Preparation and application of nitrogen and sulfur co-doped biomass porous carbon electrode material

Abstract

The invention belongs to the technical field of electro-adsorption materials, and particularly relates to preparation and application of a nitrogen and sulfur co-doped biomass porous carbon electrode material. The preparation method comprises the following steps: dispersing wheat straw powder in an alkaline solution, heating and stirring for reaction, washing slurry to be neutral after the reaction, carrying out solid-liquid separation, and drying to obtain wheat straw powder of which the content of lignin and hemicellulose is remarkably reduced; the method comprises the following steps: uniformly mixing wheat straw powder with ammonium sulfate, and carrying out high-temperature pyrolysis in a protective atmosphere to obtain the nitrogen and sulfur co-doped biomass porous carbon electrode material. The electrode material is prepared into an electrode plate to be assembled into a super capacitor device, voltage is applied between double electrodes of the capacitor to generate an electrostatic field, and free heavy metal ions in an aqueous solution are quickly adsorbed to the surfaces of the electrodes so as to achieve the purpose of purifying water.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electric adsorption materials, and particularly relates to a preparation method of a nitrogen and sulfur co-doped biomass porous carbon electrode material and application thereof. BACKGROUND

[0002] In the prior art, the water free heavy metal ion removal technology mainly includes a chemical precipitation method and a physical adsorption method. The chemical precipitation method mainly generates insoluble precipitates by reacting chemical agents and heavy metal ions in water to achieve the removal purpose. Although the method is simple and easy to implement, the chemical agents are easy to cause secondary pollution to the water body and increase subsequent treatment work. The physical adsorption method mainly captures heavy metal ions by active sites on the surface of adsorbents to achieve the removal purpose. Although the method is green and flexible to operate, the physical adsorbents are not renewable, and organic matters and suspended matters in the water body will compete with the active sites for the adsorption of heavy metal ions, so that the adsorption efficiency and selectivity of the heavy metal ions are significantly reduced. Therefore, it is a main goal in the industry to develop an environmentally friendly, renewable, and high-efficiency heavy metal ion removal technology.

[0003] The electric adsorption technology is a new technology based on a capacitor model. The technology generates electrostatic driving force by applying voltage between two electrodes to attract charged heavy metal ions to the electrode material, and stores the heavy metal ions in the capacitor in the form of a double electric layer on the surface of the electrode material to achieve the purpose of removing the heavy metal ions. At this time, the heavy metal ions can be desorbed by applying a reverse voltage between the two electrodes to realize the recycling of the heavy metal ions and the regeneration of the electrode material. As can be seen, the electric adsorption technology has the advantages of environmental friendliness, renewability, high utilization rate, and high adsorption efficiency, and therefore has a very broad application prospect in the fields of industrial wastewater recycling and drinking water purification. SUMMARY

[0004] To solve the shortcomings and deficiencies of the prior art, a primary purpose of the present application is to provide a preparation method of a nitrogen and sulfur co-doped biomass porous carbon electrode material. The present application uses wheat straw as a raw material, an alkaline solution as a pretreatment chemical agent, and a nitrogen and sulfur compound as a dopant to prepare the nitrogen and sulfur co-doped biomass porous carbon electrode material by an alkali pretreatment-calcination method. The method has the advantages of mild reaction conditions, low equipment requirements, and high adsorption efficiency, and has the potential for industrial production.

[0005] Another purpose of the present application is to provide a nitrogen and sulfur co-doped biomass porous carbon electrode material (APNSC) prepared by the above method. The material is an inorganic non-metallic carbon material, and has the advantages of simple preparation method, non-toxicity, large specific surface area, high porosity, and high selectivity to heavy metals.

[0006] Another purpose of the present application is to provide the application of the above-mentioned nitrogen and sulfur co-doped biomass porous carbon electrode material in the removal of free heavy metal ions in water by the electrosorption method. An electrode sheet is made of the APNSC electrode material and assembled into a super capacitor device. By applying a voltage between the two electrodes of the capacitor to generate an electrostatic field, the free heavy metal ions in the aqueous solution are quickly adsorbed to the surface of the electrode to achieve the purpose of purifying water.

[0007] The purpose of the present application is achieved by the following technical solutions: A preparation method of a nitrogen and sulfur co-doped biomass porous carbon electrode material, comprising the following steps: (1) dispersing the wheat straw powder in an alkaline solution, heating and stirring to react, washing the slurry to neutral after the reaction, and drying after solid-liquid separation to obtain wheat straw powder with significantly reduced lignin and hemicellulose content; (2) uniformly mixing the wheat straw powder with ammonium sulfate, and then pyrolyzing under a protective atmosphere to obtain a nitrogen and sulfur co-doped biomass porous carbon electrode material.

[0008] Preferably, the alkaline solution in step (1) is a KOH solution, a NaOH solution, a Ca(OH)2 solution or ammonia water.

[0009] Preferably, the molar concentration of the alkaline solution in step (1) is 0.5 mol / L to 6 mol / L.

[0010] Preferably, the solid-liquid ratio of the wheat straw and the alkaline solution in step (1) is 1:5 to 1:40 g / mL, and more preferably 1:20 g / mL.

[0011] Preferably, the heating and stirring reaction in step (1) is carried out at a temperature of 60 to 80 ℃ for 30 to 720 min; more preferably, at 80 ℃ for 3 h.

[0012] Preferably, the stirring speed of the heating and stirring reaction in step (1) is 600 r / min.

[0013] Preferably, the drying temperature in step (1) is 60 to 80 ℃, and the drying time is 48 to 120 h.

[0014] Preferably, in step (2), the wheat straw powder and ammonium sulfate are uniformly mixed by grinding.

[0015] Preferably, the mass ratio of the wheat straw powder to ammonium sulfate in step (2) is 1:1 to 3.

[0016] Preferably, the high-temperature pyrolysis in step (2) is carried out at a temperature of 900 ℃ for 120 min.

[0017] Preferably, step (2) is heated to 900 ℃ at a heating rate of 5 ℃ / min.

[0018] The application combines the wheat straw powder pretreated by alkaline solution for 3 hours with nitrogen and sulfur compounds to assist calcination, to obtain a porous carbon electrode material (APNSC) with nitrogen and sulfur heteroatoms introduced into the structure, and the APNSC is applied as a good electrode material to remove free heavy metal ions in water through electro-sorption technology.

[0019] The application of the nitrogen and sulfur co-doped biomass porous carbon electrode material (APNSC) prepared by the above method in removing free heavy metal ions in water through electro-sorption technology includes the following process: the APNSC, acetylene black and PVDF are mixed at a mass ratio of 7:2:1 and coated on the surface of a current collector to prepare an electrode sheet, a super capacitor device is assembled, and the device is placed in a heavy metal ion solution, stirring is started, a constant voltage is applied between the capacitor electrode sheets to generate an electrostatic field, and free heavy metal ions in water are adsorbed. The concentration of free heavy metal ions in the solution is determined by atomic absorption spectrometry (AAS).

[0020] Preferably, the current collector is one of foamed nickel and carbon cloth.

[0021] Preferably, the heavy metal ions are at least one of lead ions and cadmium ions.

[0022] Preferably, the specific conditions include a stirring speed of 350 r / min, a system running time of 120 min, an applied constant voltage of 1.2 V, and a current collector selected as carbon cloth.

[0023] Preferably, the concentration of heavy metal ions in water is 0-200 mg / L.

[0024] Compared with the prior art, the application has the following advantages and beneficial effects: (1) The electrode material has raw materials that are easy to obtain, wide selection, universality, and no toxicity and pollution.

[0025] (2) The APNSC electrode material for electro-sorption technology can be used as a material for adsorbing heavy metal ions with high efficiency, has a very broad prospect in the fields of treating heavy metal ion contaminated water, purifying drinking water, and treating industrial wastewater, and has great significance for the healthy growth of crops, the healthy life of humans, and the improvement of the ecological environment.

[0026] (3) The electrode material has the advantages of low equipment requirement, excellent adsorption performance, reusable electrode material, environmental friendliness, and certain industrial application prospect in removing free heavy metal ions in water. Attached Figure Description

[0027] Figure 1 The image shows a SEM image of the APNSC prepared in Example 1, in which the carbon material exhibits a rough surface morphology. Figure 2 The figures show the XRD patterns of APNSC prepared in Example 1 and PC prepared in Comparative Example 1. There is no significant difference between the XRD curves of APNSC and PC, indicating that the modification process has no significant impact on the structure and crystallinity of the carbon materials. Figure 3 The Raman spectra of APNSC prepared in Example 1 and PC prepared in Comparative Example 1 are shown. In the figure, the ID / IG ratio of APNSC (1.44) is greater than that of PC (1.08), indicating that the modification process increased the degree of defects in the carbon material. Figure 4 The N2 desorption curves of APNSC prepared in Example 1 and PC prepared in Comparative Example 1 are shown in the figure. The Sbet of APNSC is significantly larger than that of PC, indicating that the modification process increases the specific surface area of ​​the carbon material. Figure 5 The figure shows a comparison of the specific capacitance (CV) of PC prepared in Comparative Example 1, APNSC prepared in Example 1 (doped with ammonium sulfate), and APNSC-TU prepared in Comparative Example 2 (doped with thiourea). In the figure, APNSC has the largest CV area, followed by PC, and APNSC-TU has the smallest, indicating that the modification strategy of Example 1 significantly increased the specific capacitance of the carbon material. Figure 6 The graph shows the effect of different KOH pretreatment times on the specific capacitance. 0h represents the CV of the untreated sample PC with nitrogen and sulfur co-doping. 0.5h, 1h, 3h, 6h, and 12h represent the APNSC samples prepared at the corresponding KOH pretreatment times in Example 2. In the graph, the specific capacitance of the samples first increases with the increase of pretreatment time, reaches its maximum value at the 3-hour pretreatment time, and then begins to decrease with the increase of pretreatment time. Figure 7 The figure shows a comparison of the electrochemical performance of PC prepared in Comparative Example 1 and APNSC prepared in Example 1. In the figure, the CV performance (a), GCD performance (b), and rate performance (c) of APNSC are all better than those of PC, indicating that the modification process significantly improves the electrochemical performance of carbon materials. The EIS (d) in the figure shows that the electrochemical impedance of both APNSC and PC remains at a low level, indicating that the modification process has no significant impact on the EIS performance. Figure 8 The graph shows the change over time in the adsorption capacity of the electrode material prepared in Experiment 1 for free lead ions and free cadmium ions at a concentration of 10 mg / L in water. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. All raw materials involved in the present invention can be purchased directly from the market. For process parameters not specifically specified, conventional techniques can be referred to.

[0029] Example 1 (1) Accurately weigh 5g of wheat straw powder and add it to 100mL of 1mol / L KOH solution. Set the stirring speed to 800 r / min, the reaction temperature to 80℃, and the reaction time to 3h. After the reaction time is over, wash the pulp residue with deionized water until neutral, filter out the pulp residue and dry it in an 80℃ oven.

[0030] (2) Take 1g of wheat straw powder solid obtained in step (1) and mix and grind it with 3g of ammonium sulfate solid. Place the mixture in a tube furnace and heat it to 900℃ for 120min at a heating rate of 5℃ / min under an inert gas protection environment. Cool it to room temperature and finally obtain black nitrogen and sulfur co-doped porous carbon electrode material (APNSC).

[0031] Example 2 (1) Accurately weigh 5g of wheat straw powder and add it to 100mL of 1mol / L NaOH solution. Set the stirring speed to 800 r / min, the reaction temperature to 80℃, and the reaction time to 0.5h, 1h, 3h, 6h, and 12h respectively. After the reaction time is over, wash the pulp residue with deionized water until neutral, filter out the pulp residue and dry it in an 80℃ oven.

[0032] (2) Same as step (2) in Example 1.

[0033] Example 3 (1) Same as step (1) in Example 1; (2) Take 1g of wheat straw powder solid obtained in step (1) and mix and grind it with 1g of ammonium sulfate solid. Place the mixture in a tube furnace and heat it to 900℃ for 120min at a heating rate of 5℃ / min under an inert gas protection environment. Cool it to room temperature and finally obtain black nitrogen and sulfur co-doped porous carbon electrode material (APNSC).

[0034] Comparative Example 1 1g of wheat straw powder solid was placed in a tube furnace and heated to 900℃ at a heating rate of 5℃ / min under an inert gas protection environment. The high-temperature pyrolysis lasted for 120min, and carbon material (PC) was finally obtained.

[0035] Comparative Example 2 (1) Same as step (1) in Example 1; (2) Take 1g of wheat straw powder solid obtained in step (1) and mix and grind it with 3g of thiourea solid. Place the mixture in a tube furnace and heat it to 900℃ for 120min at a heating rate of 5℃ / min under an inert gas protection environment. Cool it to room temperature and finally obtain black nitrogen and sulfur co-doped porous carbon electrode material (APNSC-TU).

[0036] Electrochemical performance testing: 70 mg of the carbon electrode material prepared in the above examples or comparative examples, 20 mg of acetylene black, and 10 mg of PVDF were placed in a homogenizing box, and 0.1 mL of N-methylpyrrolidone (NMP) was injected. The homogenizing box was placed in a homogenizer, the rotation speed was set to 2000 r / min, and the homogenization was carried out for 18 min to obtain a uniform black slurry. The black slurry was uniformly coated onto a carbon cloth current collector with a size of 1 cm × 2 cm to obtain an electrode sheet. The electrode sheet was then placed in a vacuum oven at 80 °C for 12 hours to dry it. Using the prepared electrode sheet as the working electrode, a platinum sheet electrode as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode, a three-electrode system was constructed in 1 mol / L NaCl electrolyte for electrochemical performance testing. Specific tests included: cyclic voltammetry (CV) at scan rates of 2, 5, 10, 20, 50, 100, and 200 mV / s within a potential window of 0 to −1 V (vs. SCE); galvanostatic charge-discharge (GCD) at current densities of 1, 2, 5, and 10 A / g; and electrochemical impedance spectroscopy (EIS) at open-circuit potential with an AC signal of 10 mV amplitude applied in the frequency range of 10 mHz to 100 kHz. Additionally, the potential for zero charge (PZC) was determined in a 1 mol / L NaCl solution using cyclic voltammetry at a scan rate of 1 mV·s. -1 The potential window is set to -0.5 to 0.5 V (vs. SCE).

[0037] Adsorption experiment: (1) Take 70 mg of APNSC carbon electrode material (prepared in Example 1), 20 mg of acetylene black, and 10 mg of PVDF and put them into a homogenizing box, and inject 0.1 mL of N-methylpyrrolidone (NMP). Place the homogenizing box into a homogenizer, set the rotation speed to 2000 r / min, and run for 18 min to obtain a uniform black slurry. Coat the black slurry evenly on a carbon cloth current collector with a size of 1 cm × 2 cm to obtain an electrode sheet, and then place the electrode sheet in an 80℃ vacuum oven for 12 hours to dry it. Take one electrode sheet, one platinum sheet electrode, and one saturated calomel electrode to form a three-electrode system, and place it in a 1 mol / L NaCl solution for electrochemical CV activation. The CV scan rate is set to 100 mV / s, the voltage range is -1 to 0 V, and the number of activation cycles is 300 to obtain an active electrode sheet.

[0038] A parallel-plate capacitor was assembled from an active electrode and a current collector, with the active electrode serving as the working electrode and the current collector as the counter electrode. Several capacitors were assembled and placed in 90 mL salt solutions with heavy metal ion concentrations of 10, 20, 50, 100, and 200 mg / L, respectively. The stirring speed was set to 350 r / min, and a constant voltage of 1.2 V was applied between the two electrodes, ensuring the working electrode voltage was relatively negative. The system was run for 6 hours, and the adsorption effect was evaluated using atomic absorption spectrometry (AAS). The results are as follows: Figure 8 As shown, the saturated adsorption capacity of the electrode material for lead ions and cadmium ions reached 363.82 mg / g and 113.08 mg / g, respectively.

[0039] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A preparation method of nitrogen and sulfur co-doped biomass porous carbon electrode material, characterized in that, The method comprises the following steps: (1) dispersing the wheat straw in an alkaline solution, heating and stirring to react, washing the slurry to neutral after the reaction, and drying to obtain wheat straw powder after solid-liquid separation; (2) mixing the wheat straw powder with ammonium sulfate uniformly, and then pyrolyzing under a protective atmosphere to obtain a nitrogen and sulfur co-doped biomass porous carbon electrode material.

2. The production method according to claim 1, characterized by, The alkaline solution in step (1) is a KOH solution, a NaOH solution, a Ca(OH)2 solution, or ammonia water.

3. The preparation method according to claim 1, characterized in that, The molar concentration of the alkaline solution in step (1) is 0.5 mol / L to 6 mol / L. The solid-liquid ratio of the wheat straw to the alkaline solution in step (1) is 1:5 to 1:40 g / mL, and more preferably 1:20 g / mL.

4. The method of claim 1, wherein, The heating and stirring reaction in step (1) is carried out at a temperature of 60 to 80 °C for 30 to 720 min; more preferably, the reaction is carried out at 80 °C for 3 h.

5. The preparation method according to claim 1, characterized in that, The drying temperature in step (1) is 60 to 80 °C, and the drying time is 48 to 120 h.

6. The method of claim 1, wherein, The mass ratio of the wheat straw powder to ammonium sulfate in step (2) is 1:1 to 3.

7. The preparation method according to claim 1, characterized in that, The pyrolysis temperature in step (2) is 900 °C, and the pyrolysis time is 120 min; in step (2), the temperature is raised to 900 °C at a rate of 5 °C / min.

8. A nitrogen and sulfur co-doped biomass porous carbon electrode material prepared by the method of any one of claims 1 to 7.

9. The use of the nitrogen and sulfur co-doped biomass porous carbon electrode material of claim 8 in the removal of free heavy metal ions in water by electro-sorption.

10. Use according to claim 9, characterized in that, The heavy metal ions are at least one of lead ions and cadmium ions.

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