CN112723346B

CN112723346B - Preparation method of nitrogen-doped graphene quantum dot hybrid membrane for selectively adsorbing copper ions from mixed metal solution

Info

Publication number: CN112723346B
Application number: CN202011638270.7A
Authority: CN
Inventors: 刘俊生; 庞博文; 王凤侠
Original assignee: Hefei University
Current assignee: Hefei University
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2022-06-24
Anticipated expiration: 2040-12-31
Also published as: CN112723346A

Abstract

The invention discloses a preparation method of a nitrogen-doped graphene quantum dot hybrid membrane for selectively adsorbing copper ions from a mixed metal solution, which comprises the steps of firstly preparing a hybrid precursor solution by a sol-gel reaction between a nitrogen-doped graphene quantum dot N-GQDs precursor, silane WD-51 and tetraethoxysilane, then adding the hybrid precursor solution into a polyvinyl alcohol aqueous solution for reaction, standing and defoaming to obtain a membrane coating solution, and coating the membrane coating solution on a support to obtain a membrane; or dissolving the coating solution by using a solvent, coating the film to obtain a membrane, and drying to obtain the nitrogen-doped graphene quantum dot hybrid film which can be used for selectively adsorbing copper ions from the mixed metal solution, wherein the nitrogen-doped graphene quantum dot hybrid film can be provided with or without a support body; the copper ion selective adsorption material has selective adsorption on copper ions in various mixed metal ion solutions, can preferentially remove the copper ions in the mixed metal ion solutions by adopting membrane adsorption, and can be used for the fractional separation of the copper ions in wastewater containing various metal ions.

Description

Preparation method of nitrogen-doped graphene quantum dot hybrid membrane for selectively adsorbing copper ions from mixed metal solution

Technical Field

The invention belongs to the technical field of heavy metal wastewater treatment, and particularly relates to a nitrogen-doped graphene quantum dot hybrid membrane for selectively adsorbing copper ions from a mixed metal solution, which is prepared by a hydrothermal synthesis method and a sol-gel reaction.

Background

Heavy metal wastewater pollution is attracting more and more attention. How to remove heavy metal ions in wastewater and eliminate the harm of the heavy metal ions is a key technical problem in the field of wastewater treatment, so that the research and development of novel separation technologies are more and more urgent.

Chinese patent 201610260866.5 proposes a preparation method of a chitosan-modified graphene oxide quantum dot adsorption material, which comprises adding a cross-linking agent and graphene oxide quantum dots into an acetic acid solution of chitosan, magnetically stirring and mixing at a certain pH and a certain temperature, repeatedly washing with deionized water and ethanol, and freeze-drying to obtain the chitosan-modified graphene oxide quantum dot adsorption material. The obtained adsorbing material has good adsorption performance on methylene blue, but has no adsorption on heavy metal ions, so that the separation and the classification of the heavy metal ions in the wastewater are difficult, and the application value is limited.

Chinese patent 201911173039.2 proposes a method for preparing a hybrid membrane for selectively separating copper from a mixed metal solution, which comprises the steps of preparing a hybrid precursor by sol-gel reaction of graphene oxide and a silane coupling agent KH-792, adding the obtained hybrid precursor into a polyvinyl alcohol aqueous solution for reaction, standing and defoaming the obtained substance to obtain a membrane coating solution, and coating to obtain the hybrid membrane for selectively separating copper ions from the mixed metal ion solution; but the hybrid membrane is paired with Cu²⁺The adsorption amount of (2) is small, the number of times of recycling is small (paragraph [ 0047 ] of the specification, example 2, the adsorption amount of hybrid membrane B is maximum, it is to Cu²⁺The adsorption capacity of the adsorbent can reach about 3.5 mg/g), so the application value is limited.

Related invention patents and literature reports that nitrogen-doped graphene quantum dot hybrid membranes are used for preferential adsorption and removal of copper ions from mixed metal solutions are not found at present.

Disclosure of Invention

The present invention aims to provide a method for preparing a nitrogen-doped graphene quantum dot hybrid film for selectively adsorbing copper ions from a mixed metal solution, so as to overcome the above defects of the prior art, and provide a method for preparing a copper ion (Cu) hybrid film for various mixed metal solutions²⁺) The selective adsorption of (a) and the purification treatment of industrial wastewater containing a variety of mixed metal ions provide new solutions.

In order to realize the purpose, the invention adopts the following technical scheme: a preparation method of a nitrogen-doped graphene quantum dot hybrid film for selectively adsorbing copper ions from a mixed metal solution comprises the following steps:

preparation of nitrogen-doped graphene quantum dot (N-GQDs) precursor

And (3) synthesizing and preparing the N-GQDs precursor material by using citric acid as a carbon source and urea as a nitrogen source by using a hydrothermal method. The method comprises the following steps: dissolving citric acid and urea in a certain amount of water, stirring to obtain a clear solution, wherein the addition amount of the citric acid is as follows according to molar ratio: urea 1: 0.1-10, placing the mixture into a reaction kettle with a polytetrafluoroethylene lining, heating to 150-160 ℃, and keeping for 4-10 hours; putting the reacted solution into a culture dish, heating and drying at 60 ℃, taking out the dried solid, namely the nitrogen-doped graphene quantum dot N-GQDs precursor material;

secondly, adding a certain amount of N-GQDs precursor powder into water, stirring and dissolving the N-GQDs precursor powder, adding the N-GQDs precursor powder into a polyvinyl alcohol (PVA) aqueous solution with the mass percentage concentration of 5%, stirring the mixture for 1 to 5 hours at room temperature, adding glutaraldehyde, tetraethoxysilane (TEOS for short) and silane coupling agent WD-51, carrying out sol-gel reaction to obtain a hybrid precursor solution, and continuously stirring the hybrid precursor solution for 1 to 24 hours; placing the stirred solution in an ultrasonic cleaner, and carrying out ultrasonic treatment for 0.2-1 h to remove bubbles in the solution; standing and defoaming the obtained substance to obtain a coating solution;

or, adding a certain amount of N-GQDs precursor powder into water, stirring, adding a proper amount of glutaraldehyde, tetraethoxysilane (TEOS for short) and silane coupling agent WD-51 to perform sol-gel reaction after the precursor powder is completely dissolved, and continuously stirring for 1-24 hours to obtain a hybrid precursor solution; then adding the hybrid precursor solution into a polyvinyl alcohol (PVA) aqueous solution with the mass percentage concentration of 5%, stirring for 1-5 h at room temperature, placing the hybrid precursor solution into an ultrasonic cleaner under the stirring condition, and carrying out ultrasonic treatment for 0.2-1 h to remove bubbles in the hybrid precursor solution; standing and defoaming the obtained substance to obtain a coating solution;

thirdly, directly coating the coating liquid after standing and defoaming on a support body to obtain a membrane, standing at room temperature for 1-48 hours, separating the membrane from the support body, then drying the membrane at 10-60 ℃ for 1-48 hours, and cooling to obtain the nitrogen-doped graphene quantum dot hybrid membrane which is not provided with the support body and can be used for selectively adsorbing copper ions from mixed metal solution;

or directly coating the coating solution after standing and defoaming on a support to obtain a membrane, then drying the support and the membrane together for 1-48 h at the temperature of 10-60 ℃, and cooling to obtain the nitrogen-doped graphene quantum dot hybrid membrane with the support and capable of selectively adsorbing copper ions from the mixed metal solution;

or dissolving the coating solution after standing and defoaming by using a certain amount of solvent, coating the obtained substance on a support to obtain a membrane, drying the support and the membrane together at 10-60 ℃ for 1-48 h, and cooling to obtain the nitrogen-doped graphene quantum dot hybrid membrane with the support and capable of selectively adsorbing copper ions from the mixed metal solution; or separating the membrane from the support after drying to obtain the nitrogen-doped graphene quantum dot hybrid membrane which does not have the support and can be used for selectively adsorbing copper ions from the mixed metal solution.

As a preferred technical scheme of the invention, the preparation method comprises the following steps:

in the second step, the adding amount proportion of the N-GQDs precursor, glutaraldehyde, ethyl orthosilicate, silane coupling agent WD-51 and 5% polyvinyl alcohol is 0.1-0.5: 1-5: 0.05-0.25: 0.1-0.5: 50.

the solvent is selected from N, N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, ethanol, isobutanol or N-butanol.

The support body is made of polytetrafluoroethylene plate (Teflon plate), glass plate and Al₂O₃Ceramics, silicon dioxide ceramics, titanium dioxide ceramics, zirconium dioxide ceramics, polyethylene films, polyester fabrics, glass fiber fabrics, nylon fabrics or non-woven fabrics.

The drying is selected from convection drying, vacuum drying, conduction drying, ultraviolet drying, infrared drying, microwave drying or mechanical dehydration drying.

The coating film is selected from a flowing coating film, a dipping coating film, a spraying coating film, a scraping coating film or a rotating coating film.

The nitrogen-doped graphene quantum dot hybrid membrane prepared by the invention can adsorb and separate copper ions from copper ion-containing wastewater, and can also selectively adsorb and separate copper ions from mixed metal solution containing copper ions, so that copper ions (Cu) in the mixed metal solution are contained²⁺) In addition to lead ions (Pb)²⁺) Calcium ion (Ca)²⁺) Cobalt ion (Co)²⁺) Chromium ion (Cr)³⁺) One or more of (a).

The beneficial effects of the invention are as follows:

1) the prepared N-GQDs hybrid membrane for selectively adsorbing copper ions from the mixed metal solution can be provided with or without a support; the hybrid membrane has preferential adsorption for copper ions in various mixed metal ion solutions, has adjustable adsorption performance, can be used for preferential adsorption separation of copper ions in water, and can also be used for preferential separation and classification of copper ions in mixed metal ion wastewater solutions, so that metal ion pollution in water is eliminated.

2) Compared with the prior art, the invention adopts a hydrothermal synthesis method and a sol-gel reaction to prepare the N-GQDs hybrid membrane for selectively adsorbing copper ions from a mixed metal solution, and has the outstanding characteristics that the pyrrole N site of the N-GQDs has an electrochemical active site preferentially adsorbing metal cations to improve the adsorption and removal capacity of the hybrid membrane on the heavy metal ions; according to the edge effect of N-GQDs, the site activity is improved for adsorbing heavy metal ions in the wastewater. The hybrid membrane can be made into an industrial separation membrane and a membrane component for selectively separating copper ions from the mixed metal solution and then separating other residual metal ions in the mixed metal solution step by step in sequence, so the operation is simple and the hybrid membrane can be used for separating and grading the metal ions in large-scale industrial wastewater.

3) Compared with the method for preparing the graphene oxide quantum dot adsorption material by using chitosan modification, which is provided by the Chinese patent 201610260866.5, the hybrid membrane disclosed by the invention has the advantages that the membrane preparation process is simple, the obtained hybrid membrane is uniform and stable, is easy to recycle, has the capability of selectively adsorbing and separating metal ions in water, and can be prepared into an industrial membrane separation device for separation, classification and purification treatment of various mixed metal ions in industrial wastewater.

4) Compared with the method which is provided by Chinese patent 201911173039.2 and uses graphene oxide and silane coupling agent KH-792 to prepare a hybrid precursor through sol-gel reaction, and adds the obtained hybrid precursor into a polyvinyl alcohol aqueous solution to react to obtain the hybrid membrane, the hybrid membrane prepared by the method has the advantages of better selectivity, higher adsorption capacity, simpler and more feasible desorption and more recycling times.

Drawings

FIG. 1 is a comparison graph (a) of the color of the N-GQDs precursor solution and the color of the N-GQDs precursor solution under 365nm ultraviolet radiation, and a graph (b) of an ultraviolet absorption spectrum;

FIG. 2 is an XRD pattern of N-GQDs precursor powder;

FIG. 3 is an XPS analysis of N-GQDs precursor powder;

FIG. 4 is a graph showing the relationship between the adsorption amounts of mixed metal ions by the N-GQDs hybrid membranes A to G;

FIG. 5 shows Cu adsorption of N-GQDs hybrid film B²⁺、Co²⁺、Pb²⁺SEM image (a) and EDS energy spectrum (b) of the mixed metal ion rear surface;

FIG. 6 shows different N-GQDs hybrid films A-G for single Cu²⁺Solution with Cu²⁺、Co²⁺、Pb²⁺Cu in mixed solution of three metal ions²⁺A comparison graph of the adsorption amounts;

FIG. 7 shows the A-G to Cu pairs of N-GQDs hybrid films²⁺、Co²⁺、Pb²⁺Mixing Cu in metal solution²⁺Graph of the number of adsorption-desorption cycles used.

Detailed Description

The preparation method of the nitrogen-doped graphene quantum dot hybrid film for selectively adsorbing copper ions from mixed metal solution according to the present invention is further illustrated by specific examples.

Example 1

Preparation of nitrogen-doped graphene quantum dot (N-GQDs) precursor:

0.21g (1mmol) of citric acid and 0.18g (3mmol) of urea were dissolved in 5mL of water at a molar ratio of citric acid (carbon source) to urea (nitrogen source) of 1:3 and stirred to give a clear solution. Placing the mixture into a reaction kettle with a polytetrafluoroethylene lining, heating the mixture to 160 ℃, and keeping the temperature for 4 hours. The reaction solution was cooled to room temperature in the autoclave, and the solution in the autoclave was opened, whereby the solution was a clear yellow solution (as shown in the left panel of FIG. 1 (a)). The graphene quantum dots are used as zero-dimensional materials, and have abundant edge effects, and the fluorescent characteristic that the graphene quantum dots can emit bright blue fluorescence under 365nm ultraviolet lamp irradiation.

In order to further determine that the clear yellow solution taken out from the reaction kettle is the N-GQDs precursor, ultraviolet absorption spectrogram detection is carried out on the clear yellow solution, and the maximum ultraviolet absorption wavelength of the solution is about 365nm (shown in figure 1 (b)). And drying the prepared N-GQDs precursor solution at 40 ℃ to obtain N-GQDs precursor powder, wherein the powder is easy to dissolve in water and is in a dark blue color when dissolved in water. When the solution is irradiated by ultraviolet at 365nm, the solution can still have blue fluorescence (as shown in the right picture of figure 1 (a)). The dried N-GQDs precursor solution still has the fluorescence characteristic of the N-GQDs precursor.

XRD characterization of the N-GQDs precursor powder (FIG. 2) revealed from FIG. 2: a large broad peak exists at the 2 theta position of 26.9 degrees, and corresponds to a crystal face diffraction peak of graphene (002). This is illustrated as follows: the N-GQDs precursor powder has a crystal structure of graphene, and thus it can be considered that a substance similar to a graphite structure is formed.

The N-GQDs precursor powder was subjected to XPS analysis (as shown in FIG. 3). 285.7eV, 400.1eV, and 531.2eV in FIG. 3(a) of the entire spectrum correspond to C, N, O elements, respectively, and it was confirmed that the N element was successfully added to the powder material. The peak at 284.8eV of the C1s partial peak in fig. 3(b) can be considered as a C ═ C bond, a C — C bond, a peak at 286.2eV as a C — O bond and a C — N bond, a peak at 287.7eV as a C ═ O bond, and a peak at 288.9eV as an O — C ═ O bond. The peak at 400.0eV in the N1s peak partial plot in FIG. 3(c) can be attributed to pyrrole N. N is present as pyrrole nitrogen. Pyrrole nitrogen (pyrrole-N) has special optical properties, which on graphene can cause graphene to generate bright blue fluorescence, which also explains why the material emits blue fluorescence at 365nm on the molecular layer surface. Pyrrole N sites are believed to be electrochemically active sites that preferentially adsorb cations, which gives nitrogen-doped graphene good electronic and ionic conductivity. The peak at 531.6eV of the O1s partial peak in fig. 3(d) is attributable to C ═ O on the carboxyl group or carbonyl group.

In summary, the following steps: the precursor of N-GQDs with a graphene crystal structure is prepared in the embodiment.

Example 2

Under the condition of room temperature, taking a certain amount of the N-GQDs precursor powder prepared in the example 1, adding 10mL of water, stirring for 10min until the N-GQDs precursor powder is completely dissolved, adding a PVA (5 wt%) solution, stirring for 1h at room temperature, then respectively adding glutaraldehyde with the mass percentage concentration of 25%, ethyl orthosilicate and a silane coupling agent WD-51 under the stirring condition, and continuously stirring for 4h to obtain a solution. Placing the solution in an ultrasonic cleaner, performing ultrasonic treatment at 100KHz for 20min to remove bubbles in the solution, standing for 12h to obtain a film-forming solution, uniformly coating the film-forming solution on a polytetrafluoroethylene plate, separating a membrane from the polytetrafluoroethylene plate as a support, drying the membrane at 40 ℃ for 12h, and cooling to obtain the N-GQDs hybrid membrane without the support.

The contents of N-GQDs precursor, glutaraldehyde, WD-51, TEOS and other raw materials in the hybrid membrane are changed, the influence of the hybrid membrane composition on the adsorption amount of heavy metal ions is studied, and the result is shown in Table 1.

As can be seen from Table 1, the composition of the hybrid membrane does have some effect on the amount of heavy metal ions adsorbed. According to the experimental result, the composition of the raw materials for preparing the N-GQDs hybrid membrane can be optimized so as to improve the adsorption performance of the hybrid membrane.

TABLE 1 influence of the composition of the hybrid membranes on the amount of heavy metal ions adsorbed

In summary, the following steps: this example prepares N-GQDs hybrid membranes without a support, which can be used for adsorptive separation of different kinds of metal ions from solutions containing metal ions.

Example 3

According to the experimental results of example 2, it can be seen that: the addition amount of the N-GQDs precursor powder and the addition amount of the silane coupling agent WD-51 have the greatest influence on the performance of the N-GQDs hybrid film. Among them, the amount of N-GQDs precursor powder added is preferably not more than 0.5g, and the amount of silane coupling agent WD-51 added is preferably in the range of 0.2 to 0.5 mL. Accordingly, by optimizing the raw material ratio (see table 2), a series of N-GQDs hybrid membranes for adsorbing and separating metal ions from the mixed metal solution were prepared, and labeled as hybrid membranes a to G, respectively. Wherein the addition amount of the N-GQDs precursor powder in the A-D hybrid films is increased in sequence, and the addition amount of the silane coupling agent WD-51 in the E-G hybrid films is increased in sequence.

TABLE 2 raw material proportioning table for N-GQDs hybrid membranes A-G

Respectively putting the prepared N-GQDs hybrid membranes A to G without the support into 40mL of Cu with the concentration of 50mg/L²⁺、Pb²⁺、Ca²⁺、Co²⁺、Cr³⁺In a total of 5 metal ions, the adsorption amount of the membrane was measured. The experimental procedure was as follows:

0.2G of a series of N-GQDs hybrid membranes A-G without a support prepared as above are weighed and respectively placed in 250mL beakers, then 40mL of mixed metal ion solution with the concentration of 50mg/L is transferred and statically adsorbed for 24h, then a sample is filtered out of the beaker by a funnel, and the filtrate is collected. The concentration of the original solution before adsorption and the concentration of the residual solution after adsorption were detected by an atomic absorption spectrometer (model PE900T), and the adsorption amount (mg/g) of the hybrid membrane to metal ions was calculated. The calculation formula of the adsorption amount (mg/g) is as follows:

q＝(C₀-C_t)V/W

wherein, C₀Is the concentration of metal ions in the original solution mg/L, C_tThe concentration of the residual metal ions in the solution after adsorption is mg/L, V is the volume mL of the solution, and W is the mass mg of the sample.

FIG. 4 shows the results of adsorption experiments of A-G hybrid membranes on ions in 5 kinds of aqueous solutions of mixed metal ions. As can be seen from FIG. 4, the adsorption amounts of the A-G hybrid membranes to various metal ions are Cu in sequence from high to low²⁺＞Pb²⁺＞Ca²⁺＞Co²⁺＞Cr³⁺. Wherein for Cu²⁺The hybrid membrane B, A has better adsorption effect and higher adsorption quantity. For Pb²⁺Adsorption effectPreferably, the hybrid membrane A, B. Co²⁺、Ca²⁺The hybrid membrane B, A is preferred for the adsorption effect.

In comprehensive comparison, in the case of coexistence of 5 kinds of metal ions, the metal ions are added to Cu²⁺、Pb²⁺、Co²⁺The preferred adsorption is hybrid membrane B. Hybrid film B vs Cu²⁺、Pb²⁺、Ca²⁺、Co²⁺、Cr³⁺The corresponding adsorption capacity is respectively 7.4mg/g > 3.8mg/g > 2.6mg/g > 2.2mg/g > 0.19mg/g, and the difference of the adsorption capacity is obvious. Therefore, the N-GQDs hybrid membrane B has the best effect of adsorbing copper ions and obvious adsorption selectivity.

In summary, the following steps: the N-GQDs hybrid membranes A-G without the support prepared in this example can be used for selective adsorptive separation of heavy metal copper ions from mixed metal solutions.

Example 4

The N-GQDs hybrid membrane B with the best copper ion adsorption effect prepared in the example 3 is selected and put into 40mL of Cu with the concentration of 50mg/L²⁺、Co²⁺、Pb²⁺Adsorbing for 12h in the mixed solution of the three metals, and observing Cu in the mixed solution of the three metals on metal ions²⁺、Co²⁺、Pb²⁺The surface SEM appearance after adsorption is verified by an energy spectrum EDS; see if the metal ions are indeed adsorbed on the surface of the hybrid membrane.

FIG. 5 shows Cu adsorption of hybrid membrane B²⁺、Co²⁺、Pb²⁺SEM image (a) and EDS energy spectrum (b) of the mixed metal ion back surface. As can be seen from fig. 5: the EDS energy spectrum of FIG. 5 has obvious absorption peaks of Cu, Co and Pb elements, and other element peaks are basically not seen.

In summary, the following steps: the N-GQDs hybrid membrane without a support prepared in the embodiment can be used for selectively adsorbing and separating heavy metal copper ions from mixed metal solution.

Example 5

The A-G hybrid membrane prepared in example 3 is selected to be used for pairing single metal ions Cu²⁺Solution with Cu²⁺、Co²⁺、Pb²⁺Cu adsorption by three metal ion mixed solution²⁺The results of the experiment, in which the change in the amount of adsorption was examined, are shown in FIG. 6.

As can be seen from FIG. 6, for Cu²⁺The adsorption solution contains one or three metal ions, which has little influence on the adsorption effect, namely the hybrid membrane adsorbs Cu in the presence of other ions²⁺Less interference effects. This result illustrates that: in various mixed metal ion solutions, copper ions have competitive adsorption advantages and high adsorption selectivity.

In conclusion: the N-GQDs hybrid membrane without a support prepared in this example can be used for selective adsorptive separation of metallic copper ions from mixed metal solutions.

Example 6

The hybrid membranes A to G prepared in the embodiment 3 are selected, and HCl and HNO of 0.2mol/L are selected₃EDTA-2Na is used as a desorbent to carry out adsorption-desorption cyclic use experiments. The operation steps are as follows:

taking 0.2G of each of the A-G films, putting the hybrid film into Cu with the concentration of 50mg/L²⁺、Co²⁺、Pb²⁺And after the mixed metal solution is adsorbed for 12 hours, washing the hybrid membrane by ultrapure water, and washing off redundant heavy metal ions on the surface. The washed hybrid membrane is put into 40ml of 0.2mol/L HCl and HNO respectively₃And desorbing in the desorption solution of EDTA-2Na for 12 hours, and taking the desorbed solution to test the concentration of the heavy metal ions in the solution. And putting the desorbed membrane into ultrapure water to be soaked for about 4 hours. The cyclic use of the membrane material is completed through one-time adsorption and desorption.

As a result, it was found that: for Cu when HCl is used as desorption liquid²⁺、Co²⁺、Pb²⁺The adsorption amount of (2) is reduced by more than 60% in the 4 th cycle of adsorption. HNO₃As stripping liquid for Cu²⁺、Co²⁺、Pb²⁺The adsorption amount of (3) is reduced by 80% or more in the adsorption of the 3 rd cycle. EDTA-2Na is selected as desorption liquid to desorb Cu on the film²⁺，Cu²⁺The maximum adsorption amount of (2) was 9.0mg/g, the adsorption amount of the 10 th cycle was 7.8mg/g, and the adsorption amount was reduced by 13% (as shown in FIG. 7).

The experimental results show that: EDTA-2Na asCu²⁺The desorbent has the best effect, and the hybrid membrane without the support can be recycled for 10 times, thereby greatly improving the utilization rate of the N-GQDs hybrid membrane.

Example 8

Using the same experimental setup and procedure as in example 3, the coating solution prepared from the raw material mixture of hybrid film C was used to coat a support of zirconium dioxide (ZrO)₂) Immersing the ceramic wafer into the prepared coating liquid, dipping and coating the zirconium dioxide ceramic wafer to obtain a membrane, placing the membrane and the zirconium dioxide ceramic wafer together in a drying oven at 30 ℃ for convection drying for 6 hours, and cooling to ensure that the membrane is not separated from the support body, thus obtaining the N-GQDs hybrid membrane with the zirconium dioxide ceramic substrate of the support body.

0.2g of the hybrid membrane C with a support prepared in this example was taken to adsorb 40mL of CuCl with a concentration of 50mg/L₂The adsorption amount of copper ions in the solution can reach 7.71mg/g at 35 ℃ and pH 5.

In summary, the following steps: the N-GQDs hybrid membrane with the support prepared in the embodiment can be used for removing copper ions in water.

Example 9

Adopting the same experimental device and operation steps as those of example 3, preparing the obtained coating solution by adopting the raw material proportion of the hybrid membrane G, dissolving the coating solution by using 20mL of N, N-dimethylformamide solvent, continuously stirring for 2h, then flowing and coating the obtained substance on a support glass plate to obtain a membrane, standing for 24h at room temperature to dry the membrane in the air, then drying in vacuum for 6h at 40 ℃ to completely volatilize the solvent as far as possible, and separating the membrane from the glass plate after cooling to obtain the N-GQDs hybrid membrane without the support.

0.2G of the hybrid membrane G without a support prepared in this example was taken to adsorb 40mL of Cu at a concentration of 1000mg/L²⁺、Co²⁺、Pb²⁺The copper ion adsorption amount of the solution can reach 9.23mg/g at 45 ℃ and pH value of 5.

In summary, the following steps: the N-GQDs hybrid membrane without a support prepared in this example can be used for selective adsorptive separation of metallic copper ions from mixed metal solutions.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and all the related technologies that can be directly derived or suggested from the present disclosure should fall within the protection scope of the present invention.

Claims

1. A preparation method of a nitrogen-doped graphene quantum dot hybrid film for selectively adsorbing copper ions from a mixed metal solution is characterized by comprising the following steps:

preparing a nitrogen-doped graphene quantum dot precursor:

citric acid and urea are dissolved in water and stirred into a clear solution, which is added in molar ratios citric acid: urea 1: 0.1-10, placing the mixture into a reaction kettle with a polytetrafluoroethylene lining, heating to 150-160 ℃, and keeping for 4-10 hours; putting the reacted solution into a culture dish, heating and drying, taking out the dried solution, and drying to obtain a solid, namely the nitrogen-doped graphene quantum dot N-GQDs precursor material;

adding water into the N-GQDs precursor powder, stirring and dissolving, adding the N-GQDs precursor powder into a polyvinyl alcohol aqueous solution with the mass percentage concentration of 5%, stirring for 1-5 h at room temperature, adding glutaraldehyde, ethyl orthosilicate and silane coupling agent WD-51, performing sol-gel reaction to obtain a hybrid precursor solution, and continuously stirring for 1-24 h; placing the stirred solution in an ultrasonic cleaner, and carrying out ultrasonic treatment for 0.2-1 h to remove bubbles in the solution; standing and defoaming the obtained substance to obtain a coating solution;

or adding water into the N-GQDs precursor powder, stirring, adding a proper amount of glutaraldehyde, ethyl orthosilicate and silane coupling agent WD-51 for sol-gel reaction when the N-GQDs precursor powder is completely dissolved, and continuously stirring for 1-24 hours to obtain a hybrid precursor solution; then adding the hybrid precursor solution into a polyvinyl alcohol aqueous solution with the mass percentage concentration of 5%, stirring for 1-5 h at room temperature, placing the hybrid precursor solution in an ultrasonic cleaner under the stirring condition, and carrying out ultrasonic treatment for 0.2-1 h to remove bubbles in the hybrid precursor solution; standing and defoaming the obtained substance to obtain a coating solution;

in the second step, the adding amount proportion of the N-GQDs precursor, glutaraldehyde, ethyl orthosilicate, silane coupling agent WD-51 and 5% polyvinyl alcohol is 0.1-0.5: 1-5: 0.05-0.25: 0.1-0.5: 50;

thirdly, directly coating the coating liquid after standing and defoaming on a support body to obtain a membrane, standing at room temperature for 1-48 hours, separating the membrane from the support body, then drying the membrane at 10-60 ℃ for 1-48 hours, and cooling to obtain the nitrogen-doped graphene quantum dot hybrid membrane without the support body and used for selectively adsorbing copper ions from mixed metal solution;

or directly coating the coating solution after standing and defoaming on a support to obtain a membrane, then drying the support and the membrane together for 1-48 h at the temperature of 10-60 ℃, and cooling to obtain the nitrogen-doped graphene quantum dot hybrid membrane with the support and used for selectively adsorbing copper ions from the mixed metal solution;

or dissolving the coating solution after standing and defoaming by using a solvent, coating the obtained substance on a support until a membrane is obtained, drying the support and the membrane together at 10-60 ℃ for 1-48 h, and cooling to obtain the nitrogen-doped graphene quantum dot hybrid membrane with the support and used for selectively adsorbing copper ions from the mixed metal solution; or separating the membrane from the support after drying to obtain the nitrogen-doped graphene quantum dot hybrid membrane without the support and used for selectively adsorbing copper ions from the mixed metal solution;

in the step (c), the solvent is selected from N, N-dimethylformamide, tetrahydrofuran, dimethyl sulfoxide, N-methylpyrrolidone, ethanol, isobutanol or N-butanol.

2. The method of claim 1, wherein: the support body is made of polytetrafluoroethylene plate, glass plate and Al₂O₃Ceramics, silicon dioxide ceramics, titanium dioxide ceramics, zirconium dioxide ceramics, polyethylene films, polyester fabrics, glass fiber fabrics, nylon fabrics or non-woven fabrics.

3. The method of claim 1, wherein: the drying is selected from convection drying, vacuum drying, conduction drying, ultraviolet drying, infrared drying, microwave drying or mechanical dehydration drying.

4. The method of claim 1, wherein: the coating film is selected from a flowing coating film, a dipping coating film, a spraying coating film, a scraping coating film or a rotating coating film.

5. The application of the nitrogen-doped graphene quantum dot hybrid membrane prepared by the method of claim 1 in adsorptive separation of copper ions from waste water containing copper ions or selective adsorptive separation of copper ions from mixed metal solution containing copper ions.

6. Use according to claim 5, wherein the mixed metal solution contains Cu ions²⁺In addition to lead ions Pb²⁺Calcium ion Ca²⁺Cobalt ion Co²⁺Chromium ion Cr³⁺One or more of (a).