A modified tea stem hydrothermal charcoal, its preparation method, and its application in removing Cr(VI) from water.

Abstract

This invention discloses a modified tea stem hydrothermal char, its preparation method, and its application in removing Cr(VI) from water. The invention first involves uniformly mixing tea stem powder, sodium hydroxide, and an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride in an aqueous solution. Then, a simple one-step hydrothermal amination method is used to prepare modified tea stem hydrothermal char with a surface rich in quaternary ammonium groups, carboxyl groups, and hydroxyl groups. This modified char serves as an adsorbent for Cr(VI) in water, achieving an adsorption capacity of 240.85 mg / g for Cr(VI) in water. ‑1 The adsorption equilibrium time is 24 hours. It can be used in the treatment of Cr(VI)-containing wastewater. The preparation method of this invention has the advantages of simple process, abundant raw materials, low cost, and large-scale production. It also opens up new avenues for the resource utilization of tea stems, realizing waste-to-waste treatment.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and heavy metal removal technology, specifically to a modified tea stem hydrothermal char, its preparation and application in removing Cr(VI) from water. Background Technology

[0002] With rapid industrial development, the scale and scope of industrial activities such as electroplating, metallurgy, and dyeing have increased. Because these industries widely use the heavy metal chromium (Cr), they generate large amounts of chromium-containing wastewater. Therefore, the indiscriminate discharge of chromium-containing wastewater has become a growing global environmental concern. Chromium exists in water primarily in the forms of Cr(VI) and Cr(III). Cr(VI) can induce carcinogenesis and mutations, and ingestion by humans can cause acute and chronic toxicity, leading to symptoms such as vomiting, nausea, and diarrhea, and damaging internal organs, especially the liver and kidneys. Therefore, the concentration of Cr(VI) must be reduced to below 0.05 mg / L, as recommended by the World Health Organization, before wastewater discharge to prevent serious harm to human health and the ecological environment. Currently, various technologies are applied to remove Cr(VI) from wastewater, including chemical precipitation, ion exchange, membrane separation, and adsorption. Adsorption methods have been widely used due to their ease of operation, low energy consumption, and recyclability. However, traditional adsorbents are mainly coal-based activated carbon, which faces problems such as insufficient adsorption capacity and raw material shortage. There is an urgent need to develop new adsorbents that are high-performance, sustainable, green, environmentally friendly, and economical.

[0003] Hydrothermal char is a solid product obtained by hydrothermal carbonization of low-cost biomass precursors such as agricultural and forestry waste and animal manure at 150℃–350℃. Hydrothermal char possesses advantages such as low cost, low energy consumption, environmental friendliness, and abundant oxygen-containing functional groups on its surface. However, the lack of binding sites for anionic pollutants on its surface limits its application in adsorption. To improve the adsorption performance of hydrothermal char, researchers have utilized the abundant hydroxyl and carboxyl functional groups on its surface as reaction sites for further functionalization modification. Studies have shown that grafting amino and carboxyl functional groups onto the surface of hydrothermal char can significantly enhance its adsorption capacity for heavy metals. However, currently widely used functionalization modification methods, such as post-grafting and chemical oxidation, suffer from drawbacks such as cumbersome processing, difficulty in purification, and high costs. Further research is needed to find suitable modifiers, simplify the modification process, and prepare efficient and low-cost functionalized hydrothermal char.

[0004] my country boasts the world's largest tea industry. According to data from the National Bureau of Statistics, my country's tea production reached 3.35 million tons in 2022, showing a year-on-year increasing trend. Tea stems are the most significant waste product in tea production, accounting for 20% of the total output. Composed of cellulose, hemicellulose, lignin, polyphenolic compounds, and water, tea stems possess a certain porous structure and hold promise for development as a novel adsorbent. Currently, the utilization rate of tea stems is low, with most being disposed of through incineration and landfill, resulting in serious resource waste and environmental pollution. Summary of the Invention

[0005] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide a modified tea stem hydrothermal char, its preparation method, and its application in removing Cr(VI) from water. This invention successfully grafts quaternary ammonium groups onto the surface of hydrothermal char using a simple one-step hydrothermal method. Furthermore, it increases the number of active sites such as carboxyl and hydroxyl groups on the surface of the hydrothermal char, significantly enhancing its ability to remove Cr(VI) from water. This solves the problems of complex and costly existing functional modification processes for hydrothermal char, as well as the low utilization rate of tea stem resources.

[0006] This invention provides the following technical solution:

[0007] This invention provides a method for preparing modified tea stem hydrothermal charcoal, comprising the following steps:

[0008] (1) Dissolve tea stem powder in water, then add alkali and quaternary ammonium modifier to obtain a well mixed solution;

[0009] (2) The uniformly mixed solution is subjected to hydrothermal carbonization reaction, and after cooling, filtration, washing, drying and sieving, the modified tea stem hydrothermal carbon is obtained.

[0010] Preferably, the alkali in step (1) is sodium hydroxide; the quaternizing modifier is an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride with a mass fraction of 60±10%.

[0011] Preferably, the ratio of tea stem powder to water in step (1) is (5-20) g: 100 mL; the mass ratio of tea stem powder to alkali is 1: (0.1-0.2); and the mass ratio of tea stem powder to quaternization modifier is 1: (0.5-3).

[0012] Preferably, the stirring time in step (1) is 1 to 2 hours; the mesh size of the tea stem powder is 60 to 100 mesh; the temperature of the hydrothermal carbonization reaction in step (2) is 180 to 260°C; and the time is 2 to 8 hours.

[0013] More preferably, the temperature of the hydrothermal carbonization reaction in step (2) is 220°C and the time is 4 hours.

[0014] Preferably, the filtration in step (2) is vacuum filtration, and the filter is washed 3 to 4 times with water and anhydrous ethanol during the filtration process; the drying is carried out at 80±10℃ for 24±8h; and the sieving is carried out through an 80 to 100 mesh sieve.

[0015] The present invention also provides a modified tea stem hydrothermal char prepared by the above preparation method.

[0016] The present invention also provides an application of the above-mentioned modified tea stem hydrothermal charcoal, which is used as an adsorbent to remove heavy metal pollutants in water.

[0017] Preferably, the heavy metal pollutant is Cr(VI).

[0018] The present invention also provides a method for removing Cr(VI) from water, comprising the following steps:

[0019] The concentration was 0.4–0.8 g·L⁻¹ -1 The modified tea stem hydrothermal charcoal of claim 7 is added to a solution containing Cr(VI) at a concentration of 1–100 mg·L⁻¹. -1 In water, the pH of the solution was adjusted to 2±1, the temperature was set to 303~323K, and the adsorbent was filtered out after 24~48h of adsorption.

[0020] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0021] This invention selects tea stems, which are abundant in quantity, as raw material, and uses 60 wt% of an industrially produced and inexpensive aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride as a modifier. A one-step hydrothermal amination method is used to synthesize modified tea stem hydrothermal char rich in quaternary ammonium groups, carboxyl groups, hydroxyl groups, and other active sites. The preparation method of this invention is characterized by its simple process, abundant raw materials, low cost, and scalability. It also opens up new avenues for the resource utilization of tea stems, achieving waste-to-waste treatment. The modified tea stem hydrothermal char prepared by this invention exhibits a highly efficient removal capacity for Cr(VI) in water, with a maximum adsorption capacity reaching 240.85 mg·g⁻¹. -1 . Attached Figure Description

[0022] Figure 1 The graph shows the adsorption capacity of Cr(VI) in water by the quaternized modified tea stem hydrothermal carbon prepared in Examples 1-11, the tea stem hydrothermal carbon prepared in Comparative Example 1, and commercial activated carbon (AC).

[0023] Figure 2 The effect of pH on the adsorption of Cr(VI) by the quaternized modified tea stem hydrothermal char prepared in Example 10.

[0024] Figure 3The adsorption isotherms and Langmuir and Freundlich model fitting curves of the quaternized modified tea stem hydrothermal carbon prepared in Example 10 for Cr(VI) adsorption test.

[0025] Figure 4 The adsorption kinetics, pseudo-first-order kinetics, and pseudo-second-order kinetics model fitting curves of Cr(VI) adsorption test of the quaternized modified tea stem hydrothermal carbon prepared in Example 10 are shown.

[0026] Figure 5 Zeta potential test graphs of the quaternized ammonium-modified hydrothermal char of tea stem prepared in Example 10 and the hydrothermal char of tea stem prepared in Comparative Example 1 under different pH conditions.

[0027] Figure 6 Infrared spectra of the quaternized modified tea stem hydrothermal char prepared in Example 10, the quaternized modified tea stem hydrothermal char prepared in Example 10 after adsorbing Cr(VI), the tea stem hydrothermal char prepared in Comparative Example 1, and tea stem powder.

[0028] Figure 7 The N2 adsorption-desorption curves of the quaternized modified tea stem hydrothermal char prepared in Example 10 (Figure b) and the tea stem hydrothermal char prepared in Comparative Example 1 (Figure a).

[0029] Figure 8 The XPS full spectrum (Figure a) and C1s fine spectrum (Figure b) of the hydrothermal char of quaternized modified tea stem prepared in Example 10 were obtained by XPS testing. The full spectrum (Figure c) and C1s fine spectrum (Figure d) of the hydrothermal char of tea stem prepared in Comparative Example 1 were obtained by XPS testing.

[0030] Figure 9 The full spectrum (Fig. a), fine Cr2p spectrum (Fig. b), and fine O1s spectrum (Fig. c) obtained by XPS testing of the quaternized modified tea stem hydrothermal char prepared in Example 10 after adsorption of Cr(VI), and the fine O1s spectrum (Fig. d) obtained by XPS testing of the quaternized modified tea stem hydrothermal char prepared in Example 9.

[0031] Figure 10 SEM images of the quaternized modified tea stem hydrothermal char prepared in Example 10 (Figure b) and the tea stem hydrothermal char prepared in Comparative Example 1 (Figure a).

[0032] Figure 11 The changes in the Cr(VI) solution before and after adsorption were observed in the adsorption test experiment of Cr(VI) on the quaternized modified tea stem hydrothermal carbon prepared in Example 10. Detailed Implementation

[0033] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0034] Unless otherwise specified in the embodiments of this invention, the conditions shall be performed according to conventional conditions or conditions recommended by the manufacturer. All raw materials and reagents used, unless otherwise specified, are commercially available conventional products.

[0035] Example 1

[0036] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 10g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 96g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 220℃ for 2 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternized ammonium-modified tea stem hydrothermal carbon, named TSH2N6-220.

[0037] Example 2

[0038] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 10g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 96g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 220℃ for 4 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified tea stem hydrothermal carbon, named TSH4N6-220.

[0039] Example 3

[0040] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 10g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 96g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 220℃ for 6 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified tea stem hydrothermal carbon, named TSH6N6-220.

[0041] Example 4

[0042] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 10g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 96g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 220℃ for 8 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternized ammonium-modified tea stem hydrothermal carbon, named TSH8N6-220.

[0043] Example 5

[0044] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 10g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 96g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 180℃ for 4 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified tea stem hydrothermal carbon, named TSH8N6-180.

[0045] Example 6

[0046] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 10g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 96g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 200℃ for 4 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified hydrothermal carbon of tea stem, named TSH8N6-200.

[0047] Example 7

[0048] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 10g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 96g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 240℃ for 4 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified tea stem hydrothermal carbon, named TSH8N6-240.

[0049] Example 8

[0050] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 15g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 94g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 220℃ for 4 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified tea stem hydrothermal carbon, named TSH4N9-220.

[0051] Example 9

[0052] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 20g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 92g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 220℃ for 4 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified tea stem hydrothermal carbon, named TSH4N12-220.

[0053] Example 10

[0054] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 25g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 90g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 220℃ for 4 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified tea stem hydrothermal carbon, named TSH4N15-220.

[0055] Example 11

[0056] 10g of tea stem powder was dissolved in a mixed solution of 2g sodium hydroxide, 30g 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (60wt%), and 88g deionized water. After stirring for 1 hour, the solution was transferred to a hydrothermal reactor and hydrothermally carbonized at 220℃ for 4 hours. After the reaction was completed, the solution was naturally cooled to room temperature and washed three times alternately with deionized water and anhydrous ethanol. The solution was then dried in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve was the quaternary ammonium-modified hydrothermal carbon of tea stem, named TSH4N18-220.

[0057] Comparative Example 1

[0058] Dissolve 10g of tea stem powder in 100g of deionized water solution, stir for 1 hour, transfer to a hydrothermal reactor, and hydrothermally carbonize at 220℃ for 4 hours. After the reaction is complete, allow it to cool naturally to room temperature, wash it three times alternately with deionized water and anhydrous ethanol, and dry it in a drying oven at 80℃ for 24 hours. The black powder obtained after grinding through a 100-mesh sieve is the tea stem hydrothermal carbon, named TSH4-220.

[0059] Effect verification:

[0060] Cr(VI) adsorption capacity test: The quaternized ammonium-modified hydrothermal carbon of tea stems prepared in Examples 1-11, the hydrothermal carbon of tea stems prepared in Comparative Example 1, and commercial activated carbon (AC) were tested under the following conditions: pH=2, adsorption time=24h, adsorption temperature=313K, and initial Cr(VI) concentration in water=100mg·L⁻¹. -1 The adsorbent dosage is 0.4 g·L. -1 The adsorption capacity of the adsorbent for Cr(VI) was tested under the adsorption test conditions, and the adsorption amount of the adsorbent for Cr(VI) was calculated using the following formula:

[0061]

[0062] Where W represents the amount of adsorbent added (mg); V represents the volume of the Cr(VI) solution (L); Ce and C0 are the equilibrium and initial concentrations of Cr(VI) (mg·L⁻¹), respectively. -1 ).

[0063] The results are as follows Figure 1 As shown, the quaternized ammonium-modified hydrothermal activated carbon from tea stalks significantly improved the adsorption capacity of Cr(VI) compared to both hydrothermal activated carbon from tea stalks and commercial activated carbon (AC). Specifically, in Comparative Example 1, the sample named TSH4-220 achieved an adsorption capacity of 60.42 mg·g⁻¹. -1 The adsorption capacity of commercial activated carbon (AC) reached 128.26 mg·g. -1 The optimal modification conditions were those in Example 10, where the adsorption capacity of the sample named TSH4N15-220 was 240.85 mg·g. -1 It is 3.98 times that of TSH4-220 and 1.88 times that of commercial activated carbon (AC).

[0064] The effect of pH on the adsorption of Cr(VI) by the quaternized modified tea stem hydrothermal char prepared in Example 10 was further investigated. The adsorption test conditions were: solution pH = 2-12, adsorption time = 24 h, adsorption temperature = 313 K, initial concentration of Cr(VI) in water = 100 mg·L⁻¹, and adsorbent dosage = 0.4 g·L⁻¹. -1 The result is as follows Figure 2 As shown.

[0065] Further research was conducted on the adsorption isotherms and Langmuir and Freundlich model fitting curves of Cr(VI) adsorption tests on the quaternized ammonium-modified tea stem hydrothermal char prepared in Example 10. The adsorption test conditions were: solution pH = 2, adsorption time = 24 h, adsorption temperature = 313–323 K, initial Cr(VI) concentration in water = 100–600 mg·L⁻¹, and adsorbent dosage = 0.4 g·L⁻¹. -1 The adsorption amount is calculated using the following formula:

[0066]

[0067] Where K L q represents Langmuir's constant. m The theoretical saturated adsorption capacity (mg·g) -1 );

[0068]

[0069] Where n and K F It is related to adsorption strength and adsorption capacity, respectively; qm represents the theoretical saturated adsorption capacity (mg·g). -1 ).

[0070] The results are as follows Figure 3 As shown in Table 1, the relevant model parameters are presented. The Freundlich model has a high correlation coefficient R0. 2 The modified tea stem hydrothermal char can better fit the test data, indicating that the adsorption of Cr(VI) by the modified tea stem hydrothermal char is a multi-layered process. In addition, the equilibrium adsorption capacity of the modified tea stem hydrothermal char increases with increasing temperature, indicating that the adsorption is an endothermic process, and 1 / n is much less than 1, indicating that the adsorption is easy to carry out.

[0071] Table 1. Parameters related to the Langmuir and Freundlich models.

[0072]

[0073] Further investigation was conducted on the adsorption kinetics, pseudo-first-order kinetics, and pseudo-second-order kinetics fitting curves of Cr(VI) adsorption by the quaternized ammonium-modified tea stem hydrothermal char prepared in Example 10. The adsorption test conditions were: solution pH = 2, adsorption time = 24 h, adsorption temperature = 313 K, initial Cr(VI) concentration in water = 100 mg·L⁻¹, and adsorbent dosage = 0.4 g·L⁻¹. -1 The adsorption amount is calculated using the following formula:

[0074]

[0075] k1(min -1 ) represents the rate constant of the pseudo-first-order dynamic model, qt and q e Representing time t and the adsorption amount (mg·g) at equilibrium, respectively. -1 );

[0076]

[0077] Where k2(mg·g) -1 ·min -1 ) represents the rate constant of the quasi-second-order dynamic model, q t and q e Representing time t and the adsorption amount (mg·g) at equilibrium, respectively. -1 ).

[0078] The results are as follows Figure 4 As shown in Table 2, the relevant model parameters are also presented. The quasi-second-order dynamic model has a high correlation coefficient R0. 2 Meanwhile, based on the quasi-second-order dynamic model equation, q e The values ​​are also closer to the experimental values. This indicates that the pseudo-second-order kinetic model can more accurately explain the adsorption process, which is a chemisorption process.

[0079] Table 2. Relevant parameters of the pseudo-first-order and pseudo-second-order dynamical models.

[0080]

[0081] Figure 5 The Zeta potential test graphs of the quaternized ammonium-modified hydrothermal char of tea stems prepared in Example 10 and the hydrothermal char of tea stems prepared in Comparative Example 1 are shown under different pH conditions. It can be observed that the Zeta potential of TSH4N15-220 increased by 37.45 mV compared to TSH4-220 at pH=2. [pH] IEP The increase of 2.8 indicates that quaternization modification can significantly enhance the electropositivity of the hydrothermal carbon surface and improve its adsorption capacity for Cr(VI).

[0082] The hydrothermal charcoal of tea stems was characterized and analyzed by scanning electron microscopy, infrared spectroscopy, BET, XPS, and SEM.

[0083] Figure 6 The infrared spectra of the quaternized modified tea stem hydrothermal char prepared in Example 10, the quaternized modified tea stem hydrothermal char prepared in Example 10 after adsorbing Cr(VI), the tea stem hydrothermal char prepared in Comparative Example 1, and the tea stem powder show that -N(CH3) appears in TSH4N15-220. + Symmetric deformation vibration of CN in the group (1300 cm) -1 ) and stretching vibration (1390cm) -1A new signal was observed, indicating that quaternary ammonium groups were successfully grafted onto the surface of hydrothermal carbon, with a characteristic absorption peak (3430 cm⁻¹) at the active site of TSH4N15-220. -1 1610cm -1 The adsorption peaks of TSH4N15-220-Cr were all sharper than those of TSH4-220, indicating that the modification effectively increased the number of active groups on the hydrothermal carbon surface. After adsorption, TSH4N15-220-Cr showed sharper adsorption peaks at 526, 808, and 912 cm⁻¹. -1 Some new absorption peaks appeared at the Cr(VI)-O, Cr(III)-OH and Cr(VI)-O respectively, indicating that there are a large number of active sites on the surface of the quaternized modified hydrothermal carbon, which can partially reduce Cr(VI) ions to Cr(III), and Cr(III) ions are also adsorbed on the surface of the quaternized modified hydrothermal carbon.

[0084] Figure 7 The N2 adsorption-desorption curves are shown for the quaternized ammonium-modified hydrothermal char of tea stems prepared in Example 10 (Figure b) and the hydrothermal char of tea stems prepared in Comparative Example 1 (Figure a). The specific surface area of ​​TSH4N15-220 is 28.35 m². 2 ·g -1 The porosity is 0.1840 cm·g -1 The specific surface area of ​​TSH4-220 is only 6.81 m². 2 ·g -1 The porosity is only 0.0512 cm·g. -1 .

[0085] Figure 8 The XPS full spectrum (Figure a) and C1s fine spectrum (Figure b) of the hydrothermal char prepared by quaternized ammonium modification of tea stems in Example 10 were obtained by XPS testing. The XPS full spectrum (Figure c) and C1s fine spectrum (Figure d) of the hydrothermal char prepared by Comparative Example 1 of tea stems were obtained by XPS testing. The results show that the nitrogen content of TSH4N15-220 was increased to 2.43%. In addition, compared with TSH4-220, the CN / CO and O=CO contents of TSH4N15-220 increased, indicating that the quaternization modification was successful and could effectively increase the number of active groups such as hydroxyl and carboxyl groups on the surface of the hydrothermal char.

[0086] Figure 9The XPS spectra obtained from the quaternized modified tea stem hydrothermal char prepared in Example 10 after adsorption of Cr(VI) are shown in Figure a (full spectrum), Cr2p fine spectrum (Figure b), and O1s fine spectrum (Figure c), as well as the O1s fine spectrum obtained from the quaternized modified tea stem hydrothermal char prepared in Example 9 (Figure d). A Cr(III) peak can be observed in the Cr2p region after adsorption. Comparing the O1s XPS spectra before and after adsorption with TSH4N15-220, it can be found that the C=O content significantly increases and the OH content significantly decreases after adsorption, indicating that the active sites such as hydroxyl groups introduced by the quaternized modified tea stem hydrothermal process can reduce the Cr(VI) portion to Cr(III).

[0087] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An application of modified tea stem hydrothermal charcoal as an adsorbent for removing heavy metal pollutant Cr(VI) from water, characterized in that, The preparation method of the modified tea stem hydrothermal charcoal includes the following steps: (1) Dissolve tea stem powder in water, then add alkali and quaternization modifier to obtain a uniformly mixed solution; (2) The uniformly mixed solution is subjected to hydrothermal carbonization reaction, and the modified tea stem hydrothermal carbon is obtained after cooling, filtration, washing, drying and sieving. The quaternizing modifier in step (1) is an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride, and the mass fraction of the aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 60%; the alkali in step (1) is sodium hydroxide; In step (1), the mass ratio of tea stem powder to alkali is 1:0.2; the mass ratio of tea stem powder to quaternizing modifier is 1:2.

5. The temperature of the hydrothermal carbonization reaction in step (2) is 220℃; the time is 4h.

2. The application according to claim 1, characterized in that, The ratio of tea stem powder to water in step (1) is 1g:9g.

3. The application according to claim 1, characterized in that, The tea stem powder in step (1) has a mesh size of 60~100 mesh.

4. The application according to claim 1, characterized in that, The filtration in step (2) is vacuum filtration, and the filter is washed with water and anhydrous ethanol alternately 3 to 4 times during the filtration process; the drying is done at 80±10℃ for 24±8h; the sieving is done through an 80 to 100 mesh sieve.

5. A method for removing Cr(VI) from water, characterized in that, Follow these steps: At a concentration of 0.4–0.8 g·L -1 Modified tea stem hydrothermal charcoal was added to a solution containing Cr(VI) concentration of 1–100 mg·L⁻¹. -1 In water, the pH of the solution was adjusted to 2±1, the temperature was 303~323K, and after adsorption for 24~48h, the adsorbent was filtered out. The preparation method of the modified tea stem hydrothermal charcoal includes the following steps: (1) Dissolve tea stem powder in water, then add alkali and quaternization modifier to obtain a uniformly mixed solution; (2) The uniformly mixed solution is subjected to hydrothermal carbonization reaction, and the modified tea stem hydrothermal carbon is obtained after cooling, filtration, washing, drying and sieving. The quaternizing modifier in step (1) is an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride, and the mass fraction of the aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride is 60%; the alkali in step (1) is sodium hydroxide; In step (1), the mass ratio of tea stem powder to alkali is 1:0.2; the mass ratio of tea stem powder to quaternizing modifier is 1:2.

5. The temperature of the hydrothermal carbonization reaction in step (2) is 220℃; the time is 4h.

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