Method and apparatus for electrochemically enhanced transition metal-doped nickel-based phosphate-activated persulfate for degradation of pollutants

Abstract

The application discloses a method and device for degrading pollutants by electrochemically enhancing transition metal doped nickel-based phosphate activated persulfate, and belongs to the field of advanced oxidation water treatment technology. The method comprises the following steps: adding wastewater, transition metal doped nickel-based phosphate and persulfate into a reaction tank; starting the degradation reaction by supplying power to the anode and the cathode through a power supply; in the reaction process, active oxygen species generated by the transition metal doped nickel-based phosphate activated persulfate is used to degrade organic pollutants in the wastewater, the reduction of the cathode is used to promote the cyclic regeneration of transition metals in the transition metal doped nickel-based phosphate and accelerate the degradation of pollutants; and the oxidation of the anode can also achieve the degradation of pollutants. The application realizes the synergistic effect of the two processes by coupling the persulfate catalytic process and the electrochemical process, and has a good application prospect in the efficient treatment of refractory organic wastewater.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of advanced oxidation water treatment, and relates to a method and device for degrading pollutants by activating persulfate through an electrochemically enhanced transition metal doped nickel-based phosphate. BACKGROUND

[0002] Persulfate activation is a key means for degrading organic pollutants by advanced oxidation technology, and is mainly achieved by generating active oxygen species such as sulfate radicals, singlet oxygen and hydroxyl radicals. The existing technology generally uses transition metal catalysts (such as Cu, Fe and Co-based materials) to activate persulfate, but has problems such as low electron transfer rate, high metal leaching rate and poor stability.

[0003] Nickel-based phosphates are considered as potential catalysts due to their porous structure and high specific surface area, but single nickel-based materials have limited activation capacity for persulfate. Although transition metal-based catalysts (such as Fe2O3 and Fe3O4) have high activity, they face serious metal leaching under acidic or high salt conditions, leading to secondary pollution and frequent replacement problems.

[0004] In view of the above defects, it is urgent to develop a catalyst with high catalytic activity and low metal leaching rate, and to use an effective method to accelerate the recycling of the catalyst, further enhance the activation efficiency of persulfate and improve the degradation efficiency of pollutants. SUMMARY

[0005] To solve the above problems, the application provides a method and device for degrading pollutants by activating persulfate through an electrochemically enhanced transition metal doped nickel-based phosphate. The application prepares a high-activity catalyst by atomic doping (for example, iron is embedded into a nickel lattice to form a Fe-O-Ni bond), enhances the electron transfer capacity between the metal-oxygen bond and the metal nickel, promotes the enrichment of pollutants and improves the mass transfer efficiency by using the multi-stage pores of the catalyst, promotes the recycling of the catalyst by the reduction effect of the cathode, and at the same time, the oxidation effect of the anode can also achieve the degradation of pollutants. The method can effectively degrade antibiotics, dyes and most organic pollutants, and provides a new technical solution for the treatment of organic pollutants. It has good application prospect in the efficient treatment of refractory organic wastewater (such as pesticide wastewater, pharmaceutical wastewater, etc.).

[0006] To achieve the above purpose, the technical scheme adopted by the application is as follows:

[0007] The first object of the application is to provide a method for degrading pollutants by activating persulfate through an electrochemically enhanced transition metal doped nickel-based phosphate, comprising the following steps:

[0008] A reaction tank is provided, and an anode and a cathode connected with a power supply are arranged in the reaction tank;

[0009] adding wastewater containing organic pollutants, transition metal doped nickel-based phosphate and persulfate into the reaction tank;

[0010] The degradation reaction is started by supplying power to the anode and the cathode through the power supply, and the wastewater is stirred during the reaction process. The active oxygen species generated by the activation of the transition metal doped nickel-based phosphate and the persulfate degrades the organic pollutants in the wastewater. At the same time, the reduction of the cathode promotes the recycling of the transition metal in the transition metal doped nickel-based phosphate, accelerates the degradation of the pollutants. The oxidation of the anode can also achieve the degradation of the pollutants.

[0011] The transition metal doped nickel-based phosphate is prepared by the following method:

[0012] The phosphate precursor solution and the nickel salt solution are prepared respectively, the nickel salt solution is added to the phosphate precursor solution, and the reaction is carried out under stirring. After low-temperature aging, the nickel-based phosphate porous nanomaterial is obtained. Preferably, the phosphate used for preparing the phosphate precursor solution is at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate and sodium phosphate. The nickel salt used for preparing the nickel salt solution is at least one of nickel sulfate, nickel chloride and nickel nitrate.

[0013] The nickel-based phosphate porous nanomaterial is added to the transition metal salt solution, and the transition metal doped nickel-based phosphate is prepared by ion exchange. Preferably, the transition metal salt in the transition metal salt solution is a water-soluble iron salt, a cobalt salt, a manganese salt or a copper salt, etc. The transition metal salt is a chloride salt, a nitrate salt or a sulfate salt of the transition metal, etc.

[0014] As a preferred technical solution, the anode is a carbon electrode, a noble metal electrode or a metal oxide electrode. During the degradation reaction process, the anode can also achieve the degradation of the pollutants through direct oxidation and indirect oxidation of hydroxyl radicals.

[0015] As a preferred technical solution, the persulfate is permonosulfate (PMS) or perdisulfate (PDS). During the reaction process, the active oxygen species generated by permonosulfate is hydroxyl radical and sulfate radical, and the active oxygen species generated by perdisulfate is sulfate radical. They can be used for Fenton-like reaction and can be enhanced by electrochemistry.

[0016] As a preferred technical solution, the cathode is a titanium plate, a carbon electrode, an aluminum electrode or a copper electrode, etc.

[0017] As a preferred technical solution, the organic pollutants are antibiotics, dyes and other organic pollutants. The antibiotics are tetracycline antibiotics, penicillin antibiotics, cephalosporin antibiotics and macrolide antibiotics, etc.

[0018] Preferably, the current density of the power supply is 1-20 mA / cm 2 .

[0019] A second object of the present application is to provide an electrochemically enhanced transition metal doped nickel-based phosphate activated persulfate pollutant degradation device, comprising a reaction tank for containing wastewater containing organic pollutants, transition metal doped nickel-based phosphate and persulfate; an anode and a cathode connected to a power supply are arranged in the reaction tank; and a stirring device for stirring the wastewater in the reaction tank.

[0020] Preferably, the stirring device comprises a magnetic stirrer located below the reaction tank and a magnetic stirring rod placed in the reaction tank and matched with the magnetic stirrer.

[0021] The electrochemically enhanced transition metal doped nickel-based phosphate activated persulfate pollutant degradation method provided by the present application has the following core: (1) a high-activity, low-metal leaching rate transition metal doped nickel-based phosphate catalyst is prepared by atomic doping means, the electron transfer capacity between the transition metal and nickel is enhanced, the persulfate activation efficiency is promoted, at the same time, the multi-stage pores of the catalyst are used to promote the enrichment of pollutants and improve the mass transfer efficiency; (2) the cathodic reduction in the electrochemical process promotes the cyclic regeneration of the transition metal catalyst, further accelerates the persulfate activation efficiency, generates active oxygen species such as sulfate radical, singlet oxygen, and hydroxyl radical, and promotes the degradation of pollutants; (3) the anodic oxidation in the electrochemical process realizes the degradation of pollutants, including direct oxidation and indirect oxidation by generating hydroxyl radicals.

[0022] Taking PMS as the persulfate and iron as the transition metal as an example, the related chemical reactions involved in the degradation reaction process of the present application are as follows:

[0023] Transition metal doped nickel-based phosphate activated PMS (taking the generation of sulfate radical as an example):

[0024]

[0025]

[0026] (M refers to organic pollutants)

[0027] Cathodic reduction promotes the cyclic regeneration of the transition metal iron catalyst:

[0028]

[0029]

[0030] Anodic oxidation (direct oxidation / indirect oxidation) realizes degradation of pollutants:

[0031] (direct oxidation)

[0032]

[0033] (indirect oxidation)

[0034] In summary, compared with the prior art, the advantages of the present application are:

[0035] (1) The existing persulfate activation technology generally uses transition metal catalysts, which have problems such as low electron transfer rate, high metal leaching rate, and poor stability. Nickel-based phosphates are considered as potential catalysts due to their porous structure and high specific surface area, but single nickel-based materials have limited activation ability for persulfate. Although transition metal-based catalysts have high activity, they face serious metal leaching problems under acidic or high salt conditions, leading to secondary pollution and frequent replacement. The transition metal-doped nickel-based phosphate catalyst prepared by atomic doping has high activity and low metal leaching rate, which can enhance the electron transfer between transition metal and nickel, promote the activation efficiency of persulfate, and at the same time, the multi-level pores of the catalyst can promote the enrichment of pollutants and improve the mass transfer efficiency.

[0036] (2) In the process of activating persulfate, the valence state of transition metal elements will increase, which needs to be reduced again to restore the initial valence state, so as to restore the catalytic activity. The cathodic reduction of the electrochemical process can accelerate the recovery of the valence state of the transition metal, promote the recycling of the catalyst, and thus improve the activation efficiency of persulfate.

[0037] (3) At the same time, the anode in the electrochemical process can make the pollutants lose electrons directly and be degraded, or electrolyze water to produce hydroxyl radicals to realize the degradation of pollutants.

[0038] (4) The pure persulfate catalytic oxidation process is to use the active oxygen species generated after activation to degrade pollutants, and the pure electrochemical process is to use the direct / indirect oxidation of the anode to degrade pollutants. By coupling the persulfate catalytic process and the electrochemical process, in addition to the above two pollutant degradation mechanisms, the cathodic reduction of the electrochemical process promotes the recycling of the catalyst in the persulfate activation process, thereby realizing the synergistic effect of the two processes.

[0039] The device and method for degrading organic pollutants by electrochemically enhancing transition metal-doped nickel-based phosphate activation of persulfate provided by the present application can realize effective degradation of organic pollutants and has wide application prospects.

[0040] The raw materials used in the application are cheap and easy to obtain, the operation method is simple, the synthesis is convenient, the prepared transition metal doped nickel-based phosphate catalyst can be applied to heterogeneous Fenton-like oxidation reaction, and the organic pollutants can be efficiently degraded by assisting electrochemical enhancement. Since the catalyst is simple to prepare, easy to industrialize, the device is simple and has strong universality, and the degradation efficiency of pollutants is high, it has very high application value in the treatment of organic pollutant wastewater. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 SEM image of the iron-doped nickel-based phosphate catalyst prepared for example 1 of the application.

[0042] Figure 2 FT-IR spectrum of the iron-doped nickel-based phosphate catalyst prepared for example 1.

[0043] Figure 3 Effect diagram of the iron-doped nickel-based phosphate catalyst prepared for example 1 in activating PMS to degrade tetracycline under the condition of adding different active oxygen quenching agents.

[0044] Figure 4 The device structure schematic diagram of the electrochemical enhancement transition metal doped nickel-based phosphate activated persulfate for degrading pollutants provided by the application.

[0045] Figure 5 The principle schematic diagram of the electrochemical enhancement iron-doped nickel-based phosphate activated PMS for degrading organic pollutants.

[0046] Figure 6 Effect diagram of different comparative examples and example 2 in degrading tetracycline.

[0047] The figure legend: 1-reaction tank; 2-organic pollutants; 3-transition metal doped nickel-based phosphate; 4-persulfate; 5-power supply; 6-anode; 7-cathode; 8-magnetic stirrer; 9-magnetic stirring rod. DETAILED DESCRIPTION

[0048] The application will be further described below in combination with examples, so that those skilled in the art can better understand the application and implement it. However, the examples are not intended to limit the application. In addition, in the preparation process of the following examples, if not otherwise specified, it is a conventional means in the prior art, therefore, it will not be described in detail; the raw materials used in the application are commercially available products.

[0049] The transition metal doped nickel-based phosphate catalyst used in the following examples and comparative examples is iron-doped nickel-based phosphate, which is prepared by the following method.

[0050] The preparation method of the iron-doped nickel-based phosphate catalyst comprises the following steps:

[0051] (1) 21.6 mg of potassium dihydrogen phosphate, 163 mg of dipotassium hydrogen phosphate, 711 mg of sodium chloride and 18 mg of potassium chloride are dissolved in 90 mL of aqueous solution to prepare a phosphate precursor solution with a pH of 7.2-7.4; 315.4 mg of nickel sulfate hexahydrate is dissolved in 4 mL of ultrapure water to prepare a nickel salt solution with a concentration of 0.3 mol / L;

[0052] (2) The nickel salt solution is added dropwise to the phosphate precursor solution, and is fully stirred at 800 rpm to ensure that the nickel ions and phosphate ions are fully mixed;

[0053] (3) The reaction system is cooled to -4 DEG C in a refrigerator and is aged at low temperature for 12 hours to promote the formation of the nickel-based phosphate porous nanostructure;

[0054] (4) The precipitate is collected by centrifugation at a speed of 5000 rpm; the precipitate is washed with ultrapure water to remove unreacted raw materials and byproducts, and is dried under vacuum at a temperature in the range of 60 DEG C to obtain the nickel-based phosphate porous nanomaterial;

[0055] (5) 100 mg of the washed and dried nickel-based phosphate porous nanomaterial is added to 80 mL of ultrapure water, which is referred to as solution A; 111.2 mg of iron sulfate heptahydrate is added to 20 mL of ultrapure water, which is referred to as solution B; solution B is added to solution A, and is fully stirred for 12 hours; the precipitate is collected by centrifugation at a speed of 5000 rpm by ion exchange; the precipitate is washed with ultrapure water to remove unreacted raw materials, and is dried under vacuum at a temperature in the range of 60 DEG C to obtain the iron-doped nickel-based phosphate catalyst.

[0056] Figure 1 The SEM image of the iron-doped nickel-based phosphate catalyst prepared in Example 1, and it can be seen from the SEM image that the iron-doped nickel-based phosphate catalyst is spherical. The catalyst has a hierarchical pore structure, which can promote the enrichment of pollutants and improve the mass transfer efficiency.

[0057] Figure 2 The FT-IR spectrum of the iron-doped nickel-based phosphate catalyst prepared in Example 1, and the basic skeleton structure of the iron-doped nickel-based phosphate catalyst of the application can be determined from the FT-IR spectrum.

[0058] Figure 3The effect diagram of the iron-doped nickel-based phosphate catalyst prepared in Example 1 on the degradation of tetracycline activated by PMS under the condition of adding different active oxygen quenchers (tetracycline concentration: 20 mg / L; PMS dosage: 1 mM; catalyst dosage: 0.1 g / L; tert-butyl alcohol, 500 mM, used to quench hydroxyl radicals; isopropyl alcohol, 500 mM, used to quench sulfate radicals; L-histidine, 1 mM, used to quench singlet oxygen) is shown in the figure. From the results of the quenching experiment, it can be concluded that in the system of the iron-doped nickel-based phosphate catalyst prepared in Example 1 activating PMS to degrade tetracycline, sulfate radicals, singlet oxygen and hydroxyl radicals are the main active oxygen species participating in the reaction, and the contribution rate order is: sulfate radicals > singlet oxygen > hydroxyl radicals.

[0059] Example 1

[0060] An apparatus for electrochemically enhancing transition metal-doped nickel-based phosphate activated persulfate to degrade pollutants, with reference to Figure 4 , comprising a reaction tank 1 for containing wastewater containing organic pollutants 2, transition metal-doped nickel-based phosphate 3 and persulfate 4; an anode 6 and a cathode 7 connected with a power supply 5 are arranged in the reaction tank; further comprising a stirring device for stirring the wastewater in the reaction tank; in a preferred embodiment, the stirring device comprises a magnetic stirrer 8 located below the reaction tank 1 and a magnetic stirring rod 9 placed in the reaction tank and used with the magnetic stirrer.

[0061] Example 2

[0062] A method for electrochemically enhancing transition metal-doped nickel-based phosphate activated persulfate to degrade pollutants, which is based on Figure 4 the apparatus, the transition metal-doped nickel-based phosphate used is iron-doped nickel-based phosphate, and the persulfate is PMS, comprising the following steps:

[0063] adding wastewater containing organic pollutants (tetracycline), iron-doped nickel-based phosphate catalyst and PMS into the reaction tank; wherein: the total volume of wastewater is 200 mL; the concentration of tetracycline is 20 mg / L; the catalyst dosage is 0.05 g / L; the PMS dosage is 0.5 mmol / L;

[0064] The anode material of the reaction tank is a ruthenium-iridium-titanium plate, and the cathode material is a titanium plate;

[0065] Starting the degradation reaction by supplying power to the anode and cathode through the power supply, with a current density of 4 mA / cm 2 ; during the degradation reaction, the magnetic stirrer (300 rpm) is turned on to stir the wastewater.

[0066] Figure 5The schematic diagram of the principle of electrochemically enhancing the iron-doped nickel-based phosphate to activate PMS to degrade organic pollutants is shown in the figure. The degradation of the pollutants is divided into three degradation paths P1, P2 and P3. Among them, the P1 degradation path is that the iron-doped nickel-based phosphate activates PMS to generate sulfate radicals to degrade the pollutants, the P2 degradation path is that the indirect anodic oxidation realizes the degradation of the pollutants, and the P3 degradation path is that the direct anodic oxidation realizes the degradation of the pollutants.

[0067] Test result analysis: immediately after the degradation reaction for 5 minutes, the sample was filtered through a 0.45 µm filter membrane, the tetracycline concentration was measured by using an ultraviolet spectrophotometer (λ = 356 nm), the concentration was defined as the measured concentration during detection, the initial concentration was 20 mg / L, and then the removal rate = (1-measured concentration / initial concentration)*100%.

[0068] The removal rate of tetracycline in the embodiment is 56%.

[0069] Comparative Example 1

[0070] Compared with Example 2, the difference of Comparative Example 1 is only that the power supply is turned off, that is, the power supply does not supply power to the anode and the cathode, and the current density is 0. Comparative Example 1 does not apply an electric field in the tetracycline degradation process, that is, the degradation of tetracycline is only realized by the active oxygen species generated by the iron-doped nickel-based phosphate catalyst activating PMS. Other processes are the same as those in Example 2.

[0071] The removal rate of tetracycline is tested by using the same test method as that in Example 2, and the removal rate of tetracycline in Comparative Example 1 is 14%.

[0072] Comparative Example 2

[0073] Compared with Example 2, the difference of Comparative Example 2 is only that the iron-doped nickel-based phosphate catalyst and PMS are not added in the reaction tank, that is, the degradation of tetracycline is only realized by the electrochemical process. Other processes are the same as those in Example 2.

[0074] The removal rate of tetracycline is tested by using the same test method as that in Example 2, and the removal rate of tetracycline in Comparative Example 2 is 21%.

[0075] Figure 6 The effect diagram of degrading tetracycline in different comparative examples and Example 2 can be seen, and it can be seen that the removal rate of tetracycline in Example 2 is greater than the sum of Comparative Example 1 and Comparative Example 2. It is proved that by coupling the electrochemical process and the PMS catalytic process, the synergistic promotion effect of the two processes is realized, and the degradation effect of tetracycline is effectively improved.

[0076] It should be noted that in other embodiments, when the experimental process meets the following conditions, the purpose of the present application can be achieved:

[0077] For the transition metal doped nickel-based phosphate, the doping element can be selected from cobalt, manganese or copper, in addition to iron, and these transition metals have similar catalytic properties;

[0078] For the persulfate, in addition to peroxymonosulfate, peroxodisulfate can also be selected;

[0079] For the current density, it is preferably 1-20 mA / cm 2 , specifically 1 mA / cm 2 , 5 mA / cm 2 , 10 mA / cm 2 or 20 mA / cm 2 , etc.

[0080] For the pollutants, in addition to tetracycline, penicillins, cephalosporins and other antibiotics, or dyes, etc.

[0081] For the anode, carbon electrode, noble metal electrode, etc.

[0082] For the cathode, carbon electrode, aluminum electrode or copper electrode, etc.

[0083] For the above process parameters, those skilled in the art can make appropriate selection according to actual needs, and all of them can achieve the purpose of the present application.

[0084] Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

Claims

1. A method for electrochemically enhancing the degradation of pollutants by transition metal-doped nickel-based phosphate-activated persulfate, characterized in that, Includes the following steps: A reaction tank is provided, wherein an anode and a cathode connected to a power source are provided in the reaction tank; Wastewater containing organic pollutants, transition metal-doped nickel-based phosphate, and persulfate were added to the reaction tank; The degradation reaction begins by supplying power to the anode and cathode, and the wastewater is stirred during the reaction. The transition metal-doped nickel-based phosphate was prepared by the following method: Phosphate precursor solution and nickel salt solution were prepared separately. The nickel salt solution was added to the phosphate precursor solution and reacted under stirring conditions. After low-temperature aging, nickel-based phosphate porous nanomaterials were obtained. Nickel-based phosphate porous nanomaterials were added to a transition metal salt solution, and transition metal-doped nickel-based phosphates were prepared by ion exchange.

2. The method for electrochemically enhanced transition metal-doped nickel-based phosphate activation of persulfate to degrade pollutants according to claim 1, characterized in that: The phosphate used to prepare the phosphate precursor solution is at least one of disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, potassium phosphate, and sodium phosphate; the nickel salt used to prepare the nickel salt solution is at least one of nickel sulfate, nickel chloride, and nickel nitrate; the transition metal salt in the transition metal salt solution is a water-soluble iron salt, cobalt salt, manganese salt, or copper salt.

3. The method for electrochemically enhanced transition metal-doped nickel-based phosphate activation of persulfate to degrade pollutants according to claim 1, characterized in that: The anode is a carbon electrode, a noble metal electrode, or a metal oxide electrode.

4. The method for electrochemically enhanced transition metal-doped nickel-based phosphate activation of persulfate to degrade pollutants according to claim 1, characterized in that: The cathode is a titanium plate, a carbon electrode, an aluminum electrode, or a copper electrode.

5. The method for electrochemically enhanced transition metal-doped nickel-based phosphate activation of persulfate to degrade pollutants according to claim 1, characterized in that: The organic pollutant is one of antibiotics or dyes.

6. The method for electrochemically enhanced transition metal-doped nickel-based phosphate activation of persulfate to degrade pollutants according to claim 1, characterized in that: The persulfate is either permonosulfate or perdisulfate.

7. The method for electrochemically enhanced transition metal-doped nickel-based phosphate-activated persulfate degradation of pollutants according to any one of claims 1 to 6, characterized in that: The current density of the power supply is 1-20 mA / cm². 2 .

8. An apparatus for electrochemically enhanced transition metal-doped nickel-based phosphate activation of persulfate for pollutant degradation, characterized in that: The device includes a reaction tank for containing wastewater containing organic pollutants, transition metal-doped nickel-based phosphate and persulfate prepared by the method as described in claim 1; the reaction tank is provided with an anode and a cathode connected to a power source; and it also includes a stirring device for stirring the wastewater in the reaction tank.

9. The apparatus for electrochemically enhanced transition metal-doped nickel-based phosphate activation of persulfate for pollutant degradation according to claim 8, characterized in that: The stirring device includes a magnetic stirrer located below the reaction tank and a magnetic stir bar placed inside the reaction tank for use with the magnetic stirrer.

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