CN111342022A - A carbon-coated Na3MnTi(PO4)3/C composite electrode and its preparation method and application - Google Patents

Abstract

The invention relates to a carbon-coated Na₃MnTi(PO₄)₃A/C composite material electrode and a preparation method and application thereof belong to the technical field of water treatment. Carbon-coated Na₃MnTi(PO₄)₃The preparation method of the/C composite material electrode comprises the steps of mixing a binder, a conductive agent and carbonCoated with Na₃MnTi(PO₄)₃the/C composite material is uniformly mixed and then is bonded on a current collector to obtain Na₃MnTi(PO₄)₃a/C composite electrode of said Na₃MnTi(PO₄)₃the/C composite material is prepared by the following method: dissolving sodium acetate, manganese acetate, ammonium dihydrogen phosphate and citric acid in water, adding isopropyl titanate, and drying to obtain a solid intermediate product; finally, calcining the solid intermediate product in an inert atmosphere to obtain Na₃MnTi(PO₄)₃a/C composite material. In the invention, Na₃MnTi(PO₄)₃after/C is subjected to carbon coating, Na is obviously enhanced₃MnTi(PO₄)₃The electrical conductivity of the/C composite electrode is improved by increasing Na₃MnTi(PO₄)₃Faradaic reactivity with sodium ions.

Description

A carbon-coated Na3MnTi(PO4)3/C composite electrode and preparation method thereof application

technical field

The invention relates to a carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite material electrode, a preparation method and application thereof, and belongs to the technical field of water treatment.

Background technique

With the rapid growth of economy and population, human demand for freshwater resources also increases. However, in the process of human industrialization and urbanization, as well as inappropriate agricultural activities, many pollutants (such as persistent organic pollutants, heavy metals and dyes, etc.) are discharged into water bodies, causing serious water pollution, further exacerbated the problem of water scarcity. Although the earth is rich in water resources, 96.5% of it is in the form of seawater and brackish water, while freshwater resources only account for 2.5% of the total water on the earth. And among these freshwater resources, 68.7% are distributed in polar glaciers and high-altitude areas, which are difficult to obtain, and only a small part of rivers, lakes and groundwater are available for people to use. In order to alleviate the freshwater crisis, an effective strategy is to convert seawater and brackish water into freshwater, so many desalination technologies have been developed, such as reverse osmosis, multi-stage flash evaporation, multi-effect distillation and capacitive deionization technology (Capacitive Deionization). , CDI). Among these desalination technologies, CDI has attracted much attention of researchers due to its low energy consumption, high desalination efficiency and environmental friendliness.

The performance of CDI largely depends on the electrode material. According to the different electrode materials, the desalination principle of CDI is mainly divided into the electric double layer principle and the Faraday principle. The traditional CDI electrodes based on the electric double layer principle are mainly carbon materials, because carbon materials have the advantages of large specific surface area, abundant pore structure and excellent electrical conductivity. However, in the process of research, it is found that when carbon materials are used as CDI electrodes, due to factors such as the specific surface area available for ion adsorption and the ion repulsion effect of the same name, the desalination amount and cyclic regeneration performance cannot meet the needs of large-scale applications. To solve this problem, in 2014, Lee et al. designed a hybrid capacitive deionization, using Sodium Manganese Oxide (NMO) electrode to store sodium ions through Faradaic reaction, and activated carbon to store anions, and obtained excellent CDI performance. Compared with carbon materials, Faraday electrode materials based on the Faraday reaction principle have the advantages of large ion storage capacity, good cycle stability and other advantages when removing cations such as sodium ions. Therefore, we urgently need to develop more Faraday electrode materials with high adsorption capacity, excellent cycling stability, and as anode materials for hybrid capacitive deionization.

In recent years, NASICON (sodium superionic conductor) has been widely used in sodium-ion batteries due to its large theoretical capacity, stable three-dimensional framework and large sodium ion channel. During the charging and discharging process, sodium superionic conductors can provide fast ion diffusion channels and have small volume expansion. At the same time, they also have high ionic conductivity. These characteristics make sodium superionic conductors suitable for hybrid CDI. electrode. Among these sodium superion conductors, Na ₃ MnTi(PO ₄ ) ₃ has attracted much attention because of its high theoretical capacity, and it is more cheap, safe and environmentally friendly, and the research of Na ₃ MnTi(PO ₄ ) ₃ as a hybrid CDI electrode has also No reports have been seen.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a carbon-coated sodium superion conductor Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode. Since Na ₃ MnTi(PO ₄ ) ₃ has obvious disadvantages in its own electrical conductivity, Na ₃ MnTi(PO ₄ ) ₃ is composited with carbon materials with high electrical conductivity, in order to obtain composite materials with high electrical conductivity and high desalination performance. The invention provides a carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite material electrode with good electrical conductivity, good desalination ability and electrochemical stability, which is used as the negative electrode of hybrid CDI. The above hybrid CDI module contains two electrodes, one electrode is Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode, and the other electrode is commercial activated carbon.

A preparation method of carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite material electrode,

After the binder, the conductive agent and the carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite material are mixed uniformly, they are bonded on the current collector to obtain the Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode. Na ₃ MnTi(PO ₄ ) ₃ /C composite material was prepared by the following method:

Dissolve sodium acetate, manganese acetate, ammonium dihydrogen phosphate and citric acid in water according to a molar ratio of 3:1:3:3, and then add isopropyl titanate, wherein the molar ratio of isopropyl titanate to manganese acetate It is 1:1. After stirring and evaporating the water at 80 °C, it is transferred to an oven at 100 °C for drying to obtain a solid intermediate product; finally, the solid intermediate product is heated in an inert atmosphere at a temperature of 1-10 °C min ^-1 . The heating rate was increased to 500-700°C, and calcined for 12 hours to obtain Na ₃ MnTi(PO ₄ ) ₃ /C composite material.

In the above technical scheme, sodium acetate, manganese acetate, ammonium dihydrogen phosphate and citric acid are dissolved in a certain amount of deionized water in a molar ratio of 3:1:3:3, and the amount of deionized water used ensures that the raw materials can be dissolved. , those skilled in the art can make a reasonable choice by the amount of raw materials.

In the above technical solution, the current collector is graphite paper, titanium sheet or its product, stainless steel sheet or its product.

In the above technical solution, the binder is polytetrafluoroethylene, or a mixture of polyvinyl butyral and polyvinylpyrrolidone in a mass ratio of 4:1.

In the above technical scheme, the conductive agent is acetylene black or commodity Super P.

Another object of the present invention is to provide a hybrid capacitive deionization module comprising the above-mentioned Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode.

A hybrid capacitor deionization module, the module comprises two oppositely arranged end plates and two corresponding electrodes, wherein the surrounding edges of the two corresponding end plates of the same size are sealed and fixed by using a sealing material; Two corresponding planar electrodes with a certain distance in the middle are placed between the two end plates, wherein one electrode I is the Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode; the other electrode II is a commercial activated carbon electrode , an anion exchange membrane is provided between electrodes I and II, and the anion exchange membrane is in close contact with electrode II.

Further, the electrode II is prepared by the following method: after the binder, the conductive agent and the commercial activated carbon are mixed uniformly, they are bonded on the current collector to obtain a commercial activated carbon electrode,

Wherein, the current collector is graphite paper, titanium sheet or its product, stainless steel sheet or its product; the binder is polytetrafluoroethylene, or polyvinyl butyral and polyvinylpyrrolidone in a mass ratio of 4 : The mixture of 1 composition; Described conductive agent is acetylene black or commodity Super P.

In the above-mentioned electrodes I and II, when using polyvinylidene fluoride as a binder, Na ₃ MnTi(PO ₄ ) ₃ /C or activated carbon, acetylene black or Super P and polyvinylidene fluoride according to 8:1: The mass ratio of 1 was dissolved in dimethylacetamide. After mixing evenly, the slurry was coated on the current collector material, and dried at 80 °C for 12 h before use.

When using polyvinyl butyral and polyvinyl pyrrolidone as binders, mix Na ₃ MnTi(PO ₄ ) ₃ /C or activated carbon, acetylene black or Super P, polyvinyl butyral and polyvinyl pyrrolidone with 82.5 The mass ratio of :10:6:1.5 is dissolved and dispersed in ethanol. After mixing evenly, the slurry is coated on the current collector material, and dried at 80°C for 12h before use.

Further, the final electrode mass ratio of the Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode and the commercial activated carbon electrode is 2:1 to 1:2, preferably 2:1, 1:1 or 1:2.

The hybrid capacitor deionization and desalination module of the present invention is a sealed body, wherein two identical end plates are placed parallel to each other with a certain interval therebetween, and the two end plates are sealed and fixed with a sealing material. The thickness of the sealing material is the distance between two end plates placed in parallel. The end plate has at least one orifice for the inflow and outflow of the solution into the desalination module.

The two electrodes of the present invention are respectively bonded to the two end plates. There is a certain distance between the two electrodes. Further, an insulating non-woven material is arranged between two electrodes with a certain distance. The electrodes are respectively connected to titanium sheet wires for connecting to an external power source.

Preferably, the electrode I and the electrode II are respectively fixed on the inner surface of the adjacent end plates, the surrounding edges of the two end plates are sealed and fixed to each other with a sealing material, and the distance between the electrode I and the electrode II is controlled by the thickness of the sealing material .

The hybrid capacitor deionization module of the present invention adopts Na ₃ MnTi(PO ₄ ) ₃ /C composite as the negative electrode material and activated carbon as the positive electrode material to form a hybrid CDI module. Under the action of an applied electric field, Na ⁺ and Cl ^- can be effectively removed from the brine, so as to achieve desalination; when the two ends of the electrode are removed or the voltage is reversed, Na ⁺ and Cl ^- can be quickly desorbed. , to achieve electrode regeneration.

A hybrid capacitance deionization desalination method, the method performs desalination in a single hybrid capacitance deionization module or in a module group consisting of a plurality of modules in parallel or in series, the specific method is: the salt solution to be treated is removed from one end. The end plate flows into the module, and then flows out from the other end plate. While the salt solution is flowing, a certain negative voltage is applied to the electrode I and a certain positive voltage is applied to the electrode II.

Further, the method comprises the step of electrode regeneration: deionized water is flowed in from the end plate of one end of the CDI module, and then flows out from the other end plate, while the deionized water is flowing, a certain positive voltage is applied to the electrode I, A certain negative voltage is applied to electrode II.

The beneficial effects of the present invention are as follows: the present invention adopts a simple sol-gel-co-heating method to prepare a carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode. After carbon coating of Na ₃ MnTi(PO ₄ ) ₃ /C, the conductivity of Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode was significantly enhanced, and the Faradaic reactivity of Na ₃ MnTi(PO ₄ ) ₃ with sodium ions was improved , when assembled with commercial activated carbon into a hybrid CDI module, the results show that the desalination capacity can reach 31.4 mg g ^-1 in a 500 mg L ^-1 NaCl solution at a voltage of 1.2 V; and in the continuous desalination process, it exhibits excellent recycling capacity. Therefore, Na ₃ MnTi(PO ₄ ) ₃ /C composite is expected to be an efficient and economical hybrid CDI electrode material.

Description of drawings

1(a) and (b) are the typical Na ₃ MnTi(PO ₄ ) ₃ /C scanning electron microscope (SEM) and transmission electron microscope (TEM) images obtained in Example 1, respectively.

FIG. 2 is an XRD pattern of typical Na ₃ MnTi(PO ₄ ) ₃ /C obtained in Example 1. FIG.

FIG. 3 is a typical adsorption and desorption curve of Na ₃ MnTi(PO ₄ ) ₃ /C in 500 mg/L NaCl solution obtained in Example 1 under different voltages.

FIG. 4 is a graph showing the regeneration performance of Na ₃ MnTi(PO ₄ ) ₃ /C desalination cycle under typical 0.8V conditions obtained in Example 1.

Detailed ways

The following non-limiting examples may enable those of ordinary skill in the art to more fully understand the present invention, but do not limit the present invention in any way.

The test methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials can be obtained from commercial sources unless otherwise specified.

One of the specific implementations:

A preparation method of carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite material electrode, comprising the following process steps:

After dissolving sodium acetate, manganese acetate, ammonium dihydrogen phosphate and citric acid in water according to a molar ratio of 3:1:3:3, then adding isopropyl titanate, wherein the molar ratio of isopropyl titanate and manganese acetate is 1:1, after stirring and evaporating the water at 80 °C, transfer to an oven at 100 °C for drying to obtain a solid intermediate product; finally, the solid intermediate product is heated in an inert atmosphere at a temperature of 1 ~ 10 °C min ^-1 The rate was increased to 500-700°C, and calcined for 12 h to obtain Na ₃ MnTi(PO ₄ ) ₃ /C composite material. The binder, the conductive agent and the carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite material are mixed uniformly, and then bonded on the current collector to obtain a Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode.

When using PTFE as the binder, dissolve Na ₃ MnTi(PO ₄ ) ₃ /C or activated carbon, acetylene black or Super P and PTFE in dimethyl fluoride according to the mass ratio of 8:1:1 After mixing uniformly, the slurry was coated on the current collector material, and dried at 80 °C for 12 h before use.

When using polyvinyl butyral and polyvinyl pyrrolidone as binders, mix Na ₃ MnTi(PO ₄ ) ₃ /C or activated carbon, acetylene black or Super P, polyvinyl butyral and polyvinyl pyrrolidone with 82.5 The mass ratio of :10:6:1.5 is dissolved and dispersed in ethanol. After mixing evenly, the slurry is coated on the current collector material, and dried at 80°C for 12h before use.

Example 1

3 mmol of sodium acetate, 1 mmol of manganese acetate, 3 mmol of ammonium dihydrogen phosphate and 3 mmol of citric acid were successively dispersed in 80 mL of deionized water, and stirred for 20 min. In the process of stirring, isopropyl titanate was added dropwise to the above solution, the molar ratio of isopropyl titanate and manganese acetate was 1:1, and then the temperature was raised to 80 ° C until the solution evaporated to dryness, and then transferred to 100 Dry in an oven at ℃ for 12 h to obtain a solid intermediate product. The solid intermediate product was raised to 600 °C at a heating rate of 5 °C min ^-1 under nitrogen atmosphere, and kept for 12 h. After cooling, the final Na ₃ MnTi(PO ₄ ) ₃ /C electrode material was obtained (Figure 1 and Figure 1). 2). In particular, Na ₃ MnTi(PO ₄ ) ₃ /C electrode material was still obtained when the temperature was raised to 500° C. and 700° C. respectively. The Na ₃ MnTi(PO ₄ ) ₃ /C electrode material is used as the negative electrode material for hybrid capacitor deionization; while the positive electrode material for hybrid capacitor deionization is the commercial activated carbon material.

Na ₃ MnTi(PO ₄ ) ₃ /C and commercial activated carbon were respectively dissolved and dispersed in ethanol with acetylene black, polyvinyl butyral and polyvinyl pyrrolidone in a mass ratio of 82.5:10:6:1.5, and mixed. After uniform dispersion, the slurry was coated on graphite paper of the same size and dried at 80 °C for 12 h to obtain Na ₃ MnTi(PO ₄ ) ₃ /C and commercial activated carbon electrodes, respectively. The mass ratio of Na ₃ MnTi(PO ₄ ) ₃ /C and commercial activated carbon described in the two electrodes is 1:1.

A hybrid capacitive deionization module was assembled using the above Na ₃ MnTi(PO ₄ ) ₃ /C and a commercial activated carbon electrode, the module comprising two oppositely disposed end plates and two corresponding electrodes, wherein the two were sealed with a sealing material. The same size, the surrounding edges of the corresponding end plates are sealed and fixed; two corresponding plane electrodes with a certain distance in the middle are placed between the two end plates, wherein, one electrode I described Na ₃ MnTi (PO ₄ ) ₃ /C composite electrode; the other electrode II is a commercial activated carbon electrode, an anion exchange membrane is arranged between the electrodes I and II, the anion exchange membrane is in close contact with the electrode II, and the anion exchange membrane is not in contact with the electrode I. Contact, there is a certain distance between the two electrodes (that is, there is a certain distance between the anion exchange membrane and the electrode I); an insulating non-woven material is provided between the two electrodes with a certain distance. The electrodes are respectively connected to titanium sheet wires for connecting to an external power source.

A hybrid capacitor deionization desalination method. The method performs desalination in a single hybrid capacitor deionization module. The specific method is as follows: a to-be-treated sodium chloride solution with a salt concentration of 500 mg L ^-1 flows into an end plate at one end. The module then flows out from the other end plate, applying a certain negative voltage to electrode I and a certain positive voltage to electrode II while the saline solution is flowing.

The steps of electrode regeneration: deionized water flows in from the end plate at one end of the CDI module, and then flows out from the other end plate. While the deionized water flows, a certain positive voltage is applied to the electrode I, and a certain negative voltage is applied to the electrode II. Voltage.

The initial conductivity of NaCl was tested at 1000 μS cm ⁻¹ (at a concentration of 500 mg L ⁻¹ ), and the adsorption and regeneration curves were tested at different voltages ( FIG. 3 ). It was calculated that the maximum desalination capacity of Na ₃ MnTi(PO ₄ ) ₃ /C could reach 31.4 mg g ^-1 when the voltage was 1.2 V (Fig. 3). During 100 consecutive CDI desalination cycles, Na ₃ MnTi ( The PO ₄ ) ₃ /C composite also exhibited good cycling stability (Figure 4).

Example 2

3 mmol of sodium acetate, 1 mmol of manganese acetate, 3 mmol of ammonium dihydrogen phosphate and 3 mmol of citric acid were successively dispersed in 80 mL of deionized water, and stirred for 20 min. In the process of stirring, isopropyl titanate was added dropwise to the above solution, the molar ratio of isopropyl titanate and manganese acetate was 1:1, and then the temperature was raised to 80 ° C until the solution evaporated to dryness, and then transferred to 100 Dry in an oven at ℃ for 12 h to obtain a solid intermediate product. The solid intermediate product was raised to 600 °C at a heating rate of 5 °C min ^-1 under nitrogen atmosphere, and kept for 12 h. After cooling, the final Na ₃ MnTi(PO ₄ ) ₃ /C electrode material was obtained (Figure 1 and Figure 1). 2), as a hybrid capacitor deionization anode material; while the hybrid capacitor deionization cathode is a commercial activated carbon material.

Na ₃ MnTi(PO ₄ ) ₃ /C and commercial activated carbon were respectively dissolved and dispersed in ethanol with acetylene black, polyvinyl butyral, and polyvinyl pyrrolidone in a mass ratio of 82.5:10:6:1.5, and mixed and dispersed. After homogenization, the slurry was coated on graphite paper of the same size and dried at 80 °C for 12 h to obtain Na ₃ MnTi(PO ₄ ) ₃ /C and commercial activated carbon electrodes, respectively. The final electrode mass ratios of Na ₃ MnTi(PO ₄ ) ₃ /C and commercial activated carbon described in both electrodes were 2:1 and 1:2.

The assembly of the hybrid capacitor deionization module, the desalination method and the regeneration of the electrode are the same as in Example 1. The initial conductivity of NaCl is 1000 μS cm ^-1 (the concentration is 500 mg L ^-1 ), and the hybridization of two different final electrode mass ratios is tested. Desalination performance of electrodeionization modules. It was calculated that when the voltage was 1.2 V, the desalination amount of Na ₃ MnTi(PO ₄ ) ₃ /C and the final electrode mass ratio of commercial activated carbon was 2:1 was 28.8 mg g ^-1 , while Na ₃ MnTi(PO 4 ) 3 /C was 28.8 mg g -1 . ₄ ) The desalination amount of ₃ /C and commercial activated carbon was 25.2 mg g ^-1 when the final electrode mass ratio was 1:2.

Claims (9)

1. a preparation method of carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite material electrode, is characterized in that: After the binder, the conductive agent and the carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite material are mixed uniformly, they are bonded on the current collector to obtain the Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode. Na ₃ MnTi(PO ₄ ) ₃ /C composite material was prepared by the following method: Dissolve sodium acetate, manganese acetate, ammonium dihydrogen phosphate and citric acid in water according to a molar ratio of 3:1:3:3, and then add isopropyl titanate, wherein the molar ratio of isopropyl titanate to manganese acetate is 1:1, after stirring and evaporating the water at 80 °C, transfer to an oven at 100 °C for drying to obtain a solid intermediate product; finally, the solid intermediate product is heated in an inert atmosphere at a temperature of 1 ~ 10 °C min ^-1 The rate was increased to 500-700°C, and calcined for 12 h to obtain Na ₃ MnTi(PO ₄ ) ₃ /C composite material. 2. The method according to claim 1, wherein the binder is polytetrafluoroethylene, or a mixture of polyvinyl butyral and polyvinylpyrrolidone in a mass ratio of 4:1. 3 . The method according to claim 1 , wherein the conductive agent is acetylene black or commercial Super P. 4 . 4. The carbon-coated Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode prepared by the method of claim 1 . 5. A hybrid capacitor deionization module, characterized in that: the module comprises two oppositely arranged end plates and two corresponding electrodes, wherein the two same size, the corresponding end plates are separated by a sealing material. The surrounding edges are sealed and fixed; two corresponding planar electrodes with a certain distance in the middle are placed between the two end plates, wherein, one electrode I adopts the Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode described in claim 4 ; The other electrode II is a commercial activated carbon electrode, and an anion exchange membrane is arranged between the electrodes I and II, and the anion exchange membrane is in close contact with the electrode II. 6. The module according to claim 5, characterized in that: the electrode II is prepared by the following method: after the binder, the conductive agent and the commercialized activated carbon are mixed uniformly, they are bonded on the current collector to obtain a commercialized activated carbon electrode, Wherein, the current collector is graphite paper, titanium sheet or its product, stainless steel sheet or its product; the binder is polytetrafluoroethylene, or polyvinyl butyral and polyvinylpyrrolidone in a mass ratio of 4 : The mixture of 1 composition; Described conductive agent is acetylene black or commodity Super P. 7 . The module according to claim 6 , wherein the final electrode mass ratio of the Na ₃ MnTi(PO ₄ ) ₃ /C composite electrode and the commercial activated carbon electrode is 2:1 to 1:2, preferably 2. 8 . :1, 1:1 or 1:2. 8. A hybrid capacitor deionization desalination method, characterized in that: the method is in the hybrid capacitor deionization single module described in any one of claims 5 to 7 or in a module composed of multiple modules in parallel or in series The specific method is: make the salt solution to be treated flow into the module from one end plate, and then flow out from the other end plate, while the salt solution flows, apply a certain negative voltage to the electrode I, and to the electrode II Apply a certain positive voltage. 9. The method according to claim 8, characterized in that: the method comprises the step of electrode regeneration: deionized water flows into the end plate of one end of the CDI module, and then flows out from the other end plate, and the deionized water flows At the same time, a certain positive voltage is applied to the electrode I, and a certain negative voltage is applied to the electrode II.

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