Gold palladium / titanium dioxide heterojunction nano material and application thereof

Abstract

The invention discloses a gold palladium / titanium dioxide heterojunction nano material and application thereof, and belongs to the technical field of nano material growth. The gold-palladium / titanium dioxide heterojunction nano material is composed of a core composed of gold-palladium bimetallic nano particles and a shell layer coated with titanium dioxide. The gold-palladium bimetallic nanoparticles are of a core-shell structure formed by a gold core and a palladium shell. According to the gold-palladium / titanium dioxide heterojunction nano material, the photocatalytic performance of the material on specific target pollutants is improved by utilizing a gold core electronic effect, a gold-palladium interface effect and a core-shell type gold-palladium and titanium dioxide heterojunction structure; the photocatalytic effect of the gold palladium / titanium dioxide heterojunction nano material on methylene blue, methyl orange, salicylic acid, tetracycline hydrochloride and the like is promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of nano material growth, and in particular relates to a gold-palladium / titanium dioxide heterojunction nano material and an application thereof. Background Art

[0002] 4-Nitrophenol (4-NP) is not only a common nitro-based water pollutant, but also a toxic biodegradable pollutant that poses a great threat to the ecological environment and human health. Precious metal nanomaterials have attracted widespread attention in many fields due to their unique optical, electrical, and catalytic properties. Among them, nanocatalytic structural materials containing precious metals such as gold and palladium have been studied in many aspects. Methylene blue is a phenothiazine salt that has important applications in the treatment of cyanide poisoning and metabolic acidosis, as well as in the treatment of fish diseases in aquaculture. In addition, methylene blue is also a typical polluting dye in wastewater from the printing and dyeing industry. Dyes such as methylene blue discharged into water bodies have certain harmful effects on the ecological environment and human health. It is of great research value to study green and environmentally friendly photocatalytic technology to treat dyes such as methylene blue. Tetracycline hydrochloride (TH) has good water solubility and is easily discharged into the environment through feces and urine, which can easily cause pollution to water bodies and soil. Microbial degradation, physical ultrasonic degradation, and photocatalytic degradation are the main research methods at present. However, conventional semiconductor photocatalysts often have problems such as wide band gap, low light energy utilization and poor catalytic performance. Therefore, the research of environmentally friendly composite photocatalysts containing precious metal nanostructures with high light energy utilization and high degradation efficiency is the current focus of research and development.

[0003] Patent CN104492431B discloses a method for preparing Au-Pd / TiO2 NBs photocatalyst, which uses Au-Pd bimetallic modification to enhance the photocatalytic performance of TiO2 photocatalysis and improve the removal rate of rhodamine B. However, since the structures of 4-nitrophenol and tetracycline hydrochloride are different from those of rhodamine B, the degradation effect of 4-nitrophenol and tetracycline hydrochloride is not significantly improved. Therefore, the present invention explores a catalyst that can effectively improve the degradation effect of methylene blue and tetracycline hydrochloride. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the present invention provides a gold-palladium / titanium dioxide heterojunction nanomaterial.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A gold-palladium / titanium dioxide heterojunction nanomaterial, comprising a core composed of gold-palladium bimetallic nanoparticles and a shell layer coated with titanium dioxide; the gold-palladium bimetallic nanoparticles are a core-shell structure formed by a gold core and a palladium shell;

[0007] The preparation method of the gold-palladium / titanium dioxide heterojunction nanomaterial comprises the following steps:

[0008] (1) adding chloroauric acid solution to water and stirring, then adding sodium citrate solution to obtain gold seeds; adding tris(hydroxymethylaminomethane) solution to water, then adding gold seeds and HAuCl4 solution to water while stirring, and refluxing and stirring to obtain a colloidal solution of gold nanosphere particles with larger particle size and more uniform growth;

[0009] (2) adding the colloidal solution containing gold nanosphere particles to a hexadecyltrimethylammonium chloride solution, and then adding a sodium chloropalladate solution and an ascorbic acid solution for a water bath reaction. After the water bath is completed, repeating the steps of adding the sodium chloropalladate solution and the ascorbic acid solution for a water bath reaction 0-6 times to promote the uniform coating of the palladium shell layer on the surface of the nano-gold particles and to promote the improvement of the monodispersity of the gold-palladium bimetallic nanoparticles, thereby obtaining a colloidal solution of gold-palladium bimetallic nanosphere particles;

[0010] (3) The gold-palladium bimetallic nanosphere particles obtained by centrifugation of the colloidal solution of the gold-palladium bimetallic nanosphere particles are placed in isopropanol, and then glacial acetic acid and tetraisopropyl titanate are added and stirred, and finally water is added to react, and the gold-palladium / titanium dioxide heterojunction nanomaterial is obtained by centrifugation, washing and separation.

[0011] The gold-palladium / titanium dioxide heterojunction nanomaterial of the present invention comprises a core composed of gold-palladium bimetallic nanoparticles and a shell layer coated with titanium dioxide; the gold-palladium bimetallic nanoparticles are a core-shell structure formed by a gold core and a palladium shell, so that not only the monodispersity of the gold-palladium noble metal is improved, but also the photocatalytic performance is improved. The traditional composite structure photocatalyst formed by using semiconductor materials such as titanium dioxide as carriers to load precious metal gold-palladium, on the one hand, is difficult to uniformly adhere to the surface of the titanium dioxide carrier, or the morphology and size distribution of the attached gold-palladium nanoparticles are wide, and it is difficult to control and adjust the performance of the photocatalyst. On the other hand, the precious metal material on the composite nanostructure is often easy to fall off, and it is difficult to ensure the stability and cost-effectiveness of the application performance of the composite nanostructure. Most importantly, the size and morphology of the gold-palladium core structure in the gold-palladium / titanium dioxide heterojunction nanomaterial prepared by the present invention are uniformly distributed, and a gold-palladium alloy interface layer is included. This structure can significantly promote the heterogeneous catalytic hydrogenation of 4-nitrophenol by the gold-palladium bimetallic nanostructure. The gold palladium / titanium dioxide heterojunction nanomaterial prepared with the gold palladium bimetallic nanostructure as the core can also bring into play the wide spectrum absorption of the noble metal to visible light, and promote the photocatalytic effect of the outer shell titanium dioxide. And the prepared gold palladium / titanium dioxide heterojunction nanomaterial utilizes the gold palladium alloy interface effect and the inner core gold palladium and the excellent conduction and separation electron and hole ability of the heterojunction, so as to bring into play efficient photocatalytic effect, and cooperates with the surface performance of the gold palladium / titanium dioxide heterojunction nanomaterial of the present invention to realize the effective photocatalytic degradation of target pollutants methylene blue and tetracycline hydrochloride. However, the traditional composite structure photocatalyst formed by the semiconductor materials such as titanium dioxide as carrier to load the noble metal gold palladium does not have the gold palladium alloy interface effect and the inner core gold palladium effect, and only the composite structure can be obtained, and the heterojunction structure cannot be obtained, and the removal effect of the target pollutants methylene blue and tetracycline hydrochloride is not ideal.

[0012] In addition, the present invention does not adopt the nanostructure formed by the palladium core and gold shell layer in the prior art, mainly because the gold-palladium bimetallic core-shell structure in the present invention needs to form a heterojunction with titanium dioxide, but the gold-palladium bimetallic core-shell structure with the palladium core and gold shell layer is often difficult to exert the core electron effect of gold, the gold-palladium interface effect and the high catalytic performance of palladium, and because the energy band structure of the prepared material does not match, a suitable heterojunction structure cannot be obtained, and thus the target pollutants cannot be effectively removed. In the present invention, the use of gold nanospheres as the core can not only make up for the above shortcomings, but also realize the preparation of core-shell gold-palladium bimetallic nanoparticles with uniform size and morphology.

[0013] As a preferred embodiment of the present invention, the volume ratio of the chloroauric acid solution to the sodium citrate solution is 0.5:(0.5-2.5); the molar concentration of the chloroauric acid solution is 25×10 -3mol / L, the mass fraction of sodium citrate in the sodium citrate solution is 1%.

[0014] As a preferred embodiment of the present invention, the volume ratio of the tris(hydroxymethyl)aminomethane solution, the gold seed and the HAuCl4 solution is 2:(0.01-3):(0.1-1); the molar concentration of the tris(hydroxymethyl)aminomethane solution is 0.1 mol / L, and the molar concentration of the HAuCl4 solution is 25×10 -3 mol / L.

[0015] By adding different volumes of gold seeds, gold-palladium bimetallic structures of different thicknesses and sizes can be obtained, which makes it possible to maximize the core electronic effect of gold and the gold-palladium interface effect, and also ensures that the outer shell layer of titanium dioxide can be smoothly coated on the surface of the gold-palladium bimetallic.

[0016] As a preferred embodiment of the present invention, the volume ratio of the gold nanosphere particle solution, the hexadecyltrimethylammonium chloride solution, the sodium chloropalladate solution and the ascorbic acid solution is (0.1-2): (1-5): 0.026: 0.013; the molar concentration of the hexadecyltrimethylammonium chloride solution is 25×10 -3 mol / L, and its main function is to promote the dispersion of gold nanosphere particles to ensure that the palladium layer is smoothly coated on its surface, and to prevent the palladium layer from independently nucleating to form a separate palladium ball structure. The molar concentration of the sodium chloropalladate solution is 0.01 mol / L, and the molar concentration of the ascorbic acid solution is 0.1 mol / L.

[0017] As a preferred embodiment of the present invention, the temperature of the water bath reaction is 50° C. and the time is 30 min.

[0018] As a preferred embodiment of the present invention, the volume ratio of the gold-palladium bimetallic nanosphere particle solution, isopropyl alcohol, glacial acetic acid, tetraisopropyl titanate and water is (1-5): (0.2-1): (0.02-0.1): (0.0001-0.0025): (1-10).

[0019] As a preferred embodiment of the present invention, in the step (3), after adding glacial acetic acid and tetraisopropyl titanate, stirring is carried out at room temperature for 30 minutes, and after adding ultrapure water, stirring is carried out at room temperature for 8 hours.

[0020] As a preferred embodiment of the present invention, in the step (3), the reaction temperature is 70° C. and the reaction time is 48 hours.

[0021] As a preferred embodiment of the present invention, the gold-palladium / titanium dioxide heterojunction nanomaterial is spherical in shape and has a size of 80-150 nm.

[0022] As a preferred embodiment of the present invention, the gold-palladium / titanium dioxide heterojunction nanomaterial is used in removing organic pollutants, and the organic pollutants are methylene blue and / or tetracycline hydrochloride.

[0023] Compared with the prior art, the invention has the following beneficial effects: the gold-palladium / titanium dioxide heterojunction nanomaterial of the invention is composed of a core composed of gold-palladium bimetallic nanoparticles and a shell layer coated with titanium dioxide; the gold-palladium bimetallic nanoparticles are a core-shell structure formed by a gold core and a palladium shell. The gold inner core electron effect, the gold-palladium interface effect, and the core-shell type gold-palladium and titanium dioxide heterojunction structure are utilized to improve the photocatalytic performance of the material to specific target pollutants, and promote the photocatalytic effect of the gold-palladium / titanium dioxide heterojunction nanomaterial to methylene blue and tetracycline hydrochloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a schematic diagram of the preparation process of the gold-palladium / titanium dioxide heterojunction nanomaterial.

[0025] Figure 2 TEM images of the gold nanosphere particles and gold-palladium bimetallic nanosphere particles prepared in Examples 1-3 of the present invention; (a) is the gold nanosphere particles prepared in Example 1; (b) is the gold nanosphere particles prepared in Example 2; (c) is the gold nanosphere particles prepared in Example 3; (d) is the gold-palladium bimetallic nanosphere particles prepared in Example 1; (e) is the gold-palladium bimetallic nanosphere particles prepared in Example 2; (f) is the gold-palladium bimetallic nanosphere particles prepared in Example 3.

[0026] Figure 3 Element mapping, XPS and XRD diagrams of the gold-palladium bimetallic nanosphere particles prepared in Example 1; (a) is the element mapping diagram, (b) is the XPS diagram, and (c) is the XRD diagram.

[0027] Figure 4 TEM images and element distribution maps of the core-shell gold palladium / titanium dioxide heterojunction nanoparticles prepared in Example 1; (a) is a TEM image; (b) is a HAADF-STEM image; (c)-(f) are element mapping images of gold (Au), palladium (Pd), oxygen (O), and titanium (Ti), respectively; g is a nested image of gold (Au), palladium (Pd), oxygen (O) and titanium (Ti) elements; (h) is an EDS image of each element of the core-shell gold palladium / titanium dioxide heterojunction nanoparticles.

[0028] Figure 5Photos of colloidal solutions and UV-vis spectra of core-shell gold-palladium bimetallic colloidal nanoparticle materials prepared in Examples 1 and 4-6: (a) is a photo of the colloidal solution, (b) is a UV-vis spectra, where iv are actual photos of the solutions after gold nanoparticles and palladium coating 1, 3, 5 and 7 times, respectively.

[0029] Figure 6 Figure 3 is a diagram of the catalytic degradation process of 4-nitrophenol by the gold nanosphere particles and core-shell gold-palladium bimetallic colloidal nanoparticle materials prepared in Examples 1 and 4-6; (a) is the gold nanosphere particles, (b) is the gold-palladium bimetallic nanoparticles coated with palladium once, (c) is the catalytic effect diagram of the gold-palladium bimetallic nanoparticles with different palladium coating times, (d) is the catalytic process diagram of 50 microliters of gold-palladium bimetallic nanoparticles coated with palladium five times, (e) is the catalytic process diagram of 100 microliters of gold-palladium bimetallic nanoparticles coated with palladium five times, and (f) is the catalytic effect diagram of different amounts of gold-palladium bimetallic nanoparticles coated with palladium five times.

[0030] Figure 7 The diagram shows the photocatalytic effect of the gold-palladium bimetallic nanosphere particles and the core-shell gold-palladium / titanium dioxide heterojunction nanoparticles prepared in Example 1 of the present invention on methylene blue; (a) is the gold-palladium bimetallic nanosphere particles, (b) is the gold-palladium / titanium dioxide heterojunction nanoparticles, and (c) is a physical picture of the colors of methylene blue at different times under the catalysis of the core-shell gold-palladium / titanium dioxide heterojunction nanostructure prepared in Example 1.

[0031] Figure 8 The photocatalytic effect diagram of the core-shell gold palladium / titanium dioxide heterojunction nanoparticles prepared in Example 1 of the present invention on methyl orange (MO), salicylic acid (SA) and tetracycline hydrochloride (TH); (a) is methyl orange (MO), (b) is salicylic acid (SA), and (c) is tetracycline hydrochloride (TH). DETAILED DESCRIPTION

[0032] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0033] Example 1

[0034] like Figure 1 As shown, a method for preparing a gold-palladium / titanium dioxide heterojunction nanomaterial comprises the following steps:

[0035] (1) Take 0.5 mL of a 25×10 -3mol / L chloroauric acid solution was added to 48 mL boiling water and boiled for 10 minutes. Under vigorous stirring, 1.5 mL of 1% sodium citrate solution was quickly injected into it. The color of the reaction solution changed from yellow to blue-gray and then to ruby. The gold seed was obtained by stirring and reflux for 30 minutes. In addition, 2 mL of 0.1 mol / L tris(hydroxymethyl)aminomethane (TB) solution was added to 47 mL boiling water under stirring. After boiling and stirring for 5 minutes, 0.5 mL of the above gold seed and 0.5 mL of 25×10 -3 mol / L HAuCl4 solution, stirred and refluxed for 30 minutes, so that the gold seeds grew again to obtain the desired gold nanosphere particles (AuNPs) (the morphology of the nanogold is as follows Figure 2 (a) shows that the gold nanoparticles obtained after growth are relatively regular spherical in shape and have a size of 64.11±3.21 nm. The obtained colloidal solution containing gold nanosphere particles (AuNPs) can be further used as seeds to prepare gold-palladium bimetallic nanoparticles.

[0036] (2) 2 mL of the grown gold nanosphere solution was added to 3 mL of a 25×10 -3 mol / L hexadecyltrimethylammonium chloride solution, and then add 26μL of 0.01mol / L Na2PdCl4 solution and 13μL of 0.1mol / L ascorbic acid solution in sequence, and let it react in a 50℃ water bath for 30 minutes. After the water bath ends, a gold-palladium bimetallic nanosphere particle solution (Au@Pd NPs) with a repeated growth can be obtained.

[0037] like Figure 3 As shown, Figure 3 a element mapping shows that the prepared gold-palladium bimetallic nanosphere particles are composed of a core-shell structure consisting of a gold core and a palladium layer. Figure 3 The XPS image in b shows that the gold-palladium bimetallic nanosphere particles are mainly composed of gold and palladium atoms. Figure 5 a is the XRD pattern of gold-palladium bimetallic nanosphere particles.

[0038] (3) After centrifugation of 3 mL of colloidal solution containing gold-palladium bimetallic nanosphere particles, gold-palladium bimetallic nanosphere particles were obtained, and the thickness of the palladium layer was about 14.15 nm (morphology as shown in FIG. Figure 2 (d) shows that the elemental analysis is as follows Figure 3 The mixture was placed in 0.6 mL of isopropanol, and then 60 μL of glacial acetic acid and 2.5 μL of tetraisopropyl titanate were added and stirred at room temperature for 30 minutes. Finally, 2.5 mL of ultrapure water was added and stirred at room temperature for 8 hours, and then placed in a drying oven at 70°C for 2 days. The solution changed from gray-brown to light gray. The solution was washed and separated twice with a liquid mixture of water: ethanol in a ratio of 1:1 to obtain a gold-palladium / titanium dioxide heterojunction nanomaterial solution.

[0039] like Figure 4 The morphological characteristics of the AuPd / TiO2 heterojunction nanomaterials shown in the figure. Figure 4 The morphology and elemental composition of the gold-palladium / titanium dioxide heterojunction nanomaterial are shown, wherein the core is a gold-palladium bimetallic nanoparticle and the shell is a titanium dioxide coating layer. Therefore, the gold-palladium bimetallic nanoparticle is a core-shell structure formed by a gold core and a palladium shell. The gold-palladium / titanium dioxide heterojunction nanomaterial is a core-shell structure formed by a gold-palladium bimetallic core and a titanium dioxide outer shell.

[0040] Example 2

[0041] The only difference between the preparation method of gold-palladium / titanium dioxide heterojunction nanomaterials described in this embodiment and that in embodiment 1 is that in step (1), the volume of the gold seed is 0.1 mL. The morphology of the gold nanosphere particles in the obtained gold nanosphere particle solution is as follows: Figure 2 (b), Au-Pd bimetallic nanosphere particles such as Figure 2 (e) Due to the reduction in the volume of the added gold seeds, the size of the prepared growing gold nanospheres increased to 95.24±6.71nm. The size of the gold-palladium nanoparticles was about 119.11nm, and the thickness of the palladium nanolayer was 23.87nm.

[0042] Example 3

[0043] The only difference between the preparation method of gold-palladium / titanium dioxide heterojunction nanomaterials described in this example and that in Example 1 is that in step (1), the volume of the gold seed is 0.05 mL. The morphology of the gold nanosphere particles in the obtained gold nanosphere particle solution is as follows: Figure 2 (c), Au-Pd bimetallic nanosphere particles such as Figure 2 (f). As the volume of the gold nanoparticles further decreased, the gold nanoparticles grew to 139.22±9.24nm. The size of the gold-palladium nanoparticles was 166.23nm, and the thickness of the palladium nanolayer was 27.01nm. This shows that the size of the prepared gold nanoparticles can be well adjusted by changing the volume of the added gold seeds. Moreover, due to the different sizes of the growing gold nanoparticles, the thickness of the palladium layer coated on their surface is also significantly different.

[0044] Example 4

[0045] The only difference between the preparation method of gold-palladium / titanium dioxide heterojunction nanomaterials described in this embodiment and that in embodiment 1 is that in step (2), 26 μL of 0.01 mol / L Na2PdCl4 solution and 13 μL of 0.1 mol / L ascorbic acid solution are added repeatedly, and the reaction is allowed to stand in a 30°C water bath for 100 minutes twice. Thus, gold-palladium bimetallic nanosphere particles grown three times can be obtained. The UV-visible spectrum of the colloidal solution containing gold-palladium bimetallic particles and the actual color diagram are shown in FIG. Figure 5 As shown in bc.

[0046] Example 5

[0047] The only difference between the preparation method of gold-palladium / titanium dioxide heterojunction nanomaterials described in this embodiment and that in embodiment 1 is that in step (2), 26 μL of 0.01 mol / L Na2PdCl4 solution and 13 μL of 0.1 mol / L ascorbic acid solution are repeatedly added, and the reaction is allowed to stand in an 80°C water bath for 10 minutes for 4 times. Gold-palladium bimetallic nanosphere particles that have been grown 5 times can be obtained. The UV-visible spectrum of the colloidal solution containing gold-palladium bimetallic nanosphere particles and the actual color diagram are shown in FIG. Figure 5 As shown in bc.

[0048] Example 6

[0049] The only difference between the preparation method of gold-palladium / titanium dioxide heterojunction nanomaterials described in this embodiment and that in embodiment 1 is that in step (2), 26 μL of 0.01 mol / L Na2PdCl4 solution and 13 μL of 0.1 mol / L ascorbic acid solution are added repeatedly, and the reaction is allowed to stand in a 50°C water bath for 30 minutes for 6 times. Gold-palladium bimetallic nanosphere particles grown 7 times can be obtained. The UV-visible spectrum of the colloidal solution containing gold-palladium bimetallic nanosphere particles and the actual color diagram are shown in FIG. Figure 5 As shown in bc.

[0050] Example 7

[0051] The only difference between the preparation method of gold-palladium / titanium dioxide heterojunction nanomaterials described in this embodiment and that in embodiment 1 is that in step (1), the volume of the sodium citrate solution is 2.5 ml; the volume of the tris(hydroxymethyl)aminomethane (TB) solution with a concentration of 0.1 mol / L is 2 mL; the volume of the gold seed is 0.01 mL; and the volume of the HAuCl4 solution is 1 mL;

[0052] In the step (2), the volume of the gold nanosphere particle solution is 0.1 mL, and the volume of the hexadecyltrimethylammonium chloride solution is 5 mL;

[0053] In the step (3), 1 mL of the colloidal solution containing gold-palladium bimetallic nanosphere particles is centrifuged to obtain gold-palladium bimetallic nanosphere particles, which are placed in 1 mL of isopropanol, and then 20 μL of glacial acetic acid and 0.1 μL of tetraisopropyl titanate are added and stirred at room temperature for 20 minutes. Finally, 1 mL of ultrapure water is added and stirred at room temperature for 5 hours, and then placed in a drying oven at 70° C. for 2 days, the solution changes from gray-brown to light gray, and is washed and separated twice using a liquid with a water:ethanol ratio of 1:1 to obtain a gold-palladium / titanium dioxide heterojunction nanomaterial solution.

[0054] Example 8

[0055] The only difference between the preparation method of gold-palladium / titanium dioxide heterojunction nanomaterials described in this embodiment and that in embodiment 1 is that in step (1), the volume of the sodium citrate solution is 0.5 ml; the volume of the tris(hydroxymethyl)aminomethane (TB) solution with a concentration of 0.1 mol / L is 2 mL, the volume of the gold seed is 3 mL, and the volume of the HAuCl4 solution is 0.1 mL;

[0056] In the step (2), the volume of the gold nanosphere particle solution is 2 mL, and the volume of the hexadecyltrimethylammonium chloride solution is 1 mL;

[0057] In the step (3), 5 mL of the colloidal solution containing gold-palladium bimetallic nanosphere particles is centrifuged to obtain gold-palladium bimetallic nanosphere particles, which are placed in 0.2 mL of isopropanol, and then 100 μL of glacial acetic acid and 2.5 μL of tetraisopropyl titanate are added and stirred at room temperature for 60 minutes. Finally, 10 mL of ultrapure water is added and stirred at room temperature for 12 hours, and then placed in a drying oven at 70° C. for 2 days, the solution changes from gray-brown to light gray, and is washed and separated twice with a liquid having a water:ethanol ratio of 1:1 to obtain a gold-palladium / titanium dioxide heterojunction nanomaterial solution.

[0058] Effect Example 1

[0059] 0.04 mL of 0.01 mol / L 4-NP solution was added to a 1 cm thick quartz cuvette, and 1.96 mL of ultrapure water and 0.8 mL of 0.1 mol / L NaBH4 solution were added. The solution turned light yellow, and the concentration ratio of 4-NP to NaBH4 in the solution was 1:200. Then, 50 microliters of the gold nanoparticles in Example 1 and the gold-palladium bimetallic nanoparticle solution prepared in Example 1-6 were added respectively, and the instrument cover was closed to complete the heterogeneous catalytic reaction under the condition of no light. The measurement wavelength range of UV-vis is 250-500 nm, and the conversion rate of 4-NP to 4-AP is understood by monitoring the absorption peak intensity.

[0060] The conversion rate of AuNPs particles prepared in Example 1 from 4-NP to 4-AP is 54%, and the catalytic time is as high as 22.5 minutes. The conversion rate of core-shell gold-palladium bimetallic nano-spherical particles prepared in Example 1 from 4-NP to 4-AP is 80% within the same time. The conversion rate of core-shell gold-palladium bimetallic nano-spherical particles prepared in Examples 2-8 from 4-NP to 4-AP can reach 100% within 15 minutes.

[0061] like Figure 6 As shown in the figure, the surface coating of palladium significantly improves the catalytic effect of single metal gold nanoparticles on the hydrogenation reduction of 4-nitrophenol ( Figure 6 ac). In Examples 1-3, as the particle size of the nano-gold particles increases, their catalytic ability tends to decrease as the particle size increases. In the present invention, with the coating of different palladium layers, significant core-shell gold-palladium bimetallic nano-spherical particles are formed. Among them, after coating with 5 palladium layers, the core-shell gold-palladium bimetallic nano-spherical particles have the best catalytic effect ( Figure 6 c) TEM, XPS and UV-vis characterizations show that the nanostructure achieves the best gold core electron effect and gold-palladium interface effect, thereby promoting the improvement of catalytic activity. Figure 6 df is a diagram comparing the catalytic process and catalytic effect of core-shell gold-palladium bimetallic nanosphere particles on 4-NP with different dosages. It can be seen that with the increase in the dosage of the catalyst, its catalytic activity is significantly enhanced.

[0062] Effect Example 2

[0063] Under light-proof conditions, add a certain amount of NaOH solution (mainly for adjusting pH value) and methylene blue, methyl orange, salicylic acid or tetracycline hydrochloride test solution to a transparent glass vial, add the prepared gold palladium / titanium dioxide heterojunction nanomaterial, and stir to mix. Place the glass vial under a simulated sunlight xenon lamp to irradiate the mixed liquid evenly. Take out 150 μL of solution from the vial every 5 minutes and drop it into a quartz cell cuvette with a length of 1 cm. Use an ultraviolet visible spectrophotometer (UV-vis) to detect the changes in the absorption peaks of the test substances, and obtain the degradation rates of gold palladium / titanium dioxide heterojunction nanomaterials for methylene blue, methyl orange, salicylic acid and tetracycline hydrochloride, as shown in Figure 2. Figure 7-8 .

[0064] Figure 7 The gold-palladium bimetallic nanosphere particles (Au@PdNPs) in Example 1 ( Figure 7 a) and AuPd / TiO2 heterojunction nanomaterials ( Figure 7b) Photocatalytic process of methylene blue. It can be clearly seen from the figure that by coating the surface of the gold-palladium bimetallic nanosphere particles with a thin titanium dioxide layer, its photocatalytic activity is significantly improved. The photocatalytic effect on methylene blue is manifested as an increase from a conversion rate of less than 50% in 50 minutes to a catalytic effect of 94.5% in only 30 minutes. And compared with pure titanium dioxide, the effect of the gold-palladium / titanium dioxide heterojunction nanomaterial prepared by the present invention on methylene blue is also significantly improved. This shows that the gold-palladium / titanium dioxide heterojunction nanomaterial prepared by the present invention, in which the surface of the gold-palladium core-shell bimetallic nanosphere particles is coated with titanium dioxide, improves the photocatalytic performance of the material on methylene blue by utilizing the gold inner core electron effect, the gold-palladium interface effect, and the heterojunction structure of the core-shell type gold-palladium and titanium dioxide. Figure 7 c It can be seen that after the gold palladium / titanium dioxide heterojunction nanomaterial prepared in the present invention photocatalyzes methylene blue, the color of methylene blue gradually fades at 0, 15 and 30 minutes, further indicating that methylene blue is decomposed.

[0065] However, not all photocatalytic materials can degrade methylene blue and tetracycline hydrochloride for target pollutants, which mainly depends on the structure and surface properties of the photocatalytic materials. Figure 8 It can be seen that the structure and surface properties of the photocatalytic material determine that the gold palladium / titanium dioxide heterojunction nanomaterial of the present invention has good photocatalytic performance for methylene blue and tetracycline hydrochloride, and the degradation rate of tetracycline hydrochloride within 5 minutes reaches 100%, and the degradation rate of methylene blue within 30 minutes reaches more than 94.5%, but its degradation rate for methyl orange and salicylic acid is very poor, which can only reach 11% and 18% respectively. The gold palladium / titanium dioxide heterojunction nanomaterial prepared in Example 2-8 has a degradation rate of more than 94% for methylene blue; the degradation rate for tetracycline hydrochloride reaches 100%, but the degradation rate for methyl orange and salicylic acid can only reach less than 20%.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A gold-palladium / titanium dioxide heterojunction nanomaterial, characterized in that: It comprises a core composed of gold-palladium bimetallic nanoparticles and a shell layer coated with titanium dioxide; the gold-palladium bimetallic nanoparticles are a core-shell structure formed by a gold core and a palladium shell; The preparation method of the gold-palladium / titanium dioxide heterojunction nanomaterial comprises the following steps: (1) adding chloroauric acid solution to water and stirring, then adding sodium citrate solution to obtain gold seeds; adding tris(hydroxymethylaminomethane) solution to water, then adding gold seeds and HAuCl4 solution while stirring, reflux and stir to obtain a colloidal solution containing gold nanosphere particles; (2) adding the colloidal solution containing gold nanosphere particles to a hexadecyltrimethylammonium chloride solution, and then adding a sodium chloropalladate solution and an ascorbic acid solution to carry out a water bath reaction; after the water bath is completed, repeating the steps of adding the sodium chloropalladate solution and the ascorbic acid solution to carry out a water bath reaction to obtain a colloidal solution containing gold-palladium bimetallic nanosphere particles; (3) The gold-palladium bimetallic nanosphere particles obtained by centrifugation of a colloidal solution containing gold-palladium bimetallic nanosphere particles are placed in isopropanol, and then glacial acetic acid and tetraisopropyl titanate are added and stirred, and finally water is added to react, centrifuged for washing and separation, and dried to obtain a gold-palladium / titanium dioxide heterojunction nanomaterial.

2. The gold-palladium / titanium dioxide heterojunction nanomaterial according to claim 1, characterized in that: The volume ratio of the chloroauric acid solution to the sodium citrate solution is 0.5:(0.5-2.5); the molar concentration of the chloroauric acid solution is 25×10 -3 mol / L, the mass fraction of sodium citrate in the sodium citrate solution is 1%.

3. The gold-palladium / titanium dioxide heterojunction nanomaterial according to claim 1, characterized in that: The volume ratio of the tris(hydroxymethyl)aminomethane solution, the gold seeds and the HAuCl4 solution is 2:(0.01-3):(0.1-1); the molar concentration of the tris(hydroxymethyl)aminomethane solution is 0.1 mol / L, and the molar concentration of the HAuCl4 solution is 25×10 -3 mol / L.

4. The gold-palladium / titanium dioxide heterojunction nanomaterial according to claim 1, characterized in that: The volume ratio of the gold nanosphere particle solution, the hexadecyltrimethylammonium chloride solution, the sodium chloropalladate solution and the ascorbic acid solution is (0.1-2):(1-5):0.026:0.013; the molar concentration of the hexadecyltrimethylammonium chloride solution is 25×10 -3 mol / L, the molar concentration of the sodium chloropalladate solution is 0.01 mol / L, and the molar concentration of the ascorbic acid solution is 0.1 mol / L.

5. The gold-palladium / titanium dioxide heterojunction nanomaterial according to claim 1, characterized in that: The temperature of the water bath reaction is 30-80°C and the reaction time is 10-100 minutes.

6. The gold-palladium / titanium dioxide heterojunction nanomaterial according to claim 1, characterized in that: In the step (2), the number of times of repeatedly adding the sodium chloropalladate solution and the ascorbic acid solution to carry out the water bath reaction step is 0-6.

7. The gold-palladium / titanium dioxide heterojunction nanomaterial according to claim 1, characterized in that: The volume ratio of the gold-palladium bimetallic nanosphere particle solution, isopropanol, glacial acetic acid, tetraisopropyl titanate and water is (1-5): (0.2-1): (0.02-0.1): (0.0001-0.0025): (1-10).

8. The gold-palladium / titanium dioxide heterojunction nanomaterial according to claim 1, characterized in that: In the step (3), glacial acetic acid and tetraisopropyl titanate are added and stirred for 20-60 minutes, and water is added and stirred for reaction for 5-12 hours. The reaction temperature is 60-80° C. and the reaction time is 24-168 hours.

9. The gold-palladium / titanium dioxide heterojunction nanomaterial according to claim 1, characterized in that: The gold-palladium / titanium dioxide heterojunction nanomaterial is spherical or quasi-spherical, and has a size of 80-150 nm.

10. The use of the gold-palladium / titanium dioxide heterojunction nanomaterial in removing organic pollutants according to any one of claims 1 to 8, characterized in that: The organic pollutants are methylene blue and / or tetracycline hydrochloride.

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