Preparation method and application of modified cocoanut active charcoal loaded platinum nanoparticles

Abstract

The invention discloses a preparation method and application of modified cocoanut active charcoal loaded platinum nanoparticles, and belongs to the technical field of nano composite materials, the preparation process comprises the following steps: (1) performing activation pretreatment on cocoanut active charcoal by grinding, washing, boiling, drying at constant temperature and the like; (2) putting the activated carbon subjected to activation pretreatment into an acid solution, and carrying out chemical modification on the surface of the activated carbon through stirring and ultrasonic oscillation; (3) preparing platinum nano seeds on the surface of the activated and modified activated carbon; (4) realizing growth of platinum nanoparticles on the surface of the activated carbon carrier through seed-in-situ growth; and (5) testing the electro-catalytic performance of the prepared modified coconut shell activated carbon loaded platinum nanoparticle composite material on methanol by adopting cyclic voltammetry. According to the invention, the adsorption capacity of the activated carbon is optimized, the problems that the platinum nanoparticles are easy to agglomerate, the controllable growth is difficult and the like are solved, and the prepared composite material has good catalytic performance on methanol.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanocomposites, and particularly relates to a preparation method and application of platinum nanoparticles supported on modified coconut shell activated carbon. Background Art

[0002] The noble metal platinum (Pt) is an efficient catalyst with strong catalytic activity and is widely used in many fields. However, the natural resource reserves of platinum are scarce and dispersed, the processing and extraction are difficult, the output is very limited, and the price is expensive, which restricts the application of platinum. Research shows that platinum at the nanoscale has a high specific surface area and abundant surface active sites, which makes platinum nanoparticles (PtNPs) show excellent activity and selectivity during the catalytic process, thus improving the reaction rate. By making platinum into nanoparticles, the utilization rate of platinum can be significantly increased and the amount of platinum used can be reduced. However, the specific surface energy of platinum nanoparticles is very large and they are very easy to agglomerate, which will reduce the catalytic activity of platinum. At present, most of the methods for preparing platinum nanoparticles have obvious agglomeration phenomena, which is obviously not conducive to the wide application of platinum in the catalytic field. In addition, research shows that the catalytic activity of a catalyst is related to its particle size. In order to obtain platinum nanoparticles with an ideal particle size, it is necessary to achieve the controllable growth of platinum nanoparticles on the surface of the carrier, but the application in this field is relatively few at present. Therefore, in this application, through the seed-in-situ growth method, platinum nanoseeds are first prepared on the surface of activated and modified coconut shell activated carbon, and then the in-situ growth is used to achieve the controllable growth of platinum nanoparticles on the surface of the activated carbon carrier, and finally well-dispersed platinum nanoparticles are prepared to improve the utilization rate and catalytic performance of platinum.

[0003] Activated carbon (AC) is a common carbon material with a wide range of sources and low cost. Coupled with its excellent electrical conductivity, it is often used as a carrier material for catalysts. Compared with other carbon materials such as Cabot Vulcan-XC72 carbon black and powdered graphite, activated carbon has more developed pores and a large number of microporous structures (pore diameter < 2nm), with outstanding adsorption capacity. The microporous structure of activated carbon can effectively "capture" small molecule compounds, improving the contact efficiency between the catalyst and the reactant, thereby enhancing the reaction rate. By activating the activated carbon, the pore structure can be optimized, the ash in the pores can be removed, the pore diameter can be widened, the proportion of micropores in the activated carbon and the overall adsorption capacity can be improved, and the "capture" efficiency of the activated carbon for small molecule compounds can be enhanced. In addition, the surface of activated carbon is rich in nitrogen- and oxygen-containing functional groups, and the activated carbon can be chemically modified to increase the number of its surface functional groups, further enhancing its surface polarity and chemical activity. These functional groups form a large number of active centers on the surface and in the pores of the activated carbon. These active centers will complex with platinum salt ions to generate platinum precursors, producing an anchoring effect. With the help of a small amount of reducing agent, the platinum precursors are reduced to form a large number of dispersed platinum nanoseeds, providing in-situ active sites for the reduction and growth of platinum nanoparticles later. The anchoring effect can also prevent the aggregation of platinum nanoparticles during the growth process.

[0004] Chinese Patent CN 116120146A discloses a production method and system for hexafluorobutadiene. The specification mentions that the activated carbon carrier material is selected from coconut shells, the soluble salt is selected from potassium chloroplatinate K2PtCl4, etc., the nanoparticle stabilizer is selected from polyvinylpyrrolidone PVP, the liquid phase reducing agent is selected from L-ascorbic acid, etc., to prepare a supported metal nanocatalyst. However, considering the following deficiencies of this method: (1) This method lacks activation pretreatment measures for activated carbon, does not dredge the blocked pores of activated carbon, and does not fully utilize the characteristics of developed pores of activated carbon, easy adsorption of target substances, and improvement of catalytic reaction rate; (2) This method conducts reduction treatment on the surface of activated carbon, which will significantly reduce the number of oxygen-containing and nitrogen-containing functional groups on the surface of activated carbon, is not conducive to the anchoring and loading of platinum nanoparticle precursors on the surface of activated carbon, will reduce the platinum nanoparticle loading efficiency and increase the reaction loss of platinum; (3) In this method, the stabilizer is added first during the reaction process, then the metal soluble salt and the reducing agent are added, and finally the activated carbon is added. Although the stabilizer can improve the dispersion of nanoparticles, it will also cause the nanoparticles to be coated, resulting in a blocking effect, instead reducing the contact and loading of metal nanoparticles with activated carbon, and affecting the loading success rate of platinum on the surface of activated carbon; (4) This method reduces two-component metal nanoparticles at one time, and the reduction process is uncontrollable, unable to achieve the in-situ growth of metal nanoparticles on the surface of activated carbon, and the particle size of the nanoparticles is uncontrollable; (5) After the reaction is completed and washed, this method is calcined at a high temperature of 300-400°C in an inert gas environment. The specific surface energy of metal nanoparticles is very large, and high-temperature calcination is very likely to cause nanoparticle sintering or aggregation, instead reducing the nanoscale effect and catalytic activity of the material. (6) Some reducing agents used in this method, including sodium borohydride and ethylene glycol, have certain biological toxicity and environmental pollution risks.

[0005] In this application, the pore structure of activated carbon is activated to improve the overall adsorption capacity of activated carbon and the "capture" efficiency for small molecule compounds; the surface of activated carbon is modified to improve the polarity and chemical activity of the surface of activated carbon; through the seed-in-situ growth method, platinum nanoseeds are first prepared on the surface of activated carbon that has been activated and modified, and then the in-situ growth is used to achieve the controllable growth of platinum nanoparticles on the surface of the activated carbon carrier, and finally well-dispersed platinum nanoparticles are prepared. In this application, the structure and morphology of the platinum nanoparticle / activated carbon composite material are characterized by XRD, TEM, etc., and then the electrocatalytic performance of this composite material is further studied.

[0006] Compared with the prior art, (1) in the present application, the pore structure of activated carbon is first subjected to activation pretreatment to improve the overall adsorption capacity of activated carbon and the "capture" efficiency for small molecule compounds, thereby enhancing the catalytic reaction rate. (2) By chemically modifying the surface of activated carbon, the polarity and chemical activity of the activated carbon surface are improved, the anchoring and loading of platinum nanoparticle precursors on the activated carbon surface are enhanced, the reaction loss of platinum is reduced, and a large number of dispersed platinum nanoseeds are formed through preliminary reduction, providing in-situ active sites for the reduction growth of platinum nanoparticles. (3) Through the seed-in-situ growth method, platinum nanoseeds are prepared on the surface of activated carbon after activation and modification, and the controlled growth of platinum nanoparticles on the surface of the activated carbon carrier is achieved through in-situ growth, and platinum nanoparticles with an ideal particle size can be obtained. (4) All green reducing agents are used in the present application, and the reducing agents used include L-ascorbic acid, glucose, and tannic acid, all of which are green and pollution-free auxiliaries. Summary of the Invention

[0007] Aiming at the deficiencies of the above prior art, the present application provides a preparation method and application of platinum nanoparticles supported on modified coconut shell activated carbon, which solves the technical problems existing in the prior art, such as the scarce natural resource reserves, high price and limited production of platinum; the large specific surface energy and easy aggregation of platinum nanoparticles, which will reduce the catalytic activity of platinum; and the difficult realization of the controlled growth of platinum nanoparticles.

[0008] The technical solution adopted by the present invention is as follows:

[0009] A preparation method and application of platinum nanoparticles supported on modified coconut shell activated carbon, comprising the following steps:

[0010] The first step, activation pretreatment of powdered coconut shell activated carbon: Add powdered coconut shell activated carbon with a particle size of 400 mesh to a planetary ball mill and grind it evenly for 5 - 30 min until the particle size is 1 - 5 μm, and filter out large particles with a 2500 - 3000 mesh sieve; repeatedly rinse the remaining powdered coconut shell activated carbon with deionized water 4 - 10 times, then boil it with deionized water for 20 - 50 min, filter and separate it with a 0.8 - 1 μm filter membrane, and then dry it in an oven at a temperature of 80 - 110 °C for 12 - 36 h until the mass is constant;

[0011] The second step, surface modification of powdered coconut shell activated carbon: Take the powdered coconut shell activated carbon pretreated by activation, add it to an acidic solution with a mass fraction of 10 - 30%, stir it at a temperature of 20 - 30 °C and a speed of 200 - 1000 r / min for 1 - 5 h, then ultrasonically vibrate it at a temperature of 40 - 60 °C and a frequency of 40 - 80 Hz for 1 - 5 h, then repeatedly rinse it with deionized water until the pH value is neutral, and dry it in a vacuum drying oven at a temperature of 80 - 120 °C for 12 - 36 h to obtain the modified powdered coconut shell activated carbon;

[0012] Step 3: Preparation of platinum nanoparticles supported on modified coconut shell activated carbon PtNPs / AC-M:

[0013] S1. Preparation of platinum nano seeds: Take 1 - 10 g of modified powdered coconut shell activated carbon according to the mass - volume ratio, add it to 1 L of deionized water, ultrasonically vibrate at 40 - 80 Hz for 10 - 60 min, then stir at 50 - 600 r / min for 10 - 60 min, add platinum salt solution, continue stirring for 0.5 - 5 h, then add sodium citrate solution, continue stirring for 0.5 - 5 h, and then filter while washing with deionized water. The filter membrane pore size is 0.8 - 1 μm until the pH value of the filtrate is neutral;

[0014] S2. In - situ growth of platinum nanoparticles: Transfer 1 - 10 g of the reactant obtained in S1 to a reaction device, add 1 L of deionized water, stir at 100 - 600 r / min for 10 - 60 min; then add 0.01 - 0.5 mol of dispersant and continue stirring for 0.5 - 2 h; successively add platinum salt solution and reducing agent, and reflux and stir at 80 - 90 °C. The reaction lasts for 4 - 48 h; after the reaction, wash the sample repeatedly with deionized water until neutral, filter and separate the solid with a 0.8 - 1 μm filter membrane, and then transfer the separated solid to a vacuum drying oven and vacuum - dry at 20 - 30 °C until constant weight to obtain platinum nanoparticles supported on modified coconut shell activated carbon.

[0015] Preferably, in the second step, the acidic solution is hydrogen peroxide and / or phosphoric acid.

[0016] Preferably, the platinum salts in steps S1 and S2 are K2PtCl4 and / or K2PtCl6.

[0017] Preferably, the molar mass ratio of the platinum salt to the modified powdered coconut shell activated carbon in step S1 is 0.00005 - 0.005 mol:1 g.

[0018] Preferably, the molar ratio of sodium citrate to the platinum salt in step S1 is 2 - 15:1.

[0019] Preferably, the reaction device in step S2 is selected as a flask or a reaction kettle with a stirrer and a reflux device according to the amount of reactants.

[0020] Preferably, the dispersant in step S2 is at least one of polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and cetyltrimethylammonium bromide (CTAB).

[0021] Preferably, the platinum salt in step S2 is the same as the platinum salt in step S1, and its molar amount is 2 - 10 times that of the platinum salt molar amount in step S1.

[0022] Preferably, in the step S2, the reducing agent is at least one of L-ascorbic acid, glucose, and tannic acid, and the molar dosage is 2-20 times the molar dosage of the platinum salt in the step S2.

[0023] The present application also discloses the application of the modified coconut shell activated carbon supported platinum nanoparticles prepared by any of the above preparation methods in methanol catalysis, and the steps are as follows:

[0024] Step 1: Disperse 10-30 mg of modified coconut shell activated carbon supported platinum nanoparticles into 2 mL of N,N-dimethylformamide (DMF), ultrasonically vibrate for 3 min at 50 Hz, and then use a vortex mixer to oscillate and stir at a rate of 1000 r / min for 3 min to make the modified coconut shell activated carbon supported platinum nanoparticles evenly dispersed; Take 5 μL of the evenly dispersed solution and drop it onto the surface of a columnar glassy carbon electrode with a diameter of 3 mm, and dry it at room temperature; The prepared working electrode is used for electrochemical detection;

[0025] Step 2: Using PtNPs / AC-M as the catalyst, select methanol as the target catalyst, and use cyclic voltammetry to test the electrocatalytic oxidation of methanol on the surface of PtNPs / AC-M. The electrolyte solution is 0.5 M H2SO4, and the methanol concentration is 0.1-0.7 M; The scanning range is -0.2 V to 0.9 V (vs. Ag / AgCl), and the scanning speed is 50 mV·s -1 .

[0026] Principle explanation: The purpose of the activation pretreatment of activated carbon is to clean the ash in the activated carbon, widen the pore diameter, optimize the pore structure of the activated carbon, and improve the adsorption capacity of the activated carbon for compounds; The chemical modification of activated carbon can significantly increase the content of surface functional groups on the activated carbon, enhance the polarity of the activated carbon surface, form a large number of active sites, and these active sites will interact with platinum salt ions to form an anchoring effect (the anchoring effect can effectively prevent the aggregation of platinum nanoparticles during the growth process); Taking these active sites as the origin, a large number of platinum nanoseeds are formed through preliminary reduction, providing a reaction core for the in-situ growth of subsequent platinum nanoparticles; Using the platinum nanoseeds as the growth core and a green and environmentally friendly reducing agent, the platinum nanoparticles can achieve in-situ controllable growth to prepare a platinum nanoparticle / activated carbon composite material. By controlling the reaction time, platinum nanoparticles with an ideal particle size can be obtained; By adding a specific dispersant during the reaction, the dispersion of platinum nanoparticles on the surface of activated carbon is further improved.

[0027] Beneficial effects:

[0028] 1. During the preparation process, through the activation pretreatment of activated carbon, the pore structure can be optimized and the ash in the pores can be removed, improving the proportion of micropores and the overall adsorption capacity of activated carbon, enhancing the "capture" efficiency of activated carbon for small molecule compounds, and increasing the catalytic reaction rate;

[0029] 2. Further enhance the polarity and chemical activity of the activated carbon surface through chemical modification, increase the content of surface functional groups on the activated carbon, which helps to improve the loading capacity of platinum nanoparticles on the activated carbon surface. The formed anchoring effect can prevent nanoparticle aggregation;

[0030] 3. Adopt the "two-step method" to prepare the platinum nanoparticle / activated carbon composite. First, through the coordination reaction between platinum salt ions (PtCl4 2- , PtCl6 2- ) and the surface functional groups of the activated carbon, generate the precursor of platinum nanoparticles, form a large number of platinum nanoseeds through preliminary reduction. The anchoring effect produced by coordination can avoid the aggregation of subsequent platinum nanoparticles during the growth process and improve the adhesion of platinum nanoparticles to prevent shedding. Using the platinum nanoseeds as the growth core and a green and environmentally friendly reducing agent, through the seed-in-situ growth method, realize the controllable growth of platinum nanoparticles on the surface of the activated carbon carrier, and platinum nanoparticles with an ideal particle size can be obtained;

[0031] 4. During the catalyst preparation process, adding a specific dispersant can significantly improve the dispersion of platinum nanoparticles, avoid the aggregation of platinum nanoparticles, make the platinum nanoparticles smaller, and the particle size distribution narrower and more uniform;

[0032] 5. Using methanol as the catalytic target, the modified coconut shell activated carbon supported platinum nanoparticle composite (PtNPs / AC-M) shows good catalytic sensitivity and responsiveness to methanol with different concentrations;

[0033] 6. To verify the influence and improvement of the present invention on the catalytic performance of the composite material, a platinum nanoparticle / activated carbon composite (PtNPs / AC) was prepared by the general reduction method. The preparation steps include: adding activated carbon to the reaction device, adding deionized water and then ultrasonic vibrating for 10 - 60 min, then stirring for 10 - 60 min, successively adding the platinum salt solution and the reducing agent, refluxing and stirring at 80 - 90 °C, the reaction lasts for 4 - 48 h, washing the sample repeatedly with deionized water until neutral, filtering and separating the solid by suction, and then transferring the separated solid to a vacuum drying oven, vacuum drying at 20 - 30 °C until constant weight; no dispersant was added during this preparation process, and the coconut shell activated carbon used is the same as the powdered coconut shell activated carbon that has been ground and screened but not pretreated by activation in the first step described in claim 1;

[0034] 7. For further verification, carbon materials that have been widely used in catalytic carriers currently were selected: Cabot Vulcan-XC72 carbon black and powdered graphite as carriers, and carbon black-supported platinum nanoparticle composites (PtNPs / Vulcan) and graphite-supported platinum nanoparticle composites (PtNPs / Graphite) were prepared by a reduction method respectively; the preparation steps include: adding the reaction carrier into the reaction device, adding deionized water and then ultrasonic vibrating for 10 - 60 min, then stirring for 10 - 60 min, then successively adding a platinum salt solution and a reducing agent, refluxing and stirring under the condition of 80 - 90 °C, the reaction lasting for 4 - 48 h, repeatedly washing the sample with deionized water until neutral, separating the solid by suction filtration, and then transferring the separated solid to a vacuum drying oven, drying in vacuum at 20 - 30 °C until constant weight;

[0035] 8. For further comparative verification, the catalytic performances of four materials, PtNPs / AC-M, PtNPs / AC, PtNPs / Vulcan, and PtNPs / Graphite, towards methanol were tested respectively, and the results showed that PtNPs / AC-M had more excellent catalytic ability. Description of the Drawings

[0036] Figure 1 This is the X-ray diffraction (XRD) spectrum of AC and PtNPs / AC-M in this application;

[0037] Figure 2 This is the transmission electron microscopy (TEM) characterization diagram of platinum nanoparticles supported on modified coconut shell activated carbon in this application. Among them, A is the TEM diagram of PtNPs / AC, and B is the TEM characterization diagram of PtNPs / AC-M;

[0038] Figure 3 This is the cyclic voltammogram of four materials, PtNPs / AC-M, PtNPs / Vulcan, PtNPs / AC, and PtNPs / Graphite, in an electrolyte solution of 0.5 M CH3OH / 0.5 M H2SO4 with a scanning rate of 50 mV / s. Among them, a is the cyclic voltammogram of PtNPs / AC-M; b is the cyclic voltammogram of PtNPs / Vulcan; c is the cyclic voltammogram of PtNPs / AC; d is the cyclic voltammogram of PtNPs / Graphite;

[0039] Figure 4This is the cyclic voltammogram of the catalytic oxidation of PtNPs / AC-M in methanol solutions with different concentrations. The scanning rate is 50 mV / s. Among them, a is the cyclic voltammogram of catalytic oxidation of 0.1 M CH3OH / 0.5 M H2SO4; b is the cyclic voltammogram of catalytic oxidation of 0.3 M CH3OH / 0.5 M H2SO4; c is the cyclic voltammogram of catalytic oxidation of 0.5 M CH3OH / 0.5 M H2SO4; d is the cyclic voltammogram of catalytic oxidation of 0.7 M CH3OH / 0.5 M H2SO4. Detailed implementation method

[0040] The following further elaborates on the present invention in conjunction with embodiments. It should be understood that the following embodiments are only for the explanation and illustration of the present invention, but do not limit the present invention to these specific implementation manners and do not limit the scope of the present invention in any way.

[0041] Example 1

[0042] A preparation method of platinum nanoparticles supported on modified coconut shell activated carbon includes the following steps:

[0043] First step, activation pretreatment of powdered coconut shell activated carbon: Add 50 g of powdered coconut shell activated carbon with a particle size of 400 mesh to a planetary ball mill and grind evenly for 10 min until the particle size is 1 - 5 μm. Filter out large particles with a 2500-mesh sieve; repeatedly rinse the remaining powdered coconut shell activated carbon with deionized water 5 times, then boil it with deionized water for 30 min, separate it by suction filtration through a 1-μm filter membrane, and then dry it in an oven at 100 °C for 24 h until the mass is constant;

[0044] Second step, surface modification of powdered coconut shell activated carbon: Take 10 g of powdered coconut shell activated carbon pretreated by activation, add it to 100 ml of hydrogen peroxide solution with a mass fraction of 20%, stir at 25 °C and 600 r / min for 3 h, then ultrasonically vibrate at 60 °C and 60 Hz for 3 h, and then repeatedly rinse it with deionized water until the pH value is neutral, and dry it in a vacuum drying oven at 120 °C for 24 h to obtain modified powdered coconut shell activated carbon;

[0045] Third step, preparation of platinum nanoparticles PtNPs / AC-M supported on modified coconut shell activated carbon:

[0046] S1, Preparation of platinum nanoseeds: Take 0.1 g of modified powdered coconut shell activated carbon according to the mass-volume ratio, add it to 50 mL of deionized water, ultrasonically oscillate at 60 Hz for 10 min, then stir at 300 r / min for 10 min, add 0.5 mL of 0.1 M K2PtCl4 solution, continue stirring for 1 h, then add 4 mL of 0.1 M sodium citrate solution, continue stirring for 1 h, and then wash with deionized water while filtering. The filter membrane pore size is 1 μm until the pH value of the filtrate is neutral;

[0047] S2, In-situ growth of platinum nanoparticles: Transfer the reactants obtained in S1 to a flask, add 50 mL of deionized water, and stir at 300 r / min for 30 min; then add 0.4 g of polyvinylpyrrolidone and continue stirring for 30 min; sequentially add 3 mL of 0.1 M K2PtCl4 solution and 4 mL of 0.5 M ascorbic acid solution, and reflux and stir at 85 °C. The reaction lasts for 12 h; after the reaction is completed, wash the sample repeatedly with deionized water until neutral, filter and separate the solid with a 0.8 - 1 μm filter membrane, and then transfer the separated solid to a vacuum drying oven and vacuum dry at 25 °C until constant weight to obtain platinum nanoparticles supported on modified coconut shell activated carbon.

[0048] Application of platinum nanoparticles supported on modified coconut shell activated carbon in methanol catalysis, the steps are as follows:

[0049] Step 1: Disperse 20 mg of platinum nanoparticles supported on modified coconut shell activated carbon into 2 mL of N,N-dimethylformamide (DMF), ultrasonically oscillate at 50 Hz for 3 min, and then use a vortex mixer to oscillate and stir at a rate of 1000 r / min for 3 min to make the platinum nanoparticles supported on modified coconut shell activated carbon evenly dispersed; take 5 μL of the evenly dispersed solution and drop it onto the surface of a columnar glassy carbon electrode with a diameter of 3 mm, and dry it at room temperature; the prepared working electrode is used for electrochemical detection;

[0050] Step 2: Using PtNPs / AC-M as the catalyst, select methanol as the target catalytic substance, and use cyclic voltammetry to test the electrocatalytic oxidation of methanol on the surface of PtNPs / AC-M. The electrolyte solution is 0.5 M H2SO4, and the methanol concentration is 0.1 - 0.7 M; the scanning range is -0.2 V to 0.9 V (vs. Ag / AgCl), and the scanning speed is 50 mV·s -1 。

[0051] Example 2

[0052] A preparation method and application of platinum nanoparticles supported on modified coconut shell activated carbon, including the following steps:

[0053] Step 1, Activation pretreatment of powdered coconut shell activated carbon: Add 50 g of powdered coconut shell activated carbon with a particle size of 400 mesh to a planetary ball mill and grind it evenly for 10 min until the particle size is 1 - 5 μm. Filter out large particles with a 2500 - mesh sieve; repeatedly rinse the remaining powdered coconut shell activated carbon with deionized water 5 times, then boil it with deionized water for 30 min, separate it by suction filtration through a 1 - μm filter membrane, and then dry it in an oven at 100 °C for 24 h until the mass is constant;

[0054] Step 2, Surface modification of powdered coconut shell activated carbon: Take 10 g of the activated and pretreated powdered coconut shell activated carbon, add it to 100 ml of a hydrogen peroxide solution with a mass fraction of 20%, stir it at 25 °C and 600 r / min for 3 h, then ultrasonically vibrate it at 60 °C and 60 Hz for 3 h, and then repeatedly rinse it with deionized water until the pH value is neutral. Dry it in a vacuum drying oven at 120 °C for 24 h to obtain the modified powdered coconut shell activated carbon;

[0055] Step 3, Preparation of platinum nanoparticles PtNPs / AC - M supported on modified coconut shell activated carbon:

[0056] S1, Preparation of platinum nanoseeds: Take 0.1 g of the modified powdered coconut shell activated carbon according to the mass - to - volume ratio, add it to 50 mL of deionized water, ultrasonically vibrate it at 60 Hz for 10 min, then stir it at 300 r / min for 10 min, add 0.05 mL of a K2PtCl4 solution with a concentration of 0.1 M, continue to stir for 1 h, then add 0.1 mL of a sodium citrate solution with a concentration of 0.1 M, continue to stir for 1 h, and then filter and wash it with deionized water while filtering. The filter membrane pore size is 1 μm until the pH value of the filtrate is neutral;

[0057] S2, In - situ growth of platinum nanoparticles: Transfer the reactants obtained in S1 to a flask, add 50 mL of deionized water, and stir it at 300 r / min for 30 min; then add 0.056 g of polyvinylpyrrolidone and continue to stir for 30 min; sequentially add 0.1 mL of a K2PtCl4 solution with a concentration of 0.1 M and 0.2 mL of an ascorbic acid solution with a concentration of 0.1 M, and reflux and stir at 85 °C. The reaction lasts for 12 h; after the reaction, repeatedly wash the sample with deionized water until it is neutral, separate the solid by suction filtration through a 0.8 - 1 - μm filter membrane, and then transfer the separated solid to a vacuum drying oven and vacuum - dry it at 25 °C until the weight is constant to obtain platinum nanoparticles supported on modified coconut shell activated carbon.

[0058] Application of platinum nanoparticles supported on modified coconut shell activated carbon in methanol catalysis, the steps are as follows:

[0059] Step 1: Disperse 20 mg of platinum nanoparticles supported on modified coconut shell activated carbon into 2 mL of N,N-dimethylformamide (DMF), ultrasonically oscillate for 3 min at 50 Hz, and then use a vortex mixer to oscillate and stir at a rate of 1000 r / min for 3 min to evenly disperse the platinum nanoparticles supported on modified coconut shell activated carbon; Take 5 μl of the evenly dispersed solution and drop it onto the surface of a cylindrical glassy carbon electrode with a diameter of 3 mm, and dry it at room temperature; The prepared working electrode is used for electrochemical detection;

[0060] Step 2: Using PtNPs / AC-M as the catalyst, select methanol as the target catalytic substance, and use cyclic voltammetry to test the electrocatalytic oxidation of methanol on the surface of PtNPs / AC-M. The electrolyte solution is 0.5 M H2SO4, and the methanol concentration is 0.1 - 0.7 M; The scanning range is -0.2 V to 0.9 V (vs. Ag / AgCl), and the scanning rate is 50 mV·s -1 。

[0061] Example 3

[0062] A preparation method and application of platinum nanoparticles supported on modified coconut shell activated carbon, including the following steps:

[0063] First step, activation pretreatment of powdered coconut shell activated carbon: Add 50 g of powdered coconut shell activated carbon with a particle size of 400 mesh to a planetary ball mill and grind evenly for 10 min until the particle size is 1 - 5 μm, and filter out large particles with a 2500-mesh sieve; The remaining powdered coconut shell activated carbon is repeatedly rinsed 5 times with deionized water, then boiled with deionized water for 30 min, filtered and separated with a 1-μm filter membrane, and then dried in an oven at 100 °C for 24 h until the mass is constant;

[0064] Second step, surface modification of powdered coconut shell activated carbon: Take 10 g of the powdered coconut shell activated carbon pretreated by activation, add it to 100 ml of hydrogen peroxide solution with a mass fraction of 20%, stir at 25 °C and 600 r / min for 3 h, then ultrasonically oscillate at 60 °C and 60 Hz for 3 h, and then repeatedly rinse with deionized water until the pH value is neutral, and dry it in a vacuum drying oven at 120 °C for 24 h to obtain the modified powdered coconut shell activated carbon;

[0065] Third step, preparation of platinum nanoparticles supported on modified coconut shell activated carbon PtNPs / AC-M:

[0066] S1, Preparation of platinum nano-seeds: Take 0.1 g of modified powdered coconut shell activated carbon according to the mass-volume ratio, add it to 50 mL of deionized water, ultrasonically oscillate at 60 Hz for 10 min, then stir at 300 r / min for 10 min, add 5 mL of 0.1 M K2PtCl4 solution, continue stirring for 1 h, then add 7.5 mL of 1 M sodium citrate solution, continue stirring for 1 h, and then filter while washing with deionized water. The filter membrane pore size is 1 μm until the pH value of the filtrate is neutral;

[0067] S2, In-situ growth of platinum nanoparticles: Transfer the reactants obtained in S1 to a flask, add 50 mL of deionized water, and stir at 300 r / min for 30 min; then add 2.78 g of polyvinylpyrrolidone and continue stirring for 30 min; successively add 5 mL of 1 M K2PtCl4 solution and 10 mL of 10 M ascorbic acid solution, and reflux and stir at 85 °C. The reaction lasts for 12 h; after the reaction, repeatedly wash the sample with deionized water until neutral, filter and separate the solid with a 0.8 - 1 μm filter membrane, and then transfer the separated solid to a vacuum drying oven and vacuum dry at 25 °C until constant weight to obtain platinum nanoparticles supported on modified coconut shell activated carbon.

[0068] Application of platinum nanoparticles supported on modified coconut shell activated carbon in methanol catalysis, the steps are as follows:

[0069] Step 1: Disperse 20 mg of platinum nanoparticles supported on modified coconut shell activated carbon into 2 mL of N,N-dimethylformamide (DMF), ultrasonically oscillate at 50 Hz for 3 min, and then use a vortex mixer to oscillate and stir at a rate of 1000 r / min for 3 min to make the platinum nanoparticles supported on modified coconut shell activated carbon evenly dispersed; Take 5 μl of the evenly dispersed solution and drop it onto the surface of a cylindrical glassy carbon electrode with a diameter of 3 mm, and air dry at room temperature; The prepared working electrode is used for electrochemical detection;

[0070] Step 2: Using PtNPs / AC-M as the catalyst, select methanol as the target catalyst, and use cyclic voltammetry to test the electrocatalytic oxidation of methanol on the surface of PtNPs / AC-M. The electrolyte solution is 0.5 M H2SO4, and the methanol concentration is 0.1 - 0.7 M; The scanning range is -0.2 V to 0.9 V (vs. Ag / AgCl), and the scanning speed is 50 mV·s -1 。

[0071] Comparative Example 1

[0072] The composite material of platinum nanoparticles supported on activated carbon (PtNPs / AC) was prepared by a reduction method. The activated carbon used in this method was not activated or modified, and no dispersant was used. The preparation steps are as follows: Weigh 0.1 g of powdered coconut shell activated carbon with a particle size of 400 mesh, add 50 mL of deionized water, ultrasonically vibrate at a frequency of 60 Hz for 10 min, and then stir at a speed of 300 r / min for 30 min. Then, 3.5 mL of 0.1 M K2PtCl4 solution and 4 mL of 0.5 M ascorbic acid solution were added successively, and the mixture was refluxed and stirred at 85 °C for 12 h. After the reaction, the sample was repeatedly washed with deionized water until neutral, the solid was separated by suction filtration, and then the separated solid was transferred to a vacuum drying oven and dried at 25 °C under vacuum until constant weight.

[0073] The application steps of the composite material in methanol catalysis are the same as those in Example 1.

[0074] Comparative Example 2

[0075] The composite material of platinum nanoparticles supported on Vulcan-XC72 carbon black (PtNPs / Vulcan) was prepared by a reduction method. The preparation steps are as follows: Weigh 0.1 g of Vulcan-XC72 carbon black, add 50 mL of deionized water, ultrasonically vibrate at a frequency of 60 Hz for 10 min, and then stir at a speed of 300 r / min for 30 min. Then, 3.5 mL of 0.1 M K2PtCl4 solution and 4 mL of 0.5 M ascorbic acid solution were added successively, and the mixture was refluxed and stirred at 85 °C for 12 h. After the reaction, the sample was repeatedly washed with deionized water until neutral, the solid was separated by suction filtration, and then the separated solid was transferred to a vacuum drying oven and dried at 25 °C under vacuum until constant weight.

[0076] The application steps of the composite material in methanol catalysis are the same as those in Example 1.

[0077] Comparative Example 3

[0078] The composite material of platinum nanoparticles supported on graphite (PtNPs / Graphite) was prepared by a reduction method. The preparation steps are as follows: Weigh 0.1 g of graphite powder, add 50 mL of deionized water, ultrasonically vibrate at a frequency of 60 Hz for 10 min, and then stir at a speed of 300 r / min for 30 min. Then, 3.5 mL of 0.1 M K2PtCl4 solution and 4 mL of 0.5 M ascorbic acid solution were added successively, and the mixture was refluxed and stirred at 85 °C for 12 h. After the reaction, the sample was repeatedly washed with deionized water until neutral, the solid was separated by suction filtration, and then the separated solid was transferred to a vacuum drying oven and dried at 25 °C under vacuum until constant weight.

[0079] The application steps of the composite material in methanol catalysis are the same as those in Example 1.

[0080] Experimental Example:

[0081] X-ray diffraction analysis (XRD):

[0082] The XRD patterns of activated carbon (AC) and platinum nanoparticles supported on modified coconut shell activated carbon composite (PtNPs / AC-M, the preparation process is the same as in Example 1) are as Figure 1 shown. From the XRD pattern of AC, it can be seen that the diffuse broad peak appearing near 2θ = 24° corresponds to the (002) plane of the graphite structure, and the weaker characteristic peak appearing near 2θ = 45° corresponds to the (100) plane of the graphite structure, indicating that the activated carbon is essentially composed of many disordered graphite microcrystals. In addition, we further observe the XRD pattern of PtNPs / AC-M. In addition to the diffraction peaks of the (002) plane and (100) plane of the graphite structure, two strong characteristic diffraction peaks appear at 2θ = 39.9° and 2θ = 46.5°, corresponding to the (111) plane and (200) plane of the face-centered cubic structure of platinum respectively. This indicates that the platinum nanoparticles have been successfully loaded onto the activated carbon carrier.

[0083] Transmission electron microscopy (TEM) analysis:

[0084] (A) PtNPs / AC (the preparation process is the same as in Comparative Example 1); (B) PtNPs / AC-M (the preparation process is the same as in Example 1). As Figure 2 shown, a large number of black dots in the picture are platinum nanoparticles (PtNPs). From Figure 2 A, it can be seen that the particle size of the platinum nanoparticles is relatively large, the particle size distribution is about between 50 - 100 nm, and there is obvious particle agglomeration, with poor dispersibility. While Figure 2 the distribution of platinum nanoparticles in B is very uniform, the dispersibility has been significantly improved, and there is almost no agglomeration phenomenon. It can also be seen that Figure 2 the particle size distribution of platinum nanoparticles in B is about between 20 - 30 nm, the particles are smaller, and the particle size distribution is also narrower. Generally speaking, the catalytic activity of a catalyst is related to its particle size and dispersibility. The smaller the particles and the better the dispersibility, the stronger its catalytic activity.

[0085] Catalytic performance test:

[0086] As Figure 3As shown, the cyclic voltammograms of four composite materials: PtNPs / AC-M, PtNPs / Vulcan, PtNPs / AC, and PtNPs / Graphite in an electrolyte solution of 0.5 M CH3OH / 0.5 M H2SO4, with a scanning rate of 50 mV / s. Methanol was selected as the target catalyst for the catalytic performance test, and cyclic voltammetry was used to test the electrocatalytic oxidation of methanol on the catalyst surface. The electrolyte solution was 0.5 M H2SO4, and the methanol concentration was 0.5 M. The scanning range was -0.2 V to 0.9 V (vs. Ag / AgCl), and the scanning rate was 50 mV s -1 . Figure 3 Among them, curve a corresponds to PtNPs / AC-M (the preparation process is the same as in Example 1); curve b corresponds to PtNPs / Vulcan (the preparation process is the same as in Comparative Example 2); curve c corresponds to PtNPs / AC (the preparation process is the same as in Comparative Example 1); curve d corresponds to PtNPs / Graphite (the preparation process is the same as in Comparative Example 3).

[0087] As Figure 3 shown, the first peak that appears during the forward scan is caused by the oxidation of methanol, while the peak that appears during the reverse scan is caused by the secondary oxidation of the intermediate products generated by methanol oxidation. It can be seen from the figure that the oxidation onset potential of methanol on the PtNPs / AC-M working electrode is 0.15 V, which is lower than that of PtNPs / Vulcan (0.25 V), PtNPs / AC (0.2 V), and PtNPs / Graphite (0.2 V). A lower oxidation onset potential indicates that the catalyst can initiate the oxidation reaction at a lower potential, which shows that PtNPs / AC-M has stronger catalytic activity. During the forward scan, the catalytic peaks of methanol for the curves of the four catalysts all appear around 0.62 V - 0.64 V, but they show different peak current densities. The peak current density of the electrocatalytic oxidation of methanol for curve a (PtNPs / AC-M) is 6.58 mAcm -2 ; the peak current density of the electrocatalytic oxidation of methanol for curve b (PtNPs / Vulcan) is 3.82 mAcm -2 ; the peak current density of the electrocatalytic oxidation of methanol for curve c (PtNPs / AC) is 4.16 mAcm -2 ; the peak current density of the electrocatalytic oxidation of methanol for curve d (PtNPs / Graphite) is 1.66 mAcm -2 , and the results show that PtNPs / AC-M has stronger electrocatalytic activity. This further proves that the catalytic activity of the catalyst is related to its particle size and dispersion. The smaller the particles and the better the dispersion, the stronger its catalytic activity.

[0088] As Figure 4As shown, the cyclic voltammetry curves of the composite material PtNPs / AC-M (prepared in the same process as Example 1) for the catalytic oxidation in methanol solutions with different concentrations are as follows: (a) 0.1 M CH3OH / 0.5 M H2SO4; (b) 0.3 M CH3OH / 0.5 M H2SO4; (c) 0.5 M CH3OH / 0.5 M H2SO4; (d) 0.7 M CH3OH / 0.5 M H2SO4, and the scanning rate is 50 mV / s. In order to further study the electrocatalytic response of the PtNPs / AC-M composite material to methanol solutions with different concentrations, the cyclic voltammetry curves of PtNPs / AC-M in methanol solutions with different concentrations were tested in this application. The results show that as the methanol concentration increases successively, the current density of the catalytic oxidation of methanol by PtNPs / AC-M gradually increases, and the increasing trend is obvious, indicating that PtNPs / AC-M has strong catalytic sensitivity and responsiveness.

[0089] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and the descriptions in the specification are only the preferred examples of the present invention and are not used to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of platinum nanoparticles supported on modified coconut shell activated carbon, characterized in that, It includes the following steps: The first step is the activation pretreatment of powdered coconut shell activated carbon: Add powdered coconut shell activated carbon with a particle size of 400 mesh to a planetary ball mill and grind it evenly for 5 - 30 min until the particle size reaches 1 - 5 μm. Filter out large particles with a 2500 - 3000 mesh sieve; repeatedly rinse the remaining powdered coconut shell activated carbon with deionized water 4 - 10 times, then boil it with deionized water for 20 - 50 min, separate it by suction filtration through a 0.8 - 1 μm filter membrane, and then dry it in an oven at 80 - 110 °C for 12 - 36 h until the mass is constant. The second step is the surface modification of powdered coconut shell activated carbon: Take the activated and pretreated powdered coconut shell activated carbon and add it to an acidic solution with a mass fraction of 10 - 30%. Stir it at 20 - 30 °C and 200 - 1000 r / min for 1 - 5 h, then ultrasonically vibrate it at 40 - 60 °C and 40 - 80 Hz for 1 - 5 h. Then repeatedly rinse it with deionized water until the pH value is neutral, and dry it in a vacuum drying oven at 80 - 120 °C for 12 - 36 h to obtain the modified powdered coconut shell activated carbon. The third step is the preparation of modified coconut shell activated carbon loaded with platinum nanoparticles PtNPs / AC - M. S1, Preparation of platinum nanoseeds: Take 1 - 10 g of the modified powdered coconut shell activated carbon according to the mass - to - volume ratio, add it to 1 L of deionized water, ultrasonically vibrate it at 40 - 80 Hz for 10 - 60 min, then stir it at 50 - 600 r / min for 10 - 60 min, add a platinum salt solution, continue stirring for 0.5 - 5 h, then add a sodium citrate solution, continue stirring for 0.5 - 5 h, and then filter while washing with deionized water. The filter membrane pore size is 0.8 - 1 μm until the pH value of the filtrate is neutral. S2, In - situ growth of platinum nanoparticles: Transfer 1 - 10 g of the reactant obtained in S1 to a reaction device, add 1 L of deionized water, stir it at 100 - 600 r / min for 10 - 60 min; then add 0.01 - 0.5 mol of a dispersant and continue stirring for 0.5 - 2 h; sequentially add a platinum salt solution and a reducing agent, and reflux and stir under the condition of 80 - 90 °C. The reaction lasts for 4 - 48 h; after the reaction ends, repeatedly wash the sample with deionized water until it is neutral, separate the solid by suction filtration through a 0.8 - 1 μm filter membrane, and then transfer the separated solid to a vacuum drying oven and vacuum - dry it at 20 - 30 °C until the weight is constant to obtain the modified coconut shell activated carbon loaded with platinum nanoparticles.

2. The preparation method of platinum nanoparticles supported on modified coconut shell activated carbon according to claim 1, characterized in that, In the second step, the acidic solution is hydrogen peroxide and / or phosphoric acid.

3. The preparation method of platinum nanoparticles supported on modified coconut shell activated carbon according to claim 1, characterized in that, The platinum salts in steps S1 and S2 are K2PtCl4 and / or K2PtCl6.

4. The preparation method of platinum nanoparticles supported on modified coconut shell activated carbon according to claim 1, characterized in that, In step S1, the molar mass ratio of the platinum salt to the modified powdered coconut shell activated carbon is 0.00005 - 0.005 mol:1 g.

5. The preparation method of platinum nanoparticles supported on modified coconut shell activated carbon according to claim 1, characterized in that, In step S1, the molar ratio of sodium citrate to the platinum salt is 2 - 15:

1.

6. The preparation method of platinum nanoparticles supported on modified coconut shell activated carbon according to claim 1, characterized in that, In step S2, the reaction device is selected as a flask or a reaction kettle with a stirrer and a reflux device according to the amount of reactants.

7. The preparation method of platinum nanoparticles supported on modified coconut shell activated carbon according to claim 1, characterized in that, In the step S2, the dispersant is at least one of polyvinyl alcohol PVA, polyvinylpyrrolidone PVP, and cetyltrimethylammonium bromide CTAB.

8. A preparation method of platinum nanoparticles supported on modified coconut shell activated carbon according to claim 1, characterized in that, The platinum salt in the step S2 is the same as that in the step S1, and its molar dosage is 2-10 times that of the platinum salt in the step S1.

9. The preparation method of platinum nanoparticles supported on modified coconut shell activated carbon according to claim 1, characterized in that, In the step S2, the reducing agent is at least one of L-ascorbic acid, glucose, and tannic acid, and its molar dosage is 2-20 times that of the platinum salt in the step S2.

10. Use of the modified coconut shell activated carbon supported platinum nanoparticles prepared by the preparation method according to any one of claims 1-9 in methanol catalysis, characterized in that, The steps are as follows: Step 1: Disperse 10-30 mg of platinum nanoparticles supported on modified coconut shell activated carbon into 2 mL of N,N-dimethylformamide DMF, ultrasonically vibrate for 3 min at 50 Hz, and then use a vortex mixer to oscillate and stir at a rate of 1000 r / min for 3 min to uniformly disperse the platinum nanoparticles supported on modified coconut shell activated carbon; take 5 μl of the uniformly dispersed solution and drop it onto the surface of a columnar glassy carbon electrode with a diameter of 3 mm, and dry it at room temperature; the prepared working electrode is used for electrochemical detection. Step 2: Using PtNPs / AC-M as the catalyst, methanol was selected as the target catalytic substance, and cyclic voltammetry was used to test the electrocatalytic oxidation of methanol on the surface of PtNPs / AC-M. The electrolyte solution was 0.5 M H2SO4, and the methanol concentration was 0.1 - 0.7 M; the scanning range was -0.2 V to 0.9 V (vs. Ag / AgCl), and the scanning rate was 50 mV·s -1 .

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