CN114752002A - Organic modified chitosan adsorbent for removing PFASs, preparation method and application - Google Patents

Organic modified chitosan adsorbent for removing PFASs, preparation method and application Download PDF

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CN114752002A
CN114752002A CN202210356839.3A CN202210356839A CN114752002A CN 114752002 A CN114752002 A CN 114752002A CN 202210356839 A CN202210356839 A CN 202210356839A CN 114752002 A CN114752002 A CN 114752002A
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林辉
梁逸扬
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Dongguan University of Technology
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Abstract

The invention discloses an organic modified chitosan adsorbent for removing PFASs, a preparation method and application thereof, wherein chitosan is used as an original modified substrate, and is modified by 3-aminopropyltriethoxysilane and 3-chloro-2-hydroxypropylammonium chloride to obtain the organic modified chitosan adsorbent, the maximum adsorption capacity of PFOA can reach 3730.2mg/g, and the organic modified chitosan adsorbent also has better removal efficiency for other common PFASs. The invention has the characteristics of abundant raw material reserves, wide sources, low price, good chemical and mechanical stability, large amount of amino active groups on the surface and the like, and the preparation method is simple and feasible, meets the requirement of industrial development in practicability and cost benefit, and has quite industrial utilization value. The PFASs removing adsorbent provided by the invention has stable physical and chemical properties, has greater potential in the treatment of fluorine-containing industrial wastewater, and is particularly suitable for purification treatment of medium-and-low-concentration PFASs.

Description

Organic modified chitosan adsorbent for removing PFASs, preparation method and application
Technical Field
The invention relates to the technical field of environment restoration of polyfluoro and perfluoroalkyl substances, in particular to an organic modified chitosan adsorbent for removing PFASs, a preparation method and application thereof.
Background
Perfluoro and polyfluoroalkyl group compounds (perfluoroalkyl and polyfluoroalkyl subsst)Naces, PFASs) is a type of artificially synthesized compound in which all or more of the hydrogen atoms bonded to carbon atoms are completely substituted with fluorine atoms to form a compound containing C in whole or in partnF2n+1-new persistent organically combined contamination of the radicals. Because of the unique characteristics of hydrophobicity, oleophobicity, strong chemical stability, high surface activity and the like, the coating can bear illumination and high temperature, and is widely applied to daily supplies, foam extinguishment, surfactant emulsifiers and the like. It has high-energy C-F bond (116kcal/mol) and helical structure, so that it has the features of good chemical stability and strong durability, once it is made and treated, it can not be naturally degraded, so that it is known as "permanent chemical", so that it can be continuously detected in various environmental media and organisms in the global field in recent years. Among them, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are the 2 compounds currently used in the largest amount in the industry, and are representative PFASs. In addition, PFASs has long-distance transmission capability, high water solubility (PFOS and PFOA solubility are 570mg/L and 3.4g/L respectively), can cause pollution of seawater, underground water and drinking water, and PFOS/PFOA pollution in waste water of garbage percolate, fluorine chemical industry, semiconductor industry and the like is particularly serious, wherein the PFOS concentration in chromium plating waste water can reach 1380mg/L, and the PFOS-containing water is a water body with the highest PFOS content in waste water of the current industry. These compounds are of great interest for their bioaccumulation, environmental tolerance and potential toxicity in a variety of organisms as well as various toxicities.
At present, in domestic and foreign researches, no report is provided for degrading PFASs by using a biological method, and domestic and foreign removal methods aiming at PFASs in water can be divided into two main types, wherein the first type is a physical method and comprises a membrane treatment method, a coagulating sedimentation method and the like; the second type is a chemical method such as an electrochemical oxidation method, an advanced oxidation method, a photocatalytic oxidation method, and the like. Most of these methods have the disadvantages of complicated operation, high processing cost, and long time period. The adsorption method has the characteristics of high adsorption efficiency, high speed, large adsorption capacity and the like, and is widely applied to the treatment of water body environmental pollution.
The chitosan exists in the shells of crustaceans, such as shrimp shells, crab shells, cicada slough and the like in a large amount, contains a large amount of amino and hydroxyl groups on the surfaces, has a plurality of unique properties such as biodegradability, cell affinity, biological effect and the like, and is the only basic polysaccharide in natural polysaccharides. The amino group in the molecular structure of the chitosan has stronger reactivity, so that the polysaccharide has excellent biological functions and the possibility of chemical modification. In addition, the storage capacity of chitosan in the world is very rich, and the chitosan has great application value in the field of environmental protection due to the unique molecular structure, excellent adsorption performance and low cost, and the application of the chitosan in wastewater treatment is widely regarded.
However, when the existing chitosan is used in wastewater containing fluorine, the adsorption capacity of the chitosan to PFASs is relatively small, and the removal effect of the chitosan to PFASs is not obvious.
Disclosure of Invention
In view of the above, the present invention provides an organically modified chitosan adsorbent for removing pfas, a preparation method and an application thereof, which solve the problems that when chitosan is used in fluorine-containing wastewater, the adsorption amount of the chitosan on pfas is relatively small, and the removal effect on pfas is not very obvious.
In order to achieve the purpose, the invention adopts the following technical scheme: an organic modified chitosan adsorbent for removing PFASs, wherein an original chitosan matrix is modified to obtain hydrophobic and lipophilic organic modified chitosan, the organic modified chitosan comprises a plurality of modified unimers, and the chemical formula of each modified unimer is as follows:
Figure BDA0003583389560000031
in one embodiment, the chitosan original matrix is modified by 3-aminopropyltriethoxysilane and 3-chloro-2-hydroxypropylammonium chloride in sequence to obtain the organically modified chitosan; the chemical formula of the 3-aminopropyltriethoxysilane is as follows:
Figure BDA0003583389560000032
the chemical formula of the 3-chloro-2-hydroxypropyl ammonium chloride is shown as follows.
Figure BDA0003583389560000033
A preparation method of an organic modified chitosan adsorbent for removing PFASs comprises the following steps:
(1) adding 0.5-5 mL of the 3-aminopropyltriethoxysilane into a 50% ethanol organic solution, mixing and stirring for 1-3 h to obtain a prehydrolyzed aminosilane solution to obtain a solution A1;
(2) 1-5 g of the chitosan original matrix is added and dispersed in the solution A1, a sealing film is used for sealing, magnetic stirring is carried out for 6-8 h under the condition of water bath at the temperature of 70-80 ℃, then, suction filtration is carried out, the solid left on a filter membrane is an organic silicon modified chitosan crude product, and 50% ethanol solution is used for washing for 3 times;
(3) placing the crude product of the organic silicon modified chitosan obtained in the step (2) in a vacuum drying oven, and carrying out vacuum drying for 2-5 h at the temperature of 70-90 ℃ to remove the residual 50% ethanol solution on the surface of the crude product of the organic silicon modified chitosan;
(4) adding 0.5-3 g of the dry organic silicon modified chitosan crude product obtained in the step (3), 30-50 mL of 35% by mass sodium hydroxide solution and isopropanol into a flask, heating to 50-80 ℃ under stirring, and alkalifying for 4-6 h to obtain organic silicon modified chitosan alkali liquor A2;
(5) slowly dripping 1-10 mL of the 3-chloro-2-hydroxypropyl ammonium chloride solution with the mass fraction of 65% into the A2 solution, controlling the dripping speed and the material temperature to be not higher than 50 ℃, heating to 70-90 ℃ after finishing dripping, and reacting at constant temperature for 6-8 hours to obtain a modified chitosan solution A3;
(6) Adjusting the pH value of the A3 solution to 7 by using dilute hydrochloric acid, carrying out suction filtration, repeatedly soaking the obtained product by using methanol for three times, washing the product by using absolute ethyl alcohol for three times to obtain wet modified chitosan, transferring the wet modified chitosan to a vacuum drying oven, and drying the wet modified chitosan at the temperature of 70-90 ℃ for 12-18 hours to obtain a dried modified chitosan sample;
(7) and (4) grinding the modified chitosan sample dried in the step (6) and sieving the ground sample with a 200-mesh sieve to obtain a sample with the particle size of not more than 0.074mm, namely the hydrophobic and lipophilic organic modified chitosan.
In one embodiment, the amount of 3-aminopropyltriethoxysilane added in step (1) is 9.6-96 mL/L.
In one embodiment, the dosage of the chitosan in the solution A1 in the step (2) is 19.3-96.5 g/L.
In one embodiment, the amount of the sodium hydroxide added to the solution A2 in the step (4) is 300-500 mL/L, and the amount of the silicone chitosan added is 5-30 g/L.
In one embodiment, the amount of the 3-chloro-2-hydroxypropylammonium chloride added to the solution A3 in the step (5) is 10 to 100 mL/L.
The application of the organic modified chitosan adsorbent for removing PFASs comprises the following steps:
s1: directly throwing the organic modified chitosan with hydrophobicity and lipophilicity into waste water containing PFASs;
S2: adsorbing under stirring or oscillation conditions to ensure that the organic modified chitosan is fully contacted with PFASs wastewater;
s3: and naturally settling and depositing the organic modified chitosan after adsorption at the bottom, and removing the organic modified chitosan by filtering.
In one embodiment, the stirring in S2 is continued for at least 180min at 15-35 ℃ and 200-800 rpm.
In one embodiment, the concentration of PFASs in the S1 is 50mg/L, and the solid-to-liquid ratio of the organic modified chitosan to PFASs wastewater is 100 mg/L.
Compared with the prior art, the invention has obvious advantages and beneficial effects, and specifically, the technical scheme includes that:
1. according to the organic modified chitosan adsorbent for removing PFASs, chitosan is used as an original modified substrate, and is modified by 3-aminopropyltriethoxysilane and 3-chloro-2-hydroxypropylammonium chloride to obtain the organic modified chitosan adsorbent, the maximum adsorption capacity of PFOA can reach 3730.2mg/g, and the organic modified chitosan adsorbent has good removal efficiency for other common PFASs.
2. The invention has the characteristics of abundant raw material reserves, wide sources, low price, good chemical and mechanical stability, large amount of amino active groups on the surface and the like, and the preparation method is simple and feasible, meets the requirement of industrial development in practicability and cost benefit, and has quite industrial utilization value.
3. The PFASs removing adsorbent provided by the invention has stable physical and chemical properties, has greater potential in the treatment of fluorine-containing industrial wastewater, and is particularly suitable for purification treatment of medium-and-low-concentration PFASs.
In order to more clearly illustrate the structural features and effects of the present invention, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.
Drawings
FIG. 1 is a molecular structure diagram of an organic modified chitosan composed of three modified monomers;
FIG. 2 is an adsorption isotherm curve of the organically modified chitosan adsorbent prepared in the example of the present invention on perfluorooctanoic acid;
fig. 3 is a comparison of kinetic models of perfluoro caprylic acid with organically modified chitosan adsorbent, chitosan, powdered activated carbon, and granular activated carbon prepared in the examples of the present invention, wherein (a) is a pseudo first order kinetic model and (b) is a pseudo second order kinetic model.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application clearer, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
It will be understood that when an element is referred to as being "secured to" or "disposed on" another element, it can be directly on the other element or be indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or be indirectly connected to the other element.
It will be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like, as used herein, refer to an orientation or positional relationship indicated in the drawings that is solely for the purpose of facilitating the description and simplifying the description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be considered as limiting the present application.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "a plurality" means two or more unless specifically limited otherwise.
The application provides an organic modified chitosan adsorbent for removing PFASs, wherein an original chitosan matrix is modified to obtain hydrophobic and lipophilic organic modified chitosan, and the chemical formula of the organic modified chitosan is as follows:
Figure BDA0003583389560000071
for a more intuitive understanding of the chemical formula of the organically modified chitosan, fig. 1 shows the organically modified chitosan composed of three modified monomers.
The modified organic modified chitosan adsorbent effectively adsorbs PFASs in a water body under the action of hydrophobic interaction force and electrostatic interaction force. And the organic modified chitosan has high adsorption capacity and can quickly adsorb PFASs in a water body.
Illustratively, the organically modified chitosan adsorbent reaches adsorption equilibrium within 180 min; the maximum adsorption capacity of the adsorbent on the perfluorooctanoic acid is 3730.2mg/g, under the condition that the concentration of various polyfluorinated and perfluoroalkyl substances is 50mg/L, the adsorption capacity on the perfluorooctanoic acid (PFOA) can reach 437.8mg/g, the adsorption capacity on Perfluorosulfonate (PFOS) can reach 426.7mg/L, the adsorption capacity on perfluorobutyric acid (PFBA) can reach 257.2mg/g, and the adsorption capacity on perfluorobutylsulfonic acid (PFBS) can reach 419.4 mg/g.
In one embodiment, the chitosan original matrix is modified by 3-aminopropyltriethoxysilane and 3-chloro-2-hydroxypropylammonium chloride in sequence to obtain the organically modified chitosan; the chemical formula of the 3-aminopropyltriethoxysilane is as follows:
Figure BDA0003583389560000081
The chemical formula of the 3-chlorine-2-hydroxypropyl ammonium chloride is as follows.
Figure BDA0003583389560000082
3-aminopropyltriethoxysilane is a compound having a-NH group at the end2The silane coupling agent of the group can be grafted to the surface of the original chitosan matrix through organic modification, so that the hydrophobicity of the surface of the chitosan is enhanced, and the adsorption effect on the perfluorooctanoic acid is improved. The silanol hydrolyzed by 3-aminopropyltriethoxysilane is condensed with the hydroxyl on the surface of chitosan to further form a stable N-O-Si ion covalent bond, which is the direct grafting of chitosan. In addition, oligomers formed by condensation between hydrolyzed silanes may further link to chitosan through covalent and hydrogen bonds.
The 3-chlorine-2-hydroxypropyl ammonium chloride is an important quaternary ammonium salt type cation etherifying agent and an important organic intermediate, and is widely used for modifying natural high molecular compounds containing active hydrogen groups, such as chitosan, starch, cellulose, lignin and the like.
The organic modified chitosan adsorbent obtained by modifying 3-aminopropyltriethoxysilane and 3-chloro-2-hydroxypropylammonium chloride has the maximum adsorption capacity of 3730.2mg/g for PFOA, and has good removal efficiency for other common PFASs.
A preparation method of an organic modified chitosan adsorbent for removing PFASs comprises the following steps:
(1) adding 0.5-5 mL of the 3-aminopropyltriethoxysilane into a 50% ethanol organic solution, mixing and stirring for 1-3 h to obtain a prehydrolyzed aminosilane solution to obtain a solution A1;
(2) dispersing 1-5 g of the chitosan original matrix in a solution A1, sealing by using a sealing film, magnetically stirring for 6-8 h under the water bath condition of 70-80 ℃, then performing suction filtration, wherein the solid left on the filter membrane is an organic silicon modified chitosan crude product, and washing for 3 times by using a 50% ethanol solution;
(3) placing the crude product of the organic silicon modified chitosan obtained in the step (2) in a vacuum drying oven, and performing vacuum drying for 2-5 hours at the temperature of 70-90 ℃ to remove the residual 50% ethanol solution on the surface of the crude product of the organic silicon modified chitosan;
(4) adding 0.5-3 g of the dry organic silicon modified chitosan crude product obtained in the step (3), 30-50 mL of 35% sodium hydroxide solution and isopropanol into a flask, heating to 50-80 ℃ under stirring, and alkalifying for 4-6 h to obtain organic silicon modified chitosan alkali liquor A2;
(5) Slowly dripping 1-10 mL of the 3-chloro-2-hydroxypropyl ammonium chloride solution with the mass fraction of 65% into the A2 solution, controlling the dripping speed, controlling the material temperature to be not higher than 50 ℃, heating to 70-90 ℃ after finishing dripping, and reacting for 6-8 hours at constant temperature to obtain a modified chitosan solution A3;
(6) adjusting the pH value of the A3 solution to 7 by using dilute hydrochloric acid, carrying out suction filtration, repeatedly soaking the obtained product by using methanol for three times, washing the product by using absolute ethyl alcohol for three times to obtain wet modified chitosan, transferring the wet modified chitosan to a vacuum drying oven, and drying the wet modified chitosan at the temperature of 70-90 ℃ for 12-18 hours to obtain a dried modified chitosan sample;
(7) and (4) grinding the modified chitosan sample dried in the step (6) and sieving the ground sample with a 200-mesh sieve to obtain a sample with the particle size of not more than 0.074mm, namely the hydrophobic and lipophilic organic modified chitosan.
The preparation principle of the organic modified chitosan without PFASs is that silanol obtained by hydrolyzing 3-aminopropyltriethoxysilane is condensed with hydroxyl on the surface of chitosan to further form stable N-O-Si ionic covalent bonds, and oligomers formed by condensation between hydrolyzed silanes can be further connected with chitosan through covalent bonds and hydrogen bonds to improve the hydrophobic acting force on the surface of chitosan. Chitosan swells in isopropanol and then is alkalized to form an activation center, and then is modified by etherification, graft copolymerization and other reactions with an etherifying agent with a quaternary ammonium salt group, so that the quaternary ammonium salt is loaded on the surface of the chitosan, the electrostatic attraction of the surface is improved, and a large number of ion exchange sites are provided for PFASs anions.
The invention has the characteristics of abundant raw material reserves, wide sources, low price, good chemical and mechanical stability, large amount of amino active groups on the surface and the like, and the preparation method is simple and feasible, meets the requirement of industrial development in practicability and cost benefit, and has quite industrial utilization value.
The adsorbent prepared by the preparation method has stable physical and chemical properties, has greater potential in the treatment of fluorine-containing industrial wastewater, and is particularly suitable for the purification treatment of medium-low concentration PFASs.
In one embodiment, the amount of 3-aminopropyltriethoxysilane added in step (1) is 9.6-96 mL/L. The adding amount of the chitosan in the solution A1 in the step (2) is 19.3-96.5 g/L. The adding amount of the sodium hydroxide in the solution A2 in the step (4) is 300-500 mL/L, and the adding amount of the organic silicon chitosan is 5-30 g/L. In the step (5), the adding amount of the 3-chloro-2-hydroxypropyl ammonium chloride in the solution A3 is 10-100 mL/L.
The application of the organic modified chitosan adsorbent for removing PFASs comprises the following steps:
s1: directly throwing the organic modified chitosan with hydrophobicity and lipophilicity into waste water containing PFASs;
s2: adsorbing under stirring or oscillation conditions to ensure that the organic modified chitosan is fully contacted with PFASs wastewater;
S3: and naturally settling the organic modified chitosan after adsorption, depositing the organic modified chitosan at the bottom, and filtering to remove the organic modified chitosan.
In one embodiment, the stirring in S2 is continued for at least 180min at 15-35 ℃ and 200-800 rpm. The concentration of PFASs in the S1 is 50mg/L, and the solid-to-liquid ratio of the organic modified chitosan to PFASs wastewater is 100 mg/L. Under the environment, the removal rate of the organic modified chitosan to the perfluorooctanoic acid (PFOA) reaches more than 95%, the adsorption capacity reaches 437.8mg/g, the adsorption capacity to the Perfluorosulfonate (PFOS) is 426.7mg/L, the adsorption capacity to the perfluorobutyric acid (PFBA) is 257.2mg/g, and the adsorption capacity to the perfluorobutylsulfonic acid (PFBS) is 419.4 mg/g.
The following is described with reference to specific examples:
1mL of 3-aminopropyltriethoxysilane was added to 50mL of 50% ethanol organic solution and mixed for 2h to obtain a prehydrolyzed aminosilane solution to obtain solution A1.
Dispersing 2g of chitosan in the solution A1, sealing with a sealing film, magnetically stirring for 8h under the condition of a water bath at 75 ℃, performing suction filtration, wherein the solid remained on the filter membrane is an organosilicon modified chitosan crude product, and washing for 3 times with 50% ethanol solution, wherein the washing amount of ethanol for each time is 20 mL.
And (3) placing the crude product of the organic silicon modified chitosan into a vacuum drying oven, and carrying out vacuum drying for 2h at the temperature of 90 ℃ to remove the residual 50% ethanol solution on the surface of the crude product of the organic silicon modified chitosan.
Adding 1g of dry organic silicon modified chitosan, 30mL of 35% sodium hydroxide solution and isopropanol into a round-bottom flask, heating to 50 ℃ under stirring, and alkalifying for 4 hours to obtain organic silicon modified chitosan alkali liquor A2.
Slowly dropwise adding 5mL of 65 mass percent 3-chloro-2-hydroxypropyl ammonium chloride solution into the A2 solution, controlling the dropwise adding speed and the material temperature to be not higher than 50 ℃, heating to 70 ℃ after the dropwise adding is finished, and reacting at constant temperature for 7 hours to obtain a modified chitosan solution A3.
Adjusting the pH value of the A3 solution to 7 by using 0.1M dilute hydrochloric acid, then carrying out suction filtration, repeatedly soaking the obtained product by using methanol for three times, washing the product by using absolute ethyl alcohol for three times to obtain wet modified chitosan, transferring the wet modified chitosan to a vacuum drying oven, and drying the wet modified chitosan at the temperature of 90 ℃ for 12 hours to obtain a dried modified chitosan sample;
and grinding the dried modified chitosan sample and sieving the ground sample with a 200-mesh sieve to obtain a sample with the particle size of not more than 0.074mm, namely the organic modified chitosan adsorbent.
The adsorption experiment of PFASs sewage by using the organically modified chitosan prepared by the method of the embodiment further illustrates the invention, and the result shows that: when the concentration of PFOA is 0.25mg/L, 50mg of modified chitosan prepared by the method is put into 500mL of PFOA wastewater at 25 ℃ for constant-temperature adsorption for 180min to obtain the adsorption quantity of 2.5mg/g and the removal rate of 99.2%.
When the concentration of PFOA is 1mg/L, 50mg of modified chitosan prepared by the method is put into 500mL of PFOA wastewater at 25 ℃ for constant-temperature adsorption for 180min to obtain the adsorption quantity of 8.8mg/g and the removal rate of 87.6%.
When the concentration of PFOA is 10mg/L, 50mg of modified chitosan prepared by the method is put into 500mL of PFOA wastewater at 25 ℃ for constant-temperature adsorption for 180min to obtain the adsorption quantity of 84.2mg/g and the removal rate of 84.2%.
When the concentration of PFOA is 50mg/L, 50mg of the modified chitosan prepared by the method is put into 500mL of PFOA wastewater at 25 ℃ for constant-temperature adsorption for 180min to obtain the adsorption quantity of 512.8mg/g and the removal rate of 95.6%.
When the concentration of PFOA is 100mg/L, 50mg of modified chitosan prepared by the method is put into 500mL of PFOA wastewater at 25 ℃ for constant-temperature adsorption for 180min to obtain the adsorption quantity of 124.0mg/g and the removal rate of 87.6%.
When the concentration of PFOA is 400mg/L, 50mg of modified chitosan prepared by the method is put into 500mL of PFOA wastewater at 25 ℃ for constant-temperature adsorption for 180min to obtain the adsorption quantity of 3345.9mg/g and the removal rate of 67.0%.
When the concentration of PFASs is 50mg/L, 50mg of the modified chitosan prepared by the method is put into 500mL of PFASs wastewater at 25 ℃ for constant-temperature adsorption for 180min, the adsorption capacity to Perfluorosulfonate (PFOS) is 426.7mg/L, the adsorption capacity to perfluorobutyric acid (PFBA) is 257.2mg/g, and the adsorption capacity to perfluorobutylsulfonic acid (PFBS) is 419.4 mg/g.
Figure 2 is an adsorption isotherm fit curve of the example products to PFOA, experimental conditions: 50mg of organic chitosan was put into 500mL of PFOA solution of different initial concentrations (0.25-500mg/L) at 25 ℃ and the solution was adsorbed by shaking at constant temperature for 24 hours in order to bring the adsorbent into a sufficient adsorption equilibrium. In the figure, the abscissa Ce and Qe represent the concentration and the amount of adsorption after the adsorption equilibrium, respectively. The theoretical maximum adsorption amount obtained by Langmuir adsorption isothermal curve fitting of the organically modified chitosan to PFOA is 3730.2 mg/g. Freundlich adsorption isotherm gave a 1/n of 0.39, between 0.1 and 0.5, indicating that the example product readily adsorbs PFOA. Compared with the Freundlich adsorption isotherm, the adsorption process more closely follows the Langmuir adsorption isotherm, indicating that the adsorption process is monolayer adsorption.
Figure 3 is a comparison of the kinetics of PFOA adsorption of the product of the example with chitosan, powdered activated carbon, and granular activated carbon models for pseudo-first order kinetics and (b) pseudo-second order kinetics. The experimental conditions are as follows: 50mg of different adsorbents are put into PFOA solution at the temperature of 25 ℃, the concentration of PFOA is 50mg/L, the volume is 500mL, and the different adsorbents are respectively adsorbed by 1, 2, 5, 10, 30, 60, 90, 180, 360, 540, 720, 1440, 1620 and 2160min under constant temperature oscillation. In the figure, the abscissa t represents the adsorption time, and the ordinate Qe represents the adsorption amount over that time. The comparison of the adsorption amounts is: examples product > chitosan > powdered activated carbon > granular activated carbon. The pseudo-second-order kinetic fitting degrees of the products of the examples on PFOA adsorption are high, which shows that the products of the examples are mainly based on chemical adsorption and have a large amount of quaternary ammonium groups and silane groups on the surfaces. The adsorption saturation is basically achieved within 180min, and the pseudo first-order kinetic rate constant k value is 0.727min-1, which indicates that the adsorption rate is higher. The adsorption amount of the adsorbent to PFOA after 2160min is 436.7 mg/g.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims (10)

1. An organic modified chitosan adsorbent for removing PFASs is characterized in that an original chitosan matrix is modified to obtain hydrophobic and lipophilic organic modified chitosan, and the chemical formula of the organic modified chitosan is as follows.
Figure FDA0003583389550000011
2. The organically modified chitosan adsorbent for removal of PFASs according to claim 1, wherein: the chitosan original matrix is modified by 3-aminopropyltriethoxysilane and 3-chloro-2-hydroxypropylammonium chloride in sequence to obtain the organically modified chitosan; the chemical formula of the 3-aminopropyltriethoxysilane is as follows:
Figure FDA0003583389550000012
the chemical formula of the 3-chloro-2-hydroxypropyl ammonium chloride is shown as follows.
Figure FDA0003583389550000013
3. A preparation method of an organic modified chitosan adsorbent for removing PFASs is characterized by comprising the following steps:
(1) adding 0.5-5 mL of the 3-aminopropyltriethoxysilane into a 50% ethanol organic solution, mixing and stirring for 1-3 h to obtain a prehydrolyzed aminosilane solution to obtain a solution A1;
(2) Dispersing 1-5 g of the chitosan original matrix in a solution A1, sealing by using a sealing film, magnetically stirring for 6-8 h under the water bath condition of 70-80 ℃, then performing suction filtration, wherein the solid left on the filter membrane is an organic silicon modified chitosan crude product, and washing for 3 times by using a 50% ethanol solution;
(3) placing the crude product of the organic silicon modified chitosan obtained in the step (2) in a vacuum drying oven, and performing vacuum drying for 2-5 hours at the temperature of 70-90 ℃ to remove the residual 50% ethanol solution on the surface of the crude product of the organic silicon modified chitosan;
(4) adding 0.5-3 g of the dry organic silicon modified chitosan crude product obtained in the step (3), 30-50 mL of 35% sodium hydroxide solution and isopropanol into a flask, heating to 50-80 ℃ under stirring, and alkalifying for 4-6 h to obtain organic silicon modified chitosan alkali liquor A2;
(5) slowly dripping 1-10 mL of the 3-chloro-2-hydroxypropyl ammonium chloride solution with the mass fraction of 65% into the A2 solution, controlling the dripping speed, controlling the material temperature to be not higher than 50 ℃, heating to 70-90 ℃ after finishing dripping, and reacting for 6-8 hours at constant temperature to obtain a modified chitosan solution A3;
(6) adjusting the pH value of the A3 solution to 7 by using dilute hydrochloric acid, carrying out suction filtration, repeatedly soaking the obtained product by using methanol for three times, washing the product by using absolute ethyl alcohol for three times to obtain wet modified chitosan, transferring the wet modified chitosan to a vacuum drying oven, and drying the wet modified chitosan at the temperature of 70-90 ℃ for 12-18 hours to obtain a dried modified chitosan sample;
(7) And (4) grinding the modified chitosan sample dried in the step (6) and sieving the ground sample with a 200-mesh sieve to obtain a sample with the particle size of not more than 0.074mm, namely the hydrophobic and lipophilic organic modified chitosan.
4. The method for preparing the organically modified chitosan adsorbent for removing PFASs according to claim 3, wherein: the adding amount of the 3-aminopropyltriethoxysilane in the step (1) is 9.6-96 mL/L.
5. The method for preparing the organically modified chitosan adsorbent for removing PFASs according to claim 3, wherein: the adding amount of the chitosan in the solution A1 in the step (2) is 19.3-96.5 g/L.
6. The method for preparing the organically modified chitosan adsorbent for removing PFASs according to claim 3, wherein: the adding amount of the sodium hydroxide in the solution A2 in the step (4) is 300-500 mL/L, and the adding amount of the organic silicon chitosan is 5-30 g/L.
7. The method for preparing the organically modified chitosan adsorbent for removing PFASs according to claim 3, wherein: in the step (5), the adding amount of the 3-chlorine-2-hydroxypropyl ammonium chloride in the solution A3 is 10-100 mL/L.
8. The application of an organic modified chitosan adsorbent for removing PFASs is characterized in that: the method comprises the following steps:
S1: directly throwing the organic modified chitosan with hydrophobicity and lipophilicity into waste water containing PFASs;
s2: adsorbing under stirring or oscillation conditions to ensure that the organic modified chitosan is fully contacted with PFASs wastewater;
s3: and naturally settling and depositing the organic modified chitosan after adsorption at the bottom, and removing the organic modified chitosan by filtering.
9. The use of the organically modified chitosan adsorbent for the removal of PFASs according to claim 8, wherein: and in the S2, continuously stirring for at least 180min at the temperature of 15-35 ℃ and at the speed of 200-800 rpm.
10. The use of the organically modified chitosan adsorbent for the removal of PFASs according to claim 8, wherein: the concentration of PFASs in the S1 is 50mg/L, and the solid-to-liquid ratio of the organic modified chitosan to PFASs wastewater is 100 mg/L.
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