Preparation method of double-confinement hollow photocathode and application of double-confinement hollow photocathode in photoelectrocatalytic synthesis of ammonia

Abstract

The invention belongs to the technical field of photoelectrocatalysis, and particularly relates to a preparation method of a double-confinement hollow photocathode and application of the double-confinement hollow photocathode in synthesis of ammonia from nitrate wastewater through photoelectric reduction. According to the method, based on an ion exchange and in-situ growth strategy, a FeMnO3 / CuFe2O4 / Ti hollow cube integrated photocathode is constructed, hydroxyl functionalized ionic liquid (OH-ILs) is further introduced through vacuum impregnation, and an ILs (at) FeMnO3 / CuFe2O4 / Ti nanoreactor with a dual confinement effect is formed. Under ultraviolet-visible-near infrared (UV-Vis-NIR) illumination, the photocathode can remarkably promote separation of photo-induced electron-hole pairs, the charge transfer efficiency is improved, and high-selectivity and high-efficiency ammonia synthesis is achieved. Experiments show that the photocathode can almost completely convert nitrate in high-concentration nitrate wastewater (50mM) within 2.5 hours, so that the effluent reaches the drinking water standard of the World Health Organization (WHO). In a flowing electrolytic tank, the ammonia yield reaches 20.51 mg h <-1 > cm <-2 >, the Faraday efficiency reaches up to 97.75%, and excellent catalytic performance is shown.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photoelectrocatalysis, and particularly relates to a preparation method of a double-limited hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photoanode and application thereof in photoelectrocatalytic reduction of nitrate to synthesize ammonia. BACKGROUND

[0002] Globally, nitrogen pollution has become a serious problem that threatens water environment and human health. Nitrate, as one of the most common nitrogen pollutants, mainly comes from the overuse of nitrogen fertilizer in agriculture, industrial wastewater discharge and domestic sewage leakage. Excessive nitrate entering water bodies can cause water bloom, groundwater eutrophication, and even affect human health through the food chain, and is believed to be closely related to "blue baby syndrome", cancer and other diseases. Therefore, how to efficiently remove nitrate in the environment has become an important issue to be solved in the fields of environmental chemistry and energy conversion.

[0003] Traditional nitrate removal methods include biological denitrification, physical adsorption and chemical reduction. Although biological methods are widely used, the reaction process depends on microbial activity and is limited by temperature, pH and carbon source conditions, and the treatment efficiency is limited; physical methods such as ion exchange and reverse osmosis often have high energy consumption or secondary pollution problems; and chemical reduction method requires expensive reducing agents and has low selectivity. These shortcomings have prompted people to explore new green and controllable strategies.

[0004] In recent years, photoelectrochemical nitrate reduction has attracted much attention due to its mild reaction conditions, simple operation and the ability to couple green light and electricity. In particular, the nitrate reduction pathway with ammonia (NH3) as the target product is considered as a "win-win" approach to achieve environmental remediation and resource utilization. On the one hand, this process can effectively remove nitrate in water bodies and reduce environmental risks; on the other hand, ammonia, as an important nitrogen fertilizer and energy carrier, has great economic and strategic value. Currently, ammonia is mainly synthesized by the Haber-Bosch process, which requires high temperature and high pressure conditions and consumes a large amount of fossil fuels, resulting in huge carbon emissions. In contrast, electrochemical nitrate reduction can directly produce ammonia at room temperature and pressure, which is expected to become an important supplement or even replacement for traditional processes. However, existing photoelectrocatalysts generally have low charge separation efficiency, serious side reactions (HER), and poor selectivity.

[0005] Designing photoelectrocatalysts with heterojunction structure and hollow confinement effect can effectively improve charge transport and promote NO3 -The adsorption and selectivity are enhanced. In addition, the introduction of ionic liquids (ILs) can further regulate the electronic environment, provide a H*rich microenvironment, and inhibit side reactions, thereby significantly improving the yield of NH3 and the Faraday efficiency. Therefore, the application designs a hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type heterostructure photocathode with double confinement effect, which is applied to photoelectrocatalytic preparation of NH3. SUMMARY

[0006] One of the purposes of the application is to provide a hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photocathode with visible light response and effective separation of photo-generated electrons and holes and a preparation method thereof.

[0007] The second purpose of the application is to provide a method for photoelectrocatalytic preparation of NH3 by using the hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photocathode.

[0008] The technical scheme adopted by the application is:

[0009] A double confinement hollow photocathode, FeMn-PBA / Ti is synthesized by dispersing MnCl2·4H2O and K3[Fe(CN)6] in water and growing on Ti mesh in situ; FeMn-PBA@CuFe-PBA / Ti is obtained by converting part of FeMn-PBA into CuFe-PBA through ion exchange method; FeMnO3 / CuFe2O4 / Ti is obtained by calcining FeMn-PBA@CuFe-PBA / Ti; and finally OH-ILs is introduced into FeMnO3 / CuFe2O4 / Ti by vacuum impregnation to obtain a double confinement hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photocathode.

[0010] A preparation method of a double confinement hollow photocathode, comprising the following steps:

[0011] 1) Dissolve MnCl2·4H2O and K3[Fe(CN)6] in water and pour into Ti mesh, stir the reaction, centrifuge to collect the product, wash with ethanol and water, and dry to obtain FeMn-PBA / Ti;

[0012] 2) Put the FeMn-PBA / Ti prepared in step 1) into water, add Cu(NO3)2·3H2O aqueous solution thereto, stir the reaction, centrifuge to collect, wash with deionized water and ethanol, and dry to obtain FeMn-PBA@CuFe-PBA / Ti;

[0013] 3) Calcine the FeMn-PBA@CuFe-PBA / Ti prepared in step 2) to obtain FeMnO3 / CuFe2O4 / Ti;

[0014] 4) The FeMnO3 / CuFe2O4 / Ti prepared in step 3) is placed in a flask and activated in a vacuum environment, then the OH-ILs methanol solution is injected into the flask, stirred under vacuum, collected by centrifugation and washed with methanol to obtain the OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photoelectrode.

[0015] Further, in the above preparation method, in step 1), the molar ratio of MnCl2·4H2O and K3[Fe(CN)6] is 1:2, the stirring reaction condition is stirring at room temperature for 15 hours, and the drying temperature is 60℃.

[0016] Further, in the above preparation method, in step 2), the molar ratio of FeMn-PBA / Ti and Cu(NO3)2·3H2O is 1:1, the stirring reaction condition is stirring at room temperature for 3 hours, and the drying temperature is 60℃.

[0017] Further, in the above preparation method, in step 3), the calcination condition is in air, the heating rate is 2℃ / min, and the temperature is kept at 400℃ for 2 hours.

[0018] Further, in the above preparation method, in step 4), the activation temperature is 60℃, the activation time is 3 hours, and the stirring is carried out at 30℃ for 24 hours under vacuum.

[0019] Further, in the above preparation method, in step 4), the OH-ILs used is 1-hydroxyethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide salt, and the mass ratio of OH-ILs to FeMnO3 / CuFe2O4 / Ti is 1:1.

[0020] The above-mentioned double-limited hollow photoelectrode is applied to photoelectrocatalytic synthesis of NH3.

[0021] Further, in the above application, the method is as follows: the OH-ILs@FeMnO3 / CuFe2O4 / Ti is used as a working electrode, a platinum sheet is used as a counter electrode, and a silver / silver chloride electrode is used as a reference electrode, which are placed in an H-type reactor to form a three-electrode system; the cathode electrolyte is 0.5M sodium sulfate and 10-1500mM sodium nitrate, and the anode electrolyte is 0.5M sodium sulfate; the reaction is carried out under an applied voltage and simulated sunlight irradiation to catalytically synthesize NH3.

[0022] Further, in the above application, the applied voltage is-1.4V Vs. RHE, and the simulated sunlight irradiation is using a 300W xenon lamp as a light source, and the xenon lamp λ≥420nm.

[0023] 1、The hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photo-cathode is synthesized by in-situ growth, ion exchange method and vacuum impregnation method, further improves light response, inhibits the recombination of electron hole pairs, improves the utilization rate of electron hole pairs, improves the nitrate adsorption capacity, improves the local H* concentration, and improves the photocatalytic activity.

[0024] 2、Under the irradiation of visible light and the action of a specific additional bias, 20.51 mg h -1 cm -2 cm-2 is realized in a flow cell, and the super-high NH3 yield provides a green synthesis route and sustainable technology for the production of NH3.

[0025] 3、The application has the characteristics of simplicity, high efficiency and low cost, the prepared hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photo-cathode has the characteristics of good conductivity, good nitrate adsorption effect and high catalytic activity, and has good visible light absorption performance and good stability, the separation efficiency of photo-generated electron hole pairs is high, the interface charge transmission efficiency is fast, the production of NH3 is high, and the application can be applied to the field of photoelectric catalytic production of NH3. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the transmission electron microscopy (TEM) of FeMnO3 / CuFe2O4 (a) and OH-ILs@FeMnO3 / CuFe2O4 (b).

[0027] Figure 2 is the XRD (a) and XPS (b) of FeMnO3 / CuFe2O4 and OH-ILs@FeMnO3 / CuFe2O4.

[0028] Figure 3 is the EIS (a) and photocurrent (b) of FeMnO3 / CuFe2O4 and OH-ILs@FeMnO3 / CuFe2O4.

[0029] Figure 4 is the OCP change (a) and reaction order (b) of FeMnO3 / CuFe2O4 and OH-ILs@FeMnO3 / CuFe2O4.

[0030] Figure 5 is the CV (a) and EPR (b) of FeMnO3 / CuFe2O4 and OH-ILs@FeMnO3 / CuFe2O4.

[0031] Figure 6 is the concentration change graph of NO3 - , NO2 - and NH3 with the catalytic time.

[0032] Figure 7 is a catalytic performance diagram of OH-ILs@FeMnO3 / CuFe2O4 under different nitrate concentrations.

[0033] Figure 8 is a schematic diagram of the principle of synthesizing ammonia by photoelectrocatalytic reduction of nitrate by OH-ILs@FeMnO3 / CuFe2O4 double confinement. DETAILED DESCRIPTION

[0034] The application will be further described below with reference to specific examples.

[0035] Preparation of hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photoanode in Example 1

[0036] (I) Preparation of FeMn-PBA / Ti

[0037] Dissolve 1.98 g of MnCl2·4H2O and 6.59 g of trisodium citrate in 200 mL of water as solution A, and pour Ti mesh into it, dissolve 6.59 g of K3[Fe(CN)6] in 200 mL of water as solution B; then quickly add solution B to solution A at room temperature and magnetically stir for 15 h, centrifuge to collect the product, wash with ethanol and water several times, and dry in a 60°C oven to obtain FeMn-PBA / Ti.

[0038] (II) Preparation of FeMn-PBA@CuFe-PBA / Ti

[0039] Pour 3.2 g of FeMn-PBA / Ti into 400 mL of water as solution A, and dissolve 2.4 g of Cu(NO3)2·3H2O in 80 mL of deionized water as solution B; then quickly add solution B to solution A at room temperature, magnetically stir at room temperature for 3 h, centrifuge to collect the product, wash with deionized water and ethanol, and dry in a 60°C oven to obtain FeMn-PBA@CuFe-PBA / Ti.

[0040] (III) Preparation of FeMnO3 / CuFe2O4 / Ti

[0041] Place FeMn-PBA@CuFe-PBA / Ti in a muffle furnace, in air, at 2°C / min, and calcine at 400°C for 2 h to obtain FeMnO3 / CuFe2O4 / Ti.

[0042] (IV) Preparation of OH-ILs@FeMnO3 / CuFe2O4 / Ti

[0043] 0.2 g of FeMnO3 / CuFe2O4 / Ti was placed in a two-necked flask and evacuated to a vacuum state using a circulating water vacuum pump. Then, it was activated at 60 °C for 3 hours. Finally, 0.2 g of 1-hydroxyethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt (OH-ILs) was dissolved in 20 ml of methanol and injected into the flask. The mixture was stirred at 30 °C under vacuum for 24 hours. After centrifugation and washing with methanol, OH-ILs@FeMnO3 / CuFe2O4 / Ti was obtained.

[0044] (v) Testing

[0045] 1. For example Figure 1 As shown, (a) and (b) are TEM images of FeMnO3 / CuFe2O4 and OH-ILs@FeMnO3 / CuFe2O4, respectively. It can be observed that FeMnO3 / CuFe2O4 is a hollow cube with an average size of 200 nm and a shell thickness of approximately 10 nm. The lattice fringes and uniformly dispersed elements confirm the successful synthesis of FeMnO3 / CuFe2O4. After confining the ionic liquid, the lattice size did not change, but filling material was observed within the cavities, indicating that the ionic liquid successfully confined FeMnO3 / CuFe2O4. Furthermore, the dispersed S and F elements further confirm the successful confinement of the ionic liquid.

[0046] 2. For example Figure 2 As shown, (a) and (b) are XRD and XPS plots, respectively. XRD confirms successful material synthesis and that the ionic liquid does not alter the crystal structure of FeMnO3 / CuFe2O4. The displacement of lattice oxygen in XPS indicates that the ionic liquid forms hydrogen bonds with the oxygen in FeMnO3 / CuFe2O4, resulting in a tight bond.

[0047] 3. For example Figure 3 As shown, (a) and (b) are EIS and transient photocurrent plots, respectively. In Figure (a), OH-ILs@FeMnO3 / CuFe2O4 exhibits a smaller charge transfer resistance. In Figure (b), OH-ILs@FeMnO3 / CuFe2O4 exhibits a stronger transient photocurrent. This indicates that ionic liquids can enhance the conductivity of FeMnO3 / CuFe2O4 and suppress carrier recombination.

[0048] 4. For example Figure 4 As shown, (a) and (b) are the OCP change graph and the reaction order graph, respectively. OH-ILs@FeMnO3 / CuFe2O4 exhibits a larger OCP change and a smaller reaction order, indicating that ionic liquids can significantly enhance the adsorption capacity for nitrates.

[0049] 5. For example Figure 5The CV and EPR graphs are shown in (a) and (b), respectively. The OH-ILs@FeMn03 / CuFe204exhibited stronger H * characteristic peaks, indicating that the ionic liquid can promote the production of H * .

[0050] Example 2 Photoelectrocatalytic production of NH3

[0051] The method is as follows:

[0052] 1) The OH-ILs@FeMn03 / CuFe204 / Ti was used as the working electrode, a platinum sheet as the counter electrode, and a silver / silver chloride electrode as the reference electrode, which were placed in an H-type reactor to form a three-electrode system. The catholyte was 0.5 M sodium sulfate and different concentrations of sodium nitrate (10, 50, 200, 500, 100, and 1500 mM), and the anolyte was 0.5 M sodium sulfate.

[0053] 2) Before the reaction, 30 minutes of argon was introduced into the catholyte. The photoelectrocatalytic experiment was carried out under the conditions of a bias voltage of -1.4 V vs. RHE and an ambient temperature of 25°C, using a 300 W xenon lamp to simulate sunlight irradiation (λ≥420 nm). After 60 minutes of reaction, 0.5 mL of the catholyte was taken and diluted with water to 10 mL. After adding 0.2 mL of 10 M sodium hydroxide solution, the NH3concentration was detected using a gas-sensitive electrode.

[0054] (I) Conversion rate of nitrate-containing wastewater

[0055] Long-term photoelectrocatalytic experiments were carried out in simulated wastewater containing 50 mM nitrate, and the results are shown in Figure 6 .

[0056] The OH-ILs@FeMn03 / CuFe204 / Ti photo-cathode can almost completely convert 50 mM nitrate in 2.5 hours, and the photoelectrocatalytic product can meet the World Health Organization (WHO) drinking water standards.

[0057] (II) Catalytic activity in wastewater with wide concentration of nitrate

[0058] Considering the large difference in the concentration of nitrate in different wastewaters, photoelectrocatalytic experiments were carried out in electrolytes with nitrate concentrations of 10, 50, 200, 500, 100, and 1500 mM using a flow reactor, and the results are shown in Figure 7 .

[0059] OH-ILs@FeMnO3 / CuFe2O4 / Ti exhibited high Faradaic efficiency in a wide range of nitrate concentrations, demonstrating its excellent catalytic activity and practical application ability. The electrode achieved 97.75% Faradaic efficiency under 500 mM nitrate conditions, and achieved an ultra-high NH3 yield of 20.51 mg h -1 cm -2 under 1500 mM nitrate conditions.

Claims

1. A double confined field-free hollow photocathode, characterized in that, FeMn-PBA / Ti was synthesized by dispersing MnCl2·4H2O and K3[Fe(CN)6] in water and growing in situ on Ti mesh; FeMn-PBA was converted into CuFe-PBA by ion exchange method to obtain FeMn-PBA@CuFe-PBA / Ti; FeMn-PBA@CuFe-PBA / Ti was calcined to obtain FeMnO3 / CuFe2O4 / Ti; finally, OH-ILs was introduced into FeMnO3 / CuFe2O4 / Ti by vacuum impregnation method to obtain a double-confined hollow OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photo-cathode.

2. The method of claim 1, wherein the method of fabricating a double confined hollow photocathode is characterized by, The method comprises the following steps: 1) dissolving MnCl2·4H2O and K3[Fe(CN)6] in water and putting into Ti mesh, stirring reaction, centrifugal collection, washing with ethanol and water, drying to obtain FeMn-PBA / Ti; 2) putting FeMn-PBA / Ti prepared in step 1) into water, adding Cu(NO3)2·3H2O aqueous solution, stirring reaction, centrifugal collection, washing with deionized water and ethanol, drying to obtain FeMn-PBA@CuFe-PBA / Ti; 3) calcining FeMn-PBA@CuFe-PBA / Ti prepared in step 2) to obtain FeMnO3 / CuFe2O4 / Ti; 4) putting FeMnO3 / CuFe2O4 / Ti prepared in step 3) into a flask and activating in a vacuum environment, then injecting OH-ILs methanol solution into the flask, stirring under vacuum, centrifugal collection and washing with methanol to obtain an OH-ILs@FeMnO3 / CuFe2O4 / Ti Z-type photo-cathode.

3. The production method according to claim 2, characterized by, In step 1), the molar ratio of MnCl2·4H2O and K3[Fe(CN)6] is 1:2, the stirring reaction condition is stirring at room temperature for 15 hours, and the drying temperature is 60℃.

4. The preparation method according to claim 2, characterized in that, In step 2), the molar ratio of FeMn-PBA / Ti and Cu(NO3)2·3H2O is 1:1, the stirring reaction condition is stirring at room temperature for 3 hours, and the drying temperature is 60℃.

5. The preparation method according to claim 2, characterized in that, In step 3), the calcination condition is in air, the heating rate is 2℃ / min, and 400℃ is maintained for 2 hours.

6. The preparation method according to claim 2, characterized in that, In step 4), the activation temperature is 60℃, the activation time is 3 hours, and stirring is carried out at 30℃ for 24 hours under vacuum.

7. The preparation method according to claim 2, characterized in that, In step 4), the OH-ILs used is 1-hydroxyethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and the mass ratio of OH-ILs to FeMnO3 / CuFe2O4 / Ti is 1:

1.

8. The use of the double-confined hollow photo-cathode of claim 1 in photo-electro-catalytic synthesis of NH3.

9. Use according to claim 8, characterized in that, The method is as follows: OH-ILs@FeMnO3 / CuFe2O4 / Ti is used as a working electrode, a platinum sheet is used as a counter electrode, and a silver / silver chloride electrode is used as a reference electrode, which are placed in an H-type reactor to form a three-electrode system; the cathode electrolyte is 0.5M sodium sulfate and 10-1500mM sodium nitrate, and the anode electrolyte is 0.5M sodium sulfate; the reaction is carried out under an applied voltage and simulated sunlight irradiation to catalytically synthesize NH3.

10. Use according to claim 9, characterized in that, The applied voltage is-1.4 V Vs. RHE, and the simulated sunlight irradiation is that a 300W xenon lamp is used as a light source, and the xenon lamp is λ≥420 nm.

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