CN111450824B

CN111450824B - Preparation method and application of gold nano-catalyst with temperature response catalytic performance

Info

Publication number: CN111450824B
Application number: CN202010409115.1A
Authority: CN
Inventors: 温昕; 岳茹
Original assignee: Hebei University
Current assignee: Hebei University
Priority date: 2020-05-14
Filing date: 2020-05-14
Publication date: 2023-05-02
Anticipated expiration: 2040-05-14
Also published as: CN111450824A

Abstract

The invention provides a preparation method and application of a gold nano-catalyst with temperature response catalytic performance, wherein the preparation method comprises the following steps: (a) Dispersing halloysite nanotubes and tannic acid in a solvent, adding 3-aminopropyl triethoxysilane, separating a product after the reaction is finished, washing and drying to obtain a carrier; (b) Grafting the carrier with poly-N-isopropyl acrylamide to obtain a carrier with temperature response performance; (c) Adding chloroauric acid into the obtained carrier with temperature response performance, and reducing to obtain the gold nano-catalyst with temperature response performance. The preparation method of the catalyst is simple and environment-friendly, the active component Au in the obtained supported gold nano catalyst has good dispersibility in the catalyst, and the obtained catalyst has high activity, good stability and controllable temperature catalytic performance. Has important application prospect in the field of catalysis.

Description

Preparation method and application of gold nano-catalyst with temperature response catalytic performance

Technical Field

The invention relates to the technical field of nano catalysts, in particular to a preparation method and application of a gold nano catalyst with temperature response catalytic performance.

Background

The Au nano-catalyst combines the advantages of unique nano-structure, high specific surface area, electronic energy band structure, stable chemical property and the like, so that the Au nano-catalyst has excellent catalytic performance in a plurality of catalytic reactions. In recent years, au nanocatalysts are one of the hot problems of research at home and abroad. However, the Au nano-catalyst has higher surface energy, is easy to aggregate, causes the reduction of catalytic activity, and has the problems of difficult recycling and the like. Meanwhile, in the catalytic process, the activity of the Au nano-catalyst is difficult to regulate and control through external conditions such as temperature and the like. Therefore, the carrier with a special structure is constructed to prevent aggregation behavior among Au nano-particles, regulate and control catalytic activity of the Au nano-particles, meet the requirement of starting-stopping regulation and control of catalytic reaction in a specific environment, and have important significance.

At present, the temperature-responsive catalyst prepared by the traditional method is generally a homogeneous catalyst, and materials and toxic reagents with complicated preparation steps can be used in the preparation process. Therefore, the existing catalyst has the defects of complex preparation process, environment friendliness, low catalyst activity and the like, and the stability is difficult to improve. In addition, the conventional temperature-responsive catalyst has a problem that the temperature response is not sufficiently sensitive.

Disclosure of Invention

The invention aims to provide a preparation method and application of a gold nano-catalyst with temperature response catalytic performance, so as to solve the problems that the existing Au nano-catalyst is low in catalytic activity and stability, and the temperature response catalyst prepared by the existing method is insensitive to temperature response and is complex to prepare.

The technical scheme adopted by the invention is as follows: gold nano-catalyst with temperature response catalytic performance, which is prepared by the following method:

(a) Dispersing halloysite nanotubes and tannic acid in a solvent, adding 3-aminopropyl triethoxysilane, separating a product after the reaction is finished, washing and drying to obtain a carrier; wherein the mass ratio of halloysite nanotubes to tannic acid to 3-aminopropyl triethoxysilane is 0.25-2:1:1, preferably 1:1:1;

(b) Grafting the carrier with poly-N-isopropyl acrylamide to obtain a carrier with temperature response performance;

(c) Adding chloroauric acid into the obtained carrier with temperature response performance, and reducing to obtain a gold nano catalyst with temperature response performance; the loading of the active metal Au in the gold nano-catalyst is 0.5-2.07 wt%, preferably 2.07 wt%.

In the step (a), the total reaction time of the halloysite nanotube, the tannic acid and the 3-aminopropyl triethoxysilane is 6-24 hours, preferably 12 h.

In the step (a), halloysite nanotubes and tannic acid are firstly dispersed in an alkaline solvent with the pH value of 8.0-9.0 at normal temperature and reacted for 3 hours, preferably with the pH value of 8.5, and then 3-aminopropyl triethoxysilane is added for reaction.

In the step (b), the carrier and the poly-N-isopropyl acrylamide are added into a sodium hydroxide solution with the pH of 10, and stirred and reacted for 6-12 hours, preferably 12 h, at normal temperature, wherein the mass ratio of the carrier to the poly-N-isopropyl acrylamide is 1:2-4, preferably 1:3.

In the step (c), chloroauric acid and a carrier with temperature response performance are dispersed in water and reacted for 2-4 hours, preferably 4 h, at normal temperature.

A preparation method of a gold nano-catalyst with temperature response catalytic performance comprises the following steps:

(c) Adding chloroauric acid into the obtained carrier with temperature response performance, and reducing to obtain a gold nano catalyst with temperature response performance; the loading of the active metal Au in the gold nano-catalyst is 0.5-2.07 wt%, preferably 2.07-wt%.

The gold nano-catalyst is applied to reduction reaction of p-nitrophenol.

The solvent used in the reduction reaction of the p-nitrophenol is water, and the reducing agent is a newly prepared sodium borohydride solution; when the reaction rate needs to be accelerated, the temperature is regulated to 45 ℃, and when the reaction rate needs to be reduced, the temperature is regulated to 60 ℃.

The invention utilizes a large amount of phenolic hydroxyl groups in Tannic Acid (TA) to form an adhesion layer on the surface of halloysite nanotubes, and simultaneously, michael addition or Schiff base reaction is carried out between pyrogallol units in tannic acid and amino groups of 3-aminopropyl triethoxy silane, so that an amino-containing 'covalent bridge' formed by covalent bonds can be formed. In addition, tannic acid has a certain reducibility, and can directly reduce the catalyst precursor to generate the metal nano catalyst in situ, so that the activity and stability of the catalyst are obviously improved.

The invention adopts a simple, low-cost and environment-friendly method to prepare the high-activity temperature-responsive catalyst Au/HTA-P. The invention takes Halloysite Nanotubes (HNTs) coated by tannic acid-3-aminopropyl triethoxysilane (TA-APTES) coating as a carrier, and Au nano particles are loaded by an in-situ reduction method after polymer is grafted. The obtained catalyst active component Au has good dispersibility in the catalyst, shows high activity and stability in the reduction reaction of the p-nitrophenol, and can adjust the catalytic reaction rate by changing the temperature.

The catalyst disclosed by the invention has the advantages of simple preparation method, easiness in control, environment friendliness, low manufacturing cost and excellent temperature response performance, and has an important application prospect in the field of controllable catalysis.

Drawings

FIG. 1 is a FT-IR spectrum of HTA prepared in example 1, HTA-P prepared in example 3 and Au/HTA-P prepared in example 4.

FIG. 2 is an XRD spectrum of HTA prepared in example 1, HTA-P prepared in example 3 and Au/HTA-P prepared in example 4.

FIG. 3 is a TEM spectrum of HTA prepared in example 1.

FIG. 4 is a TEM spectrum of the catalyst Au/HTA-P prepared in example 4.

FIG. 5 is a graph showing the catalytic activity test data of the catalyst Au/HTA-P prepared in example 4 and the comparative catalyst Au/PDA@HNTs prepared in comparative example 1.

FIG. 6 is a graph of LCST test data of poly (N-isopropylacrylamide) prepared in example 2.

FIG. 7 is a graph showing the temperature response performance test data of the catalyst Au/HTA-P prepared in example 4.

FIG. 8 is a graph of stability test data for the catalyst Au/HTA-P prepared in example 4.

Detailed Description

The invention is further illustrated by the following examples, which are given by way of illustration only and are not intended to limit the scope of the invention in any way.

The procedures and methods not described in detail in the examples below are conventional methods well known in the art, and the reagents used in the examples are all analytically or chemically pure and are either commercially available or prepared by methods well known to those of ordinary skill in the art. The following examples all achieve the object of the invention.

Example 1

Purified halloysite nanotubes (100 mg) and tannic acid (100 mg) were added to Tirs-HCl buffer (50 ml, 0.05M, ph=8.5), mixed well and reacted 3h, followed by ethanol (50 mL) dissolved 3-aminopropyl triethoxysilane (100 mg), and stirred at room temperature 9 h. Finally, the mixture solution was centrifuged at high speed and the precipitate was collected, washed 3 times with water and ethanol, and dried in a vacuum oven at 60 ℃ for 12 h to give a brown powder, which was TA-APTES coated halloysite nanotube carrier, labeled "HTA".

Example 2

N-isopropyl acrylamide (768.40 mg,6.85 mmol) and S-1-dodecyl-S ' - (A, A ' -dimethyl-A ' -acetic acid) trithiocarbonate (59.6 mg,0.157 mmol) were dissolved in 6 mL tetrahydrofuran, and after three nitrogen runs, the initiator azobisisobutyronitrile (2.98 mg,0.0017 mmol) was added rapidly and stirred at 70℃12 h. The obtained mixture was precipitated with petroleum ether to obtain a solid product, and finally dried in a vacuum oven at 30 ℃ for 12 h to obtain poly-N-isopropyl acrylamide.

Example 3

HTA (25 mg) was first dispersed in deionized water (15 mL), poly N-isopropyl acrylamide (75 mg, mn=9000 g/mol) was added, then pH was adjusted to 10 with 50% sodium hydroxide, and the mixture was magnetically stirred at room temperature for 12 h and then centrifuged at high speed to collect a precipitate. Finally, after washing 3 times with deionized water, the precipitate was dried in a vacuum oven at 40 ℃ for 12 h, and the resulting product was a temperature-responsive catalyst support, labeled "HTA-P".

Example 4

HTA-P (9 mg) was added to an aqueous chloroauric acid solution (37.50. Mu.L, 24.30 mM), the mixture was centrifuged at high speed after reaction at 25℃for 4 h, and the precipitate was washed 3 times with water and then dispersed in water (1 mL) to obtain an Au/HTA-P catalyst.

The results of fourier infrared spectroscopy (FT-IR) analysis were performed on the HTA prepared in example 1, the HTA-P prepared in example 3, and the Au/HTA-P prepared in example 4, and are shown in fig. 1. As can be seen from the figure, 3703 and cm are present in the HTA sample ^-1 And 3625 cm ^-1 Absorption peaks, which correspond to the infrared characteristic absorption peaks of halloysite nanotubes. HTA samples at 2800-2950 and 3200-3500 cm ^-1 The absorption peaks at these correspond to the stretching vibrations of C-H, -OH and-NH in tannic acid and 3-aminopropyl triethoxysilane, respectively, indicating the presence of tannic acid and 3-aminopropyl triethoxysilane units in HTA. After grafting the poly-N-

isopropylacrylamide chains

1650 and 1540 cm appear in HTA-P ^-1 Two new peaks indicate that the polymer chains were successfully grafted onto the TA-APTES coating. By comparing HTA-P with Au/HTA-P, it can be seen that the spectra of the samples before and after loading the Au nanoparticles are very similar, indicating that the introduction of Au did not change its original structure.

Wide angle X-ray diffraction (XRD) analysis was performed on HTA prepared in example 1, HTA-P prepared in example 3 and Au/HTA-P prepared in example 4, and the results are shown in FIG. 2. As can be seen from the figure, the three samples all show characteristic diffraction peaks of halloysite nanotubes at 2θ=20.0°,24.3 °, 34.9 °, 38.0 °, 54.3 ° and 62.3 °, indicating that the crystal structure of halloysite nanotubes in the prepared samples is not destroyed. Sample Au/HTA-P exhibited characteristic diffraction peaks of Au at 2θ=38.3 °, 44.4 °, 64.7 ° and 78.0 °, indicating the formation of Au nanoparticles.

The HTA sample prepared in example 1 was analyzed by Transmission Electron Microscopy (TEM), and the result is shown in fig. 3. As can be seen from the figure, the sample was a nanotube structure showing a bright lumen and a dark tube wall, and a TA-Aplets coating of about 15-20 a nm a thickness was uniformly applied over the halloysite nanotubes. This result shows that TA-Apes coating has been successfully applied to the surface of halloysite nanotubes.

TEM analysis was performed on the Au/HTA-P sample prepared in example 4, and the results are shown in FIG. 4. As can be seen from the figure, the sample

The product is a nanotube structure with the diameter of about 70-120 and nm, and the Au nano-particles are fixed and highly dispersed on the surface of the carrier, and the average particle size is about 10.2 nm. The results indicate successful preparation of the catalyst Au/HTA-P.

Comparative example 1

Halloysite nanotubes (160 mg) were dispersed in Tris-HCl buffer (10 ml,10mm, ph=8.5) followed by dopamine hydrochloride (20 mg). The mixture was stirred at room temperature for 12 h, the product was collected by centrifugation and washed with water, and dried under vacuum at 40℃for 12 h to give the product labeled "PDA@HNTs". Pda@hnts (9 mg) were dispersed in deionized water (2 mL) at room temperature, chloroauric acid solution (37.50 μl,24.30 mM) was added, the mixture was centrifuged at high speed after 4 h, and the precipitate was washed 3 times with water and then dispersed in water (1 mL), and the comparative catalyst prepared was labeled "Au/pda@hnts".

Example 5

The catalyst Au/HTA-P prepared in example 4 and the catalyst Au/PDA@HNTs prepared in comparative example 1 were used for the reduction of P-nitrophenol. The p-nitrophenol reduction was performed in a Specord 210 plus UV-visible spectrophotometer with a temperature control system, as follows: paranitrophenol solution (0.075 ml,1 mM) and deionized water (1.375 mL) were added to a 1 x 1 cm quartz cuvette, then freshly prepared sodium borohydride solution (0.50 ml,133 mM) was added, and finally the catalyst Au/HTA-P (0.05 mL) or Au/pda@hnts (0.05 mL) was added rapidly. The progress of the reaction was monitored at specific times by means of an ultraviolet-visible spectrophotometer and spectral data were collected.

The results of the catalytic p-nitrophenol reduction reaction of example 5 were analyzed and are shown in FIG. 5. As can be seen from the graph, the reaction rate constants of the P-nitrophenol are respectively that in the presence of the catalyst Au/HTA-P and the comparative catalyst Au/PDA@HNTs

0.273 min ^-1 And 0.264 min ^-1 The TA-APTES coating has been demonstrated to have similar functions as the polydopamine coating. In addition, the conversion frequency (TOF) of the catalyst Au/HTA-P in the P-nitrophenol reaction is up to 463 h ^-1 The high efficiency of the catalyst Au/HTA-P was demonstrated over most reported Au-based catalysts.

Example 6

LCST tests were performed on poly-N-isopropylacrylamide prepared in example 2. The experimental procedure was as follows: poly-N-isopropyl acrylamide (5 mg) and p-nitrophenol solution (0.075 mL,1.0 mM) were placed in a quartz cuvette, then a suitable amount of sodium borohydride solution was added, and finally deionized water was added to make the volume of the solution 2 mL. And measuring the transmittance at the wavelength of 550 nm by an ultraviolet-visible spectrophotometer at the temperature of 20-80 ℃.

The LCST test results of example 6 were analyzed and the results are shown in fig. 6. As can be seen from the figure, the LCST in pure water was determined to be about 32 ℃. As the sodium borohydride concentration increased to 3.75 mm, the lcst increased to 45 ℃, and as the sodium borohydride concentration further increased to 9.98 mm, the lcst increased to 55 ℃. When the concentration of sodium borohydride was increased to 33.3 mM, no LCST could be detected. The results show that sodium ions in the solution affect the LCST of the polymer.

Example 7

The catalyst Au/HTA-P prepared in example 4 was used for temperature response performance testing in the reduction reaction of P-nitrophenol. Paranitrophenol solution (0.075 ml,1.0 mM), fresh sodium borohydride solution (0.075 ml,100 mM) and deionized water (1.80 mL) were placed in a 1 x 1 cm quartz cuvette, and then Au/HTF-P (0.05 mL) catalyst dispersion solution was added. To investigate the effect of temperature on catalytic activity, the temperature of the reaction solution in the cuvette was controlled to 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃, 50 ℃ and 60 ℃ respectively by a circulating water bath.

The temperature response performance results of example 7 were analyzed and are shown in fig. 7. The results show that when the reaction temperature is below 45 ℃ (LCST), the catalytic reaction rate increases with increasing temperature; the reaction rate was the fastest when the temperature was 45 ℃. At this time, the polymer chain is hydrophilic, and thus, hydrophilic sodium borohydride and p-nitrophenol are easily diffused to the Au active site through the hydrophilic polymer chain, thereby initiating the reduction reaction. However, when the temperature is more than 45 ℃, the reaction rate decreases inversely with the increase of the temperature, and the reaction is slowest at 60 ℃. This anomaly is due to shrinkage of the polymer chains and transition to hydrophobicity caused by the temperature higher than LCST, thereby forming a hydrophobic polymer layer around the Au nanoparticles. Thus, the hydrophilic substrate is hindered from contacting the Au active site, resulting in a reduction in the catalytic reaction rate value. The results show that the catalytic efficiency of the Au nanocatalyst can be adjusted by changing the reaction temperature.

Example 8

The catalyst was used repeatedly in the P-nitrophenol reduction reaction according to the conditions of example 5 as an important performance index for evaluating the stability of the catalyst, and the results are shown in fig. 8. As can be seen from FIG. 8, the Au/HTAP catalyst prepared in example 5 was used repeatedly 11 times, and the conversion rate of p-nitrophenol remained above 90%, with excellent stability.

Claims

1. The gold nano-catalyst with the temperature response catalytic performance is characterized by being prepared by the following steps:

(a) At normal temperature, firstly dispersing halloysite nanotubes and tannic acid in an alkaline solvent with the pH value of 8.0-9.0 and reacting for 3 hours, then adding 3-aminopropyl triethoxysilane for reacting, separating a product after the reaction is finished, and washing and drying to obtain a carrier; wherein the mass ratio of halloysite nanotubes to tannic acid to 3-aminopropyl triethoxysilane is 0.25-2:1:1;

(c) Adding chloroauric acid into the obtained carrier with temperature response performance, and reducing to obtain a gold nano catalyst with temperature response performance; the loading of the active metal Au in the gold nano-catalyst is 0.5-2.07 wt%.

2. The gold nano-catalyst with temperature response catalytic performance according to claim 1, wherein in the step (a), the total reaction time of the halloysite nanotube, tannic acid and 3-aminopropyl triethoxysilane is 6-24 hours.

3. The gold nano-catalyst with the temperature response catalytic performance according to claim 1, wherein in the step (b), the carrier and the poly-N-isopropyl acrylamide are added into a sodium hydroxide solution with the pH of 10, and are stirred at normal temperature for reaction for 6-12 hours, and the mass ratio of the carrier to the poly-N-isopropyl acrylamide is 1:2-4.

4. The gold nano-catalyst with temperature response catalytic performance according to claim 1, wherein in the step (c), chloroauric acid and a carrier with temperature response performance are dispersed in water and reacted for 2-4 hours at normal temperature.

5. The preparation method of the gold nano-catalyst with the temperature response catalytic performance is characterized by comprising the following steps of:

6. The preparation method of claim 5, wherein in the step (a), the total reaction time of the halloysite nanotube, tannic acid and 3-aminopropyl triethoxysilane is 6-24 hours, specifically: at normal temperature, the halloysite nanotubes and tannic acid are firstly dispersed in an alkaline solvent with the pH value of 8.0-9.0 and react for 3 hours, and then 3-aminopropyl triethoxysilane is added for reaction.

7. The preparation method of claim 5, wherein in the step (b), the carrier and the poly-N-isopropyl acrylamide are added into a sodium hydroxide solution with the pH of 10, and stirred and reacted for 6-12 hours at normal temperature, wherein the mass ratio of the carrier to the poly-N-isopropyl acrylamide is 1:2-4; in the step (c), chloroauric acid and a carrier with temperature response performance are dispersed in water and reacted for 2-4 hours at normal temperature.

8. Use of the gold nanocatalyst of any one of claims 1-4 in a reduction reaction of p-nitrophenol.

9. The use according to claim 8, wherein the solvent used in the reduction of p-nitrophenol is water and the reducing agent is a freshly prepared sodium borohydride solution; when the reaction rate needs to be accelerated, the temperature is regulated to 45 ℃, and when the reaction rate needs to be reduced, the temperature is regulated to 60 ℃.