Application of ammonia modified porous carbon adsorbent in methylene blue adsorption

Abstract

The invention relates to the technical field of adsorbent preparation and methylene blue adsorption, in particular to application of an ammonia modified porous carbon adsorbent in methylene blue adsorption. An ammonia modified porous carbon adsorbent is added into a water sample containing methylene blue for adsorption, so that the methylene blue in the water sample is removed; the preparation method of the ammonia modified porous carbon adsorbent comprises the following steps: carrying out hydrothermal acid leaching on gasified fine residues and an acid solution to obtain acid leaching residues; stirring the acid leaching residues in an alkali solution, washing and drying to obtain a porous carbon material; and dipping the porous carbon material in a tetraethylenepentamine solution, and then drying to obtain the ammonia modified porous carbon adsorbent. The ammonia modified porous carbon adsorbent is successfully constructed by taking a porous carbon material derived from coal gasification fine slag as a substrate and further adopting a surface ammonia functionalization modification strategy. The ammonia modified porous carbon adsorbent has a good adsorption effect on methylene blue.

Description

Technical Field

[0001] The invention relates to the technical field of adsorbent preparation and methylene blue adsorption, in particular to application of an ammonia-modified porous carbon adsorbent in adsorbing methylene blue. Background Art

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

[0003] The treatment of organic pollutants and heavy metal wastewater caused by rapid industrial development has become a major environmental challenge. Studies have shown that organic dyes such as methylene blue (MB) remaining in industrial wastewater are not only biologically toxic, but also pose a carcinogenic risk; and hexavalent chromium (Cr(VI)), as a strong oxidizing heavy metal pollutant, has been confirmed by a number of toxicological studies to be mutagenic and carcinogenic. For this type of pollutants, among the current mainstream technologies such as adsorption, membrane separation, and biodegradation (applicable to low-concentration wastewater), the adsorption method has become the treatment solution with the most application potential due to its advantages of simple operation, high removal efficiency and low risk of secondary pollution. This has driven the academic community to continue exploring low-cost, high-performance adsorption materials. Summary of the Invention

[0004] Based on the above content, the present invention provides an application of an ammonia-modified porous carbon adsorbent in the adsorption of methylene blue.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] The present invention provides an application of an ammonia-modified porous carbon adsorbent in adsorbing methylene blue. The ammonia-modified porous carbon adsorbent is added to a water sample containing methylene blue for adsorption, thereby removing the methylene blue from the water sample.

[0007] The preparation method of the ammonia-modified porous carbon adsorbent comprises the following steps:

[0008] hydrothermal acid leaching of the gasified fine slag with an acid solution to obtain an acid leaching residue;

[0009] Stirring the acid leaching residue in an alkaline solution, washing, and drying to obtain a porous carbon material;

[0010] The porous carbon material is immersed in a tetraethylenepentamine solution and then dried to obtain the ammonia-modified porous carbon adsorbent.

[0011] The present invention discloses the following technical effects:

[0012] This study uses a porous carbon material (CSM) derived from coal gasification slag as a substrate and further employs a surface ammonia functionalization strategy to successfully construct an ammonia-modified porous carbon adsorbent (CSM-TY). This ammonia-modified porous carbon adsorbent exhibits excellent MB adsorption, with a maximum MB adsorption capacity of 862.06 mg / g.

[0013] The present 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0015] Figure 1 This is a schematic diagram of the process flow for preparing an ammonia-modified porous carbon adsorbent according to the present invention.

[0016] Figure 2 XRD patterns of CSM and CSM-TY (Y = 5wt%, 10wt%, 20wt%, 30wt%, 50wt%, correspondingly marked as CSM-T5%, CSM-T10%, CSM-T20%, CSM-T30%, CSM-T50%) of the present invention.

[0017] Figure 3 FTIR spectra of CSM and CSM-TY of the present invention.

[0018] Figure 4 These are the XPS analysis results of CSM and CSM-TY of the present invention.

[0019] Figure 5 C1s fine spectra of CSM and CSM-TY of the present invention.

[0020] Figure 6 N1s fine spectra of CSM and CSM-TY of the present invention.

[0021] Figure 7 This is the O1s fine spectrum of CSM and CSM-TY of the present invention.

[0022] Figure 8These are scanning electron microscope images of the CSM and CSM-TY of the present invention; among them, (a) is CSM, (b) is CSM-T5%, (c) is CSM-T10%, (d) is CSM-T20%, (e) is CSM-T30%, and (f) is CSM-T50%.

[0023] Figure 9 These are the N2 adsorption-desorption curves and pore size distribution curves of the CSM and CSM-TY (Y = 5wt%, 10wt%, 20wt%) of the present invention; wherein, (a) is the N2 adsorption-desorption curve, and (b) is the pore size distribution curve.

[0024] Figure 10 The adsorption effects of the CSM and CSM-TY of the present invention on 200 mg / L MB and 50 mg / L Cr(VI) without adjusting the pH value of the system.

[0025] Figure 11 This is the influence of MB initial concentration on CSM-T5% adsorption capacity and removal rate under room temperature conditions.

[0026] Figure 12 This is the influence of the initial concentration of Cr(VI) on the adsorption capacity and removal rate of CSM-T5% under room temperature conditions.

[0027] Figure 13 The adsorption capacity and removal efficiency of MB by CSM-T5% change with time.

[0028] Figure 14 The adsorption amount and removal efficiency of Cr(VI) by CSM-T5% change with time.

[0029] Figure 15 Figure 2 shows the adsorption characteristics of MB on CSM-T5% at 298K, 308K and 318K.

[0030] Figure 16 The adsorption characteristics of CSM-T5% for Cr(VI) at 298K, 308K and 318K.

[0031] Figure 17 It is the zero charge point of CSM-T5%.

[0032] Figure 18 The influence of solution pH on MB adsorption performance.

[0033] Figure 19 The influence of solution pH on the adsorption performance of Cr(VI) is shown in Figure 4.

[0034] Figure 20 The effect of CSM-T5% dosage on MB and Cr(VI) removal rates.

[0035] Figure 21 The cyclic adsorption characteristics of MB and Cr(VI) by CSM-T5%.

[0036] Figure 22 The synergistic adsorption behavior of MB and Cr(VI) on CSM-T5%.

[0037] Figure 23 These are photos of CSM-T5% before and after adsorption in MB-Cr(VI) and Cr(VI)-MB binary systems with different concentrations.

[0038] Figure 24 (a) is the PSO model fitting correlation coefficient of MB, (b) is the linear fitting result of the intraparticle diffusion (ID) model of MB, (c) is the PSO model fitting correlation coefficient of Cr(VI), and (d) is the linear fitting result of the intraparticle diffusion (ID) model of Cr(VI).

[0039] Figure 25 FTIR spectra of CSM-T5% before and after adsorption of MB and Cr(VI).

[0040] Figure 26 Fitting results of S2p of CSM-T5% (a), XPS fitting results of Cr 2p (b), C 1s fine spectrum (c), O 1s fine spectrum (d), and N 1s fine spectrum (e).

[0041] Figure 27 Schematic diagram of the adsorption mechanism of MB (a) and Cr(VI) (b) by CSM-T5%. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] The present invention provides an application of an ammonia-modified porous carbon adsorbent in adsorbing methylene blue. The ammonia-modified porous carbon adsorbent is added to a water sample containing methylene blue for adsorption, thereby removing the methylene blue from the water sample.

[0048] The preparation method of the ammonia-modified porous carbon adsorbent comprises the following steps:

[0049] hydrothermal acid leaching of the gasified fine slag with an acid solution to obtain an acid leaching residue;

[0050] Stirring the acid leaching residue in an alkaline solution, washing, and drying to obtain a porous carbon material;

[0051] The porous carbon material is immersed in a tetraethylenepentamine solution and then dried to obtain the ammonia-modified porous carbon adsorbent.

[0052] In a preferred embodiment of the present invention, the concentration of the ammonia-modified porous carbon adsorbent in the water sample is 0.4-1.6 mg / mL.

[0053] In a preferred embodiment of the present invention, the adsorption temperature is 298-318 K; the adsorption time is 10-150 min.

[0054] In a preferred embodiment of the present invention, the pH of the water sample is 1-10; and the initial concentration of methylene blue in the water sample is 100-600 mg / L.

[0055] In a preferred embodiment of the present invention, the acid solution is a HNO3 solution with a concentration of 2 mol / L.

[0056] In a preferred embodiment of the present invention, the mass volume ratio of the gasified fine slag to the acid solution is 1 g:16 mL.

[0057] In a preferred embodiment of the present invention, the temperature of the hydrothermal acid leaching is 403K and the time is 150 minutes.

[0058] In a preferred embodiment of the present invention, after the hydrothermal acid leaching is completed, the steps of solid-liquid separation and washing the solid obtained by the solid-liquid separation to neutrality and drying are further included.

[0059] In a preferred embodiment of the present invention, the alkaline solution is a NaOH solution with a concentration of 2 mol / L.

[0060] In a preferred embodiment of the present invention, the acid leaching residue is stirred in the alkaline solution at a temperature of 362K for 6 hours. The present invention does not particularly limit the stirring speed, and the stirring speed commonly used by those skilled in the art can be adopted, such as 600 r / min.

[0061] In a preferred embodiment of the present invention, the solvent of the tetraethylene pentamine solution is ethanol; the content of tetraethylene pentamine in the tetraethylene pentamine solution accounts for 5 wt% to 50 wt% of the mass of the porous carbon material.

[0062] The present invention does not impose any particular limitation on the concentration of the tetraethylene pentamine solution, as long as the amount of the solvent in the tetraethylene pentamine solution is sufficient to dissolve the tetraethylene pentamine and immerse the porous carbon material.

[0063] In a preferred embodiment of the present invention, the porous carbon material is immersed in the tetraethylene pentamine solution for 30 minutes; and stirring is performed during the impregnation process. The purpose of stirring is to mix the tetraethylene pentamine and the porous carbon material evenly. The present invention does not impose any special limitation on the stirring speed, and the stirring speed commonly used by those skilled in the art can be adopted, such as 1000 r / min.

[0064] When preparing the porous carbon material and the ammonia-modified porous carbon adsorbent, the drying temperature is independently 350-353K.

[0065] The resource utilization of coal gasification slag and the harmless treatment of printing and dyeing wastewater and heavy metal wastewater are of great significance to the construction of a zero-emission industrial system and a resource recycling economy. The present invention uses coal gasification slag as raw material, obtains a porous carbon material (CSM) through a two-step acid-base treatment, and further uses an impregnation method to fix TEPA with different loading amounts on the CSM surface. Analysis by SEM, XRD, FTIR and other characterization methods shows that with the increase of TEPA loading, the amino content on the material surface is significantly improved, but excessive loading leads to amino group agglomeration and pore blockage. After loading 5%, the specific surface area of ​​CSM increases from 540.03m2 / g reduced to 376.20m 2 / g. The adsorption performance tests of MB and Cr(VI) found that CSM-T5% exhibited the best adsorption performance, with its equilibrium adsorption capacity increased by 8.01% and 15.91% respectively compared with the original CSM. By systematically clarifying the removal effects of MB and Cr(VI) under various influencing conditions such as initial concentration, contact time, temperature, pH value and adsorbent dosage, a theoretical support is provided for the development of printing and dyeing wastewater and heavy metal wastewater treatment technology. Kinetic analysis showed that the adsorption process of MB and Cr(VI) conformed to the quasi-second-order kinetic model, indicating that the adsorption process was mainly caused by chemical adsorption. Isothermal adsorption studies of the Langmuir model showed that the maximum adsorption capacity of CSM-T5% for MB and Cr(VI) at 318K was 862.06 mg / g and 233.10 mg / g respectively. Thermodynamic analysis confirmed the spontaneity and endothermic nature of the adsorption process, accompanied by an increase in entropy. Furthermore, regeneration experiments showed that after five cycles, CSM-T5% retained 71.37% and 63.68% of its adsorption capacity for MB and Cr(VI). The adsorption mechanism involves a synergistic effect between physical and chemical adsorption, with physical adsorption attributed to the pore filling of CSM-T5% and chemical adsorption primarily due to surface functional groups and intermolecular interactions. In summary, amino-modified porous carbon has great potential for the removal of printing and dyeing wastewater and heavy metal wastewater.

[0066] Unless otherwise specified, the technical solutions described in the present invention are all conventional solutions in the field, and the reagents or raw materials used, unless otherwise specified, are purchased from commercial channels or have been disclosed.

[0067] The technical solutions provided by the present invention are 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.

[0068] Example 1

[0069] 1. Materials and Methods

[0070] Materials and reagents

[0071] 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), tetraethylenepentamine (TEPA, C8H 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.

[0072] 1.2. Preparation of ammonia-modified porous carbon adsorbent

[0073] 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 to neutrality and dried at 378 K for 12 h to obtain an acid-leaching residue. The acid-leaching residue was stirred with 40 mL of 2 mol / L NaOH solution at 362 K for 6 h, finally washed to neutrality, and dried at 353 K for 12 h to obtain a porous carbon material (CSM).

[0074] TEPA was loaded on the CSM material by 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 minutes; 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 mass of the CSM material, respectively), and stirring was continued for 30 minutes; finally, it was dried at 350 K for 12 hours to remove ethanol to obtain an ammonia-modified porous carbon adsorbent. The obtained ammonia-modified porous carbon adsorbent is marked as CSM-TY, where T represents TEPA and Y represents the TEPA loading amount (5 wt%, 10 wt%, 20 wt%, 30 wt%, and 50 wt%), correspondingly marked as CSM-T5%, CSM-T10%, CSM-T20%, CSM-T30%, and CSM-T50%. The preparation process is as follows Figure 1 shown.

[0075] Characterization methods

[0076] A field emission scanning electron microscope (SEM, SIGMA 300) was used to observe the surface morphology of the samples at different magnifications to obtain detailed microstructural characteristics. At the same time, the energy dispersive spectrometer (EDS) equipped with the scanning electron microscope is a device used to analyze the elemental composition and distribution on the surface of the sample. The mineral phase composition of the sample was analyzed by X-ray diffraction (XRD, Bruker D8 Advance), using a Cu-Kα radiation source with a scanning range of 10° to 80° and a step size of 0.02°. The relevant calculation and analysis were completed using Jade 6 software. The composition of the surface functional groups was analyzed by Fourier transform infrared spectroscopy (FTIR, Bruker Tensor 27) with a wavenumber range of 4000 cm -1 Up to 400cm -1 , with a resolution of 4cm -1 The surface chemical composition of the samples was determined by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha) with an analysis chamber pressure below 2.0×10 -7mbar, using a non-monochromatic Al Kα X-ray source. Full-spectrum scans were performed at a flux energy of 150 eV with a step size of 1 eV, and narrow-spectrum scans were performed at a flux energy of 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. The micropore surface area was quantified using the t-plot method, while the mesopore surface area was determined using the BJH method.

[0077] 1.4. Adsorption experiments of single systems

[0078] This study systematically investigated the adsorption characteristics of CSM-TY for methylene blue (MB) and hexavalent chromium (Cr(VI)). The MB system parameters were as follows: solution volume of 50 mL, initial concentration of 100-600 mg / L (all other adsorption experiments used a MB concentration of 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 a characteristic wavelength of 665 nm using a UV-visible spectrophotometer. Blank controls were included in all experiments to ensure data reliability. Cr(VI) system: solution volume 50 mL, initial concentration 50–150 mg / L (all other adsorption characterization experiments used a 50 mg / L Cr(VI) concentration), adsorption time (30–1920 min), temperature (298–318 K), pH (1–10), adsorbent dosage (0.02–0.08 g), and regeneration times (1–5). Concentration was determined using visible spectrophotometry (540 nm). Each experiment was repeated three times to control for error.

[0079] During the regeneration process of CSM-Ty, 95% (v / v) ethanol was used as the eluent for the MB system, and desorption was performed at a solid-to-liquid ratio of 5:2 (m / V, mg / mL). The sample was ultrasonically treated for 15 minutes in an ultrasonic cleaner to achieve efficient desorption. 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. Saturated CSM-T5% was treated in an ultrasonic cleaner at a solid-to-liquid ratio of 5:2 (m / V, mg / mL) for 15 minutes. Desorption was repeated three times, and the regeneration efficiency of the material was measured.

[0080] The adsorption capacity (q) at a given time was determined using equations (1) and (2) respectively. t ) and MB and Cr(VI) removal efficiencies (R).

[0081]

[0082] Among them, 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 concentration of MB and Cr(VI) at time t. At adsorption equilibrium, the equilibrium concentration of MB and Cr(VI) in the solution is C e (mg / L), the corresponding adsorption capacity is q e (mg / g).

[0083] 1.5. Adsorption experiments of binary systems

[0084] Using the binary composite pollution system of MB and Cr(VI), the selective separation efficiency of adsorbent CSM-T5% in two competitive adsorption systems (MB-Cr(VI)) and Cr(VI)-MB) was systematically investigated.

[0085] In the MB-Cr(VI) system, the experimental group consisted of 25 mL of MB solution (200-600 mg / L) placed in a 150 mL conical flask, and 25 mL of a 50 mg / L fixed Cr(VI) solution was added to create a total system of 50 mL. The blank control group consisted of 25 mL of MB solution with the same concentration gradient (200-600 mg / L) but without the addition of Cr(VI) solution.

[0086] In the Cr(VI)-MB system, the experimental group was prepared by placing 25 mL of a 50-130 mg / L Cr(VI) solution in a conical flask and adding 25 mL of a 200 mg / L MB solution, for a total volume of 50 mL. The blank control group was prepared by adding 25 mL of a 50-130 mg / L Cr(VI) solution alone, without the addition of MB.

[0087] Subsequently, 0.02 g of CSM-TY adsorbent was accurately 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 that adsorption equilibrium was achieved.

[0088] 2. Results and Discussion

[0089] Structural characterization of CSM-TY

[0090] Phase composition analysis

[0091] Figure 2The XRD patterns of the original CSM and its modified samples, CSM-TY (Y = 5wt%, 10wt%, 20wt%, 30wt%, and 50wt%), were compared. All samples exhibited broad diffraction peaks near 2θ≈26° and 43°, which correspond to the characteristic peaks of amorphous carbon and indicate the presence of a small amount of residual inorganic minerals, primarily quartz (SiO2). Furthermore, even when the loading was increased from 5wt% to 50wt%, the CSM phase (e.g., SiO2) did not undergo significant changes, indicating that the modification process did not induce a crystalline phase transition.

[0092] 2.1.2. Functional group composition analysis

[0093] Figure 3 This is a comparative analysis of the FTIR spectra of CSM and its TEPA modified material CSM-TY (Y = 5 to 50 wt%). -1 The broad peak near the material is the stretching vibration characteristic peak of the hydroxyl group (-OH); 3400~3000cm -1 The absorption peaks in the range of 1650-1540 cm correspond to the stretching vibration mode of amino group (-NH2), while the absorption peaks in the range of 1650-1540 cm -1 The signal in the range 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 increase, which directly reflects the cumulative effect of -NH2 and NH rich in TEPA molecules on the CSM surface, confirming the positive correlation between loading and characteristic peak intensity.

[0094] Further analysis revealed that the modified material CSM-TY has a -1 A new characteristic absorption peak appears at 1130cm, which is the stretching vibration peak of -CH2. -1 The peak at 630-600cm is the characteristic peak of CN bond. -1 The above spectral characteristics, including the appearance of new characteristic peaks and the regular change of the main peak intensity with the loading amount, confirm that TEPA is successfully loaded on the surface of the CSM carrier and that its loading amount can cause the change of the characteristic peak intensity.

[0095] Surface chemical analysis

[0096] XPS analysis was performed on CSM and CSM-TY series samples with different TEPA loadings (5-50 wt%). Figure 4As shown in the graph, compared to CSM, CSM-TY exhibits a significant enhancement in 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 enhancing the electrostatic interaction between the adsorbent and MB and Cr(VI).

[0097] Table 1

[0098]

[0099] Figure 5 The C1s fine spectrum shows that the C1s peak of CSM can be deconvoluted 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 the 286.28 eV (C–O / C–N) peak in CSM-TY increased significantly with increasing tetraethylenepentamine loading (see Table 2), directly confirming the successful introduction of amino groups.

[0100] Table 2

[0101]

[0102] Figure 6 The N1s fine spectrum shows that after the CSM was modified with TEPA, the peak intensities of -NH at 399.98 eV and -NH2 at 400.49 eV were significantly enhanced. As shown in Table 2, with the increase of TEPA loading, the -NH and -NH2 contents increased synchronously, indicating that the amino content can be controlled and adjusted. Further studies found that the N / C ratios of CSM and the aminated material (such as CSN-T5%) were 0.016 and 0.031, respectively. With the increase of loading, the N / C ratio also increased, indicating that the amino group on the CSM was successfully modified, and also indicating that the fixed amino group on the material has accumulated.

[0103] Figure 7 The O1s fine spectrum shows that the oxygen-containing functional groups of CSM and CSM-TY are mainly hydroxyl (–OH, 533.27 eV) and carbonyl (C=O, 532.25 eV), indicating that the surface modification process has not changed the type of oxygen-containing functional groups.

[0104] 2.1.4. Micromorphology analysis

[0105] Figure 8 This is a scanning electron microscope morphology image of CSM and its TEPA-modified material CSM-TY (Y=5~50wt%). Figure 8(a) is the unmodified CSM. The material surface is smooth and has a porous structure. There are a large number of holes inside the pores and some of the holes are interconnected. Figure 3 Figures (b) through (f) show the modified materials after varying TEPA loadings. As can be seen, the modified materials retain their porous structure, with pores still visible within the channels, indicating that the addition of TEPA does not disrupt the material's pore framework. However, as the loading increases from 5% to 50%, the number of pores in the material decreases, pore blockage increases, and the surface roughness increases.

[0106] 2.1.5. Pore structure analysis

[0107] Figure 9 The N2 adsorption-desorption curves and pore size distribution curves of CSM and CSM-TY (Y = 5wt%, 10wt%, 20wt%) are shown in Figure 2. Figure 9 As shown in (a), the N2 adsorption / desorption curves of all samples are type IV isotherms. According to the IUPAC classification, the hysteresis loop shape belongs to the H3 type, and the closing point is located at P / P0≈0.40, indicating the presence of slit-shaped mesopores. When P / P0>0.4, the N2 adsorption amount continues to rise, especially when it is close to the saturation pressure, which indicates that there are some large pores in both CSM and CSM-TY. In addition, the hysteresis loop area of ​​CSM-TY is smaller than that of CSM, and with the increase of TEPA loading, the hysteresis loop gradually narrows, indicating that the mesopore volume decreases. This is because the TEPA molecules are loaded in the CSM pores or covered on the surface, resulting in partial mesopore blockage. Figure 9 As can be seen in (b), the pore size distribution after TEPA loading is lower than that of CSM, which further proves that TEPA does play a role in amino modification of the CSM surface.

[0108] 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. As can be seen from the table, the specific surface area of ​​CSM before modification is 540.03 m 2 / g, and a total pore volume of 0.5550 cm 3 / g, pore size is 4.1110nm. After TEPA modification, the specific surface area, total pore volume and pore size are reduced, and with the increase of loading, the specific surface area, total pore volume and pore size are gradually reduced. When the loading is increased to 20wt%, the specific surface area is reduced to 203.77m 2 / g, and the total pore volume is reduced to 0.3294 cm 3 / g, the pore size was reduced to 3.192nm. This indicates that TEPA occupies a portion of the pore space after loading, but the pore is not completely blocked.

[0109] Table 3

[0110]

[0111] Adsorption performance

[0112] Effect of TEPA loading on MB and Cr(VI) adsorption

[0113] The adsorption effect of 0.02g of TEPA modified material CSM-TY (Y = 5-50wt%) on 50mL 200mg / L MB and 50mL 50mg / L Cr(VI) after 1440min adsorption at room temperature without adjusting the pH value of the system is as follows: Figure 10 As shown. For the adsorption of MB, when the TEPA loading was 5% (CSM-T5%), the removal rate reached a maximum of 92.03%, which was 8.01% higher than the removal rate of 84.02% of the unmodified CSM; while the adsorption of Cr(VI) reached the best effect at a loading of 10% (CSM-T10%), with a removal rate of 31.74%, a significant increase of 15.91% compared to the removal rate of 15.83% of the original CSM. 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, at too high a loading, TEPA molecules aggregated on the surface of the material, resulting in pore blockage and a reduction in specific surface area, resulting in a decrease in removal efficiency. Taking into account the pollutant removal efficiency and the harm of excessive TEPA to the environment, CSM-T5% was selected for subsequent experiments.

[0114] 2.2.2. Adsorption characteristics of MB and Cr(VI) by CSM-T5% in a single system

[0115] Figure 11 and Figure 12The effects of initial MB and Cr(VI) concentrations on the adsorption capacity and removal efficiency of CSM-T5% at room temperature are shown. For the MB system (pH 7.84), the CSM-T5% dosage was 0.02 g, and the solution volume was 50 mL. When the initial concentration increased from 100 mg / L to 700 mg / L, the equilibrium adsorption capacity significantly increased from 249.77 mg / g to 784.03 mg / g after 150 minutes of adsorption. In the Cr(VI) system (pH 5.34), the dosage was 0.02 g, and the solution volume was 50 mL. When the initial concentration increased from 50 mg / L to 150 mg / L, the adsorption capacity increased from 112.73 mg / g to 188.32 mg / g after 1440 minutes of adsorption. This increase in adsorption capacity with concentration is primarily attributed to an enhanced mass transfer driving force. At high concentrations, MB and Cr(VI) form a larger concentration gradient on the adsorbent surface, promoting diffusion and mass transfer, thereby enhancing adsorption capacity. Despite the upward trend in adsorption, the removal rates of MB and Cr(VI) gradually decreased. This is because when MB and Cr(VI) concentrations are low, the amino groups and pore structure on the CSM-T5% surface fully expose active sites, resulting in high removal rates. However, as the concentrations continue to rise, the limited adsorption sites gradually become occupied, eventually reaching a dynamic equilibrium state, leading to a decrease in removal rates.

[0116] Figure 13 and Figure 14 The adsorption capacity and removal efficiency of 50 mL of 200 mg / L MB (pH 7.84) and 50 mL of 50 mg / L Cr(VI) (pH 5.34) were measured over time using 0.02 g of CSM-T5% at room temperature. During the initial adsorption period (0-30 min), MB exhibited a rapid adsorption rate, attributed to the lack of active sites on the adsorbent surface and the strong mass transfer driving force resulting from the high initial concentration. From 30 to 150 min, the adsorption rate decreased as the active sites gradually saturated, eventually leveling off. For Cr(VI), the adsorption rate of CSM-T5% initially increased and then leveled off with increasing adsorption time, reaching equilibrium after 1140 min.

[0117] 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 are shown. For the 200 mg / L MB system, the adsorption capacity increased with increasing temperature, reaching 466.24 mg / g at 298 K and 487.59 mg / g at 318 K, a 4.37% increase. Similarly, the adsorption capacity for 50 mg / L Cr(VI) also increased with increasing temperature, from 110.75 mg / g at 298 K to 119.03 mg / g at 318 K, a 6.95% increase. These trends indicate that increasing the temperature effectively enhances the adsorption capacity of CSM-T5% for both MB and Cr(VI).

[0118] Figure 17 The zero potential point of CSM-T5% is 7.01. When the pH value of the solution is lower than 7.01, the -NH2, -COOH and -OH active groups on the surface of the material are protonated to form -NH3 + 、-COOH2 + and -OH2 + , resulting in a positive charge on the surface of CSM-T5%. This is conducive to the effective adsorption of anionic forms of Cr(VI), such as HCrO4, by electrostatic attraction. - 、Cr2O7 2- and CrO4 2- , thus significantly improving the removal efficiency of Cr(VI) under acidic conditions. However, the positive charge on the surface of the material and MB + Electrostatic repulsion occurs between the Cr(VI) anions and the negatively charged CSM-T5% surface, significantly reducing the adsorption effect. In addition, under high pH conditions, the high concentration of -OH in the solution will react with CrO4 2- The negative charge on the surface of the material significantly enhances the adsorption of MB. + At the same time, the deprotonated hydroxyl groups can produce 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) are shown respectively. As the pH value increases from 1 to 10, the removal rate of MB continues to increase from 74.02% to 91.30%, while the removal rate of Cr(VI) drops sharply from 95.62% to 1.47%. The results show that under acidic conditions (pH < 7.01), the electrostatic attraction between the positive charge formed by the protonation of the material surface and the Cr(VI) anion dominates the adsorption process, while repelling MB. + Under alkaline conditions (pH>7.01), the negatively charged surface generated by deprotonation enhances the + The adsorption of Cr(VI) anions was inhibited by electrostatic repulsion and competitive adsorption of hydroxyl groups.

[0119] Figure 20 Figure 3 shows the effect of CSM-T5% dosage on the removal efficiency 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. 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. At this point, removal efficiencies were 65.59% and 55.52%, respectively, indicating significant adsorption incompleteness at low dosages. Increasing the CSM-T5% dosage to 0.06 g significantly increased the MB and Cr(VI) removal efficiencies 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, significantly improving the MB and Cr(VI) removal efficiencies. However, when the dosage was too high, the adsorption capacity decreased, primarily due to the agglomeration of the adsorbent particles, which reduced the specific surface area and resulted in insufficient utilization of the excess active sites. Therefore, in practical applications, the optimal dosage must be determined through experiments to ensure efficient removal of pollutants while avoiding waste of adsorbent resources.

[0120] 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 studied at room temperature. Figure 21 As shown in the figure, after three cycles, the removal efficiency of MB and Cr(VI) by CSM-T5% decreased, which was due to the gradual reduction of the effective active sites of CSM-T5% with the increase in the number of cycles. Nevertheless, after five cycles, the removal efficiency of MB and Cr(VI) remained at 71.37% and 63.68%, respectively, indicating that CSM-T5% has good cyclic performance.

[0121] 2.2.3. Synergistic effect of binary adsorption

[0122] Through binary system adsorption experiments, the synergistic adsorption behavior of 0.02g of CSM-T5% on 25mL 200mg / L MB and 25mL 50mg / L Cr(VI) was studied at room temperature. The experimental results show that in the MB-Cr(VI) and Cr(VI)-MB binary systems, the removal efficiency and adsorption capacity of pollutants are significantly improved compared with the single system. Figure 22 As shown in (a), when the Cr(VI) concentration in the MB-Cr(VI) system was fixed at 50 mg / L, the removal efficiency of CSM-T5% for 300 mg / LMB increased from 86.89% of the single system to 95.61%, while the Cr(VI) removal efficiency remained stable at above 95%. Figure 22 As shown in (b), in the Cr(VI)-MB system, at a fixed MB concentration of 200 mg / L, the removal efficiency of 130 mg / L Cr(VI) increased from 59.67% in the single system to 72.13%, while the MB removal efficiency remained at a high level of 99%. This phenomenon confirms the existence of a significant synergistic effect in the adsorption process of the binary system. On the one hand, MB preferentially adsorbs the negative surface charge of CSM-T5%, partially neutralizing the surface charge of the material and reducing the electrostatic repulsion between Cr(VI) anions and the adsorbent, thereby promoting the adsorption of Cr(VI). 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 the adsorption of Cr(VI).

[0123] Photos of CSM-T5% before and after adsorption in MB-Cr(VI) and Cr(VI)-MB binary systems with different concentrations are shown in the figure below. Figure 23 shown.

[0124] Adsorption kinetics

[0125] To clarify the key factors affecting the adsorption rate and its mechanism, the present invention used 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 PSO model fitting correlation coefficient (R 2 MB =0.994, R 2 Cr(VI) =0.995) was significantly better than 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) is consistent with the experimental value (q e,cal,MB =606.62mg / g;q e,cal,Cr(VI) =145.32 mg / g), indicating that the adsorption of MB and Cr(VI) by CSM-T5% conforms to the pseudo-second-order kinetic model. This result confirms that the adsorption process is dominated by chemical adsorption, which may involve mechanisms such as electrostatic interaction, electron transfer, or chemical bond formation.

[0126] Table 4

[0127]

[0128] Figure 24 (b) and (d) are the linear fitting results of the intraparticle diffusion (ID) model. The adsorption process can be segmented 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. Among them, the first straight line segment corresponds to the external surface diffusion process of MB or Cr(VI) from the liquid phase to the surface of CSM-T5%, and the second straight line segment reflects the intraparticle diffusion behavior of MB or Cr(VI) to the internal pores of CSM-T5%. The slope of the first straight line segment is significantly greater than that of the second straight line segment (k id,1 >k id,2 ), indicating a faster external surface diffusion rate. Therefore, in the initial stages of adsorption, intraparticle diffusion is the dominant rate-determining step. As the reaction proceeds, the MB or Cr(VI) concentration decreases, leading to a decrease in the concentration gradient between the inside and outside of the adsorbent. External surface diffusion weakens, and surface diffusion gradually becomes the rate-limiting factor. As MB or Cr(VI) continues to accumulate within the pores, the diffusion resistance increases, and the adsorption rate gradually decreases until dynamic equilibrium is reached. Furthermore, the boundary layer diffusion parameter c2 in the ID model is greater than c1, indicating that the boundary layer effect has a more significant impact on the adsorption rate during intraparticle diffusion.

[0129] Adsorption isotherms

[0130] Adsorption isotherm analysis was performed using the Langmuir isotherm model and the Freundlich isotherm model. The results showed that both models fitted well, and the Freundlich heterogeneity coefficient (n>1) indicated that the adsorption was effective. The Langmuir model had a high correlation coefficient (R 2 >0.99), indicating that it better represents the adsorption of MB or Cr(VI) on CSM-T5%, which means monolayer adsorption on a homogeneous surface. The Langmuir model fitting results show that the maximum adsorption amount (q m ) and Langmuir constant (K L) increases with increasing temperature. m,MB =862.06mg / g;q m,Cr(VI) =233.10 mg / g), maximum K L Value (K L,MB =0.2003; K L,Cr(VI) =0.243), indicating that the interaction between the adsorbent and the adsorbate is enhanced at higher temperatures, and the adsorption efficiency is improved. The adsorption performance of CSM-T5% of the present invention is shown in Table 5.

[0131] Table 5

[0132]

[0133] Thermodynamics

[0134] The thermodynamic parameters of the adsorption process, Gibbs free energy change (ΔG θ ), enthalpy change (ΔH θ ) and entropy change (ΔS θ ) and other thermodynamic parameters, the thermodynamic nature of MB or Cr(VI) adsorption on CSM-T5% was analyzed, and the relevant parameters are shown in Table 6. In the temperature range of 298K, 308K and 318K, the ΔG θ are all negative, indicating that the adsorption of MB or Cr(VI) on CSM-T5% is spontaneous. In addition, ΔG θ The absolute value of ΔG increases with increasing temperature, indicating that higher temperature promotes spontaneous reaction and thus enhances the adsorption of MB or Cr(VI). θ In the range of -20 to 0 kJ / mol, it indicates that the adsorption is physical in nature. Positive ΔH θ The value indicates that the adsorption process is endothermic, confirming the trend of the isotherm. In addition, the positive ΔS θ The values ​​correspond to the increase in entropy during the adsorption process, indicating an increase in randomness at the solid / liquid interface during MB or Cr(VI) adsorption.

[0135] Table 6

[0136]

[0137] 2.3. Adsorption mechanism analysis

[0138] The adsorption mechanism of CSM-T5% was systematically studied by FTIR and XPS. Figure 25 Comparison of FTIR characteristic peaks of the materials before and after adsorption of MB and Cr(VI). CSM-T5%-MB (after adsorption of MB) and CSM-T5%-Cr(VI) (after adsorption of Cr(VI)), 3430 cm -1The characteristic peak of -OH stretching vibration at 1636 cm-1 was red-shifted, and the peak intensity was significantly reduced, indicating that the hydroxyl group was the key adsorption site. At the same time, in the complex system of MB & Cr (VI) coexisting, the characteristic peak shift and intensity change trend of -OH were consistent with those of the single system, confirming that -OH was still the key adsorption site in different adsorption environments. After CSM adsorbed MB, Cr (VI) and the binary system of MB & Cr (VI), the peak shift and intensity change trend of -OH were consistent with those of the single system, confirming that -OH was still the key adsorption site in different adsorption environments. -1 The NH vibration peaks at -1 、1621cm -1 and 1626cm -1 , and the intensity is weakened. The main reason is that after NH is protonated, it interacts with the negatively charged groups, resulting in a decrease in the vibrational freedom of NH and a weakening of the intensity of the infrared absorption peak. -1 The CN stretching vibration peaks at 1452 cm-1 were all weakened after adsorption, indicating that the N atoms on the surface of the material participated in the adsorption process. For the MB-specific adsorption site, the peak at 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 at 1383 cm -1 The CH bending vibration peak of -CH3 and 543cm -1 The appearance of CSC characteristic peaks at 791 cm-1 and 792 cm-2 correspond to the vibration peaks of MB molecular structure, which confirm the successful adsorption of MB molecules on the surface of the material. -1 and 910cm -1 The new characteristic peaks at - The vibration peak of Cr-O and the asymmetric vibration mode of Cr=O indicate that CSM-T5% can also successfully adsorb Cr(VI).

[0139] Through the XPS full spectrum scan of the materials before and after the addition of MB and Cr(VI), it can be seen that the characteristic peaks of S2p and Cr 2p appear on CSM-T5%, which once again confirms that MB and Cr(VI) are successfully adsorbed on CSM-T5%. Figure 26 (a) is the fitting result of S2p. CSM-T5% shows peaks corresponding to C-SO2-C and C-SO3-Na at 168.11eV and 169.17eV, respectively. After MB adsorption, CSM-T5%-MB shows a C-SO3-H peak at 169.19eV and a CSC characteristic peak at 164.53eV, and the content increases by 0.21%, confirming the adsorption of MB, which is consistent with the enhancement of the C–SC stretching vibration peak in FTIR. The XPS fitting results of Cr 2p are shown in Figure 2. Figure 26As shown in (b). Cr 2p spectrum at 587.4eV (Cr 2p 1 / 2 ) and 577.6eV(Cr 2p 3 / 2 ) show two broad peaks, Cr(III) and Cr(VI). 3 / 2 In the region, the peaks with binding energies of 577.13eV and 579.08eV are Cr(III) in Cr(OH)3 and Cr(VI) in K2Cr2O7, respectively. 1 / 2 The fitted peak at 588.24 eV is Cr(VI) in Cr2O3, and 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, indicate that the Cr(VI) on the material surface is partially reduced to Cr(III) after adsorption.

[0140] Figure 26 (c) shows the C1s fine spectrum. The binding energies corresponding to 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 corresponding to 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 that ionic interactions contribute to MB adsorption. For Cr(VI) adsorption, the CO / CN content decreases, indicating that amino groups are active binding sites for Cr(VI). Furthermore, when MB and Cr(VI) coexist, the binding energy corresponding to CSM-T5%-MB&Cr(VI) lies between the two, indicating that CSM-T5% exhibits a synergistic adsorption effect on MB and Cr(VI).

[0141] Figure 26 (d) shows the O1s fine spectrum. The binding energies of 533.39 eV and 532.07 eV on CSM-T5% correspond to the functional groups -OH and C=O. After MB adsorption, the oxygen-containing functional groups on CSM-T5%-MB shift toward higher binding energies, indicating their participation 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 C=O electron-donating group participates in the reduction of Cr(VI) to Cr(III) and oxidizes to form carboxyl groups.

[0142] Figure 26(e) shows the N1s fine spectrum. After MB adsorption, CSM-T5%-MB shows a pyridine nitrogen characteristic peak at 399.20eV, confirming MB adsorption. At the same time, -NH3 appears at 401.56eV. + , indicating that the functional groups were protonated during MB adsorption. The -NH content at 400.08eV increased from 1.23% before MB adsorption to 1.34%, indicating that hydrogen bonds were formed during MB adsorption. After Cr(VI) adsorption, -NH3 appeared at 401.35eV. + The peak of α-amino group confirmed that the amino group was protonated and had electrostatic adsorption ability for Cr(VI).

[0143] To further illustrate the adsorption mechanism, Figure 27 As shown in the figure, by systematically exploring the key influencing factors of adsorption performance, combining adsorption kinetics, isothermal adsorption model fitting, thermodynamic parameter calculation and FTIR and XPS characterization, the synergistic adsorption mechanism of CSM-T5% on MB and Cr(VI) was revealed, and its adsorption process was a physical-chemical synergistic effect of physical adsorption and chemical adsorption.

[0144] Figure 27 (a) is a schematic diagram of the adsorption mechanism of MB by CSM-T5%. The pore structure of CSM-T5% promotes capillary action and synergistic effect. MB migrates into the pore structure of CSM-T5% during the adsorption process, that is, pore filling. The doping of nitrogen breaks the original chemical equilibrium, and the redistribution of spin state and charge density produces more active sites, which improves the adsorption efficiency. In addition to the hydrogen bond between N in MB molecules and NH groups in CSM-T5%, the ionic interaction between oxygen-containing functional groups such as carboxyl groups and MB molecules, and the π-π interaction between the benzene ring in MB molecules and the conjugated structure in the adsorbent, under acidic conditions, part of -NH2 is protonated to -NH3 + , and Cl in MB - Produces weak electrostatic attraction. Because the multi-amino characteristics of TEPA lead to charge dispersion, the charge density of a single site is reduced, weakening the Cl - electrostatic attraction.

[0145] Figure 27 (b) is a schematic diagram of the adsorption mechanism of Cr(VI) by CSM-T5%. The removal of Cr(VI) by CSM-T5% mainly includes three aspects: the negatively charged Cr(VI) ions and the positively charged surface functional groups (-NH3 + and -COOH + ) and then reduce Cr(VI) to Cr(III), allowing Cr(III) to complex with the functional groups on the adsorbent. The reduction of Cr(VI) to Cr(III) can be expressed as follows:

[0146] HCrO4 - +7H + +3e - →Cr3 + +4H2O

[0147] Cr2O7 2- +14H + +6e - →2Cr3 + +7H2O

[0148] 3. Conclusion

[0149] The present invention uses a porous carbon material (CSM) derived from coal gasification fine slag as a substrate, further adopts a surface ammonia functionalization modification strategy, and successfully constructs an ammonia-modified composite material (CSM-TY) by regulating the TEPA loading (Y = 5% wt%, 10% wt%, 20% wt%, 30% wt% and 50% wt%). By comprehensively using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption and desorption analysis and X-ray photoelectron spectroscopy (XPS) and other characterization methods, the structural evolution law of the material is systematically revealed: with the increase of TEPA loading, the amino content on the surface of the material is significantly improved, but excessive loading will cause amino group agglomeration and accumulation, causing pore blockage. When the loading is 5%, the specific surface area increases from the initial 540.03 m 2 / g reduced to 376.20m 2 / g.

[0150] Through the adsorption performance tests of MB and Cr(VI), it was found that CSM-T5% exhibited the best adsorption performance, and its equilibrium adsorption capacity increased by 8.01% and 15.91% respectively compared with the original CSM, confirming that the amino functionalization successfully enhanced the surface active sites. The pH value of the solution plays a crucial role in the adsorption of MB and Cr(VI). The removal rate of MB increased with the increase of pH value, while the opposite was true for Cr(VI). The adsorption process of MB and Cr(VI) conformed to the pseudo-second-order kinetic model (PSO), indicating chemical adsorption involving electrostatic interaction and electron transfer. The intraparticle diffusion model further revealed that the external surface diffusion and intraparticle diffusion jointly affect the overall adsorption rate. Thermodynamic analysis confirmed that the adsorption process was a spontaneous endothermic behavior.

[0151] Adsorption isotherms based on the Langmuir model showed that the maximum adsorption capacities of MB and Cr(VI) on CSM-T5% at 318 K reached 862.06 mg / g and 233.10 mg / g, respectively, showing a better fit than the Freundlich model, indicating a predominantly homogeneous surface adsorption. Analysis of surface properties before and after adsorption elucidated the adsorption mechanisms of MB and Cr(VI). For MB, synergistic effects include pore filling, electrostatic attraction, ionic interactions, and π-π conjugation. For Cr(VI), electrostatic interactions between Cr(VI) and the protonated CSM-T5% surface, reduction of Cr(VI) to Cr(III), and complexation of Cr(III) were implicated.

[0152] In the MB-Cr(VI) / Cr(VI)-MB binary system, both pollutant removal efficiency and adsorption capacity were significantly improved compared to the single-agent system, demonstrating the synergistic adsorption behavior of CSM-T5% for MB and Cr(VI). Regeneration experiments showed that after five cycles, CSM-T5% retained adsorption rates of 71.37% for MB and 63.68% for Cr(VI).

[0153] In summary, the adsorbent developed based on coal gasification fine slag has good potential in industrial production and application.

[0154] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. Application of an ammonia-modified porous carbon adsorbent in adsorbing methylene blue, characterized in that: Adding ammonia-modified porous carbon adsorbent to a water sample containing methylene blue for adsorption to achieve the removal of methylene blue from the water sample; The preparation method of the ammonia-modified porous carbon adsorbent comprises the following steps: hydrothermal acid leaching of the gasified fine slag with an acid solution to obtain an acid leaching residue; Stirring the acid leaching residue in an alkaline solution, washing, and drying to obtain a porous carbon material; The porous carbon material is immersed in a tetraethylenepentamine solution and then dried to obtain the ammonia-modified porous carbon adsorbent.

2. The use according to claim 1, characterized in that The concentration of the ammonia-modified porous carbon adsorbent in the water sample is 0.4-1.6 mg / mL.

3. The use according to claim 1, characterized in that The adsorption temperature is 298-318K; the adsorption time is 10-150 minutes.

4. The use according to claim 1, characterized in that The pH of the water sample is 1-10; the initial concentration of methylene blue in the water sample is 100-600 mg / L.

5. The use according to claim 1, characterized in that The acid solution is a HNO3 solution with a concentration of 2 mol / L; The mass volume ratio of the gasified fine slag to the acid solution is 1 g:16 mL; The temperature of the hydrothermal acid leaching is 403K and the time is 150 minutes.

6. The use according to claim 1, characterized in that After the hydrothermal acid leaching is completed, the steps of solid-liquid separation and washing the solid obtained by the solid-liquid separation to neutrality and drying are also included.

7. The use according to claim 1, characterized in that The alkaline solution is a NaOH solution with a concentration of 2 mol / L.

8. The use according to claim 1, characterized in that The acid leaching residue is stirred in the alkaline solution at a temperature of 362K for 6 hours.

9. The use according to claim 1, characterized in that The solvent of the tetraethylene pentamine solution is ethanol; the content of tetraethylene pentamine in the tetraethylene pentamine solution accounts for 5 wt% to 50 wt% of the mass of the porous carbon material.

10. The use according to claim 1, characterized in that The porous carbon material is immersed in the tetraethylenepentamine solution for 30 minutes; When preparing the porous carbon material and the ammonia-modified porous carbon adsorbent, the drying temperature is independently 350-353K.

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