WO2020006814A1 - Self assembling heavy metal adsorbent and preparation method and use thereof - Google Patents

Abstract

Disclosed are a self assembling heavy metal adsorbent, and a preparation method and a use thereof. The adsorbent is prepared by a concentrated water-in-oil emulsion process, whereby a polyamine amphiphile having a plurality of active amino hydrogens, used as an emulsion stabilizer, self assemble at an oil-water interface to obtain a concentrated water-in-oil emulsion, with the active amino hydrogens being expressed at the oil-water interface and facing a water phase; then the concentrated water-in-oil emulsion solidifies to form a matrix, and the active amino hydrogens are substituted by acetate radicals, forming aminopolycarboxylate groups which are expressed on a pore surface of the matrix. The adsorbent is useful for treating wastewater or soil containing heavy metals. In comparison to the prior art, the present invention involves expressing the active amino hydrogens at an interface of the concentrated water-in-oil emulsion by means of self assembling of the macromolecular polyamine amphiphile, and during or after formation of a porous matrix, converting an amino group into an aminopolycarboxylate structure have a high metal adsorption efficiency. The synthesis process is simpler, the surface coverage rate of functional groups is higher, the adsorption rate is faster, and the adsorbent is easy to regenerate.

Description

Self-assembling heavy metal adsorbent, preparation method and application thereof Technical field

The invention belongs to the technical field of heavy metal treatment, and relates to a self-assembled heavy metal adsorbent, and a preparation method and application thereof.

Background technique

Heavy metals have attracted increasing attention for their non-degradation, easy bioaccumulation, and long-lasting toxicity. Due to the heavy use of modern industrial activities such as metallurgy, mining, batteries, paper, fertilizers, pesticides and modern electronics, heavy metals have entered the ecosystem from the lithosphere, and their pollution effects are increasingly becoming the focus of global attention. Many heavy metals are widely used, but at the same time they are toxic. Heavy metals exist in various forms such as elementary or compound states. Common forms of the compound state include simple cations, complex ionic groups, and organometallic compounds. High-valent heavy metal ions are mostly hard acids, many of which are oxygen anion groups; low-valent states are mostly free ions, and zero-valent ones are mostly soft acids, which are easy to combine with organic groups. There are different morphologies, different metabolic pathways in the ecosystem, and significant differences in toxicity. Heavy metals can cause cancer, anemia, insomnia, headaches, mental retardation, organ dysfunction, and failure. Heavy metals in wastewater can be enriched by aquatic organisms and enter the human body through the food chain (such as fish). The well-known Japanese Minamata Disease is caused by the release of catalytic mercury for industrial production, which is converted into methylmercury during the ecological transfer process and passed to the human body through the food chain. It has a variety of side effects, including toxic nerves. Heavy metals in the soil may also be enriched by certain food crops and passed on to humans. Due to the gradual accumulation of many heavy metals in the food chain transmission process, endemic metal-rich areas usually do not immediately show symptoms of crowd poisoning, and more likely to be a characteristic of a sudden large-scale outbreak after a certain period of time disease.

Common methods for treating heavy metals in wastewater include chemical deposition, ion exchange, chemical oxidation / reduction, reverse osmosis, electrochemical treatment, electrodialysis, ultrafiltration, etc. At present, each technology still has different limitations, such as low processing efficiency, harsh operating conditions, secondary pollution, and difficult post-processing, etc., making the treatment of heavy metals a high-cost activity. Alkali deposition is effective for a variety of metal ions, but has the following problems: (1) a large amount of low-density slurry is produced; (2) because many hydroxides exhibit zwitterionic characteristics, their water solubility is more sensitive to pH, and each The optimal deposition pH of different metal species hydroxides is not the same, and the result is usually only one metal species at a time. Because low-cost heavy metals are mostly soft acids or intermediate acids, the soft alkali sulfur anion deposition effect is good. Metal ion sulfides have a much lower water solubility than their hydroxide counterparts and are less sensitive to pH, which is very welcome. However, hydrogen sulfide itself is toxic, volatile, and flammable; at the same time, some metal sulfides can form colloidal particles, making separation difficult. Chemical deposition often changes the material structure and physical form, and often needs to be combined with physical processing to achieve the desired effect. At the same time, it is easy to cause secondary pollution. Low-priced sulfur as a soft base has other forms such as dithiocarbonate, dithiocarbamate, and xanthate. These groups have strong chelating ability with metals, which reflects a better metal processing ability. However, metal residues are still relatively high and generally cannot meet the emission standards established by most countries (Matlock, MM, Henke, KR, Atwood, DA, .Effectiveness of commercial agents) J]. J. Hazard. Mater., 2002, 92, 129-142). However, it is worth noting that these treatment agents show high leakage rates; most of these treatment agents are unstable under acidic conditions, releasing toxicants and making regeneration difficult. Technologies such as ultrafiltration have also gained practical application. Ultrafiltration is a technique that achieves separation through the pore size selectivity at low pressure differences. Ultrafiltration is based on size selection, but the metal ions themselves are relatively small in size and place high demands on the size and uniformity of the membrane pores. In short, the removal of metals in water involves multidisciplinary principles and technologies, and large-scale production and low-cost operation are currently urgent needs.

Sorbents are a representative class of water treatment agents. Adsorption methods generally do not cause secondary pollution. The adsorbent is usually composed of a matrix and an adsorption functional group on its surface. Common substrates such as porous silica, chitosan, paramagnetic iron oxide, high surface polymers, activated carbon, kaolin, carbon nanotubes, (oxidized) graphene, etc. The matrix needs to provide high specific surface and mechanical strength. The nano-matrix with high specific surface is difficult to separate due to its small size, but the large-sized high-specific surface porous materials often have poor mechanical strength, which is an important challenge for matrix production. In general, achieving surface expression of functional groups on the adsorbent matrix often involves multi-step heterogeneous reactions, which can easily lead to low yields, high costs, and low surface functional group coverage. In addition, many adsorbents require strong acid or alkali treatment during regeneration, and some substrates will be destroyed or functional groups will fall off, which will gradually reduce the performance of the regenerated adsorbent. The mesoporous silica synthesized by the template (surfactant) method is very attractive. Its characteristics are uniform pore size, surface area up to 600-1000m ² / g, pore size 5-30nm, and the size can be controlled. The method has low cost and mature technology. However, after surface modification, the surface area of the substrate will decrease by half, mainly due to the blockage of nanopores; the surface coverage of functional groups is typically 30%; because the channels are nanopores, adsorption is controlled by capillary diffusion, and adsorption equilibrium typically takes 2-48 hour. The matrix prepared by the thick emulsion method belongs to a block-like ultra-large pore material and is easy to separate. The material is inexpensive and has a medium surface area. For a long time, the pore surface of this type of material is usually expressed by small molecule surfactants. Such small molecules are easy to fall off, have no real value in adsorption, and only provide a porous skeleton.

The adsorption functional groups of the existing adsorbents are often introduced chemically after the matrix is formed. This is because most active adsorption functional groups are difficult to undergo the baptism of the matrix synthesis process and remain unchanged. Amino, carboxyl, hydroxyl, thiol, trithiocarbonate, xanthate, dithiocarbamate, etc. are some typical adsorption functional groups. However, many of these functional groups have shortcomings. For example, the mercapto group is easily oxidized by air and it is not easy to store; esters, especially thioesters, are easily decomposed by acid and alkali, and difficult to regenerate. Although the fatty amino group is relatively stable, it will still be gradually oxidized by the air or deteriorate due to rapid absorption of acid gases such as carbon dioxide in the air. The lone pair of electrons of the amino group has medium-strength coordination to many metals, but it should be used under alkaline conditions. Dense fatty polyamines have been widely used as the core group of metal adsorbents (Alain Walcarius, Louis Mercier, Mesoporous organosilica adsorbents: nanoengineered materials for removal of organic and inorganic pollutants [J] .J.Mater.Chem., 2010,20 4478-4511). However, the effect of this dense amino group on the removal of heavy metals is generally not satisfactory, and the metal residue is still high. Amino polycarboxylic acids are very important metal chelating agents. Typical are iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), and diethylenetriaminepentaacetic acid (DTPA). )Wait. The bond strength with metals generally increases with the increase of acetic acid groups, that is: IDA <NTA <EDTA <DPTA (typical pK value increases from 10 to 20 with the increase of carboxyl groups), of which EDTA and DTPA are more widely used. The strong metal affinity of this type of metal chelator is closely related to its special topological conformation in addition to its multiple coordination sites. The amino group of the amino polycarboxylic acid is usually in a protonated state, and its oxidation resistance and acid-base stability are more prominent. Amino polycarboxylic acids have been widely used as metal masking agents. Although these small molecules can efficiently bind metals themselves, they are difficult to separate from water. To be applied to the adsorption of metal wastewater, these groups must be fixed on the surface of the substrate by chemical bonds, and related research has been reviewed (E.Repo, JK

A. Bhatnagar, A. Mudhoo, M. Sillanpaa. Aminopolycarboxylic acid functionalized adsorbents for heavy metals removal from water [J] .water research, 2013,47,4812-4832). However, there are still many limitations of amino polycarboxylic acid-based metal sorbents: one is that they usually adopt solid-phase synthesis. As mentioned earlier, in view of the reactivity of primary and secondary amines, the general approach is to introduce the amino group after the formation of a solid phase matrix, and then to derive it into an amino polycarboxylic acid. This solid-phase multi-step synthesis strategy resulted in insufficient surface density and surface coverage of the functional groups adsorbed on the surface of the matrix, and low efficiency. The second is that amino polycarboxylic acids are connected to the substrate through chemical bonds that are not resistant to acids and bases, and are prone to hydrolysis and fall off. Some amino polycarboxylic acid-based adsorbents have been commercialized, such as

IRC-748, Chelex-100 and Lewatit are modified solid-liquid-phase reaction method on the cross-linked polymer matrix, which is resistant to hydrolysis of iminodiacetic acid, and can treat calcium and magnesium ions in the chlor-alkali industry.

Summary of the invention

The purpose of the present invention is to provide an efficient self-assembling heavy metal adsorbent for toxic cationic metals in water or soil in order to overcome the defects existing in the prior art, and a preparation method and application thereof.

The object of the present invention can be achieved by the following technical solutions:

A method for preparing a self-assembling heavy metal adsorbent. The method is: using a water-in-oil thick emulsion method, using a polyamine amphiphile with multiple active amino hydrogens as an emulsion stabilizer, and the emulsion stabilizer After assembly, a water-in-oil concentrated emulsion is obtained, and the active amino hydrogen is expressed at the oil-water interface and faces the water phase; then the water-in-oil concentrated emulsion is solidified to form a matrix, and the active amino hydrogen is replaced by acetate to form amino polycarboxylic acid groups. And expressed on the pore surface of the matrix. The polyamine amphiphile contains a primary amine and / or a secondary amine group, and an oil-soluble polyamine amphiphile obtained by any method may be selected. The active amino hydrogen is derived into a dense polyaminopolycarboxylic acid structure during or after curing of the water-in-oil thick emulsion, and is expressed on the pore surface of the through-hole adsorbent.

As an emulsion stabilizer, a part of the amino hydrogens in the fatty polyamine is modified by a lipophilic chain to form a polyamine amphiphile. Polyamine amphiphiles are oil-soluble macromolecules. The amphiphile can stabilize the water-in-oil type emulsion by assembling at the oil-water interface, and express active amino hydrogen at the oil-water interface, and the active amino hydrogen faces the water phase. Polyamine amphiphiles are prepared first, and then polyamine amphiphiles are used to stabilize the emulsion. Stabilizing concentrated emulsions has two purposes. One is to arrange the active amino hydrogen residues in the polyamine amphiphile to face the water phase so that it can be easily replaced by acetate. The other is that the concentrated emulsion can be easily derived into a porous solid matrix. The fraction of the amino hydrogen in the fatty polyamine modified by the lipophilic chain should be between 10 and 60% by mole to ensure that the obtained polyamine amphiphile has good solubility in the oil phase, and at the same time, the amino There is enough residual hydrogen for later conversion to amino polycarboxylic acid. In the polyamine amphiphile, the mass of the polyamine component accounts for 5-49% of the total mass of the polyamine amphiphile. When the lipophilic chain is long, the dosage of the epoxy functional group relative to the amino hydrogen can be as low as 10% molar equivalent; when the lipophilic chain is short, it should be above 15% but not more than 60% (molar fraction) .

As a preferred technical solution, the lipophilic chain of the polyamine amphiphile may be one or any of the following chains coexisting: a linear / branched fatty chain having more than 9 carbon atoms, an aromatic group-containing fat Chain, olefin-containing aliphatic chain, any polymer incompatible with water, such as styrene, (meth) acrylate, (meth) acrylamide, or any of them Proportion of copolymers, polypropylene oxide, polytetrahydrofuran, polysiloxane, etc. The fatty polyamine may be a compound containing several fatty amino groups obtained in any manner, such as linear / branched polyethyleneimine, dendrimer polypropyleneimine, polyallylamine, and the like. The prepared polyamine amphiphiles should be stored under an inert gas such as nitrogen.

Further, the method includes the following steps:

1) Preparation of water-in-oil thick emulsion: adding an emulsion stabilizer to the oil phase, and then adding the water phase with stirring to obtain a water-in-oil thick emulsion;

2) react at room temperature or under heating conditions to solidify the oil phase to form a matrix, and at the same time, the active amino hydrogen is replaced by acetate in the water phase to form an amino polycarboxylic acid group to obtain a solid material;

3) The solid material is washed to obtain the adsorbent. The solid material was washed successively with water and ethanol, and then the ethanol was evaporated to obtain an adsorbent.

During the above preparation process, oil and water react at the same time. The amino hydrogen at the water droplet interface is replaced by acetate to form an amino polycarboxylic acid structure. The continuous oil phase solidifies to form an open porous matrix with pore diameters around the micron level. By controlling the amount of amphiphile, a block adsorbent or a debris adsorbent can be obtained; the debris adsorbent can adsorb metal ions faster.

Alternatively, the method includes the following steps:

1) Preparation of water-in-oil thick emulsion: adding an emulsion stabilizer to the oil phase, and then adding the water phase with stirring to obtain a water-in-oil thick emulsion;

2) react at room temperature or under heating to solidify the oil phase to form a matrix to obtain a solid material;

3) The solid material is immersed in an aqueous solution containing acetate to perform the reaction, so that the active amino hydrogen is replaced by the acetate in the aqueous solution to form an amino polycarboxylic acid group, and the adsorbent is obtained.

In the above preparation process, the modification of the interfacial amino hydrogen can also be carried out after the oil phase is solidified. During the preparation, no halogenated acetic acid is added to the water phase but the pH value is appropriately adjusted to maintain the stability of the thick emulsion. After the formation, the solution is immersed in an aqueous solution containing halogenated acetic acid and a weak base (including a buffer solution), the pH is not lower than 7.0, and the reaction temperature is selected from room temperature to 90 ° C depending on the halogen.

Further, in step 1), after adding the emulsion stabilizer to the oil phase, a mixed oil phase is obtained, and the mass percentage content of the emulsion stabilizer in the mixed oil phase is 5-49%.

Further, the acetate is provided by halogenated acetic acid, and the molar amount of the halogenated acetic acid is 1-4 equivalents based on the molar amount of amino hydrogen in the polyamine amphiphile.

Further, the volume of the water phase accounts for more than 74% of the total volume of the water-in-oil thick emulsion, forming a thick paste.

In the water-in-oil type emulsion, the continuous phase (oil phase) includes the following components: components that can be cured by any means (monomer, crosslinker, optional initiator), optional solvents, optional Additives; the oil phase can also consist of organic solvents and amphiphiles only. The aqueous phase consists of water, (mono) haloacetic acid XCH ₂ COOH (X = Cl, Br or I) and a weak base. The feeding amount of the weak base should be such that the pH value of the aqueous phase is not lower than 6.5. The weak base can be a buffer solution (such as phosphate), carbonate or triethylamine with a pH of 7-7.5. When preparing a water-in-oil thick emulsion, the aqueous phase is dropped into the strongly stirred oil phase, which stimulates the polymerizable components of the oil phase to solidify. In general, when the mass content of hydrophilic polyamines in the polyamine amphiphile is high, a suitable increase in pH is beneficial to the stability of the thick emulsion. This is because raising the pH will appropriately deprotonate the amino group and reduce hydrophilicity. As the reaction proceeds, the pH of the system decreases.

The oil phase can be cured by radical polymerization or polycondensation.

The oil phase can be polymerized and solidified by radically excited olefinic monomers. When the free radical excitation is used to solidify the oil phase, the oil phase is composed of water-insoluble olefinic monomers (such as styrene and its derivatives, O-vinylalkanoates, N-vinylalkanoamides, etc.), and water-insoluble Crosslinking agents (divinylbenzene, 1,4-diallyloxybenzene, 4-allyloxystyrene, etc.), oil-soluble free radical initiators, optional solvents / porosity agents (accounting for oil phase mass 0-30%, which can be toluene, xylene, cyclohexane, halogenated hydrocarbons or mixtures thereof), optional organic / inorganic additives and amphiphiles, and polymerize and solidify under thermal excitation. The molar ratio of the monomer to the crosslinking agent is an arbitrary ratio.

The oil phase can also be cured by polycondensation of heterofunctional water-insoluble monomers. Heterofunctional water-insoluble monomers are difunctional monomers and polyfunctional monomers mixed at any ratio; the functional group combination of the two monomers that are polycondensed with each other can be mercapto / ene, mercapto / alkyne, epoxy / aliphatic hydrogen ( The equivalent number of epoxy groups is not lower than amino hydrogen).

The oily phase may also consist of a solvent and optional organic / inorganic additives. Solvent assisted formation of concentrated emulsions is conducive to the enrichment of amino hydrogen at the oil-water interface and acceptance of modification. After the polyamine amphiphile amino hydrogen is replaced by carboxyethyl, the solvent is removed to obtain the corresponding debris-like adsorbent.

The sorbent can be a block or chip. When the dosage of the polyamine amphiphile in the water-in-oil thick emulsion is low (typically, the fraction of the equivalent polyamine to the total mass of the oil phase is less than 3.5%), porous blocks are generally obtained; and when equivalent When the fraction of the polyamine in the total mass of the oil phase is greater than 3.8%, and when the pH of the thick emulsion system is 7-14, the porous emulsion tends to form after the thick emulsion polymerization.

A self-assembling heavy metal adsorbent is prepared by using the method.

Further, in the adsorbent, the molecular weight of the polyamine amphiphilic derivative is ≧ 1000. In order to prevent polyamine amphiphiles and polyamine amphiphilic derivatives formed by the substitution of active amino hydrogen with acetate, the final molecular weight should be above 1,000, especially above 5000.

An application of a self-assembling heavy metal adsorbent, which is used for the treatment of wastewater or soil containing heavy metals. The time for the adsorbent to reach adsorption equilibrium is generally within 80 minutes, and the saturated adsorption amount is 0.06-1.35 mmol / g adsorbent. The adsorbent has an adsorption effect on many cationic metals, among which common metal ions such as Cu ²⁺ , Cr ³⁺ , Ni ²⁺ , Pb ²⁺ , M _n ²⁺ , Zn ²⁺ , and Co ²⁺ can be directly reached Emission standards, some directly meet drinking water standards. The adsorbent can be regenerated by treatment with an inorganic acid (pH is not higher than 1), and most of the metal is released. Regeneration has not seen performance degradation.

When the adsorbent is used in the treatment of wastewater containing toxic metal ions, the adsorbent is put into water for adsorption. Generally, adsorption is performed at pH = 5.6-7.0 (the pH should be just enough to avoid the formation of metal hydroxides), or the adsorbent debris is packed in the column as an ion exchange resin. Laboratory tests under static conditions found that the adsorbent usually completes the adsorption equilibrium within 80 minutes, and the debris-like adsorbent generally reaches the adsorption equilibrium within 50 minutes. Scanning electron microscopy showed that the minimum debris size was 2 microns, and the adsorbent was collected by filtration after adsorption equilibrium.

The adsorbent is immersed in an aqueous solution of an inorganic acid (such as hydrochloric acid, nitric acid, sulfuric acid, or a mixed acid), and the pH is adjusted to about 1. Generally, the adsorbent can be filtered within 1 hour to obtain a regenerated adsorbent. The release rate of most kinds of heavy metals is above 90%. This process can be repeated multiple times.

When the adsorbent is used for the treatment of soil containing heavy metals, the debris of the adsorbent is directly scattered on the soil. Under the action of rainwater and groundwater, metal ions migrate into the adsorbent. The adsorbent has a slow-release effect on the metal without the need for separation.

After the adsorbent adsorbs the metal, it can be regenerated with an inorganic acid. The adsorbent was leached with inorganic acid (pH <1), and left to stand under laboratory conditions, and the release was completed within 1 hour. The release rate of most metals was 90-100%. The adsorbent was filtered and reused, and the above process was repeated 10 times without any decrease in the adsorption amount. The sorbent can also be regenerated by immersion in EDTA-containing water under neutral conditions, and the operation is similar.

The invention uses a self-assembly method to arrange a large amount of active amino hydrogen at the oil-water interface. The active amino hydrogen is in the water phase and is unlikely to be interfered by the solidification of the oil phase. At the same time, the water phase reaction is unlikely to interfere with the oil phase system. The two-phase system The oil phase and the water phase can be reacted with different properties at the same time, which may modify the functional groups on the surface of the pores while the matrix is being formed, and convert the amino group into a stable amino polycarboxylic acid. This strategy makes the process easier, with higher functional group density and surface coverage.

The present invention provides a porous matrix by a water-in-oil type thick emulsion method. Different from the general thick emulsion method, the present invention uses a linear or dendritic amphiphile macromolecule instead of a conventional small molecule surfactant as an emulsion stabilizer. The prominent feature of macromolecule amphiphiles is their high migration energy, which makes it difficult to fall off the matrix. The amphiphiles of the present invention carry multiple active amino hydrogens, which are converted into amino polycarboxylic acids during matrix formation without protection. The route adopted by the invention is characterized in that the oil and water phases of the thick emulsion can react with different properties at the same time: the oil phase is solidified to form a porous matrix, and the amino hydrogen of the water phase is modified into an amino polycarboxylic acid group having a high affinity for heavy metals. It is also possible to perform amino modification after the matrix is formed. The first step of the present invention is to prepare an oil-soluble polyamine amphiphile so that it can self-assemble at the oil-water interface of a thick emulsion to stabilize the thick emulsion. The amphiphilic synthesis using amino-hydrogen and epoxy-like click reactions is very effective. In the second step, the solidification of the oil phase is stimulated after the formation of the concentrated emulsion, and the amino hydrogen at the water phase interface is simultaneously or subsequently modified into an amino polycarboxylic acid group having a strong affinity for metal ions. For convenience, the main synthesis strategy adopted by the present invention can be supplemented by an example (Figure 1).

In Figure 1, the gray particles represent water droplets, and the interface is expressed by the amphiphile assembly. Polyamine amphiphiles can be assembled at the oil-water interface to obtain a water-in-oil thick emulsion. At the same time as the oil phase of the thick emulsion polymerizes, the amino group at the water phase interface is modified to an amino polycarboxylic acid. After removing the water droplets, the pore surface will be completely The polyaminopolycarboxylic acid is expressed, and the multiple lipophilic chains on the polyamine play a physical riveting action so that they do not fall off the substrate. In Figure 1, water droplets are densely arranged in the oil continuous phase as dispersed particles, serve as a soft template, and are eventually replaced by air into pores. At the same time, the water droplets also act as microreactors, under the action of haloacetic acid and weak base, the amino hydrogen facing the water droplets is replaced by carboxymethyl. The oil continuous phase consists of a monomer, a cross-linking agent, and an initiator, and is converted into a solid matrix upon excitation. Polyamine-containing amphiphiles were initially expressed at the oil-water interface to stabilize thick emulsions, and then converted to polyaminopolycarboxylic acids, which could exert metal adsorption. The multiple lipophilic chains of the amphiphiles play a physical riveting effect, so that they are not adsorbed on the substrate and will not fall off. Due to the shrinkage caused by curing or the pressure difference between the inside and outside of the water droplet, the water droplets break and communicate with the adjacent water droplets, so that the matrix forms a through-hole material. Typical water droplet sizes range from a few microns to tens of microns.

Generally, thick emulsion polymerization often forms porous agglomerates. Such blocks are usually pulverized to allow faster adsorption of contaminants. However, crushing easily generates dust, which is also an energy-consuming process. In the present invention, by selecting appropriate synthesis conditions, a crumb-shaped adsorbent having a size ranging from micrometers to centimeters can be directly obtained, and the adsorption rate of this adsorbent is faster than that of agglomerates. There are several conditions that need to be met for the formation of crumbs: (1) the equivalent polyamine in the total mass of the oil phase is greater than 3.5% in the amphiphile; (2) the pH of the concentrated emulsion is moderate, generally between 7-14. The adsorption rate of heavy metal by the debris is significantly accelerated relative to the bulk adsorbent. Although there is no conclusive evidence for the mechanism, the possible reason for the formation of debris is that as the amino group in the stabilizer is gradually converted to an amino polycarboxylic acid, the interface stabilization effect is reduced, and the interface microphase separation is enhanced; oil phase polymerization can also induce oil The phases undergo some degree of phase separation. On the other hand, amphiphiles are more likely to exist as single molecules at the appropriate pH, which helps to increase the interface area, which is equivalent to thinning the oil phase matrix between any two water droplets. The thinning of the pore wall and the occurrence of severe micro-phase separation lead to multiple local fractures of the matrix and the formation of debris. Debris formation does not require the presence of a solvent / porosity agent; it is difficult to change the pH alone to promote the formation of debris; if no haloacetic acid is present in the aqueous phase, it is also difficult to form the debris. The crumbs were washed with water and alcohol, and stored in packages.

Compared with the prior art, the present invention has the following characteristics:

1) The metal adsorbent production process is simple, only two steps are required, and the functional density of the adsorbent pore surface is high, and the coverage is nearly 100%;

2) The invention can directly prepare porous adsorbent debris without crushing, and the adsorption balance for metal ions can generally be completed within 80 minutes; it can also prepare bulk and elastic porous materials with easy separation;

3) The adsorbent of the present invention contains a structure similar to EDTA and IDA, and the metal residue after adsorption is low; adsorption of Cu ²⁺ , Cr ³⁺ , Ni ²⁺ , Pb ²⁺ , Mn ²⁺ , Zn ²⁺ , and Co ²⁺ Directly reach discharge standards, and some directly reach drinking water standards;

4) The adsorbent of the present invention is resistant to oxidation, acid and alkali, simple to store, and does not generate secondary pollution during use;

5) The adsorbent is easy to regenerate. It is soaked with inorganic acid with a pH below 1. For most adsorbents, more than 92% of the metal is released within 1 hour. The adsorption capacity and release amount do not change after repeated times. Repeated use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a preparation process of a through-hole adsorbent expressed by an amino polycarboxylic acid on the surface; FIG.

FIG. 2 is a scanning electron microscope image of the porous block adsorbent PolyHIPE-2 (a) and the porous debris adsorbent PolyHIPE-5 (b) prepared in Example 2 and Example 5, respectively, during the preparation of general porous blocks The amount of stabilizer is low, and to obtain porous debris, the amount of stabilizer should be high.

detailed description

The present invention is described in detail below with reference to the drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

Example 1:

(1) Synthesis of dendritic amphiphiles. Weigh hyperbranched polyethyleneimine, abbreviated as PEI (M _n = 10000, a product of Sigma, vacuum dried at 60 ° C to remove carbon dioxide that may be absorbed in advance) (2.88 g, 0.067 mol equivalent of NH) and dissolved in chloroform (30 mL ), Add cetyl glycidyl ether, abbreviated C16 (7.04g, 0.0235mol), stir at room temperature for 3 days, remove chloroform by rotary evaporation, or dry with ethanol precipitation to obtain a white solid (9.92g, 100%), named PEI @ C16 _0.35 (0.35 means that 35% of the amino hydrogen is alkylated, the same applies hereinafter). The amphiphile is apparently soluble in non-polar or weakly polar solvents such as chloroform, toluene, methylene chloride, carbon tetrachloride, cyclohexane, n-hexane, and ether, and is insoluble in ethanol, N, N-dimethyl Non-polar solvents such as carboxamide, dimethylformite, water, etc. The binding energy and molar fraction of carbon, nitrogen and oxygen measured by X-ray photoelectron spectroscopy (XPS) were C _1s (284.93eV, 83.18%), N _1s (398.76eV, 9.66%), O _1s (531.94eV, 6.69 %). The alkylation rate of PEI was calculated from the molar fraction of N atoms to 35%, which was consistent with the charge.

(2) Synthesis of powdery adsorbent. A solution of chloroacetic acid (8.36g) and potassium carbonate (8.1g) in water (300mL) was dropped into a vigorously stirred solution of PEI @ C16 _0.35 (9g) in cyclohexane (70mL), which was completed in about 1 hour. Continue stirring for 15 minutes. The formed thick emulsion was heated at 70-80 ° C for 36 hours with standing or stirring. The concentrated emulsion was poured into a large amount of ethanol and the precipitate was collected. It was washed several times with water and methanol and dried to obtain a powdery solid. This solid is insoluble in any conventional organic-inorganic solvents. The binding energy and molar fraction of carbon, nitrogen, and oxygen measured by XPS were C _1s (285.08, 288.70 eV, 68.1%), N _1s (398.63, 398.89, 401.26 eV, 10.32%), O _1s (531.68, 530.38 eV, 16.49 %). Based on the molar fractions of N and O atoms, the carboxymethylation rate of PEI was 58.5%. The adsorbent was named PolyHIPE-1.

(3) Metal ion adsorption. The saturation adsorption amounts of PolyHIPE-1 on Co ²⁺ , Pb ²⁺ , Cd ²⁺ , and Ni ²⁺ were 102 mg / g, 134.8 mg / g, 159.5 mg / g, and 79.4 mg / g, respectively. Adsorption equilibrium was completed in 80 minutes. Adsorption kinetics is usually manifested as secondary.

Several kinds of metal ion stock solutions were prepared. The initial concentrations are shown in Table 1. Take 5.5 ml of the stock solution and add 20 mg of adsorbent PolyHIPE-1. After 1 hour, filter through a hydrophilic modified polytetrafluoroethylene membrane (0.45 micron pore), and determine the metal in the filtrate by inductively induced plasma spectroscopy (ICP-ms). Residual results are shown in Table 1. The metal residue was low.

Table 1 Adsorption of several metal ions by PolyHIPE-1 adsorbent (unit: ppm), pH = 6.0-7.0

Zh	Co 2+	Cr 3+	Mn 2+	Ni 2+	Cd 2+	Cu 2+	Zn 2+	Pb 2+
Before adsorption	15.3	10.2	13.9	11.2	30.5	49.6	7.3	31.0
After adsorption	0.3	0.8	0.01	0.03	1.05	0.7	0.8	0.04

Example 2:

(1) The dendritic amphiphile is the same as in Example 1, and is PEI @ C16 _0.35 .

(2) Synthesis of block adsorbent

Styrene (1.8 g), divinylbenzene (0.36 g), azobisisobutylcyanide (12 mg), PEI @ C16 _0.35 (0.24 g, ~ 1.05 mmol NH) were mixed to form an oil phase. Water (10 mL), chloroacetic acid (0.17 g, 1.8 mmol), and potassium carbonate (0.5 g, 3.6 mmol) were mixed to form an aqueous phase. The aqueous phase was dropped into the vigorously stirred oil phase, and the dripping was completed within 20 minutes. Stirring was continued for 15 minutes to form a paste-like viscous emulsion. The paste was transferred into a polyethylene plastic cup and left to heat at 70-80 ° C for 24 hours to obtain a solid block. It was sequentially washed with water and ethanol, dried, and named PolyHIPE-2. The partial scanning electron microscope image is shown as a in FIG. 2.

Mercury intrusion method (usually can only measure large pores) has a specific surface area of 46m ² / g, and the pore size is mainly distributed in 0.5-12 microns. The specific surface measured by the nitrogen method (usually only measuring pores below 50 nm) is 1.5 m ² / g. The actual surface area is likely to be close to or slightly larger than the sum of the two.

(3) Adsorption of metals

An aqueous solution of Pb (NO ₃ ) ₂ with a concentration of 0.49 mmol / L was prepared and adsorbed with PolyHIPE-2 at a pH of 3.0-6.8 (Pb ²⁺ will not precipitate). As a result, it was found that the higher the pH, the greater the amount of adsorption. The maximum adsorption capacity of Pb ²⁺ was 36 mg / g at pH 6.8. Adsorption equilibrium was reached within 80 minutes.

Take 5.5mL of several kinds of metal ion stock solutions, add 0.12g PolyHIPE-2, filter after 1.5 hours, and measure the metal residues in water by ICP. The results are shown in Table 2.

Table 2 Adsorption of several metal ions by PolyHIPE-2 (unit: ppm), pH = 6.0-7.0

Zh	Co 2 +	Cr 3 +	Mn 2 +	Ni 2 +	Cd 2 +	Cu 2 +	Fe 3+	Pb 2 +
Before adsorption	15.3	10.2	13.9	11.2	30.5	49.6	7.3	31.0
After adsorption	0.086	0.308	0.003	0.004	1.28	0.32	1.30	0.004

Example 3:

Same as in Example 2, except that bromoacetic acid was used instead of chloroacetic acid during the synthesis of the porous block, and a block adsorbent PolyHIPE-3 was obtained.

Table 3 Adsorption of several metal ions by PolyHIPE-3 adsorbent (unit: ppm), pH = 6.0-7.0

Zh	Co 2 +	Cr 3 +	Mn 2 +	Ni 2 +	Cd 2 +	Cu 2 +	Fe 3+	Pb 2 +
Before adsorption	15.3	10.2	13.9	11.2	30.5	49.6	7.3	31.0
After adsorption	1.1	0.3	0.46	0.06	2.55	0.99	0.24	0.05

Example 4:

(1) Synthesis of dendritic amphiphile PEI @ PS _0.15 (15% of amino groups are alkylated with polystyrene (PS)). Weigh hyperbranched polyethylenimine (pre-vacuum drying at 60 ° C to remove carbon dioxide that may be absorbed) (1.44g, 0.033mol NH) was dissolved in chloroform (60mL), and glyceryl ether-terminated polystyrene (M _n = 4800, 23.76g, 5mmol, synthesis see literature: D Wan, J Yuan, H Pu. Macromolecular Nanocapsule Derived from Hyperbranched Polyethylenimine (HPEI): Mechanism of Guest Encapsulation versus Molecular Parameters [J] .Macromolecules, 2009,42,1533-1540 ), Stirred at room temperature for 4 days, and precipitated with ethanol to obtain a white solid (25.2 g, 100%), named PEI @ PS _0.15 . The amphiphile obtained was apparently soluble in non-polar solvents such as chloroform, toluene, dichloromethane, carbon tetrachloride, and cyclohexane solvents, but was poorly soluble in N, N-dimethylformamide.

(2) Adsorbent synthesis

Styrene (4.5 g), divinylbenzene (0.9 g), azobisisobutylcyanide (30 mg), PEI @ PS _0.15 (0.55 g, containing 0.6 mmol NH) were mixed to form an oil phase. Bromoacetic acid (0.092 g, 0.66 mmol) was added to PB (phosphate buffer 0.2M, pH 7.4) (26 mL) to form an aqueous phase. The water phase was dropped into the vigorously stirred oil phase, and the dripping was completed within 20 minutes. Stirring was continued for 15 minutes to form a paste-like viscous emulsion. The paste was transferred into a polyethylene plastic cup and heated at 70-80 ° C for 24 hours to obtain a solid block. Wash with water and ethanol, then dry. Named PolyHIPE-4.

PolyHIPE-4 was used to adsorb metals, and metal adsorption was performed similarly to Example 2. The results are shown in Table 4.

Table 4 Adsorption of several metal ions by PolyHIPE-4 (unit: ppm), pH = 6.0-7.0

Zh	Co 2 +	Cr 3 +	Mn 2 +	Ni 2 +	Cd 2 +	Cu 2 +	Fe 3+	Pb 2 +
Before adsorption	15.3	10.2	13.9	11.2	30.5	49.6	7.3	31.0
After adsorption	0.34	0.19	1.46	1.04	4.68	2.82	0.38	0.34

Example 5:

(1) The amphiphile is the same as in Example 1, and is PEI @ C16 _0.35 .

(2) Detrital adsorbent synthesis. Styrene (50 g), divinylbenzene (10 g), azobisisobutylcyanide (0.5 g), and PEI @ C16 _0.35 (9 g) were mixed to form an oil phase. Water (300 mL), chloroacetic acid (9.83 g, 0.104 mol), and potassium carbonate (9.2 g, 0.067 mol) were mixed to form an aqueous phase. The aqueous phase was dropped into the vigorously stirred oil phase, and the dripping was completed within 60 minutes. Stirring was continued for 15 minutes to form a paste-like viscous emulsion with a pH of 9.2. Transfer the paste into a polyethylene plastic cup and heat at 70-80 ° C for 24 hours. Partial phase separation can be seen when heating to about 10 hours, and this state has been maintained. After 24 hours, wash with water and stir slightly to obtain a crumb-like solid. Filter through filter paper, wash once with ethanol, and dry. Named PolyHIPE-5. A scanning electron microscope image of a typical sample is shown in Figure 2b.

The specific surface measured by the mercury intrusion method was 53.5 m ² / g, and the specific surface measured by the nitrogen method was 1.4 m ² / g.

(3) Heavy metal adsorption. PolyHIPE-5 was added into an excess of Pb (NO ₃ ) ₂ aqueous solution (0.49 mmol / L, pH 6.8) and it was found that the highest adsorption capacity was 39.5 mg / g. Adsorption equilibrium was reached within 60 minutes.

0.12 g of PolyHIPE-5 was added to a Pb ^{2 +} -containing stock solution (5.5 mL, concentration: 31 ppm), and filtered after 1 hour. The residue of lead in water was measured by ICP, and the result was 0.004 ppm.

(4) Regeneration and reuse

The adsorbent PolyHIPE-5 after the adsorption of lead ions was placed in an aqueous solution of HCl (5.5 mL), the pH was about 1, soaked for 45 minutes, filtered through a polytetrafluoroethylene membrane containing 0.45 micron hydrophilic pores, and Pb ²⁺ in the filtrate Quantified by ICP, the release amount reached 99%. Repeating the above process 10 times, the saturated adsorption capacity was still 39 ± 1.5mg / g, and the residual amount of lead ions in water remained at 0.01 ± 0.006ppm. The properties did not change within the error range.

Example 6-8:

In Example 5, the pH was sequentially adjusted from 9.2 to 7.5, 11 or 12, and similar operations were performed to obtain debris-like adsorbents PolyHIPE-6, PolyHIPE-7, and PolyHIPE-8.

Example 9:

In Example 5, no halogenated acetic acid was added to the water phase, and similar operation was performed. As a result, a block solid PolyHIPE-9 was obtained.

Example 10:

In Example 2, a PEI @ C16 _0.20 (15% of the amino hydrogen in the PEI was alkylated with C16) was used instead of PEI @ C16 _0.35 to obtain a porous block PolyHIPE-10.

Example 11:

Preparation containing 1,6-hexanedithiol (0.9 g, 12 mmol SH), pentaerythritol allyl ether (0.704 g, ~ 6.6 mmol allyl), allyl dimethylsilane (0.35 g, 5 mmol allyl ), Azobisisobutyronitrile (1.64g, 10mmol) and a solution of PEI @ C16 _0.20 (0.6g) in 1,2-dichloroethane (2.8mL) and vigorously stirred, and chloroacetic acid ( 10 mmol), potassium carbonate (9.5 mmol) in water (25 mL). Finish dripping in 15 minutes and continue stirring for 10 minutes. The thick emulsion was heated at 70 ° C for 36 hours. The solid was immersed in water and ethanol, respectively, and dried under vacuum at normal temperature to obtain an elastic solid PolyHIPE-11. 0.12 g of PolyHIPE-11 was added to a Pb ²⁺ stock solution (5.5 mL, concentration: 31 ppm). After 1 hour, the solution was filtered with ordinary filter paper, and the residue of lead in water was measured by ICP. The result was 0.008 ppm.

The foregoing description of the embodiments is to facilitate understanding and use of the invention by those skilled in the art. It will be apparent to those skilled in the art that various modifications can be easily made to these embodiments and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications that do not depart from the scope of the present invention within the scope of the present invention.

Claims (10)

1. A method for preparing a self-assembling heavy metal adsorbent, which is characterized in that the method is: using a water-in-oil type thick emulsion method, using a polyamine amphiphile with multiple active amino hydrogens as an emulsion stabilizer, and the emulsion stabilizer Self-assembly at the oil-water interface to obtain a water-in-oil thick emulsion with active amino hydrogen expressed at the oil-water interface and facing the water phase; the water-in-oil thick emulsion solidifies to form a matrix, and the active amino hydrogen is replaced by acetate to form amino poly Carboxylic acid groups are expressed on the pore surface of the matrix.
2. The method for preparing a self-assembling heavy metal adsorbent according to claim 1, wherein a part of the amino hydrogens in the fatty polyamine is modified with a lipophilic chain to form a polyamine amphiphile.
3. The method for preparing a self-assembled heavy metal adsorbent according to claim 1, wherein the method comprises the following steps:

   1) Preparation of water-in-oil thick emulsion: adding an emulsion stabilizer to the oil phase, and then adding the water phase with stirring to obtain a water-in-oil thick emulsion;

   2) react at room temperature or under heating conditions to solidify the oil phase to form a matrix, and at the same time, the active amino hydrogen is replaced by acetate in the water phase to form an amino polycarboxylic acid group to obtain a solid material;

   3) The solid material is washed to obtain the adsorbent.
4. The method for preparing a self-assembled heavy metal adsorbent according to claim 1, wherein the method comprises the following steps:

   1) Preparation of water-in-oil thick emulsion: adding an emulsion stabilizer to the oil phase, and then adding the water phase with stirring to obtain a water-in-oil thick emulsion;

   2) react at room temperature or under heating to solidify the oil phase to form a matrix to obtain a solid material;

   3) The solid material is immersed in an aqueous solution containing acetate to perform the reaction, so that the active amino hydrogen is replaced by the acetate in the aqueous solution to form an amino polycarboxylic acid group, and the adsorbent is obtained.
5. The method for preparing a self-assembled heavy metal adsorbent according to claim 3 or 4, characterized in that in step 1), after adding an emulsion stabilizer to the oil phase, a mixed oil phase is obtained, and the emulsion is stabilized The mass percentage of the agent in the mixed oil phase is 5-49%.
6. The method for preparing a self-assembled heavy metal adsorbent according to claim 1, wherein the acetate is provided by haloacetic acid, and the molar amount of the haloacetic acid is the mole of amino hydrogen in the polyamine amphiphile 1-4 equivalents.
7. The method for preparing a self-assembling heavy metal adsorbent according to claim 1, wherein the volume of the water phase accounts for more than 74% of the total volume of the water-in-oil thick emulsion.
8. A self-assembled heavy metal adsorbent, characterized in that the adsorbent is prepared by the method according to claim 1.
9. The self-assembled heavy metal adsorbent according to claim 8, wherein the molecular weight of the polyamine amphiphilic derivative in the adsorbent is ≥1000.
10. The use of a self-assembled heavy metal adsorbent according to claim 8, wherein the adsorbent is used for the treatment of wastewater or soil containing heavy metals.

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