulfate to the organic pollutant solution to prepare a ferric sulfate solution of the organic pollutant; the organic pollutant is Direct Yellow 12 dye. Step 2: Oxygen is bubbled into the ferric sulfate solution of organic pollutants for a certain period of time to keep the reaction system in an oxygen-saturated state, and oxygen is continuously bubbled into the reaction. Step 3: Using the prepared carbon-based titanium dioxide catalytic electrode as the working electrode, the graphite electrode as the counter electrode, and the standard silver chloride electrode as the reference electrode, a three-electrode system is constructed. A voltage is applied to the working electrode through an electrochemical workstation to carry out an electro-Fenton-like reaction. Step 4: After the power is turned on, continue the reaction for a period of time. The organic pollutants are flocculated and settled through the catalytic effect of the flocs themselves, and finally removed by filtration.

2. The method for removing organic pollutants using the Fenton reaction pathway of flocs according to claim 1, characterized in that, The concentration of ferric sulfate in the solution in step 1 is 200 mg / L.

3. The method for removing organic pollutants using the Fenton reaction pathway of flocs according to claim 1, characterized in that, In step 2, oxygen is bubbled into the ferric sulfate solution containing organic pollutants for 30 minutes.

4. The method for removing organic pollutants using the Fenton reaction pathway of flocs according to claim 1, characterized in that, The dimensions of the working electrode and the counter electrode are 4 cm × 4 cm × 0.3 cm.

5. The method for removing organic pollutants using the Fenton reaction pathway of flocs according to claim 1, characterized in that, The electrochemical workstation is powered by an external voltage of -0.55 V for 1 hour.

6. The method for removing organic pollutants using the Fenton reaction pathway of flocs according to claim 1, characterized in that, In step 4, after the power is applied, the reaction continues for 1 hour.

7. The method for removing organic pollutants using the Fenton reaction pathway of flocs according to claim 1, characterized in that, The reaction was stirred using a magnetic stirrer at a speed of 500 rpm throughout.

8. The method for removing organic pollutants using the Fenton reaction pathway of flocs according to claim 1, characterized in that, The preparation method of the carbon-based titanium dioxide catalytic electrode is as follows: (1) Pretreatment of graphite powder: Mix 10g of graphite powder with deionized water and heat it in a constant temperature water bath for 1 hour. After cooling, rinse it repeatedly with deionized water to remove impurities. After the impurities are removed, filter it with a vacuum pump and then dry it in an oven at 105℃ for 8 hours. (2) Preparation of carbon-based TiO2 powder: Take 5g of pretreated graphite powder and mix it with 45mL of anhydrous ethanol and 15mL of tetrabutyl titanate. After mixing, react with a magnetic stirrer for 30min to prepare mixed solution A; then mix 1.2mL of concentrated nitric acid, 45mL of anhydrous ethanol and 6mL of deionized water. After mixing, react with a magnetic stirrer for 30min to prepare mixed solution B; add mixed solution B dropwise to mixed solution A, and then let it stand until a gel is formed; dry it in an oven at 105℃ for 8h to obtain granular material; then grind it into powder and calcine it in a muffle furnace at 500℃ for 2h to obtain carbon-based TiO2 powder; (3) Preparation of carbon-based TiO2 electrode: Weigh 20 mg of carbon-based TiO2 powder and mix it with 80 μL of Nafion. After mixing evenly, coat it on the surface of graphite sheet electrode and let it air dry at room temperature to obtain carbon-based TiO2 catalytic electrode.

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