Fe-Fe3C-coated rGO carbon nanoelectrode material and preparation method and application thereof

Abstract

The invention provides a Fe-Fe3C-coated rGO carbon nanoelectrode material as well as a preparation method and application thereof, and belongs to the technical field of electrode materials. Aiming at the problem that an existing electrode material is difficult to be used as a CDI electrode material for removing heavy metals, the CDI electrode material is prepared by utilizing the characteristic that multivalent metal iron ions can be subjected to cross-linking reaction with a sodium alginate solution, and the preparation method comprises the following steps: obtaining a graphene oxide dispersion liquid; under a water bath condition, adding sodium alginate into the graphene oxide dispersion liquid, dropwise adding the obtained gel liquid into a ferric salt solution, stirring, and freeze-drying to obtain aerogel microspheres; and carrying out high-temperature carbonization on the aerogel microspheres to obtain the Fe-Fe3C-coated rGO carbon nanomaterial. When the material is used as a CDI electrode material, aggregation of an iron compound on the surface of graphene can be effectively reduced, the specific capacitance, the conductivity and the cycling stability of the electrode material are improved, and a good Cr (VI) removal effect is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and in particular to a Fe-Fe3C@rGO carbon nanoelectrode material and a preparation method and application thereof. Background Art

[0002] With the rapid development of today's industry, excessive discharge of chromium-containing wastewater from industries such as electroplating, metallurgy, leather making, and chemicals has led to serious chromium pollution. As an important industrial raw material, the recycling of chromium is a crucial issue. Capacitive deionization (CDI), a new water treatment technology, has rapidly developed in areas such as seawater desalination, industrial wastewater, and domestic sewage treatment due to its ease of operation, high efficiency, low energy consumption, zero secondary pollution, and long service life. Its application in heavy metal wastewater treatment and resource recovery overcomes the inherent drawbacks and limitations of traditional technologies.

[0003] Graphene, with its large specific surface area, rich pore structure, and high conductivity, has been extensively studied as a CDI electrode material. However, when graphene is used alone for capacitive deionization (CDI) based solely on physical adsorption and double-layer adsorption, its adsorption capacity is low, and its high cost makes it unsuitable for industrial applications. Transition metal compounds (such as iron, cobalt, and nickel) have large pseudocapacitance. When combined with graphene, they can effectively enhance the material's specific capacitance and increase its adsorption capacity. Furthermore, the metal ions dispersed between graphene sheets can reduce the aggregation and stacking of graphene sheets, thereby improving the material's electrochemical performance. Traditional transition metal / graphene composites are prepared using hydrothermal or solvothermal methods, using graphene and metal salt solutions as precursors. The metal compounds exhibit strong agglomeration and uneven distribution. Furthermore, due to structural collapse during charge and discharge, the metal compounds are easily dissolved from the material, which reduces the composite's adsorption performance and stability.

[0004] Sodium alginate is a natural biomass material characterized by abundant resources, strong hydrophilicity, environmental friendliness, and low price. Due to the presence of negatively charged cavities in its structure, it easily cross-links with divalent cations to form a three-dimensional network hydrogel structure (commonly known as an "egg-lattice" structure). As a carbon material precursor, it cross-links with metal ions and carbonizes to form a unique carbon-coated morphology. The overall structure exhibits a well-developed three-dimensional network, which effectively improves the dispersibility of other active components, overcomes the shortcomings of graphene and metal compounds that are prone to agglomeration, and fully utilizes the synergistic effects between the components to enhance the electrochemical properties of carbon nanocomposites.

[0005] In the prior art, sodium alginate, graphene and metal salts are cross-linked to form aerogels, which are then applied to the fields of lithium batteries and electrocatalysis. For example, Chinese patent CN109244379B discloses a method for preparing LiFePO4 ultra-thin nanosheets@graphene aerogels, wherein the aqueous solution obtained by mixing sodium alginate and graphene is mixed with Fe 3+ PO4 3- 、Li + The obtained product is subjected to ion exchange, freeze drying and high temperature calcination, and can be used as a positive electrode material for batteries. For example, Chinese patent CN107715883A discloses a method for preparing Ni3FeN@graphene / algae aerogel, which combines graphene / sodium alginate with Fe 3+ 、Ni 2+ The product is prepared through ion exchange, freeze drying, and high-temperature calcination for use as an electrocatalytic material. However, there are still few technologies that can use these existing technologies as CDI electrode materials for heavy metal removal. In addition, the doping of precious metals such as lithium and nickel in these existing technologies leads to high material costs, making large-scale production and application difficult.

[0006] Therefore, developing a CDI electrode material with low cost and high adsorption performance is of great practical significance in heavy metal removal. Summary of the Invention

[0007] In order to overcome the shortcomings of graphene-based electrode materials in the above-mentioned prior art, such as high cost, easy agglomeration, and low adsorption capacity, the present invention provides a low-cost, easy-to-industrially-produce Fe-Fe3C@rGO carbon nanoelectrode material, as well as a preparation method and application, to solve the problems existing in the background technology.

[0008] The present invention utilizes the property of sodium alginate and transition metal ions to form a gel by cross-linking. The sodium alginate-derived carbon after high-temperature carbonization forms a coating layer on the surface of the metal compound, reducing the agglomeration effect of the metal compound between graphene sheets, and effectively improving the electrochemical properties and stability of the electrode material.

[0009] In order to achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0010] In a first aspect, the present invention discloses a method for preparing a Fe-Fe3C@rGO carbon nanoelectrode material, comprising the following steps:

[0011] S1: pretreating graphene oxide to obtain a graphene oxide dispersion;

[0012] S2: adding sodium alginate to the graphene oxide dispersion in a water bath to obtain a sodium alginate / graphene oxide gel solution;

[0013] S3: dropping the sodium alginate / graphene oxide gel solution into the iron salt solution and stirring to obtain the sodium alginate / graphene oxide gel spheres cross-linked with iron ions;

[0014] S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres to obtain aerogel microspheres;

[0015] S5: Carbonizing the aerogel microspheres at high temperature to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0016] As a further preferred solution: in step S1, the mass fraction of the graphene oxide dispersion is 0.1% to 1%.

[0017] As a further preferred embodiment: in step S2, the water bath condition is 50-80°C.

[0018] As a further preferred embodiment: in step S3, the iron salt solution is any one of FeCl3, Fe(NO3)3 or Fe2(SO4)3.

[0019] Furthermore, in step S3, the concentration of the iron salt solution is 0.1M to 0.6M.

[0020] Furthermore, in step S3, the stirring method is magnetic stirring, and the stirring time is 12 to 24 hours.

[0021] As a further preferred embodiment: in step S4, the freeze-drying time is 36 to 72 hours, and the freeze-drying temperature is -60°C to -80°C.

[0022] As a further preferred solution: in step S5, the high-temperature carbonization temperature is 600°C to 1000°C, the heating rate is 6°C / min, the constant temperature reaction time is 1-3h, and the protective gas is either nitrogen or argon.

[0023] In a second aspect, the present invention discloses a Fe-Fe3C@rGO carbon nanoelectrode material, characterized in that the specific surface area of the Fe-Fe3C@rGO carbon nanoelectrode material is 200-400m 2 / g, and the specific capacitance is 70~100F / g.

[0024] In a third aspect, the present invention discloses a Fe-Fe3C@rGO carbon nanoelectrode material as an electrode anode material for use in CDI, which can be widely used in CDI to remove heavy metal ions in Cr(VI)-containing wastewater, thereby realizing resource utilization of valuable metals. The specific steps are as follows:

[0025] (1) Weigh carbon nanocomposite, conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1, and grind the mixed powder of the three materials in a quartz mortar until they are completely mixed;

[0026] (2) Add an appropriate amount of dimethylformamide (DMF) to the mixed powder, stir thoroughly to make the powder into a viscous slurry, and evenly apply it on a conductive graphite paper, dry it at 120°C for 2 hours, and then place it in a vacuum drying oven at 80°C for 12 hours to obtain a CDI anode.

[0027] (3) Fe-Fe3C@rGO carbon nanomaterials were used as anode materials and commercial activated carbon was used as cathode materials to assemble a CDI module. Potassium dichromate solutions of different concentrations were prepared. The flow rate was controlled by a peristaltic pump, the working voltage was provided by a regulated DC power supply, and the Cr(VI) concentration in the solution was detected regularly.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. The Fe-Fe3C@rGO carbon nanomaterial of the present invention uses the cheap and readily available natural polysaccharide sodium alginate as a template, and utilizes the property that multivalent metal iron ions can undergo a cross-linking reaction with sodium alginate solution to mix sodium alginate / graphene oxide and then cross-link to form an Fe / graphene oxide / sodium alginate hydrogel, which is then prepared through processes such as washing, freeze-drying, and high-temperature carbonization. The Fe-Fe3C@rGO carbon nanoelectrode material prepared by the method of the present invention has iron compounds uniformly dispersed between the graphene sheets, reducing the agglomeration effect of metal compounds between the graphene sheets and improving the electrochemical properties and stability.

[0030] 2. The Fe-Fe3C@rGO carbon nanoelectrode material of the present invention has a well-developed network pore structure, a large specific surface area and a high specific capacitance. Its specific surface area is 200-400m 2 / g, and the specific capacitance reaches 70~100F / g.

[0031] 3. The present invention not only has a simple preparation process, a wide source of raw materials, low production cost, and is easy to industrialize, but also has a good Cr(VI) removal effect. The removal rate of Cr(VI)-containing wastewater solution is over 96%, and the Cr(VI) adsorption capacity is over 90%. It can be well used in CDI to remove heavy metal wastewater and realize the resource recovery and utilization of valuable metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments or the prior art.

[0033] Figure 1This is a SEM image of the Fe-Fe3C@rGO carbon nanomaterial prepared in Example 1 of the present invention;

[0034] Figure 2 TEM image of the Fe-Fe3C@rGO carbon nanomaterial prepared in Example 1 of the present invention;

[0035] Figure 3 This is the adsorption isotherm of the Fe-Fe3C@rGO carbon nanomaterial prepared in Example 1 of the present invention;

[0036] Figure 4 The cyclic voltammetry curves of Fe-Fe3C@rGO carbon nanomaterials prepared in Example 1 of the present invention at different scan rates are shown;

[0037] Figure 5 This is a SEM image of the Fe-Fe3C@rGO carbon nanomaterial in the comparative example of the present invention without adding sodium alginate;

[0038] Figure 6 This is a TEM image of the Fe-Fe3C@rGO carbon nanomaterial in the comparative example of the present invention without the addition of sodium alginate;

[0039] Figure 7 This is a comparison chart of the effects of the CDI electrode materials prepared in Example 1 of the present invention and the comparative example in treating Cr(VI) wastewater. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0041] It should be noted that any process not specifically described below can be implemented or understood by those skilled in the art with reference to existing technologies. Reagents or instruments used without manufacturer indication are considered to be commercially available conventional products.

[0042] Example 1:

[0043] Reference Figure 1-4 The present invention provides a method for preparing Fe-Fe3C@rGO carbon nanomaterials, and the specific steps are as follows:

[0044] S1: 80 mg of graphene oxide was ultrasonically dispersed in 80 ml of deionized water, followed by the addition of 0.8 g of sodium alginate powder. The mixture was stirred thoroughly in a 60°C water bath to dissolve the sodium alginate powder, and the bubbles in the sodium alginate / graphene oxide gel solution were removed by ultrasonication.

[0045] S2: The sodium alginate / graphene oxide gel solution was added dropwise into a 0.1 M FeCl3 solution using an injection, with continuous magnetic stirring, to obtain iron ion cross-linked sodium alginate / graphene oxide gel spheres;

[0046] S3: After the iron ion cross-linked sodium alginate / graphene oxide gel balls were magnetically stirred for 12 h, they were washed with secondary deionized water and anhydrous ethanol until the effluent was free of Cl - ;

[0047] S4: freeze-drying the sodium alginate / graphene oxide gel spheres cross-linked with iron ions after treatment in step S3 at -60°C for 48 hours to obtain aerogel microspheres;

[0048] S5: The aerogel microspheres were placed in a tubular furnace and heated to 800°C at a heating rate of 6°C / min under nitrogen protection. The temperature was maintained constant for 2 hours and then naturally cooled to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0049] Specifically, during the implementation of Example 1, the following morphology and performance tests were performed:

[0050] observe Figure 1-2 It can be seen that Fe3C and other iron compounds are evenly distributed on the surface of Fe-Fe3C@rGO carbon nanomaterials, and the pores are obvious. Moreover, Fe3C and other iron compounds are wrapped by a layer of nanocarbon. The specific surface area of Fe-Fe3C@rGO carbon nanomaterials is 382m 2 / g, and the specific capacitance is 88F / g.

[0051] The Fe-Fe3C@rGO carbon nanomaterial prepared in Example 1 was used as a CDI electrode. At a voltage of 1.5 V, it was operated for 3 hours. The removal rate of the Cr(VI)-containing wastewater solution with an initial concentration of 50 mg / L reached 95.4%, and the Cr(VI) adsorption capacity reached 89.65 mg / g.

[0052] Example 2:

[0053] A method for preparing Fe-Fe3C@rGO carbon nanomaterials, the specific steps are as follows:

[0054] S1: 80 mg of graphene oxide was ultrasonically dispersed in 80 ml of deionized water, followed by the addition of 0.8 g of sodium alginate powder. The mixture was stirred thoroughly in a 60°C water bath to dissolve the sodium alginate powder, and the bubbles in the sodium alginate / graphene oxide gel solution were removed by ultrasonication.

[0055] S2: The sodium alginate / graphene oxide gel solution was added dropwise into a 0.1 M FeCl3 solution using an injection, with continuous magnetic stirring, to obtain iron ion cross-linked sodium alginate / graphene oxide gel spheres;

[0056] S3: After the iron ion cross-linked sodium alginate / graphene oxide gel balls were magnetically stirred for 12 h, they were washed with secondary deionized water and anhydrous ethanol until the effluent was free of Cl - ;

[0057] S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres treated in step S3 at -60°C for 48 hours to obtain aerogel microspheres;

[0058] S5: The aerogel microspheres were placed in a tubular furnace and heated to 700°C at a heating rate of 6°C / min under nitrogen protection. The temperature was maintained constant for 2 hours and then naturally cooled to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0059] The Fe-Fe3C@rGO carbon nanomaterial prepared in Example 2 was used as a CDI electrode. At a voltage of 1.5 V, it was operated for 3 hours. The removal rate of the Cr(VI)-containing wastewater solution with an initial concentration of 50 mg / L reached 84.4%, and the Cr(VI) adsorption capacity reached 80.35 mg / g.

[0060] Example 3:

[0061] A method for preparing Fe-Fe3C@rGO carbon nanomaterials, the specific steps are as follows:

[0062] S1: 80 mg of graphene oxide was ultrasonically dispersed in 80 ml of deionized water, followed by the addition of 0.8 g of sodium alginate powder. The mixture was stirred thoroughly in a 60°C water bath to dissolve the sodium alginate powder, and the bubbles in the sodium alginate / graphene oxide gel solution were removed by ultrasonication.

[0063] S2: The sodium alginate / graphene oxide gel solution was added dropwise into a 0.1 M FeCl3 solution using an injection, with continuous magnetic stirring, to obtain iron ion cross-linked sodium alginate / graphene oxide gel spheres;

[0064] S3: After the iron ion cross-linked sodium alginate / graphene oxide gel balls were magnetically stirred for 12 h, they were washed with secondary deionized water and anhydrous ethanol until the effluent was free of Cl - ;

[0065] S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres treated in step S3 at -60°C for 48 hours to obtain aerogel microspheres;

[0066] S5: The aerogel microspheres were placed in a tubular furnace and heated to 900°C at a heating rate of 6°C / min under nitrogen protection. The temperature was maintained constant for 2 hours and then naturally cooled to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0067] The Fe-Fe3C@rGO carbon nanomaterial prepared in Example 3 was used as a CDI electrode. At a voltage of 1.5 V, it was operated for 3 hours. The removal rate of the Cr(VI)-containing wastewater solution with an initial concentration of 50 mg / L reached 87.4%, and the Cr(VI) adsorption capacity reached 82.35 mg / g.

[0068] Example 4:

[0069] A method for preparing Fe-Fe3C@rGO carbon nanomaterials, the specific steps are as follows:

[0070] S1: 160 mg of graphene oxide was ultrasonically dispersed in 80 ml of deionized water, followed by the addition of 0.8 g of sodium alginate powder. The mixture was stirred thoroughly in a 60°C water bath to dissolve the sodium alginate powder, and the bubbles in the sodium alginate / graphene oxide gel solution were removed by ultrasonication.

[0071] S2: The sodium alginate / graphene oxide gel solution was added dropwise into a 0.1 M FeCl3 solution using an injection, with continuous magnetic stirring, to obtain iron ion cross-linked sodium alginate / graphene oxide gel spheres;

[0072] S3: After the iron ion cross-linked sodium alginate / graphene oxide gel balls were magnetically stirred for 12 h, they were washed with secondary deionized water and anhydrous ethanol until the effluent was free of Cl - ;

[0073] S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres treated in step S3 at -60°C for 48 hours to obtain aerogel microspheres;

[0074] S5: The aerogel microspheres were placed in a tubular furnace and heated to 800°C at a heating rate of 6°C / min under nitrogen protection. The temperature was maintained constant for 2 hours and then naturally cooled to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0075] The Fe-Fe3C@rGO carbon nanomaterial prepared in Example 4 was used as a CDI electrode. At a voltage of 1.5 V, it was operated for 3 hours. The removal rate of the Cr(VI)-containing wastewater solution with an initial concentration of 50 mg / L reached 93.2%, and the Cr(VI) adsorption capacity reached 87.15 mg / g.

[0076] Example 5:

[0077] A method for preparing Fe-Fe3C@rGO carbon nanomaterials, the specific steps are as follows:

[0078] S1: 320 mg of graphene oxide was ultrasonically dispersed in 80 ml of deionized water. 0.8 g of sodium alginate powder was then added and stirred in a 60°C water bath to fully dissolve the sodium alginate powder. The bubbles in the sodium alginate / graphene oxide gel solution were then removed by ultrasonication.

[0079] S2: The sodium alginate / graphene oxide gel solution was added dropwise into a 0.1 M FeCl3 solution using an injection, with continuous magnetic stirring, to obtain iron ion cross-linked sodium alginate / graphene oxide gel spheres;

[0080] S3: After the iron ion cross-linked sodium alginate / graphene oxide gel balls were magnetically stirred for 12 h, they were washed with secondary deionized water and anhydrous ethanol until the effluent was free of Cl - ;

[0081] S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres treated in step S3 at -60°C for 48 hours to obtain aerogel microspheres;

[0082] S5: The aerogel microspheres were placed in a tubular furnace and heated to 800°C at a heating rate of 6°C / min under nitrogen protection. The temperature was maintained constant for 2 hours and then naturally cooled to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0083] The Fe-Fe3C@rGO carbon nanomaterial prepared in Example 5 was used as a CDI electrode. At a voltage of 1.5 V, it was operated for 3 hours. The removal rate of the Cr(VI)-containing wastewater solution with an initial concentration of 50 mg / L reached 81.2%, and the Cr(VI) adsorption capacity reached 76.78 mg / g.

[0084] Example 6:

[0085] A method for preparing Fe-Fe3C@rGO carbon nanomaterials, the specific steps are as follows:

[0086] S1: 80 mg of graphene oxide was ultrasonically dispersed in 80 ml of deionized water, followed by the addition of 0.8 g of sodium alginate powder. The mixture was stirred thoroughly in a 60°C water bath to dissolve the sodium alginate powder, and the bubbles in the sodium alginate / graphene oxide gel solution were removed by ultrasonication.

[0087] S2: The sodium alginate / graphene oxide gel solution was added dropwise into a 0.2 M FeCl3 solution using an injection, with continuous magnetic stirring, to obtain iron ion cross-linked sodium alginate / graphene oxide gel spheres;

[0088] S3: After the iron ion cross-linked sodium alginate / graphene oxide gel balls were magnetically stirred for 12 h, they were washed with secondary deionized water and anhydrous ethanol until the effluent was free of Cl - ;

[0089] S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres treated in step S3 at -60°C for 48 hours to obtain aerogel microspheres;

[0090] S5: The aerogel microspheres were placed in a tubular furnace and heated to 800°C at a heating rate of 6°C / min under nitrogen protection. The temperature was maintained constant for 2 hours and then naturally cooled to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0091] The Fe-Fe3C@rGO carbon nanomaterial prepared in Example 6 was used as a CDI electrode. At a voltage of 1.5 V, it was operated for 3 hours. The removal rate of the Cr(VI)-containing wastewater solution with an initial concentration of 50 mg / L reached 95.4%, and the Cr(VI) adsorption capacity reached 89.35 mg / g.

[0092] Example 7:

[0093] A method for preparing Fe-Fe3C@rGO carbon nanomaterials, the specific steps are as follows:

[0094] S1: 80 mg of graphene oxide was ultrasonically dispersed in 80 ml of deionized water, followed by the addition of 0.8 g of sodium alginate powder. The mixture was stirred thoroughly in a 60°C water bath to dissolve the sodium alginate powder, and the bubbles in the sodium alginate / graphene oxide gel solution were removed by ultrasonication.

[0095] S2: The sodium alginate / graphene oxide gel solution was added dropwise into a 0.3 M FeCl3 solution using an injection, with continuous magnetic stirring, to obtain iron ion cross-linked sodium alginate / graphene oxide gel spheres;

[0096] S3: After the iron ion cross-linked sodium alginate / graphene oxide gel balls were magnetically stirred for 12 h, they were washed with secondary deionized water and anhydrous ethanol until the effluent was free of Cl - ;

[0097] S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres treated in step S3 at -60°C for 48 hours to obtain aerogel microspheres;

[0098] S5: The aerogel microspheres were placed in a tubular furnace and heated to 800°C at a heating rate of 6°C / min under nitrogen protection. The temperature was maintained constant for 2 hours and then naturally cooled to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0099] The Fe-Fe3C@rGO carbon nanomaterial prepared in Example 7 was used as a CDI electrode. At a voltage of 1.5 V, it was operated for 3 hours. The removal rate of the Cr(VI)-containing wastewater solution with an initial concentration of 50 mg / L reached 96.4%, and the Cr(VI) adsorption capacity reached 90.67 mg / g.

[0100] Example 8:

[0101] A method for preparing Fe-Fe3C@rGO carbon nanomaterials, the specific steps are as follows:

[0102] S1: 80 mg of graphene oxide was ultrasonically dispersed in 80 ml of deionized water, followed by the addition of 0.8 g of sodium alginate powder. The mixture was stirred thoroughly in a 60°C water bath to dissolve the sodium alginate powder, and the bubbles in the sodium alginate / graphene oxide gel solution were removed by ultrasonication.

[0103] S2: The sodium alginate / graphene oxide gel solution was added dropwise into a 0.6 M FeCl3 solution using an injection, with continuous magnetic stirring, to obtain iron ion cross-linked sodium alginate / graphene oxide gel spheres;

[0104] S3: After the iron ion cross-linked sodium alginate / graphene oxide gel balls were magnetically stirred for 12 h, they were washed with secondary deionized water and anhydrous ethanol until the effluent was free of Cl - ;

[0105] S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres treated in step S3 at -60°C for 48 hours to obtain aerogel microspheres;

[0106] S5: The aerogel microspheres were placed in a tubular furnace and heated to 800°C at a heating rate of 6°C / min under nitrogen protection. The temperature was maintained constant for 2 hours and then naturally cooled to obtain Fe-Fe3C@rGO carbon nanomaterials.

[0107] The Fe-Fe3C@rGO carbon nanomaterial prepared in Example 8 was used as a CDI electrode. At a voltage of 1.5 V, it was operated for 3 hours. The removal rate of the Cr(VI)-containing wastewater solution with an initial concentration of 50 mg / L reached 97.2%, and the Cr(VI) adsorption capacity reached 92.5 mg / g.

[0108] Comparative Example:

[0109] Compared with Example 1, the only difference is that in step S1, no sodium alginate powder is added, but 80 mg of graphene oxide is directly dispersed in 80 ml of deionized water by ultrasonication to obtain Fe-Fe3C@rGO carbon nanomaterials, such as Figure 5 、 Figure 6 shown.

[0110] Depend on Figure 5-6 It can be observed that the surface of the Fe-Fe3C@rGO carbon nanomaterial prepared in this comparative example has serious agglomeration of iron compounds, underdeveloped pores, and the phenomenon of nanocarbon wrapping Fe3C and other iron compounds is not obvious.

[0111] Comparison of the effects of Fe-Fe3C@rGO carbon nanomaterials prepared in Example 1 of the present invention and the comparative example as CDI electrode materials for treating Cr(VI) wastewater Figure 7 As shown, from Figure 7 It can be seen from the observation that under the same operating conditions, the Fe-Fe3C@rGO carbon nanomaterial in the comparative example without the addition of sodium alginate has a removal rate of only 57.4% for an initial Cr(VI) concentration of 50 mg / L, and a Cr(VI) adsorption capacity of only 54.52 mg / g. Therefore, the treatment effect of the material obtained in the comparative example on Cr(VI) is much lower than that in Example 1.

[0112] The detailed description of the above embodiments is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the invention. Based on the embodiments of the present invention, they are only used to illustrate the technical solution of the present invention and are not limiting. Other modifications or equivalent substitutions made by ordinary technicians in this field to the technical solution of the present invention should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for preparing Fe-Fe3C@rGO carbon nanoelectrode material, characterized in that: The following steps are involved: S1: pretreating graphene oxide to obtain a graphene oxide dispersion; S2: adding sodium alginate to the graphene oxide dispersion in a water bath to obtain a sodium alginate / graphene oxide gel solution; S3: dropping the sodium alginate / graphene oxide gel solution into the iron salt solution and stirring to obtain the sodium alginate / graphene oxide gel spheres cross-linked with iron ions; S4: freeze-drying the iron ion cross-linked sodium alginate / graphene oxide gel spheres to obtain aerogel microspheres; S5: Carbonizing the aerogel microspheres at high temperature to obtain Fe-Fe3C@rGO carbon nanomaterials.

2. The method for preparing a Fe-Fe3C@rGO carbon nanoelectrode material according to claim 1, characterized in that: In step S1, the mass fraction of the graphene oxide dispersion is 0.1% to 1%.

3. The method for preparing a Fe-Fe3C@rGO carbon nanoelectrode material according to claim 1, characterized in that: In step S2, the water bath condition is 50-80°C.

4. The method for preparing a Fe-Fe3C@rGO carbon nanoelectrode material according to claim 1, characterized in that: In step S3, the iron salt solution is any one of FeCl3, Fe(NO3)3 or Fe2(SO4)3.

5. The method for preparing a Fe-Fe3C@rGO carbon nanoelectrode material according to claim 4, characterized in that: In step S3, the concentration of the iron salt solution is 0.1M to 0.6M.

6. The method for preparing a Fe-Fe3C@rGO carbon nanoelectrode material according to claim 5, characterized in that: In step S3, the stirring method is magnetic stirring, and the stirring time is 12 to 24 hours.

7. The method for preparing a Fe-Fe3C@rGO carbon nanoelectrode material according to claim 1, characterized in that: In step S4, the freeze-drying time is 36 to 72 hours, and the freeze-drying temperature is -60°C to -80°C.

8. The method for preparing a Fe-Fe3C@rGO carbon nanoelectrode material according to claim 1, characterized in that: In step S5, the high-temperature carbonization temperature is 600° C. to 1000° C., the heating rate is 6° C. / min, the constant temperature reaction time is 1-3 hours, and the protective gas is either nitrogen or argon.

9. The Fe-Fe3C@rGO carbon nanoelectrode material obtained by the preparation method according to any one of claims 1 to 8, characterized in that: The specific surface area of Fe-Fe3C@rGO carbon nanoelectrode material is 200~400m 2 / g, and the specific capacitance is 70~100F / g.

10. Use of the Fe-Fe3C@rGO carbon nanoelectrode material according to claim 9 in capacitive deionization treatment of Cr(VI)-containing wastewater.

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