CN107552008B - Method for adsorbing heavy metal ions by corncob cellulose-based hydrogel - Google Patents
Method for adsorbing heavy metal ions by corncob cellulose-based hydrogel Download PDFInfo
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Abstract
The invention discloses a method for adsorbing heavy metal ions by corncob cellulose-based hydrogel. Dissolving corncob cellulose, adding montmorillonite, heating and stirring to insert the corncob cellulose into a montmorillonite layer, adding tetramethylethylenediamine and ammonium persulfate, stirring, then adding acrylic acid and N, N' -methylene bisacrylamide, continuously heating and stirring to obtain hydrogel, the corn cob cellulose is pure cellulose extracted from corn cobs by a nitric acid-ethanol method, the corncob cellulose-based hydrogel with the best structure and adsorption performance is obtained by optimizing the use amounts of montmorillonite, N' -methylene-bisacrylamide and acrylic acid, and optimizing different concentrations, pH values and adsorption time of the heavy metal ion solution to determine the optimal adsorption condition of the hydrogel for the heavy metal ions.
Description
Technical Field
The invention relates to a corncob cellulose-based hydrogel and a heavy metal ion (Zn)2+，Cd2+And Cr3+) AdsorptionInfluence of performance, in particular to the Zn of hydrogel prepared by nitric acid-ethanol corncob cellulose under different optimized conditions2+，Cd2+And Cr3+And (5) adsorbing heavy metal ions.
Technical Field
The corncob cellulose (LNC) is a natural high molecular material with rich reserves and reproducibility, has the characteristics of good biodegradability and nontoxicity, is natural gramineae cellulose, and is easier to remove lignin and hemicellulose than other lignocellulose in the preparation process. The renewable corncob cellulose is used for developing and producing the degradable hydrogel, so that the maximization of the utilization value of the degradable hydrogel can be realized. Hydroxyl on the corn core cellulose macromolecules can participate in carboxylation, acidification and other reactions, and various active groups such as carbonyl, carboxyl and the like are introduced into the corn core cellulose to form various derivatives. The corncob cellulose has large surface gaps, strong hydrophobicity and water absorption, and high specific surface area, which is beneficial to preparing hydrogel.
In recent years, the problem of environmental pollution caused by heavy metals such as cadmium, lead, nickel, zinc, chromium, etc. has attracted much attention worldwide. Unlike organic waste, heavy metal pollutants have the characteristics of strong toxicity, difficult degradation, easy enrichment and the like, and can enter human bodies through food chains, so that the human health is harmed. Therefore, the prevention and control of heavy metal contaminants has become a focus of research. Conventional methods for removing metal ions from aqueous solutions include chemical precipitation, ion exchange, chemical oxidation/reduction, reverse osmosis, electrodialysis, ultrafiltration, and the like. However, the traditional coagulation and chemical precipitation produce a large amount of waste residues, which easily causes secondary pollution; the electrolysis and ion exchange have high energy consumption and high cost. The adsorbent has the advantages of strong adsorbability, simple operation, low investment, small secondary pollution and the like, so that the development of cheaper, efficient and environment-friendly adsorbent for improving the removal effect of heavy metal ions in the aqueous solution is continuously required.
The prior art (preparation of lignocellulose-g-acrylic acid/montmorillonite hydrogel and research on adsorption performance) discloses a preparation method of lignocellulose-g-acrylic acid/montmorillonite hydrogel and an effect of the hydrogel on adsorbing methylene blue dye in sewage treatment. Lignocellulose comprises cellulose, hemicellulose and lignin, the structure is complex, functional groups are complex, the hemicellulose is easy to hydrolyze in an acid solution, the lignin can also be hydrolyzed in the acid solution, and the lignocellulose needs to be subjected to high-temperature chemical treatment in the preparation process, so that the working procedures are complex, and certain adverse effects are caused on the structure and the performance of the cellulose. In the prior art, sodium hydroxide is needed to adjust the neutralization degree of acrylic acid when preparing hydrogel, so that the adsorption effect of the hydrogel under an acidic condition is influenced.
Disclosure of Invention
The invention provides a novel corncob cellulose based montmorillonite modified hydrogel, aiming at solving the problems of low adsorption capacity, slow adsorption rate, unstable structure, poor adsorption capacity and the like of the traditional plant fiber based heavy metal adsorbent, improving the adsorption performance of the hydrogel and improving the adsorption effect of the hydrogel on heavy metal ions.
One of the purposes of the invention is to provide a corncob cellulose-based hydrogel which has the advantages of stable structure, high adsorption capacity, high adsorption rate, good cyclability and strong selective adsorption capacity.
The invention also aims to provide a preparation method of the corncob cellulose-based hydrogel, which can simply and conveniently obtain the corncob cellulose-based hydrogel and is convenient to use.
The invention also aims to provide an application method of the corncob cellulose-based hydrogel for adsorbing heavy metal ions, which can determine the optimal adsorption condition and the maximum adsorption quantity.
In order to achieve the technical purpose, the invention specifically relates to the following technical scheme:
the invention discloses a preparation method of corncob cellulose-based hydrogel, which comprises the following steps:
(1) weighing a proper amount of corncob cellulose (LNC) and putting into a three-neck flask, and adding distilled water to dissolve;
(2) adding montmorillonite (MMT) into the solution obtained in the step (1) in inert gas N2Heating and stirring under protection;
(3) adding tetramethylethylenediamine and ammonium persulfate into the mixed liquid obtained in the step (2), uniformly stirring, adding Acrylic Acid (AA) and N, N' -Methylene Bisacrylamide (MBA), and continuously heating and stirring to obtain hydrogel;
(4) adding the obtained hydrogel into absolute ethyl alcohol, standing, washing with deionized water, and drying.
Preferably, the preparation method of the corncob cellulose-based hydrogel comprises the following steps:
(1) weighing a proper amount of corncob cellulose, putting the corncob cellulose into a three-neck flask, and adding distilled water to dissolve the corncob cellulose;
(2) adding MMT into the solution obtained in the step (1), wherein the mass ratio of MMT to LNC is 0.03-0.11, and the mass ratio is N2Heating and stirring under protection, wherein the heating temperature is 75-90 ℃, and the stirring temperature is 50-70 min;
(3) adding tetramethylethylenediamine (the volume/mass ratio of tetramethylethylenediamine/LNC is 0.2mL/g) and ammonium persulfate (the mass ratio of ammonium persulfate/LNC is 0.2) into the mixed liquid obtained in the step (2), stirring uniformly, adding AA (the mass ratio of AA/LNC is 8-24) and MBA (the mass ratio of MBA/LNC is 0.1-0.5), and continuing heating and stirring to obtain hydrogel;
(4) adding the obtained hydrogel into anhydrous ethanol, standing for 24h, washing with deionized water, and drying at 50-70 deg.C for 24 h.
Preferably, the MMT/LNC mass ratio is 0.08.
Preferably, the AA/LNC mass ratio is 16.
Preferably, the mass ratio MBA/LNC is 0.2.
The invention also provides a preparation method of the corncob cellulose, which comprises the following steps:
(1) weighing a certain amount of corncobs, putting the corncobs into a conical flask, adding a mixed solution of nitric acid and ethanol (95%), and heating in a water bath for reaction;
(2) transferring the residue obtained in the step (1) into a G2 glass filter, and pumping out the filtrate, wherein the process is repeated for 2 times;
(3) and (3) finally, transferring the filtered product obtained in the step (2) into an oven, and drying to constant weight.
Preferably, the mass ratio of nitric acid to ethanol (95%) in step (1) is 1: 4.
Preferably, the water bath reaction temperature in the step (1) is 75-90 ℃, and the reaction time is 1 h.
Preferably, the drying temperature in step (3) is 100-120 ℃.
The invention also provides an application method of the corncob cellulose-based hydrogel for adsorbing heavy metal ions, which comprises the following steps:
adding the corn cob cellulose-based hydrogel prepared by the method into Zn with the pH value of 3.5-6.52+，Cd2+And Cr3+Adsorbing in heavy metal solution with ion concentration of 50-800mg/L for 60-120 min.
Preferably, the corn cob cellulose-based hydrogel prepared by the method of the invention is added to pH 6.5, Zn2+，Cd2+And Cr3+Adsorbing in heavy metal solution with concentration of 200mg/L, 400mg/L and 800mg/L respectively for 60 min.
The invention has the beneficial effects that:
(1) the corn cob cellulose and the MMT are combined to prepare the hydrogel, the corn cob cellulose is inserted into the lamellar montmorillonite to destroy the lamellar structure of the montmorillonite, the cellulose and the acrylic polymer form a three-dimensional network structure with a complex structure, the hydrogel structure is stable, the adsorption capacity of the hydrogel is increased, basic units of the montmorillonite are uniformly dispersed in a polymer matrix, the nano-scale compounding with the polymer can be realized, the water absorption and the specific surface area of the hydrogel are increased, and a new thought is expanded for the performance research of the hydrogel.
(2) The corn cob cellulose extracted by the nitric acid-ethanol method is pure cellulose, high-temperature chemical treatment is not needed like the traditional lignocellulose, the purity of the cellulose is high, the structure is complete, and the structure is stable after the corn cob cellulose is prepared into hydrogel.
(3) In the hydrogel preparation process, sodium hydroxide is not needed to adjust the neutralization degree of acrylic acid, the dosage of chemical agents is reduced, and the adsorption effect of the hydrogel is improved under an acidic condition. In the preparation process, sodium hydroxide is not used for adjusting the neutralization degree of acrylic acid, so that the structural stability of the high-purity cellulose-based hydrogel under an acidic condition can be improved, the carboxylic acid group of polyacrylic acid is weak acid, the pH value of the hydrogel which undergoes a swelling sudden transition is higher, and the pH sensitivity of the hydrogel under the acidic condition is less influenced by the dissociation balance of polyacrylic acid in the gel, the ionic electrostatic repulsion on a network chain and the internal and external Donnan balance of the gel, so that the adsorption effect of the hydrogel is improved.
(4) The hydrogel is applied to the adsorption of heavy metal ions, the pollution load of the wastewater is reduced, and the hydrogel serving as a biological adsorbent can be recycled and degraded, so that the wastewater treatment cost can be reduced;
(5) a new method and thought are provided for the application of the hydrogel, the adsorption performance of the hydrogel is improved, and the application channel of the hydrogel is widened;
(6) the invention improves the utilization value of the corncob cellulose, expands the application range of the corncob cellulose, enhances the adsorption performance of the hydrogel and can solve the problem of heavy metal ion pollution of a water body.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. 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 invention 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 exemplary embodiments according to the invention. 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 the stated features, steps, operations, and/or combinations thereof, unless the context clearly indicates otherwise.
Herein, the term "corn cob cellulose" refers to pure cellulose extracted from corn cobs.
The term "corncob cellulose-based hydrogel" refers to a hydrogel prepared from corncob cellulose, montmorillonite, acrylic acid and N.N' -methylenebisacrylamide as main raw materials.
As described in the background art, the heavy metal adsorption hydrogel prepared from the traditional lignocellulose as the raw material in the prior art has the problems of low adsorption capacity, slow adsorption rate, unstable structure, poor adsorption capacity and the like, so the invention mainly develops a novel preparation method of the cellulose-based hydrogel with stable structure and good cyclability.
The invention discloses a preparation method of corncob cellulose-based hydrogel, which comprises the steps of extracting corncob cellulose from corncobs by a nitric acid-ethanol method, dissolving the corncob cellulose in distilled water, adding MMT in N2Heating in water bath under protection for reaction; and after the reaction is finished, adding ammonium sulfate and tetramethylethylenediamine, uniformly stirring, adding AA and MBA, and heating and stirring to obtain the hydrogel.
According to the preparation method, corncob cellulose is selected as one of main raw materials for preparing the hydrogel, the content of cellulose in the corncobs is up to 35%, the corncobs are natural gramineous cellulose, and hemicellulose and lignin are easy to remove, so that the cellulose with high purity is obtained without high-temperature chemical treatment.
The preparation method of the invention starts to make the corncob cellulose and MMT in N2Under protection, water bath heating is carried out for reaction, the corn cob cellulose is promoted to be inserted between montmorillonite layers and the montmorillonite sheet structure is promoted to be broken, so that the basic unit of the montmorillonite is smaller and more uniformly compounded on the corn cob cellulose.
According to the preparation method, the neutralization degree of AA does not need to be adjusted by sodium hydroxide, AA, MBA and an initiator are directly added into the corncob cellulose/MMT mixed solution, the polymerization and crosslinking of AA monomers and the hydroxyl condensation on the corncob cellulose are simultaneously carried out, and the activity of AA is reduced by the condensation of AA and the hydroxyl on the corncob cellulose, so that the reaction speed does not need to be controlled by adjusting the neutralization degree of AA. AA polymerization and grafting are carried out simultaneously, so that the three-dimensional structure of the hydrogel is more complex and the structure is more stable. According to the preparation method, the step of regulating the neutralization degree of AA by using sodium hydroxide is omitted, the AA is not subjected to neutralization treatment by using the sodium hydroxide, and the prepared hydrogel has a more stable structure.
In a preferred embodiment of the present invention, it is preferable to prepare the corncob cellulose-based hydrogel that the MMT/LNC mass ratio is 0.08, the AA/LNC mass ratio is 16, and the MBA/LNC mass ratio is 0.2.
The inventor finds that the content of MMT cannot be too low or too high, and the MMT content is too low to absorb heavy metal ions; the excessive MMT can not be well dispersed in the corncob cellulose, the cellulose and the MMT can not be well interpenetrated and combined, the MMT interlamellar spacing can not be modified, the particle size is larger, the adsorbability can not be improved, the structural stability of the hydrogel can also be influenced, and the preferable mass ratio of the MMT to the corncob cellulose is 0.08.
The preferred mass ratio of AA/LNC is 16, the stable three-dimensional structure cannot be formed due to too low AA content, the molecular weight of the polymerized side chain is increased easily due to too high AA content, the system viscosity is increased, the molecular chains are easy to tangle, the crosslinking degree is improved, and the adsorption performance of the product is reduced.
The preferable mass ratio of MBA/LNC is 0.2, and when the content of MBA is lower, the crosslinking degree of hydrogel is small, the water solubility is good, and the adsorption quantity is low; when the content of MBA is too high, the crosslinking density of the hydrogel is too high, the relaxation of a molecular network is limited, heavy metal ions are difficult to enter the hydrogel from the surface of the hydrogel, the swelling degree of the hydrogel is reduced, and the adsorption capacity is reduced.
The invention also provides an application method of the corncob cellulose-based hydrogel for adsorbing heavy metal ions, and in a preferred embodiment, the pH of a heavy metal solution is 6.5, Zn2+，Cd2+And Cr3+The concentrations were 200mg/L, 400mg/L and 800mg/L, respectively, and the adsorption time was 60 min.
The pH value of the heavy metal solution is 6.5, and when the pH value is small, the solution contains a large amount of H+，H+On the other hand, carboxyl and hydroxyl in the hydrogel are inhibited from ionizing in a solution with larger acidity, which is not beneficial to generating a complex, so that the adsorption quantity is small; when gradually increased, the adsorption sites are relatively increased by the gradual decrease in the solutionIonization of the carboxyl groups to COO-The formation of the complex is facilitated, and therefore the amount of adsorption is increased.
The application method of the invention is Zn in heavy metal solution2+，Cd2+And Cr3+The concentrations are respectively 200mg/L, 400mg/L and 800mg/L, when the concentration of the heavy metal ions is smaller, the ion concentration adsorption capacity is increased, the mass transfer driving force of the metal ions is increased along with the increase of the concentration of the metal ions, the adsorption resistance is reduced, and meanwhile, the contact area between the metal ions and adsorption sites is increased, so that the adsorption capacity is gradually increased; when the ion concentration is too high, the hydrolysis degree is increased, the combination with active groups is reduced, and meanwhile, the too high metal ion concentration is not beneficial to the swelling of the composite material, so that the active groups on the adsorbent are wrapped, and the adsorption quantity is reduced. In addition, in the heavy metal solution with various ions coexisting, different ions have inhibition effects, and the binding capacity of different metal ions and the hydrogel active groups is different, so that the optimal concentration of different metal ions is different.
The optimal adsorption time of the application method is 60min, the adsorption of the hydrogel on the metal ions mainly occurs on active sites on the outer surface of the adsorbent, and the adsorption rate is high; on the other hand, the adsorption of the adsorbate can also occur in the inner hole of the adsorbent, the reaction rate is slow, the time consumption is high, and the hydrogel can adsorb Zn in 60min2+，Cd2+And Cr3+The adsorption of (2) reaches the equilibrium, and the adsorption quantity cannot be increased by continuously prolonging the adsorption time.
In the following examples, all percentages are by mass unless otherwise specified.
Example 1:
the nitric acid-ethanol corncob cellulose is extracted according to the following steps:
weighing a certain amount of corncob, placing into a conical flask, adding a nitric acid-ethanol (nitric acid: ethanol is 1:4) mixed solution, heating at 85 deg.C for 1h by reflux condensing device, transferring the residue into G2 glass filter, and removing the filtrate. The above process was repeated 2 times. Finally, the filter filled with the cellulose is moved into an oven and dried at 105 ℃ to constant weight.
Example 2:
the corncob cellulose-based hydrogel is prepared by the following steps:
optimizing the mass ratio of MMT/LNC: 1. weighing appropriate amount of corncob cellulose, placing into a three-neck flask, adding distilled water to dissolve, adding MMT (mass ratio of MMT to LNC is 0, 0.03, 0.05, 0.08 and 0.11), introducing N at 85 deg.C2Stirring for 60min, then adding tetramethyl ethylene diamine (the mass ratio of tetramethyl ethylene diamine/LNC is 0.2mL/g) and ammonium persulfate (the mass ratio of ammonium persulfate/LNC is 0.2), stirring for 10min, then adding AA (the mass ratio of AA/LNC is 16) and MBA (the mass ratio of MBA/LNC is 0.2), and continuing heating and stirring to obtain the corncob cellulose-based hydrogel. Adding the obtained hydrogel into absolute ethyl alcohol, standing for 24h, washing with deionized water, drying at 60 ℃ for 24h, and cutting into blocks for later use.
2. Putting the prepared corncob cellulose-based hydrogel into a heavy metal ion solution (Zn) with the concentration of 800mg/L and the pH value of 6.52+，Cd2+And Cr3+) Stirring and adsorbing for 120 min.
As a result: through an adsorption experiment, the corn cob cellulose-based hydrogel LNC-g-AA/MMT obtained in the treatment step is a heavy metal ion solution (Zn)2+，Cd2+And Cr3+) The adsorption is carried out, the adsorption capacity of the hydrogel is increased along with the continuous increase of the mass ratio (charge ratio) of MMT/LNC, namely the increase of the MMT dosage, when the mass ratio of MMT/LNC is 0.08, the adsorption of heavy metal ions by the hydrogel is maximum, and when the mass ratio is more than 0.08, the adsorption capacity is in a descending trend along with the increase of the ratio, so that the MMT/LNC is more suitable for being in a mass ratio of 0.08. Under the mass ratio, the corn cob cellulose-based hydrogel LNC-g-AA/MMT is heavier than the traditional lignocellulose-based hydrogel LNC-g-AA/MMT by heavy metal ions (Zn)2+，Cd2+And Cr3+) The adsorption amount of (2) was increased by 16.2%.
Example 3:
the corncob cellulose-based hydrogel is prepared by the following steps:
optimizing the AA/LNC mass ratio: 1. weighing appropriate amount of corncob fiberDissolving vitamin in distilled water in three-neck flask, adding MMT (MMT/LNC mass ratio of 0.08), introducing N at 85 deg.C2Stirring for 60min, then adding tetramethyl ethylene diamine (the volume/mass ratio of tetramethyl ethylene diamine/LNC is 0.2mL/g) and ammonium persulfate (the mass ratio of ammonium persulfate/LNC is 0.2), stirring for 10min, then adding AA (the mass ratio of AA/LNC is 8, 12, 16, 20 and 24 respectively) and MBA (the mass ratio of MBA/LNC is 0.2), and continuing heating and stirring to obtain the corncob cellulose-based hydrogel. Adding the obtained hydrogel into absolute ethyl alcohol, standing for 24h, washing with deionized water, drying at 60 ℃ for 24h, and cutting into blocks for later use.
2. Putting the prepared corncob cellulose-based hydrogel into a heavy metal ion solution (Zn) with the concentration of 800mg/L and the pH value of 6.52+，Cd2+And Cr3+) Stirring and adsorbing for 120 min.
As a result: through an adsorption experiment, the corn cob cellulose-based hydrogel LNC-g-AA/MMT obtained in the treatment step is a heavy metal ion solution (Zn)2+，Cd2+And Cr3+) Adsorption was carried out, and it was found that the adsorption amount of the corncob cellulose-based hydrogel (LNC-g-AA) to heavy metal ions increased with the increase in the amount of the acrylic acid monomer, but the adsorption amount of the hydrogel tended to decrease when the mass ratio of AA/LNC exceeded 16, and therefore, the mass ratio of AA/LNC should be suitably controlled at 16. Under the mass ratio, the corn cob cellulose-based hydrogel LNC-g-AA/MMT is heavier than the traditional lignocellulose-based hydrogel LNC-g-AA/MMT by heavy metal ions (Zn)2+，Cd2+And Cr3+) The adsorption amount of (2) was improved by 13.8%.
Example 4:
the corncob cellulose-based hydrogel is prepared by the following steps:
and (3) optimizing the MBA/LNC mass ratio: 1. weighing appropriate amount of corncob cellulose, placing into a three-neck flask, adding distilled water for dissolving, placing into MMT (mass ratio of MMT to LNC is 0.08), introducing N at 85 deg.C2Stirring for 60min, adding tetramethylethylenediamine (the volume/mass ratio of tetramethylethylenediamine/LNC is 0.2mL/g) and ammonium persulfate (the mass ratio of ammonium persulfate/LNC is 0.2), stirring for 10min, adding AA (the mass ratio of AA/LNC is 16) and MBA (the mass ratio of MBA/LNC is 0.1, 0.2 and 0.3 respectively,0.4 and 0.5), and continuously heating and stirring to obtain the corncob cellulose-based hydrogel. Adding the obtained hydrogel into absolute ethyl alcohol, standing for 24h, washing with deionized water, drying at 60 ℃ for 24h, and cutting into blocks for later use.
2. Putting the prepared corncob cellulose-based hydrogel into a heavy metal ion solution (Zn) with the concentration of 800mg/L and the pH value of 6.52+，Cd2+And Cr3+) Stirring and adsorbing for 120 min.
As a result: through an adsorption experiment, the corn cob cellulose-based hydrogel LNC-g-AA/MMT obtained in the treatment step is a heavy metal ion solution (Zn)2+，Cd2+And Cr3+) The adsorption was carried out, and it was found that the adsorption amount of the hydrogel tended to increase and decrease with the increase in the amount of the crosslinking agent, and the adsorption amount of the hydrogel reached the maximum value when the mass ratio of MBA/LNC was 0.2. Thus, the MBA/LNC ratio is preferably 0.2 volume/mass. Under the mass ratio, the corn cob cellulose-based hydrogel LNC-g-AA/MMT is heavier than the traditional lignocellulose-based hydrogel LNC-g-AA/MMT by heavy metal ions (Zn)2+，Cd2+And Cr3+) The adsorption amount of (2) was improved by 14.6%.
Example 5:
the adsorption of the corncob cellulose-based hydrogel on heavy metal ions is prepared by the following steps:
optimizing the concentration of heavy metal ions: 1. weighing appropriate amount of corncob cellulose, placing into a three-neck flask, adding distilled water for dissolving, placing into MMT (mass ratio of MMT to LNC is 0.08), introducing N at 85 deg.C2Stirring for 60min, then adding tetramethyl ethylene diamine (the volume/mass ratio of tetramethyl ethylene diamine/LNC is 0.2mL/g) and ammonium persulfate (the mass ratio of ammonium persulfate/LNC is 0.2), stirring for 10min, then adding AA (the mass ratio of AA/LNC is 16) and MBA (the mass ratio of MBA/LNC is 0.2), and continuing heating and stirring to obtain the corncob cellulose-based hydrogel. Adding the obtained hydrogel into absolute ethyl alcohol, standing for 24h, washing with deionized water, drying at 60 ℃ for 24h, and cutting into blocks for later use.
2. Placing the prepared corncob cellulose-based hydrogel into heavy metal ion solution (Zn) with concentration of 50, 100, 200, 400, 600 and 800mg/L and pH of 6.52+，Cd2+And Cr3+) Middle stirringStirring and adsorbing for 120 min.
As a result: through adsorption experiments, the corn cob cellulose-based hydrogel LNC-g-AA/MMT obtained in the treatment step adsorbs heavy metal ions, and the result shows that Zn is adsorbed when Zn is adsorbed2+，Cd2+And Cr3+The adsorption effect of the LNC-g-AA/MMT hydrogel is better when the concentration is respectively 200mg/L, 400mg/L and 800 mg/L. At the concentration, the corn cob cellulose-based hydrogel LNC-g-AA/MMT is heavier than the traditional lignocellulose-based hydrogel LNC-g-AA/MMT by heavy metal ions (Zn)2+，Cd2+And Cr3+) The adsorption amount of (2) was increased by 11.7%.
Example 6:
the adsorption of the corncob cellulose-based hydrogel on heavy metal ions is prepared by the following steps:
optimizing the pH value of the heavy metal ion solution: 1. weighing appropriate amount of corncob cellulose, placing into a three-neck flask, adding distilled water for dissolving, placing into MMT (mass ratio of MMT to LNC is 0.08), introducing N at 85 deg.C2Stirring for 60min, then adding tetramethyl ethylene diamine (the volume/mass ratio of tetramethyl ethylene diamine/LNC is 0.2mL/g) and ammonium persulfate (the mass ratio of ammonium persulfate/LNC is 0.2), stirring for 10min, then adding AA (the mass ratio of AA/LNC is 16) and MBA (the mass ratio of MBA/LNC is 0.2), and continuing heating and stirring to obtain the corncob cellulose-based hydrogel. Adding the obtained hydrogel into absolute ethyl alcohol, standing for 24h, washing with deionized water, drying at 60 ℃ for 24h, and cutting into blocks for later use.
2. Putting the prepared corncob cellulose-based hydrogel into Zn2+、Cd2+、Cr3+Stirring and adsorbing in solutions with concentrations of 200mg/L, 400mg/L and 800mg/L and pH of 3.5, 4.5, 5.5 and 6.5 for 120 min.
As a result: through adsorption experiments, the corn cob cellulose-based hydrogel LNC-g-AA/MMT obtained in the treatment step adsorbs heavy metal ions, and when the pH value of the solution is 6.5, the LNC-g-AA/MMT hydrogel adsorbs Zn2+，Cd2+And Cr3+The adsorption effect is better. Under the pH value, the corn cob cellulose-based hydrogel LNC-g-AA/MMT is heavier than the traditional lignocellulose-based hydrogel LNC-g-AA/MMT by heavy metal ions (Zn)2+，Cd2+And Cr3+) Adsorption of (2)The amount was increased by 12.9%.
Example 7:
the adsorption of the corncob cellulose-based hydrogel on heavy metal ions is prepared by the following steps:
optimizing the adsorption time of the heavy metal ion solution: 1. weighing appropriate amount of corncob cellulose, placing into a three-neck flask, adding distilled water for dissolving, placing into MMT (mass ratio of MMT to LNC is 0.08), introducing N at 85 deg.C2Stirring for 60min, then adding tetramethyl ethylene diamine (the volume/mass ratio of tetramethyl ethylene diamine/LNC is 0.2mL/g) and ammonium persulfate (the mass ratio of ammonium persulfate/LNC is 0.2), stirring for 10min, then adding AA (the mass ratio of AA/LNC is 16) and MBA (the mass ratio of MBA/LNC is 0.2), and continuing heating and stirring to obtain the corncob cellulose-based hydrogel. Adding the obtained hydrogel into absolute ethyl alcohol, standing for 24h, washing with deionized water, drying at 60 ℃ for 24h, and cutting into blocks for later use.
2. Putting the prepared corncob cellulose-based hydrogel into Zn2+，Cd2+And Cr3+The solution with the concentration of 200mg/L, 400mg/L and 800mg/L and the pH of 6.5 is stirred and adsorbed for 10, 20, 40, 60, 90 and 120 min.
As a result: through an adsorption experiment, the corn cob cellulose-based hydrogel LNC-g-AA/MMT obtained in the treatment step adsorbs heavy metal ions, and when the adsorption time is 60min, the LNC-g-AA/MMT hydrogel adsorbs Zn2+，Cd2+And Cr3+The adsorption effect is better. At this time, the corn cob cellulose-based hydrogel LNC-g-AA/MMT is heavier than the traditional lignocellulose-based hydrogel LNC-g-AA/MMT by heavy metal ions (Zn)2+，Cd2+And Cr3+) The adsorption amount of (2) was increased by 15.6%.
In summary, when Zn is used2+，Cd2+And Cr3+The concentration is respectively 200mg/L, 400mg/L and 800mg/L, the pH value of the solution is 6.5, and the adsorption time is 60min, the corn cob cellulose-based hydrogel LNC-g-AA/MMT is used for Zn2+，Cd2+And Cr3+The maximum adsorption amounts of (a) to (b) are 229.6mg/g, 479.3mg/g and 121 mg/g. And the adsorption capacity is not obviously changed after the multi-time cyclic use. Compared with traditional lignocellulose-based hydrogel LNC-g-AA/MMT, the corncob cellulose-based hydrogelHydrogel LNC-g-AA/MMT heavy metal ion (Zn)2+，Cd2+And Cr3+) The adsorption amount of (A) is improved by 11-16%.
Example 8:
the adsorption-desorption cycle of the corncob cellulose-based hydrogel under the desorption of nitric acid is carried out according to the following steps:
adding a suitable amount of xerogel particles to the preferred Zn2+，Cd2+And Cr3+In the solution concentration, the mixture is stirred under the conditions of a better pH value and balance time to achieve adsorption balance, the hydrogel particles are washed by deionized water for 3 times, stirred, soaked and desorbed in a nitric acid solution (0.5mol/L) for 2 hours, then washed by 0.01mol/L NaOH for 8 hours, finally washed by deionized water, the gel particles are used for adsorption experiments again, and the adsorption-desorption process is repeated for 8 times.
As a result: after the LNC-g-AA/MMT hydrogel is circularly used for 8 times through adsorption-desorption, Cr is added3+、Cd2+And Zn2+The adsorption capacities of the hydrogel are 214.9mg/g, 449.8mg/g and 110.7mg/g respectively, and the adsorption capacity is slightly reduced compared with the first adsorption effect of the hydrogel, which shows that the adsorption effect of the LNC-g-AA/MMT hydrogel is less influenced by the recycling of the LNC-g-AA/MMT hydrogel because of the HNO at 0.5mol/L3When the heavy metal ions are analyzed in the solution, protons and carboxyl metal ions are easy to compete, and due to the existence of electrostatic attraction, the heavy metal ions are adsorbed on the surface of the adsorbent and are replaced with the original fixed ions. As can be seen, the LNC-g-AA/MMT hydrogel has better stability, and can adsorb and desorb heavy metal ions (Zn) after being recycled for 8 times compared with the traditional lignocellulose-based hydrogel LNC-g-AA/MMT2+，Cd2+And Cr3+) The adsorption amount of (A) is improved by 8-12%.
Example 9:
the desorption recycling of the corncob cellulose-based hydrogel under EDTA desorption is carried out according to the following steps:
adding a suitable amount of xerogel particles to the preferred Zn2+，Cd2+And Cr3+In the solution concentration, the mixture is stirred under the conditions of a preferred pH value and an equilibrium time to reach an adsorption equilibrium, the hydrogel particles are washed 3 times with deionized water, in a 0.1M EDTA solution,and (3) oscillating and desorbing for 3h at normal temperature, then washing with deionized water for several times, and reusing the gel particles in the adsorption experiment for 6 times in an adsorption-desorption cycle.
As a result: after the LNC-g-AA/MMT hydrogel is circularly used for 6 times through adsorption-desorption, Cr is added3+、Cd2+And Zn2+The adsorption capacities of the hydrogel are 216.9mg/g, 455.6mg/g and 114.7mg/g respectively, and the adsorption capacity is slightly reduced compared with the first adsorption effect of the hydrogel, which shows that the adsorption effect of the LNC-g-AA/MMT hydrogel is slightly influenced by the cyclic use of the LNC-g-AA/MMT hydrogel. As can be seen, the LNC-g-AA/MMT hydrogel has better stability, and can adsorb and desorb heavy metal ions (Zn) after being recycled for 6 times compared with the traditional lignocellulose-based hydrogel LNC-g-AA/MMT2+，Cd2+And Cr3+) The adsorption amount of (A) is improved by 11-17%.
Claims (9)
1. The preparation method of the corncob cellulose-based hydrogel is characterized by comprising the following steps of:
(1) weighing a proper amount of corncob cellulose, putting the corncob cellulose into a three-neck flask, and adding distilled water to dissolve the corncob cellulose;
(2) adding montmorillonite into the solution obtained in the step (1), and heating and stirring under the protection of inert gas;
(3) adding tetramethylethylenediamine and ammonium persulfate into the mixed liquid obtained in the step (2), uniformly stirring, adding acrylic acid and N, N' -methylene-bisacrylamide, and continuously heating and stirring to obtain hydrogel;
(4) adding the obtained hydrogel into absolute ethyl alcohol, standing, washing with deionized water, and drying;
wherein the mass ratio of each component is respectively as follows: the mass ratio of the montmorillonite to the corncob cellulose is 0.03-0.11; the mass ratio of the acrylic acid to the corncob cellulose is 8-24; the mass ratio of the N' -methylene bisacrylamide to the corncob cellulose is 0.1-0.5; the volume/mass ratio of the tetramethylethylenediamine to the corncob cellulose is 0.2 mL/g; the mass ratio of the ammonium persulfate to the corncob cellulose is 0.2.
2. The method for preparing the corncob cellulose-based hydrogel according to claim 1, comprising the steps of:
(1) weighing a proper amount of corncob cellulose, putting the corncob cellulose into a three-neck flask, and adding distilled water to dissolve the corncob cellulose;
(2) adding montmorillonite into the solution obtained in the step (1) and adding N2Heating and stirring under protection, wherein the heating temperature is 75-90 ℃, and the stirring time is 50-70 min;
(3) adding tetramethylethylenediamine and ammonium persulfate into the mixed liquid obtained in the step (2), uniformly stirring, adding acrylic acid and N, N' -methylene bisacrylamide, and continuously heating and stirring to obtain hydrogel;
(4) adding the obtained hydrogel into anhydrous ethanol, standing for 24h, washing with deionized water, and drying at 50-70 deg.C for 24 h.
3. The method for preparing the corncob cellulose-based hydrogel according to claim 2, wherein: in the step (2), the heating temperature is 85 ℃, and the stirring time is 60 min.
4. The method for preparing a corncob cellulose-based hydrogel according to claim 1, wherein: the mass ratio of each component is as follows: the mass ratio of the montmorillonite to the corncob cellulose is 0.05-0.08; the mass ratio of the acrylic acid to the corncob cellulose is 12-20; the mass ratio of the N, N' -methylene bisacrylamide to the corncob cellulose is 0.2-0.4.
5. The method for preparing a corncob cellulose-based hydrogel according to claim 4, wherein: the mass ratio of each component is as follows: the mass ratio of the montmorillonite to the corncob cellulose is 0.08; the mass ratio of the acrylic acid to the corncob cellulose is 16; the mass ratio of the N, N' -methylene bisacrylamide to the corncob cellulose is 0.2.
6. The method for preparing a corncob cellulose-based hydrogel according to claim 1, wherein: the corn cob cellulose extracting process includes: putting the corncobs into a nitric acid-ethanol mixed solution, reacting under a heating condition, filtering an obtained reaction product, and drying to constant weight.
7. The method for preparing a corncob cellulose-based hydrogel according to claim 6, wherein: the mass ratio of nitric acid to ethanol in the nitric acid-ethanol mixed solution is 1: 4; the heating condition is water bath heating, the temperature is 85 ℃, and the heating reaction time is 1 h; the filtration is carried out by adopting a G2 glass filter and repeated for 2 times; the drying temperature is 100-120 ℃.
8. The method for applying the corncob cellulose-based hydrogel prepared by the preparation method of claim 1 to adsorb heavy metal ions, which is characterized by comprising the following steps of: adding corn cob cellulose-based hydrogel into the mixture with pH of 3.5-6.5 and Zn2+，Cd2+And Cr3+Adsorbing in heavy metal solution with ion concentration of 50-800mg/L for 60-120 min.
9. The method of application of claim 8, wherein: adding the corncob cellulose-based hydrogel to the pH 6.5, Zn2+，Cd2+And Cr3+Adsorbing in heavy metal solution with concentration of 200mg/L, 400mg/L and 800mg/L respectively for 60 min.
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