Methods and applications for preparing porous carbon materials from cotton pulp black liquor

Abstract

This invention discloses a method for preparing porous carbon materials using cotton pulp black liquor as raw material and its application. The preparation method is as follows: Step (1) Add inorganic acid to cotton pulp black liquor and adjust the pH for acid precipitation. After acid precipitation, centrifuge to separate the biomass precipitate in the cotton pulp black liquor and dry it to obtain cotton pulp black liquor biomass; Step (2) Mix the cotton pulp black liquor biomass with an activator to obtain a mixed raw material; Step (3) Calcine the mixed raw material under a nitrogen atmosphere. After calcination, grind the solid calcined product to obtain a solid powder; Step (4) Soak the solid powder in hydrochloric acid solution and then wash it with deionized water until neutral; dry the neutralized solid powder to obtain a porous carbon material. This porous carbon material can be applied to the electrocatalytic hydrogen evolution of urea. This invention can solve the problem of low utilization rate of biomass resources in existing cotton pulp black liquor.

Description

Technical Field

[0001] This invention relates to the field of porous carbon materials technology. Specifically, it relates to a method for preparing porous carbon materials using cotton pulp black liquor as raw material and its application. Background Technology

[0002] Cotton pulp black liquor is a waste liquid produced by the alkaline cooking process of cotton linters to produce cotton pulp. It has a pH of approximately 14 and an organic matter content as high as 65%. Industrially, it is often treated by concentration and then thoroughly dried to be used as a raw material for organic compound fertilizer. However, this wastewater treatment method has many drawbacks: high treatment costs, the need for large amounts of energy for evaporation and concentration, and extremely low utilization rates. Therefore, the cotton textile industry currently faces the problems of difficult waste liquor treatment, significant pollution, and high energy consumption.

[0003] Porous carbon materials possess advantages such as high chemical stability (resistance to acids and alkalis), large specific surface area, well-developed pore structure, and adjustable pore size. They also feature simple synthesis steps, low preparation costs, and high thermal and electrical conductivity, making them widely used in electrochemistry. Furthermore, the preparation of porous carbon materials using waste biomass resources such as rice husks, cotton stalks, kapok, and willow catkins has been extensively reported in the literature. Utilizing waste biomass resources not only develops high-value-added applications for biomass materials but also significantly reduces raw material costs. Biomass porous carbon materials, with their abundant raw materials, lack of pollution, simple preparation methods, and low preparation costs, have become a research hotspot in carbon materials. Therefore, finding a method to prepare porous carbon materials using the organic matter in cotton pulp black liquor is an effective way to improve the utilization value of cotton pulp black liquor. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to provide a method and application for preparing porous carbon materials using cotton pulp black liquor as raw material, so as to solve the problem of low utilization rate of biomass resources in existing cotton pulp black liquor.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A method for preparing porous carbon materials using cotton pulp black liquor as raw material includes the following steps:

[0007] Step (1): Add inorganic acid dropwise to cotton pulp black liquor and adjust the pH for acid precipitation. After acid precipitation, centrifuge to separate the biomass precipitate in cotton pulp black liquor and dry it to obtain cotton pulp black liquor biomass.

[0008] Step (2): Thoroughly mix the cotton pulp black liquor biomass with the activator to obtain a mixed raw material;

[0009] Step (3): Place the mixed raw materials under a nitrogen atmosphere for calcination. After calcination, grind the solid calcined product to obtain solid powder.

[0010] Step (4): Soak the solid powder in the soaking solution, then wash it with deionized water until it is neutral; dry the washed solid powder to obtain porous carbon material.

[0011] In the above method for preparing porous carbon materials using cotton pulp black liquor as raw material, in step (1), the inorganic acid is one or a mixture of two or more of phosphoric acid, sulfuric acid, hydrochloric acid, or nitric acid; the pH of the cotton pulp black liquor is adjusted to 1-7 by adding the inorganic acid. Compared with other inorganic acids such as sulfuric acid, hydrochloric acid, or nitric acid, phosphoric acid has the following advantages: after adjusting the pH, phosphoric acid will partially remain in the cotton pulp black liquor biomass, and can act as an activator in the subsequent calcination process, working together with potassium hydroxide to activate the cotton pulp black liquor biomass to form an excellent pore structure.

[0012] In the above method for preparing porous carbon materials using cotton pulp black liquor as raw material, in step (1), the centrifugation conditions are 5000-6000 rpm and the centrifugation time is 3-5 min; the drying temperature is 50-90℃ and the drying time is 12-48 h; the cotton pulp black liquor biomass is passed through a 40-mesh sieve; if the particle size of the cotton pulp black liquor biomass is too large, it will not be conducive to its uniform mixing with the activator and will lead to uneven heat and mass transfer.

[0013] In the above method for preparing porous carbon materials using cotton pulp black liquor as raw material, in step (2), the activator is potassium hydroxide, zinc chloride, or phosphoric acid; in step (4), when potassium hydroxide or zinc chloride is used as the activator, hydrochloric acid solution is used as the soaking solution; when phosphoric acid is used as the activator, sodium hydroxide solution is used as the soaking solution; when zinc chloride is used as the activator, zinc salts are recovered by acid washing and water washing; when phosphoric acid is used as the activator, phosphoric acid can be extracted and recovered or phosphate can be recovered after alkali neutralization. The porous carbon material prepared using zinc chloride as the activator has many large pores and has zinc pollution problems; phosphoric acid as the activator can make the porous carbon material have finer pores, but it is not ideal in terms of the number of pores; the porous carbon material prepared using potassium hydroxide as the activator has a moderate pore size and high porosity, and the largest specific surface area.

[0014] In the above method for preparing porous carbon materials using cotton pulp black liquor as raw material, in step (2), the activator is potassium hydroxide; the mass ratio of cotton pulp black liquor biomass to activator is 1:(0.5~2).

[0015] In the above method for preparing porous carbon materials using cotton pulp black liquor as raw material, when the activator in step (2) is potassium hydroxide, the soaking solution in step (4) is a hydrochloric acid solution with a molar concentration of 1-2 mol / L, the soaking time is 1-2 h, the drying temperature is 70-80℃, and the drying time is 12-48 h.

[0016] In the above method for preparing porous carbon materials using cotton pulp black liquor as raw material, in step (3), during calcination, the mixed raw materials are placed in a tube furnace and heated to 400-500℃ and held for 30-60 minutes, with a heating rate of 5-10℃ / min; after the holding period, the materials are cooled to room temperature; the solid powder is the undersize obtained by grinding the calcined product and passing it through an 80-mesh sieve.

[0017] In the above method for preparing porous carbon materials using cotton pulp black liquor as raw material, in step (1), the cotton pulp black liquor contains: lead 1.15 mg / kg, cadmium 0.11 mg / kg, chromium 3.96 mg / kg, arsenic 0.35 mg / kg, magnesium 839.28 mg / kg, zinc 133.77 mg / kg, manganese 13.87 mg / kg, copper 1.98 mg / kg, and iron 490.49 mg / kg.

[0018] In the above method for preparing porous carbon materials using cotton pulp black liquor as raw material, in step (1), the inorganic acid is phosphoric acid; the pH of the cotton pulp black liquor is adjusted to 1 by adding inorganic acid for acid precipitation (compared to other acid precipitation conditions, the porous carbon materials generated from the cotton pulp black liquor biomass obtained by acid precipitation at pH 1 after activation and calcination have better pore structure and higher electrocatalytic activity, which may be because the biochar prepared from the cotton pulp black liquor biomass obtained under the acid precipitation conditions under the activation and carbonization conditions of this invention has a higher specific surface area, excellent pore structure and contains more electrocatalytic active sites); the centrifugation conditions are 5000 rpm and centrifugation time. The drying time is 48 hours, with a drying temperature of 65℃ and a drying time of 5 minutes. If the drying temperature is too high or the drying time is too long, the structure of the biomass in the cotton pulp black liquor will collapse, affecting the subsequent formation of the pore structure. The cotton pulp black liquor contains: lead 1.15 mg / kg, cadmium 0.11 mg / kg, chromium 3.96 mg / kg, arsenic 0.35 mg / kg, magnesium 839.28 mg / kg, zinc 133.77 mg / kg, manganese 13.87 mg / kg, copper 1.98 mg / kg, and iron 490.49 mg / kg.

[0019] In step (2), the activator is potassium hydroxide; the mass ratio of biomass to activator in cotton pulp black liquor is 1:1;

[0020] In step (3), during calcination, the mixed raw materials are placed in a tubular furnace and heated to 400℃ and held for 1 hour. The heating rate is 10℃ / min. Under these calcination conditions, the cotton pulp black liquor biomass can be carbonized to obtain biochar with excellent pore structure under the activation of the activator, and the biochar yield is relatively high. If the heating rate is too fast, the carbonization temperature is too low, or the holding time is too short, the generated porous carbon will not be completely carbonized and the pore structure will be poor. If the heating rate is too slow, the carbonization temperature is too high, or the holding time is too long, the biomass will be pyrolyzed more and the biochar yield will be low. After the holding time is completed, the furnace is cooled to room temperature. The solid powder is the undersize obtained by grinding the calcined product and passing it through an 80-mesh sieve.

[0021] In step (4), the soaking solution is a hydrochloric acid solution with a molar concentration of 1 mol / L, and the soaking time is 2 h. Under these washing conditions, the residual activator in the porous carbon can be completely removed. The drying temperature is 80℃ and the drying time is 48 h. If the drying temperature is too high or the drying time is too long, it may damage the porous structure formed by the porous carbon.

[0022] The application of porous carbon materials prepared from cotton pulp black liquor will be carried out by using the above-mentioned method of preparing porous carbon materials from cotton pulp black liquor for electrocatalytic urea hydrogen evolution.

[0023] The technical solution of the present invention achieves the following beneficial technical effects:

[0024] 1. This invention uses cotton pulp black liquor as a raw material for preparing porous carbon materials. The biomass from the cotton pulp black liquor is precipitated through acid precipitation. By controlling the pH of the acid precipitation, the extracted cotton pulp black liquor biomass, under the preparation process conditions of this invention, can form a porous carbon material with uniform pores, a complete pore structure, a large number of micropores, and suitable pore size. Furthermore, this porous carbon material can stably generate hydrogen gas in alkaline solution and can efficiently degrade urea in wastewater. This method of preparing porous carbon materials using cotton pulp black liquor as a raw material solves the problems of high cost, significant pollution, and extremely low utilization rate associated with traditional cotton pulp black liquor concentration and treatment.

[0025] 2. This invention extracts specific components of cotton pulp black liquor biomass by controlling the pH of acid precipitation during cotton pulp black liquor acidification. By controlling the type and amount of activator, the heating rate during calcination, the calcination temperature, and the calcination time, a porous carbon material with excellent pore structure is finally prepared. This porous carbon material has a large number of active sites for urea electrolysis and a large effective active area, which makes the material have high electrocatalytic activity in electrochemical catalysis and can stably degrade urea hydrogen evolution.

[0026] 3. This invention selects phosphoric acid to adjust the pH of cotton pulp black liquor to 1 during acid precipitation. The resulting cotton pulp black liquor biomass contains a suitable amount of residual phosphoric acid, which can act as an activator in the subsequent calcination process, synergistically with potassium hydroxide. By controlling the amount of potassium hydroxide and the calcination conditions, the prepared porous carbon material exhibits a higher micropore content and a complete pore structure (specific surface area as high as 1139.33 m²). 2 / g, pore volume reaches 0.47cm³. 3 / g, with an average pore size of 1.61nm).

[0027] 4. In this invention, phosphoric acid is selected for acid precipitation of cotton pulp black liquor. By controlling the addition of phosphoric acid dropwise, the cotton pulp black liquor is acid precipitated at a pH of 1, which can prevent metal elements such as lead, cadmium, and arsenic contained in the cotton pulp black liquor from entering the cotton pulp black liquor biomass along with the precipitate. The porous carbon material prepared from this cotton pulp black liquor biomass is soaked in a 1 mol / L hydrochloric acid solution, which can not only effectively remove the residual activator in the porous carbon, but also further dissolve the small amount of metal elements contained in the cotton pulp black liquor biomass, so that the final porous carbon material is free of various metal elements contained in the cotton pulp black liquor. Attached Figure Description

[0028] Figure 1 FT-IR spectra of different porous carbon materials in the embodiments of the present invention;

[0029] Figure 2a SEM image of PCMA-1 in this embodiment of the invention;

[0030] Figure 2b SEM image of PCMA-4 in this embodiment of the invention;

[0031] Figure 2c SEM image of PCMA-7 in this embodiment of the invention;

[0032] Figure 2d SEM image of PCMA-11 in this embodiment of the invention;

[0033] Figure 3a SEM images of CARB-1 in embodiments of the present invention;

[0034] Figure 3b SEM images of CARB-2 in embodiments of the present invention;

[0035] Figure 3c SEM images of CARB-3 in embodiments of the present invention;

[0036] Figure 4a The N2 adsorption-desorption curves of PCMA-1, PCMA-4, PCMA-7 and PCMA-11 in the embodiments of the present invention;

[0037] Figure 4b Aperture distribution diagrams (0-100nm) of PCMA-1, PCMA-4, PCMA-7 and PCMA-11 in embodiments of the present invention;

[0038] Figure 4c Aperture distribution diagrams (0-20nm) of PCMA-1, PCMA-4, PCMA-7 and PCMA-11 in embodiments of the present invention;

[0039] Figure 5 XRD distribution diagrams of CARB-1, CARB-2, and CARB-3 in embodiments of the present invention;

[0040] Figure 6a LSV diagrams of UOR and OER of CARB-1 in this embodiment of the invention;

[0041] Figure 6b LSV diagrams of UOR and OER of CARB-2 in embodiments of the present invention;

[0042] Figure 6c LSV diagrams of UOR and OER of CARB-3 in embodiments of the present invention;

[0043] Figure 7a The UOR performance diagrams (LSV curves and overpotential diagrams) of CARB-1, CARB-2 and CARB-3 in the embodiments of the present invention;

[0044] Figure 7b UOR performance plots (Tafel slopes) of CARB-1, CARB-2 and CARB-3 in this embodiment of the invention;

[0045] Figure 8a HER performance diagrams (LSV curves and overpotential diagrams) of CARB-1, CARB-2, and CARB-3 in embodiments of the present invention;

[0046] Figure 8b HER performance plots (Tafel slopes) of CARB-1, CARB-2, and CARB-3 in embodiments of the present invention;

[0047] Figure 9a In the embodiments of the present invention, C of CARB-1, CARB-2, and CARB-3 dl Line graph;

[0048] Figure 9b ECSA diagram of CARB-1 in this embodiment of the invention;

[0049] Figure 10a and Figure 10bThe LSV curves of CARB-1 in a mixed solution of 1M potassium hydroxide and 0.33M urea and a 1M potassium hydroxide solution are shown in the embodiments of the present invention.

[0050] Figure 11 Nyquist plots of CARB-1 and Pt / IrO2 in embodiments of the present invention;

[0051] Figure 12 Chronopotential (CP) curve of CARB-1 porous material in this embodiment of the invention. Detailed Implementation

[0052] 1. Materials and Methods

[0053] 1.1 Reagents and Instruments

[0054] Potassium hydroxide (KOH), Luoyang Chemical Reagent Factory; Phosphoric acid (H3PO4), Yantai Shuangshuang Chemical Co., Ltd.; Hydrochloric acid (HCl), Xi'an Chemical Reagent Factory; n-Hexane (C6H 14 Sinopharm Industrial Co., Ltd.; Cyclopentane (C5H) 10 ), Tianjin Zhiyuan Chemical Technology Co., Ltd.; Ethyl acetate (C4H8O2), Tianjin Xinbote Chemical Co., Ltd.; Acetone (CH3COCH3), Tianjin Xinbote Chemical Co., Ltd.; n-Propanol (CH3CH2H2OH), Sinopharm Industrial Co., Ltd.; all were analytical grade. Cotton pulp black liquor, Xinjiang Zhongtai Textile Co., Ltd., the metal content in cotton pulp black liquor is shown in Table 1; Distilled water (H2O), double distilled, supplied by the Equipment Department of Tarim University.

[0055] Table 1

[0056]

[0057] Multi-head magnetic stirrer, HJ-6A, Jintan Medical Instrument Factory; Electronic balance PL303 / AL104, Mettler Toledo Instruments Shanghai Co., Ltd.; Electric drying oven, GZX-9246MBE, Shanghai Boxun Industrial Co., Ltd.; Tube furnace, OTF-1200X, Hefei Kejing Materials Technology Co., Ltd.; pH meter, PHS-3C, Shanghai Instrument & Electronics Science Co., Ltd.; Room temperature centrifuge, TD-4M, Jinan Oulaibo E-commerce Co., Ltd.; Fourier transform infrared spectrometer, Frontier mid-infrared spectrometer, PerkinElmer, USA; Scanning electron microscope, Aprio S, Thermo Fisher Scientific, USA; Rotary evaporator, RE-52C, Shanghai Yarong Biochemical Instrument Factory; Three-station multi-functional adsorption analyzer, 3Flex, Mack, USA; X-ray diffractometer, D8 Advance, Bruker, Germany.

[0058] 1.2 Experiment

[0059] 1.2.1 Acid precipitation method for extracting biomass from cotton pulp black liquor

[0060] Cotton pulp black liquor is sensitive to pH changes. Biomass was extracted from the black liquor by adjusting the pH with phosphoric acid. Phosphoric acid was added dropwise to 100 mL of black liquor to adjust the pH to 11. The liquor was then centrifuged (5000 rpm, 5 min), and the solid at the bottom of the centrifuge tube was scraped off. The solid was then dried in an oven (48 h). The resulting solution was poured into a beaker and adjusted to pH 9 with concentrated phosphoric acid. This process was repeated, adjusting the pH of the supernatant solution after centrifugation to 7, 4, 9, and 1, respectively, to obtain black liquor extracts at different pH values. Experiments showed that organic biomass could not be separated at pH 9. Finally, black liquor biomass at pH values ​​of 11, 7, 4, and 1 was obtained.

[0061] 1.2.2 Preparation of porous carbon materials with different pH values

[0062] Using KOH as an activator, the extracted cotton pulp black liquor biomass was mixed with KOH at a 1:1 ratio (the cotton pulp black liquor biomass was passed through a 40-mesh sieve to collect the undersize material). 1g of each mixture was weighed using an electronic balance and placed in a covered porcelain boat. The mixture was then calcined at 400℃ in a tube furnace under nitrogen protection for 1 hour, with a heating rate of 10℃ / min. -1 After the tube furnace cooled to room temperature, the porous carbon material was removed and scraped from the ceramic rim with a spatula. It was then ground in an agate mortar and sieved through an 80-mesh sieve. The porous carbon material was then soaked in a 1 mol / L hydrochloric acid solution for 2 hours, filtered, and washed 6-8 times with deionized water until neutral. It was then dried in an oven at 80°C for 48 hours to obtain the porous carbon material. The prepared porous carbon materials were named PCMA-1, PCMA-4, PCMA-7, and PCMA-11 (named according to the different pH values ​​of cotton pulp black liquor biomass at 1, 4, 7, and 11 as biochar raw materials). Electron microscopy analysis was used to identify the organic raw material with the most suitable pH value.

[0063] 1.2.3 Preparation of porous carbon materials with different amounts of activator

[0064] To investigate whether the amount of KOH affects porous carbon materials, this embodiment prepared porous carbon materials by varying the amounts of KOH and cotton pulp black liquor biomass, followed by activation and carbonization treatment. Cotton pulp black liquor biomass at pH 1 was used as raw material, and the ratio of organic matter to KOH was changed to 1:2 and 2:1. The materials were placed in a tube furnace and calcined at 400°C for 1 hour to prepare porous carbon materials. Finally, the prepared porous carbon materials were used in electrochemical tests. The porous carbon materials with organic matter to KOH ratios of 1:1, 1:2, and 2:1 at pH 1 were named CARB-1, CARB-2, and CARB-3, respectively.

[0065] 2. Applications of Characterization and Electrochemical Properties of Porous Carbon Materials

[0066] 2.1 Characterization of porous carbon materials

[0067] 2.1.1 SEM characterization of porous carbon materials

[0068] Scanning electron microscopy (SEM) is the most effective and direct testing method for observing and studying differences in material shape, particle size, and microstructure. In this embodiment, SEM analysis revealed that pH 1 was the optimal pH for porous carbon materials. Under these pH conditions, approximately 0.03 g of porous carbon material with organic matter to KOH ratios of 1:2 and 2:1 was placed on the sample stage and sputtered with gold in a vacuum for approximately 90 seconds. The sample, coated with conductive adhesive, was then placed on a sample holder for scanning observation.

[0069] 2.1.2 FT-IR characterization of porous carbon materials

[0070] The infrared spectra of PAM porous microspheres were determined using a Nicolet 380 Fourier transform infrared (FT-IR) spectrometer. The prepared porous carbon material was ground and sieved. High-purity KBr was dried at 120℃ for 4 h, mixed with the treated porous carbon material, and ground uniformly before infrared characterization.

[0071] 2.1.3 XRD Characterization of Porous Carbon Materials

[0072] This embodiment employs X-ray diffraction (XRD) analysis to analyze the crystal structure of the material. By analyzing its diffraction pattern, information such as the material's phase composition, internal atomic or molecular structure, and morphology is obtained. A powder sample is placed in an XRD instrument, and X-ray diffraction patterns at different angles are recorded.

[0073] 2.1.4 BET characterization of porous carbon materials

[0074] Specific surface area (BET) measurement is one of the important methods for characterizing particulate materials. This study uses nitrogen low-temperature adsorption to measure the specific surface area and pore size distribution curves of porous materials.

[0075] 2.2 Applications of the electrochemical properties of porous carbon materials

[0076] Electrochemical testing and analysis were performed using a WaveDrive10 electrochemical workstation from PINE Corporation, USA. A Hg / HgO electrode was selected as the reference electrode, a platinum sheet electrode as the counter electrode, and nickel foam with catalyst support as the working electrode. Electrochemical tests were conducted in a three-electrode system using 1 mol / L KOH solution and 1 mol / L KOH + 0.33 mol / L urea solution as electrolytes.

[0077] 2.2.1 Treatment of Nickel Foam

[0078] First, cut the nickel foam into cubes with an area of ​​1cm*1cm and a thickness of about 0.02cm. Then, ultrasonically wash them with 1mol / L hydrochloric acid solution, anhydrous ethanol and deionized water for 10 minutes each. Place them in a petri dish and dry them in a forced-air drying oven at 80℃ for later use.

[0079] 2.2.2 Preparation of working electrode

[0080] Porous carbon material was placed in a small centrifuge tube, followed by the addition of 5 μL of polytetrafluoroethylene binder and an appropriate amount of ethanol solvent. Then, 0.015 g of accurately weighed acetylene black was added. The solution was then sealed, shaken well, and sonicated at room temperature for 30 min to obtain a uniformly dispersed suspension. The suspension was then applied to nickel foam using a pipette. The coated working electrode in the culture dish was sealed with plastic wrap and then dried in an 80°C oven until ready for testing.

[0081] 2.2.3 Linear Scan Voltammetry (LSV)

[0082] All tests in this embodiment were conducted at a scan rate of 10 mV / s. To better obtain the reaction characteristic curves, the potentials were converted into reversible hydrogen electrode potentials: the formula is as follows:

[0083] Evs RHE=Evs Hg / HgO+PH*0.059+0.095

[0084] 2.2.4 Tafel Slope

[0085] By analyzing and fitting the polarization curve, the current density j and overpotential η are obtained. The Tafel slope b can be calculated using the formula η = a + blogj, where a, b, and j are constants, the Tafel slope (mV / dec), and the current density (mA·cm²), respectively. -2 ).

[0086] 2.2.5 Electrochemical impedance spectroscopy (EIS)

[0087] The AC impedance test was performed using a PARSTAT 4000A electrochemical workstation manufactured by Ametek Corporation, with a measurement frequency range of 0.01 Hz to 500,000 Hz.

[0088] 2.2.6 Timing Potential Test (CP)

[0089] Stability was assessed by recording the relationship between electrode potential and time during electrocatalysis under constant current conditions and analyzing the stability. This example uses a 10 mA cm⁻¹ current. -2 Tests conducted at current density.

[0090] 3 Results and Analysis

[0091] 3.1 Analysis of Characterization Results of Porous Carbon Materials

[0092] 3.1.1 FT-IR Analysis of Porous Carbon Materials

[0093] Figure 1 It can be seen that the peak value of the four groups of porous carbon materials with different pH values ​​is 2923 cm⁻¹. -1 and 2844cm -1 The peaks appearing on the left and right correspond to the absorption peaks of the -CH2 stretching vibration, at 1588 cm⁻¹. -1 and 1712cm -1 The peaks appearing on the left and right correspond to the -C=C- stretching vibration, 1086cm. -1 and 1081cm -1 The peaks appearing on the left and right correspond to CO. The results show that as the pH decreases, starting from the porous carbon material at pH=4, the CO peak disappears. As the pH decreases, the total content of functional groups on the surface of the porous carbon material decreases.

[0094] 3.1.2 SEM Analysis of Porous Carbon Materials

[0095] Figure 2a , Figure 2b , Figure 2c and Figure 2d The images show scanning electron microscope (SEM) images of PCMA-1, PCMA-4, PCMA-7, and PCMA-11 at 2000x magnification. The pH of the organic matter significantly affects the porous carbon material. At pH 1, the porous carbon material exhibits a uniform pore distribution, intact structure, suitable pore size, and a large number of pores. As the pH increases, the surface pore structure of the porous carbon material decreases, the number of pores decreases, and the surface roughness increases.

[0096] Figure 3a , Figure 3b , Figure 3c The images shown are, in order, scanning electron microscope (SEM) images of CARB-1, CARB-2, and CARB-3 at 5000x magnification. KOH, as an activator, directly affects the surface morphology and porous structure of porous carbon materials by changing its proportion and amount. Figure 3a It can be seen that when the ratio of KOH to PCMA is 1:1, the porous carbon surface has a highly porous structure with small, uniformly distributed, and consistent pore size. Figure 3b It can be clearly seen that when the ratio of PCMA to KOH is 1:2, the excessive amount of KOH leads to the cracking of the porous carbon skeleton and the collapse of the pore structure. Figure 3c It can be seen that when the ratio of PCMA to KOH is 2:1, the amount of KOH used is too small, resulting in fewer and uneven pores.

[0097] 3.1.3 BET Analysis of Porous Carbon Materials

[0098] N2 adsorption-desorption isotherms and pore size distributions of PCMA-1, PCMA-4, PCMA-7, and PCMA-11 are shown below. Figure 4a and Figure 4b As shown, in Figure 4a The nitrogen adsorption-desorption curves of porous carbon materials PCMA-1, PCMA-4, and PCMA-7 exhibit typical Type I isotherms, and these isotherms increase sharply at very low relative pressures (<0.12), demonstrating the presence of numerous microporous structures. The nitrogen adsorption-desorption curve of PCMA-11 shows a typical Type IV isotherm, with a distinct H4-type hysteresis loop at P / P0 = 0.1, indicating that the adsorbent material contains both micropores and mesopores. The calculated specific surface area of ​​PCMA-1 is 1139.33 m². 2 / g, the specific surface area of ​​PCMA-4 is 801.56m². 2 / g, the specific surface area of ​​PCMA-7 is 759.82m². 2 / g, the specific surface area of ​​PCMA-11 is 51.97m². 2 / g.

[0099] like Figure 4b and Figure 4cAs shown in Table 2, the pore volume of PCMA-1 is higher than that of PCMA-4, PCMA-7, and PCMA-11 in the 0.4 to 1 nm range. The pore volumes of PCMA-4 and PCMA-7 are higher than those of PCMA-11 in the 1 to 2 nm range, but the pore volumes of PCMA-4 and PCMA-7 are similar within this range. When the pore size is greater than 2 nm, the pore volumes of PCMA-4 and PCMA-7 are significantly higher than those of PCMA-11. Furthermore, Table 2 shows that the pore volumes of PCMA-4 and PCMA-7 are similar in the range below 1.70 nm, while the pore volume of PCMA-1 in this range is 0.47 cm³. 3 The micropore content ( / g) is higher than the other three groups. In summary, porous carbon materials at pH=1 have a higher micropore content and a larger specific surface area. This is because the acid etching process consumes impurities, increasing the porosity of the porous carbon material. Therefore, the porous structure of porous carbon materials can provide more active sites and greatly expand the contact area for electrochemical reactions, facilitating the permeation and adsorption of biomolecules and the transfer of mass and charge, thereby achieving higher electrocatalytic activity.

[0100] Table 2 Pore volume and pore size distribution of porous carbon materials

[0101]

[0102] 3.1.4 XRD Analysis of Porous Carbon Materials

[0103] Depend on Figure 5 XRD diffraction peak analysis of the three ratios of porous carbon materials revealed broad peaks around 20°, indicating the successful synthesis of structurally excellent porous carbon materials. Although some strong crystalline peaks were present, this was mainly due to the use of phosphoric acid for initial material treatment and KOH as an activator in the subsequent preparation of the porous carbon materials, resulting in a residual amount of sodium phosphate in the materials and causing these strong crystalline peaks. Since peak intensity is positively correlated with content, CARB-1 showed the least residual sodium phosphate, therefore this ratio of porous carbon material can be considered the most superior. The carbon peak should be relatively weak and broad, indicating a weaker peak intensity for sodium phosphate, which also suggests a lower residual amount.

[0104] 3.2 Application Analysis of Electrochemical Performance

[0105] 3.2.1 Investigating the activities of CARB-1, CARB-2, and CARB-3 on UOR and OER

[0106] Figure 6a , Figure 6b , Figure 6cThe LSV plots show the OER and UOR of CARB-1, CARB-2, and CARB-3 in 1M KOH solution and a mixed solution of 1M KOH and 0.33 MUrea, respectively. The catalytic electrolysis performance of the porous carbon materials was evaluated using linear sweep voltammetry (LSV). From the LSV curves in the figures, it can be seen that the porous carbon materials exhibit excellent performance at a current density of 10 mA / cm². -2 Under the given conditions, the potential required for UOR of CARB-1 (1.37V) is much smaller than that required for OER (1.52V). Similarly, the potential required for UOR of CARB-2 (1.39V) is much smaller than that required for OER (1.53V), and the potential required for UOR of CARB-3 (1.56V) is smaller than that required for OER (1.58V). This indicates that porous carbon materials with different ratios of raw materials and activators have lower electrochemical activation barriers for UOR than OER, meaning they all have the ability to electrolyze urea and exhibit better electrochemical activity than water electrolysis.

[0107] 3.2.2 Investigating the UOR performance of CARB-1, CARB-2, and CARB-3

[0108] Depend on Figure 7a and Figure 7b It can be seen that porous carbon materials can achieve a current density of 10 mA / cm². -2 Under the specified conditions, CARB-1 requires a potential of 1.37V, lower than the 1.39V required by CARB-2 to achieve the same current density, and significantly lower than the 1.56V required by CARB-3. This indicates that CARB-1 exhibits the highest activity in urea electrolysis. This is largely due to the significant influence of KOH as an activator and pore-forming agent. As the KOH concentration increases, the overpotential for urea electrolysis decreases, meaning the number of active sites in the porous material increases. This demonstrates that the less energy required for the porous carbon material to stabilize the reaction, the greater its catalytic activity in urea electrolysis. In conclusion, CARB-1 demonstrates the optimal performance in urea electrolysis.

[0109] 3.2.3 Investigating the hydrogen evolution reaction (HER) performance of CARB-1, CARB-2, and CARB-3

[0110] Depend on Figure 8a and Figure 8b It can be seen that porous carbon materials in 1M KOH solution, such as CARB-1, only require a potential of -0.13V to achieve a current density of 10 mA cm⁻¹. -2 The potential required for the reaction of porous carbon materials is much higher than the -0.14V required for CARB-2 to achieve the same current density, and the -0.21V required for CARB-3. The higher the potential required for the reaction of porous carbon materials, the less energy is needed, and the easier it is to produce hydrogen. Therefore, CARB-1 has a better hydrogen evolution capacity. Electrolyzing urea to produce hydrogen offers the possibility that hydrogen can be used as a new energy source to replace traditional energy.

[0111] 3.2.4 Electrochemical Active Surface Area (ECSA) Test

[0112] Optimization of porous carbon materials generally involves two aspects: increasing the number of active sites and enhancing the activity of existing active sites. To investigate the optimization mechanism of CARB's catalytic activity, the effective electrochemical active surface area of ​​the material was determined by calculating the electric double-layer capacitance (Cdl) over the non-Radida potential range. In this embodiment, the potential range was selected from -0.40V (vs. RHE) to -0.50V (vs. RHE), and scan rates of 20, 40, 60, 80, and 100 mV·s were performed in a 1 mol / L KOH + 0.33 mol / L urea solution. -1 The cyclic voltammetry test results are as follows: Figure 9a and Figure 9b As shown, the CV curve of the CARB-1 sample exhibits the typical rectangular characteristics of an electric double-layer capacitor. The charge / discharge current density difference (Δj = j) at a voltage of 0.45V (vs. RHE) was calculated from the CV curve. anode -j cathode According to formula C dl The slope of the fitted straight line is C = Δj / 2v. dl .Depend on Figure 9a and Figure 9b It can be seen that CARB-1's C dl The value is 1.94 mF cm -2 CARB-2 C dl Value 0.81mF cm -2 CARB-3 C dl Value 0.82mF cm -2 Furthermore, the larger the double-layer capacitance value, the larger the effective active area of ​​the material. Therefore, the composite CARB-1 catalyst has a large effective active area.

[0113] 3.2.5 Performance Comparison of UOR and OER of CARB-1 Catalyst

[0114] The activity of the target catalyst in water electrolysis (OER) and urea electrocatalysis (UOR) was analyzed by linear sweep voltammetry (LSV). Figure 10a and Figure 10b The LSV curves of CARB-1 in a 1M KOH mixed solution with 0.33M urea and in a 1M KOH solution were compared. The UOR of the catalyst reached 10 mA cm⁻¹ at a potential of 1.360 V. -2 The current density is much lower than that of OER reaching 10 mA cm under the same conditions. -2The required voltage is 1.580V. Furthermore, the current density in the UOR curve increases rapidly with increasing potential, almost completely covering the Ni. 2+ The oxidation peaks of the components indicate that CARB-1 has highly efficient urea electrolysis activity, and that the UOR catalyzed by the target catalyst is more energy-efficient than the OER. Notably, under almost all test conditions, the "anodic peak" consistently appeared near the onset point of the OER, suggesting a possible competition between OCRs and OER, which could lead to undesirable overall activity degradation in the OER region.

[0115] 3.2.6 Electrochemical Impedance Spectroscopy (EIS) Test

[0116] To obtain the UOR process kinetics information of CARB-1, EIS testing was performed, and the results are as follows: Figure 11 As shown. The equivalent circuit diagram of the composite structure is as follows. Figure 11 As shown in the illustration, the system resistance is generated in the high-frequency or mid-to-low-frequency region, corresponding to the solution resistance (Rs) and charge transfer resistance (Rct), respectively. A smaller semicircle diameter in the Nyquist plot corresponds to a lower Rct value, indicating that the catalyst has better electron transfer performance. The impedance diagram shows that CARB-1 has an Rct of only 5.21 Ω, less than the 14.45 Ω of the PT / IrO2 catalyst, indicating that CARB-1 has better electron transfer performance and can effectively accelerate the system's reaction kinetics.

[0117] 3.2.6 Timing Potential (CP) Test

[0118] Depend on Figure 12 To evaluate the performance of CARB-1 porous carbon material (KOH to organic raw material ratio 1:1, preparation time 1 h, preparation temperature 400℃) in electrolyzing urea, chronopotential (CP) tests were performed in a 1 mol / L KOH + 0.33 mol / L urea solution. The results showed that the porous material exhibited good performance at 10 mA·cm⁻¹. -2 Under certain conditions, it can work stably with the voltage remaining basically unchanged, indicating that the porous material has stable urea degradation performance.

[0119] This embodiment describes the preparation of porous carbon materials from organic matter extracted from cotton pulp black liquor and their application in electrochemistry. The following conclusions were drawn: the porous carbon materials have a rich porous structure with uniform pores and intact pore structure. The porous carbon materials prepared from pH values ​​ranging from 11 to 7 exhibited uneven pore structure and a small number of pores. For porous carbon materials with different activator ratios, decreasing the KOH ratio resulted in fewer pores and uneven distribution; conversely, increasing the KOH ratio led to rupture of the porous carbon framework and collapse of the pore structure. At pH 1, the pore structure of the porous carbon material with a 1:1 ratio of biomass feedstock to activator was optimal. The porous carbon prepared in this embodiment had a specific surface area of ​​1139.33 m². 2 / g, pore volume is 0.47cm³ 3 The porous carbon material UOR has an average pore size of 1.61 nm, mostly micropores, and a density of 10 mA / cm². Furthermore, the UOR exhibits a current density of 10 mA / cm². -2 At that time, CARB-1 requires a potential of 1.37V. Under the same conditions, CARB-1's HER requires only a potential of -0.13V. Furthermore, it can operate at 10mAcm. -2 The reaction remained stable for 10 hours at a given current density. This indicates that the porous carbon material prepared in the experiment can not only stably generate hydrogen in alkaline solution, but also efficiently degrade urea in wastewater, providing a new source of biomass porous carbon and solving the problem of organic matter recovery from cotton pulp black liquor.

Claims

1. A method for preparing porous carbon materials using cotton pulp black liquor as raw material, characterized in that, Includes the following steps: Step (1): Add inorganic acid dropwise to cotton pulp black liquor and adjust the pH for acid precipitation. After acid precipitation, centrifuge to separate the biomass precipitate in cotton pulp black liquor and dry it to obtain cotton pulp black liquor biomass. Step (2): Thoroughly mix the cotton pulp black liquor biomass with the activator to obtain a mixed raw material; Step (3): Place the mixed raw materials under a nitrogen atmosphere for calcination. After calcination, grind the solid calcined product to obtain solid powder. Step (4): Soak the solid powder in the soaking solution, and then wash it with deionized water until neutral; The porous carbon material can be obtained by drying the solid powder after washing until it is neutral. In step (1), the inorganic acid is phosphoric acid; the pH of the cotton pulp black liquor is adjusted to 1 by adding inorganic acid; the centrifugation conditions are 5000-6000 rpm and centrifugation time is 3-5 min; the drying temperature is 50-90℃ and the drying time is 12-48 h; after drying, the cotton pulp black liquor biomass is passed through a 40-mesh sieve. In step (2), the activator is potassium hydroxide, zinc chloride or phosphoric acid; in step (4), when potassium hydroxide or zinc chloride is used as the activator, hydrochloric acid solution is used as the soaking solution; when phosphoric acid is used as the activator, sodium hydroxide solution is used as the soaking solution.

2. The method for preparing porous carbon materials using cotton pulp black liquor as raw material according to claim 1, characterized in that, In step (2), the activator is potassium hydroxide; the mass ratio of cotton pulp black liquor biomass to activator is 1:(0.5~2).

3. The method for preparing porous carbon materials using cotton pulp black liquor as raw material according to claim 2, characterized in that, In step (4), the soaking solution is a hydrochloric acid solution with a molar concentration of 1-2 mol / L, and the soaking time is 1-2 h; the drying temperature is 70-80℃, and the drying time is 12-48 h.

4. The method for preparing porous carbon materials using cotton pulp black liquor as raw material according to claim 1, characterized in that, In step (3), during calcination, the mixed raw materials are placed in a tube furnace and heated to 400-500°C and held for 30-60 minutes, with a heating rate of 5-10°C / min. After the holding period, the mixture is cooled to room temperature. The solid powder is the undersize obtained by grinding the calcined product and passing it through an 80-mesh sieve.

5. The method for preparing porous carbon materials using cotton pulp black liquor as raw material according to claim 1, characterized in that, In step (1), the cotton pulp black liquor contains: lead 1.15 mg / kg, cadmium 0.11 mg / kg, chromium 3.96 mg / kg, arsenic 0.35 mg / kg, magnesium 839.28 mg / kg, zinc 133.77 mg / kg, manganese 13.87 mg / kg, copper 1.98 mg / kg, and iron 490.49 mg / kg.

6. The method for preparing porous carbon materials using cotton pulp black liquor as raw material according to claim 1, characterized in that, In step (1), the inorganic acid is phosphoric acid; inorganic acid is added to adjust the pH of the cotton pulp black liquor to 1 for acid precipitation; the centrifugation conditions are 5000 rpm and 5 min; the drying temperature is 65℃ and the drying time is 48 h; the cotton pulp black liquor biomass is passed through a 40-mesh sieve. The black liquor from cotton pulp contained the following elements: lead 1.15 mg / kg, cadmium 0.11 mg / kg, chromium 3.96 mg / kg, arsenic 0.35 mg / kg, magnesium 839.28 mg / kg, zinc 133.77 mg / kg, manganese 13.87 mg / kg, copper 1.98 mg / kg, and iron 490.49 mg / kg. In step (2), the activator is potassium hydroxide; the mass ratio of biomass to activator in cotton pulp black liquor is 1:1; In step (3), during calcination, the mixed raw materials are placed in a tube furnace and heated to 400°C and held for 1 hour, with a heating rate of 10°C / min; after the holding period, the materials are cooled to room temperature; the solid powder is the undersize obtained by grinding the calcined product and passing it through an 80-mesh sieve. In step (4), the soaking solution is a hydrochloric acid solution with a molar concentration of 1 mol / L, and the soaking time is 2 h; the drying temperature is 80℃, and the drying time is 48 h.

7. The application of porous carbon materials prepared from cotton pulp black liquor, characterized in that, The porous carbon material prepared by the method described in any one of claims 1-6 using cotton pulp black liquor as raw material will be used for electrocatalytic urea hydrogen evolution.

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