阅读说明：本技术 一种还原氧化石墨烯修饰电极及其制备方法和应用 (Reduced graphene oxide modified electrode and preparation method and application thereof ) 是由 曾建平 陈亮 陈涵 周臣 谢红艳 刘弘宇 陈雨航 陈松 徐友胜 于 2020-12-03 设计创作，主要内容包括：本发明公开了一种还原氧化石墨烯修饰电极及其制备方法和应用,还原氧化石墨烯修饰电极包括还原氧化石墨烯、导电碳黑、环氧树脂和集流体；还原氧化石墨烯以抗坏血酸与L-半胱氨酸混合物化学还原制备,反应时间短、反应条件温和、环境友好；还原氧化石墨烯、导电碳黑、环氧树脂以质量比为3～8:1:1集流体表面形成薄膜,具有优良的电子传输特性,显著提高电催化还原芳香硝基化合物电催化性能,使还原反应转化率和选择性均达到80%以上。(The invention discloses a reduced graphene oxide modified electrode and a preparation method and application thereof, wherein the reduced graphene oxide modified electrode comprises reduced graphene oxide, conductive carbon black, epoxy resin and a current collector; the reduced graphene oxide is prepared by chemically reducing a mixture of ascorbic acid and L-cysteine, and has the advantages of short reaction time, mild reaction conditions and environmental friendliness; the reduced graphene oxide, the conductive carbon black and the epoxy resin form a film on the surface of the current collector in a mass ratio of 3-8: 1:1, the film has excellent electron transmission characteristics, the electrocatalytic performance of electrocatalytic reduction of the aromatic nitro compound is remarkably improved, and the conversion rate and the selectivity of the reduction reaction are both more than 80%.)

1. The reduced graphene oxide modified electrode is characterized by comprising reduced graphene oxide, conductive carbon black, epoxy resin and a current collector, wherein the reduced graphene oxide, the conductive carbon black and the epoxy resin form a film on the surface of the current collector, and the mass ratio of the reduced graphene oxide to the conductive carbon black to the epoxy resin is 3-8: 1: 1.

2. The method for preparing a reduced graphene oxide modified electrode according to claim 1, comprising the steps of:

the method comprises the following steps: preparation of GO: graphite is used as an initial raw material, potassium permanganate and concentrated sulfuric acid are used as oxidants, GO is prepared by a Hummers method, repeated centrifugation is carried out, water washing is carried out until the mixture is neutral, vacuum drying treatment is carried out, and then grinding is carried out to obtain GO powder;

step two: preparation of rGO: ultrasonically dispersing the GO powder obtained in the step one in deionized water; adding a mixture of ascorbic acid and L-cysteine for reduction reaction, controlling the reaction temperature to be 40-60 ℃ under the water bath condition, keeping vigorous stirring, and obtaining a black solid reduction product rGO in the solution after the reduction reaction is finished; repeatedly washing and centrifuging, carrying out vacuum drying treatment, and grinding into powder to obtain rGO powder;

step three: preparing an rGO modified electrode: and (3) mixing the rGO powder obtained in the step two, conductive carbon black and epoxy resin, adding a solvent, grinding and dispersing uniformly, coating the mixture on the surface of a current collector, and drying, shearing and tabletting to obtain the rGO modified electrode.

3. The preparation method of the reduced graphene oxide modified electrode according to claim 2, wherein in the second step, the addition amount of the GO powder is 1-2 g/L, and the addition amount of the mixture of ascorbic acid and L-cysteine is 4-20 g/L.

4. The method for preparing a reduced graphene oxide modified electrode according to claim 2, wherein the rGO powder obtained in the second step is of a layered porous nanostructure, the interlayer spacing is 0.51-0.77 nm, and the pore diameter is 3-11 nm.

5. The method for preparing a reduced graphene oxide modified electrode according to claim 2, wherein the solvent in step three is ethanol or ethyl acetate.

6. The application of the reduced graphene oxide modified electrode of claim 1, which comprises the step of immersing the rGO modified electrode in an ionic liquid dissolved with an aromatic nitro compound to carry out electrocatalytic reduction reaction, wherein the reaction conversion rate and the selectivity both reach more than 80%.

7. The use of the reduced graphene oxide-modified electrode of claim 6, wherein the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate or 1-butyl-3-methylimidazolium hexafluorophosphate.

8. The application of the reduced graphene oxide modified electrode according to claim 6, wherein the concentration of the aromatic nitro compound is 0.5-1.0 mol/L, and the temperature of the electrocatalytic reduction reaction is 30-70 ℃.

9. The use of the reduced graphene oxide-modified electrode according to claim 6, wherein the aromatic nitro compound is any one of nitrobenzene, p-nitrotoluene, m-nitroaniline, 2, 4-dinitrochlorobenzene, 2, 4-dinitrophenol, and 2,4, 6-trinitrophenol.

Technical Field

The invention relates to an electrochemical reduction electrode material, in particular to a reduced graphene oxide modified electrode and a preparation method and application thereof.

Background

The reduction of the aromatic nitro compound to prepare aromatic compounds such as amines, azos, aminophenols and the like is an important organic synthesis reaction and has higher economic and social benefits. At present, the main reduction methods of nitro compounds include a sodium sulfide reduction method, a metal reduction method, a catalytic hydrogenation reduction method, an electrochemical reduction method, a photocatalytic reduction method and the like. The electrochemical reduction method is a green chemical process which takes electrons as a reaction reagent and consumes few reactants, and is more and more concerned by people. However, the electro-reduction process of nitro compounds has many limiting factors: firstly, the traditional electrode material has limited sources and high price, such as platinum, tin, copper electrodes and the like; secondly, the use of the traditional organic solvent and the generated by-products thereof cause serious environmental pollution; finally, the interaction between the electrode and the solute and the solvent causes the mass transfer process to be undesirable, so that the electroreduction reaction rate is low. Therefore, it is of great significance to research and develop electrodes and solvents suitable for the electroreduction of aromatic nitro compounds.

Graphene Oxide (GO) has higher specific surface area and oxygen-containing functional groups such as-COOH, -OH and epoxy groups, so that GO has better amphiprotic (hydrophilic and hydrophobic) properties and electronegative properties and can be used for coating and modifying the surface of an electrode. CN109046460A discloses a graphene oxide @ polymeric metalloporphyrin composite nano-catalyst with a core-shell type coating structure, which can efficiently carry out electrocatalytic reduction on nitrobenzene.

And proper reduction is carried out on GO, the number of oxygen-containing groups and band gap can be adjusted, a graphene plane conjugated structure is formed, and further the conductivity and the electrocatalysis performance are enhanced. However, the current reduction means mainly include chemical reduction, thermal annealing decomposition or hydrothermal treatment, and high temperature and high pressure conditions are mostly adopted. Therefore, a simple method with mild conditions and environmental friendliness for preparing reduced graphene oxide (rGO) is needed to be developed for modifying electrodes and improving the reaction efficiency of electrocatalytic reduction of aromatic nitro compounds.

Disclosure of Invention

The invention aims to solve the technical problem of providing a reduced graphene oxide modified electrode and a preparation method and application thereof.

The reduced graphene oxide modified electrode comprises reduced graphene oxide, conductive carbon black, epoxy resin and a current collector, wherein the reduced graphene oxide, the conductive carbon black and the epoxy resin form a film on the surface of the current collector, and the mass ratio of the reduced graphene oxide to the conductive carbon black to the epoxy resin is 3-8: 1: 1.

A preparation method of a reduced graphene oxide modified electrode comprises the following steps:

the method comprises the following steps: preparation of GO:

graphite is used as an initial raw material, potassium permanganate and concentrated sulfuric acid are used as oxidants, GO is prepared by a Hummers method, repeated centrifugation is carried out, water washing is carried out until the GO is neutral, vacuum drying treatment is carried out, and then grinding is carried out to obtain GO powder.

Step two: preparation of rGO:

ultrasonically dispersing the GO powder obtained in the step one in deionized water; adding a mixture of ascorbic acid and L-cysteine for reduction reaction, controlling the reaction temperature to be 40-60 ℃ under the water bath condition, keeping vigorous stirring, and obtaining a black solid reduction product rGO in the solution after the reduction reaction is finished; repeatedly washing and centrifuging, vacuum drying, and grinding into powder to obtain rGO powder.

Step three: preparing an rGO modified electrode:

and (3) mixing the rGO powder obtained in the step two, conductive carbon black and epoxy resin, adding a solvent, grinding and dispersing uniformly, coating the mixture on the surface of a current collector, and drying, shearing and tabletting to obtain the rGO modified electrode.

Preferably, the adding amount of the GO powder in the second step is 1-2 g/L, and the adding amount of the mixture of the ascorbic acid and the L-cysteine is 4-20 g/L.

Preferably, the rGO powder obtained in the second step is of a layered porous nano structure, the interlayer spacing is 0.51-0.77 nm, and the pore diameter is 3-11 nm.

Preferably, the solvent in the third step is ethanol or ethyl acetate.

The application of the reduced graphene oxide modified electrode comprises the step of immersing the rGO modified electrode in an ionic liquid dissolved with an aromatic nitro compound to carry out electrocatalytic reduction reaction, wherein the reaction conversion rate and the selectivity both reach over 80 percent.

Preferably, the ionic liquid is 1-butyl-3-methylimidazolium tetrafluoroborate ([ BMIM ] [ BF4]) or 1-butyl-3-methylimidazolium hexafluorophosphate ([ BMIM ] [ PF6 ]).

Preferably, the concentration of the aromatic nitro compound is 0.5-1.0 mol/L, and the temperature of the electrocatalytic reduction reaction is 30-70 ℃.

Preferably, the aromatic nitro compound is any one of nitrobenzene, p-nitrotoluene, m-nitroaniline, 2, 4-dinitrochlorobenzene, 2, 4-dinitrophenol and 2,4, 6-trinitrophenol.

Compared with the prior art, the invention has the beneficial effects that:

1) according to the invention, the electrode is modified by the surface of rGO, and the rGO has good dispersibility and can be uniformly distributed on the surface of the electrode; the rGO forms a conjugated layered porous nano structure, the interlayer spacing is 0.51-0.77 nm, the pore diameter is 3-11 nm, the excellent electron transmission characteristic is achieved, and the electrode conductivity is enhanced under the combined action of the rGO and conductive carbon black.

2) According to the invention, the mixture of ascorbic acid and L-cysteine is adopted to reduce GO to prepare rGO, compared with hydrazine hydrate reduction, the reaction time is short, the reaction condition is mild, the environment is friendly, and the prepared rGO has higher conductivity.

3) The prepared rGO surface modified electrode is applied to electrocatalytic reduction of aromatic nitro compounds, so that the electrocatalytic performance is remarkably improved, and the conversion rate and the selectivity of the reduction reaction reach more than 80%.

Drawings

FIG. 1 is a schematic diagram of an experimental apparatus for electrocatalysis of nitrobenzene by an rGO modified electrode in example 3-10;

FIG. 2 shows cyclic voltammograms of examples 3 and 4.

The device comprises a 1-rGO modified electrode, a 2-Pt electrode, a 3-saturated calomel electrode, a 4-water bath, a 5-beaker, a 6-electrochemical workstation and a 7-computer.

Detailed Description

The invention is further described with reference to the following figures and examples.

Example 1

A preparation method of a reduced graphene oxide modified electrode comprises the following steps:

the method comprises the following steps: graphite is used as an initial raw material, potassium permanganate and concentrated sulfuric acid are used as oxidants, GO is prepared by a Hummers method, repeated centrifugation is carried out, water washing is carried out until the GO is neutral, vacuum drying treatment is carried out, and then grinding is carried out to obtain GO powder.

Step two: adding 1g of GO powder obtained in the first step into 1L of deionized water, performing ultrasonic dispersion uniformly, adding 2g of ascorbic acid and 2g L-cysteine, controlling the reaction temperature to be 40 ℃ in a water bath, continuously stirring at 500rpm for 1h to obtain a black solid reduction product rGO, repeatedly washing with water, performing centrifugation at 6000rpm, performing vacuum freeze drying at-90 ℃ to-110 ℃, and grinding into powder to obtain rGO powder.

The obtained rGO powder is of a layered porous nano structure, the interlayer spacing is 0.51 nm, and the pore diameter is 3 nm.

Step three: and (3) mixing 6g of the rGO powder obtained in the step two, 2g of conductive carbon black and 2g of epoxy resin, adding 30mL of ethyl acetate, grinding and dispersing uniformly, coating the mixture on the surface of a copper foil, and drying, shearing and tabletting to obtain the rGO modified electrode.

Example 2

A preparation method of a reduced graphene oxide modified electrode comprises the following steps:

the method comprises the following steps: graphite is used as an initial raw material, potassium permanganate and concentrated sulfuric acid are used as oxidants, GO is prepared by a Hummers method, repeated centrifugation is carried out, water washing is carried out until the GO is neutral, vacuum drying treatment is carried out, and then grinding is carried out to obtain GO powder.

Step two: adding 2g of GO powder obtained in the step one into 1L of deionized water, performing ultrasonic dispersion uniformly, adding 10g of ascorbic acid and 10g L-cysteine, controlling the reaction temperature in a water bath to be 60 ℃, continuously stirring at 600rpm for 2h to obtain a black solid reduction product rGO, repeatedly washing with water, performing centrifugation at 6000rpm, performing vacuum freeze drying at-90 to-110 ℃, and grinding into powder to obtain rGO powder.

The obtained rGO powder is of a layered porous nano structure, the interlayer spacing is 0.77nm, and the pore diameter is 11 nm.

Step three: and (3) mixing 8g of the rGO powder obtained in the step two, 1g of conductive carbon black and 1g of epoxy resin, adding 30mL of ethanol, grinding and dispersing uniformly, coating the mixture on the surface of a copper foil, and drying, shearing and tabletting to obtain the rGO modified electrode.

Example 3

As shown in figure 1, a three-electrode electro-catalytic reduction system is formed by taking the rGO modified electrode as a working electrode, a platinum wire as an auxiliary electrode and a saturated calomel electrode as a reference electrode, and is used for investigating the electrochemical behavior of the rGO electrode in the ionic liquid for electrically reducing the aromatic nitro compound. Dissolving reactant nitrobenzene in hydrophilic ionic liquid BMIM][BF₄]The solution with the concentration of 0.5mol/L is placed in a beaker, the electrode plate is kept immersed in the solution, and the beaker is placed in a constant-temperature water bath kettle at the temperature of 30 ℃. And (3) measuring the electrochemical characteristics of nitrobenzene in the electrocatalytic reduction reaction of the rGO modified electrode by adopting a cyclic voltammetry method. Setting parameters of cyclic voltammetry: scanning rate: 100 mV/s; scanning voltage: 0V-2V; cycle number: 1 time.

As shown in FIG. 2, nitrobenzene in hydrophilic ionic liquid [ BMIM][BF₄]When electrochemical reduction reaction is carried out, two peaks appear at-0.75V and-1.25V, which are respectively a single-electron reversible process and a multi-electron irreversible process, and the peak current is respectively 3.0 muA and 5.5 muA.

The nitrobenzene conversion was 87.52% and the aniline selectivity was 82.77%.

Example 4

The difference from example 3 is that: the ionic liquid is hydrophobic ionic liquid [ BMIM][PF₆]。

As shown in FIG. 2, nitrobenzene in hydrophobic ionic liquid BMIM][PF₆]When electrochemical reduction reaction is carried out, two peaks appear at-0.90V and-1.50V, which are respectively a single-electron reversible process and a multi-electron irreversible process, and the peak current is respectively 2.3 muA and 5.0 muA. Nitrobenzene in hydrophilic ionic liquid BMIM][BF₄]Peak current ratio of middle [ BMIM ]][PF₆]Medium and large, the peak potential is more positive than that, which indicates that in the electric reduction of nitrobenzene, [ BMIM ]][BF₄]The performance is better.

The nitrobenzene conversion was 83.37% and the aniline selectivity was 80.42%.

Examples 5 to 8

Examples 5 to 8 differ from example 3 in that the nitrobenzene concentration was 1.0mol/L and the temperature of the constant temperature water bath was 40 ℃, 50 ℃, 60 ℃ and 70 ℃.

Examples 9 to 13

Examples 9 to 13 differ from example 3 in that: the reactants are p-nitrotoluene, m-nitroaniline, 2, 4-dinitrochlorobenzene, 2, 4-dinitrophenol and 2,4, 6-trinitrophenol respectively, the concentration of the reactants is 1.0mol/L, and the temperature of the thermostatic water bath is 60 ℃.