A gradient pore activated carbon for adsorbing formaldehyde-benzene series and a preparation method thereof

Abstract

The application provides a gradient-pore activated carbon for adsorbing formaldehyde-benzene series and a preparation method thereof, and belongs to the technical field of activated carbon. In the application, a chitosan-tannic acid network is constructed on a sawdust skeleton, a nano MnOx catalyst is synthesized in situ, and sulfonated pitch is compounded. Then, the gradient pores are constructed through multi-stage heat treatment of nitrogen pre-carbonization, carbon dioxide activation for micropores, and water vapor expansion for mesopores. There are double synergistic mechanisms in the system. One is that the nitrogen-doped sites converted from chitosan and MnOx are synergistic, and formaldehyde is continuously removed through adsorption-catalytic oxidation circulation. The other is that functional partition is realized, the nitrogen-doped / MnOx system is specialized in formaldehyde, and the graphite-like micro area converted from the sulfonated pitch and micropores are synergistically adsorbed with benzene series through pi-pi stacking and confinement effect. This design integrates various functional sites in a single material, and realizes efficient hierarchical adsorption of composite pollutants.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon technology, and relates to a gradient pore size activated carbon for adsorbing formaldehyde-benzene series compounds and its preparation method. Background Technology

[0002] Formaldehyde and benzene compounds often coexist in indoor and industrial organic waste gases, but their physicochemical properties differ significantly: formaldehyde has a small molecular weight, strong polarity, and is electrophilic, readily interacting with basic / Lewis basic sites and being further oxidized; benzene compounds are nonpolar, rich in π electrons, and more sensitive to pore size matching and π–π interactions with aromatic / graphite-like surfaces. Real-world scenarios also involve humidity fluctuations, long-term release from low concentrations, and competitive adsorption of multiple components, requiring purification materials not only to "capture" but also to "transfer quickly, separate clearly, and remain stable for a long time."

[0003] Existing technologies often suffer from insufficient functional separation and coupling. Single-adsorption activated carbon or nitrogen-doped carbon has a certain chemical adsorption capacity for formaldehyde, but its regeneration and mineralization capabilities are limited, and it is prone to saturation and efficiency decay. Although impregnation-loaded transition metal oxides can catalyze the oxidation of formaldehyde, their activity and cycle stability often decrease due to particle agglomeration, weak binding, or dissolution under acidic / humid environments. High specific surface area carbon or molecular sieves for benzene series compounds often have a single pore size distribution and an excessively high proportion of micropores, resulting in limited mass transfer, short breakthrough time, and high sensitivity to humidity and competition from multiple components.

[0004] Furthermore, the spatial separation and weak interaction between adsorption sites and catalytic sites are also key bottlenecks restricting the purification efficiency of complex pollutants. If formaldehyde captured by adsorption sites cannot be rapidly activated and oxidized in the vicinity, it easily leads to site occupancy and capacity decay; if the catalytic sites have poor dispersion or weak interfacial interaction with the carbon skeleton, stability and selectivity are difficult to guarantee under cyclic operating conditions. Summary of the Invention

[0005] To address the above problems, the present invention aims to provide a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds and a method for preparing the same. This application constructs a chitosan-tannic acid composite network on a wood chip skeleton, where chitosan provides the nitrogen source and tannic acid serves as both a reducing agent and a carbon source. Utilizing the confinement effect of this network, a highly dispersed nano-MnOx catalyst is synthesized in situ. Sulfonated pitch is introduced as a binder and a precursor for subsequent π-π adsorption sites. Subsequently, a gradient pore size structure is constructed through a multi-stage heat treatment process: nitrogen pre-carbonization to solidify nitrogen-doped sites, carbon dioxide activation to etch micropores, and steam activation to construct mesopores. The material's efficiency stems from its dual synergistic mechanism: firstly, nitrogen-doped sites synergistically remove formaldehyde through a cycle of "chemical adsorption-catalytic oxidation-site regeneration" in conjunction with neighboring MnOx sites; secondly, the material achieves functional partitioning, with the nitrogen-doped / MnOx system specifically targeting formaldehyde, while the graphite-like microregions and microporous structure synergistically adsorb benzene compounds through π-π stacking and confinement effects, thereby achieving efficient hierarchical adsorption of complex pollutants.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds, the method comprising:

[0008] S1: Prepare an acetic acid solution, add chitosan to obtain a chitosan solution, immerse the sawdust in the chitosan solution, ultrasonically treat it, remove it, and wash it to obtain pre-treated sawdust; prepare a tannic acid solution, adjust the pH with acetic acid and sodium acetate to obtain a tannic acid buffer solution, add the pre-treated sawdust to obtain reaction solution A, stir and react, filter, wash, and dry to obtain chitosan-tannic acid network-coated sawdust;

[0009] S2: Chitosan-tannic acid network-coated wood chips are added to acetic acid buffer solution, and potassium permanganate solution is added dropwise to obtain reaction solution B. The reaction is stirred at room temperature, washed, and allowed to stand for aging to obtain wood chip composite material. It is then mixed with sulfonated asphalt powder to obtain a mixture, hot water is added to obtain a paste, kneaded and allowed to stand for degassing, extruded and granulated to obtain the material, and dried to obtain functional composite precursor particles.

[0010] S3: The single-layer spread functional composite precursor particles are heated to a first temperature at a first heating rate and held in a nitrogen atmosphere, and then heated to a second temperature at a second heating rate and held in a carbon dioxide atmosphere. The atmosphere is switched to a mixture of nitrogen and water vapor and held in this atmosphere. Heating is stopped and the atmosphere is switched to nitrogen atmosphere for cooling to obtain crude gradient pore size activated carbon.

[0011] S4: The crude gradient pore size activated carbon is placed in hydrochloric acid solution to obtain reaction solution C. After stirring at room temperature, it is filtered to obtain pre-acid-washed activated carbon. It is then rinsed with acetic acid solution to obtain secondary acid-washed activated carbon. The crude product is repeatedly washed with deionized water and dried to obtain gradient pore size activated carbon for adsorbing formaldehyde-benzene series compounds.

[0012] As a preferred technical solution of the present invention, in step S1, the volume fraction of the acetic acid solution is 1-2%, for example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2.0%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0013] In some optional embodiments, the chitosan solution contains 1-2 wt.% chitosan by mass, for example, 1.0 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, 1.6 wt.%, 1.7 wt.%, 1.8 wt.%, 1.9 wt.%, or 2.0 wt.%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0014] In some optional embodiments, the particle size of the wood chips is 40-80 mesh, for example, 40 mesh, 44 mesh, 48 mesh, 52 mesh, 56 mesh, 60 mesh, 64 mesh, 68 mesh, 72 mesh, 76 mesh or 80 mesh, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0015] In some optional embodiments, the solid-liquid mass ratio of the sawdust to the chitosan solution is 1:(10-20), for example, it can be 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0016] In some optional embodiments, the ultrasonic treatment time after the sawdust is impregnated in the chitosan solution is 30-60 min, for example, 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0017] In some optional embodiments, the concentration of the tannic acid solution is 1-5 g / L, for example, it can be 1.0 g / L, 1.4 g / L, 1.8 g / L, 2.2 g / L, 2.6 g / L, 3.0 g / L, 3.4 g / L, 3.8 g / L, 4.2 g / L, 4.6 g / L or 5.0 g / L, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0018] In some alternative embodiments, the pH value of the tannic acid buffer solution is 4-5, for example, it may be 4.0, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9 or 5.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0019] In some optional embodiments, the mass-to-volume ratio of the pretreated sawdust to the tannic acid buffer solution is 1:(10-20) g / mL, for example, it can be 1:10 g / mL, 1:11 g / mL, 1:12 g / mL, 1:13 g / mL, 1:14 g / mL, 1:15 g / mL, 1:16 g / mL, 1:17 g / mL, 1:18 g / mL, 1:19 g / mL or 1:20 g / mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0020] In some optional embodiments, the temperature of the reaction mixture A during stirring is 20-40°C, for example, it can be 20°C, 22°C, 24°C, 26°C, 28°C, 30°C, 32°C, 34°C, 36°C, 38°C or 40°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0021] In some optional embodiments, the reaction time of the reaction solution A is 2-4 hours, for example, it can be 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4.0 hours, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0022] As a preferred technical solution of the present invention, in step S2, the pH value of the acetic acid buffer solution is 5-6, for example, it can be 5, 5.1, 5.2, 5.3, 5.4, 5.5, 5.6, 5.7, 5.8, 5.9 or 6, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] In some alternative embodiments, the concentration of the potassium permanganate solution is 1-10 mM, for example, it can be 1.0 mM, 1.9 mM, 2.8 mM, 3.7 mM, 4.6 mM, 5.5 mM, 6.4 mM, 7.3 mM, 8.2 mM, 9.1 mM or 10.0 mM, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0024] In some optional embodiments, the molar ratio of tannic acid to potassium permanganate is (1-2):1, for example, it can be 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2.0:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0025] In some optional embodiments, the reaction solution B is stirred at room temperature for 2-4 hours, for example, 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, or 4.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0026] In some optional embodiments, the static aging time is 30-60 minutes, for example, it can be 30 minutes, 33 minutes, 36 minutes, 39 minutes, 42 minutes, 45 minutes, 48 ​​minutes, 51 minutes, 54 minutes, 57 minutes or 60 minutes, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0027] In some optional embodiments, the mass ratio of the sulfonated bitumen powder to the wood chip composite material is (0.2-0.8):1, for example, it can be 0.20:1, 0.26:1, 0.32:1, 0.38:1, 0.44:1, 0.50:1, 0.56:1, 0.62:1, 0.68:1, 0.74:1 or 0.80:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0028] In some alternative embodiments, the temperature of the hot water is 60-80°C, for example, it can be 60°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C or 80°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0029] In some alternative embodiments, the mass ratio of the hot water to the mixture is (0.2-0.4):1, for example, it can be 0.20:1, 0.22:1, 0.24:1, 0.26:1, 0.28:1, 0.30:1, 0.32:1, 0.34:1, 0.36:1, 0.38:1 or 0.40:1, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0030] In some optional embodiments, the kneading time is 15-30 min, for example, it can be 15.0 min, 16.5 min, 18.0 min, 19.5 min, 21.0 min, 22.5 min, 24.0 min, 25.5 min, 27.0 min, 28.5 min or 30.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0031] In some optional embodiments, the settling and degassing time is 10-15 min, for example, it can be 10.0 min, 10.5 min, 11.0 min, 11.5 min, 12.0 min, 12.5 min, 13.0 min, 13.5 min, 14.0 min, 14.5 min or 15.0 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0032] In some alternative embodiments, the diameter of the material is 2-4 mm, for example, it can be 2.0 mm, 2.2 mm, 2.4 mm, 2.6 mm, 2.8 mm, 3.0 mm, 3.2 mm, 3.4 mm, 3.6 mm, 3.8 mm or 4.0 mm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0033] In some optional embodiments, the material drying temperature is 60-70°C, for example, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C or 70°C, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0034] In some optional embodiments, the drying time of the material is 12-24 hours, for example, 12.0 hours, 13.2 hours, 14.4 hours, 15.6 hours, 16.8 hours, 18.0 hours, 19.2 hours, 20.4 hours, 21.6 hours, 22.8 hours, or 24.0 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0035] As a preferred technical solution of the present invention, in step S3, the flow rate of the nitrogen atmosphere is 150-180 mL / min, for example, it can be 150 mL / min, 153 mL / min, 156 mL / min, 159 mL / min, 162 mL / min, 165 mL / min, 168 mL / min, 171 mL / min, 174 mL / min, 177 mL / min or 180 mL / min, but it is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0036] In some alternative embodiments, the first heating rate is 1-3 °C / min, for example, it can be 1.0 °C / min, 1.2 °C / min, 1.4 °C / min, 1.6 °C / min, 1.8 °C / min, 2.0 °C / min, 2.2 °C / min, 2.4 °C / min, 2.6 °C / min, 2.8 °C / min or 3.0 °C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0037] In some alternative embodiments, the first temperature is 430-450°C, for example, it can be 430°C, 432°C, 434°C, 436°C, 438°C, 440°C, 442°C, 444°C, 446°C, 448°C or 450°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0038] In some optional embodiments, the heat preservation time at the first temperature is 1-2 hours, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0039] In some optional embodiments, the flow rate of the carbon dioxide atmosphere is 100-200 mL / min, for example, it can be 100 mL / min, 110 mL / min, 120 mL / min, 130 mL / min, 140 mL / min, 150 mL / min, 160 mL / min, 170 mL / min, 180 mL / min, 190 mL / min or 200 mL / min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0040] In some alternative embodiments, the second heating rate is 5-8°C / min, for example, it can be 5.0°C / min, 5.3°C / min, 5.6°C / min, 5.9°C / min, 6.2°C / min, 6.5°C / min, 6.8°C / min, 7.1°C / min, 7.4°C / min, 7.7°C / min or 8.0°C / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0041] In some alternative embodiments, the second temperature is 780-810°C, for example, it can be 780°C, 783°C, 786°C, 789°C, 792°C, 795°C, 798°C, 801°C, 804°C, 807°C or 810°C, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0042] In some optional embodiments, the heat preservation time at the second temperature is 0.7-1.2h, for example, it can be 0.70h, 0.75h, 0.80h, 0.85h, 0.90h, 0.95h, 1.00h, 1.05h, 1.10h, 1.15h or 1.20h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0043] In some optional embodiments, the total gas flow rate of the mixed gas is 200-300 mL / min, for example, it can be 200 mL / min, 210 mL / min, 220 mL / min, 230 mL / min, 240 mL / min, 250 mL / min, 260 mL / min, 270 mL / min, 280 mL / min, 290 mL / min or 300 mL / min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0044] In some optional embodiments, the partial pressure of water vapor in the mixture is 0.2-0.5 atm, for example, it can be 0.20 atm, 0.23 atm, 0.26 atm, 0.29 atm, 0.32 atm, 0.35 atm, 0.38 atm, 0.41 atm, 0.44 atm, 0.47 atm or 0.50 atm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0045] In some optional embodiments, the heat preservation time under the mixed gas atmosphere is 0.3-0.8h, for example, it can be 0.30h, 0.35h, 0.40h, 0.45h, 0.50h, 0.55h, 0.60h, 0.65h, 0.70h, 0.75h or 0.80h, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0046] As a preferred technical solution of the present invention, in step S4, the concentration of the hydrochloric acid solution is 0.1-0.3M, for example, it can be 0.10M, 0.12M, 0.14M, 0.16M, 0.18M, ​​0.20M, 0.22M, 0.24M, 0.26M, 0.28M or 0.30M, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] In some optional embodiments, the mass-to-volume ratio of the crude gradient pore size activated carbon to the hydrochloric acid solution is 1:(20-30) g / mL, for example, it can be 1:20 g / mL, 1:21 g / mL, 1:22 g / mL, 1:23 g / mL, 1:24 g / mL, 1:25 g / mL, 1:26 g / mL, 1:27 g / mL, 1:28 g / mL, 1:29 g / mL or 1:30 g / mL, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0048] In some optional embodiments, the reaction solution C is stirred at room temperature for 30-60 min, for example, 30 min, 33 min, 36 min, 39 min, 42 min, 45 min, 48 min, 51 min, 54 min, 57 min or 60 min, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0049] In some optional embodiments, the concentration of the acetic acid solution is 1-2 wt%, for example, it may be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, or 2.0 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0050] In some optional embodiments, the rinsing time is 10-30 min, for example, it can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min or 30 min, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0051] In some optional embodiments, the secondary acidic activated carbon is washed with deionized water until the pH of the washing effluent is 6.5-7.0, for example, it can be 6.5, 6.55, 6.6, 6.65, 6.7, 6.75, 6.8, 6.85, 6.9, 6.95 or 7.0, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0052] Secondly, the present invention provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds.

[0053] This application constructs a chitosan-tannic acid functional network on a three-dimensional sawdust framework: Under acidic conditions, the amino groups on the chitosan molecular chains are protonated to form positively charged groups, which are initially fixed on the sawdust surface and pore walls mainly through multi-point hydrogen bonding with cellulose / lignin and pore penetration; subsequently, tannic acid is introduced, and under pH 4-5 conditions, it forms a stable and dense chitosan-tannic acid composite network mainly through hydrogen bonding accompanied by limited ion pairing / deprotonation, through electrostatic attraction and hydrogen bonding between the chitosan and chitosan layers. This application constructs an integrated platform for functional precursors: chitosan serves as a precursor for subsequent nitrogen doping sites, providing a nitrogen source for the chemical adsorption of formaldehyde; while tannic acid serves as a reducing agent and part of the carbon source for subsequent in-situ synthesis, laying the foundation for the introduction of catalysts and the formation of the carbon framework.

[0054] This application utilizes the spatial environment provided by the chitosan-tannic acid composite network to achieve in-situ synthesis of catalytically active centers: under mild acidic conditions, permanganate ions diffuse into the interior of the chitosan-tannic acid composite network and are efficiently reduced by the tannic acid (polyphenol structure) within the network, generating nanoscale mixed-valence MnOx particles. The confinement and multi-point coordination of the chitosan-tannic acid composite network inhibits the migration and aggregation of the nascent phase, maintaining high dispersion of MnOx and spatial proximity to the organic layer. The subsequently introduced sulfonated pitch plays a dual role: firstly, as a functional binder at high temperatures, ensuring the macroscopic shaping of the precursor; secondly, as an intermediate carbon precursor, its rich aromatic ring structure evolves into locally ordered graphite / aromatic carbon microdomains during subsequent thermal conversion. These microdomains provide sites for π-π electron stacking interactions for the adsorption of benzene compounds.

[0055] This application achieves the simultaneous construction of material structure and function through a multi-stage thermal activation process. The first stage, nitrogen pre-carbonization, transforms chitosan in situ into a more thermodynamically stable nitrogen-doped carbon structure, solidifying the chemical sites for formaldehyde adsorption within the carbon framework. The second stage, carbon dioxide activation, primarily through micropore etching, forms micropores on the carbon matrix, constructing a confined space for adsorbing benzene compounds. The third stage, water vapor activation, performs confined pore expansion under maintained temperature conditions, opening up some micropores into mesopores, forming a mesoporous network connecting macroscopic channels and microscopic adsorption domains. This three-step heat treatment is a gradient pore size construction method. Through the synergistic combination of activator types and their order, it achieves an ordered distribution from transport macropores to distribution mesopores and then to adsorption micropores.

[0056] After two stages of mild acid washing, inorganic ash / alkaline earth metals and soluble salt residues can be selectively removed, and inorganic blockages formed in the pores or channels during the steam activation stage can be cleared, thereby restoring / improving the effective accessibility and connectivity of micro-mesopores. At the same time, free or weakly bound manganese salts can be washed away, while the in-situ anchored nano-MnOx confined in the chitosan-tannic acid composite network is retained due to the presence of multiple interfacial interactions with the matrix, which ensures the stability of the catalytic active center under cyclic conditions.

[0057] This application employs multiple synergistic mechanisms. Firstly, there is a synergistic effect of chemical adsorption-catalytic oxidation for formaldehyde: nitrogen-doped sites transformed from chitosan provide Lewis basic centers and promote oxygen adsorption activation (forming surface peroxide / superoxide species). Synergistically with adjacent highly dispersed MnOx, adsorbed formaldehyde is gradually oxidized to formic acid / intermediates and ultimately mineralized, achieving in-situ regeneration of the sites; this cycle continues under an oxygen-containing atmosphere. This dynamic cycle enhances the continuous removal capacity and total removal capacity of formaldehyde. Secondly, there is "functional zoning and synergistic adsorption" for different pollutants: nitrogen-doped sites synergistically work with MnOx to remove formaldehyde, while the ordered microdomains of graphite-like / aromatic carbon transformed from sulfonated pitch synergistically work with micropores formed by carbon dioxide activation (and connected via mesoporous expansion through water vapor confinement) to efficiently adsorb benzene compounds through π-π stacking and spatial confinement effects. This integration of multiple functional sites in a single material, both spatially adjacent and structurally integrated, is key to achieving efficient hierarchical adsorption of complex pollutants.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] This application constructs a chitosan-tannic acid functional network by layer-by-layer compounding of chitosan and tannic acid on a wood chip skeleton through hydrogen bonding and electrostatic interactions. This network serves as an integrated precursor platform, in which chitosan provides the nitrogen source for subsequent nitrogen doping, while tannic acid also acts as a reducing agent and part of the carbon source for the in-situ synthesis catalyst.

[0060] This application utilizes the confinement effect of the chitosan-tannic acid network to synthesize highly dispersed nano-MnOx catalysts in situ via the reduction of permanganate by tannic acid. The subsequently introduced sulfonated pitch plays a dual role: acting as a binder to shape the precursor and as a carbon precursor to lay the foundation for the subsequent formation of π-π interaction sites for the adsorption of benzene compounds.

[0061] This application constructs the structure and function of the material simultaneously through a multi-stage thermal activation process: nitrogen pre-carbonization converts chitosan into solidified nitrogen-doped adsorption sites; carbon dioxide activation etches micropores that adsorb benzene compounds; and water vapor activation expands some micropores into mesopores. This achieves an ordered distribution from transport macropores to distribution mesopores and then to adsorption micropores.

[0062] This application employs a dual synergistic mechanism. First, for formaldehyde, the nitrogen-doped sites synergize with adjacent MnOx sites to achieve a cycle of "chemisorption-catalytic oxidation-site regeneration," enhancing continuous removal capacity. Second, for complex pollutants, the material achieves functional specialization: the nitrogen-doped / MnOx system removes formaldehyde, while the graphite-like microdomains and microporous structure synergistically adsorb benzene compounds through π-π stacking and confinement effects. This integration of spatially adjacent functional sites within a single material is key to achieving efficient hierarchical adsorption. Detailed Implementation

[0063] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include technical solutions that employ any obvious substitutions and modifications made to the embodiments described herein.

[0064] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone further purification or processing.

[0065] Example 1

[0066] This embodiment provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds and its preparation method. The preparation method of the gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds specifically includes the following steps:

[0067] S1: Prepare a 1.2% (v / v) acetic acid solution, add chitosan to obtain a chitosan solution with a chitosan mass fraction of 1.3 wt.%, immerse 70-mesh sawdust in the chitosan solution with a solid-liquid mass ratio of sawdust to chitosan solution of 1:12, sonicate for 55 min, remove and wash to obtain pre-treated sawdust; prepare a 2 g / L tannic acid solution, adjust the pH to 4.2 using acetic acid and sodium acetate to obtain a tannic acid buffer solution, add the pre-treated sawdust to obtain reaction solution A with a mass-volume ratio of pre-treated sawdust to tannic acid buffer solution of 1:18 g / mL, stir and react at 25℃ for 2.5 h, filter, wash and dry to obtain chitosan-tannic acid network-coated sawdust;

[0068] S2: Chitosan-tannic acid network-coated wood chips were added to an acetic acid buffer solution with a pH of 5.8, and a 4 mM potassium permanganate solution was added dropwise to obtain reaction solution B, wherein the molar ratio of tannic acid to potassium permanganate was 1.2:1. The reaction was stirred at room temperature for 2.5 h, washed, and allowed to stand for aging for 40 min to obtain a wood chip composite material. This composite material was then mixed with sulfonated asphalt powder to obtain a mixture, and hot water at 65 °C was added to obtain a paste, wherein the mass ratio of sulfonated asphalt powder to wood chip composite material was 0.4:1, and the mass ratio of hot water to the mixture was 0.25:1. After kneading for 20 min, the mixture was allowed to stand for degassing for 11 min, and then extruded and granulated to obtain a material with a diameter of 2.5 mm. The paste was then dried at 62 °C for 16 h to obtain functional composite precursor particles.

[0069] S3: The single-layer spread functional composite precursor particles were heated to a first temperature of 435℃ at a first heating rate of 1.5℃ / min under a nitrogen atmosphere with a flow rate of 160mL / min and held for 1.2h. Then, under a carbon dioxide atmosphere with a flow rate of 120mL / min, the temperature was raised to a second temperature of 790℃ at a second heating rate of 6℃ / min and held for 0.8h. The atmosphere was then switched to a mixture of nitrogen and water vapor, with a total gas flow rate of 220mL / min and a water vapor partial pressure of 0.3atm. The mixture was held for 0.4h under this atmosphere. Heating was then stopped and the mixture was switched to a nitrogen atmosphere for cooling to obtain crude gradient pore size activated carbon.

[0070] S4: The crude gradient pore size activated carbon was placed in a 0.15M hydrochloric acid solution to obtain reaction solution C, wherein the mass-volume ratio of the crude gradient pore size activated carbon to the hydrochloric acid solution was 1:22 g / mL. After stirring at room temperature for 40 min, the mixture was filtered to obtain pre-acid-washed activated carbon. The activated carbon was then rinsed with a 1.2wt% acetic acid solution for 15 min to obtain secondary acid-washed activated carbon. The activated carbon was repeatedly washed with deionized water to obtain the crude product. After drying, the gradient pore size activated carbon for adsorbing formaldehyde-benzene series compounds was obtained.

[0071] Example 2

[0072] This embodiment provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds and its preparation method. The preparation method of the gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds specifically includes the following steps:

[0073] S1: Prepare a 2% (v / v) acetic acid solution, add chitosan to obtain a chitosan solution, wherein the mass fraction of chitosan is 2 wt.%, immerse 40-mesh sawdust in the chitosan solution, wherein the solid-liquid mass ratio of sawdust to chitosan solution is 1:20, sonicate for 30 min, remove and wash to obtain pre-treated sawdust; prepare a 5 g / L tannic acid solution, adjust the pH to 5 using acetic acid and sodium acetate to obtain a tannic acid buffer solution, add the pre-treated sawdust to obtain reaction solution A, wherein the mass-volume ratio of pre-treated sawdust to tannic acid buffer solution is 1:10 g / mL, stir and react at 40℃ for 4 h, filter, wash and dry to obtain chitosan-tannic acid network coated sawdust;

[0074] S2: Chitosan-tannic acid network-coated wood chips were added to an acetic acid buffer solution with a pH of 5.5, and a 10 mM potassium permanganate solution was added dropwise to obtain reaction solution B, wherein the molar ratio of tannic acid to potassium permanganate was 2:1. The reaction was stirred at room temperature for 4 h, washed, and allowed to stand for aging for 60 min to obtain a wood chip composite material. This composite material was mixed with sulfonated asphalt powder to obtain a mixture, and hot water at 80 °C was added to obtain a paste, wherein the mass ratio of sulfonated asphalt powder to wood chip composite material was 0.8:1, and the mass ratio of hot water to the mixture was 0.4:1. After kneading for 30 min, the mixture was allowed to stand for degassing for 15 min, and then extruded and granulated to obtain a material with a diameter of 4 mm. The paste was dried at 70 °C for 24 h to obtain functional composite precursor particles.

[0075] S3: The single-layer spread functional composite precursor particles are heated to a first temperature of 450℃ at a first heating rate of 3℃ / min under a nitrogen atmosphere with a flow rate of 180mL / min and held for 2h. Then, under a carbon dioxide atmosphere with a flow rate of 200mL / min, the temperature is raised to a second temperature of 810℃ at a second heating rate of 8℃ / min and held for 1.2h. The atmosphere is then switched to a mixture of nitrogen and water vapor, with a total gas flow rate of 300mL / min and a water vapor partial pressure of 0.5atm. The mixture is held for 0.8h under this atmosphere. Heating is then stopped and the atmosphere is switched to nitrogen for cooling to obtain crude gradient pore size activated carbon.

[0076] S4: The crude gradient pore size activated carbon was placed in a 0.3M hydrochloric acid solution to obtain reaction solution C, wherein the mass-volume ratio of the crude gradient pore size activated carbon to the hydrochloric acid solution was 1:30 g / mL. After stirring at room temperature for 60 min, the mixture was filtered to obtain pre-acid-washed activated carbon. The activated carbon was then rinsed with a 2wt% acetic acid solution for 30 min to obtain secondary acid-washed activated carbon. The activated carbon was repeatedly washed with deionized water to obtain the crude product. After drying, the gradient pore size activated carbon for adsorbing formaldehyde-benzene series compounds was obtained.

[0077] Example 3

[0078] This embodiment provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds and its preparation method. The preparation method of the gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds specifically includes the following steps:

[0079] S1: Prepare an acetic acid solution with a volume fraction of 1.8%, add chitosan to obtain a chitosan solution with a chitosan mass fraction of 1.7 wt.%, immerse 50-mesh sawdust in the chitosan solution with a solid-liquid mass ratio of sawdust to chitosan solution of 1:18, sonicate for 40 min, remove and wash to obtain pre-treated sawdust; prepare a tannic acid solution with a concentration of 4 g / L, adjust the pH to 4.8 using acetic acid and sodium acetate to obtain a tannic acid buffer solution, add the pre-treated sawdust to obtain reaction solution A with a mass-volume ratio of pre-treated sawdust to tannic acid buffer solution of 1:15 g / mL, stir and react at 35℃ for 3.5 h, filter, wash and dry to obtain chitosan-tannic acid network coated sawdust;

[0080] S2: Chitosan-tannic acid network-coated wood chips were added to an acetic acid buffer solution with a pH of 5, and an 8 mM potassium permanganate solution was added dropwise to obtain reaction solution B, wherein the molar ratio of tannic acid to potassium permanganate was 1.8:1. The reaction was stirred at room temperature for 3.5 h, washed, and allowed to stand for 50 min to age to obtain a wood chip composite material. This composite material was mixed with sulfonated asphalt powder to obtain a mixture, and hot water at 75 °C was added to obtain a paste, wherein the mass ratio of sulfonated asphalt powder to wood chip composite material was 0.7:1, and the mass ratio of hot water to the mixture was 0.35:1. After kneading for 25 min, the mixture was allowed to stand for 14 min to degas, and then extruded and granulated to obtain a material with a diameter of 3.5 mm. The paste was dried at 68 °C for 20 h to obtain functional composite precursor particles.

[0081] S3: The single-layer spread functional composite precursor particles were heated to a first temperature of 445℃ at a first heating rate of 2.5℃ / min under a nitrogen atmosphere with a flow rate of 175mL / min and held for 1.8h. Then, they were heated to a second temperature of 805℃ at a second heating rate of 7.5℃ / min under a carbon dioxide atmosphere with a flow rate of 180mL / min and held for 1.1h. The atmosphere was then switched to a mixture of nitrogen and water vapor, with a total gas flow rate of 280mL / min and a water vapor partial pressure of 0.45atm. The mixture was held for 0.7h under this atmosphere, heating was stopped, and the atmosphere was switched to nitrogen for cooling to obtain crude gradient pore size activated carbon.

[0082] S4: The crude gradient pore size activated carbon was placed in a 0.25M hydrochloric acid solution to obtain reaction solution C, wherein the mass-volume ratio of the crude gradient pore size activated carbon to the hydrochloric acid solution was 1:28 g / mL. After stirring at room temperature for 55 min, the solution was filtered to obtain pre-acid-washed activated carbon. The activated carbon was then rinsed with a 1.8wt% acetic acid solution for 25 min to obtain secondary acid-washed activated carbon. The activated carbon was repeatedly washed with deionized water to obtain the crude product. After drying, the gradient pore size activated carbon for adsorbing formaldehyde-benzene series compounds was obtained.

[0083] Example 4

[0084] This embodiment provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds and its preparation method. The preparation method of the gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds specifically includes the following steps:

[0085] S1: Prepare a 1% (v / v) acetic acid solution, add chitosan to obtain a chitosan solution, wherein the mass fraction of chitosan is 1 wt.%, immerse 80-mesh wood chips in the chitosan solution, wherein the solid-liquid mass ratio of wood chips to chitosan solution is 1:10, sonicate for 60 min, remove and wash to obtain pre-treated wood chips; prepare a 1 g / L tannic acid solution, adjust the pH to 4 using acetic acid and sodium acetate to obtain a tannic acid buffer solution, add the pre-treated wood chips to obtain reaction solution A, wherein the mass-volume ratio of pre-treated wood chips to tannic acid buffer solution is 1:20 g / mL, stir and react at 20℃ for 2 h, filter, wash and dry to obtain chitosan-tannic acid network coated wood chips;

[0086] S2: Chitosan-tannic acid network-coated wood chips were added to an acetic acid buffer solution with a pH of 6, and a 1 mM potassium permanganate solution was added dropwise to obtain reaction solution B, wherein the molar ratio of tannic acid to potassium permanganate was 1:1. The reaction was stirred at room temperature for 2 hours, washed, and allowed to stand for 30 minutes to age to obtain a wood chip composite material. This composite material was mixed with sulfonated asphalt powder to obtain a mixture, and hot water at 60°C was added to obtain a paste, wherein the mass ratio of sulfonated asphalt powder to wood chip composite material was 0.2:1, and the mass ratio of hot water to the mixture was 0.2:1. After kneading for 15 minutes, the mixture was allowed to stand for 10 minutes to degas, and then extruded and granulated to obtain a material with a diameter of 2 mm. The paste was dried at 60°C for 12 hours to obtain functional composite precursor particles.

[0087] S3: The single-layer spread functional composite precursor particles are heated to a first temperature of 430℃ at a first heating rate of 1℃ / min under a nitrogen atmosphere with a flow rate of 150mL / min and held for 1h. Then, under a carbon dioxide atmosphere with a flow rate of 100mL / min, the temperature is raised to a second temperature of 780℃ at a second heating rate of 5℃ / min and held for 0.7h. The atmosphere is then switched to a mixture of nitrogen and water vapor, with a total gas flow rate of 200mL / min and a water vapor partial pressure of 0.2atm. The mixture is held for 0.3h under this atmosphere. Heating is then stopped and the atmosphere is switched to nitrogen for cooling to obtain crude gradient pore size activated carbon.

[0088] S4: The crude gradient pore size activated carbon was placed in a 0.1M hydrochloric acid solution to obtain reaction solution C, wherein the mass-volume ratio of the crude gradient pore size activated carbon to the hydrochloric acid solution was 1:20 g / mL. After stirring at room temperature for 30 min, the mixture was filtered to obtain pre-acid-washed activated carbon. The activated carbon was then rinsed with a 1wt% acetic acid solution for 10 min to obtain secondary acid-washed activated carbon. The activated carbon was repeatedly washed with deionized water to obtain the crude product. After drying, the gradient pore size activated carbon for adsorbing formaldehyde-benzene series compounds was obtained.

[0089] Comparative Example 1

[0090] This comparative example provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds. The difference from Example 1 is that the step of adding potassium permanganate solution in step S2 is omitted, while the other operation steps and process parameters are exactly the same as in Example 1.

[0091] Comparative Example 2

[0092] This comparative example provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds. The difference from Example 1 is that the step of adding potassium permanganate solution to reaction solution B is omitted in S2. The crude gradient pore size activated carbon obtained in S3 is impregnated in manganese nitrate solution, dried after impregnation, and calcined at 350°C for 2 hours in air atmosphere. Other operation steps and process parameters are exactly the same as in Example 1.

[0093] Comparative Example 3

[0094] This comparative example provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds. The difference from Example 1 is that a carbon dioxide atmosphere is used instead of a mixed gas atmosphere in step S3. Other operating steps and process parameters are exactly the same as in Example 1.

[0095] Comparative Example 4

[0096] This comparative example provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds. The difference from Example 1 is that a mixed atmosphere is used instead of a carbon dioxide atmosphere in step S3. Other operating steps and process parameters are exactly the same as in Example 1.

[0097] Comparative Example 5

[0098] This comparative example provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds. The difference from Example 1 is that sulfonated pitch powder is not added, but other operating steps and process parameters are exactly the same as in Example 1.

[0099] Comparative Example 6

[0100] This comparative example provides a gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds. The difference from Example 1 is that the step of impregnating wood chips with chitosan solution in step S1 is omitted. Other operating steps and process parameters are exactly the same as in Example 1.

[0101] The performance of the gradient pore size activated carbons used for adsorbing formaldehyde-benzene compounds in Examples 1-4 and Comparative Examples 1-6 was tested, and the specific process is as follows:

[0102] The method for testing the single-pass purification rate is as follows:

[0103] a) Formaldehyde single-pass purification rate: 1.000 g of the gradient pore size activated carbon sample to be used for adsorbing formaldehyde-benzene series compounds was evenly spread in an open glass weighing bottle. The weighing bottle was placed in an environment pre-equilibrated at 25℃ and 50% relative humidity (RH) for 24 h, where a stable formaldehyde concentration (C0, 2.0 mg / m³) had been established. 3 The bottom of a 10 L sealed glass desiccator was placed. The desiccator was quickly sealed and timing was started. The formaldehyde concentration inside the desiccator was monitored and recorded in real time over time using a formaldehyde detector. At the first hour, the formaldehyde concentration C1 in the desiccator was recorded. At the same time, a desiccator without the sample was placed under the same initial conditions as a blank control, and its formaldehyde concentration C-blank after 1 hour was recorded to correct for natural decay. Formaldehyde single-pass purification rate (1h, %) = [(C0 – C1) / C0] × 100%.

[0104] b) Single-pass purification rate of benzene series compounds (represented by toluene):

[0105] 1.000 g of gradient pore size activated carbon sample to be used for adsorbing formaldehyde-benzene series compounds was evenly spread in an open glass weighing bottle. The weighing bottle was placed in an environment pre-equilibrated for 24 h at 25°C and 50% relative humidity (RH) to establish a stable toluene concentration (C0, 4.0 mg / m³). 3 The bottom of a 10 L sealed glass desiccator was placed. The desiccator was quickly sealed and timing was started. The toluene concentration inside the desiccator was monitored and recorded in real time over time using a volatile organic compound (VOC) detector. At the first hour, the toluene concentration C1 in the desiccator was recorded. Simultaneously, a desiccator without the sample was placed under the same initial conditions as a blank control, and its toluene concentration C-blank was recorded after 1 hour to correct for natural decay. The toluene single-pass purification rate (1h, %) = [(C0 – C1) / C0] × 100%.

[0106] Cyclic performance test method: Place 1.000 g of the test sample in a 10 L sealed desiccator with a stable pollutant concentration (formaldehyde or toluene, CO, 100 ppm) established, and follow the same method as above. Continuously monitor until the concentration no longer changes significantly (or reaches the preset 24 hours), and record the final equilibrium concentration C-final. At the same time, record the final concentration C-blank of the blank control group. Calculate the initial static saturated adsorption capacity q. Static saturated adsorption capacity qn (mg / g) = [(C-blank – C-final) × V × M / 24.45] / 1.000, where V is the effective volume of the desiccator, M is the molar mass of formaldehyde or toluene, and 24.45 is the gas molar volume at 25℃ and 1 atm. Remove the activated carbon sample that has completed the initial adsorption test, and perform desorption regeneration by heat treatment at 150℃ for 60 minutes under a nitrogen atmosphere, then cool to room temperature. The regenerated sample was subjected to adsorption testing again according to the single-cycle purification rate test method, and its static saturated adsorption capacity qn (n is the number of cycles) after regeneration was determined. The "adsorption-regeneration" process was repeated for 10 cycles, and the capacity retention rate (%) of the 10th cycle was calculated as (q10 / q1) × 100%.

[0107] The test results are shown in Table 1.

[0108] Table 1: Performance test results of gradient pore size activated carbon for adsorbing formaldehyde-benzene series compounds in Examples 1-4 and Comparative Examples 1-6

[0109]

[0110] Based on the test results of Example 1 and Comparative Example 1, it can be seen that by omitting the step of adding potassium permanganate solution in step S2, and without in-situ oxidation and fixation with potassium permanganate, the carbonized surface lacks N / O-rich polar active sites and dispersed MnOx sites. This reduces the high affinity adsorption capacity of small molecule polar pollutants such as formaldehyde, resulting in a significant decrease in the single-pass purification rate of formaldehyde. Since weak physical adsorption is the main method, the desorption is more thorough, and the cycle retention rate is relatively higher.

[0111] The test results of Example 1 and Comparative Example 2 show that the MnOx after impregnation-air calcination mainly accumulates on the carbon surface and is not embedded in the pore walls. At the same time, air calcination will oxidize / ablaze the carbon skeleton, causing pore collapse and blockage, reducing the specific surface area and effective diffusion channels, resulting in a decrease in the initial purification rate. Furthermore, the sites are prone to deactivation, and the cycle retention rate also deteriorates.

[0112] The test results of Example 1 and Comparative Example 3 show that carbon dioxide activation alone mainly forms a large number of micropores, allowing small molecule formaldehyde to enter quickly, thus maintaining a high formaldehyde purification rate; however, the lack of subsequent water vapor activation leads to insufficient mesopores / macropores, restricting the diffusion of larger molecules such as toluene, reducing the purification rate of benzene series compounds, making the framework more compact and stable, and resulting in a relatively higher cycle retention rate.

[0113] The test results of Example 1 and Comparative Example 4 show that direct activation with water vapor will drastically enlarge the pore size and generate a loose structure dominated by mesopores / macropores, which is conducive to the rapid entry of benzene series compounds such as toluene and increases the benzene series purification rate. However, the micropore volume fraction is insufficient, the high affinity adsorption sites of small molecules such as formaldehyde are greatly reduced, the formaldehyde purification rate decreases, and the skeleton becomes brittle and easy to decay, resulting in a decrease in cycle retention rate.

[0114] The test results of Example 1 and Comparative Example 5 show that the lack of sulfonated asphalt makes it difficult to form a mesoporous network with a rich aromatic π surface after carbonization, which leads to a significant weakening of π–π adsorption and mesoporous diffusion of hydrophobic aromatic pollutants (toluene), resulting in a decrease in the purification rate of benzene series compounds. However, formaldehyde mainly relies on polar sites and microporous adsorption and is less affected, and the formaldehyde purification rate and cycle stability are basically maintained.

[0115] The test results of Example 1 and Comparative Example 6 show that without the introduction of chitosan, sufficient nitrogen-containing functional group sites cannot be retained in the framework. The directional binding of formaldehyde to amine / pyridine sites is weakened, and the single purification rate of formaldehyde decreases. Benzene compounds mainly rely on hydrophobic π–π interactions and mesoporous diffusion, so the impact is relatively small. Since the adsorption is mainly reversible physical adsorption, the cycle retention rate is actually higher.

[0116] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds, characterized in that, The preparation method includes: S1: Prepare an acetic acid solution, add chitosan to obtain a chitosan solution, immerse the sawdust in the chitosan solution, ultrasonically treat it, remove it, and wash it to obtain pre-treated sawdust; prepare a tannic acid solution, adjust the pH with acetic acid and sodium acetate to obtain a tannic acid buffer solution, add the pre-treated sawdust to obtain reaction solution A, stir and react, filter, wash, and dry to obtain chitosan-tannic acid network-coated sawdust; S2: Chitosan-tannic acid network-coated wood chips are added to acetic acid buffer solution, and potassium permanganate solution is added dropwise to obtain reaction solution B. The reaction is stirred at room temperature, washed, and allowed to stand for aging to obtain wood chip composite material. It is then mixed with sulfonated asphalt powder to obtain a mixture, hot water is added to obtain a paste, kneaded and allowed to stand for degassing, extruded and granulated to obtain the material, and dried to obtain functional composite precursor particles. S3: The single-layer spread functional composite precursor particles are heated to a first temperature at a first heating rate and held in a nitrogen atmosphere, and then heated to a second temperature at a second heating rate and held in a carbon dioxide atmosphere. The atmosphere is switched to a mixture of nitrogen and water vapor and held in this atmosphere. Heating is stopped and the atmosphere is switched to nitrogen atmosphere for cooling to obtain crude gradient pore size activated carbon. S4: The crude gradient pore size activated carbon is placed in hydrochloric acid solution to obtain reaction solution C. After stirring at room temperature, it is filtered to obtain pre-acid-washed activated carbon. It is then rinsed with acetic acid solution to obtain secondary acid-washed activated carbon. The crude product is repeatedly washed with deionized water and dried to obtain gradient pore size activated carbon for adsorbing formaldehyde-benzene series compounds.

2. The method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds according to claim 1, characterized in that, In S1: The solid-liquid mass ratio of the wood chips to the chitosan solution is 1:(10-20).

3. The method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds according to claim 1, characterized in that, In S1: The mass-to-volume ratio of the pretreated sawdust to the tannic acid buffer solution is 1:(10-20)g / mL.

4. The method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds according to claim 1, characterized in that, In S2: The molar ratio of tannic acid to potassium permanganate is (1-2):

1.

5. The method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds according to claim 1, characterized in that, In S2: The mass ratio of the sulfonated asphalt powder to the wood chip composite material is (0.2-0.8):

1.

6. The method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds according to claim 1, characterized in that, In S3: The flow rate of the nitrogen atmosphere is 150-180 mL / min; The first temperature is 430-450℃.

7. The method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds according to claim 1, characterized in that, In S3: The flow rate of the carbon dioxide atmosphere is 100-200 mL / min; The second temperature is 780-810℃.

8. The method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds according to claim 1, characterized in that, In S3: The total gas flow rate of the mixed gas is 200-300 mL / min; The partial pressure of water vapor in the mixture is 0.2-0.5 atm.

9. The method for preparing gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds according to claim 1, characterized in that, In S4: The mass-to-volume ratio of the crude gradient pore size activated carbon to the hydrochloric acid solution is 1:(20-30)g / mL.

10. A gradient pore size activated carbon for adsorbing formaldehyde-benzene compounds prepared by the preparation method according to any one of claims 1-9.

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