CN116237022A - Preparation method and application of fixed nano-hydrated cerium oxide - Google Patents
Preparation method and application of fixed nano-hydrated cerium oxide Download PDFInfo
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- CN116237022A CN116237022A CN202310159029.3A CN202310159029A CN116237022A CN 116237022 A CN116237022 A CN 116237022A CN 202310159029 A CN202310159029 A CN 202310159029A CN 116237022 A CN116237022 A CN 116237022A
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- hydrated cerium
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- 229910000420 cerium oxide Inorganic materials 0.000 title claims abstract description 106
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 title claims abstract description 99
- 238000002360 preparation method Methods 0.000 title claims abstract description 9
- 238000001179 sorption measurement Methods 0.000 claims abstract description 51
- 229920002678 cellulose Polymers 0.000 claims abstract description 42
- 239000001913 cellulose Substances 0.000 claims abstract description 42
- 229910052731 fluorine Inorganic materials 0.000 claims abstract description 32
- 239000011737 fluorine Substances 0.000 claims abstract description 32
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 claims abstract description 29
- 238000000034 method Methods 0.000 claims abstract description 29
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 27
- -1 fluoride ions Chemical class 0.000 claims abstract description 26
- 239000002105 nanoparticle Substances 0.000 claims abstract description 15
- BRLQWZUYTZBJKN-UHFFFAOYSA-N Epichlorohydrin Chemical compound ClCC1CO1 BRLQWZUYTZBJKN-UHFFFAOYSA-N 0.000 claims abstract description 5
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 39
- 239000000243 solution Substances 0.000 claims description 31
- 239000011259 mixed solution Substances 0.000 claims description 14
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims description 9
- 239000004202 carbamide Substances 0.000 claims description 9
- 239000000843 powder Substances 0.000 claims description 9
- 238000003756 stirring Methods 0.000 claims description 9
- 239000000725 suspension Substances 0.000 claims description 8
- 230000002860 competitive effect Effects 0.000 claims description 7
- 150000002500 ions Chemical class 0.000 claims description 7
- 238000005303 weighing Methods 0.000 claims description 7
- 230000000694 effects Effects 0.000 claims description 5
- 238000004108 freeze drying Methods 0.000 claims description 4
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 3
- 239000008367 deionised water Substances 0.000 claims description 3
- 229910021641 deionized water Inorganic materials 0.000 claims description 3
- 239000005457 ice water Substances 0.000 claims description 3
- 230000007935 neutral effect Effects 0.000 claims description 3
- 238000005406 washing Methods 0.000 claims description 3
- LRWZZZWJMFNZIK-UHFFFAOYSA-N 2-chloro-3-methyloxirane Chemical compound CC1OC1Cl LRWZZZWJMFNZIK-UHFFFAOYSA-N 0.000 claims description 2
- 239000002253 acid Substances 0.000 claims 2
- 230000001172 regenerating effect Effects 0.000 claims 1
- 238000004065 wastewater treatment Methods 0.000 claims 1
- 239000006260 foam Substances 0.000 abstract description 9
- 239000002351 wastewater Substances 0.000 abstract description 6
- 238000004132 cross linking Methods 0.000 abstract description 5
- 230000002378 acidificating effect Effects 0.000 abstract description 4
- 239000002270 dispersing agent Substances 0.000 abstract description 3
- 239000000463 material Substances 0.000 abstract description 3
- 230000002776 aggregation Effects 0.000 abstract description 2
- 238000004220 aggregation Methods 0.000 abstract description 2
- 239000003431 cross linking reagent Substances 0.000 abstract description 2
- 239000002114 nanocomposite Substances 0.000 abstract description 2
- 229920006395 saturated elastomer Polymers 0.000 abstract description 2
- 239000003513 alkali Substances 0.000 abstract 1
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 15
- 239000007788 liquid Substances 0.000 description 9
- 239000013078 crystal Substances 0.000 description 8
- 238000003795 desorption Methods 0.000 description 7
- 230000008569 process Effects 0.000 description 6
- 239000006228 supernatant Substances 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 230000008901 benefit Effects 0.000 description 4
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 3
- 239000003463 adsorbent Substances 0.000 description 3
- 238000006115 defluorination reaction Methods 0.000 description 3
- 238000011065 in-situ storage Methods 0.000 description 3
- 238000005342 ion exchange Methods 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 2
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 238000010668 complexation reaction Methods 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000002349 favourable effect Effects 0.000 description 2
- 238000005189 flocculation Methods 0.000 description 2
- 230000016615 flocculation Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- YPJKMVATUPSWOH-UHFFFAOYSA-N nitrooxidanyl Chemical compound [O][N+]([O-])=O YPJKMVATUPSWOH-UHFFFAOYSA-N 0.000 description 2
- 230000006911 nucleation Effects 0.000 description 2
- 238000010899 nucleation Methods 0.000 description 2
- 239000002243 precursor Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910002651 NO3 Inorganic materials 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000004581 coalescence Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 150000004696 coordination complex Chemical class 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 239000003651 drinking water Substances 0.000 description 1
- 235000020188 drinking water Nutrition 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 230000036541 health Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
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- 238000000733 zeta-potential measurement Methods 0.000 description 1
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- 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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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- 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
- B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
- B01J20/06—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising oxides or hydroxides of metals not provided for in group B01J20/04
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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
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- B01J20/28016—Particle form
- B01J20/28019—Spherical, ellipsoidal or cylindrical
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/28—Treatment of water, waste water, or sewage by sorption
- C02F1/288—Treatment of water, waste water, or sewage by sorption using composite sorbents, e.g. coated, impregnated, multi-layered
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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Abstract
The invention discloses a preparation method and application of fixed nano-hydrated cerium oxide, which relate to the technical field of environment functional nano-composite materials, and are characterized in that cellulose is used as a dispersing agent, epichlorohydrin is used as a crosslinking agent, hydrated cerium oxide nano-particles are uniformly fixed into cellulose foam by a dissolving-dispersing-crosslinking-pore-forming method, the prepared fixed nano-hydrated cerium oxide has a unique cellulose reticular crosslinking structure, can wrap around the hydrated cerium oxide nano-particles to prevent self aggregation in water and endow the hydrated cerium oxide with good hydraulic property, breaks through the bottleneck of nano-hydrated cerium oxide in practical engineering application, the fixed nano-hydrated cerium oxide is environment-friendly, has excellent adsorption capacity for fluoride ions in an acidic polluted water body, is convenient to adsorb and recycle after being saturated in a spherical shape, can keep unchanged form and stable performance after being regenerated repeatedly by alkali liquor, and is suitable for treating practical fluorine polluted wastewater.
Description
Technical Field
The invention relates to the technical field of environment functional nano composite materials, in particular to a preparation method and application of fixed nano hydrated cerium oxide.
Background
Fluorine is one of 14 microelements necessary for human body and one of the constituent components of human body, but excessive intake of fluorine causes fluoriasis, thyropathy and even death. According to the investigation, the problem of how to treat fluorine-containing wastewater is urgently solved, wherein the fluorine content of daily drinking water in at least one eighth of countries in the world is far beyond the standard (1.5 mg/L) regulated by the world health organization.
The current treatment methods of fluorine-containing wastewater mainly comprise precipitation and flocculation, a membrane treatment method, an adsorption method and an ion exchange method. Among them, the adsorption method has been considered as one of the most effective methods for treating fluorine-containing wastewater because of the advantages of low material cost, controllable operating conditions, large adsorption capacity, potential for reuse and reproducibility. The common adsorbents such as activated alumina, bone charcoal and the like have the problems of low adsorption capacity, poor adsorption specificity and secondary pollution. It was found that nano-hydrated cerium oxide (NCO) can bind to fluorine through Lewis acid-base complexation, ion exchange, and thus exhibit high selectivity for fluorine in water.
However, in actual water treatment, NCO tends to be high, solid-liquid separation is difficult, and pressure drop is too large, which hinders large-scale application. The in-situ precipitation method for introducing inorganic nano particles into a large-size porous main body to construct a three-dimensional macroscopic structure is a common idea for solving the problems. However, the nucleation and growth process in the special pore canal of the method is very likely to cause the difference of NCO crystal structures in the composite material and NCO crystal structures directly prepared from the outside, so that the exclusive adsorption capacity of NCO on fluoride ions is limited. In addition, the NCO layer initially grown on the surface of the porous body can prevent the precursor from diffusing inwards further, the mass transfer function of the body is reduced, the NCO content is maintained at a lower level, and the removal rate cannot be further improved. Therefore, a preparation method and application of the immobilized nano-hydrated cerium oxide are needed.
Disclosure of Invention
The purpose of the application is to provide a preparation method and application of fixed nano-hydrated cerium oxide, so as to solve the problems that NCO in the background art is serious in self aggregation, difficult in solid-liquid separation, excessive in pressure drop and energy-consuming in continuous dynamic water treatment, and the change of NCO crystal structure is difficult to control in the introduction process of the existing in-situ precipitation method for introducing NCO into a large-size host, so that the NCO cannot exert the F - Is specific to the adsorption capacity of F in complex water environment - The targeted removal rate is low, and the problems of complex preparation method, toxic substances generation and the like often exist.
The prepared NCO is uniformly fixed in the cellulose foam by using cellulose as a dispersing agent and epichlorohydrin as a cross-linking agent through a method of dissolution, dispersion, cross-linking and pore-forming. The NCO can keep the original crystal structure in the foam, and the prepared fixed nano-hydrated cerium oxide can keep the complete form in the liquid under compression, so that fluoride ions in the wastewater can be efficiently removed and the fluoride ions are not interfered by sulfate ions, chloride ions and nitrate ions coexisting in the water body. The millimeter-scale spherical shape is easy to separate and recycle, and has good reproducibility.
In order to achieve the above purpose, the present application provides the following technical solutions: the preparation process of fixed nanometer hydrated cerium oxide includes the following steps:
s1, placing a sodium hydroxide/urea mixed solution into a refrigerator to reach the temperature of minus 18 ℃, taking out, weighing cellulose, adding the cellulose into the precooled mixed solution, and stirring at a high speed for 2 hours to obtain a clear and transparent cellulose solution;
s2, weighing the hydrated cerium oxide powder, adding the hydrated cerium oxide powder into the cellulose solution of S1, and stirring for 1 hour to uniformly disperse the hydrated cerium oxide powder in the cellulose solution to obtain a hydrated cerium oxide/cellulose mixed suspension;
s3, dropwise adding epoxy chloropropane into the hydrated cerium oxide/cellulose mixed suspension obtained in the step S2 by using a dropping funnel in an ice-water bath with the temperature of 0-3 ℃ at the rotating speed of 500-600 rpm, transferring the mixed solution into a spherical mold by using a plastic dropper after stirring for 1 hour, and reacting at the temperature of 60 ℃ until demoulding is achieved, thus obtaining the hydrous fixed nanometer hydrated cerium oxide;
s4, repeatedly washing the water-containing fixed nano-hydrated cerium oxide obtained in the S3 to be neutral by using deionized water and absolute ethyl alcohol, and then freeze-drying at the temperature of-40 ℃ for 48 hours, and dehydrating to obtain the fixed nano-hydrated cerium oxide.
Preferably, in S1, the mass ratio of sodium hydroxide, urea and water in the sodium hydroxide/urea mixed solution is 7:12:81.
preferably, in S1, the dosage of the cellulose is 1/24-3/47 of the mass of the sodium hydroxide/urea mixed solution.
Preferably, in S2, the dosage of the nano-hydrated cerium oxide is 1/3-1/9 of the mass of the cellulose solution obtained in S1.
Preferably, in S3, the dosage of the epichlorohydrin is 3/20-3/10 of the mass of the cellulose suspension obtained in S2.
Preferably, in S4, the nanoparticle size of the hydrated cerium oxide is between 40 and 200nm.
The application of the fixed nano-cerium oxide hydrate is that the fixed nano-cerium oxide hydrate is applied to the treatment of fluorine-containing wastewater and is used for deep removal of fluorine in fluorine-polluted water.
Preferably, the fixed nano-hydrated cerium oxide is suitable for deep removal of fluorine in a moderately acidic fluorine-polluted water body, and the pH value of the moderately acidic fluorine-polluted water body is=2-6.
Preferably, the immobilized nano-hydrated cerium oxide is suitable for deep removal of fluorine in fluorine-polluted water containing strong competitive ions, and the strong competitive ions are ions with strong competitive adsorption effect with fluorine ions.
Preferably, after the fixed nano-hydrated cerium oxide is saturated in adsorption, the fixed nano-hydrated cerium oxide is desorbed and regenerated by using a 5% NaOH solution.
In summary, the invention has the technical effects and advantages that:
1. according to the invention, the cellulose is taken as a dispersing agent, NCO is dispersed in the cellulose, after crosslinking and freeze drying, the NCO is fixed in the cellulose foam, and the whole process enables the cellulose to form a netlike crosslinking structure to surround the surface of the NCO, so that flocculation and coalescence among nano particles are prevented, the contact area of the NCO and fluoride ions is increased, more adsorption sites of the NCO are exposed, the NCO utilization rate is improved, and the economic feasibility is better.
2. According to the invention, the NCO is uniformly fixed in the cellulose foam by utilizing the fluorine removal advantage of the NCO, so that the capability of purifying fluoride ions is maintained, and the fixed nano-hydrated cerium oxide has higher fluorine adsorption capacity in a water body polluted by medium acidity (pH=2-6) and has specific adsorption on fluoride ions in a strongly competitive ion system. Fluorine is removed by electrostatic action, ion exchange and inner sphere complexation of NCO.
3. In the invention, the good hydraulic property of the cellulose foam and the exclusive adsorption capacity of NCO to fluoride ions are combined. NCO is independently and stably distributed in cellulose foam, so that the fixed nano-hydrated cerium oxide has excellent mechanical strength and high-efficiency separation and purification performance, and can be applied in wider scenes. Meanwhile, the used fixed nano-hydrated cerium oxide can be desorbed and regenerated through desorption liquid, so that the practical application value of the nano-hydrated cerium oxide is ensured.
4. In the invention, the problems that a nano-hydration cerium oxide layer on the surface of a host formed in situ firstly prevents the precursor from diffusing further inwards and a special crystal nucleation and growth process in a nano hole cause the finally synthesized composite adsorbent to show poor fluorine selectivity due to low NCO content and uncontrolled crystal structure are solved. The NCO content in the prepared fixed nano-hydrated cerium oxide is controllable, and the crystal structure is kept unchanged.
5. The method has the advantages of simple steps, low cost and industrial expansion production value. And the mechanical stability of the immobilized nano-hydrated cerium oxide is enhanced due to covalent crosslinking of cellulose, and the spherical geometrical characteristic is favorable for the adsorption reaction in the reactor.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is an SEM topography of the fixed nano-ceria hydrate of example 1 of the invention;
FIG. 2 is an XRD pattern of the fixed nano-sized hydrated cerium oxide in example 1 of the present invention;
FIG. 3 is a graph showing the defluorination adsorption performance of the pH-affected fixed nano-sized hydrated cerium oxide according to example 2 of the present invention;
FIG. 4 is a zeta potential map of example 3 of the present invention;
FIG. 5 is a graph showing adsorption isotherms of example 4 of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1:
referring to fig. 1 to 5, a method for preparing the immobilized nano-sized hydrated cerium oxide includes the steps of:
s1, mixing 96g of sodium hydroxide/urea/water in a mass ratio of 7:12:81, putting the mixed solution into a refrigerator until the temperature reaches-18 ℃, taking out, weighing 4g of cellulose, adding the cellulose into the pre-cooled mixed solution, and stirring at 1000rpm for 2 hours at a high speed to obtain a clear and transparent cellulose solution;
s2, weighing 25g of hydrated cerium oxide powder, adding the weighed 25g of hydrated cerium oxide powder into 75g of cellulose solution of S1, and stirring at 500-600 rpm for 1 hour to uniformly disperse the hydrated cerium oxide powder in the cellulose solution, so as to obtain a hydrated cerium oxide/cellulose mixed suspension;
s3, dropwise adding 16.875g of epichlorohydrin into the mixed suspension of the hydrated cerium oxide and the cellulose obtained in the S2 by using a dropping funnel in an ice-water bath with the temperature of 0-3 ℃ at the rotating speed of 500-600 rpm, transferring the mixed solution into a 6mm spherical mold by using a plastic dropper after stirring for 1 hour, and reacting at the temperature of 60 ℃ until the mixed solution can be easily demoulded to obtain the hydrated fixed nanometer hydrated cerium oxide;
s4, repeatedly washing the water-containing fixed nano-hydrated cerium oxide obtained in the S3 to be neutral by using deionized water and absolute ethyl alcohol, and then freeze-drying at the temperature of-40 ℃ for 48 hours, and dehydrating to obtain the fixed nano-hydrated cerium oxide.
The fixed nano-hydrated cerium oxide has a zero charge point of 3.1, a diameter of 6mm and a content of 67.70%. As shown in FIG. 1, the scanning electron microscope image shows that the hydrated cerium oxide nano particles are respectively separated in the cellulose foam, the contact surface with the outside is totally exposed, and the particle size of the hydrated cerium oxide is 40-200 nm. In addition, as shown in fig. 2, the X-ray diffraction ratio shows that the fixed-type nano-hydrated cerium oxide can correspond to the (111) (200) (220) (311) (400) and (331) crystal planes of the hydrated cerium oxide. Overall, it was shown that the hydrated cerium oxide nano-ions were successfully dispersed and immobilized into the cellulose foam.
Example 2:
adsorption effect of fixed nano-hydrated cerium oxide on fluoride ions at different pH values:
the solid-liquid ratio is kept to be 0.5g/L, the fixed nano-hydrated cerium oxide is respectively added into fluoride ion solution with pH value of 2-12.10 mg/L, and the mixture is vibrated at 180rpm for 24 hours at 25 ℃ to ensure that the adsorption balance is achieved. And taking the supernatant to measure the concentration of residual fluoride ions in the solution, and obtaining the equilibrium adsorption quantity at different pH values.
As shown in fig. 3, the adsorption amount of the immobilized nano-ceria to fluoride ions increases first with the increase of pH, reaches the highest point at ph=3, and then gradually decreases, and the fluoride removal effect in the medium-acidic range of ph=2 to 6 is optimal, and the average adsorption amount per gram of fluoride is 10 to 20mg based on the immobilized nano-ceria. This is because the acidic conditions enhance the electrostatic attraction and ligand exchange between NCO and fluorine. Fluorine exists in different forms under different pH conditions. At a pH of < 3.18, fluorine exists predominantly in the form of HF with less fluoride ion participating in the reaction. At this point, the adsorption of fluorine is mainly dependent on the internal coordination complex between NCO and HF, and at pH > 3.18, fluorine exists mainly in the form of fluoride ions. With increasing pH, the surface of the NCO is deprotonated and negatively charged, creating electrostatic repulsion between the NCO and fluoride ions, thereby reducing the adsorption capacity. Meanwhile, a large amount of hydroxyl free radicals and fluoride ions compete for limited active adsorption sites on the surface of the adsorbent in the solution, so that the defluorination performance of the immobilized nano-cerium oxide hydrate is obviously reduced.
Example 3:
zeta potential measurement of fixed nano-hydrated cerium oxide:
weighing 0.05g of fixed nano-hydrated cerium oxide, putting into 500mL of 3mmol/L KCl solution, carrying out ultrasonic treatment until the solution is uniformly dispersed, precipitating for 12 hours, taking supernatant, adjusting the pH to be 2-12, putting the supernatant with the pH adjusted into a shaking table, shaking at 180rpm at 25 ℃ for 24 hours, measuring balance pH, measuring zeta potential, and establishing a relationship diagram of zeta potential and balance pH, as shown in figure 4.
The result shows that the zero charge point of the immobilized nano-cerium oxide hydrate is 3.1. When the pH is less than 3.1, the immobilized nano-hydrated cerium oxide is positively charged, and when the pH is more than 3.1, the immobilized nano-hydrated cerium oxide is negatively charged. This shows that the higher the pH, the more likely the immobilized nano-hydrated cerium oxide is to electrostatically repel fluoride ions, resulting in a decrease in the adsorption amount, validating the experimental results of example two.
Example 4:
adsorption isotherm of fixed nano-hydrated cerium oxide:
the solid-liquid ratio is kept at 0.5g/L, the fixed nanometer hydrated cerium oxide is respectively added into fluorine ion solutions with different concentrations, the concentration range of the solution is 5-150 mg/L, the temperature is 25 ℃, and the pH is controlled at 4.0+/-0.2 and 6.0+/-0.2. Shaking for 24 hours ensures that adsorption equilibrium is reached. And taking the supernatant to measure the concentration of the residual fluoride ions of the solution, and obtaining the equilibrium adsorption quantity under different initial fluoride ion concentrations.
The results show that, as shown in FIG. 5, the pH is 4.0.+ -. 0.2 and the maximum adsorption fitted by Langmuir model at 25 ℃ is 103mg/g; the pH was 6.0.+ -. 0.2 and the maximum adsorption fitted by Langmuir model at 25 ℃ was 66mg/g. Notably, the Freundlich model can better describe the adsorption process of fluorine on the immobilized nano-hydrated cerium oxide, R 2 The values are higher, indicating that the adsorption process is more likely to be multi-layer chemisorption and heterogeneous surface adsorption and heterogeneous active sites are present.
Example 5:
adsorption thermodynamics of fixed nano-hydrated cerium oxide:
the solid-liquid ratio is kept at 0.5g/L, the fixed nanometer hydrated cerium oxide is respectively added into fluoride ion solutions with different concentrations, the concentration range of the solution is 5-150 mg/L, the temperature is 10 ℃, the temperature is 25 ℃, the pH is controlled at 4.0+/-0.2 and 6.0+/-0.2. Shaking for 24 hours ensures that adsorption equilibrium is reached. And taking the supernatant to measure the concentration of the residual fluoride ions of the solution, and obtaining the equilibrium adsorption quantity under different initial fluoride ion concentrations.
The result shows that the increased temperature is favorable for the adsorption of the fixed nano-hydrated cerium oxide to fluoride ions. ΔG 0 The negative values of (a) and Δh0 further confirm that the immobilized nano-ceria is a spontaneous and feasible endothermic reaction, and that higher temperature conditions favor adsorption.
Example 6:
adsorption selectivity evaluation of immobilized nano-hydrated cerium oxide:
the initial concentration of fluorine in water is 10mg/L, the adding amount of the fixed nano-hydrated cerium oxide is 0.5g/L, sulfate radical, chloride ion and nitrate radical with the molar amount of 0, 1, 5, 10, 25 and 50 times of that of fluorine ion are respectively added into the solution under the conditions that the reaction temperature is 25 ℃ and the pH value is=4.0+/-0.2, and the solution is oscillated for 24 hours to ensure that the adsorption balance is achieved. The supernatant was taken to measure the residual fluoride ion concentration of the solution.
The result shows that even when sulfate radical, chloride ion and nitrate radical reach 50 times of fluoride ion, the adsorption amount of the immobilized nanometer hydrated cerium oxide is still stable, and the immobilized nanometer hydrated cerium oxide has excellent fluoride ion adsorption selectivity. Wherein the most influence on the defluorination of the fixed nano-hydrated cerium oxide is sulfate radical, when the molar ratio of the sulfate radical to the fluoride ion is 50, the adsorption quantity of the fixed nano-hydrated cerium oxide to the fluoride is 17.1mg/g, and the adsorption quantity of the common active alumina to the fluoride is 1.6mg/g under the same condition.
Example 7:
desorption and reuse of the fixed nano-hydrated cerium oxide:
the initial concentration of fluorine in water is 10mg/L, the addition amount of the fixed nano hydrated cerium oxide is 0.5g/L, and the desorption is carried out by using 5% NaOH solution to oscillate for 24 hours after the adsorption equilibrium under the conditions that the reaction temperature is 25 ℃ and the pH=4.0+/-0.2, wherein the total amount of the desorption is 1 cycle, and 10 cycles are carried out. And (5) respectively measuring the concentration of fluorine ions in the adsorption liquid and the desorption liquid, and calculating the adsorption rate and the desorption rate.
The result shows that the spherical fixed nano-hydrated cerium oxide is simple to recover and can be recycled, the adsorption rate of the fixed nano-hydrated cerium oxide to fluoride ions is still above 75% after 10 cycles, and the 5% NaOH solution can effectively desorb the fluoride ions adsorbed by the fixed nano-hydrated cerium oxide, so that the desorption rate is more than 90%.
Finally, it should be noted that: the foregoing description is only illustrative of the preferred embodiments of the present invention, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications may be made to the embodiments described, or equivalents may be substituted for elements thereof, and any modifications, equivalents, improvements or changes may be made without departing from the spirit and principles of the present invention.
Claims (10)
1. The preparation method of the fixed nano-hydrated cerium oxide is characterized by comprising the following steps:
s1, placing a sodium hydroxide/urea mixed solution into a refrigerator to reach the temperature of minus 18 ℃, taking out, weighing cellulose, adding the cellulose into the precooled mixed solution, and stirring at a high speed for 2 hours to obtain a clear and transparent cellulose solution;
s2, weighing the hydrated cerium oxide powder, adding the hydrated cerium oxide powder into the cellulose solution of S1, and stirring for 1 hour to uniformly disperse the hydrated cerium oxide powder in the cellulose solution to obtain a hydrated cerium oxide/cellulose mixed suspension;
s3, dropwise adding epoxy chloropropane into the hydrated cerium oxide/cellulose mixed suspension obtained in the step S2 by using a dropping funnel in an ice-water bath with the temperature of 0-3 ℃ at the rotating speed of 500-600 rpm, transferring the mixed solution into a spherical mold by using a plastic dropper after stirring for 1 hour, and reacting at the temperature of 60 ℃ until demoulding is achieved, thus obtaining the hydrous fixed nanometer hydrated cerium oxide;
s4, repeatedly washing the water-containing fixed nano-hydrated cerium oxide obtained in the S3 to be neutral by using deionized water and absolute ethyl alcohol, and then freeze-drying at the temperature of-40 ℃ for 48 hours, and dehydrating to obtain the fixed nano-hydrated cerium oxide.
2. The method for preparing the immobilized nano-sized hydrated cerium oxide according to claim 1, wherein the method comprises the steps of: in the S1, the mass ratio of the sodium hydroxide to the urea to the water in the sodium hydroxide/urea mixed solution is 7:12:81.
3. the method for preparing the immobilized nano-sized hydrated cerium oxide according to claim 2, wherein the method comprises the steps of: in S1, the dosage of the cellulose is 1/24-3/47 of the mass of the sodium hydroxide/urea mixed solution.
4. The method for preparing the immobilized nano-sized hydrated cerium oxide according to claim 1, wherein the method comprises the steps of: in S2, the dosage of the nano-hydrated cerium oxide is 1/3-1/9 of the mass of the cellulose solution obtained in S1.
5. The method for preparing the immobilized nano-sized hydrated cerium oxide according to claim 1, wherein the method comprises the steps of: in the step S3, the dosage of the epichlorohydrin is 3/20-3/10 of the mass of the cellulose suspension obtained in the step S2.
6. The method for preparing the immobilized nano-sized hydrated cerium oxide according to claim 1, wherein the method comprises the steps of: in S4, the nano particle size of the hydrated cerium oxide is between 40 and 200nm.
7. An application of fixed nano-hydrated cerium oxide is characterized in that: the fixed nano-hydrated cerium oxide is applied to fluorine-containing wastewater treatment and is used for deep removal of fluorine in fluorine-polluted water.
8. The use of a fixed nano-hydrated cerium oxide according to claim 7, characterized in that: the fixed nano-hydrated cerium oxide is suitable for deep removal of fluorine in a medium-acid fluorine-polluted water body, and the pH value of the medium-acid fluorine-polluted water body is=2-6.
9. The use of a fixed nano-hydrated cerium oxide according to claim 8, characterized in that: the immobilized nano-cerium oxide hydrate is suitable for deep removal of fluorine in fluorine-polluted water containing strong competitive ions, and the strong competitive ions are ions with strong competitive adsorption effect with fluorine ions.
10. The use of a fixed nano-hydrated cerium oxide according to any one of claims 7 to 9, characterized in that: and after the adsorption saturation of the fixed nano-cerium oxide hydrate, desorbing and regenerating the nano-cerium oxide hydrate by using a 5% NaOH solution.
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