Polyelectrolyte multilayer film loaded metal nanoparticle catalyst and application thereof in treatment of printing and dyeing wastewater

Abstract

The invention discloses a polyelectrolyte multilayer film loaded metal nanoparticle catalyst, which is characterized in that cationic polyelectrolyte poly (diallyldimethylammonium chloride) PDDA and anionic polyelectrolyte sodium polystyrenesulfonate (PSS) are selected 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 or (PDDA / PSS) n + 0.5, and then loading metal nanoparticles silver or palladium on the multilayer film through an ion exchange-in-situ reduction method to obtain the catalyst (PDDA / PSS) n / Ag or (PDDA / PSS) n + 0.5 / Pd for the oxidation-reduction reaction. According to the polyelectrolyte multilayer film loaded metal nanoparticle catalyst disclosed by the invention, by selecting and designing the material and the number of layers of the multilayer film carrier, the synergistic catalysis of the polyelectrolyte and the metal nanoparticles is exerted, the catalytic performance of the catalyst is remarkably improved, and especially the degradation effect on methylene blue in printing and dyeing wastewater is improved.

Description

Technical Field

[0001] The invention relates to the technical field of catalysis, in particular to a polyelectrolyte multilayer film-loaded metal nanoparticle catalyst, as well as the preparation of the catalyst and the application of methylene blue in treating printing and dyeing wastewater. Background Art

[0002] With the development of industrialization, the pollution of industrial wastewater to the environment is becoming increasingly serious. Among them, printing and dyeing wastewater has become the most difficult type of industrial wastewater to degrade due to its high chroma, difficulty in biodegradation and high toxicity. Among the many pollutants in printing and dyeing wastewater, methylene blue (MB) is a widely used and difficult to treat one. It belongs to the thiazine pollutant and has serious toxicity and carcinogenicity. The commonly used treatment methods currently include adsorption flocculation technology, membrane separation technology and redox technology, but these treatment technologies generally have problems such as complicated treatment process, long treatment time, low removal efficiency and high treatment cost. For example, the treatment effect of adsorbents and flocculants is easily affected by suspended matter, pollutants, oils and greases in the wastewater. They require large amounts of usage and high costs. In addition, the treatment mechanism is to achieve phase transfer of pollutants, which can easily cause secondary pollution and make it difficult to fundamentally solve the problem. The membrane separation operation process consumes a lot of energy and is itself costly, making it unsuitable for industrial treatment of large amounts of printing and dyeing wastewater. Redox technology is limited by redox reactions and the catalytic activity of catalysts. Usually, highly active catalysts are not easy to separate, recover and reuse, which is not only costly but also increases secondary pollution, limiting industrial applications. Therefore, in order to improve the effective removal or degradation of dyes in wastewater, highly active and easily recoverable catalysts remain a research focus. Summary of the invention

[0003] In order to solve the problems of low degradation rate of methylene blue in printing and dyeing wastewater and complicated catalytic degradation operation, the present invention develops a polyelectrolyte multilayer film-supported metal nanoparticle catalyst for catalytic redox reaction, which can simplify the reaction operation and facilitate catalyst separation and recovery. In addition, the polyelectrolyte content is controlled by selecting and designing the material and number of layers of the multilayer film carrier to exert the synergistic catalytic effect of the polyelectrolyte and the metal nanoparticles, thereby significantly improving the catalytic performance of the catalyst, especially the degradation effect of methylene blue in printing and dyeing wastewater.

[0004] In order to achieve the above-mentioned object, the present invention provides a polyelectrolyte multilayer film loaded with metal nanoparticle catalysts, selects cationic polyelectrolyte polydiallyl dimethyl ammonium chloride PDDA and anionic polyelectrolyte sodium polystyrene sulfonate PSS as construction materials, and adopts layer-by-layer self-assembly technology to prepare the polyelectrolyte multilayer film, which is marked as (PDDA / PSS) n or (PDDA / PSS) n+0.5 Then, metal nanoparticles silver or palladium are loaded on the multilayer film by ion exchange-in-situ reduction method to obtain a catalyst for redox reaction (PDDA / PSS)n / Ag or (PDDA / PSS) n+0.5 / Pd;

[0005] (PDDA / PSS) n The outermost polyelectrolyte membrane is PSS, and the (PDDA / PSS) n+0.5 The polyelectrolyte membrane representing the outermost layer is PDDA; and n represents a positive integer.

[0006] The present invention utilizes layer-by-layer self-assembly technology to prepare a polyelectrolyte multilayer membrane with cationic polyelectrolyte PDDA and anionic polyelectrolyte PSS as construction materials, and then loads metal nanoparticles on the multilayer membrane. By designing the matching of the polyelectrolyte multilayer membrane material, especially the outermost membrane material, and the metal nanoparticles, the catalytic activity of the metal nanoparticles is effectively dispersed and stabilized, and the catalytic efficiency is significantly improved, while simplifying the reaction operation and facilitating the separation and recovery of the catalyst.

[0007] As a limitation of the above technical solution, in the prepared (PDDA / PSS) n / Ag was further subjected to secondary deposition of polyelectrolyte multilayers by layer-by-layer self-assembly technology to obtain (PDDA / PSS) n / Ag / (PDDA / PSS) m ;

[0008] Or in the prepared (PDDA / PSS) n+0.5 / Pd, and then the polyelectrolyte multilayer film was deposited again by layer-by-layer self-assembly technology to obtain (PDDA / PSS) n+0.5 / Pd / (PSS / PDDA) s+0.5 ;

[0009] The m and s both represent natural numbers.

[0010] As a limitation of the above technical solution, the n is preferably 1-5.

[0011] As a limitation of the above technical solution, the catalyst (PDDA / PSS) n / Ag / (PDDA / PSS) m Here, m is preferably 1 to 6, and more preferably 4.

[0012] As a limitation of the above technical solution, the catalyst (PDDA / PSS) n+0.5 / Pd / (PSS / PDDA) s+0.5 Here, s is preferably 0 to 2, and more preferably 1.

[0013] As a limitation of the above technical solution, the layer-by-layer self-assembly technology is to soak the negatively charged substrate in PDDA solution and PSS solution successively to obtain a layer of polyelectrolyte PDDA / PSS membrane, or soak it in PSS solution and PDDA solution successively to obtain a layer of polyelectrolyte PSS / PDDA membrane, and repeat this process multiple times to prepare a polyelectrolyte multilayer membrane with the required number of layers; wherein 0.5 represents the preparation of only one layer of PDDA membrane or one layer of PSS membrane.

[0014] To further optimize the catalytic performance of the catalyst, (PDDA / PSS) n / Ag, (PDDA / PSS) n+0.5 / Pd is used for secondary deposition of polyelectrolyte multilayer films, which creates a synergistic effect between the metal nanoparticles and the multilayer film carrier, not only exerting the catalytic effect of the metal nanoparticles, but also making full use of the significant promoting effect of the polyelectrolyte on the catalytic reaction with the help of the matching of the secondary deposited thin film, especially the outermost film material and the metal nanoparticles, thereby greatly increasing the catalytic reaction rate.

[0015] As a limitation of the above technical solution, the concentration of the PDDA solution is 0.1-10 mg / mL, the concentration of the PSS solution is 0.1-10 mg / mL, and / or the PDDA solution and the PSS solution also contain salt, the concentration of the salt is 0.01-5 mol / L, and the salt is at least one of NaCl and NaBr; preferably, the concentration of the PDDA solution and the PSS solution are both 1 mg / mL, and the concentration of the salt is 1.5 mol / L.

[0016] Further improve the preparation conditions of the catalyst and optimize the activity and stability of the catalyst.

[0017] At the same time, the present invention provides a method for preparing the polyelectrolyte multilayer film-supported metal nanoparticle catalyst as described above, comprising the following steps:

[0018] a. Preparation of polyelectrolyte multilayer film: Using layer-by-layer self-assembly technology, the negatively charged substrate is immersed in a cationic polyelectrolyte PDDA solution and an anionic polyelectrolyte PSS solution in sequence, each time for 5 to 30 minutes, and the polyelectrolyte film is deposited. The polyelectrolyte multilayer film is prepared by repeating the process for multiple times;

[0019] Preferably, the substrate is a quartz sheet or a glass sheet, and the substrate is immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 7:3, and heated at 80° C. to 100° C. for 1 to 2 hours to make the surface negatively charged;

[0020] b. Preparation of polyelectrolyte multilayer films loaded with metal nanoparticles

[0021] The substrate with the deposited polyelectrolyte multilayer film is immersed in a solution containing metal ions, and then immersed in a reducing solution, each time for 1 to 10 minutes, to reduce the metal ions to metal nanoparticles, and obtain a polyelectrolyte multilayer film loaded with metal nanoparticles (PDDA / PSS) n / Ag or (PDDA / PSS) n+0.5 / Pd, used as a catalyst for redox reactions;

[0022] Preferably, the solution containing metal ions is a silver nitrate solution or a chloropalladic acid solution, and the reducing solution is a sodium borohydride solution;

[0023] Preferably, the concentrations of the silver nitrate solution, the chloropalladic acid solution, and the sodium borohydride solution are all in the range of 1 to 100 mmol / L; more preferably, the concentration of the silver nitrate solution is 5 to 20 mmol / L, the chloropalladic acid solution is 1 mmol / L, and the concentration of the sodium borohydride solution is 5 to 20 mmol / L.

[0024] As a limitation of the above technical solution, the present invention further comprises step c, in which the prepared (PDDA / PSS) n / Ag or (PDDA / PSS) n+0.5 / Pd was again deposited by layer-by-layer self-assembly technology to obtain (PDDA / PSS) n / Ag / (PDDA / PSS) m or (PDDA / PSS) n+0.5 / Pd / (PSS / PDDA) s+0.5 , used as a catalyst for redox reactions.

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

[0026] In addition, the present invention also provides the use of the polyelectrolyte multilayer film-supported metal nanoparticle catalyst in treating printing and dyeing wastewater, which is used to catalyze the degradation of methylene blue in the wastewater.

[0027] The polyelectrolyte multilayer film loaded with silver nanoparticles and polyelectrolyte multilayer film loaded with palladium nanoparticles prepared by the invention are used as catalysts for treating printing and dyeing wastewater by redox method, and especially exhibit excellent catalytic degradation activity and degradation effect for methylene blue in wastewater.

[0028] In summary, the present invention adopts layer-by-layer self-assembly technology, uses cationic polyelectrolyte PDDA and anionic polyelectrolyte PSS as construction materials to prepare polyelectrolyte multilayer films, loads metal nanoparticles in the multilayer films, controls the polyelectrolyte content by selecting and designing the material and number of layers of the multilayer film carrier, controls the matching of the outermost film material and the metal nanoparticles, and increases the matching of the secondary deposited multilayer film and the metal nanoparticles, so that the metal nanoparticles and the polyelectrolyte multilayer film carrier have a synergistic effect on the catalytic degradation of methylene blue, significantly improves the treatment effect of methylene blue, and realizes rapid and efficient degradation of methylene blue. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 , prepared in Example 1 (PDDA / PSS) 3 UV-visible spectra of MB reduction by sodium borohydride catalyzed by / Ag at different times.

[0030] Figure 2 , Examples 1 to 6, and Comparative Examples 1 and 2 prepared polyelectrolyte multilayer films loaded with silver nanoparticles samples catalyzed by sodium borohydride reduction of MB at different times.

[0031] Figure 3 , Examples 7 to 10, Comparative Tables 3 and 4 are absorbance variation trends of the polyelectrolyte multilayer membrane-supported palladium nanoparticle samples prepared at different times when catalyzed by sodium borohydride to reduce MB.

[0032] Figure 4 , absorbance variation trend diagram of the polyelectrolyte multilayer film loaded with silver nanoparticles prepared in Examples 11 to 14 at different times when catalyzed by sodium borohydride to reduce MB.

[0033] Figure 5 , Examples 7, 9 and Examples 15 to 20 prepared polyelectrolyte multilayer film loaded with palladium nanoparticles samples catalyzed by sodium borohydride reduction of MB at different times.

[0034] Figure 6 , Polyelectrolyte multilayer film loaded with silver nanoparticles (PDDA / PSS) prepared in Example 1 3 Transmission electron micrograph of the Ag / Ag sample.

[0035] Figure 7 , Example 7 Polyelectrolyte multilayer film loaded with palladium nanoparticles (PDDA / PSS) 3.5 Transmission electron micrograph of the / Pd sample. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] The experimental methods in the following examples and comparative examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from conventional reagent stores unless otherwise specified. The quantitative tests in the following examples are repeated three times, and the results are averaged.

[0038] The following examples and comparative examples relate to different polyelectrolyte multilayer films loaded with metal nanoparticles and their preparation.

[0039] Example 1

[0040] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 The preparation of the Ag / Ag samples was performed as follows:

[0041] a. Use a quartz wafer as a substrate and place it in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3. Heat it at 90°C for 1 hour to make the surface of the quartz wafer negatively charged. Place the quartz wafer with negative surface charge in PDDA solution and PSS solution with a concentration of 1 mg / mL, respectively, and soak for 30 minutes. After each soaking, wash off the excess solution with deionized water. Repeat this step 3 times. The outermost layer is PSS. Deposit (PDDA / PSS) on the quartz wafer 3 Multilayer film.

[0042] b. Prepared above (PDDA / PSS) 3 The multilayer film was successively placed with 10mmol / L AgNO 3 and 10mmol / L NaBH 4 The solution was immersed in water for 5 minutes each time, and the excess solution was washed off with deionized water. 2 After drying, the polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) was obtained. 3 / Ag samples.

[0043] Example 2

[0044] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag / (PDDA / PSS) 1 The sample preparation was performed as follows:

[0045] a, b: Steps a and b are the same as in Example 1;

[0046] c. In the prepared (PDDA / PSS) 3 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3 / Ag was successively placed in PDDA solution and PSS solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. The outermost layer was PSS, and a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) was prepared. 3 / Ag / (PDDA / PSS) 1 sample.

[0047] Example 3

[0048] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag / (PDDA / PSS) 2 The sample preparation was performed as follows:

[0049] a, b: Steps a and b are the same as in Example 1;

[0050] c. In the prepared (PDDA / PSS) 3 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3 / Ag was successively placed in PDDA solution and PSS solution with a concentration of 1 mg / mL, and each solution was immersed for 30 minutes. After each immersion, the excess solution was washed away with deionized water. This step was repeated twice, and the outermost layer was PSS to obtain a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS). 3 / Ag / (PDDA / PSS) 2 sample.

[0051] Example 4

[0052] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag / (PDDA / PSS) 3 The sample preparation was performed as follows:

[0053] a, b: Steps a and b are the same as in Example 1;

[0054] c. In the prepared (PDDA / PSS) 3 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3 / Ag was successively placed in PDDA solution and PSS solution with a concentration of 1 mg / mL, and each solution was immersed for 30 minutes. After each immersion, the excess solution was washed away with deionized water. This step was repeated 3 times, and the outermost layer was PSS to obtain a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag / (PDDA / PSS) 3 sample.

[0055] Example 5

[0056] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag / (PDDA / PSS) 4 The sample preparation was performed as follows:

[0057] a, b: Steps a and b are the same as in Example 1;

[0058] c. In the prepared (PDDA / PSS) 3 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3 / Ag was successively placed in PDDA solution and PSS solution with a concentration of 1 mg / mL, and each solution was immersed for 30 minutes. After each immersion, the excess solution was washed away with deionized water. This step was repeated 4 times, and the outermost layer was PSS to obtain a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag / (PDDA / PSS) 4 sample.

[0059] Example 6

[0060] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag / (PDDA / PSS) 6 The sample preparation was performed as follows:

[0061] a, b: Steps a and b are the same as in Example 1;

[0062] c. In the prepared (PDDA / PSS) 3 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3 / Ag was successively placed in a PDDA solution and a PSS solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. This step was repeated 6 times, and the outermost layer was PSS to obtain a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS). 3 / Ag / (PDDA / PSS) 6 sample.

[0063] Comparative Example 1

[0064] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 The preparation of / Ag / PDDA samples was performed as follows:

[0065] a, b: Steps a and b are the same as in Example 1;

[0066] c. In the prepared (PDDA / PSS) 3 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3 / Ag was placed in a PDDA solution with a concentration of 1 mg / mL and immersed for 30 min to deposit a layer of PDDA film. After the immersion was completed, the excess solution was washed away with deionized water to obtain a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS). 3 / Ag / PDDA samples.

[0067] Comparative Example 2

[0068] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag / (PDDA / PSS) 1.5 The sample preparation was performed as follows:

[0069] a, b: Steps a and b are the same as in Example 1;

[0070] c. In the prepared (PDDA / PSS) 3 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3 / Ag was successively placed in PDDA solution and PSS solution with a concentration of 1 mg / mL, and each solution was immersed for 30 minutes. 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 a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) was obtained. 3 / Ag / (PDDA / PSS) 1.5 sample

[0071] Example 7

[0072] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 3.5 The preparation of Pd / Pd samples was performed as follows:

[0073] a. Use a glass sheet as a substrate and place it in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3. Heat it at 90°C for 1 hour to make the surface of the glass sheet negatively charged. Place the glass sheet with negative surface charge in PDDA solution and PSS solution with a concentration of 1 mg / mL respectively, and soak them for 30 minutes respectively. After each soaking, wash off the excess solution with deionized water. Repeat this step 3.5 times. The outermost layer is PDDA, and (PDDA / PSS) is deposited on the glass sheet. 3.5 Multilayer film.

[0074] b. Prepared above (PDDA / PSS) 3.5 The multilayer membrane was successively placed in 1mmol / L H 2 PdCl 4 solution and 10mmol / L NaBH 4 The solution was immersed in water for 5 minutes each time. After each immersion, the excess solution was washed away with deionized water. 2 After drying, polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS) was obtained. 3.5 / Pd samples.

[0075] Example 8

[0076] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 3.5 The preparation of Pd / PSS samples was performed as follows:

[0077] a, b: Steps a and b are the same as in Example 7;

[0078] c. In the prepared (PDDA / PSS) 3.5 / Pd was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3.5 / Pd was placed in a PSS solution with a concentration of 1 mg / mL and soaked for 30 min. After the soaking was completed, the excess solution was washed away with deionized water, and a layer of PSS film was deposited to prepare a polyelectrolyte multilayer film loaded with palladium particles (PDDA / PSS) 3.5 / Pd / PSS samples.

[0079] Example 9

[0080] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 3.5 / Pd / (PSS / PDDA) 1.5 The sample preparation was performed as follows:

[0081] a, b: Steps a and b are the same as in Example 7;

[0082] c. In the prepared (PDDA / PSS) 3.5 / Pd was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3.5 / Pd was successively placed in a PSS solution and a PDDA solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. This step was repeated 1.5 times, and the outermost layer was a PSS membrane to obtain a polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS). 3.5 / Pd / (PSS / PDDA) 1.5 sample.

[0083] Example 10

[0084] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 3.5 / Pd / (PSS / PDDA) 2.5 The sample preparation was performed as follows:

[0085] a, b: Steps a and b are the same as in Example 7;

[0086] c. In the prepared (PDDA / PSS) 3.5 / Pd was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3.5 / Pd was successively placed in a PSS solution and a PDDA solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. This step was repeated 2.5 times. The outermost layer was a PSS membrane, and polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS) was obtained. 3.5 / Pd / (PSS / PDDA) 2.5 sample.

[0087] Comparative Example 3

[0088] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 3.5 / Pd / (PSS / PDDA) 1 The sample preparation was performed as follows:

[0089] a, b: Steps a and b are the same as in Example 7;

[0090] c. In the prepared (PDDA / PSS) 3.5 / Pd was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3.5 / Pd was successively placed in a PSS solution and a PDDA solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. The outermost layer was a PDDA membrane, and polyelectrolyte multilayer membrane-loaded palladium particles (PDDA / PSS) were prepared. 3.5 / Pd / (PSS / PDDA) 1 sample.

[0091] Comparative Example 4

[0092] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 3.5 / Pd / (PSS / PDDA) 2 The sample preparation was performed as follows:

[0093] a, b: Steps a and b are the same as in Example 7;

[0094] c. In the prepared (PDDA / PSS) 3.5 / Pd was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 3.5 / Pd was successively placed in a PSS solution and a PDDA solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. This step was repeated twice, and the outermost layer was a PDDA membrane to obtain a polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS). 3.5 / Pd / (PSS / PDDA) 2 sample.

[0095] Embodiment 11

[0096] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 2 The preparation of the Ag / Ag samples was performed as follows:

[0097] a. Use a quartz wafer as a substrate and place it in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3. Heat it at 90°C for 1 hour to make the surface of the quartz wafer negatively charged. Place the quartz wafer with negative surface charge in PDDA solution and PSS solution with a concentration of 1 mg / mL, respectively, and soak for 20 minutes. After each soaking, wash off the excess solution with deionized water. Repeat this step twice. The outermost layer is PSS. Deposit (PDDA / PSS) on the quartz wafer 2 Multilayer film.

[0098] b. Prepared above (PDDA / PSS) 2 The multilayer film was successively placed with 5mmol / L AgNO 3 and 5mmol / L NaBH 4 The solution was immersed in water for 3 minutes each time, and the excess solution was washed off with deionized water. 2 After drying, the polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) was obtained. 2 / Ag samples.

[0099] Example 12

[0100] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 2 / Ag / (PDDA / PSS) 4 The sample preparation was performed as follows:

[0101] a, b: Steps a and b are the same as in Example 11;

[0102] c. In the prepared (PDDA / PSS) 2 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 2 / Ag was successively placed in PDDA solution and PSS solution with a concentration of 1 mg / mL, and each solution was immersed for 20 minutes. After each immersion, the excess solution was washed away with deionized water. This step was repeated 4 times, and the outermost layer was PSS to obtain a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 2 / Ag / (PDDA / PSS) 4 sample.

[0103] Embodiment 13

[0104] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 4 The preparation of the Ag / Ag samples was performed as follows:

[0105] a. Use a quartz wafer as a substrate and place it in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3. Heat it at 90°C for 1 hour to make the surface of the quartz wafer negatively charged. Place the quartz wafer with negative surface charge in PDDA solution and PSS solution with a concentration of 1 mg / mL, respectively, and soak for 25 minutes. After each soaking, wash off the excess solution with deionized water. Repeat this step 4 times. The outermost layer is PSS. Deposit (PDDA / PSS) on the quartz wafer 4 Multilayer film.

[0106] b. Prepared above (PDDA / PSS) 4 The multilayer film was successively placed in 20mmol / L AgNO 3 and 20mmol / L NaBH 4 The solution was immersed in water for 10 min each time, and the excess solution was washed off with deionized water. 2 After drying, the polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) was obtained. 4 / Ag samples.

[0107] Embodiment 14

[0108] Polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS)4 / Ag / (PDDA / PSS) 2 The sample preparation was performed as follows:

[0109] a, b: Steps a and b are the same as in Example 13;

[0110] c. In the prepared (PDDA / PSS) 4 / Ag was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 4 / Ag was successively placed in PDDA solution and PSS solution with a concentration of 1 mg / mL, and each solution was immersed for 25 min. After each immersion, the excess solution was washed away with deionized water. This step was repeated twice, and the outermost layer was PSS to obtain a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS). 4 / Ag / (PDDA / PSS) 2 sample.

[0111] Embodiment 15

[0112] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 1.5 The preparation of Pd / Pd samples was performed as follows:

[0113] a. Use a glass sheet as a substrate and place it in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3. Heat it at 90°C for 1 hour to make the surface of the glass sheet negatively charged. Place the glass sheet with negative surface charge in PDDA solution and PSS solution with a concentration of 1 mg / mL respectively, and soak them for 30 minutes respectively. After each soaking, wash off the excess solution with deionized water. Repeat this step 1.5 times. The outermost layer is PDDA, and (PDDA / PSS) is deposited on the glass sheet. 1.5 Multilayer film.

[0114] b. Prepared above (PDDA / PSS) 1.5 The multilayer membrane was successively placed in 1mmol / L H 2 PdCl 4 solution and 10mmol / L NaBH 4 The solution was immersed in water for 5 minutes each time. After each immersion, the excess solution was washed away with deionized water. 2 After drying, polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS) was obtained. 1.5 / Pd samples.

[0115] Example 16

[0116] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 1.5 / Pd / (PSS / PDDA)1.5 The sample preparation was performed as follows:

[0117] a, b: Steps a and b are the same as in Example 15;

[0118] c. In the prepared (PDDA / PSS) 1.5 / Pd was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 1.5 / Pd was successively placed in a PSS solution and a PDDA solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. This step was repeated 1.5 times, and the outermost layer was a PSS membrane to obtain a polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS). 1.5 / Pd / (PSS / PDDA) 1.5 sample.

[0119] Embodiment 17

[0120] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 2.5 The preparation of Pd / Pd samples was performed as follows:

[0121] a. Use a glass sheet as a substrate and place it in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3. Heat it at 90°C for 1 hour to make the surface of the glass sheet negatively charged. Place the glass sheet with negative surface charge in PDDA solution and PSS solution with a concentration of 1 mg / mL, respectively, and soak for 30 minutes. After each soaking, wash off the excess solution with deionized water. Repeat this step 2.5 times. The outermost layer is PDDA. Deposit (PDDA / PSS) on the glass sheet 2.5 Multilayer film.

[0122] b. Prepared above (PDDA / PSS) 2.5 The multilayer membrane was successively placed in 1mmol / L H 2 PdCl 4 solution and 10mmol / L NaBH 4 The solution was immersed in water for 5 minutes each time. After each immersion, the excess solution was washed away with deionized water. 2 After drying, polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS) was obtained. 2.5 / Pd samples.

[0123] Embodiment 18

[0124] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 2.5 / Pd / (PSS / PDDA) 1.5 The sample preparation was performed as follows:

[0125] a, b: Steps a and b are the same as in Example 17;

[0126] c. In the prepared (PDDA / PSS) 2.5 / Pd was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 2.5 / Pd was successively placed in a PSS solution and a PDDA solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. This step was repeated 1.5 times, and the outermost layer was a PSS membrane to obtain a polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS). 2.5 / Pd / (PSS / PDDA) 1.5 sample.

[0127] Embodiment 19

[0128] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 4.5 The preparation of Pd / Pd samples was performed as follows:

[0129] a. Use a glass sheet as a substrate and place it in a mixed solution of concentrated sulfuric acid and hydrogen peroxide with a volume ratio of 7:3. Heat it at 90°C for 1 hour to make the surface of the glass sheet negatively charged. Place the glass sheet with negative surface charge in PDDA solution and PSS solution with a concentration of 1 mg / mL, respectively, and soak for 30 minutes. After each soaking, wash off the excess solution with deionized water. Repeat this step 4.5 times. The outermost layer is PDDA, and (PDDA / PSS) is deposited on the glass sheet. 4.5 Multilayer film.

[0130] b. Prepared above (PDDA / PSS) 4.5 The multilayer membrane was successively placed in 1mmol / L H 2 PdCl 4 solution and 10mmol / L NaBH 4 The solution was immersed in water for 5 minutes each time. After each immersion, the excess solution was washed away with deionized water. 2 After drying, polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS) was obtained. 4.5 / Pd samples.

[0131] Embodiment 20

[0132] Polyelectrolyte multilayer films supported on palladium particles (PDDA / PSS) 4.5 / Pd / (PSS / PDDA) 1.5 The sample preparation was performed as follows:

[0133] a, b: Steps a and b are the same as in Example 19;

[0134] c. In the prepared (PDDA / PSS) 4.5 / Pd was used for secondary deposition of polyelectrolyte multilayers to form (PDDA / PSS) 4.5 / Pd was successively placed in a PSS solution and a PDDA solution with a concentration of 1 mg / mL, and each solution was immersed for 30 min. After each immersion, the excess solution was washed away with deionized water. This step was repeated 1.5 times, and the outermost layer was a PSS membrane to obtain a polyelectrolyte multilayer membrane loaded with palladium particles (PDDA / PSS). 4.5 / Pd / (PSS / PDDA) 1.5 sample.

[0135] Note: The PDDA solution and PSS solution used in the above Examples 1 to 20 and Comparative Examples 1 to 4 both contain 1.5 mol / L of sodium chloride.

[0136] Example 1 is a polyelectrolyte multilayer film loaded with silver particles (PDDA / PSS) 3 / Ag sample; Examples 2 to 6 are (PDDA / PSS) loaded with the same content of Ag nanoparticles 3 On the Ag / Ag, (1, 2, 3, 4, 6) layers of PDDA / PSS double-layer films were deposited respectively, and the outermost layer was all PSS film.

[0137] Comparative Examples 1 and 2 are (PDDA / PSS) loaded with the same content of Ag nanoparticles. 3 On the Ag / Ag, (0.5, 1.5) layers of PDDA / PSS double-layer films were deposited respectively, and the outermost layer was PDDA.

[0138] Example 7 is a polyelectrolyte multilayer film loaded with palladium particles (PDDA / PSS) 3.5 / Pd sample; Examples 8 to 10 are (PDDA / PSS) loaded with the same content of Pd nanoparticles 3.5 On the Pd / Pd, (0.5, 1.5, 2.5) layers of PSS / PDDA double-layer films were deposited respectively, and the outermost layer was PSS.

[0139] Comparative Examples 3 and 4 are (PDDA / PSS) loaded with the same content of Pd nanoparticles. 3.5 On the Pd / Pd, (1, 2) layers of PSS / PDDA double-layer films are deposited respectively, and the outermost layer is PDDA.

[0140] Examples 11 and 12 are (PDDA / PSS) loaded with the same content of Ag nanoparticles. 2 / Ag and (PDDA / PSS) 2 / Ag / (PDDA / PSS) 4 Samples, Examples 13 and 14 are (PDDA / PSS) loaded with the same content of Ag nanoparticles 4 / Ag and (PDDA / PSS) 4 / Ag / (PDDA / PSS) 2 sample.

[0141] Examples 15 and 16 are (PDDA / PSS) loaded with the same content of Pd nanoparticles. 1.5 / Pd and (PDDA / PSS) 1.5 / Pd / (PSS / PDDA) 1.5 Samples, Examples 17 and 18 are (PDDA / PSS) loaded with the same content of Pd nanoparticles 2.5 / Pd and (PDDA / PSS) 2.5 / Pd / (PSS / PDDA) 1.5 Samples, Examples 19 and 20 are (PDDA / PSS) loaded with the same content of Pd nanoparticles 4.5 / Pd and (PDDA / PSS) 4.5 / Pd / (PSS / PDDA) 1.5 sample.

[0142] Regarding the number of polyelectrolyte film layers deposited at one time in each embodiment and comparative example, it is based on the fact that as the number of film layers increases, the content of nanoparticles in the film increases, which can optimize the catalytic effect; but considering that the nanoparticle content is too high, the dispersion and density of the nanoparticles are too high and may have an adverse effect on the catalytic effect, according to application requirements (such as different nanoparticle contents, catalytic performance requirements, etc.), the number of polyelectrolyte film layers deposited at one time can be 1 to 5 layers.

[0143] The above embodiments and comparative examples only give one concentration and composition of PDDA solution and PSS solution for the convenience of reflecting the experimental effect. According to the application requirements (such as different nanoparticle contents, catalytic performance requirements, etc.), the concentration of PDDA solution used in the preparation process can be 0.1-10 mg / mL, the concentration of PSS solution can be 0.1-10 mg / mL, the salt concentration in PDDA solution and PSS solution can be 0.01-5 mol / L, the concentration of silver nitrate solution can be 1-100 mmol / L, the concentration of chloropalladic acid solution can be 1-100 mmol / L, and the concentration of sodium borohydride solution can be 1-100 mmol / L.

[0144] The catalytic activity of the polyelectrolyte multilayer film-supported metal nanoparticles of the examples and comparative examples was verified. A mixed solution of a sodium borohydride solution with a concentration of 10 mmol / L and a volume of 2 mL and a methylene blue solution with a concentration of 0.1 mmol / L and a volume of 1 mL was used as a reaction system, and the polyelectrolyte multilayer film-supported metal nanoparticle samples prepared in each example and comparative example were added to the reaction system for catalytic reaction, and the absorbance of methylene blue at 664 nm of the reaction solution at different reaction times was monitored by ultraviolet-visible spectroscopy to determine the degradation of methylene blue and the progress of the catalytic reaction.

[0145] According to the degradation rate formula To reflect the catalytic effect, C t represents the degradation rate, A t A represents the absorbance of the solution at time t. 0 It indicates the absorbance of the solution at the initial time 0 min.

[0146] Figure 1 Prepared as in Example 1 (PDDA / PSS) 3 UV-visible spectra of MB reduction by sodium borohydride catalyzed by Ag at different times, such as Figure 1 As shown in Figure 2, the absorbance of MB at 664 nm gradually decreased over time, indicating that the MB content was decreasing, but the reaction was slow. 90 (ie the degradation rate in 90 min) is only 28%.

[0147] Figure 2 The absorbance variation trend diagram of the polyelectrolyte multilayer film loaded with silver nanoparticles prepared in Examples 1 to 6 and Comparative Examples 1 and 2 catalyzed by sodium borohydride to reduce MB at different times. Figure 2 As shown in the figure, after the number of secondary deposited PDDA / PSS film layers is 0, 1, 2, 3, and 4, as the number of secondary deposited film layers increases, the MB absorbance at the same reaction time decreases significantly, indicating that the catalytic reaction rate is accelerated; when the number of secondary deposited film layers is 6, 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 fastest when the number of secondary deposited film layers is 4, compared with (PDDA / PSS) 3 C / Ag catalyst 90 28%, (PDDA / PSS) 3 / Ag / (PDDA / PSS) 4 Catalyst C 90 As high as 80%, an increase of nearly 3 times. However, when the secondary deposition is 0.5 or 1.5 layers, that is, the outermost layer of the film is the PDDA film, the catalytic reaction rate decreases instead, indicating that in addition to the catalytic effect of Ag nanoparticles on the degradation reaction of methylene blue, the outermost layer of the film, the PSS film, has a significant promoting effect on the degradation reaction of methylene blue.

[0148] Figure 3 The absorbance variation trend diagram of the polyelectrolyte multilayer film supported palladium nanoparticle samples prepared in Examples 7 to 10 and Comparative Examples 3 and 4 catalyzed by sodium borohydride to reduce MB at different times. Figure 3 As shown in the figure, when the number of layers of the secondary deposited PSS / PDDA film is 0, 0.5, and 1.5, the absorbance of MB decreases significantly at the same reaction time, and the degradation rates are 31%, 82%, and 99% respectively after 10 minutes of reaction. 1.5 After 10 minutes of reaction, MB was basically completely degraded, with a degradation rate of up to 99%. The catalytic degradation efficiency was greatly improved, compared with the (PDDA / PSS) without secondary deposition treatment. 3.5 / Pd catalyst, its C 10 (i.e., the degradation rate in 10 minutes) value increased by more than 3 times. However, when the secondary deposition is 1 or 2 layers, that is, the outermost layer of the film is a PDDA film, the catalytic reaction rate also increased, but was significantly lower than that of the catalyst whose outermost layer of the secondary deposition film is a PSS film, indicating that in addition to the catalytic effect of Pd nanoparticles on the degradation reaction of methylene blue, the PSS in the film, especially the outermost PSS film, has a significant promoting effect on the degradation reaction of methylene blue.

[0149] Figure 4 The absorbance variation trend diagram of the polyelectrolyte multilayer film loaded with silver nanoparticles prepared in Examples 11 to 14 at different time periods when sodium borohydride was used to reduce MB is shown in FIG. Figure 4 As shown in the figure, as the number of layers of the first deposited polyelectrolyte film increases, the content of Ag nanoparticles in the film increases, so the catalytic degradation efficiency is improved; and as the number of layers of the second deposited film increases, the outermost PSS film of the film greatly improves the catalytic degradation efficiency. Comparing Examples 12 and 14, the number of layers of the first deposited and second deposited films is 6 layers in total, and the (PDDA / PSS) with less Ag nanoparticle content 2 / Ag / (PDDA / PSS) 4 The sample has a higher catalytic degradation efficiency, indicating that too high Ag nanoparticle density has an adverse effect on the catalytic effect.

[0150] Figure 5 The absorbance variation trend diagram of the polyelectrolyte multilayer film supported palladium nanoparticle samples prepared in Examples 7, 9 and Examples 15 to 20 catalyzing the reduction of MB by sodium borohydride at different times is shown in FIG. Figure 5As shown, as the number of layers of the first deposited polyelectrolyte film increases, the content of Pd nanoparticles in the film increases, and thus the catalytic degradation efficiency is improved; when the number of layers of the first deposited polyelectrolyte film changes, the second deposited polyelectrolyte multilayer film can improve the catalytic degradation efficiency, indicating that the synergistic catalytic effect of Pd nanoparticles and the multilayer film carrier is not affected by the number of layers of the first deposited film.

[0151] Figure 6 This is a transmission electron microscope photograph of the polyelectrolyte multilayer film loaded with silver particles prepared in Example 1, proving that the silver particles loaded on the polyelectrolyte multilayer film are nanoscale. Examples 2 to 6 and Comparative Examples 1 and 2 are the same as Example 1.

[0152] Figure 7 This is a transmission electron microscope photograph of the polyelectrolyte multilayer membrane loaded with palladium particles prepared in Example 7, proving that the palladium particles loaded on the polyelectrolyte multilayer membrane are nanoscale. Examples 8 to 10 and Comparative Examples 3 and 4 are the same as Example 7.

[0153] The results show that the catalytic reaction rate of the secondary deposited film of polyelectrolyte multilayer film loaded with metal nanoparticles is reduced when the outermost layer is PDDA, while the catalytic reaction rate increases when the outermost layer is PSS, and the catalytic rate shows a trend of first increasing and then decreasing with the increase of the number of film layers, and the optimal degradation rate is increased by more than 3 times. In addition to the catalytic effect of metal nanoparticles in the catalyst, the PSS in the polyelectrolyte multilayer film carrier, especially the outermost PSS film, has a very obvious promoting effect on the reaction. The synergistic catalytic effect between the metal nanoparticle catalyst and the multilayer film carrier accelerates the degradation of methylene blue. Since the catalyst is directly deposited on the substrate, the substrate can be directly taken out of the solution after the reaction is completed, which easily realizes the separation of the catalyst from the reaction solution and the recovery of the catalyst.

[0154] In summary, the polyelectrolyte multilayer film loaded with metal nanoparticle catalyst of the present invention uses cationic polyelectrolyte PDDA and anionic polyelectrolyte PSS as construction materials to prepare a carrier with a multilayer film structure, and loads metal nanoparticles on the multilayer film. By designing the polyelectrolyte membrane material and the number of layers, especially the matching of the outermost membrane material and the metal nanoparticles, and adding secondary deposited multilayer films and their matching relationship, the metal nanoparticles and the polyelectrolyte multilayer film carrier can fully exert the catalytic degradation effect on methylene blue, and can also produce a synergistic effect, thereby significantly improving the treatment effect on methylene blue and realizing rapid and efficient degradation treatment of methylene blue.

Claims

1. A polyelectrolyte multilayer film supported metal nanoparticle catalyst, characterized in that: Cationic polyelectrolyte polydiallyl dimethyl ammonium chloride (PDDA) and anionic polyelectrolyte sodium polystyrene sulfonate (PSS) were selected as building materials, and polyelectrolyte multilayers were prepared by layer-by-layer self-assembly technology, which was labeled as (PDDA / PSS). n or (PDDA / PSS) n+0.5 Then, metal nanoparticles silver or palladium are loaded on the multilayer film by ion exchange-in-situ reduction method to obtain a catalyst for redox reaction (PDDA / PSS) n / Ag or (PDDA / PSS) n+0.5 / Pd; (PDDA / PSS) n The outermost polyelectrolyte membrane is PSS, and the (PDDA / PSS) n+0.5 The polyelectrolyte membrane representing the outermost layer is PDDA; and n represents a positive integer.

2. The polyelectrolyte multilayer film-supported metal nanoparticle catalyst according to claim 1, characterized in that: In the prepared (PDDA / PSS) n / Ag was further subjected to secondary deposition of polyelectrolyte multilayers by layer-by-layer self-assembly technology to obtain (PDDA / PSS) n / Ag / (PDDA / PSS) m ; Or in the prepared (PDDA / PSS) n+0.5 / Pd, and then the polyelectrolyte multilayer film was deposited again by layer-by-layer self-assembly technology to obtain (PDDA / PSS) n+0.5 / Pd / (PSS / PDDA) s+0.5 ; The m and s both represent natural numbers.

3. The polyelectrolyte multilayer film supported metal nanoparticle catalyst according to claim 1, characterized in that: The above n is preferably 1-5.

4. The polyelectrolyte multilayer film supported metal nanoparticle catalyst according to claim 2, characterized in that: Catalyst (PDDA / PSS) n / Ag / (PDDA / PSS) m Here, m is preferably 1 to 6, and more preferably 4.

5. The polyelectrolyte multilayer film supported metal nanoparticle catalyst according to claim 2, characterized in that: Catalyst (PDDA / PSS) n+0.5 / Pd / (PSS / PDDA) s+0.5 Here, s is preferably 0 to 2, and more preferably 1.

6. The polyelectrolyte multilayer film supported metal nanoparticle catalyst according to any one of claims 1 to 5, characterized in that: The layer-by-layer self-assembly technology is to soak the negatively charged substrate in PDDA solution and PSS solution successively to prepare a layer of polyelectrolyte PDDA / PSS membrane, or soak it in PSS solution and PDDA solution successively to prepare a layer of polyelectrolyte PSS / PDDA membrane, and repeat it many times to prepare the required number of polyelectrolyte multilayer membranes; where 0.5 represents the preparation of only one PDDA membrane or one PSS membrane.

7. The polyelectrolyte multilayer film supported metal nanoparticle catalyst according to claim 6, characterized in that: The concentration of the PDDA solution is 0.1-10 mg / mL, and the concentration of the PSS solution is 0.1-10 mg / mL; and / or, the PDDA solution and the PSS solution further contain salt, the concentration of the salt is 0.01-5 mol / L, and the salt is at least one of NaCl and NaBr; Preferably, the concentrations of the PDDA solution and the PSS solution are both 1 mg / mL, and the concentration of the salt is 1.5 mol / L.

8. A method for preparing a polyelectrolyte multilayer film-supported metal nanoparticle catalyst as claimed in any one of claims 1 to 7, characterized in that: The following steps are involved: a. Preparation of polyelectrolyte multilayer film: Using layer-by-layer self-assembly technology, the negatively charged substrate is immersed in a cationic polyelectrolyte PDDA solution and an anionic polyelectrolyte PSS solution in sequence, each time for 5 to 30 minutes, and the polyelectrolyte film is deposited. The polyelectrolyte multilayer film is prepared by repeating the process for multiple times; Preferably, the substrate is a quartz sheet or a glass sheet, and the substrate is immersed in a mixed solution of concentrated sulfuric acid and hydrogen peroxide in a volume ratio of 7:3, and heated at 80° C. to 100° C. for 1 to 2 hours to make the surface negatively charged; b. Preparation of polyelectrolyte multilayer films loaded with metal nanoparticles The substrate with the deposited polyelectrolyte multilayer film is immersed in a solution containing metal ions, and then immersed in a reducing solution, each time for 1 to 10 minutes, to reduce the metal ions to metal nanoparticles, and obtain a polyelectrolyte multilayer film loaded with metal nanoparticles (PDDA / PSS) n / Ag or (PDDA / PSS) n+0.5 / Pd, used as a catalyst for redox reactions; Preferably, the solution containing metal ions is a silver nitrate solution or a chloropalladic acid solution, and the reducing solution is a sodium borohydride solution; Preferably, the concentrations of the silver nitrate solution, the chloropalladic acid solution, and the sodium borohydride solution are all in the range of 1 to 100 mmol / L; more preferably, the concentration of the silver nitrate solution is 5 to 20 mmol / L, the chloropalladic acid solution is 1 mmol / L, and the concentration of the sodium borohydride solution is 5 to 20 mmol / L.

9. The method for preparing the polyelectrolyte multilayer film-supported metal nanoparticle catalyst according to claim 8, characterized in that: The step also includes step c, in which the prepared (PDDA / PSS) n / Ag or (PDDA / PSS) n+0.5 / Pd was again deposited by layer-by-layer self-assembly technology to obtain (PDDA / PSS) n / Ag / (PDDA / PSS) m or (PDDA / PSS) n+0.5 / Pd / (PSS / PDDA) s+0.5 , used as a catalyst for redox reactions.

10. Use of the polyelectrolyte multilayer film supported metal nanoparticle catalyst as claimed in any one of claims 1 to 7 in treating printing and dyeing wastewater, characterized in that: Polyelectrolyte multilayer films loaded with metal nanoparticle catalysts were used to catalyze the degradation of methylene blue in wastewater.

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