Dendritic polyethyleneimine surface modified GO / MXene nano adsorbent as well as preparation method and application thereof

Abstract

The invention belongs to the field of heavy metal adsorption separation and solid adsorbents, and provides a dendritic polyethyleneimine surface modified GO / MXene nano adsorbent as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing a graphene oxide dispersion liquid with a Ti3C2Tx colloidal solution, and carrying out dispersion treatment to obtain a GO-Ti3C2Tx mixed solution with a certain concentration; adding dendritic polyethyleneimine, and carrying out covalent modification and electrostatic assembly strategy reaction to obtain a dendritic polyethyleneimine modified GO / MXene reaction solution; and centrifuging, washing and drying to obtain the dendritic polyethyleneimine surface modified GO / MXene adsorbent. According to the invention, the nitrogen-rich cationic polymer is introduced, so that the adsorption capacity of graphene oxide to Cr (VI) is improved; the preparation process is simple, green and environment-friendly; the obtained adsorbent can efficiently remove Cr (VI) in a water body, and has a good adsorption effect on Cr (VI).

Description

Technical Field

[0001] This invention belongs to the field of heavy metal adsorption and separation and solid adsorbent technology, specifically relating to a dendritic polyethyleneimine surface-modified graphene oxide / MXene nano-adsorbent, its preparation method and application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the rapid advancement of industrialization, chromium-containing wastewater discharged from industries such as electroplating, metallurgy, and leather tanning has caused serious harm to the aquatic environment. Among them, hexavalent chromium (Cr(VI)) is listed as a priority pollutant due to its extreme toxicity, high mobility, and strong carcinogenicity. Therefore, the efficient removal of Cr(VI) or its reduction to trivalent chromium (Cr(III)) has become an urgent need for water pollution control.

[0004] Among numerous water treatment technologies, graphene oxide (GO) is considered an ideal adsorption carrier due to its high specific surface area and abundant oxygen-containing functional groups (hydroxyl, carboxyl, and epoxy groups). However, its inherent defects severely limit its Cr(VI) adsorption performance. These include structural defects: interlayer van der Waals forces induce self-agglomeration, masking active sites; and charge repulsion: the strong negative surface charge interacts with Cr(VI) anions (hydrogen chromate ions / chromate ions HCrO4). - / CrO4 2- Electrostatic repulsion significantly reduces adsorption capacity; sluggish kinetics: mass transfer resistance at the solid-liquid interface leads to excessively long adsorption equilibrium times, making it difficult to meet the efficiency requirements of practical wastewater treatment. To address this, researchers have attempted to improve the heavy metal adsorption performance of GO through functionalization. For example, the introduction of nitrogen-rich polymer polyethyleneimine (PEI), whose primary / secondary amine groups can capture Cr(VI) under acidic conditions through electrostatic attraction and chelation. However, existing modification strategies have still failed to systematically resolve the core contradiction of sluggish mass transfer kinetics.

[0005] Furthermore, the preparation of GO-based composite materials generally suffers from problems such as cumbersome procedures, high energy consumption, and high reagent toxicity, and also lacks sufficient adsorption selectivity. Some studies have employed multi-step reactions to bond magnetic iron oxide (Fe3O4) to the PEI-GO surface, which improves separation convenience, but the process is cumbersome and dependent on high temperatures / toxic reagents, and the adsorption capacity and rate remain unsatisfactory. Novel two-dimensional materials such as MXene (e.g., monolayer titanium carbide Ti3C2T) are being explored. x Although it possesses excellent hydrophilicity and abundant surface groups (hydroxyl / fluorine), its combination with GO as a single two-dimensional material can easily lead to the problem of heavy metal ion intercalation, resulting in poor selectivity and reducing its targeted adsorption capacity for Cr(VI).

[0006] Therefore, there is an urgent need to develop a composite adsorption material system that has a simple preparation process and high selective adsorption performance for Cr(VI). Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a dendritic polyethyleneimine surface-modified GO / MXene nano-adsorbent, its preparation method, and its application. This invention uses polyethyleneimine as the modifier and MXene-Ti3C2T... x Using covalent modification and electrostatic assembly as the main intercalation reagent, the chemical modification of graphene oxide was achieved, resulting in the synthesis of a nitrogen-rich cationic polymer-modified GO / MXene nanocomposite material as an adsorbent for chromium. Furthermore, the introduction of modified molecules enhanced the adsorption capacity of graphene oxide for Cr(VI). This invention features a simple and environmentally friendly preparation process; the resulting adsorbent can efficiently remove Cr(VI) from water, exhibiting excellent adsorption performance for Cr(VI).

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent, comprising: GO dispersion with Ti3C2T x Colloidal solutions according to GO and Ti3C2T x A mixture with a mass ratio of 3-5:1 yields GO-Ti3C2T. x Mixture; The GO-Ti3C2T x The mixture was mixed with an aqueous solution of dendritic polyethyleneimine and reacted to obtain a reaction solution containing GO / MXene modified with dendritic polyethyleneimine. The reaction solution containing GO / MXene modified with dendritic polyethyleneimine was subjected to solid-liquid separation, washed, and dried to obtain the final product.

[0009] In a second aspect, the present invention provides a dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent prepared by the above method.

[0010] A third aspect of the present invention provides the application of the above-described dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent in the adsorption of heavy metal Cr(VI).

[0011] Beneficial effects of the present invention (1) In this invention, dendritic polyethyleneimine is used as a modifier, and MXene-Ti3C2T is used as a modifier. xThis invention utilizes GO and MXene nanocomposite adsorbents with nitrogen-rich cationic polymer surface modification as the main intercalation reagent. x The layers intercalate to form a unique composite structure. At the same time, the specific modifier of this invention (dendritic polyethyleneimine) is rich in nitrogen-containing groups such as primary amines, secondary amines and tertiary amines on the chain, which can provide abundant active sites for fixing toxic metal ions under low acid conditions.

[0012] (2) In the preparation process of the adsorbent of the present invention, MXene-Ti3C2T x The GO sheets modified with intercalation and dendritic polyethyleneimine had a 2θ angle of 5.1° and increased interlayer spacing. Furthermore, the N (nitrogen) content of the GO sheets modified with dendritic polyethyleneimine was 11.08%. This modification of the nitrogen-rich cationic polymer laid the foundation for the subsequent adsorption of Cr(VI) in the solution.

[0013] (3) In a Cr(VI)-containing solution, the amino group on the adsorbent is protonated and becomes positively charged, which can effectively attract Cr anions electrostatically. In addition, the reduction of the amino group can reduce some Cr(VI) to Cr(III) and fix Cr(III) through chelation. Therefore, the adsorption of Cr(VI) by the composite material is a mechanism of coexistence of electrostatic and chelation effects, thereby achieving the adsorption and removal of Cr(VI) and showing good adsorption performance. Furthermore, the overall structure of the adsorbent of this invention makes it have a certain anti-interference ability against other anions and has adsorption selectivity.

[0014] (4) This invention uses covalent modification and electrostatic assembly to prepare a nitrogen-rich cationic polymer-modified GO / MXene nanocomposite material with a richly wrinkled layered structure. The adsorption capacity of GO for Cr(VI) is enhanced by the introduction of modifier molecules. The adsorbent of this invention has excellent adsorption performance and anti-interference performance for the heavy metal Cr(VI), and the removal rate of heavy metal Cr(VI) reaches 98.9%. The maximum adsorption capacity in the experiment can reach 320.2 mg / g. By optimizing the adsorption conditions, efficient adsorption of heavy metal Cr(VI) can be achieved.

[0015] (5) The synthesis steps of the adsorbent of the present invention are simple, and the raw materials used are inexpensive, readily available, green and environmentally friendly. Attached Figure Description

[0016] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. Exemplary embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0017] Figure 1 This is a scanning electron microscope image of the adsorbent in Example 1.

[0018] Figure 2 The image shows the infrared spectrum of the adsorbent in Example 1.

[0019] Figure 3 The image shows the energy dispersive X-ray (EDS) spectrum of the adsorbent in Example 1.

[0020] Figure 4 This is the adsorption isotherm diagram of Cr(VI) by the adsorbent in Example 2. Detailed Implementation

[0021] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they are used in accordance with conventional methods in the art or product instructions. Similarly, unless otherwise specified, the test methods of this invention are performed in accordance with conventional methods in the art or industry-standard methods or practices. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0023] As described in the background section, novel two-dimensional materials MXene (such as Ti3C2T) x Although GO and MXene possess excellent hydrophilicity and abundant surface groups (hydroxyl / fluorine groups), there are serious stacking and heavy metal ion intercalation problems during the assembly process. This leads to a significant loss of specific surface area and accessibility of active sites, reducing the overall adsorption performance of the composite material, especially the reduced targeted adsorption capacity for Cr(VI).

[0024] Therefore, this invention provides a method for preparing a dendritic polyethyleneimine surface-modified graphene oxide / MXene nano-adsorbent, comprising: GO dispersion with Ti3C2T x Colloidal solutions according to GO and Ti3C2T x A mixture with a mass ratio of 3-5:1 yields GO-Ti3C2T. x Mixture; The GO-Ti3C2T x The mixture was mixed with an aqueous solution of dendritic polyethyleneimine and reacted to obtain a reaction solution containing GO / MXene modified with dendritic polyethyleneimine. The reaction solution containing GO / MXene modified with dendritic polyethyleneimine was subjected to solid-liquid separation, washed, and dried to obtain the final product.

[0025] This invention utilizes the large three-dimensional structure of dendritic PEI to provide stronger steric hindrance between GO and MXene sheets and on the sheet surface, more effectively suppressing the recombination of GO and MXene nanosheets. At the same time, the stronger steric hindrance helps to form a more stable and looser porous three-dimensional hybrid nanosheet structure, which is beneficial to ion diffusion and mass transfer and improves the overall adsorption performance of the composite material.

[0026] The adsorption mechanism of Cr(VI) in this invention is as follows: electrostatic interaction between Cr(VI) and protonated amine groups (derived from PEI) or hydroxyl groups (derived from GO or MXene) in the adsorbent; the synergistic effect of the nitrogen-containing groups of PEI and the oxygen-containing groups of GO and MXene chemically reduces Cr(VI) to Cr(III); Cr(III) is immobilized through coordination; simultaneously, the adsorption process involves Cr(VI) (HCrO4) - and CrO4 2- It interacts with hydrogen bonds of various functional groups.

[0027] GO and Ti3C2T x The ratio of GO to Ti3C2T affects the performance of the adsorbent; therefore, this invention focuses on the ratio of GO to Ti3C2T. x The mass ratio of GO and Ti3C2T was studied, and preferably, the mass ratio of GO and Ti3C2T was... x The mass ratio is 3-5:1, more preferably 4:1, to better improve the adsorption performance.

[0028] To ensure GO and Ti3C2T x To improve the mixing effect and facilitate subsequent reactions, this invention studied the concentration of the GO dispersion. Preferably, the mass concentration of the GO dispersion is 10 mg / L-15 mg / L to obtain a better mixing effect.

[0029] To ensure GO and Ti3C2T x The mixing effect of Ti3C2T is to facilitate subsequent reactions. This invention relates to Ti3C2T. x The concentration of the colloidal solution was studied, and preferably, the Ti3C2T x The mass concentration of the colloidal solution is 8 mg / L - 12 mg / L to obtain a better mixing effect.

[0030] To ensure that the dendritic polyethyleneimine reacts with GO and Ti3C2T xTo improve the mixing effect and facilitate subsequent reactions, this invention studies the mass concentration of the branched polyethyleneimine aqueous solution. Preferably, the mass concentration of the branched polyethyleneimine aqueous solution is 20%-50%, and more preferably, it is 50%, to obtain a better mixing effect.

[0031] The mass ratio of dendritic polyethyleneimine to graphene oxide affects the adsorption performance of the adsorbent. Therefore, this invention studies the mass ratio of dendritic polyethyleneimine to graphene oxide. Preferably, the mass ratio of dendritic polyethyleneimine to graphene oxide is 8-12:1, and more preferably, it is 10:1, to obtain better adsorption performance.

[0032] The molecular weight of dendritic polyethyleneimine affects the adsorption performance and stability of the adsorption material. Therefore, this invention studies the molecular weight of dendritic polyethyleneimine. Preferably, the number average molecular weight of the dendritic polyethyleneimine is 60,000-80,000, so that the material has both better adsorption performance and stability.

[0033] The reaction of the present invention can be carried out at room temperature. Preferably, the reaction temperature is 20°C-25°C and the reaction time is 20-30 hours, more preferably 24 hours, to ensure complete reaction.

[0034] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.

[0035] In the following examples, after the adsorption separation process is completed, the concentration of metal ions in the solution after centrifugation is determined by ICP-OES (inductively coupled plasma optical emission spectrometry). The formula for calculating the metal ion removal rate (E) is as follows: , Among them, C0 and C e (mg / L) represents the concentration of metal ions in the solution before and after adsorption, respectively.

[0036] The formula for calculating the adsorption capacity (Q) used is as follows: , Where C0 and C e (mg / L) represents the concentration of metal ions in the solution before and after adsorption, respectively; V is the volume of the solution (mL), and m is the mass of the adsorbent added (mg).

[0037] In the following examples, the aqueous solution of dendritic polyethyleneimine (PEI) had a mass concentration of 50% and a molecular weight of 70,000, and was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0038] Example 1 1. Synthesis of GO / MXene adsorbent with dendritic polyethyleneimine surface modification A modified Hummers method was used to perform strong acid oxidative exfoliation on 325-mesh graphite powder to obtain an aqueous dispersion of graphene oxide (GO).

[0039] A nitrogen-rich cationic polymer-modified GO / MXene nanocomposite adsorbent (GMP) was prepared using covalent modification and electrostatic assembly. The process included mixing 11.5 mg / mL GO dispersion with 10 mg / mL Ti3C2T... x The colloidal solutions were mixed and sonicated at room temperature for 2 hours to obtain GO-Ti3C2T at a concentration of 8 mg / mL. x The mixture, in which Ti3C2T x The mass ratio of graphene oxide to GO was 1:4. Subsequently, a 50% (w / w) aqueous solution of dendritic polyethyleneimine (number average molecular weight approximately 70,000) was added to the above mixture at a mass ratio of graphene oxide to dendritic polyethyleneimine aqueous solution of 1:10. The mixture was stirred vigorously for 24 h to obtain dendritic polyethyleneimine-modified GO / MXene composite two-dimensional nanomaterials. The resulting solid material was washed with deionized water until the washing solution became clear. The washed product was then freeze-dried under vacuum for 48 h to obtain a nitrogen-rich cationic polymer surface-modified GO / MXene nanocomposite adsorbent (GMP).

[0040] The synthesized materials were characterized by... Figure 1 Scanning electron microscopy (SEM) images of the adsorbent reveal that its microstructure exhibits a layered structure with abundant surface folds. Through... Figure 2 The characteristic peaks in the infrared spectrum confirm the successful synthesis of GO / MXene nanocomposites with nitrogen-rich cationic polymer surface modification. Figure 3 The EDS spectrum of the adsorbent indicates that the nitrogen content of the adsorbent GMP is 11.08%. The specific surface area of ​​the adsorbent prepared in this example is 30.89 m². 2 / g.

[0041] 2. Adsorption process of Cr(VI) To prepare a Cr(VI)-containing solution: Weigh 0.2829 g of potassium dichromate dried at 110℃ for 2 hours, dissolve it in water, transfer it to a 100 mL volumetric flask, dilute it with deionized water to a 1000 mg / L Cr(VI)-containing solution, and adjust the pH to 3 with concentrated hydrochloric acid.

[0042] Take 1.6 mL of 1000 mg / L Cr(VI) solution and dilute it in a centrifuge tube to 10 mL of 160 mg / L Cr(VI) solution. During the above process, the pH of the obtained Cr(VI) solution is controlled to 3 by adding concentrated hydrochloric acid. Then add 10 mg of the adsorbent prepared in this example and adsorb for 2 hours under mechanical shaking at 30 °C and 220 rpm to ensure that the adsorbent is in full contact with the aqueous phase. After the adsorption is completed, centrifuge to separate the adsorbent and test the remaining concentration of Cr(VI) in the aqueous phase and calculate the adsorption capacity.

[0043] During the above adsorption and separation process, the dendritic polyethyleneimine surface-modified GO / MXene nanocomposite material prepared in this embodiment achieved an adsorption capacity of 149.8 mg / g in the above 160 mg / L Cr(VI)-containing solution.

[0044] Example 2 1. Synthesis of GO / MXene adsorbent with dendritic polyethyleneimine surface modification The method for synthesizing the adsorbent in this embodiment is the same as in Example 1.

[0045] 2. Adsorption process of Cr(VI) Preparation of Cr(VI)-containing solutions: Weigh 0.2829 g of potassium dichromate dried at 110℃ for 2 hours, dissolve it in water, transfer it to a 100 mL volumetric flask, and dilute with deionized water to a 1000 mg / L Cr(VI)-containing solution. Dilute with deionized water to prepare Cr(VI)-containing solutions of 40 mg / L, 80 mg / L, 120 mg / L, 160 mg / L, 240 mg / L, 280 mg / L, 320 mg / L, 360 mg / L, and 400 mg / L, respectively. In all the above processes, the pH of the final Cr(VI)-containing solution was controlled to be 3 using concentrated hydrochloric acid.

[0046] Take 10 mL of each of the above-mentioned Cr(VI)-containing solutions of different concentrations into centrifuge tubes, add 10 mg of the adsorbent prepared in this example, and adsorb for 2 hours under mechanical shaking at 30 ℃ and 220 rpm to ensure sufficient contact between the adsorbent and the aqueous phase. After adsorption, centrifuge to separate the solutions, test the remaining concentration of Cr(VI) in the aqueous phase, and calculate the adsorption capacity. Obtain the correspondence between equilibrium concentration and adsorption capacity. Plot the adsorption capacity obtained at different concentrations of Cr(VI)-containing solutions against the equilibrium concentration (…). Figure 4 R was obtained by fitting the Freundlich adsorption isotherm. 2 The value is 0.9920. The maximum adsorption capacity of the dendritic polyethyleneimine surface-modified GO / MXene nanocomposite adsorbent prepared in this embodiment reaches 320.2 mg / g.

[0047] Example 3 1. Synthesis of GO / MXene adsorbent with dendritic polyethyleneimine surface modification The method for synthesizing the adsorbent in this embodiment is the same as in Example 1.

[0048] 2. Adsorption process of Cr(VI) Preparation of Cr(VI)-containing solution: Weigh 0.2829 g of potassium dichromate dried at 110℃ for 2 hours, dissolve it in water, transfer it to a 100 mL volumetric flask, and dilute with deionized water to a 1000 mg / L Cr(VI)-containing solution. Then dilute with deionized water to an 80 mg / L Cr(VI)-containing solution. Throughout the above process, the pH of the final Cr(VI)-containing solution is controlled from 1 to 10 using concentrated hydrochloric acid or sodium hydroxide aqueous solution.

[0049] The main forms of Cr(VI) in aqueous solutions at different pH values ​​are as follows: at pH ≤ 7, Cr(VI) exists as HCrO4. - Cr2O7 2- It exists, in the form of HCrO4 - Primarily; at pH > 7, Cr(VI) is mainly produced as CrO4. 2- HCrO4 - It exists, in CrO4 2- Mainly.

[0050] Take 10 mL of the above-mentioned Cr(VI)-containing solutions at different pH values ​​into centrifuge tubes, add 10 mg of the above-prepared adsorbent, and adsorb for 2 hours under mechanical shaking at 30 ℃ and 220 rpm to ensure that the adsorbent is in full contact with the aqueous phase. After the adsorption is completed, centrifuge to separate the solutions, test the remaining concentration of Cr(VI) in the aqueous phase, and calculate the adsorption capacity at different initial pH values.

[0051] Table 1. Adsorption capacity of adsorbent for Cr(VI) at different pH values pH 1 2 3 4 5 6 7 8 9 10 Adsorption capacity (mg / g) 28.2 61.6 79.1 57.4 53.2 48.5 32.6 26.4 25.7 22.9 In the above adsorption and separation process, the adsorption capacity of Cr(VI) under different pH conditions is shown in Table 1. As the pH increases, the adsorption capacity of the adsorbent for Cr(VI) first increases and then decreases, and the optimal adsorption capacity is achieved at pH 3.

[0052] Example 4 1. Synthesis of GO / MXene adsorbent with dendritic polyethyleneimine surface modification The method for synthesizing the adsorbent in this embodiment is the same as in Example 1.

[0053] 2. Adsorption process of Cr(VI) Preparation of Cr(VI)-containing solution: Weigh 0.2829 g of potassium dichromate dried at 110℃ for 2 hours, dissolve it in water, transfer it to a 100 mL volumetric flask, and dilute with deionized water to a 1000 mg / L Cr(VI)-containing solution. Then dilute with deionized water to a 160 mg / L Cr(VI)-containing solution. During the above process, the pH of the final Cr(VI)-containing solution is controlled to be 3 using concentrated hydrochloric acid.

[0054] Take 10 mL of the above Cr(VI) solution into centrifuge tubes, add 10 mg of the adsorbent prepared above, and adsorb for 2 hours at different temperatures of 30 ℃, 40 ℃, 50 ℃, and 60 ℃ with mechanical shaking at 220 rpm to ensure that the adsorbent is in full contact with the aqueous phase. After the adsorption is completed, centrifuge to separate the adsorbents, test the remaining concentration of Cr(VI) in the aqueous phase, and calculate the adsorption capacity at different temperatures.

[0055] In the above adsorption separation process, the adsorption capacity of Cr(VI) under different temperature conditions is shown in Table 2. As the temperature increases, the adsorption capacity of the adsorbent for Cr(VI) gradually increases. However, considering cost factors, 30℃ was selected for subsequent experiments.

[0056] Table 2. Adsorption capacity of adsorbent for Cr(VI) at different temperatures Temperature (°C) 30 40 50 60 Adsorption capacity (mg / g) 149.8 151.9 153.5 156.2 Example 5 1. Synthesis of GO / MXene adsorbent with dendritic polyethyleneimine surface modification The method for synthesizing the adsorbent in this embodiment is the same as in Example 1.

[0057] 2. Adsorption process of Cr(VI) Preparation of Cr(VI)-containing solution: Weigh 0.2829 g of potassium dichromate dried at 110℃ for 2 hours, dissolve it in water, transfer it to a 100 mL volumetric flask, and dilute with deionized water to a 1000 mg / L Cr(VI)-containing solution. Then dilute with deionized water to a 80 mg / L Cr(VI)-containing solution. Throughout the above process, the pH of the final Cr(VI)-containing solution is controlled to be 3 using concentrated hydrochloric acid.

[0058] Take 10 mL of the above Cr(VI) solution into centrifuge tubes, and then add 2 mg, 6 mg, 10 mg, 14 mg and 18 mg of the adsorbent prepared above, respectively. Adsorb for 2 hours under mechanical shaking at 30 ℃ and 220 rpm to ensure that the adsorbent is in full contact with the aqueous phase. After the adsorption is completed, centrifuge to separate the adsorbents and test the remaining concentration of Cr(VI) in the aqueous phase. Calculate the adsorption capacity and removal rate at different adsorbent dosages.

[0059] In the above adsorption and separation process, the removal rate of Cr(VI) by the adsorbent increased with the increase of the dosage when different amounts of adsorbent were added. The results are shown in Table 3.

[0060] Table 3. Removal rate of Cr(VI) by different adsorbent masses Adsorbent dosage (mg) 2 6 10 14 18 Removal rate 48.4% 91.9% 98.5% 99.7% 99.8% Example 6 1. Synthesis of GO / MXene adsorbent with dendritic polyethyleneimine surface modification The method for synthesizing the adsorbent in this embodiment is the same as in Example 1.

[0061] 2. Adsorption process of Cr(VI) Preparation of Cr(VI)-containing solutions: Weigh 0.2829 g of potassium dichromate dried at 110℃ for 2 hours, dissolve it in water, transfer it to a 100 mL volumetric flask, and dilute with deionized water to a 1000 mg / L Cr(VI)-containing solution. Then dilute with deionized water to a 120 mg / L Cr(VI)-containing solution. Prepare Cr(VI)-containing solutions with a concentration of 120 mg / L and containing four different concentrations (0 mM, 5 mM, 10 mM, 20 mM) of Cl. - SO4 2- NO3 - The solution is prepared, and the pH of the final Cr(VI)-containing solution is controlled to 3 by concentrated hydrochloric acid or sodium hydroxide aqueous solution during the above process.

[0062] Take 10 mL of the above Cr(VI) solution into a centrifuge tube, add 10 mg of the adsorbent prepared above, and adsorb for 2 hours under mechanical shaking at 30 ℃ and 220 rpm to ensure that the adsorbent is in full contact with the aqueous phase. After the adsorption is completed, centrifuge to separate the Cr(VI) solution and test the remaining concentration of Cr(VI) and the concentration of other ions in the aqueous phase.

[0063] In the above adsorption separation process, different concentrations of Cl - SO4 2- NO3 - All of these have a certain impact on the adsorption capacity of the adsorbent, among which NO3... - The most affected is SO4. 2- The impact is secondary, Cl - The effect was minimal. The results are shown in Table 4. Therefore, hydrochloric acid was chosen to adjust the solution pH in the batch adsorption experiment.

[0064] Table 4. Effect of different concentrations of coexisting anions on the adsorption capacity of the adsorbent. Concentration / Adsorption Capacity <![CDATA[Cl - ]]> <![CDATA[SO4 2- ]]> <![CDATA[NO3 - ]]> 0 mM 116.2 mg / g 116.2 mg / g 116.2 mg / g 5 mM 114.4 mg / g 114.0 mg / g 73.2 mg / g 10 mM 112.7 mg / g 112.2 mg / g 69.6 mg / g 20 mM 110.3 mg / g 109.8 mg / g 67.9 mg / g Example 7 1. Synthesis of GO / MXene adsorbent with dendritic polyethyleneimine surface modification The method for synthesizing the adsorbent in this embodiment is the same as in Example 1.

[0065] 2. Adsorption process of Cr(VI) Preparation of Cr(VI)-containing solutions: Weigh 0.2829 g of potassium dichromate dried at 110℃ for 2 hours, dissolve it in water, transfer it to a 100 mL volumetric flask, and dilute it with deionized water to a 1000 mg / L Cr(VI)-containing solution. Then dilute it with deionized water to a 60 mg / L Cr(VI)-containing solution. Prepare solutions containing 60 mg / L Cr(VI) and 70 mg / L of each of the following eight different metal cations: Fe(III) trivalent, Cd(II) divalent, Co(II) divalent, Cu(II) divalent, Mn(II) divalent, Ni(II) divalent, Zn(II) divalent, and Mg(II) divalent. In the above process, the pH of the final Cr(VI)-containing solution is controlled to be 3 using concentrated hydrochloric acid or sodium hydroxide aqueous solution.

[0066] Take 10 mL of the above Cr(VI) solution into a centrifuge tube, add 10 mg of the adsorbent prepared above, and adsorb for 2 hours under mechanical shaking at 30 ℃ and 220 rpm to ensure that the adsorbent is in full contact with the aqueous phase. After the adsorption is completed, centrifuge to separate the Cr(VI) solution and test the remaining concentration of Cr(VI) and the concentration of other ions in the aqueous phase.

[0067] In the above adsorption and separation process, various cations have a certain influence on the adsorption capacity of the adsorbent, with Fe(III) having the greatest impact. The removal rates of Cr(VI) by the other metal cations are all less than 5%. The results are shown in Table 5. Therefore, in water systems where multiple cations coexist, the adsorbent still exhibits high affinity and efficient removal capacity for Cr(VI).

[0068] Table 5. Effect of polymetallic cations on adsorption efficiency of adsorbents Metal cations Cr(VI) Fe(III) Cd(II) Co(II) Cu(II) Mn(II) Ni(II) Zn(II) Mg(II) Adsorption efficiency 63.7% 37.2% 1.28% 1.78% 3.49% 0.75% 1.57% 1.28% 1.36% Example 8 1. Synthesis of GO / MXene adsorbent with dendritic polyethyleneimine surface modification The method for synthesizing the adsorbent in this embodiment is the same as in Example 1.

[0069] 2. Adsorption process of Cr(VI) Preparation of Cr(VI)-containing solution: Weigh 0.2829 g of potassium dichromate dried at 110℃ for 2 hours, dissolve it in water, transfer it to a 100 mL volumetric flask, and dilute with deionized water to a 1000 mg / L Cr(VI)-containing solution. Then dilute with deionized water to a 40 mg / L Cr(VI)-containing solution, and control the pH of the final Cr(VI)-containing solution to 3 using concentrated hydrochloric acid or sodium hydroxide aqueous solution during the above process.

[0070] Take 10 mL of the above Cr(VI) solution into a centrifuge tube, add 10 mg of the adsorbent prepared above, and adsorb for 2 hours under mechanical shaking at 30 ℃ and 220 rpm to ensure that the adsorbent is in full contact with the aqueous phase. After the adsorption is completed, centrifuge to separate the Cr(VI) solution and test the remaining concentration of Cr(VI) and the concentration of other ions in the aqueous phase.

[0071] In the above adsorption and separation process, the removal efficiency remained basically unchanged in the first two adsorption-desorption experiments. From the third cycle onwards, the removal efficiency decreased; however, the purification efficiency remained at 91.5% after six cycles. This indicates that the GMP adsorbent exhibits good cycle stability and is suitable for the removal of Cr(VI) in wastewater systems. The results are shown in Table 6.

[0072] Table 6 Effect of cycle number on adsorption efficiency Loop count 1 2 3 4 5 6 Adsorption efficiency 98.9% 98.5% 97.4% 95.1% 94.0% 91.5% Example 9 The difference from Example 1 is that the GO and Ti3C2T x The mass ratio of dendritic polyethyleneimine to graphene oxide is 3:1, and the mass ratio of dendritic polyethyleneimine to graphene oxide is 12:1.

[0073] The prepared adsorbent had an adsorption capacity of 145.3 mg / g in a Cr(VI)-containing solution with an initial concentration of 160 mg / L.

[0074] Example 10 The difference from Example 1 is that the GO and Ti3C2T x The mass ratio of dendritic polyethyleneimine to graphene oxide is 5:1, and the mass ratio of dendritic polyethyleneimine to graphene oxide is 8:1.

[0075] The prepared adsorbent had an adsorption capacity of 134.8 mg / g in a Cr(VI)-containing solution with an initial concentration of 160 mg / L.

[0076] Comparative Example 1 1. The synthesis of the adsorbent is as described in Example 1, except that: no dendritic polyethyleneimine modification and MXene intercalation are performed; the specific method is as follows: 325 mesh graphite powder is subjected to deep oxidation and exfoliation using the modified Hummers method to obtain graphene oxide aqueous dispersion, and graphene oxide powder is obtained by freeze drying, denoted as GO, and GO is used as adsorbent for the adsorption process of Cr(VI).

[0077] 2. The adsorption process of Cr(VI) is as described in Example 1.

[0078] In the above adsorption and separation process, the GO prepared in this comparative example exhibited an adsorption capacity of 49 mg / g in a Cr(VI)-containing solution with an initial concentration of 160 mg / L. This demonstrates that surface modification of dendritic polyethyleneimine and MXene intercalation can significantly enhance the Cr(VI) adsorption capacity.

[0079] Comparative Example 2 The difference from Example 1 is that linear polyethyleneimine (molecular weight 2500) is used instead of dendritic PEI.

[0080] The GO prepared in this comparative example had an adsorption capacity of 130.1 mg / g in a Cr(VI)-containing solution with an initial concentration of 160 mg / L.

[0081] Therefore, compared with linear polyethyleneimine, surface modification with dendritic polyethyleneimine can better improve the adsorption capacity of the adsorbent for Cr(VI).

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent, characterized in that, The method comprises the following steps: The GO dispersion liquid and Ti3C2T x are mixed in a mass ratio of 3-5:1 to obtain a GO-Ti3C2T x mixed solution. x ​ The GO-Ti3C2T x The mixed solution is mixed with the aqueous branched polyethyleneimine solution to perform a reaction, and a reaction solution containing branched polyethyleneimine modified GO / MXene is obtained. The reaction solution containing the branched polyethyleneimine modified GO / MXene is subjected to solid-liquid separation, washing and drying to obtain the branched polyethyleneimine surface modified GO / MXene nanoadsorbent.

2. The method of claim 1, wherein the dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent is prepared by the steps of: The mass ratio of the GO and Ti3C2T x is 3-5:

1.

3. The method of claim 1, wherein the dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent is prepared by the steps of: The mass concentration of the GO dispersion solution is 10 mg / L-15 mg / L.

4. The method of claim 1, wherein the dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent is prepared by the steps of: The Ti3C2T x The mass concentration of the colloidal solution is 8 mg / L-12 mg / L.

5. The method of claim 1, wherein the dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent is prepared by the steps of: The mass concentration of the branched polyethyleneimine aqueous solution is 20%-50%.

6. The method of claim 1, wherein the dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent is prepared by the steps of: The mass ratio of the branched polyethyleneimine to the graphene oxide is 8-12:

1.

7. The method of claim 1, wherein the dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent is prepared by the steps of: The number average molecular weight of the branched polyethyleneimine is 60000-80000.

8. The method of claim 1, wherein the dendritic polyethyleneimine surface-modified graphene oxide / MXene nanoadsorbent is prepared by the steps of: The reaction temperature is 20℃-25℃, and the reaction time is 20-30 hours. 9.The branched polyethyleneimine surface modified graphene oxide / MXene nanoadsorbent prepared by the method of any one of claims 1-8. 10.The application of the branched polyethyleneimine surface modified graphene oxide / MXene nanoadsorbent of claim 9 in adsorbing heavy metal Cr(VI).

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