CN114733491A - Phosphated chitosan loaded magnetic nano-iron composite material and preparation method and application thereof - Google Patents
Phosphated chitosan loaded magnetic nano-iron composite material and preparation method and application thereof Download PDFInfo
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- CN114733491A CN114733491A CN202210213823.7A CN202210213823A CN114733491A CN 114733491 A CN114733491 A CN 114733491A CN 202210213823 A CN202210213823 A CN 202210213823A CN 114733491 A CN114733491 A CN 114733491A
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- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
- B01J20/22—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising organic material
- B01J20/24—Naturally occurring macromolecular compounds, e.g. humic acids or their derivatives
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- B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
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- B01J20/305—Addition of material, later completely removed, e.g. as result of heat treatment, leaching or washing, e.g. for forming pores
- B01J20/3064—Addition of pore forming agents, e.g. pore inducing or porogenic agents
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Abstract
The invention belongs to the technical field of uranium-containing wastewater treatment, and particularly relates to a phosphated chitosan loaded magnetic nano-iron composite material, and a preparation method and application thereof. According to the invention, firstly, the chitosan is subjected to phosphorylation treatment, phosphate radicals and hydroxyl groups on the chitosan are subjected to substitution reaction, so that a large amount of phosphate radicals are arranged on the surface of the chitosan, then, the phosphorylated chitosan, the nano zero-valent iron and the pore-forming agent are uniformly mixed, and the mixture is dried to prepare the sponge-type composite gel material with a pore structure, meanwhile, the nano zero-valent iron is loaded on the sponge-type phosphorylated chitosan matrix, and the pore structure enables the phosphorylated chitosan-loaded magnetic nano iron composite material prepared by the invention to have a large specific surface area, and the surface of the phosphorylated chitosan-loaded magnetic nano iron composite material has abundant hydroxyl groups, amino groups and phosphate groups introduced after phosphorylation modification, so that the phosphorylated chitosan-loaded magnetic nano iron composite material has high reaction activity and excellent adsorption performance on hexavalent uranium.
Description
Technical Field
The invention belongs to the technical field of uranium-containing wastewater treatment, and particularly relates to a phosphated chitosan loaded magnetic nano-iron composite material, and a preparation method and application thereof.
Background
Uranium is a main source of nuclear fuel, nuclear energy is used as a clean and efficient energy source, and the development of nuclear industry can be guaranteed only by enough uranium. The relatively scarce uranium content on land has turned the eye to recovering uranium from seawater and uranium-bearing wastewater. Wherein the content of uranium in seawater reaches 4-4.5 multiplied by 109t, several thousand times the total uranium content on land.
Although the reserves of uranium in the ocean are quite large, seawater is a highly complex matrix, rich in high ionic strength (average content of salt about 3.5%), large amounts of competing ions (Na)+、Mg2+、Ca2+、Cu2+Etc.) and extremely low uranium concentrations (3.3mg · m)-3). The adsorption method is one of the main methods for extracting uranium from a uranium solution due to its advantages of low cost, simple operation, and high practicability. At present, various adsorbing materials for uranyl ion extraction are available, such as clay minerals, mesoporous silica, resins, chitosan, synthetic polymers, carbon materials, porous framework materials and the like. However, in aqueous environments, the predominant form of uranium present is soluble hexavalent uranium (U (vi)). The adsorption material has poor selectivity and adsorbability to hexavalent uranium, and the adsorbed hexavalent uranium is easily desorbed from the adsorption material due to the fact that the hexavalent uranium is dissolved in water and enters the water solution again, so that extraction of uranium is not facilitated.
Disclosure of Invention
In view of the above, the present invention aims to provide a magnetic nano-iron composite loaded with phosphorylated chitosan, and a preparation method and an application thereof.
In order to achieve the purpose, the invention provides the following technical scheme:
the invention provides a preparation method of a phosphorylated chitosan loaded magnetic nano-iron composite material, which comprises the following steps:
(1) mixing chitosan, a phosphorylation modifier and a catalyst for the first time, and then carrying out phosphorylation reaction to obtain phosphorylated chitosan;
(2) and after the phosphorylated chitosan, the nano zero-valent iron and the pore-forming agent are mixed for the second time, freeze drying is carried out, and the phosphorylated chitosan loaded magnetic nano iron composite material is obtained.
Preferably, in the step (1), the phosphorylation modifier includes phosphorus pentoxide; the mass ratio of the chitosan to the phosphorylation modifier is (1-10) to (1-10).
Preferably, in the step (1), the catalyst comprises methanesulfonic acid, and the ratio of the mass of the chitosan to the volume of the catalyst is 1g to (1-14) mL.
Preferably, in the step (2), the mass ratio of the chitosan to the phosphorylated chitosan is (0.1-2): (0.05-1).
Preferably, in the step (2), the mass ratio of the phosphorylated chitosan to the nano zero-valent iron is (0.05-1): (0.05-1).
Preferably, in the step (2), the pore-forming agent includes NH4CO3A solution; the NH4CO3The mass concentration of the solution was 10%.
Preferably, in the step (2), the ratio of the mass of the nanoscale zero-valent iron to the volume of the pore-forming agent is (0.05-1) g to (1-10) mL.
Preferably, in the step (2), the temperature of the freeze drying is-85.5 ℃; the freeze drying time is 12-24 hours.
The invention also provides a phosphorylated chitosan loaded magnetic nano-iron composite material prepared by the preparation method of the technical scheme, which comprises a sponge chitosan substrate with phosphate groups and nano zero-valent iron loaded on the sponge chitosan substrate; the sponge-type chitosan matrix is a phosphorylated chitosan-chitosan compound.
The invention also provides application of the phosphorylated chitosan loaded magnetic nano-iron composite material in the technical scheme in extraction of uranium in seawater or uranium-containing wastewater.
The invention provides a preparation method of a phosphorylated chitosan loaded magnetic nano-iron composite material, which comprises the following steps: (1) mixing chitosan, a phosphorylation modifier and a catalyst for the first time, and then carrying out phosphorylation reaction to obtain phosphorylated chitosan; (2) and after the phosphorylated chitosan, the nano zero-valent iron and the pore-forming agent are mixed for the second time, freeze drying is carried out, and the phosphorylated chitosan loaded magnetic nano iron composite material is obtained. According to the method, firstly, the chitosan is subjected to phosphorylation treatment, the phosphate radical and hydroxyl on the chitosan are subjected to substitution reaction, so that a large amount of phosphate radical is arranged on the surface of the chitosan, then, the phosphorylated chitosan, the nano zero-valent iron and the pore-forming agent are uniformly mixed and dried, the pore-forming agent generates a large amount of gas in the drying process, so that the chitosan and the phosphorylated chitosan jointly generate a sponge type composite gel material with a pore structure, meanwhile, the nano zero-valent iron is loaded on a sponge type phosphorylated chitosan matrix, and the pore structure enables the phosphorylated chitosan loaded magnetic nano iron composite material prepared by the method to have a large specific surface area and can provide a larger reaction platform; in addition, the surface of the phosphorylated chitosan loaded magnetic nano-iron composite material has rich hydroxyl and amino groups of chitosan and phosphate groups introduced after phosphorylation modification, so that the phosphorylated chitosan loaded magnetic nano-iron composite material has high reaction activity and excellent adsorption performance on hexavalent uranium.
In the phosphorylated chitosan loaded magnetic nano-iron composite material prepared by the invention, nano zero-valent iron is loaded on the sponge type phosphorylated chitosan matrix, and the abundant pore structure can reduce the contact of the nano zero-valent iron and air, thereby solving the problems that the nano zero-valent iron is easy to oxidize and agglomerate.
The phosphorylated chitosan loaded magnetic nano-iron composite material is used for extracting uranium from seawater or uranium-containing wastewater, abundant hydroxyl, amino and phosphate groups contained in the material have high affinity to hexavalent uranium, the chelation effect of the amino and phosphate groups and the protonation/deprotonation effect of the hydroxyl can enable the hexavalent uranium to be chemically adsorbed on the phosphorylated chitosan loaded magnetic nano-iron composite material, and the reducibility of nano zero-valent iron can reduce soluble hexavalent uranium into insoluble tetravalent uranium, so that the uranium is extracted from a solution.
Drawings
FIG. 1 shows different masses of chitosan, phosphorylated chitosan, zero-valent nano-iron and different volumes of NH4CO3A change diagram of the influence on the adsorption performance of the phosphorylated chitosan loaded magnetic nano-iron composite material;
FIG. 2 is a surface morphology representation and element distribution mapping diagram of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 before and after uranium adsorption;
FIG. 3 is an EDS diagram of C, N, O, P, Fe, U in the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 after uranium adsorption;
FIG. 4 is a Fourier transform infrared spectrum of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 before and after uranium adsorption;
FIG. 5 is an XPS plot of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 before and after uranium adsorption;
FIG. 6 is a graph showing the effect of pH change on Zeta potential and U (VI) adsorption of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1;
FIG. 7 is a graph showing the effect of initial uranium concentration on U (VI) adsorption of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1;
FIG. 8 is a graph showing the effect of contact time and temperature on U (VI) adsorption of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1;
fig. 9 is a graph showing the influence of coexisting ions on the U (vi) adsorption of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1.
Detailed Description
The invention provides a preparation method of a phosphorylated chitosan loaded magnetic nano-iron composite material, which comprises the following steps:
(1) mixing chitosan, a phosphorylation modifier and a catalyst for the first time, and then carrying out phosphorylation reaction to obtain phosphorylated chitosan;
(2) and after the phosphorylated chitosan, the nano zero-valent iron and the pore-forming agent are mixed for the second time, freeze drying is carried out, and the phosphorylated chitosan loaded magnetic nano iron composite material is obtained.
Unless otherwise specified, the present invention does not require any particular source of the starting materials for the preparation, and commercially available products known to those skilled in the art may be used.
According to the invention, the phosphorylation reaction is carried out after the chitosan, the phosphorylation modifier and the catalyst are firstly mixed, so as to obtain the phosphorylation chitosan. In the present invention, in the step (1), the phosphorylation modifier preferably includes phosphorus pentoxide; the catalyst preferably comprises methane sulfonic acid; the mass ratio of the chitosan to the phosphorylation modifier is preferably (1-10) to (1-10), and more preferably 1: 1; the ratio of the mass of the chitosan to the volume of the catalyst is preferably 1g to (1-14) mL, and more preferably 1g to 7 mL.
In the present invention, the first mixing process is preferably to dissolve chitosan into the catalyst, then add the phosphorylation modifier, and stir uniformly. The process of adding the phosphorylation modifier is not particularly limited in the invention, and a process well known in the art can be adopted, and in the embodiment of the invention, the process of adding the phosphorylation modifier is specifically that the phosphorylation modifier is added in small amount for multiple times; the stirring process is not particularly limited in the present invention, and a stirring process well known in the art is employed until the phosphorylation modifier is completely reacted. In the embodiment of the present invention, the stirring process is specifically manual stirring at room temperature.
Preferably, the product obtained by the first mixing is cooled in the phosphorylation reaction process to obtain a phosphorylation reaction product; the cooling mode is preferably ice water bath; the cooling time is preferably 3 hours; in the invention, the product obtained by mixing is preferably stirred once every 5min in the cooling process; the time of each stirring is preferably 1-2 min, and more preferably 2 min; the stirring process is not particularly limited in the present invention, and a process well known in the art may be used. In the embodiment of the invention, the process of each stirring is specifically manual stirring at room temperature. The phosphorylation modifier can release a large amount of heat in the phosphorylation reaction process, and the ice-water bath is adopted to cool the phosphorylation reaction process so as to prevent the phosphorylation effect of the chitosan from being influenced by overhigh temperature.
After the phosphorylation reaction is finished, the phosphorylation reaction product is preferably washed and freeze-dried in sequence to obtain the phosphorylated chitosan. In the present invention, the washing solution used for the washing preferably includes anhydrous diethyl ether, acetone and methanol; the washing process is preferably to adopt each washing liquid to wash for three times in sequence; the present invention does not specifically limit the amount of the washing solution used for washing, and the phosphorylation reaction product is sufficiently washed. The invention adopts anhydrous ether, acetone and methanol to clean phosphorylation reaction products, and has the functions of precipitating phosphorylation reactants and washing away unreacted catalyst.
In the invention, the freeze drying time is preferably 12-24 h, and more preferably 12 h; the temperature of the freeze drying is preferably-85.5 ℃; the freeze drying mode is preferably low-temperature freeze drying; the freeze drying apparatus is preferably a vacuum drying oven.
After obtaining the phosphorylated chitosan, the nano zero-valent iron and the pore-forming agent are mixed for the second time, and then freeze-dried to obtain the phosphorylated chitosan loaded magnetic nano-iron composite material.
In the present invention, in the step (2), the chitosan and phosphorylated chitosanThe mass ratio of the sugar is preferably (0.1-2) to (0.05-1), more preferably (0.7-1.5) to (0.093-0.213); the mass ratio of the phosphorylated chitosan to the nano zero-valent iron is preferably (0.05-1) to (0.05-1), and more preferably (0.093-0.213) to (0.05-0.4); the pore former preferably comprises NH4CO3A solution; the NH4CO3The mass concentration of the solution is preferably 10%; the ratio of the mass of the nano zero-valent iron to the volume of the pore-forming agent is preferably (0.05-1) g to (1-10) mL, and more preferably (0.05-0.4) g to (0.5-3) mL. The pore-forming agent used in the invention has the function of generating gas in the second mixing process, so that air holes are formed in the mixed material of the phosphorylated chitosan, the chitosan and the nano zero-valent iron, the specific surface area of the mixed material of the phosphorylated chitosan, the chitosan and the nano zero-valent iron is increased, the adsorption performance of the phosphorylated chitosan-loaded magnetic nano iron composite material is improved, more reaction sites are provided, and the adsorption performance of hexavalent uranium is improved.
In the present invention, in the step (2), the phosphorylated chitosan is preferably used in the form of a phosphorylated chitosan aqueous solution; the preparation method of the phosphorylated chitosan aqueous solution is preferably that the phosphorylated chitosan is dissolved in water; the ratio of the mass of the phosphorylated chitosan to the volume of water is preferably (0.1 to 1) g to (1 to 10) mL, and more preferably (0.5 to 1) g to (2 to 7) mL. The invention adopts deionized water to dissolve phosphorylated chitosan so as to prevent other impurities from being introduced.
In the present invention, in the step (2), the chitosan is preferably used in the form of a chitosan acetic acid dispersion; the preparation method of the chitosan acetic acid dispersion liquid is preferably that chitosan is dispersed in acetic acid; the ratio of the mass of the chitosan to the volume of the acetic acid in the step (2) is preferably (0.1-1) g to (1-10) mL, and more preferably (0.5-1) g to (2-7) mL; the process of dispersing is not particularly limited in the present invention, and chitosan may be uniformly dispersed in acetic acid by using a dispersing process well known in the art.
In the invention, in the step (2), preferably, the second mixing process is to mix the phosphorylated chitosan and the chitosan, add the nano zero-valent iron, stir the mixture uniformly, add the pore-forming agent, and continue stirring for 2-5 min to obtain the second mixture. The mixing mode of the phosphorylated chitosan and the chitosan is preferably stirring, and the stirring time is preferably 3-5 min; the stirring is preferably performed by hand at room temperature.
In the present invention, in the step (2), the temperature of the freeze-drying is preferably-85.5 ℃; the freeze drying time is preferably 12-24 hours, and more preferably 12-13 hours; the freeze drying mode is preferably low-temperature freeze drying; the freeze drying apparatus is preferably a vacuum drying oven.
After the freeze drying is finished, preferably soaking the freeze-dried material in absolute ethyl alcohol twice to obtain the phosphorylated chitosan loaded magnetic nano-iron composite material; the time of each soaking is preferably 20-30 min, and more preferably 20 min. The invention has no special limitation on the dosage of the absolute ethyl alcohol, and the dried material is completely immersed. The invention adopts absolute ethyl alcohol to soak the dried material, so as to extract residual moisture, acetic acid and pore-forming agent.
The invention also provides a phosphorylated chitosan loaded magnetic nano-iron composite material prepared by the preparation method in the technical scheme, which comprises a sponge chitosan matrix with phosphate groups and nano zero-valent iron loaded on the sponge chitosan matrix; the sponge-type chitosan matrix is a phosphorylated chitosan-chitosan compound.
The acid resistance of the phosphorylated chitosan loaded magnetic nano-iron composite material is preferably tested by adopting an acid solution; preferably, the testing process comprises the steps of soaking the phosphorylated chitosan loaded magnetic nano-iron composite material in an acid solution, and then sequentially cleaning and drying; the pH value of the acid solution is preferably 1-6, and more preferably 4; the acid solution is preferably a hydrochloric acid solution or a nitric acid solution, and more preferably a hydrochloric acid solution. The dosage of the hydrochloric acid solution is not specially limited, and the phosphorylated chitosan loaded magnetic nano-iron composite material is completely immersed; the cleaning process is preferably carried out by adopting deionized water for washing; the drying temperature is preferably 15-35 ℃, and more preferably 25 ℃; the drying time is preferably 12-72 hours, and more preferably 48-72 hours; the drying mode is preferably vacuum drying. The acid resistance of the phosphorylated chitosan loaded magnetic nano-iron composite material prepared by the method is tested by adopting an acid solution soaking mode, and when the pH value is less than 4, the phosphorylated chitosan loaded magnetic nano-iron composite material can be dissolved in the acid solution to damage the pore structure of the phosphorylated chitosan loaded magnetic nano-iron composite material, so that the adsorption performance of the phosphorylated chitosan loaded magnetic nano-iron composite material is influenced.
The invention also provides application of the phosphorylated chitosan loaded magnetic nano-iron composite material in extraction of uranium in seawater or low-concentration uranium-containing wastewater.
The method of the present invention is not particularly limited, and the method may be applied by a method known in the art.
The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.
Example 1
Dissolving 2g of Chitosan (CS) into 14mL of methanesulfonic acid, then weighing 2g of phosphorus pentoxide, adding a small amount of phosphorus pentoxide for multiple times, manually stirring uniformly at room temperature, placing in ice water for 3h, stirring for 2min every five min, then washing with anhydrous ether, acetone and methanol for three times respectively, and finally freeze-drying at the low temperature of-85.5 ℃ in a vacuum drying oven for 12h to obtain phosphorylated Chitosan (CSP);
dispersing 0.8g of chitosan into 4.25mL of acetic acid with the mass concentration of 1% to obtain chitosan acetic acid dispersion liquid; dissolving 0.133g of phosphorylated chitosan in 4.25mL of deionized water to obtain a phosphorylated chitosan aqueous solution; mixing chitosan acetic acid dispersion solution and phosphorylated chitosan aqueous solution, manually stirring at room temperature for 4min, and adding 0.2g of nano zero-valent iron (Fe)0) After stirring the mixture at room temperature, 1.5mL of 10 wt% NH was added4CO3Manually stirring the solution at room temperature for 3min, drying the obtained material in a vacuum drying oven at-85.5 deg.C for 12 hr, and soaking in anhydrous ethanol twice each timeSoaking for 20min in HCl solution with pH of 4 for 30min, washing with deionized water, and vacuum drying at 25 deg.C for 72h to obtain magnetic nano-iron composite material (CSP/Fe) loaded with phosphorylated chitosan0Composite materials).
Examples 2 to 10
The difference from example 1 is that the chitosan masses were 0.7g, 0.8g, 0.825g, 0.875g, 0.9g, 0.925g, 1g, 1.25g, and 1.5g, respectively, and the rest was the same as example 1.
Examples 11 to 17
The difference from example 1 is that the masses of phosphorylated chitosan were 0.093g, 0.113g, 0.133g, 0.153g, 0.173g, 0.193g, and 0.213g, respectively, and the rest was the same as example 1.
Examples 18 to 22
The difference from example 1 is that the mass of the zero-valent nano-iron is 0.05g, 0.1g, 0.2g, 0.3g and 0.4g, and the rest is the same as example 1.
Examples 23 to 28
The difference from example 1 is that NH4CO3The volume of the solution was 0.5mL, 1mL, 1.5mL, 2mL, 2.5mL, and 3mL, respectively, and the remainder was the same as in example 1.
Application example 1
The phosphorylated chitosan loaded magnetic nano-iron composite material prepared in the embodiment 1 with the mass range of 20g is weighed as an adsorbent, and is put into a uranium solution with the pH of 90ml and the pH of 6 and the concentration of 10mg/L for adsorption for 12 hours at the temperature of 308.15k and the rotating speed of 175 r/min.
Application examples 2 to 28
The difference from the application example 1 is that the adsorbent is replaced by the phosphorylated chitosan loaded magnetic nano-iron composite material prepared in the embodiments 2 to 28, and the rest is consistent with the application example 1.
Performance test
(1) FIG. 1 shows different masses of chitosan, phosphorylated chitosan, zero-valent nano-iron and different volumes of NH4CO3Change chart of influence on adsorption performance of phosphorylated chitosan loaded magnetic nano-iron composite material, and method for preparing phosphorylated chitosan loaded magnetic nano-iron composite materialWherein a is the influence of chitosan with different masses on the adsorption performance of the phosphorylated chitosan-loaded magnetic nano-iron composite material (application examples 2-10), b is the influence of the phosphorylated chitosan with different masses on the adsorption performance of the phosphorylated chitosan-loaded magnetic nano-iron composite material (application examples 18-22), c is the influence of zero-valent nano-iron with different masses on the adsorption performance of the phosphorylated chitosan-loaded magnetic nano-iron composite material, and d is NH with different volumes4CO3Influence of the solution on adsorption performance of the phosphorylated chitosan loaded magnetic nano-iron composite material (application examples 23-28), wherein e is NH with different volumes4CO3Influence of the solution on the morphology of the phosphorylated chitosan loaded magnetic nano-iron composite material (application examples 23-28).
As can be seen from a in FIG. 1, the mass range of chitosan is 0.7-1.5 g, and under the influence of different masses of chitosan, CSP/Fe0The adsorption rate of the composite material to uranium is over 90 percent, which shows that the content of CS has no obvious influence on the adsorption capacity of the material. The adsorption rates of the materials containing 0.800g, 0.8250g, 0.8750g and 0.9000g of CS were 95% or more.
As shown in a b in FIG. 1, the mass range of the phosphorylated chitosan is 0.093-0.213 g, and the phosphorylated Chitosan (CSP) improves the selectivity of uranium by providing abundant phosphate radicals on one hand, and improves the characteristic that CS is easy to dissolve in an acidic environment due to chemical modification on the other hand. However, the adsorption of uranium is also affected by too much CSP content, the adsorption capacity of uranium is greatly reduced when the content exceeds 0.1930g, and the adsorption rate of uranium is the highest when the content is 0.1330 g.
As can be seen from c in FIG. 1, the mass range of the nano-iron is 0.05-0.4 g, and the nano-iron has large specific surface area and high reactivity, and is used for CSP/Fe0The adsorption effect of the composite material is remarkably influenced, and the adsorption rate of the material to uranium can be effectively increased within a certain amount range. However, if the nano-iron content is too high, the adsorption rate may be lowered by self-oxidation, and the molding of the material may be affected.
As can be seen in FIG. 1 d, NH4CO3The volume range is 0.5-3.0 mL, NH4CO3Addition amount of the solution CSP/Fe0The adsorption effect of the composite material has a remarkable influence.
As can be seen in FIG. 1, e is NH4CO3The insufficient addition amount of the solution can cause the water content of the material to be too large, a stable gel structure cannot be formed, and the specific surface area is influenced due to insufficient pore formation, so that the active sites are reduced, and the adsorption rate is further influenced. NH (NH)4CO3An excessive amount of the additive hardens the material to form chips, which makes it difficult to maintain the stability of the structure, and thus the adsorption rate is lowered. Therefore, 1.5mL was selected as the optimum amount.
(2) The surface morphology of the phosphorylated chitosan loaded magnetic nano-iron composite material prepared in example 1 before and after uranium adsorption was characterized by SEM, and the result is shown in a in fig. 2.
As can be seen from a in fig. 2, the surface of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 has a porous structure in a random distribution, and a large number of irregular protrusions are present on the surface to form a rough surface. After the phosphorylated chitosan loaded magnetic nano-iron composite material prepared in example 1 adsorbs uranium, the surface voids are filled, the surface roughness is reduced, and it is proved that U (vi) is adsorbed on the surface.
(3) The distribution of each element of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 after uranium adsorption was analyzed by mapping, as shown in b in fig. 2.
As can be seen from b in fig. 2, the content of zero-valent nano-iron in the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 after uranium adsorption is highest, C, O times, and detection of 0.486 wt.% of U proves that a part of U (vi) is successfully adsorbed.
(4) EDS analysis is carried out on C, N, O, P, Fe and U in the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 after uranium adsorption, and the result is shown in FIG. 3.
As can be seen from fig. 3, the distribution positions of C, N, O elements in the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 after uranium adsorption are relatively consistent, the distribution of P element proves that chitosan is completely phosphorylated, Fe element is uniformly loaded by phosphorylated chitosan, and U element is uniformly distributed on the whole surface, but more concentrated in pores on the surface of the phosphorylated chitosan-loaded magnetic nano-iron composite material.
(5) Using 400-4000 cm-1The FT-IR of (a) was used to analyze the functional groups on the surface of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 before and after uranium adsorption, and the results are shown in fig. 4.
As can be seen from FIG. 4, the length of the groove is 3450 to 3400cm-1The peak appears in the stretching vibration peak of amino and hydroxyl, the peak shape is sharp, and no other peak interference exists. 1636cm-1Has secondary amino absorption peak at 2900-2863 cm-1A C-H stretching vibration peak appears, and both curves are 1400-1000 cm-1The stretching vibration spectrum of P ═ O and P-O-H appears in the range, and the curve after adsorption is 1092cm-1The absorption peak of the phosphate radical is weakened, and the fact that the phosphate radical is successfully introduced into the phosphorylated chitosan loaded magnetic nano iron composite material is confirmed, and P ═ O is complexed with uranyl ions. The adsorbed phosphorylated chitosan loaded magnetic nano-iron composite material is 1591cm-1The peak value is weakened, which indicates that the amino group and U (VI) are also subjected to complexation reaction.
(6) An X-ray photoelectron spectrometer is used to test the phosphorylated chitosan loaded magnetic nano-iron composite material prepared in example 1 before and after uranium adsorption, and the result is shown in fig. 5, wherein a is a total spectrum, b-f are XPS spectra of C, N, O, P, Fe elements, and g is an XPS spectrum of U.
As can be seen from a in fig. 5, the atomic contents of C (62.15%) and O (23.60%) on the surface of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 are the highest, the atomic content of P element is about 0.24%, and the atomic content of Fe is about 1.80%.
As can be seen from the spectra of C1s, N1s, and O1s in fig. 5 b to d, the main components of the phosphorylated chitosan-supported magnetic nano-iron composite material prepared in example 1 are C — C peaks at 284.88ev, which are the main species of the surface C, and C ═ NOH peaks and COOH peaks at 282.88ev, 286.17ev, and 288.46ev, respectively. The N1s spectrum represented N-H peaks and N-C-N peaks at 399.24eV and 400.04eV, respectively. The O1s spectrum has major components at 531.28ev, 532.21ev and 533.12 ev-COOH, C ═ O, -OH, respectively.
As can be seen from e in FIG. 5, 133.78ev and 134.78ev prove that-PO in the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 14Is present.
As is clear from f in FIG. 5, Fe2P3/2And Fe2P1/2Two strong bands with binding energies of 710.05ev and 725.36ev, respectively, are formed by Fe2+(FeO) and Fe3+(Fe3O4) Has a peak composition of Fe3O4Typical features of (a). CSP/Fe after adsorption0U4f appearing above5/2And U4f7/2The peak shows that U (VI) is successfully adsorbed on the surface of the phosphorylated chitosan loaded magnetic nano-iron composite material.
As can be seen from g in FIG. 5, the two peaks of U (VI) and U (IV) are further subdivided into four components, U (VI) U4f5/2At 392.79ev, U (IV) U4f5/2At 391.51ev, U (VI) U4f7/2At 381.89ev, U (IV) U4f7/2Located at 380.72 ev. According to the relative areas of the peaks, the proportion of U (VI) to U (IV) is 72.93 percent and 27.06 percent, which shows that the adsorption of the phosphorylated chitosan loaded magnetic nano-iron composite material reduces part of U (VI) to U (IV).
(7) Influence of pH value of U (VI) solution on Zeta potential and U (VI) adsorption of phosphorylated chitosan loaded magnetic nano-iron composite material prepared in example 1
The phosphorylation chitosan load magnetic nano-iron composite material prepared in the example 1 is studied on the U (VI) adsorption condition under different conditions of pH 4-9 and temperature 288.15-308.15 k. In the adsorption experiment, the phosphorylated chitosan loaded magnetic nano-iron composite material prepared in the example 1 with the mass range of 0.0005-0.0045 g is weighed and put into 90mL of uranium solution with the concentration range of 5-600 mg/L for adsorption, and Na is used for adsorption2CO3、HNO3Adjusting the pH value of the solution, and uniformly keeping the adsorption process at the rotating speed of 170-180 r/min for vibration. Then, the concentration of the uranium solution is analyzed by a spectroscopic method, and the adsorption rate (R)e) And adsorption capacity (Q)e) From the formulae (1) and(2) and (6) calculating. Wherein, C0And CeThe initial and equilibrium concentrations (mg/L) of the uranium solution, respectively.
Re＝(C0-Ce)/C0×100％ (1)
Qe＝(C0-Ce)×V/m (2)
The pH of the U (VI) solution is selected to be in the range of 4-9 for carrying out an adsorption experiment, and the change conditions of the CSP/Fe0 on the U (VI) adsorption quantity and the Zeta potential under different pH values are studied, and the result is shown in FIG. 6.
The pH of the U (VI) solution is closely related to the shape of a solute and the Zate potential, and the U (VI) solution has an important influence on the adsorption effect of the phosphorylated chitosan loaded magnetic nano-iron composite material. As shown in fig. 6, when the pH is less than 5, the adsorption effect is poor, mainly because the surface of the phosphorylated chitosan loaded magnetic nano-iron composite material is positively charged, and a repulsive force exists between the phosphorylated chitosan loaded magnetic nano-iron composite material and adsorbate cations, so that a double-layer film between the phosphorylated chitosan loaded magnetic nano-iron composite material and the solution is thickened. When the pH value exceeds the zero charge, the attraction between negative charges and positive ions on the surface of the phosphorylated chitosan loaded magnetic nano iron composite material causes the contraction of the double-layer film, so that the opportunity of the surface action of adsorbate and the adsorbent is increased, and the adsorption effect is improved. When the pH value of the solution exceeds 5.5, the surface of the phosphorylated chitosan loaded magnetic nano-iron composite material is negatively charged due to the increase of the hydroxide concentration in the solution.
The phosphorylated chitosan loaded magnetic nano-iron composite material has strong pH dependence, and the effect is optimal when the pH is 6. At lower pH concentrations, H+And H3O+Occupies a large number of adsorption sites and UO2 2+Competition, the amino group being highly protonated at lower pH decreases for UO2 2+The affinity of (a). In addition, the lower pH also causes the adsorbent to dissolve to a certain extent, which affects the adsorption effect. As pH increases, the adsorbent surface becomes more negatively charged resulting in more favorable adsorption of positively charged species, and the protonation of the phosphate groups decreases to facilitate complex formation. When the pH value is more than 5, the U (VI) adsorption can be related to the protonation/deprotonation of the hydroxyl on the surface of the nano iron particle. When the pH value is more than 7, the adsorption effect is goodThe sharp drop is mainly due to uranium and CO in solution3 2+Combined to form UO2(CO3)2 2-Electrostatic repulsion between the uranyl ions and the adsorption effect is influenced, and the uranyl ions are hydrolyzed under the condition of high pH (UO)2)3(OH)5+And (UO)2)4(OH)7+And precipitating. For zero-valent iron to exert reducibility, uranium exists mainly as uranyl ions more suitable for being reduced under acidic or weakly acidic conditions, and the presence of uranium in the form of these complex ions inhibits the reduction of uranium by zero-valent iron when the pH is raised.
(8) Influence of initial uranium concentration of U (VI) solution on adsorption effect of phosphorylated chitosan loaded magnetic nano-iron composite material
The adsorption condition of the phosphorylated chitosan loaded magnetic nano-iron composite material prepared in the example 1 on U (VI) under the conditions that the initial uranium concentration is 5-600 mg/L and the temperature is 298.15K is studied. In the adsorption experiment, 0.0200g of the phosphorylated chitosan loaded magnetic nano-iron composite material prepared in example 1 is weighed and put into 90mL of uranium solution with the concentration range of 5-600 mg/L for adsorption, and Na is used2CO3、HNO3Adjusting the pH value of the solution, uniformly maintaining the adsorption process at a rotating speed of 170-180 r/min, and oscillating, and then analyzing the concentration of the adsorbed uranium solution by using a spectroscopic method, wherein the result is shown in figure 7.
As can be seen from FIG. 7, when the initial uranium concentration of the U (VI) solution is less than 100mg/L, more than 90% of the U (VI) in the solution can be adsorbed. The adsorption capacity of the phosphorylated chitosan-loaded magnetic nano-iron composite material is increased along with the increase of the initial uranium concentration, because when the uranium concentration is lower, the phosphorylated chitosan-loaded magnetic nano-iron composite material has unsaturated binding sites, and the binding sites are gradually occupied along with the increase of the U (VI) concentration. The greater the concentration gradient between the adsorbent and the solution interface, the stronger the equilibrium absorption. Finally, the phosphorylated chitosan loaded magnetic nano-iron composite material reaches the maximum adsorption capacity when the initial uranium concentration is 200 mg/L.
(9) Dynamics of
Different dynamicsThe model is usually used for predicting the adsorption mechanism of a solid-liquid system, and the quasi-first order kinetic equation (eqn (3)) and the quasi-second order kinetic equation (eqn (4)) are adopted to research U (VI) in CSP/Fe0The adsorption kinetics above are fitted and Qe (mg/g) and Qt (mg/g) represent the adsorption quantities k at equilibrium and at time t (min), respectively1And k2Are the rate constants of the quasi-first and quasi-second order equations, respectively.
Qt＝Qe(1-e-k1t) (3)
Qt＝Qe 2k2t/(1+Qek2t) (4)
Under the conditions of pH 6 and 298.15K, 0.0100g of the phosphorylated chitosan loaded magnetic nano-iron composite material prepared in example 1 adsorbs 10mg/L uranium solution, the influence of contact time and temperature on the U (vi) adsorption effect of the phosphorylated chitosan loaded magnetic nano-iron composite material is studied, and the result is shown in fig. 8, wherein a is the influence of contact time on the U (vi) adsorption effect of the phosphorylated chitosan loaded magnetic nano-iron composite material, a quasi-primary kinetic model and a quasi-secondary kinetic model are adopted for fitting, b to d are isothermal lines of the phosphorylated chitosan loaded magnetic nano-iron composite material adsorption U (vi) under the conditions of 288.15K, 289.15K and 308.15K, respectively, and the kinetic parameters fitted by the quasi-primary kinetic model and the quasi-secondary kinetic model are shown in table 1.
As can be seen from FIG. 8, the adsorption process of the phosphorylated chitosan loaded magnetic nano-iron composite material to U (VI) comprises a fast adsorption stage of 0-2 h and a second stage of slow growth to adsorption equilibrium. In the rapid adsorption stage, the adsorption efficiency is increased rapidly probably due to the high specific surface area and abundant binding sites of the phosphorylated chitosan loaded magnetic nano-iron composite material. Over time, the binding sites were heavily occupied and the adsorption efficiency gradually stabilized after 4 h.
As can be seen from Table 1, the quasi-second order kinetics R2The quasi-second-order dynamics model is more suitable for the adsorption behavior of the phosphorylated chitosan loaded magnetic nano-iron composite material, and the U (VI) is proved to be used for phosphorylating chitosan loaded magnetic nano-iron composite materialThe adsorption on the nano-iron composite material is chemical adsorption, wherein the valence force relates to the action of exchanging or sharing electrons of U (VI) on the phosphorylated chitosan loaded magnetic nano-iron composite material.
TABLE 1 kinetic parameters
(10) Thermodynamic and adsorption isotherms
The adsorption thermodynamics are of great significance to the research of the adsorption mechanism, and the related distribution coefficient and entropy change (delta H)0) Enthalpy change (Δ S)0) Gibbs free energy (Δ G)0) The equivalent thermodynamic parameters are calculated from the equations (5), (6), (7) and (8) shown in table 2. In the formula, R is an ideal gas constant (8.314J/(mol K)), and T is a Kelvin temperature.
Kd＝Qe/Ce (5)
Kc＝1000Kd (6)
lnKc＝-ΔH0/RT+ΔS0/R (7)
ΔG0＝ΔH0-TΔS0 (8)
As can be seen from Table 2,. DELTA.G0Determines whether the adsorption reaction can be performed spontaneously, is greatly influenced by temperature and pressure, and has a size depending on delta H0And Δ S0，ΔG0A negative value indicates that the adsorption reaction is spontaneous and feasible, but not. And, Δ G0Negative values and increasing spontaneity with increasing temperature, it can be concluded that the adsorption mechanism is related to chemisorption. Δ H0A positive value indicates that the adsorption process is endothermic and an increase in temperature may promote the adsorption of U (vi). Delta S0The positive value of (B) is probably due to the fact that the increase of temperature leads to the increase of intermolecular mobility, is beneficial to the complexation and stability of adsorption and promotes CSP/Fe0For U (VI) adsorption.
TABLE 2 thermodynamic parameters at different temperatures
The adsorption isotherms Langmuir and Freundlich model equations are shown in equations (9) (10). In the formula, QeAnd QmB is the Langmuir adsorption constant (L/mg), k is the Freundlich adsorption coefficient, and n is the degree of linear dependence of adsorption, reflecting the adsorption capacity of the adsorbent.
Qe＝(bQmCe)/(1+bCe) (9)
Qe＝kCe 1/n (10)
The adsorption isotherm may reflect the interaction mechanism between the adsorbent and the adsorbate. Research shows that different initial uranium solution concentrations for CSP/Fe are shown by Langmuir and Freundlich adsorption isothermal models0Influence of the adsorption effect. The Langmuir model assumes dynamic monolayer adsorption, all adsorption sites are the same and independent of each other, and there is no interaction between adsorbate molecules on the surface of the adsorbent, whereas the Freundlich model assumes multilayer adsorption, and the adsorption capacity of the adsorbent increases with increasing concentration.
With 0.020g CSP/Fe0Respectively at concentrations of 5, 10, 20, 30, 50, 100, 200, 400 and 600 mg.L-1The uranium solution (b) was adsorbed and the data were fitted using Langmuir and Freundlich models to obtain a linear relationship as shown in fig. 8. As the uranium concentration increases, the adsorption capacity increases sharply at the beginning, and then slowly to gradually level off. According to the R of Langmuir model shown in Table 32The adsorption behavior of the magnetic nano-iron composite material loaded by the phosphorylated chitosan belongs to single-layer adsorption. N in the Freundlich model is less than 1, and the phosphorylation chitosan loaded magnetic nano-iron composite material is considered to be a main adsorption mechanism for the adsorption of U (VI) by chemical adsorption, mainly because the U (VI) is related to the chelation of phosphate groups on the phosphorylation chitosan loaded magnetic nano-iron composite material.
TABLE 3 thermodynamic parameters for fitting Langmuir and Freundlich models at different temperatures
(11) Simulating influence of coexisting ions in seawater on adsorption effect of phosphorylated chitosan loaded magnetic nano-iron composite material
Because a large amount of coexisting ions exist in seawater, the research on the influence of the coexisting ions and the magnetic nano-iron loaded phosphorylated chitosan composite material on U (VI) adsorption is very important. Therefore, solutions were prepared by experimentally simulating the concentration of each ion in seawater, 0.0200g of the phosphorylated chitosan-loaded magnetic nano-iron composite material prepared in example 1 was added to the simulated seawater solution prepared at each ion concentration in 90mL of simulated seawater under the conditions of 298.15K, pH 8 and 175r/min for 12h of adsorption, competitive adsorption of the phosphorylated chitosan-loaded magnetic nano-iron composite material on U (vi), Cu (ii), Fe (iii), Zn (ii), Ca (ii), Mg (ii), V (V) and Na (i) ions was studied, and the concentration of each ion in the simulated seawater was as shown in table 4.
TABLE 4 simulation of coexisting ion concentration in seawater
Partition coefficient (K) for influence of coexisting ions on U (VI) adsorption of phosphorylated chitosan loaded magnetic nano-iron composite materiald) Expressed in mL/g, and obtained by the formula (11). C0And CeInitial and equilibrium concentrations (mg/L) of uranium solution, v (ml) is the volume of the solution, and m (g) is the dry weight of the adsorbent, respectively, the results are shown in fig. 9.
As can be seen in FIG. 9, the partition coefficient (K)d) Is commonly used for expressing the affinity of a substance to a solvent, and the phosphorylated chitosan loaded magnetic nano-iron composite material has Ca (II), Mg (II) and VThe affinity between the (V) and Na (I) ions is low, and the four ions have little influence on the U (VI) adsorption. And the existence of Cu (II), Fe (III) and Zn (II) ions with higher affinity inhibits the adsorption of the phosphorylated chitosan loaded magnetic nano-iron composite material to U (VI), which is probably caused by the existence of phosphate groups and the aggregation of metal cations due to the magnetism of nano-iron. In addition, when the pH of the solution is set to 8 in the study of the influence of the coexisting ions on the adsorption of U (vi), the adsorption of U (vi) by the nano-iron is also influenced to some extent. When the phosphorylated chitosan loaded magnetic nano-iron composite material adsorbs uranium in a solution in which seven other coexisting ions exist, the distribution coefficient of U (VI) still reaches a high level (13713.0560 mL/g). Therefore, the phosphorylated chitosan loaded magnetic nano-iron composite material has better selective adsorption on U (VI) and is expected to be applied to extraction or recovery of U (VI) from seawater or uranium-containing wastewater.
In conclusion, the main action mechanism of the phosphorylated chitosan loaded magnetic nano-iron composite material prepared by the invention for adsorbing uranium is the combined action of the complexation of amino and phosphate radical and the reduction of zero-valent iron. The phosphorylated chitosan loaded magnetic nano-iron composite material has strong adsorption performance and high selectivity on U (VI), the adsorption behavior of the phosphorylated chitosan loaded magnetic nano-iron composite material depends on pH, and the phosphorylated chitosan loaded magnetic nano-iron composite material conforms to a quasi-second-order kinetic model and a Langmuir isotherm model. The maximum adsorption capacity (627.3441mg/g) is obtained under the condition of pH 6, 308.15K and 12h, the adsorption behavior is endothermic, spontaneous and feasible, and the selective U (VI) has better selectivity, and can be applied to the work of enriching low-concentration U (VI).
Although the present invention has been described in detail with reference to the above embodiments, it is only a part of the embodiments of the present invention, not all of the embodiments, and other embodiments can be obtained without inventive step according to the embodiments, and the embodiments are within the scope of the present invention.
Claims (10)
1. A preparation method of a phosphorylated chitosan loaded magnetic nano-iron composite material comprises the following steps:
(1) mixing chitosan, a phosphorylation modifier and a catalyst for the first time, and then carrying out phosphorylation reaction to obtain phosphorylated chitosan;
(2) and after the phosphorylated chitosan, the nano zero-valent iron and the pore-forming agent are mixed for the second time, freeze drying is carried out, and the phosphorylated chitosan loaded magnetic nano iron composite material is obtained.
2. The method according to claim 1, wherein in the step (1), the phosphorylation modifier includes phosphorus pentoxide; the mass ratio of the chitosan to the phosphorylation modifier is (1-10) to (1-10).
3. The preparation method according to claim 1, wherein in the step (1), the catalyst comprises methane sulfonic acid, and the ratio of the mass of the chitosan to the volume of the catalyst is 1g to (1-14) mL.
4. The method according to claim 1, wherein in the step (2), the mass ratio of the chitosan to the phosphorylated chitosan is (0.1-2) to (0.05-1).
5. The preparation method according to claim 1, wherein in the step (2), the mass ratio of the phosphorylated chitosan to the nano zero-valent iron is (0.05-1) to (0.05-1).
6. The method according to claim 1, wherein in the step (2), the pore-forming agent comprises NH4CO3A solution; the NH4CO3The mass concentration of the solution was 10%.
7. The preparation method according to claim 1 or 6, wherein in the step (2), the ratio of the mass of the nano zero-valent iron to the volume of the pore-forming agent is (0.05-1) g to (1-10) mL.
8. The method according to claim 1, wherein the temperature of the freeze-drying in the step (2) is-85.5 ℃; the freeze drying time is 12-24 hours.
9. The phosphorylated chitosan-loaded magnetic nano-iron composite material prepared by the preparation method of any one of claims 1 to 8, which comprises a sponge chitosan matrix with phosphate groups and nano zero-valent iron loaded on the sponge chitosan matrix; the sponge-type chitosan matrix is a phosphorylated chitosan-chitosan compound.
10. The use of the phosphorylated chitosan-loaded magnetic nano-iron composite material of claim 9 in the extraction of uranium from seawater or uranium-containing wastewater.
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