CN114797786A - Preparation method, product and application of magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent - Google Patents

Preparation method, product and application of magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent Download PDF

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CN114797786A
CN114797786A CN202210209274.6A CN202210209274A CN114797786A CN 114797786 A CN114797786 A CN 114797786A CN 202210209274 A CN202210209274 A CN 202210209274A CN 114797786 A CN114797786 A CN 114797786A
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carboxypropionyl
adsorbent
chitosan sodium
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陈慧
戴炜博
马建青
陈泽龙
张琳
余岩
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College of Science and Technology of Ningbo University
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Abstract

The invention provides a preparation method, a product and application of a magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent. The preparation method comprises the following steps: from SiO 2 Encapsulated Fe 3 O 4 The nano particles and 3-aminopropyl triethoxysilane react in solvent to obtain surface aminated Fe 3 O 4 /SiO 2 A nanoparticle; by amination of Fe 3 O 4 /SiO 2 Mixing the nano particles with N-carboxypropionyl chitosan sodium, adding glutaraldehyde for crosslinking reaction to obtain the magnetic crosslinked chitosanN-carboxypropionyl chitosan sodium adsorbent. The preparation method is simple to operate and easy to realize industrialization. The magnetic cross-linking N-carboxypropionyl chitosan sodium adsorbent prepared by the preparation method has good adsorption performance, and can be applied to the selective adsorption of heavy metal ions in wastewater to Pb 2+ The method has the advantages of strong selectivity, stable property, rapid separation through an external magnetic field, simple operation, low cost and higher practical value.

Description

Preparation method, product and application of magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent
Technical Field
The invention belongs to the technical field of adsorbent preparation, and particularly relates to a preparation method, a product and application of a magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent.
Background
Heavy metals have the characteristics of high toxicity, durability, difficult degradation and the like, and the pollution problem of the heavy metals is widely concerned due to the complex chemical behavior and ecological effect and the continuously increased emission. The waste water discharged from mining, metal smelting, electroplating, tanning, plastic chemical industry, microelectronic manufacturing and other industries is the main cause of heavy metal pollution. Heavy metal ions discharged into the environment are first concentrated in organisms and are transmitted along with food chains to harm the health of animals, plants and human beings. Such as cd (ii), can cause severe kidney damage, anemia, and pain; excessive Cu (II) can stimulate mucosa, cause damage and lesion of liver and kidney, and Pb (II) can damage the central nervous system and hematopoietic system, thereby seriously affecting the growth and development of children. Therefore, safe removal of heavy metal ions from wastewater is of paramount importance.
At present, the mainstream methods for treating heavy metal ions in wastewater are chemical precipitation, coagulating sedimentation and the like, wherein the heavy metal in a dissolved state is converted into insoluble metal compounds or elements by adjusting the pH or adding a medicament, and the insoluble metal compounds or elements are removed from the water by precipitation or air flotation. However, a large amount of heavy metal sludge is generated in the technology, and the safety problem of the heavy metal sludge still needs to be solved.
The adsorption method is a heavy metal treatment method with simple process, economy and reliability, heavy metal ions in water are adsorbed by cheap materials such as chitosan, clay minerals, fly ash and biochar, and then desorbed into heavy metal concentrated solution by a proper method, so that the heavy metal can be recycled, the pollution problem of the heavy metal can be effectively solved, and the regeneration of waste resources can be realized. However, the actual industrial wastewater often contains 2 or more heavy metal ions, and the adsorbent has no selectivity, so that different heavy metals in the concentrated solution are still difficult to separate and difficult to recycle.
Disclosure of Invention
The selective adsorption of heavy metal ions in the wastewater treatment is beneficial to improving the use efficiency of the adsorbent and recycling the heavy metals. The chitosan derivative N-carboxypropionyl chitosan sodium molecule contains carboxyl and propionyl at the same time, can realize selective chelation on specific metal ions, but has good water solubility and cannot be directly used as an adsorbent. On the other hand, the material can keep smaller size by constructing the magnetic response characteristic, the mass transfer rate and the catalytic activity are ensured, and meanwhile, the material is also beneficial to quick separation and recovery, so that the use cost is effectively reduced.
Based on the analysis, the invention provides a preparation method of a magnetic cross-linking N-carboxypropionyl chitosan sodium adsorbent, which is simple to operate and easy to realize industrialization.
The invention also provides a magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent prepared by the preparation method, and the adsorbent is used for adsorbing Pb 2+ Has high selective adsorption and can realize rapid separation by magnetic field.
The invention also provides application of the magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent in selective adsorption of heavy metal ions in wastewater.
A preparation method of a magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent comprises the following steps:
(1) from SiO 2 Encapsulated Fe 3 O 4 The nano particles react with 3-aminopropyl triethoxysilane (APTES) in a solvent to obtain surface aminated Fe 3 O 4 /SiO 2 A nanoparticle;
(2) by amination of Fe 3 O 4 /SiO 2 Mixing the nano particles with N-carboxypropionyl chitosan sodium (CPCTS), adding glutaraldehyde to perform a crosslinking reaction to obtain the magnetically crosslinked N-carboxypropyleneAcyl chitosan sodium adsorbent.
In the above preparation method, in step (1):
preferably, 3-aminopropyltriethoxysilane is reacted with Fe 3 O 4 /SiO 2 The volume-mass ratio of the nanoparticles is (0.25-4): 1 mL/g. More preferably (0.5-2): 1 mL/g.
Preferably, among the solvents, SiO 2 Encapsulated Fe 3 O 4 The mass volume concentration of the nano particles is 5-20 g/L. More preferably 8 to 12 g/L. Still more preferably 10 g/L.
Preferably, the volume percentage concentration of the 3-aminopropyltriethoxysilane in the solvent is 0.5-2% (v/v). Further preferably 1.0% (v/v).
Preferably, the solvent is one or a mixture of isopropanol and absolute ethyl alcohol. More preferably, it is anhydrous ethanol.
Preferably, the operation is carried out by first using SiO 2 Encapsulated Fe 3 O 4 Nanoparticles (Fe) 3 O 4 /SiO 2 Nanoparticles) are ultrasonically dispersed in the solvent, and 3-aminopropyltriethoxysilane is added into the solvent for amination reaction.
Preferably, the amination reaction is carried out in a stirring state at room temperature, and the reaction time is 12-48 h. More preferably 18 to 28 hours. Still more preferably 24 hours.
Preferably, the material is made of SiO 2 Encapsulated Fe 3 O 4 The preparation process of the nano-particles is as follows:
adding Tetraethylorthosilicate (TEOS) to Fe 3 O 4 The SiO is prepared and obtained by the reaction in ethanol water solution of nano particles 2 Encapsulated Fe 3 O 4 And (3) nanoparticles.
Further preferably, tetraethoxysilane and Fe 3 O 4 The volume-mass ratio of the nanoparticles is (0.2-4): 1 mL/g. More preferably (0.3 to 0.8): 1 mL/g.
As a further preference, the ethanol aqueous solution is obtained by mixing absolute ethanol and water, wherein the volume ratio of the water to the absolute ethanol is 1: (3-5). More preferably 1: 4.
more preferably, Fe is contained in an aqueous solution of ethanol 3 O 4 The addition amount of the nanoparticles is 5-25 g/L in terms of mass-volume concentration. Further preferably 20 g/L.
More preferably, the amount of ethyl orthosilicate added to the aqueous ethanol solution is 0.5 to 2% (v/v) in terms of volume percentage concentration. Further preferably 1.0% (v/v).
More preferably, Fe is added first during the operation 3 O 4 And (3) adjusting the ethanol aqueous solution to be alkaline by using concentrated ammonia water, and then adding tetraethoxysilane for reaction.
More preferably, the concentration of the concentrated ammonia water is 25-28 wt/%, and the adding volume is 1% of the volume of the ethanol water solution.
Further preferably, Fe 3 O 4 SiO of nanoparticles 2 The coating reaction is carried out under stirring. Wherein the stirring time is 12-48 h. More preferably, 24 hours.
Fe as described above 3 O 4 The nano-particles can be prepared by adopting a solvothermal method, a coprecipitation method or a microemulsion method.
In order to ensure uniformity of the particle size of the nanoparticles and to facilitate control of the reaction process, preferably, Fe 3 O 4 The nanoparticles are prepared by a solution-thermal process, wherein ferric chloride hexahydrate (FeCl) 3 ·6H 2 O) is an iron source, sodium acetate (NaAc) is an alkaline reagent, and ethylene glycol is a reducing agent and a solvent.
Preferably, the addition amount of ferric chloride hexahydrate in ethylene glycol is 10-30 g/L in terms of mass-to-volume ratio. More preferably 25 to 30 g/L. Still more preferably 27 g/L.
Preferably, the addition amount of sodium acetate in ethylene glycol is 50 to 80g/L in terms of mass-to-volume ratio. More preferably 70 to 80 g/L. Still more preferably 72 g/L.
Preferably, the reaction device of the solvothermal reaction is a polytetrafluoroethylene high-temperature reaction kettle, and the heating device is an oven.
Preferably, the reaction temperature of the solvothermal reaction is 160-220 ℃, and the reaction time is 6-16 h.
Further preferably 190-210 ℃, and the reaction time is 7-9 h.
In the solvothermal reaction, the heating temperature and reaction time affect Fe 3 O 4 The particle size of the particles. Too low temperature or too short reaction time, Fe 3 O 4 Insufficient growth and waste of raw materials; if the temperature is too high or the time is too long, particles with larger particle size are easy to form. Therefore, it is more preferable that the reaction temperature is 200 ℃ and the reaction time is 8 hours.
Preferably, after the amination reaction is finished, separating by using a magnet, washing by using deionized water and ethanol, and drying to obtain the surface aminated Fe 3 O 4 /SiO 2 And (3) nanoparticles.
In the above preparation method, in the step (2):
preferably, the aminated Fe 3 O 4 /SiO 2 The aminated Fe was first added before mixing the nanoparticles with N-carboxypropionyl chitosan sodium 3 O 4 /SiO 2 The nano particles are ultrasonically dispersed in ethanol to prepare aminated Fe 3 O 4 /SiO 2 A nanoparticle dispersion; dissolving N-carboxypropionyl chitosan sodium in deionized water to prepare an N-carboxypropionyl chitosan sodium aqueous solution; then the prepared aminated Fe 3 O 4 /SiO 2 And uniformly mixing the nano-particle dispersion liquid and the N-carboxypropionyl chitosan sodium aqueous solution under the stirring state to obtain a mixed solution.
More preferably, the aminated Fe 3 O 4 /SiO 2 Aminated Fe in nanoparticle dispersions 3 O 4 /SiO 2 The mass volume concentration of the nano particles is 10-25 g/L. More preferably 15 to 18 g/L.
Preferably, the mass volume concentration of the N-carboxypropionyl chitosan sodium in the N-carboxypropionyl chitosan sodium aqueous solution is 5-20 g/L. More preferably 10 to 15 g/L.
Preferably, N-carboxypropionyl chitosan sodium is reacted with aminated Fe 3 O 4 /SiO 2 The mass ratio of the nano particles is (0.1-2): 1. more preferably (0.2 to 1.0): 1. more preferably 0.5: 1.
adding glutaraldehyde to the mixed solution, the glutaraldehyde serving to aminate Fe 3 O 4 /SiO 2 And (3) connecting the amino on the surface of the nano-particle with the residual amino in the N-carboxypropionyl chitosan sodium.
Preferably, the volume mass ratio of the glutaraldehyde to the N-carboxypropionyl chitosan sodium is (1-4): 1 mL/g. More preferably (2-3): 1 mL/g.
Preferably, the concentration of the glutaraldehyde is 25%, and the volume ratio of the addition volume of the glutaraldehyde to the volume of the mixed solution is (10-100): 1 ml/L. More preferably (40 to 60): 1 mL/L. More preferably 50: 1 mL/L.
Preferably, the crosslinking reaction time is 4-12 h. Further preferably 8 hours.
Preferably, after the reaction is finished, separating a magnet, washing with ethanol, and drying to obtain the magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent.
Specifically, the preparation method of the magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent comprises the following steps:
(1) dissolving iron salt and sodium acetate in ethylene glycol, and preparing Fe by a solvothermal method 3 O 4 Nano particles and wrapping SiO on the nano particles by using tetraethoxysilane 2 Preparation of Fe 3 O 4 /SiO 2 A nanoparticle;
(2) mixing the above Fe 3 O 4 /SiO 2 The nano particles react with 3-aminopropyl triethoxysilane to prepare surface aminated Fe 3 O 4 /SiO 2 A nanoparticle;
(3) mixing the aminated composite particles with a N-carboxypropionyl chitosan sodium solution, dropwise adding a glutaraldehyde solution, carrying out a crosslinking reaction, carrying out magnetic separation and drying after ethanol cleaning, and thus obtaining the magnetic crosslinked N-carboxypropionyl chitosan sodium adsorbent.
The preparation method of the invention utilizes the classical solvothermal method and stober method to prepare SiO 2 Wrapped magnetic core (Fe) 3 O 4 /SiO 2 Nanoparticles) and surface amination reaction on Fe 3 O 4 /SiO 2 Amino is introduced to the surface of the nano-particles, and then the magnetic inner core and the N-carboxypropionyl chitosan sodium are combined together through glutaraldehyde crosslinking. In the preparation method of the invention, the Fe is treated 3 O 4 /SiO 2 The purpose of the surface amination treatment of the nano-particles is to make SiO 2 The wrapped magnetic core is firmly combined with the N-carboxypropionyl chitosan sodium, so that the stability of the adsorbent is improved.
The magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent prepared by the preparation method has good heavy metal ion selective adsorption, and the selective order is Pb 2+ ＞Cu 2+ ＞Cd 2+ . In the three ion coexisting system, when the addition amount is 2-6 g, the adsorbent is used for adsorbing Pb 2+ All show excellent selectivity performance to Cd 2+ Ions hardly adsorb at all, Pb 2 + Relative to Cd 2+ The selectivity coefficient of the copper-copper alloy can reach 36.68, and the copper-copper alloy is applied to Cu 2+ The selectivity coefficient of (A) can also reach 19.00. The principle is that carboxyl and amido oxygen in the N-carboxypropionyl chitosan sodium at the outermost layer of the adsorbent can coordinate heavy metal at the same time and can coordinate Pb with large hydrated ion radius 2+ Cd with good chelating property and small hydration radius 2+ And Cu 2+ When chelation is carried out, the structure of the molecule needs to be distorted, so that the adsorption process is more prone to coordination and ion exchange, and the selectivity is poor.
A magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent is prepared by the preparation method of any one of the above. The magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent is applicable to adsorption and removal of heavy metal ions in wastewater containing various heavy metal ions, and is simple to operate, strong in selectivity to specific metal ions, high in speed and stable in property when being applied to selective adsorption of heavy metal ions in wastewater.
An application of the magnetic cross-linking N-carboxypropionyl chitosan sodium adsorbent in selective adsorption of heavy metal ions in wastewater.
The specific operation is as follows:
when the magnetic cross-linking N-carboxypropionyl chitosan sodium adsorbent is used for selectively adsorbing heavy metal ions in wastewater, the magnetic cross-linking N-carboxypropionyl chitosan sodium adsorbent is directly put into the wastewater to be treated (wastewater to be treated). The magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent has the advantages of high heavy metal adsorption rate, strong selectivity, simple operation and great practical value.
Preferably, the heavy metal ion is Pb 2+ 、Cu 2+ 、Cd 2+ One or more of (a).
Preferably, the addition amount of the magnetic cross-linked N-carboxypropionyl chitosan sodium in the wastewater is 1-6 g/L. More preferably 2 to 3 g/L. Still more preferably 2 g/L.
Preferably, the concentration of the heavy metal ions is 10-100 mg/L. More preferably 10 to 50 mg/L.
Preferably, the pH value of the wastewater is 2-6. At higher pH, the heavy metals will form hydroxide precipitates, while at too low a pH, H + Competitive adsorption with heavy metal ions is formed. Therefore, the pH value of the wastewater is more preferably 3 to 6.
In order to ensure that the magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent is uniformly dispersed in a reaction system (wastewater to be treated), the reaction process (heavy metal adsorption process) is carried out by oscillating reaction through a constant-temperature oscillating box, and solid-liquid separation is realized by an external magnetic field after the reaction is finished.
Compared with the prior art, the invention has the following beneficial effects:
the preparation method of the magnetic cross-linking N-carboxypropionyl chitosan sodium adsorbent selects N-carboxypropionyl chitosan sodium as a main component, the component can provide bidentate ligand (simultaneously containing carboxyl and propionyl) to coordinate with metal ions, and the adsorption of the heavy metal ions is selective; and the operation is simple, and the industrial production is easy to realizeAnd (4) transforming. The magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent prepared by the preparation method has good adsorption performance, and can be applied to selective adsorption of heavy metal ions in wastewater for Pb 2+ The method has the advantages of strong selectivity, stable property, rapid separation through an external magnetic field, simple operation, low cost and higher practical value.
Drawings
FIG. 1 shows Fe in the examples 3 O 4 /SiO 2 /CPCTS, Fe in comparative example 1 3 O 4 Fe in comparative example 2 3 O 4 /SiO 2 And Fe in comparative example 3 3 O 4 /SiO 2 /CPCTS-Cu 2+ Fourier infrared absorption spectrum (FTIR);
in fig. 2: (a) each of (a) to (b) is Fe in examples 3 O 4 /SiO 2 A scanning electron microscope image of the CPCTS under different magnification;
(c) fe in comparative example 3 to (d) 3 O 4 /SiO 2 /CPCTS-Cu 2+ Scanning electron microscope images under different magnifications;
in fig. 3: (a) is Fe in the examples 3 O 4 /SiO 2 X-ray energy Spectrum of/CPCTS (EDS); (b) is Fe in comparative example 3 3 O 4 /SiO 2 /CPCTS-Cu 2+ X-ray energy spectrum (EDS);
in fig. 4: (a) is Fe in the examples 3 O 4 /SiO 2 The dispersion condition of CPCTS in water, and clear water on the left side is used for comparison;
(b) is Fe in the examples 3 O 4 /SiO 2 The CPCTS water dispersion system is subjected to magnetic separation, and clear water is arranged on the left side for comparison;
in fig. 5: (a) is Fe in the examples 3 O 4 /SiO 2 /CPCTS to Cu 2+ 、Pb 2+ 、Cd 2+ A time-dependent change curve of the adsorption amount of (c);
(b) is Fe in the examples 3 O 4 /SiO 2 /CPCTS to Cu 2+ 、Pb 2+ 、Cd 2+ Quasi-second order kinetic equation ofFitting a curve;
(c) is Fe in the examples 3 O 4 /SiO 2 /CPCTS to Cu 2+ 、Pb 2+ 、Cd 2+ Fitting a curve to the intra-particle diffusion model;
in fig. 6: (a) is Fe in the examples 3 O 4 /SiO 2 /CPCTS vs Pb 2+ Fitting curves to adsorbed Langmuir, Freundlich and Temkin isothermal adsorption models;
(b) is Fe in the examples 3 O 4 /SiO 2 /CPCTS to Cd 2+ Fitting curves to adsorbed Langmuir, Freundlich and Temkin isothermal adsorption models;
(c) is Fe in the examples 3 O 4 /SiO 2 CPCTS vs Cu 2+ Fitting curves to adsorbed Langmuir, Freundlich and Temkin isothermal adsorption models;
(d) is Fe in the examples 3 O 4 /SiO 2 /CPCTS vs Pb 2+ 、Cd 2+ 、Cu 2+ Curves were fitted to the adsorbed Dubinin-Radushkevich (D-R) isothermal adsorption model.
Detailed Description
The invention will now be further illustrated with reference to the following examples:
the raw materials used in the examples:
n-carboxypropionyl chitosan sodium (CPCTS) is purchased from Zhejiang Chitosan Biochemical Limited company, and the carboxylation degree is more than or equal to 60 percent; tetraethoxysilane (TEOS) is available from Acros Organics, USA, and has a purity>98 percent; 3-aminopropyltriethoxysilane (3-aminopropyltriethoxysilane, APTES) was purchased from Sigma-Aldrich, USA with a purity of 98% or more. Glutaraldehyde (GLA, 25 wt.%), ammonia (NH) 3 ·H 2 25-28 wt% of O, and ferric chloride (FeCl) 3 ·6H 2 O), anhydrous sodium acetate (NaAc), copper nitrate (Cu (NO) 3 ) 2 ·3H 2 O), lead nitrate (Pb (NO) 3 ) 2 ) Cadmium nitrate (Cd (NO) 3 ) 2 ·4H 2 O), ethylene glycol, ethanol, isopropanol were analytically pure and purchased from Shanghai national drug group. The water used for the experiment is ultrapure water (resistor)≥18.2MΩ·cm -1 )。
Examples
6.75g of FeCl 3 ·6H 2 Dissolving O and 18g NaAc in 250mL of ethylene glycol, magnetically stirring until the NaAc is completely dissolved, transferring the solution into a polytetrafluoroethylene high-temperature reaction kettle, and reacting in an oven at 200 ℃ for 8 hours. Cooling to room temperature after the reaction is finished, alternately cleaning for 4 times by using ethanol and water, separating by using a magnet, drying, and marking as Fe 3 O 4 And (3) nanoparticles.
2g of Fe obtained above 3 O 4 Dissolving the nano particles in 20mL of water, adding 80mL of absolute ethyl alcohol, performing ultrasonic treatment for 20min to completely disperse the nano particles, transferring the nano particles into a 250mL three-neck flask, and dropwise adding 1mL of ammonia water with the concentration of 28 wt% under mechanical stirring. After stirring for 30min, 1mL of TEOS was slowly added and the reaction was carried out at room temperature for 24 h. Separating with magnet after reaction, washing with deionized water and ethanol for 3 times, and oven drying to obtain SiO 2 Encapsulated Fe 3 O 4 Nanoparticles, denoted Fe 3 O 4 /SiO 2 And (3) nanoparticles.
Taking thoroughly dried Fe 3 O 4 /SiO 2 2.0g of nanoparticles are placed in a 500mL three-neck flask, 200mL of absolute ethyl alcohol is added, and ultrasonic treatment is carried out for 20min to completely disperse the nanoparticles. Slowly adding 2mLAPTES under strong stirring, and stirring for 24h at room temperature to carry out amination reaction. Separating with magnet after reaction, washing with water and ethanol for 3 times, and oven drying to obtain surface aminated Fe 3 O 4 /SiO 2 And (3) nanoparticles.
Taking aminated Fe 3 O 4 /SiO 2 Dissolving 2.0g of nano particles in 120mL of ethanol, and performing ultrasonic treatment for 20min to obtain Fe 3 O 4 /SiO 2 A nanoparticle dispersion. And dissolving 1.0g of carboxylated chitosan CPCTS in 80mL of deionized water to obtain the N-carboxypropionyl chitosan sodium aqueous solution. The dispersion and the aqueous solution were slowly mixed with mechanical stirring, and 10mL of a 25% glutaraldehyde solution was added dropwise to the mixed solution, followed by crosslinking reaction for 8 hours. After the reaction is finished, separating a magnet, washing the reaction product for three times by using ethanol, and drying the reaction product to obtain the magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent marked as Fe 3 O 4 /SiO 2 /CPCTS。
Comparative example 1
Fe 3 O 4 And (3) nanoparticles.
Comparative example 2
Is Fe obtained in example 3 O 4 /SiO 2 And (3) nanoparticles.
Comparative example 3
0.2g of Fe obtained in example 3 O 4 /SiO 2 the/CPCTS solution was put into a container containing 100mL of Cu (NO) at a concentration of 10mg/L (in terms of Cu) 3 ) 2 Oscillating the solution in a 250mL conical flask at constant temperature for 4 hours at room temperature, separating by a magnet, and drying to obtain the magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent with copper ions, which is marked as Fe 3 O 4 /SiO 2 /CPCTS-Cu 2+ 。
Characterization of the adsorbent 1
FIG. 1 shows Fe in the examples 3 O 4 /SiO 2 /CPCTS, Fe in comparative example 1 3 O 4 Fe in comparative example 2 3 O 4 /SiO 2 And Fe in comparative example 3 3 O 4 /SiO 2 /CPCTS-Cu 2+ Comparison graph of Fourier infrared absorption spectrum. Wherein Fe in comparative example 1 3 O 4 The three main peaks were located at 578.4, 1603.4 and 3407.1cm respectively -1 At position of 578.4cm -1 Is Fe 3 O 4 The characteristic stretching vibration peak of the middle Fe-O part, and the other two parts are O-H bending vibration and stretching vibration respectively. Fe in comparative example 2 3 O 4 /SiO 2 At 1096 and 1221cm -1 The shoulder peak and 460.2cm -1 Respectively, are caused by the asymmetric stretching vibration and the bending vibration of the Si-O bond, thereby confirming that SiO 2 Successful coating. 798cm -1 And 950cm -1 The small peaks at both positions are due to the symmetric stretching vibration of the Si-O bond and the bending vibration of Si-OH.
Fe in example, in comparison with comparative example 2 3 O 4 /SiO 2 The main change of/CPCTS occurs at 1200- -1 But due to the matrix Fe 3 O 4 /SiO 2 The peak intensity at this point is small, and it is highly likely that a plurality of peaks overlap each other to cause difficulty in recognition. At 1560cm -1 The newly appeared peak is antisymmetric stretching vibration of the carboxylate, and the N-carboxypropionyl chitosan sodium is proved to be introduced. At 1100cm -1 The increase in the width and strength of the absorption peak of (a) is likely to be caused by superposition of C-OH bond stretching vibration and Si-O bond vibration in N-carboxypropionyl chitosan sodium. At 3420cm -1 The peaks at the left and right are significantly slowed down because the N-H stretching vibration absorption peak and the O-H stretching vibration absorption peak associated with hydrogen bonds overlap each other due to the introduction of a large amount of amino groups and hydroxyl groups, forming a broadened multiple absorption peak.
When adsorbing Cu 2+ Then, Fe in comparative example 3 3 O 4 /SiO 2 /CPCTS-Cu 2+ Does not change significantly, but is 1560cm -1 The carboxylate antisymmetric stretching vibration peak of (a) becomes complicated, indicating that the oxygen atom in the carboxyl group reacts with Cu to cause the occurrence of multiple peaks.
Characterization of the adsorbent 2
FIG. 2 shows Fe 3 O 4 /SiO 2 Scanning electron microscope photographs of the copper ions before and after adsorption of the copper ions by CPCTS. As can be seen from the figure (a), the whole adsorbent is in the shape of particles formed by aggregating nanospheres, the particle size is between several microns and tens of microns, and the surface of the adsorbent is loose and irregular; (b) FIG. 2 is an enlarged scanning electron micrograph, Fe 3 O 4 /SiO 2 The particle size of CPCTS is about 500 nm. On the other hand, when copper ions were adsorbed, it was found from (c) and (d) that the overall surface morphology of the adsorbent did not change much.
FIG. 3 shows Fe in the examples 3 O 4 /SiO 2 The X-ray energy spectrograms before and after the copper ions are adsorbed by the CPCTS are shown in the table 1. Fe in the adsorbent was roughly calculated from the contents of Fe and Si elements in the examples in Table 1 3 O 4 、SiO 2 And the contents of crosslinked carboxylated chitosan were 76.97%, 14.72%, 8.31%, respectively. The presence of Cu was detected in comparative example 3, the surface content of which was about 0.62 wt%, confirming Fe 3 O 4 /SiO 2 The adsorption of Cu by CPCTS.
TABLE 1 Fe 3 O 4 /SiO 2 Content of each element before and after copper ion adsorption by CPCTS adsorbent
Fe 3 O 4 /SiO 2 /CPCTS C O Si Fe Cu
wt％ 7.73 29.66 6.87 55.74 /
at％ 17.21 49.56 6.54 26.68 /
Fe 3 O 4 /SiO 2 /CPCTS-Cu 2+ C O Si Fe Cu
wt％ 7.16 29.00 6.27 56.94 0.62
at％ 16.28 49.51 6.10 27.85 0.27
Sorbent performance testing
Performance test example 1
To determine the optimal reaction conditions, the study first selects Fe 3 O 4 /SiO 2 The effect of the addition of the adsorbent on the removal of copper ions was examined. As can be seen from Table 2, the adsorption removal rate increased with the addition of the adsorbent, wherein the removal rate reached 96.5% for 10mg/L of copper ions for 1 hour at an addition of 2.0g/L, although Cu was added at 2.5 and 3.0g/L 2+ The removal rate was higher, 98.8% and 99.5%, respectively, but from the economical point of view, it was more appropriate to select an addition amount of 2 g/L.
At this addition amount, Fe in comparative example 1 3 O 4 And Fe in comparative example 2 3 O 4 /SiO 2 For Cu 2+ The adsorption removal rates of (a) and (b) were 61.20% and 22.31%, respectively. Fe 3 O 4 Has abundant hydroxyl on the surface, so it is good for Cu 2+ Shows a certain absorptionAdsorption capacity, but Fe under acidic conditions 3 O 4 Unstable and its selectivity is poor. Magnetic Fe by assembling layers of nuclear shell material 3 O 4 Acid-resistant SiO 2 The composite adsorbent is coated on the innermost layer, and the surface of the composite adsorbent is coated by the crosslinked N-carboxypropionyl chitosan sodium, so that the composite adsorbent has higher adsorption capacity and good stability due to the existence of carboxyl.
Fe in the examples 3 O 4 /SiO 2 the/CPCTS (2g/L) is added into 0.1mol/L hydrochloric acid, the mixture is subjected to constant temperature oscillation reaction for 12 hours, the magnet is separated, the permeation amount of Fe in the supernatant is respectively 9.5mg/L and only accounts for 0.85 percent of the total iron content by ICP-MS, the adsorbent shows stronger acid resistance, and the adsorbent can be safely applied to removal of heavy metal ions under the weak acidic condition. After the reaction is finished, the adsorbent can be rapidly separated by using an external magnetic field (the separation effect is shown in figure 4), so that the method is favorable for industrial popularization and application.
TABLE 2 different adsorbents and addition levels to Cu 2+ (10mg/L) adsorption removal rate of 1 hour
Adsorbent and process for producing the same Addition amount (g/L) Cu 2+ Removal Rate (%)
Fe 3 O 4 /SiO 2 /CPCTS 1.0 58.14
Fe 3 O 4 /SiO 2 /CPCTS 1.5 81.14
Fe 3 O 4 /SiO 2 /CPCTS 2.0 96.51
Fe 3 O 4 /SiO 2 /CPCTS 2.5 98.83
Fe 3 O 4 /SiO 2 /CPCTS 3.0 99.50
Fe 3 O 4 2.0 61.20
Fe 3 O 4 /SiO 2 2.0 22.31
Performance test example 2
Adsorption kinetics experiments were performed in 250mL erlenmeyer flasks. 0.1g of each prepared adsorbent sample was added to 50mL of a sample containing Cu 2+ 、Cd 2+ 、Pb 2+ The solution (30mg/L) was put in a constant temperature vibration box after the flask was closed, and the reaction was shaken at 135rpm at 25 ℃. And in a certain time interval, taking out a part of samples, then carrying out magnet separation, taking supernatant, immediately measuring by using a precise millivoltmeter and a copper ion selective electrode, a lead ion selective electrode and a cadmium ion selective electrode, and calculating the residual concentration of metal ions and the adsorption quantity.
Adsorption kinetics experiment researches Fe 3 O 4 /SiO 2 /CPCTS to Cu 2+ 、Cd 2+ And Pb 2+ And fitting the data by using a quasi-second order kinetic equation and an intra-particle diffusion equation, wherein the fitting result and related parameters are shown in fig. 5 and table 3.
As can be seen from the graph (a) in fig. 5, the adsorption of the three metal ions is very unstable in the first 40min, and the equilibrium is substantially reached around 180 min. According to the graphs (b) and (c) in FIG. 5 and the comparison correlation coefficient R 2 Is considered to be Cu 2+ 、Cd 2+ And Pb 2+ Adsorption on this adsorbent was more consistent with a quasi-secondary kinetic model, which is also consistent with the results of many adsorption studies with linear correlation coefficients of 0.99, 0.95 and 0.98, respectively. Generally, the quasi-second order kinetic equation includes all the adsorption processes such as external liquid film diffusion, surface adsorption and intra-particle diffusion, so that the adsorption mechanism can be more comprehensively reflected. When the particle internal diffusion model is adopted for fitting, the curve is obviously divided into two sections, and the second section adsorbs Pb 2+ 、Cd 2+ And Cu 2+ The linear correlation coefficients of (a) are 0.93, 0.91 and 0.83 respectively, indicating that the diffusion process is also divided into two stages, the first stage is mass diffusion in which the adsorbate is transferred from the solution to the surface of the adsorbent, and the second stage is diffusion of the adsorbate inside the particle. The intra-particle diffusion equation curve does not cross the origin, indicating that the process is not the only rate-dependent step, the adsorption rate is controlled by the combination of actions such as surface adsorption and liquid film diffusion, the intercept of the fitted curve is proportional to the thickness of this boundary layer, and thus the whole adsorption process is the result of a plurality of kinetic interactions.
From the above, Fe 3 O 4 /SiO 2 The adsorption process of the CPCTS on the three heavy metal ions mainly takes physical adsorption within the first 40min, the speed is high but the adsorption process is unstable, and then the physical adsorption gradually reaches the equilibrium and is replaced by chemical adsorption through complexation, coordination or chelation.
TABLE 3 fitting results of three metal ion adsorption reaction rate equations
Figure BDA0003532477550000121
Figure BDA0003532477550000131
Performance test example 3
The adsorption thermodynamics experiments were performed in 50mL Erlenmeyer flasks. 0.04g of each prepared adsorbent sample was added to 20mL of a sample containing Cu 2+ 、Cd 2+ 、Pb 2+ Sealing the conical flask in a solution (10-50 mg/L), placing in a constant temperature vibration box, oscillating at 25 ℃ at 135rpm for 12 hours, separating with a magnet after the reaction is finished, taking the supernatant, measuring the residual concentration of metal ions with an ion selective electrode, and calculating the equilibrium adsorption capacity.
Fe at 298K was analyzed by thermodynamic experiments 3 O 4 /SiO 2 /CPCTS to Cu 2+ 、Cd 2+ And Pb 2+ Three metal ion adsorption mechanisms. The adsorption thermodynamic data were fitted using Langmuir, Freundlich, Temkin and D-R isothermal adsorption models, and the fitting results and relevant parameters are shown in FIG. 6 and Table 4. By comparing R 2 Size, it can be seen that the adsorption mechanism of the three metal ions is not completely the same, among which Pb 2+ More suitable for Langmuir equation, while Cd 2+ And Cu 2+ The Freundlich and D-R equations are fit, respectively. The order of magnitude of the saturated adsorption amounts calculated by the Langmuir equation is Pb 2+ >Cu 2+ >Cd 2+ 21.01, 16.17 and 12.76mg/g, respectively. Calculation of Pb from D-R model 2+ 、Cd 2+ And Cu 2+ The average free energies of adsorption of (1) and (b) were 16.09, 11.72 and 11.36kJ/mol, respectively, indicating that the adsorbent is resistant to Pb 2+ Adsorption of (2) is chemical adsorption, and for Cd 2+ And Cu 2+ Mainly ion exchange.
TABLE 4 fitting parameters and correlation coefficients of isothermal adsorption models
Figure BDA0003532477550000132
Figure BDA0003532477550000141
Performance test example 4
Since heavy metal ions hydrolyze under neutral or basic conditions, interfering with the adsorption process, only acidic conditions are considered when investigating the effect of pH. As can be seen from Table 5, Fe at pH 6 3 O 4 /SiO 2 The removal rate of 30mg/L lead ions by/CPCTS is the maximum and is 96.3%, and the removal rate gradually decreases with the decrease of pH. According to other studies, Fe 3 O 4 /SiO 2 The carboxyl in the CPCTS adsorbent is a main adsorption active site, and adsorbs heavy metal ions through complexation or ion exchange, and H is generated along with the enhancement of acidity + The competitive adsorption with heavy metal ions is gradually enhanced, and the complexation or ion exchange action is weakened, so that the adsorption removal rate is reduced.
TABLE 5 Fe at different pH 3 O 4 /SiO 2 Adsorption removal rate of lead ions (30mg/L) by CPCTS
pH 2 3 4 5 6
Removal Rate (%) 82.1 89.6 90.6 93.8 96.3
Performance test example 5
The selective adsorption experiments were performed in 50mL erlenmeyer flasks. 0.04g, 0.08g and 0.12g of the prepared adsorbent samples were added to 20mL of a sample containing Cu 2+ 、Cd 2+ 、Pb 2+ In each 50mg/L mixed solution, the conical flask is sealed and then placed in a constant temperature vibration box, the mixture is shaken at the speed of 135rpm for 12 hours at the temperature of 25 ℃, after the reaction is finished, the magnet is separated, the supernatant is taken and used for measuring the residual concentration of metal ions by ICP-MS, and the distribution coefficient and the selectivity coefficient are calculated.
When two or more metal ions are present in a solution, competitive adsorption occurs between the different ions. In this study by adding Cu 2+ 、Cd 2+ 、Pb 2+ Different amounts of adsorbent (Fe) were added to the mixed solutions (50 mg/L each) 3 O4/SiO 2 CPCTS), selective adsorption performance was observed for different ions, and the associated results and data are shown in table 6.
TABLE 6 removal rate (%) and distribution coefficient K of each ion at different addition amounts d (L/g) and Selectivity coefficient
Figure BDA0003532477550000151
As can be seen from the removal rates and partition coefficients of the three ions in Table 6, Fe 3 O 4 /SiO 2 The selective sequence of the CPCTS adsorbent to the three ions is Pb in sequence 2+ ＞Cu 2+ ＞Cd 2+ This is consistent with the saturated adsorption data calculated from the Langmuir isothermal adsorption equation. When the adding amount is 2-6 g, the adsorbent shows excellent effect on leadGood selectivity for Cd 2+ The ions hardly adsorb. When the adding amount is 6g/L, Pb 2+ Relative to Cd 2+ Has a selectivity coefficient as high as 36.68, and for Cu 2+ The selectivity coefficient of the catalyst also reaches 19.00, so that the catalyst is hopefully applied to the separation and recovery of heavy metals in wastewater, particularly copper-lead mixed wastewater and lead-cadmium mixed wastewater.
Fe 3 O4/SiO 2 Carboxyl and amido oxygen on CPCTS at the outer layer of the/CPCTS can coordinate heavy metals at the same time, so that the adsorbent shows stronger chelation. Conjecture with thermodynamic data, Pb 2+ The larger radius of the hydrated ion may be the main reason for the higher selectivity, because of the limitation of the molecular structure, when Cd has a smaller radius of hydration 2+ And Cu 2+ When chelation is performed, the structure of the molecule needs to be distorted, and thus the adsorption process is more prone to coordination and ion exchange.

Claims (10)

1. A preparation method of a magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent is characterized by comprising the following steps:
(1) from SiO 2 Encapsulated Fe 3 O 4 The nano particles and 3-aminopropyl triethoxysilane react in solvent to obtain surface aminated Fe 3 O 4 /SiO 2 A nanoparticle;
(2) by amination of Fe 3 O 4 /SiO 2 Mixing the nano particles with N-carboxypropionyl chitosan sodium, and adding glutaraldehyde to perform a crosslinking reaction to obtain the magnetic crosslinked N-carboxypropionyl chitosan sodium adsorbent.
2. The method of claim 1, wherein the adsorbent is prepared by reacting 3-aminopropyltriethoxysilane with Fe 3 O 4 /SiO 2 The volume-mass ratio of the nanoparticles is (0.25-4): 1 mL/g;
the solvent is one or the mixture of isopropanol and absolute ethyl alcohol.
3. The method of claim 1, wherein the N-carboxypropionyl chitosan sodium is reacted with aminated Fe 3 O 4 /SiO 2 The mass ratio of the nano particles is (0.1-2): 1.
4. the preparation method of the magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent according to claim 1, wherein the volume mass ratio of the glutaraldehyde to the N-carboxypropionyl chitosan sodium is (1-4): 1 mL/g.
5. The method for preparing the magnetically cross-linked N-carboxypropionyl chitosan sodium adsorbent of claim 1, wherein the adsorbent is prepared from SiO 2 Encapsulated Fe 3 O 4 The preparation process of the nano-particles is as follows:
adding tetraethoxysilane to Fe 3 O 4 Reacting in ethanol water solution of nano particles to prepare the SiO 2 Encapsulated Fe 3 O 4 And (3) nanoparticles.
6. The method of claim 5 wherein the adsorbent is prepared by mixing tetraethoxysilane with Fe 3 O 4 The volume-mass ratio of the nanoparticles is (0.2-4): 1 mL/g.
7. A magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent, which is prepared by the preparation method of any one of claims 1 to 6.
8. Use of the magnetically cross-linked N-carboxypropionyl chitosan sodium adsorbent of claim 7 for selectively adsorbing heavy metal ions in wastewater.
9. Use according to claim 8, wherein the heavy metal ion is Pb 2+ 、Cu 2+ 、Cd 2+ AOr a plurality thereof.
10. The use of claim 8, wherein the magnetic cross-linked N-carboxypropionyl chitosan sodium is added in an amount of 1-6 g/L in wastewater; the concentration of the heavy metal ions is 10-100 mg/L; the pH value of the wastewater is 2-6.
CN202210209274.6A 2022-03-04 2022-03-04 Preparation method, product and application of magnetic cross-linked N-carboxypropionyl chitosan sodium adsorbent Pending CN114797786A (en)

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