Preparation method and application of nitrogen-doped titanium dioxide and carbon hollow sphere heterojunction photocatalyst

Abstract

The invention discloses a preparation method of a heterojunction photocatalyst with nitrogen simultaneously doped with titanium dioxide and carbon hollow spheres. The preparation method comprises the following steps: 1) preparing a carbon hollow sphere core-shell structure sample based on melamine-formaldehyde nanospheres; 2) preparing a TiO2-carbon core-shell structure sample by taking the carbon hollow sphere core-shell structure and tetrabutyl titanate as a reaction system; and (3) simultaneously doping an N element into the TiO2 at carbon core-shell structure by adopting a one-step method, and forming the N-TiO2 at N doped carbon hollow sphere heterojunction. The invention provides a preparation method and application of a heterojunction photocatalyst with nitrogen simultaneously doped with titanium dioxide and carbon hollow spheres, according to the method, uniform doping of nitrogen and effective compounding of TiO2 and carbon hollow spheres are realized through specific steps, and the prepared photocatalyst shows excellent photocatalytic performance under visible light and ultraviolet light.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalyst material preparation, and in particular to a preparation method and application of a nitrogen-doped titanium dioxide and carbon hollow sphere heterojunction photocatalyst. Background Art

[0002] With climate change and the energy crisis becoming increasingly severe, finding sustainable, clean, and efficient energy utilization methods has become a core task for scientific research and technological development. Carbon dioxide (CO2), the primary greenhouse gas, has been found to contribute significantly to global warming, sea level rise, and other serious issues. Therefore, reducing CO2 emissions and exploring ways to utilize it as a resource have become crucial tasks for researchers worldwide.

[0003] Solar-driven semiconductor photocatalytic reduction of CO₂ is a promising, environmentally friendly technology. Using semiconductor materials as catalysts under sunlight to convert CO₂ into chemical fuels (such as CO, methane, and methanol) can address the energy crisis and contribute to a green, low-carbon, and sustainable development system. The fundamental principles of photocatalytic reduction of CO₂ involve multiple steps, including light absorption, electron excitation, charge separation and migration, and surface catalytic reactions. Under illumination, photocatalysts absorb photons and generate photogenerated electrons and holes. These electrons have strong reducing properties and can react with CO₂ molecules adsorbed on the catalyst surface to produce hydrocarbons and other compounds. Meanwhile, photogenerated holes can participate in the oxidation of water to generate oxygen. By rationally designing the structure and composition of photocatalysts, their optical, electronic, and surface properties can be manipulated to improve the activity and selectivity of photocatalytic reduction of CO₂.

[0004] At present, a variety of high-efficiency semiconductor-based photocatalytic systems have been used for carbon dioxide reduction. Among the many photocatalysts, titanium dioxide is widely used in the field of photocatalysis because of its high photocatalytic activity, good chemical stability, safety and non-toxicity, easy production, and no secondary pollution. However, in the research of TiO2 materials, there are still some factors that restrict its practical application: (1) The recombination efficiency of photogenerated carriers is too high. The electrons and holes generated by TiO2 under light excitation quickly recombine, resulting in a significant reduction in the number of effective electrons actually participating in the photocatalytic or photoelectric conversion process, thereby reducing the quantum efficiency, that is, the efficiency of converting light energy into chemical energy or electrical energy is not high. (2) The spectral response range is limited. TiO2 mainly absorbs light energy in the ultraviolet band, while ultraviolet light accounts for a relatively small proportion in the solar spectrum and has a certain impact on the human body and the environment. Therefore, TiO2 cannot efficiently utilize the abundant visible light resources, limiting its potential in the field of solar energy conversion. In order to overcome this defect, researchers have tried to modify TiO2 by doping with non-metallic elements (such as nitrogen) to expand its spectral response range and improve its photocatalytic performance. In addition, compounding TiO2 with other materials (such as carbon materials) to form a heterojunction can also significantly improve the separation efficiency of photogenerated electron-hole pairs, thereby enhancing photocatalytic activity.

[0005] In summary, it is very meaningful to develop a heterojunction photocatalyst with high photocatalytic efficiency that can be used for photocatalytic reduction of CO2. Summary of the Invention

[0006] In view of this, the present invention provides a preparation method and application of a heterojunction photocatalyst of nitrogen-doped titanium dioxide and carbon hollow spheres, so as to provide a catalyst for significantly improving the separation efficiency of photogenerated electron-hole pairs and enhancing photocatalytic activity.

[0007] The technical solution provided by the present invention is specifically a method for preparing a heterojunction photocatalyst of nitrogen-doped titanium dioxide and carbon hollow spheres, comprising the following steps:

[0008] 1) Preparation of carbon hollow sphere core-shell structure samples based on melamine-formaldehyde nanospheres;

[0009] 2) Preparation of TiO2@carbon core-shell structure samples using carbon hollow sphere core-shell structure and tetrabutyl titanate as the reaction system;

[0010] 3) Using a one-step method, N is simultaneously doped into the TiO2@carbon core-shell structure to form a heterojunction.

[0011] Preferably, the preparation method of the melamine-formaldehyde nanospheres is: formaldehyde, water and NaOH solution are mixed evenly, melamine is added, and the mixture is stirred at 100°C, and then the prepared F127 solution is added, stirred at room temperature, and then transferred to a reactor for reaction at 100°C.

[0012] Preferably, the preparation of the carbon hollow sphere core-shell structure sample based on melamine-formaldehyde nanospheres comprises:

[0013] Melamine-formaldehyde nanospheres were added to a mixed solution of water and ethanol and ultrasonically dispersed uniformly. Cetyltrimethylammonium bromide, resorcinol and ammonia water were added to the mixed solution after ultrasonic dispersion. After stirring at 35°C, formaldehyde was added and continued to stir. After cooling to room temperature, the solution was allowed to stand and then washed with water and dried.

[0014] Preferably, the method of preparing a TiO2@carbon core-shell structure sample using a carbon hollow sphere core-shell structure and tetrabutyl titanate as a reaction system includes: mixing the TiO2@carbon core-shell structure sample with anhydrous ethanol and ultrasonicating the mixture to mix them evenly, then adding tetrabutyl titanate to the evenly mixed system and stirring; dripping a mixed solution of hydrochloric acid, anhydrous ethanol and water into the stirred solution system dropwise, stirring at room temperature, letting it stand for 12-24 hours, and drying at 60-100°C.

[0015] Preferably, the mass of the TiO2@carbon core-shell structure sample is 0.1-0.6 g; the amount of anhydrous ethanol is 5-10 ml; the ultrasonic time is 20-40 minutes, and the amount of tetrabutyl titanate is 2.5-5 ml;

[0016] The volumes of the components in the mixed solution of hydrochloric acid, anhydrous ethanol and water are 2.5 ml, 1 ml-4 ml and 2-5 ml respectively.

[0017] Preferably, the one-step method is used to simultaneously dope N into TiO2@carbon core-shell structure to form a heterojunction, comprising: placing the TiO2@carbon core-shell structure sample in a tube furnace, heating it to 150°C at a rate of 10-15°C / min in a nitrogen atmosphere and calcining it for 40-60 minutes, then heating it to 400°C at a rate of 1°C / min and calcining it for 240-360 minutes to obtain a heterojunction photocatalyst of nitrogen-doped titanium dioxide@carbon hollow spheres.

[0018] The present invention also provides the use of nitrogen-doped titanium dioxide@carbon hollow sphere heterojunction photocatalyst prepared by the preparation method, and the catalyst is used for photocatalytic reduction of CO2.

[0019] The present invention provides a preparation method and application of a heterojunction photocatalyst of titanium dioxide and carbon hollow spheres doped with nitrogen. The method realizes uniform doping of nitrogen and effective compounding of TiO2 and carbon hollow spheres through specific steps. The prepared photocatalyst exhibits excellent photocatalytic performance under both visible light and ultraviolet light.

[0020] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0023] Figure 1 The XRD spectrum of the nitrogen-doped titanium dioxide@carbon hollow sphere heterojunction photocatalyst prepared in Example 4 of the present invention;

[0024] Figure 2 TEM image of the catalyst prepared in Example 4 of the present invention;

[0025] Figure 3 This is the N element distribution diagram of the catalyst prepared in Example 4 of the present invention;

[0026] Figure 4 The adsorption equilibrium isotherm diagram of the catalyst prepared in Example 4 of the present invention;

[0027] Figure 5 This is a graph showing the photocatalytic reduction of CO2 yield in the ultraviolet-visible light region of the catalyst prepared in Example 4 of the present invention. DETAILED DESCRIPTION

[0028] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all possible embodiments consistent with the present invention. Rather, they are merely examples of methods consistent with certain aspects of the present invention, as detailed in the appended claims.

[0029] In order to overcome the problems in the prior art that TiO2 cannot efficiently utilize abundant visible light resources, limiting its potential in the field of solar energy conversion, this embodiment provides a method for preparing a nitrogen-doped titanium dioxide@carbon hollow sphere heterojunction photocatalyst, characterized by comprising the following steps:

[0030] 1) Preparation of carbon hollow sphere core-shell structure samples based on melamine-formaldehyde nanospheres;

[0031] 2) Preparation of TiO2@carbon core-shell structure samples using carbon hollow sphere core-shell structure and tetrabutyl titanate as the reaction system;

[0032] 3) Using a one-step method, N is simultaneously doped into the TiO2@carbon core-shell structure to form a heterojunction.

[0033] Specifically, the steps include:

[0034] 1. Preparation of carbon hollow sphere core-shell structure:

[0035] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0036] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0037] 2. Preparation of TiO2@carbon core-shell structure:

[0038] A certain amount of the above core-shell structure is mixed with anhydrous ethanol and ultrasonicated to mix them evenly. Tetrabutyl titanate is added to the above system and stirred for 30-60 minutes. Then, a mixed solution of hydrochloric acid, anhydrous ethanol and water is added dropwise into the above solution. After stirring at room temperature for 6-12 hours, the mixture is allowed to stand for 12-24 hours and then dried at 60-100°C.

[0039] In step 2, the mass of the core-shell structure is 0.1-0.6 g; the amount of anhydrous ethanol is 5-10 ml; the ultrasonic time is 20-40 minutes; the volumes of the components in the mixed solution of hydrochloric acid, ethanol and water are 2.5 ml, 1 ml-4 ml, and 2-5 ml, respectively; and the amount of tetrabutyl titanate is 2.5-5 ml.

[0040] Preferably, in step 2, the mass of the core-shell structure is 0.4 g, the amount of anhydrous ethanol is 10 ml, the ultrasonic time is 20 minutes, the amount of tetrabutyl titanate is 4 ml, the stirring time is 60 minutes, the amounts of each component in the mixed solution of hydrochloric acid, anhydrous ethanol and water are 2.5 ml, 2.5 ml, and 2 ml respectively, the stirring time is 12 hours, the mixture is allowed to stand for 24 hours, and the mixture is dried at 80°C. In step 3, the first heating rate is 15°C / min, the mixture is calcined at 150°C for 60 minutes, the second calcination temperature is 400°C, and the calcination time is 300 minutes.

[0041] Among them, the mass of the selected core-shell structure is 0.4g, which is the optimal ratio with titanium dioxide nanoparticles and shows the best photocatalytic activity; the amount of anhydrous ethanol selected is 10ml, and the core-shell structure has the best dispersion effect in the system; the ultrasonic time of 20 minutes is the shortest time to obtain the best dispersion effect; the catalyst with a calcination temperature of 400℃ has the highest activity.

[0042] 3. One-step formation of a heterojunction of nitrogen-doped hollow carbon spheres and TiO2: The above sample was placed in a tube furnace and heated at a rate of 10-15°C / min to 150°C for 40-60 minutes in a nitrogen atmosphere. Then, the temperature was raised to 400°C at a rate of 1°C / min and calcined for 240-360 minutes to obtain the target product. The product phase was analyzed by X-ray powder diffraction and transmission electron microscopy, and light absorption was analyzed by UV-visible diffuse reflectance spectroscopy. The pore distribution and specific surface area of ​​the product were analyzed by nitrogen adsorption.

[0043] In this preparation method, during high-temperature calcination, the central melamine-formaldehyde nanospheres decompose into nitrogen-rich gas. During this process, nitrogen is doped into the carbon hollow spheres and TiO2 formed by carbonization of the resorcinol-formaldehyde resin. At high temperatures, the TiO2 and carbon hollow spheres combine to form a heterojunction. The hollow structure, the small size effect of the titanium dioxide nanoparticles, the nitrogen doping, and the heterojunction structure result in a photocatalytic material with a large specific surface area, excellent visible light absorption, and high visible light photocatalytic efficiency. This material has applications in energy and environmental fields, such as photocatalytic reduction of CO2.

[0044] The specific steps for photocatalytic degradation of organic pollutants in this embodiment are as follows: 10 mg of the catalyst is mixed with 30 mg of ruthenium bipyridine, 4 ml of N,N-dimethylacetamide, 1 ml of water, and 1 ml of triethanolamine. The mixture is stirred in the dark under vacuum for 30 minutes. A light source with a 420 nm filter is used to filter out ultraviolet light. The mixture is stirred under illumination. The chromatogram is automatically sampled every 60 minutes, and the CO peak area is measured to calculate the CO production.

[0045] The present invention is further explained below with reference to specific embodiments, but is not intended to limit the scope of protection of the present invention.

[0046] Example 1

[0047] 1. Preparation of carbon hollow sphere core-shell structure:

[0048] Synthesis of melamine-formaldehyde nanospheres:

[0049] Mix 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution, add 5.0 g of melamine and stir at 100 ° C for 1 hour. Then add the prepared F127 solution (8 g F127 + 60 ml H2O) and stir at room temperature for 6 hours. Then transfer the mixture into a reactor and react at 100 ° C for 24 hours.

[0050] Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed uniformly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0051] 2. Preparation of TiO2 and carbon core-shell structure: 0.1g core-shell structure was mixed with 10ml anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4ml tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5ml hydrochloric acid, 2.5ml anhydrous ethanol and 2ml water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and dried at 80℃.

[0052] 3. One-step formation of N-doped carbon hollow spheres@TiO2 to form a heterojunction: The above samples were placed in a tube furnace, first heated to 150°C at a rate of 15°C / min in a nitrogen atmosphere for 60 minutes, and then heated to 400°C at a rate of 1°C / min and calcined for 300 minutes to obtain the target product.

[0053] Example 2

[0054] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0055] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0056] 2. Preparation of TiO2@carbon core-shell structure: 0.2 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0057] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0058] Example 3

[0059] 1. Formation of carbon hollow sphere core-shell structure:

[0060] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0061] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0062] 2. Preparation of TiO2@carbon core-shell structure: 0.3g of core-shell structure was mixed with 10ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix them evenly. 4ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5ml of hydrochloric acid, 2.5ml of anhydrous ethanol and 2ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, the mixture was allowed to stand for 24 hours and then dried at 80℃. (3) One-step formation of heterojunction of N-doped hollow carbon spheres and TiO2: The above sample was placed in a tube furnace and heated to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere for 60 minutes. Then, the mixture was heated to 400℃ at a rate of 1℃ / min and calcined for 300 minutes to obtain the target product.

[0063] Example 4

[0064] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0065] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0066] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0067] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0068] The target product was characterized by X-ray powder diffraction, transmission electron microscopy, UV-visible diffuse reflectance spectroscopy, and N2 adsorption analysis. Figure 1-5 As shown, Figure 1 From the XRD spectrum of , it can be seen that the peak around 20° is the carbon hollow sphere phase, and the other peaks are the anatase and rutile phases of titanium dioxide; Figure 2 The TEM image of the prepared material is shown, in which the hollow spheres are N-doped carbon spheres and the surface nanoparticles are N-doped titanium dioxide; Figure 3 The figure shows the distribution of N elements in the prepared material. It can be proved from this figure that both carbon spheres and surface titanium dioxide nanoparticles contain N elements, achieving simultaneous doping. Figure 4 The adsorption equilibrium isotherm diagram of the prepared material is shown in FIG. 1 , from which it can be seen that the material prepared by the method of the present invention has a mesoporous structure and a high specific surface area; Figure 5The figure shows the photocatalytic reduction of CO2 yield of the prepared material in the UV-visible light region. It can be seen from the figure that under simulated sunlight, CO2 has a high conversion rate. After 6 hours of illumination, the CO yield reaches 353 μmol g -1 .

[0069] Example 5

[0070] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0071] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0072] 2. Preparation of TiO2@carbon core-shell structure: 0.5 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0073] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0074] Example 6

[0075] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0076] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0077] 2. Preparation of TiO2@carbon core-shell structure: 0.6 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0078] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0079] Example 7

[0080] 1. Formation of carbon hollow sphere core-shell structure:

[0081] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0082] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0083] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 5 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0084] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0085] Example 8

[0086] 1. Formation of carbon hollow sphere core-shell structure:

[0087] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0088] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0089] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 6 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0090] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0091] Example 9

[0092] 1. Formation of core-shell structure of hollow carbon spheres

[0093] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0094] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0095] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 8 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0096] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0097] Example 10

[0098] 1. Formation of core-shell structure of hollow carbon spheres

[0099] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0100] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0101] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 10 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0102] A one-step method was used to form a heterojunction of N-doped carbon hollow spheres and TiO2: the above samples were placed in a tubular furnace, heated to 150°C at a rate of 15°C / min in a nitrogen atmosphere for 60 minutes, and then heated to 400°C at a rate of 1°C / min and calcined for 300 minutes to obtain the target product.

[0103] Example 11

[0104] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0105] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0106] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 20 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0107] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0108] Example 12

[0109] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0110] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0111] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 3 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0112] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0113] Example 13

[0114] 1. Formation of core-shell structure of hollow carbon spheres

[0115] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0116] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0117] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4.5 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0118] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0119] Example 14

[0120] 1. Formation of carbon hollow sphere core-shell structure:

[0121] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0122] ② Formation of core-shell structure: 0.4 g of nanospheres were added to a mixed solution of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed evenly. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of ammonia water were added to the mixed solution and stirred at 35°C for 30 minutes. After that, 0.6 ml of formaldehyde was added and continued to stir for 6 hours. After cooling to room temperature, the mixture was allowed to stand for 12 hours, washed with water, and dried.

[0123] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 30 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0124] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0125] Example 15

[0126] 1. Formation of carbon hollow sphere core-shell structure:

[0127] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0128] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0129] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 40 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0130] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0131] Example 16

[0132] 1. Formation of core-shell structure of hollow carbon spheres

[0133] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0134] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0135] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 50 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0136] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0137] Example 17

[0138] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0139] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0140] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 1 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0141] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0142] Example 18

[0143] 1. Formation of carbon hollow sphere core-shell structure:

[0144] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0145] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0146] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 1.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0147] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0148] Example 19

[0149] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0150] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0151] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0152] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0153] Example 20

[0154] 1. Formation of core-shell structure of hollow carbon spheres

[0155] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0156] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0157] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 3 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0158] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0159] Example 21

[0160] 1. Formation of carbon hollow sphere core-shell structure:

[0161] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0162] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0163] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 3.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0164] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0165] Example 22

[0166] 1. Formation of carbon hollow sphere core-shell structure:

[0167] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0168] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0169] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 4 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0170] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0171] Example 23

[0172] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0173] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0174] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 3 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0175] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0176] Example 24

[0177] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0178] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0179] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 4 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0180] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0181] Example 25

[0182] 1. Formation of carbon hollow sphere core-shell structure:

[0183] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0184] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0185] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 5 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0186] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0187] Example 26

[0188] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0189] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0190] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 6 hours, it was allowed to stand for 24 hours and dried at 80°C.

[0191] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0192] Example 27

[0193] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0194] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0195] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 7 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0196] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0197] Example 28

[0198] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0199] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0200] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 9 hours, it was allowed to stand for 24 hours and dried at 80°C.

[0201] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0202] Example 29

[0203] Formation of carbon hollow sphere core-shell structure: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml formaldehyde, 40 ml water and 0.2 ml 1M NaOH solution were mixed evenly, 5.0 g melamine was added and stirred at 100 ° C for 1 hour, and then the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours, and then transferred to a reactor and reacted at 100 ° C for 24 hours.

[0204] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0205] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 11 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0206] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0207] Example 30

[0208] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0209] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0210] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 12 hours and then dried at 80°C.

[0211] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0212] Example 31

[0213] 1. Formation of the core-shell structure of hollow carbon spheres ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0214] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0215] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 16 hours and then dried at 80°C.

[0216] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0217] Example 32

[0218] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0219] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0220] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 20 hours and then dried at 80°C.

[0221] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0222] Example 33

[0223] 1. Formation of carbon hollow sphere core-shell structure:

[0224] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0225] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0226] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 60°C.

[0227] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0228] Example 34

[0229] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0230] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0231] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and dried at 70°C.

[0232] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0233] Example 35

[0234] 1. Formation of core-shell structure of hollow carbon spheres: ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added and stirred at 100°C for 1 hour. Then, the prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. Then, the mixture was transferred to a reactor and reacted at 100°C for 24 hours.

[0235] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0236] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and dried at 90°C.

[0237] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0238] Example 36

[0239] 1. Formation of carbon hollow sphere core-shell structure:

[0240] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0241] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0242] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, the solution was allowed to stand for 24 hours and dried at 100°C.

[0243] 3. One-step method to form heterojunction of N-doped carbon hollow spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0244] Example 37

[0245] 1. Formation of carbon hollow sphere core-shell structure:

[0246] ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0247] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0248] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0249] 3. One-step formation of N-doped carbon hollow spheres and TiO2 to form a heterojunction: Place the above sample in a tube furnace, first heat it to 150℃ at a rate of 10℃ / min in a nitrogen atmosphere and calcine for 60 minutes, then heat it to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0250] Example 38

[0251] 1. Formation of the core-shell structure of hollow carbon spheres ① Synthesis of melamine-formaldehyde nanospheres: 9 ml of formaldehyde, 40 ml of water, and 0.2 ml of 1 M NaOH solution were mixed evenly, 5.0 g of melamine was added, and the mixture was stirred at 100°C for 1 hour. The prepared F127 solution (8 g F127 + 60 ml H2O) was added and stirred at room temperature for 6-10 hours. The mixture was then transferred to a reactor and reacted at 100°C for 24 hours.

[0252] ② Formation of the core-shell structure: 0.4 g of nanospheres were added to a mixture of 35 ml of water and 14 ml of ethanol and ultrasonically dispersed. 1.2 g of hexadecyltrimethylammonium bromide (CTAB), 0.2 g of resorcinol, and 0.05 ml of aqueous ammonia were added to the mixture, stirred at 35°C, and the mixture was dripped dropwise into the above solution. The mixture was stirred at room temperature for 12 hours, allowed to stand for 24 hours, and then dried at 80°C. After 30 minutes, 0.6 ml of formaldehyde was added, and stirring was continued for 6 hours. The mixture was then cooled to room temperature, allowed to stand for 12 hours, and washed with water and dried.

[0253] 2. Preparation of TiO2@carbon core-shell structure: 0.4 g of core-shell structure was mixed with 10 ml of anhydrous ethanol and ultrasonicated for 30 minutes to mix evenly. 4 ml of tetrabutyl titanate was added to the above system and stirred for 60 minutes. Then, a mixed solution of 2.5 ml of hydrochloric acid, 2.5 ml of anhydrous ethanol and 2 ml of water was dripped dropwise into the above solution. After stirring at room temperature for 12 hours, it was allowed to stand for 24 hours and then dried at 80°C.

[0254] 3. One-step method to form heterojunction of N-doped hollow carbon spheres and TiO2: Place the above samples in a tube furnace, first heat them to 150℃ at a rate of 15℃ / min in a nitrogen atmosphere and calcine for 40 minutes, then heat them to 400℃ at a rate of 1℃ / min and calcine for 300 minutes to obtain the target product.

[0255] Other embodiments of the present invention will readily occur to those skilled in the art after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

[0256] It should be understood that the present invention is not limited to the above description and that various modifications and changes can be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for preparing a heterojunction photocatalyst of nitrogen-doped titanium dioxide and carbon hollow spheres, characterized in that: The steps include: 1) Preparation of carbon hollow sphere core-shell structure samples based on melamine-formaldehyde nanospheres; 2) Using carbon hollow sphere core-shell structure and tetrabutyl titanate as the reaction system to prepare TiO2@carbon core-shell structure samples; 3) Using a one-step method, N is simultaneously doped into the TiO2@carbon core-shell structure to form a heterojunction.

2. The method for preparing a nitrogen-doped titanium dioxide and carbon hollow sphere heterojunction photocatalyst according to claim 1, characterized in that: The preparation method of the melamine-formaldehyde nanospheres is: After the formaldehyde, water and NaOH solution are evenly mixed, melamine is added and stirred at 100°C, the prepared F127 solution is added, stirred at room temperature, and then transferred to a reactor to react at 100°C.

3. The method for preparing a nitrogen-doped titanium dioxide and carbon hollow sphere heterojunction photocatalyst according to claim 1, characterized in that: The method for preparing a carbon hollow sphere core-shell structure sample based on melamine-formaldehyde nanospheres comprises: Melamine-formaldehyde nanospheres were added to a mixed solution of water and ethanol and dispersed evenly by ultrasonication. Hexadecyltrimethylammonium bromide, resorcinol and aqueous ammonia were added to the mixed solution after ultrasonic dispersion. After stirring at 35°C, formaldehyde was added and stirring was continued. After cooling to room temperature, the mixture was allowed to stand and then washed with water and dried.

4. The method for preparing a nitrogen-doped titanium dioxide and carbon hollow sphere heterojunction photocatalyst according to claim 1, characterized in that: The method of preparing a TiO2@carbon core-shell structure sample using a carbon hollow sphere core-shell structure and tetrabutyl titanate as a reaction system comprises: The TiO2@carbon core-shell structure sample was mixed with anhydrous ethanol and ultrasonicated to make the mixture uniform, and then tetrabutyl titanate was added into the uniformly mixed system and stirred; Add a mixed solution of hydrochloric acid, anhydrous ethanol and water dropwise into the stirred solution system, stir at room temperature, let stand for 12-24 hours, and dry at 60-100°C.

5. The method for preparing a nitrogen-doped titanium dioxide and carbon hollow sphere heterojunction photocatalyst according to claim 4, characterized in that: The mass of the TiO2@carbon core-shell structure sample is 0.1-0.6 g; the amount of anhydrous ethanol is 5-10 ml; the ultrasonic time is 20-40 minutes, and the amount of tetrabutyl titanate is 2.5-5 ml; The volumes of the components in the mixed solution of hydrochloric acid, anhydrous ethanol and water are 2.5 ml, 1 ml-4 ml and 2-5 ml respectively.

6. The method for preparing a nitrogen-doped titanium dioxide and carbon hollow sphere heterojunction photocatalyst according to claim 1, characterized in that: The one-step method is used to simultaneously dope N into the TiO2@carbon core-shell structure to form a heterojunction, comprising: The TiO2@carbon core-shell structure sample was placed in a tubular furnace, and the temperature was first increased to 150°C at a rate of 10-15°C / min in a nitrogen atmosphere and calcined for 40-60 minutes, and then increased to 400°C at a rate of 1°C / min and calcined for 240-360 minutes to obtain a nitrogen-doped titanium dioxide@carbon hollow sphere heterojunction photocatalyst.

7. Application of heterojunction photocatalyst of nitrogen-doped titanium dioxide and carbon hollow spheres prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The catalyst is used for photocatalytic reduction of CO2.

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