NTO / Ag / g-C3N4 multi-dimensional heterostructure as well as preparation method and application thereof

Abstract

The invention discloses an NTO / Ag / g-C3N4 multi-dimensional heterostructure as well as a preparation method and application thereof. The NTO / Ag / g-C3N4 multi-dimensional heterostructure comprises NTO nanowires, Ag nanoparticles and g-C3N4 nanosheets. A one-step hydrothermal method is adopted to prepare an NTO / Ag / g-C3N4 multi-dimensional heterostructure, one-dimensional NTO nanowires provide a flexible matrix, zero-dimensional Ag nanoparticles modify the surfaces of the NTO nanowires, the number of active sites on the surfaces of the nanowires is increased, and two-dimensional g-C3N4 nanosheets and the NTO nanowires construct heterojunctions, so that the photocatalytic efficiency and the absorption capacity to ultraviolet light and visible light are improved; the NTO / Ag / g-C3N4 multi-dimensional heterostructure catalyst film is prepared by using the NTO / Ag / g-C3N4 multi-dimensional heterostructure, the NTO / Ag / g-C3N4 multi-dimensional heterostructure catalyst film is uniform in thickness and high in strength and toughness, green hydrogen production can be realized, meanwhile, the catalyst can be recycled, and new environmental pollution caused by the catalyst is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic materials, and particularly relates to an NTO / Ag / g-C 3 N 4 multi-dimensional heterostructure and its preparation method and application. Background Art

[0002] Hydrogen has become the focus of global clean energy research because its final combustion product is only water. Currently, common hydrogen production processes mainly include electrolytic water hydrogen production, natural gas hydrogen production, methanol hydrogen production, etc., all of which have problems such as high energy consumption and a large amount of carbon dioxide emissions. Therefore, how to produce hydrogen cleanly and without pollution has become a key issue.

[0003] TiO 2 has advantages such as a suitable energy band structure, stable chemical properties, non-toxicity, and low cost, and has become the most common photocatalyst. Titanate is an oxygen-containing salt of titanium and has a structure similar to that of TiO 2 Titanate can maintain its original form and transform into TiO 2 Therefore, compact TiO 2 can be uniformly doped or molecularly assembled through the transformation of titanate.

[0004] Traditional Ti-based photocatalysts (such as TiO 2 ) have a relatively large band gap (3.0 - 3.2 eV), mainly absorb ultraviolet light (only accounting for 5% of the solar spectrum), resulting in weak visible light response and high photogenerated carrier recombination rate, which limits their practical applications. In addition, powder catalysts are difficult to recycle and are prone to causing secondary pollution. In the prior art, the photocatalytic performance can be partially improved by noble metal doping (such as Ag, Pt), nanostructure regulation, or heterostructure construction (such as type II, Z-type heterojunctions), but there are still problems such as limited light absorption range, poor stability, and difficulty in recycling.

[0005] For TiO 2 semiconductor photocatalysts, the main problems existing in the process of splitting water to produce hydrogen under visible light are:

[0006] (1) The absorption ability of visible light is weak, making the photocatalytic activity of traditional Ti-based semiconductors such as TiO 2 relatively low under visible light. In addition, the number and availability of active sites on the surface of Ti-based semiconductors have a great impact on the efficiency of catalytic water decomposition. Surface defects or doping can increase the density of active sites, but may also introduce instability and other side effects;

[0007] (2) Most of the existing Ti-based semiconductor catalysts are powders. During the process of water splitting to produce hydrogen, the catalysts may be affected by factors such as photocorrosion and redox cycling, reducing their long-term catalytic activity, and they are not easily recycled during use, easily causing secondary pollution. Summary of the Invention

[0008] To solve the technical problems existing in the prior art, the purpose of the present invention is to provide an NTO / Ag / g-C 3 N 4 multidimensional heterostructure and its preparation method and application.

[0009] To achieve the above purpose and reach the above technical effects, the technical solution adopted by the present invention is as follows:

[0010] An NTO / Ag / g-C 3 N 4 multidimensional heterostructure, including NTO nanowires, Ag nanoparticles, and g-C 3 N 4 nanosheets, wherein the Ag nanoparticles are modified on the surface of the NTO nanowires, and the NTO nanowires and g-C 3 N 4 nanosheets form a heterojunction.

[0011] Further, the diameter of the NTO nanowires is 30 - 50 nm, and the length exceeds 10 μm.

[0012] Further, the particle size of the Ag nanoparticles is 10 - 20 nm.

[0013] The present invention also discloses a preparation method of an NTO / Ag / g-C 3 N 4 multidimensional heterostructure, including the following steps:

[0014] 1) Prepare NTO nanowires, Ag nanoparticles, and g-C 3 N 4 nanosheets respectively;

[0015] 2) Add the NTO nanowires, Ag nanoparticles, and g-C 3 N 4 nanosheets obtained in step 1) into an NaOH solution, react at 100 - 150 °C for 20 - 30 h, and maintain the stirring speed at 150 - 450 rpm during the reaction, then the required NTO / Ag / g-C 3 N 4 multidimensional heterostructure can be obtained.

[0016] Further, the NTO nanowires are prepared by the following steps:

[0017] Add TiO 2 powder to the NaOH solution, stir evenly, react at 100 - 150 °C for 20 - 30 h, keep the stirring speed at 150 - 450 rpm during the reaction process, then perform pickling to remove the residual NaOH, and wash it several times with deionized water until the solution is neutral. After vacuum drying, NTO nanowires can be obtained.

[0018] Furthermore, the Ag nanoparticles are prepared by the following steps:

[0019] 11) Dissolve AgNO 3 in deionized water, add polyvinylpyrrolidone, and disperse it evenly by ultrasonic wave to obtain a mixed solution A;

[0020] 12) Dissolve NaOH and NaBH 4 in deionized water, and disperse it evenly by ultrasonic wave to obtain a mixed solution B;

[0021] 13) Place the mixed solution A in a constant temperature water bath and keep the stirring speed at 300 - 500 rpm; slowly inject the mixed solution B into the solution A. After the injection is completed, ultrasonically treat the obtained solution at room temperature, and then perform centrifugal washing with deionized water until the solution is neutral to obtain Ag nanoparticles.

[0022] Furthermore, the g-C 3 N 4 nanosheets are prepared by the following steps:

[0023] Put C 2 H 4 N 4 powder into a crucible, place the crucible in a tube furnace, pass nitrogen into the furnace, heat it to 500 - 600 °C, with a heating rate of 0.5 - 1.5 °C / min, and keep the temperature for 3 - 5 h. After the heat preservation is completed, let the tube furnace cool naturally, and then grind the calcined product to obtain g-C 3 N 4 nanosheets.

[0024] The present invention also discloses an NTO / Ag / g-C 3 N 4 multidimensional heterostructure catalyst film, which is prepared by vacuum filtration of the NTO / Ag / g-C 3 N 4 multidimensional heterostructure suspension. The thickness of the NTO / Ag / g-C 3 N 4 multidimensional heterostructure catalyst film is 50 - 100 μm.

[0025] The present invention also discloses an NTO / Ag / g-C 3 N4 Application of Multidimensional Heterostructure Catalyst Film in Photocatalytic Hydrogen Production

[0026] Further, the Ag content in the NTO / Ag / g-C 3 N 4 When the Ag content in the multidimensional heterostructure catalyst film is 5%, the cumulative hydrogen production amounts at 1 h, 2 h, and 3 h are 858.6, 2161.5, and 3504 μmol / g, respectively.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1) The present invention uses a one-step hydrothermal method to prepare NTO / Ag / g-C 3 N 4 multidimensional heterostructure. The one-dimensional NTO nanowires provide a flexible matrix, the zero-dimensional Ag nanoparticles modify the surface of the NTO nanowires and act as an electron conductor to increase the number of active sites on the nanowire surface, and the two-dimensional g-C 3 N 4 nanosheets and NTO nanowires construct a heterojunction, which promotes the effective separation, redistribution, and rapid transfer of photo-generated carriers, inhibits the combination of electrons and holes, and is beneficial to improving the photocatalytic efficiency; NTO / Ag / g-C 3 N 4 The absorption ability of the multidimensional heterostructure to ultraviolet light and visible light is improved, especially the absorption ability to visible light in the wavelength range of 400 - 750 nm is greatly improved, which is further beneficial to improving the photocatalytic efficiency; the special linear structure of NTO generates a large specific surface area, which can increase the light absorption area. At the same time, the surface of the one-dimensional NTO nanowires contains more defect structures such as vacancies, and these defects can serve as trapping centers for photo-generated electron-hole pairs, which is beneficial to improving the light absorption efficiency;

[0029] 2) Based on the vacuum filtration technology, the present invention uses NTO / Ag / g-C 3 N 4 multidimensional heterostructure to prepare an NTO / Ag / g-C 3 N 4 multidimensional heterostructure catalyst film with uniform thickness, high strength and toughness, which can realize the recovery and reuse of the catalyst while achieving green hydrogen production, and avoid new environmental pollution caused by the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is the schematic diagram of the present invention;

[0031] Figure 2 is the scanning electron microscope image of the NTO / Ag / g-C 3 N 4 multidimensional heterostructure of Example 1 of the present invention;

[0032] Figure 3 For the present invention Figure 2 Partial enlarged view at A in

[0033] Figure 4 Scanning electron microscope image of NTO nanowires in Example 1 of the present invention;

[0034] Figure 5 Scanning electron microscope image of Ag nanoparticles in Example 1 of the present invention;

[0035] Figure 6 For the g-C 3 N 4 Scanning electron microscope image of nanosheets in Example 1 of the present invention;

[0036] Figure 7 For the raw material TiO 2 Scanning electron microscope image of powder in Example 1 of the present invention;

[0037] Figure 8 For the NTO / Ag / g-C 3 N 4 Scanning electron microscope image of the multi-dimensional heterostructure in Example 2 of the present invention;

[0038] Figure 9 For the NTO / Ag / g-C 3 N 4 Physical image of the NTO / Ag / g-C multi-dimensional heterostructure catalyst film in Example 3 of the present invention;

[0039] Figure 10 For the NTO / Ag / g-C 3 N 4 Scanning electron microscope image of the dried NTO / Ag / g-C multi-dimensional heterostructure catalyst film in Example 3 of the present invention;

[0040] Figure 11 For the NTO / Ag / g-C 3 N 4 Scanning electron microscope image of the longitudinal section of the NTO / Ag / g-C multi-dimensional heterostructure catalyst film in Example 3 of the present invention;

[0041] Figure 12 Scanning electron microscope image of the NTO / Ag powder in Comparative Example 1;

[0042] Figure 13 For the TiO 2 / Ag / g-C 3 N 4 Scanning electron microscope image of the powder in Comparative Example 1;

[0043] Figure 14 Hydrogen production efficiency diagrams of Example 1 and Comparative Examples 1-2 of the present invention;

[0044] Figure 15 Hydrogen production efficiency diagrams of Examples 1-2 of the present invention;

[0045] Figure 16 For the NTO nanowires, NTO / Ag, g-C 3 N 4 nanosheets, TiO 2 / Ag / g-C 3 N 4 , NTO / Ag / g-C 3 N 4 UV-visible diffuse reflectance spectra of the NTO / Ag / g-C Detailed implementation manners

[0046] The present invention will be elaborated in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making the protection scope of the present invention more clearly defined.

[0047] A brief overview of one or more aspects is given below to provide a basic understanding of these aspects. This overview is not an exhaustive survey of all contemplated aspects, and is neither intended to identify key or decisive elements of all aspects nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that follows.

[0048] As Figure 1-16 shown, the present invention discloses an NTO / Ag / g-C 3 N 4 multidimensional heterostructure, including NTO nanowires, Ag nanoparticles and g-C 3 N 4 nanosheets, with the Ag nanoparticles modified on the surface of the NTO nanowires, and the NTO nanowires and g-C 3 N 4 nanosheets forming a heterojunction.

[0049] The diameter of the NTO nanowires is 30-50 nm, and the length exceeds 10 μm.

[0050] The particle size of the Ag nanoparticles is 10-20 nm.

[0051] The present invention also discloses a preparation method of an NTO / Ag / g-C 3 N 4 multidimensional heterostructure, comprising the following steps:

[0052] 1) Prepare NTO nanowires, Ag nanoparticles and g-C 3 N 4 nanosheets respectively;

[0053] 2) Add the NTO nanowires, Ag nanoparticles, and g-C 3 N 4 nanosheets obtained in step 1) into an NaOH solution, and react at 100 - 150 °C for 20 - 30 h. During the reaction, maintain the stirring speed at 150 - 450 rpm, and the required NTO / Ag / g-C 3 N 4 multidimensional heterostructure can be obtained.

[0054] The NTO nanowires are prepared by the following steps:

[0055] Add TiO 2 powder into an NaOH solution, stir evenly, and react at 100 - 150 °C for 20 - 30 h. During the reaction, maintain the stirring speed at 150 - 450 rpm. Then perform pickling to remove the residual NaOH, and wash with deionized water several times until the solution is neutral. After vacuum drying, the NTO nanowires can be obtained.

[0056] The Ag nanoparticles are prepared by the following steps:

[0057] 11) Dissolve AgNO 3 in deionized water, add polyvinylpyrrolidone, and disperse evenly by ultrasonic treatment to obtain a mixed solution A;

[0058] 12) Dissolve NaOH and NaBH 4 in deionized water, and disperse evenly by ultrasonic treatment to obtain a mixed solution B;

[0059] 13) Place the mixed solution A in a constant temperature water bath and maintain a stirring speed of 300 - 500 rpm; slowly inject the mixed solution B into solution A. After the injection is complete, ultrasonically treat the resulting solution at room temperature, and then perform centrifugal washing with deionized water until the solution is neutral to obtain the Ag nanoparticles.

[0060] g-C 3 N 4 The g-C

[0061] nanosheets are prepared by the following steps: 2 H 4 N 4 powder into a crucible, place the crucible in a tube furnace, introduce nitrogen into the furnace, heat to 500 - 600 °C at a heating rate of 0.5 - 1.5 °C / min, and keep the temperature for 3 - 5 h. After the heat preservation is completed, let the tube furnace cool naturally, and then grind the calcined product to obtain g-C 3 N 4 nanosheets.

[0062] The present invention also discloses an NTO / Ag / g-C 3 N 4 multidimensional heterostructure catalyst film, which is prepared by vacuum filtration of an NTO / Ag / g-C 3 N 4 multidimensional heterostructure suspension. The thickness of the NTO / Ag / g-C 3 N 4 multidimensional heterostructure catalyst film is 50 - 100 μm.

[0063] The present invention also discloses an application of an NTO / Ag / g-C 3 N 4 multidimensional heterostructure catalyst film in photocatalytic hydrogen production.

[0064] Example 1

[0065] Prepare NTO nanowires by hydrothermal method. Weigh 12 g of NaOH with an electronic balance in a beaker, slowly add 30 ml of deionized water, and stir until completely dissolved to obtain a NaOH solution. Then weigh 0.2 g of TiO 2 powder and add it to the NaOH solution. Place the above solution on a magnetic stirrer and stir for 5 min to make it evenly dispersed. Put the mixed solution into a hydrothermal reactor for hydrothermal reaction, set the hydrothermal temperature at 130 °C, the hydrothermal time at 24 h, and the stirring speed at 300 rpm. After the reaction is completed, naturally cool it to room temperature, take out the reactor. The reaction product is a white flocculent mixture, and it can be preliminarily judged that linear structure substances are formed in the reaction. Wash the generated NTO nanowires with 0.1 mol / L dilute hydrochloric acid solution to remove the residual NaOH and stabilize the nanowire structure. Then use deionized water to repeatedly wash the product until the suspension is neutral, and then vacuum dry it for 12 h to obtain NTO nanowire powder.

[0066] The flocculent product prepared by the hydrothermal method forms a stable nanowire structure during the subsequent pickling treatment process. During the hydrothermal reaction process, the Ti-O-Ti bonds of TiO 2 are broken, and react with NaOH to form Ti-OH bonds and Ti-O-Na bonds. The Ti-O-Na bonds and Ti-OH bonds form new Ti-O-Ti bonds and form fragments during the pickling process. During the pickling process, the Ti-OH bonds form Ti-O-H-O-Ti or Ti-O-Ti bonds through dehydration reaction, so that the bond length between Ti and Ti on the surface becomes shorter. Finally, the Ti-OH fragments bend and connect with other fragments to form nanowires.

[0067] Perform scanning electron microscope observation on the raw material TiO 2 powder and the obtained NTO nanowires, as shown in Figure 4 and Figure 7 shown. AsFigure 4 and Figure 7 It can be seen that the morphology of TiO 2 is uniform-sized and well-dispersed nanoparticles with an average particle size of 13 nm. After the TiO 2 nanoparticles are hydrothermally reacted with a high-concentration NaOH solution for 24 h, NTO with an ultra-long nanowire structure is formed, with a diameter of 30 nm and a length exceeding 10 μm. The NTO nanowires are intertwined with each other like "fibers" and have good mechanical properties such as strength and toughness while having good catalytic performance, which is the basis for preparing the catalyst film.

[0068] Ag nanoparticles are prepared by a chemical reduction method. Weigh 340 mg of AgNO 3 and dissolve it in 10 mL of deionized water. Add an appropriate amount of polyvinylpyrrolidone (PVP), and ultrasonically disperse for 5 min to make the solution uniformly dispersed, obtaining a mixed solution A. Weigh 80 mg of NaOH and 18.9 mg of NaBH 4 and dissolve them in 10 mL of deionized water. After ultrasonically dispersing for 5 min, a mixed solution B is obtained. Subsequently, place the mixed solution A in a constant-temperature water bath at 45 °C and maintain a stirring speed of 400 rpm. Slowly inject 10 mL of the mixed solution B into the mixed solution A at a rate of 0.1 mL / min through a syringe pump. After the injection is completed, ultrasonically treat the obtained solution at room temperature for 1 h, and then perform centrifugal washing with deionized water. The centrifugal force is 800*10 rcf, and each washing is for 10 min. Repeat the above process until the solution is neutral. The obtained Ag nanoparticles are dispersed in deionized water for subsequent use.

[0069] In the above process, AgNO 3 provides Ag ions as raw materials. NaBH 4 acts as a reducing agent to reduce Ag ions to elemental silver, forming Ag nanoparticles. PVP is a protective agent that wraps on the surface of Ag nanoparticles to prevent them from combining with each other, thereby preventing the aggregation and precipitation of Ag nanoparticles.

[0070] The scanning electron microscope image of the Ag nanoparticles obtained by the chemical reduction method is as Figure 5 shown. It can be seen that the Ag nanoparticles have uniform sizes, good dispersibility, and an average grain size of 18 nm.

[0071] Graphitic carbon nitride (g-C 3 N 4 ) nanosheets are prepared by a calcination method. Weigh an appropriate amount of C 2 H 4 N 4The powder was placed in a crucible, and the crucible was placed in a tube furnace. Nitrogen was introduced into the furnace. The heating temperature was 550 °C, the heating rate was 1 °C / min, and the holding time was 4 h. After the holding was completed, the tube furnace was naturally cooled. Subsequently, the calcined product was ground to obtain g-C 3 N 4 nanosheet powder. Its scanning electron microscope image is as shown in Figure 6 It can be seen that the microstructure of the g-C 3 N 4 nanosheets prepared by the calcination method is an irregular cluster composed of many nanosheets with different orientations.

[0072] To solve the problem that NTO ultra-long nanowires are transformed into nanorods in the further hydrothermal reaction, in this example, a one-step hydrothermal method was used to prepare NTO / Ag / g-C 3 N 4 multidimensional heterostructure. The reaction process is as shown in Figure 1 It shows. 200 mg of NTO nanowires, 5 mg of g-C 3 N 4 nanosheets and 4 mg of Ag nanoparticles were added to the NaOH solution, and then placed in a hydrothermal environment at 130 °C for reaction for 24 h. The stirring speed was maintained at 300 rpm during the reaction process to obtain an NTO / Ag / g-C 3 N 4 multidimensional heterostructure suspension. The product obtained after the reaction was a flocculent linear structure. After the solution was naturally cooled, it was washed with dilute hydrochloric acid and deionized water until neutral. The washed solution was vacuum dried to obtain NTO / Ag / g-C 3 N 4 multidimensional heterostructure powder (Ag content is 2%). Its scanning electron microscope image is as shown in Figures 2-3 It shows. It can be seen that after the hydrothermal reaction and hydrochloric acid washing, the generated NTO / Ag / g-C 3 N 4 multidimensional heterostructure has an ultra-long nanowire structure. The length of the nanowires reaches the micron level and has obvious orientations. After loading Ag nanoparticles, NTO still maintains the nanowire structure. After the Ag nanoparticles are loaded on NTO, on the one hand, a Schottky barrier is formed, which can extend the light absorption range of NTO from the ultraviolet region to the visible region, greatly improving the utilization efficiency of sunlight. On the other hand, the Ag nanoparticles serve as electron capture centers, which can effectively separate photo-generated electrons and holes, prolong the lifetime of electrons, and give them more opportunities to participate in redox reactions. The Ag nanoparticles can also serve as electron transport channels to quickly transfer photo-generated electrons to the catalyst surface to react with the reactants adsorbed on the surface, improving the catalytic reaction rate. Through the surface modification of NTO nanowires by Ag nanoparticles, and the combination of NTO nanowires and g-C 3 N 4Heterojunctions formed by nanosheets can redistribute photo-generated carriers, inhibit the recombination of electrons and holes, and thus greatly improve the catalytic efficiency of the catalyst.

[0073] Example 2

[0074] The difference between this example and Example 1 is that the dosage of Ag nanoparticles in this example is 10 mg, and the rest is the same as in Example 1.

[0075] The NTO / Ag / g-C obtained in this example 3 N 4 The scanning electron microscopy image of the multi-dimensional heterostructure (Ag content is 5%) is as Figure 8 shown. It can be seen that its microstructure is basically the same as that of the NTO / Ag / g-C 3 N 4 multi-dimensional heterostructure in Example 1, and the basic structure is NTO ultra-long nanowires.

[0076] Example 3

[0077] Open the suction filter cup, place the filter paper and then tighten it again. Slowly pour the NTO / Ag / g-C 3 N 4 multi-dimensional heterostructure suspension into the suction filter cup, turn on the vacuum pump to start suction filtration until there is no excess liquid flowing out, turn off the vacuum pump, and obtain an NTO / Ag / g-C 3 N 4 multi-dimensional heterostructure catalyst film with a thickness of 50 μm. Its thickness is relatively uniform, and the surface of the film is a flocculent fluff structure, presumably caused by the irregular entanglement of NTO nanowires, as Figure 9 shown.

[0078] After the NTO / Ag / g-C 3 N 4 multi-dimensional heterostructure catalyst film is treated with liquid nitrogen freezing and then placed in a freeze-dryer for 24 h. The shape of the dried sample is well maintained without warping or cracking. When the sample is removed from the filter paper, there is no tearing or damage, indicating that the sample is well combined, has sufficient strength and toughness, and can maintain a good self-supporting film state. The scanning electron microscopy image of the dried sample of the NTO / Ag / g-C 3 N 4 multi-dimensional heterostructure catalyst film is as Figure 10 shown. It can be seen that there is a disordered and cross-linked nanowire structure. Scanning electron microscopy observation of the longitudinal section of the sample film, as Figure 11 shown, shows that the catalyst film has a multi-layer fibrous structure in the thickness direction. This is because the NTO / Ag / g-C 3 N 4The length of the ternary composite nanowires can reach the micron level, and the catalyst film obtained after suction filtration is a nanofiber multi-layer film structure formed by the intersection of ultra-long nanowires.

[0079] Prepare the simulated seawater according to the following ratio: NaCl (27.21 g / L), MgCl 2 (3.81 g / L), MgSO 4 (1.66 g / L), CaSO 4 (1.404 g / L), K 2 SO 4 (0.577 g / L), K 2 CO 3 (0.2124 g / L) and MgBr 2 (0.08 g / L). The salinity of the prepared simulated seawater is 34.95‰, which is similar to the average salinity of the global seawater (about 35‰).

[0080] Use a xenon lamp to simulate the solar light source. As the core light source in the simulated sunlight device, the xenon lamp emits light by generating an arc through the ionization of high-pressure xenon gas. Its spectral range is wide, covering multiple bands from ultraviolet light to infrared light, and has a high similarity with the spectral characteristics of sunlight. The xenon lamp also has the characteristics of high brightness and high color temperature, and can produce bright light close to natural sunlight. This enables it to provide sufficient light intensity when simulating sunlight while maintaining a color temperature similar to natural sunlight.

[0081] The visible-light photocatalytic cracking of simulated seawater to produce hydrogen experiment is carried out in a quartz photoreactor. The photoreactor is connected to a closed gas circulation system. The xenon lamp is placed above the quartz reactor, and a filter with λ≥420 nm is loaded on the xenon lamp. Therefore, the transmitted light is mainly visible light. During the experiment, circulating water is connected to keep the reactor at room temperature throughout the reaction process. The gas in the reactor is sampled and tested every 30 minutes using a gas chromatograph. The visible-light photocatalytic cracking of simulated seawater to produce hydrogen system used in this example is obtained commercially.

[0082] Carry out the simulated seawater cracking to produce hydrogen experiment on the NTO / Ag / g-C 3 N 4 multi-dimensional heterostructure catalyst film. During the experiment, Na 2 S·9H 2 O and Na 2 SO 3As sacrificial agents, sacrificial agents play an important role in the photocatalytic reaction of seawater splitting to produce hydrogen. They promote the photocatalytic hydrogen production reaction by providing electron donors, consuming holes, improving hydrogen production efficiency, stabilizing photocatalysts, and adjusting the reaction environment. During the experiment, nitrogen was first introduced into the system for 30 minutes under dark conditions to remove the dissolved oxygen in the solution and the mixed gas in the reactor. Then the hydrogen production experiment began.

[0083] Comparative Example 1

[0084] The difference between this comparative example and Example 1 is that this comparative example adopts a two-step method. 12g NaOH is weighed in a beaker using an electronic balance, 30ml deionized water is slowly added, and stirred until completely dissolved to obtain a NaOH solution. Then 0.2g TiO 2 The powder and 4 mL of Ag nanoparticles were added to the NaOH solution, and the solution was placed on a magnetic stirrer and stirred for 5 minutes to make it evenly dispersed. The mixed solution was then placed in a reactor for hydrothermal reaction, and the hydrothermal temperature was set to 130°C, the hydrothermal time was set to 24 hours, and the stirring speed was set to 300 rpm. After the reaction was completed, it was naturally cooled to room temperature, and the reactor was taken out to obtain brown NTO / Ag powder, the scanning electron microscope image of which is shown in the figure. Figure 12 As shown, it can be seen that the NTO after loading with Ag still maintains a nanowire structure, and the curling and winding of the nanowire is more obvious, and the Ag nanoparticles are uniformly attached to the NTO nanowire. The parameters of the entire reaction process are the same as those of Example 1.

[0085] Take 30 mg of prepared NTO / Ag powder and 5 mg of gC 3 N 4 The nanosheets were placed in a beaker, deionized water was added, the solution volume was kept at 30 mL, and the solution was fully stirred. The mixed solution was placed in a hydrothermal kettle for hydrothermal reaction, the hydrothermal temperature was 130 ° C, the reaction time was 24 h, and the magnetic stirring speed was maintained at 300 rpm. The solid product after the water bath reaction was dispersed particles. After cooling, the product was centrifuged and washed with deionized water until neutral, a part of it was placed in a vacuum drying oven for 12 h, and TiO was obtained by grinding. 2 / Ag / gC 3 N 4 The powder, the scanning electron microscope photo is as follows Figure 13 As shown in the figure, it can be seen that the NTO / Ag binary composite material is prepared first and then gC is added. 3 N 4 Preparation of TiO 2 / Ag / gC 3 N 4 The original NTO ultra-long nanowire structure disappears in the ternary composite material, and the microscopic morphology is a uniformly dispersed flake gC 3 N4 is loaded with a large number of rod-shaped TiO 2 / Ag particles, which may be because after adding g-C 3 N 4 , during the hydrothermal treatment process, the NTO nanowires hydrolyze and transform into short rod-shaped TiO 2 .

[0086] The rest is the same as in Example 1.

[0087] Comparative Example 2

[0088] The difference between this comparative example and Example 1 is that this comparative example conducts a simulated seawater splitting hydrogen production experiment on the TiO 2 / Ag / g-C 3 N 4 powder obtained in Comparative Example 1. The rest is the same as in Example 1.

[0089] Comparative Example 3

[0090] The difference between this comparative example and Example 3 is that this comparative example conducts a simulated seawater splitting hydrogen production experiment on the NTO / Ag / g-C 3 N 4 powder after drying the NTO / Ag / g-C 3 N 4 multidimensional heterostructure catalyst film. The rest is the same as in Example 1.

[0091] The hydrogen production efficiencies of Example 1 and Comparative Examples 1-2 are as Figure 14 shown. Hydrogen production was detected in Example 1 and Comparative Examples 1-2. Among them, the hydrogen production efficiency of the powdered catalyst is generally higher than that of the film catalyst, which may be because the powdered catalyst is uniformly dispersed in seawater and can be fully dispersed in the simulated seawater to achieve the best catalytic effect. However, when using the powdered catalyst, the catalyst is uniformly dispersed in seawater, which is likely to cause secondary pollution. When using the powdered catalyst, the hydrogen production amount basically shows a linear growth over time. The hydrogen production amount per hour of the TiO 2 / Ag / g-C 3 N 4 powder is about 365 μmol / g, and the catalytic hydrogen production efficiency of the NTO / Ag / g-C 3 N 4 multidimensional heterostructure catalyst film is about 660 μmol / g, which is much higher than the hydrogen production efficiency of the TiO 2 / Ag / g-C 3 N 4 powder, which may be because the one-dimensional ultra-long nanowire structure of NTO is more conducive to the effective separation and rapid transfer of photo-generated carriers. Using NTO / Ag / g-C 3 N 4When the catalyst film acts as a catalyst, the hydrogen production amount in the first hour is about 225 μmol / g, the hydrogen production amount in the second hour is about 240 μmol / g, and the hydrogen production amount in the third hour has a relatively large increase compared with the previous two hours, about 395 μmol / g. As the simulated seawater cracking time progresses, the hydrogen production efficiency of the catalyst becomes higher and higher. This may be because as the reaction proceeds, the catalyst film fully adsorbs seawater, and more catalysts participate in the cracking of seawater to produce hydrogen, resulting in an increase in the hydrogen production amount. After 3 hours of reaction, NTO / Ag / g-C 3 N 4 The catalyst film is taken out from the simulated seawater, and its shape remains good. At the same time, the simulated seawater remains clean, and no suspended particles are seen. It can be seen that after 3 hours of catalytic reaction, the catalyst film does not decompose, thus ensuring that the catalyst can be recycled and ensuring that no secondary pollution will be caused.

[0092] The hydrogen production efficiency of Example 1-2 is as Figure 15 shown, and NTO / Ag(5%) / g-C 3 N 4 has significantly better catalytic performance than NTO / Ag(2%) / g-C 3 N 4 samples. Hydrogen production is significantly detected half an hour after the start of the experiment. The cumulative hydrogen production amounts at 1h, 2h, and 3h are 858.6, 2161.5, and 3504 μmol / g respectively, which are much higher than the hydrogen production amounts of NTO / Ag(2%) / g-C 3 N 4 samples. This is mainly because the addition of Ag ions is beneficial to the separation of photogenerated carriers in NTO, reducing the recombination of surface photogenerated electrons and holes, so that more electrons and holes can participate in the redox reaction. At the same time, Ag ions can also improve the visible light absorption ability of NTO, thereby improving its photocatalytic activity. The addition of more Ag ions further improves the catalytic ability of the catalyst.

[0093] The UV-visible diffuse reflectance spectra of NTO, NTO / Ag, g-C 3 N 4 , TiO 2 / Ag / g-C 3 N 4 , NTO / Ag / g-C 3 N 4 are as Figure 16As shown, it can be seen that NTO only shows obvious absorption to ultraviolet light (λ<400nm) and little absorption to visible light. NTO / Ag after adding Ag nanoparticles can not only absorb ultraviolet light, but also shows certain absorption to visible light in the wavelength range of 400 - 700nm. Among them, the absorption ability to visible light in the wavelength range of 400 - 500nm is relatively strong. This may be because of the surface plasmon resonance effect of Ag nanoparticles, which causes visible light to be strongly absorbed on the surface of Ag nanoparticles. g-C 3 N 4 shows strong absorption ability to both ultraviolet light and visible light, especially shows obvious absorption characteristics to light with a wavelength of 250 - 600nm. TiO 2 / Ag / g-C 3 N 4 and NTO / Ag / g-C 3 N 4 both show obvious absorption to visible light. Compared with pure NTO and NTO / Ag, TiO 2 / Ag / g-C 3 N 4 and NTO / Ag / g-C 3 N 4 have improved absorption ability to both ultraviolet light and visible light, especially greatly improved the absorption ability to visible light in the wavelength range of 400 - 750nm. It can be seen that the combination of NTO / Ag and g-C 3 N 4 can effectively improve the absorption ability of the composite material to visible light, thereby improving its photocatalytic efficiency. Comparing TiO 2 / Ag / g-C 3 N 4 with NTO / Ag / g-C 3 N 4 , NTO / Ag / g-C 3 N 4 shows better light absorption ability, which is mainly attributed to the special linear structure of NTO resulting in a larger specific surface area, which can increase the area of light absorption. At the same time, the surface of one-dimensional NTO contains more defect structures such as vacancies, and these defects can serve as trapping centers for photo-generated electron-hole pairs, improving the light absorption efficiency. NTO / Ag / g-C 3 N 4 shows the best visible light absorption ability and excellent optoelectronic properties, and it can be predicted that it has the optimal photocatalytic performance and the ability to split water to produce hydrogen.

[0094] For parts or structures not specifically described in the present invention, existing technologies or existing products can be adopted, and no further elaboration will be made here.

[0095] The above are only embodiments of the present invention, and thus do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the content of the specification of the present invention, or directly or indirectly applied in other related technical fields, shall similarly be included within the patent protection scope of the present invention.

Claims

1. A NTO / Ag / g-C3N4 multidimensional heterostructure, characterized in that: The invention comprises NTO nanowires, Ag nanoparticles and g-C3N4 nanosheets, wherein the Ag nanoparticles are modified on the surface of the NTO nanowires, and the NTO nanowires and the g-C3N4 nanosheets form a heterojunction.

2. The NTO / Ag / g-C3N4 multidimensional heterostructure according to claim 1, characterized in that: The diameter of the NTO nanowire is 30-50 nm and the length is more than 10 μm.

3. The NTO / Ag / g-C3N4 multidimensional heterostructure according to claim 1, characterized in that: The particle size of the Ag nanoparticles is 10-20 nm.

4. A method for preparing a NTO / Ag / g-C3N4 multidimensional heterostructure according to any one of claims 1 to 3, characterized in that: The following steps are involved: 1) Prepare NTO nanowires, Ag nanoparticles and g-C3N4 nanosheets respectively; 2) Add the NTO nanowires, Ag nanoparticles and g-C3N4 nanosheets obtained in step 1) into a NaOH solution, react at 100-150°C for 20-30h, and maintain a stirring speed of 150-450rpm during the reaction to obtain the desired NTO / Ag / g-C3N4 multidimensional heterogeneous structure.

5. The method for preparing a NTO / Ag / g-C3N4 multidimensional heterostructure according to claim 4, characterized in that: The NTO nanowires are prepared by the following steps: Add TiO2 powder to NaOH solution, stir evenly, react at 100-150°C for 20-30h, maintain a stirring speed of 150-450rpm during the reaction, then acid wash to remove residual NaOH, and then wash with deionized water several times until the solution is neutral. After vacuum drying, NTO nanowires can be obtained.

6. The method for preparing a NTO / Ag / g-C3N4 multidimensional heterostructure according to claim 4, characterized in that: The Ag nanoparticles are prepared by the following steps: 11) dissolving AgNO3 in deionized water, adding polyvinyl pyrrolidone, and uniformly dispersing by ultrasonication to obtain a mixed solution A; 12) dissolving NaOH and NaBH4 in deionized water, and uniformly dispersing by ultrasonication to obtain a mixed solution B; 13) Place the mixed solution A in a constant temperature water bath and maintain a stirring speed of 300-500 rpm; slowly inject the mixed solution B into the solution A. After the injection is completed, ultrasonicate the resulting solution at room temperature, and then centrifuge and wash with deionized water until the solution is neutral, thereby obtaining Ag nanoparticles.

7. The method for preparing a NTO / Ag / g-C3N4 multidimensional heterostructure according to claim 4, characterized in that: The g-C3N4 nanosheets are prepared by the following steps: Put C2H4N4 powder into a crucible, put the crucible into a tubular furnace, pass nitrogen into the furnace, heat to 500-600℃, with a heating rate of 0.5-1.5℃ / min and a holding time of 3-5h. After the holding is completed, the tubular furnace is naturally cooled, and then the calcined product is ground to obtain g-C3N4 nanosheets.

8. A NTO / Ag / g-C3N4 multi-dimensional heterogeneous structure catalyst membrane, characterized in that: The catalyst film is prepared by vacuum filtering a NTO / Ag / g-C3N4 multi-dimensional heterogeneous structure suspension, wherein the thickness of the NTO / Ag / g-C3N4 multi-dimensional heterogeneous structure catalyst film is 50-100 μm.

9. Application of a NTO / Ag / g-C3N4 multidimensional heterostructure catalyst film in photocatalytic hydrogen production.

10. The use of a NTO / Ag / g-C3N4 multi-dimensional heterogeneous structure catalyst film in photocatalytic hydrogen production according to claim 9, characterized in that: When the Ag content in the NTO / Ag / g-C3N4 multi-dimensional heterogeneous structure catalyst membrane is 5%, the cumulative hydrogen production in 1h, 2h and 3h is 858.6, 2161.5 and 3504 μmol / g respectively.

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