Conductive MOF / LDH heterojunction electrode material and preparation method and application thereof

Abstract

This invention proposes a conductive MOF / LDH heterojunction electrode material, its preparation method, and its application. Using iron foam as a substrate, vertically aligned and uniformly sized NiFe-LDH nanosheets are grown in situ on the substrate surface. After coordination with a hexahydroxy ligand, a conductive MOF layer is constructed in situ, forming a MOF / LDH heterojunction electrode material with a two-dimensional conductive framework and heterojunction interface control capability. The prepared electrode material is used in a device and method for coupling capacitive deionization technology with electrocatalytic technology to reduce nitrate ions to ammonia, realizing an integrated process of nitrate ion adsorption-enrichment-electrocatalytic conversion. Through the adsorption-conversion coupling mechanism, the NO3- concentration is increased. ‑ The localized concentration on the electrode surface allows the Faraday efficiency of ammonia to reach 85%.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical and environmental functional materials technology, specifically relating to a conductive MOF / LDH heterojunction electrode material constructed on the surface of foamed iron, its preparation method and application. Background Technology

[0002] Ammonia (NH3), as a basic chemical raw material and an emerging hydrogen energy carrier, has significant value in agriculture, energy, and chemical industries. The traditional Haber-Bosch process requires the production of hydrogen from fossil fuels under high temperature and pressure, followed by the synthesis of ammonia from nitrogen, resulting in high energy consumption and severe carbon emissions. In recent years, electrochemical nitrate reduction to ammonia (NO3RR) has attracted attention because it can achieve the resource conversion of nitrogen-containing wastewater under mild conditions.

[0003] There are several common methods for preparing ammonia, such as the traditional nitric acid reduction methods, including chemical reduction, biological denitrification, and electrochemical reduction. However, each method has its own disadvantages. For example, chemical reduction has the disadvantages of poor reaction rate and selectivity, biological denitrification is costly and not suitable for industrial production, and electrochemical reduction has poor low-concentration treatment efficiency, requires long-term electrolysis, has high energy consumption, and is not economical.

[0004] The invention patent CN112354541A, entitled "A Co / CoO heterojunction electrocatalyst supported on a nickel foam substrate and its preparation method and application," discloses a Co / CoO heterojunction electrocatalyst supported on a nickel foam substrate for the hydrogen reduction of nitrate in water. It utilizes a catalytic electrode material to conduct an electrocatalytic reduction reaction, converting nitrate ions into ammonium ions. However, removing nitrate ions from water and reducing them to ammonia under low concentration conditions remains a technical challenge. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a conductive MOF / LDH heterojunction electrode material and its preparation method. The prepared electrode material is then used in a device and method for coupling capacitive deionization technology and electrocatalytic technology to reduce nitrate ions to produce ammonia, thereby realizing an integrated process of nitrate ion adsorption-enrichment-electrocatalytic conversion, which significantly improves the ammonia yield and Faraday efficiency.

[0006] To achieve the purpose of the invention, the following technical solution is provided: This invention discloses a conductive MOF / LDH heterojunction electrode material. Using iron foam as a substrate, vertically arranged and uniformly sized NiFe-LDH nanosheets are grown in situ on the substrate surface. After coordination with hexahydroxy ligands, a conductive MOF layer is constructed in situ, forming a MOF / LDH heterojunction electrode material with a two-dimensional conductive framework and heterojunction interface control capability.

[0007] This invention also discloses a method for preparing a conductive MOF / LDH heterojunction electrode material, comprising the following steps: (1) Immerse the treated foamed iron in a Ni-containing solution. 2+ NiFe-LDH nanosheets were grown in situ on iron foam using a hydrothermal method in an alkaline solution of the precursor to obtain NiFe-LDH / IF. (2) NiFe-LDH / IF was immersed in a solution containing hexahydroxytriphenylene, ultrasonically treated, and then placed in a preheating furnace for reaction. After the reaction was completed, it was washed and dried to obtain a conductive MOF / LDH heterojunction electrode material, denoted as M(Ni + and Fe 2+ / Fe 3+ )-HHTP / LDH / IF.

[0008] Furthermore, the Ni-containing [item] mentioned in step (1) 2+ The precursor alkaline solution is a solution obtained by dissolving Ni(NO3)2·6H2O, NH4F and urea in deionized water and stirring until homogeneous; wherein the molar ratio of Ni(NO3)2·6H2O, NH4F and urea is 1:(1.5~2.5):(15~30).

[0009] Furthermore, the hydrothermal reaction conditions described in step (1) are 80-120 °C for 2-12 h, which can be adjusted according to the morphology and crystallinity requirements.

[0010] Furthermore, the reaction conditions of the preheating furnace in step (2) are as follows: reaction at 80-160 °C for 12-72 h. The reaction time and reaction temperature can be adjusted according to the requirements of structural growth and crystallinity.

[0011] Furthermore, the drying conditions in step (2) are drying under vacuum or inert atmosphere at 40-80 °C.

[0012] This invention also discloses the application of conductive MOF / LDH heterojunction electrode materials in capacitive deionization, specifically, using the prepared conductive MOF / LDH heterojunction as an electrode material in combination with electrostatic adsorption and electrocatalytic reduction to produce ammonia.

[0013] Furthermore, the application involves changing the access voltage, with the conductive MOF / LDH heterojunction electrode material acting as both an anode for nitrate adsorption and a cathode for electrocatalytic reduction of nitrate to produce ammonia.

[0014] This invention also discloses a method for producing ammonia by capacitive deionization coupling electrocatalytic reduction. The method uses the prepared conductive MOF / LDH heterojunction electrode material and activated carbon as two electrodes. A positive voltage is applied to the conductive MOF / LDH heterojunction electrode material as the anode, and the activated carbon as the cathode, allowing nitrate ions to be electrostatically adsorbed on the surface of the conductive MOF / LDH heterojunction electrode material. A negative voltage is then applied to the conductive MOF / LDH heterojunction electrode material as the cathode, and the activated carbon as the anode, allowing electrocatalytic reduction of nitrate ions to produce ammonia on the surface of the conductive MOF / LDH heterojunction electrode material.

[0015] Furthermore, the adsorption voltages for nitrate ions are 0.8, 1.0, 1.2, and 1.4 V, with the optimal value being 1.4 V; the negative voltages range from -1 to -1.6 V, with the optimal value being -1.45 V.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The conductive MOF / LDH heterojunction electrode material prepared in this invention uses a three-dimensional foam iron matrix as an electron transport framework, which has a large specific surface area and excellent mechanical stability. A nickel-iron double hydroxide compound is grown in situ on its surface to obtain NiFe-LDH nanosheets, which provide abundant metal active sites. Hexahydroxytriphenyl (HHTP) ligands are introduced to regulate the coordination between metal nodes and organic ligands, and a conductive MOF layer is constructed in situ. The HHTP-MOF layer endows an excellent π-conjugated conductive network, which promotes rapid electron migration. The prepared heterojunction interface regulates the electronic structure, optimizes the adsorption performance, enhances the charge transfer ability, and promotes the generation and transformation of key intermediates.

[0017] (2) In the preparation process of conductive MOF / LDH heterojunction electrode materials, the present invention, in the Ni-containing 2+ When urea and NH4F are added to an alkaline precursor solution, the urea will slowly decompose during heating, releasing OH- evenly. - Slowly increase the alkalinity of the solution, while generating CO3. 2- As an interlayer anion, ammonium fluoride enables the metal to precipitate synchronously and uniformly, forming an ordered layered structure, thus promoting the growth of LDH into a two-dimensional nanosheet structure with higher crystallinity and more uniform morphology. Ammonium fluoride plays a crucial role in LDH synthesis primarily through the deposition of F... - The weak coordination and surface regulation of F control crystal growth, enabling LDH to form a thinner, more uniform, and more dispersed two-dimensional sheet-like structure; at the same time, F - The etching effect introduces surface defects and enhances active sites; while NH4 + The buffering effect can avoid disordered precipitation caused by local strong alkali, which helps to obtain LDH materials with controllable morphology, high crystallinity and better performance.

[0018] (3) Traditional capacitive deionization technology can only adsorb / desorb → nitrate is enriched in concentrated brine, failing to truly achieve detoxification and causing secondary pollution; the capacitive deionization (CDI) coupled with electrocatalytic reduction of nitrate to ammonia proposed in this invention can efficiently enrich nitrate at low concentrations using capacitive deionization, increasing the local concentration. Nitrate reduction directly converts the nitrate ions enriched on the electrode surface into ammonia, achieving "enrichment-conversion" rather than "enrichment-emission"; coupling CDI with NO3RR can upgrade "simply removing pollutants" to "removal + resource utilization", achieving water purification and nitrogen resource recovery simultaneously under low energy consumption and short cycle conditions; through the adsorption-conversion coupling mechanism, the NO3RR is increased. - The localized concentration at the electrode surface allows for a Faradaic efficiency (FE) of up to 85% for ammonia, resulting in an ammonia yield of 0.49 mmol·cm⁻¹. -2 ·h -1 It achieves both high selectivity and high efficiency.

[0019] (4) The conductive MOF / LDH heterojunction electrode material of the present invention has high mechanical strength of foam iron substrate. During the capacitive deionization and electrocatalytic coupling reduction of nitrate reaction, the current density and ammonia yield remain stable after 10 hours of continuous operation. Moreover, the use of inexpensive foam iron as carrier makes the material and process simple, has the feasibility of large-scale preparation, and has low cost. Through CDI-electrocatalytic cycle, a closed-loop process of ion capture, conversion and electrode regeneration is realized, which has low energy consumption and high efficiency. Attached Figure Description

[0020] Figure 1 Scanning electron microscope images of iron foam-based (IF), NiFe-LDH / IF and M-HHTP / LDH / IF prepared in Example 1 of the present invention; Figure 2 The XRD patterns, FI-TR patterns, and Raman spectra of iron foam-based (IF), NiFe-LDH / IF, and M-HHTP / LDH / IF prepared in Example 1 of this invention are shown. Figure 3 The images show the Faradaic efficiency of M-HHTP / LDH / IF prepared in Example 1 of this invention and NiFe-LDH / IF prepared in Comparative Example 1 at different voltages, the ammonia yield at different voltages, and the Faradaic efficiency and ammonia yield over 30 catalytic cycles. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0022] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0023] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0024] Example 1 This embodiment provides a conductive MOF / LDH heterojunction electrode material. Using iron foam as a substrate, vertically aligned and uniformly sized NiFe-LDH nanosheets are grown in situ on the substrate surface. After coordination with a hexahydroxy ligand, a conductive MOF layer is constructed in situ. The conductive MOF / LDH heterojunction electrode material possesses a two-dimensional conductive framework and the ability to control the heterojunction interface. The specific preparation method includes the following steps: (1) Cut a piece of foamed iron (IF) into 2.5 cm × 2.5 cm pieces and wash them with 1.0 M hydrochloric acid, ethanol and deionized water for 10 min each. (2) Dissolve 0.75 mM Ni(NO3)2·6H2O, 1.5 mM NH4F and 15 mM urea in 30 mL of deionized water and stir for 20 min to obtain a uniform Ni-containing solution. 2+ The precursor was placed in an alkaline solution; the solution was poured into a 50 mL high-pressure reactor, and the treated foamed iron was placed into the reactor at an angle; the reactor was placed in an oven and reacted at 90 °C for 3 h; after the reaction was completed and cooled to room temperature, the sample was repeatedly washed with deionized water and ethanol, and then dried under vacuum at 60 °C to obtain NiFe-LDH / IF; (3) NiFe-LDH / IF was immersed in a mixed solution containing 55 mg of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 4 mL of deionized water and sonicated for 30 min. Then, the mixed solution containing NiFe-LDH / IF was placed in a preheated furnace at 100 °C and reacted fully for 48 h. After the reaction was completed, the temperature was lowered to the ambient temperature, and the reacted NiFe-LDH / IF was rinsed with deionized water several times. Then, it was vacuum dried at 60 °C for 12 h to obtain conductive MOF / LDH heterojunction electrode material. The sample was named M-HHTP / LDH / IF.

[0025] In this embodiment, the morphology images of the foamed iron (IF) treated in step (1) and the NiFe-LDH / IF and sample M-HHTP / LDH / IF generated by the reaction in step (2) are as follows. Figure 1 As shown in (a)-(c), the original foamed iron exhibits a smooth, clean, rib-like network structure. Figure 1a); After hydrothermal growth, a dense array of vertically aligned and uniformly sized NiFe-LDH nanosheets is distributed on the substrate surface, forming a hierarchical nanostructure resembling a tree trunk. Figure 1 b); Subsequently, after coordination with HHTP, ultrathin c-MOF nanodendrons grow radially and form a uniform coating on the LDH framework, giving the material surface a rough, flower-like characteristic structure, reflecting the typical morphology of the target heterostructure. Figure 1 c).

[0026] In this embodiment, the XRD, FI-TR, and Raman spectra of the foamed iron (IF) treated in step (1), the NiFe-LDH / IF generated by the reaction in step (2), and the prepared sample M-HHTP / LDH / IF are shown below. Figure 2 As shown in (a)-(c), the phase composition and crystal structure of NiFe-LDH / IF and M-HHTP / LDH / IF were characterized by XRD. Figure 2 a) The optimized original NiFe-LDH / IF template shows diffraction peaks at 10.4°, 23.2°, 25.57°, 33.30° and 36.3°, which correspond to the (003), (001), (002), (101) and (104) crystal planes of NiFe-LDH, respectively (JCPDS No.). (40-0215); After coordination with HHTP ligands, three new diffraction peaks of 4.9°, 9.6° and 27.3° were added to M-HHTP / LDH / IF, which correspond to the (100), (200) and (001) crystal plane diffraction of conductive MOF, respectively. These diffraction peaks are attributed to typical π-π stacking and the ordered arrangement of the interlayer structure, which further proves the successful construction of ordered hierarchical covalent metal-organic framework. These new peaks appeared together with the characteristic peaks of NiFe-LDH / IF template, which confirmed that c-MOF nanoshells have been successfully grown on the surface of NiFe-LDH / IF template.

[0027] To verify the successful growth of c-MOF nanobranches on NiFe-LDH nano-"trunks", Fourier transform infrared (FTIR) spectroscopy analysis was further performed, such as... Figure 2 As shown in b, M-HHTP / LDH / IF exhibits characteristic vibrational absorption peaks of the HHTP ligand, including obvious CO stretching vibrations and aromatic ring vibrations, proving that effective coordination occurred between the organic ligand and the metal center; Raman spectroscopy ( Figure 2 c) also provides corroborating evidence: the original NiFe-LDH / IF ratio is between 261 and 311 cm⁻¹. -1The sample exhibited characteristic peaks within the specified range, corresponding to the M–OH (M = Ni, Fe) stretching vibration, confirming the presence of the LDH layered structure. After coordination with HHTP, a new 900.9 cm⁻¹ peak appeared in the sample. -1 The Raman peak, attributed to the CC stretching vibration of the HHTP ligand, further demonstrates the successful introduction and integration of the c-MOF component.

[0028] Example 2 This embodiment provides a conductive MOF / LDH heterojunction electrode material, which has the same structural features as in Embodiment 1. The specific preparation method includes the following steps: (1) Cut a piece of foamed iron (IF) into 2.5 cm × 2.5 cm pieces and wash them with 2.0 M hydrochloric acid, ethanol and deionized water for 10 min each. (2) Dissolve 0.75 mM Ni(NO3)2·6H2O, 1.2 mM NH4F and 20 mM urea in 30 mL of deionized water and stir for 20 min to obtain a uniform Ni-containing solution. 2+ A precursor alkaline solution was prepared and poured into a 50 mL high-pressure reactor. The treated iron foam was then placed into the reactor at an angle. The reactor was placed in an oven and reacted at 120 °C for 2 h. After the reaction was completed and cooled to room temperature, the sample was repeatedly washed with deionized water and ethanol, and then dried under vacuum at 60 °C to obtain NiFe-LDH / IF. (3) NiFe-LDH / IF was immersed in a mixed solution containing 55 mg of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 4 mL of deionized water and sonicated for 30 min. Then, the mixed solution containing NiFe-LDH / IF was placed in a preheated furnace at 80 °C and reacted fully for 72 h. After the reaction was completed, the temperature was lowered to the ambient temperature and the reacted NiFe-LDH / IF was rinsed with deionized water several times. Then, it was dried in a nitrogen atmosphere at 80 °C for 12 hours to obtain a conductive MOF / LDH heterojunction electrode material. The sample was named M-HHTP / LDH / IF.

[0029] Example 3 This embodiment provides a conductive MOF / LDH heterojunction electrode material, which has the same structural features as in Embodiment 1. The specific preparation method includes the following steps: (1) Cut a piece of foamed iron (IF) into 2.5 cm × 2.5 cm pieces and wash them with 1.0 M hydrochloric acid, ethanol and deionized water for 10 min each. (2) Dissolve 0.75 mM Ni(NO3)2·6H2O, 1.5 mM NH4F and 13 mM urea in 30 mL of deionized water and stir for 20 min to obtain a uniform Ni-containing solution. 2+ Precursor alkaline solution; pour the solution into a 50 mL high-pressure reactor, and place the pretreated foamed iron into the reactor at an angle; place the reactor in an oven and react fully at 80°C for 10 h; after the reaction is completed and cooled to room temperature, the sample is repeatedly washed with deionized water and ethanol, and then vacuum dried at 60 °C to obtain NiFe-LDH / IF; (3) NiFe-LDH / IF was immersed in a mixed solution containing 55 mg of 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 4 mL of deionized water and sonicated for 30 min. Then, the mixed solution containing NiFe-LDH / IF was placed in a preheated furnace at 120 °C and reacted fully for 36 hours. After the reaction was completed, the temperature was lowered to the ambient temperature, and the reacted NiFe-LDH / IF was rinsed with deionized water several times. Then, it was dried in vacuum at 80 °C for 12 hours to obtain conductive MOF / LDH heterojunction electrode material. The sample was named M-HHTP / LDH / IF.

[0030] Comparative Example 1 This embodiment provides a NiFe-LDH / IF electrode material, the preparation method of which specifically includes the following steps: (1) Cut a piece of foamed iron (IF) into 2.5 cm × 2.5 cm pieces and wash them with 1.0 M hydrochloric acid, ethanol and deionized water for 10 min each. (2) Dissolve 0.75 mM Ni(NO3)2·6H2O, 1.5 mM NH4F and 15 mM urea in 30 mL of deionized water and stir for 20 min to obtain a uniform Ni-containing solution. 2+ Precursor solution; pour the solution into a 50 mL high-pressure reactor, and place the pretreated foamed iron into the reactor at an angle; place the reactor in an oven and react fully at 90 °C for 3 h; after the reaction is completed and cooled to room temperature, the sample is repeatedly washed with deionized water and ethanol, and then vacuum dried at 60 °C to obtain NiFe-LDH / IF.

[0031] Example 4 The M-HHTP / LDH / IF electrode materials prepared in Example 1 and the NiFe-LDH / IF electrode materials prepared in Comparative Example 1 were applied in capacitive deionization (CDI) coupled electrocatalytic nitrate to ammonia production: First, the prepared electrode materials M-HHTP / LDH / IF and NiFe-LDH / IF were used as anodes, and activated carbon as cathodes. The electrolyte was a 50 mg-N / L sodium nitrate solution. A positive voltage (+0.8V, +1V, +1.2V, +1.4V, preferably 1.4V) was applied to the device. Due to electrostatic adsorption, nitrate ions were adsorbed onto the anode, resulting in a low concentration of nitrate ions accumulating on the electrode surface. Then, the power supply was reversed, with activated carbon as the anode and the electrode with adsorbed nitrate ions as the cathode. A negative voltage (-1.0 to -1.6V, preferably -1.45V) was applied to catalytically reduce nitrate ions to ammonia. The concentrations of nitrate ions and ammonia were quantitatively measured using a visible-ultraviolet spectrophotometer.

[0032] Test results are as follows Figure 3 As shown, by comparing the nitrate electroreduction performance of NiFe-LDH / IF and M-HHTP / LDH / IF electrodes at different voltages, it can be seen that the M-HHTP / LDH / IF heterostructure electrode constructed in this invention has higher Faraday efficiency and ammonia yield. Figure 3 Both ab) showed significant improvements. When a voltage range of -1.0 to -1.6 V was applied, the Faradaic efficiency of this electrode increased from about 25% to about 80%, significantly higher than the 15% to 35% of the comparative NiFe-LDH / IF; at the same voltage, the ammonia yield reached about 0.50 mmol·cm⁻¹. -2 ·h -1 The control group was only about 0.28 mmol·cm⁻¹. -2 ·h -1 This indicates that the structure can significantly enhance the conversion rate of nitrate to ammonia. Furthermore, in 30 consecutive cycles of testing, the Faraday efficiency of the electrode of this invention remained consistently between 80-85%, and the ammonia yield remained stable at 0.45–0.55 mmol·cm⁻¹. -2 ·h -1 No significant degradation was observed, which fully demonstrates that this heterostructure possesses excellent electrochemical stability and long-term operational reliability. Figure 3 c); In summary, by constructing a MOF / LDH synergistic interface, this invention achieves high selectivity, high yield, and excellent stability in the nitrate electroreduction reaction, which is significantly superior to existing technologies.

[0033] The above-described embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above-described embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present patent shall be considered equivalent substitutions and shall be included within the protection scope of the present patent.

Claims

1. A conductive MOF / LDH heterojunction electrode material, characterized in that, Using iron foam as a substrate, vertically aligned and uniformly sized NiFe-LDH nanosheets are grown in situ on the substrate surface. After coordination with hexahydroxy ligands, a conductive MOF layer is constructed in situ, forming a MOF / LDH heterojunction electrode material with a two-dimensional conductive framework and heterojunction interface control capability.

2. The method for preparing a conductive MOF / LDH heterojunction electrode material as described in claim 1, characterized in that, Includes the following steps: (1) Immerse the treated foamed iron in a Ni-containing solution. 2+ NiFe-LDH nanosheets were grown in situ on iron foam using a hydrothermal method in an alkaline solution of the precursor to obtain NiFe-LDH / IF. (2) NiFe-LDH / IF was immersed in a solution containing hexahydroxytriphenyl (HHTP), ultrasonically treated, and then placed in a preheating furnace for reaction. After the reaction was completed, it was washed and dried to obtain a conductive MOF / LDH heterojunction electrode material.

3. The method for preparing a conductive MOF / LDH heterojunction electrode material as described in claim 2, characterized in that, The Ni-containing component mentioned in step (1) 2+ The precursor alkaline solution is a solution obtained by dissolving Ni(NO3)2·6H2O, NH4F and urea in deionized water and stirring until homogeneous; the molar ratio of Ni(NO3)2·6H2O, NH4F and urea is 1:(1.5~2.5):(15~30).

4. The method for preparing a conductive MOF / LDH heterojunction electrode material as described in claim 2, characterized in that, The hydrothermal reaction conditions described in step (1) are 80-120℃ for 2-12 hours.

5. The method for preparing a conductive MOF / LDH heterojunction electrode material as described in claim 2, characterized in that, The reaction conditions of the preheating furnace in step (2) are 80-160℃ for 12-72h.

6. The method for preparing a conductive MOF / LDH heterojunction electrode material as described in claim 2, characterized in that, The drying conditions described in step (2) are vacuum or inert atmosphere drying at 40-80℃.

7. The application of the conductive MOF / LDH heterojunction electrode material as described in claim 1 in capacitor deionization and desalting, characterized in that, As an electrode material, it combines electrostatic adsorption and electrocatalytic reduction to produce ammonia.

8. The application as described in claim 7, characterized in that, By changing the input voltage, nitrate adsorption is achieved as an anode and electrocatalytic reduction of nitrate to produce ammonia is achieved as a cathode.

9. A method for producing ammonia by capacitive deionization coupled electrocatalytic reduction, characterized in that: Using the conductive MOF / LDH heterojunction electrode material as described in claim 1 and activated carbon as the two electrodes, a positive voltage is applied to the conductive MOF / LDH heterojunction electrode material as the anode and activated carbon as the cathode, and nitrate ions are electrostatically adsorbed on the surface of the conductive MOF / LDH heterojunction electrode material; a negative voltage is applied to the conductive MOF / LDH heterojunction electrode material as the cathode and activated carbon as the anode, and electrocatalytic reduction of nitrate ions to ammonia is performed on the surface of the conductive MOF / LDH heterojunction electrode material.

Images