CN113634220B - Preparation method and application of nonmetal water-soluble heavy metal adsorbent based on reversible phase transition - Google Patents

Preparation method and application of nonmetal water-soluble heavy metal adsorbent based on reversible phase transition Download PDF

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CN113634220B
CN113634220B CN202110743620.4A CN202110743620A CN113634220B CN 113634220 B CN113634220 B CN 113634220B CN 202110743620 A CN202110743620 A CN 202110743620A CN 113634220 B CN113634220 B CN 113634220B
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heavy metal
adsorbent
water
graphite
carbon nitride
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CN113634220A (en
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兰华春
安晓强
刘会娟
曲久辉
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Tsinghua University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/0203—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising compounds of metals not provided for in B01J20/04
    • B01J20/0259—Compounds of N, P, As, Sb, Bi
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/28—Treatment of water, waste water, or sewage by sorption
    • C02F1/281—Treatment of water, waste water, or sewage by sorption using inorganic sorbents
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/10—Inorganic compounds
    • C02F2101/20—Heavy metals or heavy metal compounds

Abstract

The application provides a preparation method and application of a nonmetal water-soluble heavy metal adsorbent based on reversible phase transition, wherein the preparation method of the adsorbent comprises the following steps: (1) evenly mixing melamine and alkaline substances; (2) heating the mixture in the step (1) to 250-600 ℃ for 1-5 h, and cooling to room temperature; (3) and (3) dissolving the solid obtained in the step (2) in ultrapure water, dialyzing the solution in the ultrapure water through a dialysis bag, and drying the liquid in the dialysis bag to obtain the adsorbent. The technical scheme provided by the application has the advantages of cheap and easily-obtained raw materials, simple preparation process, no need of secondary activation and other steps. The adsorbent material has a reversible phase inversion function that is not possessed by other adsorbent materials. And greatly improves the mass transfer rate of the adsorption micro-interface and enhances the interface action between the adsorption micro-interface and molecules and ions adsorbed in water. And no metal ion is needed in the preparation process of the adsorption material, so that the adsorption material has the characteristic of environmental friendliness.

Description

Preparation method and application of nonmetal water-soluble heavy metal adsorbent based on reversible phase transition
Technical Field
The invention relates to a method for removing heavy metal ions in water and treating water pollution, in particular to a method for preparing a nonmetal dissolved heavy metal adsorbent based on reversible phase transition and application thereof in pollutant removal.
Background
With the rapid development of social economy, various waste water containing high-toxicity, harmful and difficultly-degradable substances is continuously discharged into natural water, thereby bringing serious harm to the safety of an ecosystem and the health of human beings. Adsorption technology based on physical separation is the most common method for removing pollutants such as heavy metals and organic matters in water. Currently, adsorbents based on porous solids such as activated carbon, zeolites, molecular sieves, resins, etc. are widely used in practical wastewater treatment processes. Nevertheless, insufficient adsorption capacity, poor selectivity and difficult regeneration remain major problems in the application of this technology. By developing a novel adsorption material, a new principle and a new method for removing harmful substances in water are searched, and the method is an important breakthrough direction for future development of the technology.
It is easy to find that the existing adsorption water purification process is implemented by accumulating the accumulation of pollutant molecules and ions on the surface of the solid adsorbent, and the liquid/solid multiphase interface process is undoubtedly influenced by the water-soluble processes of adsorbate diffusion, mass transfer and the like in water. Especially for low-concentration pollutants, how to realize strong interfacial interaction between a solid adsorbent and a soluble adsorbate still remains one of the difficult problems faced by adsorption technology. Compared with the prior art, the water-soluble system has the characteristics of high mass transfer rate, high reaction rate and the like, and has the unique advantage that the heterogeneous reaction process is difficult to compare favorably in important operation units such as catalysis, rectification, extraction and the like. The rapid mass transfer and interaction of molecules and ions in a water-soluble medium are used for realizing the high-efficiency capture of substances, and the method is undoubtedly an effective way for separating harmful substances. However, the separation of soluble substances in water based on conventional water-soluble intermolecular interaction often requires the coupling with processes such as precipitation and flocculation to separate the products, which not only causes the formation of secondary pollutants, but also makes it difficult to recycle the capture agent molecules. If the adsorption material which can meet the requirements of water-soluble adsorption and heterogeneous separation phase fusion can be developed and the cyclic regeneration can be realized, the method is expected to become a novel means for efficiently separating pollutants in water.
Disclosure of Invention
The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the present application.
The invention aims to provide a preparation method of a nonmetal water-soluble heavy metal adsorbent based on reversible phase transition, which is used for adsorbing and removing heavy metal ions in water.
A preparation method of a nonmetal water-soluble heavy metal adsorbent based on reversible phase transition comprises the following steps:
(1) evenly mixing melamine and alkaline substances;
(2) heating the mixture in (1) to 250-600 ℃ for 1-5 h, and cooling to room temperature;
(3) dissolving the solid obtained in the step (2) in ultrapure water, dialyzing the solution in the ultrapure water through a dialysis bag, and drying the liquid in the dialysis bag to obtain the adsorbent;
alternatively, the preparation method consists of the above steps.
In one embodiment provided herein, the alkaline substance in step (1) is selected from one or both of sodium hydroxide and potassium hydroxide.
In one embodiment provided herein, the molar ratio of the melamine to the basic species is from 0.3 to 3;
in one embodiment provided herein, the heating rate is 1 ℃/min to 10 ℃/min;
in one embodiment provided herein, the heating rate is 5 ℃/min to 10 ℃/min;
in one embodiment provided herein, the heating temperature is 330 ℃.
In one embodiment provided herein, the dialysis bag has a molecular weight cut-off of 3500 to 12000;
in one embodiment provided herein, the mass ratio of the ultrapure water to the melamine is (60-70): 1;
in one embodiment provided herein, the dialysis is for a period of 2 to 4 days.
In yet another aspect, the present application provides a graphite-phase carbon nitride prepared by the above-described preparation method.
In one embodiment provided herein, the graphite-phase carbon nitride is added to the heavy metal wastewater, such that the heavy metal is adsorbed by the graphite-phase carbon nitride;
in an embodiment provided by the present application, cations may be further added to recover the graphite-phase carbon nitride adsorbed with the heavy metal, so that the graphite-phase carbon nitride is precipitated;
in one embodiment provided herein, the cation is selected from one or more of calcium, sodium, potassium, and magnesium.
In one embodiment provided by the application, the concentration of heavy metal ions in the heavy metal wastewater is 1mg/L to 500mg/L, and the dosage of the graphite phase carbon nitride is 10mg/L to 500 mg/L;
in one embodiment provided herein, the pH of the heavy metal wastewater is 2 to 6;
in one embodiment provided herein, the final concentration of the cation in the heavy metal wastewater is 0.2mmol/L to 1 mol/L;
in one embodiment provided herein, the heavy metal ions are selected from any one or more of pb (ii), cu (ii), and cd (ii), ni (ii), zn (ii).
In one embodiment of the present invention, the graphite-phase carbon nitride adsorbed with the heavy metal precipitated after the addition of the cation is regenerated by the following method:
1) placing the graphite-phase carbon nitride after the heavy metal is adsorbed into an acid solution to obtain a mixed solution;
2) adding the cation solution into the mixed solution obtained in the step 1) to enable the final concentration of cations to be 0.2mmol/L to 1 mol/L; and then centrifuging to collect precipitate, adjusting the pH value of the precipitate to be neutral or alkaline, and finishing regeneration.
In one embodiment provided herein, the concentration of the acidic solution is 0.05mol/L to 0.5mol/L, and the amount ratio of the acidic solution to the graphite phase carbon nitride is 1g of the acidic solution in 10ml to 200ml of the graphite phase carbon nitride;
in one embodiment provided herein, the acidic solution is selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, and a mixed solution thereof;
in one embodiment provided herein, the centrifugation speed is 3000rpm to 10000rpm, and the centrifugation time is 2min to 20 min;
in one embodiment provided herein, the solution for adjusting the pH of the precipitate is one or more of sodium hydroxide and potassium hydroxide.
Compared with the prior art, the method has the following advantages and beneficial effects:
(1) reversible phase-shifting (graphitic carbon nitride) g-C made herein 3 N 4 The polymer adsorbent is a non-metal water-soluble heavy metal adsorbent, the raw materials are cheap and easy to obtain, the preparation process is simple, and the steps of secondary activation and the like are not needed, so that the polymer adsorbent has a great cost advantage.
(2) The application is by g-C 3 N 4 The soluble water-soluble adsorbent is obtained by adjusting the molecular morphology, so that the mass transfer rate of the adsorption micro-interface is greatly improved, and the interface action between the adsorption micro-interface and molecules and ions adsorbed in water is enhanced.
(3) The adsorbing material provided by the application does not need any metal ions in the preparation process, and has the characteristic of environmental friendliness.
(4) The non-metal water-soluble adsorbent can realize out-phase separation through ion strength adjustment after saturated adsorption, further obtains desorption regeneration and dissolution in water, and has a reversible phase conversion function which is not possessed by other adsorption materials.
(5) The water-soluble adsorbent prepared by the method has good selectivity on heavy metal ions and charged molecules in water, and the adsorption capacity is obviously superior to that of a conventional bulk phase carbon nitride material.
Additional features and advantages of the application will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the application. Other advantages of the present application may be realized and attained by the invention in its aspects as described in the specification.
Drawings
The accompanying drawings are included to provide an understanding of the present disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the examples serve to explain the principles of the disclosure and not to limit the disclosure.
FIG. 1 is a schematic representation of the preparation of water-soluble polymers according to the examples of the present applicationSchematic diagram of adsorbent water purification process (with Pb) 2+ For example);
FIG. 2 is a graph showing the evaluation of the performance of the non-metallic water-soluble adsorbent prepared in example 1 of the present application in removing heavy metal lead from water;
FIG. 3 is a comparison of the lead ion removal effect of different types of adsorbents in comparative examples; the adsorption performance of the adsorbent of example 1, the adsorbent of example 8, the commercial activated carbon and the conventional bulk-phase carbon nitride at an initial concentration of 1mg/L of the contaminant are compared with that of different heavy metal ions (pH 5.0 ± 0.1, m/V50 mg/L, T298K);
FIG. 4 is a graph showing the evaluation of the removal of lead ions from water after the adsorbent in application example 3 was regenerated for a plurality of times (hydrochloric acid and nitric acid regenerated adsorbents for Pb at different cycles) 2+ Adsorption performance comparison).
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, embodiments of the present application are described in detail below. It should be noted that the embodiments and features of the embodiments in the present application may be arbitrarily combined with each other without conflict.
In the examples of the present application, melamine was purchased from welengi technologies ltd; sodium hydroxide and potassium hydroxide chemical reagents were purchased from pharmaceutical group reagents;
the dialysis bag was purchased from sigma aldrich (shanghai) trade ltd;
example 1
The preparation method of the non-metal water-soluble dissolved adsorbent comprises the following steps:
(1) 6g (0.048mol) of melamine, 0.8g (0.02mol) of sodium hydroxide and 2.24g (0.04mol) of potassium hydroxide were weighed out and sufficiently ground in a mortar to obtain a mixture.
(2) Adding the mixture obtained in (1) into a crucible with a cover, putting into a muffle furnace, raising the temperature from room temperature to 330 ℃ at the speed of 5 ℃/min, keeping for 2h, cooling to room temperature, and fully grinding into powder.
(3) Dissolving the powder obtained in the step (2) in 400ml of ultrapure water, and then filling the solution into a 3500Da dialysis bag for dialysis for 4 days to obtain the non-metallic water-soluble adsorbent based on the reversible phase transition function.
Example 2
The difference between the present application and example 1 is only that the amount of raw materials used in this example is different from that in example 1, and the difference is as follows: 6g (0.048mol) of melamine and 0.8g (0.02mol) of sodium hydroxide were sufficiently ground in a mortar to obtain a mixture, and then the calcination and dialysis procedures of example 1 were carried out to obtain a non-metallic water-soluble adsorbent.
Example 3
The difference between the present application and example 1 is only that the amount of raw materials used in this example is different from that in example 1, and the difference is as follows: 6g (0.048mol) of melamine and 2.44g (0.04mol) of potassium hydroxide were sufficiently ground in a mortar to obtain a mixture, and then the calcination and dialysis procedures of example 1 were carried out to obtain a non-metallic water-soluble adsorbent.
Example 4
The difference between the present application and example 1 is only that the amount of the raw materials used in the present example is different from that in example 1, and the differences are as follows: 6g (0.048mol) of melamine, 0.4g of sodium hydroxide (0.01mol) and 1.22g of potassium hydroxide (0.02mol) were sufficiently pulverized in a mortar to obtain a mixture, and then the calcination and dialysis procedures of example 1 were carried out to obtain a non-metallic water-soluble adsorbent.
Example 5
The present application differs from embodiment 1 only in that the temperature increase rate of the present embodiment differs from embodiment 1 as follows: a mixture of 6g of melamine, 0.8g of sodium hydroxide and 2.24g of potassium hydroxide was placed in a crucible with a lid, heated from room temperature to 330 ℃ in a muffle furnace at a rate of 10 ℃/min and held for 2 hours, cooled to room temperature and ground to a powder thoroughly. Then dialyzed in a dialysis bag (same specification as example 1) to obtain the non-metal water-soluble adsorbent.
Example 6
The present application differs from embodiment 1 only in that the temperature after temperature rise in the present embodiment differs from embodiment 1 as follows: a mixture of 6g of melamine, 0.8g of sodium hydroxide and 2.24g of potassium hydroxide was placed in a crucible with a lid, heated from room temperature to 450 ℃ in a muffle furnace at a rate of 10 ℃/min and held for 2 hours, cooled to room temperature and ground to a powder thoroughly. Then dialyzed in a dialysis bag (same specification as example 1) to obtain the non-metal water-soluble adsorbent.
Example 7
The present application differs from embodiment 1 only in that the temperature after temperature rise in the present embodiment differs from embodiment 1 as follows: a mixture of 6g of melamine, 0.8g of sodium hydroxide and 2.24g of potassium hydroxide was placed in a crucible with a lid, heated from room temperature to 400 ℃ at a rate of 10 ℃/min in a muffle furnace and maintained for 2 hours, cooled to room temperature and then ground to a powder. Then dialyzed in a dialysis bag (same specification as example 1) to obtain the non-metallic water-soluble adsorbent.
Example 8
The present application differs from example 1 only in that the method of obtaining a specific molecular weight adsorbent of this example differs from example 1 as follows: the powder obtained by calcination is dissolved in 400ml of ultrapure water, and then is filled into a 6000Da dialysis bag for dialysis for 4 days, so that the nonmetal water-soluble adsorbent based on the reversible phase transition function is obtained.
Comparative example 1 preparation method of bulk phase non-metallic carbon nitride adsorbent
The preparation method of the conventional bulk-phase carbon nitride non-metallic adsorbent without reversible phase transformation function provided by the comparative example comprises the following steps:
(1) 10g of melamine are weighed out and ground thoroughly in a mortar.
(2) And (3) adding the raw material obtained in the step (1) into a crucible with a cover, putting the crucible into a muffle furnace, raising the temperature from room temperature to 550 ℃ at the speed of 5 ℃/min, keeping the temperature for 4 hours, cooling to room temperature, and fully grinding into powder to obtain the conventional non-metal carbon nitride adsorbent without the reversible phase conversion function.
Comparative example 2
Purchase of coconut shell amorphous activated carbon from Baike water treatment materials Co., Ltd, Baozhi City, parameter iodine value ≥ 700 mg/g, stacking specific gravity of 0.50-0.6 g/cubic centimeter and pH value of more than or equal to 7, which are used as comparison of common active carbon adsorption materials, as shown in FIG. 3.
Application example 1 heavy Metal Pb 2+ Adsorption removal of ions
Taking 5mg/L Pb 2+ 40mL of the solution was put in a 50mL Erlenmeyer flask, 50mg/L and 15mg/L of the adsorbent prepared in example 1 were added, and the mixture was adjusted to pH 5 with HCl and NaOH and shaken in a shaker at a constant temperature of 25 ℃ for 24 hours. Taking out the mixed solution, adding calcium ion-containing solution to make Ca 2+ The final concentration of the heavy metal ions is 2mmol/L, the heavy metal ions are centrifuged for 5 minutes at 8000rpm, and the supernatant is taken to detect the heavy metal ions Pb 2+ The residual concentration after adsorption is determined by the initial concentration C of Pb (II) in the solution 0 And Pb in the adsorbed solution 2+ Concentration C of e Calculating Pb 2+ Removal rate of (2).
Application example 2 heavy Metal ion Cu 2+ Adsorption removal of
Taking 5mg/L of Cu 2+ 40mL of the solution was put in a 50mL Erlenmeyer flask, 50mg/L and 15mg/L of the adsorbent prepared in example 2 were added, and the mixture was adjusted to pH 5 with HCl and NaOH and shaken in a shaker at a constant temperature of 25 ℃ for 24 hours. Taking out the mixed solution, adding calcium ion-containing solution to make Ca 2+ The final concentration of the heavy metal ions is 2mmol/L, the heavy metal ions are detected by taking supernate and centrifuging the supernate for 5 minutes at 8000rpm 2+ Residual concentration after adsorption, in terms of Cu in solution 2+ Initial concentration C of 0 And Cu in the post-adsorption solution 2+ Concentration C of e Calculating Cu 2+ Removal rate of (2) (fig. 2).
Test of Pb according to application example 2 2+ 、Cd 2+ 、Cu 2+ 、Ni 2+ 、Zn 2+ The amounts of the adsorbents added were 15mg/L and 50mg/L, respectively, and the subsequent operations were the same as in application example 2, and the removal rates of the heavy metals in the mixed solution (1 mg/L, respectively) are shown in FIG. 2.
Cd was tested separately according to application example 2 2+ 、Ni 2+ 、Zn 2+ (concentration: 5mg/L) was adsorbed and removed, the amounts of adsorbent added were 15mg/L and 50mg/L, respectively, the subsequent operations were the same as in application example 2, and the removal rates of each heavy metal in the mixed solution are shown in FIG. 2.
Pb Using Water-soluble adsorbent of example 3 2+ Desorption regeneration
Adsorbing Pb in application example 2 2+ Adsorbent precipitated by post-centrifugationCollecting 0.1g, adding into 10mL of 0.1mol/L nitric acid solution, shaking on a turnover shaking table for 2h, and adding calcium ion-containing solution to make Ca 2+ Was centrifuged at 8000rpm for 5 minutes at a final concentration of 2 mmol/L. Collecting the centrifuged precipitate, adding 5ml of 0.1mol/L sodium hydroxide solution, shaking on a turnover shaking table for 2h, adjusting the pH to 7 to complete regeneration, performing solid-liquid separation, and drying to obtain powder which can be continuously used for adsorption. Adsorbent pair Pb after regeneration 2+ The adsorption experiments were carried out again (the experimental parameters were all the same as in application example 1) without a significant decrease in the adsorption capacity (fig. 4).
Cu of Water-soluble adsorbent of application example 4 2+ Desorption regeneration
Will adsorb Cu in application example 3 2+ Collecting 0.1g of adsorbent precipitated by centrifugation, adding into 10mL of 0.1mol/L nitric acid solution, shaking for 2h on a turnover shaking table, and adding calcium ion-containing solution to make Ca 2+ Was centrifuged at 8000rpm for 5 minutes at a final concentration of 2 mmol/L. Collecting the centrifuged precipitate, adding 5mL of 0.1mol/L sodium hydroxide solution, shaking on a turnover shaking table for 2h, adjusting the pH to 7 to complete regeneration, performing solid-liquid separation, and drying to obtain powder which can be continuously used for adsorption. Adsorbent pair Cu after regeneration 2+ The adsorption experiment was performed again (the test parameters were all the same as in application example 2), and the adsorption capacity was not significantly reduced.
Application example 5 regenerated adsorbent for adsorption removal of heavy metal Cd 2+ Ion(s)
Taking 5mg/L Cd 2+ 40mL of the solution was put in a 50mL Erlenmeyer flask, 50mg/L of the regenerated adsorbent obtained in application example 3 was added, pH of the mixture was adjusted to 5 with HCl and NaOH, and the mixture was shaken in a constant temperature shaker at 25 ℃ for 24 hours. Taking out the mixed solution, adding solution containing calcium ions to make Ca 2+ The final concentration of the heavy metal ion is 2mmol/L, the heavy metal ion is centrifuged for 5 minutes at 8000rpm, and the supernatant is taken to detect the heavy metal ion Cd 2+ The residual concentration after adsorption is determined by the initial concentration C of Cd (II) in the solution 0 And Cd in the adsorbed solution 2+ Concentration C of e Calculating Cd 2+ The removal rate of (3).
Application example 6 five times of regenerated adsorbents to adsorb and remove heavy metal Pb 2+ Ion(s) in a substrate
Method for adsorbing Pb by combining application example 1 and application example 3 2+ The water-soluble adsorbent is used for 5 times of adsorption and regeneration, and 5mg/L of Pb is taken each time 2+ 40mL of the solution was put in a 50mL Erlenmeyer flask, 50mg/L of the adsorbent recovered was added, the pH of the mixture was adjusted to 5 with HCl and NaOH, and the mixture was shaken in a shaker at a constant temperature of 25 ℃ for 24 hours. Taking out the mixed solution, adding solution containing calcium ions to make Ca 2+ The final concentration of the heavy metal ion is 2mmol/L, the heavy metal ion is centrifuged for 5 minutes at 8000rpm, and the supernatant is taken to detect the heavy metal ion Cd 2+ The residual concentration after adsorption is determined according to the initial concentration C of Cd (II) in the solution 0 And Cd in the adsorbed solution 2+ Concentration C of e Calculating Cd 2+ The removal rate of (3).
Although the embodiments disclosed in the present application are described above, the descriptions are only for the convenience of understanding the present application, and are not intended to limit the present application. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the disclosure as defined by the appended claims.

Claims (18)

1. A preparation method of a reversible phase-transition water-soluble heavy metal adsorbent comprises the following steps:
(1) evenly mixing melamine and alkaline substances;
(2) heating the mixture in (1) to 250-600 ℃ for 1-5 h, and cooling to room temperature;
(3) dissolving the solid obtained in the step (2) in ultrapure water, dialyzing the solution in the ultrapure water through a dialysis bag, and drying the liquid in the dialysis bag to obtain the adsorbent;
the molar ratio of the melamine to the alkaline substance is 0.3 to 3;
the cut-off molecular weight of the dialysis bag is 3500 to 12000;
the mass ratio of the ultrapure water to the melamine is 60-70: 1;
in the step (1), the alkaline substance is selected from one or two of sodium hydroxide and potassium hydroxide.
2. The production method according to claim 1, wherein the heating is performed at a temperature increase rate of 1 ℃/min to 10 ℃/min.
3. The production method according to claim 1, wherein the heating is performed at a temperature increase rate of 5 ℃/min to 10 ℃/min.
4. The production method according to claim 1, wherein the heating temperature is 330 ℃.
5. The production method according to any one of claims 1 to 4, wherein the dialysis is performed for 2 to 4 days.
6. The water-soluble heavy metal adsorbent prepared by the preparation method according to any one of claims 1 to 5, wherein the water-soluble heavy metal adsorbent is graphite-phase carbon nitride.
7. The use of the water-soluble heavy metal adsorbent according to claim 6 in the treatment of heavy metal wastewater,
adding graphite-phase carbon nitride into the heavy metal wastewater, so that the heavy metal is adsorbed by the graphite-phase carbon nitride.
8. The use of claim 7, wherein the concentration of heavy metal ions in the heavy metal wastewater is 1mg/L to 500mg/L, and the amount of the graphite-phase carbon nitride is 10mg/L to 500 mg/L.
9. The use according to claim 7, wherein the pH value of the heavy metal wastewater is 2 to 6.
10. The use according to claim 7, wherein the heavy metal ions are selected from any one or more of Pb (II), Cu (II) and Cd (II), Ni (II), Zn (II).
11. The use according to claim 7, wherein a cation is added to the heavy metal wastewater to recover the graphite-phase carbon nitride having adsorbed the heavy metal, thereby precipitating the graphite-phase carbon nitride.
12. Use according to claim 11, wherein the cation is selected from one or more of calcium, sodium, potassium and magnesium.
13. Use according to claim 11, wherein the final concentration of the cation in the heavy metal wastewater is from 0.2 to 1 mol/L.
14. The use according to any one of claims 11 to 13, wherein the graphite-phase carbon nitride having the heavy metal adsorbed thereon, which is precipitated after the addition of the cation, is regenerated according to the following method:
1) placing the graphite-phase carbon nitride after the heavy metal is adsorbed into an acid solution to obtain a mixed solution;
2) adding the cation solution into the mixed solution obtained in the step 1) to enable the final concentration of cations to be 0.2mmol/L to 1 mol/L; and then centrifuging to collect precipitate, adjusting the pH value of the precipitate to be neutral or alkaline, and finishing regeneration.
15. The use according to claim 14, wherein the concentration of the acidic solution in step 1) is 0.05 to 0.5mol/L, and the ratio of the amount of the acidic solution to the amount of the graphite phase carbon nitride is 10 to 200ml of the acidic solution per 1g of the graphite phase carbon nitride.
16. The use according to claim 14, wherein the acidic solution is selected from one or more of a nitric acid solution, a sulfuric acid solution and a hydrochloric acid solution.
17. The use according to claim 14, wherein the centrifugation is performed at 3000rpm to 10000rpm for 2min to 20 min.
18. The use according to claim 14, wherein the solution for adjusting the precipitation pH is one or more of sodium hydroxide and potassium hydroxide.
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