CN110841632B - Controllable synthesis method and application of palladium-carbon nano composite catalyst - Google Patents
Controllable synthesis method and application of palladium-carbon nano composite catalyst 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
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
- B01J23/44—Palladium
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- C—CHEMISTRY; METALLURGY
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- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C213/00—Preparation of compounds containing amino and hydroxy, amino and etherified hydroxy or amino and esterified hydroxy groups bound to the same carbon skeleton
- 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
Abstract
The invention relates to a controllable synthesis method of a palladium-carbon nano composite catalyst, which adopts sucrose as a carbon source to synthesize a high water-solubility carbon quantum dot by a hydrothermal method, utilizes a reductive oxygen-containing group on the surface of the carbon quantum dot to reduce bivalent palladium ions Pd (II) into zero-valent metal palladium without adding other reducing agents, and promotes the groups on the surface of the carbon quantum dot to be mutually crosslinked in a reflux mode in an oil bath to form a carbon thin layer to fix and disperse generated palladium nano particles to obtain the novel palladium-carbon nano composite catalyst. Has the advantages that: the metal palladium can be fixed without adding a stabilizer and other carriers, the activity of metal palladium particles in the palladium-carbon nano composite catalyst is not weakened, and the capability of the palladium-carbon nano composite catalyst in catalytic reduction of nitroaromatic compounds is further improved. The metal palladium particle size in the palladium-carbon nano composite catalyst obtained by the method can be controlled below 5nm by changing conditions, the activity is good, and the catalyst effect of reducing the nitroaromatic compound is excellent.
Description
Technical Field
The invention relates to a catalyst applied to hydrogenation reduction of nitroaromatic compounds, in particular to a controllable synthesis method and application of a palladium-carbon nano composite catalyst.
Background
The palladium-carbon catalyst is a supported catalyst formed by loading metal nano palladium into a carbon material, is widely applied to the chemical industry, and particularly has a good catalytic effect on hydrogenation of nitroaromatic compounds. Research shows that the catalytic activity of the nano-catalyst is strongly influenced by factors such as the size, the shape, the surface performance and the like of the nano-catalyst (Synthetic Communications,2008, 38 (17), 2889-2897). According to the characteristics of the nano particles, the smaller the particles are, the more the surface dangling bonds are, the more the active sites are, the higher the catalytic activity is, however, the particle size is less than 5nm, the synthesis of the monodisperse metal nano material needs harsh conditions, some organic long-chain molecules are required to be added as stabilizers to reduce the surface energy, and the addition of the stabilizers can occupy the active sites on the surface of the nano palladium particles to further reduce the catalytic effect. In addition, the unsupported metal palladium nano-catalyst also faces the problems of agglomeration, inactivation, difficult recovery and the like in the catalytic reaction, and the use of the excessive metal palladium catalyst causes great pollution to water. Therefore, the synthesis of the metal palladium composite catalyst which has high activity, stability and reusability has great practical significance. The palladium-carbon catalysts reported in the literature or referred in the patent at present mostly use activated carbon as a carrier, and adopt an immersion reduction method to load metal palladium, although the method is simple, the defects are that the particle size of metal nano palladium and the uniform dispersion of the metal nano palladium on the activated carbon carrier can not be effectively controlled, thereby greatly limiting the activity of the palladium-carbon catalysts. Other methods for synthesizing carbon-based/palladium (Pd) composite materials, such as reduction under supercritical conditions (US patent No. US 5973206a), ignition by introducing a reducing gas, addition of a large amount of a strong reducing agent, and photoreduction, etc. (New Journal of Chemistry,2018,421771-1778, nanoscale, 2014,6, 6609-6616. Therefore, how to simply and controllably uniformly and stably load the metal palladium nanoparticles on the surface of the carbon material still has a challenge.
Disclosure of Invention
The invention aims to provide a simple, economic and controllable method aiming at the problems of the existing palladium-carbon catalyst, wherein the rich oxygen-containing groups on the surface of carbon quantum dots are utilized to reduce and fix metal palladium nano particles with the size less than 5nm on the surface of a carbon layer to form a palladium-carbon material with uniformly dispersed palladium nano particles, and the palladium-carbon material shows high-efficiency hydrogenation reduction activity for catalyzing nitro-aromatic compounds.
The invention provides a controllable synthesis method of a novel palladium-carbon nano composite catalyst, which is characterized by comprising the following steps: sucrose is used as a carbon source, a hydrothermal method is used for synthesizing a high-water-solubility carbon quantum dot, a reductive oxygen-containing group on the surface of the carbon quantum dot is used for reducing bivalent palladium ions Pd (II) into zero-valent metal palladium without adding other reducing agents, and groups on the surface of the carbon quantum dot are mutually crosslinked in a reflux mode in an oil bath to form a carbon thin layer for fixing and dispersing generated palladium nanoparticles, so that the novel palladium-carbon nano composite catalyst is obtained.
Further, the method specifically comprises the following steps:
s1, preparing carbon quantum dots, synthesizing the carbon quantum dots with surfaces rich in reducing groups by a hydrothermal method, weighing a certain amount of sucrose to dissolve in deionized water, transferring the solution into a high-pressure reaction kettle after the sucrose is completely dissolved, and heating to 160-200 ℃ for 4-6 hours. Then naturally cooling the reaction kettle to room temperature, passing the reaction product through a microporous filter membrane with the aperture of 0.15-0.30 μm, centrifuging the obtained filtrate, and taking the supernatant as the stock solution of the carbon quantum dots, wherein the concentration is 6.6-11 mg/mL;
S2、H 2 PdCl 4 preparing solution with H concentration of 1.8782mg/mL-3.1302mg/mL 2 PdCl 4 Solution: a certain amount of PdCl 2 Dispersing in hydrochloric acid solution of certain concentration to make PdCl 2 The molar part ratio of the HCl to the HCl is 1:2, placing the dispersion liquid in a water bath at 35-45 ℃, continuously heating and stirring until the solution becomes clear and transparent, and then cooling the solution to room temperature for later use;
s3, preparing the palladium-carbon nano composite catalyst by taking prepared H 2 PdCl 4 Mixing the aqueous solution with a certain amount of carbon quantum dot stock solution, and stirring and reacting for 1.5h-2.5h under the conditions of an oil bath at the temperature of 80-120 ℃ and the rotating speed of 500-1000 rmp (revolutions per minute); then stirring the reaction mixed liquid and naturally cooling to room temperature, centrifugally separating the black precipitate at the rotating speed of 5000-20000 rpm, and respectively washing with deionized water and ethanol for 3-6 times so as to remove unreacted metal salt and carbon quantum dots on the surface of the catalyst; finally, the obtained black precipitate is dried in vacuum at the temperature of 60-80 ℃.
In particular, the steps
S1, preparing carbon quantum dots, synthesizing the carbon quantum dots with surfaces rich in reducing groups by a hydrothermal method, weighing a certain amount of sucrose, dissolving the sucrose in deionized water to prepare a sucrose solution with the concentration of 25mg/mL, transferring the solution to a high-pressure reaction kettle with a proper volume after the sucrose is completely dissolved, heating to 180 ℃, keeping the temperature for 5 hours, naturally cooling the reaction kettle to room temperature, passing the reaction solution through a microporous filter membrane with the pore diameter of 0.18-0.26 mu m, centrifuging the obtained filtrate, and removing large particles at the bottom, namely the stock solution of the carbon quantum dots, wherein the concentration of the stock solution is 8.8mg/mL.
In particular, the steps
S2、H 2 PdCl 4 Preparing solution with H concentration of 1.8782mg/mL-3.1302mg/mL 2 PdCl 4 Solution: a certain amount of PdCl 2 Dispersing in 0.5468mg/mL-0.9113mg/mL (0.015 mol/L-0.025 mol/L) hydrochloric acid solution to obtain PdCl 2 The molar part ratio of the HCl to the HCl is 1:2, then placing the dispersion in a water bath at 35-45 ℃ to continuously heat and stir until the solution becomes clear and transparent, and waiting for the solution to be cooled to room temperature for standby.
Preferably, said step
S2、H 2 PdCl 4 Preparation of a solution, preparing H at a preferred concentration of 2.5042mg/mL 2 PdCl 4 Solution: a certain amount of PdCl 2 Dispersing in 0.729mg/mL (0.02 mol/L) hydrochloric acid solution to obtain PdCl 2 The molar part ratio of the HCl to the HCl is 1:2, the dispersion is then placed in a water bath at 40 ℃ with continuous heating and stirring until the solution becomes clear and transparent, and then it is allowed to cool to room temperature for further use.
In particular, the steps
S3, preparing the palladium-carbon nano composite catalyst by taking prepared H 2 PdCl 4 Mixing the water solution with the carbon quantum dot stock solution, and adjusting the added carbon quantum dots and H 2 PdCl 4 The volume ratio of the solution (2.5-0.5): 1; then stirring the mixed solution in an oil bath at 100 +/-1 ℃ at the rotating speed of 600-900 rmp (revolutions per minute) for reaction for 1.5-2.5 h; then, the mixed solution is stirred and naturally cooled to room temperature, and black precipitates obtained by centrifugation at 10000rpm (revolutions per minute) are respectively washed for 3-5 times by deionized water and ethanol so as to remove unreacted metal salts and carbon quantum dots on the surface of the catalyst; finally, the black precipitate obtained is dried in vacuum at 70 ℃. + -. 1 ℃ for future use. The samples are marked as Carbon-x/Pd in sequence, wherein x is the added Carbon quantum dot and H 2 PdCl 4 X =2.5-0.5.
Preferably, said step
S3, preparing the palladium-carbon nano composite catalyst by taking prepared H 2 PdCl 4 Mixing the water solution with the carbon quantum dot stock solution, and adjusting the added carbon quantum dots and H 2 PdCl 4 The volume ratio of the solution (2.5): 1, stirring the mixed solution in an oil bath at 100 +/-1 ℃ and at the rotating speed of 800rmp (revolutions per minute) for 2-2.5 h; stirring the mixed solution, naturally cooling to room temperature, and centrifuging at 10000rpm (revolutions per minute) to obtain black precipitate, and washing with deionized water and ethanol for 3 times respectively to remove unreacted metal salt and carbon quantum dots on the surface of the catalyst; finally, the resulting black precipitate was dried under vacuum at 70 ℃. + -. 1 ℃ for future use, and the sample was labeled as Carbon-2.5/Pd.
The palladium-carbon nano composite catalyst synthesized by the controllable synthesis method of the palladium-carbon nano composite catalyst has the advantages that other carriers are not required to be added, the carbon thin layer for fixing and dispersing palladium nano particles is formed by mutually crosslinking groups on the surface of carbon quantum dots, the size of the carbon thin layer contained in the components of the palladium-carbon nano composite catalyst is 50-100nm, the particle size range of the carbon quantum dot raw material is 1-3nm, and the size of the palladium nano particles is formed by synthesizing carbon quantum dots and H 2 PdCl 4 Controlling the volume ratio of the solution to be 4-20nm; in the palladium-carbon nano composite catalyst, the mass fraction of palladium nano particles is 5-30%. Preferably, the mass fraction of the palladium nanoparticles is 10%.
Specifically, controllable synthesis method of palladium-carbon nano composite catalyst comprises step S3 of carbon quantum dots and H 2 PdCl 4 When the volume ratio of the original solution is controlled to be more than or equal to 1.8, namely x is more than or equal to 1.8 in Carbon-x/Pd, the concentration of Carbon Quantum Dots (CQDs) in the reaction mixed solution is more than or equal to 4.6mg/mL, and the metal palladium particle size of the generated palladium-Carbon nano composite catalyst is controlled to be less than 5 nm.
Preferably, the mass fraction of the palladium nanoparticles is 10%.
The invention also provides application of the novel palladium-carbon nano composite material, which is characterized in that: the novel palladium-carbon nano composite material is used for selective catalytic hydrogenation reduction of nitroaromatic compounds.
Preferably, the nitroaromatic compound is p-nitro aromatic compoundNitrobenzene 4-NP, the reducing agent is NaBH 4 The specific reduction reaction steps are as follows:
s41, firstly, a certain amount of NaBH is added 4 Dissolving in 4-NP aqueous solution with certain mass concentration to obtain yellow solution;
s51, adding the palladium-carbon nano composite material serving as a catalyst into the reaction liquid, wherein the color of the reaction liquid is completely changed from yellow to colorless, namely the reaction is completely carried out;
s61, centrifuging the reaction solution, and taking supernatant fluid to obtain the reduction product p-aminophenol 4-AP.
Optionally, the nitroaromatic compound is 4-NP and the reducing agent is HCOONH 4 The specific reduction reaction steps are as follows:
s42, firstly, a certain amount of HCOONH is added 4 Dissolving in 4-NP aqueous solution with certain mass concentration;
s52, adding a palladium-carbon nano composite catalyst serving as a catalyst into the reaction solution, and stirring in the dark for 25-35 min to achieve adsorption-desorption balance of 4-NP on the surface of the catalyst;
s62, transferring the reaction liquid into a quartz tube, and introducing N 2 Under the condition of illumination, within a certain time interval, when the reaction liquid becomes colorless, the reaction is completely carried out;
s72, centrifuging the reaction solution, and taking supernatant fluid, namely the reduction product p-aminophenol 4-AP.
Optionally, the nitroaromatic compound is m-nitrophenol 2-NP, and the reducing agent is NaBH 4 The specific reduction reaction steps are as follows:
s43, firstly, a certain amount of NaBH is added 4 Dissolving in 2-NP aqueous solution with certain mass concentration;
s53, adding a palladium-carbon nano composite catalyst serving as a catalyst into the reaction solution, and introducing N 2 The reaction is performed under illumination;
s63, centrifuging the reaction solution, and taking the supernatant fluid to obtain the reduction product o-aminophenol 2-AP. And measuring the ultraviolet-visible absorption spectrum of the supernatant to determine the reduced product o-aminophenol 2-AP.
After the scheme is adopted, the invention has the beneficial effects that:
1. the carbon quantum dots have the advantages of strong photostability, nontoxicity, high water solubility and the like; cheap carbon sources are adopted, the surface obtained by a simple hydrothermal synthesis method contains rich functional groups, which is very beneficial to the synthesis of functional composite materials, and the oxygen-containing reducing groups on the surface of the water-soluble carbon quantum dots can reduce Pd (II) into metal palladium nano particles without other reducing agents;
2. the method is simple and economical, and the interaction among the groups can fix and disperse the metal palladium nano particles to prevent the metal palladium particles from agglomerating so as to play a role in high-efficiency catalysis;
3. the size of metal palladium particles in the palladium-Carbon nano composite catalyst obtained by the method can be controlled below 5nm by changing conditions, and the concentration of Carbon Quantum Dots (CQDs) in the reaction mixed liquid in the step S3 in the controllable synthesis method of the palladium-Carbon nano composite catalyst is more than or equal to 4.6mg/mL, namely when x is not less than 1.8 in the sample labeled Carbon-x/Pd, the size of the metal palladium particles of the generated palladium-Carbon nano composite catalyst is below 5nm, the activity is good, and the catalyst effect as a reduction catalyst for nitro-aromatic compounds is excellent;
4. according to the invention, the metal palladium can be fixed without adding a stabilizer and an additional carrier, the activity of metal palladium particles in the palladium-carbon nano composite catalyst is not weakened, and the capability of the palladium-carbon nano composite catalyst in catalytic reduction of nitro-aromatic compounds is further improved.
Drawings
FIG. 1 (a) is an XRD pattern of Carbon-2.5/Pd;
FIG. 1 (b) Raman plot of Carbon-2.5/Pd;
FIG. 2 (a) is a TEM image of Carbon Quantum Dots (CQDs);
FIG. 2 (b) is a TEM image of Carbon-2.5/Pd;
FIG. 2 (c) is a TEM image of Carbon-1.8/Pd;
FIG. 2 (d) is a TEM image of Carbon-1.2/Pd;
FIG. 2 (e) is a TEM image of Carbon-0.5/Pd;
FIG. 2 (f) is an HRTEM image of Carbon-2.5/Pd;
FIG. 3 is an infrared spectrum of Carbon Quantum Dots (CQDs) and Carbon-2.5/Pd;
FIG. 4 (a) is a C1s XPS plot of Carbon-2.5/Pd;
FIG. 4 (b) Pd3d XPS plot of Carbon-2.5/Pd;
FIG. 5 (a) the ultraviolet-visible absorption spectrum of Carbon-2.5/Pd catalyzed 4-NP (reaction conditions: 5mg of catalyst, 40.025g of NaBH, concentration of 4-NP is 50 mg/mL);
FIG. 5 (b) UV-visible absorption spectrum of 4-NP with time in the absence of catalyst (reaction conditions: catalyst 5mg, naBH40.025g, 4-NP concentration 50 mg/mL);
FIG. 5 (c) is a time comparison graph of catalytic reduction of different nitroaromatic compounds by Carbon-2.5/Pd (reaction conditions: 5mg of catalyst, 40.025g of NaBH, and 50mg/mL of substrate concentration);
FIG. 5 (d) time chart of catalytic reduction of 4-NP with different Carbon-x/Pd materials (reaction conditions: catalyst 5mg, naBH40.025g, substrate concentration 50mg/mL; carbon-in the chart 2.5 Pd, i.e. Carbon-2.5/Pd, carbon 1.8 Pd, i.e. Carbon-1.8/Pd, carbon 1.2 Pd, i.e. Carbon-1.2/Pd, carbon 0.5 Pd, i.e. Carbon-0.5/Pd; the four points on the abscissa of the graph represent x values of 2.5,1.8,1.2, 0.5);
FIG. 6 (a) the UV-VIS absorption spectrum of Carbon-2.5/Pd photocatalytic 4-NP reduction (reaction conditions: catalyst 5mg, HCOONH40.05g, 4-NP concentration 50 mg/mL);
FIG. 6 (b) is a graph comparing the conversion of 4-NP to p-nitrophenol ion under light and dark conditions (reaction conditions: 5mg of catalyst, HCOONH40.05g, 4-NP concentration 50 mg/mL).
Detailed Description
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, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
The embodiments of the present invention were carried out based on the following experimental reagents and experimental instruments:
TABLE 1 Experimental reagents
TABLE 2 Experimental instruments
Example 1:
the preparation method of the palladium-carbon nano composite catalyst provided by the invention adopts sucrose as a carbon source, synthesizes high water-solubility carbon quantum dots by a hydrothermal method, utilizes reductive oxygen-containing groups on the surfaces of the carbon quantum dots to reduce bivalent palladium ions Pd (II) into metal nano palladium under the condition of no other reducing agent, and promotes the mutual crosslinking of the groups on the surfaces of the carbon quantum dots by an oil bath to form a carbon thin layer to fix and disperse the generated palladium nano particles to obtain the palladium-carbon composite material.
The method specifically comprises the following steps:
s1, preparing carbon quantum dots, synthesizing the carbon quantum dots with surfaces rich in reductive oxygen-containing groups by a hydrothermal method, weighing 1g +/-0.0001 g of sucrose, dissolving the sucrose in 40mL +/-0.01 mL of deionized water to prepare a 25mg/mL sucrose solution, transferring the solution to a 50mL +/-0.01 mL high-pressure reaction kettle after all the sucrose in a beaker is dissolved, and heating to 180 ℃ for 5 hours; when the reaction kettle is naturally cooled to room temperature, the reaction solution passes through a microporous filter membrane with the aperture of 0.22 mu m, the obtained filtrate is centrifuged to remove large particles, and the large particles are the stock solution of carbon quantum dots, and the concentration is 8.8mg/mL;
S2、H 2 PdCl 4 preparation of a solution, preparing H at a preferred concentration of 2.5042mg/mL 2 PdCl 4 Solution, 0.1770 g. + -. 0.0001g of PdCl 2 Dispersing in 100mL +/-0.01 mL hydrochloric acid solution with concentration of 0.729mg/mL (0.02 mol/L), then placing the dispersion in a water bath at 40 ℃, continuously heating and stirring until the solution becomes clear and transparent, and cooling to room temperature for later use;
s3, preparing the palladium-carbon nano composite catalyst by taking 30mL +/-0.01 mL of prepared H 2 PdCl 4 Mixing the aqueous solution with 75mL or 55mL or 35mL or 15mL of carbon quantum dot stock solution, simultaneously adding corresponding volume of water to keep the total volume of the reaction solution consistent, and keeping 105mL, thereby adjusting the carbon quantum dot added and H 2 PdCl 4 The volume ratio of the solution (2.5): 1 or 1.8:1 or 1.2:1 or 0.5:1; then transferred to a three-necked flask and reacted for 2 hours in an oil bath at 100 ℃. + -. 1 ℃ and at a speed of 800rmp (revolutions per minute). The mixed solution is transferred to a beaker and is stirred and naturally cooled to the room temperature, and then black precipitates obtained by centrifugation at the rotation speed of 10000rpm (revolutions per minute) are respectively washed for 3 times by deionized water and ethanol so as to remove unreacted metal salts and carbon quantum dots on the surface of the catalyst. Finally, the obtained black precipitate is dried in vacuum at 70 +/-1 ℃ for standby, the samples are marked as Carbon-x/Pd in sequence, x is the added Carbon quantum dot and H 2 PdCl 4 The volume ratio of the solution in this example was x =2.5, and in the other three examples, x =1.8, x =1.2, and x =0.5, respectively.
The embodiment also provides a palladium-carbon nano composite catalyst prepared by the preparation method of the palladium-carbon nano composite catalyst, other carriers are not needed to be added, a carbon thin layer is formed by mutual crosslinking of surface groups of carbon quantum dots to fix and disperse the generated palladium nano particles, the size of the carbon thin layer of the palladium-carbon nano composite catalyst component is 50-100nm, the particle size range of the carbon quantum dot raw material is 1-3nm, and the size of the palladium nano particles is determined by the carbon quantum dots and H in the synthesis process 2 PdCl 4 Controlling the volume ratio of the solution to be 4-20nm; in the palladium-carbon nano composite catalyst, the mass fraction of palladium nano particles is 10%.
Specifically, carbon quantum dots and H in step S3 of controllable synthesis method of palladium-carbon nano composite catalyst 2 PdCl 4 When the volume ratio of the original solution is controlled to be more than or equal to 1.8, namely x is more than or equal to 1.8 in Carbon-x/Pd, the concentration of Carbon Quantum Dots (CQDs) in the reaction mixed solution is more than or equal to 4.6mg/mL, and the metal palladium particle size of the generated palladium-Carbon nano composite catalyst is controlled to be less than 5 nm.
The embodiment also provides application of the palladium-carbon nano composite catalyst, and the palladium-carbon nano composite catalyst is used for selective catalytic reduction of reducing nitroaromatic compounds.
The nitroaromatic compound is 4-NP (p-nitrophenol), and the reducing agent is NaBH 4 The specific reaction steps of catalytic reduction of 4-NP are as follows:
s41, first 0.025g of NaBH 4 Dissolved in 50mL of solution at a concentration of 50 mg.L -1 The solution turns yellow in the 4-NP solution, and the change of an ultraviolet-visible light absorption curve is measured;
s51, adding 5mg of catalyst into the reaction solution, tracking and testing the change of the maximum absorbance value of the reaction solution within a certain time interval, and stopping recording for a while when the maximum absorbance value of the solution does not change along with time any more, namely the reaction is completed; the Carbon-2.5/Pd nano composite catalyst is added in the embodiment, and the Carbon-1.8/Pd, carbon-1.2/Pd and Carbon-0.5/Pd nano composite catalysts are respectively added in the other three embodiments;
FIG. 1 (a) is an XRD pattern of a Carbon-2.5/Pd sample, and three strong diffraction peaks appear at 40.1 deg., 46.6 deg., 68.1 deg., respectively assigned to (111), (200), (220) crystal planes of cubic system Pd (JCPDS: 46-1043). In addition, a very weak diffraction peak appears at 22 ° and is attributed to the (002) crystal face of graphitic carbon, which indicates that Carbon Quantum Dots (CQDs) successfully reduce Pd (II) to Pd (0) in the oil bath, and amorphous Carbon Quantum Dots (CQDs) undergo surface group crosslinking to form a carbon material with a graphite phase structure having low crystallinity.
FIG. 1 (b) is a Raman spectrum of Carbon-2.5/Pd, from which the present invention can find that two distinct characteristic peaks are at 1365cm -1 and 1566cm -1 This is consistent with the previously reported D-band and G-band positions, respectively, of carbon nanomaterials (e.g., graphene), where the D-band represents sp 3 Hybridized defective or disordered carbon, the G band representing sp 2 The in-plane vibration of the hybrid Carbon is obviously higher than that of a D band, and the strength of the G band in the figure shows that the synthesized Carbon-2.5/Pd has a good graphite phase structure, so that the transfer of electrons on the surface of the material is very goodAdvantageously, the D band in the figure is caused by defects generated when Carbon Quantum Dots (CQDs) reduce Pd (II).
FIG. 2 (a) is a TEM image of hydrothermally synthesized Carbon Quantum Dots (CQDs), which are relatively uniform in size and around 3nm in size. Fig. 2 (b-e) are TEM images of various Carbon-x/Pd materials obtained under different synthesis conditions by changing the concentration of Carbon Quantum Dots (CQDs), respectively, and it is found by comparison that the concentration of the Carbon Quantum Dots (CQDs) in the synthesis significantly affects the thickness of the Carbon layer in the composite material, the size of the palladium nanoparticles and the dispersion thereof on the surface of the Carbon layer. FIG. 2 (b) shows a morphology of Carbon-2.5/Pd, and palladium nanoclusters (single palladium nanoparticle size is below 5 nm) like flowers are uniformly embedded on the surface of the Carbon layer; as the concentration of Carbon Quantum Dots (CQDs) in the synthesis decreased, the Carbon layer became gradually thinner and the size of the palladium nanoparticles became gradually larger, and when the concentration of Carbon Quantum Dots (CQDs) was decreased to 1.26 mg/L, fig. 2 (e) shows that the size of the palladium nanoparticles of Carbon-0.5/Pd material was about 20nm or so. FIG. 2 (f) is an HRTEM image of Carbon-2.5/Pd, from which it is evident that the lattice fringes attributed to metallic Pd demonstrate the successful recombination of the Carbon layer with the palladium nanoparticles, consistent with the results of XRD.
FIG. 3 is an infrared spectrum of Carbon Quantum Dots (CQDs) and Carbon-2.5/Pd, reflecting the composition and changes of the surface groups of Carbon Quantum Dots (CQDs) and Carbon-2.5/Pd, and clearly observed in an infrared spectrum of Carbon Quantum Dots (CQDs) belonging to-OH (3400 cm) -1 )、C＝O(1708cm -1 ) And C = C (1631 cm) -1 ) The stretching vibration peak of (1); and is at 1360cm -1 And 1404cm -1 Indicates the presence of a C-H bond; 1030cm -1 The peak at (A) then belongs to the vibration of the C-O-C bond. 1708cm after Carbon-2.5/Pd formation -1 The peak at (a) hardly disappears because the Carbon Quantum Dots (CQDs) surface having the reducing C = O group successfully reduces Pd (II), resulting in a decrease in peak intensity. Meanwhile, the characteristic absorption peaks belonging to C-O-C bonds and O-H are also obviously weakened, which indicates that Carbon Quantum Dots (CQDs) are condensed and crosslinked in the reflux process. In contrast, the characteristic peaks of C-H bond and C = C bond are obviously enhanced, and further prove the existence of graphite phase Carbon layer, the increase of pi-pi conjugated structure and Carbon-2.5/Pd complex formation.
XPS spectra are often used to analyze the surface chemical composition of materials in depth, such as the XPS spectra of C1s and Pd3d (binding energy of orbital electrons) for Carbon-2.5/Pd, respectively, in FIGS. 4 (a) and 4 (b). Fig. 4 (a) as can be seen from the C1s XPS plot of the compound, the Carbon layer in Carbon-2.5/Pd consists mainly of C-C/C = C (284.7 eV), with small amounts of C-O (286.4 eV) and C = O groups (288.6 eV) present; FIG. 4 (b) is a Pd3d XPS plot, with two strong peaks at 335.4eV and 340.7eV demonstrating the generation of metallic palladium, indicating that Carbon Quantum Dots (CQDs) successfully reduce Pd (II) to Pd (0), while the other two weak peaks at higher electron binding energies 337.5eV and 342.6eV may result from a small amount of Pd (II) bonded to the carbon layer.
The synthesized Carbon-2.5/Pd material has very good activity of reducing p-nitrophenol (4-NP) at room temperature. As shown in FIG. 5 (a), an excess of NaBH is added 4 (0.025 g) when added to 50mL of 4-NP solution at a concentration of 50mg/L, the solution immediately turned yellow-green and its maximum absorption peak red-shifted from 310nm to 400nm due to the addition of NaBH 4 The p-nitrophenol is changed into p-nitrophenol ions. When 5mg of Carbon-2.5/Pd catalyst was added, the reaction solution rapidly changed from yellow-green to colorless (about 65 s), and the peak at 400nm disappeared, and a new absorption peak appeared at 298nm, which should be attributed to p-aminophenol (4-AP) obtained after catalytic reduction hydrogenation of 4-NP. In the absence of the catalyst, as shown in FIG. 5 (b), the peak at 400nm did not change significantly after 40min, which indicates that Carbon-2.5/Pd has a strong ability to catalyze the reduction of 4-NP for hydrogenation.
Example 2:
the preparation method of the palladium-carbon nano composite catalyst provided by the invention adopts sucrose as a carbon source, synthesizes high water-solubility carbon quantum dots by a hydrothermal method, utilizes reductive oxygen-containing groups on the surfaces of the carbon quantum dots to reduce bivalent palladium ions Pd (II) into metal nano palladium under the condition of no other reducing agent, and promotes the mutual crosslinking of the groups on the surfaces of the carbon quantum dots by an oil bath to form a carbon thin layer to fix and disperse the generated palladium nano particles to obtain the palladium-carbon composite material.
The method specifically comprises the following steps:
s1, preparing carbon quantum dots, synthesizing the carbon quantum dots with surfaces rich in reductive oxygen-containing groups by a hydrothermal method, weighing 0.75g +/-0.0001 g of sucrose, dissolving the sucrose in 30mL +/-0.01 mL of deionized water, transferring the solution to a 50mL +/-0.01 mL high-pressure reaction kettle after the sucrose in a beaker is completely dissolved, and heating to 160 ℃ for 4 hours; then naturally cooling the reaction kettle to room temperature, passing the reaction solution through a microporous filter membrane with the aperture of 0.15 mu m, centrifuging the obtained filtrate, and taking supernatant as stock solution of the carbon quantum dots, wherein the concentration is 6.6mg/mL;
S2、H 2 PdCl 4 preparation of a solution, preparing H with a preferred concentration of 1.8782mg/mL 2 PdCl 4 Solution, 0.1328 g. + -. 0.0001g of PdCl 2 Is dispersed in 100mL +/-0.01 mL of hydrochloric acid solution with the concentration of 0.5468mg/mL (0.015 mol/L), then the dispersion is placed in a water bath with the temperature of 35 ℃ for continuous heating and stirring until the solution becomes clear and transparent, and then the solution is cooled to the room temperature for standby;
s3, preparing the palladium-carbon nano composite catalyst by taking 30mL +/-0.01 mL of prepared H 2 PdCl 4 Mixing the aqueous solution with 75mL or 55mL or 35mL or 15mL of carbon quantum dot stock solution, simultaneously adding corresponding volume of water to keep the total volume of the reaction solution consistent, and keeping 105mL, thereby adjusting the carbon quantum dot added and H 2 PdCl 4 The volume ratio of the solution (2.5): 1 or 1.8:1 or 1.2:1 or 0.5:1; then transferring the mixture into a three-neck flask, and reacting for 1.5h under the conditions of an oil bath at the temperature of 80 ℃ and the rotating speed of 1000rmp (revolutions per minute); transferring the mixed solution into a beaker, naturally cooling to room temperature while stirring, centrifuging at the rotating speed of 5000rpm (revolutions per minute) to obtain black precipitates, and respectively washing with deionized water and ethanol for 6 times so as to remove unreacted metal salts and carbon quantum dots on the surface of the catalyst; finally, the obtained black precipitate is dried in vacuum at 80 +/-1 ℃ for standby, the samples are marked as Carbon-x/Pd in sequence, and x is the added Carbon quantum dot stock solution and H 2 PdCl 4 The volume ratio of the solution in this example was x =2.5, and in the other three examples, x =1.8, x =1.2, and x =0.5, respectively.
The invention also provides a palladium-carbon nano composite catalyst prepared by the preparation method of the palladium-carbon nano composite catalyst, which has no other carrier, the surface groups of the carbon quantum dots are mutually crosslinked to form a carbon thin layer for fixing and dispersing the generated palladium nano particles, the size of the carbon thin layer contained in the palladium-carbon nano composite catalyst component is 50-100nm, the particle size range of the carbon quantum dot raw material is 1-3nm, and the size of the palladium nano particles is determined by the carbon quantum dots and H in the synthesis process 2 PdCl 4 Controlling the volume ratio of the solution to be 4-20nm; in the palladium-carbon nano composite catalyst, the mass fraction of palladium nano particles is 5%.
In this example, carbon-2.5/Pd reduced other nitroaromatic compounds such as: 2-NP, and the reducing agent is NaBH 4 The specific reduction reaction steps of the catalytic reduction 2-NP are as follows:
s41, first 0.025g of NaBH 4 Dissolved in 50mL of solution at a concentration of 50 mg.L -1 Measuring the change in absorbance of the aqueous solution of 2-NP of (1);
s51, adding 5mg of catalyst into the reaction solution, starting to record time, sampling within a certain time interval, and measuring the change of the absorbance value of the reaction solution, wherein the reaction is complete when the maximum absorption peak value does not change any more; the catalyst of Carbon-2.5/Pd nano composite material is added in the embodiment, and Carbon-1.8/Pd, carbon-1.2/Pd and Carbon-0.5/Pd nano composite material are respectively added in the other three embodiments;
s61, taking 4mL of reaction liquid for centrifugation, obtaining supernatant liquid which is the reduction product p-aminophenol 2-AP, and measuring the absorbance change of the reduction product p-aminophenol 2-AP.
In this example, carbon-2.5/Pd reduced other nitroaromatic compounds: 2-NP (o-nitrophenol), in another example 4-NA (p-nitroaniline) was reduced, all with 5mg catalyst, naBH 4 0.025g, the volume of the solution is 50mL, the concentration of the substrate is 50mg/mL, the time required for the complete reaction and transformation of the three (4-NP, 2-NP and 4-NA) is shown in figure 5 (c), 65s is required for catalytic reduction of 4-NP, 30s is required for catalytic reduction of 2-NP, and only 28s is required for catalytic reduction of 4-NA, which is superior to the reported Pd supported catalyst, and shows that the Carbon-2.5 synthesized by the inventionPd has super-strong capability of catalyzing and reducing nitro-aromatic compounds. In addition, the effect of different amounts of Carbon Quantum Dots (CQDs) on the Carbon/Pd activity was also examined, and as shown in FIG. 5 (d), the shortest catalytic reduction time effect of Carbon-2.5/Pd was the best. With the continuous decrease of the dosage of Carbon Quantum Dots (CQDs), the catalytic reduction time of the 4-NP is firstly obviously increased and then gradually shortened, and the catalytic reduction time sequence is Carbon-2.5/Pd (65 s)<Carbon-0.5/Pd (99s)<Carbon-1.2/Pd(240s)<Carbon-1.8/Pd (315 s), which is greatly related to the morphology of Carbon/Pd material, because the size of palladium nanoparticles, their distribution on Carbon layer, exposed active sites, etc. directly affect the catalytic activity of palladium-Carbon nanomaterial.
Example 3:
the preparation method of the palladium-carbon nano composite catalyst provided by the invention adopts sucrose as a carbon source, synthesizes high water-solubility carbon quantum dots by a hydrothermal method, utilizes reductive oxygen-containing groups on the surfaces of the carbon quantum dots to reduce bivalent palladium ions Pd (II) into metal nano palladium under the condition of no other reducing agent, and promotes the mutual crosslinking of the groups on the surfaces of the carbon quantum dots by an oil bath to form a carbon thin layer to fix and disperse the generated palladium nano particles to obtain the palladium-carbon composite material.
The method specifically comprises the following steps:
s1, preparing a carbon quantum dot, synthesizing the carbon quantum dot with the surface rich in reducing groups by a hydrothermal method, weighing 1.25g +/-0.0001 g of sucrose, dissolving the sucrose in 50mL +/-0.01 mL of deionized water to prepare a sucrose solution with the concentration of 25mg/mL, transferring the solution to a 70mL +/-0.01 mL high-pressure reaction kettle after all the sucrose in a beaker is dissolved, and heating to 200 ℃ for 6 hours; then naturally cooling the reaction kettle to room temperature, passing the reaction solution through a microporous filter membrane with the aperture of 0.30 mu m, centrifuging the obtained filtrate, and taking supernatant as stock solution of the carbon quantum dots, wherein the concentration is 11mg/mL;
S2、H 2 PdCl 4 preparation of a solution, preparing H with a preferred concentration of 3.1302mg/mL 2 PdCl 4 Solution, 0.2213g +/-0.0001 g of PdCl 2 Is dispersed in a hydrochloric acid solution of 100 mL. + -. 0.01mL and a concentration of 0.9113mg/mL (0.025 mol/L), and then the dispersion is placed inContinuously heating and stirring in a water bath at 45 ℃ until the solution becomes clear and transparent, and then cooling to room temperature for later use;
s3, preparing the palladium-carbon nano composite catalyst by taking 30mL +/-0.01 mL of prepared H 2 PdCl 4 Mixing the aqueous solution with 75mL or 55mL or 35mL or 15mL of carbon quantum dot stock solution, simultaneously adding corresponding volume of water to keep the total volume of the reaction solution consistent, and keeping 105mL, thereby adjusting the carbon quantum dot added and H 2 PdCl 4 The volume ratio of the solution (2.5): 1 or 1.8:1 or 1.2:1 or 0.5:1; then transferring the mixture into a three-neck flask, and reacting for 2.5h in an oil bath at the temperature of 120 ℃ and at the rotating speed of 500rpm (revolutions per minute); transferring the mixed solution into a beaker, naturally cooling to room temperature while stirring, centrifuging at the rotation speed of 20000rpm to obtain black precipitate, and respectively washing with deionized water and ethanol for 5 times in order to remove unreacted metal salt and carbon quantum dots on the surface of the catalyst; finally, the obtained black precipitate is dried in vacuum at 70 +/-1 ℃ for later use, the sample is marked as Carbon-x/Pd in sequence, x is the added Carbon quantum dot and H 2 PdCl 4 In the present example, x =2.5, and in the other three examples, x =1.8, x =1.2, and x =0.5, respectively.
The invention also provides a palladium-carbon nano composite catalyst prepared by the preparation method of the palladium-carbon nano composite catalyst, which has the advantages that other carriers are not required to be added, the carbon thin layer for fixing and dispersing palladium nano particles is formed by mutually crosslinking groups on the surfaces of carbon quantum dots, namely, the groups on the surfaces of the carbon quantum dots are mutually crosslinked to form a carbon thin layer for fixing and dispersing the generated palladium nano particles, the size of the carbon thin layer of the palladium-carbon nano composite catalyst component is 50-100nm, the particle size range of the carbon quantum dot raw material is 1-3nm, and the size of the palladium nano particles is determined by the carbon quantum dots and H in the synthesis process 2 PdCl 4 Controlling the volume ratio of the solution to be 4-20nm; in the palladium-carbon nano composite catalyst, the mass fraction of palladium nano particles is 30%.
In this example, HCOONH is used 4 A reducing agent for carrying out photocatalytic hydrogenation reduction on the nitroaromatic compound 4-NPThe bulk reduction reaction comprises the following steps:
s42, firstly, 0.05g of HCOONH 4 Dissolving in 50mL of 50 mg/L4-NP aqueous solution;
s52, adding 5mg of palladium-carbon nano composite catalyst serving as a catalyst into the reaction solution, and stirring for 30min in the dark, wherein the stirring time is 25min and 35min in the other two embodiments respectively, so as to achieve the adsorption-desorption balance of 4-NP on the surface of the catalyst; the Carbon-2.5/Pd nano composite material catalyst is added in the embodiment, and the Carbon-1.8/Pd, carbon-1.2/Pd and Carbon-0.5/Pd nano composite materials are respectively added in the other three embodiments;
s62, transferring the reaction solution into a quartz tube, and introducing N 2 At 5min intervals, 4mL of the solution was centrifuged to remove the catalyst, and the absorbance curve of the supernatant was determined, the conversion being determined according to (A) t /A 0 ) X 100% calculation, wherein A t The absorbance value, A, at the maximum absorption wavelength in the reaction time interval 0 Is the absorbance value of the initial solution; the reduction rate reaches 100 percent in 25 minutes;
s72, centrifuging the reaction solution, and taking supernatant fluid, namely the reduction product p-aminophenol 4-AP.
As can be seen from FIG. 6 (a), the catalyst is added and stirred for 30min under dark conditions, the maximum absorption peak of 4-NP is still at 310nm and has a small red shift, after 5min of illumination, 4-NP is completely converted into p-nitrophenol anion, the maximum absorption peak is red-shifted to 400nm, the absorption peak at 400nm gradually weakens until the absorption peak disappears with the increase of illumination time, the absorption peak of 4-AP appears at 298nm and the intensity gradually increases, which shows that 4-NP is gradually reduced, and the reduction rate of 4-NP reaches 100% after 25min of illumination. Furthermore, it was found that the single Carbon/Pd catalyst did not promote the conversion of 4-NP to the p-nitrophenol anion, whereas the large amount of HCOONH 4 Can result in slow dehydrogenation of 4-NP. FIG. 6 (b) compares Carbon-2.5/Pd with HCOONH 4 When the reaction solution exists simultaneously, the conversion rate of 4-NP converted into anion thereof under the conditions of illumination and darkness shows that the reaction solution reacts for 5min under visible light, 4-NP is completely converted into corresponding anion, and only 20.2 percent of 4-NP is converted into corresponding anion after reaction for 30min under the dark conditionThis shows that under visible light-assisted conditions, the Carbon/Pd catalysis accelerates HCOONH 4 The H atom in-OH of the 4-NP molecule is abstracted, so that the p-nitrophenol ion can be quickly converted.
The reinforced catalysis mechanism of the palladium-carbon nano composite catalyst prepared by the preparation method of the palladium-carbon nano composite catalyst is as follows: the mechanism of catalytic hydrogenation reduction of aromatic nitro compounds can often be explained when NaBH is used 4 Dissociating by hydration to form B (OH) 4 - When active hydrogen is used, the bonding of the metal palladium catalyst to the active hydrogen and the electron transfer determine the reduction rate of 4-NP; for Carbon-2.5/Pd and Carbon-1.8/Pd catalysts, the size of the formed palladium nano-particles can be controlled to be less than 5nm, and the structure can provide a large number of active sites, and the combination comes from NaBH 4 Active hydrogen formed by hydrolysis; the large specific surface area of the carbon layer not only facilitates the adsorption of 4-NP, but also conducts electrons rapidly, resulting in the rapid reduction of 4-NP.
In a word, the palladium-carbon nano composite catalyst is synthesized by adopting an oil bath reflux mode and taking Carbon Quantum Dots (CQDs) as a reducing agent and a carbon source. At different carbon quantum dots and H 2 PdCl 4 Among the palladium-Carbon nano composite catalysts generated by the reaction of the volume ratio of the solution, the palladium-Carbon nano composite catalyst marked as Carbon-2.5/Pd has the best catalytic activity under the conditions (5 mg of catalyst, naBH 4 0.025g, solution volume 50mL, substrate concentration 50 mg/mL), 4-NP, 2-NP, and 4-NA were rapidly catalyzed within 65s, 30s, and 28s, respectively. In addition, carbon-2.5/Pd can accelerate HCOONH under the action of visible light 4 By dehydrogenation of (2) to form CO 2 - The free radical causes the 4-NP to be rapidly converted into p-nitrophenol ions, the H bonded on the surface of the palladium nano particle causes the effective reduction of the 4-NP, and the reduction rate of the 4-NP reaches 100% after illumination for 25 min. The enhanced catalytic activity of Carbon-2.5/Pd is mainly due to the unique structure and the synergistic effect of the Carbon layer and Pd: (1) The size of palladium nano particles in the composite material can be controlled to be less than 5nm, and active hydrogen can be effectively adsorbed; (2) The carbon layer formed by crosslinking Carbon Quantum Dots (CQDs) has strong conductive ability and can rapidly conduct electrons to promoteAnd (4) reducing. In a word, the method for synthesizing Carbon-2.5/Pd and Carbon-1.8/Pd in the invention is simple and economic, has excellent catalytic activity, and can generate great economic benefit when being popularized and applied to industrial production.
Claims (11)
1. A controllable synthesis method of a palladium-carbon nano composite catalyst is characterized by comprising the following steps: sucrose is used as a carbon source, a hydrothermal method is used for synthesizing a high-water-solubility carbon quantum dot, a reducing oxygen-containing group on the surface of the carbon quantum dot is utilized, a divalent palladium ion Pd (II) is reduced to zero-valent metal palladium under the condition that other reducing agents are not added, groups on the surface of the carbon quantum dot are mutually crosslinked in a reflux mode in an oil bath, a carbon thin layer is formed to fix and disperse generated palladium nano particles, and the palladium-carbon nano composite catalyst is obtained;
the method specifically comprises the following steps:
s1, preparing carbon quantum dots, synthesizing the carbon quantum dots with surfaces rich in reducing groups by a hydrothermal method, weighing a certain amount of sucrose to dissolve in deionized water, transferring the solution into a high-pressure reaction kettle after the sucrose is completely dissolved, and heating to 160 DEG C o C-200 o C, keeping for 4-6 h; then naturally cooling the reaction kettle to room temperature, passing the reaction product through a microporous filter membrane with the aperture of 0.15-0.30 μm, centrifuging the obtained filtrate, and taking the supernatant as the stock solution of the carbon quantum dots, wherein the concentration is 6.6-11 mg/mL;
S2、H 2 PdCl 4 preparing solution with H concentration of 1.8782mg/mL-3.1302mg/mL 2 PdCl 4 Solution: a certain amount of PdCl 2 Dispersing in hydrochloric acid solution with certain concentration to make PdCl 2 The molar part ratio of the HCl to the HCl is 1:2, then placing the dispersion at 35 o C-45 o C, continuously heating and stirring in the water bath until the solution becomes clear and transparent, and then cooling to room temperature for later use;
s3, preparing the palladium-carbon nano composite catalyst by taking prepared H 2 PdCl 4 Mixing the aqueous solution with a certain amount of carbon quantum dot stock solution at 80 deg.C o C-120 o C, stirring and reacting for 1.5-2.5 h under the conditions of oil bath and the rotating speed of 500-1000 rpm; then the reaction mixture is addedNaturally cooling to room temperature while stirring, centrifugally separating to obtain black precipitate at 5000-20000 rpm, and washing with deionized water and ethanol for 3-6 times to remove unreacted metal salt and carbon quantum dots on the surface of the catalyst; finally, the resulting black precipitate was precipitated at 60 o C-80 o And C, vacuum drying.
2. The controllable synthesis method of palladium-carbon nanocomposite catalyst according to claim 1, characterized in that: said step (c) is
S1, preparing carbon quantum dots, synthesizing the carbon quantum dots with surfaces rich in reducing groups by a hydrothermal method, weighing a certain amount of sucrose, dissolving the sucrose in deionized water to prepare a sucrose solution with the concentration of 25mg/mL, transferring the solution to a high-pressure reaction kettle with a proper volume after all the sucrose is dissolved, and heating to 180 DEG C o And C, keeping the temperature for 5 hours, naturally cooling the reaction kettle to room temperature, passing the reaction solution through a microporous filter membrane with the pore diameter of 0.18-0.26 mu m, centrifuging the obtained filtrate, and removing large particles at the bottom, namely the stock solution of the carbon quantum dots, wherein the concentration is 8.8mg/mL.
3. The controllable synthesis method of palladium-carbon nanocomposite catalyst according to claim 1, characterized in that: said step (c) is
S2、H 2 PdCl 4 Preparing solution with H concentration of 1.8782mg/mL-3.1302mg/mL 2 PdCl 4 Solution: a certain amount of PdCl 2 Dispersing in hydrochloric acid solution with concentration of 0.5468mg/mL-0.9113mg/mL to obtain PdCl 2 The molar part ratio of the HCl to the HCl is 1:2, then placing the dispersion at 35 o C-45 o And C, continuously heating and stirring in the water bath until the solution becomes clear and transparent, and waiting for the solution to be cooled to the room temperature for standby.
4. The controllable synthesis method of palladium-carbon nanocomposite catalyst according to claim 1, characterized in that: said step (c) is
S3, preparing the palladium-carbon nano composite catalyst by taking prepared H 2 PdCl 4 Mixing the aqueous solution with the carbon quantum dot stock solutionAdjusting the carbon quantum dots added and H 2 PdCl 4 The volume ratio of the solution (2.5-0.5): 1; then the mixed solution is mixed at 100 o C±1 o C, stirring and reacting for 1.5-2.5 h in an oil bath at the rotating speed of 600-900 rpm; stirring the mixed solution, naturally cooling to room temperature, and centrifuging at 10000rpm to obtain black precipitate, and washing with deionized water and ethanol for 3-5 times to remove unreacted metal salt and carbon quantum dots on the surface of the catalyst; finally, the resulting black precipitate was precipitated at 70 o C±1 o And C, vacuum drying.
5. The controllable synthesis method of palladium-carbon nanocomposite catalyst according to claim 4, characterized in that: said step (c) is
S3, preparing the palladium-carbon nano composite catalyst by taking prepared H 2 PdCl 4 Mixing the water solution with the carbon quantum dot stock solution, and adjusting the added carbon quantum dots and H 2 PdCl 4 The volume ratio of the solution of (2.5): 1, then the mixed solution is added to 100 o C±1 o C, stirring and reacting for 2-2.5 h in an oil bath at the rotating speed of 800 rpm; then, the mixed solution is naturally cooled to room temperature while stirring, and black precipitates obtained by centrifugation at the rotation speed of 10000rpm are respectively washed by deionized water and ethanol for 3 times so as to remove unreacted metal salts and carbon quantum dots on the surface of the catalyst; finally, the resulting black precipitate was precipitated at 70 o C±1 o And C, vacuum drying.
6. A palladium carbon nanocomposite catalyst obtained by the method for the controlled synthesis of a palladium carbon nanocomposite catalyst according to any one of claims 1 to 5, wherein: the carbon thin layer for fixing and dispersing the palladium nano-particles is formed by mutually crosslinking groups on the surfaces of the carbon quantum dots without adding other carriers, the size of the carbon thin layer of the palladium-carbon nano-composite catalyst component is between 50 and 100nm, the particle size of the carbon quantum dot raw material is between 1 and 3nm, and the palladium nano-particles are synthesized from carbon quantum dots and H 2 PdCl 4 Controlling the volume ratio of the solution to be 4-20nm; the palladium-carbon nano compositeIn the composite catalyst, the mass fraction of the palladium nano-particles is 5-30%.
7. Use of a palladium on carbon nanocomposite catalyst according to claim 6, characterized in that: the palladium-carbon nano composite catalyst is used for selective catalytic hydrogenation reduction of nitroaromatic compounds,
specifically, the nitroaromatic compound is p-nitrophenol 4-NP, and the reducing agent is NaBH 4 The specific reduction reaction steps are as follows:
s41, firstly, a certain amount of NaBH is added 4 Dissolving in 4-NP aqueous solution with certain mass concentration to obtain yellow solution;
s51, adding a palladium-carbon nano composite material serving as a catalyst into the reaction liquid, wherein the color of the reaction liquid is completely changed from yellow to colorless, namely the reaction is completely carried out;
s61, centrifuging the reaction liquid, and taking the supernatant to obtain the reduction product p-aminophenol 4-AP.
8. Use of the palladium-carbon nanocomposite catalyst according to claim 6, wherein: the palladium-carbon nano composite catalyst is used for selective catalytic hydrogenation reduction of nitroaromatic compounds, the nitroaromatic compounds are 4-NP, and the reducing agent is HCOONH 4 The specific reduction reaction steps are as follows:
s42, firstly, a certain amount of HCOONH is added 4 Dissolving in 4-NP aqueous solution with certain mass concentration;
s52, adding a palladium-carbon nano composite catalyst serving as a catalyst into the reaction solution, and stirring in the dark for 25-35 min to achieve adsorption-desorption balance of 4-NP on the surface of the catalyst;
s62, transferring the reaction liquid into a quartz tube, and introducing N 2 Under the condition of illumination, within a certain time interval, when the reaction liquid becomes colorless, the reaction is completely carried out;
s72, centrifuging the reaction solution, and taking supernatant fluid, namely the reduction product p-aminophenol 4-AP.
9. A kind ofThe use of the palladium on carbon nanocomposite catalyst according to claim 6, wherein: the palladium-carbon nano composite catalyst is used for selective catalytic hydrogenation reduction of a nitroaromatic compound, wherein the nitroaromatic compound is m-nitrophenol 2-NP, and the reducing agent is NaBH 4 The specific reduction reaction steps are as follows:
s43, firstly, a certain amount of NaBH is added 4 Dissolving in 2-NP aqueous solution with certain mass concentration;
s53, adding a palladium-carbon nano composite catalyst serving as a catalyst into the reaction solution, and introducing N 2 The reaction is carried out under the condition of illumination;
s63, centrifuging the reaction liquid, and taking the supernatant to obtain the reduced product o-aminophenol 2-AP.
10. The controllable synthesis method of palladium-carbon nanocomposite catalyst according to claim 3, characterized in that: in said step S2, the dispersion is placed at 40 o And C, continuously heating and stirring in the water bath until the solution becomes clear and transparent.
11. The palladium-carbon nanocomposite catalyst according to claim 6, wherein: the mass fraction of the palladium nanoparticles is 10%.
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