CN114752002B - 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 PDFInfo
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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 matrix, and the chitosan is modified by 3-aminopropyl triethoxysilane and 3-chloro-2-hydroxypropyl ammonium chloride to obtain the organic modified chitosan adsorbent, wherein the maximum adsorption capacity of PFOA can reach 3730.2mg/g, and the organic modified chitosan adsorbent has better removal efficiency for other common PFASs. The invention has the characteristics of rich raw material reserves, wide sources, low price, good chemical and mechanical stability, large amount of amino active groups on the surface, simple and feasible preparation method, meets the requirements of industrial development in practicality and cost benefit, and has industrial utilization value. The adsorbent for removing PFASs has stable physical and chemical properties, has great potential in the treatment of fluorine-containing industrial wastewater, and is particularly suitable for the purification treatment of PFASs with medium and low concentration.
Description
Technical Field
The invention relates to the technology in the field of environmental remediation 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 compounds (perfluoroalkyl and poly fluoroalkyl substances, PFASs) are synthetic and contain in whole or in part C by complete substitution of all or more hydrogen atoms bound to carbon atoms by fluorine atoms n F 2n+1 Novel persistent organic compound pollutants of the radicals. The water-based fire extinguishing agent has the unique characteristics of being hydrophobic and oleophobic, strong in chemical stability, high in surface activity and the like, can bear illumination and high temperature, and is widely used in the aspects of daily necessities, foam fire extinguishment, surfactant emulsifying agents and the like. The material has a high-energy C-F bond (116 kcal/mol) and a spiral structure, so that the material has the characteristics of good chemical stability and strong durability, and once the material is manufactured and processed, the material cannot be naturally degraded, and the material is known as an 'always chemical', so that various environmental media and organisms in the global scope are detected in recent years. Of these, perfluorooctanoic acid (perfluorooctanoic acid, PFOA) and perfluorooctane sulfonate (perfluorooctane sulfonate, PFOS) are the 2 most industrially used compounds at present, and are representative PFASs. In addition, PFASs have long-distance transmission capability, high water solubility (PFOS and PFOA solubility are 570mg/L and 3.4g/L respectively), and can cause pollution of seawater, groundwater and drinking water, and can be used for treating various diseasesPFOS/PFOA pollution is particularly serious in waste water of garbage percolate, fluorine chemical industry, semiconductor industry and the like, wherein the PFOS concentration in chromium plating waste water can reach 1380mg/L, and the waste water is the water body with the highest PFOS content in the waste water of the industry at present. These compounds are of great concern for bioaccumulation, environmental tolerance, and potential toxicity in a variety of organisms.
At present, in domestic and foreign researches, no report is made on PFASs degradation by using a biological method, and the method for removing PFASs in water at home and abroad can be divided into two main types, wherein the first type is a physical method comprising a membrane treatment method, a coagulating sedimentation method and the like; the second type is chemical methods such as electrochemical oxidation, advanced oxidation, photocatalytic oxidation, and the like. Most of these methods have the disadvantages of complex operation, high processing cost, long time period, and the like. The adsorption method has the characteristics of high adsorption efficiency, high speed, large adsorption capacity and the like, and has been widely applied to the treatment of water environmental pollution.
Chitosan exists in a large amount in shells of crustaceans, such as shrimp shells, crab shells, cicada slough and the like, 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 alkaline polysaccharide in natural polysaccharide. The amino groups in the chitosan molecular structure have stronger reactivity, so that the polysaccharide has excellent biological functions and the possibility of chemical modification. In addition, the chitosan has very abundant reserves in the world, has great application value in the environment-friendly field due to the unique molecular structure, excellent adsorption performance and low cost, and has been widely paid attention to the application of chitosan in wastewater treatment.
However, when chitosan is used in wastewater containing fluorine, the adsorption amount of PFASs is relatively small, and the effect of PFASs removal is not obvious.
Disclosure of Invention
In view of the above, the present invention aims at overcoming the disadvantages of the prior art, and its main objective is to provide an organically modified chitosan adsorbent for removing pfacs, a preparation method and an application thereof, which solve the problems that the adsorption amount to pfacs is relatively small and the removal effect to pfacs is not obvious when chitosan is used in wastewater containing fluorine.
In order to achieve the above purpose, the present invention adopts the following technical scheme: an organic modified chitosan adsorbent for removing PFASs, wherein an original chitosan matrix is modified to obtain organic modified chitosan with hydrophobic and oleophilic properties, and the organic modified chitosan comprises a plurality of modified monomers, and the chemical formula of the single modified monomer is as follows:
in one embodiment, the chitosan raw matrix is modified by 3-aminopropyl triethoxysilane and 3-chloro-2-hydroxypropyl ammonium chloride in sequence to obtain the organically modified chitosan; the chemical formula of the 3-aminopropyl triethoxysilane is as follows:
the chemical formula of the 3-chloro-2-hydroxypropyl ammonium chloride is as follows.
The preparation method of the organic modified chitosan adsorbent for removing PFASs comprises the following steps:
(1) Adding 0.5-5 mL of 3-aminopropyl triethoxysilane 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 into the solution A1, sealing by using a sealing film, magnetically stirring for 6-8 h under the water bath condition of 70-80 ℃, then carrying out suction filtration, wherein the solid left on the filter membrane is an organosilicon modified chitosan crude product, and washing for 3 times by using 50% ethanol solution;
(3) Placing the crude product of the organosilicon modified chitosan obtained in the step (2) in a vacuum drying oven, and vacuum drying for 2-5 h at 70-90 ℃ to remove the 50% ethanol solution remained on the surface of the crude product of the organosilicon modified chitosan;
(4) Adding 0.5-3 g of dry organosilicon 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 alkalizing for 4-6 h to obtain organosilicon modified chitosan alkali liquor A2;
(5) Slowly dripping 1-10 mL of 3-chloro-2-hydroxypropyl ammonium chloride solution with the mass fraction of 65% into the solution A2, controlling the dripping speed, heating to 70-90 ℃ after the dripping is finished, and reacting at constant temperature for 6-8 h to obtain modified chitosan solution A3;
(6) Regulating the pH value of the solution A3 to 7 by using dilute hydrochloric acid, performing suction filtration, repeatedly soaking the obtained product in methanol for three times, washing the product with 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) Grinding the dried modified chitosan sample in the step (6) and sieving the ground modified chitosan sample with a 200-mesh sieve to obtain a sample with the particle size not more than 0.074mm, namely the organic modified chitosan with the hydrophobicity and the lipophilicity.
In one embodiment, the 3-aminopropyl triethoxysilane in step (1) is added in an amount of 9.6-96 mL/L.
In one embodiment, the chitosan in the solution A1 in the step (2) is added in an amount of 19.3-96.5 g/L.
In one embodiment, the adding amount of sodium hydroxide in the solution A2 in the step (4) is 300-500 mL/L, and the adding amount of the organosilicon chitosan is 5-30 g/L.
In one embodiment, the 3-chloro-2-hydroxypropyl ammonium chloride in the solution A3 in the step (5) is added in an amount of 10-100 mL/L.
An application of an organically modified chitosan adsorbent for removing PFASs, which comprises the following steps:
s1: directly adding organic modified chitosan with hydrophobicity and lipophilicity into waste water containing PFASs;
s2: adsorption is carried out under the condition of stirring or oscillation, so that the organic modified chitosan is ensured to be fully contacted with the PFASs wastewater;
s3: and naturally settling and depositing the organically modified chitosan after the adsorption is finished at the bottom, and removing the organically modified chitosan through filtration.
In one embodiment, stirring is continued in S2 at 15-35℃and 200-800 rpm for at least 180min.
In one embodiment, the concentration of PFASs in the S1 is 50mg/L, and the solid-to-liquid ratio of the organically modified chitosan to the PFASs wastewater is 100mg/L.
Compared with the prior art, the invention has obvious advantages and beneficial effects, and in particular, the technical scheme can be as follows:
1. according to the organic modified chitosan adsorbent for removing PFASs, chitosan is used as an original modified matrix, and the chitosan is modified by 3-aminopropyl triethoxysilane and 3-chloro-2-hydroxypropyl ammonium chloride to obtain the organic modified chitosan adsorbent, so that the maximum adsorption capacity of PFOA can reach 3730.2mg/g, and the organic modified chitosan adsorbent has better removal efficiency for other common PFASs.
2. The invention has the characteristics of rich raw material reserves, wide sources, low price, good chemical and mechanical stability, large amount of amino active groups on the surface, simple and feasible preparation method, meets the requirements of industrial development in practicality and cost benefit, and has industrial utilization value.
3. The adsorbent for removing PFASs has stable physical and chemical properties, has great potential in the treatment of fluorine-containing industrial wastewater, and is particularly suitable for the purification treatment of PFASs with medium and low concentration.
In order to more clearly illustrate the structural features and efficacy of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and examples.
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 perfluoro caprylic acid by the organic modified chitosan adsorbent prepared in the example of the present invention;
fig. 3 shows a comparison of the kinetic model of perfluoro caprylic acid by the organically modified chitosan adsorbent prepared in the embodiment of the invention with the kinetic model of chitosan, powdered activated carbon and granular activated carbon, wherein (a) is a pseudo-primary kinetic model, and (b) is a pseudo-secondary kinetic model.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved by the present application more clear, 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 for purposes of illustration only and are not intended to limit the present application.
It will be understood that when an element is referred to as being "mounted" 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 is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate or are based on the orientation or positional relationship shown in the drawings, merely to facilitate description of the present application and simplify description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be configured and operated in a particular orientation, and therefore should not be construed as limiting the present application.
Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.
The application provides an organic modified chitosan adsorbent for removing PFASs, which is characterized in that an original chitosan matrix is modified to obtain organic modified chitosan with hydrophobic and oleophilic properties, and the chemical formula of the organic modified chitosan is as follows:
for a more visual understanding of the chemical formula of organically modified chitosan, fig. 1 shows organically modified chitosan composed of three modified monomers.
The modified organic modified chitosan adsorbent effectively adsorbs PFASs in the water body under the action of hydrophobic acting force and electrostatic interaction force. And the organic modified chitosan has high adsorption capacity and can rapidly adsorb PFASs in the water body.
Illustratively, the organically modified chitosan adsorbent reaches adsorption equilibrium within 180 min; the maximum adsorption capacity of the adsorbent to the perfluorooctanoic acid is 3730.2mg/g, the adsorption capacity to the perfluorooctanoic acid (PFOA) can reach 437.8mg/g, the adsorption capacity to the Perfluorosulfonate (PFOS) can reach 426.7 mg/g, the adsorption capacity to the perfluorobutyric acid (PFBA) can reach 257.2mg/g, and the adsorption capacity to the perfluorobutylsulfonic acid (PFBS) can reach 419.4mg/g under the condition that the concentration of various polyfluoro and perfluoroalkyl substances is 50 mg/g.
In one embodiment, the chitosan raw matrix is modified by 3-aminopropyl triethoxysilane and 3-chloro-2-hydroxypropyl ammonium chloride in sequence to obtain the organically modified chitosan; the chemical formula of the 3-aminopropyl triethoxysilane is as follows:
the chemical formula of the 3-chloro-2-hydroxypropyl ammonium chloride is as follows.
The 3-aminopropyl triethoxysilane is a catalyst having an end with-NH 2 Silane coupling agent of groupThe hydrophobic property of the chitosan surface can be enhanced and the adsorption effect on the perfluorooctanoic acid can be improved by organically modifying and grafting the chitosan to the surface of the original chitosan substrate. The silanol after the hydrolysis of the 3-aminopropyl triethoxy silane is condensed with the hydroxyl on the surface of the chitosan to further form a stable N-O-Si ion covalent bond, which is the direct grafting of the chitosan. In addition, oligomers formed by condensation between hydrolyzed silanes may further link to chitosan via covalent and hydrogen bonds.
The 3-chloro-2-hydroxypropyl ammonium chloride is an important quaternary ammonium salt cationic etherifying agent and an important organic intermediate, is widely used for modifying high molecular compounds containing active hydrogen groups such as natural high molecular compounds including chitosan, starch, cellulose, lignin and the like, the chitosan is swelled in isopropanol and then alkalized to form an activation center, and then the activation center is modified with the etherifying agent with the quaternary ammonium salt groups through etherification, graft copolymerization and other reactions, so that the quaternary ammonium salt is loaded on the surface of the chitosan, and the electrostatic attraction of the surface is improved.
The organic modified chitosan adsorbent obtained by modifying 3-aminopropyl triethoxysilane and 3-chloro-2-hydroxypropyl ammonium chloride has a maximum adsorption capacity of 3730.2mg/g to PFOA and has good removal efficiency to other common PFASs.
The preparation method of the organic modified chitosan adsorbent for removing PFASs comprises the following steps:
(1) Adding 0.5-5 mL of 3-aminopropyl triethoxysilane 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 into the solution A1, sealing by using a sealing film, magnetically stirring for 6-8 h under the water bath condition of 70-80 ℃, then carrying out suction filtration, wherein the solid left on the filter membrane is an organosilicon modified chitosan crude product, and washing for 3 times by using 50% ethanol solution;
(3) Placing the crude product of the organosilicon modified chitosan obtained in the step (2) in a vacuum drying oven, and vacuum drying for 2-5 h at 70-90 ℃ to remove the 50% ethanol solution remained on the surface of the crude product of the organosilicon modified chitosan;
(4) Adding 0.5-3 g of dry organosilicon 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 alkalizing for 4-6 h to obtain organosilicon modified chitosan alkali liquor A2;
(5) Slowly dripping 1-10 mL of 3-chloro-2-hydroxypropyl ammonium chloride solution with the mass fraction of 65% into the solution A2, controlling the dripping speed, heating to 70-90 ℃ after the dripping is finished, and reacting at constant temperature for 6-8 h to obtain modified chitosan solution A3;
(6) Regulating the pH value of the solution A3 to 7 by using dilute hydrochloric acid, performing suction filtration, repeatedly soaking the obtained product in methanol for three times, washing the product with 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) Grinding the dried modified chitosan sample in the step (6) and sieving the ground modified chitosan sample with a 200-mesh sieve to obtain a sample with the particle size not more than 0.074mm, namely the organic modified chitosan with the hydrophobicity and the lipophilicity.
According to the organic modified chitosan for removing PFASs and the preparation method thereof, the preparation principle is that silanol after hydrolysis of 3-aminopropyl triethoxy silane is condensed with hydroxyl on the surface of chitosan to further form a stable N-O-Si ionic covalent bond, and an oligomer formed by condensation between hydrolyzed silanes is further connected with chitosan through covalent bonds and hydrogen bonds to improve the hydrophobic acting force on the surface of chitosan. Swelling chitosan in isopropanol, alkalizing to form an activation center, and then modifying the activation center with an etherifying agent with quaternary ammonium salt groups through etherification, graft copolymerization and other reactions, 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 rich raw material reserves, wide sources, low price, good chemical and mechanical stability, large amount of amino active groups on the surface, simple and feasible preparation method, meets the requirements of industrial development in practicality and cost benefit, and has industrial utilization value.
The adsorbent prepared by the preparation method has stable physical and chemical properties, has great potential in the treatment of fluorine-containing industrial wastewater, and is particularly suitable for the purification treatment of low-concentration PFASs.
In one embodiment, the 3-aminopropyl triethoxysilane in step (1) is added in an amount of 9.6-96 mL/L. The adding amount of chitosan in the solution A1 in the step (2) is 19.3-96.5 g/L. The adding amount of sodium hydroxide in the solution A2 in the step (4) is 300-500 mL/L, and the adding amount of the organosilicon chitosan is 5-30 g/L. The adding amount of the 3-chloro-2-hydroxypropyl ammonium chloride in the solution A3 in the step (5) is 10-100 mL/L.
An application of an organically modified chitosan adsorbent for removing PFASs, which comprises the following steps:
s1: directly adding organic modified chitosan with hydrophobicity and lipophilicity into waste water containing PFASs;
s2: adsorption is carried out under the condition of stirring or oscillation, so that the organic modified chitosan is ensured to be fully contacted with the PFASs wastewater;
s3: and naturally settling and depositing the organically modified chitosan after the adsorption is finished at the bottom, and removing the organically modified chitosan through filtration.
In one embodiment, stirring is continued in S2 at 15-35℃and 200-800 rpm for at least 180min. The concentration of PFASs in the S1 is 50mg/L, and the solid-liquid ratio of the organic modified chitosan to the PFASs wastewater is 100mg/L. In this environment, the removal rate of the organic modified chitosan to perfluorooctanoic acid (PFOA) is more than 95%, the adsorption amount is 437.8mg/g, the adsorption amount to Perfluorosulfonate (PFOS) is 426.7mg/L, the adsorption amount to perfluorobutyric acid (PFBA) is 257.2mg/g, and the adsorption amount to perfluorobutylsulfonic acid (PFBS) is 419.4mg/g.
The following description is made in connection with specific embodiments:
50mL of 50% ethanol organic solution was added in an amount of 1mL of 3-aminopropyl triethoxysilane, and the mixture was stirred for 2 hours to obtain a pre-hydrolyzed aminosilane solution to obtain solution A1.
2g of chitosan is added into the solution A1, the solution A1 is sealed by a sealing film, the solution A is magnetically stirred for 8 hours under the water bath condition of 75 ℃, the solution A is filtered by suction, the solid remained on the filter film is the crude product of the organosilicon modified chitosan, and the solution A is washed for 3 times by 50% ethanol solution, wherein the washing amount of ethanol is 20mL each time.
And (3) placing the crude product of the organosilicon modified chitosan in a vacuum drying oven, and vacuum drying for 2 hours at 90 ℃ to remove the residual 50% ethanol solution on the surface of the crude product of the organosilicon modified chitosan.
Adding 1g of dry organosilicon modified chitosan, 30mL of 35% sodium hydroxide solution and isopropanol into a round-bottom flask, heating to 50 ℃ with stirring, and alkalizing for 4h to obtain organosilicon modified chitosan alkali liquor A2.
Slowly dripping 5mL of 3-chloro-2-hydroxypropyl ammonium chloride solution with the mass fraction of 65% into the solution A2, controlling the dripping speed, heating to 70 ℃ after the dripping is finished, and reacting at constant temperature for 7h to obtain the modified chitosan solution A3.
Regulating the pH value of the A3 solution to 7 by using 0.1M dilute hydrochloric acid, performing suction filtration, repeatedly soaking the obtained product in methanol for three times, washing the product with 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 90 ℃ for 12 hours to obtain a dried modified chitosan sample;
and grinding the dried modified chitosan sample, and sieving with a 200-mesh sieve to obtain a sample with the particle size not more than 0.074mm, namely the organic modified chitosan adsorbent.
The organic modified chitosan prepared by the method of the embodiment is used for carrying out adsorption experiments on PFASs sewage, and further illustrates the invention, and the results show that: when the PFOA concentration is 0.25mg/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, and the adsorption capacity is 2.5mg/g, and the removal rate is 99.2%.
When the PFOA concentration is 1mg/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, so that the adsorption capacity is 8.8mg/g, and the removal rate is 87.6%.
When the PFOA concentration is 10mg/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, and the adsorption capacity is 84.2mg/g, and the removal rate is 84.2%.
When the PFOA concentration 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, so that the adsorption capacity is 512.8mg/g, and the removal rate is 95.6%.
When the PFOA concentration is 100mg/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, so that the adsorption capacity is 124.0mg/g, and the removal rate is 87.6%.
When the PFOA concentration is 400mg/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, and the adsorption capacity is 3345.9mg/g, and the removal rate is 67.0%.
When the PFASs concentration 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 amount of Perfluorosulfonate (PFOS) is 426.7mg/L, the adsorption amount of perfluorobutyric acid (PFBA) is 257.2mg/g, and the adsorption amount of perfluorobutylsulfonic acid (PFBS) is 419.4mg/g.
FIG. 2 is an adsorption isothermal fit curve of the example product to PFOA, experimental conditions: 50mg of organic chitosan was put into 500mL of PFOA solution of different initial concentrations (0.25-500 mg/L) at 25℃and the adsorption was continued for 24 hours with constant temperature shaking in order to allow the adsorbent to fully adsorb and equilibrate. In the figure, the abscissa Ce and Qe are the concentration and adsorption amount after adsorption equilibrium, respectively. The theoretical maximum adsorption capacity of the organic modified chitosan obtained by the Langmuir adsorption isothermal curve fitting of PFOA is 3730.2mg/g. The 1/n obtained from the Freundlich adsorption isotherm curve is 0.39, between 0.1 and 0.5, indicating that the example product is readily adsorbed to PFOA. Compared with the Freundlich adsorption isothermal curve, the adsorption process is more in line with the Langmuir adsorption isothermal curve, which shows that the adsorption process is monolayer adsorption.
FIG. 3 is a kinetic model comparison of the example product with chitosan, powdered activated carbon, and granular activated carbon to PFOA adsorption, where (a) is a pseudo-first order kinetic fit and (b) is a pseudo-second order kinetic fit. Experimental conditions: 50mg of each of the different adsorbents was put into a PFOA solution at 25℃and PFOA concentrations were 50mg/L and volumes were 500mL, and the adsorbents were adsorbed by constant-temperature shaking for 1,2,5, 10, 30, 60, 90, 180, 360, 540, 720, 1440, 1620 and 2160min, respectively. In the figure, the abscissa t represents the adsorption time, and the ordinate Qe represents the amount of adsorption at that time. The comparison of the adsorption amount is: example product > chitosan > powdered activated carbon > granular activated carbon. The pseudo-secondary dynamics fitting degree of the product of the example to PFOA adsorption is higher, which shows that the product of the example mainly adopts chemical adsorption, and the surface of the product of the example is provided with a large number of quaternary ammonium groups and silane groups. The adsorption saturation is basically reached within 180min, and the k value of the pseudo first-order kinetic rate constant is 0.727min < -1 >, which shows that the adsorption rate is faster. After 2160min, the adsorption quantity of the adsorbent to PFOA is 436.7mg/g.
The foregoing description of the preferred embodiments of the present application is not intended to be limiting, but is intended to cover any and all modifications, equivalents, and alternatives falling within the spirit and principles of the present application.
Claims (8)
1. An organically modified chitosan adsorbent for removing PFASs, which is characterized in that: the original chitosan matrix is modified by 3-aminopropyl triethoxysilane and 3-chloro-2-hydroxypropyl ammonium chloride in sequence to obtain the organically modified chitosan; the chemical formula of the 3-aminopropyl triethoxysilane is as follows:
the chemical formula of the 3-chloro-2-hydroxypropyl ammonium chloride is as follows:
the preparation method of the organic modified chitosan adsorbent comprises the following steps:
(1) Adding 0.5-5 mL of 3-aminopropyl triethoxysilane 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 into the solution A1, sealing by using a sealing film, magnetically stirring for 6-8 h under the water bath condition of 70-80 ℃, then carrying out suction filtration, wherein the solid left on the filter membrane is an organosilicon modified chitosan crude product, and washing for 3 times by using 50% ethanol solution;
(3) Placing the crude product of the organosilicon modified chitosan obtained in the step (2) in a vacuum drying oven, and vacuum drying for 2-5 h at 70-90 ℃ to remove the 50% ethanol solution remained on the surface of the crude product of the organosilicon modified chitosan;
(4) Adding 0.5-3 g of dry organosilicon 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 alkalizing for 4-6 h to obtain an organic modified chitosan alkali liquor A2;
(5) Slowly dripping 1-10 mL of 3-chloro-2-hydroxypropyl ammonium chloride solution with the mass fraction of 65% into the solution A2, controlling the dripping speed, heating to 70-90 ℃ after the dripping is finished, and reacting at constant temperature for 6-8 h to obtain modified chitosan solution A3;
(6) Regulating the pH value of the solution A3 to 7 by using dilute hydrochloric acid, performing suction filtration, repeatedly soaking the obtained product in methanol for three times, washing the product with 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) Grinding the dried modified chitosan sample in the step (6) and sieving the ground modified chitosan sample with a 200-mesh sieve to obtain a sample with the particle size not more than 0.074mm, namely the organic modified chitosan with the hydrophobicity and the lipophilicity.
2. The organically modified chitosan adsorbent for removing pfacs according to claim 1, wherein: the adding amount of the 3-aminopropyl triethoxysilane in the step (1) is 9.6-96 mL/L.
3. The organically modified chitosan adsorbent for removing pfacs according to claim 1, wherein: the adding amount of chitosan in the solution A1 in the step (2) is 19.3-96.5 g/L.
4. The organically modified chitosan adsorbent for removing pfacs according to claim 1, wherein: the adding amount of sodium hydroxide in the solution A2 in the step (4) is 300-500 mL/L, and the adding amount of the organosilicon chitosan is 5-30 g/L.
5. The organically modified chitosan adsorbent for removing pfacs according to claim 1, wherein: the adding amount of the 3-chloro-2-hydroxypropyl ammonium chloride in the solution A3 in the step (5) is 10-100 mL/L.
6. An application of an organically modified chitosan adsorbent for removing PFASs, which is characterized in that: the method comprises the following steps:
s1: directly adding organic modified chitosan with hydrophobicity and lipophilicity into waste water containing PFASs;
s2: adsorption is carried out under the condition of stirring or oscillation, so that the organic modified chitosan is ensured to be fully contacted with the PFASs wastewater;
s3: and naturally settling and depositing the organically modified chitosan after the adsorption is finished at the bottom, and removing the organically modified chitosan through filtration.
7. The use of the organically modified chitosan adsorbent for removing pfas defined in claim 6, wherein: and in the step S2, stirring is continuously carried out for at least 180min under the conditions of 15-35 ℃ and 200-800 rpm.
8. The use of the organically modified chitosan adsorbent for removing pfas defined in claim 6, wherein: the concentration of PFASs in the S1 is 50mg/L, and the solid-liquid ratio of the organic modified chitosan to the PFASs wastewater is 100mg/L.
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