Polyelectrolyte multilayer film loaded gold-palladium bimetallic nanoparticle catalyst and application thereof in degradation of p-nitrophenol

Abstract

The invention discloses a polyelectrolyte multilayer film loaded gold-palladium bimetallic nanoparticle catalyst, which is characterized in that cationic polyelectrolyte poly (diallyldimethylammonium chloride) PDDA and anionic polyelectrolyte sodium polystyrenesulfonate (PSS) are used as construction materials, a layer-by-layer self-assembly technology is adopted to prepare a polyelectrolyte multilayer film, and the polyelectrolyte multilayer film is marked as (PDDA / PSS) n + 0.5, and firstly loading gold nanoparticles on the multilayer film through an ion exchange-in-situ reduction method, and then loading palladium nanoparticles on the multilayer film to obtain the catalyst (PDDA / PSS) (n + 0.5 / a) AubPd for catalyzing the degradation of p-nitrophenol. According to the polyelectrolyte multilayer film loaded gold-palladium bimetallic nanoparticle catalyst disclosed by the invention, by selecting and designing the material and the layer number of the multilayer film carrier and the proportion of gold and palladium bimetallic, the synergistic catalysis of the polyelectrolyte film and the gold-palladium bimetallic nanoparticles is exerted; the catalytic efficiency and the degradation effect of the catalyst in the p-nitrophenol degradation process are obviously improved.

Description

Technical Field

[0001] The present invention relates to the field of catalytic technology, specifically to a polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst, and the preparation of the catalyst and its application in the catalytic degradation of p-nitrophenol. Background Art

[0002] p-Nitrophenol (4-NP) is an important organic chemical raw material and product, widely used in the fields of pesticides, insecticides, dyes, etc. However, it is a toxic and harmful substance, and its chemical structure is stable, making it difficult to be biodegradable, which will cause environmental pollution. p-Nitrophenol has a certain water solubility and can enter water bodies through industrial wastewater discharge, landfill leachate and other channels, and accumulate in water bodies, threatening the survival and reproduction of aquatic organisms and possibly affecting the safety of drinking water sources. If industrial waste, pesticides containing p-nitrophenol and the like are not properly treated, they will seep into the soil, remain in the soil, affect the physical and chemical properties of the soil and the structure of the microbial community, inhibit the growth and development of plants, and may also cause harm to organisms at higher trophic levels through the transfer of the food chain.

[0003] Currently, the commonly used methods for treating 4-NP include physical adsorption, chemical treatment and biodegradation, etc. Physical adsorption usually uses adsorbents such as activated carbon and resin to adsorb and remove p-nitrophenol. Chemical treatment includes Fenton oxidation, photocatalytic oxidation, electrochemical oxidation, etc. Fenton oxidation is to use ferrous ions and hydrogen peroxide to react to generate hydroxyl radicals to oxidize and decompose p-nitrophenol into harmless substances such as carbon dioxide and water; photocatalytic oxidation is to use light energy to excite electron-hole pairs under the action of a photocatalyst, and then generate strongly oxidizing free radicals to degrade p-nitrophenol; electrochemical oxidation is to generate an oxidant through an electrode reaction or directly oxidize and degrade p-nitrophenol on the electrode surface. Biodegradation uses strains with the ability to degrade p-nitrophenol, so screening and culturing strains is the key.

[0004] Traditional methods such as physical adsorption and biodegradation often have problems such as low efficiency, high cost and secondary pollution. The catalytic oxidation-reduction technology of chemical treatment has become a research hotspot due to its high efficiency and greenness. Among them, noble metal nanocatalysts (such as Au, Ag, Pd, Pt) have been widely studied due to their high catalytic activity. However, the existing metal nanoparticles have the following problems: (1) High surface energy leads to easy aggregation and insufficient exposure of active sites; (2) Serious oxidation inactivation and poor stability during recycling. Therefore, in order to effectively degrade 4-NP and remove pollution, developing a catalyst with high activity and easy recycling and reuse is the current research focus. Summary of the Invention

[0005] To solve the problems of low degradation rate of p-nitrophenol, complex catalytic degradation operation and poor catalyst recycling in the existing technology, the present invention develops a polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst for catalyzing the degradation reaction of p-nitrophenol, which can simplify the reaction operation, facilitate the separation and recycling of the catalyst, and by selecting and designing the materials and number of layers of the multilayer film support to control the polyelectrolyte content, the synergistic catalytic effect of the polyelectrolyte film and the gold-palladium bimetallic nanoparticles is exerted, thereby significantly improving the catalytic efficiency and degradation effect of the catalyst in the degradation process of p-nitrophenol.

[0006] To achieve the above object, the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst provided by the present invention uses the cationic polyelectrolyte poly(diallyldimethylammonium chloride) PDDA and the anionic polyelectrolyte sodium polystyrene sulfonate PSS as building materials, and adopts the layer-by-layer self-assembly technology to prepare the polyelectrolyte multilayer film, denoted as (PDDA / PSS) n+0.5 , and then the gold nanoparticles are first loaded on the polyelectrolyte multilayer film by the ion exchange-in-situ reduction method, and then the palladium nanoparticles are loaded to obtain the catalyst (PDDA / PSS) n+0.5 / aAubPd for catalyzing the degradation of p-nitrophenol;

[0007] The (PDDA / PSS) n+0.5 represents that the outermost polyelectrolyte film is PDDA, and n represents a positive integer; the (PDDA / PSS) n+0.5 / aAubPd represents the amount of gold nanoparticles loaded on the (PDDA / PSS) n+0.5 polyelectrolyte film through a times of ion exchange-in-situ reduction operations, and b represents the amount of palladium nanoparticles loaded on the polyelectrolyte film (PDDA / PSS) n+0.5 / aAu that has already loaded gold nanoparticles through b times of ion exchange-in-situ reduction operations. Both a and b are positive integers.

[0008] The present invention uses the layer-by-layer self-assembly technology to prepare a polyelectrolyte multilayer film with the cationic polyelectrolyte PDDA and the anionic polyelectrolyte PSS as building materials, and then loads the gold-palladium bimetallic nanoparticles on the multilayer film successively. By designing the matching of the polyelectrolyte multilayer film materials, especially the outermost film material, and the gold-palladium bimetallic nanoparticles, the catalytic activity of the gold-palladium bimetallic nanoparticles is effectively dispersed and stabilized, while significantly improving the catalytic efficiency, simplifying the reaction operation, and facilitating the separation and recycling of the catalyst.

[0009] As a limitation to the above technical solution, on the prepared (PDDA / PSS) n+0.5 / aAubPd, the secondary deposition of the polyelectrolyte multilayer film is continued by the layer-by-layer self-assembly technology to obtain (PDDA / PSS) n+0.5 / aAubPd / (PSS / PDDA) m ; where m represents a natural number.

[0010] As a limitation of the above technical solution, n is preferably 1 to 5, a is preferably 1 to 4, and b is preferably 2 to 4; further preferably, a is 1 and b is 2.

[0011] As a limitation of the above technical solution, m is preferably 0 to 2, and further preferably 2.

[0012] As a limitation of the above technical solution, the layer-by-layer self-assembly technique is to soak the substrate successively in PDDA solution and PSS solution to prepare a layer of polyelectrolyte PDDA / PSS film, or successively soak it in PSS solution and PDDA solution to prepare a layer of polyelectrolyte PSS / PDDA film, and repeat multiple times to prepare a polyelectrolyte multilayer film with the required number of layers; where 0.5 represents preparing only one layer of PDDA film or one layer of PSS film.

[0013] To further optimize the catalytic performance of the catalyst, through secondary deposition of the polyelectrolyte multilayer film on the gold-palladium bimetallic nanoparticles, a synergistic catalytic effect is generated between the gold-palladium bimetallic nanoparticles and the multilayer film carrier, not only exerting the catalytic effect of the gold-palladium bimetallic nanoparticles, but also fully exerting the significant promoting effect of the polyelectrolyte on the catalytic reaction by virtue of the matching between the secondary deposition film, especially the outermost film material, and the gold-palladium bimetallic nanoparticles, greatly improving the catalytic reaction rate.

[0014] As a limitation of the above technical solution, the concentration of the PDDA solution is 0.1 to 10 mg / mL, the concentration of the PSS solution is 0.1 to 10 mg / mL, and the PDDA solution and the PSS solution also contain salts with a concentration of 0.01 to 5 mol / L. Common salts include NaCl, NaBr, etc.

[0015] Further improve the preparation conditions of the catalyst and optimize the activity and stability of the catalyst.

[0016] Meanwhile, the present invention provides a preparation method of the catalyst of the gold-palladium bimetallic nanoparticles supported on the polyelectrolyte multilayer film as described above, including the following steps:

[0017] a. Preparation of the polyelectrolyte multilayer film: Using the layer-by-layer self-assembly technique, soak the negatively charged substrate successively in the cationic polyelectrolyte PDDA solution and the anionic polyelectrolyte PSS solution, soak for 5 to 30 minutes each time, and wash off the excess polyelectrolyte solution with water after each soak to deposit the polyelectrolyte film, and repeat multiple times to prepare the polyelectrolyte multilayer film (PDDA / PSS) n+0.5 ;

[0018] Preferably, the substrate is selected as a quartz sheet or a glass sheet. The substrate is immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3 and heated at 80 °C to 100 °C for 1 to 2 hours to make the surface carry negative charges.

[0019] b. Preparation of polyelectrolyte multilayer film loaded with gold-palladium bimetallic nanoparticles

[0020] The substrate deposited with the polyelectrolyte multilayer film is immersed in a solution containing Au ions, and then immersed in a strong reducing solution to reduce the Au ions to gold nanoparticles, obtaining a polyelectrolyte multilayer film (PDDA / PSS) loaded with gold nanoparticles n+0.5 / 1Au;

[0021] The polyelectrolyte multilayer film (PDDA / PSS) n+0.5 / 1Au is immersed in a solution containing Au ions, and then immersed in a weak reducing agent, repeating a - 1 times, obtaining a polyelectrolyte multilayer film (PDDA / PSS) n+0.5 / aAu;

[0022] The polyelectrolyte multilayer film (PDDA / PSS) n+0.5 / aAu is immersed in a solution containing Pd ions, and then immersed in a weak reducing solution to reduce the Pd ions to palladium nanoparticles, repeating b times, obtaining a polyelectrolyte multilayer film (PDDA / PSS) loaded with gold-palladium bimetallic nanoparticles n+0.5 / aAubPd;

[0023] Preferably, the solution containing Au ions is selected as chloroauric acid (HAuCl4) solution, the solution containing Pd ions is selected as chloropalladic acid (H2PdCl4) solution, the strong reducing solution is selected as sodium borohydride (NaBH4) solution, and the weak reducing solution is selected as ascorbic acid (AA) solution.

[0024] As a limitation to the above technical solution, it further includes step c. On the prepared (PDDA / PSS) n+0.5 / aAubPd, the layer-by-layer self-assembly technology is used again. It is successively immersed in an anionic polyelectrolyte PSS solution and a cationic polyelectrolyte PDDA solution, each immersion for 5 to 30 minutes. After each immersion, the excess polyelectrolyte solution is washed off with water, and the polyelectrolyte film is deposited secondarily. Repeat multiple times to prepare (PDDA / PSS) n+0.5 / aAubPd / (PSS / PDDA) m catalyst.

[0025] The preparation of the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst of the present invention is simple and convenient. By combining the layer-by-layer self-assembly technique and the ion exchange-in-situ reduction method, a catalyst with high activity and high stability can be obtained, which is conducive to industrial preparation and application.

[0026] The present invention also provides the application of the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst as described above in the degradation of p-nitrophenol, which uses the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle as the catalyst for the p-nitrophenol degradation reaction.

[0027] As a limitation to the above technical solution, the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle is used as the catalyst for the reduction of p-nitrophenol by sodium borohydride degradation reaction. The number of repeated uses of this catalyst is not less than 5 times, and the recycling and reuse efficiency reaches more than 95%.

[0028] The polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst not only has a high efficiency in catalytically degrading p-nitrophenol, but also is convenient for recycling, separation and reuse, and has practical application prospects and value.

[0029] In summary, the present invention adopts the layer-by-layer self-assembly technique, uses the cationic polyelectrolyte PDDA and the anionic polyelectrolyte PSS as the building materials to prepare the polyelectrolyte multilayer film, and successively loads the gold-palladium bimetallic nanoparticles in the multilayer film. By selecting and designing the materials of the multilayer film carrier, controlling the number of layers to control the polyelectrolyte content, and controlling the matching of the outermost layer film material and the gold-palladium bimetallic nanoparticles, as well as the ratio of the two metals of gold and palladium, the bimetallic synergistic effect is achieved, so that the activity of the bimetallic particles is significantly improved compared with that of the single metal particles; in addition, the matching of the secondary deposited multilayer film and the gold-palladium nanoparticles is increased, so that the catalytic degradation effect of the gold-palladium bimetallic nanoparticles and the polyelectrolyte multilayer film carrier on 4-NP produces a synergistic effect again, further improving the degradation effect on 4-NP and realizing the rapid and efficient degradation treatment of 4-NP. In addition, the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticles of the present invention, used as a catalyst, also have the advantages of being conducive to separation, recovery and reuse, thereby enhancing the practical application value. Description of the Drawings

[0030] Figure 1 The ultraviolet-visible spectra of (PDDA / PSS) 3.5 / 1Au2Pd catalyzing the reduction of 4-NP by sodium borohydride at different times.

[0031] Figure 2, Absorbance change trend diagrams at different times of the sample of polyelectrolyte multilayer film - supported gold - palladium bimetallic nanoparticles prepared in Example 2 and the samples of polyelectrolyte multilayer film - supported gold nanoparticles and polyelectrolyte multilayer film - supported palladium nanoparticles prepared in Comparative Examples 1 and 2 for the reduction of 4 - NP by sodium borohydride.

[0032] Figure 3 , A is the absorbance change trend diagram at different times of the samples of polyelectrolyte multilayer film - supported gold - palladium bimetallic nanoparticles with different ion - exchange in - situ reduction times prepared in Examples 1 - 4 for the reduction of 4 - NP by sodium borohydride; B is the absorbance change trend diagram at different times of the samples of polyelectrolyte multilayer film - supported gold - palladium bimetallic nanoparticles with different ion - exchange in - situ reduction times prepared in Examples 1, 5 - 7 for the reduction of 4 - NP by sodium borohydride.

[0033] Figure 4 , Absorbance change trend diagram at different times of the sample of polyelectrolyte multilayer film - supported gold - palladium bimetallic nanoparticles prepared in Example 1 for the reduction of 4 - NP by sodium borohydride after being recycled 5 times.

[0034] Figure 5 , Absorbance change trend diagram at different times of the sample of polyelectrolyte multilayer film - supported gold nanoparticles prepared in Comparative Example 1 for the reduction of 4 - NP by sodium borohydride after being recycled 5 times.

[0035] Figure 6 , Absorbance change trend diagrams at different times of the samples of polyelectrolyte multilayer film - supported gold - palladium bimetallic nanoparticles prepared in Examples 1, 8 - 11 and Comparative Examples 3, 4 for the reduction of 4 - NP by sodium borohydride.

[0036] Figure 7 , Transmission electron microscope photograph of the sample of polyelectrolyte multilayer film - supported gold - palladium nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd prepared in Example 1.

[0037] Figure 8 , Line - scan diagram of the sample of polyelectrolyte multilayer film - supported gold - palladium nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd prepared in Example 1.

[0038] Figure 9 , Absorbance change trend diagrams at different times of the samples of polyelectrolyte multilayer film - supported gold - palladium bimetallic nanoparticles with different numbers of layers prepared in Examples 1, 12 - 15 for the reduction of 4 - NP by sodium borohydride.

[0039] Figure 10 , Absorbance change trend diagrams at different times of the samples of polyelectrolyte multilayer film - supported gold - palladium and palladium - gold bimetallic nanoparticles prepared in Example 1 and Comparative Example 5 for the reduction of 4 - NP by sodium borohydride. Detailed implementation manners

[0040] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0041] The experimental methods in the following embodiments and comparative examples are all conventional methods unless otherwise specified. The test materials used in the following embodiments are all obtained from regular reagent stores unless otherwise specified. The quantitative tests in the following embodiments are all set with three repeated experiments, and the results are averaged.

[0042] The following embodiments and comparative examples relate to the preparation of gold-palladium bimetallic nanoparticles and gold and palladium monometallic nanoparticles loaded on different polyelectrolyte multilayers and the polyelectrolyte multilayers.

[0043] Example 1

[0044] Preparation of gold-palladium bimetallic nanoparticles (PDDA / PSS) loaded on polyelectrolyte multilayers 3.5 / 1Au2Pd sample was prepared according to the following operations:

[0045] a. Using a glass slide as a substrate, it was placed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3 and heated at 90 °C for 1 hour to make the surface of the glass slide carry negative charges. The negatively charged glass slide was successively placed in PDDA solutions and PSS solutions with a concentration of 1 mg / mL, and each was soaked for 30 min. After each soaking, the excess solution was washed away with deionized water. This step was cycled 3.5 times, and the outermost layer was PDDA, and a (PDDA / PSS) 3.5 multilayer film was deposited on the glass slide.

[0046] b. The above-prepared (PDDA / PSS) 3.5 multilayer film was successively placed in a 1 mmol / L HAuCl4 solution and a 10 mmol / L NaBH4 solution, and each was soaked for 5 min. After each soaking, the excess solution was washed away with deionized water. The HAuCl4 solution and the NaBH4 solution were only soaked once, and finally dried with N2 to obtain polyelectrolyte multilayer-loaded gold nanoparticles (PDDA / PSS) 3.5 / 1Au sample.

[0047] c. The above-prepared (PDDA / PSS) 3.5The / 1Au sample was successively placed into 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution, and soaked for 5 min respectively. After each soaking, the excess solution was washed away with deionized water. Both the H2PdCl4 solution and the AA solution were soaked twice. Finally, it was dried with N2 to obtain polyelectrolyte multilayer film supported gold and palladium nanoparticles (PDDA / PSS). 3.5 / 1Au2Pd sample.

[0048] The amount of metal supported on the polyelectrolyte film is limited by the number of ion exchange-in-situ reduction operations because the amount of each reduction of the same metal is fixed. The solution with metal elements enters the film through ion exchange, and the amount of electric charge that the film can provide for ion exchange is fixed. Moreover, the electric charge will be released after each in-situ reduction. Therefore, the metal content of each ion exchange / in-situ reduction of the same metal is fixed. Even if the metal solution concentration is changed, the content of the supported metal nanoparticles will not be changed, but only the completion time of ion exchange will be changed. The higher the concentration, the shorter the ion exchange time.

[0049] When loading metal particles on the polyelectrolyte multilayer film, a strong reducing solution is required for the first ion exchange-in-situ reduction operation. The purpose is to ensure the rapid generation of well-dispersed and small-sized nanoparticles as seeds inside the film through strong reduction. When loading metal particles later, a weak reducing agent is needed to ensure that subsequent in-situ reduction can continue to load metal on the seeds, causing the seeds to grow.

[0050] Example 2

[0051] Polyelectrolyte multilayer film supported Au and Pd bimetallic particles (PDDA / PSS) 3.5 The preparation of the / 1Au1Pd sample was carried out according to the following operations:

[0052] a, b: The operations in steps a and b are the same as those in Example 1;

[0053] c. The prepared (PDDA / PSS) 3.5 The / 1Au sample was successively placed into 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution, and soaked for 5 min respectively. After each soaking, the excess solution was washed away with deionized water. Both the H2PdCl4 solution and the AA solution were soaked only once. Finally, it was dried with N2 to obtain polyelectrolyte multilayer film supported gold and palladium nanoparticles (PDDA / PSS). 3.5 / 1Au1Pd sample.

[0054] Example 3

[0055] Polyelectrolyte multilayer film supported Au and Pd bimetallic particles (PDDA / PSS) 3.5The preparation of the (PDDA / PSS) / 1Au3Pd sample was carried out as follows:

[0056] a, b: The operations in steps a and b are the same as those in Example 1;

[0057] c. The prepared (PDDA / PSS) / 1Au sample was successively placed into a 1 mmol / L H2PdCl4 solution and a 10 mmol / L AA solution, and soaked for 5 min respectively. After each soaking, the excess solution was washed away with deionized water. Both the H2PdCl4 solution and the AA solution were soaked 3 times. Finally, it was dried with N2 to obtain the polyelectrolyte multilayer film supported gold and palladium nanoparticles (PDDA / PSS) / 1Au3Pd sample. 3.5 3.5 sample.

[0058] Example 4

[0059] The preparation of the polyelectrolyte multilayer film supported Au and Pd bimetallic particles (PDDA / PSS) / 1Au4Pd sample was carried out as follows: 3.5

[0060] a, b: The operations in steps a and b are the same as those in Example 1;

[0061] c. The prepared (PDDA / PSS) / 1Au sample was successively placed into a 1 mmol / L H2PdCl4 solution and a 10 mmol / L AA solution, and soaked for 5 min respectively. After each soaking, the excess solution was washed away with deionized water. Both the H2PdCl4 solution and the AA solution were soaked 4 times. Finally, it was dried with N2 to obtain the polyelectrolyte multilayer film supported gold and palladium nanoparticles (PDDA / PSS) / 1Au4Pd sample. 3.5 3.5 sample.

[0062] Example 5

[0063] The preparation of the polyelectrolyte multilayer film supported Au and Pd bimetallic particles (PDDA / PSS) / 2Au2Pd sample was carried out as follows: 3.5

[0064] a, b: The operations in steps a and b are the same as those in Example 1;

[0065] c. The prepared (PDDA / PSS) / 1Au sample was successively placed into a 1 mmol / L HAuCl4 solution and a 10 mmol / L AA solution, and soaked for 5 min respectively. After each soaking, the excess solution was washed away with deionized water. Both the HAuCl4 solution and the AA solution were soaked only 1 time. Finally, it was dried with N2 to obtain the polyelectrolyte multilayer film supported gold nanoparticles (PDDA / PSS) / 1Au sample. 3.5 3.5 ​​​​​ / 2Au sample.

[0066] d. Put the prepared (PDDA / PSS) 3.5 / 2Au sample into 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution successively, soak for 5 min respectively each time. After each soaking, wash away the excess solution with deionized water. Both the H2PdCl4 solution and the AA solution are soaked twice. Finally, dry it with N2 to obtain polyelectrolyte multilayer film supported gold and palladium nanoparticles (PDDA / PSS) 3.5 / 2Au2Pd sample.

[0067] When loading gold nanoparticles on the polyelectrolyte multilayer film multiple times, a strong reducing solution is needed for the first time, and then a weak reducing agent is used to ensure that the seeds continue to grow on the in-situ reduced seeds in the first time.

[0068] Example 6

[0069] Polyelectrolyte multilayer film supported Au and Pd bimetallic particles (PDDA / PSS) 3.5 / 3Au2Pd sample is prepared according to the following operations:

[0070] a, b: The operations of steps a and b are the same as those in Example 1;

[0071] c. Put the prepared (PDDA / PSS) 3.5 / 1Au sample into 1 mmol / L HAuCl4 solution and 10 mmol / L AA solution successively, soak for 5 min respectively each time. After each soaking, wash away the excess solution with deionized water. Both the HAuCl4 solution and the AA solution are soaked twice. Finally, dry it with N2 to obtain polyelectrolyte multilayer film supported gold nanoparticles (PDDA / PSS) 3.5 / 3Au sample.

[0072] d. Put the prepared (PDDA / PSS) 3.5 / 3Au sample into 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution successively, soak for 5 min respectively each time. After each soaking, wash away the excess solution with deionized water. Both the H2PdCl4 solution and the AA solution are soaked twice. Finally, dry it with N2 to obtain polyelectrolyte multilayer film supported gold and palladium nanoparticles (PDDA / PSS) 3.5 / 3Au2Pd sample.

[0073] Example 7

[0074] Polyelectrolyte multilayer film supported Au and Pd bimetallic particles (PDDA / PSS) 3.5The preparation of the / 4Au2Pd sample is carried out according to the following operations:

[0075] a, b: The operations in steps a and b are the same as those in Example 1;

[0076] c. The prepared (PDDA / PSS) 3.5 / 1Au sample is successively placed into a 1 mmol / L HAuCl4 solution and a 10 mmol / L AA solution, and each is soaked for 5 min. After each soaking, the excess solution is washed away with deionized water. Both the HAuCl4 solution and the AA solution are soaked 3 times. Finally, after drying with N2, the polyelectrolyte multilayer film loaded with gold particles (PDDA / PSS) 3.5 / 4Au sample is obtained.

[0077] d. The prepared (PDDA / PSS) 3.5 / 3Au sample is successively placed into a 1 mmol / L H2PdCl4 solution and a 10 mmol / L AA solution, and each is soaked for 5 min. After each soaking, the excess solution is washed away with deionized water. Both the H2PdCl4 solution and the AA solution are soaked 2 times. Finally, after drying with N2, the polyelectrolyte multilayer film loaded with gold and palladium nanoparticles (PDDA / PSS) 3.5 / 4Au2Pd sample is obtained.

[0078] Example 8

[0079] The preparation of the polyelectrolyte multilayer film loaded with Au and Pd bimetallic particles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA)1 sample is carried out according to the following operations:

[0080] a, b, c: The operations in steps a, b, and c are the same as those in Example 1;

[0081] d. On the prepared (PDDA / PSS) 3.5 / 1Au2Pd, secondary deposition of the polyelectrolyte multilayer film is carried out. The (PDDA / PSS) 3.5 / 1Au2Pd is successively placed into a PSS solution and a PDDA solution with a concentration of 1 mg / mL each, and each is soaked for 30 min. After each soaking, the excess solution is washed away with deionized water. The outermost layer is a PDDA film, and the polyelectrolyte multilayer film loaded with gold and palladium nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA)1 sample is prepared.

[0082] Example 9

[0083] The preparation of the polyelectrolyte multilayer film loaded with Au and Pd bimetallic particles (PDDA / PSS) 3.5The preparation of the / 1Au2Pd / (PSS / PDDA)2 sample is carried out according to the following procedures:

[0084] a, b, c: The operations of steps a, b, and c are the same as those in Example 1;

[0085] d. Perform secondary deposition of the polyelectrolyte multilayer film on the prepared (PDDA / PSS) 3.5 / 1Au2Pd. Place the (PDDA / PSS) 3.5 / 1Au2Pd into PSS solution and PDDA solution with a concentration of 1 mg / mL respectively, soak for 30 min each time, and wash away the excess solution with deionized water after each soaking. Repeat this step 2 times. The outermost layer is the PDDA film, and the polyelectrolyte multilayer film loaded with gold and palladium nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA)2 sample is obtained.

[0086] Example 10

[0087] The preparation of the polyelectrolyte multilayer film loaded with Au and Pd bimetallic particles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA)3 sample is carried out according to the following procedures:

[0088] a, b, c: The operations of steps a, b, and c are the same as those in Example 1;

[0089] d. Perform secondary deposition of the polyelectrolyte multilayer film on the prepared (PDDA / PSS) 3.5 / 1Au2Pd. Place the (PDDA / PSS) 3.5 / 1Au2Pd into PSS solution and PDDA solution with a concentration of 1 mg / mL respectively, soak for 30 min each time, and wash away the excess solution with deionized water after each soaking. Repeat this step 3 times. The outermost layer is the PDDA film, and the polyelectrolyte multilayer film loaded with gold and palladium nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA)3 sample is obtained.

[0090] Example 11

[0091] The preparation of the polyelectrolyte multilayer film loaded with Au and Pd bimetallic particles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA)4 sample is carried out according to the following procedures:

[0092] a, b, c: The operations of steps a, b, and c are the same as those in Example 1;

[0093] d. Perform secondary deposition of the polyelectrolyte multilayer film on the prepared (PDDA / PSS) 3.5Secondary deposition of polyelectrolyte multilayers was carried out on / 1Au2Pd, and (PDDA / PSS) 3.5 / 1Au2Pd was successively and alternately immersed in PSS solution and PDDA solution with a concentration of 1 mg / mL for 30 min each. After each immersion, the excess solution was washed away with deionized water. This step was repeated 4 times. The outermost layer was the PDDA film, and polyelectrolyte multilayer-loaded gold and palladium nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA)4 sample was prepared.

[0094] Example 12

[0095] Preparation of polyelectrolyte multilayer-loaded Au and Pd bimetallic particles (PDDA / PSS) 1.5 / 1Au2Pd sample was prepared according to the following procedures:

[0096] a. Using a glass slide as a substrate, it was placed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3 and heated at 90 °C for 1 hour to make the surface of the glass slide carry negative charges. The negatively charged glass slide was successively immersed in PDDA solution and PSS solution with a concentration of 1 mg / mL for 30 min each. After each immersion, the excess solution was washed away with deionized water. This step was repeated 1.5 times. The outermost layer was PDDA, and (PDDA / PSS) 1.5 multilayers were deposited on the glass slide.

[0097] b. The prepared (PDDA / PSS) 1.5 multilayers were successively immersed in 1 mmol / L HAuCl4 solution and 10 mmol / L NaBH4 solution for 5 min each. After each immersion, the excess solution was washed away with deionized water. The HAuCl4 solution and NaBH4 solution were only immersed once. Finally, it was dried with N2 to obtain polyelectrolyte multilayer-loaded gold nanoparticles (PDDA / PSS) 1.5 / 1Au sample.

[0098] c. The prepared (PDDA / PSS) 1.5 / 1Au sample was successively immersed in 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution for 5 min each. After each immersion, the excess solution was washed away with deionized water. The H2PdCl4 solution and AA solution were immersed 2 times. Finally, it was dried with N2 to obtain polyelectrolyte multilayer-loaded gold and palladium nanoparticles (PDDA / PSS) 1.5 / 1Au2Pd sample.

[0099] Example 13

[0100] Polyelectrolyte multilayer film supported Au and Pd bimetallic particles (PDDA / PSS) 2.5 The preparation of the / 1Au2Pd sample is carried out according to the following procedures:

[0101] a. Using a glass slide as the substrate, it is placed into a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3, and heated at 90 °C for 1 hour to make the surface of the glass slide carry negative charges. The negatively charged glass slide is successively placed into PDDA solutions and PSS solutions with a concentration of 1 mg / mL respectively, and each is soaked for 30 min. After each soaking, the excess solution is washed away with deionized water. This step is repeated 2.5 times. The outermost layer is PDDA, and the (PDDA / PSS) 2.5 multilayer film is deposited on the glass slide.

[0102] b. The prepared (PDDA / PSS) 2.5 multilayer film is successively placed into 1 mmol / L HAuCl4 solution and 10 mmol / L NaBH4 solution, and each is soaked for 5 min. After each soaking, the excess solution is washed away with deionized water. The HAuCl4 solution and the NaBH4 solution are each soaked only once. Finally, it is dried with N2 to obtain the polyelectrolyte multilayer film supported gold nanoparticles (PDDA / PSS) 2.5 / 1Au sample.

[0103] c. The prepared (PDDA / PSS) 2.5 / 1Au sample is successively placed into 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution, and each is soaked for 5 min. After each soaking, the excess solution is washed away with deionized water. The H2PdCl4 solution and the AA solution are each soaked 2 times. Finally, it is dried with N2 to obtain the polyelectrolyte multilayer film supported gold and palladium nanoparticles (PDDA / PSS) 2.5 / 1Au2Pd sample.

[0104] Example 14

[0105] Polyelectrolyte multilayer film supported Au and Pd bimetallic particles (PDDA / PSS) 4.5 The preparation of the / 1Au2Pd sample is carried out according to the following procedures:

[0106] a. Using a glass slide as the substrate, it is placed into a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3, and heated at 90 °C for 1 hour to make the surface of the glass slide carry negative charges. The negatively charged glass slide is successively placed into PDDA solutions and PSS solutions with a concentration of 1 mg / mL respectively, and each is soaked for 30 min. After each soaking, the excess solution is washed away with deionized water. This step is repeated 4.5 times. The outermost layer is PDDA, and the (PDDA / PSS)4.5 Multilayer film.

[0107] b. Sequentially immerse the prepared (PDDA / PSS) 4.5 multilayer film into 1 mmol / L HAuCl4 solution and 10 mmol / L NaBH4 solution, each for 5 min. After each immersion, wash away the excess solution with deionized water. Both the HAuCl4 solution and the NaBH4 solution are only immersed once. Finally, dry it with N2 to obtain the polyelectrolyte multilayer film loaded with gold nanoparticles (PDDA / PSS) 4.5 / 1Au sample.

[0108] c. Sequentially immerse the prepared (PDDA / PSS) 4.5 / 1Au sample into 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution, each for 5 min. After each immersion, wash away the excess solution with deionized water. Both the H2PdCl4 solution and the AA solution are immersed twice. Finally, dry it with N2 to obtain the polyelectrolyte multilayer film loaded with gold and palladium nanoparticles (PDDA / PSS) 4.5 / 1Au2Pd sample.

[0109] Example 15

[0110] Polyelectrolyte multilayer film loaded with Au and Pd bimetallic particles (PDDA / PSS) 5.5 The preparation of the / 1Au2Pd sample is carried out according to the following operations:

[0111] a. Use a glass slide as the substrate and place it into a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3. Heat at 90 °C for 1 hour to make the surface of the glass slide carry negative charges. Sequentially immerse the negatively charged glass slide into PDDA solution and PSS solution with a concentration of 1 mg / mL each, for 30 min each. After each immersion, wash away the excess solution with deionized water. Repeat this step 5.5 times. The outermost layer is PDDA, and deposit the (PDDA / PSS) 5.5 multilayer film on the glass slide.

[0112] b. Sequentially immerse the prepared (PDDA / PSS) 5.5 multilayer film into 1 mmol / L HAuCl4 solution and 10 mmol / L NaBH4 solution, each for 5 min. After each immersion, wash away the excess solution with deionized water. Both the HAuCl4 solution and the NaBH4 solution are only immersed once. Finally, dry it with N2 to obtain the polyelectrolyte multilayer film loaded with gold nanoparticles (PDDA / PSS) 5.5 / 1Au sample.

[0113] c. Place the prepared (PDDA / PSS) 5.5 / 1Au sample into 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution successively, and soak for 5 min respectively. After each soaking, wash away the excess solution with deionized water. Both the H2PdCl4 solution and the AA solution are soaked twice. Finally, dry with N2 to obtain polyelectrolyte multilayer film supported gold and palladium nanoparticles (PDDA / PSS) 5.5 / 1Au2Pd sample.

[0114] Comparative Example 1

[0115] Preparation of polyelectrolyte multilayer film supported Au nanoparticles (PDDA / PSS) 3.5 / 1Au sample is prepared according to the following operations:

[0116] a. The operation in step a is the same as that in Example 1;

[0117] b. Place the prepared (PDDA / PSS) 3.5 multilayer film into 1 mmol / L HAuCl4 solution and 10 mmol / L NaBH4 solution successively, and soak for 5 min respectively. After each soaking, wash away the excess solution with deionized water. Both the HAuCl4 solution and the NaBH4 solution are soaked only once. Finally, dry with N2 to obtain polyelectrolyte multilayer film supported gold nanoparticles (PDDA / PSS) 3.5 / 1Au sample.

[0118] Comparative Example 2

[0119] Preparation of polyelectrolyte multilayer film supported Pd nanoparticles (PDDA / PSS) 3.5 / 1Pd sample is prepared according to the following operations:

[0120] a. The operation in step a is the same as that in Example 1;

[0121] b. Place the prepared (PDDA / PSS) 3.5 multilayer film into 1 mmol / L H2PdCl4 solution and 10 mmol / L NaBH4 solution successively, and soak for 5 min respectively. After each soaking, wash away the excess solution with deionized water. Both the H2PdCl4 solution and the NaBH4 solution are soaked only once. Finally, dry with N2 to obtain polyelectrolyte multilayer film supported palladium nanoparticles (PDDA / PSS) 3.5 / 1Pd sample.

[0122] Comparative Example 3

[0123] Preparation of polyelectrolyte multilayer film supported Au and Pd bimetallic nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA) 1.5 The preparation of the sample is carried out according to the following operations:

[0124] a, b, c: The operations of steps a, b, and c are the same as those in Example 1;

[0125] d. Perform secondary deposition of the polyelectrolyte multilayer film on the prepared (PDDA / PSS) 3.5 / 1Au2Pd. Put (PDDA / PSS) 3.5 / 1Au2Pd into PSS solution and PDDA solution with a concentration of 1 mg / mL respectively, soak for 30 min each time, and wash away the excess solution with deionized water after each soaking. Repeat this step 1.5 times. The outermost layer is the PSS film, and the polyelectrolyte multilayer film loaded with gold and palladium nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA) 1.5 sample is obtained.

[0126] Comparative Example 4

[0127] The preparation of the polyelectrolyte multilayer film loaded with Au and Pd bimetallic particles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA) 2.5 sample is carried out according to the following operations:

[0128] a, b, c: The operations of steps a, b, and c are the same as those in Example 1;

[0129] d. Perform secondary deposition of the polyelectrolyte multilayer film on the prepared (PDDA / PSS) 3.5 / 1Au2Pd. Put (PDDA / PSS) 3.5 / 1Au2Pd into PSS solution and PDDA solution with a concentration of 1 mg / mL respectively, soak for 30 min each time, and wash away the excess solution with deionized water after each soaking. Repeat this step 2.5 times. The outermost layer is the PSS film, and the polyelectrolyte multilayer film loaded with gold and palladium nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd / (PSS / PDDA) 2.5 sample is obtained.

[0130] Comparative Example 5

[0131] The preparation of the polyelectrolyte multilayer film loaded with Pd and Au bimetallic particles (PDDA / PSS) 3.5 / 2Pd1Au sample is carried out according to the following operations:

[0132] a. The operation of step a is the same as that in Example 1;

[0133] b. Immerse the prepared (PDDA / PSS) multilayers prepared above 3.5 into 1 mmol / L H2PdCl4 solution and 10 mmol / L NaBH4 solution successively, each for 5 minutes. After each immersion, wash away the excess solution with deionized water. Both the H2PdCl4 solution and the NaBH4 solution are only immersed once. Finally, dry with N2 to obtain polyelectrolyte multilayer-supported palladium nanoparticles (PDDA / PSS) 3.5 / 1Pd sample.

[0134] c. Immerse the prepared (PDDA / PSS) 3.5 / 1Pd sample into 1 mmol / L H2PdCl4 solution and 10 mmol / L AA solution successively, each for 5 minutes. After each immersion, wash away the excess solution with deionized water. Both the H2PdCl4 solution and the AA solution are immersed once. Finally, dry with N2 to obtain polyelectrolyte multilayer-supported palladium nanoparticles (PDDA / PSS) 3.5 / 2Pd sample.

[0135] d. Immerse the prepared (PDDA / PSS) 3.5 / 2Pd sample into 1 mmol / L HAuCl4 solution and 10 mmol / L AA solution successively, each for 5 minutes. After each immersion, wash away the excess solution with deionized water. Both the HAuCl4 solution and the AA solution are immersed once. Finally, dry with N2 to obtain polyelectrolyte multilayer-supported palladium and gold nanoparticles (PDDA / PSS) 3.5 / 2Pd1Au sample.

[0136] Note: In the above Examples 2-15 and Comparative Examples 1-5, the PDDA solution and the PSS solution used both contain 1.5 mol / L sodium chloride. Besides the glass slides provided in the examples, quartz slides can also be used as the substrates.

[0137] Example 1 is a polyelectrolyte multilayer-supported Au and Pd bimetallic nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd sample.

[0138] Examples 2-7 are Au and Pd bimetallic nanoparticles with different ion exchange-in situ reduction operation times loaded onto the polyelectrolyte multilayer (PDDA / PSS) 3.5 .

[0139] Examples 8-11 are based on the polyelectrolyte multilayer-supported Au and Pd bimetallic nanoparticles (PDDA / PSS) in Example 1 3.5On the / 1Au2Pd sample, (1, 2, 3, 4) layers of PSS / PDDA bilayer films were redeposited respectively, and the outermost layer was a PDDA film in each case.

[0140] Examples 12 to 15 were (PDDA / PSS) with bimetallic nanoparticles loaded on different numbers of polyelectrolyte multilayers through the same number of ion exchange-in-situ reduction operations as in Example 1. 1.5 / 1Au2Pd, (PDDA / PSS) 2.5 / 1Au2Pd, (PDDA / PSS) 4.5 / 1Au2Pd, (PDDA / PSS) 5.5 / 1Au2Pd samples, and the ratio of the Au and Pd metal contents loaded on each sample was the same.

[0141] Comparative Example 1 was a polyelectrolyte multilayer film loaded with gold nanoparticles (PDDA / PSS) 3.5 / 1Au sample.

[0142] Comparative Example 2 was a polyelectrolyte multilayer film loaded with palladium nanoparticles (PDDA / PSS) 3.5 / 1Pd sample.

[0143] Comparative Examples 3 and 4 were on the polyelectrolyte multilayer film of Example 1 loaded with Au and Pd bimetallic nanoparticles (PDDA / PSS) 3.5 / 1Au2Pd samples, and (1.5, 2.5) layers of PSS / PDDA bilayer films were redeposited respectively, and the outermost layer was a PSS film in each case.

[0144] Comparative Example 5 was a polyelectrolyte multilayer film of Example 1 loaded with Pd and Au bimetallic nanoparticles (PDDA / PSS) 3.5 / 2Pd1Au sample.

[0145] Regarding the number of layers of the polyelectrolyte film deposited at one time in each example and comparative example, it was based on the fact that as the number of film layers increased, the content of metal nanoparticles in the film increased, which could optimize the catalytic effect; however, considering that if the content of metal nanoparticles was too high, the dispersibility and density of metal nanoparticles were too high, which might instead have an adverse effect on the catalytic effect. Considering comprehensively, the number of layers of the polyelectrolyte film deposited at one time selected for the experiment was 3.5 layers. And according to application requirements (such as different metal nanoparticle contents, catalytic performance requirements, etc.), the number of layers of the polyelectrolyte film deposited at one time could be implemented within the range of 1.5 to 5.5 layers.

[0146] In the above-mentioned examples and comparative examples, only one concentration and composition of the PDDA solution and the PSS solution, as well as one concentration of the chloroauric acid solution, the chloropalladic acid solution, the sodium borohydride solution, and the ascorbic acid solution are given for the convenience of reflecting the experimental effects. However, according to application requirements (such as different nanoparticle contents, catalytic performance requirements, etc.), the concentration of the PDDA solution used in the preparation process can be 0.1 - 10 mg / mL, the concentration of the PSS solution can be 0.1 - 10 mg / mL, the salt concentration in the PDDA solution and the PSS solution can be 0.01 - 5 mol / L, the concentration of the chloroauric acid solution can be 1 - 100 mmol / L, the concentration of the chloropalladic acid solution can be 1 - 100 mmol / L, the concentration of the sodium borohydride solution can be 1 - 100 mmol / L, and the concentration of the ascorbic acid solution can be 1 - 100 mmol / L, all of which can be implemented.

[0147] Verify the catalytic activities of the polyelectrolyte multilayer films loaded with gold and palladium nanoparticles in the examples and comparative examples. Using a mixed solution of a sodium borohydride solution with a concentration of 10 mmol / L and a volume of 2 mL and a p-nitrophenol solution with a concentration of 0.2 mmol / L and a volume of 1 mL as the reaction system, add the samples of the polyelectrolyte multilayer films loaded with gold and palladium nanoparticles prepared in each example and comparative example to the reaction system for catalytic reaction. Monitor the absorbance of p-nitrophenol at 400 nm in the reaction solution at different reaction times through ultraviolet-visible spectroscopy to judge the degradation situation of p-nitrophenol and the progress of the catalytic reaction.

[0148] According to the degradation rate formula to reflect the catalytic effect, where C t represents the degradation rate, A t represents the absorbance of the solution at time t, and A0 represents the absorbance of the solution at the initial 0 min.

[0149] Figure 1 For the (PDDA / PSS) 3.5 / 1Au2Pd sample prepared in Example 1, the ultraviolet-visible spectrum of the catalytic reduction of p-nitrophenol by sodium borohydride at different times is shown in Figure 1 As shown, with the passage of time, the absorbance of 4-NP at 400 nm gradually decreases, indicating that the content of 4-NP is decreasing, but the reaction is relatively slow, and C 20 (i.e., the degradation rate at 20 min) is only 67%.

[0150] Figure 2 For the samples of the polyelectrolyte multilayer films loaded with gold-palladium bimetallic nanoparticles prepared in Example 2, the samples of the polyelectrolyte multilayer films loaded with gold nanoparticles prepared in Comparative Example 1, and the samples of the polyelectrolyte multilayer films loaded with palladium nanoparticles prepared in Comparative Example 2, the trend chart of the absorbance change of the catalytic reduction of 4-NP by sodium borohydride at different times. From Figure 2The results show that the catalytic activity of Au, Pd bimetallic nanoparticles is higher than that of Au and Pd monometallic nanoparticles.

[0151] Figure 3 It is the absorbance change trend diagram of the samples of polyelectrolyte multilayer films loaded with Au-Pd bimetallic nanoparticles with different exchange and reduction times prepared in Examples 1-7 for the reduction of 4-NP by sodium borohydride at different times. As Figure 3 shown in A, on the basis of (PDDA / PSS) 3.5 , when the Au content is fixed and the exchange and reduction times of Pd are 1-2 times, the absorbance of 4-NP at the same reaction time decreases significantly, indicating that the catalytic reaction rate increases; when the exchange and reduction times of Pd are 3-4 times, the absorbance at the same reaction time gradually increases instead, indicating that the reaction rate slows down accordingly. As Figure 3 shown in B, on the basis of (PDDA / PSS) 3.5 , when the Pd content is fixed and the exchange and reduction times of Au are 1-4 times, the absorbance at the same reaction time gradually increases instead, indicating that the reaction rate slows down accordingly. It can be concluded that the catalytic activity of the optimal exchange and reduction times of 1 time for Au and 2 times for Pd, that is, 1Au2Pd, is the highest.

[0152] Figure 4 And Figure 5 are respectively the absorbance change trend diagrams of (PDDA / PSS) 3.5 / 1Au2Pd and (PDDA / PSS) 3.5 / 1Au for 5 cycles of catalytic reduction of 4-NP by sodium borohydride at different times. As Figure 4 shown, the degradation rates C 3.5 of (PDDA / PSS) 20 / 1Au2Pd for 1-5 times of catalytic reaction for 20 min are 93%, 91%, 90%, 90%, 89% respectively, and after 5 times of catalysis, C 20 only decreases by 4%, and the recycling efficiency is as high as over 95%. And as Figure 5 shown, the degradation rates C 3.5 of (PDDA / PSS) 20 / 1Au for 1-5 times of catalytic reaction for 20 min are 52%, 42%, 38%, 37%, 35% respectively, and after 5 times of catalysis, C 20 decreases by 17%, which is much higher than that of the bimetallic nanoparticles. From the degradation rates of the monometallic and bimetallic nanoparticles for 5 cycles of catalytic reduction of 4-NP by sodium borohydride, it can be seen that the Au, Pd bimetallic nanoparticles have good reusability.

[0153] Figure 6Absorbance change trend graphs of the samples of polyelectrolyte multilayers loaded with 1Au2Pd bimetallic nanoparticles prepared in Example 1, Examples 8 to 11 and Comparative Examples 3 and 4 for the reduction of 4-NP by sodium borohydride at different times. As Figure 6 shown, when the number of secondary deposited PSS / PDDA thin film layers is 0, 1, or 2, the absorbance of 4-NP at the same reaction time decreases significantly, and the degradation rates at 10 min of reaction are 67%, 94%, and 99% respectively. When the number of secondary deposited thin film layers is 3 or 4, the absorbance at the same reaction time increases instead, indicating that the catalytic reaction rate slows down. It can be concluded that the catalytic reaction rate is the fastest when the number of secondary deposited thin film layers is 2. After 10 min of reaction with secondary deposition of (PSS / PDDA)2, 4-NP is basically completely degraded, and the degradation rate is as high as 99%, and the catalytic degradation efficiency is greatly improved. Compared with the (PDDA / PSS) 3.5 / 1Au2Pd catalyst without secondary deposition treatment, its C 10 (i.e., the degradation rate at 10 min) is greatly improved. However, when the secondary deposition is 1.5 or 2.5 layers, that is, the outermost layer of the thin film is a PSS film, the catalytic reaction rate decreases instead, indicating that in addition to the catalytic effect of Au and Pd bimetallic nanoparticles on the degradation reaction of p-nitrophenol, the outermost PDDA film of the thin film has an obvious promoting effect on the degradation reaction of p-nitrophenol.

[0154] Figure 7 Transmission electron microscope photos of the polyelectrolyte multilayers loaded with 1Au2Pd bimetallic nanoparticles prepared in Example 1, Examples 8 to 11 and Comparative Examples 3 and 4, proving that the metal particles loaded on the polyelectrolyte multilayers are nanoscale.

[0155] Figure 8 Line scan graphs of the polyelectrolyte multilayers loaded with 1Au2Pd bimetallic nanoparticles prepared in Example 1, Examples 8 to 11 and Comparative Examples 3 and 4, proving that the nanoparticles loaded on the polyelectrolyte multilayers are Au and Pd bimetals.

[0156] Figure 9 Absorbance change trend graphs of the samples of polyelectrolyte multilayers loaded with 1Au2Pd bimetallic nanoparticles prepared in Example 1, Examples 12 to 15 for the reduction of 4-NP by sodium borohydride at different times. As Figure 9 shown, 1Au2Pd bimetallic nanoparticles loaded on thin films with different numbers of layers all have strong catalytic effects on the reduction of 4-NP by sodium borohydride. Since the reaction rate of (PDDA / PSS) 4.5 and (PDDA / PSS) 5.5 loaded with 1Au2Pd is too fast to carry out further research, (PDDA / PSS) 3.5 / 1Au2Pd is selected as the basic experiment.

[0157] Figure 10 Absorbance change trend graphs of the samples of polyelectrolyte multilayer films loaded with 1Au2Pd and 2Pd1Au bimetallic nanoparticles prepared in Example 1 and Comparative Example 5 during the reduction of 4-NP by sodium borohydride at different times. As Figure 10 shown, the catalytic efficiency of loading Au first is higher than that of loading Pd first. The C 20 values after 20 min of reaction are 93% and 62% respectively. This is because in the metal activity series, Pd is more active than Au. During the ion exchange process, a part of Pd will be displaced by Au, resulting in the inability of the two metals Au and Pd to reach the optimal ratio and thus affecting the catalytic rate. Therefore, the loading order of the bimetals cannot be interchanged. If Pd is loaded first and then Au, a displacement reaction will occur between Pd and chloroauric acid, making it impossible to control the ratio of Au and Pd, and ultimately affecting the catalytic effect.

[0158] The results show that in the system of catalytic reduction of 4-NP by sodium borohydride, the catalytic activity of Au, Pd bimetallic nanoparticles is stronger than that of Au and Pd monometallic nanoparticles. The optimal number of ion exchange-in-situ reduction times for Au, Pd bimetallic nanoparticles is 1Au2Pd. The reusability of Au, Pd bimetallic nanoparticles is better than that of Au monometallic nanoparticles. In the secondary deposition film of the polyelectrolyte multilayer film loaded with gold-palladium bimetallic nanoparticles, when the outermost layer is PSS, the catalytic reaction rate decreases, while when the outermost layer of the film is PDDA, the catalytic reaction rate increases, and with the increase of the number of film layers, the catalytic rate shows a trend of first increasing and then decreasing. The optimal degradation rate C 10 is as high as 99%. In addition to the catalytic effect of the gold-palladium bimetallic nanoparticles in the catalyst, PDDA in the polyelectrolyte multilayer film carrier, especially when the outermost layer of the film is PDDA film, has a very obvious promoting effect on the reaction. The synergistic catalytic effect between the gold-palladium bimetallic nanoparticle catalyst and the multilayer film carrier accelerates the degradation of p-nitrophenol. Since the catalyst is directly deposited on the substrate, after the reaction is completed, the substrate can be directly taken out of the solution, easily realizing the separation of the catalyst from the reaction solution and the recycling of the catalyst.

[0159] In summary, for the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst of the present invention, a carrier with a multilayer film structure is prepared using the cationic polyelectrolyte PDDA and the anionic polyelectrolyte PSS as construction materials. Gold-palladium bimetallic nanoparticles are loaded on the multilayer film. By designing the polyelectrolyte membrane material, the number of layers, and the ratio of gold and palladium bimetallic nanoparticles, bimetallic nanoparticles with higher catalytic performance and reusability than single-metal nanoparticles in the catalytic sodium borohydride reduction of 4-NP system are obtained. The optimal ion exchange-in-situ reduction ratio is 1Au2Pd. In particular, the matching of the outermost layer membrane material deposited once and the gold-palladium bimetallic nanoparticles, as well as the addition of the second-deposited multilayer film and its matching relationship, enable both the gold-palladium bimetallic nanoparticles and the polyelectrolyte multilayer film carrier to fully exert their catalytic degradation effects on 4-NP, while also producing a synergistic effect, significantly enhancing the degradation effect and the recycling effect of 4-NP, and achieving rapid, efficient, and convenient treatment of 4-NP.

Claims

1. A polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst, characterized in that: The cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) and the anionic polyelectrolyte sodium polystyrene sulfonate (PSS) were selected as the building materials, and polyelectrolyte multilayers were prepared by the layer-by-layer self-assembly technique, denoted as (PDDA / PSS). n+0.5 Then, gold nanoparticles were first loaded onto the polyelectrolyte multilayers by ion exchange-in-situ reduction method, and then palladium nanoparticles were loaded to obtain the catalyst (PDDA / PSS) / aAubPd for catalytic degradation of p-nitrophenol. n+0.5 / aAubPd; The (PDDA / PSS) n+0.5 represents that the outermost polyelectrolyte membrane is PDDA, and n represents a positive integer; the (PDDA / PSS) n+0.5 / aAubPd represents the amount of gold nanoparticles loaded on the (PDDA / PSS) n+0.5 polyelectrolyte membrane through a ion exchange-in-situ reduction operations, and b represents the amount of palladium nanoparticles loaded on the polyelectrolyte membrane (PDDA / PSS) n+0.5 / aAu through b ion exchange-in-situ reduction operations, where a and b are both positive integers.

2. The polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst according to claim 1, wherein: On the prepared (PDDA / PSS) n+0.5 / aAubPd, the secondary deposition of polyelectrolyte multilayers is continued by the layer-by-layer self-assembly technique to obtain (PDDA / PSS) n+0.5 / aAubPd / (PSS / PDDA) m , where m represents a natural number.

3. The polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst according to claim 1, wherein: Preferably, n is 1 to 5, a is 1 to 4, and b is 2 to 4; more preferably, a is 1 and b is 2.

4. The polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst according to claim 2, wherein: Preferably, m is 0 to 2, and more preferably 2.

5. The polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst according to any one of claims 1 to 4, characterized in that: The layer-by-layer self-assembly technique involves successively immersing a substrate in a PDDA solution and a PSS solution to obtain a layer of polyelectrolyte PDDA / PSS film, or successively immersing it in a PSS solution and a PDDA solution to obtain a layer of polyelectrolyte PSS / PDDA film, and repeating this process multiple times to prepare a polyelectrolyte multilayer film with the desired number of layers; where 0.5 represents preparing only one layer of PDDA film or one layer of PSS film.

6. The polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst according to claim 5, wherein: The concentration of the PDDA solution is 0.1 to 10 mg / mL, and the concentration of the PSS solution is 0.1 to 10 mg / mL; the PDDA solution and the PSS solution also contain a salt with a concentration of 0.01 to 5 mol / L, and the salt is preferably at least one of NaCl and NaBr.

7. A method for preparing a polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst according to any one of claims 1 to 6, characterized in that: It includes the following steps: a. Preparation of polyelectrolyte multilayer films: Using the layer-by-layer self-assembly technique, the negatively charged substrate was successively immersed in a cationic polyelectrolyte PDDA solution and an anionic polyelectrolyte PSS solution, each immersion for 5 - 30 min. After each immersion, the excess polyelectrolyte solution was washed away with water to deposit the polyelectrolyte film. This process was repeated multiple times to prepare the polyelectrolyte multilayer film (PDDA / PSS). n+0.5 ; Preferably, the substrate is a quartz wafer or a glass slide. The substrate is immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3 and heated at 80°C to 100°C for 1 to 2 hours to make the surface carry negative charges. b. Preparation of polyelectrolyte multilayer film loaded with gold-palladium bimetallic nanoparticles The substrate with the deposited polyelectrolyte multilayer film was immersed in a solution containing Au ions, and then in a strong reducing solution to reduce the Au ions to gold nanoparticles, obtaining a polyelectrolyte multilayer film (PDDA / PSS) loaded with gold nanoparticles n+0.5 / 1Au; Immerse the polyelectrolyte multilayer film (PDDA / PSS) n+0.5 / 1Au in a solution containing Au ions, and then immerse it in a weak reducing agent, repeating a - 1 times, to obtain the polyelectrolyte multilayer film (PDDA / PSS) n+0.5 / aAu; Soak the polyelectrolyte multilayer film (PDDA / PSS) n+0.5 / aAu in a solution containing Pd ions, and then soak it in a weak reducing solution to reduce the Pd ions to palladium nanoparticles. Repeat this process b times to obtain a polyelectrolyte multilayer film (PDDA / PSS) loaded with gold-palladium bimetallic nanoparticles n+0.5 / aAubPd; Preferably, the solution containing Au ions is chloroauric acid solution, the solution containing Pd ions is chloropalladic acid solution, the strong reducing solution is sodium borohydride solution, and the weak reducing solution is ascorbic acid solution.

8. The preparation method of the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst according to claim 7, characterized in that: It also includes step c. On the prepared (PDDA / PSS) n+0.5 / aAubPd, the layer-by-layer self-assembly technique is used again. It is successively immersed in an anionic polyelectrolyte PSS solution and a cationic polyelectrolyte PDDA solution, with each immersion lasting 5 to 30 minutes. After each immersion, the excess polyelectrolyte solution is washed away with water, and the polyelectrolyte film is deposited secondarily. This is repeated multiple times to obtain the (PDDA / PSS) n+0.5 / aAubPd / (PSS / PDDA) m catalyst.

9. Use of a polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst as described in any one of claims 1 to 6 in the degradation of p-nitrophenol, characterized in that: The polyelectrolyte multilayer film loaded with gold-palladium bimetallic nanoparticles is used as a catalyst for the degradation reaction of p-nitrophenol.

10. Use of the polyelectrolyte multilayer film-supported gold-palladium bimetallic nanoparticle catalyst as described in claim 9 in the degradation of p-nitrophenol, characterized in that: The polyelectrolyte multilayer film loaded with gold-palladium bimetallic nanoparticles is used as a catalyst for the degradation reaction of sodium borohydride-reduced p-nitrophenol. The number of times this catalyst can be reused is not less than 5 times, and the recycling and reuse efficiency is over 95%.

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