An ammonia-modified porous carbon adsorbent and its preparation method

Abstract

This invention relates to the field of adsorbent preparation technology, and in particular to an ammonia-modified porous carbon adsorbent and its preparation method. The preparation method of the ammonia-modified porous carbon adsorbent includes the following steps: hydrothermal acid leaching of gasification fine slag with an acid solution to obtain an acid leaching residue; stirring the acid leaching residue in an alkaline solution, followed by washing and drying to obtain a porous carbon material; and immersing the porous carbon material in a tetraethylenepentamine solution, followed by drying to obtain the ammonia-modified porous carbon adsorbent. This invention uses porous carbon material derived from coal gasification fine slag as a substrate and further employs a surface ammonia functionalization modification strategy to successfully construct an ammonia-modified porous carbon adsorbent. The preparation method of this invention is simple, the raw materials are readily available, and the prepared ammonia-modified porous carbon adsorbent has good adsorption effects on methylene blue and hexavalent chromium. This invention not only realizes the high-value-added resource utilization of coal gasification solid waste but also provides a solution for the treatment of dye wastewater and heavy metal wastewater.

Description

Technical Field

[0001] This invention relates to the field of adsorbent preparation technology, and in particular to an ammonia-modified porous carbon adsorbent and its preparation method. Background Technology

[0002] Coal gasification technology, a core process in coal chemical industry, generates gasification slag, which accounts for over 95% of the industry's total solid waste. Currently, this type of solid waste is mainly disposed of through open-air stockpiling. Large-scale stockpiling not only occupies land resources but also causes environmental problems such as dust and water pollution. Analysis shows that coal gasification slag mainly contains metal oxides such as SiO2, CaO, and Al2O3, as well as residual carbon. Therefore, promoting the resource utilization of coal gasification slag has become a key path to solving environmental problems and achieving comprehensive utilization of solid waste.

[0003] The treatment of organic pollutants and heavy metal wastewater resulting from rapid industrial development has become a major environmental challenge. Studies show that residual organic dyes such as methylene blue (MB) in industrial wastewater not only possess biotoxicity but also pose a carcinogenic risk; while hexavalent chromium (Cr(VI)), as a strong oxidizing heavy metal pollutant, has had its mutagenic and carcinogenic properties confirmed by numerous toxicological studies. Among the current mainstream technologies for treating these pollutants, such as adsorption, membrane separation, and biodegradation (suitable for low-concentration wastewater), adsorption stands out as the most promising treatment solution due to its advantages of simple operation, high removal efficiency, and low risk of secondary pollution. This drives the academic community to continuously explore low-cost, high-performance adsorption materials. Summary of the Invention

[0004] Based on the above, this invention provides an ammonia-modified porous carbon adsorbent and its preparation method. The ammonia-modified porous carbon adsorbent of this invention exhibits good adsorption effects on MB and Cr(VI), while simultaneously realizing the resource utilization of coal gasification slag.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] One of the technical solutions of this invention is a method for preparing an ammonia-modified porous carbon adsorbent, comprising the following steps:

[0007] The gasification residue is subjected to hydrothermal acid leaching with an acid solution to obtain acid leaching residue;

[0008] The acid leaching residue was stirred in an alkaline solution, washed, and dried to obtain a porous carbon material.

[0009] The porous carbon material is impregnated in a tetraethylenepentamine solution and then dried to obtain the ammonia-modified porous carbon adsorbent.

[0010] In a preferred embodiment of the present invention, the acid solution is an HNO3 solution with a concentration of 2 mol / L.

[0011] The second technical solution of the present invention is an ammonia-modified porous carbon adsorbent prepared according to the above preparation method.

[0012] The present invention discloses the following technical effects:

[0013] This invention uses porous carbon material (CSM) derived from coal gasification fine slag as a substrate and further employs a surface ammonia functionalization modification strategy to successfully construct an ammonia-modified porous carbon adsorbent (CSM-TY).

[0014] The preparation method of this invention is simple, the raw materials are readily available, and the prepared ammonia-modified porous carbon adsorbent has good adsorption effect on MB and Cr(VI).

[0015] This invention not only realizes the high-value-added resource utilization of coal gasification solid waste, but also provides a solution for the treatment of dye wastewater and heavy metal wastewater. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the process flow for preparing ammonia-modified porous carbon adsorbent according to the present invention.

[0018] Figure 2 The XRD patterns of CSM and CSM-TY (Y = 5wt%, 10wt%, 20wt%, 30wt%, 50wt%, corresponding to CSM-T5%, CSM-T10%, CSM-T20%, CSM-T30%, CSM-T50%) of the present invention are shown.

[0019] Figure 3 The FTIR spectra of the CSM and CSM-TY of this invention are shown.

[0020] Figure 4 The XPS analysis results for CSM and CSM-TY of this invention are shown.

[0021] Figure 5 This is the C1s fine spectrum of the CSM and CSM-TY of this invention.

[0022] Figure 6 The N1s fine spectrum of CSM and CSM-TY of this invention.

[0023] Figure 7 This is the O1s fine spectrum of CSM and CSM-TY of the present invention.

[0024] Figure 8 The images are scanning electron microscope (SEM) images of the CSM and CSM-TY of the present invention; wherein, (a) is CSM, (b) is CSM-T5%, (c) is CSM-T10%, (d) is CSM-T20%, (e) is CSM-T30%, and (f) is CSM-T50%.

[0025] Figure 9 The N2 adsorption-desorption curves and pore size distribution curves of CSM and CSM-TY (Y = 5wt%, 10wt%, 20wt%) of the present invention are shown; wherein, (a) is the N2 adsorption-desorption curve and (b) is the pore size distribution curve.

[0026] Figure 10 The adsorption effects of CSM and CSM-TY on 200 mg / L MB and 50 mg / L Cr(VI) under conditions where the pH of the system was not adjusted.

[0027] Figure 11 The effect of initial MB concentration on the adsorption capacity and removal rate of CSM-T5% under room temperature conditions is shown.

[0028] Figure 12 The effect of initial Cr(VI) concentration on the adsorption capacity and removal rate of CSM-T5% under room temperature conditions is shown.

[0029] Figure 13 The changes in the adsorption capacity and removal efficiency of CSM-T5% for MB over time.

[0030] Figure 14 The adsorption capacity and removal efficiency of CSM-T5% for Cr(VI) change over time.

[0031] Figure 15 The adsorption characteristics of CSM-T5% for MB at 298K, 308K and 318K.

[0032] Figure 16 The adsorption characteristics of CSM-T5% for Cr(VI) at 298K, 308K and 318K are shown.

[0033] Figure 17 The zero charge point is 5% of CSM-T.

[0034] Figure 18 The effect of solution pH on MB adsorption performance is shown.

[0035] Figure 19 The effect of solution pH on the adsorption performance of Cr(VI) is shown.

[0036] Figure 20The effect of a 5% CSM-T dosage on the removal rates of MB and Cr(VI).

[0037] Figure 21 The cyclic adsorption characteristics of CSM-T5% for MB and Cr(VI) are shown.

[0038] Figure 22 The synergistic adsorption behavior of CSM-T5% for MB and Cr(VI) was studied.

[0039] Figure 23 Photographs of CSM-T5% before and after adsorption in different concentrations of MB-Cr(VI) and Cr(VI)-MB binary systems.

[0040] Figure 24 In the table, (a) is the correlation coefficient of the PSO model fitting for MB, (b) is the linear fitting result of the intraparticle diffusion (ID) model for MB, (c) is the correlation coefficient of the PSO model fitting for Cr(VI), and (d) is the linear fitting result of the intraparticle diffusion (ID) model for Cr(VI).

[0041] Figure 25 The FTIR spectra of CSM-T5% before and after adsorption of MB and Cr(VI) are shown.

[0042] Figure 26 Fitting results for S2p of CSM-T5% (a), XPS fitting results for Cr2p (b), C 1s fine spectrum (c), O 1s fine spectrum (d), N 1s fine spectrum (e).

[0043] Figure 27 This is a schematic diagram of the adsorption mechanism of CSM-T5% on MB(a) and Cr(VI)(b). Detailed Implementation

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0046] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0047] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] The first aspect of this invention provides a method for preparing an ammonia-modified porous carbon adsorbent, comprising the following steps:

[0050] The gasification residue is subjected to hydrothermal acid leaching with an acid solution to obtain acid leaching residue;

[0051] The acid leaching residue was stirred in an alkaline solution, washed, and dried to obtain a porous carbon material.

[0052] The porous carbon material is impregnated in a tetraethylenepentamine solution and then dried to obtain the ammonia-modified porous carbon adsorbent.

[0053] In a preferred embodiment of the present invention, the acid solution is an HNO3 solution with a concentration of 2 mol / L.

[0054] In a preferred embodiment of the present invention, the mass-to-volume ratio of the gasified fine residue to the acid solution is 1 g: 16 mL.

[0055] In a preferred embodiment of the present invention, the hydrothermal acid leaching temperature is 403K and the time is 150min.

[0056] In a preferred embodiment of the present invention, the hydrothermal acid leaching process further includes solid-liquid separation and washing the solid obtained from the solid-liquid separation until neutral and then drying it.

[0057] In a preferred embodiment of the present invention, the alkaline solution is a 2 mol / L NaOH solution.

[0058] In a preferred embodiment of the present invention, the acid leaching residue is stirred in an alkaline solution at a temperature of 362K for 6 hours. The present invention does not impose any particular limitation on the stirring speed; a stirring speed commonly used by those skilled in the art can be adopted, such as not less than 600 r / min.

[0059] In a preferred embodiment of the present invention, the solvent of the tetraethylenepentamine solution is ethanol; the content of tetraethylenepentamine in the tetraethylenepentamine solution accounts for 5 wt% to 50 wt% of the mass of the porous carbon material.

[0060] The present invention does not impose a particular limitation on the concentration of the tetraethylenepentamine solution, as long as the amount of solvent in the tetraethylenepentamine solution is sufficient to fully dissolve the tetraethylenepentamine and impregnate the porous carbon material.

[0061] In a preferred embodiment of the present invention, the porous carbon material is immersed in the tetraethylenepentamine solution for 30 minutes; and stirring is performed during the immersion process to mix the tetraethylenepentamine and the porous carbon material evenly; the present invention does not impose a particular limitation on the stirring speed, and a stirring speed commonly used by those skilled in the art, such as 1000 r / min, can be used.

[0062] When preparing the porous carbon material and ammonia-modified porous carbon adsorbent, the drying temperature is independently 350-353K.

[0063] A second aspect of the present invention provides an ammonia-modified porous carbon adsorbent prepared according to the above-described preparation method.

[0064] The resource utilization of coal gasification slag and the harmless treatment of dyeing and printing wastewater and heavy metal wastewater are of great significance for building a zero-emission industrial system and a resource circular economy. This invention uses coal gasification slag as raw material and obtains porous carbon material (CSM) through a two-step acid-base treatment. Further, TEPA with different loadings is fixed onto the CSM surface using an impregnation method. Characterization analysis using SEM, XRD, and FTIR shows that with increasing TEPA loading, the amino content on the material surface significantly increases. However, excessive loading leads to amino agglomeration and pore blockage. After a 5% loading, the specific surface area of ​​the CSM decreases from 540.03 m² / s. 2 / g decreased to 376.20m 2Adsorption performance tests of MB and Cr(VI) revealed that CSM-T5% exhibited the best adsorption performance, with equilibrium adsorption capacities increasing by 8.01% and 15.91% respectively compared to the original CSM. The removal efficiency of MB and Cr(VI) under various influencing conditions, including initial concentration, contact time, temperature, pH, and adsorbent dosage, was systematically elucidated, providing theoretical support for the development of technologies for treating dyeing and printing wastewater and heavy metal wastewater. Kinetic analysis showed that the adsorption process of MB and Cr(VI) conformed to a pseudo-second-order kinetic model, indicating that the adsorption process was mainly chemisorption. Isothermal adsorption studies using the Langmuir model showed that CSM-T5% achieved maximum adsorption capacities of 862.06 mg / g for MB and 233.10 mg / g for Cr(VI) at 318 K. Thermodynamic analysis confirmed the spontaneous and endothermic nature of the adsorption process, accompanied by an increase in entropy. Furthermore, regeneration experiments showed that after five cycles, CSM-T5% retained adsorption rates of 71.37% for MB and 63.68% for Cr(VI). The adsorption mechanism involved a synergistic effect between physical and chemical adsorption; physical adsorption was attributed to the pore-filling properties of CSM-T5%, while chemical adsorption was mainly due to surface functional groups and intermolecular interactions. In conclusion, amino-modified porous carbon has great potential for the removal of dyeing and printing wastewater and heavy metal wastewater.

[0065] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0066] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0067] Example 1

[0068] 1. Materials and Methods

[0069] 1.1. Materials and Reagents

[0070] Gasification fine slag (CGFS) was purchased from Shaanxi Coal and Chemical Industry Group Co., Ltd.; the chemical reagents used in the experiment included: nitric acid (HNO3), sodium hydroxide (NaOH), ethanol (CH3CH2OH), and tetraethylenepentamine (TEPA, C8H2O). 23 N5), methylene blue (MB, C) 16 H 18 ClN3S), potassium dichromate (K2Cr2O7), phosphoric acid (H3PO4), and sulfuric acid (H2SO4) were all analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd.

[0071] 1.2. Preparation of Ammonia-Modified Porous Carbon Adsorbent

[0072] 4 g of 200-mesh CGFS was hydrothermally acid-leached with 64 mL of 2 mol / L HNO3 in a polytetrafluoroethylene reactor (403 K, 150 min). After solid-liquid separation, the resulting solid was washed until neutral and dried at 378 K for 12 h to obtain the acid-leaching residue. The acid-leaching residue was stirred with 40 mL of 2 mol / L NaOH solution at 362 K for 6 h, and finally washed until neutral and dried at 353 K for 12 h to obtain porous carbon material (CSM).

[0073] TEPA was loaded onto CSM material using a physical impregnation method. The specific preparation process is as follows: A certain amount of TEPA was dispersed in 30 mL of ethanol and stirred at room temperature for 30 min; then 2 g of CSM material was added (the amount of TEPA added was 5 wt%, 10 wt%, 20 wt%, 30 wt%, and 50 wt% of the CSM material mass), and stirring was continued for 30 min; finally, it was dried at 350 K for 12 h to remove the ethanol, obtaining an ammonia-modified porous carbon adsorbent. The obtained ammonia-modified porous carbon adsorbent was labeled CSM-TY, where T represents TEPA and Y represents the TEPA loading (5 wt%, 10 wt%, 20 wt%, 30 wt%, and 50 wt%), corresponding to the labels CSM-T5%, CSM-T10%, CSM-T20%, CSM-T30%, and CSM-T50%. The preparation process is as follows: Figure 1 As shown.

[0074] 1.3. Characterization Methods

[0075] The surface morphology of the samples was observed at different magnifications using a field emission scanning electron microscope (SEM, SIGMA 300) to obtain detailed microstructural features. Simultaneously, an energy dispersive spectroscopy (EDS) instrument equipped with the scanning electron microscope was used to analyze the elemental composition and distribution of the sample surface. The mineral phase composition of the samples was analyzed by X-ray diffraction (XRD, Bruker D8 Advance) using a Cu-Kα radiation source, with a scanning range of 10°–80° and a step size of 0.02°. Related calculations and analyses were performed using Jade 6 software. The composition of surface functional groups was analyzed by Fourier transform infrared spectroscopy (FTIR, Bruker Tensor 27) in the wavenumber range of 4000 cm⁻¹. -1 Up to 400cm -1 The resolution is 4cm. -1 The surface chemical composition of the samples was determined by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha), with the analysis chamber pressure below 2.0 × 10⁻⁶. -7mbar was used with a non-monochromatic Al Kα X-ray source. The full-spectrum scan flux energy was 150 eV with a step size of 1 eV; the narrow-spectrum scan flux energy was 50 eV with a step size of 0.1 eV. Nitrogen adsorption-desorption isotherms were measured using a nitrogen adsorption analyzer (ASAP 260), and the specific surface area and pore structure of the samples were determined using the BET (Brunauer-Emmett-Teller) and BJH (Barrett-Joyner-Halenda) methods. Micropore surface area was quantified using the t-plot method, while mesopore surface area was determined using the BJH method.

[0076] 1.4. Adsorption experiments of a single system

[0077] This invention systematically investigated the adsorption characteristics of CSM-TY for methylene blue (MB) and hexavalent chromium (Cr(VI)). MB system parameters included: solution volume 50 mL, initial concentration 100–600 mg / L (except for other adsorption characteristic experiments, the MB concentration used was 200 mg / L), contact time (10–150 min), temperature (298–318 K), pH (1–10), adsorbent dosage (0.02–0.08 g), and number of cycles (1–5). The absorbance of the solution was measured at the characteristic wavelength of 665 nm using a UV-Vis spectrophotometer. A blank control group was included in all experiments to ensure data reliability. Cr(VI) system: solution volume 50 mL, initial concentration 50–150 mg / L (the concentration of Cr(VI) used in all other adsorption characteristic experiments was 50 mg / L), adsorption time (30–1920 min), temperature (298–318 K), pH (1–10), adsorbent dosage (0.02–0.08 g), and regeneration times (1–5 times). Concentration was determined using visible spectrophotometry (540 nm), with each experiment performed in triplicate to control for error.

[0078] In the regeneration process of CSM-TY, 95% (v / v) ethanol was used as the eluent for the MB system, and the desorption process was carried out at a solid-liquid ratio of 5:2 (m / v, mg / mL). The sample was ultrasonically treated in an ultrasonic cleaner for 15 min to achieve efficient desorption, and this process was repeated three times to ensure consistency and thoroughness. For the Cr(VI) system, 0.05 mol / L sodium hydroxide solution was used as the eluent. The saturated adsorbed CSM-T5% was placed in an ultrasonic cleaner for 15 min at a solid-liquid ratio of 5:2 (m / v, mg / mL), and the desorption was repeated three times before the material regeneration efficiency was measured.

[0079] The adsorption capacity (q) at a given time is determined using equations (1) and (2), respectively. t ) and MB and Cr(VI) removal efficiency (R).

[0080]

[0081] Where, q t (mg / g) represents the adsorption capacity of the adsorbent at time t, C0 (mg / L) represents the initial concentrations of MB and Cr(VI), and C t (mg / L) represents the concentrations of MB and Cr(VI) at time t. At adsorption equilibrium, the equilibrium concentrations of MB and Cr(VI) in the solution are C. e (mg / L), the corresponding adsorption capacity is q e (mg / g).

[0082] 1.5. Adsorption Experiments of Binary Systems

[0083] The selective separation efficiency of adsorbent CSM-T5% in two competing adsorption systems (MB-Cr(VI) and Cr(VI)-MB) was systematically investigated using a binary composite pollution system of MB and Cr(VI).

[0084] In the MB-Cr(VI) system, the experimental group: 25 mL of MB solution with a concentration of 200–600 mg / L was placed in a 150 mL Erlenmeyer flask, and 25 mL of Cr(VI) solution with a fixed concentration of 50 mg / L was added to form a total system of 50 mL. The blank control group: 25 mL of MB solution with the same concentration gradient (200–600 mg / L) was prepared separately, without the addition of Cr(VI) solution.

[0085] In the Cr(VI)-MB system, the experimental group: 25 mL of Cr(VI) solution with a concentration of 50–130 mg / L was measured into an Erlenmeyer flask, and 25 mL of MB solution with a constant concentration of 200 mg / L was added, for a total system volume of 50 mL. The blank control group: 25 mL of Cr(VI) solution with the same concentration gradient (50–130 mg / L) was prepared separately, without the addition of MB solution.

[0086] Subsequently, 0.02 g of CSM-TY adsorbent was precisely added to all experimental groups and the blank control group, and the mixture was shaken at 130 rpm for 1440 min at room temperature to ensure adsorption equilibrium was reached.

[0087] 2. Results and Discussion

[0088] 2.1. Structural Characterization of CSM-TY

[0089] 2.1.1. Phase Composition Analysis

[0090] Figure 2XRD patterns of the original CSM and its modified sample CSM-TY (Y = 5 wt%, 10 wt%, 20 wt%, 30 wt%, 50 wt%) were compared. All samples exhibited broad diffraction peaks near 2θ≈26° and 43°, corresponding to typical characteristic peaks of amorphous carbon, indicating the presence of small amounts of inorganic minerals, primarily quartz (SiO2). Furthermore, even as the loading increased from 5 wt% to 50 wt%, the phase composition of CSM (e.g., SiO2) did not change significantly, suggesting that the modification process did not induce a phase transformation.

[0091] 2.1.2. Functional Group Composition Analysis

[0092] Figure 3 Comparative FTIR spectra of CSM and its TEPA-modified material CSM-TY (Y = 5–50 wt%). In the spectra, 3430 cm⁻¹... -1 The broad peaks in the vicinity are characteristic peaks of the stretching vibration of hydroxyl groups (-OH) in the material; 3400–3000 cm⁻¹ -1 The absorption peaks within the range correspond to the stretching vibration mode of amino (-NH2), while those in the 1650–1540 cm⁻¹ range correspond to the stretching vibration mode of amino groups. -1 The signal in the interval is the bending vibration response of the NH bond. As the TEPA loading increases, the characteristic peak intensities of -NH2 and NH show a gradient increasing trend, which directly reflects the cumulative effect of the abundant -NH2 and NH in the TEPA molecule on the CSM surface, confirming the positive correlation between loading and characteristic peak intensity.

[0093] Further analysis revealed that the modified material CSM-TY at 2930 cm⁻¹ -1 A new characteristic absorption peak appears at 1130 cm⁻¹, which is the stretching vibration peak of -CH₂. -1 The peak at 630-600 cm⁻¹ is a characteristic peak of the CN bond. -1 The range corresponds to the CS bond vibration peak. The above spectral characteristics, including the appearance of new characteristic peaks and the regular change in the intensity of the main peak with the loading amount, confirm that TEPA was successfully loaded onto the surface of the CSM support, and that the loading amount can cause changes in the intensity of the characteristic peaks.

[0094] 2.1.3. Surface Chemical Analysis

[0095] XPS analysis was performed on CSM and CSM-TY series samples with different TEPA loadings (5–50 wt%). Wide-scan spectra were obtained, such as… Figure 4As shown, compared to CSM, CSM-TY exhibits a significant enhancement of the N1s signal at 400.0 eV, confirming the successful introduction of amino / amine functional groups onto the material surface. Furthermore, the N1s peak intensity increases positively with increasing TEPA loading (see Table 1). The introduction of nitrogen significantly enhances the adsorption performance of pollutants by strengthening the electrostatic interaction between the adsorbent and MB and Cr(VI).

[0096] Table 1

[0097]

[0098] Figure 5 The C1s fine spectrum shows that the C1s peak of CSM can be unconvoluted into four components: 284.8 eV (C–C / C=C / C–H), 286.28 eV (C–O / C–N), 288.23 eV (C=O), and 290.48 eV (COO-). After TEPA modification, the peak area and atomic percentage of CSM-TY at 286.28 eV (C–O / C–N) significantly increased with increasing tetraethylenepentamine loading (see Table 2), directly proving the successful introduction of amino groups.

[0099] Table 2

[0100]

[0101] Figure 6 The N1s fine spectrum shows that after TEPA modification, the intensities of the -NH peak at 399.98 eV and the -NH2 peak at 400.49 eV of CSM are significantly enhanced. Table 2 shows that the contents of -NH and -NH2 increase synchronously with increasing TEPA loading, indicating that the amino content can be controlled. Further research revealed that the N / C ratios of CSM and the aminated material (e.g., CSN-T5%) are 0.016 and 0.031, respectively. The N / C ratio increases with increasing loading, indicating successful amino modification on CSM and accumulation of fixed amino groups on the material.

[0102] Figure 7 The O1s fine spectrum shows that the oxygen-containing functional groups of both CSM and CSM-TY are mainly hydroxyl (–OH, 533.27 eV) and carbonyl (C=O, 532.25 eV), indicating that the surface modification process did not change the type of oxygen-containing functional groups.

[0103] 2.1.4. Microscopic Morphology Analysis

[0104] Figure 8 Scanning electron microscope (SEM) images of CSM and its TEPA-modified material CSM-TY (Y = 5–50 wt%). Figure 8In the middle (a), there is unmodified CSM. The material surface is smooth and has a porous structure with a large number of pores inside the channels, and some of the pores are interconnected. Figure 8 Figures (b) to (f) show the materials modified with different TEPA loadings. It can be seen that the modified materials still maintain a porous structure, and the pores inside the channels are still visible, indicating that the addition of TEPA does not destroy the pore framework of the material itself. However, as the loading increases from 5% to 50%, the number of pores in the material decreases, the pore blockage becomes stronger, and the surface roughness of the material increases.

[0105] 2.1.5. Pore Structure Analysis

[0106] Figure 9 The N2 adsorption-desorption curves and pore size distribution curves are for CSM and CSM-TY (Y = 5 wt%, 10 wt%, 20 wt%). Figure 9 As shown in (a), the N2 adsorption / desorption curves of all samples were type IV isotherms. According to IUPAC classification, the hysteresis loop shape belongs to type H3, with the closure point located at P / P0≈0.40, indicating the presence of slit-like mesopores. When P / P0>0.4, the N2 adsorption capacity continuously increases, especially significantly near the saturation pressure, indicating the presence of some macropores in both CSM and CSM-TY. Furthermore, the hysteresis loop area of ​​CSM-TY is smaller than that of CSM, and the hysteresis loop gradually narrows with increasing TEPA loading, indicating a reduction in mesopore volume. This is due to partial mesopore blockage caused by TEPA molecules loading within the CSM channels or surface covering. Figure 9 As can be seen in (b), the pore size distribution of TEPA after loading is lower than that of CSM, which further proves that TEPA does indeed play a role in modifying the amino group on the surface of CSM.

[0107] Table 3 compares the effects of different TEPA loadings (Y = 5 wt%, 10 wt%, 20 wt%) on the specific surface area, pore size, and total pore volume of CSM. The table shows that the specific surface area of ​​unmodified CSM is 540.03 m². 2 / g, total pore volume is 0.5550cm³ 3 / g, pore size 4.1110nm. After TEPA modification, the specific surface area, total pore volume, and pore size all decreased, and these parameters gradually decreased with increasing loading. When the loading increased to 20wt%, the specific surface area decreased to 203.77m². 2 / g, the total pore volume decreased to 0.3294cm³. 3 / g, the pore size decreased to 3.192nm. This indicates that TEPA loading occupied part of the pores, but the pores were not completely blocked.

[0108] Table 3

[0109]

[0110] 2.2. Adsorption performance

[0111] 2.2.1. Effect of TEPA loading on the adsorption efficiency of MB and Cr(VI)

[0112] The adsorption effects of 0.02 g of TEPA-modified material CSM-TY (Y = 5–50 wt%) at room temperature on 50 mL of 200 mg / L MB and 50 mL of 50 mg / L Cr(VI) after 1440 min of adsorption were as follows: Figure 10 As shown in the figure, for MB adsorption, the removal rate reached its highest value of 92.03% when the TEPA loading was 5% (CSM-T5%), an improvement of 8.01% compared to the 84.02% removal rate of unmodified CSM. Cr(VI) adsorption achieved its best effect at a loading of 10% (CSM-T10%), with a removal rate of 31.74%, a significant improvement of 15.91% compared to the original CSM removal rate of 15.83%. When the TEPA loading exceeded 5%, the removal efficiency of MB showed a downward trend, and the adsorption effect of Cr(VI) also gradually decreased after the loading exceeded 10%. This is because, under excessively high loading, TEPA molecules aggregate on the material surface, leading to pore blockage and a reduction in specific surface area, resulting in a decrease in removal efficiency. Considering both pollutant removal efficiency and the environmental hazards of excessive TEPA, CSM-T5% was selected for subsequent experiments.

[0113] 2.2.2. Adsorption characteristics of CSM-T5% for MB and Cr(VI) in a single system

[0114] Figure 11 and Figure 12The effects of initial concentrations of MB and Cr(VI) on the adsorption capacity and removal rate of CSM-T5% at room temperature were investigated. For the MB system (pH 7.84), with a CSM-T5% dosage of 0.02 g and a solution volume of 50 mL, the equilibrium adsorption capacity significantly increased from 249.77 mg / g to 784.03 mg / g after 150 min of adsorption when the initial concentration increased from 100 mg / L to 700 mg / L. In the Cr(VI) system (pH 5.34), with a dosage of 0.02 g and a solution volume of 50 mL, the adsorption capacity increased from 112.73 mg / g to 188.32 mg / g after 1440 min of adsorption when the initial concentration increased from 50 mg / L to 150 mg / L. The increase in adsorption capacity with increasing concentration is mainly attributed to enhanced mass transfer driving forces. The increased concentration gradient between MB and Cr(VI) at higher concentrations and the adsorbent surface promotes diffusion mass transfer, thereby enhancing the adsorption capacity. Although the adsorption capacity showed an upward trend, the removal rates of MB and Cr(VI) gradually decreased. This is because when the concentrations of MB and Cr(VI) are low, the amino groups and pore structures on the surface of CSM-T5% can fully expose the active sites, resulting in a high removal rate; however, as the concentration continues to increase, the limited adsorption sites are gradually occupied, eventually reaching a dynamic equilibrium state, leading to a decrease in the removal rate.

[0115] Figure 13 and Figure 14 The adsorption capacity and removal efficiency of 0.02 g of CSM-T5% for 50 mL of 200 mg / L MB (pH 7.84) and 50 mL of 50 mg / L Cr(VI) (pH 5.34) at room temperature, respectively, changed over time. In the initial adsorption phase (0–30 min), the adsorption rate of MB was relatively fast, attributed to the lack of occupied active sites on the adsorbent surface and the strong mass transfer driving force resulting from the high initial concentration. From 30–150 min, as the active sites gradually became saturated, the adsorption rate decreased accordingly and eventually leveled off. For Cr(VI), the adsorption rate of CSM-T5% for Cr(VI) showed a trend of first increasing and then leveling off with increasing adsorption time, reaching adsorption equilibrium after 1140 min.

[0116] Figure 15 and Figure 16The adsorption characteristics of 0.02 g of CSM-T5% for 50 mL of 200 mg / L MB (pH 7.84) and 50 mL of 50 mg / L Cr(VI) (pH 5.34) at 298 K, 308 K, and 318 K were studied. For the 200 mg / L MB system, the adsorption capacity increased with increasing temperature, from 466.24 mg / g at 298 K to 487.59 mg / g at 318 K, an increase of 4.37%. Similarly, the 50 mg / L Cr(VI) system also showed an increase in adsorption capacity with increasing temperature, from 110.75 mg / g at 298 K to 119.03 mg / g at 318 K, an increase of 6.95%. These trends indicate that increasing the temperature can effectively enhance the adsorption capacity of CSM-T5% for MB and Cr(VI).

[0117] Figure 17 The zero potential point of CSM-T5% is shown to be 7.01. When the solution pH is below 7.01, the -NH2, -COOH, and -OH active groups on the material surface undergo protonation, forming -NH3, etc. + -COOH2 + and -OH2 + This results in a positive charge on the surface of CSM-T5%. This facilitates the effective adsorption of anionic forms of Cr(VI), such as HCrO4, via electrostatic attraction. - Cr2O7 2- and CrO4 2- This significantly improves the removal efficiency of Cr(VI) under acidic conditions. However, the positive charge on the material surface and MB... + Electrostatic repulsion occurs between the Cr(VI) anions and the negatively charged CSM-T5% surface, inhibiting its adsorption capacity for MB. When the solution pH is above 7.01, a deprotonation reaction occurs on the CSM-T5% surface, resulting in a negatively charged surface. At this time, electrostatic repulsion occurs between the Cr(VI) anions and the negatively charged CSM-T5% surface, significantly reducing adsorption. Furthermore, under high pH conditions, the high concentration of -OH groups in the solution reacts with CrO4. 2- The competition for adsorption sites between anions and ions further reduces the removal efficiency of Cr(VI). Conversely, the negative charge on the material surface significantly enhances the adsorption of MB. + Electrostatic attraction, along with the deprotonated hydroxyl groups, can also generate a synergistic adsorption effect with MB through hydrogen bonding, thereby significantly improving the removal performance of MB under alkaline conditions. Figure 18 and Figure 19The effects of solution pH on the adsorption performance of MB and Cr(VI) were investigated. As the pH increased from 1 to 10, the removal rate of MB steadily increased from 74.02% to 91.30%, while the removal rate of Cr(VI) decreased sharply from 95.62% to 1.47%. These results indicate that under acidic conditions (pH < 7.01), the electrostatic attraction between the positively charged protonated particles on the material surface and the Cr(VI) anions dominates the adsorption process, while simultaneously repelling MB. + Under alkaline conditions (pH>7.01), the negative charge generated by deprotonation enhances the surface effect on MB. + It exhibits adsorption, but shows a dual inhibitory effect on Cr(VI) anions through electrostatic repulsion and competitive adsorption by hydroxyl groups.

[0118] Figure 20 The effect of CSM-T5% dosage on the removal rates of 50 mL of 200 mg / L MB (pH 7.84) and 50 mL of 50 mg / L Cr(VI) (pH 5.34) at room temperature was investigated. At a dosage of 0.02 g, the limited active sites on the material surface were rapidly occupied by MB and Cr(VI), leading to adsorption saturation. The removal rates at this point were 65.59% and 55.52%, respectively, indicating significant incomplete adsorption under low dosage conditions. As the CSM-T5% dosage increased to 0.06 g, the removal rates of MB and Cr(VI) significantly improved to 99.78% and 86.05%, respectively. These results indicate that increasing the adsorbent dosage effectively expands the adsorption interface contact area and exposes more unoccupied active sites, thus significantly improving the removal rates of MB and Cr(VI). However, when the dosage was too high, the adsorption capacity decreased. This is mainly attributed to the agglomeration effect of the adsorbent particles, leading to a decrease in specific surface area, and the underutilization of excess active sites. Therefore, in practical applications, the optimal dosage needs to be determined through experiments to ensure efficient removal of pollutants while avoiding waste of adsorbent resources.

[0119] In addition, the cyclic adsorption characteristics of 0.02 g of CSM-T5% on 50 mL of 200 mg / L MB (pH 7.84) and 50 mL of 50 mg / L Cr(VI) (pH 5.34) were investigated at room temperature. The results are as follows: Figure 21 As shown, after three cycles, the removal rates of MB and Cr(VI) by CSM-T5% decreased, which is due to the gradual reduction of the effective active sites of CSM-T5% with increasing cycle number. Nevertheless, after five cycles, the removal rates of MB and Cr(VI) remained at 71.37% and 63.68%, respectively, indicating that CSM-T5% has good cycling performance.

[0120] 2.2.3. Synergistic effect of adsorption in binary systems

[0121] The synergistic adsorption behavior of 0.02 g of CSM-T5% on 25 mL of 200 mg / L MB and 25 mL of 50 mg / L Cr(VI) was investigated using binary adsorption experiments at room temperature. The results showed that both the MB-Cr(VI) and Cr(VI)-MB binary systems exhibited significantly improved pollutant removal efficiency and adsorption capacity compared to the single-system adsorption. Figure 22 As shown in (a), when the Cr(VI) concentration in the MB-Cr(VI) system is fixed at 50 mg / L, the removal rate of 300 mg / LMB by CSM-T5% increases from 86.89% in the single system to 95.61%, while the removal rate of Cr(VI) remains stable at over 95%. Figure 22 As shown in Figure (b), in the Cr(VI)-MB system, with a fixed MB concentration of 200 mg / L, the removal rate of 130 mg / L Cr(VI) increased from 59.67% in the single system to 72.13%, while the MB removal rate remained at a high level of 99%. These phenomena confirm a significant synergistic effect in the adsorption process of the binary system. On the one hand, MB preferentially adsorbs the negative charge on the surface of CSM-T5%, partially neutralizing the surface charge and reducing the electrostatic repulsion between Cr(VI) anions and the adsorbent, thereby promoting Cr(VI) adsorption. On the other hand, MB preferentially occupies the mesopores of CSM-T5%, while Cr(VI) is mainly adsorbed in the micropores. This hierarchical adsorption reduces competition for active sites and promotes Cr(VI) adsorption.

[0122] Photos of CSM-T5% before and after adsorption in binary systems of MB-Cr(VI) and Cr(VI)-MB at different concentrations are shown below. Figure 23 As shown.

[0123] 2.2.4. Adsorption Kinetics

[0124] To elucidate the key influencing factors and their mechanisms of action on the adsorption rate, this invention employs pseudo-first-order kinetics (PFO), pseudo-second-order kinetics (PSO), and intraparticle diffusion (ID) models to conduct kinetic analysis on the adsorption of MB and Cr(VI) by CSM-T5%. The kinetic fitting parameters are summarized in Table 4. Figure 24 As shown in (a) and (c), the correlation coefficient (R²) of the PSO model fit between MB and Cr(VI) is... 2 MB =0.994, R 2 Cr(VI) =0.995) significantly outperformed the PFO model (R 2 MB =0.711, R 2 Cr(VI)=0.592). The theoretical equilibrium adsorption capacity calculated by the PSO model (MB: 609.66 mg / g; Cr(VI): 145.51 mg / g) and the experimental value (q) e,cal,MB =606.62mg / g; q e,cal,Cr(VI) The results (145.32 mg / g) show a high degree of agreement, indicating that the adsorption processes of MB and Cr(VI) by CSM-T5% conform to a pseudo-second-order kinetic model. This confirms that the adsorption process is primarily chemisorption, possibly involving mechanisms such as electrostatic interactions, electron transfer, or chemical bond formation.

[0125] Table 4

[0126]

[0127] Figure 24 Figures (b) and (d) show the linear fitting results of the intraparticle diffusion (ID) model. The adsorption process can be piecewise fitted by two straight lines that do not pass through the origin, indicating that the process is not only controlled by intraparticle diffusion but also related to surface diffusion. The first straight line segment corresponds to the diffusion process of MB or Cr(VI) from the liquid phase to the outer surface of the CSM-T5% surface, while the second straight line segment reflects the intraparticle diffusion behavior of MB or Cr(VI) into the internal pores of the CSM-T5% surface. The slope of the first straight line segment is significantly greater than that of the second segment (k...). id,1 >k id,2 The higher concentration of MB or Cr(VI) in the ID model indicates that the diffusion rate is faster at the outer surface. Therefore, in the initial stage of adsorption, intraparticle diffusion is the dominant rate-controlling step. As the reaction proceeds, the decrease in MB or Cr(VI) concentration leads to a reduction in the concentration gradient between the adsorbent and the interior, weakening the diffusion effect at the outer surface, and surface diffusion gradually becomes the rate-limiting factor. When MB or Cr(VI) continues to accumulate in the pores, the diffusion resistance increases, and the adsorption rate gradually decreases until a dynamic equilibrium is reached. Furthermore, the boundary layer diffusion parameter c2 in the ID model is greater than the value of c1, indicating that the boundary layer effect has a more significant impact on the adsorption rate during intraparticle diffusion.

[0128] 2.2.5. Adsorption Isotherm

[0129] Adsorption isotherm analysis was performed using both the Langmuir and Freundlich isotherm models. The results showed that both models fit well, and the Freundlich inhomogeneity coefficient (n>1) indicated effective adsorption. The Langmuir model exhibited a high correlation coefficient (R²). 2 >0.99), indicating that it better represents the adsorption of MB or Cr(VI) on CSM-T5%, which implies monolayer adsorption on a homogeneous surface. Langmuir model fitting results show that the maximum adsorption amount (q) m ) and Langmuir constant (K LAll of these increase with increasing temperature. Maximum adsorption capacity (q) m,MB =862.06mg / g; q m,Cr(VI) =233.10mg / g), maximum K L Value (K) L,MB =0.2003; K L,Cr(VI) =0.243), indicating that the interaction between the adsorbent and adsorbate is enhanced at higher temperatures, resulting in improved adsorption efficiency. The adsorption performance of CSM-T5% of this invention is shown in Table 5.

[0130] Table 5

[0131]

[0132] 2.2.6. Thermodynamics

[0133] The thermodynamic parameters of the adsorption process, specifically the Gibbs free energy change (ΔG), were analyzed from a thermodynamic perspective. θ ), enthalpy change (ΔH) θ and entropy change (ΔS) θ The thermodynamic parameters, such as ΔG, were analyzed to determine the thermodynamic nature of MB or Cr(VI) adsorption on CSM-T5%. The relevant parameters are shown in Table 6. Within the temperature ranges of 298 K, 308 K, and 318 K, the ΔG of MB or Cr(VI) adsorption was... θ All values ​​are negative, indicating that the adsorption of MB or Cr(VI) on CSM-T5% is spontaneous. Furthermore, ΔG θ The absolute value of ΔG increases with increasing temperature, indicating that higher temperatures promote spontaneous reactions, thereby enhancing the adsorption of MB or Cr(VI). θ Within the range of -20 to 0 kJ / mol, this indicates that the adsorption is essentially physisorption. Positive ΔH θ The value indicates that the adsorption process is endothermic, confirming the trend of the isotherm. Furthermore, the positive ΔS... θ The value corresponds to the increase in entropy during adsorption, indicating an increase in randomness at the solid / liquid interface during MB or Cr(VI) adsorption.

[0134] Table 6

[0135]

[0136] 2.3. Adsorption Mechanism Analysis

[0137] The adsorption mechanism of CSM-T5% was systematically studied using FTIR and XPS. Figure 25 Comparison of FTIR characteristic peaks of the materials before and after MB and Cr(VI) adsorption. CSM-T5%-MB (after MB adsorption) and CSM-T5%-Cr(VI) (after Cr(VI) adsorption), 3430 cm⁻¹ -1The characteristic peak of the -OH stretching vibration showed a red shift and a significant decrease in intensity, indicating that the hydroxyl group is the key adsorption site. Simultaneously, in the complex system of MB & Cr(VI) binary coexistence, the shift and intensity trends of the -OH characteristic peak were consistent with those in the single system, confirming that -OH remains a key adsorption site in different adsorption environments. After adsorbing MB, Cr(VI), and the MB & Cr(VI) binary system, CSM showed a peak at 1636 cm⁻¹. -1 The NH vibration peaks at various locations all exhibited a redshift, changing to 1631 cm⁻¹. -1 1621cm -1 and 1626cm -1 Furthermore, the intensity decreases, mainly because after NH is protonated, it interacts with negatively charged groups, leading to a reduction in the vibrational degrees of freedom of NH and thus weakening the intensity of the infrared absorption peak. At 1116 cm⁻¹ -1 The CN stretching vibration peaks at the adsorption sites all decreased after adsorption, indicating that N atoms on the material surface participated in the adsorption process. For MB-specific adsorption sites, a peak of 1452 cm⁻¹ was observed in both the single MB system and the MB&Cr(VI) coexistence system. -1 The C=C vibration peak of the benzene ring skeleton is at 1383 cm⁻¹. -1 The CH bending vibration peak at -CH3 and 543 cm⁻¹ -1 The appearance of the CSC characteristic peaks, which correspond to the vibrational peaks of the MB molecule structure, confirms the successful adsorption of MB molecules on the material surface. Regarding the adsorption characteristics of Cr(VI), in both single Cr(VI) systems and MB&Cr(VI) coexistence systems, the peak at 791 cm⁻¹... -1 and 910cm -1 The newly appearing characteristic peaks correspond to HCrO4 respectively - The vibrational peaks of Cr-O and the asymmetric vibrational modes of Cr=O indicate that CSM-T5% can also successfully adsorb Cr(VI).

[0138] XPS full-spectrum scanning of the materials before and after MB and Cr(VI) adsorption revealed characteristic peaks of S2p and Cr2p on CSM-T5%, further confirming the successful adsorption of MB and Cr(VI) on CSM-T5%. Figure 26 (a) shows the fitting results for S2p. CSM-T5% showed peaks corresponding to C-SO2-C and C-SO3-Na at 168.11 eV and 169.17 eV, respectively. After MB adsorption, CSM-T5%-MB showed a C-SO3-H peak at 169.19 eV and a CSC characteristic peak at 164.53 eV, with an increase in content of 0.21%, confirming MB adsorption, consistent with the enhancement of the C–SC stretching vibration peak in FTIR. The XPS fitting results for Cr 2p are shown below. Figure 26As shown in (b), the Cr 2p spectrum at 587.4 eV (Cr 2p 1 / 2 ) and 577.6eV (Cr 2p 3 / 2 Two broad peaks are observed at Cr2p, indicating the presence of Cr(III) and Cr(VI). 3 / 2 In the region, the peaks with binding energies of 577.13 eV and 579.08 eV represent Cr(III) in Cr(OH)3 and Cr(VI) in K2Cr2O7, respectively. Cr 2p 1 / 2 The fitted peak at 588.24 eV indicates Cr(VI) in Cr₂O₃, while the peak at 586.95 eV indicates the presence of Cr(III). The coexistence of Cr(VI) and Cr(III) on the material surface, and the absence of Cr(III) in the initial solution, suggests that Cr(VI) on the material surface was partially reduced to Cr(III) after adsorption.

[0139] Figure 26 Figure (c) shows the C1s fine spectrum. The binding energies of CC / C=C / CH, CO / CN, C=O, and -COOH in CSM-T5% are 284.80 eV, 286.05 eV, 287.79 eV, and 290.19 EV, respectively. After MB adsorption, the binding energies of CSM-T5% shift to higher positions to 284.80 eV, 286.09 eV, 287.80 eV, and 290.36 eV, and the -COOH content decreases significantly, indicating the presence of ion interactions in MB adsorption. For Cr(VI) adsorption, the CO / CN content decreases, indicating that the amino group is the active binding site for Cr(VI). Furthermore, when MB and Cr(VI) coexist, the binding energy of CSM-T5%-MB&Cr(VI) falls between the two, indicating that CSM-T5% has a synergistic adsorption effect on MB and Cr(VI).

[0140] Figure 26 The O1s fine spectrum is shown in (d). The functional groups corresponding to the binding energies of CSM-T5% at 533.39 eV and 532.07 eV are -OH and C=O. After MB adsorption, the oxygen-containing functional groups of CSM-T5%-MB shift towards higher binding energies, indicating that oxygen-containing functional groups participate in MB adsorption. After Cr(VI) adsorption, the binding energy of C=O shifts from 532.07 eV to 532.17 eV, and the C=O content increases from 2.27% to 6.35%, indicating that the electron-donating C=O group participates in the reduction of Cr(VI) to Cr(III) and self-oxidation to generate carboxyl groups.

[0141] Figure 26The N1s fine spectrum is shown in (e). After MB adsorption, CSM-T5%-MB shows a pyridine nitrogen characteristic peak at 399.20 eV, confirming MB adsorption. Simultaneously, a -NH3 peak appears at 401.56 eV. + This indicates that functional groups undergo protonation during MB adsorption. The -NH content at 400.08 eV increases from 1.23% before MB adsorption to 1.34%, indicating hydrogen bond formation during MB adsorption. After Cr(VI) adsorption, -NH3 appears at 401.35 eV. + The peak indicates that the amino group is protonated and has electrostatic adsorption capacity for Cr(VI).

[0142] To further explain the adsorption mechanism, such as Figure 27 As shown, by systematically exploring the key influencing factors of adsorption performance, and combining adsorption kinetics, isothermal adsorption model fitting, thermodynamic parameter calculation, and FTIR and XPS characterization, the synergistic adsorption mechanism of CSM-T5% for MB and Cr(VI) was revealed. The adsorption process is a physicochemical synergistic effect of physical adsorption and chemical adsorption.

[0143] Figure 27 (a) shows a schematic diagram of the adsorption mechanism of MB by CSM-T5%. The pore structure of CSM-T5% promotes capillary and synergistic effects, and MB migrates into the pore structure of CSM-T5% during adsorption, i.e., pore filling. Nitrogen doping disrupts the original chemical equilibrium, and the redistribution of spin states and charge density generates more active sites, improving adsorption efficiency. In addition to the hydrogen bonds formed between N in the MB molecule and NH groups in CSM-T5%, the ionic interactions between oxygen-containing functional groups such as carboxyl groups and MB molecules, and the π-π interactions between the benzene ring in the MB molecule and the conjugated structure in the adsorbent, under acidic conditions, some -NH2 is protonated to -NH3. + TEPA exhibits a weak electrostatic attraction with Cl- ions in MB. Because the polyamine nature of TEPA leads to charge dispersion, the charge density at individual sites decreases, weakening the attraction to Cl- ions. - Electrostatic attraction.

[0144] Figure 27 Figure (b) shows a schematic diagram of the adsorption mechanism of Cr(VI) by CSM-T5%. The removal of Cr(VI) by CSM-T5% mainly involves three aspects: the negatively charged Cr(VI) ions react with the positively charged surface functional groups (-NH3). + and -COOH + The electrostatic interaction between Cr(VI) and Cr(III) leads to the reduction of Cr(VI) to Cr(III), which then complexes with the functional groups on the adsorbent. The reduction of Cr(VI) to Cr(III) can be represented as follows:

[0145] HCrO4 - +7H + +3e - →Cr3 + +4H2O

[0146] Cr2O7 2- +14H + +6e - →2Cr3 + +7H2O

[0147] 3. Conclusion

[0148] This invention uses porous carbon material (CSM) derived from coal gasification fine slag as a substrate and further employs a surface ammonia functionalization modification strategy. By controlling the loading of TEPA (Y = 5% wt%, 10% wt%, 20% wt%, 30% wt%, and 50% wt%), an ammonia-modified composite material (CSM-TY) was successfully constructed. Using a combination of characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption-desorption analysis, and X-ray photoelectron spectroscopy (XPS), the structural evolution of the material was systematically revealed: with increasing TEPA loading, the amino content on the material surface significantly increases; however, excessive loading leads to amino agglomeration and accumulation, causing pore blockage. When the loading is 5%, the specific surface area increases from the initial 540.03 m². 2 / g decreased to 376.20m 2 / g.

[0149] Adsorption performance tests of MB and Cr(VI) revealed that CSM-T5% exhibited the best adsorption performance, with equilibrium adsorption capacities increasing by 8.01% and 15.91% respectively compared to the original CSM, confirming that amino functionalization successfully enhanced the surface active sites. Solution pH played a crucial role in the adsorption of MB and Cr(VI). The removal rate of MB increased with increasing pH, while the opposite was true for Cr(VI). The adsorption process of MB and Cr(VI) conformed to a pseudo-second-order kinetic model (PSO), indicating chemisorption involving electrostatic interactions and electron transfer. Intraparticle diffusion modeling further revealed that both external surface diffusion and intraparticle diffusion jointly influenced the overall adsorption rate. Thermodynamic analysis confirmed that the adsorption process was spontaneously endothermic.

[0150] Isothermal adsorption studies based on the Langmuir model showed that CSM-T5% exhibited maximum adsorption capacities of 862.06 mg / g for MB and 233.10 mg / g for Cr(VI) at 318 K, demonstrating a higher fit than the Freundlich model, indicating that adsorption primarily occurred on a homogeneous surface. Analysis of surface characteristics before and after adsorption elucidated the adsorption mechanisms of MB and Cr(VI). For MB, synergistic effects included pore filling, electrostatic attraction, ionic interactions, and π-π conjugation. For Cr(VI), electrostatic interactions between Cr(VI) and the protonated CSM-T5% surface led to the reduction of Cr(VI) to Cr(III) and the formation of Cr(III) complexes.

[0151] In the MB-Cr(VI) / Cr(VI)-MB binary system, both the removal efficiency and adsorption capacity of pollutants were significantly improved compared to the single system, indicating the synergistic adsorption behavior of CSM-T5% for MB and Cr(VI). Regeneration experiments showed that after 5 cycles, the adsorption retention rates of CSM-T5% for MB and Cr(VI) remained at 71.37% and 63.68%, respectively.

[0152] In summary, adsorbents developed based on coal gasification fine slag have good potential in industrial production and application.

[0153] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. The application of an ammonia-modified porous carbon adsorbent in the synergistic adsorption of Cr(VI) and MB, characterized in that, The preparation method of the ammonia-modified porous carbon adsorbent includes the following steps: The gasification residue is subjected to hydrothermal acid leaching with an acid solution to obtain acid leaching residue; The acid leaching residue was stirred in an alkaline solution, washed, and dried to obtain a porous carbon material. The porous carbon material was impregnated in a tetraethylenepentamine solution and then dried to obtain the ammonia-modified porous carbon adsorbent. The acid solution is a 2 mol / L HNO3 solution; The mass-to-volume ratio of the gasified fine residue to the acid solution is 1g:16mL; The hydrothermal acid leaching temperature was 403K and the time was 150min; After the hydrothermal acid leaching is completed, the process also includes solid-liquid separation and washing the solid obtained from the solid-liquid separation to neutral and drying. The alkaline solution is a 2 mol / L NaOH solution; The acid leaching residue was stirred in an alkaline solution at a temperature of 362K for 6 hours. The solvent for the tetraethylenepentamine solution is ethanol; the content of tetraethylenepentamine in the tetraethylenepentamine solution is 5 wt% to 50 wt% of the porous carbon material. The porous carbon material was immersed in the tetraethylenepentamine solution for 30 minutes. When preparing the porous carbon material and ammonia-modified porous carbon adsorbent, the drying temperature is independently 350-353K.

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