Lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial and low-temperature preparation method

Abstract

The application provides a lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial and a preparation method thereof. The preparation method comprises the following steps: preparing fluorine-doped titanium dioxide material, preparing lead iodine calcium perovskite material, and preparing the lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial. The application provides a photocatalytic degradation nanomaterial with high photocatalytic activity, and the photocatalytic degradation nanomaterial has high commercial value and popularization value.

Description

TECHNICAL FIELD

[0001] The application relates to the field of photocatalytic degradation of nanomaterials, in particular to a lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterostructure photocatalytic degradation nanomaterial and a low-temperature preparation method. BACKGROUND

[0002] An ecological system is the material basis for human survival and development. Due to the influence of human activities, the internal mechanism of the ecological system is changing, and this change will simultaneously react on human beings, so it is particularly important to repair the damaged ecological system and realize the benign circulation of the ecological system. With the wide use of drugs and cosmetics, the potential harm of drugs and personal care products to human beings and the ecological system has attracted more and more attention, but they are difficult to be quickly removed in the environment, they can enter the environment through various channels, and are accumulated through the biological amplification of the food chain, and finally harm the water environment and human health. Therefore, scientific researchers have invested a large number of advanced technical means such as physics, chemistry and biology to solve the related environmental problems, among which the photocatalyst as a way of using solar energy to decompose organic matter and eliminate unnecessary chemical substances has been deeply studied. For example, the titanium dioxide semiconductor photocatalyst has become one of the powerful choices for photocatalytic degradation of pollutants due to its advantages of non-toxicity, low cost and stable physical and chemical properties. However, titanium dioxide is still limited by characteristics such as wide band gap (3.2-3.3 eV), high recombination rate of photo-generated carriers, low reusability and limited response in the ultraviolet region, which makes it not have the performance of a high-efficiency semiconductor photocatalyst. Therefore, the research on modified titanium dioxide has never stopped in the past two or three decades, such as doping transition metals (iron, copper, zinc), rare earth metals (lanthanum, scandium, cerium, praseodymium, neodymium), noble metals (silver, platinum), non-metals (nitrogen, fluorine, carbon, iodine, chlorine, sulfur) and co-doping or multi-doping (C-N, N-F, S-F, N-La, La-Fe, N-B-Fe) and the like.

[0003] Lead iodine perovskite materials such as CH3NH3PbX3 (X = Cl, Br, I) have excellent properties such as narrow band gap, wide visible light region absorption range, long carrier diffusion distance and carrier lifetime, and have become the focus of research in the field of optoelectronics in recent years. However, according to our knowledge, due to the problem of chemical stability such as decomposition into PbX2, methylammonium cations and halide anions when meeting water and heat, lead iodine perovskite is rarely applied to the field of photocatalysts.

[0004] Further studies have found that the crystal form of the halide material finally decomposed at different temperatures will be different. For example, when the temperature reaches a certain height, the by-product lead iodide exhibits a coexistence of hexagonal and rhombohedral crystal forms. Literature indicates that a phase junction can be established under the condition of close contact between different crystal phases, which will lead to effective electron-hole separation and more excellent catalytic efficiency, such as the phase junction structure of the brookite / anatase polymorphic compound in nano-titanium dioxide exhibits excellent photocatalytic efficiency for hydrogen production and degradation of rhodamine B, etc.

[0005] However, whether it is the doping modification of semiconductor catalysts or the preparation experiment of mixed crystal formation, the experiment is often carried out at high temperature calcination (> 300℃), which usually leads to the increase of crystal size and the decrease of specific surface area, thereby hindering the enhancement of photocatalytic activity. In addition, the doping modification application of organic carbonitride under low temperature conditions is often difficult to form, which limits its development in the field of photocatalysis. Therefore, it is urgent to develop a low-temperature preparation method and construct an efficient organic doping modification heterojunction photocatalytic system. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a preparation method of lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterojunction photocatalytic degradation nanomaterials, to solve the problem that the conventional preparation method needs to be carried out at high temperature, which leads to the increase of crystal size and the decrease of specific surface area, thereby hindering the enhancement of photocatalytic activity.

[0007] In order to solve the above problems, the present application provides a preparation method of lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterojunction photocatalytic degradation nanomaterials, comprising the following steps:

[0008] S11: Preparation of fluorine-doped titanium dioxide material: hydrofluoric acid solution is added to tetrabutyl titanate and stirred to obtain a mixture, the mixture is subjected to a heating reaction to obtain granules, the granules are washed with ethanol and deionized water respectively, and the precipitate is collected by centrifugation, and the fluorine-doped titanium dioxide material is obtained after drying;

[0009] S12: Preparation of lead iodine perovskite material: the mixed solution of methylamine iodide and lead iodide dissolved in N,N-dimethylformamide is stirred until the solution presents clear yellow-green color, and then the mixed solution is baked until the solid changes to dark black, thereby obtaining the lead iodine perovskite material;

[0010] S2: Preparation of lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterojunction photocatalytic degradation nanomaterials: the fluorine-doped titanium dioxide material and the lead iodine perovskite material prepared in step S1 are uniformly mixed in a grinding process to obtain a mixture, and the lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterojunction photocatalytic degradation nanomaterials are obtained after baking the mixture.

[0011] As a preferred scheme, in the step S1, the volume ratio of the hydrofluoric acid solution to the tetrabutyl titanate is 1:(4-5).

[0012] As a preferred scheme, in the step S11, the heating reaction is carried out in an autoclave.

[0013] As a preferred scheme, in the step S1, the stirring time is 30 minutes, the autoclave is a Teflon-lined autoclave, and the heating condition is heating to 240 DEG C and keeping for 24 hours.

[0014] As a preferred scheme, in the step S1, the drying condition is placing the precipitate in a 60 DEG C oven for continuous drying for 12 hours.

[0015] As a preferred scheme, in the step S12, the molar ratio of the methylamine iodine to the lead iodide is 1:1.

[0016] As a preferred scheme, in the step S12, the stirring condition is stirring at a temperature of 60 DEG C for 1 hour, and the baking temperature is 60 DEG C.

[0017] As a preferred scheme, in the step S2, the mass ratio of the fluorine-doped titanium dioxide material to the lead iodine calcium perovskite material is 1:1.

[0018] As a preferred scheme, in the step S2, the baking condition is continuous calcination at 150-160 DEG C for 48 hours.

[0019] Another technical problem to be solved by the present application is to provide a lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial to solve the problem of general photocatalytic activity of conventional materials.

[0020] To solve the above problems, the present application provides a lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial, which is prepared by the above preparation method.

[0021] Compared with the prior art, the present application has the following beneficial technical effects:

[0022] (1) The application provides a preparation method of a lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial, and in the thermal degradation process, a hexagonal rhombohedral heterojunction mixed crystal phenomenon of lead iodide is formed due to a size-related path of possible nanocrystal decomposition, under sunlight, photo-generated electrons are transferred from the conduction band of fluorine-doped titanium dioxide to the conduction band of lead iodide with a lower Fermi level, and meanwhile, the electrons are further transferred from rhombohedral phase lead iodide to hexagonal phase lead iodide, so that three-way transfer of photo-generated electrons is realized; on the contrary, holes are transferred from the valence band of hexagonal phase lead iodide to the valence band of rhombohedral phase lead iodide, so that the transfer of holes is realized. Through the above-mentioned transfer, the migration of photo-generated electrons and holes between the two composite materials and the hexagonal rhombohedral heterojunction can effectively separate the photo-generated carriers, which is beneficial to the further absorption of visible light, so as to improve the photocatalytic degradation effect of the material.

[0023] (2) In the preparation method of the lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial, fluorine doping promotes the formation of nitrogen doping, and the interstitially doped nitrogen and oxygen share the unpaired electrons to form a local occupied state of a π characteristic antibonding state (π*) above 0.7eV above the top of the O 2p valence band, which further narrows the band gap of titanium dioxide and enhances the visible light absorption; nitrogen doping is also beneficial to the increase of the content of hydroxyl groups on the material surface, so that more photo-generated holes are captured to increase the number of hydroxyl radicals, and thus the photocatalytic activity of the nanomaterial is enhanced.

[0024] (3) The lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial prepared by the application is synthesized at low temperature, so that the problem of increase of crystal size and decrease of specific surface area of the photocatalytic material caused by high-temperature calcination is effectively inhibited, so that the problem of adverse effect on photocatalytic efficiency is solved. In addition, the preparation method provided by the application uses an organic nitrogen-containing material as a modified doping nitrogen source, which provides a new preparation method of organic carbonitride as a modified doping source under low-temperature conditions, and provides a more green and environmentally friendly method for degradation of organic pollutants, promotes the sustainable development of the ecological system, and has high popularization value. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A flow chart of the low-temperature preparation method of the lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial;

[0026] Figure 2 A transmission electron microscope image of lead iodine calcium perovskite@titanium-based (1:1 160 DEG C);

[0027] Figure 3XPS comparison chart of fluorine doping in nanomaterials obtained with different mass ratios of lead iodine perovskite / titanium base;

[0028] Figure 4 XPS comparison chart of nitrogen doping in nanomaterials obtained with different mass ratios of lead iodine perovskite / titanium base;

[0029] Figure 5 XPS comparison chart of oxygen element in nanomaterials obtained with different mass ratios of lead iodine perovskite / titanium base;

[0030] Figure 6 Comparison chart of degradation efficiency of composite materials obtained with different mass ratios of lead iodine perovskite / titanium base and temperature, titanium base, lead iodide and lead iodine perovskite. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0032] The present application provides a preparation method of nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial based on lead iodine perovskite@titanium base, as shown in Figure 1 , and Figure 1 is a flow chart of the low-temperature preparation method of nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial based on lead iodine perovskite@titanium base of the present application. The preparation method comprises the following steps:

[0033] S11: Preparation of fluorine-doped titanium dioxide material: hydrofluoric acid solution is added to tetrabutyl titanate and stirred to obtain a mixture, the mixture is subjected to heating reaction to obtain granules, the granules are washed by ethanol and deionized water respectively, and the precipitate is collected by centrifugation, and the fluorine-doped titanium dioxide material is obtained after drying;

[0034] S12: Preparation of lead iodine perovskite material: the mixed solution of methylamine iodide and lead iodide dissolved in N,N-dimethylformamide is stirred until the solution presents clear yellow-green color, and then the mixed solution is baked until the solid changes to dark black, thereby obtaining the lead iodine perovskite material;

[0035] S2: Preparation of nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial based on lead iodine perovskite@titanium base: the fluorine-doped titanium dioxide material and the lead iodine perovskite material prepared in step S1 are uniformly mixed in grinding treatment to obtain a mixture, and the lead iodine perovskite@titanium base nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial is obtained after baking the mixture.

[0036] Preferably, in the step S1, the volume ratio of the hydrofluoric acid solution to the tetrabutyl titanate is 1:(4-5).

[0037] Preferably, in the step S11, the heating reaction is carried out in an autoclave.

[0038] Preferably, in the step S1, the stirring time is 30 minutes, the autoclave is a Teflon-lined autoclave, and the heating condition is heating to 240℃ and holding for 24 hours.

[0039] Preferably, in the step S1, the drying condition is placing the precipitate in a 60℃ oven for continuous drying for 12 hours.

[0040] Preferably, in the step S12, the molar ratio of the methylamine iodine to the lead iodide is 1:1.

[0041] Preferably, in the step S12, the stirring condition is stirring at a temperature of 60℃ for 1 hour, and the baking temperature is 60℃.

[0042] Preferably, in the step S2, the mass ratio of the fluorine-doped titanium dioxide material to the lead iodine calcium perovskite material is 1:1.

[0043] Preferably, in the step S2, the baking condition is continuous calcination at 150-160℃ for 48 hours.

[0044] The application provides a lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nano material.

[0045] The above technical solutions of the application are described below in combination with actual data:

[0046] Example 1

[0047] Example 1 mainly includes four parts: preparation of a fluorine-doped titanium dioxide material, preparation of a lead iodine calcium perovskite material, preparation of a lead iodine calcium perovskite@titanium-based composite nano material, and performance evaluation of a lead iodine calcium perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nano material.

[0048] The preparation process of the lead iodine calcium perovskite@titanium-based composite nano material with a mass ratio of 1:1 at 160℃ in a hot atmosphere is as follows:

[0049] S1: Preparation of fluorine-doped titanium dioxide material: The fluorine-doped titanium dioxide nanoplatelets were synthesized by a simple hydrothermal method. 10 mL of hydrofluoric acid solution was added to 50 mL of tetrabutyl orthotitanate at room temperature, and after magnetic stirring for 30 minutes, the mixture was transferred to a dry 100 mL Teflon-lined autoclave. Subsequently, the autoclave was heated to 240°C for 24 hours. After that, the obtained granules were washed several times with ethanol and deionized water, respectively, the precipitate was collected by centrifugation, and finally the sample was placed in a 60°C oven for drying for 12 hours to obtain fluorine-doped titanium dioxide nanoparticles.

[0050] S12: Preparation of lead iodine perovskite material: The preparation of the lead iodine perovskite sample first mixed a methy lammonium iodide and lead iodide solution dissolved in N,N-dimethylformamide at a molar ratio of 1:1, and stirred at a temperature of 60°C for 1 hour until the solution appeared clear yellow-green, and then the solution was placed in a 60°C oven to dry until all the solids turned dark black to obtain lead iodine perovskite nanoparticles.

[0051] S2: Preparation of lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterojunction photocatalytic degradation nanomaterial: The fluorine-doped titanium dioxide nanoparticles and lead iodine perovskite nanoparticles were mixed uniformly at a mass ratio of 1:1 under the action of a ball mill at room temperature. After that, the mixture was placed in an oven at 160°C for continuous calcination for 48 hours to obtain lead iodine perovskite@titanium-based (160°C 1:1) nanocomposite.

[0052] The performance of the lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterojunction photocatalytic degradation nanomaterial is as follows:

[0053] This example uses a 500W xenon lamp as a light source, weighs 50mg of the nanomaterial, and carries out a paracetamol (100mL, 10mg / L) photocatalytic degradation experiment under dark reaction conditions and visible light irradiation, uses a high-performance liquid chromatograph to test the concentration of paracetamol in the solution, and calculates the degradation rate. As shown in Figure 6 After 30 minutes of treatment under dark reaction conditions, the nanomaterial did not show a significant degradation trend. After 100 minutes of visible light irradiation, the degradation rate of the composite material was 58.3%. The degradation rates of fluorine-doped titanium dioxide, lead iodine perovskite, lead iodide, and lead iodine perovskite@titanium-based (60°C 1:1) nanocomposite were 24.3%, 47.2%, 56.8%, and 35.4%, respectively. The results show that the photocatalytic activity of the lead iodine perovskite@titanium-based (160°C 1:1) composite material is the highest, and the degradation efficiency is 2.4 times that of fluorine-doped titanium dioxide. This indicates that the synthesis of nitrogen and fluorine co-doping and hexagonal-rhombohedral heterojunction helps to improve the photocatalytic performance of the catalytic material.

[0054] Comparative Example 2

[0055] The comparative examples mainly include four parts: preparation of fluorine-doped titanium dioxide material, preparation of lead iodine perovskite material, preparation of lead iodine perovskite@titanium-based composite nanomaterial, and performance evaluation of lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial.

[0056] The preparation process of the lead iodine perovskite@titanium-based composite nanomaterial with a mass ratio of 1:1 in a 60°C thermal atmosphere is as follows:

[0057] S1: Preparation of fluorine-doped titanium dioxide material: fluorine-doped titanium dioxide nanosheets are synthesized by a simple hydrothermal method. At room temperature, 10 mL of hydrofluoric acid solution is added to 50 mL of tetrabutyl orthotitanate, and after magnetic stirring for 30 minutes, the mixture is transferred to a dry 100 mL Teflon-lined autoclave. Then, the autoclave is heated to 240°C for 24 hours. After that, the obtained particulate matter is washed several times with ethanol and deionized water, respectively, the precipitate is collected by centrifugation, and finally the sample is placed in a 60°C oven for drying for 12 hours, obtaining fluorine-doped titanium dioxide nanoparticles.

[0058] S12: Preparation of lead iodine perovskite material: the preparation of lead iodine perovskite sample first mixes a methy lammonium iodide and lead iodide solution with a molar ratio of 1:1 in N,N-dimethylformamide, and stirs continuously at 60°C for 1 hour until the solution appears clear yellow-green, and then places the solution in a 60°C oven to dry until all the solids turn dark black, obtaining lead iodine perovskite nanoparticles.

[0059] S2: Preparation of lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial: at room temperature, fluorine-doped titanium dioxide nanoparticles and lead iodine perovskite nanoparticles are mixed uniformly in a ball mill under the action of a ball mill. After that, the mixture is placed in a 60°C oven for continuous calcination for 48 hours, obtaining lead iodine perovskite@titanium-based (60°C 1:1) nanocomposite material.

[0060] The performance of the lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial is as follows:

[0061] This comparative example uses a 500W xenon lamp as a light source, weighs 50mg of the nanomaterial, and carries out a paracetamol (100mL, 10mg / L) photocatalytic degradation experiment under dark reaction conditions and visible light irradiation, uses a high-performance liquid chromatograph to test the concentration of paracetamol in the solution, and calculates the degradation rate. As Figure 6As shown, after 30 min of treatment under dark reaction conditions, the nanomaterial did not exhibit an obvious degradation trend. After 100 min of visible light irradiation, the degradation rate of the composite material was 35.4%. The degradation rates of fluorine-doped titanium dioxide and lead iodine perovskite were 24.3% and 47.2%, respectively. Test results show that the photocatalytic activity of the lead iodine perovskite@titanium-based composite nanomaterial with a mass ratio of 1:1 at 60°C thermal atmosphere is similar to the performance characteristics of the simple mechanical mixture of the two materials.

[0062] Comparative Example 2

[0063] The present comparative example mainly includes four parts: preparation of fluorine-doped titanium dioxide material, preparation of lead iodine perovskite material, preparation of lead iodine perovskite@titanium-based composite nanomaterial, and performance evaluation of lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial.

[0064] Preparation process of lead iodine perovskite@titanium-based composite nanomaterial with a mass ratio of 1:0.5 at 160°C thermal atmosphere is as follows:

[0065] S1: Preparation of fluorine-doped titanium dioxide material: fluorine-doped titanium dioxide nanosheets are synthesized by a simple hydrothermal method. At room temperature, 10 mL of hydrofluoric acid solution is added to 50 mL of tetrabutyl orthotitanate, and after magnetic stirring for 30 minutes, the mixture is transferred to a dry 100 mL Teflon-lined autoclave. Subsequently, the autoclave is heated to 240°C for 24 hours. After that, the obtained particulate matter is washed several times with ethanol and deionized water, respectively, the precipitate is collected by centrifugation, and finally the sample is placed in a 60°C oven for drying for 12 hours, obtaining fluorine-doped titanium dioxide nanoparticles.

[0066] Preparation of lead iodine perovskite material: the preparation of lead iodine perovskite sample first mixes a methyamine iodine and lead iodide mixed solution with a molar ratio of 1:1 in N,N-dimethylformamide, and stirs continuously at 60°C for 1 hour until the solution appears clear yellow-green. Then, the solution is placed in a 60°C oven to dry until all the solids turn dark black, obtaining lead iodine perovskite nanoparticles.

[0067] S2: Preparation of lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial: at room temperature, fluorine-doped titanium dioxide nanoparticles and lead iodine perovskite nanoparticles are mixed uniformly in a ball mill under the action of a ball mill. After that, the mixture is placed in a 160°C oven for continuous calcination for 48 hours, obtaining lead iodine perovskite@titanium-based (160°C 1:0.5) nanocomposite material.

[0068] The performance of the lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial is as follows:

[0069] The para-example uses a 500W xenon lamp as a light source, weighs 50mg of the nanomaterial, and carries out a paracetamol (100mL, 10mg / L) photocatalytic degradation experiment under dark reaction conditions and visible light irradiation, uses a high-performance liquid chromatograph to test the concentration of paracetamol in the solution, and calculates the degradation rate. As shown in the figure, after 30min of treatment under dark reaction conditions, the nanomaterial does not exhibit an obvious degradation trend. After 100min of visible light irradiation, the degradation rate of the composite material is 49.0%, and the degradation rate of the lead iodine perovskite@titanium-based (60℃ 1:1) nanocomposite material is 35.4%. The test results show that the photocatalytic activity of the lead iodine perovskite@titanium-based (160℃ 1:0.5) composite material is higher than that of the mechanically mixed lead iodine perovskite@titanium-based composite material, which indicates that the synthesis of nitrogen and fluorine co-doped and hexagonal-rhombohedral heterophase junctions helps to improve the photocatalytic performance of the catalytic material. Figure 6

[0070] Through relevant structure and performance analysis of the lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterophase junction photocatalytic degradation nanomaterial obtained by the preparation method of the embodiment of the present application, the following conclusions can be drawn:

[0071] (1) The lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterophase junction photocatalytic degradation nanomaterial, through the transmission electron microscope graph (TEM) of the lead iodine perovskite@titanium-based (1:1 160℃) in the present application, Figure 2 ), analyzes that the hexagonal-rhombohedral heterophase junction mixed crystal phenomenon of lead iodide is formed in the thermal degradation process due to the size-related path of the possible nanocrystal decomposition. Under sunlight, photo-generated electrons are transferred from the conduction band of fluorine-doped titanium dioxide to the conduction band of lead iodide with a lower Fermi level, and at the same time, electrons are further transferred from the rhombohedral phase lead iodide to the hexagonal phase lead iodide, realizing three-way transfer of photo-generated electrons; conversely, holes are transferred from the valence band of the hexagonal phase lead iodide to the valence band of the rhombohedral phase lead iodide, thereby realizing the transfer of holes. In this case, the migration of photo-generated electrons and holes between the two composite materials and the hexagonal-rhombohedral heterophase junction can effectively separate the photo-generated carriers, which is conducive to the further absorption of visible light and improves the photocatalytic degradation effect.

[0072] (2) In the lead iodine perovskite@titanium-based nitrogen and fluorine co-doped hexagonal-rhombohedral heterophase junction photocatalytic degradation nanomaterial, through the XPS comparison graph (XPS) of fluorine, nitrogen doping and oxygen elements in the nanomaterial obtained by different lead iodine perovskite / titanium-based mass ratios in the present application, Figures 3-5 ), analyzes that:

[0073] (a) Fluorine-doped titanium dioxide, lead iodine perovskite@titanium-based (160℃ 1:1) and lead iodine perovskite@titanium-based (160℃ 1:0.5) nanomaterials all form interstitial doping of fluorine and nitrogen. ​

[0074] (b) Fluorine doping promotes the formation of nitrogen doping, and the interstitial doping nitrogen shares the unpaired electrons formed by oxygen to form a localized occupied state with a π characteristic antibonding state (π*) located about 0.7 eV above the top of the O2p valence band, which further narrows the band gap of titanium dioxide and enhances the visible light absorption.

[0075] (c) Meanwhile, through the XPS comparison chart of oxygen elements in the nanomaterials obtained by different lead iodine perovskite / titanium base mass ratios in the application, it is analyzed that the mass fraction of hydroxyl in fluorine-doped titanium dioxide, lead iodine perovskite@titanium base (160℃ 1:1) and lead iodine perovskite@titanium base (160℃ 1:0.5) is 5.1%, 15.2% and 9.5% respectively, which shows that the formation of nitrogen doping promotes more hydroxyl to combine on the surface of the nanomaterial, so as to capture more photo-generated holes and improve the number of hydroxyl radicals, thereby enhancing the photocatalytic activity of the nanomaterial.

[0076] (3) The nitrogen and fluorine co-doped hexagonal-rhombohedral heterojunction photocatalytic degradation nanomaterial of lead iodine perovskite@titanium base is synthesized at low temperature, which effectively inhibits the problem that the increase of crystal size and the decrease of specific surface area caused by high-temperature calcination of the commonly existing photocatalytic materials, thereby being not conducive to the photocatalytic efficiency. Meanwhile, the nanomaterial uses an organic nitrogen-containing material as a modified doping nitrogen source, which provides a new preparation method for the organic carbon nitride as a modified doping source under low temperature conditions, and provides a more green and environmentally friendly method for the degradation of organic pollutants, thereby promoting the sustainable development of the ecological system.

[0077] (4) The nitrogen and fluorine co-doped hexagonal-rhombohedral heterojunction photocatalytic degradation nanomaterial of lead iodine perovskite@titanium base prepared under low-temperature heat atmosphere, through the comparison chart of degradation efficiency of the composite material under different lead iodine perovskite / titanium base mass ratios and temperatures in the application and titanium base, lead iodide and lead iodine perovskite (Fig. Figure 6 ), it is analyzed that compared with the lead iodine perovskite@titanium base composite material simply mechanically mixed, the photocatalytic degradation efficiency of paracetamol of the lead iodine perovskite@titanium base (160℃) nanomaterial is obviously improved. Therefore, the synergistic effect between nitrogen and fluorine co-doping and hexagonal-rhombohedral heterojunction improves the photocatalytic activity of the catalytic material.

[0078] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited to this. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications shall fall within the protection scope of the present disclosure.

Claims

1. A low-temperature preparation method for nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterials based on lead-iodide perovskite@titanium, characterized in that: Includes the following steps: S11: Preparation of fluorine-doped titanium dioxide material: Hydrofluoric acid solution was added to tetrabutyl titanate and stirred to obtain a mixture. The mixture was heated to obtain particulate matter. The particulate matter was washed with ethanol and deionized water respectively. The precipitate was collected by centrifugation and dried to obtain fluorine-doped titanium dioxide material. S12: Preparation of lead-iodine perovskite material: Stir the mixed solution of methylamine iodine and lead iodide dissolved in N,N-dimethylformamide until the solution turns a clear yellow-green color, and then bake the mixed solution until the solid turns into a dark black color to obtain lead-iodine perovskite material. S2: Preparation of nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterials based on lead-iodine perovskite@titanium: The fluorine-doped titanium dioxide material and lead-iodine perovskite material prepared in step S1 are mixed evenly in a grinding process to obtain a mixture. The mixture is then baked to obtain nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterials based on lead-iodine perovskite@titanium. In step S11, the volume ratio of the hydrofluoric acid solution to the tetrabutyl titanate is 1:(4-5). In step S12, the molar ratio of methylamine iodine to lead iodide is 1:1; In step S2, the mass ratio of the fluorine-doped titanium dioxide material to the lead-iodine perovskite material is 1:

1.

2. The low-temperature preparation method of nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterials based on lead-iodide perovskite@titanium according to claim 1, characterized in that: In step S11, the heating reaction is carried out in a high-pressure reactor.

3. The low-temperature preparation method of nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterials based on lead-iodide perovskite@titanium according to claim 2, characterized in that: In step S11, the stirring time is 30 minutes, the autoclave is a Teflon-lined autoclave, and the heating conditions are: heating to 240°C and holding at that temperature for 24 hours.

4. The low-temperature preparation method of nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterials based on lead-iodide perovskite@titanium according to claim 1, characterized in that: In step S11, the drying conditions are as follows: the precipitate is placed in an oven at 60°C and dried continuously for 12 hours.

5. The low-temperature preparation method of nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterials based on lead-iodide perovskite@titanium according to claim 1, characterized in that: In step S12, the stirring conditions are: stirring at 60°C for 1 hour, and the baking temperature is 60°C.

6. The low-temperature preparation method of nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterials based on lead-iodide perovskite@titanium according to claim 1, characterized in that: In step S2, the baking conditions are continuous calcination in an oven at 150-160°C for 48 hours.

7. A nitrogen-fluorine co-doped hexagonal rhombohedral heterojunction photocatalytic degradation nanomaterial based on lead-iodide perovskite@titanium, characterized in that: The nanomaterial is prepared by any one of the preparation methods of claims 1-6.

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