CN113234197B

CN113234197B - Preparation method and application of cellulose-based cationic adsorbent

Info

Publication number: CN113234197B
Application number: CN202110484152.3A
Authority: CN
Inventors: 马庆林; 张萌; 王新刚; 孟凡君
Original assignee: Shandong University
Current assignee: Shandong University
Priority date: 2021-04-30
Filing date: 2021-04-30
Publication date: 2022-07-01
Anticipated expiration: 2041-04-30
Also published as: CN113234197A

Abstract

The invention relates to the technical field of macromolecules, in particular to a preparation method and application of a cellulose-based cationic adsorbent, wherein the preparation method comprises the following steps: adding hydroxyethyl acrylate monomer into cellulose, and reacting under the action of an initiator to obtain cellulose-graft-polyhydroxyethyl acrylate; continuously adding thionyl chloride to react to obtain a cellulose-graft-polyhydroxyethyl acrylate cation derivative; and then adding a trimethylamine aqueous solution, and reacting under the action of a catalyst to generate the cellulose-graft-polyhydroxyethyl acrylate cationic derivative. Practice of the inventionThe maximum adsorption capacity of the cellulose-graft-polyhydroxyethyl acrylate cation derivative prepared in the method on methyl orange solution can reach 1103.053mg g^‑1The performance of the adsorbent is very excellent; the adsorption regeneration performance is good, and the adsorption rate of methyl orange after being recycled for four times can still reach 76%.

Description

Preparation method and application of cellulose-based cationic adsorbent

Technical Field

The invention relates to the technical field of macromolecules, and particularly relates to a preparation method and application of a cellulose-based cationic adsorbent.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

Water is a basic resource for maintaining human survival, but increasing water pollution causes serious shortage of safe drinking water, and thus improvement of the water pollution problem is imminent. Water pollution refers to the change of any beneficial water due to physical, chemical or biological factors, and the like, and the sewage can cause harm and influence on public health. The main factor of water pollution is the dyes produced in the textile and cosmetic industries.

Common ways of treating water pollution are precipitation, membrane separation, ion exchange, electrochemistry, photocatalysis, adsorption, coagulation, and microbial degradation, where chemisorption occurs through chemical bond bonding between the adsorbate and the adsorbent, is essentially irreversible, and the material adsorbed on the solid surface is not easily shed. The adsorbent has the advantages of low cost, high efficiency and the like, and can treat a large amount of dye wastewater.

The common types of the adsorbents at present comprise activated carbon, minerals, inorganic molecules, organic polymers and the like, but the adsorbents all have certain defects: the powdery active carbon is not easy to separate from water and difficult to recover, and is easy to cause secondary pollution, and the granular active carbon is expensive and cannot be used for treating industrial water pollution; the mineral adsorbent is dispersed in the solution after adsorption, is difficult to collect and cannot be reused; when the inorganic adsorbent is used for treating wastewater, metal ions can remain in the wastewater, and subsequent treatment is needed; acrylamide is commonly used as a monomer of the organic polymer adsorbent, which is toxic and non-degradable, and is forbidden by some countries at present.

The adsorbents required today should meet two criteria: firstly, the dye wastewater can be efficiently treated, and is easy to separate from the treated water body; secondly, the coating is green and environment-friendly, and can be regenerated and biodegraded. Natural polymer adsorbents have the advantages of wide sources, low cost, no toxicity and the like, and are increasingly widely researched. Cellulose is the most abundant natural polymer in the world, is cheap and easily available, is insoluble in water, is renewable, has excellent mechanical properties, and is a good adsorbent matrix.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention provides a cellulose-based cationic adsorbent which has excellent adsorption performance on methyl orange dye and can be applied to treatment of dye wastewater.

In order to achieve the above object, the technical solution of the present invention is as follows:

in a first aspect of the present invention, there is provided a method for preparing a cellulose-based cationic adsorbent, the method comprising:

adding hydroxyethyl acrylate monomer into cellulose, and reacting under the action of an initiator to obtain cellulose-graft-polyhydroxyethyl acrylate (Cell-g-PHEA); continuously adding thionyl chloride to react to obtain cellulose-graft-poly (chloroethyl acrylate) (Cell-g-PCEA); and then adding trimethylamine aqueous solution, and reacting under the action of a catalyst to generate the cellulose-graft-polyhydroxyethyl acrylate cation derivative (CD-Cell-g-PHEA).

According to the invention, hydroxyethyl acrylate with good hydrophilicity is selected as a monomer, and the hydroxyethyl acrylate is easy to graft and polymerize on cellulose in a water system adopted by the invention; thionyl chloride is a good reagent commonly used in the chlorine replacement reaction of alcohol, and the reaction needs to be carried out in an anhydrous system; DMF is selected as a solvent for chlorination, the chlorination belongs to an anhydrous system, and hydrogen chloride and sulfur dioxide generated in the reaction are gases and are easily volatilized to be removed without residues.

The adsorbent structure obtained by the invention is prepared by graft polymerization of easily-reacted hydroxyethyl acrylate monomer and chlorination, quaternization and other reactions, and the obtained adsorbent has more cationic groups.

In the prior art, researches are made to directly graft and polymerize cationic monomer DMC on cotton fiber, and the grafting rate is only 2.37%; in addition, the research also comprises the step of graft polymerizing the dimethylaminoethyl methacrylate on the cellulose, wherein the grafting rate can reach 65.1%; then quaternary ammonification is carried out to prepare the cationic cellulose-based adsorbent, the quaternization degree reaches 58.3 percent at most, which is equivalent to that the grafting rate of direct graft polymerization of DMC on cellulose reaches 38 percent, although the cationic group is greatly improved, the maximum adsorption capacity of the adsorbent on MO is 118.82mg g^-1There are still large differences compared to other kinds of adsorbents. The grafting rate of the adsorbent prepared by the invention is equivalent to that of direct grafting polymerization of DMC on cellulose, and the grafting rate reaches 245.97%, and the maximum adsorption capacity can reach 1103.053mg g^-1And the improvement is about 10 times compared with the prior art. The initial adsorption rate and the maximum adsorption capacity of the adsorbent of the invention are excellent.

Specifically, the preparation method comprises the following steps:

(1) cellulose pretreatment: soaking cellulose in water for 10-14h to obtain a cellulose suspension;

(2) adding an initiator into the cellulose suspension, then slowly dropwise adding a hydroxyethyl acrylate monomer, and reacting under a certain temperature condition to obtain cellulose-graft-polyhydroxyethyl acrylate (Cell-g-PHEA);

(3) adding thionyl chloride into the Cell-g-PHEA synthesized in the step (2), and reacting at a certain temperature to obtain cellulose-graft-poly (chloroethyl acrylate) (Cell-g-PCEA);

(4) adding a proper amount of catalyst into the Cell-g-PCEA synthesized in the step (3), and slowly dropwise adding a trimethylamine aqueous solution for reaction to obtain a cellulose-graft-polyhydroxyethyl acrylate cationic derivative (CD-Cell-g-PHEA);

preferably, the initiator is potassium persulfate;

preferably, the catalyst is potassium iodide.

In one or more embodiments, the potassium persulfate is recrystallized prior to use; potassium persulfate has deliquescence and is impure after being placed for a long time, so that the effect is influenced.

In one or more embodiments, the mass ratio of cellulose to hydroxyethyl acrylate monomers is 1: 1-1: 6;

in one or more embodiments, in step (2), the initiator is selected from potassium persulfate;

the concentration of the potassium persulfate is 0.005-0.06 mol L^-1Preferably 0.015 to 0.04mol L^-1More preferably 0.0285mol L^-1(ii) a The concentration of the initiator has great influence on the grafting rate and the grafting efficiency of the cellulose-graft-polyhydroxyethyl acrylate, and the excessive or insufficient concentration of the initiator can reduce the grafting rate and the grafting efficiency of the cellulose-graft-polyhydroxyethyl acrylate, so that the amount of products obtained by the reaction is influenced;

in one or more embodiments, in the step (2), the concentration of the monomer hydroxyethyl acrylate is 0.5-3.5 mol L^-1Preferably 1.5 to 3.0mol L^-1More preferably 2.5835mol L^-1；

In one or more embodiments, in the step (2), the reaction temperature is 30-70 ℃, preferably 50 ℃; after the temperature reaches 30 ℃, the grafting rate and the grafting efficiency of the cellulose-graft-polyhydroxyethyl acrylate start to increase, and the grafting rate and the grafting efficiency start to slowly decrease after reaching the highest point at 50 ℃; the grafting rate and the grafting efficiency can be kept higher within the temperature range of 30-70 ℃.

The grafting rate of the cellulose-graft-polyhydroxyethyl acrylate prepared by the method can reach 535.34% to the maximum, and meanwhile, the grafting efficiency also reaches 89.19%.

In one or more embodiments, the purification of the product cellulose-graft-polychlorinated ethyl acrylate (Cell-g-PCEA) in step (2) is performed by solvent displacement with water-ethanol-acetone to remove unreacted initiator, monomers, and homopolymers;

in one or more embodiments, in step (3), the concentration of thionyl chlorideThe degree of the reaction is 0.25 to 2.25mol L^-1Preferably 0.75 to 2.0mol L^-1More preferably 1.8910mol L^-1(ii) a The concentration of thionyl chloride has a great influence on the chlorinity of the cellulose-graft-poly (chloroethyl acrylate), and the chlorinity of the cellulose-graft-poly (chloroethyl acrylate) is higher in the concentration range selected in the embodiment;

in one or more embodiments, in step (3), the reaction temperature is 40 to 75 ℃, preferably 70 ℃;

in the embodiment, the concentration of thionyl chloride and the reaction temperature are important factors influencing the chlorination degree of the cellulose-graft-polyacrylic acid chloroethyl ester, and the chlorination degree of the cellulose-graft-polyacrylic acid chloroethyl ester is higher and can reach as high as 98.05% in the selected concentration and temperature range of the thionyl chloride in the embodiment of the invention.

In one or more embodiments, in the step (4), the concentration of trimethylamine is 2 to 10mol L^-1Preferably 4.0 to 8.0mol L^-1More preferably 6.7797mol L^-1；

In one or more embodiments, in the step (4), the concentration of the potassium iodide catalyst is 0-0.075 mol L^-1Preferably 0.025 to 0.045mol L^-1More preferably 0.0361mol L^-1；

In one or more embodiments, in step (4), the reaction temperature is 50 to 70 ℃, preferably 60 ℃.

The influence of the concentration of trimethylamine, the concentration of a catalyst and the reaction temperature on the quaternization degree of the cellulose-graft-poly (chloroethyl acrylate) is large, the quaternization degree of the cellulose-graft-poly (chloroethyl acrylate) is high in the concentration range and the temperature range selected by the embodiment of the invention, and the quaternization degree can reach 46.86% optimally.

In one or more embodiments, step (2) is replaced with water-absolute ethanol-acetone solvent to provide the product; settling the product obtained in the step (3) by using absolute ethyl alcohol; and (4) after the reaction in the step (4) is finished, settling the product by using absolute ethyl alcohol.

In one or more embodiments, inert gas is introduced to protect the reaction in steps (2) - (4) throughout the reaction; preferably, the inert gas is nitrogen.

In a second aspect of the present invention, there is provided a cellulose-based cationic adsorbent prepared by the method for preparing the cellulose-based cationic adsorbent of the first aspect.

In a third aspect of the invention, there is provided a use of the cellulose-based cationic adsorbent of the second aspect in dye wastewater treatment.

In one or more embodiments, the dye wastewater comprises methyl orange wastewater.

The specific embodiment of the invention has the following beneficial effects:

the grafting rate of the cellulose-graft-polyhydroxyethyl acrylate prepared in the embodiment of the invention can reach 535.34% to the maximum, and meanwhile, the grafting efficiency also reaches 89.19%; the degree of chlorination of cellulose-graft-polychloroethyl acrylate (Cell-g-PCEA) was 98.05%; the quaternization degree of the cellulose-graft-polyhydroxyethyl acrylate cationic derivative (CD-Cell-g-PHEA) is optimally 46.86%, and the maximum adsorption capacity of the cellulose-graft-polyhydroxyethyl acrylate cationic derivative on methyl orange solution can reach 1103.053mg g^-1The performance of the adsorbent is very excellent;

the cellulose-based cationic adsorbent prepared in the embodiment of the invention is an effective reproducible adsorbent, the adsorption and reproduction performance is good, and the adsorption rate of methyl orange after being recycled for four times can still reach 76%.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.

FIG. 1 is an infrared spectrum of Cell, Cell-g-PHEA, Cell-g-PCEA and CD-Cell-g-PHEA in example 1 of the present invention;

FIG. 2 is a scanning electron micrograph of Cell, Cell-g-PHEA, Cell-g-PCEA, CD-Cell-g-PHEA and MO-adsorbed CD-Cell-g-PHEA in example 1 of the present invention;

wherein, FIG. 2(a) is a scanning electron micrograph of Cell;

FIG. 2(b) is a scanning electron micrograph of Cell-g-PHEA;

FIG. 2(c) is a scanning electron micrograph of Cell-g-PCEA;

FIG. 2(d) is a scanning electron micrograph of CD-Cell-g-PHEA;

FIG. 2(e) is a scanning electron micrograph of CD-Cell-g-PHEA after adsorption of MO;

FIG. 3 is a graph showing the adsorption effect of CD-Cell-g-PHEA prepared in example 1 on MO at different pH values;

FIG. 4 is a quasi-first order kinetic model of CD-Cell-g-PHEA prepared in example 1 of the present invention;

FIG. 5 is a model of the quasi-secondary kinetics of CD-Cell-g-PHEA prepared in example 1 of the present invention;

FIG. 6 is a Freundlich adsorption isotherm of CD-Cell-g-PHEA prepared in example 1 of the present invention;

FIG. 7 is a Langmuir adsorption isotherm of CD-Cell-g-PHEA prepared in example 1 of the present invention;

FIG. 8 is a graph showing the effect of temperature on the thermodynamic performance of CD-Cell-g-PHEA prepared in example 1 of the present invention in adsorbing methyl orange;

FIG. 9 is a graph showing the adsorption regeneration performance of CD-Cell-g-PHEA prepared in example 1 of the present invention.

Detailed Description

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

The invention will be further explained and illustrated with reference to specific examples.

Example 1

A method of preparing a cellulose-based cationic adsorbent, the method comprising the steps of:

(1) pretreatment process

Pretreatment of an initiator: adding 150mL of deionized water into a 250mL beaker, heating the beaker in a 30 ℃ water bath kettle, gradually adding potassium persulfate into the beaker until the potassium persulfate can not be dissolved, filtering to remove insoluble substances, naturally cooling the beaker at room temperature, putting the beaker in a 4 ℃ refrigerator for recrystallization, and simultaneously preparing a proper amount of ice deionized water for cleaning. And taking out after 24 hours, cleaning, filtering, and placing the obtained crystal in a vacuum drying oven for drying.

Cellulose pretreatment: 1g of cellulose was soaked in a 100mL three-necked round bottom flask to which an appropriate amount of deionized water had been added in advance for 12 hours.

(2) Synthesis of cellulose-graft-polyhydroxyethyl acrylate (Cell-g-PHEA):

and (3) placing the three-neck round-bottom flask containing the cellulose suspension wetted in the step (1) into a constant-temperature water bath kettle, heating to 50 ℃, and introducing nitrogen for protection. After the temperature was constant, 0.1g of potassium persulfate was added to the three-necked flask to initiate the reaction for 30min, and then 6g of hydroxyethyl acrylate monomer was slowly added dropwise thereto. After reacting for 6h, the water bath kettle is stopped heating. The nitrogen protection is introduced and the stirring is continued throughout the synthesis, taking care that the nitrogen flux can be increased appropriately when initiator and monomer are added. And taking out the product after the water bath is cooled to room temperature, and performing solvent replacement through water-ethanol-acetone to remove unreacted initiator, monomer and homopolymer. And (4) carrying out suction filtration on the obtained crude product, and drying in a vacuum drying oven to constant weight. The product was then removed and weighed.

(3) Synthesis of cellulose-graft-Chloroethyl polyacrylate (Cell-g-PCEA):

and (3) adding 1g of the Cell-g-PHEA synthesized in the step (2) into a three-neck round-bottom flask containing 40mL of DMF, placing the three-neck flask into a constant-temperature water bath kettle, heating to 70 ℃, and introducing nitrogen for protection in the whole reaction process. Adding 9g of thionyl chloride into the three-neck flask after the temperature is constant, stopping heating the water bath after reacting for 12 hours, taking out the three-neck flask after cooling to room temperature, settling the product in absolute ethyl alcohol for a certain time, and drying the obtained crude product in a vacuum drying oven to constant weight after suction filtration. The product was then removed and weighed.

(4) Synthesis of cellulose-graft-Polyhydroxyethyl acrylate cationic derivative (CD-Cell-g-PHEA):

weighing 1g of Cell-g-PCEA synthesized in the step (3), adding the Cell-g-PCEA into a three-neck round-bottom flask filled with 50mL of DMF, soaking for 12 hours, placing the three-neck round-bottom flask into a constant-temperature water bath kettle, heating to 60 ℃, and introducing nitrogen for protection in the whole reaction process. And after the temperature of the water bath kettle is constant, adding 0.3g of KI serving as a catalyst into the flask, slowly dropwise adding 20g of trimethylamine aqueous solution into the flask after a period of time, stopping heating after reacting for 12 hours, and cooling to room temperature. And (3) settling the product by using absolute ethyl alcohol, and after the product is subjected to suction filtration, putting the product into a vacuum drying oven to be dried to constant weight.

The infrared spectra of cellulose, Cell-g-PHEA, Cell-g-PCEA and CD-Cell-g-PHEA in example 1 are shown in FIG. 1, and the scanning electron micrographs are shown in (a) to (d) of FIG. 2; FIG. 2(e) is a scanning electron micrograph of the CD-Cell-g-PHEA after adsorbing methyl orange.

FIG. 1(a) is a spectrum of cellulose: 3381cm^-1The infrared stretching vibration absorption peak is widened due to the hydrogen bond interaction between hydroxyl groups; 2897cm^-1Is a symmetric stretching vibration peak of a C-H bond; 1642cm^-1Is the bending stretching vibration peak of the O-H bond. FIG. 1(b) is a spectrum of Cell-g-PHEA: 1726cm^-1Is a stretching vibration peak of carbonyl C ═ O bond, and the stretching vibration peak of carbonyl C ═ O bond of saturated fatty acid ester is usually located at 1740cm^-1On the left and right, the graft polymerization of hydroxyethyl acrylate on cellulose is illustrated; 1164cm^-1Is a symmetric stretching vibration peak of C-O-C, and the carbonyl group of the hydroxyethyl acrylate and an unshared electron pair of an O atom in the C-O-C form p-pi conjugation, so that the C-O-C bond has partial double bond characteristic, therefore, the peak value is higher, and the fact that the hydroxyethyl acrylate is successfully grafted on the cellulose is also confirmed. FIG. 1(c) is a spectrum of Cell-g-PCEA: as can be seen from the figure, at 3400cm^-1The nearby hydroxyl stretching vibration peak is greatly weakened, and at the same time, 750cm^-1A stretching vibration peak of a C-Cl bond appears to prove that the chlorination reaction is successful, and the hydroxyethyl group in the Cell-g-PHEA is replaced by chloroethyl. FIG. 1(d) is a spectrum of CD-Cell-g-PHEA: 1481cm^-1A stretching vibration peak of a C-N bond appears at the same time of 750cm^-1The stretching vibration peak of the C-Cl bond is greatly weakened, which confirms the success of the quaternization reaction, namely the cationic derivative of the cellulose grafted poly hydroxyethyl acrylate is successfully obtained.

FIG. 2(a) is a schematic diagram of the surface morphology of cellulose, and since the particle size of the cellulose used in the experiment is not more than 25 μm, and is not a specific value, the particle size and length of the cellulose may be different, and the cellulose is rod-shaped and has different sizes under a lower magnification. The surface of the cellulose was observed to be smooth and even at high magnification. FIG. 2(b) is a scanning electron micrograph of Cell-g-PHEA, which shows that the Cell-g-PHEA is much larger in size than cellulose due to the high grafting ratio, and the Cell-g-PHEA molecular chains are intertwined with each other to roughen the surface. FIG. 2(c) shows that the surface morphology of Cell-g-PCEA is still rough, indicating that the chloro groups do not affect the surface morphology of the polymer. FIG. 2(d) is a scanning electron microscope image of QD-Cell-g-PCEA, and strong electrostatic repulsion exists between cationic groups of the polymer after quaternization, so that the polymer structure is looser, and a pore structure appears on the surface, thereby confirming the success of quaternization reaction. FIG. 2(e) is a scanning electron micrograph of QD-Cell-g-PCEA after adsorption of MO, and it can be seen that the surface of QD-Cell-g-PCEA after adsorption of methyl orange becomes flat because the positive charges of the adsorbent combine with the negative charges of methyl orange, the electrostatic repulsive force is reduced, the pore structure disappears, and the polymer structure becomes dense.

The content of organic chlorine and total chlorine in cellulose-graft-poly (chloroethyl acrylate) (Cell-g-PCEA) was measured as shown in the table:

table 1:

the C, H, N content in cellulose, Cell-g-PHEA, Cell-g-PCEA, and CD-Cell-g-PHEA is determined as shown in Table 2:

table 2:

the results of C, H, N elemental analyses of the cellulose and the products of each stage are shown in the following table. The C, H content in the Cell-g-PHEA sample was increased compared to cellulose, further confirming the successful grafting of hydroxyethyl acrylate onto cellulose. The H content in the Cell-g-PCEA sample is lower than that in the Cell-g-PHEA sample, indicating that the hydroxyl groups in the Cell-g-PHEA sample are replaced by chlorine. The content of N element in the CD-Cell-g-PHEA sample is 3.650 percent, namely 2.607mmol g^-1Indicating that the quaternization reaction was successful and that the number of cationic groups was considerable.

Testing of adsorption performance and regeneration performance:

the cellulose-based cationic adsorbent prepared in example 1 was subjected to adsorption test of methyl orange:

the pH values are respectively 2.45, 3.52, 4.64, 5.12, 5.62, 7.25, 9.47 and 10.80, and the concentration is 100mg L^-150mL of the methyl orange solution is respectively filled into 100mL conical flasks, and 50mg of CD-Cell-g-PHEA adsorbent is respectively added into each conical flask; placing the conical flask into a constant-temperature shaking box with the temperature stabilized at 28 ℃, and adsorbing for 8 hours at the speed of 150 rpm; standing for a period of time after the reaction is finished, taking a proper amount of supernatant to measure the absorbance of the supernatant, and calculating the concentration of the methyl orange after adsorption equilibrium through a known standard curve equation so as to calculate the removal rate of the methyl orange.

The adsorption effect of the cellulose-based cationic adsorbent prepared in example 1 on methyl orange is shown in fig. 3, and as can be seen from fig. 3, the cellulose-based cationic adsorbent prepared in example 1 has a good adsorption effect on methyl orange at a ph of 2.45-10.8, and the removal rate of methyl orange is over 93%, and the maximum removal rate can reach 99.55%.

The cellulose-based cationic adsorbent prepared in example 1 was subjected to an adsorption kinetics experiment to explore the adsorption type of the adsorbent to a methyl orange solution:

the pH value is 5.62, and the concentration is 200mg L^-1100mL of the methyl orange solution was charged into 250mL Erlenmeyer flasks, and 50mg of CD-Cell-g-PHEA adsorbent was added to each Erlenmeyer flask. The flask was placed in a constant temperature shaking chamber at a temperature stabilized at 28 ℃ and the adsorption was carried out at a speed of 150 rpm. And (4) taking a proper amount of supernatant liquid at each period of time, measuring the absorbance of the supernatant liquid, and calculating the adsorption capacity of the adsorbent to the methyl orange solution at the known time and the final adsorption equilibrium capacity.

Fitting parameters of quasi-first-order dynamics and quasi-second-order dynamics models

Example 1 isothermal adsorption model experiment of cellulose-based cationic adsorbent prepared, adsorption isotherm was used to study the adsorption capacity of the adsorbent CD-Cell-g-PHEA for methyl orange solutions of different initial concentrations, and the adsorption capacity of CD-Cell-g-PHEA for methyl orange solutions of that concentration could be estimated:

the pH value is 5.62, and the concentration is 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200 and 1300mg L^-150mL of the methyl orange solution was charged into 100mL Erlenmeyer flasks, and then 50mg of CD-Cell-g-PHEA adsorbent was added to each Erlenmeyer flask. The flask was placed in a constant temperature shaking chamber at a temperature stabilized at 28 ℃ and the adsorption was carried out at a speed of 150 rpm. After the adsorption is balanced, taking a proper amount of supernatant to measure the absorbance of the supernatant, and calculating corresponding equilibrium concentration and equilibrium adsorption capacity.

Freundlich and Langmuir isothermal adsorption model fitting parameters

The cellulose-based cationic adsorbent prepared in example 1 was subjected to adsorption thermodynamic experiments: the pH of the solution filled with 50mg of the adsorbent is 5.62, and the concentration is 1000mg L^-1Volume of 50mL methyl orangePlacing the solution in a constant temperature shaking box with the temperature of 20 ℃, 30 ℃, 35 ℃, 40 ℃ and 50 ℃, adsorbing the solution to saturation at 150rpm, taking the supernatant of the solution, measuring the absorbance of the supernatant, and calculating related parameters.

Thermodynamic parameters of methyl orange adsorbed by adsorbent at different temperatures

The cellulose-based cationic adsorbent prepared in example 1 was subjected to a regenerability test: 50mg of the adsorbent is weighed, mixed with a proper amount of silica gel and placed in a glass adsorption column. 50mL of 300mg L was delivered by a micropump^-1The methyl orange solution is injected into an adsorption column, a mixed solution of sodium hydroxide and sodium chloride is used as an eluent, the adsorption-desorption process is circulated for 4 times, and the regenerability of the adsorbent is evaluated.

The regenerability of the cellulose-based cationic adsorbent prepared in example 1 to methyl orange is shown in fig. 9, and it can be seen from fig. 9 that the removal rate of methyl orange by the cellulose-based cationic adsorbent prepared in example 1 is still as high as 76% after the adsorption-desorption process is cycled for 4 times, which indicates that the cellulose-based cationic adsorbent has better regenerability.

The initial adsorption rate and the maximum adsorption capacity of the cellulose-based cationic adsorbent prepared in example 1 were compared with those of the adsorbents existing in the prior art, and the results are shown in the following table:

maximum adsorption capacity of various adsorbents

Example 2

(1) pretreatment process

Pretreatment of an initiator: adding 150mL of deionized water into a 250mL beaker, heating in a 30 ℃ water bath kettle, gradually adding potassium persulfate into the beaker until the potassium persulfate can not be dissolved, filtering to remove insoluble substances, naturally cooling at room temperature, putting into a 4 ℃ refrigerator for recrystallization, and simultaneously preparing a proper amount of ice deionized water for cleaning. And taking out after 24 hours, cleaning, filtering, and placing the obtained crystal in a vacuum drying oven for drying.

(2) Synthesis of cellulose-graft-polyhydroxyethyl acrylate (Cell-g-PHEA):

and (3) placing the three-neck round-bottom flask containing the cellulose suspension wetted in the step (1) into a constant-temperature water bath kettle, heating to 50 ℃, and introducing nitrogen for protection. After the temperature was constant, 0.15g of potassium persulfate was added to the three-necked flask to initiate the reaction for 30min, and then 5.5g of hydroxyethyl acrylate monomer was slowly added dropwise to the three-necked flask. After reacting for 6h, the water bath kettle is stopped heating. The nitrogen protection is introduced and the stirring is continued throughout the synthesis, taking care that the nitrogen flux can be increased appropriately when initiator and monomer are added. And taking out the product after the water bath is cooled to room temperature, and performing solvent replacement through water-ethanol-acetone to remove unreacted initiator, monomer and homopolymer. And (4) filtering the obtained crude product, and drying in a vacuum drying oven to constant weight. The product was then removed and weighed.

(3) Synthesis of cellulose-graft-Chloroethyl polyacrylate (Cell-g-PCEA):

and (3) adding 1g of the Cell-g-PHEA synthesized in the step (2) into a three-neck round-bottom flask containing 40mL of DMF, placing the three-neck flask into a constant-temperature water bath kettle, heating to 70 ℃, and introducing nitrogen for protection in the whole reaction process. Adding 9.5g of thionyl chloride into the three-neck flask after the temperature is constant, reacting for 12 hours, stopping heating the water bath kettle, cooling to room temperature, taking out the three-neck flask, settling the product in absolute ethyl alcohol for a certain time, filtering the obtained crude product, and drying in a vacuum drying oven to constant weight. The product was then removed and weighed.

weighing 1g of Cell-g-PCEA synthesized in the step (3), adding the Cell-g-PCEA into a three-neck round-bottom flask filled with 50mL of DMF, soaking for 12 hours, placing the three-neck round-bottom flask into a constant-temperature water bath kettle, heating to 60 ℃, and introducing nitrogen for protection in the whole reaction process. After the temperature of the water bath kettle is constant, 0.35g of KI is added into the flask as a catalyst, a certain amount of trimethylamine aqueous solution is slowly dripped into the flask after a period of time, the heating is stopped after the reaction is carried out for 12 hours, and the flask is cooled to the room temperature. And (3) settling the product by using absolute ethyl alcohol, and after the product is subjected to suction filtration, putting the product into a vacuum drying oven to be dried to constant weight.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A preparation method of a cellulose-based cationic adsorbent is characterized by comprising the following steps:

adding hydroxyethyl acrylate monomer into cellulose, and reacting under the action of an initiator to obtain cellulose-graft-polyhydroxyethyl acrylate; continuously adding thionyl chloride to react to obtain cellulose-graft-poly (chloroethyl acrylate); then adding trimethylamine aqueous solution, and reacting under the action of a catalyst to generate a cellulose-graft-polyhydroxyethyl acrylate cation derivative; the mass ratio of the cellulose to the hydroxyethyl acrylate monomer is 1: 1-1: 6; the concentration of the thionyl chloride is 0.25-2.25 mol L^-1(ii) a The concentration of the trimethylamine is 2-10 mol L^-1。

2. The method of claim 1, comprising the steps of:

(1) cellulose pretreatment: soaking cellulose in water to obtain a cellulose suspension;

(2) adding an initiator into the cellulose suspension, then slowly dropwise adding a hydroxyethyl acrylate monomer, and reacting under a certain temperature condition to obtain cellulose-graft-polyhydroxyethyl acrylate;

(3) adding thionyl chloride into the cellulose-graft-polyhydroxyethyl acrylate synthesized in the step (2), and reacting at a certain temperature to obtain cellulose-graft-polyhydroxyethyl acrylate;

(4) and (4) adding a proper amount of catalyst into the cellulose-graft-poly (chloroethyl acrylate) synthesized in the step (3), and slowly dropwise adding a trimethylamine aqueous solution for reaction to obtain the cellulose-graft-poly (hydroxyethyl acrylate) cationic derivative.

3. The method of claim 2, wherein the initiator is potassium persulfate.

4. The method of claim 2, wherein the catalyst is potassium iodide.

5. The method of claim 2, wherein the soaking time of the cellulose in water is 10 to 14 hours.

6. The process according to claim 3, wherein the concentration of potassium persulfate is 0.005 to 0.06mol L^-1。

7. The process according to claim 3, wherein the concentration of potassium persulfate is 0.015 to 0.04mol L^-1。

8. The process according to claim 3, wherein the concentration of potassium persulfate is 0.0285mol L^-1。

9. The method according to claim 2, wherein the concentration of the monomeric hydroxyethyl acrylate is 0.5 to 3.5mol L^-1。

10. The method according to claim 2, wherein the concentration of the monomeric hydroxyethyl acrylate is 1.5 to 3.0mol L^-1。

11. The method of claim 2, wherein the concentration of the monomeric hydroxyethyl acrylate is 2.5835mol L^-1。

12. The method according to claim 2, wherein the reaction temperature in the step (2) is 30 to 70 ℃.

13. The method according to claim 2, wherein in the step (2), the reaction temperature is 50 ℃.

14. The method of claim 2, wherein the purification of the product cellulose-graft-polychlorinated acrylic acid ethyl ester in step (2) is performed by solvent displacement with water-ethanol-acetone to remove unreacted initiator, monomer and homopolymer.

15. The method according to claim 2, wherein the concentration of thionyl chloride is 0.75 to 2.0mol L^-1。

16. The process according to claim 2, wherein the concentration of thionyl chloride is 1.8910mol L^-1。

17. The method according to claim 2, wherein the reaction temperature in the step (3) is 40 to 75 ℃.

18. The method according to claim 2, wherein in the step (3), the reaction temperature is 70 ℃.

19. The method according to claim 2, wherein the concentration of trimethylamine is 4.0 to 8.0mol L^-1。

20. The method of claim 2, wherein the trimethylamine is present in a concentration of6.7797mol L^-1。

21. The preparation method according to claim 2, wherein the concentration of the potassium iodide catalyst is 0 to 0.075mol L^-1。

22. The method of claim 2, wherein the concentration of potassium iodide as a catalyst is 0.025 to 0.045mol L^-1。

23. The method of claim 2, wherein the concentration of potassium iodide as a catalyst is 0.0361mol L^-1。

24. The method according to claim 2, wherein in the step (4), the reaction temperature is 50 to 70 ℃.

25. The method according to claim 2, wherein in the step (4), the reaction temperature is 60 ℃.

26. The method according to claim 2, wherein in the step (4), the product is precipitated with absolute ethanol after completion of the reaction.

27. The method of claim 2, wherein the inert gas is introduced to protect the reaction in steps (2) to (4) over the whole course of the reaction.

28. The method of claim 27, wherein the inert gas introduced throughout the reactions of steps (2) - (4) is nitrogen.

29. A cellulose-based cationic adsorbent prepared by the method of any one of claims 1-28.

30. Use of the cellulose-based cationic adsorbent of claim 29 in dye wastewater treatment.

31. Use of the cellulose-based cationic adsorbent of claim 30 in dye wastewater treatment, wherein the dye wastewater comprises methyl orange wastewater.