阅读说明：本技术 一种新型钯碳纳米复合催化剂的可控合成方法及应用 (Controllable synthesis method and application of novel palladium-carbon nano composite catalyst ) 是由 田丽红 于 2019-11-18 设计创作，主要内容包括：本发明涉及钯碳纳米复合催化剂的可控合成方法,采用蔗糖为碳源,水热法合成高水溶性的碳量子点,利用碳量子点表面的还原性含氧基团,在不加其它还原剂的情况下还原正二价钯离子Pd(Ⅱ)为零价金属钯,并通过油浴中回流的方式促使碳量子点表面的基团相互交联,形成碳薄层来固定和分散生成的钯纳米颗粒而得到一种新型钯碳纳米复合催化剂。有益效果在于：不加稳定剂和另外的载体就能固定金属钯,不会减弱钯碳纳米复合催化剂中的金属钯颗粒的活性,进一步提高了其催化还原硝基芳香类化合物的能力。本发明的方法得到的钯碳纳米复合催化剂中的金属钯颗粒尺寸可通过改变条件控制在5nm以下,活性好,作为还原硝基芳香类化合物的催化剂效果优良。(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.)

1. A controllable synthesis method of a novel 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 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.

2. The controllable synthesis method of the novel palladium-carbon nanocomposite catalyst according to claim 1, characterized in that: 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, dissolving the sucrose in deionized water, transferring the solution to a high-pressure reaction kettle after the sucrose is completely dissolved, and heating to 160-200 ℃ 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、H₂PdCl₄preparing solution with H concentration of 1.8782mg/mL-3.1302mg/mL₂PdCl₄Solution: adding a certain amount of PdCl₂Dispersing in hydrochloric acid solution with certain concentration to make PdCl₂The molar part ratio of the HCl to the HCl is 1: 2, placing the dispersion liquid in a water bath at 35-45 ℃ to be heated and stirred continuously until the solution becomes clear and transparent, and then cooling the solution to room temperature for later use;

s3, preparing Pd/C nano composite catalyst, taking prepared H₂PdCl₄Mixing the aqueous solution with a certain amount of carbon quantum dot stock solution, and stirring and reacting for 1.5-2.5 h under the conditions of an oil bath at the temperature of 80-120 ℃ and the rotating speed of 500-1000 rmp; then stirring the reaction mixed solution, naturally cooling to room temperature, centrifugally separating at the rotation speed of 5000-20000 rpm to obtain black precipitate, and respectively washing with deionized water and ethanol for 3-6 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 the temperature of 60-80 ℃.

3. The controllable synthesis method of the novel 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 to dissolve 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, heating to 180 ℃ 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 to remove large particles at the bottom, namely the stock solution of the carbon quantum dots, wherein the concentration is 8.8 mg/mL.

4. The controllable synthesis method of the novel palladium-carbon nanocomposite catalyst according to claim 1, characterized in that: said step (c) is

S2、H₂PdCl₄Preparing solution with H concentration of 1.8782mg/mL-3.1302mg/mL₂PdCl₄Solution: adding a certain amount of PdCl₂Dispersing in hydrochloric acid solution with concentration of 0.5468mg/mL-0.9113mg/mL to obtain PdCl₂The molar part ratio of the HCl to the HCl is 1: 2, the dispersion is then placed in a water bath at 35 ℃ to 45 ℃, preferably 40 ℃, with continuous heating and stirring until the solution becomes clear and transparent, and it is waited to cool to room temperature for use.

5. The controllable synthesis method of the novel palladium-carbon nanocomposite catalyst according to claim 1, characterized in that: said step (c) is

S3, preparing Pd/C nano composite catalyst, taking prepared H₂PdCl₄Mixing the water solution with the carbon quantum dot stock solution, and adjusting the added carbon quantum dots and H₂PdCl₄The volume ratio of the solution (2.5-0.5): 1; then dissolving the mixture in an oil bath at 100 +/-1 ℃ and stirring for reaction for 1.5-2.5 h at the rotating speed of 600-900 rmp; 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 obtained black precipitate is dried under vacuum at 70 ℃. + -. 1 ℃.

6. The controllable synthesis method of the novel palladium-carbon nanocomposite catalyst according to claim 5, characterized in that: said step (c) is

S3, preparing Pd/C nano composite catalyst, taking prepared H₂PdCl₄Mixing the water solution with the carbon quantum dot stock solution, and adjusting the added carbon quantum dots and H₂PdCl₄The 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 for reaction for 2-2.5 h; then, the mixed solution is stirred and naturally cooled to room temperature, and black precipitates obtained by centrifugation at the rotation speed of 10000rpm 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 under vacuum at 70 ℃. + -. 1 ℃.

7.A palladium carbon nanocomposite catalyst prepared by the controllable synthesis method of the novel palladium carbon nanocomposite catalyst according to claims 1 to 6, characterized in that: 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 50-100nm, the particle size range of the raw material of the carbon quantum dots is 1-3nm, and the size of the Pd nano-particles is formed by synthesizing the carbon quantum dots and H₂PdCl₄Controlling the volume ratio of the solution to be 4-20 nm; in the palladium-carbon nanocomposite catalyst, the mass fraction of palladium nanoparticles is 5-30%, and preferably, the mass fraction of palladium nanoparticles is 10%.

8. Use of a palladium on carbon nanocomposite catalyst according to claim 7, characterized in that: the palladium-carbon nano composite catalyst is used for selective catalytic reduction of nitroaromatic compounds, and is particularly used for selective catalytic hydrogenation reduction of the nitroaromatic compounds;

specifically, the nitroaromatic compound is p-nitrobenzene 4-NP, and the reducing agent is NaBH₄The specific reduction reaction steps are as follows:

s41, firstly, a certain amount of NaBH is added₄Dissolving 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 solution, wherein the color of the reaction solution is completely changed from yellow to colorless, namely the reaction is completely carried out;

s61, centrifuging the reaction solution, and taking the supernatant fluid to obtain the reduction product p-aminophenol 4-AP.

9. Use of a palladium on carbon nanocomposite catalyst according to claim 7, characterized in that: the nitroaromatic compound is 4-NP, and the reducing agent is HCOONH₄The specific reduction reaction steps are as follows:

s42, firstly, a certain amount of HCOONH is added₄Dissolving in 4-NP aqueous solution with certain mass concentration;

s52, adding the palladium-carbon nano composite catalyst as a catalyst into the reaction solution, and stirring in the dark for 25-35 min to achieve the adsorption-desorption balance of 4-NP on the surface of the catalyst;

s62, transferring the reaction solution into a quartz tube, and introducing N₂Under 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 the supernatant fluid to obtain the reduction product p-aminophenol 4-AP.

10. Use of a palladium on carbon nanocomposite catalyst according to claim 7, characterized in that: the nitroaromatic compound is m-nitrophenol 2-NP, and the reducing agent is NaBH₄The specific reduction reaction steps are as follows:

s43, firstly, a certain amount of NaBH is added₄Dissolving in 2-NP aqueous solution with certain mass concentration;

s53, adding palladium-carbon nano composite catalyst as catalyst into the reaction solution, and introducing N₂The reaction is carried out under illumination.

S63, centrifuging the reaction solution, and taking the supernatant fluid to obtain the reduction product o-aminophenol 2-AP.

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 morphology and the surface performance 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. US5973206a), ignition by introducing a reducing gas, addition of a large amount of a strong reducing agent, and photoreduction (New Journal of chemistry,2018, 421771-1778; Nanoscale,2014,6, 6609-containing 6616; Tetrahedron,2017,73, 5585-containing 5592), have high energy consumption and complicated operation. 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 solve the problems of the existing palladium-carbon catalyst, and provides a simple, economic and controllable method, which utilizes rich oxygen-containing groups on the surface of carbon quantum dots 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, dissolving the sucrose in deionized water, transferring the solution to a high-pressure reaction kettle after the sucrose is completely dissolved, and heating to 160-200 ℃ 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、H₂PdCl₄preparing solution with H concentration of 1.8782mg/mL-3.1302mg/mL₂PdCl₄Solution: adding a certain amount of PdCl₂Dispersing in hydrochloric acid solution with certain concentration to make PdCl₂The molar part ratio of the HCl to the HCl is 1: 2, placing the dispersion liquid in a water bath at 35-45 ℃ to be heated and stirred continuously until the solution becomes clear and transparent, and then cooling the solution to room temperature for later use;

s3, preparing Pd/C nano composite catalyst, taking prepared H₂PdCl₄Mixing 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 precipitated at 60-8 DEG CVacuum drying at 0 deg.C.

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 to dissolve 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, heating to 180 ℃ 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 to remove large particles at the bottom, namely the stock solution of the carbon quantum dots, wherein the concentration is 8.8 mg/mL.

In particular, the steps

S2、H₂PdCl₄Preparing solution with H concentration of 1.8782mg/mL-3.1302mg/mL₂PdCl₄Solution: adding a certain amount of PdCl₂Dispersing in hydrochloric acid solution with concentration of 0.5468mg/mL-0.9113mg/mL (0.015mol/L-0.025mol/L) to make PdCl₂The 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、H₂PdCl₄Preparation of a solution, preparing H with a preferred concentration of 2.5042mg/mL₂PdCl₄Solution: adding a certain amount of PdCl₂Dispersing in 0.729mg/mL (0.02mol/L) hydrochloric acid solution to obtain PdCl₂The 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 Pd/C nano composite catalyst, taking prepared H₂PdCl₄Mixing the water solution with the carbon quantum dot stock solution, and adjusting the added carbon quantum dots and H₂PdCl₄The volume ratio of the solution (2.5-0.5): 1; then the mixed solution is put in a strip with the rotating speed of 600rmp (revolutions per minute) to 900rmp (revolutions per minute) in an oil bath with the temperature of 100 +/-1 DEG CStirring and reacting 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 H₂PdCl₄X is 2.5-0.5.

Preferably, said step

S3, preparing Pd/C nano composite catalyst, taking prepared H₂PdCl₄Mixing the water solution with the carbon quantum dot stock solution, and adjusting the added carbon quantum dots and H₂PdCl₄The 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 needed 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, 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 formed by synthesizing carbon quantum dots and H₂PdCl₄Controlling the volume ratio of the solution to be 4-20 nm; 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 H₂PdCl₄When 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-nitrobenzene 4-NP, and the reducing agent is NaBH₄The specific reduction reaction steps are as follows:

s41, firstly, a certain amount of NaBH is added₄Dissolving 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 solution, wherein the color of the reaction solution is completely changed from yellow to colorless, namely the reaction is completely carried out;

s61, centrifuging the reaction solution, and taking the supernatant fluid to obtain the reduction product p-aminophenol 4-AP.

Optionally, the nitroaromatic compound is 4-NP and the reducing agent is HCOONH₄The specific reduction reaction steps are as follows:

s42, firstly, a certain amount of HCOONH is added₄Dissolving in 4-NP aqueous solution with certain mass concentration;

s52, adding the palladium-carbon nano composite catalyst as a catalyst into the reaction solution, and stirring in the dark for 25-35 min to achieve the adsorption-desorption balance of 4-NP on the surface of the catalyst;

s62, transferring the reaction solution into a quartz tube, and introducing N₂Under 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 the supernatant fluid to obtain the reduction product p-aminophenol 4-AP.

Optionally, the nitroaromatics are of the nitroaromatic typeThe compound is m-nitrophenol 2-NP, and the reducing agent is NaBH₄The specific reduction reaction steps are as follows:

s43, firstly, a certain amount of NaBH is added₄Dissolving in 2-NP aqueous solution with certain mass concentration;

s53, adding palladium-carbon nano composite catalyst as catalyst into the reaction solution, and introducing N₂The reaction is carried out under the condition of 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 between 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 metal palladium particle size in the palladium-Carbon nano composite catalyst obtained by the method can be controlled below 5nm by changing conditions, 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 in Carbon-x/Pd is not less than 1.8 marked by a sample, the metal palladium particle size of the generated palladium-Carbon nano composite catalyst is below 5nm, the activity is good, and the catalyst effect as a reduction nitro aromatic compound 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) is a diagram showing an ultraviolet-visible absorption spectrum of Carbon-2.5/Pd catalyzed 4-NP (reaction conditions: catalyst 5mg, NaBH40.025g, 4-NP concentration 50 mg/mL);

FIG. 5(b) is a graph showing a UV-VIS absorption spectrum of 4-NP with time in the absence of a 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 50 mg/mL; Carbon-in the chart_2.5Pd, i.e. Carbon-2.5/Pd, Carbon_1.8Pd, i.e. Carbon-1.8/Pd, Carbon_1.2Pd, i.e. Carbon-1.2/Pd, Carbon_0.5Pd, i.e. Carbon-0.5/Pd; the abscissa of the graph has four points representing x values of 2.5, 1.8, 1.2, 0.5);

FIG. 6(a) 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 examples of the invention were carried out on the basis of the following experimental reagents and instruments:

TABLE 1 Experimental reagents

TABLE 2 Experimental instruments