A hydrothermal carbon-based composite material, its preparation method and application

Abstract

The present application belongs to the technical field of adsorbing materials, and particularly relates to a hydrothermal carbon-based composite material and a preparation method and application thereof. The present application provides a preparation method of a hydrothermal carbon-based composite material, comprising the following steps: first mixing a biomass raw material and a metal salt solution, performing a hydrothermal reaction to obtain hydrothermal carbon; second mixing the hydrothermal carbon, an active agent and water, and performing calcination treatment to obtain the hydrothermal carbon-based composite material. The present application uses biomass as a raw material, and prepares hydrothermal carbon by adding a metal salt through one-pot hydrothermal carbonization; then the hydrothermal carbon solid is mixed with an active agent, and after calcination, a hydrothermal carbon-based composite material with a multi-level pore structure can be obtained. The combination of hydrothermal treatment and activation can obtain a rich multi-level pore structure, which can significantly improve the specific surface area of the composite material and improve the adsorption effect on ammonium nitrogen.

Description

Technical Field

[0001] This invention belongs to the field of adsorption materials technology, specifically relating to a hydrothermal carbon-based composite material, its preparation method, and its application. Background Technology

[0002] Ammonium nitrogen, a form of ammonia nitrogen, is both a nutrient and a major pollutant in water bodies. Excessive ammonium nitrogen can cause eutrophication, which is harmful to humans, animals, and plants. Therefore, the removal of ammonium nitrogen from water bodies has long been a concern for various industries.

[0003] Currently, various methods have emerged for the removal of ammonium nitrogen, including chemical precipitation, aeration, biological nitrification and denitrification, membrane separation, and adsorption. Biological nitrification and denitrification are suitable for nitrogen-rich wastewater, but require long sludge retention times. Other physicochemical methods have drawbacks in terms of treatment efficiency, cost, and safety. Adsorption, due to its simple process, has attracted widespread attention. Commonly used adsorbents in current research include zeolite, activated carbon, biochar, diatomaceous earth, and ion exchange resins. Although these adsorbents have shown some effectiveness in ammonium nitrogen removal, the high cost of some products means that ammonium nitrogen removal methods require further exploration and development. In recent years, research on the preparation of hydrothermal carbon for adsorbing pollutants in wastewater using hydrothermal carbonization technology has emerged. However, the pollutants currently adsorbed by hydrothermal carbon are mainly heavy metals and organic matter. Studies have shown that hydrothermal carbon possesses abundant oxygen- and nitrogen-containing functional groups, which is a key factor affecting the performance of adsorbent materials. At the same time, hydrothermal carbon is also considered an environmentally friendly, inexpensive, and cost-effective adsorbent material, so its application in ammonium nitrogen adsorption has great potential.

[0004] However, the hydrothermal carbon produced by conventional hydrothermal carbonization processes can no longer meet the target requirements. Ammonium nitrogen cannot fully contact the hydrothermal carbon to achieve effective adsorption, resulting in reduced adsorption efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a hydrothermal carbon-based composite material, its preparation method, and its application. The hydrothermal carbon-based composite material prepared by the method provided by this invention has a high adsorption efficiency for ammonium nitrogen.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a hydrothermal carbon-based composite material, comprising the following steps:

[0008] Biomass raw materials and metal salt solution are first mixed and subjected to hydrothermal reaction to obtain hydrothermal carbon;

[0009] The hydrothermal carbon, activator, and water are mixed and calcined to obtain the hydrothermal carbon-based composite material.

[0010] Preferably, the biomass raw material includes one or more of corn stalks, rice stalks, and sorghum stalks;

[0011] The biomass raw material has a particle size of 40 mesh.

[0012] Preferably, the metal salt in the metal salt solution includes aluminum salt, magnesium salt, or iron salt;

[0013] The concentration of the metal salt solution is 0.5–1 mol / L;

[0014] The ratio of biomass raw material to metal salt solution is 1g:5-100mL.

[0015] Preferably, the temperature of the hydrothermal reaction is 160–260°C, and the holding time is 3–7 hours.

[0016] Preferably, the activator includes potassium carbonate and / or potassium bicarbonate.

[0017] Preferably, the mass ratio of the hydrothermal char to the activator is 1:0.5 to 3;

[0018] The ratio of hydrothermal char to water is 1g:30-150mL.

[0019] Preferably, the second mixing time is 0.5 to 4 hours;

[0020] The second mixing is carried out under stirring conditions, wherein the stirring speed is 60 to 500 rpm.

[0021] Preferably, the calcination temperature is 550–750°C, and the holding time is 1–2 hours.

[0022] The heating rate to the calcination temperature is 5°C / min.

[0023] The present invention also provides a hydrothermal carbon-based composite material prepared by the preparation method described above, wherein the hydrothermal carbon-based composite material has a hierarchical porous structure;

[0024] The specific surface area of ​​the hydrothermal carbon-based composite material is 300–600 m². 2 / g.

[0025] The present invention also provides the application of the hydrothermal carbon-based composite material described in the above technical solution in the adsorption of ammonium nitrogen.

[0026] This invention provides a method for preparing a hydrothermal carbon-based composite material, comprising the following steps: first, mixing biomass raw materials and a metal salt solution, and carrying out a hydrothermal reaction to obtain hydrothermal carbon; second, mixing the hydrothermal carbon, an activator, and water, and carrying out calcination to obtain the hydrothermal carbon-based composite material. This invention uses biomass as raw material and prepares hydrothermal carbon through a one-pot hydrothermal carbonization process by adding metal salts; then, the hydrothermal carbon solid is mixed with an activator, and after calcination, a multi-level porous hydrothermal carbon-based composite material is obtained. The combination of hydrothermal treatment and activation yields a rich multi-level porous structure, which can significantly increase the specific surface area of ​​the composite material. During the adsorption of ammonium nitrogen, the multi-level porous hydrothermal carbon-based adsorbent material mainly relies on the multi-level porous structure and the functional groups within the pores and on the surface of the hydrothermal carbon to exert its adsorption effect. Therefore, the composite material obtained by this invention has high adsorption performance for ammonium nitrogen in water; and it can rapidly and massively adsorb ammonium nitrogen in a short time, and is easily desorbed, making it suitable for rapid adsorption and desorption processes of ammonium nitrogen. Attached Figure Description

[0027] Figure 1 The graph shows the change in the adsorption effect of the hydrothermal carbon-based materials obtained in Examples 1-3 on ammonium nitrogen over time.

[0028] Figure 2 The graph shows the adsorption effect of the hydrothermal carbon-based material obtained in Example 2 on ammonium nitrogen at different addition amounts.

[0029] Figure 3 SEM images of the hydrothermal carbon-based adsorbent materials obtained in Examples 1-3 and Comparative Example 3;

[0030] Figure 4 The following are characterizations of the hydrothermal carbon-based adsorbent materials obtained in Examples 1-3 and Comparative Examples 3-5, where (a) is a nitrogen adsorption / desorption isotherm curve and (b) is the relationship between cumulative pore volume and pore size. Detailed Implementation

[0031] This invention provides a method for preparing a hydrothermal carbon-based composite material, comprising the following steps:

[0032] Biomass raw materials and metal salt solution are first mixed and subjected to hydrothermal reaction to obtain hydrothermal carbon;

[0033] The hydrothermal carbon, activator, and water are mixed and calcined to obtain the hydrothermal carbon-based composite material.

[0034] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0035] This invention involves first mixing biomass raw materials and a metal salt solution, and then carrying out a hydrothermal reaction to obtain hydrothermal carbon.

[0036] In this invention, the biomass raw material preferably includes one or more of corn stalks, rice stalks, and sorghum stalks. In this invention, the particle size of the biomass raw material is preferably 40 mesh.

[0037] Before mixing, the present invention preferably includes pretreatment of the biomass raw material; the pretreatment preferably includes sequential ash removal, air drying, crushing and sieving.

[0038] In this invention, the metal salt in the metal salt solution preferably includes aluminum salt, magnesium salt, or iron salt; the aluminum salt is more preferably aluminum chloride or aluminum sulfate. In this invention, the concentration of the metal salt solution is preferably 0.5–1 mol / L, more preferably 0.6–0.9 mol / L, and even more preferably 0.7–0.8 mol / L. In this invention, the ratio of the biomass raw material to the metal salt solution is preferably 1 g: 5–100 mL, more preferably 1 g: 20–80 mL, and even more preferably 1 g: 30–50 mL.

[0039] In this invention, the temperature of the hydrothermal reaction is preferably 160–260°C, more preferably 180–220°C, and even more preferably 200–220°C; the holding time is preferably 3–7 hours, more preferably 4–5 hours. In this invention, the hydrothermal reaction is preferably carried out under stirring conditions; the stirring speed is preferably 100–300 rpm. In this invention, the hydrothermal reaction is preferably carried out in a high-temperature, high-pressure reactor. After the hydrothermal reaction, this invention further preferably includes sequentially cooling, washing, filtering, and drying the obtained reaction solution; the cooling method is preferably natural cooling to room temperature; the filtering is preferably vacuum filtration; the drying process is preferably drying in an oven at 105°C for at least 6 hours.

[0040] After obtaining the hydrothermal carbon, the present invention mixes the hydrothermal carbon, activator and water, and performs calcination treatment to obtain the hydrothermal carbon-based composite material.

[0041] In this invention, the water is preferably purified water. In this invention, the active agent preferably includes potassium carbonate and / or potassium bicarbonate.

[0042] In this invention, the mass ratio of the hydrothermal char to the activator is preferably 1:0.5-3, more preferably 1:0.5-2, and even more preferably 1:1-2. In this invention, the amount ratio of the hydrothermal char to water is preferably 1g:30-150mL, more preferably 1g:60-120mL. In this invention, the second mixing time is preferably 0.5-4h, more preferably 1-3h. In this invention, the second mixing is preferably carried out under stirring conditions, and the stirring speed is preferably 60-500rpm.

[0043] Following the second mixing, the present invention preferably further includes drying the resulting liquid. The present invention does not specifically limit the drying process; any process well known to those skilled in the art can be used. In a specific embodiment of the present invention, the drying conditions are preferably: drying in an oven at 105°C for at least 6 hours.

[0044] In this invention, the calcination temperature is preferably 550–750°C, more preferably 600–680°C, and even more preferably 620–650°C; the holding time is 1–2 hours; and the heating rate to the calcination temperature is preferably 5°C / min. In this invention, the calcination is preferably carried out in a nitrogen atmosphere. In a specific embodiment of this invention, the nitrogen flow rate is preferably 120 mL / min. In this invention, the calcination is preferably carried out in a tube furnace.

[0045] Following the calcination treatment, the present invention preferably further includes sequentially cooling, washing with water, and drying the obtained material; the cooling method is preferably natural cooling to room temperature. The washing process is not particularly limited in the present invention; pure water is used for washing until the filtrate is clear and transparent. In the present invention, the drying method is preferably: drying in an oven at 105°C for at least 6 hours.

[0046] In this invention, the liquid obtained from the water washing process can be recycled as a raw material for hydrothermal reactions, which reduces costs and alleviates environmental pressure, providing a new approach for the green and sustainable production of hydrothermal carbon-based composite materials.

[0047] The present invention also provides a hydrothermal carbon-based composite material prepared by the preparation method described above, wherein the hydrothermal carbon-based composite material has a hierarchical porous structure.

[0048] In this invention, the specific surface area of ​​the hydrothermal carbon-based composite material is 300–600 m². 2 / g, further preferably 400-580m 2 / g, more preferably 500-550m 2 / g. In this invention, the hierarchical pore structure preferably includes a microporous structure, a mesoporous structure, and a macroporous structure; the pore volume ratio of the microporous structure, mesoporous structure, and macroporous structure is preferably 1:0.1-0.5:0.05-0.8, more preferably 1:0.2-0.4:0.1-0.7, and even more preferably 1:0.25-0.3:0.2-0.6.

[0049] The present invention also provides the application of the hydrothermal carbon-based composite material described in the above technical solution in the adsorption of ammonium nitrogen.

[0050] In this invention, the ammonium nitrogen is preferably ammonium chloride.

[0051] In this invention, the application process preferably includes:

[0052] The hydrothermal carbon-based composite material was mixed with a solution containing ammonium nitrogen. The container containing the mixture was placed in a shaker and shaken. The ammonium nitrogen content in the liquid was determined using an ultraviolet spectrophotometer.

[0053] In this invention, the concentration of the solution containing ammonium nitrogen is preferably p. N =100~1000mg / L.

[0054] In this invention, the preferred ratio of the hydrothermal carbon-based composite material to the solution containing ammonium nitrogen is 1g:150-3000mL.

[0055] In this invention, the shaking temperature is preferably 30°C, the shaking speed is preferably 150 rpm, and the shaking time is preferably 10 to 2880 min, more preferably 10 to 180 min.

[0056] In this invention, the detection process preferably includes:

[0057] The liquid obtained after shaking was drawn with a disposable needle, filtered through a 0.22μm needle filter and collected in a centrifuge tube. The ammonium nitrogen in the liquid was quantitatively determined by a UV spectrophotometer. The specific experimental steps and parameter settings were in accordance with the national standard method "HJ535-2009".

[0058] The present invention provides an effective method for modifying hydrothermal carbon. The modified hydrothermal carbon-based ammonium nitrogen adsorbent material has a significant hierarchical porous structure. This structure significantly increases the specific surface area of ​​the hydrothermal carbon and improves its adsorption performance for ammonium nitrogen in water. It can rapidly and massively adsorb ammonium nitrogen in a short time and is easy to desorb, making it suitable for rapid adsorption and desorption processes of ammonium nitrogen.

[0059] This invention uses abundant and inexpensive agricultural waste as raw material and prepares it into functional biomass-based hydrothermal char through a simple one-step method, which has significant environmental and social benefits.

[0060] To further illustrate the present invention, a hydrothermal carbon-based composite material, its preparation method, and its application are described in detail below with reference to the accompanying drawings and embodiments. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0061] Example 1

[0062] The corn stalks are deashed, air-dried and crushed, and then sieved through a 40-mesh screen to obtain pre-treated corn stalks.

[0063] 10g of pretreated corn stalks and 100mL of 0.5mol / L AlCl3 solution were placed in a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at a stirring rate of 200rpm and a temperature of 180℃ for 4h. After the reaction was completed, the reaction solution was naturally cooled to room temperature, washed with water and vacuum filtered, and then dried in an oven at 105℃ for more than 6h to obtain hydrothermal carbon.

[0064] Place 0.5g of hydrothermal charcoal and 1g of potassium bicarbonate in a beaker, add 60mL of purified water, and stir on a magnetic stirrer at room temperature for 4 hours at a stirring speed of 200rpm. After stirring, place in an oven at 105℃ to dry for more than 6 hours.

[0065] The dried material was placed in a tube furnace for calcination in a nitrogen atmosphere at a flow rate of 120 mL / min. The calcination temperature was 650℃, the heating rate was 5℃ / min, and the holding time was 1 h. The material was then naturally cooled to room temperature, rinsed with pure water, and dried in an oven at 105℃ for more than 6 h to obtain the hydrothermal carbon-based composite material (denoted as (CS+Al)-180-650).

[0066] Example 2

[0067] The corn stalks are deashed, air-dried and crushed, and then sieved through a 40-mesh screen to obtain pre-treated corn stalks.

[0068] 10g of pretreated corn stalks and 100mL of 0.5mol / L AlCl3 solution were placed in a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at a stirring rate of 200rpm and a temperature of 220℃ for 4h. After the reaction was completed, the reaction solution was naturally cooled to room temperature, washed with water and vacuum filtered, and then dried in an oven at 105℃ for more than 6h to obtain hydrothermal carbon.

[0069] Place 0.5g of hydrothermal charcoal and 1g of potassium bicarbonate in a beaker, add 60mL of purified water, and stir on a magnetic stirrer at room temperature for 4 hours at a stirring speed of 200rpm. After stirring, place in an oven at 105℃ to dry for more than 6 hours.

[0070] The dried material was placed in a tube furnace for calcination in a nitrogen atmosphere at a flow rate of 120 mL / min. The calcination temperature was 650℃, the heating rate was 5℃ / min, and the holding time was 1 h. The material was then allowed to cool naturally to room temperature. The modified carbon was rinsed with pure water and dried in an oven at 105℃ for more than 6 h to obtain the hydrothermal carbon-based composite material (denoted as (CS+Al)-220-650).

[0071] Example 3

[0072] The corn stalks are deashed, air-dried and crushed, and then sieved through a 40-mesh screen to obtain pre-treated corn stalks.

[0073] 10g of pretreated corn stalks and 100mL of 0.5mol / L AlCl3 solution were placed in a high-temperature and high-pressure reactor and subjected to hydrothermal reaction at a stirring rate of 200rpm and a temperature of 260℃ for 4h. After the reaction was completed, the resulting reaction solution was naturally cooled to room temperature, washed with water and vacuum filtered, and then dried in an oven at 105℃ for more than 6h to obtain hydrothermal carbon.

[0074] Place 0.5g of hydrothermal charcoal and 1g of potassium bicarbonate in a beaker, add 60mL of purified water, and stir on a magnetic stirrer at room temperature for 4 hours at a stirring speed of 200rpm. After stirring, place in an oven at 105℃ to dry for more than 6 hours.

[0075] The dried material was placed in a tube furnace for calcination in a nitrogen atmosphere at a flow rate of 120 mL / min. The calcination temperature was 650 °C, the heating rate was 5 °C / min, and the holding time was 1 h. The material was then allowed to cool naturally to room temperature. The modified carbon was rinsed with pure water and dried in an oven at 105 °C for more than 6 h to obtain the hydrothermal carbon-based composite material (denoted as (CS+Al)-260-650).

[0076] Comparative Example 1

[0077] The hydrothermal carbon-based material (denoted as CS-220) was prepared according to Example 2, except that the 0.5 mol / L AlCl3 solution was replaced with deionized water, and the hydrothermal carbon was not impregnated or calcined after preparation by the hydrothermal reaction.

[0078] Comparative Example 2

[0079] Corn stalks were dust-removed, air-dried, crushed, and sieved through a 40-mesh sieve to obtain pretreated corn stalks. 10g of the pretreated corn stalks were calcined under a nitrogen atmosphere at a flow rate of 120mL / min, a calcination temperature of 650℃, a heating rate of 5℃ / min, and a holding time of 1h. After calcination, the modified char was rinsed with pure water and dried to obtain pyrolytic char, designated CS-650.

[0080] Comparative Example 3

[0081] Hydrothermal carbon-based material (denoted as (CS+Al)-220) was prepared according to Example 2, except that after the hydrothermal reaction to prepare hydrothermal carbon, no impregnation and calcination reactions were carried out.

[0082] Comparative Example 4

[0083] The hydrothermal carbon-based material (denoted as CS-220-650) was prepared according to Example 2, except that the aluminum chloride solution in the hydrothermal carbonization process was replaced with deionized water.

[0084] Comparative Example 5

[0085] The hydrothermal carbon-based material (denoted as (CS+Al)-220-650 without KHCO3) was prepared according to Example 2, the difference being that the step of blending hydrothermal carbon with KHCO3 was reduced.

[0086] Performance testing

[0087] Test Example 1

[0088] The carbon materials obtained in Examples 1-3 and Comparative Examples 1-5, and pretreated corn stalks (denoted as CS) were used as adsorbents to verify the adsorption effect on ammonium nitrogen in water.

[0089] Weigh 0.1g of the above material and add it to 30mL of ammonium chloride (ρN=1000mg / L) solution. Place the conical flask in a shaker at 30℃ and shake at 150rpm for 180min. After shaking, draw up the liquid after the reaction through a disposable syringe, filter it through a 0.22μm syringe filter, and collect the liquid in a centrifuge tube.

[0090] The ammonium nitrogen content in the liquid was determined using Nessler's reagent spectrophotometry. The filtrate was diluted 100 times, and its absorbance was measured using a UV spectrophotometer. Before testing, Nessler's reagent and potassium sodium tartrate were added to mask other impurities. The ammonium nitrogen content was calculated using an ammonium nitrogen standard curve; specific testing procedures and parameter settings were referenced in the national standard method HJ535-2009.

[0091] The test results are shown in Table 1.

[0092] Table 1. Adsorption properties of carbon materials obtained in Examples 1-3 and Comparative Examples 1-5

[0093]

[0094] Table 1 shows that corn stalks, a biomass raw material, inherently possess a certain adsorption capacity for ammonium nitrogen (2.36 mg / g). After hydrothermal or calcination treatment, the adsorption performance of corn stalks for ammonium nitrogen is enhanced; the adsorption capacity of corn stalks after hydrothermal treatment is higher than that of pyrolytic char. Comparisons between CS-220 and (CS+Al)-220, and between CS-220-650 and (CS+Al)-220-650, highlight the importance of adding metals during the hydrothermal process. The regulation of the physicochemical properties of the char material by aluminum ions improves its overall adsorption performance. Further combining hydrothermal treatment with impregnation and oxygen-free calcination can further enhance its ammonium nitrogen adsorption performance. When the hydrothermal temperature is 180℃, the ammonium nitrogen adsorbent material already exhibits relatively excellent adsorption performance. As the hydrothermal temperature increases, the hydrothermal carbon-based adsorbent material prepared at 220℃ shows even better adsorption performance. However, when the hydrothermal temperature is further increased to 260℃, the adsorption performance of the prepared adsorbent material for ammonium nitrogen decreases significantly. The comparison between (CS+Al)-220-650 and (CS+Al)-220-650 without KHCO3 emphasizes the importance of KHCO3 impregnation for improving the adsorption performance of ammonium nitrogen. The comparison between (CS+Al)-220 and (CS+Al)-220-650 clarifies that impregnation combined with oxygen-free calcination is the key to significantly improving the adsorption performance of ammonium nitrogen. Therefore, the preparation process of the high-efficiency ammonium nitrogen adsorbent material mainly includes three steps: hydrothermal treatment, impregnation, and calcination, and each step is a major factor affecting the adsorption performance of ammonium nitrogen.

[0095] Test Example 2

[0096] Using the hydrothermal carbon-based composite materials obtained in Examples 1-3 as adsorbents, the adsorption effect of these materials on ammonium nitrogen in water over time was verified.

[0097] Weigh 0.1g of the above material and add it to 30mL of ammonium chloride (ρ). N In a 1000 mg / L solution, place the conical flask in a shaker at 30°C and shake at 150 rpm for 2880 min. After shaking, extract the reacted liquid using a disposable syringe, filter it through a 0.22 μm syringe filter, and collect the liquid in a centrifuge tube.

[0098] The ammonium nitrogen content in the liquid was determined using Nessler's reagent spectrophotometry. The filtrate was diluted 100 times, and its absorbance was measured using a UV spectrophotometer. Before testing, Nessler's reagent and potassium sodium tartrate were added to mask other impurities. The ammonium nitrogen content was calculated using an ammonium nitrogen standard curve; specific testing procedures and parameter settings were referenced in the national standard method HJ535-2009.

[0099] The obtained test results are shown in the figure below. Figure 1 As shown in Table 2;

[0100] Table 2 Adsorption properties of hydrothermal carbon-based composite materials obtained in Examples 1-3

[0101]

[0102] from Figure 1 As shown in Table 2, the hydrothermal carbon-based adsorbent material undergoes an adsorption and desorption process throughout the early stages of adsorption, resulting in a sawtooth-shaped decrease in its adsorption capacity for ammonium nitrogen. This indicates that the adsorbent material can rapidly adsorb ammonium nitrogen within a short period. However, due to the unstable adsorption, only a small amount of ammonium nitrogen can stably bind to the active sites, while a large amount of ammonium nitrogen undergoes repeated adsorption-desorption processes. Although this adsorbent material is unstable in its adsorption of ammonium nitrogen, it possesses the characteristics of rapid and large-scale adsorption of ammonium nitrogen within a short period and can autonomously desorb. This will solve the problems of many existing adsorbent materials being unable to be reused and potentially causing secondary pollution. Furthermore, the hydrothermal carbon-based adsorbent materials prepared at hydrothermal temperatures of 180 and 220℃ exhibit slightly better adsorption performance for ammonium nitrogen than those prepared at 260℃.

[0103] Test Example 3

[0104] Using the hydrothermal carbon-based material obtained in Example 2 as the adsorbent, the adsorption effect of different amounts of adsorbent added on ammonium nitrogen in water was verified.

[0105] Weigh 0.01–0.2 g of the above material and add it to 30 mL of ammonium chloride (ρ). N In a 1000 mg / L solution, place the conical flask in a shaker at 30°C and shake at 150 rpm for 180 min. After shaking, extract the reacted liquid using a disposable syringe, filter it through a 0.22 μm syringe filter, and collect the liquid in a centrifuge tube.

[0106] The ammonium nitrogen content in the liquid was determined using Nessler's reagent spectrophotometry. The filtrate was diluted 100 times, and its absorbance was measured using a UV spectrophotometer. Before testing, Nessler's reagent and potassium sodium tartrate were added to mask other impurities. The ammonium nitrogen content was calculated using an ammonium nitrogen standard curve; specific testing procedures and parameter settings were referenced in the national standard method HJ535-2009.

[0107] The obtained test results are shown in the figure below. Figure 2 As shown in Table 3;

[0108] Table 3 Adsorption performance of the hydrothermal carbon-based adsorbent material obtained in Example 2

[0109]

[0110] from Figure 2As shown in Table 3, the adsorption capacity of ammonium nitrogen increases with the increase of adsorbent material. When the amount of adsorbent material added is 0.2 g, the adsorption capacity of ammonium nitrogen increases to 41.55 mg / g, more than twice the adsorption capacity when the amount of adsorbent material added is 0.1 g. This is mainly because the more adsorbent material added, the more adsorption sites it carries, allowing ammonium nitrogen to bind rapidly. However, the current data results are inconsistent with many adsorption studies. Some studies indicate that as the amount of adsorbent material increases, the adsorption capacity of the target pollutant generally increases first and then decreases. This is because when the amount of adsorbent material added is too large, it will cause overlap of adsorption sites, affecting the diffusion of pollutants to the adsorbent material. However, in this study, no decreasing trend was observed. This may be because, in the adsorption system of this study, the amount of adsorbent material added at 0.2 g does not cause overlap of adsorption sites, and more adsorbent material may be needed to achieve a decrease in adsorption capacity. Figure 2 It can be inferred that (CS+Al)-220-650 has good dispersion in this system, or that (CS+Al)-220-650 carries relatively few adsorption sites that can bind to ammonium nitrogen, thus making it difficult for overlap to occur.

[0111] Test Example 4

[0112] The hydrothermal carbon-based composite materials obtained in Examples 1-3 and Comparative Example 3 were examined by scanning electron microscopy (SEM), and the resulting SEM images are shown below. Figure 3 As shown, from Figure 3 It can be seen that corn stalks, when treated hydrothermally only, form a large number of cross-linked carbon microspheres loaded on the undegraded solid structure. However, when hydrothermal treatment is combined with impregnation and calcination, the microstructure of the prepared carbon material undergoes a significant change. Firstly, the spherical shape of the carbon particles becomes more pronounced. For example, at a hydrothermal temperature of 180℃, the (CS+Al)-180-650 morphology is observed to be relatively regular, with larger carbon microspheres attached to the network structure formed by the cross-linking of nanoscale carbon microspheres. Simultaneously, numerous channels and pores are observed; some of these pores are due to CO2 produced by the decomposition of KHCO3 at high temperatures escaping from the structure. When the hydrothermal temperature rises to 220℃, the size of the spherical particles increases, and cross-linking relatively decreases. When the hydrothermal temperature is further increased to 260℃, plate-like metal clusters appear on the surface of the hydrothermal char. This structure is generated during the hydrothermal process. Because it covers the surface of the hydrothermal char during formation, it hinders pore formation during calcination and also prevents contact between active sites or functional groups within the pores and pollutants during adsorption, thus reducing the adsorption of ammonium nitrogen pollutants by the adsorbent material. In summary, this demonstrates that the combination of aluminum salt-assisted hydrothermal treatment, impregnation, and calcination can significantly improve the microstructure of biochar materials, forming distinct carbon microspheres and porous structures, which is beneficial for the adsorption of pollutants.

[0113] Test Example 5

[0114] Nitrogen isothermal adsorption tests were performed on the hydrothermal carbon-based adsorbents obtained in Examples 1-3 and Comparative Examples 3-5. The obtained nitrogen adsorption / desorption isotherm curves, cumulative pore volume versus pore size graphs, and specific surface area and pore structure parameters obtained by BET calculation are shown below. Figure 4 As shown in Tables 4 and 5;

[0115] Table 4 Specific surface area and pore structure parameters of hydrothermal carbon-based composite materials

[0116] sample <![CDATA[Specific surface area m 2 / g]]> <![CDATA[Pore volume cm 3 / g]]> Most probable aperture (nm) (CS+Al)-180-650 521.95 0.29 2.20 (CS+Al)-220-650 456.37 0.27 3.07 (CS+Al)-260-650 396.36 0.25 2.51 (CS+Al)-220 10.99 0.04 5.89 CS-220-650 229.05 0.16 3.29 <![CDATA[(CS + Al)-220 - 650 (without KHCO3 added)]]> 152.44 0.15 3.84

[0117] Table 5 Hierarchical Pore Structure Parameters of Hydrothermal Carbon-Based Composite Materials

[0118] sample Micropores: Mesopores: Macropores (pore volume) (CS+Al)-180-650 1:0.30:0.27 (CS+Al)-220-650 1:0.16:0.09 (CS+Al)-260-650 1:0.40:0.54 (CS+Al)-220 1:10.63:8.04 CS-220-650 1:0.23:0.17 <![CDATA[(CS + Al)-220 - 650 (without KHCO3 added)]]> 1:0.67:0.22

[0119] from Figure 4 As can be seen from Tables 4 and 5, after calcination, the specific surface area and pore volume of the carbon material are significantly increased, and the pore structure is mainly micropores and smaller mesopores. Figure 4 In (a), when P / P0 < 0.1, the microporous adsorption of the corresponding material is... Figure 4 Table 5 shows that hydrothermal carbon itself has relatively obvious mesoporous and macroporous structures, while the microporous structure of calcined carbon materials significantly increases, exhibiting a distinct hierarchical pore structure. Micropores can promote electron transfer, while mesopores and macropores are more conducive to molecular adsorption and diffusion. Furthermore, the abundant functional groups within the pores possess strong adsorption potential; therefore, the hierarchical pore structure is beneficial for the adsorption of pollutants. Table 4 reveals that carbon materials with better adsorption performance correspond to larger specific surface areas and pore volumes. On this basis, if the proportion of micropores increases, its adsorption performance will be further improved (corresponding to Table 5). Therefore, low-temperature aluminum salt-assisted hydrothermal reaction, combined with impregnation and calcination modification, can increase the specific surface area, pore volume, and exposed active sites of the material, while also optimizing the pore size distribution, increasing the micropore structure potential, and improving adsorption performance. This is an effective method for the preparation and modification of ammonium nitrogen adsorbent materials.

[0120] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a hydrothermal carbon-based composite material, characterized by, The method comprises the following steps: mixing a biomass raw material and a metal salt solution to perform a hydrothermal reaction to obtain a hydrothermal carbon, wherein the biomass raw material comprises one or more of corn stalks, rice stalks and sorghum stalks; mixing the hydrothermal carbon, an active agent and water to perform a calcination treatment to obtain the hydrothermal carbon-based composite material; the active agent comprises potassium carbonate and / or potassium bicarbonate; the calcination treatment is performed at a temperature of 550-750 ℃ for 1-2 h, the temperature is raised to the calcination treatment temperature at a rate of 5 ℃ / min, and the calcination treatment is performed in a nitrogen atmosphere; the hydrothermal carbon-based composite material has a hierarchical pore structure comprising microporous structure, mesoporous structure and macroporous structure, and the pore volume ratio of the microporous structure, mesoporous structure and macroporous structure is 1:0.1-0.5:0.05-0.

8.

2. The production method according to claim 1, characterized by, The particle size of the biomass raw material is 40 mesh.

3. The preparation method according to claim 1, characterized in that, The metal salt in the metal salt solution comprises an aluminum salt, a magnesium salt or an iron salt; the concentration of the metal salt solution is 0.5-1 mol / L; the use amount ratio of the biomass raw material to the metal salt solution is 1 g:5-100 mL.

4. The method of claim 1, wherein, The hydrothermal reaction is performed at a temperature of 160-260 ℃ for 3-7 h.

5. The preparation method according to claim 1, characterized in that, The mass ratio of the hydrothermal carbon to the active agent is 1:0.5-3; The use amount ratio of the hydrothermal carbon to water is 1 g:30-150 mL.

6. The method of claim 1, wherein, The second mixing is performed for 0.5-4 h; The second mixing is performed under stirring at a stirring speed of 60-500 rpm.

7. The hydrothermal carbon-based composite material produced by the production process according to any one of claims 1 to 6, characterized by The hydrothermal carbon-based composite material has a hierarchical pore structure; The hydrothermal carbon-based composite has a specific surface area of 300-600 m 2 / g.

8. Application of the hydrothermal carbon-based composite material of claim 7 to adsorption of ammonium nitrogen.

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