CN110918067B - Grafted cellulose adsorbent and preparation method and application thereof - Google Patents
Grafted cellulose adsorbent and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the technical field of functional polymers, and particularly discloses a grafted cellulose adsorbent and a preparation method and application thereof. The preparation method of the grafted cellulose adsorbent comprises the following steps: the method comprises the steps of taking cheap and easily-obtained cellulose as a raw material, taking ionic liquid as a solvent to dissolve the cellulose, preparing a cellulose macroinitiator by reacting the cellulose with 2-bromoisobutyryl bromide, and grafting acrylamide molecules into a molecular chain of the cellulose macroinitiator under the action of a cross-linking agent by adopting a traditional ATRP method. The maximum adsorption capacity of the grafted cellulose adsorbent prepared by the method is 55.03mg/g for copper ions and 90.12mg/g for chromium ions, and after the grafted cellulose adsorbent is repeatedly used for five times, the maximum adsorption capacity of the grafted cellulose adsorbent for copper ions and chromium ions can still reach 81.4% and 74.8% of the maximum adsorption capacity of the first test, so that the grafted cellulose adsorbent has high adsorption performance and multiple recycling performance, and has good economic benefit and environmental protection benefit.
Description
Technical Field
The invention relates to the technical field of functional polymers, in particular to a grafted cellulose adsorbent and a preparation method and application thereof.
Background
With the continuous progress of society, resources are continuously developed and utilized, and environmental problems become more severe, wherein the problem of water pollution becomes the most severe environmental problem at present. Heavy metal ions in sewage are one of the most serious pollutants affecting the environment, seriously affect the water safety and threaten the life health of people. Conventional water treatment materials have become increasingly incapable of meeting the ever-increasing demand for clean water. The problem to be solved at present is to develop a water treatment material with high efficiency, low cost and no secondary pollution.
Aiming at the pollution problem of heavy metal ions in sewage, more and more researchers select an adsorption method which is wide in raw material source, large in adsorption capacity, low in economic cost and convenient in regeneration treatment to remove the heavy metal ions in the sewage. The cellulose has the advantages of high yield, biodegradability, good biocompatibility, capability of enriching pollutants, capability of adsorbing a small amount of heavy metal ions, environmental friendliness and the like, and is widely applied to being used as an adsorbent for the heavy metal ions. However, the high molecular structure of cellulose has a large number of hydroxyl groups, which form intramolecular and intermolecular hydrogen bonds, thus seriously affecting the reactivity thereof, resulting in unsatisfactory adsorption effect. Graft modification is an important method for improving the adsorption effect of cellulose. However, the existing graft-modified cellulose has poor adsorption performance on heavy metal ions, the reusability of the adsorbent is poor, and the sewage treatment cost is still high. Therefore, the development of the cellulose-based adsorbent which has large heavy metal ion adsorption capacity and can be recycled is of great significance.
Disclosure of Invention
Aiming at the problems of poor heavy metal ion adsorption performance and poor reusability of the existing cellulose-based adsorbent, the invention provides a grafted cellulose adsorbent and a preparation method and application thereof.
In order to solve the technical problems, the technical scheme provided by the invention is as follows:
a preparation method of a grafted cellulose adsorbent comprises the following steps:
dissolving cellulose in chlorinated 1-allyl-3-methylimidazole ([ AMIM ] Cl ionic liquid), adding 2-bromoisobutyryl bromide and toluene, and reacting to obtain a cellulose macroinitiator; the reaction principle is as follows:
and step two, dissolving the cellulose macroinitiator in N, N-dimethylformamide, adding acrylamide, uniformly mixing, adding a catalyst, a reaction ligand and a cross-linking agent, uniformly mixing, and reacting at 60-70 ℃ for 15-17h under an inert atmosphere to obtain the grafted cellulose adsorbent. The reaction principle is as follows:
compared with the prior art, the preparation method of the grafted cellulose adsorbent provided by the invention firstly dissolves cellulose in [ AMIM]In Cl ion liquid, [ AMIM]Cl in Cl ion liquid - Reacts with-OH in cellulose molecule to generate hydrogen bond and reacts in [ AMIM ]] + The crystalline region in the cellulose molecule is opened under the synergistic effect of the two, so that the cellulose is fully dissolved, the accessibility of hydroxyl is increased, the full reaction of the cellulose and the 2-bromoisobutyryl bromide is facilitated, and the grafting rate of the subsequent grafting reaction is improved; then functional monomer acrylamide is grafted on a cellulose framework through a conventional Atom Transfer Radical Polymerization (ATRP) method, atoms containing lone pair electrons such as N, O and the like in the acrylamide can be chelated with heavy metal ions and cooperate with-OH on the surface of cellulose, so that the adsorption capacity of the adsorbent to the heavy metal ions is obviously enhanced, and the preparation method of the grafted cellulose provided by the invention can also improve the roughness of the surface of the cellulose, make the surface of the cellulose loose and porous, increase the surface area of the cellulose adsorbent, further increase the contact area of the cellulose adsorbent and the heavy metal ions, and further improve the adsorption performance to the heavy metal ions. Meanwhile, the grafted cellulose adsorbent prepared by the invention can be desorbed and regenerated in a strong acid aqueous solution, and has good regeneration and reutilization properties.
The maximum adsorption capacity of the grafted cellulose adsorbent prepared by the method is 55.03mg/g for copper ions and 90.12mg/g for chromium ions, the grafted cellulose adsorbent after adsorbing heavy metal ions is desorbed and regenerated in a strong acid aqueous solution, and after the regenerated grafted cellulose adsorbent is reused for five times, the maximum adsorption capacity of the grafted cellulose adsorbent for copper ions and chromium ions can still reach 81.4 percent and 74.8 percent of the maximum adsorption capacity of the grafted cellulose adsorbent for the first time, so that the grafted cellulose adsorbent has high adsorption performance and recycling performance for multiple times, has good economic benefit and environmental protection benefit, and has wide application prospect in the field of sewage treatment.
The inert gas atmosphere in the invention is formed by introducing inert gas which is conventional in the field into the reactor, and the inert gas can be nitrogen, argon or helium, etc.
Preferably, in the first step, the cellulose is microcrystalline cellulose.
Preferably, in the first step, the reaction temperature is 20-30 ℃, and the reaction time is 23-25 h.
Preferably, in the first step, the mass ratio of the cellulose to the 1-allyl-3-methylimidazole chloride is 1: 10-30.
Preferably, in the first step, the mass ratio of the cellulose to the toluene is 1: 1-2.
Preferably, in the first step, the mass ratio of the cellulose to the 2-bromoisobutyryl bromide is 1: 4-10.
The optimized reaction temperature, reaction time and the ratio of the substances are favorable for improving the accessibility of hydroxyl on the surface of the cellulose, so that the cellulose and the 2-bromoisobutyryl bromide fully react, and further the grafting rate of the subsequent grafting reaction is favorably improved.
Preferably, in the second step, the catalyst is copper bromide.
Preferably, in the second step, the reaction ligand is diethylenetriamine.
Preferably, in the second step, the crosslinking agent is N, N-methylene bisacrylamide.
The preferable compounding of the catalyst, the reaction ligand and the cross-linking agent can lead the grafting monomer acrylamide and the cellulose macroinitiator to be properly cross-linked, avoid the problem of excessive cross-linking or insufficient cross-linking and obtain the cellulose adsorbent with excellent grafting rate.
Preferably, in the second step, the mass ratio of the cellulose macroinitiator to the acrylamide is 1: 10-15.
If the amount of the monomer is too large, on the one hand, swelling of the cellulose can be reduced, so that polymerization reaction of the grafted cellulose cannot go deep into the cellulose substrate but mainly occurs in the outer layer of the cellulose, so that acrylamide is relatively more prone to participate in the reaction for forming a homopolymer, and the grafting rate is reduced; on the other hand, when the acrylamide monomer is too much, the steric hindrance of the grafted chain is increased, the efficiency of the grafted chain reaching the active site on the cellulose skeleton is reduced, the difficulty of forming a branched chain is increased, and the grafting rate is also reduced. In addition, an excessive amount of the monomer increases the viscosity of the reaction system, decreases the diffusion rate of the acrylamide monomer into the cellulose skeleton, and decreases the graft ratio. When the mass ratio of the cellulose macroinitiator to the acrylamide is 1:10-15, the grafting rate of the reaction reaches the highest.
Preferably, in the second step, the mass ratio of the catalyst to the cellulose macroinitiator is 0.2-0.3: 1.
Preferably, in the second step, the mass ratio of the N, N-dimethylformamide to the cellulose macroinitiator is 20-30: 1.
The N, N-dimethylformamide is selected as a solvent, and the specific proportion is selected, so that the cellulose macroinitiator, the N, N-methylene bisacryloyl cross-linking agent, the diethylenetriamine reaction ligand and the acrylamide monomer are fully dissolved to form a uniform reaction system, the controllable polymerization of the cellulose grafting reaction is realized, the polyacrylamide is uniformly grafted on a cellulose molecular skeleton to form a grafted cellulose polymer with controllable molecular size and uniform molecular weight distribution, the grafting rate is improved, the density of an acrylamide functional group is improved, the chelating effect of atoms containing lone pair electrons such as N, O on the functional group on heavy metal ions is fully exerted, and the heavy metal ions in the sewage are effectively removed.
Preferably, in the second step, the mass ratio of the reaction ligand to the cellulose macroinitiator is 1-2: 1.
Preferably, in the second step, the mass ratio of the cross-linking agent to the cellulose macroinitiator is 0.004-0.005: 1.
The optimized proportion of the substances is favorable for fully reacting the acrylamide grafting monomer with the cellulose macroinitiator and improving the grafting rate.
The invention also provides a grafted cellulose adsorbent prepared by any one of the preparation methods of the grafted cellulose adsorbent.
The grafted cellulose adsorbent provided by the invention has stable performance, is environment-friendly, has excellent adsorption capacity on heavy metal ions, and has good renewable recycling performance, so that the added value of cellulose is obviously improved, the cost of sewage treatment is obviously reduced, and the grafted cellulose adsorbent has good economic and social benefits.
Drawings
Fig. 1 is an infrared spectrum of the grafted cellulose adsorbent, the cellulose macroinitiator, and the microcrystalline cellulose prepared in example 1 of the present invention: (a) microcrystalline cellulose, (b) a cellulose macroinitiator, (c) a grafted cellulose adsorbent;
FIG. 2 is a nuclear magnetic hydrogen spectrum of the cellulose macroinitiator prepared in example 1;
FIG. 3 is a nuclear magnetic hydrogen spectrum of the grafted cellulose adsorbent prepared in example 1;
FIG. 4 is a scanning electron micrograph of a grafted cellulose adsorbent prepared according to example 1 of the present invention;
FIG. 5 is a scanning electron micrograph of microcrystalline cellulose;
FIG. 6 is a graph of the effect of the adsorption capacity of grafted cellulose adsorbent and microcrystalline cellulose prepared in example 1 of the present invention on copper ions over time: (a) microcrystalline cellulose, (b) a grafted cellulose adsorbent;
FIG. 7 is a graph of the effect of adsorption capacity of grafted cellulose adsorbent and microcrystalline cellulose prepared in example 1 of the present invention on chromium ions over time: (a) microcrystalline cellulose, (b) a grafted cellulose adsorbent;
FIG. 8 is a graph showing the effect of adsorption capacity of copper ions on the number of times of adsorption by the grafted cellulose adsorbent prepared in example 1 of the present invention;
FIG. 9 is a graph showing the effect of adsorption capacity of the grafted cellulose adsorbent prepared in example 1 of the present invention on chromium ions as a function of the number of times of adsorption.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
In order to better illustrate the invention, the following examples are given by way of further illustration.
Example 1
A preparation method of a grafted cellulose adsorbent comprises the following steps:
step one, weighing 4g of microcrystalline cellulose, adding the weighed cellulose into a 500mL three-necked bottle filled with 100g of [ AMIM ] Cl ionic liquid for 3 times, heating at a constant temperature of 80 ℃, magnetically stirring until the microcrystalline cellulose is completely dissolved, taking out the three-necked bottle, cooling to room temperature, transferring the three-necked bottle into an ice water bath, slowly adding 24g of 2-bromoisobutyryl bromide and 6g of toluene, reacting for 24 hours under the condition of constant-temperature magnetic stirring at 25 ℃, washing with distilled water, carrying out suction filtration, and carrying out vacuum drying to obtain a cellulose macroinitiator (MCC-BiB);
step two, weighing 5g of MCC-BiB and 125g of DMF, adding the MCC-BiB and the DMF into a 500mL three-necked bottle, connecting a condensation and nitrogen protection device, stirring at a constant temperature of 70 ℃ until the MCC-BiB is completely dissolved, adding 65g of acrylamide at 65 ℃, uniformly mixing, slowly adding 1g of copper bromide, 5g of bisacrylamide and 0.023g N, N-methylene bisacrylamide, reacting for 16h at 65 ℃ under a nitrogen atmosphere, cooling to room temperature, transferring all reaction liquid in the three-necked bottle into a dialysis bag with molecular weight cutoff of 3000-plus 4000, placing the dialysis bag into a beaker filled with deionized water, dialyzing for 72h, changing water once every 6h, and then drying in vacuum to obtain the grafted microcrystalline cellulose adsorbent.
The graft ratio of the grafted microcrystalline cellulose prepared in this example was 74.29%.
Meter of graft Rate (GE)The calculation formula is as follows: GE ═ m 2 -m 0 )/m 1 ×100％；
Wherein m is 2 Mass of grafted cellulose, g; m is 1 Mass of acrylamide monomer, g; m is 0 Is the mass of the cellulose macroinitiator, g.
FIG. 1 is an infrared spectrum of the grafted cellulose adsorbent, cellulose macroinitiator and microcrystalline cellulose prepared in this example, from which it can be seen that 3300cm -1 The peak is hydroxyl peak on cellulose, compared with cellulose macroinitiator, the-OH stretching vibration peak of the cellulose is obviously weakened at the position, and the cellulose macroinitiator is 1750cm -1 The peak with larger intensity is a stretching vibration peak of (C ═ O) of the 2-bromoisobutyryl bromide, which indicates that the 2-bromoisobutyryl bromide is grafted to the microcrystalline cellulose through acylation reaction to generate a cellulose macroinitiator.
Grafted cellulose adsorbent at 3194cm -1 The characteristic peak of amide appears at 1668cm -1 The peak of stretching vibration of (C ═ O) in the amide appears at 1471cm -1 The expansion vibration peak of (C-N) bond in amide appears, which indicates that the polyacrylamide grafted microcrystalline cellulose adsorbent is synthesized by the ATRP method.
Fig. 2 and fig. 3 are nuclear magnetic hydrogen spectra of the cellulose macroinitiator and the grafted cellulose adsorbent prepared in this example, respectively, and it can be seen from the nuclear magnetic hydrogen spectra of the cellulose macroinitiator that two hydrogen spectra with chemical shifts δ ═ 1.70ppm and 1.90ppm are the bismethyl peak of the acyl bromide group in 2-bromoisobutyryl bromide; the proton peak between the chemical shift delta being 4.0-6.0ppm is a multiple hydrogen proton peak on a microcrystalline cellulose framework, and the structure of the cellulose macroinitiator is further confirmed by further analyzing the nuclear magnetic hydrogen spectrum of the cellulose macroinitiator.
The nuclear magnetic hydrogen spectrum of the grafted cellulose adsorbent is analyzed, and the proton peak with chemical shift delta-5.695 is-CONH on the side chain of polyacrylamide 2 The proton peak in (1) is the proton peak in the polyacrylamide molecular chain, and the proton peak between chemical shifts delta-3.572-4.631 ppm is the proton peak in the polyacrylamide molecular chain. Combined infrared spectroscopyThe figure and nuclear magnetic hydrogen spectrum analysis can confirm that the polyacrylamide grafted microcrystalline cellulose adsorbent is successfully grafted and synthesized on the surface of cellulose by using an ATRP method.
Fig. 4 is a scanning electron microscope image of the grafted cellulose adsorbent prepared in this embodiment, and fig. 5 is a scanning electron microscope image of microcrystalline cellulose, and it can be seen from the image that before participating in the ATRP graft modification reaction, the surface of microcrystalline cellulose is relatively smooth, and compared with the cellulose after graft modification, the surface is very rough, which is because polyacrylamide is grafted on the surface of microcrystalline cellulose, so that the surface appearance of the microcrystalline cellulose is significantly changed, the surface appearance of the microcrystalline cellulose is rough and porous, the contact area between the grafted cellulose product and heavy metal ions is increased, and meanwhile, a large number of chelating groups are present on the surface of the grafted cellulose, and the adsorption performance of the grafted cellulose adsorbent to heavy metal ions is significantly improved.
Testing of adsorption performance and regeneration performance:
the test method comprises the following steps:
1. preparation of the solution
Mixing CuSO 4 ·5H 2 O is prepared into 100mg/L copper ion standard stock solution; the potassium dichromate is prepared into a chromium ion standard stock solution of 100 mg/L.
21.396g of ammonium chloride is dissolved in 29.9mL of concentrated ammonia water with the mass concentration of 22-25%, 100mL of deionized water is added for complete dissolution, and the volume is determined to be 500mL by absolute ethyl alcohol, so as to obtain 0.8mol/L ammonia water-ammonium chloride buffer solution (the pH value is 8-10).
0.5g of diphenyl carbodihydrazide (DPCI) is dissolved in 50mL of absolute ethyl alcohol, the volume is determined to be 100mL by the absolute ethyl alcohol, and a chromium ion color developing agent solution with the concentration of 0.02mol/L is prepared.
0.5g of sodium diethyldithiocarbamate (DDTC) reagent is dissolved in 100mL of sodium hydroxide solution to obtain a copper ion color developing agent solution, and the solution is prepared on site.
Sulfuric acid (1+1) solution: sulfuric acid (density 1.84g/mL) was slowly added to the same volume of water and mixed well.
Phosphoric acid (1+1) solution: phosphoric acid (density 1.69g/mL) was slowly added to the same volume of water and mixed well.
Taking a copper ion standard stock solution, adding 0.2mL of copper ion color development agent solution and 0.4mL of ammonia water-ammonium chloride buffer solution into each milliliter of copper ion standard stock solution to prepare a series of standard copper ion solutions with the concentrations of 1mg/L, 2mg/L, 3mg/L, 4mg/L, 5mg/L and 6mg/L respectively.
Taking a chromium ion standard stock solution, adding 0.4mL of chromium ion color development agent solution, 0.125mL of sulfuric acid (1+1) solution and 0.125mL of phosphoric acid (1+1) solution into each milliliter of chromium ion standard stock solution to prepare a series of standard chromium ion solutions with the concentrations of 0.2mg/L, 0.4mg/L, 0.6mg/L, 0.8mg/L and 1.0mg/L respectively.
And respectively measuring the absorbance of the series of labeled copper ion solutions and chromium ion solutions in an ultraviolet spectrophotometer, and performing linear fitting according to different concentrations and absorbances to obtain a standard curve.
The standard curve equation of copper ion is Y ═ 0.059+1.796X (R) 2 0.9992), the standard curve equation of chromium ion is Y0.017 +0.991X (R) 2 ＝0.9989)。
2. Calculation of the adsorption amount of the grafted cellulose adsorbent:
and measuring the absorbance of the metal ion solution to be measured by using an ultraviolet spectrophotometer, and calculating the metal ion concentration of the solution to be measured by using the obtained standard curve. The adsorption capacity was calculated according to the following formula:
wherein Q is the adsorption capacity (mg/g);
C 0 initial metal ion concentration (mg/L);
C 1 the metal ion concentration (mg/L) after the adsorption experiment is obtained;
v is the volume of the experimental solution (L);
and m is the mass (g) of the adsorbent sample.
3. Comparison of adsorption Properties of grafted microcrystalline cellulose and microcrystalline cellulose
12 100mL beakers were charged with copper ions (Cu) at an initial concentration of 300mg/L and pH4.5, respectively 2+ ) Solution, 0.5g of the grafted microcrystalline cellulose adsorbent prepared in example 1 was added to 6 beakers, the same mass of microcrystalline cellulose was added to the remaining 6 beakers, the same adsorption time (40min, 80min, 120min, 160min and 200min) was controlled, and the adsorption was measured after the adsorption was completed. The results are shown in FIG. 6.
12 100mL beakers were charged with chromium ions (Cr) at an initial concentration of 300mg/L and pH4.5, respectively 6+ ) Solution, 0.5g of the grafted microcrystalline cellulose adsorbent prepared in example 1 was added to 6 beakers, the same mass of microcrystalline cellulose was added to the remaining 6 beakers, the same adsorption time (40min, 80min, 120min, 160min and 200min) was controlled, and the adsorption was measured after the adsorption was completed. The results are shown in FIG. 7.
As can be seen from FIG. 6, compared with unmodified microcrystalline cellulose, the adsorption capacity of microcrystalline cellulose modified by ATRP method is greatly improved, the maximum adsorption capacity of microcrystalline cellulose to copper ions reaches 5.00mg/g, while the maximum adsorption capacity of graft-modified microcrystalline cellulose reaches 55.03mg/g, and the adsorption capacity is improved by 11 times.
As can be seen from FIG. 7, the maximum adsorption amount of chromium ions by unmodified microcrystalline cellulose is 12.68mg/g, while the maximum adsorption amount of ionic chromium by the microcrystalline cellulose modified by the ATRP method reaches 90.12mg/g, and the adsorption amount is improved by nearly 8 times.
The results prove that although-OH in the microcrystalline cellulose can be used as a chelating site to be combined with heavy metal ions so as to enable the microcrystalline cellulose to have certain adsorption performance, the adsorption performance is low. The acrylamide molecular side chain is uniformly grafted on the surface of the microcrystalline cellulose by utilizing the ATRP technology, so that the content of N, O atoms containing lone pair electrons is increased, the chelating sites of the microcrystalline cellulose and heavy metal ions are increased, the surface area of the microcrystalline cellulose is increased, and the contact probability of the microcrystalline cellulose and the heavy metal ions is further increased, and therefore, the adsorption capacity of the polyacrylamide graft modified microcrystalline cellulose to the heavy metal ions is far higher than that of the unmodified microcrystalline cellulose.
4. Desorption and reutilization properties of grafted microcrystalline cellulose adsorbent
And desorbing the grafted microcrystalline cellulose after adsorbing the heavy metal by using 0.5mol/L hydrochloric acid solution as an eluent, then adjusting the pH value to be neutral, cleaning and drying to obtain the desorbed grafted microcrystalline cellulose adsorbent. The test of the recycling performance is carried out according to the test condition of '3 comparison of the adsorption performance of the grafted microcrystalline cellulose and the microcrystalline cellulose'.
Respectively weighing the same mass (0.5g) of grafted microcrystalline cellulose adsorbent, grafted microcrystalline cellulose adsorbent desorbed after first adsorption, grafted microcrystalline cellulose adsorbent desorbed after two times of adsorption, grafted microcrystalline cellulose adsorbent desorbed after three times of adsorption, grafted microcrystalline cellulose adsorbent desorbed after four times of adsorption and grafted microcrystalline cellulose adsorbent desorbed after five times of adsorption, adding the materials into a 100mL beaker, and respectively adding 300mg/L of copper ion (Cu) with pH4.5 (Cu) 2+ ) The solution was adsorbed for 120min, and the results are shown in FIG. 8.
Respectively weighing the same mass (0.5g) of grafted microcrystalline cellulose adsorbent, grafted microcrystalline cellulose adsorbent desorbed after first adsorption, grafted microcrystalline cellulose adsorbent desorbed after two times of adsorption, grafted microcrystalline cellulose adsorbent desorbed after three times of adsorption, grafted microcrystalline cellulose adsorbent desorbed after four times of adsorption and grafted microcrystalline cellulose adsorbent desorbed after five times of adsorption, adding the materials into a 100mL beaker, and respectively adding 300mg/L of chromium ions (Cr ions) with pH of 4.5 (Cr ions/L) 6+ ) Solution, adsorption for 120min, shown in FIG. 9
It can be obtained from the figure that the grafted microcrystalline cellulose adsorbent is repeatedly used for 6 times, and the adsorption capacity can still reach 81.4% of the maximum adsorption capacity of the first adsorption. After the grafted microcrystalline cellulose adsorbent adsorbs chromium ions for 6 times, the adsorption capacity of the grafted microcrystalline cellulose adsorbent can also reach 74.8% of the maximum adsorption capacity of the first adsorption, and experimental data can show that the grafted microcrystalline cellulose adsorbent has excellent regeneration performance, the cost of the adsorbent in the production process can be reduced, and resources are saved.
According to experimental phenomena, the grafted microcrystalline cellulose adsorbent can be desorbed and regenerated in a strong acidic solution, possibly in a strong acidic aqueous solution, H + Will react with heavy metal ionsCompete for adsorption sites while allowing-CONH in the grafted microcrystalline cellulose adsorbent 2 Protonation occurs to form-CONH 3+ Formation of-CONH 3+ Due to the electrostatic repulsion effect with the heavy metal ions, the chelation stability of the adsorbent and the heavy metal ions is reduced under the dual action, so that the adsorbed heavy metal ions are desorbed into the solution, and the regeneration of the grafted microcrystalline cellulose adsorbent is realized.
Example 2
A preparation method of a grafted microcrystalline cellulose adsorbent comprises the following steps:
step one, weighing 4g of microcrystalline cellulose, adding the weighed cellulose into a 500mL three-necked bottle filled with 120g of [ AMIM ] Cl ionic liquid for 3 times, heating at a constant temperature of 80 ℃, magnetically stirring until the microcrystalline cellulose is completely dissolved, taking out the three-necked bottle, cooling to room temperature, transferring the three-necked bottle into an ice-water bath, slowly adding 16g of 2-bromoisobutyryl bromide and 8g of toluene, reacting for 25 hours under the condition of constant-temperature magnetic stirring at 20 ℃, washing with distilled water, performing suction filtration, and performing vacuum drying to obtain a cellulose macroinitiator (MCC-BiB);
step two, weighing 5g of MCC-BiB and 100g of DMF, adding the MCC-BiB and the DMF into a 500mL three-necked bottle, connecting a condensation and nitrogen protection device, stirring at a constant temperature of 70 ℃ until the MCC-BiB is completely dissolved, adding 50g of acrylamide at 60 ℃, uniformly mixing, slowly adding 1.5g of copper bromide, 10g of bisacrylamide and 0.02g of N, N-methylene bisacrylamide, reacting for 17h at 60 ℃ under a nitrogen atmosphere, cooling to room temperature, transferring all reaction liquid in the three-necked bottle into a dialysis bag with molecular weight cutoff of 3000-plus 4000, placing the dialysis bag into a beaker filled with deionized water, dialyzing for 72h, changing water once every 6h, and then drying in vacuum to obtain the grafted microcrystalline cellulose adsorbent.
The graft ratio of the grafted microcrystalline cellulose prepared in this example was 73.19%.
Example 3
A preparation method of a grafted microcrystalline cellulose adsorbent comprises the following steps:
step one, weighing 4g of microcrystalline cellulose, adding the weighed cellulose into a 500mL three-necked bottle filled with 40g of [ AMIM ] Cl ionic liquid for 3 times, heating at a constant temperature of 80 ℃, magnetically stirring until the microcrystalline cellulose is completely dissolved, taking out the three-necked bottle, cooling to room temperature, transferring the three-necked bottle into an ice water bath, slowly adding 40g of 2-bromoisobutyryl bromide and 4g of methylbenzene, reacting for 23 hours under the condition of constant-temperature magnetic stirring at 30 ℃, washing with distilled water, carrying out suction filtration, and carrying out vacuum drying to obtain a cellulose macroinitiator (MCC-BiB);
step two, weighing 5g of MCC-BiB and 150g of DMF, adding the MCC-BiB and the DMF into a 500mL three-necked bottle, connecting a condensing and nitrogen protection device, stirring at a constant temperature of 70 ℃ until the MCC-BiB is completely dissolved, adding 75g of acrylamide, uniformly mixing, slowly adding 1.25g of copper bromide, 7.5g of divinylamide and 0.025g N, N-methylene bisacrylamide, reacting at 70 ℃ under a nitrogen atmosphere for 15 hours, cooling to room temperature, transferring all reaction liquid in the three-necked bottle into a dialysis bag with molecular weight cutoff of 3000-minus 4000, placing the dialysis bag into a beaker filled with deionized water, dialyzing for 72 hours, changing water once every 6 hours, and then drying in vacuum to obtain the grafted microcrystalline cellulose adsorbent.
The graft ratio of the grafted microcrystalline cellulose prepared in this example was 73.84%.
Example 4
A preparation method of a grafted microcrystalline cellulose adsorbent comprises the following steps:
step one, weighing 4g of microcrystalline cellulose, adding the weighed cellulose into a 500mL three-necked bottle filled with 40g of [ AMIM ] Cl ionic liquid for 3 times, heating at a constant temperature of 80 ℃, magnetically stirring until the microcrystalline cellulose is completely dissolved, taking out the three-necked bottle, cooling to room temperature, transferring the three-necked bottle into an ice-water bath, slowly adding 40g of 2-bromoisobutyryl bromide and 4g of toluene, reacting for 24 hours under the condition of constant-temperature magnetic stirring at 25 ℃, washing with distilled water, performing suction filtration, and performing vacuum drying to obtain a cellulose macroinitiator (MCC-BiB);
step two, weighing 5g of MCC-BiB and 150g of DMF, adding the MCC-BiB and the DMF into a 50mL three-necked bottle, connecting a condensation and nitrogen protection device, stirring at a constant temperature of 70 ℃ until the MCC-BiB is completely dissolved, adding 75g of acrylamide, uniformly mixing, slowly adding 1.25g of copper bromide, 7.5g of divinylamide and 0.025g of epichlorohydrin cross-linking agent, reacting at 70 ℃ under a nitrogen atmosphere for 15 hours, cooling to room temperature, transferring all reaction liquid in the three-necked bottle into a dialysis bag with molecular weight cutoff of 3000-4000, placing the dialysis bag into a beaker filled with deionized water, dialyzing for 72 hours, changing water once every 6 hours, and then drying in vacuum to obtain the grafted microcrystalline cellulose adsorbent.
The graft ratio of the grafted microcrystalline cellulose prepared in this example was 56.25%. For copper ion (Cu) 2+ ) Has a maximum adsorption amount of 42.05mg/g, and can adsorb chromium ions (Cr) 6+ ) The maximum adsorption amount of (2) was 76.24 mg/g.
Comparative example 1
This comparative example provides a method for preparing a grafted microcrystalline cellulose adsorbent, which is the same as in example 1, except that the mass ratio of the cellulose macroinitiator to acrylamide was replaced with 1: 5.
The graft ratio of the grafted microcrystalline cellulose prepared in this comparative example was 31.59%. For copper ion (Cu) 2+ ) Has a maximum adsorption amount of 25.33mg/g, and has a chromium ion (Cr) adsorption capacity 6+ ) The maximum adsorption amount of (A) was 41.69 mg/g.
Comparative example 2
This comparative example provides a method of preparing a grafted microcrystalline cellulose adsorbent, which is the same as in example 1, except that the mass ratio of the cellulose macroinitiator to acrylamide was replaced with 1: 20.
The graft ratio of the grafted microcrystalline cellulose prepared in this comparative example was 49.87%. For copper ion (Cu) 2+ ) Has a maximum adsorption amount of 41.32mg/g, and has a chromium ion (Cr) adsorption capacity 6+ ) The maximum adsorption amount of (2) was 65.02 mg/g.
Comparative example 3
This comparative example provides a process for the preparation of a grafted microcrystalline cellulose adsorbent, which is the same as that of example 1, except that acrylamide is replaced by an equal amount of glycidyl methacrylate.
The graft ratio of the grafted microcrystalline cellulose prepared in this comparative example was 52.18%. For copper ion (Cu) 2+ ) Has a maximum adsorption amount of 44.25mg/g, and has a high adsorption capacity for chromium ions (Cr) 6+ ) The maximum adsorption amount of (a) was 63.02 mg/g.
Comparative example 4
This comparative example provides a method of making a grafted microcrystalline cellulose adsorbent, which is the same as example 1, except that acrylamide is replaced with an equal amount of acrylic acid.
The graft ratio of the grafted microcrystalline cellulose prepared in this comparative example was 43.05%. For copper ion (Cu) 2+ ) Has a maximum adsorption amount of 31.91mg/g, and has a chromium ion (Cr) adsorption capacity of 6+ ) The maximum adsorption amount of (A) was 48.26 mg/g.
From the above results, compared with the case that glycidyl methacrylate and acrylic acid are used as the grafting monomers, the cellulose is grafted and modified by using acrylamide as the grafting monomer, so that the adsorption performance of the cellulose on copper ions and chromium ions can be remarkably improved, and the removal of the copper ions and chromium ions in sewage is facilitated.
The grafted microcrystalline cellulose adsorbents prepared in examples 2-3 of the present invention all achieved substantially the same results as example 1.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (6)
1. The application of the grafted cellulose adsorbent in removing heavy metal ions in sewage is characterized in that the preparation method of the grafted cellulose adsorbent comprises the following steps:
dissolving cellulose in chlorinated 1-allyl-3-methylimidazole, adding 2-bromoisobutyryl bromide and toluene, and reacting to obtain a cellulose macroinitiator; the mass ratio of the cellulose to the chlorinated 1-allyl-3-methylimidazole is 1: 10-30; the mass ratio of the cellulose to the toluene is 1: 1-2;
dissolving the cellulose macroinitiator in N, N-dimethylformamide, adding acrylamide, uniformly mixing, adding a catalyst, a reaction ligand and a cross-linking agent, uniformly mixing, and reacting at 60-70 ℃ for 15-17 hours under an inert atmosphere to obtain the grafted cellulose adsorbent; in the second step, the mass ratio of the cross-linking agent to the cellulose macroinitiator is 0.004-0.005: 1;
wherein the cellulose is microcrystalline cellulose; the reaction ligand is diethylenetriamine, and the cross-linking agent is N, N-methylene-bisacrylamide; the mass ratio of the cellulose macroinitiator to the acrylamide is 1: 10-15.
2. The application of the grafted cellulose adsorbent in removing heavy metal ions in sewage as claimed in claim 1, wherein in the first step, the reaction temperature is 20-30 ℃ and the reaction time is 23-25 h.
3. The application of the grafted cellulose adsorbent in removing heavy metal ions in sewage according to claim 1, wherein in the first step, the mass ratio of the cellulose to the 2-bromoisobutyryl bromide is 1: 4-10.
4. The use of the grafted cellulose adsorbent of claim 1 for removing heavy metal ions from wastewater, wherein in step two, the catalyst is cupric bromide.
5. The application of the grafted cellulose adsorbent in removing heavy metal ions in sewage as claimed in claim 1, wherein in step two, the mass ratio of the catalyst to the cellulose macroinitiator is 0.2-0.3: 1; and/or
In the second step, the mass ratio of the N, N-dimethylformamide to the cellulose macroinitiator is 20-30: 1.
6. The application of the grafted cellulose adsorbent in removing heavy metal ions in sewage water according to claim 1, wherein in the second step, the mass ratio of the reaction ligand to the cellulose macroinitiator is 1-2: 1.
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