Method, device for co-production of urea from power plant exhaust gas-nitrogen-containing wastewater and multi-component metal-based photoelectrocatalyst

Abstract

The application discloses a kind of power plant exhaust-nitrogen-containing wastewater synergic urea preparation method, device and multi-component metal-based photoelectrocatalyst, power plant exhaust-nitrogen-containing wastewater synergic urea preparation method includes: step S1, after being pretreated, into micro-nano bubble generator, with nitrogen-containing wastewater as medium, preparation load CO2 micro-nano bubble suspension.The step S2, micro-nano bubble suspension is introduced into photoelectrocatalytic reactor, reactor is filled with multi-component metal-based photoelectrocatalyst, under the synergistic effect of light and bias, generate urea.Step S3, after reaction, mixed liquor is separated by solid-liquid, and the catalyst in solid phase is recycled, and liquid phase is separated to obtain urea product.According to the power plant exhaust-nitrogen-containing wastewater synergic urea preparation method of embodiment of the application, increase the residence time of bubble in water, improve the specific surface area of micro-nano bubble, improve the efficiency of preparation urea.

Description

Technical Field

[0001] This invention relates to the fields of photoelectrocatalysis technology and synergistic treatment of industrial waste gas and wastewater, and in particular to a method, apparatus, and multi-component metal-based photoelectrocatalyst for the synergistic production of urea from power plant waste gas and nitrogen-containing wastewater. Background Technology

[0002] Urea (CO(NH2)2) is the world's most important nitrogen fertilizer and basic chemical raw material. my country is the world's largest producer and consumer of urea, with an annual output exceeding 55 million tons, accounting for more than one-third of global production. Currently, industrial urea production relies entirely on the Bosch-Meiser process, which requires extreme high-temperature and high-pressure conditions of 150 atm and 200 °C to synthesize urea using NH3 and CO2 as raw materials. This process not only consumes 1%-2% of global fossil energy but also generates massive carbon emissions, with approximately 1.6 tons of carbon emitted per ton of urea produced, fundamentally contradicting my country's "dual-carbon" strategic goals.

[0003] In recent years, the photoelectrocatalytic coupling of CO2 with nitrogen-containing species to synthesize urea has become a cutting-edge research area at the intersection of new energy and chemical engineering. Photoelectrocatalysis technology, with its core advantages of being clean, mild, and capable of directly utilizing renewable energy sources such as solar energy to drive the reaction, can synthesize urea in one step via CN coupling reaction under ambient temperature and pressure, using CO2 as the carbon source and nitrate / nitrite nitrogen from nitrogen-containing wastewater as the nitrogen source. Compared to traditional processes, this technology does not require extreme high-temperature and high-pressure conditions, has no additional carbon emissions throughout the entire process, and offers environmental, economic, and social benefits.

[0004] However, existing photoelectrocatalytic urea synthesis technology still faces the following core technical bottlenecks: gas-liquid mass transfer efficiency severely restricts the kinetics of CO2 reduction reaction. The low solubility of CO2 in water (approximately 0.033 mol / L, 25 ℃, 1 atm) and slow diffusion rate lead to severe mass transfer limitations. In power plant exhaust gas systems, the CO2 concentration is only 10%-15% (volume ratio), and SO2 and NO coexist. x Impurities such as dust prevent traditional aeration methods from effectively delivering sufficient CO2 to the catalyst's active interface, leading to a severe imbalance in carbon and nitrogen source activation efficiency and extremely low CN coupling selectivity. Therefore, improvements are needed. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one objective of this invention is to propose a method for the synergistic production of urea from power plant exhaust gas and nitrogen-containing wastewater. This method involves carrying CO2 from the power plant exhaust gas into the nitrogen-containing wastewater system in the form of micro-nano bubbles. These micro-nano bubbles can remain in the water for several hours, increasing the residence time of the bubbles in the water, prolonging the contact time between CO2 and the catalyst, and significantly increasing the specific surface area of ​​the micro-nano bubbles. This, in turn, greatly improves the gas-liquid mass transfer efficiency of CO2 and enhances the efficiency of photoelectrocatalytic production of urea from CO2 and nitrogen-containing wastewater.

[0006] The present invention also proposes an apparatus for the co-production of urea from power plant exhaust gas and nitrogen-containing wastewater in the above-mentioned method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater.

[0007] The present invention also proposes a multi-component metal-based photocatalyst for the above-mentioned method of synergistic production of urea from power plant exhaust gas and nitrogen-containing wastewater.

[0008] According to a first aspect of the present invention, a method for co-producing urea from power plant waste gas and nitrogen-containing wastewater includes: step S1, pre-treating power plant waste gas and then introducing it into a micro / nano bubble generator, using nitrogen-containing wastewater as a medium to prepare a CO2-carrying micro / nano bubble suspension; step S2, introducing the micro / nano bubble suspension into a photoelectrocatalytic reactor, wherein the photoelectrocatalytic reactor is filled with a multi-component metal-based photoelectrocatalyst, and under the synergistic effect of light and bias voltage, CO2 in the micro / nano bubbles undergoes a photoelectrocatalytic CN coupling reaction with nitrate nitrogen / nitrite nitrogen in the nitrogen-containing wastewater to generate urea; step S3, after the reaction mixture is subjected to solid-liquid separation, the catalyst in the solid phase is recovered, and the liquid phase is separated to obtain urea product and nitrogen-containing liquid, and the nitrogen-containing liquid is introduced into the CO2-carrying micro / nano bubble suspension in step S1 to continue participating in the reaction.

[0009] The method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to embodiments of the present invention involves introducing CO2 from power plant exhaust gas into the nitrogen-containing wastewater system in the form of micro-nano bubbles. These micro-nano bubbles can remain in the water for several hours, increasing their residence time and prolonging the contact time between CO2 and the catalyst. This significantly improves the specific surface area of ​​the micro-nano bubbles, thereby greatly enhancing the gas-liquid mass transfer efficiency of CO2 and increasing the efficiency of photoelectrocatalytic CO2 and nitrogen-containing wastewater urea production. By simultaneously consuming CO2 from power plant exhaust gas and nitrogen pollutants from nitrogen-containing wastewater and converting them into high-value-added urea products, the method operates at ambient temperature and pressure, is solar-powered throughout, and produces no additional carbon emissions, demonstrating significant environmental and economic benefits.

[0010] According to some embodiments of the present invention, the diameter of the micro-nano bubbles is 100 nm to 10 μm, the volume fraction of the micro-nano bubbles in the suspension is 1% to 20%, and the operating pressure of the micro-nano bubble generator is 0.1 MPa to 1.0 MPa.

[0011] According to some embodiments of the present invention, in step S1, the power plant exhaust gas pretreatment method includes electrostatic precipitator dust removal, wet desulfurization, and selective catalytic reduction denitrification. The volume fraction of CO2 in the pretreated exhaust gas is 10%-15%, and the SO2 concentration is less than 50 mg / m³. 3 NOx concentration below 100 mg / m³ 3 Dust concentration below 30 mg / m³ 3 .

[0012] According to some embodiments of the present invention, in step S2, the conditions for the photoelectrocatalytic reaction include: a reaction temperature of 15 ℃ to 60 ℃, a reaction pH of 4.0 to 10.0, an applied bias voltage relative to the Ag / AgCl reference electrode of -0.5 V to -1.5 V, and a light source intensity of 50 mW / cm². 2 ~200 mW / cm 2 .

[0013] According to a second aspect of the present invention, the photoelectrocatalytic reaction device is used in the method for co-producing urea from power plant waste gas and nitrogen-containing wastewater according to a first aspect of the present invention. The photoelectrocatalytic reaction device includes: a micro / nano bubble generating module, which includes a waste gas pretreatment unit, a micro / nano bubble generator, and a gas-liquid mixing reactor. The micro / nano bubble generating module is used to prepare CO2-carrying micro / nano bubbles, and the gas-liquid mixing reactor is used to prepare a CO2-carrying micro / nano bubble suspension using the micro / nano bubbles and the nitrogen-containing wastewater; a photoelectrocatalytic reaction module, which includes a photoelectrocatalytic reactor and a light source system. The photoelectrocatalytic reactor includes a working electrode, a counter electrode, a reference electrode, and a potentiostat. The working electrode is loaded with the multi-component metal-based photoelectrocatalyst; and a product separation and recovery module, which includes a solid-liquid separator, a membrane separation device or an evaporator / crystallizer, and a circulating pump. The product separation and recovery module is used for the separation and recovery of urea products and the recycling of the reaction liquid.

[0014] According to the photoelectrocatalytic reactor of the present invention, by providing a micro-nano bubble distributor at the bottom of the photoelectrocatalytic reactor, carbon dioxide is carried into the nitrogen-containing wastewater system in the form of micro-nano bubbles. This allows the micro-nano bubble suspension to be uniformly distributed on the catalyst surface, ensuring sufficient contact between the gas, liquid, and solid phases. By integrating the micro-nano bubble generation module, the photoelectrocatalytic reaction module, and the product separation and recovery module, continuous operation of urea production from power plant waste gas and nitrogen-containing wastewater can be achieved.

[0015] According to some embodiments of the present invention, the photoelectrocatalytic reaction device further includes a micro / nano bubble distributor, which is used to uniformly distribute the micro / nano bubble suspension onto the catalyst surface.

[0016] According to some embodiments of the present invention, the photoelectrocatalytic reactor has a single-chamber or double-chamber structure, and the working electrode and the counter electrode are separated by a proton exchange membrane or a glass fiber membrane.

[0017] According to a third aspect of the present invention, a multi-component metal-based photocatalyst is used in a method for co-producing urea from power plant waste gas and nitrogen-containing wastewater according to a first aspect of the present invention. The multi-component metal-based photocatalyst comprises: an N-doped MXene substrate; multi-component metal-based semiconductor nanocrystals supported on the substrate, the semiconductor nanocrystals having a crystal plane co-activation structure, the crystal plane co-activation structure including a carbon source activated crystal plane and a nitrogen source activated crystal plane; and bimetallic active sites anchored on the crystal planes of the semiconductor nanocrystals.

[0018] The multi-component metal-based photocatalyst of the present invention, by doping the N-doped MXene substrate, enhances the specific adsorption capacity of the lone pair electrons on the N atom surface for the target substrate, thereby enabling the substrate to have good adsorption and sieving capabilities. The substrate can pre-enrich the target substrate and shield impurity ions. By giving the semiconductor nanocrystals a crystal plane synergistic structure, the built-in electric field formed at the heterocrystalline interface can promote the separation of photogenerated carriers.

[0019] According to some embodiments of the present invention, intrinsic defects are further introduced on the characteristic crystal faces of the semiconductor nanocrystals, including oxygen vacancies, sulfur vacancies or metal vacancies; and / or, the bimetallic active sites are atomically dispersed heteronuclear bimetallic sites selected from at least one combination of Fe-Co, Co-Ni, Cu-Bi, Ni-Cu, and the loading of bimetallic sites is 0.1wt% to 5wt% of the total mass of the catalyst.

[0020] According to some embodiments of the present invention, the multi-component metal-based semiconductor nanocrystals are selected from composite semiconductors composed of at least two of the oxides, sulfides, or selenides of transition metals such as Fe, Co, Ni, Cu, Bi, and In; and / or, the characteristic active crystal facets include the {001} / {110} crystal facets of metal oxides and the {010} / {110} crystal facets of metal sulfides, the carbon source activated crystal facets are crystal facets with adsorption capacity for CO2 and its intermediates, and the nitrogen source activated crystal facets are crystal facets with adsorption capacity for NO3. - Crystal planes of the crystals and their intermediates have selective adsorption and activation capabilities.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a flowchart of a method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to some embodiments of the present invention; Figure 2 This is a simplified schematic diagram of the photoelectrocatalytic reaction module in an apparatus for the co-production of urea from power plant exhaust gas and nitrogen-containing wastewater, according to some embodiments of the present invention.

[0023] Figure label: 100. Photoelectrocatalytic reaction module; 1. Photoelectrocatalytic reactor; 11. Working electrode; 12. Counter electrode; 13. Reference electrode; 14. Potentiostat; 15. Proton exchange membrane; 2. Light source system; 3. Micro-nano bubble distributor. Detailed Implementation

[0024] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0025] The following is for reference. Figures 1-2 A method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to an embodiment of the present invention is described.

[0026] Reference Figure 1 According to a first aspect of the present invention, a method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater includes: Step S1: After pretreatment, the power plant exhaust gas is introduced into a micro-nano bubble generator, and a micro-nano bubble suspension carrying CO2 is prepared using nitrogen-containing wastewater as a medium.

[0027] Step S2: The micro-nano bubble suspension is introduced into the photoelectrocatalytic reactor 1, which is filled with a multi-component metal-based photoelectrocatalyst. Under the synergistic effect of light and bias voltage, CO2 in the micro-nano bubbles undergoes a photoelectrocatalytic CN coupling reaction with nitrate nitrogen / nitrite nitrogen in nitrogen-containing wastewater to generate urea.

[0028] Step S3: After the reaction, the mixture is subjected to solid-liquid separation to recover the catalyst in the solid phase. The liquid phase is separated to obtain urea product and nitrogen-containing liquid. The nitrogen-containing liquid is then passed into the micro-nano bubble suspension carrying CO2 from step S1 to continue participating in the reaction.

[0029] By carrying CO2 from power plant exhaust gas into a nitrogen-containing wastewater system in the form of micro- and nano-bubbles, the huge specific surface area of ​​micro- and nano-bubbles can significantly increase the gas-liquid contact area and enhance mass transfer efficiency; the ultra-long residence time of micro- and nano-bubbles can stay in water for several hours, extending the contact time between CO2 and the catalyst; the self-pressurization and dissolution effect of micro- and nano-bubbles can make the partial pressure of CO2 inside the bubbles higher than the ambient pressure, promoting CO2 dissolution. The method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to embodiments of the present invention involves introducing CO2 from power plant exhaust gas into the nitrogen-containing wastewater system in the form of micro-nano bubbles. These micro-nano bubbles can remain in the water for several hours, increasing their residence time and prolonging the contact time between CO2 and the catalyst. This significantly improves the specific surface area of ​​the micro-nano bubbles, thereby greatly enhancing the gas-liquid mass transfer efficiency of CO2 and increasing the efficiency of photoelectrocatalytic CO2 and nitrogen-containing wastewater urea production. By simultaneously consuming CO2 from power plant exhaust gas and nitrogen pollutants from nitrogen-containing wastewater and converting them into high-value-added urea products, the method operates at ambient temperature and pressure, is solar-powered throughout, and produces no additional carbon emissions, demonstrating significant environmental and economic benefits.

[0030] According to some embodiments of the present invention, the diameter of the micro / nanobubbles is 100 nm to 10 μm, the volume fraction of the micro / nanobubbles in the suspension is 1% to 20%, and the operating pressure of the micro / nanobubble generator is 0.1 MPa to 1.0 MPa. By making the diameter of the micro / nanobubbles 100 nm to 10 μm, the bubbles can have both a sufficiently large specific surface area and an appropriate rising velocity, ensuring effective bubble circulation and renewal while enhancing mass transfer; by making the gas content 1% to 20%, sufficient CO2 supply can be provided for the photoelectrocatalytic reaction; and by making the operating pressure 0.1 MPa to 1.0 MPa, sufficient bubble cutting and refinement can be ensured.

[0031] According to some embodiments of the present invention, the diameter of the micro / nanobubbles is 500 nm to 5 μm, the gas content is 5% to 10%, and the operating pressure is 0.3 MPa to 0.6 MPa. By making the diameter of the micro / nanobubbles 500 nm to 5 μm, the bubbles can achieve the optimal mass transfer efficiency within this size range; by making the gas content 5% to 10%, excessive aggregation between bubbles can be avoided, which would lead to a decrease in mass transfer efficiency, while ensuring sufficient CO2 supply; and by making the operating pressure 0.3 MPa to 0.6 MPa, the micro / nanobubble generator can achieve the optimal energy consumption-efficiency balance within this pressure range.

[0032] According to some embodiments of the present invention, in step S1, the power plant exhaust gas pretreatment method includes electrostatic precipitator dust removal, wet desulfurization, and selective catalytic reduction denitrification. The volume fraction of CO2 in the pretreated exhaust gas is 10%-15%, and the SO2 concentration is less than 50 mg / m³. 3 NOx concentration below 100 mg / m³ 3 Dust concentration below 30 mg / m³ 3 By pre-treating the power plant exhaust gas to meet the above-mentioned standards, harmful impurities in the exhaust gas can be effectively removed, avoiding the generation of SO2 and NO. x And the interference of dust on photoelectrocatalytic reactions and the poisoning of catalysts.

[0033] According to some embodiments of the present invention, in step S2, the conditions for the photoelectrocatalytic reaction include: a reaction temperature of 15℃ to 60℃, a reaction pH of 4.0 to 10.0, an applied bias voltage relative to the Ag / AgCl reference electrode of -0.5 V to -1.5 V, and a light source intensity of 50 mW / cm². 2 ~200 mW / cm 2 By keeping the reaction conditions within the above range, the photoelectrocatalytic CN coupling reaction can be ensured to proceed efficiently at room temperature and pressure.

[0034] According to some embodiments of the present invention, in step S2, the conditions for the photoelectrocatalytic reaction include: a reaction temperature of 20°C to 40°C, a pH value of 6.0 to 8.5, and an applied bias voltage of -0.8 V to -1.2 V. By keeping the reaction conditions within the above-mentioned preferred range, the redox potentials of CO2 reduction and nitrogen species reduction can be better matched, and the reaction kinetics can be more balanced, thereby further improving the CN coupling selectivity.

[0035] Reference Figure 2According to a second aspect of the present invention, a photoelectrocatalytic reaction apparatus is used in a method for co-producing urea from power plant waste gas and nitrogen-containing wastewater according to a first aspect of the present invention. The photoelectrocatalytic reaction apparatus includes: a micro / nano bubble generating module, a photoelectrocatalytic reaction module 100, and a product separation and recovery module. The micro / nano bubble generating module includes a waste gas pretreatment unit, a micro / nano bubble generator, and a gas-liquid mixing reactor. The micro / nano bubble generating module is used to prepare CO2-carrying micro / nano bubbles. The gas-liquid mixing reactor is used to prepare a CO2-carrying micro / nano bubble suspension using micro / nano bubbles and nitrogen-containing wastewater. The photoelectrocatalytic reaction module 100 includes a photoelectrocatalytic reactor 1 and a light source system 2. The photoelectrocatalytic reactor 1 includes a working electrode 11, a counter electrode 12, a reference electrode 13, and a potentiostat 14. A multi-component metal-based photoelectrocatalyst is loaded on the working electrode 11. The product separation and recovery module includes a solid-liquid separator, a membrane separation device or an evaporator / crystallizer, and a circulating pump. The product separation and recovery module is used for the separation and recovery of urea products and the recycling of the reaction liquid.

[0036] By integrating the micro-nano bubble generation module, the photoelectrocatalytic reaction module 100, and the product separation and recovery module, continuous operation of urea production from power plant exhaust gas and nitrogen-containing wastewater can be achieved.

[0037] By equipping the bottom of the photoelectrocatalytic reactor 1 with a micro-nano bubble distributor 3, the micro-nano bubble suspension can be evenly distributed onto the catalyst surface, ensuring sufficient contact between the gas, liquid, and solid phases.

[0038] According to the photoelectrocatalytic reaction device of the present invention, by providing a micro-nano bubble distributor 3 at the bottom of the photoelectrocatalytic reactor 1, carbon dioxide is carried into the nitrogen-containing wastewater system in the form of micro-nano bubbles, and the micro-nano bubble suspension can be uniformly distributed on the catalyst surface to ensure sufficient contact between the gas, liquid and solid phases; by integrating the micro-nano bubble generation module, the photoelectrocatalytic reaction module 100 and the product separation and recovery module, continuous operation of urea production from power plant exhaust gas and nitrogen-containing wastewater can be realized.

[0039] According to some embodiments of the present invention, the photoelectrocatalytic reaction device further includes a micro / nano bubble distributor 3, which is used to uniformly distribute the micro / nano bubble suspension onto the catalyst surface. By providing the micro / nano bubble distributor 3 at the bottom of the photoelectrocatalytic reactor 1, the micro / nano bubbles can rise uniformly from the bottom of the reactor and fully contact the catalyst surface, thereby improving mass transfer efficiency and reaction uniformity.

[0040] According to some embodiments of the present invention, the photoelectrocatalytic reactor 1 has a single-chamber or double-chamber structure, and the working electrode 11 and the counter electrode 12 are separated by a proton exchange membrane 15 or a glass fiber membrane. By separating the working electrode 11 and the counter electrode 12 by a proton exchange membrane 15 or a glass fiber membrane, the occurrence of reverse reaction can be suppressed and the selectivity of the product can be improved.

[0041] According to a third aspect of the present invention, a multi-component metal-based photocatalyst is used in a method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to a first aspect of the present invention. The multi-component metal-based photocatalyst comprises: a substrate, semiconductor nanocrystals, and bimetallic active sites. The substrate is an N-doped MXene substrate. The semiconductor nanocrystals are multi-component metal-based semiconductor nanocrystals supported on the substrate. The semiconductor nanocrystals have a crystal plane co-activation structure, which includes a carbon source activated crystal plane and a nitrogen source activated crystal plane. The bimetallic active sites are anchored on the crystal planes of the semiconductor nanocrystals.

[0042] By doping the MXene substrate with N, the lone pair electrons on the surface of the N atom have a stronger specific adsorption capacity for the target substrate, which can make the substrate have good adsorption and sieving capabilities. This allows the substrate to accumulate near the substrate, ensuring that the active sites of the semiconductor nanocrystals anchored on the substrate are always surrounded by a high concentration of the target substrate. This increases the effective collision frequency between the substrate and the active center, thereby significantly improving the reaction rate.

[0043] By giving semiconductor nanocrystals a synergistic crystal plane structure, the built-in electric field formed at the heterocrystalline interface can promote the separation of photogenerated carriers and suppress the recombination of electrons and holes. This allows electrons to fully promote the reduction reaction, while holes can prevent the reduction reaction from going too far and causing an increase in by-products. As a result, the synergistic urea production process of power plant waste gas and nitrogen-containing wastewater catalyzed by the catalyst has a faster reaction rate and higher yield.

[0044] The multi-component metal-based photocatalyst of the present invention, by doping the N-doped MXene substrate, enhances the specific adsorption capacity of the lone pair electrons on the N atom surface for the target substrate, thereby enabling the substrate to have good adsorption and sieving capabilities. The substrate can pre-enrich the target substrate and shield impurity ions. By giving the semiconductor nanocrystals a crystal plane synergistic structure, the built-in electric field formed at the heterocrystalline interface can promote the separation of photogenerated carriers.

[0045] According to some embodiments of the present invention, intrinsic defects, including oxygen vacancies, sulfur vacancies, or metal vacancies, are also introduced on the characteristic crystal faces of the semiconductor nanocrystals. By introducing intrinsic defects on the characteristic crystal faces, the band structure of the material can be altered. These intrinsic defects induce local charge rearrangement, thereby lowering the reaction energy barrier and acting as highly active centers to enhance reactant adsorption. This can further optimize the substrate adsorption energy and carrier separation efficiency, thereby improving catalytic activity and selectivity.

[0046] According to some embodiments of the present invention, the bimetallic active sites are atomically dispersed heteronuclear bimetallic sites, selected from at least one combination of Fe-Co, Co-Ni, Cu-Bi, and Ni-Cu, and the loading of bimetallic sites is 0.1wt% to 5wt% of the total mass of the catalyst. By making the bimetallic active sites atomically dispersed heteronuclear bimetallic sites, different reactant molecules can be activated by electronic coupling or orbital hybridization between the bimetals, breaking the linear constraint relationship of a single active site and making the reaction easier to proceed.

[0047] According to some embodiments of the present invention, the multi-component metal-based semiconductor nanocrystals are composite semiconductors composed of at least two of the oxides, sulfides, or selenides of transition metals such as Fe, Co, Ni, Cu, Bi, and In. By selecting the multi-component metal-based semiconductor nanocrystals from the aforementioned composite semiconductors of transition metals, the light absorption range can be extended and the separation of photogenerated carriers can be promoted by utilizing the electronic coupling and band matching between different metals.

[0048] According to some embodiments of the present invention, the multi-component metal-based semiconductor nanocrystals are selected from the Bi2S3-In2S3, Cu2O-NiO, and Co3O4-Fe2O3 systems. By selecting the multi-component metal-based semiconductor nanocrystals from the above-mentioned preferred systems, the multi-component metal-based semiconductor can have suitable band structure and crystal plane growth characteristics, which is beneficial to the construction of crystal plane synergistic structures.

[0049] According to some embodiments of the present invention, the characteristic active crystal faces include the {001} / {110} crystal faces of metal oxides and the {010} / {110} crystal faces of metal sulfides; the carbon source activated crystal faces are crystal faces that have the ability to adsorb CO2 and its intermediates; and the nitrogen source activated crystal faces are crystal faces that adsorb NO3. - The crystal facets and their intermediates possess selective adsorption and activation capabilities. By activating the crystal facets with carbon and nitrogen sources, respectively, CO2 and NO3 are effectively adsorbed and activated. - It has selective adsorption and activation capabilities, which can spatially separate CO2 reduction and nitrogen reduction and achieve precise kinetic equilibrium, effectively avoiding the direct reduction of NO3. - The production of N2 or other byproducts reduces the yield, thus improving the selectivity of the reaction.

[0050] The following describes a method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to a first aspect of the present invention, with reference to some specific embodiments.

[0051] Example 1 8.73 g Bi(NO3)3·5H2O and 0.5 mmol InCl3 were mixed with 50 mL ethylene glycol, and 3 mmol thioacetamide and 0.5 mmol L-cysteine ​​were added as crystal plane guiding agents. After ultrasonic dispersion for 30 min, the mixture was transferred to a polytetrafluoroethylene-lined high-pressure reactor, and 50 mg N-doped MXene substrate was added. The mixture was hydrothermally reacted at 160 °C for 18 h, and then naturally cooled to room temperature. The mixture was washed alternately with deionized water and ethanol until the supernatant was clear, and then dried under vacuum at 60 °C to obtain the Bi2S3-In2S3 / N-MXene composite catalyst precursor.

[0052] 100 mg of the above precursor was dispersed in 100 mL of a methanol-water mixture (volume ratio 1:3) containing 0.1 mmol Cu(NO3)2 and 0.05 mmol Bi(NO3)3. The reaction was carried out under xenon lamp irradiation (300 W, visible light band) and nitrogen protection with stirring for 2 h, allowing Cu and Bi atoms to be selectively deposited on the {110} crystal plane. After the reaction was completed, the catalyst was obtained by washing and drying, denoted as Cu-Bi / Bi2S3-In2S3 / N-MXene.

[0053] Simulated power plant exhaust gas (CO2 concentration 12%, N2 balance, pretreated by dust removal, desulfurization, and denitrification) was used as the carbon source, and simulated power plant desulfurization wastewater containing nitrate nitrogen (NO3-N concentration 500 mg / L) was used as the liquid medium. A cavitation-type micro / nano bubble generator (operating pressure 0.4 MPa, gas-liquid ratio 1:15) was used to prepare a CO2 micro / nano bubble suspension.

[0054] The aforementioned CO2 micro / nano bubble suspension was introduced into a photoelectrocatalytic reactor. The working electrode in the reactor was an FTO conductive glass plate loaded with a Cu-Bi / Bi₂S₃-In₂S₃ / N-MXene catalyst (catalyst loading of 1 mg / cm²), the counter electrode was a platinum sheet, the reference electrode was an Ag / AgCl electrode, and the light source was a 300 W xenon lamp (equipped with an AM 1.5G filter). The reaction conditions were: temperature 25 °C, pH 7.0, applied bias voltage -1.0 V vs. Ag / AgCl, and light intensity 100 mW / cm². Samples were taken every 1 h, and the urea concentration was determined using the diacetyl monooxime spectrophotometric method.

[0055] After 8 h of reaction, the urea yield reached 186.5 μmol / g-cat / h, with a Faraday efficiency of 42.3% and a CN coupling selectivity of 38.7%. XRD characterization results showed that Bi₂S₃ nanocrystals mainly exposed {010} crystal planes, while In₂S₃ nanocrystals mainly exposed {110} crystal planes. STEM-EDS characterization showed that Cu and Bi existed in an atomically dispersed state, with a bimetallic site loading of approximately 1.2 wt%.

[0056] Example 2 Following the method in Example 1, the effects of different micro / nano bubble parameters on the photoelectrocatalytic urea production performance were investigated. The results showed that when the bubble diameter increased from 500 nm to 50 μm, the urea yield initially increased and then decreased, reaching its maximum value in the range of 2-5 μm. As the gas holdup increased from 1% to 20%, the urea yield exhibited a trend of first linear growth and then stabilization, reaching its optimum at a gas holdup of 8%-10%. The optimal urea yield could be obtained when the operating pressure of the micro / nano bubble generator was in the range of 0.3-0.6 MPa.

[0057] Example 3 Following the method in Example 1, Bi₂S₃-In₂S₃ / N-MXene catalysts with different crystal facet exposure ratios were prepared, and the effect of crystal facet synergy on CN coupling performance was investigated. The results showed that when the exposure area ratio of Bi₂S₃{010} crystal facets to In₂S₃{110} crystal facets was 1:1.5, the CN coupling selectivity and urea yield were optimal. This is because the {010} crystal facets preferentially adsorb and activate NO₃⁻. - The formation of amino intermediates is achieved by preferentially adsorbing and activating CO2 on the {110} crystal facet to generate carbonyl intermediates. The synergistic ratio of the two crystal facets is optimally matched with the reaction kinetics.

[0058] Example 4 Long-term stability tests were conducted under the optimal conditions of Example 1 for 10 consecutive reaction cycles (8 h per cycle). After each cycle, the catalyst on the working electrode was collected, washed with deionized water, and reloaded for the next round of reaction. The results showed that after 10 cycles, the photocurrent density of the catalyst remained at approximately 91.5%, the urea yield remained at approximately 88.3%, and the CN coupling selectivity remained above 35%. XRD and TEM characterization showed that the crystal structure and bimetallic site dispersion of the catalyst did not change significantly, confirming that the catalyst of the present invention has excellent long-term cycling stability.

[0059] Example 5 Actual flue gas and desulfurization wastewater were collected from a coal-fired power plant. The CO2 concentration in the pretreated flue gas was 13.2%, and the NO3-N concentration in the desulfurization wastewater was 685 mg / L, with SO4 also present. 2- Concentration of 3200 mg / L, Cl - Concentration of 1200 mg / L, trace heavy metals (Cu) 2+ Zn 2+ Ni 2+The total concentration was approximately 15 mg / L. The photoelectrocatalytic urea production reaction was carried out using the method described in Example 1. After 8 hours of reaction, the urea yield reached 152.8 μmol / g-cat / h, with a Faraday efficiency of 36.5% and a CN coupling selectivity of 31.2%. The results indicate that the method and apparatus of this invention have good adaptability and anti-interference capabilities for complex real power plant systems.

[0060] Example 6 Following the method of Example 1, but replacing the micro / nanobubble carrier gas with a traditional aeration method (aeration stone bubble diameter 1-3 mm, gas-liquid ratio same), all other conditions remained unchanged. After 8 h of reaction, the urea yield was only 52.3 μmol / g-cat / h, the Faraday efficiency was 15.6%, and the CN coupling selectivity was 12.4%. The comparative results show that the micro / nanobubble technology can increase the urea yield by about 3.6 times and the CN coupling selectivity by about 3.1 times.

[0061] Example 7 The method of Example 1 was followed, but the Cu-Bi / Bi2S3-In2S3 / N-MXene catalyst was replaced with a Bi2S3-In2S3 / N-MXene catalyst without crystal facet regulation (no crystal facet directing agent, crystal faces randomly exposed), while other conditions remained unchanged. After 8 hours of reaction, the urea yield was 118.2 μmol / g-cat / h, and the CN coupling selectivity was 24.5%. The comparative results show that synergistic crystal facet regulation can improve the CN coupling selectivity by approximately 58%.

[0062] Example 8 The method of Example 1 was followed, but the Cu-Bi bimetallic site was replaced with a single Cu metal site, while all other conditions remained unchanged. After 8 h of reaction, the urea yield was 142.6 μmol / g-cat / h, and the CN coupling selectivity was 28.3%. The comparative results show that the synergistic catalytic effect of the bimetallic site can further improve the CN coupling selectivity and urea yield.

[0063] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0064] In the description of this invention, "first feature" and "second feature" may include one or more of the features.

[0065] In the description of this invention, "a plurality of" means two or more.

[0066] In the description of this invention, the first feature being "above" or "below" the second feature may include the first and second features being in direct contact, or it may include the first and second features not being in direct contact but being in contact through another feature between them.

[0067] In the description of this invention, the terms "above," "over," and "on top" for the first feature and the second feature include the first feature being directly above or diagonally above the second feature, or simply indicating that the first feature is at a higher horizontal level than the second feature.

[0068] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0069] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater, characterized in that, include: Step S1: After pretreatment, the power plant exhaust gas is introduced into a micro-nano bubble generator, and a micro-nano bubble suspension carrying CO2 is prepared using nitrogen-containing wastewater as a medium. Step S2: The micro-nano bubble suspension is introduced into a photoelectrocatalytic reactor, which is filled with a multi-component metal-based photoelectrocatalyst. Under the synergistic effect of light and bias voltage, CO2 in the micro-nano bubbles undergoes a photoelectrocatalytic CN coupling reaction with nitrate nitrogen / nitrite nitrogen in nitrogen-containing wastewater to generate urea. Step S3: After the reaction, the mixture is subjected to solid-liquid separation to recover the catalyst in the solid phase. The liquid phase is separated to obtain urea product and nitrogen-containing liquid. The nitrogen-containing liquid is then passed into the CO2-carrying micro / nano bubble suspension from step S1 to continue participating in the reaction.

2. The method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to claim 1, characterized in that, The diameter of the micro-nano bubbles is 100 nm to 10 μm, the volume fraction of the micro-nano bubbles in the suspension is 1% to 20%, and the working pressure of the micro-nano bubble generator is 0.1 MPa to 1.0 MPa.

3. The method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to claim 1, characterized in that, In step S1, the power plant exhaust gas pretreatment method includes electrostatic precipitator dust removal, wet desulfurization, and selective catalytic reduction denitrification. After pretreatment, the volume fraction of CO2 in the exhaust gas is 10%-15%, and the SO2 concentration is less than 50 mg / m³. 3 NO x Concentration below 100 mg / m 3 Dust concentration below 30 mg / m³ 3 .

4. The method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to claim 1, characterized in that, In step S2, the conditions for the photoelectrocatalytic reaction include: a reaction temperature of 15 ℃ to 60 ℃, a reaction pH of 4.0 to 10.0, an applied bias voltage relative to the Ag / AgCl reference electrode of -0.5 V to -1.5 V, and a light source intensity of 50 mW / cm². 2 ~200 mW / cm 2 .

5. A photoelectrocatalytic reaction apparatus for the method of co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to any one of claims 1-4, characterized in that, include: The micro-nano bubble generating module includes a waste gas pretreatment unit, a micro-nano bubble generator, and a gas-liquid mixing reactor. The micro-nano bubble generating module is used to prepare micro-nano bubbles carrying CO2, and the gas-liquid mixing reactor is used to prepare a micro-nano bubble suspension carrying CO2 using the micro-nano bubbles and the nitrogen-containing wastewater. A photoelectrocatalytic reaction module, comprising a photoelectrocatalytic reactor and a light source system, wherein the photoelectrocatalytic reactor comprises a working electrode, a counter electrode, a reference electrode, and a potentiostat, and the multi-component metal-based photoelectrocatalyst is loaded on the working electrode; The product separation and recovery module includes a solid-liquid separator, a membrane separation device or an evaporator crystallizer, and a circulating pump. The product separation and recovery module is used for the separation and recovery of urea products and the recycling of reaction liquid.

6. The photoelectrocatalytic reaction apparatus for the co-production of urea from power plant exhaust gas and nitrogen-containing wastewater according to claim 5, characterized in that, It also includes a micro / nano bubble distributor, which is used to uniformly distribute the micro / nano bubble suspension onto the catalyst surface.

7. The photoelectrocatalytic reaction apparatus for the co-production of urea from power plant waste gas and nitrogen-containing wastewater according to claim 5, characterized in that, The photoelectrocatalytic reactor has a single-chamber or double-chamber structure, and the working electrode and the counter electrode are separated by a proton exchange membrane or a glass fiber membrane.

8. A multi-component metal-based photocatalyst used in the method for co-producing urea from power plant exhaust gas and nitrogen-containing wastewater according to any one of claims 1-4, characterized in that, include: N-doped MXene substrate; Multi-component metal-based semiconductor nanocrystals loaded on the substrate, wherein the semiconductor nanocrystals have a crystal plane synergistic structure, the crystal plane synergistic structure including a carbon source activated crystal plane and a nitrogen source activated crystal plane; Bimetallic active sites are anchored on the crystal surface of the semiconductor nanocrystal.

9. The multi-component metal-based photocatalyst according to claim 8, characterized in that, The semiconductor nanocrystals also have intrinsic defects introduced on their characteristic crystal surfaces, including oxygen vacancies, sulfur vacancies, or metal vacancies; and / or, the bimetallic active sites are atomically dispersed heteronuclear bimetallic sites selected from at least one combination of Fe-Co, Co-Ni, Cu-Bi, and Ni-Cu, and the loading of the bimetallic sites is 0.1wt% to 5wt% of the total mass of the catalyst.

10. The multi-component metal-based photocatalyst according to claim 8, characterized in that, The multi-component metal-based semiconductor nanocrystals are composite semiconductors selected from at least two of the oxides, sulfides, or selenides of transition metals such as Fe, Co, Ni, Cu, Bi, and In; and / or, the characteristic active crystal facets include the {001} / {110} crystal facets of metal oxides and the {010} / {110} crystal facets of metal sulfides, the carbon source activated crystal facets are crystal facets with adsorption capacity for CO2 and its intermediates, and the nitrogen source activated crystal facets are crystal facets with adsorption capacity for NO3. - Crystal planes of the crystals and their intermediates have selective adsorption and activation capabilities.

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