Preparation and application of ferroelectric ultrathin layered nanosheet photocatalyst

Abstract

The application relates to a preparation method of a ferroelectric ultrathin layered nanosheet photocatalyst and application thereof, and belongs to the field of photocatalysis. The application provides a hydrothermal preparation method of the catalyst and subsequent reduction to obtain the layered ultrathin nanosheet catalyst Bi5FeTi3O 15 The thickness of the nanosheet is 3.6 nm, and the formation of the ultrathin nanosheet promotes the spontaneous induction of the formation of surface vacancies by surface atoms. The prepared ferroelectric layered catalyst in the form of an ultrathin nanosheet is used for the reduction of low-concentration and high-toxicity atmospheric pollutants NO, and high NO reduction activity is achieved under visible light irradiation. The preparation of the ferroelectric ultrathin nanosheet catalyst and the photocatalytic NO reduction operation process / method are simple, low in cost, efficient and fast in the photocatalytic reduction of low-concentration and high-toxicity atmospheric pollutants NO and the obtaining of non-toxic and selective nitrogen product, and have a positive promoting effect on atmospheric environmental protection.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysis, specifically relating to the controllable preparation of a ferroelectric layered ultrathin nanosheet catalyst and its application in the field of photocatalytic environmental remediation. Background Technology

[0002] Nitrogen oxides (NO) x NO is a precursor to atmospheric aerosols, and its pollution of the environment has become an increasingly serious global problem, contributing to events such as acid rain and photochemical smog. Meanwhile, NO... x NO is also a major component of urban air pollution, seriously affecting people's quality of life and physical and mental health. Currently, the more mature NO... x Removal technologies include selective reduction and adsorption. These technologies primarily target NO. x Source control, and for NO already released into the air x Or the actual trace amounts of NO present in the air x Removal at (ppb level) levels is not economically feasible.

[0003] As a simple and green alternative technology, photocatalysis has been proven effective in reducing NO emissions. x Potential applications in NO removal. Existing research indicates that NO removal using photocatalysis primarily involves two reaction pathways: photocatalytic oxidation and photocatalytic reduction. [This is] for NO removal... x The photocatalytic material systems for transformation can be summarized into the following four aspects: (i) Photocatalytic systems based on classical TiO2. These catalysts fail to fully utilize sunlight due to their photoresponse being limited to the ultraviolet region, but they provide a good framework for studying surface and interface mechanisms. They are promising systems worthy of in-depth exploration and represent the starting point for this project; (ii) Bi-based photocatalytic materials such as metal halide oxides BiOX (X = Cl, Br, and I), Bi2MoO6, and BiVO4. These materials exhibit excellent photoresponse, but are still far from practical application; (iii) Novel non-metallic photocatalysts g-C3N4 and metal-supported (Au, Pb, and Bi) photocatalytic systems. These catalysts exhibit excellent NO... x Conversion efficiency, but the intermediate products generated during the conversion process cause secondary pollution, leading to catalyst passivation; (iv) Ti-based composite metal oxides with similar compositions to TiO2, such as Ag-SrTiO3, ATiO3 (A=Pb, Sr and Ba) and Pb2Bi4Ti5O 18 Currently, research on this type of catalytic system is in its early stages. Photocatalytic oxidation of NO can convert NO to NO3 at room temperature. - The products that are easily detected, unfortunately, include the NO3 formed during the transformation. -Residue on the catalyst surface will passivate it, reducing catalytic activity, and may also produce highly toxic byproducts such as NO2 and N2O. In fact, during photocatalysis, in addition to reactive oxygen species, reducing electrons can also directly react with NO. x The function is to activate and reduce NO to N2. That is, it is thermodynamically feasible to directly decompose NO into non-toxic N2 using only light irradiation, while simultaneously inhibiting the formation of byproducts. This is similar to the photocatalytic oxidation of NO. x In comparison, its reduction reaction does not produce NO3. - It has advantages such as no need for washing and regeneration, but the reaction conditions are relatively harsh, especially the reduction of NO to N2, which requires energy (632kJ / mol). How to achieve the breaking of N–O bond and the formation of N≡N triple bond to obtain a single reduction product N2 by relying solely on light is a challenging topic.

[0004] "Sandwich" type perovskites with flexible and tunable structures, especially those composed of [A m-1 M m O 3m+1 ] 2- (m is the number of layers) and [Bi2O2] 2+ Alternating layered ferroelectric materials exhibit excellent polarization and electron delocalization tunability. These layered catalysts have shown promising progress in environmental remediation, particularly in NO oxidation processes. For example, layered catalysts rich in oxygen vacancies have successfully achieved a one-step process to produce the deep oxidation product nitric acid, with a selectivity reaching 99%. However, while the thermodynamic feasibility of layered ferroelectric catalysts for the reduction of NO to non-toxic N2 is theoretically feasible, it remains unstudied. Summary of the Invention

[0005] To address the aforementioned bottlenecks, this invention provides a controllable preparation of ferroelectric layered ultrathin nanosheet catalyst bismuth iron titanate and its application in the field of photocatalysis. It is mainly used in the treatment of potential air pollutants with high toxicity and low concentration, providing a promising method and approach for environmental governance.

[0006] This invention also provides a controllable preparation of a ferroelectric layered ultrathin nanosheet catalyst, specifically comprising the following steps:

[0007] Bismuth source, iron source, and reducing agent were dissolved in an acidic solution, and a titanium source was added to the solution. The pH was adjusted to 4.0-6.0 with an alkaline solution. After hydrothermal reaction, the layered ultrathin nanosheet catalyst Bi5FeTi3O was obtained. 15 ;

[0008] According to an embodiment of the present invention, the required precursor iron source can be at least one of ferric nitrate, ferric oxide, and ferric chloride;

[0009] According to an embodiment of the present invention, the bismuth precursor source for preparing the required precursor can be selected from at least one of bismuth oxide and bismuth nitrate;

[0010] According to an embodiment of the present invention, the reducing agent may be a mild reducing agent, such as at least one of ascorbic acid, glyoxal, and methanol;

[0011] According to an embodiment of the present invention, the acid may be nitric acid;

[0012] According to an embodiment of the present invention, the titanium source may be at least one of titanium trichloride, titanium tetrachloride, and tetrabutyl titanate;

[0013] According to an embodiment of the present invention, the alkali may be at least one of an alkali metal or an alkaline earth metal hydroxide;

[0014] According to an embodiment of the present invention, the molar volume ratio of the bismuth source to the acid is 5:3 (mmol / mL).

[0015] According to an embodiment of the present invention, the molar ratio of bismuth, iron and titanium in the bismuth source, iron source and titanium source is 10:1:50;

[0016] According to an embodiment of the present invention, the molar mass ratio of bismuth element to reducing agent in the bismuth source is 10:1 (mmol / g).

[0017] According to an embodiment of the present invention, the temperature of the hydrothermal reaction can be 180°C;

[0018] According to an embodiment of the present invention, the hydrothermal reaction time can be 24 hours.

[0019] This invention also provides the application of the defective perovskite material in the photocatalytic reduction of NO to nitrogen gas. A ferroelectric layered ultrathin nanosheet catalyst for the photocatalytic reduction of NO involves placing the catalyst in a reactor, introducing NO-containing gas into the reactor, and conducting the reaction under light irradiation. Nitrogen gas is produced without the addition of an additional reducing agent, thus reducing NO concentration and its harmful effects.

[0020] The catalyst described in this invention is a ferroelectric layered ultrathin nanosheet material;

[0021] The concentration of NO in the NO-containing gas described in this invention can be 10-10000 ppb, with an example of 600 ppb;

[0022] The light described in this invention can be visible light, and the wavelength of the visible light is 380-780nm, for example, 420-780nm;

[0023] According to the present invention, the light energy density of the xenon lamp is 380 mW / cm². 2 .

[0024] According to the present invention, the efficiency of visible light photocatalytic reduction of NO by the ferroelectric layered ultrathin nanosheets can reach 99% selectivity.

[0025] According to the present invention, the NO photocatalytic reduction method specifically includes the following steps:

[0026] a. Place the ferroelectric layered ultrathin nanosheet catalyst powder of the present invention in a reactor, exhaust the air in the reaction chamber by exhaust method, and at the same time achieve a vacuum atmosphere in the system by using the inside of the nitrogen oxide analyzer, while introducing a mixed gas containing nitric oxide and high-purity helium.

[0027] b. Ensure a constant flow rate of the mixed gas using a mass flow meter, and irradiate it with a xenon lamp as the visible light source, gradually reading the changes in the concentrations of N and O species such as NO, NO2, and NOx;

[0028] d. During the reaction, 1.0 mL of gas was taken out from the sampling port, and the concentrations of NO decomposition products such as N2 and O2 were obtained through online analysis;

[0029] d. After the reaction is complete, the catalyst powder is slowly scraped off and further dispersed by ultrasound to ensure that the catalyst is fully dissolved in deionized water; then the supernatant is separated by filtration and quantitatively analyzed with nitric acid.

[0030] e. Calculate the NO photocatalytic reduction selectivity based on the N and O species concentrations obtained in the above steps;

[0031] According to the present invention, in step a, a low concentration of NO standard gas is selected for photocatalytic NO reduction. The mixed gas is balanced with helium and has a concentration of 13.5 μmol / mol.

[0032] According to the present invention, the NO concentration in the mixed gas in step a can be 100-20000 ppb, and in the example, the NO concentration is controlled at 730 ppb;

[0033] According to the present invention, the flow rate of the mixed gas in step b can be 0.3 mL / min to 1.0 mL / min, and in this example, the flow rate of the mixed gas is controlled at 1.0 mL / min;

[0034] According to the present invention, in step b, a nitrogen oxide analyzer is used for real-time online monitoring, with a sampling interval of 1 minute;

[0035] According to the present invention, in step c, the NO photocatalytic reduction product is monitored in real time using an Agilent 7890 online gas chromatograph, with a sampling interval of 20 min;

[0036] According to the present invention, in step d, filtration is performed using a 0.45 μL microporous filter membrane, and the concentration of nitric acid generated during the NO photocatalytic reduction process is further analyzed using an ion chromatograph.

[0037] The beneficial effects of this invention are:

[0038] To fully realize the potential application of ferroelectric layered ultrathin catalysts in environmental remediation, this invention provides a controllable preparation of ferroelectric layered ultrathin nanosheet catalysts and their application in the field of photocatalysis, which has the following characteristics:

[0039] 1. The ferroelectric layered ultrathin nanosheet catalyst described in this invention achieves catalyst dimension and surface active site regulation in hydrothermal synthesis using only the mild reducing agent glyoxal. This ferroelectric layered photocatalytic material, prepared by a simple synthesis method involving the addition of a small amount of reducing agent, stirring, calcination, and washing, with low catalyst dimension control through a mild reducing agent, has advantages such as high yield (98%), uniform distribution, and good crystallinity, and is expected to be extended to the synthesis of other inorganic compounds.

[0040] 2. The ferroelectric layered ultrathin nanosheet catalyst described in this invention exhibits significant visible light absorption and is rich in surface active sites such as surface oxygen vacancies. Without doping or using cumbersome preparation processes, the prepared nanosheets are approximately 3.6 nm thick. The formation of these ultrathin nanosheets facilitates the easy departure of surface atoms from their crystallographic positions, thereby spontaneously inducing the formation of surface vacancies. This abundant surface area is expected to serve as adsorption sites for atmospheric pollutants, thus facilitating further photocatalytic redox reactions.

[0041] 3. According to the present invention, the prepared ultrathin nanosheet ferroelectric layered catalyst is used for the removal of low-concentration, highly toxic air pollutants; it achieves high NO reduction activity under visible light irradiation, with a reaction selectivity of up to 99%; the preparation process / method of the ferroelectric ultrathin nanosheet catalyst and the photocatalytic NO reduction operation of the present invention is simple, low-cost, and can be used efficiently and rapidly for the rapid photocatalytic reduction of low-concentration, highly toxic air pollutant NO to obtain non-toxic selective product nitrogen, which has a positive promoting effect on atmospheric environmental protection;

[0042] 4. The preparation method and its application in environmental governance described in this invention will provide a promising approach to reduce NO emissions at room temperature and atmospheric pressure, enrich the catalyst system for NO reduction, and, more importantly, liberate NO removal methods based on precious metal deposition and high-temperature treatment, meet the requirements of my country's ambient air quality standards, strengthen source emission reduction, and actively develop suitable new technologies to treat NO already emitted into the atmosphere, overcoming limitations such as low reactivity and numerous byproducts. Attached Figure Description

[0043] Figure 1 This is an X-ray powder diffraction pattern of a ferroelectric layered catalyst described in the comparative example of this invention;

[0044] Figure 2 This is an X-ray powder diffraction pattern of a ferroelectric layered ultrathin nanosheet catalyst described in an embodiment of the present invention;

[0045] Figure 3 This is a transmission electron microscope image of a ferroelectric layered ultrathin nanosheet catalyst described in the comparative example of this invention;

[0046] Figure 4 This is a transmission electron microscope image of a ferroelectric layered ultrathin nanosheet catalyst described in an embodiment of the present invention;

[0047] Figure 5 This is a visible light photocatalytic NO reduction effect diagram of a ferroelectric layered catalyst described in the comparative example of the present invention;

[0048] Figure 6 This is a visible light photocatalytic NO reduction effect diagram of a ferroelectric layered ultrathin nanosheet catalyst described in Example 1 of the present invention.

[0049] Figure 7 This is a visible light photocatalytic NO reduction effect diagram of a ferroelectric layered catalyst described in Example 2 of the present invention. Detailed Implementation

[0050] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0051] Comparative Example 1:

[0052] a) Accurately weigh 5.0 mmol of bismuth nitrate and 1.0 mmol of ferric nitrate and dissolve them in an aqueous solution containing 3.0 mL of nitric acid (0.56 M). Stir magnetically for 40 min. Then, add 3.0 mL of titanium tetrachloride to the above solution and stir for 30 min. Adjust the pH to 5.0 with 1.0 mol / L sodium hydroxide solution. While continuing to stir, slowly add 0.0 mL of glyoxal to the obtained solution and continue stirring for 30 min. Transfer the above solution to a hydrothermal reactor and place it in an oven to heat at 180 °C for 24 h. After the reaction is complete, allow it to cool naturally to room temperature. Wash, dry, and grind the sample to obtain the comparative target product, the ferroelectric layered catalyst bismuth iron titanate Bi5FeTi3O. 15 ;

[0053] b) According to the present invention, 60.0 mg of the ferroelectric layered catalyst obtained in Comparative Example 1 was uniformly spread in a petri dish with a diameter of 6.0 cm and placed together with the petri dish in a quartz glass reactor; simultaneously, in order to achieve a vacuum state, a high-vacuum grease was uniformly coated on the surface of the reactor inlet ring; then a certain proportion of NO standard gas (13.0 × 10⁻⁶) was introduced. -6 The NO concentration was stably controlled at 640 ppb using high-purity helium (99.999%) and μmol / mol, and the gas flow rate was monitored at any time. Then, NO gas was introduced into the sample in the reactor under dark conditions for about 45 min to ensure that the catalyst surface could fully absorb NO, and wait for the adsorption-desorption equilibrium to be established.

[0054] c) After establishing equilibrium, continue to introduce the NO-He mixture at a constant flow rate (1.0 mL / min), while irradiating the catalyst with a xenon lamp as a visible light source (λ = 420 nm - 780 nm); use NO... x The analyzer observes and records NO, NO2, and NO every 1.0 min. x Changes in species concentrations were observed; simultaneously, 1.0 mL of gas was injected into a gas chromatograph to observe the concentrations and ratios of N2 and O2; after 280 min of light irradiation, the concentrations of NO, NO2, and NO were observed. x The corresponding concentrations were 609 ppb, 28.93 ppb and 630.623 ppb, respectively. The concentrations of N2 and O2 have not yet been detected.

[0055] d) According to the method of the present invention, the catalyst powder collected after the reaction is weighed and added to deionized water and ultrasonically dispersed for 30 min; then filtered with a 0.45 μL microporous filter membrane, and the supernatant is tested by ion chromatography; based on the fact that no N2O or other products were detected in step c), the photocatalytic reduction reaction activity of NO is determined and calculated to be 0.001% and the percentage of NO2 produced is 4.57%, corresponding to a selectivity of 0.00% for N2 production;

[0056] Example 1:

[0057] a) Accurately weigh 5.0 mmol of bismuth nitrate and 1.0 mmol of ferric nitrate and dissolve them in an aqueous solution containing 3.0 mL of nitric acid (0.56 M). Stir magnetically for 40 min. Then, add 3.0 mL of titanium tetrachloride to the above solution and stir for 30 min. Adjust the pH to 5.0 with 1.0 mol / L sodium hydroxide solution. While continuing to stir, slowly add 2.4 mL of glyoxal to the obtained solution and continue stirring for 30 min. Transfer the above solution to a hydrothermal reactor and place it in an oven to heat at 180 °C for 24 h. After the reaction is complete, allow it to cool naturally to room temperature. Wash, dry, and grind the sample to obtain the target product, ferroelectric layered ultrathin nanosheet catalyst bismuth iron titanate Bi5FeTi3O4. 15 ;

[0058] b) According to the present invention, 60.0 mg of the ferroelectric layered catalyst obtained in Comparative Example 1 was uniformly spread in a petri dish with a diameter of 6.0 cm and placed together with the petri dish in a quartz glass reactor; simultaneously, in order to achieve a vacuum state, a high-vacuum grease was uniformly coated on the surface of the reactor inlet ring; then a certain proportion of NO standard gas (13.0 × 10⁻⁶) was introduced. -6 The NO concentration was stably controlled at 640 ppb using high-purity helium (99.999%) and μmol / mol, and the gas flow rate was monitored at any time. Then, NO gas was introduced into the sample in the reactor under dark conditions for about 45 min to ensure that the catalyst surface could fully absorb NO, and wait for the adsorption-desorption equilibrium to be established.

[0059] c) After establishing equilibrium, continue to introduce the NO-He mixture at a constant flow rate (1.0 mL / min), while irradiating the catalyst with a xenon lamp as a visible light source (λ = 420 nm - 780 nm); use NO... x The analyzer observes and records NO, NO2, and NO every 1.0 min. x Changes in species concentration were observed; simultaneously, 1.0 mL of gas was injected into a gas chromatograph to observe the concentrations and ratios of N2 and O2; after 150 min of illumination, NO, NO2, and NO were observed. x The corresponding concentrations changed very subtly, at 280 ppb, 33 ppb, and 315 ppb, respectively, indicating a loss of approximately 320 ppb of NO during the reaction. Combined with online detection of N2 and O2 signals by gas chromatography, when the initial NO concentration was restored after the light was turned off and visible light irradiation was repeated, NO, NO2, and NO were observed to be present in the concentrations. x The corresponding concentrations still showed similar changes, with concentrations of 287 ppb, 11 ppb, and 320 ppb, respectively. According to the chromatographic data, the concentrations of NO decomposition to produce N2 and O2 are consistent with the concentration of NO lost (3.35%), and nitrogen is conserved.

[0060] d) According to the method described in this invention, the catalyst powder collected after the reaction is weighed and added to deionized water and sonicated for 30 min to disperse it evenly; then filtered through a 0.45 μL microporous membrane, and the supernatant is used for ion chromatography testing; based on the absence of N2O and other products detected in step c), the photocatalytic reduction activity of NO is further determined and calculated to be 45.59%, the percentage of NO2 produced is 1.94%, and the corresponding selectivity for N2 production is 95.92%.

[0061] Example 2:

[0062] a) Accurately weigh 5.0 mmol of bismuth nitrate and 1.0 mmol of ferric nitrate and dissolve them in an aqueous solution containing 3.0 mL of nitric acid (0.56 M) and stir magnetically for 40 min. Then, add 3.0 mL of titanium tetrachloride to the above solution and stir for 30 min, and adjust the pH to 5.0 with 1.0 mol / L sodium hydroxide solution. While continuing to stir, slowly add 0.6 g of ascorbic acid to the obtained solution and continue stirring for 30 min. Transfer the above solution to a hydrothermal reactor and place it in an oven to heat at 180 °C for 24 h. After the reaction is completed, allow it to cool naturally to room temperature. Wash, dry, and grind the sample to obtain the target product, the layered ferroelectric catalyst bismuth iron titanate Bi5FeTi3O. 15 ;

[0063] b) According to the present invention, 60.0 mg of the ferroelectric layered catalyst obtained in Comparative Example 1 was uniformly spread in a petri dish with a diameter of 6.0 cm and placed together with the petri dish in a quartz glass reactor; simultaneously, in order to achieve a vacuum state, a high-vacuum grease was uniformly coated on the surface of the reactor inlet ring; then a certain proportion of NO standard gas (13.0 × 10⁻⁶) was introduced. -6 The NO concentration was stably controlled at 640 ppb using high-purity helium (99.999%) and μmol / mol, and the gas flow rate was monitored at any time. Then, NO gas was introduced into the sample in the reactor under dark conditions for about 45 min to ensure that the catalyst surface could fully absorb NO, and wait for the adsorption-desorption equilibrium to be established.

[0064] c) After establishing equilibrium, continue to introduce the NO-He mixture at a constant flow rate (1.0 mL / min), while irradiating the catalyst with a xenon lamp as a visible light source (λ = 420 nm - 780 nm); use NO... x The analyzer observes and records NO, NO2, and NO every 1.0 min. x Changes in species concentration were observed; simultaneously, 1.0 mL of gas was injected into a gas chromatograph to observe the concentrations and ratios of N2 and O2; after 400 min of illumination, NO, NO2, and NO were observed.x The corresponding concentrations changed very clearly, at 561 ppb, 24 ppb, and 582 ppb, respectively, indicating that approximately 51 ppb of NO was lost in the reaction. Combined with the online detection of N2 and O2 signals by gas chromatography, the chromatographic data showed that the concentrations of N2 and O2 produced by NO decomposition were consistent with the concentration of 8.21% lost NO, and nitrogen was conserved.

[0065] d) According to the method described in this invention, the catalyst powder collected after the reaction is weighed and added to deionized water, and ultrasonicated for 30 min to disperse it evenly; then filtered through a 0.45 μL microporous membrane, and the supernatant is used for ion chromatography testing; based on the absence of N2O and other products detected in step c), the photocatalytic reduction activity of NO is further determined and calculated to be 8.21%, the percentage of NO2 produced is 3.63%, and the corresponding selectivity for N2 production is 58.9%.

[0066] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. The use of ferroelectric ultrathin layered nanosheet photocatalyst to reduce nitrogen to nitrogen in the photocatalytic of NO with helium as the balance gas, the preparation method of the ferroelectric ultrathin layered nanosheet photocatalyst comprising the following steps: Dissolving a bismuth source, an iron source and a reducing agent in an acid solution, adding a titanium source to the above solution, adjusting the pH value of the solution to 4.0-6.0 by an alkali solution, and obtaining the layered ultrathin nanosheet catalyst Bi5FeTi3O 15 ; The reducing agent is glyoxal; and the thickness of the nanosheet is 3.6 nm.

2. Use according to claim 1, characterized in that, The precursor iron source is at least one of ferric nitrate, ferric oxide and ferric chloride; the bismuth source is at least one of bismuth oxide and bismuth nitrate, and the acid is nitric acid.

3. Use according to claim 1, characterized in that, The titanium source is at least one of titanium trichloride, titanium tetrachloride and tetrabutyl titanate; and the base is at least one of alkali metal or alkaline earth metal hydroxide.

4. Use according to claim 1, characterized in that, The molar volume ratio mmol / mL of the bismuth source to the acid is 5:3; the molar ratio of bismuth element, iron element and titanium element in the bismuth source, the iron source and the titanium source is 10:1:50; and the molar mass ratio mmol / g of bismuth element in the bismuth source to the reducing agent is 10:

1.

5. The use according to claim 1, characterized in that, The temperature of the hydrothermal reaction is 180 DEG C; and the time of the hydrothermal reaction is 24 h.

6. The application according to claim 1, wherein the catalyst is placed in a reactor, a gas containing NO is introduced into the reactor, and the reaction is carried out under visible light irradiation to produce nitrogen without adding an additional reducing agent, thereby reducing the concentration of NO.

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