CN113736080A - Hierarchical pore covalent organic polymer material and preparation method and application thereof - Google Patents

Hierarchical pore covalent organic polymer material and preparation method and application thereof Download PDF

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CN113736080A
CN113736080A CN202111172240.6A CN202111172240A CN113736080A CN 113736080 A CN113736080 A CN 113736080A CN 202111172240 A CN202111172240 A CN 202111172240A CN 113736080 A CN113736080 A CN 113736080A
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郑红
任雪莹
师艳召
张煜
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China University of Geosciences Beijing
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Abstract

The invention relates to a hierarchical pore covalent organic polymer material and a preparation method and application thereof, belonging to the technical field of material preparation and deep purification of drinking water. The covalent organic polymer is a two-dimensional reticular polymer, and the repeating unit of the covalent organic polymer is as follows:
Figure DDA0003293712290000011
the preparation method comprises the steps of dropwise adding concentrated hydrochloric acid into an ETTA aqueous solution under the ice-water bath condition, and continuously stirring for a certain time; adding NaNO under the condition of ice-water bath2The solution is stirred and then added with NaNeutralizing the OH solution to be neutral and slightly alkaline to obtain a solution A; dissolving 1, 4-phenyl dithiol in NaOH solution, and performing ultrasonic treatment to obtain solution B; adding B into A dropwise under stirring; carrying out reaction under inert atmosphere; washing the solid sample with water and an organic solvent in sequence; the solid sample was freeze dried. The material can quickly and selectively adsorb low-concentration mercury in water, and has mild preparation conditions and good chemical stability.

Description

Hierarchical pore covalent organic polymer material and preparation method and application thereof
Technical Field
The invention relates to a hierarchical pore covalent organic polymer material, a preparation method and application thereof, in particular to a mercapto-directly-modified hierarchical pore covalent organic polymer material for quickly and selectively adsorbing low-concentration mercury in water, and a preparation method and application thereof.
Background
Heavy metals are characterized by difficult biodegradation, high stability, accumulation, high toxicity and the like, and are important pollutants for causing the water quality of drinking water to be reduced. The mercury is one of heavy metals which have great harm to human health, and as a nervous system poison, the mercury can enter cells through a blood brain barrier and can also be reversely transported through a nerve axon to accumulate in neurons, so that the central nervous system is seriously damaged. Prolonged exposure to low concentrations of mercury can affect a variety of neurobehavioral functions such as psychomotor ability, motor coordination, memory, responsiveness, etc. Especially for women of childbearing age and pregnant women, premature labor, abortion, gestational poisoning, etc. are easily caused. Many studies have shown that drinking water has become an important exposure route for mercury to enter human body, and it is necessary to take effective measures to control and remove low-concentration mercury in drinking water. At present, membrane separation technologies (including electrodialysis, reverse osmosis, ultrafiltration, microfiltration, nanofiltration and the like), ion exchange technologies and adsorption technologies are important aspects of deep treatment research of heavy metals in water, but most of the technologies have the problems of high purification cost, short material life, poor selectivity, unsatisfactory purification effect and the like. In contrast, the adsorption technology is considered to be a good technical choice because of simple and convenient operation, controllable selectivity and difficult generation of secondary pollution. The common adsorbents mainly comprise active carbon, active carbon fibers, zeolite molecular sieves and the like, and although the adsorbents have good adsorption effects on organic micro-pollutants, residual chlorine and the like in drinking water, the materials cannot meet the requirement for removing low-concentration mercury in the drinking water due to the adsorption sites with low density and low bonding capacity of heavy metals and the slow diffusion speed of micro/trace heavy metals in the drinking water.
Among the most reported materials for adsorbing micro/trace mercury so far, some sulfide-type adsorbing materials, such as KMS-1, KMS-2, K-MPS-1, LHMS-1, MoS4-LDH，Fe-MoS4LDH, porous amorphous metal chalcogenide, 3D MoS2Aerogel, graphene/SnS2The composite material and the like show excellent removal effect on micro/trace mercury by utilizing the strong affinity of Lewis soft alkali sulfur to Lewis soft acid mercury. However, due to the low specific surface area and low functional group density of these materials, the adsorption rate is still slow and selective and rapid reduction of micro/trace mercury concentrations to drinking water standards over a wide pH range cannot be achieved. The porous material has a large specific surface area, abundant pore channel structures and easily accessible active sites, can greatly promote the eddy diffusion of low-concentration pollutants, and the functionalization of the porous material becomes the focus of attention of researchers. Among them, Metal Organic Frameworks (MOFs) and covalent organic porous polymer (COPs) are porous materials discovered in recent years and have great adsorption potential, and compared with traditional materials such as activated carbon, mesoporous silicon, zeolite, activated carbon fiber and cross-linked polyethyleneimine, the materials have larger porosity and specific surface area, especially adjustable pore diameter, variable functional groups, high-density chelating sites, surface modification characteristics and the like, are widely favored by researchers, and show greater advantages in heavy metal adsorption. Compared with crystalline Covalent Organic Frameworks (COFs) in MOFs and COPs, amorphous COPs have better thermal stability and chemical stability, and the preparation method is relatively simple, convenient and various, the condition is mild and easy to control, and the application prospect is better.
However, the currently reported amorphous COPs materials are mostly limited to the preparation and functionalization of single-pore COPs, on one hand, the reported COPs materials do not fully exert the excellent mass transfer and diffusion performance of pore channels on the aspect of physical and chemical structures, and micro/trace mercury is not better close to an adsorption site, so that the capture and mass transfer of the micro/trace mercury by the adsorption site of COPs are influenced, and the adsorption rate is not fast enough; on the other hand, the functional group density of the conventional COPs material is low, the soft-soft strong affinity effect of Lewis soft base on soft acid is not fully exerted, and the affinity effect of the COPs material on micro/trace mercury cannot be fully exerted, so that the selective adsorption of mercury is not sufficient, and the preparation steps are complicated, a large amount of organic solvent is consumed, or the catalysis of noble metal is required, so that the conventional COPs material is not suitable for large-scale application.
Disclosure of Invention
The invention aims to solve the problems that the existing adsorbing material is slow in adsorbing rate of low-concentration mercury or poor in adsorption selectivity. Therefore, the invention aims to provide a sulfhydryl directly-modified hierarchical pore covalent organic polymer (hp-COP-SH) material capable of quickly and selectively adsorbing low-concentration mercury in water, a preparation method and application thereof, so that the obtained hp-COP-SH material can quickly and selectively adsorb low-concentration mercury in water, the concentration of the mercury in the outlet water meets the requirements of sanitary water quality standards for drinking water (2001), and the adsorbing material is mild in preparation conditions and good in stability.
A multi-level hole covalent organic polymer material, in particular to a hp-COP-SH material, the covalent organic polymer is a two-dimensional reticular polymer, the repeating unit of which is as follows:
Figure BDA0003293712270000021
the covalent organic polymer is prepared by diazo coupling reaction of synthetic monomers tetra- (4-aminostyrene) Ethylene (ETTA) and 1, 4-phenyldithiol, wherein the tetra- (4-aminostyrene) Ethylene (ETTA) is subjected to diazotization treatment, and amino (-NH)2) The reaction is changed into diazo (-NN-), the diazo is symmetrically grafted on a benzene ring of the 1, 4-phenyl dithiol, and the diazo has a hierarchical pore structure and contains rich sulfhydryl adsorption sites.
Further, the tetra- (4-aminostyrene) Ethylene (ETTA) contains four mutually symmetrical amino groups-NH2) The two mercapto groups of phenyl dithiol are located at the para positions of the benzene ring.
Further, after diazotization, ETTA and 1, 4-phenyl dithiol are subjected to coupling reaction in an alkaline environment, and the generated hp-COP-SH contains abundant and uniformly distributed sulfydryl functional groups and a micropore-mesopore structure.
Compared with a single-pore material, the multi-level pore material has higher specific surface area, extremely easy-to-approach active sites, excellent mass transfer and diffusion performance, can better promote the eddy diffusion of micro/trace mercury, and greatly improves the adsorption speed. The monomer 1, 4-phenyl dithiol is provided with two sulfydryl groups, after the monomer 1, 4-phenyl dithiol and ETTA have diazo coupling reaction under mild reaction conditions only by using water as a reaction solvent without heating or noble metal catalysis, a sulfydryl directly modified hierarchical pore covalent organic polymer with a micropore-mesopore structure can be generated, the hierarchical pore structure can greatly promote the mass transfer and diffusion performance of low-concentration mercury, so that the micro/trace mercury is better close to an adsorption site, the capture and mass transfer of the adsorption site of COPs to the micro/trace mercury are promoted, meanwhile, the large specific surface area of the hierarchical pore COPs enables the density of the directly modified sulfydryl functional groups to be increased, more adsorption active sites are increased, the strong affinity effect of the sulfydryl groups is fully exerted, the affinity between the material and the micro/trace mercury is enhanced, the mass transfer resistance of the low-concentration mercury is effectively overcome, and the mercury capturing capacity of the material is greatly improved, The speed and the selectivity have important significance for developing micro/trace mercury adsorption materials with fast adsorption and diffusion and good selectivity and drinking water mercury deep purification.
A method for preparing a hierarchical porous covalent organic polymeric material, comprising the steps of:
(1) dissolving tetra- (4-aminostyrene) (ETTA) in water, dropwise adding concentrated hydrochloric acid under the condition of ice-water bath, and stirring for reaction under the condition of ice-water bath; then adding NaNO2Stirring the solution again for reaction, and neutralizing the solution with NaOH solution until the solution is neutral and slightly alkaline to obtain solution A;
(2) dissolving 1, 4-phenyl dithiol in NaOH solution, and performing ultrasonic dispersion to obtain solution B;
(3) keeping the ice-water bath condition, dropwise adding the solution B into the solution A under stirring, and reacting the reaction system for a period of time under an inert gas environment;
(4) after the reaction is finished, washing with water and an organic solvent in sequence;
(5) and (4) carrying out freeze drying on the solid sample to obtain the target product hp-COP-SH.
In the step (1), ETTA, concentrated hydrochloric acid and NaNO2The molar ratio of the acid to the base is 1:11: 4-1: 12:5.5, namely the molar ratio of ETTA to hydrochloric acid is 1: 11-1: 12, and ETTA to NaNO2The molar ratio of (A) to (B) is 1: 4-1: 5.5; wherein the molar ratio of ETTA to water (preferably deionized water) is 1: 5555-1: 5556, and the molar concentration of concentrated hydrochloric acid is preferably 12 mol.L-1，NaNO2NaNO in solution2The molar ratio of the deionized water to the deionized water is 1: 134-1: 135; dropwise adding concentrated hydrochloric acid, stirring for 10-15 minutes, and dropwise adding NaNO2Stirring the solution for 25-30 minutes. And neutralizing the solution with NaOH solution until the pH value is 7.8-8.2.
The monomer ETTA used has four-NH groups which are symmetrical to one another2Two mercapto groups in the monomer 1, 4-phenyl dithiol (benzene dithiol) are located at para positions of benzene ring.
In the step (2), the molar ratio of 1, 4-phenyl dithiol to NaOH is 1: 2-1.5: 2, and the ultrasonic time is 20-40 minutes; the concentration of the NaOH solution is 0.08-0.12 mol.L-1。
In the step (3), the molar ratio of ETTA to 1, 4-phenyl dithiol is 1:2, the solution A and the solution B are mixed, the ice-water bath condition is kept, and the solid sample is separated after stirring for 10-12 hours at a constant temperature of 0-5 ℃.
In the step (4), the organic solvent is absolute ethyl alcohol, and the solid sample is washed by ethyl alcohol and water.
In the step (5), the solid sample is frozen and dried to obtain hp-COP-SH; the freeze-drying time varied depending on the sample size until drying.
The multi-level pore covalent organic polymer material can be better applied to quickly and selectively adsorbing low-concentration mercury (the concentration of the mercury is less than or equal to 80ppb) in water.
The invention provides an excellent transmission channel for low-concentration mercury by utilizing the micropore-mesopore structure of the prepared material, promotes the eddy diffusion of the material, and simultaneously enriches the sulfydryl adsorption sites, thereby greatly enhancing the affinity between the material and the mercury and greatly improving the speed and the selectivity of the material for capturing the low-concentration mercury. When the prepared hp-COP-SH material is used for purifying low-concentration mercury in drinking water, the material has the advantages of high adsorption rate, good selective adsorption and stable material structure, and the concentration of the mercury in the outlet water meets the requirements of sanitary Specification for quality of drinking water (2001).
The hp-COP-SH material obtained by the invention can quickly and selectively adsorb low-concentration mercury (the concentration of the mercury is less than or equal to 80ppb) in water, and the adsorption material is simple to prepare and good in stability.
The advantages of the invention are mainly reflected in that:
(1) the method for constructing COPs by diazo coupling reaction only needs water as a reaction solvent, does not need heating or metal catalysis, has mild reaction conditions, can avoid the use of an organic solvent, greatly shortens the synthesis period, is a green, environment-friendly and convenient preparation method, has simple process and lower cost, and is easy for practical application.
(2) The prepared hp-COP-SH material contains uniform and rich sulfydryl functional groups, so that the adsorption active sites are greatly increased, the strong affinity effect of sulfur on heavy metal mercury is exerted, and the affinity between the material and micro/trace mercury is enhanced, thereby greatly improving the selective adsorption capacity of the material on mercury.
(3) The prepared hp-COP-SH material contains micropores (2 nm) and mesopores (2-50 nm) at the same time, so that the material has very quick adsorption kinetics, the problems of mass transfer and diffusion in the mass transfer process are solved, and the adsorption rate of low-concentration mercury is improved.
(4) The prepared hp-COP-SH material has good chemical stability and is suitable for drinking water purification.
Drawings
FIG. 1 is a photograph of a sample of hp-COP-SH;
FIG. 2 is a Fourier transform infrared (FT-IR) spectrum of hp-COP-SH and its synthetic monomers;
FIG. 3 shows N of hp-COP-SH2An adsorption-desorption curve and an aperture distribution diagram in a DFT mode;
FIG. 4 is an XRD spectrum of hp-COP-SH;
FIGS. 5a and 5b are XPS high resolution spectra of hp-COP-SH, wherein: FIG. 5 a: n1 s; FIG. 5 b: s2 p;
FIG. 6 is an SEM picture of hp-COP-SH;
FIG. 7 is a graph of the separation factor and corresponding removal rate for different competitor ions in a mixture;
FIGS. 8a and 8b are graphs showing the effect of hp-COP-SH on mercury adsorption at different pH values and initial concentrations;
FIG. 9 is a graph showing the adsorption kinetics of hp-COP-SH;
FIG. 10 is an adsorption isotherm plot of hp-COP-SH;
FIG. 11 is a graph showing the results of the adsorption experiment and the regeneration effect of hp-COP-SH;
FIG. 12 is an XPS survey spectrum before and after mercury adsorption by hp-COP-SH;
fig. 13a and 13b are high resolution XPS spectra of hp-COP-SH-Hg, wherein fig. 13 a: hg4 f; FIG. 13 b: s2 p;
FIG. 14 is a FT-IR spectrum before and after adsorption of mercury by hp-COP-SH;
FIG. 15 is a FT-IR spectrum of hp-COP-SH after soaking for 24 hours under different pH conditions.
Detailed Description
The invention relates to a hp-COP-SH material for quickly and selectively adsorbing low-concentration mercury in water, wherein synthetic monomers are ETTA and 1, 4-phenyl dithiol, and a covalent organic polymer prepared through diazo coupling reaction has a multi-stage pore structure and contains rich sulfydryl adsorption sites.
The hp-COP-SH material is a two-dimensional reticular polymer, and the repeating unit of the hp-COP-SH material is as follows:
Figure BDA0003293712270000051
dropwise adding concentrated hydrochloric acid into an ETTA aqueous solution with a certain concentration under the ice-water bath condition, and continuously stirring for a certain time; adding NaNO with a certain concentration under the condition of ice-water bath2Stirring the solution for a certain time, and neutralizing the solution with NaOH solution until the solution is neutral and slightly alkaline to obtain solution A; dissolving 1, 4-phenyl dithiol in a certain amount of 0.1M NaOH solution, and performing ultrasonic treatment for a certain time to obtain a solutionB; adding B into A dropwise under stirring; carrying out reaction under inert atmosphere; washing the solid sample with water and an organic solvent in sequence; and (3) freeze-drying the solid sample to obtain the thiol-directly modified hierarchical pore covalent organic polymer.
A method for preparing a hierarchical porous covalent organic polymeric material, comprising the steps of:
(1) dissolving tetra- (4-aminostyrene) (ETTA) in water according to a certain proportion, and dropwise adding a certain amount of concentrated hydrochloric acid into the solution under the condition of ice-water bath. The mixture was stirred for a period of time under an ice-water bath. Then, a certain concentration of NaNO is added2Solution, stirring the mixture for a certain time, and neutralizing the mixture to be neutral and slightly alkaline by using NaOH solution to obtain solution A;
the reaction process is as follows:
Figure BDA0003293712270000061
(2) dissolving a certain amount of 1, 4-phenyl dithiol in a certain volume of NaOH solution, and performing ultrasonic treatment for a certain time to obtain a solution B;
(3) keeping the ice-water bath condition, dropwise adding the solution B into the solution A under stirring, and reacting the reaction system for a period of time under an inert gas environment;
the reaction process is as follows:
Figure BDA0003293712270000062
(4) after the reaction is finished, washing with water and an organic solvent in sequence;
(5) and (4) carrying out freeze drying on the solid sample to obtain the target product hp-COP-SH.
Specifically, the preparation method of the hp-COP-SH material for rapidly and selectively adsorbing low-concentration mercury in water comprises the following steps:
(1) reacting tetra- (4-aminostyrene) (ETTA) in a ratio of 1: 5555-1: 5556 in water and under ice-water bath conditions according to ETTA: concentrated hydrochloric acid 1: 11-1: 12 ofTo which concentrated hydrochloric acid was added dropwise in a molar ratio. The mixture is stirred at 0-5 ℃ for 10-15 minutes. Then, according to ETTA: NaNO21: 4-1: 5.5 molar ratio of NaNO added2Solution (NaNO)2The mol ratio of the deionized water to the deionized water is 1: 134-135), stirring the mixture for 25-30 minutes, and neutralizing the mixture with NaOH solution until the pH value is 7.8-8.2 to obtain solution A;
(2) according to the following steps: 2-1.5: 2, adding 0.08-0.12 mol L of benzene dithiol-1Performing ultrasonic treatment on the NaOH solution for 20-40 minutes to obtain a solution B;
(3) according to ETTA: benzenedithiol ═ 1:2, adding the solution B into the solution A under stirring at the temperature of 0-5 ℃. Reacting the reaction system for 10-12 h in an inert gas environment;
(4) centrifuging, and washing a solid sample with water and absolute ethyl alcohol;
(5) and (5) freeze-drying to obtain the hp-COP-SH material.
The present invention will be described in further detail with reference to the accompanying drawings.
Example 1:
ETTA (0.25mmol) was dissolved in water (25mL) and 0.23mL of concentrated hydrochloric acid was added dropwise thereto under ice-water bath conditions. The mixture was stirred for 15 minutes in an ice bath (0-5 ℃ C., 0 ℃ C.). Then, 2.5mL of NaNO was added while maintaining the rate of one drop for two seconds2(1.03mmol) and the mixture was stirred for 30 minutes and neutralized with 1M NaOH solution to pH 8.0 to give solution a. On the other hand, benzenedithiol (0.5mmol) was dissolved in 10mL of a 0.1M NaOH solution to obtain a solution B. Solution B was sonicated for 20 minutes and then added dropwise to solution a with stirring at 0 ℃. And (3) reacting the reaction system for 12 hours in a nitrogen environment, sequentially carrying out centrifugal washing with water and absolute ethyl alcohol for multiple times, and carrying out freeze drying for 48 hours to obtain the target product hp-COP-SH.
As shown in FIG. 1, which is a photograph of hp-COP-SH, the color of the sample is reddish brown. The sample is not dissolved after being soaked in toluene and tetrahydrofuran for 3 days, is slowly heated to 500 ℃ and is kept warm for 3 hours, and the sample is not in a molten state but is directly carbonized, so that the sample is a planar reticular polymer.
The preparation strategy of hp-COP-SH is as follows, and COPs material with mercapto directly modifying multi-level pores is obtained by ETTA and terephthalyl mercaptan through diazo coupling reaction according to the topological principle.
Figure BDA0003293712270000071
As shown in FIG. 2, which is a Fourier transform infrared (FT-IR) spectrum of hp-COP-SH and its monomer, amino group (-NH) in ETTA after the reaction can be seen by comparing the IR spectra of hp-COP-SH and monomer23356 and 3310cm-1) The characteristic peak of (2) disappears, and the nitrogen-nitrogen double bond (N ═ N, 1592 cm)-1) The characteristic peak of the method is generated, and obvious sulfydryl (-SH, 2558 cm) appears in hp-COP-SH-1) Characteristic peaks, indicating that two monomers successfully prepare hp-COP-SH by N ═ N ligation.
As shown in FIG. 3, is the N of hp-COP-SH2The pore size distribution diagram under the absorption and desorption curve and the non-local Density Functional Theory (DFT) mode can be clearly seen, and the hp-COP-SH shows the isotherms of mixed type I and IV, which represents the existence of micropores and mesopores. At a lower relative pressure (0)<P/P0<0.15), hp-COP-SH adsorbs N2Due to the relatively large adsorption potential of the micropores, consistent with the type i isotherms. Intermediate P/P0The H4 type hysteresis loop appears in the region, which indicates that the region contains a certain amount of mesopores, and indicates that IV type isotherms exist at the same time. Based on the DFT pore size distribution, pores with a maximum probable pore size of 1.48nm and 4.52nm, respectively, can be seen, indicating the simultaneous presence of micropores and mesopores with N in the structure2The results of the adsorption-desorption isotherms were consistent. Meanwhile, mesopores of various sizes occur in the range of 5 to 50nm, possibly due to stacking of amorphous polymers. Brunauer-Emmett-Teller (BET) surface area of hp-COP-SH is 348m2 g-1. The abundant micropores and mesopores enable high-density-SH sites to be symmetrically dispersed on the surface of the whole hp-COP-SH channel, and the method is favorable for quickly and effectively adsorbing micro/trace mercury.
As shown in FIG. 4, the XRD spectrum of hp-COP-SH is shown. As can be seen from the figure, no obvious characteristic peak appears in hp-COP-SH, and the material is a polymer existing in an amorphous state.
As shown in FIGS. 5a and 5b, the XPS spectra are high resolution for hp-COP-SH. As can be seen from the figure, peaks with the bonding energy of 400.25 eV and peaks with the bonding energy of 164.2eV in an XPS spectrum of the hp-COP-SH correspond to N1S and S2 p respectively, and an infrared spectrum is combined to further prove that-N ═ N-and-SH exist, and the results show that the thiol functionalized covalent organic polymer hp-COP-SH is successfully synthesized through diazo coupling reaction.
As shown in fig. 6, which is an SEM image of hp-COP-SH, it can be seen that hp-COP-SH is a stacked, less ordered material with wider interstitial pores, which is further illustrated as an amorphous polymer, combining the XRD pattern and DFT mode pore size distribution pattern.
FIG. 15 shows FT-IR spectra of hp-COP-SH after 24 hours immersion at different pH. As can be seen, the FT-IR spectrum of the sample after 24 hours of soaking in the solution with pH 2, 6 and 12 is basically consistent with that of the prepared sample, and the hp-COP-SH has structural stability in a wide pH range and is suitable for purifying drinking water.
Example 2:
the application test of the hp-COP-SH material of the invention is carried out as follows:
(1) 10mg of the hp-COP-SH sample prepared in example 1 was added to a solution containing 30mL of Hg (II) at a concentration of 30ppb, Na+Concentration 30ppm, K+Concentration 80ppm, Ca2+、Mg2+、Cu2+Concentration of 20ppm, Pb2+A solution with a concentration of 150ppb and a pH of 6.5. + -. 0.25 in erlenmeyer flasks. Oscillating in 20 ℃ water bath at constant temperature for 10min, centrifuging 5.00mL, filtering the supernatant through a 0.22-micron filter membrane, adding 2% nitric acid to acidify, fixing the volume to 10.00mL, measuring various ion concentrations in the solution by ICP-MS, and multiplying the measurement result by the dilution factor 2 to obtain the actual concentration in the solution. Thus, the adsorption selectivity of hp-COP-SH to Hg (II) was evaluated.
FIG. 7 shows the separation factor and corresponding removal rate for different competing ions in a mixture. The selective adsorption capacity of the adsorbent for different ions can be determined by the partition coefficient Kd MAnd (4) showing. In combination with Table 1, as can be seen from FIG. 7, hp-COP-SH is present against other cations in the coexistence of a plurality of high-concentration cationsThe factor for the separation of the subunits is very high, up to 103Of order of magnitude, indicating that hg (ii) is highly selective for hp-COP-SH in the presence of co-existing cations. It is notable that the removal rate of hp-COP-SH to Hg (II) is very high (>98%) with a water concentration well below 1ppb, but with a relatively low efficiency for the removal of other ions (<10%) which can be explained by Pearson's soft and hard acid-base theory. This result demonstrates that hp-COP-SH is an excellent material for separating micro/traces of hg (ii) from other high concentrations of competing metal ions.
TABLE 1 result of adsorption selectivity experiment of hp-COP-SH to Hg (II)
Figure BDA0003293712270000091
Note: the dosage of hp-COP-SH is 10mg/30 mL.
(2) 10mg of each of the hp-COP-SH samples prepared in example 1 were introduced into erlenmeyer flasks containing 30mL of a solution having a Hg (II) concentration of 30ppb, a Ca hardness of 20ppm and a pH of 3.5, 4.5, 5.5, 6.5, 7.5, 8.5, 9.5, prepared according to drinking water treatment unit standard NSF/ANSI 53-2020 a. Oscillating in 20 ℃ water bath at constant temperature for 3min, centrifuging 5.00mL, filtering the supernatant through a 0.22-micron filter membrane, adding 2% nitric acid to acidify, fixing the volume to 10.00mL, measuring various ion concentrations in the solution by ICP-MS, and multiplying the measurement result by the dilution factor 2 to obtain the actual concentration in the solution. The adsorption effect of hp-COP-SH on Hg (II) at different pH values was evaluated.
FIG. 8a shows the effect of hp-COP-SH on mercury adsorption at different pH. As can be seen, the removal rate of hp-COP-SH to trace Hg (II) in a wide pH range is always kept above 98% within 3 minutes, and the water outlet concentration is lower than the mercury concentration limit (less than or equal to 1ppb) required by the sanitary Specification for quality of drinking water (2001), which shows that the hp-COP-SH can stably capture the trace Hg (II) at different pH values.
(3) 10mg of each of the hp-COP-SH samples prepared in example 1 was added to a conical flask containing 30mL of a solution having hg (ii) of initial concentration of 6, 10, 30, 60, 80, 100, 150ppb, Ca hardness of 20ppm, and pH of 6.5 ± 0.25. Oscillating in 20 ℃ water bath at constant temperature for 3min, centrifuging 5.00mL, filtering the supernatant through a 0.22-micron filter membrane, adding 2% nitric acid to acidify, fixing the volume to 10.00mL, measuring various ion concentrations in the solution by ICP-MS, and multiplying the measurement result by the dilution factor 2 to obtain the actual concentration in the solution. Thus, the adsorption effect of hp-COP-SH on different initial concentrations of Hg (II) was evaluated.
FIG. 8b shows the adsorption effect of hp-COP-SH on mercury at different initial concentrations. As can be seen from the figure, after the hp-COP-SH adsorbs 6-70ppb Hg (II) solution in 3 minutes, the effluent concentration can reach the requirement (less than or equal to 1ppb) of the sanitary Standard for Water quality of Drinking Water (2001) on the mercury concentration, which shows that the hp-COP-SH has good adsorption effect on micro/trace Hg (II) with different initial concentrations.
(4) 10mg of the hp-COP-SH sample prepared in example 1 was added to a conical flask containing 30mL of a solution having a Hg (II) concentration of 30ppb, a Ca hardness of 20ppm and a pH of 6.5. + -. 0.25. Respectively oscillating in a water bath at 20 ℃ for 10s, 30s, 1min, 3min, 5min, 10min and 30min at constant temperature, centrifuging 5.00mL of each solution, filtering the supernatant through a filter membrane of 0.22 mu m, adding 2% nitric acid for acidification, fixing the volume to 10.00mL, measuring the concentration of Hg (II) in the solution by ICP-MS, and multiplying the measurement result by the dilution factor 2 to obtain the actual Hg (II) concentration in the solution at different adsorption times. Thus, the adsorption rate of hp-COP-SH to Hg (II) was evaluated.
As shown in FIG. 9, the adsorption kinetics of hp-COP-SH are shown. As can be seen, hp-COP-SH has very fast adsorption kinetics on low concentrations of Hg (II), and the initial concentration of 30ppb Hg (II) effluent can be reduced to 0.72ppb within 10s, which is far below the mercury concentration limit (less than or equal to 1ppb) required by the Drinking Water quality sanitation Specification (2001), in the case of the adsorbent dosage of only 10mg/30 mL. As can be seen from fig. 9, the adsorption process can be well fitted with a pseudo-second order kinetic model.
(5) 10mg of each of the hp-COP-SH samples prepared in example 1 was added to a flask containing 30mL of a solution having hg (ii) concentration of 6, 10, 30, 60, 80, 100, 150, 200, 500, 1000ppb, Ca hardness of 20ppm, pH 6.5 ± 0.25. Oscillating in 20 ℃ water bath at constant temperature for 3min, centrifuging 5.00mL, filtering the supernatant through a 0.22-micron filter membrane, adding 2% nitric acid to acidify, fixing the volume to 10.00mL, measuring various ion concentrations in the solution by ICP-MS, and multiplying the measurement result by the dilution factor 2 to obtain the actual concentration in the solution. Thus, the adsorption isotherms of hp-COP-SH against Hg (II) were evaluated.
FIG. 10 shows the adsorption isotherm diagram of hp-COP-SH. It can be seen that the Freundlich adsorption model can better fit the isothermal adsorption result (R) of hp-COP-SH on low-concentration mercury2＝0.99，1/n＝0.58<1)。
(6) 10mg of the hp-COP-SH sample prepared in example 1 was charged into a conical flask containing 30mL of a solution having an Hg (II) concentration of 30ppb, a Ca hardness of 20ppm and a pH of 6.5. + -. 0.25. Oscillating in a water bath at the constant temperature of 20 ℃ for 10min, recovering a sample, repeatedly adsorbing for 6 times, centrifuging 5.00mL each time, filtering the supernatant through a filter membrane of 0.22 mu m, adding 2% nitric acid for acidification, fixing the volume to 10.00mL, measuring the concentration of Hg (II) in the solution by using ICP-MS, and multiplying the measurement result by the dilution factor 2 to obtain the actual concentration of Hg (II) in the solution. Thus, the standard adsorption quantity of hp-COP-SH is evaluated.
Regenerating the sample with the outlet water mercury concentration exceeding the standard of sanitary Standard of Drinking Water quality (2001) after 6 times of adsorption by adopting the following method: 10mg of the hp-COP-SH sample after repeating the adsorption 6 times was added to 10mL of 1M hydrochloric acid containing 1% thiourea, and shaken at room temperature for 30 minutes.
As shown in FIG. 11, the results of the adsorption experiment and the regeneration effect of hp-COP-SH were repeated. As can be seen from the figure, under the condition that the dosage of the adsorbent is 10mg/30mL, the outlet water concentration is 0.74ppb after repeated adsorption for 3 times, and the requirement of sanitary standard for drinking water quality (2001) on the mercury concentration (less than or equal to 1ppb) is still met. The number of times of use is continuously increased, although the effluent concentration exceeds 1ppb, the adsorption effect is still good, and the adsorption amount still tends to be continuously increased after the reuse for 6 times. In addition, the regeneration scheme has a good regeneration effect on a sample repeatedly adsorbed for 6 times, the concentration of the regenerated effluent meets the requirement of sanitary Specification for Water quality of Drinking Water (2001) on the concentration of mercury (less than or equal to 1ppb), and the concentration of the effluent is 0.85ppb, which shows that the material can be effectively regenerated.
As shown in FIG. 12, the XPS full spectrum before and after the hp-COP-SH adsorbs mercury, it can be seen that the hp-COP-SH-Hg has a more obvious characteristic peak of Hg4f compared with the hp-COP-SH without adsorbing mercury, and the effective adsorption of the hp-COP-SH to the mercury is proved.
As shown in FIGS. 13a and 13b, the XPS spectra are high resolution XPS spectra of hp-COP-SH-Hg. As can be seen from FIG. 13a, the strong characteristic peaks of Hg4f 5/2 and 4f at 106 and 101.9eV after adsorption of mercury by hp-COP-SH indicate that hp-COP-SH successfully captures Hg (II). The S2 p peak of Hg (II) -loaded samples shifted to higher binding energies (-0.4 eV) compared to the original hp-COP-SH (FIG. 13b), indicating that-SH in hp-COP-SH binds to Hg (II).
As shown in FIG. 14, which is a FT-IR spectrum before and after the adsorption of mercury to hp-COP-SH, it can be seen that the Hg (II) -loaded hp-COP-SH-Hg is 1385cm higher than the prepared hp-COP-SH-1The nearby strong peaks correspond to Hg-S, further demonstrating the successful capture of Hg (ii) by the adsorbent in conjunction with fig. 13a and 13 b.
Example 3:
actual water application test: 10mg of each of the hp-COP-SH samples prepared in example 1 were introduced into Erlenmeyer flasks containing 30mL of a solution having a Hg (II) concentration of 6, 10, 30ppb each, prepared with tap water. Oscillating in a water bath at the constant temperature of 20 ℃ for 10s, centrifuging 5.00mL, filtering the supernatant through a filter membrane of 0.22 mu m, adding 2% nitric acid for acidification, fixing the volume to 10.00mL, measuring various ion concentrations in the solution by ICP-MS, and multiplying the measurement result by the dilution factor 2 to obtain the actual concentration in the solution. Therefore, the adsorption capacity of the hp-COP-SH to low-concentration mercury in an actual water environment is evaluated.
Table 2 shows the adsorption effect of hp-COP-SH on tap water at different initial concentrations of Hg (II). As can be seen from the table, within 10s, the hp-COP-SH shows high removal rate to micro/trace mercury with different initial concentrations in tap water, and the outlet water concentration reaches the requirement (less than or equal to 1ppb) of sanitary Standard for Water quality of Drinking Water (2001) on the mercury concentration, which shows that the material also has rapid and selective adsorption effect on low-concentration Hg (II) in the actual water body.
TABLE 2 adsorption Effect of hp-COP-SH on Hg (II) in tap water
Figure BDA0003293712270000121
Note: the dosage of hp-COP-SH is 10mg/30 mL.
Comparative example:
in order to examine the effect of hierarchical pores, a single-pore covalent organic polymer material (sp-COP-SH) was prepared by using 1,3, 5-tris (4-aminophenyl) benzene and 1, 4-phenyldithiol as monomers, and the effect of adsorbing low-concentration mercury was compared.
(1) Preparation of sp-COP-SH: first, 1.0mmol of 1,3, 5-tris (4-aminophenyl) benzene was added to 100mL of water, 0.7mL of concentrated HCl was added dropwise under ice-water bath conditions, and 30mL of NaNO was added dropwise after 15 minutes of reaction2(0.1M) solution, after 30 minutes of reaction, the reaction was adjusted to neutral off-base with NaOH solution, which was solution 1. Adding 1.5mmol of terephthalyl mercaptan into 30mL of 0.1M NaOH solution, performing ultrasonic treatment for 20 minutes, dropwise adding into the reaction solution 1, and finally obtaining the reaction system in N2Reacting for 12 hours in the environment, washing with water and ethanol in sequence after the reaction is finished, and finally drying to obtain sp-COP-SH.
(2) 10mg of the sp-COP-SH sample prepared in comparative example (1) was put in a conical flask containing 30mL of a solution of Hg (II) having a concentration of 30ppb, Ca hardness of 20ppm and pH 6.5. + -. 0.25. Shaking in 20 deg.C water bath at constant temperature for 10s, 30s, 1min, centrifuging 5.00mL each, filtering the supernatant with 0.22 μm filter membrane, adding 2% nitric acid to acidify and fix volume to 10.00mL, measuring Hg (II) concentration in the solution by ICP-MS, and multiplying the measurement result by dilution multiple 2 to obtain actual Hg (II) concentration in the solution at different adsorption time. Thereby evaluating the effect of the multi-stage pores.
TABLE 3 comparison of the adsorption effects of hp-COP-SH and sp-COP-SH
Figure BDA0003293712270000122
Note: hg (II) initial concentration 30ppb, adsorbent amount 10mg/30mL
Table 3 shows the comparison of the adsorption effect of hp-COP-SH and sp-COP-SH on Hg (II) at 10s, 30s, 1 min. sp-COP-SH is a covalent organic polymer directly modified by sulfydryl, and is different from hp-COP-SH in that the sp-COP-SH only contains mesopores instead of a multi-level pore material. As can be seen from the table, the hp-COP-SH of the multi-level hole obviously shows more excellent adsorption advantage under the same low concentration, the effluent concentration of 30ppb Hg (II) solution can be reduced to be less than 1ppb required by the specification within 10s, and the sp-COP-SH of the single hole can be reached within 1min, so that the rate of the material for adsorbing low-concentration mercury can be greatly improved by the structure of the multi-level hole, and the material has better application prospect in the technical field of deep purification of drinking water.
The hp-COP-SH material prepared by the invention can quickly and selectively adsorb low-concentration mercury in water, the effluent meets the requirements of sanitary Specification for quality of Drinking Water (2001), and the material has mild preparation conditions and good chemical stability.
After diazotization treatment, tetra- (4-aminostyrene) (ETTA) and 1, 4-phenyl dithiol are subjected to coupling reaction in an alkaline environment to obtain the sulfydryl directly modified hierarchical pore covalent organic polymer. Dissolving tetra- (4-aminostyrene) (ETTA) in water according to a certain proportion, and dropwise adding a certain amount of concentrated hydrochloric acid into the solution under the condition of ice-water bath. The mixture was stirred for a period of time under an ice-water bath. Then, adding NaNO with a certain concentration under the condition of ice-water bath2Solution, stirring the mixture for a certain time, and neutralizing the mixture to be neutral and slightly alkaline by using NaOH solution to obtain solution A; on the other hand, a certain amount of terephthalyl mercaptan is dissolved in a certain volume of NaOH solution with a certain concentration, and the solution B is obtained by ultrasonic treatment for a certain time. Keeping the ice-water bath condition, dropwise adding the solution B into the solution A under stirring, reacting the reaction system in an inert gas environment for a period of time, sequentially washing a solid sample with water and an organic solvent for multiple times, and freeze-drying to obtain the target product hp-COP-SH. The material can quickly and selectively adsorb low-concentration mercury in water, and has mild preparation conditions and good chemical stability.

Claims (10)

1. A multi-cellular covalent organic polymeric material, characterized in that: the covalent organic polymer is a two-dimensional reticular polymer, and the repeating unit of the covalent organic polymer is as follows:
Figure FDA0003293712260000011
2. the multi-cellular covalent organic polymeric material of claim 1, wherein: the covalent organic polymer is prepared from tetra- (4-aminostyrene) and 1, 4-phenyldithiol through diazo coupling reaction, wherein the tetra- (4-aminostyrene) is subjected to diazotization treatment, amino reaction in the diazo treatment is changed into diazo, the diazo is symmetrically grafted on a benzene ring of the 1, 4-phenyldithiol, and the covalent organic polymer has a multi-level pore structure and contains abundant sulfhydryl adsorption sites.
3. A method for preparing a hierarchical porous covalent organic polymeric material, comprising the steps of:
(1) dissolving tetra- (4-aminostyrene) in water, dropwise adding concentrated hydrochloric acid under the ice-water bath condition, and stirring for reaction under the ice-water bath condition; then adding NaNO2Stirring the solution again for reaction, and neutralizing the solution with NaOH solution until the pH value is 7.8-8.2 to obtain solution A;
(2) dissolving 1, 4-phenyl dithiol in NaOH solution, and performing ultrasonic dispersion to obtain solution B;
(3) keeping the ice-water bath condition, dropwise adding the solution B into the solution A under stirring, and reacting the reaction system in an inert gas environment;
(4) after the reaction is finished, washing with water and an organic solvent in sequence;
(5) and (4) carrying out freeze drying on the solid sample to obtain a target product.
4. The method of preparing a hierarchical porous covalent organic polymer material of claim 3, wherein: tetra- (4-aminostyrene), concentrated hydrochloric acid and NaNO2The molar ratio of (A) to (B) is 1:11:4 to 1:12: 5.5.
5. The method of preparing a hierarchical porous covalent organic polymer material of claim 3, wherein: the molar ratio of the tetra- (4-aminostyrene) to the water is 1: 5555-1: 5556, and the molar concentration of concentrated hydrochloric acid is 12 mol.L-1，NaNO2NaNO in solution2The molar ratio of the deionized water to the deionized water is 1: 134-1:135。
6. the method of preparing a hierarchical porous covalent organic polymer material of claim 3, wherein: dropwise adding concentrated hydrochloric acid, stirring for 10-15 minutes, and dropwise adding NaNO2Stirring the solution for 25-30 minutes.
7. The method of preparing a hierarchical porous covalent organic polymer material of claim 3, wherein: the monomer tetra- (4-aminostyrene) employed has four-NH groups which are symmetrical to one another2The two mercapto groups in the monomer 1, 4-phenyl dithiol are located at the para positions of the benzene ring.
8. The method of preparing a hierarchical porous covalent organic polymer material of claim 3, wherein: the molar ratio of 1, 4-phenyl dithiol to NaOH is 1: 2-1.5: 2, the ultrasonic time is 20-40 minutes, and the concentration of NaOH solution is 0.08-0.12 mol.L-1。
9. The method of preparing a hierarchical porous covalent organic polymer material of claim 3, wherein: the molar ratio of the tetra- (4-aminostyrene) to the 1, 4-phenyldithiol is 1:2, the solution A and the solution B are mixed, stirred at a constant temperature of 0-5 ℃ for 10-12 hours, and then a solid sample is separated; the organic solvent is absolute ethyl alcohol.
10. Use of the hierarchical porous covalent organic polymeric material according to claim 1 or 2 for adsorbing low concentrations of mercury in water.
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