CN109126869B - Chitosan modified active coke in-situ supported nano-gold catalyst and preparation method thereof - Google Patents
Chitosan modified active coke in-situ supported nano-gold catalyst and preparation method thereof Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
- B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
- B01J31/06—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides containing polymers
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- B01J35/61—
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- C07C213/02—Preparation of compounds containing amino and hydroxy, amino and etherified hydroxy or amino and esterified hydroxy groups bound to the same carbon skeleton by reactions involving the formation of amino groups from compounds containing hydroxy groups or etherified or esterified hydroxy groups
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J2231/00—Catalytic reactions performed with catalysts classified in B01J31/00
- B01J2231/60—Reduction reactions, e.g. hydrogenation
- B01J2231/64—Reductions in general of organic substrates, e.g. hydride reductions or hydrogenations
Abstract
The invention discloses a chitosan modified active coke in-situ loaded nano-gold catalyst and a preparation method thereof. The preparation method comprises the steps of preparing the chitosan/active coke compound and loading the nano-gold on the chitosan/active coke compound. The catalyst has the advantages of good nano-gold particle dispersibility, high mechanical strength, good catalytic activity, good stability and the like, is a novel supported nano-gold catalyst, has very high application value and wider application range, has the advantages of simple preparation process, easy operation, cheap raw materials, short production period, low production cost, environmental protection and the like, can realize large-scale preparation at normal temperature, and is suitable for industrial production.
Description
Technical Field
The invention belongs to the technical field of preparation of nano metal catalysts, and relates to a chitosan modified active coke in-situ supported nano gold catalyst and a preparation method thereof.
Technical Field
In the existing nano-gold catalyst, the nano-gold has small particle size and high surface activation energy, and is easy to agglomerate, so that the reaction activity is obviously reduced. Based on the above problems, researchers have tried to load gold nanoparticles on a carrier to improve the activity and stability of a catalyst, wherein carbon materials such as carbon nanotubes, carbon nanofibers, graphene (graphene oxide), mesoporous carbon and the like are often used as carrier materials of the gold nanoparticles, but these carrier materials have the problems of high cost, low mechanical strength, poor pore structure and the like, and the carbon materials are difficult to obtain due to complicated obtaining routes. In addition, the existing preparation methods of the supported nano gold catalyst comprise an impregnation method, a deposition-precipitation method, a coprecipitation method, a chemical vapor deposition method and the like, and the methods have the following defects: the nano-gold has incomplete loading, poor repeatability in the preparation process and high possibility of being influenced by solvation effect and cluster effect of metal components, so that the nano-gold has poor dispersibility, unstable catalyst structure (poor stability) and high noble metal consumption, and chemical reagents such as sodium borohydride and hydrazine need to be added in the preparation process, so that the chemical reagents cause secondary pollution to the environment and do not accord with the theme of green chemistry. In addition, the existing deposition-precipitation method, impregnation method and other methods are difficult to realize the high dispersion loading of the nanogold on the carbon support material. Therefore, the supported nano-gold catalyst with good nano-gold particle dispersibility, high mechanical strength, good stability and good catalytic activity is obtained, and has important significance for expanding the application field of the supported nano-gold catalyst.
Disclosure of Invention
The invention aims to solve the technical problems of the prior art, provides a chitosan modified active coke in-situ loaded nano-gold catalyst with good nano-gold particle dispersibility, high mechanical strength, good catalytic activity and good stability, and also provides a chitosan modified active coke in-situ loaded nano-gold catalyst with simple process, cheap raw materials and low production cost.
In order to solve the technical problems, the invention adopts the following technical scheme:
a chitosan modified active coke in-situ loaded nano-gold catalyst comprises active coke, chitosan and nano-gold particles; the surface of the active coke is modified with chitosan to form a chitosan/active coke compound; and the chitosan/active coke compound is loaded with nano gold particles.
In the chitosan modified active coke in-situ supported nano-gold catalyst, the mass percentage of nano-gold particles in the chitosan modified active coke in-situ supported nano-gold catalyst is further improved to be 0.84wt% -13.40 wt%; the mass ratio of the chitosan to the active coke is 0.1-0.6.
The chitosan modified active coke in-situ supported nano-gold catalyst is further improved, and the average particle size of the nano-gold particles is 5.27 +/-2.02 nm-30.61 +/-13.58 nm.
As a general inventive concept, the invention also provides a preparation method of the chitosan modified active coke in-situ supported nano gold catalyst, which comprises the following steps:
s1, mixing the chitosan suspension and the active coke suspension, performing ultrasonic treatment, stirring, centrifuging, washing and drying to obtain a chitosan/active coke compound;
and S2, preparing the chitosan/active coke compound obtained in the step S1 into a chitosan/active coke compound suspension, dropwise adding a chloroauric acid solution, performing ultrasonic treatment, stirring, centrifuging, washing and drying to obtain the chitosan modified active coke in-situ loaded nanogold catalyst.
In the above preparation method, further improvement is provided, in the step S1, the volume ratio of the chitosan suspension to the active coke suspension is 1: 5-2: 5;
the chitosan suspension is prepared by ultrasonically dispersing chitosan in an acetic acid solution; the ratio of the chitosan to the acetic acid solution is 0.2-0.6 g: 20 mL; the mass concentration of the acetic acid solution is 0.1-1%; the ultrasonic dispersion time in the preparation process of the chitosan suspension is 10-30 min;
the active coke suspension is prepared by ultrasonically dispersing active coke in water; the ratio of the active coke to the water is 0.5-1.5 g: 50 mL; the ultrasonic dispersion time in the preparation process of the active coke suspension is 10-30 min.
In the preparation method, the improvement is that the active coke also comprises the following pretreatment before use: cleaning, drying, ball milling and sieving the active coke; ultrapure water is adopted for cleaning; the ball milling is carried out at the rotating speed of 50 r/h-200 r/h; the ball milling time is 1-2 h; the sieving is 200 mesh sieving.
In the above preparation method, further improvement is provided, in the step S1, the ultrasound time is 10min to 30 min; the stirring time is 12-24 h; the drying is vacuum drying for 12 to 24 hours at the temperature of between 20 and 50 ℃.
In a further improvement of the above preparation method, in step S2, the chitosan/active coke complex suspension is prepared by ultrasonically dispersing chitosan/active coke complex in water; the ratio of the chitosan/active coke compound to water is 0.1-0.5 g: 60 mL; the ultrasonic dispersion time in the preparation process of the chitosan/active coke compound suspension is 10 min-30 min.
In the above preparation method, further improvement is provided, in the step S2, the volume ratio of the chitosan/activated coke complex suspension to the chloroauric acid solution is 60: 0.35-5.6; the concentration of the chloroauric acid solution is 24.3 mmol/L.
In the above preparation method, further improvement is provided, in the step S2, the ultrasound time is 10min to 30 min; the stirring time is 12-24 h; the drying is vacuum drying for 12 to 24 hours at the temperature of between 20 and 50 ℃.
Compared with the prior art, the invention has the advantages that:
(1) the invention provides a chitosan modified active coke in-situ loaded nano-gold catalyst, which comprises active coke, chitosan and nano-gold particles, wherein the chitosan is modified on the active cokeThe surface of the active coke forms a chitosan/active coke compound, and the chitosan/active coke compound is loaded with nano gold particles. In the invention, the activated coke has the characteristics of low cost, stable chemical property, high mechanical strength, large specific surface area, developed void structure and the like, so the chitosan/activated coke compound formed by modifying chitosan on the surface of the activated coke has the advantages of large specific surface area, high mechanical strength and the like, and the chitosan has better adhesive force, so that the chitosan can be firmly attached to the surface of the activated coke, the mechanical stability of the chitosan can be greatly improved, and the stable loading of the subsequent nano-gold is facilitated. On the basis, the chitosan surface is rich in hydroxyl (-OH) and amino (-NH)2) When the nano-gold particles are loaded on the chitosan/active coke composite, the nano-gold is uniformly distributed and fixed on the chitosan by utilizing the interaction of the nano-gold and hydrophilic groups (hydroxyl and amino) on the surface of the chitosan, the dispersibility of the nano-gold is improved, and the nano-gold is effectively protected, so that the particle size of the nano-gold particles is smaller and the nano-gold particles are uniformly dispersed on the surface of the chitosan/active coke composite. Meanwhile, the chitosan has certain viscosity and surface electropositivity, so that electrostatic interaction exists between the gold nanoparticles and the chitosan, and the chitosan with larger steric hindrance effect can prevent the gold nanoparticles from agglomerating, thereby being beneficial to improving the gold nanoparticles and keeping better catalytic activity. Based on the characteristics of chitosan, the nano-gold is functionalized, and high mechanical strength, high catalytic activity and high stability are maintained. In the invention, the chitosan has excellent biocompatibility and degradability, so that the obtained supported nano gold catalyst has low toxicity to the environment. In addition, the active coke has a mesoporous and macroporous structure, is not easy to be blocked by the nano-gold particles, and the rich pore channel structure of the active coke is beneficial to reducing the influence of internal diffusion on adsorption and a catalysis process, and can also strengthen the interaction between a catalyst interface and organic matters through the pi-pi stacking effect, thereby improving the catalysis efficiency. Therefore, the chitosan modified active coke in-situ supported nano-gold catalyst has the advantages of good nano-gold particle dispersibility, high mechanical strength, good catalytic activity, good stability and the likeThe method has the advantages of being a novel supported nano-gold catalyst, and having high application value and wide application range. Meanwhile, compared with other carbon-supported nano-gold catalysts, the chitosan modified active coke in-situ supported nano-gold catalyst has higher catalytic efficiency and obviously improved cycle stability.
(2) In the chitosan modified active coke in-situ supported nano gold catalyst, the mass ratio of chitosan to active coke is optimized to be 0.1-0.6, so that the load stability of nano gold can be obviously improved, the catalytic performance of nano gold is easier to show, the mass transfer performance of the catalyst can be improved, the mass transfer process of pollutants in the catalyst is smoother, and higher catalytic efficiency is finally obtained, because a small amount of chitosan is not beneficial to anchoring of nano gold, nano gold is easy to separate, the catalytic efficiency is reduced, and the excessive chitosan hinders the mass transfer process of pollutants, so that the catalytic efficiency is reduced. In addition, the invention optimizes the mass percent of the nano-gold particles in the chitosan modified active coke in-situ supported nano-gold catalyst to be 0.84wt% -13.40 wt%, and can exert the performance of nano-gold to the maximum extent under the condition, so that the chitosan modified active coke in-situ supported nano-gold catalyst obtains better catalytic performance.
(3) The invention also provides a preparation method of the chitosan modified active coke in-situ loaded nano gold catalyst, which takes active coke, chitosan and chloroauric acid solution as raw materials, utilizes the good adhesive force of the chitosan to firmly modify the chitosan on the surface of the active coke to form a chitosan/active coke compound, simultaneously, the chitosan modified on the surface of the active coke serves as a reducing agent and a stabilizing agent in the forming and distributing process of nano gold, adsorbs and enriches gold ions through abundant hydroxyl and amino groups on the surface of the chitosan, and reduces the gold ions into nano gold, thereby the nano gold is in-situ loaded on the chitosan/active coke compound, after the nano gold is formed, the amino group on the surface of the chitosan can be combined with the nano gold to play a good role in dispersing and protecting the nano gold particles, and simultaneously, the viscosity and the surface electropositivity of the chitosan can ensure that the electrostatic effect exists between the chitosan and the gold nano particles, therefore, the agglomeration of the nano gold particles can be prevented, the nano gold is functionalized, the advantages of high activity and stability are kept, and the chitosan modified active coke in-situ loaded nano gold catalyst with good nano gold particle dispersibility, high mechanical strength, good catalytic activity and good stability is finally prepared. Meanwhile, the chitosan has excellent biocompatibility and degradability, and can reduce secondary pollution to the environment in the preparation process and subsequent treatment and disposal of the catalyst. The preparation method has the advantages of simple preparation process, easy operation, cheap raw materials, short production period, low production cost, environmental protection and the like, can realize large-scale preparation at normal temperature, and is suitable for industrial production.
Drawings
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.
FIG. 1 shows the chitosan modified activated coke in-situ loaded nano-gold catalyst (AuNPs/CTS/AC) prepared in example 3 of the present invention(3)) Transmission electron micrographs of Active Coke (AC) and chitosan/active coke complex (CTS/AC), where a is AC, b is CTS/AC, and c is Au NPs/CTS/AC(3)D is Au NPs/CTS/AC(3)High power transmission electron microscopy.
FIG. 2 is a transmission electron microscope image of the chitosan modified active coke in-situ supported nano-gold catalyst prepared in embodiments 1 to 5 of the present invention, wherein a to e are Au NPs/CTS/AC in sequence(1)、Au NPs/CTS/AC(2)、Au NPs/CTS/AC(3)、AuNPs/CTS/AC(4)、Au NPs/CTS/AC(5)。
FIG. 3 is a particle size distribution diagram of the chitosan modified active coke in-situ supported nano-gold catalyst prepared in embodiments 1 to 5 of the present invention, wherein (a) to (e) are Au NPs/CTS/AC in sequence(1)、Au NPs/CTS/AC(2)、Au NPs/CTS/AC(3)、AuNPs/CTS/AC(4)、Au NPs/CTS/AC(5)。
FIG. 4 shows the chitosan modified activated coke in-situ supported nano-gold catalyst (AuN)Ps/CTS/AC(4)) Active Coke (AC) and chitosan/active coke complex (CTS/AC).
FIG. 5 is an infrared spectrum of the chitosan-modified activated coke in-situ supported nano-gold catalyst prepared in examples 1 to 5 of the present invention.
FIG. 6 shows the chitosan modified activated coke in-situ loaded nano-gold catalyst (AuNPs/CTS/AC) prepared in example 4 of the present invention(4)) Active Coke (AC) and chitosan/active coke complex (CTS/AC).
FIG. 7 is a graph showing the change of the reaction rate constant with time during the catalytic reduction of 4-nitrophenol by the chitosan modified activated coke in-situ supported nano-gold catalyst in example 6 of the present invention.
FIG. 8 shows the chitosan modified activated coke in-situ loaded nano-gold catalyst (Au NPs/CTS/AC) in example 6 of the present invention（4）) A change curve diagram of the ultraviolet spectrum of the solution along with the reaction time in the process of catalytic reduction of 4-nitrophenol.
Fig. 9 is a recycling cycle chart of the chitosan modified activated coke in-situ supported nano-gold catalyst in the catalytic reduction of 4-nitrophenol in example 7 of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
The starting materials and equipment used in the following examples are commercially available. In the following examples, unless otherwise specified, the data obtained are the average of three or more repeated experiments.
Example 1:
the chitosan modified active coke in-situ loaded nano-gold catalyst comprises active coke, chitosan and nano-gold particles, wherein the chitosan is modified on the surface of the active coke to form a chitosan/active coke compound, and the chitosan/active coke compound is loaded with the nano-gold particles.
In this embodiment, in the chitosan modified activated coke in-situ supported nanogold catalyst, the mass percentage of the nanogold particles is 0.84wt%, and the mass ratio of the chitosan to the activated coke is 0.5.
In this example, the average particle diameter of the gold nanoparticles was 5.27 ± 2.02 nm.
The preparation method of the chitosan modified active coke in-situ supported nano-gold catalyst comprises the following steps:
(1) pretreatment of active coke:
cleaning the active coke with ultrapure water, and drying in a vacuum drying oven; ball-milling the dried active coke for 2 hours at the ball-milling rotating speed of 200 r/h; and (4) sieving the powder subjected to ball milling by a sieve with 200-mesh sieve pores to obtain activated coke powder, wherein the serial number of the activated coke powder is AC.
(2) Preparing a chitosan modified active coke compound:
(2.1) 0.5g of chitosan is weighed and placed in a 100 mL round bottom beaker, 0.2 mL of acetic acid and 20mL of ultrapure water (namely, the mass concentration of the acetic acid solution is 1%) are added, and the chitosan is dispersed uniformly by ultrasonic treatment for 30min to obtain a chitosan suspension.
(2.2) weighing 1g of the activated coke powder prepared in the step (1) and placing the weighed activated coke powder in a 100 mL round-bottom flask, adding 50mL of ultrapure water, and carrying out ultrasonic treatment for 30min to uniformly disperse the activated coke powder to obtain an activated coke suspension.
And (2.3) mixing the solutions obtained in the step (2.1) and the step (2.2), performing ultrasonic treatment for 30min, placing the mixture on a magnetic stirrer to stir for 24h, centrifuging and washing the stirred product, and performing vacuum drying at the temperature of 50 ℃ for 24h to obtain a chitosan modified active coke compound, namely a chitosan/active coke compound, which is numbered CTS/AC.
(3) Preparing a chitosan modified active coke in-situ supported nano gold catalyst:
(3.1) weighing 0.2g of the chitosan/active coke compound prepared in the step (2) and placing the chitosan/active coke compound in a 100 mL round-bottom flask, adding 60mL of ultrapure water, and carrying out ultrasonic treatment for 30min to obtain a chitosan/active coke compound suspension.
(3.2) placing the chitosan/active coke compound suspension obtained in the step (3.1) on a magnetic stirrer for stirring, and dropwise adding 0.35 mL of chloroauric acid with the concentration of 24.3 mmol/LAnd (3) carrying out ultrasonic treatment on the acid solution for 30min, and continuing stirring for 24h, namely carrying out in-situ reduction reaction in the stirring process, wherein the generated nano gold is directly loaded on the chitosan/active coke compound. Centrifuging and washing the product solution after the reaction is finished, and drying for 24h in vacuum at the temperature of 50 ℃ to obtain the chitosan modified active coke in-situ loaded nano-gold catalyst which is numbered as Au NPs/CTS/AC(1)。
Example 2
The chitosan modified active coke in-situ supported nano-gold catalyst is basically the same as the chitosan modified active coke in-situ supported nano-gold catalyst in the embodiment 1, and the differences are only that: in example 2, the mass percentage of the gold nanoparticles in the chitosan modified activated coke in-situ supported gold nanoparticle catalyst is 1.68 wt%, and the average particle size of the gold nanoparticles is 6.78 ± 2.31 nm.
The preparation method of the chitosan modified active coke in-situ supported nanogold catalyst in the embodiment is basically the same as the preparation method in the embodiment 1, and the difference is only that: the amount of the chloroauric acid solution added in the preparation method of example 2 was 0.7 mL.
The chitosan modified active coke in-situ loaded nano-gold catalyst prepared in example 2 is numbered Au NPs/CTS/AC(2)。
Example 3
The chitosan modified active coke in-situ supported nano-gold catalyst is basically the same as the chitosan modified active coke in-situ supported nano-gold catalyst in the embodiment 1, and the differences are only that: in example 3, the mass percentage of the gold nanoparticles in the chitosan modified activated coke in-situ supported gold nanoparticle catalyst is 3.35 wt%, and the average particle size of the gold nanoparticles is 13.05 ± 5.82 nm.
The preparation method of the chitosan modified active coke in-situ supported nanogold catalyst in the embodiment is basically the same as the preparation method in the embodiment 1, and the difference is only that: the amount of the chloroauric acid solution added in the preparation method of example 3 was 1.4 mL.
The chitosan modified active coke in-situ loaded nano-gold catalyst prepared in example 3 is numbered Au NPs/CTS/AC(3)。
Example 4
The chitosan modified active coke in-situ supported nano-gold catalyst is basically the same as the chitosan modified active coke in-situ supported nano-gold catalyst in the embodiment 1, and the differences are only that: in example 4, the mass percentage of the gold nanoparticles in the chitosan modified activated coke in-situ supported gold nanoparticle catalyst is 6.70wt%, and the average particle size of the gold nanoparticles is 27.65 ± 16.81 nm.
The preparation method of the chitosan modified active coke in-situ supported nanogold catalyst in the embodiment is basically the same as the preparation method in the embodiment 1, and the difference is only that: the amount of the chloroauric acid solution added in the preparation method of example 4 was 2.8 mL.
The chitosan modified active coke in-situ loaded nano-gold catalyst prepared in example 4 is numbered Au NPs/CTS/AC(4)。
Example 5
The chitosan modified active coke in-situ supported nano-gold catalyst is basically the same as the chitosan modified active coke in-situ supported nano-gold catalyst in the embodiment 1, and the differences are only that: in example 5, the mass percent of Au in the chitosan modified active coke in-situ supported nano-gold catalyst is 13.40 wt%; the average particle diameter of the nano gold particles is 30.61 +/-13.58 nm.
The preparation method of the chitosan modified active coke in-situ supported nanogold catalyst in the embodiment is basically the same as the preparation method in the embodiment 1, and the difference is only that: the amount of the chloroauric acid solution added in the preparation method of example 5 was 5.6 mL.
The chitosan modified active coke in-situ loaded nano-gold catalyst prepared in example 5 is numbered Au NPs/CTS/AC(5)。
FIG. 1 shows the chitosan modified activated coke in-situ loaded nano-gold catalyst (AuNPs/CTS/AC) prepared in example 3 of the present invention(3)) Transmission electron micrographs of Active Coke (AC) and chitosan/active coke complex (CTS/AC), where a is AC, b is CTS/AC, and c is Au NPs/CTS/AC(3)D is Au NPs/CTS/AC(3)High power transmission electron microscopy. As can be seen from the view in figure 1,the surface of the active coke consists of uneven folds; after the active coke is modified by the chitosan, the surface of the active coke becomes smooth; a layer of nano gold particles is uniformly distributed on the chitosan/active coke compound, and the nano gold particles do not have the agglomeration phenomenon; the high power transmission electron microscope image shows the clear lattice stripes of the nano-gold, and the interplanar spacing is 0.204 nm and 0.235 nm respectively.
FIG. 2 is a transmission electron microscope image of the chitosan modified active coke in-situ supported nano-gold catalyst prepared in embodiments 1 to 5 of the present invention, wherein a to e are Au NPs/CTS/AC in sequence(1)、Au NPs/CTS/AC(2)、Au NPs/CTS/AC(3)、AuNPs/CTS/AC(4)、Au NPs/CTS/AC(5). FIG. 3 is a particle size distribution diagram of the chitosan modified active coke in-situ supported nano-gold catalyst prepared in embodiments 1 to 5 of the present invention, wherein (a) to (e) are Au NPs/CTS/AC in sequence(1)、Au NPs/CTS/AC(2)、Au NPs/CTS/AC(3)、Au NPs/CTS/AC(4)、Au NPs/CTS/AC(5). As shown in fig. 2 and 3, as the addition amount of chloroauric acid increases, the concentration of the gold nanoparticles supported on the chitosan/active coke becomes denser, and the particle size of the gold nanoparticles also increases.
FIG. 4 shows the chitosan modified activated coke in-situ loaded nano-gold catalyst (AuNPs/CTS/AC) prepared in example 4 of the present invention(4)) Active Coke (AC) and chitosan/active coke complex (CTS/AC). FIG. 5 is an infrared spectrum of the chitosan-modified activated coke in-situ supported nano-gold catalyst prepared in examples 1 to 5 of the present invention. As can be seen from fig. 4, chitosan is successfully modified on the surface of the active coke, and there is a coordination between the gold nanoparticles and the chitosan/active coke complex, which indicates that the gold nanoparticles are successfully loaded on the chitosan/active coke complex. As can be seen from FIG. 5, 2146 cm corresponding to the C-N bond increased with the amount of nanogold loaded-1The peak of (a) disappears, indicating that a large amount of nanogold occupies the N — H bond. At the same time, 800 cm-1～520 cm-1This band number was slightly changed due to the interaction between nanogold and the chitosan/active coke complex, thereby further verifying nanogold and chitosan/active coke complex-NH2The interaction between them.
FIG. 6 shows the chitosan modified activated coke in-situ loaded nano-gold catalyst (AuNPs/CTS/AC) prepared in example 4 of the present invention(4)) Active Coke (AC) and chitosan/active coke complex (CTS/AC). As can be seen from fig. 6, four diffraction peaks appear at 38.18 °, 44.38 °, 64.52 ° and 77.54 °, corresponding to the different four crystal planes (111), (200), (311) and (222) of Au, respectively, which are in good agreement with the standard diffraction peaks of the face centered cubic (fcc) structure of Au (JCPDS No. 04-0784).
Example 6
Investigating the catalytic performance of the chitosan modified active coke in-situ supported nano-gold catalyst, in particular to the method for catalytically reducing 4-nitrophenol at room temperature by using the chitosan modified active coke in-situ supported nano-gold catalyst, which comprises the following steps:
(1) respectively weighing 5mg of the chitosan modified active coke in-situ loaded nano-gold catalyst (Au NPs/CTS/AC) prepared in examples 1-5(1)、Au NPs/CTS/AC(2)、Au NPs/CTS/AC(3)、Au NPs/CTS/AC(4)、Au NPs/CTS/AC(5)) Adding the solution into 50mL of 4-nitrophenol solution with the concentration of 0.2mM, and stirring for 30min to ensure that the chitosan modified active coke in-situ loaded nano-gold catalyst achieves adsorption balance.
(2) Weighing 0.0757g of 5 parts of sodium borohydride, and adding the weighed 0.0757g of sodium borohydride into the mixed solution obtained in the step (1) after stirring (the molar ratio of 4-nitrophenol to sodium borohydride in the mixed solution is = 1: 200) respectively to perform catalytic reduction reaction, so as to complete the treatment of 4-nitrophenol in the water body. Adding sodium borohydride, mixing, immediately timing, sampling and filtering at certain time intervals (0 min, 1min, 2 min, 4 min, 6 min and 7.67 min), and performing ultraviolet spectrum determination.
FIG. 7 is a graph showing the change of the reaction rate constant with time during the catalytic reduction of 4-nitrophenol by the chitosan modified activated coke in-situ supported nano-gold catalyst in example 6 of the present invention. As can be seen from fig. 7, as the loading amount of the nanogold increases, the catalytic efficiency increases, but if the nanogold particles are excessively loaded, the catalytic efficiency is decreased, because the excessive nanogold particles cause the chitosan to be blocked, so that the process of transferring the 4-nitrophenol to the catalytically active site is hindered.
FIG. 8 shows the chitosan modified activated coke in-situ loaded nano-gold catalyst (Au NPs/CTS/AC) in example 6 of the present invention（4）) A change curve diagram of the ultraviolet spectrum of the solution along with the reaction time in the process of catalytic reduction of 4-nitrophenol. As can be seen from FIG. 8, when Au NPs/CTS/AC(4)When present, the intensity of the absorption peak at 400 nm (characteristic peak of p-nitrophenol) gradually becomes weaker with the lapse of reaction time, and the absorption peak at 300 nm (characteristic peak of p-aminophenol) is formed. When the reaction time reaches 7.67 min, the reaction is completed, which shows that the system can catalyze and reduce the 4-nitrophenol into the p-aminophenol in a shorter time.
Example 7
The method is used for investigating the stability of the chitosan modified active coke in-situ supported nano-gold catalyst, and specifically comprises the following steps of carrying out catalytic treatment on 4-nitrophenol (4-NP) in a water body by adopting the chitosan modified active coke in-situ supported nano-gold catalyst:
(1) 5mg of the chitosan modified active coke in-situ loaded nano-gold catalyst (Au NPs/CTS/AC) prepared in example 1 was weighed(1)) Adding the solution into 50mL of 4-nitrophenol solution with the concentration of 0.2mM, and stirring until the chitosan modified active coke in-situ loaded nano-gold catalyst reaches adsorption balance.
(2) 0.0757g of sodium borohydride is weighed and added into the mixed solution obtained after stirring in the step (1), the mixture is stirred uniformly, and catalytic reduction reaction is carried out at room temperature, so that the treatment of the 4-nitrophenol in the water body is completed. Adding sodium borohydride, mixing uniformly, immediately timing, sampling at a certain time interval, filtering, and detecting the change of the characteristic peak of the 4-nitrophenol in the filtrate by an ultraviolet-visible spectrophotometer. The solution faded to the end of the colorless reaction, and the reaction time was 7.7 min.
Fig. 9 is a recycling cycle chart of the chitosan modified activated coke in-situ supported nano-gold catalyst in the catalytic reduction of 4-nitrophenol in example 7 of the present invention. As can be seen from fig. 9, after 6 times of recycling, the chitosan modified active coke in-situ supported nanogold catalyst still has better activity, which indicates that the square chitosan modified active coke in-situ supported nanogold catalyst has good cycling stability and reusability.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-described embodiments. All technical schemes belonging to the idea of the invention belong to the protection scope of the invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention, and such modifications and embellishments should also be considered as within the scope of the invention.
Claims (8)
1. The chitosan modified active coke in-situ loaded nano-gold catalyst is characterized in that the chitosan modified active coke in-situ loaded nano-gold catalyst comprises active coke, chitosan and nano-gold particles; the surface of the active coke is modified with chitosan to form a chitosan/active coke compound; the chitosan/active coke compound is loaded with nano gold particles; the mass percentage of the nano-gold particles in the chitosan modified active coke in-situ supported nano-gold catalyst is 6.70wt% -13.40 wt%; the mass ratio of the chitosan to the active coke is 0.5-0.6; the average grain diameter of the nano gold particles is 27.65 +/-16.81 nm-30.61 +/-13.58 nm.
2. The preparation method of the chitosan modified active coke in-situ supported nano-gold catalyst as claimed in claim 1, characterized by comprising the following steps:
s1, mixing the chitosan suspension and the active coke suspension, performing ultrasonic treatment, stirring, centrifuging, washing and drying to obtain a chitosan/active coke compound;
and S2, preparing the chitosan/active coke compound obtained in the step S1 into a chitosan/active coke compound suspension, dropwise adding a chloroauric acid solution, performing ultrasonic treatment, stirring, centrifuging, washing and drying to obtain the chitosan modified active coke in-situ loaded nanogold catalyst.
3. The preparation method according to claim 2, wherein in the step S1, the volume ratio of the chitosan suspension to the activated coke suspension is 1: 5-2: 5;
the chitosan suspension is prepared by ultrasonically dispersing chitosan in an acetic acid solution; the ratio of the chitosan to the acetic acid solution is 0.2-0.6 g: 20 mL; the mass concentration of the acetic acid solution is 0.1-1%; the ultrasonic dispersion time in the preparation process of the chitosan suspension is 10-30 min;
the active coke suspension is prepared by ultrasonically dispersing active coke in water; the ratio of the active coke to the water is 0.5-1.5 g: 50 mL; the ultrasonic dispersion time in the preparation process of the active coke suspension is 10-30 min.
4. The method of claim 3, wherein the activated coke further comprises the following pretreatment before use: cleaning, drying, ball milling and sieving the active coke; ultrapure water is adopted for cleaning; the ball milling is carried out at the rotating speed of 50 r/h-200 r/h; the ball milling time is 1-2 h; the sieving is 200 mesh sieving.
5. The method according to any one of claims 2 to 4, wherein in the step S1, the ultrasonic treatment is performed for 10 to 30 min; the stirring time is 12-24 h; the drying is vacuum drying for 12 to 24 hours at the temperature of between 20 and 50 ℃.
6. The preparation method according to any one of claims 2 to 4, wherein in the step S2, the chitosan/active coke complex suspension is prepared by ultrasonically dispersing chitosan/active coke complex in water; the ratio of the chitosan/active coke compound to water is 0.1-0.5 g: 60 mL; the ultrasonic dispersion time in the preparation process of the chitosan/active coke compound suspension is 10 min-30 min.
7. The method according to any one of claims 2 to 4, wherein in the step S2, the volume ratio of the chitosan/activated coke complex suspension to the chloroauric acid solution is 60: 0.35-5.6; the concentration of the chloroauric acid solution is 24.3 mmol/L.
8. The method according to any one of claims 2 to 4, wherein in the step S2, the ultrasonic treatment is performed for 10 to 30 min; the stirring time is 12-24 h; the drying is vacuum drying for 12 to 24 hours at the temperature of between 20 and 50 ℃.
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