Preparation method of polyelectrolyte brush for rapid treatment of heavy metal complex wastewater

Abstract

The application discloses a preparation method of a polyelectrolyte brush for quickly treating heavy metal complex wastewater, and belongs to the water treatment adsorption technical field in the environmental protection field. The specific steps of the method are as follows: (1) after dopamine hydrochloride is dissolved in DMF, an initiator and triethylamine are added, and stirring is carried out for 3 hours, and the solution is recorded as solution A. Solution A is poured into a graphene oxide hydrochloride buffer solution (pH=8.5), mixed and stirred for 1 day, and then solid A is obtained through separation and drying. (2) solid A is ultrasonically dispersed in a solution of methanol and water, and then monomers, copper bromide, a solution initiator and a ligand are added in sequence. After stirring and dissolving, ascorbic acid is added, and stirring is carried out at 30 DEG C for 1 day. After separation and drying, the polyelectrolyte brush is obtained. The polyelectrolyte brush can synergistically adsorb heavy metal complexes by regulating the electrostatic interaction of the polyelectrolyte chain, the organic molecule interaction and the nanometer interface effect of the substrate, so that the heavy metal complexes are quickly adsorbed and enriched in the polyelectrolyte brush, and low-concentration complex heavy metal ions can be efficiently removed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, and particularly relates to graphene polyelectrolyte brush as an adsorbent for deep treatment of heavy metal complex wastewater. BACKGROUND

[0002] Wastewater discharged from the electroplating, metal smelting, mining and pharmaceutical industries always contains a large amount of chelating agents and heavy metal ions, thus forming heavy metal complexes. Chelating agents, such as citrate, tartrate and ethylenediaminetetraacetic acid (EDTA), increase the solubility of heavy metal ions and are stable in a wide range of pH values. Traditional wastewater treatment technologies, including chemical precipitation and coagulation, are inefficient and difficult to meet increasingly stringent standards. More seriously, chelated metals in the water environment exhibit serious toxicity to specific cells, aquatic plants and microorganisms. The most commonly used heavy metal complex treatment technology at present is the advanced oxidation process, such as Fenton oxidation, ozone oxidation, photochemical oxidation, electrochemical oxidation and photoelectrocatalytic oxidation. However, these technologies often have incomplete mineralization, and the effluent after oxidation treatment often still contains low concentrations of heavy metal complexes, partially degraded organic complexing agents and free heavy metal ions. This will cause secondary pollution because the organic complexing agent is recombined with the free heavy metal ions after degradation. Therefore, further deep treatment is needed to meet the discharge standards.

[0003] The most commonly used deep treatment technology for heavy metal complex wastewater is adsorption and membrane separation. Adsorption has great application prospects for deep treatment of wastewater due to easy operation, high cost-effectiveness and low long-term stability. Among them, ion exchange resins have been widely used to remove metal ions by electrostatic attraction due to their large ion exchange capacity, great stability and excellent mechanical properties. However, ion exchange resins also have some inherent challenges, such as slow mass transfer rate, easy clogging and difficulty in regeneration. The low mass transfer rate may be due to their irregular pores, which are not conducive to the free and rapid diffusion of metal complexes and the exposure of active sites. Heavy metal complexes, i.e. the combination of heavy metal ions and organic ligands, increase the possibility of contaminating ion exchange resins, making it difficult to regenerate the resins. Therefore, for the treatment of wastewater containing heavy metal complexes, innovative adsorbents with higher adsorption rate and regenerability are still worth further exploration.

[0004] Polyelectrolytes are chain-like polymers with ionizable groups, which are widely used in wastewater treatment (such as polymer flocculants, nanofiltration membranes, ion exchange resins) due to low cost and environmental friendliness. Polyelectrolyte brushes, defined as one end of a single polyelectrolyte chain is tethered to a substrate. Polyelectrolyte chains are free to stretch under low external charge, while they are strongly contracted under multivalent ions or high concentrations of counterions. Through the elasticity and electrostatic interaction of polyelectrolyte chains, polyelectrolyte brushes can fully expose active sites, quickly capture ions (such as metal ions) in the solution, and then contract to enrich them inside. Using polyelectrolyte brushes can easily adsorb and regenerate, however, there is no related report on using polyelectrolyte brush composites to treat heavy metal complex wastewater. SUMMARY

[0005] In view of the above problems, the present application provides a novel polyelectrolyte brush for deep treatment of heavy metal complex wastewater, which is grafted with cationic polyelectrolyte chains on graphene oxide as a flat substrate and dopamine as a bridge.

[0006] In the present application, the graphene polyelectrolyte brush is obtained by the following method:

[0007] (1) Grafting initiator on graphene oxide

[0008] In a three-necked flask, 400 mg of dopamine hydrochloride was added and degassed for 5 minutes with nitrogen. 20 ml of N,N-dimethylformamide was added to dissolve dopamine hydrochloride, and stirred for 20 minutes under nitrogen atmosphere. Then 520 μl of bromoisobutyryl bromide and 600 μl of triethylamine (molar ratio of bromoisobutyryl bromide and triethylamine is 1:1) were added, and the mixture was stirred at room temperature for 3 hours under nitrogen, which was recorded as solution A. 0.1 g of graphene oxide was dispersed in 100 ml of hydrochloric acid buffer (480 mg of tris-hydroxymethyl aminomethane, and the pH was adjusted to 8.5 with 0.1 mol / L HCl solution) and ultrasonicated for 60 minutes, which was recorded as solution B. Solution A was poured into solution B and mixed and stirred at room temperature for 24 hours. The mixture was separated by centrifugation (10000 rpm for 5 minutes), and washed with ethanol and water by centrifugation for 5 times. Finally, the solid was freeze-dried for 24 hours to obtain solid A;

[0009] (2) Grafting polyelectrolyte chains to the graphene initiator composite material obtained in step (1)

[0010] The graphene polyelectrolyte brush is polymerized from monomer methacryloyloxyethyl trimethyl ammonium chloride. The operation method is as follows: 0.1 gram of solid A obtained in step (1) is dispersed in 10 milliliters of mixed solution of methanol and water with a volume ratio of 1:2 for 10 minutes under ultrasonic, and then is transferred into a 250 milliliter three-necked flask. Then 10 milliliters of methacryloyloxyethyl trimethyl ammonium chloride, 3.6 grams of copper bromide, 45 microliters of ethyl alpha-bromoisobutyrate and 5 milligrams of 2,2-bipyridine are sequentially added, and stirring is carried out under nitrogen atmosphere for 30 minutes. Then 30 milligrams of ascorbic acid is added, and the mixture is stirred at 30°C under nitrogen for 24 hours. The reaction mixture is exposed to air, and the reaction is stopped. The mixture is separated by centrifugation (10000 rpm for 5 minutes), and is washed with methanol and water for 5 times to remove unattached polymer, copper / ligand complex and unreacted monomer. The black solid is freeze-dried for 24 hours, and finally the graphene polyelectrolyte brush composite material is obtained.

[0011] Compared with the prior art, the present application has the following advantages:

[0012] (1) Based on the electrostatic adsorption of charged polymer chains and the "remote claw" function of flexible polyelectrolyte chains, the heavy metal complex in the solution is enriched, and the capture and aggregation ability for low concentration heavy metal complex in water can be improved simply by adjusting the polyelectrolyte brush grafting density, chain structure and charge density;

[0013] (2) The abundant functional group structure and intermolecular forces (such as hydrogen bond, hydrophobic interaction between organic molecules, etc.) of the polymer chain are used to realize selective adsorption of charged organic pollution molecules such as complexing agent and complex heavy metal ion;

[0014] (3) The polyelectrolyte chain can be stably grafted on graphene to form a multifunctional, structurally stable and controllable composite material, and the interface effect of the substrate is used to enhance the adsorption and fixation of heavy metal complex;

[0015] (4) Compared with channel materials (such as membrane materials and ion exchange resins), the polyelectrolyte brush has stronger flexibility, larger specific surface area and controllable morphology transformation, which is beneficial to the reversible adsorption and desorption of adsorbate, and makes the adsorbent easy to regenerate. BRIEF DESCRIPTION OF DRAWINGS

[0016] The specific embodiments of the present application will be further described in detail below with reference to the accompanying drawings.

[0017] Figure 1 The scanning electron microscope image of the graphene polyelectrolyte brush composite material obtained in Example 1.

[0018] Figure 2 The removal effect diagram of different materials on heavy metal complex Cu-EDTA.

[0019] Figure 3 Figure 4 is a graph of the removal of heavy metal complex Cu-EDTA by graphene polyelectrolyte brushes of different grafting densities.

[0020] Figure 4 Figure 5 is a graph of the removal of heavy metal complex Cu-EDTA by graphene polyelectrolyte brushes of different grafting lengths.

[0021] Figure 5 Figure 6 is a graph of the adsorption of Cu-EDTA by graphene polyelectrolyte brushes over time, pH = 6.

[0022] Figure 6 Figure 7 is an isotherm graph of the adsorption of Cu-EDTA by graphene polyelectrolyte brushes, pH = 6. DETAILED DESCRIPTION

[0023] Example 1 Preparation of graphene polyelectrolyte brush composite

[0024] (1) Grafting initiator on graphene oxide

[0025] Into a three-necked flask was added 400 mg of dopamine hydrochloride, which was degassed with nitrogen for 5 minutes. 20 ml of N,N-dimethylformamide was added to dissolve the dopamine hydrochloride, which was stirred for 20 minutes under a nitrogen atmosphere. Subsequently, 520 μΐ of bromoiso-butyryl bromide and 600 μΐ of triethylamine (molar ratio of bromoiso-butyryl bromide to triethylamine was 1 : 1) were added, and the mixture was stirred for 3 hours at room temperature under nitrogen, which was denoted as solution A. 0.1 g of graphene oxide was dispersed in 100 ml of hydrochloric acid buffer (480 mg of tris-hydroxymethyl aminomethane, pH was adjusted to 8.5 with 0.1 mol / L HC1) and ultrasonicated for 60 minutes, which was denoted as solution B. Solution A was poured into solution B and mixed, and the reaction was stirred for 24 hours at room temperature. The mixture was separated by centrifugation (10000 rpm for 5 minutes), and washed with ethanol and water by centrifugation for 5 times. Finally, the solid was freeze-dried for 24 hours to obtain solid A;

[0026] (2) Grafting polyelectrolyte chains on the graphene initiator composite obtained in step (1)

[0027] The graphene polyelectrolyte brush was polymerized from monomer methacryloyloxyethyl trimethyl ammonium chloride. The operation method was as follows: 0.1 gram of solid A obtained in step (1) was dispersed in 10 milliliters of a mixed solution of methanol and water with a volume ratio of 1:2 by ultrasonic for 10 minutes, and then transferred to a 250 milliliter three-necked flask. Then 10 milliliters of methacryloyloxyethyl trimethyl ammonium chloride, 3.6 grams of copper bromide, 45 microliters of ethyl alpha-bromoisobutyrate and 5 milligrams of 2,2-bipyridine were sequentially added, and stirred for 30 minutes under nitrogen atmosphere. Then 30 milligrams of ascorbic acid was added, and the mixture was stirred at 30°C for 24 hours under nitrogen atmosphere. The reaction mixture was exposed to air to stop the reaction. The mixture was separated by centrifugation (10000 rpm for 5 minutes), and washed with methanol and water for 5 times to remove unattached polymer, copper / ligand complex and unreacted monomer. The black solid was freeze-dried for 24 hours to obtain the graphene polyelectrolyte brush composite material.

[0028] Example 2: Preparation of graphene polyelectrolyte brush composites with different grafting densities

[0029] The operation steps of this example were the same as those of example 1, except that in step (1) of example 1, the amount of bromoisobutyryl bromide was adjusted to 130 microliters and 260 microliters.

[0030] Example 3: Preparation of graphene polyelectrolyte brush composites with different grafting lengths

[0031] The operation steps of this example were the same as those of example 1, except that in step (2) of example 1, the reaction time was adjusted to 3 hours and 6 hours.

[0032] Example 4: Adsorption experiment of heavy metal complex

[0033] Preparation of simulated heavy metal complex Cu-EDTA solution: 362.4 milligrams of copper nitrate trihydrate and 558.4 milligrams of ethylenediaminetetraacetic acid disodium salt (molar ratio of 1:1) were dissolved in 250 milliliters of ultrapure water, stirred until completely dissolved, and placed for 48 hours to obtain a Cu-EDTA mother liquor with a concentration of 6 mmol / L; 2.5 milliliters of Cu-EDTA mother liquor was diluted to 100 milliliters to obtain a Cu-EDTA solution with a concentration of 0.15 mmol / L, and the pH of the solution was adjusted to 6.0, then 0.1 gram of graphene polyelectrolyte brush composite material of example 1 was added, and placed in a constant temperature oscillator at 25°C for 30 minutes. The supernatant was obtained by filtration, and the residual copper content was measured by inductively coupled plasma spectrometer (ICP).

[0034] The above merely illustrates the preferred embodiments of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a polyelectrolyte brush for rapidly treating heavy metal complexed wastewater, characterized in that, The specific steps are as follows: (1) Grafting initiators onto graphene oxide 400 mg of dopamine hydrochloride was added to a three-necked flask and degassed with nitrogen for 5 minutes. 20 mL of N,N-dimethylformamide was added to dissolve the dopamine hydrochloride, and the mixture was stirred for 20 minutes under a nitrogen atmosphere. Subsequently, 520 μL of bromoisobutyryl bromide and 600 μL of triethylamine were added, with a molar ratio of bromoisobutyryl bromide to triethylamine of 1:

1. The mixture was stirred at room temperature under nitrogen for 3 hours, and this solution was denoted as solution A. 0.1 g of graphene oxide was dispersed in 100 mL of hydrochloric acid buffer, which was prepared by adjusting the pH of 480 mg of tris(hydroxymethyl)aminomethane to 8.5 with 0.1 mol / L hydrochloric acid. After sonication for 60 minutes, solution B was obtained. Solution A was poured into solution B and mixed, and the mixture was stirred at room temperature for 24 hours. The reaction mixture was centrifuged at 10,000 rpm for 5 minutes to achieve solid-liquid separation, and washed five times with ethanol and water. Finally, the solid was freeze-dried for 24 hours to obtain solid A. (2) Graft polyelectrolyte chains onto the graphene initiator composite material obtained in step (1). The graphene polyelectrolyte brush is polymerized from the monomer methacryloyloxyethyltrimethylammonium chloride. The operation method is as follows: 0.1 g of solid A obtained in step (1) is ultrasonically dispersed for 10 minutes in 10 mL of a mixed solution of methanol and water with a volume ratio of 1:2, and then transferred to a 250 mL three-necked flask; then 10 mL of methacryloyloxyethyltrimethylammonium chloride, 3.6 g of copper bromide, 45 μL of ethyl α-bromoisobutyrate and 5 mg of 2,2-bipyridine are added in sequence, and stirred in a nitrogen atmosphere for 30 minutes; then 30 mg of ascorbic acid is added, and the mixture is stirred at 30 °C for 24 hours under nitrogen; the reaction mixture is exposed to air to stop the reaction; the reaction mixture is centrifuged at 10,000 rpm for 5 minutes to achieve solid-liquid separation, and washed 5 times with methanol and water to remove unattached polymer, copper / ligand complex and unreacted monomer; the black solid is freeze-dried for 24 hours to finally obtain the graphene polyelectrolyte brush composite material.

2. The application of the graphene polyelectrolyte brush composite material according to claim 1 in the deep treatment of heavy metal complex wastewater, characterized in that: The Cu-EDTA wastewater concentration is 5-80 mg / L, the dosage of the graphene polyelectrolyte brush composite material is 1 g / L, and the pH range is 2-12.

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