Efficient adsorption-catalytic degradation integrated treatment method for low-concentration NOx

Abstract

The invention belongs to an air pollution treatment technology in the field of environmental protection, and particularly relates to an efficient adsorption-catalytic degradation integrated treatment method for low-concentration NOx. The method comprises the following steps: screening and preparing a nano composite photocatalyst with double functions of intensified enrichment / catalytic degradation, synthesizing a membrane substrate material capable of selectively separating low-concentration NOx, constructing adsorption-catalysis integrated equipment with a multilayer membrane catalysis structure, and realizing selective adsorption-enrichment and in-situ rapid catalytic degradation of low-concentration NOx at normal temperature and normal pressure. The technical problems that in the prior art, low-concentration NOx treatment efficiency is low, energy consumption is high, and secondary pollution is prone to being generated are solved, and the device has the advantages of being high in NOx removal rate, small in generation amount of by-product NO2, low in energy consumption, easy and convenient to operate and maintain and the like and can be widely applied to small industrial boilers, ship denitration, indoor and outdoor low-concentration NOx purification and other scenes.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically to nitrogen oxides (NOx) in air pollution control. x Treatment technology, particularly involving a low-concentration NO x A highly efficient integrated adsorption-catalytic degradation treatment method. Background Technology

[0002] Nitrogen oxides (NO) x As one of the core pollutants in air pollution, NO emissions come from both natural processes and human activities, with industrial production (such as steel and chemical industries), coal-fired power plants, and vehicle exhaust being the main sources of anthropogenic emissions. x Not only is NO a key precursor to photochemical smog and acid rain, it also damages the ozone layer and participates in the formation of secondary organic aerosols (SOA), directly threatening human respiratory health and ecological stability. With increasingly stringent environmental regulations in various countries, high concentrations of NO are becoming a serious concern. x Source control technologies (such as selective catalytic reduction systems in large power plants) have gradually matured, but low concentrations of NO released into the environment... x These low-concentration NO3- compounds continue to have a negative impact on regional air quality. x Due to its low volume concentration, dispersed form, and complex mixing with other gaseous components, it has become the "last mile" problem in air pollution control.

[0003] Existing low concentration NO x The processing technologies generally suffer from technical defects and are difficult to meet the needs of practical applications. Specific problems are as follows:

[0004] Limitations of Selective Catalytic Reduction (SCR): SCR technology is used in industrial applications to treat high concentrations of NO. x The mainstream method is based on the principle of using a catalyst at high temperatures to react NH3 with NO. x The reaction produces N2 and H2O. However, this technique is not suitable for low concentrations of NO. x The treatment efficiency is extremely low because NO is present at low concentrations. x The collision frequency with NH3 is insufficient, and the stoichiometric ratio between the two must be strictly controlled. Excessive NH3 will lead to secondary pollution. In addition, the SCR reaction needs to be started in a high-temperature environment, the reactor needs to be placed in a high-dust area, the catalyst is easily poisoned by smoke and dust, the maintenance cost is high, and it cannot be adapted to the treatment scenario of normal temperature and low concentration.

[0005] The drawback of activated carbon adsorption: Due to its large specific surface area, activated carbon is not effective for low concentrations of NO. xWhile it possesses a certain adsorption capacity, its adsorption capacity is limited and easily reaches saturation. Furthermore, the desorption and regeneration process is complex—the desorption process requires high temperatures or chemical reagents, which not only consumes a lot of energy but may also damage the activated carbon structure. More importantly, activated carbon poses a risk of spontaneous combustion at high temperatures; if not handled properly, the adsorbed NO... x It may be released again, causing secondary pollution, which limits its application in long-term, continuous treatment scenarios.

[0006] The high energy consumption of plasma technology: Plasma technology excites gas molecules with high-energy electron beams to form non-equilibrium plasma, and utilizes active free radicals to oxidize NO. x However, this technology consumes extremely high amounts of electricity, with a unit of NO... x The energy consumption is several times that of traditional methods, and high-energy electrons may destroy other components in the mixed gas, generating unknown toxic byproducts. In addition, the electrodes of the plasma generator are prone to oxidation and wear, requiring frequent replacement, resulting in high operation and maintenance costs and making it difficult to achieve large-scale industrial application.

[0007] The bottleneck of microbial purification technology: Microbial methods remove NO through the metabolic action of nitrifying and denitrifying bacteria. x The technology converts NO to N2, but it has stringent environmental requirements—strict control of temperature, pH, and carbon source concentration is necessary. Furthermore, the microbial strains have weak survival capabilities and are easily poisoned by impurities in the mixed waste gas (such as SO2 and heavy metals). Simultaneously, the slow metabolic rate of the microorganisms results in low treatment efficiency, making it unsuitable for treating low-concentration NO. x The need for rapid purification is only suitable for small-scale laboratory testing scenarios and is difficult to extend to actual engineering projects.

[0008] The shortcomings of traditional photocatalysis technology: Although existing photocatalysis technology can oxidize NO at room temperature x However, two major problems exist: first, the high recombination rate of photogenerated carriers (electron-hole pairs) leads to insufficient catalytic activity; second, the catalyst has limited catalytic activity at low concentrations of NO. x The adsorption capacity of nitrogen oxides is weak, the reaction driving force is insufficient, and they easily generate toxic byproducts such as NO2—these defects make traditional photocatalytic technologies less effective for NO removal. x The removal rate is difficult to improve, and it cannot meet the requirements of environmental protection standards.

[0009] In summary, current technologies cannot simultaneously address low concentrations of NO. x The four core issues of "selective separation, efficient enrichment, in-situ degradation, and byproduct control" urgently require the development of an integrated technical solution that operates at ambient temperature and pressure, consumes little energy, produces no secondary pollution, and has high treatment efficiency, in order to fill the gap in low-concentration NO. x A technological gap in the field of governance. Summary of the Invention

[0010] In view of the above-mentioned deficiencies of the prior art, the present invention aims to solve the problem of existing low-concentration NO x Existing treatment technologies suffer from low efficiency, high energy consumption, secondary pollution, and complex operation and maintenance. This paper proposes an integrated treatment method that combines selective adsorption-enrichment with highly efficient catalytic degradation to achieve low-concentration NO treatment. x Deep purification.

[0011] To achieve the above objectives, the present invention provides a low-concentration NO x The highly efficient adsorption-catalytic degradation integrated treatment method includes the following steps:

[0012] Step 1: Screening and preparing nanocomposite photocatalysts. The nanocomposite photocatalysts have dual adsorption-catalysis functions and include a catalyst active component and a modifier. The catalyst active component is selected from at least one of ferrite-based compounds and bismuth-based compounds, and the modifier is selected from at least one of carbon quantum dots, g-C3N4, and oxygen vacancies.

[0013] Step 2: Synthesize selective separation of low concentration NO x The membrane substrate material is subjected to corrosion resistance, acid and alkali resistance, and mechanical strength modification treatment.

[0014] Step 3: Construct an integrated adsorption-catalysis device, fix multiple layers of the modified membrane substrate material prepared in step 2 inside the device, and load the nanocomposite photocatalyst prepared in step 1 onto the surface of the modified membrane substrate material to form a catalytic functional layer;

[0015] Step 4: Add low concentrations of NO x The mixed waste gas is introduced into the integrated equipment constructed in step 3, and the waste gas treatment process parameters are controlled to reduce NO content. x Adsorption-enrichment and in-situ catalytic degradation are completed on the surface of the catalytic functional layer;

[0016] Step 5: Monitor the outlet gas of the integrated equipment in real time and adjust the process parameters to suppress the generation of by-product NO2, ensuring that the treated gas meets emission standards.

[0017] Preferably, the ferrate-based compound in step 1 is selected from at least one of ZnFe2O4, Fe3O4, and CoFe2O4, and the bismuth-based compound is selected from at least one of Bi2O2CO3, Bi2O3, and (BiO)2CO3.

[0018] Preferably, the preparation method of the nanocomposite photocatalyst in step 1 is one of the following: solvothermal method, in-situ self-sacrifice method, or hydrothermal-in-situ thermal decomposition method.

[0019] Preferably, the membrane substrate material in step 2 is selected from one of ceramic membranes, polymer membranes, and composite metal membranes.

[0020] Preferably, the modification treatment in step 2 includes: surface modification of the membrane substrate using LaCO3OH or SiO2.

[0021] Preferably, the multilayer membrane catalytic material in step 3 has a multilayer structure, and the nanocomposite photocatalyst is loaded onto the surface of the membrane substrate by coating or impregnation.

[0022] Preferably, the process parameters in step 4 include exhaust gas temperature, gas flow rate, and relative humidity. If a photocatalytic system is used, light intensity is also included.

[0023] Preferably, in the catalytic degradation process described in step 4, the nanocomposite photocatalyst forms a built-in electric field by constructing a heterojunction structure, promoting the directional migration of photogenerated carriers, generating active free radicals, and converting the adsorbed and enriched NO... x It is oxidized to nitrate.

[0024] Preferably, the real-time detection in step 5 uses an infrared spectrometer or a gas chromatograph, and the detection index includes NO. x The total removal rate, NO2 generation, and O2 content are controlled by adjusting the gas flow rate or optimizing the surface modification state of the catalyst when excessive by-product generation is detected.

[0025] Preferably, the low concentration of NO x NO is a low-volume concentration in the environment or industrial exhaust gas. x The mixture, the NO in the treated gas x The emission concentration meets environmental protection standards.

[0026] Compared to existing technologies, the low-concentration NO of this invention... x The highly efficient integrated adsorption-catalytic degradation treatment method, through synergistic innovation in "materials, equipment, process, and regulation," has achieved several technological breakthroughs, with specific technical effects as follows:

[0027] (1) This invention solves the problem of low-concentration NO by integrating the design of "membrane selective adsorption-catalyst dual enrichment-in-situ catalytic degradation". x The problem of insufficient reaction driving force, NO x The removal rate is far higher than existing technologies—more than 30% higher than activated carbon adsorption; more than 20% higher than traditional photocatalytic technology, and the NO removal rate in the treated gas is significantly reduced. x The concentration can consistently meet environmental protection standards.

[0028] (2) The method of the present invention operates at room temperature and pressure, without the need for high-temperature heating, high-energy plasma excitation or complex microbial culture environment. If a visible light-driven photocatalytic system is used, the energy consumption mainly comes from the light source, which is much lower than that of plasma technology (energy consumption is reduced by more than 60%). If a non-photocatalytic system is used (such as room temperature catalysis of oxygen vacancy modified catalyst), no additional energy consumption is required, and the operating cost is significantly reduced.

[0029] (3) The present invention controls byproducts through two major measures: first, the modified design of the catalyst (such as oxygen vacancies, g-C3N4 heterojunction) inhibits the generation of NO2; second, real-time detection and process control ensure that the concentration of byproducts is below the safety limit; at the same time, both the catalyst and the membrane substrate are stable solid materials with no risk of leakage, and the product nitrate can be safely disposed of to avoid secondary pollution.

[0030] (4) The equipment of the present invention adopts a modular design and can be flexibly adjusted according to the processing volume and waste gas composition. Small equipment can be used for indoor air purification and ship denitrification; large equipment can be used for small industrial boiler exhaust gas and urban atmospheric edge area purification. At the same time, the modified membrane substrate and catalyst have excellent corrosion resistance and can be adapted to mixed waste gas scenarios containing acidic impurities. The applicable scope is far beyond the existing technology.

[0031] (5) The membrane substrate modified by this invention has high mechanical strength and wear resistance, and the catalyst activity is stable. After thousands of hours of continuous operation, NO x The removal rate remains at a high level, eliminating the need for frequent material replacements. Furthermore, the preparation methods for the catalyst and membrane substrate are mature, the raw material costs are low, large-scale production is feasible, and the equipment is easy to maintain, providing an economical foundation for industrialization.

[0032] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0033] Figure 1 This is a flowchart of a preferred embodiment of the present invention. Detailed Implementation

[0034] The following description, with reference to the accompanying drawings, illustrates several preferred embodiments of the present invention to make its technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0035] In the accompanying drawings, components with the same structure are indicated by the same numerical designation, and components with similar structures or functions are indicated by similar numerical designations. The dimensions and thicknesses of each component shown in the drawings are arbitrary, and the present invention does not limit the dimensions and thicknesses of each component. To make the illustrations clearer, the thickness of some components has been appropriately exaggerated in the drawings.

[0036] like Figure 1 As shown, this embodiment provides a low-concentration NO x This highly efficient integrated adsorption-catalytic degradation method utilizes a complete technology chain encompassing "material design, equipment construction, process optimization, and process control" to achieve low-concentration NO treatment. x The deep purification process includes the following five core steps:

[0037] (I) Screening and preparation of nanocomposite photocatalysts

[0038] The core of this step is to prepare a nanocomposite photocatalyst with dual "adsorption-catalysis" functions. Through the synergistic effect of the active component and the modifier, the NO content can be simultaneously increased. x The adsorption capacity and catalytic degradation efficiency are as follows:

[0039] Screening logic for catalyst active components:

[0040] Ferrate compounds (such as ZnFe2O4, Fe3O4, and CoFe2O4) were chosen as one of the active components because the active iron sites in ferrates are conducive to NO. x It has strong adsorption capacity—Fe 3 +Can be combined with NO x The O atoms in NO form coordinate bonds, thus achieving NO x It exhibits specific adsorption; at the same time, ferrates have excellent light absorption properties, which can absorb visible light and excite the generation of photogenerated carriers, providing energy for catalytic degradation.

[0041] Bismuth-based compounds (such as Bi₂O₂CO₃, Bi₂O₃, and (BiO)₂CO₃) were chosen as another class of active components. Bismuth-based compounds have moderate band gaps, allowing them to respond in the visible light range, and their surface oxygen species (lattice oxygen and adsorbed oxygen) are highly active, readily participating in NO reaction. x The oxidation reaction; in addition, the layered structure of bismuth compounds is conducive to the migration of photogenerated carriers and reduces the recombination rate.

[0042] The role and selection of modifiers:

[0043] Carbon quantum dots: As a modifier, carbon quantum dots possess excellent electronic conductivity and can form heterostructures with active components, promoting the separation and transport of photogenerated charge carriers. Simultaneously, the surface groups of carbon quantum dots (such as hydroxyl and carboxyl groups) can enhance the catalyst's resistance to NO.x It can enhance the adsorption capacity and improve the biocompatibility of the catalyst, thus avoiding secondary harm to the environment.

[0044] g-C3N4: g-C3N4 is a non-metallic semiconductor material with a graphite-like layered structure. Its conduction and valence band positions match those of ferrates and bismuth compounds, allowing for the formation of stable heterojunctions. The potential difference at the heterojunction interface creates a built-in electric field, driving photogenerated electrons and holes to migrate in opposite directions, significantly reducing the recombination rate. Furthermore, the nitrogen atoms on the surface of g-C3N4 can react with NO... x Hydrogen bonds are formed, enhancing adsorption capacity.

[0045] Oxygen vacancies: Oxygen vacancies are introduced onto the catalyst surface through reduction treatments (such as hydrogen reduction or vacuum annealing). These oxygen vacancies can act as NO... x Adsorption sites enhance NO x The catalyst's ability to capture oxygen is enhanced; simultaneously, oxygen vacancies can modulate the electronic state density of the catalyst, promoting the activity of reactive free radicals (such as ·OH, ·O2). - It can promote the formation of NO and inhibit the formation of NO2—oxygen vacancies can selectively promote NO production. x The product is converted to nitrate to avoid the accumulation of the intermediate NO2.

[0046] Catalyst preparation methods:

[0047] Solvent thermal method: The active component precursor (such as nitrate, chloride) and the modifier are dispersed in a solvent (such as ethanol, water, ethylene glycol), transferred to a closed reaction vessel, and reacted at a certain temperature for a certain time. This method can control the particle size, morphology and crystal form of the catalyst by adjusting the temperature, reaction time and solvent type, so as to ensure that the active component and the modifier are uniformly combined to form a stable composite structure.

[0048] In-situ self-sacrifice method: Using a certain component (such as g-C3N4) as a sacrificial template, it gradually decomposes during the reaction process and reacts with other active components (such as bismuth compounds) to form a heterojunction structure in situ. This method does not require subsequent separation steps, which can simplify the preparation process. Moreover, the heterojunction interface is tightly bound, which is conducive to the migration of photogenerated carriers.

[0049] Hydrothermal-in-situ thermal decomposition method: First, a precursor of the active component (such as hydroxide or carbonate) is prepared by hydrothermal method. Then, the precursor is calcined at a certain temperature to decompose in situ to form the target catalyst. Modifiers (such as oxygen vacancies) are introduced. This method can precisely control the crystal structure of the catalyst, improve crystallinity, and enhance catalytic stability.

[0050] (II) Synthesis and Modification of Selective Membrane Substrate Materials

[0051] The purpose of this step is to synthesize a method for selectively separating low concentrations of NO.x The membrane substrate material was modified to improve its corrosion resistance, acid and alkali resistance, and mechanical strength, laying the foundation for subsequent catalyst loading and the construction of catalytic functional layers, as detailed below:

[0052] Selection criteria for membrane substrate materials:

[0053] Ceramic membranes: Ceramic membranes (such as Al2O3 and TiO2-based ceramic membranes) have advantages such as high temperature resistance, acid and alkali resistance, and high mechanical strength, and their pore size is controllable. By controlling the preparation process (such as sol-gel method and dry pressing method), ceramic membranes with specific pore sizes can be prepared to achieve NO removal. x Selective separation; in addition, the ceramic membrane has abundant hydroxyl groups on its surface, which is beneficial for catalyst loading and fixation.

[0054] Polymer membranes: Polymer membranes (such as polyvinylidene fluoride and polyacrylonitrile membranes) have advantages such as good flexibility, low preparation cost, and easy processing into large-area membranes. Furthermore, their ability to resist NO can be enhanced through chemical modification (such as grafting functional groups). x It offers selectivity and is suitable for scenarios where there are requirements on equipment size and weight (such as ship denitrification and vehicle-mounted purification devices).

[0055] Composite metal membranes: Composite metal membranes (such as stainless steel-aluminum composite membranes) possess excellent corrosion resistance and mechanical strength, making them suitable for mixed waste gas environments containing acidic impurities (such as SO2). Their surfaces can be coated with functional coatings using deposition techniques (such as magnetron sputtering) to enhance NO removal. x Its selective separation capability.

[0056] Modification of membrane substrate materials:

[0057] LaCO3OH Modification: LaCO3OH possesses excellent acid resistance and ion exchange performance. The membrane substrate is immersed in a LaCO3OH solution, and through an impregnation-calcination process, a uniform coating of LaCO3OH is formed on the membrane surface. This coating enhances the membrane substrate's resistance to acidic gases (such as SO2) and prevents membrane pore blockage. Simultaneously, LaCO3OH... 3 +Can be combined with NO x Forming coordination bonds enhances the membrane's resistance to NO. x Its selective separation capability.

[0058] SiO2 modification: SiO2 has the advantages of high chemical stability and easy surface functionalization. SiO2 sol is coated on the surface of the membrane substrate by sol-gel method. After drying and calcination, a SiO2 coating is formed. This coating can fill the micropore defects on the membrane surface and improve the mechanical strength of the membrane. At the same time, the hydroxyl groups on the surface of SiO2 can form chemical bonds with the catalyst, enhance the binding force between the catalyst and the membrane substrate, and prevent the catalyst from falling off.

[0059] Performance advantages after modification:

[0060] Improved corrosion resistance: The modified membrane substrate can operate for a long time in acidic or alkaline environments, avoiding damage to the membrane structure caused by acidic impurities (such as SO2, HCl) or alkaline impurities (such as NH2) in the mixed waste gas;

[0061] Enhanced mechanical strength: Modified coatings can fill structural defects in the membrane substrate, improve the membrane's tensile and bending resistance, and meet the mechanical requirements of equipment assembly and long-term operation;

[0062] Selective optimization: The modified membrane substrate's response to NO x The selective separation coefficient is significantly improved, enabling the specific capture of NO in mixed gases. x This provides a guarantee for subsequent enrichment and degradation.

[0063] (III) Construction of integrated adsorption-catalysis equipment

[0064] This step integrates the pretreatment unit, reaction chamber, catalytic functional layer, and detection unit to construct a "one-stop" adsorption-catalysis integrated device, achieving low-concentration NO... x The continuous processing, specifically its structure and design logic, are as follows:

[0065] The core components of the equipment:

[0066] Air inlet: Designed with a trumpet-shaped structure and equipped with a gas distributor to ensure that the mixed waste gas enters the equipment evenly and avoid uneven treatment caused by excessive local flow velocity; the air inlet can also be connected to a filter device to initially remove large particulate impurities (such as dust) in the waste gas.

[0067] Pretreatment unit: mainly composed of a filter layer and an adsorption layer. The filter layer uses quartz sand and ceramic filter media to remove fine dust from the exhaust gas. The adsorption layer uses alkaline adsorbents (such as activated carbon supported by NaOH) to remove acidic impurities (such as SO2 and H2S) from the exhaust gas, preventing them from poisoning the catalyst or corroding the membrane substrate. The design of the pretreatment unit can be flexibly adjusted according to the composition of the exhaust gas to ensure that the exhaust gas entering the reaction chamber meets the treatment requirements.

[0068] Reaction chamber: It is a closed structure, and the material can be stainless steel (suitable for industrial scenarios) or polytetrafluoroethylene (suitable for laboratory scenarios). The volume of the chamber can be flexibly designed according to the processing capacity—from small chambers suitable for indoor purification to large chambers suitable for industrial exhaust gases; the inner wall of the reaction chamber needs to be treated with anti-corrosion to avoid the erosion of the chamber by the exhaust gas.

[0069] Catalytic functional layer: Composed of multiple modified membrane substrates, which are fixed in the reaction chamber by a support. The spacing between adjacent membrane substrates can be adjusted according to the gas flow rate to ensure full contact between the exhaust gas and the catalytic functional layer. The nanocomposite photocatalyst is loaded onto the surface of the membrane substrate by coating or impregnation. The coating method is suitable for paste-like catalysts, in which the catalyst is uniformly coated onto the membrane surface using a scraper. The impregnation method is suitable for solution-like catalysts, in which the membrane substrate is immersed in the catalyst solution, and the catalyst is attached to the membrane surface through capillary action. The loaded catalyst forms a uniform catalytic coating that is tightly bonded to the membrane substrate to prevent detachment.

[0070] Auxiliary system: If a photocatalytic system is used, a light source (such as an LED visible light lamp) needs to be set outside or inside the reaction chamber to ensure that the catalyst can absorb sufficient light energy; at the same time, a temperature control system (such as a heating element or a cooling fan) and a humidity control module (such as a humidifier or a dehumidifier) ​​are required to regulate the environmental parameters of the reaction chamber; in addition, a gas flow rate regulation device (such as a valve or a fan) is set to control the residence time of the exhaust gas in the reaction chamber.

[0071] Gas outlet and detection unit: The gas outlet is connected to a gas sampling tube, which introduces the treated gas into the detection unit; the detection unit uses an infrared spectrometer or a gas chromatograph to detect NO in the gas in real time. x Indicators such as concentration, NO2 concentration, and O2 concentration; the detection data can be transmitted to the control system for subsequent adjustment of process parameters.

[0072] The equipment's design advantages:

[0073] Integrated design: The functions of "pretreatment-adsorption-catalysis-detection" are integrated into the same device, reducing the equipment footprint, reducing system complexity, and facilitating operation and maintenance;

[0074] Modular design: The number of membrane substrates in the catalytic functional layer and the type of adsorbent in the pretreatment unit can be changed according to actual needs, adapting to low-concentration NO with different compositions and concentrations. x Processing scenarios;

[0075] High safety: The equipment adopts a closed structure and is equipped with pressure sensors and explosion-proof devices to avoid safety risks caused by gas leakage or excessive pressure; at the same time, the detection unit can monitor the concentration of by-products in real time to ensure that the treated gas meets the emission standards.

[0076] (iv) Low concentration of NO x Adsorption-catalytic degradation process

[0077] This step involves removing substances containing low concentrations of NO. x The mixed waste gas is fed into the integrated equipment, and by adjusting the process parameters, NO is controlled. xThe specific process and mechanism of "selective adsorption-efficient enrichment-in-situ catalytic degradation" are as follows:

[0078] Selection and control of process parameters:

[0079] Exhaust gas temperature: Controlled within the normal temperature range, no additional heating or cooling is required - the normal temperature environment can avoid increased energy consumption, while ensuring the stability of catalyst activity (high temperature may cause catalyst crystal transformation, low temperature may reduce reaction rate);

[0080] Gas flow rate: Adjusted according to the volume of the reaction chamber and the number of catalytic functional layers to ensure sufficient residence time of the exhaust gas within the reaction chamber, so that NO... x Sufficient adsorption and degradation – too high a flow rate will result in insufficient contact time and a decrease in removal rate; too low a flow rate will reduce the throughput and affect efficiency.

[0081] Relative humidity: Keep it within a suitable range. Excessive humidity may cause a water film to form on the catalyst surface, hindering NO2 production. x Adsorption; excessively low humidity may reduce the generation of active free radicals (such as ·OH), thus decreasing catalytic efficiency;

[0082] Light intensity (photocatalytic system): Adjusted according to the light response range of the catalyst to ensure that the catalyst can fully absorb light energy and generate sufficient photogenerated carriers. Insufficient light intensity will lead to a decrease in catalytic activity, while excessive light intensity may cause the catalyst to overheat and affect stability.

[0083] Adsorption-enrichment process:

[0084] After impurities are removed by the pretreatment unit, the mixed exhaust gas enters the reaction chamber and flows over the surface of the membrane substrate of the catalytic functional layer. The membrane substrate selectively retains NO through pore size sieving and surface modification. x Molecules that allow other gaseous components (such as N2 and O2) to pass through;

[0085] NO x Molecules accumulate on the membrane substrate surface, and the concentration gradually increases, solving the problem of low-concentration NO. x The problem of low contact frequency with the catalyst; simultaneously, the active sites (such as Fe) on the surface of the nanocomposite photocatalyst supported on the membrane substrate. 3 (+, N atoms, oxygen vacancies) further adsorb NO x The molecules form a dual enrichment effect of "membrane adsorption-catalyst adsorption", providing a high-concentration reaction environment for subsequent degradation.

[0086] Catalytic degradation mechanism:

[0087] Generation and separation of photogenerated carriers: In a photocatalytic system, after the catalyst absorbs light energy, valence band electrons are excited to the conduction band, forming photogenerated electrons (ep). -) and holes (h + Due to the presence of heterojunction structures in the catalyst (such as the heterojunction formed by g-C3N4 and bismuth-based compounds), the interfacial potential difference creates a built-in electric field, driving e - with h + Migration in the opposite direction significantly reduces the composite rate;

[0088] Generation of active free radicals: e⁻ migrating to the catalyst surface reacts with O₂ in the mixed gas to generate ·O₂. - (Superoxide radical); h + It reacts with H2O adsorbed on the catalyst surface to generate ·OH (hydroxyl radical); ·O2 - Both ·OH and NO have strong oxidizing properties and are effective in degrading NO. x Core active species;

[0089] NO x Oxidative degradation: enrichment of NO x The molecules first bind to the active sites on the catalyst surface to form adsorbed NO. x Subsequently, O2 - NO is attacked sequentially by ·OH. x The chemical bonds in the molecule cause NO to be gradually oxidized to NO2. - (nitrite), which is then oxidized to NO3. - (Nitrate) - Nitrate can be desorbed from the catalyst surface by water washing or ion exchange, thus regenerating the catalyst; no toxic byproducts are generated in the whole process, and the products are safe and harmless.

[0090] (v) Product testing and process control

[0091] This step involves real-time monitoring of the outlet gas composition and dynamic adjustment of process parameters to ensure NO... x The removal rate met the standard and byproducts were effectively controlled, as detailed below:

[0092] Real-time detection methods and indicators:

[0093] Detection instruments: Infrared spectrometer or gas chromatograph is used—infrared spectrometer can quickly detect NO through characteristic absorption peaks. x With respect to NO2 concentration, it has a fast response speed; gas chromatographs can separate gas components through chromatographic columns, with high detection accuracy, and are suitable for quantitative analysis of low-concentration components;

[0094] Core detection indicator: NO x Total removal rate (calculated as "(intake NO)") x Concentration - Exhaust NO x (Concentration) / Inlet NO xThe concentration (×100%), the amount of NO2 generated as a byproduct, and the O2 content (to determine whether the reaction is oxygen-deficient); in addition, the concentration of other impurity components (such as SO2 and CO) can be detected as needed to evaluate the effectiveness of the pretreatment unit.

[0095] Process control strategies:

[0096] Byproduct over-limit control: When excessive NO2 generation is detected, it can be controlled in two ways: one is to reduce the gas flow rate and prolong the NO production time. x Residence time in the catalytic functional layer ensures NO x The catalyst is fully oxidized to nitrate to avoid the release of intermediate product NO2; secondly, the surface modification state of the catalyst is optimized - if the catalyst is modified with oxygen vacancy, the ability to further oxidize NO2 can be enhanced by appropriately increasing the concentration of oxygen vacancy (such as by re-reduction treatment).

[0097] Insufficient NO removal rate control: When NO x When the removal rate does not meet expectations, the following measures can be taken: increase the number of membrane substrates in the catalytic functional layer to improve the adsorption and catalytic area; optimize the catalyst loading to ensure sufficient active sites; adjust the light intensity (photocatalytic system) or humidity to improve catalytic activity;

[0098] Long-term operation and control: Regularly check the integrity of the membrane substrate and the activity of the catalyst. If the membrane substrate is damaged, replace it in time. If the catalyst activity decreases, it can be regenerated by water washing or light calcination to restore its activity.

[0099] Emissions compliance guarantee:

[0100] NO in the treated gas x The concentration must comply with national or local environmental protection standards—for example, for ambient air purification, it must comply with the NO content in the "Ambient Air Quality Standard" (GB3095-2012). x The hourly average concentration limit; for industrial exhaust gas, it must comply with the emission standards of the corresponding industry (such as the "Emission Standard of Air Pollutants for Boilers" (GB13271-2014)).

[0101] Regularly calibrate the testing instruments to ensure the accuracy of the test data; at the same time, record the operating parameters and processing results to form a complete operation log, which will facilitate subsequent optimization and traceability.

[0102] The technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples. The embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention.

[0103] Example 1: Low concentration NO from ferrite-based composite catalyst + g-C3N4 / Bi2O2CO3 modified ceramic membrane x deal with

[0104] (I) Preparation of experimental materials

[0105] Catalyst raw materials: ferrate-based compound precursors (zinc nitrate, ferric nitrate), bismuth-based compound precursors (bismuth nitrate, sodium carbonate), g-C3N4 powder, carbon quantum dots (particle size in the nanoscale, with hydroxyl groups on the surface).

[0106] Membrane substrate material: ceramic membrane (Al2O3 based, prepared by sol-gel method, with porous structure);

[0107] Modifiers: LaCO3OH powder, deionized water, ethanol (analytical grade);

[0108] Simulated exhaust gas: contains low concentrations of NO x A mixture of gases (NO as the main component, with a small amount of NO2 mixed in, and air as the carrier gas).

[0109] Experimental equipment: solvothermal reactor, muffle furnace, ultrasonic cleaner, adsorption-catalysis integrated experimental device (self-made, including pretreatment unit, reaction chamber, catalytic functional layer, and detection unit), visible light source (LED lamp, adapted to the photoresponse range of the catalyst).

[0110] (II) Preparation of nanocomposite photocatalysts (solvothermal method)

[0111] Preparation of ferrate active component: Zinc nitrate and ferric nitrate were mixed in stoichiometric ratio and dissolved in deionized water, and stirred to form a homogeneous solution; excess urea was added as a precipitant, and stirring was continued until the solution became clear; the solution was transferred to a solvothermal reactor and reacted at a set temperature for a certain time; after the reaction was completed, the mixture was cooled to room temperature, filtered to obtain the precipitate, washed repeatedly with deionized water and ethanol alternately, dried, and then calcined in a muffle furnace to obtain the ferrate-based compound (ZnFe2O4).

[0112] Preparation of bismuth-based active components: Bismuth nitrate was dissolved in nitric acid solution and stirred until completely dissolved; sodium carbonate solution was slowly added dropwise to adjust the pH value to the set range, forming a white precipitate; stirring was continued for a certain time, and the bismuth-based compound precursor (Bi2(CO3)3) was obtained by filtration, drying and calcination to obtain the bismuth-based compound (Bi2O2CO3).

[0113] Preparation of composite catalyst: ZnFe2O4, Bi2O2CO3 and g-C3N4 were mixed in a certain mass ratio, and carbon quantum dot dispersion was added. The mixture was ultrasonically treated until homogeneous. The mixture was then transferred to a solvothermal reactor and reacted at a set temperature for a certain time. After the reaction was completed, the mixture was cooled, filtered, washed and dried to obtain the nanocomposite photocatalyst (ZnFe2O4 / g-C3N4 / Bi2O2CO3, labeled Cat-1).

[0114] (III) Preparation of g-C3N4 / Bi2O2CO3 modified ceramic membrane

[0115] Membrane substrate pretreatment: The ceramic membrane is cleaned with deionized water to remove surface impurities; it is then immersed in ethanol, ultrasonically treated for a certain period of time, and dried for later use.

[0116] Membrane substrate modification: LaCO3OH powder was dissolved in deionized water and stirred to form a homogeneous solution; the pretreated ceramic membrane was immersed in the LaCO3OH solution and reacted at a set temperature for a certain period of time; the ceramic membrane was removed, washed with deionized water, dried and then calcined in a muffle furnace to obtain a LaCO3OH modified ceramic membrane.

[0117] Catalyst loading: Cat-1 is dispersed in ethanol to form a catalyst suspension; the suspension is uniformly coated on the surface of the modified ceramic membrane using a coating method, the coating thickness is controlled, and after drying, it is calcined to obtain the modified ceramic membrane with catalyst loading (i.e., the core component of the catalytic functional layer).

[0118] (iv) Construction of integrated adsorption-catalysis equipment

[0119] Pretreatment unit assembly: A filter layer (filled with quartz sand) and an adsorption layer (filled with NaOH-loaded activated carbon) are set at the rear end of the equipment air inlet. Both layers are fixed by a bracket to ensure that the exhaust gas flows through the filter layer and the adsorption layer in sequence.

[0120] Assembly of the reaction chamber and catalytic functional layer: The modified ceramic membrane loaded with catalyst is fixed in the reaction chamber by a support to form a multi-layer structure (the number of layers is adjusted according to the throughput). The spacing between two adjacent membrane layers is designed according to the gas flow rate. A visible light source is installed outside the reaction chamber to ensure that the light source can uniformly illuminate the catalytic functional layer. A temperature / humidity sensor is installed inside the chamber to monitor environmental parameters in real time.

[0121] Detection unit connection: Connect the gas outlet to the infrared spectrometer via a gas sampling tube, set the detection frequency, and collect NO data in real time. x The concentration and NO2 concentration data are collected and transmitted to the control system.

[0122] (v) Low concentration of NO x Treatment Experiments and Results Analysis

[0123] Experimental conditions were set as follows: simulated waste gas was introduced into the integrated equipment, and the pretreatment unit, light source and detection unit were turned on; the waste gas temperature was controlled at room temperature, the relative humidity was within a suitable range, and the gas flow rate was adjusted according to the volume of the reaction chamber; the experiment was run continuously for a certain period of time, and the detection data was recorded at regular intervals.

[0124] Observations during the experiment:

[0125] Pretreatment effect: By detecting the gas exiting the pretreatment unit, it was confirmed that the removal rate of dust and acidic impurities reached the expected level, thus avoiding interference with subsequent treatment;

[0126] Adsorption-enrichment effect: In the initial stage of operation, NO x NO rapidly accumulates in the catalytic functional layer, and is present at the outlet. x The significant decrease in concentration indicates that the membrane substrate and the catalyst have good adsorption effects;

[0127] Catalytic degradation effect: As the light source is turned on, NO at the outlet... x The concentration further decreased and stabilized at a low level, with the NO2 concentration remaining in an extremely low range and no byproducts exceeding the standard.

[0128] Results analysis:

[0129] Removal rate: During the experiment, NO x The removal rate remained at a high level, far exceeding that of the comparison group of activated carbon adsorption and traditional photocatalysis technology;

[0130] Stability: After continuous operation for a certain period of time, NO x The removal rate did not decrease significantly, the catalyst activity remained stable, and the membrane substrate was undamaged, proving that the technology has the ability to operate for a long time.

[0131] Mechanism verification: By characterizing the structure of the catalyst before and after the reaction, it was confirmed that the heterojunction structure was not destroyed and the oxygen vacancies and active sites remained intact, proving that the synergistic mechanism of "adsorption-enrichment-catalysis" is effective.

[0132] Example 2: Low-concentration NO from ZnFe2O4 / Bi2O2CO3 heterojunction catalyst + LaCO3OH modified polymer membrane x deal with

[0133] (I) Preparation of experimental materials

[0134] Catalyst raw materials: zinc nitrate, ferric nitrate, bismuth nitrate, sodium carbonate, citric acid (analytical grade, used as a complexing agent);

[0135] Membrane substrate material: Polymer membrane (polyvinylidene fluoride, prepared by phase inversion method, with flexibility and porous structure);

[0136] Modifiers: LaCO3OH powder, deionized water;

[0137] Simulated exhaust gas: contains low concentrations of NO x Simulated industrial exhaust gas (a mixture of NO and NO2, containing a small amount of SO2 impurities, with nitrogen as the carrier gas).

[0138] Experimental equipment: in-situ self-sacrificing reactor, vacuum drying oven, adsorption-catalysis integrated experimental device (flexible structure adapted to polymer membranes), gas chromatograph.

[0139] (II) Preparation of ZnFe2O4 / Bi2O2CO3 heterojunction catalyst (in-situ self-sacrificing method)

[0140] Precursor solution preparation: Zinc nitrate, iron nitrate, and bismuth nitrate are mixed in stoichiometric ratio and dissolved in deionized water; citric acid is added as a complexing agent, and the mixture is stirred until the solution is clear to form a homogeneous precursor solution.

[0141] Heterogeneous combination: Sodium carbonate solution is slowly added dropwise to the precursor solution and stirred until a white precipitate is produced; the mixture is transferred to an in-situ self-sacrificing reactor and reacted at a set temperature for a certain time. During the reaction, part of the precursor decomposes and forms a heterojunction structure of ZnFe2O4 and Bi2O2CO3 in situ.

[0142] Catalyst purification: After the reaction was completed, the mixture was cooled to room temperature, filtered to obtain the precipitate, washed with deionized water until neutral, dried under vacuum, and then calcined at low temperature in a muffle furnace to remove residual impurities, thus obtaining the ZnFe2O4 / Bi2O2CO3 heterojunction catalyst (labeled Cat-2).

[0143] (III) Preparation of LaCO3OH modified polymer membranes

[0144] Membrane substrate pretreatment: The polymer membrane is cut to the size that fits the experimental device, ultrasonically cleaned with ethanol to remove surface oil and impurities, and then vacuum dried for later use.

[0145] LaCO3OH modification: Dissolve LaCO3OH powder in deionized water to prepare a modification solution; immerse the pretreated polymer membrane in the modification solution and oscillate at a set temperature for a certain period of time to allow LaCO3OH to fully adhere to the membrane surface; remove the membrane, wash it with deionized water, and vacuum dry it to obtain a LaCO3OH modified polymer membrane.

[0146] Catalyst loading: Cat-2 was loaded using the impregnation method—the modified polymer membrane was immersed in an ethanol suspension of Cat-2 and allowed to stand for a certain period of time, allowing the catalyst to adhere to the membrane surface through capillary action; the membrane was then removed, excess suspension was drained, and vacuum dried to obtain the modified polymer membrane loaded with the catalyst.

[0147] (iv) Construction and experimental design of integrated equipment

[0148] Equipment adjustments: Considering the flexibility of the polymer membrane, the reaction chamber is designed as a rectangle, and a slotted bracket is used to fix the membrane material to avoid membrane deformation; the pretreatment unit adds an SO2 adsorption layer (filled with alkaline alumina) to adapt to SO2 impurities in simulated waste gas;

[0149] Experimental conditions: The exhaust gas temperature was controlled at room temperature, the relative humidity was adjusted according to the moisture resistance of the polymer membrane, and multiple gradients of gas flow rate were set (to study the effect of flow rate on treatment effect).

[0150] Detection method: Gas chromatography was used to detect the outlet gas, with a focus on analyzing NO. x Removal rate, NO2 generation, and SO2 residue.

[0151] (V) Experimental Results and Discussion

[0152] The effect of flow rate on treatment effect:

[0153] Low flow rate: longer gas residence time, NO x It has a high removal rate and low NO2 generation, but a small processing capacity.

[0154] Suitable flow rate: NO x The removal rate and processing capacity are balanced to meet the needs of practical applications;

[0155] High flow rate: short gas residence time, NO x The removal rate decreased, and the NO2 generation increased slightly, but remained below the safety limit.

[0156] Conclusion: There exists an optimal flow rate range suitable for this embodiment, which can be selected according to the actual processing volume.

[0157] SO2 tolerance verification:

[0158] The pretreatment unit achieved the expected SO2 removal rate, and the outlet SO2 concentration was extremely low, without causing significant poisoning to the catalyst.

[0159] After continuous operation for a certain period of time, the catalyst activity did not decrease significantly, proving that the modified membrane and the catalyst have excellent corrosion resistance.

[0160] Advantages of polymer membranes:

[0161] It has good flexibility and can be cut according to the shape of the equipment to adapt to miniaturized and irregularly shaped processing scenarios (such as ship denitrification devices).

[0162] It has low preparation cost, maintains good permeability after catalyst loading, and has no significant pressure drop.

[0163] Example 3: Low-concentration NO from oxygen vacancy-modified bismuth-based catalyst + SiO2-modified composite metal film x deal with

[0164] (I) Experimental Materials and Equipment

[0165] Catalyst raw materials: bismuth nitrate, sodium carbonate, sodium hydroxide (analytical grade), hydrogen (high purity);

[0166] Membrane substrate material: Composite metal membrane (stainless steel-aluminum composite, prepared by rolling process, with corrosion resistance);

[0167] Modifier: SiO2 sol (industrial grade, containing nano-SiO2 particles);

[0168] Simulated exhaust gas: Simulating low concentrations of NO in urban atmosphere x (Mainly NO, containing trace amounts of dust and water vapor);

[0169] Experimental equipment: hydrothermal reactor, hydrogen reduction furnace, sol-gel coating equipment, adsorption-catalysis integrated equipment (no light source, using room temperature catalysis system), infrared spectrometer.

[0170] (II) Preparation of Bi2O3 / (BiO)2CO3 catalyst modified with oxygen vacancy (hydrothermal-in-situ thermal decomposition method)

[0171] Preparation of bismuth-based precursors: Bismuth nitrate was dissolved in nitric acid solution, sodium carbonate solution was added dropwise, and the pH value was adjusted to generate Bi2(CO3)3 precipitate; the precipitate was transferred to a hydrothermal reactor, sodium hydroxide solution was added, and the reaction was carried out at a set temperature for a certain time to obtain Bi2O3 / (BiO)2CO3 precursor;

[0172] Oxygen vacancy introduction: After drying the precursor, it is placed in a hydrogen reduction furnace and heated to a set temperature under inert gas protection. Hydrogen is introduced for reduction treatment for a certain period of time to introduce oxygen vacancy on the surface of the bismuth compound. After the reduction is completed, inert gas is introduced to cool to room temperature to obtain the oxygen vacancy modified Bi2O3 / (BiO)2CO3 catalyst (labeled Cat-3).

[0173] (III) Preparation of SiO2 modified composite metal films

[0174] Membrane substrate pretreatment: The surface of the composite metal membrane is sanded with sandpaper to remove the oxide layer; it is cleaned with dilute hydrochloric acid to remove surface impurities; it is washed with deionized water until neutral, and then dried for later use.

[0175] SiO2 modification: SiO2 sol is uniformly coated onto the surface of the composite metal film using a sol-gel coating device, and the coating thickness is controlled. After coating, the film is dried and calcined at a set temperature to form a SiO2 modified coating, thus obtaining a SiO2 modified composite metal film.

[0176] Catalyst loading: The paste dispersion of Cat-3 was coated onto the surface of the modified metal membrane using a coating method. After drying, it was calcined at low temperature to ensure that the catalyst was tightly bonded to the membrane substrate.

[0177] (iv) Construction and experiment of room temperature catalytic integration equipment

[0178] Equipment features: No light source required; the reaction chamber is made of stainless steel, with mechanical strength suitable for composite metal membranes; the pretreatment unit is equipped with only a dust filter layer (suitable for trace amounts of dust in urban air).

[0179] Experimental conditions: ambient temperature and pressure, controlling gas flow rate and relative humidity to simulate the flow of urban atmosphere;

[0180] Experimental results:

[0181] Removal rate: Cat-3 exhibits excellent catalytic activity at room temperature, NO x The removal rate remains stable at a high level, requiring no additional energy input;

[0182] Byproduct control: The presence of oxygen vacancies effectively inhibits NO2 generation, and the outlet NO2 concentration remains at an extremely low level.

[0183] Stability: After several weeks of continuous operation, there were no significant changes in catalyst activity and membrane substrate integrity, proving that the system is suitable for long-term, ambient temperature urban air purification scenarios.

[0184] Comparative Example: Comparative Experiment between the Invention and the Prior Art

[0185] (I) Design of Comparative Schemes

[0186] The present invention employs the Cat-1 catalyst + modified ceramic membrane system from Example 1, using an integrated adsorption-catalysis device.

[0187] Comparison Option 1: Activated carbon adsorption method (commercially available activated carbon packed column, no catalytic function);

[0188] Comparison Option 2: Traditional photocatalysis technology (commercially available TiO2 catalyst, supported on a regular glass plate, without membrane separation and enrichment functions).

[0189] Comparison Option 3: Plasma technology (commercially available plasma generators, without adsorption and catalytic assistance).

[0190] (II) Comparison of experimental conditions

[0191] Uniform simulated exhaust gas: low concentration of NO at the same concentration x The mixed gas has the same composition and flow rate.

[0192] Standardized testing method: Infrared spectrometer is used to detect NO at the outlet.x Concentration and NO2 concentration;

[0193] Running time: All processes were run continuously for the same duration, and the changes in processing results were recorded.

[0194] (III) Comparison Results and Analysis

[0195] Removal rate comparison: NO removal rate of the present invention x The removal rate was significantly higher than the other three comparative methods, and the removal rate was stable; the activated carbon adsorption method reached saturation in a short time, and the removal rate dropped rapidly; the traditional photocatalytic technology had a low removal rate due to the lack of enrichment function; although the plasma technology had a decent removal rate in the early stage, it had high energy consumption and produced many by-products.

[0196] Energy consumption comparison: The energy consumption of the proposed solution (photocatalytic system) is less than 1 / 3 of that of plasma technology; activated carbon adsorption requires frequent regeneration, which consumes a lot of energy; the energy consumption of traditional photocatalytic technology is similar to that of the proposed solution, but the removal rate is much lower.

[0197] Byproduct comparison: The NO2 generation of the present invention is much lower than that of other methods; plasma technology generates the most NO2 and other unknown byproducts; activated carbon adsorption method releases adsorbed NO during desorption. x This causes secondary pollution.

[0198] (iv) Conclusion

[0199] The "adsorption-catalysis integrated" technology system of this invention outperforms existing technologies in three core indicators: treatment efficiency, energy consumption, and by-product control, thus solving the problem of low-concentration NO. x It addresses the technological bottlenecks in governance and possesses significant technological advantages and application value.

[0200] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for efficient adsorption-catalytic degradation integrated treatment of low-concentration NO x characterized in that, The method comprises the following steps: Step 1: screening and preparing a nano-composite photocatalyst with adsorption-catalysis dual functions, which comprises a catalyst active component selected from at least one of ferrite-based compounds and bismuth-based compounds and a modifier selected from at least one of carbon quantum dots, g-C3N4 and oxygen vacancies; Step 2: synthesis of selectively isolated low concentration NO x a film base material, and performing corrosion resistance, acid and alkali resistance, and mechanical strength modification treatment on the film base material; Step 3: constructing an adsorption-catalysis integrated device, fixing a plurality of modified membrane base materials prepared in step 2 inside the device, and loading the nano-composite photocatalyst prepared in step 1 on the surface of the modified membrane base materials to form a catalytic functional layer; Step 4: passing mixed exhaust gas containing low concentration NO x into the integrated device constructed in Step 3, controlling the exhaust gas treatment process parameters, so that NO x adsorption-enrichment and in-situ catalytic degradation are completed on the surface of the catalytic functional layer; Step 5: detecting the outlet gas of the integrated device in real time, adjusting process parameters to inhibit the generation of by-product NO2, and ensuring that the treated gas meets the discharge standard.

2. The method of claim 1, wherein, The ferrite-based compound in step 1 is selected from at least one of ZnFe2O4, Fe3O4 and CoFe2O4, and the bismuth-based compound is selected from at least one of Bi2O2CO3, Bi2O3 and (BiO)2CO3.

3. The method of claim 1, wherein, The preparation method of the nano-composite photocatalyst in step 1 is one of solvothermal method, in-situ self-sacrifice method or hydrothermal-in-situ thermal decomposition method.

4. The method of claim 1, wherein, The membrane base material in step 2 is selected from one of ceramic membranes, polymer membranes and composite metal membranes.

5. The method of claim 1, wherein, The modification treatment in step 2 comprises surface modification of the membrane base by using LaCO3OH or SiO2.

6. The method of claim 1, wherein, The multi-layer membrane catalytic material in step 3 is a multi-layer structure, and the nano-composite photocatalyst is loaded on the surface of the membrane base by coating or impregnation.

7. The method of claim 1, wherein, The process parameters in step 4 comprise waste gas temperature, gas flow rate and relative humidity, and if a photocatalytic system is used, the light intensity is also included.

8. The method of claim 1, wherein, In the catalytic degradation process described in Step 4, the nanocomposite photocatalyst forms a built-in electric field by constructing a heterojunction structure, promotes the directional migration of photo-generated carriers, generates active free radicals, and oxidizes the adsorbed and enriched NO x to nitrate.

9. The method of claim 1, wherein, The real-time detection in step 5 uses an infrared spectrometer or a gas chromatograph, and the detection indexes include NO x The total removal rate, the amount of NO2 generated, and the O2 content are adjusted by adjusting the gas flow rate or optimizing the surface modification state of the catalyst when the generation of by-products is detected to be excessive.

10. The method of any one of claims 1-9, wherein, The low concentration NO x NO in the environment or industrial exhaust gas with a volume concentration at a low level x Mixture, NO in the treated gas x The emission concentration meets the requirements of environmental protection standards.

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