Sludge-based hydrothermal carbon adsorbent for adsorbing micro-plastics as well as preparation method and application of sludge-based hydrothermal carbon adsorbent

Abstract

The invention relates to a sludge-based hydrothermal carbon adsorbent for adsorbing micro-plastics as well as a preparation method and application of the sludge-based hydrothermal carbon adsorbent. The method comprises the following steps: respectively drying sewage sludge and livestock and poultry manure to constant weight, crushing, and sieving with a 100-mesh sieve to obtain a sludge base material and a livestock and poultry manure base material; mixing the sludge base material and the livestock and poultry manure base material, adding deionized water, carrying out a hydrothermal reaction at 220-240 DEG C, cooling, carrying out suction filtration, drying, and sieving to obtain primary hydrothermal carbon; mixing the primary hydrothermal carbon with an activating agent, transferring the mixture into a tubular furnace, heating to 800-820 DEG C in an inert atmosphere, keeping the temperature for 1-2 hours, cooling, putting into an acid solution, standing for 24-30 hours, separating, washing to be neutral, and drying to obtain the sludge-based hydrothermal carbon adsorbent for adsorbing the micro-plastics. According to the sludge-based hydrothermal carbon adsorbent for adsorbing the micro-plastics and the preparation method of the sludge-based hydrothermal carbon adsorbent, the technical problem that no adsorbent for the micro-plastics with high hydrophobicity and surface inertia exists in the prior art is solved.

Description

Technical Field

[0001] This invention relates to the field of hydrothermal carbon adsorbent technology, and in particular to a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics, its preparation method and application. Background Technology

[0002] With the acceleration of global urbanization and the booming development of intensive livestock farming, the generation of sewage sludge and livestock manure has reached an alarming scale. Statistics show that China generated approximately 60 million tons of raw wastewater sludge in 2019, and this figure is projected to increase to 90 million tons by 2025. This sewage sludge and livestock manure contain large amounts of pathogens, parasites, and heavy metals, posing potential risks to the environment. Traditional methods for disposing of sewage sludge and livestock manure include sanitary landfill and incineration. However, sanitary landfill not only occupies a large amount of land resources, but its leachate may also cause groundwater pollution, and the anaerobic process emits large amounts of methane (CH4). Incineration, while significantly reducing volume, has high investment and operating costs and is prone to causing heavy metal accumulation in fly ash and the emission of toxic gases such as dioxins, resulting in secondary pollution. Therefore, seeking a green, low-carbon, and resource-efficient disposal pathway has become a major demand in the field of environmental engineering.

[0003] Hydrothermal carbonization, as an emerging thermochemical conversion technology, utilizes water as a reaction medium under mild conditions (typically 180-250 °C and autogenous pressure) to directly convert high-moisture biomass (such as sludge and feces) into carbon-rich solid products—hydrothermal carbon. This technology typically produces hydrothermal carbon with stable structures and good heavy metal solidification effects, reducing the environmental risks associated with subsequent utilization. Furthermore, hydrothermal carbon can serve as a soil conditioner, low-grade fuel, or precursor for functional materials. However, research and practice have shown that hydrothermal carbon prepared from a single raw material (such as pure sludge or pure feces) suffers from drawbacks as an adsorbent material, including low specific surface area, underdeveloped pore structure, and limited surface functional groups. These limitations severely restrict its application in high-efficiency adsorption, particularly in the treatment of emerging pollutants.

[0004] Microplastics (plastic particles with a diameter <5 mm) have emerged as a global, persistent pollutant, widely detected in oceans, freshwater, soil, and even the atmosphere. Aquatic and terrestrial organisms, as well as humans, may ingest microplastics through various pathways, causing physical damage, inflammatory responses, and physiological disorders. Current mainstream microplastic removal technologies have significant limitations. For example, physical filtration / sieving has low retention efficiency for nanoscale microplastics and produces high-concentration concentrates requiring secondary treatment; chemical flocculation, if using large amounts of chemicals, can introduce new chemical substances, potentially altering aquatic ecosystems and generating chemical sludge; and biodegradation is a lengthy process (months or even years) and has extremely low degradation efficiency for many synthetic plastics (such as PE and PP). Therefore, developing an adsorbent material that can actively capture, efficiently enrich, easily separate, be environmentally friendly, and cost-effective is one of the key breakthroughs in overcoming the challenge of microplastic pollution control.

[0005] Although some scholars have explored the use of hydrothermal carbonization of sludge or feces for adsorbing dyes, heavy metals or phosphates, research on specific adsorbent materials for microplastics with strong hydrophobicity and inert surfaces is still in its early stages, especially research on using the synergistic effect of co-hydrothermal carbonization of the two to specifically improve the adsorption performance of microplastics.

[0006] Therefore, in view of the above problems, the present invention urgently needs to provide a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics, its preparation method and application. Summary of the Invention

[0007] The purpose of this invention is to provide a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics, its preparation method and application. By proposing a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics and its preparation method, the invention aims to solve the technical problem in the prior art of not having an adsorbent for microplastics with strong hydrophobicity and inert surface.

[0008] This invention provides a method for preparing a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics, comprising the following steps:

[0009] Sewage sludge and livestock manure are dried to constant weight, crushed and passed through a 100-mesh sieve to obtain sludge base material and livestock manure base material.

[0010] Sludge substrate and livestock and poultry manure substrate are mixed, deionized water is added, and hydrothermal reaction is carried out at 220-240℃. After cooling, filtration, drying and sieving, primary hydrothermal carbon is obtained.

[0011] The primary hydrothermal carbon is mixed with an activator and transferred to a tube furnace. Under an inert atmosphere, the temperature is raised to 800-820℃ and held for 1-2 hours. After cooling, the mixture is placed in an acid solution and allowed to stand for 24-30 hours. The mixture is then separated, rinsed until neutral, and dried to obtain a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics.

[0012] Preferably, the activator is one or more of NaOH, KOH, ZnCl2 or H3PO4.

[0013] Preferably, the mass ratio of primary hydrothermal char to activator is 1:(3-4).

[0014] Preferably, the mass ratio of sludge substrate to livestock and poultry manure substrate is (2-3):1.

[0015] Preferably, during the preparation of primary hydrothermal carbon, 0.1-1.0 mol / L of acid or base is added as a catalyst.

[0016] Preferably, the acid is citric acid or oxalic acid, and the base is NaOH or KOH.

[0017] Preferably, the livestock and poultry manure is one or more of pig manure, chicken manure, or cow manure.

[0018] Preferably, the inert gas is argon;

[0019] Argon gas was introduced and purged at a flow rate of 20 mL / min for 15 min, followed by a temperature increase to 800 °C at a rate of 10 °C / min.

[0020] The present invention also provides a sludge-based hydrothermal carbon adsorbent prepared by the method described in any one of the above-mentioned methods for adsorbing microplastics.

[0021] The present invention also provides an application of sludge-based hydrothermal carbon adsorbent as described above in the adsorption of microplastics.

[0022] The present invention provides a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics, and its preparation method and application have the following advantages compared with the prior art:

[0023] The sludge-based hydrothermal carbon adsorbent provided by this invention utilizes the proteins and polysaccharides in sludge and the cellulose and lignin in feces to promote the formation of carbon skeleton and pore development. Subsequent activation treatment further expands the specific surface area and enriches the surface functional groups, enhancing the hydrophobic adsorption, pore capture and surface complexation of microplastics, thus achieving a triple effect of "raw material synergy - process enhancement - performance improvement". Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] This invention provides a method for preparing a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics, comprising the following steps:

[0026] S1) The sewage sludge and livestock manure are dried to constant weight, crushed and passed through a 100-mesh sieve to obtain sludge base material and livestock manure base material.

[0027] S2) Sludge substrate and livestock and poultry manure substrate are mixed, deionized water is added, and hydrothermal reaction is carried out at 220-240℃. After cooling, filtration, drying and sieving, primary hydrothermal carbon is obtained.

[0028] S3) Mix the primary hydrothermal carbon with the activator, transfer it to a tube furnace, heat it to 800-820℃ under an inert atmosphere, keep it at that temperature for 1-2 hours, cool it, place it in an acid solution and let it stand for 24-30 hours, separate it, rinse it until neutral, dry it, and obtain a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics.

[0029] Specifically, the activator is one or more of NaOH, KOH, ZnCl2 or H3PO4.

[0030] Specifically, the mass ratio of primary hydrothermal carbon to activator is 1:(3-4).

[0031] Specifically, the mass ratio of sludge substrate to livestock and poultry manure substrate is (2-3):1.

[0032] Specifically, in the primary hydrothermal carbon preparation process, 0.1-1.0 mol / L of acid or base is added as a catalyst.

[0033] Specifically, the acid is citric acid or oxalic acid, and the base is NaOH or KOH.

[0034] Specifically, livestock and poultry manure is one or more of pig manure, chicken manure, or cow manure.

[0035] Specifically, the inert gas is argon;

[0036] Argon gas was introduced and purged at a flow rate of 20 mL / min for 15 min, followed by a temperature increase to 800 °C at a rate of 10 °C / min.

[0037] The present invention also provides a sludge-based hydrothermal carbon adsorbent prepared by the method described in any one of the above-mentioned methods for adsorbing microplastics.

[0038] The present invention also provides an application of sludge-based hydrothermal carbon adsorbent as described above in the adsorption of microplastics.

[0039] The sludge-based hydrothermal carbon adsorbent provided by this invention utilizes the proteins and polysaccharides in sludge and the cellulose and lignin in feces to promote the formation of carbon skeleton and pore development. Subsequent activation treatment further expands the specific surface area and enriches the surface functional groups, enhancing the hydrophobic adsorption, pore capture and surface complexation of microplastics, thus achieving a triple effect of "raw material synergy - process enhancement - performance improvement".

[0040] Example 1

[0041] The specific steps for preparing a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics are as follows:

[0042] 101) Dry the sewage sludge and livestock and poultry manure separately to constant weight, crush them and pass them through a 100-mesh sieve to obtain sludge base material and livestock and poultry manure base material;

[0043] 102) Sludge substrate and livestock and poultry manure substrate are mixed at a ratio of 2:1, deionized water is added, the solid-liquid ratio is 1:5, and hydrothermal reaction is carried out at 220℃ for 1 hour. After cooling, filtration, drying and sieving, primary hydrothermal carbon is obtained.

[0044] 103) The primary hydrothermal carbon and activator were mixed at a ratio of 1:3, introduced into an alumina disk, transferred to a tube furnace, and purged with argon gas at a flow rate of 20 mL / min for 15 min. Then, the temperature was increased to 800℃ at a rate of 10℃ / min, held for 1 hour, cooled, placed in acid solution and allowed to stand for 24 hours, separated, rinsed until neutral, and dried at 105℃ to obtain a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics.

[0045] The activator in this embodiment is NaOH.

[0046] In the primary hydrothermal carbon preparation process of this embodiment, 0.1 mol / L of acid is added as a catalyst.

[0047] The acid in this embodiment is citric acid.

[0048] The livestock and poultry manure in this embodiment is pig manure.

[0049] Before mixing the primary hydrothermal char with the activator in this embodiment, the primary char is treated by washing it with deionized water until the pH is neutral, drying it at 105°C to constant weight, and grinding it through a 20-mesh sieve.

[0050] The sludge-based hydrothermal carbon adsorbent obtained in this embodiment can be applied to the adsorption of microplastics.

[0051] The specific process of microplastic adsorption is as follows:

[0052] Select plastic powder with a diameter of 10-100 μm, remove surface impurities with organic solvent, dry it, add it to 1 L of ultrapure water, and add 0.01 mol / L NaCl (to simulate the ionic environment of natural water). Use a magnetic stirrer or an ultrasonic cell disruptor (100 W, 10 min) to fully and uniformly disperse the microplastics to obtain a 50 mg / L microplastic stock solution (the microplastic stock solution needs to be used on-site or continuously stirred at low speed to prevent sedimentation).

[0053] Take several conical flasks and add 100 mL of microplastic stock solution to each flask. Adjust the initial pH of the microplastic stock solution in each flask to 7.0 using 0.1 mol / L HCl or NaOH solution. Add 0.5 g of sludge-based hydrothermal carbon adsorbent to each flask. Place the flasks on a constant temperature shaker and shake at 150 rpm. Remove the flasks at different time points and filter them using a 0.45 μm glass fiber membrane or a mixed cellulose ester membrane to separate the adsorbent and unadsorbed microplastics. Measure the concentration of residual microplastics in the filtrate.

[0054] The specific surface area of ​​the sludge-based hydrothermal carbon adsorbent in this embodiment is 60 m². 2 / g, with an adsorption rate of 90% for microplastics.

[0055] Example 2

[0056] The specific steps for preparing a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics are as follows:

[0057] 201) The sewage sludge and livestock and poultry manure are dried to constant weight, crushed and passed through a 100-mesh sieve to obtain sludge base material and livestock and poultry manure base material;

[0058] 202) Sludge substrate and livestock and poultry manure substrate are mixed at a ratio of 3:1, deionized water is added, the solid-liquid ratio is 1:5, and hydrothermal reaction is carried out at 240℃ for 1 hour. After cooling, filtration, drying and sieving, primary hydrothermal carbon is obtained.

[0059] 203) The primary hydrothermal carbon and activator were mixed at a ratio of 1:4, introduced into an alumina disk, transferred to a tube furnace, and purged with argon gas at a flow rate of 20 mL / min for 15 min. Then, the temperature was increased to 820℃ at a rate of 10℃ / min and held for 2 hours. After cooling, the mixture was placed in acid solution and allowed to stand for 30 hours. After separation, the mixture was rinsed until neutral and dried at 105℃ to obtain a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics.

[0060] The activator in this embodiment is ZnCl2.

[0061] In the primary hydrothermal carbon preparation process of this embodiment, 1.0 mol / L of acid is added as a catalyst.

[0062] The acid in this embodiment is oxalic acid.

[0063] The livestock and poultry manure in this embodiment is chicken manure.

[0064] Before mixing the primary hydrothermal char with the activator in this embodiment, the primary char is treated by washing it with deionized water until the pH is neutral, drying it at 105°C to constant weight, and grinding it through a 20-mesh sieve.

[0065] The sludge-based hydrothermal carbon adsorbent obtained in this embodiment can be applied to the adsorption of microplastics.

[0066] The specific process of microplastic adsorption is as follows:

[0067] Select plastic powder with a diameter of 10-100 μm, remove surface impurities with organic solvent, dry it, add it to 1 L of ultrapure water, and add 0.01 mol / L NaCl (to simulate the ionic environment of natural water). Use a magnetic stirrer or an ultrasonic cell disruptor (100 W, 10 min) to fully and uniformly disperse the microplastics to obtain a 50 mg / L microplastic stock solution (the microplastic stock solution needs to be used on-site or continuously stirred at low speed to prevent sedimentation).

[0068] Take several conical flasks and add 100 mL of microplastic stock solution to each flask. Adjust the initial pH of the microplastic stock solution in each flask to 7.0 using 0.1 mol / L HCl or NaOH solution. Add 0.5 g of sludge-based hydrothermal carbon adsorbent to each flask. Place the flasks on a constant temperature shaker and shake at 150 rpm. Remove the flasks at different time points and filter them using a 0.45 μm glass fiber membrane or a mixed cellulose ester membrane to separate the adsorbent and unadsorbed microplastics. Measure the concentration of residual microplastics in the filtrate.

[0069] The specific surface area of ​​the sludge-based hydrothermal carbon adsorbent in this embodiment is 62 m². 2 / g, with an adsorption rate of 92% for microplastics.

[0070] Example 3

[0071] The specific steps for preparing a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics are as follows:

[0072] 301) Dry the sewage sludge and livestock manure to constant weight, crush them and pass them through a 100-mesh sieve to obtain sludge base material and livestock manure base material;

[0073] 302) Sludge substrate and livestock and poultry manure substrate are mixed at a ratio of 2.5:1, deionized water is added, the solid-liquid ratio is 1:5, and hydrothermal reaction is carried out at 230℃ for 1 hour. After cooling, filtration, drying and sieving, primary hydrothermal carbon is obtained.

[0074] 303) The primary hydrothermal carbon and activator were mixed at a ratio of 1:4, introduced into an alumina disk, transferred to a tube furnace, and purged with argon gas at a flow rate of 20 mL / min for 15 min. Then, the temperature was increased to 810℃ at a rate of 10℃ / min and held for 1.5 hours. After cooling, the mixture was placed in acid solution and allowed to stand for 26 hours. After separation, the mixture was rinsed until neutral and dried at 105℃ to obtain a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics.

[0075] The activators in this embodiment are KOH and ZnCl2.

[0076] In the primary hydrothermal carbon preparation process of this embodiment, 1.0 mol / L of alkali is added as a catalyst.

[0077] The alkali in this embodiment is NaOH.

[0078] The livestock and poultry manure in this embodiment is chicken manure and cow manure.

[0079] Before mixing the primary hydrothermal char with the activator in this embodiment, the primary char is treated by washing it with deionized water until the pH is neutral, drying it at 105°C to constant weight, and grinding it through a 20-mesh sieve.

[0080] The sludge-based hydrothermal carbon adsorbent obtained in this embodiment can be applied to the adsorption of microplastics.

[0081] The specific process of microplastic adsorption is as follows:

[0082] Select plastic powder with a diameter of 10-100 μm, remove surface impurities with organic solvent, dry it, add it to 1 L of ultrapure water, and add 0.01 mol / L NaCl (to simulate the ionic environment of natural water). Use a magnetic stirrer or an ultrasonic cell disruptor (100 W, 10 min) to fully and uniformly disperse the microplastics to obtain a 50 mg / L microplastic stock solution (the microplastic stock solution needs to be used on-site or continuously stirred at low speed to prevent sedimentation).

[0083] Take several conical flasks and add 100 mL of microplastic stock solution to each flask. Adjust the initial pH of the microplastic stock solution in each flask to 7.0 using 0.1 mol / L HCl or NaOH solution. Add 0.5 g of sludge-based hydrothermal carbon adsorbent to each flask. Place the flasks on a constant temperature shaker and shake at 150 rpm. Remove the flasks at different time points and filter them using a 0.45 μm glass fiber membrane or a mixed cellulose ester membrane to separate the adsorbent and unadsorbed microplastics. Measure the concentration of residual microplastics in the filtrate.

[0084] The specific surface area of ​​the sludge-based hydrothermal carbon adsorbent in this embodiment is 64 m². 2 / g, with an adsorption rate of 93% for microplastics.

[0085] Comparative Example 1

[0086] Compared to Example 1, this method uses no sludge substrate, only livestock and poultry manure substrate.

[0087] The specific surface area of ​​the hydrothermal carbon adsorbent in this embodiment is 54 m². 2 / g, with an adsorption rate of 84% for microplastics.

[0088] Comparative Example 2

[0089] Compared to Example 1, there is no livestock and poultry manure substrate, only sludge substrate;

[0090] The specific surface area of ​​the hydrothermal carbon adsorbent in this embodiment is 52 m². 2 / g, with an adsorption rate of 80% for microplastics.

[0091] Comparative Example 3

[0092] Compared to Example 1, step 103 is omitted.

[0093] The specific surface area of ​​the primary hydrothermal carbon in this embodiment is 30 m². 2 / g, with an adsorption rate of 50% for microplastics.

[0094] Compared to Example 1, Comparative Example 1, which only used livestock and poultry manure as a substrate, yielded a hydrothermal carbon adsorbent with a specific surface area of ​​54 m². 2 / g, the adsorption rate of microplastics is 84%, which is lower than that of the sludge-based hydrothermal carbon adsorbent obtained in Example 1. This is mainly because the proteins and polysaccharides in sludge and the cellulose and lignin in feces jointly promote the formation of carbon skeleton and pore development. Subsequent activation treatment further expands the specific surface area and enriches the surface functional groups, enhancing the hydrophobic adsorption, pore capture and surface complexation of microplastics, and realizing the triple effect of "raw material synergy - process enhancement - performance improvement".

[0095] Compared to Example 1, Comparative Example 2, which only used sludge as a substrate, yielded a hydrothermal carbon adsorbent with a specific surface area of ​​52 m². 2 The adsorption rate of microplastics was 80% (g), which is lower than that of the sludge-based hydrothermal carbon adsorbent obtained in Example 1. This is mainly because the proteins and polysaccharides in sludge, together with the cellulose and lignin in feces, promote the formation of carbon skeleton and pore development. Subsequent activation treatment further expands the specific surface area and enriches the surface functional groups, enhancing the hydrophobic adsorption, pore trapping and surface complexation of microplastics, thus achieving a triple effect of "raw material synergy - process enhancement - performance improvement".

[0096] Compared to Example 1, Comparative Example 3 did not employ step 103 of Example 1, i.e., it did not undergo activation treatment, resulting in significantly lower performance. Therefore, activation treatment further expands the specific surface area, enriches surface functional groups, and enhances the hydrophobic adsorption, pore trapping, and surface complexation of microplastics.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics, characterized in that: Includes the following steps: Sewage sludge and livestock manure are dried to constant weight, crushed and passed through a 100-mesh sieve to obtain sludge base material and livestock manure base material. Sludge substrate and livestock and poultry manure substrate are mixed, deionized water is added, and hydrothermal reaction is carried out at 220-240℃. After cooling, filtration, drying and sieving, primary hydrothermal carbon is obtained. The primary hydrothermal carbon is mixed with an activator and transferred to a tube furnace. Under an inert atmosphere, the temperature is raised to 800-820℃ and held for 1-2 hours. After cooling, the mixture is placed in an acid solution and allowed to stand for 24-30 hours. The mixture is then separated, rinsed until neutral, and dried to obtain a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics.

2. The method for preparing sludge-based hydrothermal carbon adsorbent for adsorbing microplastics according to claim 1, characterized in that: The activator is one or more of NaOH, KOH, ZnCl2 or H3PO4.

3. The method for preparing sludge-based hydrothermal carbon adsorbent for adsorbing microplastics according to claim 1, characterized in that: The mass ratio of primary hydrothermal carbon to activator is 1:(3-4).

4. The method for preparing sludge-based hydrothermal carbon adsorbent for adsorbing microplastics according to claim 1, characterized in that: The mass ratio of sludge substrate to livestock and poultry manure substrate is (2-3):

1.

5. The method for preparing sludge-based hydrothermal carbon adsorbent for adsorbing microplastics according to claim 1, characterized in that: In the primary hydrothermal carbon preparation process, 0.1-1.0 mol / L of acid or base is added as a catalyst.

6. The method for preparing sludge-based hydrothermal carbon adsorbent for adsorbing microplastics according to claim 5, characterized in that: The acid is citric acid or oxalic acid, and the base is NaOH or KOH.

7. The method for preparing sludge-based hydrothermal carbon adsorbent for adsorbing microplastics according to claim 1, characterized in that: Livestock and poultry manure is one or more of pig manure, chicken manure, or cow manure.

8. The method for preparing sludge-based hydrothermal carbon adsorbent for adsorbing microplastics according to claim 1, characterized in that: The inert gas is argon; Argon gas was introduced and purged at a flow rate of 20 mL / min for 15 min, followed by a temperature increase to 800℃ at a rate of 10 ℃ / min.

9. A sludge-based hydrothermal carbon adsorbent obtained by the preparation method of a sludge-based hydrothermal carbon adsorbent for adsorbing microplastics as described in any one of claims 1-8.

10. An application of the sludge-based hydrothermal carbon adsorbent as described in claim 9 in the adsorption of microplastics.