Photoelectrocatalysis membrane electrode for nitrate nitrogen wastewater treatment, preparation method thereof and ammonia recovery coupling integrated device

Abstract

The invention discloses a photoelectrocatalysis membrane electrode for nitrate nitrogen wastewater treatment, a preparation method of the photoelectrocatalysis membrane electrode and an ammonia recovery coupling integrated device, and belongs to the technical field of photoelectrocatalysis. The photoelectrocatalysis membrane electrode disclosed by the invention has a photoelectrocatalysis synergistic effect. The high dispersity of metal single atoms on carbon nitride enhances the adsorption and activation capability of the membrane electrode to nitrate, and meanwhile, improves the carrier separation efficiency and the photo-induced electron utilization rate, and can realize efficient and stable reduction of nitrate into ammonia with low energy consumption. The continuous flow type photoelectrocatalysis membrane reactor and the ammonia recovery device are integrated, nitrate wastewater is reduced into ammonia at a cathode after entering the photoelectrocatalysis membrane reactor, the ammonia flows out of the ammonia recovery device through a water outlet hole, the ammonia in the wastewater overflows from a hollow fiber membrane and is collected by acid, and the remaining wastewater is recycled to a wastewater pool again. The processes of nitrate photoelectric catalytic reduction and ammonia separation and recovery are realized.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalysis technology, specifically relating to a photoelectrocatalytic membrane electrode for nitrate wastewater treatment, its preparation method, and an integrated device coupled with ammonia recovery. Background Technology

[0002] The excessive use of nitrogen fertilizers and improper treatment and discharge of industrial and domestic wastewater have led to a continuous increase in nitrate pollution in water bodies. In some surface waters and groundwaters, nitrate concentrations have reached over 100 mg / L. This not only causes eutrophication and damages aquatic ecosystems but also seriously endangers human health and may even induce cancer. Therefore, removing excess nitrates from water bodies or reducing nitrate levels in industrial wastewater discharge at the source has become a crucial task in controlling water pollution.

[0003] Currently, commonly used water denitrification technologies include ion exchange, physical adsorption, reverse osmosis, electrodialysis, chemical reduction, and biological denitrification. However, these technologies all have certain drawbacks, such as generating high-concentration wastewater, low reaction efficiency, high operating costs, and severe susceptibility to environmental conditions. These problems hinder the large-scale application of the above water denitrification technologies, therefore, there is an urgent need to develop an efficient, harmless, and resource-efficient method for treating nitrates in water bodies.

[0004] Compared to the aforementioned denitrification technologies, photoelectrocatalytic nitrate treatment is a promising green process due to its ability to achieve highly efficient denitrification without the need for chemical reagents and powered by renewable energy sources. Furthermore, photoelectrocatalytic nitrate reduction leads to ammonia synthesis, and ammonia, as an important basic chemical raw material, can be recycled as a value-added product. Therefore, photoelectrocatalytic nitrate treatment is considered a resource recovery strategy that "turns waste into treasure."

[0005] However, existing research on photoelectrocatalytic nitrate reduction is typically conducted in batch reactors, focusing primarily on the synthesis of ammonia from nitrates while neglecting subsequent ammonia recovery steps. This limits its industrial-scale application. Therefore, there is an urgent need to develop a continuous-flow reactor to adapt to the characteristics of large volumes and flow-type flow in natural water bodies or industrial wastewater, and to combine it with an ammonia recovery device for resource recovery. Summary of the Invention

[0006] In order to solve the technical problem that batch reactors cannot operate continuously in the photoelectrocatalytic treatment of nitrate wastewater, this invention provides a photoelectrocatalytic membrane electrode for nitrate wastewater treatment, its preparation method, and an integrated device coupled with ammonia recovery.

[0007] The technical solution of the present invention is as follows: One objective of this invention is to provide a method for preparing a photoelectrocatalytic membrane electrode for treating nitrate-nitrogen wastewater, comprising the following steps: (1) Melamine solution, cyanuric acid solution, citric acid solution and metal salt solution are stirred and reacted to form a precursor mixture; (2) Centrifuge the precursor mixture, collect the precipitate, wash, dry and grind the precipitate to obtain precursor powder; (3) The precursor powder was calcined in an inert gas atmosphere to obtain a carbon nitride powder catalyst modified with metal single atoms; (4) The carbon nitride powder catalyst modified with metal single atom and the multi-walled carbon nanotubes are ultrasonically dispersed in an organic solvent containing polyacrylonitrile to obtain a mixed dispersion. The mixed dispersion is vacuum filtered on a ceramic membrane substrate, and after peeling, washing and drying, a photoelectrocatalytic membrane electrode is obtained.

[0008] Further specifying, (1) the metal salt is one or two of Ni(NO3)2, Cu(NO3)2, Fe(NO3)2, Co(NO3)2, and AgNO3.

[0009] Further specifying, the molar ratio of melamine, cyanuric acid, citric acid and metal salt in (1) is (10-12): (9-10): 1: (0.05-0.2).

[0010] Further specified, the stirring speed in (1) is 500-600 rpm and the time is 4-6 h.

[0011] Further specified, (3) the inert gas is argon or nitrogen, the heating rate of the calcination process is 2-5 ℃ / min, the calcination temperature is 500-600 ℃, and the holding time is 3-5 h.

[0012] Further specifying, the mass ratio of the metal single-atom modified carbon nitride powder catalyst to the multi-walled carbon nanotube in (4) is (1-2): (1-2).

[0013] Further specified, (4) the organic solvent is dimethylformamide, and the mass percentage of polyacrylonitrile in the organic solvent is 0.1-0.3 wt%.

[0014] Further specifying, the total concentration of the metal single-atom modified carbon nitride powder catalyst and multi-walled carbon nanotubes in the organic solvent in (4) is 5-8 g / L.

[0015] The second objective of this invention is to provide a photoelectrocatalytic membrane electrode for treating nitrate wastewater prepared by the above method.

[0016] The third objective of this invention is to provide an integrated ammonia recovery device, which includes a photoelectrocatalytic membrane reactor 1, an ammonia recovery device 2, a wastewater tank 3, an acid capture tank 4, a power supply 5, and a light source 6. The photoelectrocatalytic membrane reactor 1 consists of a membrane reactor inlet 7, a membrane reactor outlet 8, an anode region 9, a cathode region 10, an anode 11, a cathode 12, and a light-transmitting surface 14. The positive and negative terminals of the power supply 5 are connected to the anode 11 and the cathode 12, respectively, to supply electrical energy. The light source 6 supplies light energy and is vertically positioned above the photoelectrocatalytic membrane reactor 1. The ammonia recovery device 2 includes one or more bundles of hollow fiber membranes 13.

[0017] Further defined, nitrate wastewater enters the photoelectrocatalytic membrane reactor through the inlet of the membrane reactor, where oxidation and reduction reactions occur at the anode and cathode, respectively. Nitrate is reduced to ammonia at the cathode and flows out through the outlet of the membrane reactor into the ammonia recovery device. Ammonia in the wastewater overflows from the hollow fiber membrane and is collected by the acid in the chamber of the ammonia recovery device, where the acid capture tank serves as the source of the acidic solution. The remaining wastewater enters the wastewater pool and then continues to be circulated back into the photoelectrocatalytic membrane reactor for photoelectrocatalytic treatment, thereby realizing the photoelectrocatalytic reduction of nitrate and the separation and recovery of ammonia.

[0018] Furthermore, the light-transmitting surface 14 of the photoelectrocatalytic membrane reactor 1 is made of quartz glass.

[0019] Further specifying, the anode 11 is a porous titanium sheet or porous carbon cloth, connected to the positive terminal of the power supply, to ensure that the nitrate wastewater has sufficient contact and flow with the cathode.

[0020] Further defining the cathode 12 as a metal single-atom modified carbon nitride photocatalytic membrane electrode, it is connected to the negative terminal of the power supply, and the light source shines vertically onto the surface of the metal single-atom modified carbon nitride photocatalytic membrane electrode through the light-transmitting surface 14.

[0021] Further specifying, the hollow fiber membrane is a hydrophobic and breathable membrane, and the membrane material is polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF).

[0022] The beneficial effects of this invention are as follows: (1) The photoelectrocatalytic membrane electrode of the present invention is a metal single-atom modified carbon nitride photoelectrocatalytic membrane electrode, which is prepared by metal single-atom modified carbon nitride powder catalyst and multi-walled carbon nanotubes. Therefore, the photoelectrocatalytic membrane electrode not only has excellent photoelectrocatalytic synergistic effect, but also has catalytic effect. The uniform distribution of metal single atoms on the carbon nitride support significantly enhances the adsorption and activation ability of the photoelectrocatalytic membrane electrode for nitrate in wastewater, while improving the carrier separation efficiency and photogenerated electron utilization rate, thereby achieving a highly efficient and stable nitrate reduction to ammonia reaction with low energy consumption.

[0023] (2) This invention integrates a continuous flow photoelectrocatalytic membrane reactor with an ammonia recovery device, realizing continuous and automated operation of nitrate wastewater treatment and ammonia resource recovery. The integrated device is compact and easy to operate, and is suitable for actual wastewater treatment scenarios with large flow and continuous discharge, overcoming the shortcomings of traditional batch reactors with limited treatment capacity and inability to adapt to industrial continuous flow operation.

[0024] (3) This invention achieves efficient in-situ separation and recovery of ammonia through hydrophobic hollow fiber membrane, avoiding the accumulation of ammonia in the system from inhibiting the catalytic process. At the same time, the reduction product can be recycled in the form of ammonium salt (determined by the type of acid; when the acid is hydrochloric acid, the recovered ammonium salt is ammonium chloride). This realizes a closed-loop treatment mode of "pollutant removal - product recovery - wastewater recycling", which has both environmental benefits and resource recovery value, and has good prospects for engineering application. Attached Figure Description

[0025] Figure 1 The metal single-atom modified carbon nitride catalyst (Ni) prepared in Example 1 0.1 SEM and EDS plots of -CN); Figure 2 For example Ni in application 1 0.1 Comparison chart of nitrate removal performance of CN / CM under different conditions; Figure 3 For example Ni in application example 2 0.05 -CN / CM、Ni 0.1 -CN / CM、Ni 0.15 -CN / CM and Ni 0.2 Comparison of photoelectrocatalytic nitrate reduction performance on CN / CM; Figure 4 For example Ni in application example 2 0.1 Comparison of nitrate levels over time on CN / CM and CN / CM; Figure 5 For example Ni in application example 2 0.1 Comparison of ammonia levels over time on CN / CM and CN / CM; Figure 6 This invention relates to an integrated ammonia recovery coupling device; Among them, 1. Photoelectrocatalytic membrane reactor; 2. Ammonia recovery device; 3. Wastewater pool; 4. Acid capture pool; 5. Power supply; 6. Light source; 7. Membrane reactor inlet; 8. Membrane reactor outlet; 9. Anode area; 10. Cathode area; 11. Anode; 12. Cathode; 13. Hollow fiber membrane; 14. Transmitting surface. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0028] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0029] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0030] Example 1 (1) Weigh out 1.261 g (10 mmol) of melamine, 1.226 g (9.5 mmol) of cyanuric acid, 0.192 g (1 mmol) of citric acid and 0.0291 g (0.1 mmol) of Ni(NO3)2·6H2O respectively, and dissolve them in 40 mL of deionized water. Stir magnetically until each substance is completely dissolved to obtain four solutions. Mix the above four solutions and stir continuously at 500 rpm for 6 h at room temperature to allow the four substances to react fully and form a homogeneous precursor mixture. (2) The precursor mixture was transferred to a centrifuge tube and centrifuged at 10,000 rpm for 10 min. The supernatant was discarded, and the precipitate was collected. The precipitate was washed three times each with deionized water and anhydrous ethanol, and then dried in an oven at 80 °C for 12 h. The dried sample was ground into a fine powder to obtain the precursor powder. (3) The above precursor powder was placed in an alumina ceramic boat, placed in a tube furnace, and heated to 550 °C at a heating rate of 5 °C / min under argon atmosphere protection, and held at that temperature for 4 h for calcination. After calcination, it was naturally cooled to room temperature to obtain metal single-atom modified carbon nitride (Ni). 0.1 -CN) powdered catalyst; (4) Take 50 mg of Ni-NC powder and 50 mg of multi-walled carbon nanotubes, add them together to 20 mL of dimethylformamide (DMF) solution containing 0.1 wt% polyacrylonitrile, and ultrasonically disperse for 1 h to obtain a uniform catalyst slurry. Pour the slurry into a vacuum filtration device containing a ceramic membrane substrate (50 mm in diameter, 200 nm in average pore size), filter under vacuum to form a membrane, then peel the membrane off the substrate, rinse it three times with deionized water, and dry it in a vacuum drying oven at 60 ℃ for 6 h to obtain Ni 0.1 -CN film electrode, denoted as Ni 0.1 -CN / CM.

[0031] Figure 1 The Ni single-atom modified carbon nitride (Ni) prepared in this embodiment 0.1 The SEM and EDS images of the -CN catalyst show that the catalyst surface exhibits a porous, polymeric microstructure with abundant active sites. The Ni element distribution map in the EDS image indicates that trace amounts of Ni atoms and carbon nitride have been successfully doped into the catalyst.

[0032] Example 2 The difference between this embodiment and Embodiment 1 is that in step (1), Ni(NO3)2·6H2O is 0.05 mmol, i.e., 0.01455 g. The remaining process steps and parameter settings are the same as in Embodiment 1, and Ni is finally obtained. 0.05 -CN film electrode, denoted as Ni 0.05 -CN / CM.

[0033] Example 3 The difference between Example 3 and Example 1 is that in step (1), Ni(NO3)2·6H2O is 0.15 mmol, i.e., 0.04365 g. The remaining process steps and parameter settings are the same as in Example 1, and Ni is finally obtained. 0.15 -CN film electrode, denoted as Ni 0.15 -CN / CM.

[0034] Example 4 The difference between Example 4 and Example 1 is that in step (1), Ni(NO3)2·6H2O is 0.2 mmol, i.e., 0.0582 g. The remaining process steps and parameter settings are the same as in Example 1, and Ni is finally obtained. 0.2 -CN film electrode, denoted as Ni 0.2 -CN / CM.

[0035] Comparative Example 1 The difference between this comparative example and Example 1 is that Ni(NO3)2·6H2O and citric acid are not added in step (1), while the remaining process steps and parameter settings are the same as in Example 1, and a carbon nitride film electrode is finally obtained, denoted as CN / CM.

[0036] Application Example 1 This application example is used to study the effect of the electrode of the present invention on nitrate removal performance under different environmental conditions, in order to elucidate the photoelectric synergistic effect.

[0037] The continuous flow membrane reactor and ammonia recovery integrated device of the present invention, such as Figure 6 As shown, this application example uses this device, wherein the Ni prepared in Example 1 0.1 -CN / CM was used as the cathode 12, and a porous titanium sheet electrode with a pore area of ​​3 mm × 6 mm and a porosity of 70% was used as the anode 11. The wastewater to be treated was a mixed aqueous solution of 100 mL of 0.1 mol / L Na2SO4 and 200 mg N / L NaNO3, simulating nitrate wastewater. The solution was pumped through a peristaltic pump at a flow rate of 5 mL / min. Figure 6 The light flows in the direction indicated by the middle arrow. Light source 6 is a 300 W xenon lamp (equipped with an AM 1.5G filter to simulate sunlight), which shines perpendicularly onto the surface of cathode 12 through the light-transmitting surface 14, with a light intensity of 100 mW / cm². 2 The power supply 6 applies a potential of 3.5 V between the positive and negative electrodes. The mixed aqueous solution enters the photoelectrocatalytic membrane reactor 1 through the inlet 7 of the membrane reactor, where oxidation and reduction reactions occur at the anode 11 and cathode 12, respectively. Nitrate is reduced to ammonia at the cathode 12 and flows out through the outlet 8 of the membrane reactor into the ammonia recovery device 2. Ammonia in the wastewater overflows from the hollow fiber membrane 13 made of PVDF and is collected by 1 M hydrochloric acid in the chamber of the ammonia recovery device 2 and recovered as ammonium chloride. The acid capture tank 4 serves as the source of the acidic solution. The remaining wastewater is recycled back to the wastewater tank 3, realizing the photoelectrocatalytic reduction of nitrate and the separation and recovery of ammonia.

[0038] This application example sets up three sets of comparative experiments: ① Illumination only: Light source 6 is turned on (light intensity 100 mW / cm²) 2 ① No external voltage is applied; ② Electrochemical conditions only: A voltage of 3.5 V is applied, and the photoelectrocatalytic membrane reactor 1 is in a completely light-proof state; ③ Photoelectrochemical synergistic conditions: Light source 6 is turned on simultaneously (light intensity 100 mW / cm²). 2 A voltage of 3.5 V was applied. The reaction time for each group of experiments was 90 min. After the reaction, the NO3 in the solution was determined by ultraviolet-visible spectrophotometry. ﹣ -N and NH4 + -N concentration.

[0039] Figure 2 For this application example, Ni 0.1 Using -CN / CM as the working electrode, the ammonia recovery coupling integrated device of this invention yielded the results of nitrate reduction to ammonia production under three conditions: illumination, applied voltage, and photoelectric synergy. From... Figure 4 It can be seen from this that Ni 0.1 Under photoelectric synergistic conditions, the nitrate removal rate, ammonia selectivity, and ammonia production rate of -CN / CM reached 98.53%, 98.16%, and 257.90 mg·h, respectively. -1 ·mg cat -1 The value is far higher than that under conditions of light exposure only and voltage application only, proving that Ni 0.1 -CN / CM exhibits highly efficient photoelectrochemical synergistic catalytic performance in the reduction of nitrate to ammonia.

[0040] Application Example 2 This application example compares the differences in the photoelectrocatalytic nitrate removal performance of membrane electrodes modified with different amounts of metal.

[0041] This application example also uses the following... Figure 6 The device shown was subjected to performance testing. The wastewater to be treated and the flow rate were the same as in Application Example 1. The difference was that the cathode 12 in this application example was a Ni-CN / CM electrode prepared in Examples 1, 2, 3, and 4, and a CN / CM electrode prepared in Comparative Example 1, for comparison. The reaction conditions were photoelectrocatalysis, i.e., the light source 6 (light intensity 100 mW / cm²) was turned on simultaneously. 2 A voltage of 3.5 V was applied to power supply 5, and the reaction time was 90 min. 2 mL water samples were taken every 10 min to determine the NO3 content in the solution. ﹣ -N and NH4 + -N concentration.

[0042] The photoelectrocatalytic nitrate reduction performance of the membrane electrode under different Ni dosage modifications is as follows: Figure 3 As shown, after 90 min of reaction, the nitrate removal rate and ammonia production rate exhibited a volcano-like relationship with the Ni dosage, reaching their maximum at a Ni dosage of 0.1 mM. Furthermore, Ni... 0.1 The results of the nitrate nitrogen concentration change over time between -CN / CM and CN / CM are as follows: Figure 4 As shown, the results of ammonia nitrogen concentration changing over time are as follows: Figure 5 As shown. The results indicate that Ni within 0-90 min 0.1 The reduction of nitrate to ammonia on -CN / CM is superior to that on CN / CM. At 90 minutes after the reaction ends, Ni... 0.1The nitrate nitrogen concentration on the CN / CM was only 2.942 mg N / L, and the ammonia nitrogen concentration was 193.425 mg N / L, with a nitrate removal rate as high as 98.53%, almost completely removed; while the nitrate nitrogen concentration on the CN / CM was 19.464 mg N / L, and the ammonia nitrogen concentration was 167.001 mg N / L, with a nitrate removal rate of 90.27%. This demonstrates that the Ni prepared in this invention... 0.1 The introduction of metallic Ni atoms in -CN / CM improves the photoelectrocatalytic activity of carbon nitride materials for nitrate reduction and the selectivity of ammonia production.

[0043] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a photoelectrocatalytic membrane electrode for treating nitrate-nitrogen wastewater, characterized in that, Includes the following steps: (1) Melamine solution, cyanuric acid solution, citric acid solution and metal salt solution are stirred and reacted to form a precursor mixture; (2) Centrifuge the precursor mixture, collect the precipitate, wash, dry and grind the precipitate to obtain precursor powder; (3) The precursor powder was calcined in an inert gas atmosphere to obtain a carbon nitride powder catalyst modified with metal single atoms; (4) The carbon nitride powder catalyst modified with metal single atom and the multi-walled carbon nanotubes are ultrasonically dispersed in an organic solvent containing polyacrylonitrile to obtain a mixed dispersion. The mixed dispersion is vacuum filtered on a ceramic membrane substrate, and after peeling, washing and drying, a photoelectrocatalytic membrane electrode is obtained.

2. The preparation method according to claim 1, characterized in that, (1) The metal salt is one or two of Ni(NO3)2, Cu(NO3)2, Fe(NO3)2, Co(NO3)2, and AgNO3. The stirring speed is 500-600 rpm and the time is 4-6 h.

3. The preparation method according to claim 1, characterized in that, (1) The molar ratio of melamine, cyanuric acid, citric acid and metal salt in the mixture is (10-12): (9-10): 1: (0.05-0.2).

4. The preparation method according to claim 1, characterized in that, (3) The inert gas is argon or nitrogen. The heating rate during the calcination process is 2-5 ℃ / min, the calcination temperature is 500-600 ℃, and the holding time is 3-5 h.

5. The preparation method according to claim 1, characterized in that, (4) The mass ratio of the metal single-atom modified carbon nitride powder catalyst to the multi-walled carbon nanotube is (1-2): (1-2).

6. The preparation method according to claim 1, characterized in that, (4) The organic solvent is dimethylformamide, the mass percentage of polyacrylonitrile in the organic solvent is 0.1-0.3 wt%, and the total concentration of metal single-atom modified carbon nitride powder catalyst and multi-walled carbon nanotubes in the organic solvent is 5-8 g / L.

7. A photoelectrocatalytic membrane electrode for treating nitrate wastewater, obtained by the preparation method according to any one of claims 1-6.

8. An integrated ammonia recovery coupling device, characterized in that, The device includes a photoelectrocatalytic membrane reactor (1), an ammonia recovery device (2), a wastewater pool (3), an acid capture pool (4), a power supply (5), and a light source (6). The photoelectrocatalytic membrane reactor (1) consists of a membrane reactor inlet (7), a membrane reactor outlet (8), an anode region (9), a cathode region (10), an anode (11), a cathode (12), and a light-transmitting surface (14); The positive and negative terminals of the power supply (5) are connected to the anode (11) and the cathode (12), respectively; The ammonia recovery device (2) includes one or more hollow fiber membranes (13). The cathode (12) is the photoelectrocatalytic membrane electrode as described in claim 7.

9. The apparatus according to claim 8, characterized in that, The anode (11) is a porous titanium sheet or a porous carbon cloth.

10. The apparatus according to claim 8, characterized in that, The hollow fiber membrane (13) is a hydrophobic and breathable membrane, and the membrane material is polytetrafluoroethylene or polyvinylidene fluoride.

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