Silicon-rich biomass electrode material, preparation method thereof and application of silicon-rich biomass electrode material in adjusting pH of papermaking wastewater

Abstract

The invention discloses a silicon-rich biomass electrode material, a preparation method thereof and application of the silicon-rich biomass electrode material in adjusting the pH value of papermaking wastewater, and belongs to the technical field of functional materials and wastewater treatment. The method comprises the following steps: mixing the silicon-rich biomass with a molybdenum salt solution, stirring and reacting at 50-80 DEG C for 2-6 hours, and drying the obtained reactant; carbonizing the dried product in an inert atmosphere at 500-600 DEG C for 1-3 hours; activating a carbonized product in a CO2 or water vapor atmosphere at 700-900 DEG C for 0.5-2 hours, and naturally cooling to room temperature; and performing acid washing and water washing to be neutral, and drying to obtain the silicon-rich biomass electrode material. According to the method, silicon retention and molybdenum doping are synchronously realized by adopting a one-step carbonization-activation method, a silicon-molybdenum synergistic active site is formed, the conductivity and catalytic activity of a carbon electrode are remarkably improved, a catalytic energy barrier is effectively reduced, the problems of poor conductivity and low silicon utilization rate of traditional biomass charcoal are solved, and effective adjustment of the pH value of the papermaking wastewater is realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional materials and wastewater treatment, and more particularly relates to a silicon-rich biomass electrode material, a preparation method thereof and application thereof in adjusting the pH of papermaking wastewater. BACKGROUND

[0002] In the papermaking wastewater treatment process, pH adjustment is a crucial link. Different sections need to add acid or alkali according to the characteristics of the wastewater to achieve efficient treatment or resource recovery. For example, the pulp-making section wastewater (black liquor) is strongly alkaline, and acid needs to be added to reduce the pH to 2-3 during the lignin precipitation recovery process, which is conducive to the precipitation of lignin and facilitates separation and recovery. The pH needs to be adjusted to 10-11 before alkali recovery to reduce evaporator fouling and improve alkali recovery efficiency. Alkali needs to be supplemented to maintain high alkalinity during black liquor concentration and combustion to prevent silicate precipitation from clogging equipment. For bleaching section wastewater, bleaching wastewater is usually weakly alkaline, and sulfuric acid is added to adjust the pH to 6-7 to reduce the toxicity of chlorophenol and improve the efficiency of subsequent biological treatment. Fenton reaction needs to be carried out under acidic conditions, and sulfuric acid is added to activate H2O2 to degrade difficult-to-treat organic matter. However, after oxidation treatment, the wastewater needs to be adjusted to neutral with NaOH or lime to avoid equipment corrosion. In the white water recycling system, acid is occasionally added to inhibit bacterial reproduction and prevent slurry problems. Calcium carbonate filler needs to be added with alkali to make the pH at 7.5-8.5, at which point the stability is best and precipitation is avoided. For comprehensive wastewater treatment, if the wastewater is alkaline, sulfuric acid is added to 6-7 to improve the flocculation effect of aluminum / iron coagulants. If the wastewater is acidic, alkali is added to 6.5-7.5 to optimize microbial activity. At the same time, alkali is added to make heavy metals form hydroxide precipitates. Therefore, adjusting the pH of papermaking wastewater is not only an environmental protection requirement, but also a core technology for resource recycling. By precisely controlling the pH, enterprises can achieve water saving, byproduct value increase (recovery of alkali, lignin, etc.), compliance reduction, and process stability.

[0003] In the papermaking wastewater treatment process, if the pH of the wastewater can be effectively adjusted by carbon composite electrodes, both the amount of acid and alkali used can be reduced to achieve recycling, and the required pH can be specifically controlled to achieve resource recycling. Electrolytic water is a process that uses electrical energy to decompose water into hydrogen and oxygen. In the hydrogen evolution process, OH - is generated at the cathode, which adjusts the pH of the wastewater. Therefore, using the hydrogen evolution reaction raw material is expected to achieve controllable adjustment of the pH of the wastewater. However, the core challenge is the limitation of electrode materials. Currently, catalysts generally use noble metal electrodes such as platinum and transition metal sulfides to adsorb H atoms and promote the formation of H-H bonds to accelerate the reaction, but the cost is high and the post-treatment of metals is not environmentally friendly. Biomass composite electrodes can efficiently utilize biomass waste and provide active sites to optimize the reaction path, and have received widespread attention.

[0004] Patent CN113838678A discloses a doped porous biomass charcoal electrode material and its preparation method and application, including dogtail grass, potassium hydroxide, Co(NO3)2 and Ni(NO3)2, dogtail grass and potassium hydroxide, to make a super capacitor electrode material, which has high specific capacitance, reversibility and good conductivity, and the dogtail grass effectively reduces the cost of the electrode material; but the reaction is complex, and two kinds of metals are needed to effectively improve the process. Patent CN109003828A discloses a wheat straw derived porous biomass charcoal electrode material and its preparation method, which mixes wheat straw, citric acid and NaH2PO4, stirs the mixture to form a slurry; the slurry is freeze-dried and carbonized, and the carbonized product is activated with KOH at high temperature to obtain a porous biomass charcoal electrode material suitable for super capacitors, which has excellent electrochemical performance and effectively realizes the effective utilization of biological waste resources, but the electrode has low active sites in the catalytic field, limiting its expansion and application. Patent CN118993260A discloses a lignin activated carbon electrode material for capacitive deionization and its preparation method and application, which mixes lignin, Bi precursor or Ag precursor with a solvent, and exchanges the mixed solution in water to complete the dialysis, which has good prospects in the field of capacitive deionization desalination, but the electrode still uses metal materials and dialysis membranes to realize capacitive deionization technology, which has high dialysis cost and metal pollution. SUMMARY

[0005] In view of the problems in the prior art, the present application provides a silicon-rich biomass electrode material, a preparation method thereof and an application thereof in adjusting the pH of papermaking wastewater. The silicon-rich biomass electrode material is prepared by using wheat straw (a natural silicon-rich biomass) as a raw material and modifying it with ammonium molybdate. In the carbonization process, silicon-molybdenum synergistic active sites are formed, which significantly improve the conductivity and catalytic activity of the carbon electrode and effectively reduce the catalytic energy barrier, thereby achieving effective adjustment of the pH of papermaking wastewater.

[0006] Specifically, the technical solutions of the present application are as follows.

[0007] In a first aspect of the present application, a silicon-rich biomass electrode material is provided. The silicon content of the silicon-rich biomass electrode material is 20-25wt% of the total mass of the material, and the molybdenum element is uniformly doped in the carbon skeleton with a content of 20-30wt%.

[0008] Further, the silicon-rich biomass electrode material has a micropore pore size of <2nm, and the proportion of micropores with a pore size of <2nm is 75-90%.

[0009] In a second aspect of the present application, a preparation method of the silicon-rich biomass electrode material is provided, which comprises the following steps: (1) mixing a silicon-rich biomass material with a molybdenum salt solution, stirring at 50-80℃ for 2-6h, and drying the obtained reaction product; (2) The product after drying in step (1) is subjected to staged heating under inert atmosphere, the first stage is heating to 300-400 DEG C at a heating rate of 2-5 DEG C / min, and the temperature is kept for 30-60 min; the second stage is continuously heating to 500-600 DEG C at a heating rate of 5-10 DEG C / min, and carbonization is carried out at 500-600 DEG C for 0.5-2 h to form stable carbon material; (3) The product after carbonization in step (2) is subjected to activation by heating to 700-900 DEG C under CO2 or steam atmosphere at a heating rate of 2-5 DEG C / min, and the temperature is kept for 30-120 min, so as to improve the pore structure of the carbon material; (4) The product after activation in step (3) is subjected to acid washing, water washing to neutral, and drying to obtain the silicon-rich biomass electrode material.

[0010] Further, the heating rate in the first stage of step (2) is 2-5 DEG C / min, and the heating rate in the second stage is 5-10 DEG C / min.

[0011] Further, the silicon-rich biomass material in step (1) is rice husk and / or wheat straw, and the molybdenum salt solution is ammonium molybdate and / or sodium molybdate.

[0012] Further, the silicon-rich biomass material in step (1) is wheat straw, and the molybdenum salt solution is ammonium molybdate solution; the wheat straw is wheat straw or wheat chaff, and the silicon content in the dry basis of the wheat straw is ≥3 wt%.

[0013] Further, the concentration of the molybdenum salt solution in step (1) is 1-5 mol / L; and the ratio of the silicon-rich biomass material to the molybdenum salt solution is 1 g:10-30 mL.

[0014] In a third aspect, the application provides use of the silicon-rich biomass electrode material in preparation of a silicon-rich biomass electrode; the silicon-rich biomass electrode is a three-electrode system, the working electrode is composed of the electrode material, the counter electrode is a platinum sheet or a graphite sheet, and the reference electrode is a calomel electrode, Ag / AgCl or Hg / HgO.

[0015] In a fourth aspect, the application provides use of the silicon-rich biomass electrode material or the silicon-rich biomass electrode in adjusting the pH of papermaking wastewater.

[0016] Compared with the prior art, the application has at least the following beneficial technical effects: (1) The application uses wheat straw (a natural silicon-rich biomass) as raw material, and realizes silicon retention and molybdenum doping simultaneously by molybdate complex modification and one-step carbonization-activation method, forms silicon-molybdenum synergistic active sites, significantly improves the conductivity and catalytic activity of the carbon electrode, and effectively reduces the catalytic energy barrier, solves the problems of poor conductivity and low silicon utilization rate of traditional biomass carbon, and realizes effective adjustment of the pH of papermaking wastewater.

[0017] (2) The silicon-rich biomass electrode material prepared by the method of the application is prepared into a silicon-rich biomass electrode of a three-electrode system, avoiding the compatibility problem of heterogeneous electrodes, resisting alkali corrosion, and prolonging the cycle life.

[0018] (3) The application is directed to the high salt characteristics of papermaking wastewater, and through the desalination cycle test of the silicon-molybdenum composite electrode in the wastewater, the electrode maintains high cycle stability after 10000 cycles of adjustment. BRIEF DESCRIPTION OF DRAWINGS

[0019] The drawings constituting a part of the specification of the application are used to provide further understanding of the application, and the illustrative embodiments of the application and the description thereof are used to explain the application, and do not constitute an improper limitation on the application.

[0020] Figure 1 XRD pattern of the silicon-rich biomass electrode material prepared for Example 1; Figure 2 Infrared spectrum of the silicon-rich biomass electrode material prepared for Example 2; Figure 3 Structure schematic diagram of the electrode test device constructed for the application; Figure 4 Variation diagram of the pH adjustment of the silicon-rich biomass electrode material to the pulp washing wastewater; Figure 5 Cycle performance test diagram of the silicon-rich biomass electrode material. DETAILED DESCRIPTION

[0021] The application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the application and not to limit the scope of the application. The experimental methods not specified in the following examples are usually carried out according to the conventional conditions or according to the conditions recommended by the manufacturers.

[0022] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as familiar to those skilled in the art. The reagents or raw materials used in the application can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in the application are used according to the conventional methods in the art or according to the product instructions.

[0023] The application will be further described in conjunction with the drawings and specific embodiments of the specification.

[0024] In the following examples and comparative examples, the dry basis moisture content of wheat straw is 15wt%, and the silicon content is 4wt%.

[0025] Example 1 (1) 10 g wheat straw (dry basis) was mixed with 10 mL ammonium molybdate 1 mol / L solution, and stirred at 50°C for 5 h, and the obtained reaction product was dried; (2) The dried product of step (1) was heated to 300°C at a heating rate of 2°C / min in an inert atmosphere in the first stage, and kept at 300°C for 60 min; in the second stage, the temperature was continuously increased to 600°C at a heating rate of 10°C / min, and carbonized at 600°C for 2 h to form a stable carbon material; (3) The carbonized product of step (2) was activated at 800°C for 2 h in a CO2 atmosphere at a heating rate of 5°C / min, and kept at 800°C for 120 min; (4) The activated product of step (3) was dried after being washed with hydrochloric acid and water until neutral to obtain a silicon-rich biomass electrode material.

[0026] The XRD pattern and infrared spectrum of the silicon-rich biomass electrode material prepared in Example 1 are shown in Figure 1 and Figure 2 It can be seen from Figure 1 and Figure 2 that the silicon-rich biomass electrode material contains Si and Mo elements, and the content of Si is 20% and the content of Mo is 22% by testing. The pore size of the silicon-rich biomass electrode material is tested, and the micropore (<2 nm) is 85%.

[0027] Example 2 (1) 10 g wheat straw (dry basis) was mixed with 10 mL ammonium molybdate salt 1 mol / L solution, and stirred at 60°C for 4 h, and the obtained reaction product was dried; (2) The dried product of step (1) was heated to 400°C at a heating rate of 3°C / min in an inert atmosphere in the first stage, and kept at 400°C for 40 min; in the second stage, the temperature was continuously increased to 600°C at a heating rate of 8°C / min, and carbonized at 600°C for 1 h to form a stable carbon material; (3) The carbonized product of step (2) was activated at 900°C for 1 h in a CO2 atmosphere at a heating rate of 4°C / min, and kept at 900°C for 100 min; (4) The activated product of step (3) was dried after being washed with hydrochloric acid and water until neutral to obtain a silicon-rich biomass electrode material.

[0028] The wheat straw electrode material prepared in Example 2 has a micropore (<2 nm) of 90%, and the content of Si is 20% and the content of Mo is 20% by testing.

[0029] Example 3 (1) 10 g wheat straw (dry basis) was mixed with 10 mL ammonium molybdate 1 mol / L solution, and stirred at 50°C for 6 h, and the obtained reaction product was dried; (2) The product after drying in step (1) is heated to 300℃ in the first stage under an inert atmosphere at a heating rate of 2℃ / min and held for 60min; the second stage is to continue heating to 500℃ at a heating rate of 5℃ / min and carbonize at 500℃ for 2h to form a stable carbon material. (3) The carbonized product in step (2) was activated at 900 °C for 1.5 h in a CO2 atmosphere, with a heating rate of 8 °C / min and a holding time of 90 min; (4) The activated product in step (3) is washed with hydrochloric acid and water until neutral, and then dried to obtain silicon-rich biomass electrode material.

[0030] The straw electrode material prepared in Example 3 has a micropore size (<2nm) of 75%, and the tested Si content is 20% and the Mo content is 25%.

[0031] Comparative Example 1 (1) In step (1), the dried wheat straw (dry basis) is heated to 300℃ in the first stage under an inert atmosphere at a heating rate of 2℃ / min and held for 60min; the second stage is to continue heating to 600℃ at a heating rate of 10℃ / min and carbonize at 600℃ for 2h to form a stable carbon material. (2) The carbonized product of step (1) was activated at 800 °C for 2 h in a CO2 atmosphere, with a heating rate of 5 °C / min and a holding time of 120 min; (3) The activated product in step (3) is washed with hydrochloric acid and water until neutral, and then dried to obtain silicon-rich biomass electrode material.

[0032] Application Example 1 An electrode testing device was constructed using the electrode material prepared in this invention, as shown in the schematic diagram below. Figure 3 As shown, the specific method is as follows: (1) Electrode slurry preparation: Mix silicon-rich biomass powder, conductive agent (acetylene black), and binder (polyvinylidene fluoride PVDF, which needs to be dissolved in N-methylpyrrolidone NMP) at a mass ratio of 8:1:1, and grind / stir thoroughly in an agate mortar to form a uniform slurry without particle agglomeration; (2) Electrode coating and molding: The prepared slurry is uniformly coated on the surface of the current collector (copper foil) with a scraper, and the coating is controlled to be 20 micrometers. Then it is placed in a vacuum drying oven (100℃) to dry for 8 hours. (3) Electrode pressing and cutting: The dried current collector along with the coating is taken out and pressed with a tablet press (10 MPa pressure) to enhance the bonding force between the coating and the current collector. Then it is cut into circular or square working electrodes of a specific size (e.g., 1cm×1cm), and the mass of the active material is weighed and recorded. The prepared material is used as the working electrode, with a platinum sheet as the counter electrode and Hg / HgO as the reference electrode.

[0033] (4) Using the silicon-rich biomass electrode materials prepared in Example 1 and Comparative Example 1 as electrode materials, respectively, an electrode testing device was constructed according to the above method. Cyclic voltammetry curves of the washing wastewater were tested using an electrochemical workstation (CHI660E) (current density 20 mA·cm). -2 The solution was subjected to a voltage window of -0.9 to 0.1 V for 85 hours, and the pH value of the solution was tracked and recorded using a pH meter. The pH adjustment change graph is shown below. Figure 4 As shown, by Figure 4 It can be seen that the silicon-rich biomass electrode material prepared by the method of the present invention can regulate pH changes and achieve effective pH regulation of papermaking wastewater, while the silicon-rich biomass electrode material prepared in the comparative proportion does not show significant pH changes and does not possess this property.

[0034] (5) Using the silicon-rich biomass electrode material prepared in Example 1 as the electrode material, an electrode testing device was constructed according to the above method. The device was then used with an electrochemical workstation (CHI660E) to perform cycle performance testing in a 6M potassium hydroxide solution at a current density of 20 mA·cm⁻¹. -2 Under the following conditions, a voltage window of -0.9 to 0.1V was used for 10,000 charge-discharge cycles, and the results are as follows: Figure 5 As shown, by Figure 5 As shown, the electrode prepared by the silicon-rich biomass electrode material of the present invention still maintains good electrochemical performance and good resistance to alkali corrosion after 10,000 cycles.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-rich biomass electrode material, characterized in that, The silicon element content of the silicon-rich biomass electrode material is 20-25wt% of the total mass of the material, and the molybdenum element is uniformly doped in the carbon skeleton, with a content of 20-30wt%.

2. The silicon-rich biomass electrode material of claim 1, wherein, The micropore aperture of the silicon-rich biomass electrode material is less than 2nm, accounting for 75-90%.

3. A method of producing the silicon-rich biomass electrode material of claim 1 or 2, characterized by, The method comprises the following steps: (1) mixing the silicon-rich biomass with a molybdate solution, stirring and reacting at 50-80℃ for 2-6h, and drying the obtained reaction product; (2) substage heating the dried product of step (1) in an inert atmosphere, the first stage being heating to 300-400℃ at a heating rate of 2-5℃ / min, and holding for 30-60min; the second stage being continuously heating to 500-600℃ at a heating rate of 5-10℃ / min, and carbonizing at 500-600℃ for 0.5-2h to form a stable carbon material; (3) heating the carbonized product of step (2) to 700-900℃ in a CO2 or steam atmosphere for activation at a heating rate of 2-5℃ / min, and holding for 30-120min to improve the pore structure of the carbon material; (4) drying the activated product of step (3) after acid washing and water washing to neutral to obtain the silicon-rich biomass electrode material.

4. The method for preparing the silicon-rich biomass electrode material according to claim 3, characterized in that, The heating rate of the first stage of step (2) is 2-5℃ / min; and the heating rate of the second stage is 5-10℃ / min.

5. The method for preparing the silicon-rich biomass electrode material according to claim 3, characterized in that, The silicon-rich biomass material in step (1) is rice husk and / or wheat straw, and the molybdate solution is ammonium molybdate and / or sodium molybdate.

6. The method for preparing the silicon-rich biomass electrode material according to claim 5, characterized in that, In step (1), the silicon-rich biomass material is wheat straw, and the molybdate solution is ammonium molybdate solution; the wheat straw is wheat straw stalk or wheat straw bran, and the silicon content in the dry basis of the wheat straw is ≥3wt%.

7. The method for preparing the silicon-rich biomass electrode material according to claim 3, characterized in that, The concentration of the molybdate solution in step (1) is 1-5mol / L; and the ratio of the silicon-rich biomass material to the molybdate solution is 1g:10-30mL.

8. Use of the silicon-rich biomass electrode material of claim 1 or 2 or the silicon-rich biomass electrode material prepared by the preparation method of any one of claims 3-7 in the preparation of a silicon-rich biomass electrode.

9. Use of the silicon-rich biomass electrode material of claim 1 or 2 or the silicon-rich biomass electrode material prepared by the preparation method of any one of claims 3-7 or the silicon-rich biomass electrode of claim 8 in adjusting the pH of papermaking wastewater.

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