O / N co-doped ultramicroporous carbon material adsorbent and preparation method and application thereof

Abstract

The invention discloses an O / N co-doped ultra-microporous carbon material adsorbent and a preparation method and application thereof, and belongs to the technical field of adsorbents, the preparation method of the O / N co-doped ultra-microporous carbon material adsorbent comprises the following steps: uniformly mixing waste high-density polyethylene, waste coffee grounds, a catalyst and an activator to obtain a mixture; and calcining the mixture in a protective atmosphere, cooling, pickling, carrying out suction filtration, and drying to prepare the O / N co-doped ultra-microporous carbon material adsorbent. The O / N co-doped ultra-microporous carbon material adsorbent PECG-PC2 is successfully prepared by introducing nickel chloride for catalysis and potassium acetate for activation on the basis of the synergistic pyrolysis effect of two carbon sources, namely waste high-density polyethylene and waste coffee grounds. The main aperture of the material is concentrated at 0.635 nm, the specific surface area of micropores is up to 97.7%, and the material has excellent CO2 adsorption performance. Under the conditions of 0 DEG C and 1 bar, the CO2 adsorption capacity is as high as 5.37 mmol / g; and in a dynamic adsorption experiment of simulating 15% CO2 flue gas at 25 DEG C, the adsorption capacity reaches 1.49 mmol / g. Meanwhile, after eight times of adsorption-desorption cycles, the CO2 adsorption capacity can still be kept at 97.3% of the initial value.

Description

Technical Field

[0001] The invention belongs to the technical field of adsorbents, and in particular relates to an O / N co-doped ultra-microporous carbon material adsorbent and a preparation method and application thereof. Background Art

[0002] CCUS technology provides an effective solution to reduce CO2 emissions by capturing, utilizing and storing CO2. At present, common CO2 capture technologies mainly include amine washing, membrane separation, ionic liquid absorption and adsorption. Among them, adsorption is considered to be a CO2 capture technology with greater development potential due to its advantages such as high chemical stability, high heat resistance, strong wear resistance, high CO2 selectivity, low heat capacity and flexible operation. Porous carbon materials (PCs) show great industrial application potential among many adsorption materials due to their moderate preparation cost, simple synthesis process, good stability, customizable pore structure and adjustable surface. Ultramicropores (<1nm) are the key factor determining the CO2 adsorption capacity of porous carbon adsorbents. In particular, micropores with a pore size between 0.35-0.7nm can significantly improve the CO2 adsorption performance of porous carbon adsorbents. In addition, the presence of heteroatoms (such as N, S, B, O or P) on porous carbon helps to enhance the basicity and surface polarity of the carbon surface, further enhancing the interaction between CO2 molecules and the carbon surface. In addition to the adsorption performance of the adsorbent, another factor that needs to be considered is the production cost of the adsorbent. Developing low-cost adsorbents is an effective way to reduce the overall operating cost of the carbon capture process.

[0003] At the same time, about 100 million tons of plastic products are produced worldwide each year, but only 9% of them are recycled, 12% are incinerated, and 79% are landfilled or discharged into the environment. Common plastics such as polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) may take decades to hundreds of years to completely degrade in the natural environment. Byproducts produced during the degradation process, such as microplastics, toxic chemicals (such as bisphenol A and phthalates) and greenhouse gases (such as methane and carbon dioxide) will also cause further pollution to the environment. In addition, solid waste such as spent coffee grounds (SCGs) produced in the coffee manufacturing process are mostly not utilized and enter landfills. The toxic substances (such as tannins and polyphenols) generated by their accumulation and decomposition not only occupy a large amount of land resources, but also cause serious pollution to the soil, water and atmosphere.

[0004] Therefore, how to provide an adsorbent preparation method that can not only solve the waste disposal problem but also significantly reduce the research and development cost of carbon capture adsorbents is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] The purpose of the present invention is to provide an O / N co-doped ultra-microporous carbon material adsorbent and a preparation method and application thereof to solve the problems existing in the above-mentioned prior art. The present invention prepares an O / N co-doped ultra-microporous carbon material adsorbent by catalytic reaction and high-temperature activation of waste high-density polyethylene and waste coffee grounds.

[0006] One of the technical solutions provided by the present invention:

[0007] A method for preparing an O / N co-doped ultra-microporous carbon material adsorbent comprises the following steps: uniformly mixing waste high-density polyethylene (HDPE), waste coffee grounds (SCGs), a catalyst and an activator, calcining the mixture in a protective atmosphere, cooling, acid washing, filtering and drying the mixture to prepare the O / N co-doped ultra-microporous carbon material, which is recorded as PECG-PC2.

[0008] The present invention uses waste high-density polyethylene and waste coffee grounds as carbon sources to prepare an O / N co-doped ultra-microporous carbon material adsorbent, which significantly improves the CO2 adsorption performance through multiple synergistic effects. During the pyrolysis process, the mixing of the two carbon sources triggers a complex decomposition and recombination reaction, forming more carbon defects in the initially generated derivative carbon material. Under high-temperature catalytic conditions, the decomposition and structural reorganization of polyethylene are promoted, and the number of carbon defects is further increased by the generated local stress. These carbon defects are in a high-energy state at high temperatures, and gas escape or further chemical reactions are prone to occur. At the same time, KAc, as an activator, decomposes and releases a large amount of small molecule gases in a high-temperature environment, which generates expansion pressure when precipitated inside the carbon material, significantly promoting the generation of carbon skeleton pores. As the expansion proceeds, the defect sites are gradually transformed into a uniformly distributed and highly controllable microporous structure.

[0009] Preferably, the mass ratio of the waste high-density polyethylene to the waste coffee grounds is 1:2; and / or,

[0010] The mass ratio of the waste high-density polyethylene to the catalyst is 1:2.56; and / or,

[0011] The mass ratio of the waste high-density polyethylene to the activator is 1:5.

[0012] Preferably, the catalyst is NiCl2·6H2O; and the activator is KAc.

[0013] NiCl2·6H2O can promote the decomposition and structural reorganization of polyethylene at high temperature, forming local stress and defects. KAc, as an activator, decomposes at high temperature and releases a large amount of small molecular gas. When it precipitates inside the carbon material, the expansion pressure generated promotes the formation of carbon skeleton pores and further improves the formation of microporous structure.

[0014] Preferably, the calcination includes secondary calcination; wherein the first calcination temperature is 300°C and the time is 60 min, the second calcination temperature is 664°C and the time is 91.2 min, and the heating rate of the secondary calcinations is 5°C / min.

[0015] The first calcination was carried out at 300 °C for 60 min, which helped the waste to be evenly mixed and fully contacted with the catalyst and activator, and at the same time removed the bound water in NiCl2·6H2O.

[0016] Waste high-density polyethylene and waste coffee grounds interact with each other during the calcination pyrolysis process. The mixing of the two carbon sources triggers complex decomposition and recombination reactions, forming more carbon defects in the initially generated derivative carbon materials.

[0017] Preferably, the solution used for pickling is hydrochloric acid with a mass concentration of 20%.

[0018] Preferably, the protective atmosphere is nitrogen with a flow rate of 200 mL / min.

[0019] The second technical solution provided by the present invention is:

[0020] An O / N co-doped ultra-microporous carbon material adsorbent prepared by the method.

[0021] The pore size of the O / N co-doped ultra-microporous carbon material adsorbent finally obtained by the present invention is concentrated at 0.635 nm, and the micropore specific surface area accounts for as high as 97.7%.

[0022] The third technical solution provided by the present invention is:

[0023] An application of the above O / N co-doped ultra-microporous carbon material adsorbent in capturing CO2 in flue gas.

[0024] The pore size of the O / N co-doped ultra-microporous carbon material adsorbent finally obtained by the present invention is concentrated at 0.635 nm, and the micropore specific surface area accounts for as high as 97.7%, which provides superior pore structure advantages and abundant adsorption active sites for the efficient capture of CO2.

[0025] Compared with the prior art, the present invention has the following advantages and technical effects:

[0026] The present invention uses a catalytic reaction and a high-temperature activation method to synergistically treat HDPE and SCGs to prepare an O / N co-doped ultra-microporous carbon material adsorbent (PECG-PC2). Based on the synergistic pyrolysis of two carbon sources, waste high-density polyethylene and waste coffee grounds, the present invention successfully prepared an O / N co-doped ultra-microporous carbon material adsorbent PECG-PC2 with significant ultra-microporous structural characteristics by introducing nickel chloride catalysis and potassium acetate activation. The main pore size of the material is concentrated at 0.635nm, and the micropore specific surface area accounts for as high as 97.7%, with excellent CO2 adsorption performance. Under the conditions of 0°C and 1bar, its CO2 adsorption capacity is as high as 5.37mmol / g; in the dynamic adsorption experiment at 25°C and simulating 15% CO2 flue gas, the adsorption capacity reaches 1.49mmol / g. At the same time, after 8 adsorption-desorption cycles, its CO2 adsorption capacity can still maintain 97.3% of the initial value, showing excellent cycle stability. The invention realizes the efficient capture and reuse of CO2, providing important support for the development of low-cost, high-performance carbon capture technology. The preparation of this material provides a strong reference for the high-value utilization of solid waste, while achieving efficient and low-cost CO2 capture, showing broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0028] Figure 1 is a flow chart of the preparation process of Example 1;

[0029] Figure 2 The scanning electron microscope images of PECF-PC2 prepared in Example 1, wherein the scale of (a) is 10 um, the scale of (b) is 1 um, the scale of (c) is 500 nm, and the scale of (d) is 300 nm;

[0030] Figure 3 Element mapping diagram of PECG-PC2 prepared in Example 1, wherein (a) is a superimposed diagram of the distribution of C, O, and N elements, (b) is a C element distribution diagram, (c) is an O element distribution diagram, and (d) is an N element distribution diagram;

[0031] Figure 4 N2 adsorption-desorption isotherms of the adsorbents prepared in Example 1, Comparative Example 1 and Comparative Example 9;

[0032] Figure 5XRD patterns of the adsorbent samples prepared in Comparative Example 1, Comparative Example 9 and Example 1;

[0033] Figure 6 The Raman spectra of the adsorbent samples prepared in Comparative Example 1, Comparative Example 9 and Example 1 are shown;

[0034] Figure 7 FT-IR spectrum result diagram of the adsorbent samples prepared in Comparative Example 1, Comparative Example 2, Comparative Example 7, Comparative Example 9 and Example 1;

[0035] Figure 8 The surface chemical composition and element chemical valence analysis results of the adsorbent samples prepared in Comparative Example 1, Comparative Example 2, Comparative Example 7, Comparative Example 9 and Example 1 are shown;

[0036] Fig. 9 This is a diagram of a fixed bed adsorption device for simulating 15% CO2 flue gas;

[0037] Fig.10 This is a comparison chart of the adsorption performance of the adsorbents (PECG-PCx, x is the ratio of waste coffee grounds to waste high-density polyethylene) prepared in Example 1 and Comparative Examples 1-9 under the conditions of simulating 15% CO2 flue gas at 25°C;

[0038] Fig.11 This is a comparison chart of the CO2 adsorption performance of PECG-PC2 adsorbent and other materials (CS-700-2 / 3, C-PP-750-1, NPC-4 and PFKC-700-2) under simulated flue gas;

[0039] Fig.12 It is a comparison chart of the adsorption performance of Example 1 and Comparative Example 1 (PE-PC), Comparative Example 2 (PECG-PC0.5), Comparative Example 7 (PECG-PC6) and Comparative Example 9 (CG-PC) under pure CO2 (0-1 bar) conditions, wherein (a) is the adsorption performance measurement result at 0°C and 1 bar, and (b) is the adsorption performance measurement result at 25°C and 1 bar;

[0040] Fig.13 The adsorption energy diagram of CO2 by C-OH, C=O, C-N5, C-N6, and COOH functional groups, where (a) is the adsorption energy comparison when the functional group is located outside the pore, and (b) is the adsorption energy comparison when the functional group is located inside the pore;

[0041] Fig.14 This is the stability diagram of PECG-PC2 adsorbent obtained in Example 1 after 8 cycles of adsorption;

[0042] Fig.15The pore size distribution diagram of the adsorbents obtained in Example 1, Comparative Example 1 and Comparative Example 9 analyzed by HK method;

[0043] Fig.16 The adsorption selectivity diagram of the PECG-PC2 adsorbent obtained in Example 1 for CO2 and N2;

[0044] Fig.17 These are O1s spectra and N1s spectra of the adsorbent samples prepared by Comparative Example 1 (PE-PC), Comparative Example 2 (PECF-PC0.5), Comparative Example 7 (PECF-PC6), Comparative Example 9 (CG-PC) and Example 1 (PECF-PC2), wherein (a) is the C1s spectrum and (b) is the O1s spectrum. DETAILED DESCRIPTION

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0047] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0048] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0049] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0050] The room temperature in the present invention refers to 25±2°C.

[0051] The sources of raw materials and reagents in the embodiments of the present invention are as follows:

[0052] Waste high-density polyethylene (HDPE0) (50-150 mesh) was provided by Dongguan Jinheng Plastic Co., Ltd.;

[0053] Waste coffee grounds (SCGs) were provided by Lixing Coffee Shop in Dongguan;

[0054] Nickel chloride hexahydrate (NiCl2·6H2O, AR, ≥98.0%) was purchased from Tianjin Fuchen Chemical Reagent Co., Ltd.;

[0055] Potassium acetate (KAc, AR, ≥98.0%) was purchased from Tianjin Kemeiou Chemical Reagent Co., Ltd.;

[0056] Hydrochloric acid (AR, mass fraction 36%-38%) was purchased from Tianjin Komiou Chemical Reagent Co., Ltd.

[0057] Deionized water was used to prepare all solutions in the present invention; all reagents and solutions were commercially available and were used directly without further purification.

[0058] Example 1 A method for preparing an O / N co-doped ultra-microporous carbon material

[0059] (1) Waste high-density polyethylene and waste coffee grounds are mixed in a mass ratio of 1:2, and 2.56 times the mass of catalyst NiCl2·6H2O and 5 times the mass of activator KAc are added based on the waste high-density polyethylene, and the mixture is mixed uniformly by grinding;

[0060] (2) The mixture was placed in a porcelain ark of a tube furnace, and the temperature was raised to 300 °C at 5 °C / min and maintained for 1 h in a 200 mL / min N2 flow, and then continued to be raised to 664 °C at 5 °C / min and maintained for 91.2 min, and cooled with the furnace temperature to obtain a carbonized sample;

[0061] (3) The carbonized sample was ground, added to 20% (wt.) hydrochloric acid (the ratio of hydrochloric acid solution to carbonized sample was 5 mL: 1 g) and stirred for 8 h to completely remove the residual NiCl2 and KAc. The black solid was then filtered and dried at 100 °C to obtain O / N co-doped ultraporous carbon material. The obtained material was named PECF-PC2.

[0062] Figure 1 This is a flow chart of the preparation process of Example 1.

[0063] Comparative Example 1

[0064] The same as Example 1, except that no waste coffee grounds were added, and the prepared adsorbent material was recorded as PE-PC.

[0065] Comparative Example 2

[0066] The same as Example 1, except that the mass ratio of waste high-density polyethylene to waste coffee grounds is 1:0.5, and the obtained material is named PECF-PC0.5.

[0067] Comparative Example 3

[0068] The same as Example 1, except that the mass ratio of waste high-density polyethylene to waste coffee grounds is 1:1, and the obtained material is named PECF-PC1.

[0069] Comparative Example 4

[0070] The same as Example 1, except that the mass ratio of waste high-density polyethylene to waste coffee grounds is 1:3, and the obtained material is named PECF-PC3.

[0071] Comparative Example 5

[0072] The same as Example 1, except that the mass ratio of waste high-density polyethylene to waste coffee grounds is 1:4, and the obtained material is named PECF-PC4.

[0073] Comparative Example 6

[0074] The same as Example 1, except that the mass ratio of waste high-density polyethylene to waste coffee grounds is 1:5, and the obtained material is named PECF-PC5.

[0075] Comparative Example 7

[0076] The same as Example 1, except that the mass ratio of waste high-density polyethylene to waste coffee grounds is 1:6, and the obtained material is named PECF-PC6.

[0077] Comparative Example 8

[0078] The same as Example 1, except that the mass ratio of waste high-density polyethylene to waste coffee grounds is 1:7, and the obtained material is named PECF-PC7.

[0079] Comparative Example 9

[0080] The same as Example 1, except that no waste high-density polyethylene was added, and the prepared adsorbent material was recorded as CG-PC.

[0081] 1. Material performance test

[0082] The morphology and structure of PECF-PC2 prepared in Example 1 were observed by scanning electron microscopy (SEM; GeminiSEM300, ZEISS, Germany).

[0083] Figure 2 The SEM images of the PECF-PC2 adsorbent prepared in Example 1, where the scale of (a) is 10 um, the scale of (b) is 1 um, the scale of (C) is 500 nm, and the scale of (D) is 300 nm; Figure 2 It can be seen that the adsorbent material has a rough surface and is rich in carbon defects. Its highly porous multilayer structure makes the pores interconnected and evenly distributed, providing more active sites for CO2 adsorption.

[0084] The PECF-PC2 prepared in Example 1 was characterized by elemental mapping using a high-resolution transmission electron microscope (HRTEM, JEM-2100F, JEOL, Japan) to analyze the types of elements in the sample and their spatial distribution characteristics.

[0085] Figure 3 Element mapping diagram of the PECG-PC2 adsorbent prepared in Example 1, where (a) is a distribution summary diagram of the three elements C, O, and N, (b) is a C element distribution diagram, (c) is an O element distribution diagram, and (d) is an N element distribution diagram. Figure 3 It can be seen that the carbon, oxygen and nitrogen elements are evenly distributed in the adsorbent prepared in Example 1.

[0086] The elemental compositions of the adsorbents prepared in Comparative Example 1, Comparative Example 9 and Example 1 were analyzed by an elemental analyzer (EA, Unicube, Germany). The analysis results are shown in Table 1.

[0087] Table 1

[0088] sample C％ N％ O％ H％ PE-PC 91.97 0.00 7.46 0.57 CG-PC 83.66 0.92 14.06 1.36 PECG-PC2 78.85 1.94 17.43 1.78

[0089] It can be seen from Table 1 that the adsorbent prepared in Example 1 contains a higher proportion of oxygen and nitrogen.

[0090] The specific surface area and pore distribution of the adsorbents prepared in Comparative Example 1, Comparative Example 9 and Example 1 were analyzed by N2 isothermal adsorption and desorption experiments. The N2 adsorption and desorption isotherms of the adsorbents prepared in Example 1, Comparative Example 1 and Comparative Example 9 are shown in Figure 2. Figure 4As shown. In the low-pressure region (P / P0 < 0.01), the isotherms of all adsorbent samples show a sharp increase in adsorption, which is a typical characteristic of type I isotherms according to the classification of the International Union of Pure and Applied Chemistry (IUPAC). In the range of 0.4 < P / P < 0.9, all three adsorbents exhibit small H4-type hysteresis loops, indicating the presence of a small amount of mesoporous structure in the adsorbents. Among them, the hysteresis loop of Example 1 (PECG-PC2) is smaller, indicating that its mesoporous structure is more reasonable and the pore size distribution is more uniform. This optimized pore characteristic not only helps the rapid transmission of gas but also can improve the adsorption efficiency. In addition, it can be seen from the isotherm characteristics that as the pressure increases, the isotherm of PECG-PC2 shows a slower rising trend, indicating that it has better structural stability under high-pressure conditions. At high pressure, PECG-PC2 can maintain the integrity of the pore structure and provide continuous and stable site support for gas adsorption.

[0091] The specific surface area, pore size, and pore volume of the adsorbent were measured by a high-throughput specific surface area and pore size analyzer (ASAP 2460, Micromeritics, USA); the specific surface area of the sample was calculated by the Brunauer-Emmett-Teller (BET) equation, the microporous specific surface area of the sample was calculated by the Thickness Plot (t-plot) equation, and the pore size distribution of the sample was calculated by the Horvath-Kawazoe (HK) equation. Fig.15 Figure 5 is the pore size distribution diagram of the adsorbents obtained in Example 1, Comparative Example 1, and Comparative Example 9 analyzed by the H-K method; the pore size distribution obtained by Horvath-Kawazoe (HK) shows that the pore size of PECG-PC2 is mainly distributed at 0.635 nm, the pore size of CG-PC is mainly distributed at 0.655 nm, and there is almost no pore size for PE-PC at this stage. The rich and regular ultramicroporous structure of PECG-PC2 can provide more sites for CO2 adsorption.

[0092] Table 2 shows the specific surface area and pore size distribution of the adsorbents prepared in Example 1, Comparative Example 1, and Comparative Example 9.

[0093] Table 2

[0094]

[0095] It can be seen from Table 2 that the average pore size of PECG-PC2 is 1.96 nm, and the proportion of the microporous specific surface area is 97.7%, indicating that the adsorbent contains a large number of microporous structures.

[0096] The crystal structure of the adsorbent was determined by X-ray diffractometer (XRD, SmartLAB9, Japan). The XRD patterns of the adsorbent samples prepared in Comparative Example 1, Comparative Example 9 and Example 1 are shown in FIG. Figure 5 As shown, from Figure 5 It can be seen that the peak angles of the adsorbent prepared in Example 1 near 2θ26° and 43° are significantly broadened, and the peak intensity is significantly weakened, indicating that its degree of graphitization is low and the structure is more disordered. This disordered structure brings more amorphous carbon pores and defect sites, providing a large number of active sites for CO2 adsorption.

[0097] The molecular structure and amorphous properties of the adsorbent were determined by Raman spectrometer (LabRAM HR Evolution, France). The Raman spectra of the adsorbent samples prepared in Comparative Example 1, Comparative Example 9 and Example 1 are as follows: Figure 6 As shown, the ID / IG of the adsorbent prepared in Example 1 is the highest, which is 0.959. This indicates that in the high-temperature activation reaction, the most defects are generated at this ratio, and this result is consistent with the XRD characterization results.

[0098] The chemical composition and functional groups of the adsorbent were determined by Fourier transform infrared (FT-IR) spectrometer (Nicolet iZ10, Thermo Fisher Scientific, USA). The FT-IR spectra of the adsorbent samples prepared in Comparative Example 1, Comparative Example 2, Comparative Example 7, Comparative Example 9 and Example 1 are shown in FIG. Figure 7 As shown, the results indicate that hydroxyl, carbonyl, and carboxyl groups exist in all adsorbents, and the samples doped with coffee grounds may contain a small amount of CN bonds.

[0099] X-ray photoelectron spectroscopy (XPS, EscaLab 250xi, USA) was used to further determine the chemical composition and functional groups of the adsorbent. The surface chemical composition and element chemical valence state of the adsorbent samples prepared in Comparative Example 1 (PE-PC), Comparative Example 2 (PECF-PC0.5), Comparative Example 7 (PECF-PC6), Comparative Example 9 (CG-PC) and Example 1 (PECF-PC2) were analyzed. The results are as follows: Figure 8 As shown, with the increase of the amount of waste coffee grounds added, the intensity of the O1s and N1s peaks in the adsorbent gradually increased, verifying that waste coffee grounds can be used as an effective dopant. The adsorbent sample prepared in Example 1 has a higher proportion of oxygen and nitrogen functional groups than the undoped Comparative Examples 1 and 9.

[0100] Fig.17The O1s spectra and N1s spectra of the adsorbent samples prepared in Comparative Example 1 (PE-PC), Comparative Example 2 (PECF-PC0.5), Comparative Example 7 (PECF-PC6), Comparative Example 9 (CG-PC) and Example 1 (PECF-PC2) are shown in Figure 1; (a) is the C1s spectrum; (b) is the O1s spectrum. Fig.17 (a) shows that the CC ratio of the C1s spectrum of the sample of Example 1 (PECG-PC2) is low, indicating that its carbon structure has more defects and disorder, providing more active sites for CO2 adsorption, which is consistent with XRD ( Figure 5 ) and Raman spectroscopy ( Figure 6 ) is consistent with the results. The deconvolution results of the O1s spectrum ( Fig.17 In (b), the main oxygen-containing functional groups in the samples are revealed, including hydroxyl, carbonyl and carboxyl. Among the five samples, the trend of the change in the functional group ratio is consistent with the C1s spectrum results, showing that hydroxyl and carbonyl are dominant, while carboxyl is relatively less. Example 1 (PECG-PC2) shows the highest carboxyl ratio, in contrast to other adsorbent samples. In addition, compared with Comparative Example 1 (PE-PC) and Comparative Example 9 (CG-PC), the hydroxyl ratio in Example 1 (PECG-PC2) is lower, while the carbonyl and carboxyl ratios are higher. Since the alkalinity of the carboxyl group is stronger than that of the carbonyl group, and the carbonyl group is stronger than the hydroxyl group, CO2, as a weakly acidic gas with a high electric quadrupole moment, needs to be adsorbed under stronger alkaline conditions. Therefore, PECG-PC2 provides more effective alkaline sites for CO2 adsorption through its higher carbonyl and carboxyl ratios. Through the above characterization results, it can be confirmed that the present invention synthesized O / N co-doped ultra-microporous carbon material. The pore size of the material is concentrated at 0.635nm, and the micropore specific surface area accounts for as high as 97.7%. The high content of carbonyl and carboxyl groups in PECG-PC2 materials provides abundant basic sites for CO2 adsorption. In addition, the presence of nitrogen-containing functional groups enhances the Lewis acid sites and basic sites in the carbon framework, further promoting the interaction between PECG-PC2 and CO2.

[0101] 2.CO2 dynamic adsorption performance test

[0102] The dynamic capture capacity of the sample under the simulated conditions of mixed gas (CO2 / N2=0.15 / 0.85) was measured by using a self-made fixed bed adsorption device and a multifunctional dynamic adsorption instrument (GXH-3011, China Huayun). Fig. 9As shown, before the adsorption experiment, 0.5g of the adsorbent sample was placed in the tubular furnace adsorption column, and a quantitative amount of 0.2g of quartz wool was stuffed into the top and bottom of the sample for fixation. The temperature of the tubular furnace was set to 120°C, and high N2 (27mL / min) was introduced for desorption for 2h, in order to remove a small amount of water vapor and CO2 adsorbed in the sample. After the desorption was completed, the tubular furnace was cooled to room temperature and adjusted to 25°C, and a mixed gas of CO215% / N285% (27mL / min) was introduced for the adsorption experiment, and the outlet concentration was detected by an online CO2 analyzer. A blank control group was set up, and only a quantitative amount of quartz wool (0.2g) was added to the tubular furnace adsorption column without adding adsorbent. Each set of data was measured 3 times, and the uncertainty of the CO2 adsorption data was calculated to be 2% or less to ensure the accuracy of the data. The results are shown in Fig.10 As shown, it can be seen that the penetration time of the PECG-PC2 sample doped with twice the coffee grounds (Example 1) is longer than that of the other samples (Comparative Examples 1-9). The longer the penetration time, the higher the corresponding dynamic adsorption amount of CO2. Among them, the adsorption amount of Example 1 is higher than that of the other samples, which is 1.49 mmol / g.

[0103] Fig.11 This is a comparison chart of the CO2 adsorption performance of PECG-PC2 adsorbent and other materials (CS-700-2 / 3, C-PP-750-1, NPC-4 and PFKC-700-2) under simulated flue gas;

[0104] CS-700-2 / 3 (J.Shao, J.Wang, Q.Yu, F.Yang, M.Demir, OCAltinci, A.Umay, L.Wang and X.Hu, Unlocking the potential of N-doped porous Carbon: Facilesynthesis and superior CO2 adsorption performance, Sep Purif Technol, 2024, 333.)

[0105] C-PP-750-1 (C.Liu, Y.Zhi, Q.Yu, L.Tian, ​​M.Demir, SGColak, AAFarghaly, L.Wang and X.Hu, Sulfur-Enriched Nanoporous Carbon: ANovel Approach to CO2Adsorption, ACS Applied Nano Materials, 2024, 7, 5434-5441.)

[0106] NPC-4 (J.Gong, H.Lin, K.Grygiel and J.Yuan, Main-chain poly(ionicliquid)-derived nitrogen-doped micro / mesoporous carbons for CO2 capture and selective aerobic oxidation of alcohols, Applied Materials Today, 2017, 7, 159-168.)

[0107] PFKC-700-2 (C.Ma, J.Bai, M.Demir, Q.Yu, X.Hu, W.Jiang and L.Wang, Polyacrylonitrile-derived nitrogen enriched porous carbon fiber with highCO2capture performance, Sep Purif Technol, 2022, 303.)

[0108] 3.CO2 BET static adsorption performance test

[0109] The CO2 adsorption capacity of ultra-microporous carbon was evaluated by Autosorb-iQ / ASAP 2460 at 0°C and 25°C and in the pressure range of 0-1 bar. The samples selected were Example 1 and Comparative Example 1, Comparative Example 2, Comparative Example 7 and Comparative Example 9. The results are shown in Figure 2. Fig.12 As shown, the CO2 adsorption capacity of PECG-PC2 obtained in Example 1 is the most significant, reaching 3.71mmol / g at 25°C and 1bar, and up to 5.37mmol / g at 0°C and 1bar. The adsorption capacity of PECG-PC2 is much higher than that of polyethylene-derived ultra-microporous carbon PE-PC (Comparative Example 1) and coffee grounds-derived ultra-microporous carbon CG-PC (Comparative Example 9), which verifies that coffee grounds doping can effectively improve the CO2 adsorption capacity of polyethylene-derived carbon materials.

[0110] 4. Model analysis of functional groups located within the pore size

[0111] Models with functional groups located outside and inside the pore were constructed, and the results are shown in Fig.13As shown. The adsorption energy ranking of both for CO2 is basically the same. Specifically, the adsorption energy ranking of the model with functional groups located outside the pore size is: carboxyl (-COOH) > pyrrolic nitrogen (C-N5) > pyridinic nitrogen (C-N6) > carbonyl (C=O) > hydroxyl (-OH); while the adsorption energy ranking of the model with functional groups located inside the pore size is: PECG-PC2+COOH (carboxyl functionalized PECG-PC2) > PECG-PC2+N5 (pyrrolic N functionalized PECG-PC2) > PECG-PC2+C=O (carbonyl functionalized PECG-PC2) > PECG-PC2+N6 (pyridinic nitrogen functionalized PECG-PC2) > PECG-PC2+OH (hydroxyl functionalized PECG-PC2) > PECG-PC2 (non-functionalized PECG-PC2) > Nonporous (non-functionalized PECG-PC2 without micropores).

[0112] The main controlling factor for CO2 adsorption is the electrostatic attraction between the micropores and the functional groups formed by the doping elements. The presence of functional groups significantly improves the adsorption capacity of porous carbon materials for CO2, especially the carboxyl group has the strongest adsorption capacity for CO2. In the PECG-PC2 adsorbent material obtained in Example 1, the percentage of O and N elements is the highest, and the percentage of carboxyl nitrogen and pyridinic nitrogen is the highest among all samples. Therefore, from the perspective of heteroatom doping, PECG-PC2 is most likely to adsorb CO2 through functional groups.

[0113] 5. Cycle test

[0114] Using the homemade adsorption bed, multiple cyclic adsorption experiments were carried out to evaluate the stability and recyclability of the adsorbent PECG-PC2 prepared in Example 1. Before each test, the adsorbent sample was heated at 120°C for 2 hours with nitrogen. Fig.14 As shown, the adsorbent was subjected to 8 dynamic adsorption experiments at 25°C, and the adsorption amount remained relatively stable, and after 8 cycles, the adsorption amount was still about 97% of the original adsorption amount. This shows that the PECG-PC2 obtained in Example 1 has good recyclability and stability.

[0115] 6. Select adsorption test

[0116] Fig.16 The adsorption selectivity diagram of the PECG-PC2 adsorbent obtained in Example 1 for CO2 and N2;

[0117] Fig.16The CO2 and N2 adsorption isotherms and selectivity of PECG-PC2 prepared in Example 1 are shown. The CO2 and N2 adsorption properties of the PECG-PC2 ultra-microporous carbon material were measured at 0°C and 25°C and in the pressure range of 0-1bar using the Autosorb-iQ / ASAP 2460 device. The results show that at 25°C and 1bar, the CO2 adsorption capacity of PECG-PC2 is 3.71mmol / g, while the N2 adsorption capacity is only 0.38mmol / g. Based on IAST calculation analysis, under typical flue gas ratios (CO2 / N2=15:85, by volume), the CO2 / N2 selectivity of the material at 1bar is as high as 56, and can reach 172 at low pressure, which is significantly better than traditional porous carbon materials.

[0118] The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing an O / N co-doped ultra-microporous carbon material adsorbent, characterized in that: The method comprises the following steps: uniformly mixing waste high-density polyethylene, waste coffee grounds, a catalyst and an activator, calcining, cooling, acid washing, filtering and drying the mixture in a protective atmosphere to prepare the O / N co-doped ultra-microporous carbon material.

2. The method for preparing the O / N co-doped ultra-microporous carbon material adsorbent according to claim 1, characterized in that: The mass ratio of the waste high-density polyethylene to the waste coffee grounds is 1:

2.

3. The method for preparing the O / N co-doped ultra-microporous carbon material adsorbent according to claim 2, characterized in that: The mass ratio of the waste high-density polyethylene to the catalyst is 1:2.56; and / or, The mass ratio of the waste high-density polyethylene to the activator is 1:

5.

4. The method for preparing the O / N co-doped ultra-microporous carbon material adsorbent according to claim 1, characterized in that: The catalyst is NiCl2·6H2O.

5. The method for preparing the O / N co-doped ultra-microporous carbon material adsorbent according to claim 1, characterized in that: The activating agent is KAc.

6. The method for preparing the O / N co-doped ultra-microporous carbon material adsorbent according to claim 1, characterized in that: The calcination includes two calcinations; wherein the first calcination temperature is 300°C and the time is 60 min, the second calcination temperature is 664°C and the time is 91.2 min, and the heating rate of the two calcinations is 5°C / min.

7. The method for preparing the O / N co-doped ultra-microporous carbon material adsorbent according to claim 1, characterized in that: The pickling solution is hydrochloric acid with a mass concentration of 20%.

8. The method for preparing the O / N co-doped ultra-microporous carbon material adsorbent according to claim 1, characterized in that: The protective atmosphere was nitrogen with a flow rate of 200 mL / min.

9. An O / N co-doped ultra-microporous carbon material adsorbent, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the O / N co-doped ultra-microporous carbon material adsorbent according to claim 9 in capturing CO2 in flue gas.

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