Polydopamine/pullulan composite hydrogel as well as preparation method and application thereof
Technical Field
The invention relates to the field of heavy metal adsorbents, in particular to a polydopamine/pullulan composite hydrogel as well as a preparation method and application thereof.
Background
Heavy metals are highly toxic, non-degrading and bioaccumulating and are considered to be one of the most harmful pollutants in the environment. Heavy metal pollution is caused by a plurality of sources, mainly caused by industries such as petroleum refining, paint and pigment, paper making and paper pulp, steel plants, chemical industry, metallurgy mining, electroplating and the like.
The removal of heavy metal pollution in industrial wastewater and environment is becoming more and more of a concern. Currently accepted methods for removing heavy metals from wastewater include precipitation methods, ion exchange methods, membrane filtration methods, adsorption methods (physical adsorption methods, chemical adsorption methods and biological adsorption methods), and electrodeposition methods.
The adsorption method has the advantages of simple operation, high efficiency, economy, effectiveness and the like, and is widely applied. In recent years, various adsorbent materials have been reported to remove heavy metal contamination, such as Qi, et al (X.Qi, R.Liu, M.Chen, et al.Removal of counter from water using polysaccharide-bound molecules [ J ], Carbohydrate polymers,2019,209: 101-. Awual et al (M.R.Awual, M.M.Hasan, M.M.Rahman, et al.novel composition for selective copper (II) detection and removal from a water medium [ J ]. Journal of Molecular Liquires, 2019,283:772-780.) A mesoporous composite was prepared by direct conjugation to porous silica as an effective material for removing copper ions in water media, with a maximum adsorption of 197.1mg/g.Sani, M.B.Ahmad, M.Z.Hussein, of Nanocomposition of ZnO with a porous adsorption for removal of ions of clay and adsorption of zinc in water, as a combined mineral adsorption of clay and adsorption of clay, 2017,109 mg of nano-oxide in water. Generally, the existing adsorbents have the defects of difficult recovery, complicated preparation, poor biocompatibility and the like, so that the application of the adsorbents is limited.
Disclosure of Invention
The invention aims to solve the defects that the preparation of an adsorbent is complicated and the recovery is difficult when heavy metal pollution is removed. The polydopamine-doped pullulan hydrogel and the preparation method thereof can be applied to heavy metal absorption in sewage treatment, and the method can realize good biocompatibility of the adsorbent, is simple to prepare, and can recover the adsorbent without means such as centrifugation and filtration.
5-10 parts of dopamine;
10-15 parts of pullulan;
0.2-2 parts of ethylene glycol diglycidyl ether;
200 portions of 1.2mol/L sodium hydroxide solution.
The invention also provides a preparation method of the polydopamine-doped pullulan hydrogel, which comprises the following steps:
step one, 5-10 parts of dopamine are added into 100-150 parts of sodium hydroxide solution with the concentration of 1.2mol/L, and the obtained dopamine solution is stirred and polymerized at room temperature to form polydopamine solution.
And step two, adding 10-20 parts of pullulan into 100-150 parts of sodium hydroxide solution with the concentration of 1.2mol/L, stirring at room temperature until the pullulan is fully dissolved, and preparing the pullulan solution.
And step three, uniformly mixing the polydopamine solution obtained in the step one and the pullulan solution obtained in the step two, adding 0.2-2 parts of ethylene glycol diglycidyl ether, uniformly stirring, and placing in an oven at 30 ℃ for heat preservation for 3-24 hours to form the polydopamine/pullulan composite hydrogel.
And step four, soaking the polydopamine/pullulan composite hydrogel obtained in the step three in deionized water, changing water for multiple times, and removing unreacted products.
And step five, freezing and drying the soaked hydrogel obtained in the step four to obtain a final product.
Further, the mass ratio of the polydopamine solution to the pullulan solution in the third step is 1-3: 3.
The invention also provides an application of the polydopamine-doped pullulan hydrogel, wherein the polydopamine-doped pullulan hydrogel is used as a metal adsorbent.
The invention also provides a method for recovering the polydopamine-doped pullulan hydrogel, which comprises the steps of adding the polydopamine-doped pullulan hydrogel which adsorbs heavy metals into 0.1M HCl solution for soaking, recovering the polydopamine-doped pullulan hydrogel and cleaning the polydopamine-doped pullulan hydrogel with deionized water.
The invention has the following advantages:
(1) the preparation method is simple, the reaction condition is mild, only stirring, constant temperature at room temperature and other conditions are needed, and the power consumption of wastewater treatment can be greatly reduced.
(2) The dopamine and the pullulan have good biocompatibility, can be naturally degraded, and cannot cause secondary pollution to the environment.
(3) The polydopamine can be combined with heavy metal ions through electrostatic adsorption and coordination, the porous pullulan hydrogel has a large specific surface area and can provide more adsorption sites for copper ions, and the polydopamine adsorbent with high adsorption capacity on the heavy metals and the pullulan hydrogel carrier with the large specific surface area are combined to synthesize the dopamine-doped pullulan hydrogel composite adsorption material, so that the adsorption efficiency is greatly improved.
(4) The adsorption rate of the adsorption material of the invention to heavy metal is greatly increased, and particularly, the copper ion adsorption capacity reaches higher 100.9 mg/g.
(5) Pullulan is added with ethylene glycol diglycidyl ether, hydrogel with a 3D structure cross-linked network is formed through cross-linking, the adsorption effect is enhanced through doping polydopamine, the adsorbent can be recovered without means such as centrifugation and filtration, and the recovery mode is simple.
Drawings
FIG. 1 is a schematic diagram of the preparation and adsorption of polydopamine/pullulan composite hydrogel;
FIG. 2 is a graph showing the adsorption results of polydopamine/pullulan composite hydrogels prepared in examples 1 to 3 and comparative example 1 on copper ions;
fig. 3 shows the adsorption of the polydopamine/pullulan composite hydrogel on copper ions at different times.
Detailed Description
The present invention will be further described in detail with reference to examples and effect examples, but the scope of the present invention is not limited thereto.
Example 1: and (3) preparing the polydopamine/pullulan composite hydrogel composite adsorption material.
The preparation method comprises the following steps:
1)6g of dopamine is added into 100mL of 1.2mol/L sodium hydroxide solution, and the obtained dopamine solution is stirred at room temperature for 24 hours to polymerize to form polydopamine solution.
2)20g of pullulan is added into 100mL of 1.2mol/L sodium hydroxide solution, and the solution is stirred for 1 hour at room temperature to be fully dissolved.
3) Uniformly mixing the polydopamine solution obtained in the step 1 and the pullulan solution obtained in the step 2, wherein the mass ratio of the dopamine solution to the pullulan solution is 1: and 3, adding 0.6g of ethylene glycol diglycidyl ether into 6g of the total mass, uniformly stirring, and then placing the mixture in an oven at the temperature of 30 ℃ for heat preservation for 6 hours to form the polydopamine/pullulan composite hydrogel.
4) And (4) placing the polydopamine/pullulan composite hydrogel obtained in the step (3) into deionized water to be soaked for three days, and changing water three times every day to remove unreacted products.
5) And (4) freeze-drying the soaked hydrogel obtained in the step (4) to obtain a final product.
Example 2
The difference from example 1 is that the mass ratio of the dopamine solution to the pullulan solution in step 3 is 2: 3, the total mass is 6 g.
Example 3
The difference from example 1 is that the mass ratio of the dopamine solution to the pullulan solution in step 3 is 3:3, the total mass is 6 g.
Comparative example 1
The difference from example 1 is that the mass ratio of the dopamine solution to the pullulan solution in step 3 is 0: 3, the total mass is 6 g.
Example 4
The effect of the polydopamine/pullulan composite hydrogel prepared in examples 1 to 3 and comparative example 1 on the adsorption of heavy metal ions, and the preparation and adsorption principles are shown in fig. 1.
The adsorption steps are as follows:
0.1g of the dopamine/pullulan hydrogel prepared in examples 1 to 3 and comparative example 1 was added to 60mL of a copper sulfate solution having a copper ion concentration of 200mg/L, and the mixture was placed in a 37 ℃ constant temperature shaker and shaken at a speed of 100 rpm/min. After 200min of adsorption, the adsorption results of the dopamine/pullulan hydrogels of examples 1 to 3 and comparative example 1 are shown in fig. 2, where the ratio of the dopamine solution to the pullulan polysaccharide is 1:1, the adsorption effect on metal ions is best.
Example 5
The adsorption effect of the polydopamine/pullulan composite hydrogel prepared in example 3 on different metal ions comprises the following adsorption steps:
0.1g of the dopamine/pullulan hydrogel prepared in example 3 was added to 60mL of copper sulfate having a copper ion concentration of 200mg/L, 60mL of nickel sulfate having a nickel ion concentration of 200mg/L, and 60mL of a cobalt sulfate solution having a cobalt ion concentration of 200mg/L, respectively, and the mixture was placed in a 37 ℃ constant temperature oscillator and oscillated at a speed of 100 rpm/min. After adsorbing for 200min, the dopamine/pullulan hydrogel is used for treating Cu2+,Co2+And Ni2+The maximum adsorption amounts are 100.9mg/g, 96.3mg/g and 97.1mg/g respectively, and the best adsorption effect of the dopamine/pullulan hydrogel on copper ions can be seen.
Example 6:
and adsorbing the copper ions by the polydopamine/pullulan composite hydrogel composite adsorption material at different time points.
0.1g of the dopamine/pullulan hydrogel prepared in example 3 was added to 60mL of a copper sulfate solution having a copper ion concentration of 200mg/L, and the mixture was placed in a 37 ℃ constant temperature shaker and shaken at a speed of 100 rpm/min. The amount of remaining copper ions at different time points is shown in fig. 3. As can be seen from fig. 3, the adsorption was rapid for the first one hundred minutes, reaching adsorption equilibrium around 200 min. The adsorbent is high in adsorption speed, and compared with the adsorbent in the prior art, the adsorption efficiency is greatly improved.
Example 7: recovery effect of polydopamine/pullulan composite hydrogel
The polydopamine/pullulan composite hydrogel after saturated adsorption in example 6 was soaked in 0.1M HCl solution for regeneration, and then washed with deionized water to remove the HCl solution until neutral conditions. Five cycles of adsorption-desorption measurements were repeated, all following the same procedure. In a strong acid environment, negative electricity of polydopamine is preferentially competed with heavy metal by H + protons in hydrochloric acid to desorb the heavy metal. Calculated by the original adsorption bivalent copper 100.9mg/g (100%), the adsorption amount of the adsorption material on bivalent copper after the first recovery is 98.5mg/g (recovery utilization rate is 97.6%, the adsorption amount of the adsorption material on bivalent copper after the second recovery is 95.4mg/g (recovery utilization rate is 94.5%, the adsorption amount of the adsorption material on bivalent copper after the third recovery is 93.1mg/g (recovery utilization rate is 92.3%), the adsorption amount of the adsorption material on bivalent copper after the fourth recovery is 91.2mg/g (recovery utilization rate is 90.4%), and the adsorption amount of the adsorption material on bivalent copper after the fifth recovery is 89.7mg/g (recovery utilization rate is 88.9%).
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.