Polydopamine / noble metal catalyst as well as preparation method and application thereof

Abstract

The invention discloses a polydopamine / noble metal catalyst and a preparation method and application thereof.The preparation method comprises the steps that firstly, a PDA monomer solution serves as electrolyte, electrochemical polymerization is conducted on a conductive substrate through cyclic voltammetry, and conductive substrate loaded polydopamine is obtained; and by taking a noble metal salt solution as a precursor solution, loading noble metal nanoparticles on the conductive substrate loaded polydopamine to obtain the conductive substrate loaded polydopamine / noble metal catalyst. The prepared catalyst can delay inactivation of noble metal under high potential, realizes preparation of glycollic acid through electro-catalysis of ethylene glycol under high potential and coupled hydrogen production, realizes full utilization of PET plastic monomer ethylene glycol, and converts ethylene glycol into more valuable glycollic acid under high potential.

Description

Technical Field

[0001] The invention belongs to the technical field of polyol acid production, and specifically relates to a polydopamine / noble metal catalyst and a preparation method and application thereof. Background Art

[0002] Converting discarded polyethylene terephthalate (PET) plastics into monomers or high-value-added chemicals by chemical means is one of the effective ways to solve the increasingly serious plastic pollution and alleviate the depletion of fossil resources. Ethylene glycol is a key monomer of PET, and electrochemical oxidation driven by renewable electricity provides a sustainable strategy to directly oxidize ethylene glycol into high-value-added chemicals in alkaline solution, while producing hydrogen at the cathode.

[0003] Glycolic acid is widely used in chemical cleaning and the production of polyglycolic acid-lactic acid, polyglycolic acid, etc. Its related products have excellent properties such as biodegradability, biocompatibility, and low toxicity, and the market demand is significant. However, at present, high-value-added glycolic acid is generally obtained by chemical or biological oxidation of ethylene glycol. The production method often relies on irritating, carcinogenic and consumable petrochemical products, and the process often requires harsh reaction conditions and low glycolic acid selectivity. The electrochemical preparation of glycolic acid has more advantages, such as high glycolic acid yield, few by-products, and short reaction time. Therefore, the electrocatalytic ethylene glycol selective oxidation method has become a potential method for preparing glycolic acid, and then a path for preparing degradable plastics.

[0004] The current electrocatalytic ethylene glycol selective oxidation technology requires the use of precious metals such as platinum, palladium and gold to improve the activity of the catalytic material. However, at high potentials, the precious metals will be rapidly converted into an oxidized state, resulting in catalyst deactivation (e.g. Au is oxidized to AuO at high potentials). x ), which leads to a significant decrease in current density and glycolic acid selectivity. Therefore, it is urgent to develop a new technical means to delay the deactivation of precious metal catalysts and promote the electrooxidation of ethylene glycol to produce glycolic acid at high potential. Summary of the invention

[0005] The present invention is proposed to overcome the disadvantage of easy deactivation in the existing technology of preparing glycolic acid by electrocatalyzing ethylene glycol with noble metal-based catalysts, and its purpose is to provide a polydopamine / noble metal catalyst and its preparation method and application.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a polydopamine / noble metal catalyst comprises the following steps:

[0008] (I) dissolving PDA monomer in a solvent to obtain a PDA monomer solution;

[0009] (II) using PDA monomer solution as electrolyte, electrochemical polymerization is carried out on a conductive substrate by cyclic voltammetry to obtain polydopamine supported on the conductive substrate;

[0010] (III) Using a noble metal salt solution as a precursor solution, noble metal nanoparticles are loaded on polydopamine loaded on a conductive substrate by electrodeposition or liquid phase reduction, thereby obtaining a polydopamine / noble metal catalyst loaded on a conductive substrate; the polyhydroxy structure of polydopamine can inhibit the deactivation of noble metals during the reaction.

[0011] In the above technical scheme, the PDA monomer is dopamine hydrochloride; the solvent is deionized water or a weak alkaline buffer solution; the weak alkaline buffer solution is a phosphate buffer solution, Tris-HCl buffer solution, carbonate buffer solution or ammonia solution with a pH of 6.8 to 10; the concentration of the PDA monomer in the PDA monomer solution is 0.5 g / L to 10 g / L, and the pH value of the PDA monomer solution is 6.8 to 10.

[0012] In the above technical solution, the conductive substrate is any one of carbon cloth, carbon paper, nickel foam, nickel sheet, nickel mesh, copper foam, copper sheet, copper mesh, titanium sheet, titanium mesh, stainless steel sheet, stainless steel mesh, ITO conductive glass or FTO conductive glass.

[0013] In the above technical solution, the conductive substrate needs to be pretreated before electrochemical polymerization. The specific pretreatment method is: first, the conductive substrate is ultrasonically cleaned in dilute hydrochloric acid, ethanol and deionized water for 15 minutes to remove the surface oxide layer and oil stains, and then vacuum dried.

[0014] In the above technical scheme, the cyclic voltammetry in step (II) is specifically as follows: using a conductive substrate as a working electrode, a counter electrode, and a reference electrode to form a three-electrode system, and depositing in a PDA monomer solution at a potential of -1V to 1V vs Ag / AgCl for 1min to 60min.

[0015] In the above technical solution, the counter electrode is a platinum sheet; and the reference electrode is a silver / silver chloride electrode.

[0016] In the above technical solution, the thickness of the polydopamine loaded on the conductive substrate is 0.1 nm to 10 nm.

[0017] In the above technical solution, the precious metal is any one or more of platinum, gold, silver, ruthenium, iridium, palladium, copper or rhodium; the concentration of the precious metal salt solution is 2mmol / L to 50mmol / L.

[0018] In the above technical scheme, the cyclic voltammetry electrodeposition method in step (III) is specifically as follows: polydopamine supported on a conductive substrate is used as a working electrode, and a three-electrode system is formed with a counter electrode and a reference electrode, and is deposited in a noble metal salt solution at a potential of -1VvsAg / AgCl for 1min to 60min.

[0019] In the above technical scheme, the liquid phase reduction method in step (III) refers to immersing the polydopamine supported on a conductive substrate in a precious metal salt solution, and then adding sodium borohydride as a reducing agent to obtain a polydopamine / precious metal catalyst supported on a conductive substrate.

[0020] A polydopamine / noble metal catalyst is prepared by the method.

[0021] A method for preparing glycolic acid from ethylene glycol by electrocatalysis and producing hydrogen by coupling is disclosed. The method comprises the following steps:

[0022] (I) Assembling the electrolytic cell

[0023] The polydopamine / precious metal catalyst supported on a conductive substrate is used as an anode, the cathode catalyst is used as a cathode, and they are assembled into an electrolytic cell with an electrolyte;

[0024] (II) Electrocatalytic reaction

[0025] Ethylene glycol is added to the electrolyte. Under voltage conditions, the polyol is oxidized at the anode to produce glycolic acid, and water is reduced at the cathode to produce hydrogen.

[0026] In the above technical solution, the electrolyte is an aqueous solution of any one or more of sodium hydroxide, potassium hydroxide, potassium bicarbonate, potassium carbonate, sodium bicarbonate or sodium carbonate, and the concentration of the electrolyte in the electrolyte is 1g / L to 50g / L.

[0027] In the above technical scheme, the cathode catalyst is any one of transition metal oxides, transition metal phosphides, transition metal sulfides, transition metal nitrides, transition metal borides, platinum-based catalysts, palladium-based catalysts, ruthenium-based catalysts, rhodium-based catalysts, nickel-based catalysts or copper-based catalysts, or a mixture of several of them; when the cathode catalyst is a powder, the cathode is composed of a conductive substrate loaded with the cathode catalyst.

[0028] In the above technical solution, the concentration of ethylene glycol in the electrolyte is 1 g / L to 50 g / L; and the voltage condition is 0 V to 2 V vsAg / AgCl.

[0029] The beneficial effects of the present invention are:

[0030] The present invention provides a polydopamine / noble metal catalyst and a preparation method and application thereof. The catalyst can delay the deactivation of the noble metal at a high potential, realize the coupled hydrogen production of preparing glycolic acid from ethylene glycol at a relatively high potential, realize the full utilization of PET plastic monomer ethylene glycol, and convert ethylene glycol into more valuable glycolic acid at a relatively high potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the reaction principle of the catalyst of the present invention;

[0032] Figure 2 is a SEM image of the anode catalyst in Example 1 of the present invention;

[0033] Figure 3 is the X-ray diffraction pattern of the anode catalyst in Example 1 of the present invention;

[0034] Figure 4 is an infrared spectrum of the anode catalyst in Example 1 of the present invention;

[0035] Figure 5 is a current-time curve in the reaction of preparing glycolic acid from ethylene glycol in Example 1 of the present invention;

[0036] Figure 6 is a high performance liquid chromatogram of the ethylene glycol oxidation product of Example 1 of the present invention;

[0037] Figure 7 is a high performance liquid chromatogram of the ethylene glycol oxidation product of Example 2 of the present invention;

[0038] Figure 8 It is the high performance liquid chromatogram of the ethylene glycol oxidation product of Example 3 of the present invention.

[0039] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0041] The chemicals used in the embodiments of the present invention and the comparative examples were purchased from Aladdin Reagent Company with a purity of >98.0 wt%.

[0042] Example 1

[0043] A method for preparing glycolic acid and co-producing hydrogen by electrochemical oxidation of ethylene glycol, using Au / PDA catalyst as an anode catalyst, specifically comprising the following steps:

[0044] (I) Preparation of anode and cathode

[0045] A. Preparation of anode (Au / PDA supported on nickel foam)

[0046] Firstly, PDA loaded with nickel foam was prepared. The specific method was as follows: firstly, the nickel foam was ultrasonically cleaned in dilute hydrochloric acid, ethanol and deionized water for 15 min respectively to remove the oxide layer and oil on the surface, and then vacuum dried for later use.

[0047] Dissolve 0.2g dopamine hydrochloride in 50mL deionized water and stir thoroughly. Use the cleaned nickel foam as the working electrode, platinum sheet as the counter electrode, and silver / silver chloride electrode as the reference electrode to form a three-electrode system, and deposit at a potential of -0.8V to 0.8V vs Ag / AgCl for 20min to obtain PDA loaded on nickel foam.

[0048] Then, Au / PDA loaded on nickel foam was prepared. The specific method was as follows: a 10 mM chloroauric acid solution was prepared, and a three-electrode system was composed of PDA loaded on nickel foam as a working electrode, a platinum sheet as a counter electrode, and a silver / silver chloride electrode as a reference electrode; and electroplating was performed at -1 V vsAg / AgCl for 600 s to obtain an anode, i.e., Au / PDA loaded on nickel foam.

[0049] The scanning electron microscope, X-ray diffraction and infrared spectra of the obtained anode catalyst Au / PDA are shown in Figures 1 to 3 As shown, it can be seen that Au nanoparticles are loaded on nickel foam, with a particle size of about 300nm, and there is an adhesive substance at the bottom of the nanoparticles, which is PDA. The X-ray diffraction spectrum also has diffraction peaks of nickel foam and Au, but PDA is an organic polymer and is amorphous, so there is no diffraction peak. The infrared spectrum confirms the existence of PDA.

[0050] B. Preparation of cathode (platinum sheet)

[0051] Cut the platinum sheet into a size of 15mm*15mm*2mm. After cutting, rinse the platinum sheet with deionized water and it can be used.

[0052] (II) Ethylene glycol oxidation catalytic activity test

[0053] 2 g of ethylene glycol was added to 100 mL of a 5.6 g / L aqueous NaOH solution to obtain an electrolyte. The anode (Au / PDA loaded with nickel foam) and cathode (platinum sheet) obtained in step (1) and an Ag / AgCl reference electrode were placed in the obtained electrolyte to form an electrolytic cell. A voltage was applied using an electrochemical workstation (CHI 760E) and the reaction was carried out using the current-time (it) mode at room temperature and normal pressure, wherein the potential E RHE =1.5V, the time was set to 3600 seconds, and the preparation of glycolic acid was completed.

[0054] The current-time curve of the reaction of preparing glycolic acid from ethylene glycol is shown in Figure 4 As shown, it can be seen that the catalyst electrode without PDA modification loses its catalytic activity at 2400s and the current density decreases rapidly, while Au / PDA still maintains a high catalytic activity.

[0055] (III) Product Detection

[0056] Take 1 mL of the above electrolyte and neutralize it to pH 7 with acid, filter it with a nylon 66 filter membrane, place it in a sample bottle, and analyze the product using high performance liquid chromatography. Figure 5 As shown, it can be seen that at 1.5V RHE After reacting for 1 h at the potential, the oxidation product of ethylene glycol was mainly glycolic acid with a selectivity of more than 96%.

[0057] Example 2

[0058] A method for preparing glycolic acid and co-producing hydrogen by electrochemical oxidation of ethylene glycol, using a Pd / PDA catalyst as an anode catalyst, specifically comprising the following steps:

[0059] (I) Preparation of anode and cathode

[0060] A. Preparation of anode (Pd / PDA supported on FTO conductive glass)

[0061] Firstly, PDA loaded with FTO conductive glass was prepared. The specific method was as follows: firstly, the FTO conductive glass was ultrasonically cleaned in acetone, ethanol and deionized water for 15 min respectively to remove oil and dust on the surface, and then vacuum dried for later use.

[0062] Dissolve 0.1g dopamine hydrochloride in 50mL Tris-HCl buffer solution with pH=7.4 and stir thoroughly. Use the cleaned FTO conductive glass as the working electrode, platinum sheet as the counter electrode, and silver / silver chloride electrode as the reference electrode to form a three-electrode system, and deposit for 10min at a potential of -1V~1VvsAg / AgCl.

[0063] Then, a 2 mM potassium chloropalladate solution was prepared, the PDA loaded on the nickel foam was placed in the solution, and 0.5 g of sodium borohydride was added under stirring to prepare Pd / PDA loaded on the nickel foam.

[0064] B. Preparation of cathode (cobalt phosphide supported on carbon paper)

[0065] Prepare 0.2M cobalt nitrate solution, use carbon paper as working electrode, platinum sheet as counter electrode, and saturated calomel electrode as reference electrode to form a three-electrode system. Electrodeposit for 300s at -1.2V to obtain carbon paper loaded Co(OH) 2; 1g sodium hypophosphite and carbon paper-loaded Co(OH) 2 At the same time, the mixture was placed in a tubular furnace, purged with Ar gas, and calcined at 300° C. for 2 h to obtain carbon paper-supported cobalt phosphide.

[0066] (II) Ethylene glycol oxidation catalytic activity test

[0067] 2 g of ethylene glycol was added to 100 mL of a 5 g / L aqueous NaOH solution to obtain an electrolyte. The anode (Pd / PDA supported by FTO conductive glass) and cathode (cobalt phosphide supported by carbon cloth) obtained in step (1) and an Ag / AgCl reference electrode were placed in the obtained electrolyte to form an electrolytic cell. A voltage was applied using an electrochemical workstation (CHI 760E) and the reaction was carried out using the current-time (it) mode at room temperature and normal pressure, wherein the potential E RHE =1.5V, the time was set to 3600 seconds, and the preparation of glycolic acid was completed.

[0068] (III) Product Detection

[0069] Take 1 mL of the above electrolyte and neutralize it to pH 7 with acid, filter it with a nylon 66 filter membrane, place it in a sample bottle, and analyze the product using high performance liquid chromatography. Figure 6 As shown, it can be seen that at 1.5V RHE After reacting for 1 h at the potential, the oxidation product of ethylene glycol is mainly glycolic acid, with a selectivity of more than 90%.

[0070] Example 3

[0071] A method for preparing lactic acid from glycerol by electrocatalysis and coupling hydrogen production, using a Pd / PDA catalyst as an anode catalyst, specifically comprising the following steps:

[0072] (I) Preparation of anode and cathode

[0073] A. Preparation of anode (Pt / PDA supported on carbon paper)

[0074] First, prepare carbon paper-supported Pt / PDA, specifically, dissolve 0.2 g dopamine hydrochloride in 50 mL phosphate buffer solution, the pH of the buffer solution is 8.0. Use carbon paper as the working electrode, platinum sheet as the counter electrode, and silver / silver chloride electrode as the reference electrode to form a three-electrode system, and deposit at a potential of -1V to 1V vs Ag / AgCl for 5 minutes to obtain carbon paper-supported PDA.

[0075] Then, Pt / PDA loaded on carbon paper was prepared. The specific method was as follows: a 10 mM chloroplatinic acid solution was prepared and 0.15 M sodium chloride was added as the electrolyte. The PDA loaded on carbon paper was used as the working electrode, the platinum sheet was used as the counter electrode, and a saturated calomel electrode was used as the reference electrode to form a three-electrode system. The electrodeposition was performed at -1 V for 600 s to obtain the anode, i.e., the Pt / PDA loaded on carbon paper.

[0076] B. Preparation of cathode (nickel sulfide supported by nickel foam)

[0077] A 0.2M nickel nitrate solution was prepared as the electrolyte, and the nickel foam was used as the working electrode, the platinum sheet was used as the counter electrode, and the saturated calomel electrode was used as the reference electrode to form a three-electrode system. Electrodeposition was performed at -1.2V for 300s to obtain Ni(OH) loaded on the nickel foam. 2 ; Ni(OH) loaded on nickel foam 2 and 0.1 g of thioacetamide were placed in a high-pressure reactor and reacted at 120° C. for 6 h to obtain nickel sulfide supported on nickel foam, i.e., a cathode.

[0078] (II) Ethylene glycol oxidation catalytic activity test

[0079] 2 g of ethylene glycol was added to 100 mL of a 5 g / L aqueous NaOH solution to obtain an electrolyte. The anode (Pt / PDA supported on carbon paper) and cathode (nickel sulfide supported on nickel mesh) obtained in step (1) and an Ag / AgCl reference electrode were placed in the obtained electrolyte to form an electrolytic cell. A voltage was applied using an electrochemical workstation (CHI 760E) and the reaction was carried out using the current-time (it) mode at room temperature and normal pressure, wherein the potential E RHE =1.4 V, the time was set to 3600 seconds, and the preparation of glycolic acid was completed.

[0080] (III) Product Detection

[0081] Take 1 mL of the above electrolyte and neutralize it to pH 7 with acid, filter it with a nylon 66 filter membrane, place it in a sample bottle, and analyze the product using high performance liquid chromatography. Figure 7 As shown, it can be seen at: 1.5V RHE After reacting for 1 h at the potential, the oxidation product of ethylene glycol is mainly glycolic acid, with a selectivity of more than 80%.

[0082] like Figure 1As shown, the noble metal / polydopamine constructed in the present invention is used as an anode electrocatalyst, and the hydrogen bonding between the polyhydroxy structure of polydopamine and the hydroxyl group of ethylene glycol is utilized to adsorb and enrich ethylene glycol on the catalyst surface, thereby promoting the reaction kinetics, inhibiting the oxidative deactivation of the noble metal at high potential, and promoting the oxidation activity of ethylene glycol. At the same time, water is reduced to hydrogen at the cathode, further improving its industrial application potential. High-efficiency electrocatalytic production of glycolic acid from ethylene glycol can be achieved at room temperature and atmospheric pressure, and hydrogen is co-produced at the cathode, providing a new idea and method for the green and efficient preparation of glycolic acid.

[0083] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0084] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a polydopamine / noble metal catalyst, characterized in that: The following steps are involved: (I) dissolving PDA monomer in a solvent to obtain a PDA monomer solution; (II) using PDA monomer solution as electrolyte, electrochemical polymerization is carried out on a conductive substrate by cyclic voltammetry to obtain polydopamine supported on the conductive substrate; (III) Using a noble metal salt solution as a precursor solution, noble metal nanoparticles are loaded on the polydopamine loaded on a conductive substrate to obtain a polydopamine / noble metal catalyst loaded on a conductive substrate.

2. The method for preparing a polydopamine / noble metal catalyst according to claim 1, characterized in that: The PDA monomer is dopamine hydrochloride; the solvent is deionized water or a weak alkaline buffer solution; the weak alkaline buffer solution is a phosphate buffer solution, a Tris-HCl buffer solution, a carbonate buffer solution or an ammonia solution with a pH of 6.8 to 10; the concentration of the PDA monomer in the PDA monomer solution is 0.5 g / L to 10 g / L, and the pH value of the PDA monomer solution is 6.8 to 10.

3. The method for preparing a polydopamine / noble metal catalyst according to claim 1, characterized in that: The conductive substrate is any one of carbon cloth, carbon paper, nickel foam, nickel sheet, nickel mesh, copper foam, copper sheet, copper mesh, titanium sheet, titanium mesh, stainless steel sheet, stainless steel mesh, ITO conductive glass or FTO conductive glass.

4. The method for preparing a polydopamine / noble metal catalyst according to claim 1, characterized in that: The cyclic voltammetry in step (II) is specifically as follows: using a conductive substrate as a working electrode, a counter electrode, and a reference electrode to form a three-electrode system, and depositing in a PDA monomer solution at a potential of -1V to 1V vsAg / AgCl for 1min to 60min.

5. The method for preparing a polydopamine / noble metal catalyst according to claim 1, characterized in that: The noble metal is any one or more of platinum, gold, silver, ruthenium, iridium, palladium, copper or rhodium; the concentration of the noble metal salt solution is 2mmol / L to 50mmol / L.

6. The method for preparing a polydopamine / noble metal catalyst according to claim 1, characterized in that: The method for loading the noble metal nanoparticles in the step (III) is an electrodeposition method or a liquid phase reduction method.

7. A polydopamine / noble metal catalyst, characterized in that: Prepared by the method according to any one of claims 1 to 5.

8. Use of a polydopamine / noble metal catalyst prepared by the method of any one of claims 1 to 5 in the electrocatalytic production of ethylene glycol to produce glycolic acid coupled with hydrogen production, characterized in that: The method for preparing glycolic acid by electrocatalysis of ethylene glycol and coupling hydrogen production specifically comprises the following steps: (I) Assembling the electrolytic cell The polydopamine / precious metal catalyst supported on a conductive substrate is used as an anode, the cathode catalyst is used as a cathode, and they are assembled into an electrolytic cell with an electrolyte; (II) Electrocatalytic reaction Ethylene glycol is added to the electrolyte. Under voltage conditions, the polyol is oxidized at the anode to produce glycolic acid, and water is reduced at the cathode to produce hydrogen.

9. The use of the polydopamine / noble metal catalyst according to claim 8 in the electrocatalytic production of ethylene glycol to produce glycolic acid coupled with hydrogen production, characterized in that: The electrolyte is an aqueous solution of any one or more of sodium hydroxide, potassium hydroxide, potassium bicarbonate, potassium carbonate, sodium bicarbonate or sodium carbonate, and the concentration of the electrolyte in the electrolyte is 1g / L to 50g / L; the cathode catalyst is any one or a mixture of transition metal oxides, transition metal phosphides, transition metal sulfides, transition metal nitrides, transition metal borides, platinum-based catalysts, palladium-based catalysts, ruthenium-based catalysts, rhodium-based catalysts, nickel-based catalysts or copper-based catalysts; when the cathode catalyst is a powder, the cathode is composed of a conductive substrate loaded with the cathode catalyst.

10. The use of the polydopamine / noble metal catalyst according to claim 8 in the electrocatalytic production of ethylene glycol to produce glycolic acid coupled with hydrogen production, characterized in that: The concentration of ethylene glycol in the electrolyte is 1 g / L to 50 g / L; the voltage condition is 0 V to 2 V vsAg / AgCl.

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