Ammonia modified porous carbon adsorbent and preparation method thereof

Abstract

The invention relates to the technical field of adsorbent preparation, in particular to an ammonia modified porous carbon adsorbent and a preparation method thereof. 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 preparation method is simple, the raw materials are easy to obtain, and the prepared ammonia modified porous carbon adsorbent has a good adsorption effect on methylene blue and hexavalent chromium. According to the method, high-added-value resource utilization of the coal gasification solid waste is achieved, and a solution is provided for treatment of the dye wastewater and the heavy metal wastewater.

Description

Technical Field

[0001] The present invention relates to the technical field of adsorbent preparation, and particularly to an ammonia-modified porous carbon adsorbent and a preparation method thereof. Background Art

[0002] As a core process of coal chemical industry, coal gasification technology produces coal gasification slag, which accounts for more than 95% of the total solid waste in the industry. At present, such solid wastes are mainly disposed of by open stacking. A large amount of stacking not only occupies land resources, but also causes environmental problems such as dust pollution and water pollution. Analysis shows that coal gasification slag mainly contains metal oxides such as SiO2, CaO, Al2O3 and residual carbon. Therefore, promoting the resource utilization of coal gasification slag has become the key path to solve environmental problems and realize the comprehensive utilization of solid waste.

[0003] The treatment of organic pollutants and heavy metal wastewater brought about by the rapid development of industry has become a major environmental challenge. Research shows that organic dyes such as methylene blue (MB) remaining in industrial wastewater not only have biological toxicity, but also pose a carcinogenic risk; while hexavalent chromium (Cr(VI)), as a strong oxidizing heavy metal pollutant, its mutagenicity and carcinogenicity have been confirmed by a number of toxicological studies. For such pollutants, among the current mainstream technologies such as adsorption method, membrane separation method, and biodegradation method (applicable to low-concentration wastewater), the adsorption method has become the most promising treatment solution due to its advantages of simple operation, high removal efficiency and low risk of secondary pollution. This drives the continuous exploration of low-cost and high-performance adsorption materials in the academic community. Summary of the Invention

[0004] Based on the above, the present invention provides an ammonia-modified porous carbon adsorbent and a preparation method thereof. The ammonia-modified porous carbon adsorbent of the present invention has good adsorption effects on MB and Cr(VI), and at the same time realizes the resource utilization of coal gasification slag.

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

[0006] One of the technical solutions of the present invention, a preparation method of an ammonia-modified porous carbon adsorbent, includes the following steps:

[0007] Hydrothermally acid-leach the gasified fine slag with an acid solution to obtain an acid-leached residue;

[0008] After stirring the acid-leached residue in an alkali solution, wash and dry it to obtain a porous carbon material;

[0009] Immerse the porous carbon material in a tetraethylenepentamine solution, and then dry it to obtain the ammonia-modified porous carbon adsorbent.

[0010] In a preferred embodiment of the present invention, the acid solution is a 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 by the above-mentioned preparation method.

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

[0013] Based on the porous carbon material (CSM) derived from coal gasification fine slag, the present invention further adopts a surface ammonia-functionalization modification strategy to successfully construct an ammonia-modified porous carbon adsorbent (CSM-TY).

[0014] The preparation method of the present invention is simple, and the raw materials are easy to obtain. The prepared ammonia-modified porous carbon adsorbent has good adsorption effects on MB and Cr(VI).

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

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

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

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

[0019] Figure 3 It is the FTIR spectrum of CSM and CSM-TY of the present invention.

[0020] Figure 4 It is the XPS analysis result of CSM and CSM-TY of the present invention.

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

[0022] Figure 6 It is the N1s fine spectrum of CSM and CSM-TY of the present invention.

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

[0024] Figure 8 Scanning electron microscope images of 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%.

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

[0026] Figure 10 Adsorption effects of CSM and CSM-TY of the present invention on 200 mg / L of MB and 50 mg / L of Cr(VI) under the condition of not adjusting the pH value of the system.

[0027] Figure 11 Effect of initial concentration of MB on adsorption capacity and removal rate of CSM-T5% at room temperature.

[0028] Figure 12 Effect of initial concentration of Cr(VI) on adsorption capacity and removal rate of CSM-T5% at room temperature.

[0029] Figure 13 Variation of adsorption capacity and removal efficiency of CSM-T5% for MB with time.

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

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

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

[0033] Figure 17 Zero charge point of CSM-T5%.

[0034] Figure 18 Effect of solution pH value on adsorption performance of MB.

[0035] Figure 19 Effect of solution pH value on adsorption performance of Cr(VI).

[0036] Figure 20Effect of the dosage of CSM-T5% on the removal rates of MB and Cr(VI).

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

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

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

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

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

[0042] 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), N 1s fine spectrum (e).

[0043] Figure 27 Schematic diagrams of the adsorption mechanism of CSM-T5% for MB (a) and Cr(VI) (b). Detailed implementation manners

[0044] Now, various exemplary implementation manners of the present invention will 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, characteristics, and implementation schemes of the present invention.

[0045] It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0046] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to those documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0047] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this invention are merely exemplary.

[0048] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but 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] Performing hydrothermal acid leaching on gasified fine slag with an acid solution to obtain an acid-leached residue;

[0051] After stirring the acid-leached residue in an alkali solution, washing and drying it to obtain a porous carbon material;

[0052] Impregnating the porous carbon material in a tetraethylenepentamine solution and then drying it to obtain the ammonia-modified porous carbon adsorbent.

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

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

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

[0056] In a preferred embodiment of this invention, after the hydrothermal acid leaching, it further includes the steps of solid-liquid separation and washing the solid obtained from the solid-liquid separation to neutrality and drying.

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

[0058] In a preferred embodiment of the present invention, the temperature of stirring the acid leaching residue in the alkaline solution is 362K, and the time is 6h; the present invention does not make a special limitation on the stirring speed, and the stirring speed commonly used by those skilled in the art can be adopted, such as not less than 600r / 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 5wt% - 50wt% of the mass of the porous carbon material.

[0060] The present invention does not make a special limitation on the concentration of the tetraethylenepentamine solution, and the amount of the solvent in the tetraethylenepentamine solution can sufficiently dissolve tetraethylenepentamine and immerse the porous carbon material.

[0061] In a preferred embodiment of the present invention, the impregnation time of the porous carbon material in the tetraethylenepentamine solution is 30min; and stirring is carried out during the impregnation process, and the purpose of stirring is to mix tetraethylenepentamine and the porous carbon material evenly; the present invention does not make a special limitation on the stirring speed, and the stirring speed commonly used by those skilled in the art can be adopted, such as 1000r / min.

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

[0063] The second aspect of the present invention provides an ammonia-modified porous carbon adsorbent prepared by the above preparation method.

[0064] The resource utilization of coal gasification fine slag and the harmless treatment of printing and dyeing wastewater and heavy metal wastewater are of great significance for building a zero-emission industrial system and a resource recycling economy. The present invention uses coal gasification fine slag as a raw material, and through two-step acid-base treatment, a porous carbon material (CSM) is obtained, and different loadings of TEPA are further fixed on the surface of CSM by an impregnation method. Analysis by characterization means such as SEM, XRD, and FTIR shows that with the increase of the TEPA loading, the amino group content on the material surface increases significantly, but excessive loading leads to the agglomeration of amino groups and the blockage of pores. After loading 5%, the specific surface area of CSM decreases from 540.03m 2 / g to 376.20m 2 / g. The adsorption performance tests for MB and Cr(VI) found that CSM-T5% exhibited the optimal adsorption performance, with its equilibrium adsorption capacity increased by 8.01% and 15.91% respectively compared to the original CSM. By systematically elucidating the removal effects of MB and Cr(VI) under various influencing conditions such as initial concentration, contact time, temperature, pH value, and adsorbent dosage, it provided theoretical support for the development of treatment technologies for printing and dyeing wastewater and heavy metal wastewater. Kinetic analysis showed that the adsorption processes of MB and Cr(VI) conform to the pseudo-second-order kinetic model, indicating that the adsorption process is mainly chemisorption. The isothermal adsorption study of the Langmuir model showed that the maximum adsorption capacities of CSM-T5% for MB and Cr(VI) reached 862.06 mg / g and 233.10 mg / g respectively at 318 K. Thermodynamic analysis confirmed the spontaneity and endothermic nature of the adsorption process, accompanied by an increase in entropy. In addition, the regeneration experiment showed that the adsorption retention rates of CSM-T5% for MB and Cr(VI) still reached 71.37% and 63.68% after 5 cycles. The adsorption mechanism involves the synergistic effect between physical and chemical adsorption. Physical adsorption is attributed to the pore filling of CSM-T5%, and chemical adsorption is mainly 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.

[0065] The technical solutions described in the present invention are all conventional solutions in the art unless otherwise specified, 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 in conjunction with the embodiments, but they cannot be construed as limiting the protection scope of the present invention.

[0067] Example 1

[0068] 1. Materials and Methods

[0069] 1.1. Materials and Reagents

[0070] The 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), all of which were 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 and 64 mL of 2 mol / L HNO3 were subjected to hydrothermal acid leaching (403 K, 150 min) in a polytetrafluoroethylene reaction kettle. After solid-liquid separation, the obtained solid was washed to neutrality and dried at 378 K for 12 h to obtain the acid-leached residue. The acid-leached residue was stirred with 40 mL of 2 mol / L NaOH solution at 362 K for 6 h, and finally washed to neutrality and dried at 353 K for 12 h to obtain the porous carbon material (CSM).

[0073] The TEPA was loaded onto the CSM material by the physical impregnation method. The specific preparation process was 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 addition amounts of TEPA were 5 wt%, 10 wt%, 20 wt%, 30 wt%, 50 wt% of the mass of the CSM material), and stirring was continued for 30 min; finally, it was dried at 350 K for 12 h to remove ethanol, and the ammonia-modified porous carbon adsorbent was obtained. The obtained ammonia-modified porous carbon adsorbent was labeled as CSM-TY, where T represents TEPA and Y represents the TEPA loading amount (5 wt%, 10 wt%, 20 wt%, 30 wt%, 50 wt%), and the corresponding labels were CSM-T5%, CSM-T10%, CSM-T20%, CSM-T30%, CSM-T50%. The preparation process was as Figure 1 shown.

[0074] 1.3. Characterization methods

[0075] The surface morphology of the samples at different magnifications was observed by field emission scanning electron microscopy (SEM, SIGMA 300) to obtain detailed microstructural features. 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 its distribution on the surface of the samples. 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° to 80° and a step size of 0.02°. The relevant calculation and analysis were completed using Jade 6 software. The composition of surface functional groups was analyzed by Fourier transform infrared spectroscopy (FTIR, Bruker Tensor 27), with a wavenumber range of 4000 cm -1 to 400 cm -1 and a resolution of 4 cm -1 . The surface chemical composition of the samples was detected by X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha), and the pressure in the analysis chamber was lower than 2.0×10 -7mbar, using a non-monochromatic Al Kα X-ray source. The full-spectrum scanning flux energy was 150 eV with a step size of 1 eV; the narrow-spectrum scanning flux energy was 50 eV with a step size of 0.1 eV. The nitrogen adsorption-desorption isotherm was measured using a nitrogen adsorption analyzer (ASAP 260), and the specific surface area and pore structure of the samples were determined by the BET (Brunauer-Emmett-Teller) and BJH (Barrett-Joyner-Halenda) methods. The micropore surface area was quantified by the t-plot method, while the mesopore surface area was determined by the BJH method.

[0076] 1.4. Adsorption experiments for a single system

[0077] The present invention systematically investigated the adsorption characteristic parameters of CSM-TY for methylene blue (MB) and hexavalent chromium (Cr(VI)). MB system: The solution volume was 50 mL, the initial concentration was 100 - 600 mg / L (the concentration of the MB system used in other adsorption characteristic experiments was 200 mg / L), the contact time was (10 - 150 min), the temperature was (298 - 318 K), the pH was (1 - 10), the adsorbent dosage was (0.02 - 0.08 g), and the number of cycles was (1 - 5 times). The absorbance of the solution was measured using a UV-visible spectrophotometer at the characteristic wavelength of 665 nm, and all experiments were set with blank control groups to ensure data reliability. Cr(VI) system: The solution volume was 50 mL, the initial concentration was 50 - 150 mg / L (the concentration of the Cr(VI) system used in other adsorption characteristic experiments was 50 mg / L), the adsorption time was (30 - 1920 min), the temperature was (298 - 318 K), the pH was (1 - 10), the adsorbent dosage was (0.02 - 0.08 g), and the number of regeneration times was (1 - 5 times). The concentration was determined by visible spectrophotometry (540 nm), and each group of experiments was performed in parallel 3 times to control errors.

[0078] During the regeneration process of CSM-TY, 95% (v / v) ethanol was used as the eluent for the MB system, and the operation was carried out according to the solid-liquid ratio of 5:2 (m / V, mg / mL) during the desorption process. The sample was placed in an ultrasonic cleaner and ultrasonically treated for 15 min to achieve efficient desorption, and this process was repeated three times to ensure the consistency and thoroughness of the operation. For the Cr(VI) system, 0.05 mol / L sodium hydroxide solution was used as the eluent, and the saturated adsorbed CSM-T5% was placed in an ultrasonic cleaner and treated for 15 min according to the solid-liquid ratio of 5:2 (m / V, mg / mL). After repeating the desorption 3 times, the regeneration efficiency of the material was measured.

[0079] Equations (1) and (2) were used to determine the adsorption capacity (q t ) and the removal efficiency (R) of MB and Cr(VI) at a given time.

[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), and the corresponding adsorption capacity is q e (mg / g).

[0082] 1.5. Adsorption experiments for binary systems

[0083] Through the binary composite pollution system of MB and Cr(VI), the selective separation efficiency of the adsorbent CSM-T5% in two competitive adsorption systems (MB-Cr(VI)) and Cr(VI)-MB) was systematically investigated.

[0084] In the MB-Cr(VI) system, experimental group: Measure 25 mL of MB solution with a concentration of 200 - 600 mg / L and place it in a 150 mL conical flask, add 25 mL of Cr(VI) solution with a fixed concentration of 50 mg / L to form a total system of 50 mL. Blank control group: Separate 25 mL of MB solution with the same concentration gradient (200 - 600 mg / L) was set alone without adding Cr(VI) solution.

[0085] In the Cr(VI)-MB system, experimental group: Measure 25 mL of Cr(VI) solution with a concentration of 50 - 130 mg / L in a conical flask, add 25 mL of MB solution with a constant concentration of 200 mg / L, and the total system is 50 mL. Blank control group: Separate 25 mL of Cr(VI) solution with the same concentration gradient (50 - 130 mg / L) was set alone without adding MB solution.

[0086] Subsequently, accurately add 0.02 g of CSM-TY adsorbent to all experimental groups and blank control groups, and oscillate at 130 rpm for 1440 min at room temperature to ensure adsorption equilibrium is reached.

[0087] 2. Results and discussion

[0088] 2.1. Structural characterization of CSM-TY

[0089] 2.1.1. Phase composition analysis

[0090] Figure 2The XRD patterns of the original CSM and its modified samples CSM-TY (Y = 5 wt%, 10 wt%, 20 wt%, 30 wt%, 50 wt%) were compared. All samples presented broad diffraction peaks near 2θ ≈ 26° and 43°, which corresponded to the typical characteristic peaks of amorphous carbon and simultaneously indicated that a small amount of inorganic minerals remained in the materials, mainly quartz (SiO2). In addition, even when the loading amount increased from 5 wt% to 50 wt%, the phase of CSM (such as SiO2) did not change significantly, indicating that the modification process did not cause a phase transformation.

[0091] 2.1.2. Analysis of functional group composition

[0092] Figure 3 This is the comparative analysis of the FTIR spectra of CSM and its TEPA-modified materials CSM-TY (Y = 5 - 50 wt%). In the spectra, the broad peak near 3430 cm -1 is the characteristic peak of the stretching vibration of hydroxyl groups (-OH) in the material; the absorption peaks in the range of 3400 - 3000 cm -1 correspond to the stretching vibration mode of amino groups (-NH2), while the signals in the range of 1650 - 1540 cm -1 are the bending vibration responses of N-H bonds. With the increase in the TEPA loading amount, the characteristic peak intensities of -NH2 and N-H show a gradient enhancement trend, which directly reflects the cumulative effect of the rich -NH2 and N-H in the TEPA molecule on the surface of CSM, verifying the positive correlation between the loading amount and the characteristic peak intensity.

[0093] Further analysis found that the modified material CSM-TY showed a new characteristic absorption peak at 2930 cm -1 for the stretching vibration peak of -CH2. At 1130 cm -1 is the characteristic peak of the C-N bond. The range of 630 - 600 cm -1 is the vibration peak of the C-S bond. 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 was successfully loaded on the surface of the CSM carrier, and its loading amount can cause changes in the characteristic peak intensity.

[0094] 2.1.3. Surface chemical analysis

[0095] XPS analysis was carried out on CSM and the CSM-TY series samples with different TEPA loading amounts (5 - 50 wt%). The wide-scan spectra, such as Figure 4As shown, compared with CSM, the N 1s signal of CSM-TY is significantly enhanced at 400.0 eV, confirming the successful introduction of amino / amine functional groups onto the material surface. Moreover, with the increase in TEPA loading, the intensity of the N 1s peak shows a positive correlation (see Table 1). The introduction of nitrogen elements significantly improves the adsorption performance of pollutants by enhancing the electrostatic interaction between the adsorbent and MB and Cr(VI).

[0096] Table 1

[0097]

[0098] Figure 5 Figure 10 shows the C 1s fine spectrum. The results indicate that the C 1s 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 modification with TEPA, the peak area and atomic percentage of CSM-TY at 286.28 eV (C–O / C–N) increase significantly with the increase in tetraethylenepentamine loading (see Table 2), directly demonstrating the successful introduction of amino groups.

[0099] Table 2

[0100]

[0101] Figure 6 Figure 11 shows the N 1s fine spectrum. After modification of CSM with TEPA, the peak intensities of -NH at 399.98 eV and -NH2 at 400.49 eV are significantly enhanced. As can be seen from Table 2, with the increase in TEPA loading, the contents of -NH and -NH2 increase synchronously, indicating that the amino content can be controllably adjusted. Further research finds that the N / C ratios of CSM and the ammoniated material (such as CSN-T5%) are 0.016 and 0.031, respectively. With the increase in loading, the N / C ratio also increases, indicating the successful modification of amino groups on CSM and the accumulation of immobilized amino groups on the material.

[0102] Figure 7 Figure 12 shows the O 1s fine spectrum. The results show that the oxygen-containing functional groups of CSM and CSM-TY are mainly hydroxyl groups (–OH, 533.27 eV) and carbonyl groups (C=O, 532.25 eV), indicating that the type of oxygen-containing functional groups remains unchanged during the surface modification process.

[0103] 2.1.4. Microscopic Morphology Analysis

[0104] Figure 8 Figure 13 shows the SEM morphology diagrams of CSM and its TEPA-modified materials CSM-TY (Y = 5 - 50 wt%). Figure 8In (a), it is unmodified CSM. The material surface is smooth, presenting a porous structure. There are a large number of holes inside the pores, and some of the pores communicate with each other. Figure 8 In (b)-(f), they are materials modified with different TEPA loadings. It can be seen that the modified materials still maintain a porous structure, and the pores inside the pores are still visible, indicating that the addition of TEPA does not damage 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 roughness of the material surface increases.

[0105] 2.1.5. Pore structure analysis

[0106] Figure 9 are the N2 adsorption-desorption curves and pore size distribution curves of CSM and CSM-TY (Y = 5wt%, 10wt%, 20wt%). As Figure 9 shown in (a), the N2 adsorption / desorption curves of all samples are type IV isotherms. According to the IUPAC classification, the shape of the hysteresis loop belongs to type H3, and the closing point is located at P / P0 ≈ 0.40, indicating the existence of slit-shaped mesopores. When P / P0 > 0.4, the N2 adsorption amount continues to increase, especially rising significantly near the saturation pressure, indicating that there are some macropores in both CSM and CSM-TY. In addition, the hysteresis loop area of CSM-TY is smaller than that of CSM, and as the TEPA loading increases, the hysteresis loop gradually narrows, indicating a decrease in the mesopore volume. This is because the TEPA molecules are loaded in the CSM pores or cover the surface, resulting in partial blockage of some mesopores. From Figure 9 it can be seen from (b) that the pore size distribution after TEPA loading is lower than that of CSM, further proving that TEPA does play an amino modification role on the CSM surface.

[0107] Table 3 compares the effects of different TEPA loadings (Y = 5wt%, 10wt%, 20wt%) on the specific surface area, pore size and total pore volume of CSM. It can be seen from the table that the specific surface area of unmodified CSM is 540.03 m 2 / g, the total pore volume is 0.5550 cm 3 / g, and the pore size is 4.1110 nm. After TEPA modification, the specific surface area, total pore volume and pore size all decrease, and as the loading increases, the specific surface area, total pore volume and pore size all gradually decrease. When the loading increases to 20wt%, the specific surface area decreases to 203.77 m 2 / g, the total pore volume drops to 0.3294 cm 3 / g, and the pore size shrinks to 3.192 nm. It shows that TEPA occupies a part of the position in the pores after loading. However, the pores are not completely blocked.

[0108] Table 3

[0109]

[0110] 2.2. Adsorption performance

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

[0112] At room temperature, with a dosage of 0.02 g of TEPA-modified material CSM-TY (Y = 5 - 50 wt%) and without adjusting the pH value of the system, the adsorption effects on 50 mL of 200 mg / L MB and 50 mL of 50 mg / L Cr(VI) after 1440 min of adsorption are as Figure 10 shown. For the adsorption of MB, when the TEPA loading is 5% (CSM-T5%), the removal rate reaches the highest value of 92.03%, which is 8.01% higher than the removal rate of 84.02% of unmodified CSM; while for the adsorption of Cr(VI), the best effect is achieved when the loading is 10% (CSM-T10%), and the removal rate is 31.74%, which is significantly increased by 15.91% compared with the removal rate of 15.83% of the original CSM. When the TEPA loading exceeds 5%, the removal efficiency of MB shows a downward trend, and the adsorption effect of Cr(VI) also gradually decreases after the loading exceeds 10%. This is because at high loadings, TEPA molecules aggregate on the material surface, resulting in pore blockage and a reduction in specific surface area, causing a decrease in the removal effect. Considering the pollutant removal efficiency and the harm of excessive TEPA to the environment, CSM-T5% was selected for subsequent experiments.

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

[0114] Figure 11 and Figure 12The effects of the initial concentrations of MB and Cr(VI) on the adsorption capacity and removal rate of CSM-T5% at room temperature are presented respectively. For the MB system (pH 7.84), with a CSM-T5% dosage of 0.02 g and a solution volume of 50 mL each, when the initial concentration increased from 100 mg / L to 700 mg / L, after 150 min of adsorption, the equilibrium adsorption capacity increased significantly from 249.77 mg / g to 784.03 mg / g. In the Cr(VI) system (pH 5.34), with a dosage of 0.02 g and a solution volume of 50 mL each, when the initial concentration increased from 50 mg / L to 150 mg / L, after 1440 min of adsorption, the adsorption capacity increased from 112.73 mg / g to 188.32 mg / g. The increase in adsorption capacity with increasing concentration is mainly attributed to the enhanced mass transfer driving force. The concentration gradient formed between high-concentration MB and Cr(VI) and the adsorbent surface increases, promoting the diffusion mass transfer process and thus enhancing the adsorption capacity. Although the adsorption capacity shows an upward trend, the removal rates of MB and Cr(VI) gradually decrease. 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, and finally a dynamic equilibrium state is reached, leading to a decrease in the removal rate.

[0115] Figure 13 and Figure 14 The changes in 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) with time at room temperature are presented respectively. In the initial adsorption stage of 0 - 30 min, the adsorption rate of MB is relatively fast, which is attributed to the unoccupied active sites on the adsorbent surface and the strong mass transfer driving force formed by the high initial concentration. Between 30 - 150 min, as the active sites gradually become saturated, the adsorption rate decreases accordingly and finally levels off. For Cr(VI), as the adsorption time increases, the adsorption rate of CSM-T5% for Cr(VI) shows a trend of first increasing and then leveling off, reaching the 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. For the 200 mg / L MB system, the adsorption capacity increases with increasing temperature, reaching 466.24 mg / g at 298 K and increasing to 487.59 mg / g at 318 K, with a 4.37% increase in adsorption capacity. Similarly, for the 50 mg / L Cr(VI) system, the adsorption capacity also increases with increasing temperature, from 110.75 mg / g at 298 K to 119.03 mg / g at 318 K, with an increase of 6.95%. These trends indicate that increasing the temperature can effectively improve the adsorption capacity of CSM-T5% for MB and Cr(VI).

[0117] Figure 17 shows that the zero potential point of CSM-T5% is 7.01. When the solution pH is below 7.01, the active groups -NH2, -COOH, and -OH on the material surface are protonated, forming -NH3 + , -COOH2 + and -OH2 + , resulting in a positively charged surface of CSM-T5%. This is beneficial for the effective adsorption of the anionic forms of Cr(VI) through electrostatic attraction, such as HCrO4 - , Cr2O7 2- and CrO4 2- , thus significantly improving the removal efficiency of Cr(VI) under acidic conditions. However, the electrostatic repulsion between the positively charged surface of the material and MB + results in the inhibition of its adsorption capacity for MB. When the solution pH is above 7.01, deprotonation occurs on the surface of CSM-T5%, resulting in a negatively charged surface of the material. At this time, electrostatic repulsion occurs between the anions of Cr(VI) and the negatively charged surface of CSM-T5%, significantly reducing the adsorption effect. In addition, at high pH, the high concentration of -OH in the solution competes with anions such as CrO4 2- for adsorption sites, further reducing the removal efficiency of Cr(VI). On the contrary, the negative charge on the material surface significantly enhances the electrostatic attraction for MB + , and the deprotonated hydroxyl groups can also produce a synergistic adsorption effect with MB through hydrogen bonding, thus significantly improving the removal performance of MB under alkaline conditions. Figure 18 and Figure 19The influence rules of solution pH on the adsorption performance of MB and Cr(VI) are as follows. As the pH value increases from 1 to 10, the removal rate of MB continuously increases from 74.02% to 91.30%, while the removal rate of Cr(VI) sharply decreases from 95.62% to 1.47%. The results show that under acidic conditions (pH < 7.01), the electrostatic attraction between the positive charges formed by the protonation of the material surface and the Cr(VI) anions dominates the adsorption process, while repelling MB + ; under alkaline conditions (pH > 7.01), the negatively charged surface generated by deprotonation enhances the adsorption of MB + , while showing a dual inhibitory effect of electrostatic repulsion and hydroxyl competitive adsorption on Cr(VI) anions.

[0118] Figure 20 At room temperature, the influence of the dosage of CSM-T5% 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) is shown. When the dosage is 0.02 g, the limited active sites on the material surface are quickly occupied by MB and Cr(VI), resulting in the adsorption saturation phenomenon. At this time, the removal rates are 65.59% and 55.52% respectively, indicating that there is an obvious incomplete adsorption phenomenon under low dosage conditions. As the dosage of CSM-T5% increases to 0.06 g, the removal rates of MB and Cr(VI) increase significantly to 99.78% and 86.05% respectively. The results show that increasing the adsorbent dosage can effectively expand the contact area of the adsorption interface and expose more unoccupied active sites, thereby significantly improving the removal rates of MB and Cr(VI). However, when the dosage is too high, the adsorption capacity shows a downward trend, which is mainly due to the agglomeration effect of the adsorbent particles leading to a decrease in specific surface area and the underutilization of excessive active sites. Therefore, in practical applications, the optimal dosage needs to be determined through experiments to ensure the efficient removal of pollutants while avoiding the waste of adsorbent resources.

[0119] In addition, at room temperature, the cyclic 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) were also studied, and the results are as Figure 21 shown. After 3 cycles, the removal rates of CSM-T5% for MB and Cr(VI) decrease because the effective active sites of CSM-T5% gradually decrease with the increase in the number of cycles. Nevertheless, after 5 cycles, the removal rates of MB and Cr(VI) still remain at 71.37% and 63.68%, indicating that CSM-T5% has good cyclic performance.

[0120] 2.2.3. Synergistic effect of binary system adsorption

[0121] Through binary system adsorption experiments, the co-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 studied at room temperature. The experimental results showed that in both the MB-Cr(VI) and Cr(VI)-MB binary systems, the removal efficiency and adsorption capacity of the pollutants were significantly improved compared to the single systems. As Figure 22 shown in (a) below, when the Cr(VI) concentration in the MB-Cr(VI) system was fixed at 50 mg / L, the removal rate of 300 mg / L MB by CSM-T5% increased from 86.89% in the single system to 95.61%, while the removal rate of Cr(VI) remained stable at over 95%; Figure 22 as shown in (b) below, in the Cr(VI)-MB system, when the MB concentration was fixed at 200 mg / L, the removal rate of 130 mg / L Cr(VI) increased from 59.67% in the single system to 72.13%, and at the same time, the removal rate of MB remained at a high level of 99%. The above phenomena confirmed the existence of a significant synergistic effect during the binary system adsorption process. On the one hand, MB preferentially adsorbed the negative charges on the surface of CSM-T5%, partially neutralizing the surface charges of the material and reducing the electrostatic repulsion between Cr(VI) anions and the adsorbent, thus promoting the adsorption of Cr(VI). On the other hand, MB preferentially occupied the mesopores of CSM-T5%, while Cr(VI) was mainly adsorbed in the micropores. This hierarchical adsorption form reduced the competition for active sites and promoted the adsorption of Cr(VI).

[0122] The photos of CSM-T5% before and after adsorption in different concentrations of MB-Cr(VI) and Cr(VI)-MB binary systems are as Figure 23 shown.

[0123] 2.2.4. Adsorption kinetics

[0124] To clarify the key influencing factors of the adsorption rate and their action mechanisms, the present invention used the pseudo-first-order kinetics (PFO), pseudo-second-order kinetics (PSO), and intraparticle diffusion (ID) models to conduct kinetic analysis on the adsorption processes of CSM-T5% for MB and Cr(VI). The kinetic fitting parameters are summarized in Table 4. As Figure 24 shown in (a) and (c) below, the correlation coefficients (R 2 MB = 0.994, R 2 Cr(VI) = 0.995) of the PSO model for MB and Cr(VI) were significantly better than those of the PFO model (R 2 MB = 0.711, R 2 Cr(VI)= 0.592). The theoretical equilibrium adsorption capacities calculated by the PSO model (MB: 609.66 mg / g; Cr(VI): 145.51 mg / g) are in good agreement with the experimental values (q e,cal,MB = 606.62 mg / g; q e,cal,Cr(VI) = 145.32 mg / g), indicating that the adsorption processes of MB and Cr(VI) onto CSM-T5% both conform to the pseudo-second-order kinetic model. This result confirms that the adsorption process is dominated by chemisorption and may involve mechanisms such as electrostatic interaction, electron transfer, or chemical bond formation.

[0125] Table 4

[0126]

[0127] Figure 24 In (b) and (d) are the linear fitting results of the intraparticle diffusion (ID) model. The adsorption process can be segmented and 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. 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) into the internal pores of CSM-T5%. The slope of the first straight line is significantly greater than that of the second (k id,1 > k id,2 ), indicating that the external surface diffusion rate is faster. Therefore, the rate-limiting step is dominated by intraparticle diffusion at the initial stage of adsorption; as the reaction proceeds, the decrease in the concentration of MB or Cr(VI) leads to a reduction in the concentration gradient inside and outside the adsorbent, weakening the external surface diffusion effect, and surface diffusion gradually becomes the rate-limiting factor. When MB or Cr(VI) continuously accumulates in the pores, the diffusion resistance increases, and the adsorption rate gradually decreases until dynamic equilibrium is reached. In addition, the boundary layer diffusion parameter c2 value in the ID model is greater than the c1 value, indicating that the boundary layer effect has a more significant impact on the adsorption rate during the intraparticle diffusion process.

[0128] 2.2.5. Adsorption isotherm

[0129] The adsorption isotherm analysis was carried out using the Langmuir isotherm model and the Freundlich isotherm model. The results show that both models fit well, and the Freundlich heterogeneity coefficient (n > 1) indicates effective adsorption. The Langmuir model has a relatively high correlation coefficient (R 2 > 0.99), indicating that it better represents the adsorption of MB or Cr(VI) onto CSM-T5%, which means monolayer adsorption on a homogeneous surface. The fitting results of the Langmuir model show that the maximum adsorption capacity (q m ) and the Langmuir constant (K L) increase with the increase of temperature. The maximum adsorption capacity (q m,MB = 862.06 mg / g; q m,Cr(VI) = 233.10 mg / g), the 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.

[0130] Table 5

[0131]

[0132] 2.2.6. Thermodynamics

[0133] The thermodynamic parameters of the adsorption process, such as the change in Gibbs free energy (ΔG θ ), enthalpy change (ΔH θ ), and entropy change (ΔS θ ), were analyzed from a thermodynamic perspective to analyze the thermodynamic nature of the adsorption of MB or Cr(VI) by CSM-T5%. The relevant parameters are shown in Table 6. In the temperature range of 298 K, 308 K, and 318 K, the ΔG θ of MB or Cr(VI) is negative, indicating that the adsorption of MB or Cr(VI) on CSM-T5% is spontaneous. In addition, the absolute value of ΔG θ increases with the increase of temperature, indicating that a higher temperature promotes the spontaneous reaction, thereby enhancing the adsorption of MB or Cr(VI). ΔG θ is in the range of -20 to 0 kJ / mol, indicating that the adsorption is physically adsorbed in nature. The positive ΔH θ value indicates that the adsorption process is endothermic, confirming the changing trend of the isotherm. In addition, the positive ΔS θ value corresponds to an increase in entropy during the adsorption process, indicating an increase in randomness at the solid / liquid interface during the adsorption process of MB or Cr(VI).

[0134] Table 6

[0135]

[0136] 2.3. Adsorption mechanism analysis

[0137] The adsorption mechanism of CSM-T5% was systematically studied by FTIR and XPS. Figure 25 is the comparative spectrum of the FTIR characteristic peaks of the material before and after adsorbing MB and Cr(VI). CSM-T5%-MB (after adsorbing MB) and CSM-T5%-Cr(VI) (after adsorbing Cr(VI)), 3430 cm -1The characteristic peak of -OH stretching vibration undergoes a red shift, and the peak intensity decreases significantly, indicating that the hydroxyl group is a key adsorption site. Meanwhile, in the complex system of coexisting MB&Cr(VI), the displacement and intensity change trend of the -OH characteristic peak are consistent with those in the single system, confirming that -OH remains a key adsorption site in different adsorption environments. After CSM adsorbs MB, Cr(VI), and the binary system of MB&Cr(VI), the N-H vibration peak at 1636 cm -1 undergoes a red shift and is respectively shifted to 1631 cm -1 , 1621 cm -1 and 1626 cm -1 , and the intensity weakens. The main reason is that after N-H protonation, it forms an interaction with the negatively charged group, resulting in a decrease in the vibration freedom of N-H and weakening the intensity of the infrared absorption peak. The C-N stretching vibration peak at 1116 cm -1 weakens after adsorption, indicating that the N atoms on the material surface participate in the adsorption process. For the specific adsorption site of MB, the benzene ring skeleton C=C vibration peak at 1452 cm -1 , the C-H bending vibration peak of -CH3 at 1383 cm -1 , and the C-S-C characteristic peak at 543 cm -1 are observed in both the single MB system and the coexisting MB&Cr(VI) system. These vibration peaks corresponding to the MB molecular structure confirm the successful adsorption of MB molecules on the material surface. Regarding the adsorption characteristics of Cr(VI), in both the single Cr(VI) system and the coexisting MB&Cr(VI) system, the newly emerged characteristic peaks at 791 cm -1 and 910 cm -1 correspond to the vibration peak of Cr-O in HCrO4 - and the asymmetric vibration mode of Cr=O respectively, indicating that CSM-T5% can also successfully adsorb Cr(VI).

[0138] Through the XPS full-spectrum scanning of the material before and after adsorbing MB and Cr(VI), the characteristic peaks of S2p and Cr 2p appear on CSM-T5%, further confirming the successful adsorption of MB and Cr(VI) on CSM-T5%. Figure 26 (a) in it is the fitting result of S2p. CSM-T5% shows peaks corresponding to C-SO2-C and C-SO3-Na at 168.11 eV and 169.17 eV respectively. After MB adsorption, for CSM-T5%-MB, a peak of C-SO3-H appears at 169.19 eV, and a C-S-C characteristic peak appears at 164.53 eV, and the content increases by 0.21%, confirming the adsorption of MB, which is consistent with the enhancement of the C–S-C stretching vibration peak in FTIR. The XPS fitting result of Cr 2p is as shown in Figure 26As shown in (b). The Cr 2p spectrum shows two broad peaks at 587.4 eV (Cr 2p 1 / 2 ) and 577.6 eV (Cr 2p 3 / 2 ), indicating the presence of Cr(III) and Cr(VI). In the Cr 2p 3 / 2 region, the peaks with binding energies of 577.13 eV and 579.08 eV are Cr(III) in Cr(OH)3 and Cr(VI) in K2Cr2O7, respectively. The fitting peak of Cr 2p 1 / 2 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 Cr(VI) on the material surface is partially reduced to Cr(III) after adsorption.

[0139] Figure 26 As shown in (c) is the C1s fine spectrum. The binding energies corresponding to C-C / C═C / C-H, C-O / C-N, C═O, and -COOH in CSM-T5% are 284.80 eV, 286.05 eV, 287.79 eV, and 290.19 eV, respectively. After adsorbing MB, the binding energies corresponding to CSM-T5% shift to higher values to 284.80 eV, 286.09 eV, 287.80 eV, and 290.36 eV, and the content of -COOH decreases significantly, indicating the existence of ionic interactions in the adsorption of MB. For the adsorption of Cr(VI), the content of C-O / C-N decreases, indicating that the amino group is the active binding site for Cr(VI). In addition, when MB and Cr(VI) coexist, the binding energies corresponding to CSM-T5%-MB&Cr(VI) are between the two, indicating that CSM-T5% has a synergistic adsorption effect on MB and Cr(VI).

[0140] Figure 26 As shown in (d) is the O1s fine spectrum. The functional groups corresponding to the binding energies of 533.39 eV and 532.07 eV in CSM-T5% are -OH and C═O. After adsorbing MB, the oxygen-containing functional groups of CSM-T5%-MB shift to higher binding energies, indicating that the oxygen-containing functional groups participate in the adsorption of MB. For the adsorption of Cr(VI), the binding energy of C═O migrates from 532.07 eV to 532.17 eV, and the content of C═O 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 is oxidized to form carboxyl groups itself.

[0141] Figure 26As shown in (e), the N1s fine spectrum is presented. After the adsorption of MB, a characteristic peak of pyridine nitrogen appears at 399.20 eV for CSM-T5%-MB, confirming the adsorption of MB. Meanwhile, -NH3 appears at 401.56 eV + , indicating that the functional groups are protonated during the adsorption process of MB. The content of -NH at 400.08 eV increases from 1.23% before the adsorption of MB to 1.34%, which indicates the formation of hydrogen bonds during the adsorption process of MB. After the adsorption of Cr(VI), a peak of -NH3 appears at 401.35 eV + , confirming the protonation of amino groups and their electrostatic adsorption ability for Cr(VI).

[0142] To further illustrate the adsorption mechanism, as Figure 27 shown, by systematically exploring the key influencing factors of the adsorption performance, combining adsorption kinetics, isothermal adsorption model fitting, calculation of thermodynamic parameters, and FTIR and XPS characterizations, the synergistic adsorption mechanism of CSM-T5% for MB and Cr(VI) is revealed, and its adsorption process is a physical-chemical synergistic effect of the combined action of physical adsorption and chemical adsorption.

[0143] Figure 27 In (a), it is a schematic diagram of the adsorption mechanism of CSM-T5% for MB. The pore structure of CSM-T5% promotes capillary action and synergistic action, and MB migrates into the pore structure of CSM-T5% during the adsorption process, namely pore filling. The doping of nitrogen breaks the original chemical equilibrium, and the redistribution of spin states and charge densities generates more active sites, improving the adsorption efficiency. In addition to the formation of hydrogen bonds between N in the MB molecule and the N-H group in CSM-T5%, the ionic interaction between oxygen-containing functional groups such as carboxyl groups and the MB molecule, and the π-π interaction between the benzene ring in the MB molecule and the conjugated structure in the adsorbent, under acidic conditions, part of -NH2 is protonated to -NH3 + , generating a weak electrostatic attraction with Cl- in MB. Due to the multi-amino characteristics of TEPA leading to charge dispersion, the charge density of a single site decreases, weakening the electrostatic attraction to Cl - .

[0144] Figure 27 In (b), it is a schematic diagram of the adsorption mechanism of CSM-T5% for Cr(VI). The removal of Cr(VI) by CSM-T5% mainly includes three aspects: the electrostatic interaction between negatively charged Cr(VI) ions and positively charged surface functional groups (-NH3 + and -COOH + ), and then the reduction of Cr(VI) to Cr(III), enabling Cr(III) to complex with the functional groups on the adsorbent. The reduction of Cr(VI) to Cr(III) can be expressed as follows:

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

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

[0147] 3. Conclusion

[0148] In this invention, a porous carbon material (CSM) derived from fine slag of coal gasification is used as the substrate, and further a surface ammonia functionalization modification strategy is adopted. By regulating the loading amount of TEPA (Y = 5% wt%, 10% wt%, 20% wt%, 30% wt% and 50% wt%), an ammonia-modified composite material (CSM-TY) is successfully constructed. By comprehensively using characterization means such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption and desorption analysis, and X-ray photoelectron spectroscopy (XPS), the structural evolution law of the material is systematically revealed: with the increase of the TEPA loading amount, the amino group content on the material surface increases significantly, but excessive loading will cause agglomeration and accumulation of amino groups, leading to pore blockage. When the loading amount is 5%, the specific surface area decreases from the initial 540.03 m 2 / g to 376.20 m 2 / g.

[0149] Through the adsorption performance tests of MB and Cr(VI), it is found that CSM-T5% exhibits the optimal adsorption performance, and its equilibrium adsorption capacity is increased by 8.01% and 15.91% respectively compared with the original CSM, which confirms that amino functionalization has successfully enhanced the surface active sites. The solution pH value plays a crucial role in the adsorption of MB and Cr(VI). For MB, the removal rate increases with the increase of the pH value, while for Cr(VI), it is the opposite. The adsorption processes of MB and Cr(VI) conform to the pseudo-second-order kinetic model (PSO), indicating chemical adsorption involving electrostatic interaction and electron transfer. The intraparticle diffusion model further reveals that the overall adsorption rate is jointly affected by external surface diffusion and intraparticle diffusion. Thermodynamic analysis confirms that the adsorption process is a spontaneous endothermic behavior.

[0150] Isothermal adsorption studies based on the Langmuir model showed that the maximum adsorption capacities of CSM-T5% for MB and Cr(VI) at 318 K reached 862.06 mg / g and 233.10 mg / g, respectively, with a higher degree of fit compared to the Freundlich model, indicating mainly homogeneous surface adsorption. Through the analysis of surface characteristics before and after adsorption, the adsorption mechanisms of MB and Cr(VI) were elucidated. For MB, the synergistic effects include pore filling, electrostatic attraction, ion interaction, and π-π conjugation, etc.; for Cr(VI), the electrostatic interaction between Cr(VI) and the protonated CSM-T5% surface, the reduction of Cr(VI) to Cr(III), and the complexation of Cr(III).

[0151] In the MB-Cr(VI) / Cr(VI)-MB binary system, 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). The regeneration experiment showed that after 5 cycles, the adsorption retention rates of CSM-T5% for MB and Cr(VI) still reached 71.37% and 63.68%.

[0152] In summary, the adsorbent developed based on coal gasification fine slag has good potential in industrial production and applications.

[0153] The embodiments described above are only for describing the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A preparation method of an ammonia-modified porous carbon adsorbent, characterized in that, It includes the following steps: Subject the gasified fine slag to hydrothermal acid leaching with an acid solution to obtain an acid leaching residue; After stirring the acid leaching residue in an alkali solution, wash and dry it to obtain a porous carbon material; Immerse the porous carbon material in a tetraethylenepentamine solution and then dry it to obtain the ammonia-modified porous carbon adsorbent.

2. The preparation method of the ammonia-modified porous carbon adsorbent according to claim 1, characterized in that, The acid solution is a HNO3 solution with a concentration of 2 mol / L.

3. The preparation method of the ammonia-modified porous carbon adsorbent according to claim 1, characterized in that, The mass-volume ratio of the gasified fine slag to the acid solution is 1 g∶16 mL.

4. The preparation method of the ammonia-modified porous carbon adsorbent according to claim 1, characterized in that, The temperature of the hydrothermal acid leaching is 403 K and the time is 150 min.

5. The preparation method of the ammonia-modified porous carbon adsorbent according to claim 1, characterized in that, After the hydrothermal acid leaching, it also includes the steps of solid-liquid separation and washing the solid obtained from the solid-liquid separation to neutrality and drying.

6. The preparation method of the ammonia-modified porous carbon adsorbent according to claim 1, wherein, The alkali solution is a NaOH solution with a concentration of 2 mol / L.

7. The preparation method of the ammonia-modified porous carbon adsorbent according to claim 1, characterized in that, The temperature for stirring the acid leaching residue in the alkali solution is 362 K and the time is 6 h.

8. The preparation method of the ammonia-modified porous carbon adsorbent according to claim 1, characterized in that, The solvent of the tetraethylenepentamine solution is ethanol; the content of tetraethylenepentamine in the tetraethylenepentamine solution accounts for 5 wt% - 50 wt% of the mass of the porous carbon material.

9. The preparation method of the ammonia-modified porous carbon adsorbent according to claim 1, wherein, The impregnation time of the porous carbon material in the tetraethylenepentamine solution is 30 min; When preparing the porous carbon material and the ammonia-modified porous carbon adsorbent, the drying temperature is independently 350 - 353 K.

10. An ammonia-modified porous carbon adsorbent prepared by the preparation method according to any one of claims 1 to 9.

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