CN116809036A - Preparation method, product and application of ammonium phosphomolybdate-polyethylene glycol magnetic nano material - Google Patents
Preparation method, product and application of ammonium phosphomolybdate-polyethylene glycol magnetic nano material Download PDFInfo
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Abstract
The invention relates to the technical field of environmental remediation, in particular to a preparation method, a product and application of an ammonium phosphomolybdate-polyethylene glycol magnetic nanomaterial. The method comprises the following steps: step 1, adding citric acid into a solution system of ferrous chloride and ferric chloride, stirring, separating a product, and drying to obtain citric acid coated ferroferric oxide nano particles; step 2, dispersing the citric acid coated ferroferric oxide nano particles in water, and then adding polyethylene glycol to obtain a suspension; and adding ammonium phosphomolybdate into the suspension, stirring, collecting a product, and drying to obtain the ammonium phosphomolybdate-polyethylene glycol magnetic nanomaterial. PEG prepared by the method of the inventionAMPMNs composite material can be used for treating Cs in the pH range of 2.0-12.0 + The removal rate of the catalyst can reach 99.8%, and the adsorption rate of the AMP to the Cs is widened + And is capable of maintaining the material stable after adsorption.
Description
Technical Field
The invention relates to the technical field of environmental remediation, in particular to a preparation method, a product and application of an ammonium phosphomolybdate-polyethylene glycol magnetic nanomaterial.
Background
The safety of nuclear energy is always a topic of concern, and cesium in high-level waste liquid 137 Cs have large heat generation and long half-life, can release beta rays and gamma rays in the decay process, and have strong radiation. If appropriate, can be used 137 Cs is extracted and recovered from the high-level radioactive waste liquid, so that the nuclear waste liquid disposal cost and the harm to the environment can be reduced, and the Cs can be used as a radioactive source in the fields of industry, agriculture, medicine and the like, and considerable economic benefits are brought.
Various methods of cesium removal have been developed so far and applied to Gao Fang waste streams, including precipitation, solvent extraction and ion exchange. Among these methods, the ion exchange method has been widely studied because of its advantages of high efficiency, low cost, good selectivity, and the like. Various inorganic ion exchangers have therefore been developed, such as: titanosilicate zeolite, hexacyanoferrate, prussian blue analogues and tungsten molybdenum heteropolyacid salts. Wherein ammonium phosphomolybdate (AMP) is a cation exchanger with Keggin skeleton structure, 12 MoOs 6 Octahedron forms a hollow sphere, PO 4 3- Located in the center of the sphere, [ P (Mo) 12 O 40 )] 3- NH is arranged in the gap between 4 + . AMP vs Cs + Has good selectivity and extremely high exchange capacity, and has excellent stability under strong acid environment, and is used for Cs + Ideal materials for adsorption. However, AMP has a small particle size, a small surface activity, and is easily agglomerated, and is also difficult to separate from the solution after adsorption. Thus, AMPs are typically immobilized on various supports, such as sodium alginate, polyacrylonitrile, polyvinyl alcohol, silica. Then allowing AMP to adsorb Cs by centrifugation or filtration + And then separated from the solution.
Compared with the centrifugal filtering method, the magnetic filter has the advantages thatThe separation method has the advantages of high speed, low energy consumption, simple operation and the like. The magnetic carrier can be easily separated from the solvent or complex matrix by an externally applied magnetic field. Magnetic Fe 3 O 4 As a carrier in combination with an adsorbent and for wastewater treatment is possible. However, at present, fe is magnetic 3 O 4 The adsorption material prepared by combining the carrier and the adsorbent is easy to form large clusters in the cesium adsorption process, and the chemical stability and the dispersibility of the adsorption material are required to be improved.
Disclosure of Invention
Based on the above, the invention provides a preparation method, a product and application of an ammonium phosphomolybdate-polyethylene glycol magnetic nanomaterial. The invention adopts a coprecipitation method to graft ammonium phosphomolybdate on Fe 3 O 4 Surface, a novel Cs is synthesized + The adsorbent, ammonium phosphomolybdate-polyethylene glycol magnetic nano material (PEG-AMPMNs), has good chemical stability and dispersibility in nuclear waste liquid and high cesium adsorption removal rate.
In order to achieve the above object, the present invention provides the following solutions:
according to one of the technical schemes, the preparation method of the ammonium phosphomolybdate-polyethylene glycol magnetic nanomaterial comprises the following steps:
step 1, adding citric acid into a solution system of ferrous chloride and ferric chloride, stirring, separating a product, and drying to obtain citric acid coated ferroferric oxide nano particles;
step 2, dispersing the citric acid coated ferroferric oxide nano particles in water, and then adding polyethylene glycol to obtain a suspension; and adding ammonium phosphomolybdate into the suspension, stirring, collecting a product, and drying to obtain the ammonium phosphomolybdate-polyethylene glycol magnetic nanomaterial.
Further, the molar ratio of the ferrous chloride to the ferric chloride is 1:2.
Further, in the step 1, the concentration of citric acid in the solution system of ferrous chloride and ferric chloride is 1.7-2.2M; the concentration of ferrous chloride in the solution system of ferrous chloride and ferric chloride is 0.344g/mL.
The main function of citric acid is to form smaller and monodisperse magnetic Fe 3 O 4 And (3) particles. Too low a concentration of citric acid would reduce the coating effect. In addition, the concentration of citric acid affects the pH of the solution system; under the non-oxidizing condition, synthesizing nano Fe 3 O 4 The pH value of (2) should be 8-11, the pH environment is provided by ammonia water and hydrazine hydrate, the acidity of citric acid is strong (acidity coefficient is 4.7), and the too high concentration can destroy the alkaline environment to generate Fe 2 O 3 . The citric acid solution concentration must not be too high nor too low.
Further, in the step 1, the solution system of ferrous chloride and ferric chloride also contains ammonia water and hydrazine hydrate; the solvent of the solution system of ferrous chloride and ferric chloride is water; the volume ratio of the water to the ammonia water to the hydrazine hydrate is 50:5:3.
The function of ammonia and hydrazine hydrate is to provide a strong alkaline environment. Possible equations are as follows:
Fe 3+ +3OH - →Fe(OH) 3
Fe(OH) 3 →FeOOH+H 2 O
Fe 2+ +2OH - →Fe(OH) 2
2FeOOH+Fe(OH) 2 →Fe 3 O 4 ↓+2H 2 O。
in the step 2, the mass ratio of the citric acid coated ferroferric oxide nano particles to polyethylene glycol to ammonium phosphomolybdate is 1:3:1-1.5.
Further, in the step 2, the stirring is specifically 1000rpm for 10 hours.
Further, in the step 2, the drying is specifically drying to constant weight at 30-100 ℃ under vacuum.
The drying temperature cannot exceed 100 ℃, and too high a temperature damages the structure of the ammonium phosphomolybdate.
According to the second technical scheme, the ammonium phosphomolybdate-polyethylene glycol magnetic nanomaterial is prepared by the preparation method.
In a third aspect of the present invention, the ammonium phosphomolybdate-polyethylene glycol magnetic materialCesium removal from high-level radioactive waste liquid by nano material 137 Application in Cs.
The invention discloses the following technical effects:
polyethylene glycol (PEG) is a readily available, nontoxic and biodegradable copolymer, and the invention selects PEG to be magnetic Fe 3 O 4 Surface functionalization treatment is carried out, so that on one hand, magnetic Fe can be reduced 3 O 4 Preventing the formation of large clusters due to hydrophobic interactions between particles; on the other hand, the magnetic particles can be tightly combined with the AMP as an intermediate carrier, so that the combination stability of the magnetic particles and the AMP is improved. In the use of PEG for magnetic Fe 3 O 4 Before the surface functionalization treatment, the invention also uses citric acid to make the magnetic Fe 3 O 4 Pretreatment is carried out to prepare the citric acid coated ferroferric oxide nano particles (CA-Fe 3 O 4 ). The citric acid can be used as a surfactant to chelate with iron ions to prepare water-based stable ferric oxide nano particles, and finally, the synthesis of the PEG-AMPMNs composite material is realized.
PEG-AMP MNs composite material prepared by the method of the invention can be used for preparing Cs in the pH range of 2.0-12.0 + The removal rate of the catalyst can reach 99.8%, and the adsorption rate of the AMP to the Cs is widened + And is capable of maintaining the material stable after adsorption.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a sample of PEG-AMP MNs and CA-Fe prepared in example 1 3 O 4 X-ray diffraction spectrum (a) of (C) and pure AMP, CA-Fe 3 O 4 And the infrared spectrum of PEG-AMP MNs (b).
FIG. 2 is an XPS spectrum of C1s (a), N1s (b), O1s (C) and Mo3d (d) of PEG-AMP MNs prepared in example 1.
FIG. 3 is a PEG-AMP MNs prepared in example 1 to adsorb Cs + SEM images and EDS spectra of the previous (a), (b) and after adsorption (c), (d).
FIG. 4 is a PEG-AMP MNs prepared from example 1 to adsorb Cs + A subsequent Fe, mo, cs, P energy spectrum EDS element map.
FIG. 5 shows the nitrogen adsorption and desorption curve (a), pore size distribution (b) and hysteresis loop (c) of PEG-AMP MNs prepared in example 1.
FIG. 6 is a nonlinear fit (a) of the adsorption kinetics of PEG-AMP MNs prepared in example 1, a Langmuir and Freundlich model fit (b) of adsorption experimental data, an effect of temperature on PEG-AMP MNs (c) and a thermodynamic fit (d).
FIG. 7 shows the adsorption of Cs by PEG-AMP MNs prepared in example 1 under different conditions + Is a function of (1); wherein (a) is pH vs. Cs + Influence of adsorption (c0=100 mg/L, contact time t=30 min, room temperature), (b) adsorption efficiency at different competing ions, (C) partition coefficient of PEG-amps to various competing ions (C 0 =100 mg/L, natural pH, room temperature).
FIG. 8 is a PEG-AMP MNs prepared in example 1 to adsorb Cs + Front and rear XPS spectra (a), cs3d XPS spectra (b), and Zeta potential of PEG-AMP MNs at different pH values (c).
FIG. 9 shows Cs on PEG-AMP MNs prepared in example 1 + Schematic diagram of switching mechanism.
FIG. 10 is a schematic diagram showing the process for preparing PEG-AMPMNs and adsorbing Cs by PEG-AMP MNs according to the present invention + Is a schematic diagram of (a).
Detailed Description
Various exemplary embodiments of the invention will now be described in detail, which should not be considered as limiting the invention, but rather as more detailed descriptions of certain aspects, features and embodiments of the invention.
It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. In addition, for numerical ranges in this disclosure, it is understood that each intermediate value between the upper and lower limits of the ranges is also specifically disclosed. Every smaller range between any stated value or stated range, and any other stated value or intermediate value within the stated range, is also encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.
It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the invention described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from consideration of the specification of the present invention. The specification and examples of the present invention are exemplary only.
As used herein, the terms "comprising," "including," "having," "containing," and the like are intended to be inclusive and mean an inclusion, but not limited to.
The raw materials used in the examples and comparative examples of the present invention, unless otherwise specified, were all available commercially.
As used herein, the term "room temperature", unless otherwise indicated, means 15 to 30 ℃.
Cesium standard solutions (1000 mg/L) used in the examples of the present invention were purchased from Beijing northern Weijingsu technical institute; ferric chloride hexahydrate (FeCl) 3 ·6H 2 O), ferrous chloride tetrahydrate (FeCl) 2 ·4H 2 O), ammonium phosphomolybdate (AMP), polyethylene glycol (PEG-4000), citric acid monohydrate (CA) were purchased from adult colone chemical company, ltd, and used without further purification. During the whole experiment, deionized water was prepared by ULPARE-H pure water purification System (ULPARE, china)。
The process for preparing the PEG-AMP MNs is schematically shown and the PEG-AMP MNs adsorbs Cs + A schematic diagram of (2) is shown in figure 10.
Example 1
Step 1, citric acid coated ferroferric oxide nanoparticles (CA-Fe 3 O 4 ) Is prepared from
50mL of deionized water is placed into a two-neck flask for preheating, the temperature is raised to 45 ℃, 5mL of ammonia water and 3mL of hydrazine hydrate are measured and dissolved in the heated deionized water. 1.72g FeCl was added 2 ·4H 2 O and 4.68g FeCl 3 ·6H 2 O, the system turned black and was vigorously stirred for 30 minutes. Then, 1.9M citric acid was added to the two-necked flask, and stirring was continued for 1.5 hours. The black product was separated with a permanent magnet and washed three times with deionized water and ethanol. And (3) drying in vacuum at 50 ℃ for 12 hours to obtain the citric acid coated ferroferric oxide nano particles.
Step 2, preparation of ammonium phosphomolybdate-polyethylene glycol magnetic nanomaterial (PEG-AMP MNs)
Taking 2.5g of CA-Fe prepared in the step 1 3 O 4 Dispersing with ultrasound in 20mL DW (distilled water), adding 7.5g PEG, and stirring with strong magnetic force (800 rpm) at 25deg.C for 1 hr to obtain a solution containing PEG-Fe 3 O 4 A suspension of nanoparticles. To the above suspension was added 2.5g AMP and magnetic stirring (1000 rpm) was continued for 10h. Finally, collecting the product by magnet, washing with ethanol for three times, and vacuum drying at 50 ℃ for 12 hours to constant weight to obtain PEG-AMP MNs.
Characterization method
The phase of the sample was characterized by X-ray diffractometry (XRD, D/max-1400, japan). The identification of sample functionalities was performed by fourier infrared spectroscopy (FTIR, thermo Scientific Nicolet iS, usa) over a wavenumber range of 4000-400 cm-1. The composition and valence of the main elements were tested by X-ray photoelectron spectroscopy (XPS, thermo Scientific K-Alpha). The morphology and chemical composition of the samples were characterized by scanning electron microscopy (SEM, ZEISS sigma 500) and spectroscopy analysis (EDS, BRUKER xfash 6130). The magnetic properties of the samples were analyzed with a vibrating sample magnetometer (VSM, lakeShore 7404). Using a fully automatic specific surface and porosity analyser (BET, Q)uantachrome Autosorb-IQ) was investigated for specific surface area. Measurement of Cs in solution before and after adsorption by inductively coupled plasma mass spectrometry (ICP-MS, aglient 7800 MS) + Concentration.
Adsorption experiment
Due to safety problems, in the adsorption experiment, inactive cesium element is used 133 Cs) instead of radioactive cesium, to study its adsorption properties. 10mL of Cs were dispersed in a polyethylene centrifuge tube as adsorbent PEG-AMP MNs (0.09 g) + In solution (100 mg/L). The mixture was shaken at a speed of 180rmp with a constant temperature shaker, after a certain period of time, the supernatant was separated with a permanent magnet, and Cs in the supernatant was measured by ICP-MS + Concentration.
PEG-AMP MNs vs Cs under multiple factor conditions + Adsorption performance and action rule thereof. Comprising the following steps: ph=2, 3,4,5,6,7,8,9, 10, 11, 12, adsorption temperature t=290 k,300k,310k,320k, contact time t=1, 2,3,4,5, 10, 15, 20, 30min, cs + Initial concentration C 0 =100, 300, 500, 700, 800, 900mg/L. Competing ions Na + 、K + 、Ca 2+ 。
According to Cs in the solution before and after adsorption + The concentration of PEG-AMP MNs versus Cs was calculated separately + Equilibrium adsorption capacity q of (2) e Adsorption efficiency AE and partition coefficient K d The calculation formula is as follows:
wherein q is e The equilibrium adsorption capacity (mg/g), AE is the adsorption efficiency (%), K d Is the distribution coefficient, C 0 Is Cs + Initial concentration (mg/L), c e The equilibrium concentration (mg/L), V represents the volume (L) of the sample solution, and m represents the mass (g) of the adsorbent.
Results and discussion
Characterization analysis
XRD, FTIR, XPS analysis
PEG-AMPMNs and CA-Fe are shown as (a) in FIG. 1 3 O 4 Is a XRD pattern of (C). The strong characteristic peak indicates that the PEG-AMPMNs composite material has good crystal form. PEG-AMPMNs have 10 strong diffraction peaks around 2 theta, 10.7 °, 15.1 °, 21.5 °, 26.5 °, 30.6 °, 36.1 °, 39.3 °, 43.9 °, 48.1 ° and 55.7 °, respectively, which can be attributed to (110), (200), (220), (222), (400), (332), (510), (440), (532), and (550) crystal planes (JCCPDSPDF#09-0412) related to Keggin structure. CA-Fe is shown in FIG. 1 (a) 3 O 4 X-ray pattern 2 theta of 30.3 deg., 35.7 deg., 43.5 deg., 57.5 deg., and 63.2 deg. can be assigned to (220), (311), (400), (511), and (440) crystal planes (JCPDS PDF # 70-0449), respectively, indicating magnetic CA-Fe 3 O 4 Is a successful synthesis of (a). In addition, it can be seen that the crystallization peak of PEG-AMPMNs contains magnetic Fe 3 O 4 And all characteristic peaks of AMP. Indicating that AMP is successfully loaded on magnetic Fe 3 O 4 And (3) upper part.
FIG. 1 is a sample of PEG-AMPMNs and CA-Fe prepared by example 1 3 O 4 X-ray diffraction spectrum (a) of (C) and pure AMP, CA-Fe 3 O 4 And the infrared spectrum of PEG-AMPMNs (b). FIG. 1 (b) shows pure AMP, CA coated Fe 3 O 4 (CA-Fe 3 O 4 ) And FTIR spectra of PEG-AMPMNs. Clearly, the spectra of PEG-AMPMNs are comparable to those reported for pure AMP and Fe 3 O 4 Is well consistent. In the shaded portion of the figure, 1068, 966, 869, and 785cm -1 The characteristic peak at the position is [ PMo ] 12 O 40 ] 3- Is shown to have been loaded with Fe in the AMP 3 O 4 On the matrix, this is consistent with the results of XRD. 3432cm -1 The broad peak at this point can be ascribed to N-H stretching vibration, indicating NH 4 + Is present. CA-Fe 3 O 4 At 575cm -1 The absorption peak observed nearby can be attributed to Fe 3 O 4 Fe-O stretching vibration of (C). Furthermore, 1631cm -1 The strong peak at this point is attributable to the c=o asymmetric stretching vibration of the COOH group of CA, revealing that the CA radical is bound to the nano Fe by chemisorption of carboxylate ions 3 O 4 A surface. Carboxylic acid group of CA and Fe 3 O 4 The Fe atoms on the surface form a complex, giving the c=o bond a partial single bond character.
FIG. 2 is an XPS spectrum of C1s (a), N1s (b), O1s (C) and Mo3d (d) of PEG-AMP MNs prepared in example 1. FIG. 2 shows surface electron valence and composition information of PEG-AMP MNs measured by XPS. The energy spectra of C1s, N1s, O1s and Mo3d of the PEG-AMP MNS composites are shown in FIGS. 2 (a) - (d). The peak at 286.2eV in the C1s spectrum is attributed to the C-O of PEG in the PEG-AMP MNS composite, and the peak at N1s 402.1 eV is attributed to NH in AMP 4 + Peaks at 532.8eV, 531.5eV and 530.2eV in the O1s spectrum, respectively attributed to the C-O bond of PEG and MoO of AMP 4 2- 、PO 3 2- . Peaks of 232.7eV/235.8eV and 232.2eV/235.2eV in Mo3d spectrum belong to Mo of AMP respectively 4 2- And Mo (Mo) 5 + . The results showed that PEG-AMP MNS composite material was successfully synthesized.
FIG. 3 is an SEM image and EDS spectrum of PEG-AMPMNs prepared in example 1 before (a), (b) and after (c), (d) adsorption. In FIG. 3, (a) and (b) show the adsorption of Cs by PEG-AMP MNs, respectively + The front SEM image and EDS map of the corresponding region, respectively show the adsorption of Cs by PEG-AMP MNs in FIG. 3 (c) and (d) + The subsequent SEM pictures and EDS maps of the corresponding regions. PEG-AMP MNs are irregular particles, and AMP is uniformly distributed in Fe 3 O 4 A surface. The particle size of PEG-AMPMNs obtained by the laser particle sizer was mainly distributed between 1.77 and 18.8 μm (FIG. S1), and the average particle size was 3.63. Mu.m. EDS mapping of the corresponding region (FIG. 3 (b)) revealed the presence of Mo and Fe, indicating that AMP is present in Fe 3 O 4 The surface of the substrate. Furthermore, PEG-AMP MNs adsorb Cs + After that, in FIG. 3 (d), cs can be observed + Proof of Cs presence + Has been adsorbed by PEG-AMP MNs.In FIG. 4, (a), (b), (c), and (d) are Cs, respectively + After adsorption to the surface, the PEG-AMP MNs were mapped to Fe, mo, cs, P energy spectrum EDS elements from the same region. Cs and Mo are distributed in the same area, further confirming AMP and Fe 3 O 4 Bonding of substrates.
FIG. 5 shows the nitrogen adsorption and desorption curve (a), pore size distribution (b) and hysteresis loop (c) of PEG-AMP MNs prepared in example 1. In FIG. 5, (a) and (b) are specific surface area and pore size distribution diagrams of PEG-AMP MNs obtained by BET. As shown in FIG. 5 (a), the PEG-AMP MNs adsorption and desorption curve is of a typical I-type structure, which shows that the PEG-AMP MNs has a microporous structure. The specific surface area of the PEG-AMPMNs is calculated to be 35.86m 2 And/g. Further, the pore size distribution curve is shown in fig. 5 (b), and the pore size range on the nanoparticle is mainly distributed in the range of 3.41 to 5.62nm. The larger specific surface area and the wider pore size indicate that it is specific to Cs + Has better adsorption performance.
The magnetic properties of PEG-AMP MNs composites were characterized using VSM, resulting in an M-H curve. As shown in FIG. 5 (c), the sample exhibited hysteresis-free superparamagnetic behavior, with a saturation magnetization of 16.91emu/g. The lower magnetization value may be due to Fe 3 O 4 The groups are entrapped by AMP particles. In fig. 5 (c) (panels) the magnetic separation of PEG-AMP MNs is shown, indicating that the composite can be pulled from the solution on the vial sidewall by an externally applied magnetic field. Thus, the above results indicate that this magnetic property enables PEG-AMP MNs to be used for simple and efficient magnetic recovery of solutions.
Adsorption model
Adsorption kinetics
The adsorption kinetics can better reflect the adsorption rate and further reaction mechanism. At temperature t=298.15k, ph=7, cs + The initial concentration was 100mg/L, the adsorbent dosage was 9mg/mL, and the adsorption experiments were performed with a contact time t=1, 2,3,4,5, 10, 20, 30 min. As can be seen from the experimental data curves of FIG. 6 (a), PEG-AMP MNs vs. Cs + The adsorption of (C) reaches 94.96% in 5min and reaches equilibrium about 20min, indicating that PEG-AMP MNs pair Cs + Has faster adsorption kinetics. The rapid removal is due to the large number of vacanciesActive center, and Cs + And the combination probability is high.
To describe the adsorption process in more detail, adsorption kinetics curves were analyzed using a quasi-primary kinetics model and a quasi-secondary kinetics model, corresponding expressions (4) and (5):
ln(q e -q t )＝ln q t -k 1 t (4)
wherein t (min) is the contact time; q e And q t (mg·g -1 ) Is the adsorption amount of the adsorbent at equilibrium and time t; k (k) 1 (min -1 ) And k 2 (g/(mg. Min)) is the adsorption rate constant.
In fig. 6, (a) is a nonlinear fit of the quasi-first order dynamics and quasi-second order dynamics models, respectively, and the fitting parameters are shown in table 1. According to the correlation coefficient R of Table 1 2 (0.999 > 0.987) it can be seen that PEG-AMP MNs vs. Cs + The adsorption of (2) is more in accordance with a quasi-secondary kinetic model. Chemisorption might dominate during the rate-limiting phase, consistent with the reported results for other similar AMP-based adsorbents. R of quasi-first order dynamics model 2 A value of about 0.987, indicating Cs + Physical adsorption on PEG-AMP MNs is also present. In conclusion, PEG-AMP MNs vs Cs + Adsorption is a complex physicochemical co-adsorption process mainly comprising surface adsorption complexation and ion exchange, but the latter is dominant.
TABLE 1 adsorption Rate constant and correlation coefficient for pseudo first and pseudo second order kinetic models
Adsorption isotherm
Adsorption isotherms help elucidate the manner in which metal ions bind to the adsorbent surface. At temperature t=298.15K, pH =7 and Cs + Initial concentration C 0 Isothermal adsorption experiments were performed at =300, 500, 700, 800, 900 ppm. To investigate the pair of PEG-AMP MNs against Cs + The experimental data are typically fitted with Langmuir model and Freundlich model. The corresponding expressions are (6) and (7).
Wherein q is e Adsorption amount (mg/g), q of adsorbent per unit mass max For maximum single layer coverage adsorption capacity (mg/g), C e K is the equilibrium concentration of adsorbate (mg/L) b Is Langmuir adsorption constant (L/mg), K F N is the heterogeneous coefficient for the Freundlich adsorption constant.
In fig. 6 (b) is a nonlinear fit of Langmuir and Freundlich isothermal models, respectively, with the fitting parameters shown in table 2. Experimental results show that under the optimal adsorption condition, the maximum adsorption capacity can reach 53.89mg/g. Correlation coefficient R 2 (0.998 > 0.976) shows that the Langmuir isotherm model better describes the adsorption process than the Freundlich isotherm model, PEG-AMP MNs vs Cs + The adsorption of (2) is a homogeneous single-layer adsorption mechanism.
TABLE 2 adsorption isotherm constants for cesium adsorption processes
Adsorption thermodynamics
In order to evaluate the nature and thermodynamic behavior of the adsorption process, studies were made for adsorption thermodynamics. FIG. 6 (c) shows the comparison of PEG-AMP MNs with Cs in the temperature range of 290-320K + Is not limited, and adsorption efficiency of the catalyst is improved. As shown in fig. 6 (c), the adsorption efficiency slightly increases with an increase in temperature. Indicating that the adsorption process is endothermic, higher temperatures favor Cs + Is adsorbed by the adsorbent. In addition, in the case of the optical fiber,the experimental results were also fitted with a van't Hoff equation (ln K) d vs. 1/T) and the derivative of FIG. 6 (d) is plotted. The equation expression is as follows:
ΔG 0 ＝ΔH 0 -TΔS 0 (8)
wherein T is absolute temperature (K), R is universal gas constant (8.314J/mol.K), K d Is a thermodynamic equilibrium constant. ΔS 0 And DeltaH 0 Is obtained from the intercept and slope of the van der Waals plot, ΔG 0 The value of (2) can be calculated from equation (8). ΔG 0 、ΔS 0 And DeltaH 0 The results of (2) are shown in Table 3.
Table 3 Cs + Thermodynamic parameters on PEG-AMP MSs
As can be seen from Table 3, ΔS 0 And DeltaH 0 All positive values, further confirming the irreversible endothermic reaction. The gibbs free energy at all four temperatures was negative, indicating that the adsorption process was spontaneous. Taken together, these results indicate that PEG-AMP MSs vs. Cs + Is endothermic, random and spontaneous.
Influence of pH
The pH environment is a key factor affecting adsorption efficiency. The adsorption of PEG-AMP MSs on Cs was investigated by pH + Is a function of (a) and (b). Adsorption experiments were performed by adjusting the pH of the solution to a range of 2-12 with 0.1M HCl and NaOH. In FIG. 7 (a), it is shown that the adsorption efficiency does not significantly change in the pH range of 2-10, and PEG-AMP MSs have good adsorption performance even in a strong acid solution. However, at pH 11 and 12, the adsorption efficiency was slightly lowered, which may be caused by dissolution of a small amount of AMP (formula 10). Nevertheless, the adsorption efficiency can still reach 99.7%. The results show that PEG-AMP NMs have stable adsorption properties over a wide pH range.
In environmental management, secondary pollution caused by leaching of adsorbed components is not preferable. Therefore, the leaching conditions of Fe and Mo in PEG-AMP MSs under different pH values are examined. After the sample was adsorbed, the sample was suspended in a solution at pH 2-12 for 24 hours, and the ion concentrations of Fe and Mo were measured. As shown in fig. 7 (a), in the pH range of 2-10, fe and Mo ions are negligible, and even under strongly alkaline conditions (ph=12), the dissolution rate of Fe is only 0.27%. However, at pH 11-12, mo leaching rate reaches 5.90% due to small amount of dissolution of AMP. Nevertheless, PEG-AMP MSs retain good adsorption properties. Thus, even over a wide pH range, cs are treated with natural pH values + The adsorbent still has good adsorption performance and stability after adsorption.
(NH 4 ) 3 PO 4 · 12MoO 3 +27NaOH→3NH 3 · H 2 O+Na 3 PO 4 +12Na 2 MoO 4 +12H 2 O (10)
Competitive ion influence
Radioactive cesium is usually present with other ions in natural water (Na + 、K + 、Ca 2+ ). As shown in FIG. 7 (b), when Na + 、K + 、Ca 2+ Cs when the concentration of (C) varies from 100mg/L to 300mg/L + The removal rate of (C) is greater than 99.8%, indicating that PEG-AMP MNs pair Cs + Exhibits a strong selectivity. Obviously, as shown in fig. 7 (c), the partition coefficient (Kd) significantly decreases due to the competing effect of the metal ions, and decreases as the concentration of the competing ions increases. But remove K + Except that Kd values are all greater than 4.0X10 4 mL/g, which also reflects the pair of Cs by PEG-AMP MNs + Has better selectivity. The order of influence of the test ions is K + ＞Na + ＞Ca 2+ Indicating K + And Cs + Is more effective than other ions, which can be used with K + And Cs + Similar hydration radii are explained, which indirectly confirms Cs + NH with AMP 4 + Ion exchange occurs.
Adsorption mechanism
The adsorption mechanism is studied by means of XPS, quantitative analysis and the like. As shown in FIG. 8 (a), PEG-AMP MNs adsorb Cs + After that, a distinct characteristic peak of Cs3d appears, which indicates Cs + Has been successfully adsorbed. The binding energy of Cs3d5 was found to be 724eV by observation under magnification (fig. 8 (b)). Cs phosphate bound species are generated when the binding energy of 3d5 is around 723.8eV, indicating Cs + [ PMo ] in successful AMP after adsorption material 12 O 40 ] 3- And (5) combining. Possibly due to hydrated ionic radius NH 4 + () And Cs + () Similarly, they can perform ion exchange smoothly, and the adsorption process is shown in formula (11), fig. 9.
In addition, the invention also measures Cs in the supernatant before and after adsorption + And NH 4 + The concentration of ions varies. As shown in Table 4, NH 4 + Increased content of Cs + Is reduced, indicating NH in AMP 4 + And Cs + Ion exchange is performed to dissolve into the solution. Δ iNH 4 + (43.53 mg/L) below Delta dCs + (98.98mg/L)，H + Is increased due to NH 4 + Is released into solution during adsorption and generates h+ by hydrolysis. Thereby leading to NH 4 + Reduced self content of H + The content is increased. Thus, the adsorption mechanism is mainly ion exchange.
FIG. 8 (c) is the Zeta potential of PEG-AMP MNs in aqueous pH 2-12. It can be seen that the PEG-AMP MNs are negatively charged on their surface over a pH range of 2-12. The negatively charged adsorbent may be associated with positively charged Cs + Electrostatic attraction is generated, which is consistent with the results of the kinetic analysis.
In conclusion, based on XPS, zeta potential and quantitative analysis means, inhalation is combinedAnalysis of the additional kinetic model, PEG-AMP MNs vs Cs + The adsorption mechanism of (2) is a combination of weak electrostatic attraction and ion exchange.
(NH 4 ) 3 PO 4 · 12MoO 3 +xCs + Csx(NH 4 ) 3-x PMo12O 40 +x(NH 4 ) + (aq) (11)
TABLE 4 PEG-AMP MSs adsorb Cs + Front-to-back variation value
Generally, for adsorbing Cs + The adsorbents of (2) can be divided into three classes including natural materials, synthetic compound materials and modified adsorbents. Different adsorbent materials have significantly different physicochemical properties, so different adsorbent materials are not comparable. However, it is of great value to compare the adsorption properties of similar AMP adsorbent materials in the present invention to evaluate their potential applications. In this comparison, the partition coefficient and the adsorption capacity are generally used as important indicators.
Table 5 lists different types of AMP composites. The results show that the PEG-AMP MNs prepared by the invention has higher Kd value compared with other materials, which shows that the PEG-AMP MNs is Cs + Is an effective adsorbent material of (a). The PEG-AMP MNs prepared by the invention has shorter equilibrium time (20 min) when cesium ions are adsorbed, and is more beneficial to Cs in practical application + Is especially useful in the removal of emergency Cs + In the event of a leak. Furthermore, PEG-AMP MNs have strong Cs at any pH + Adsorption performance and can be quickly separated by a magnet after adsorption. Finally, the PEG-AMP MNs adsorbent can be prepared by using only environment-friendly raw materials. In conclusion, the PEG-AMP MNs synthesized by the invention can maintain high selectivity, high adsorption efficiency and stability under natural pH, can be rapidly separated from solid and liquid, and is a potential Cs possibly going to practical application + An adsorbent material.
TABLE 5 PEG-AMP prepared in example 1MNs and different types of AMP composite material pair Cs + Adsorption comparison of (2)
Comparative example 1
The difference from example 1 is that step 1 was omitted and CA-Fe in step 2 was added 3 O 4 The magnetic iron oxide nano particles with superparamagnetism of 10nm are replaced.
Results: the Kd value of PEG-AMP MNs prepared in this comparative example was 1.2X10 4 The method comprises the steps of carrying out a first treatment on the surface of the The removal rate of cesium is 95% in the pH range of 2-12; the adsorption equilibrium time is 120min; the maximum adsorption capacity was 40.45mg/g.
Comparative example 2
The preparation method of the magnetic ferric oxide/ammonium phosphomolybdate porous composite material comprises the following specific steps:
(1) Ultra-sonically dispersing 0.5g of superparamagnetic 10nm magnetic iron oxide nanoparticles to 500mL of 2M HNO 3 And (3) in the solution, uniformly stirring, standing for 35min, washing the magnetic particles with deionized water for 3 times, then ultrasonically dispersing the magnetic particles into 200mL of deionized water, adding 80mL of 135.9mM ammonium molybdate solution into the solution under the condition of mechanical stirring, and continuously stirring for 15min to obtain an intermediate solution 1.
(2) Accurately measuring 2.5mL of concentrated nitric acid, slowly adding the concentrated nitric acid into 17.5mL of deionized water, shaking uniformly, adding 1.0g of potassium pyrophosphate into the solution, and stirring to dissolve the potassium pyrophosphate to obtain an intermediate solution 2.
(3) And (3) under the condition of mechanical stirring, controlling the reaction temperature to be 35 ℃, dropwise adding the intermediate solution 2 into the intermediate solution 1, continuously stirring for 1h, separating a product by using a magnet, washing 3 times by using deionized water, and drying at 40 ℃ to obtain the magnetic ferric oxide/ammonium phosphomolybdate porous composite material.
Magnetic ferric oxide/ammonium phosphomolybdate porous composite material prepared in comparative exampleThe adsorption performance of the material was verified in the same manner as in example 1, and the result shows that the Kd value of the magnetic iron oxide/ammonium phosphomolybdate porous composite material prepared in this comparative example is 1.0X10 4 The method comprises the steps of carrying out a first treatment on the surface of the The removal rate of cesium is 91% in the pH range of 4-10; the adsorption equilibrium time is 60min; the maximum adsorption capacity was 45.62mg/g.
The invention successfully prepares the PEG-AMP MNs magnetic nanocomposite by a simple coprecipitation method, thereby solving the problem of adsorbing Cs by AMP + And then difficult to separate from the solution. And the adsorbent itself is kept stable and Cs is protected over a wide pH range (ph=2-12) + Has strong ion exchange capacity. Its selective adsorption is not affected by Na + 、K + 、Ca 2+ Interference of ions. Through research of adsorption kinetics and isotherms, the chemisorption of PEG-AMP MNs on the Cs+ monolayer is determined, and the Cs can be effectively removed in a short time (20 min) + . Adsorption mechanism studies confirm that PEG-AMP MNs remove Cs + Is a combination of weak electrostatic attraction and ion exchange mechanisms. In addition, the maximum bright point of the invention is that the magnetic nano carrier is embedded in the adsorbent, which is convenient for magnetic separation and recovery of the polluted solution. Therefore, the PEG-AMP MNs prepared by the invention can effectively remove Cs in the high-emissivity waste liquid + Has good practical application prospect in the aspect.
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the design spirit of the present invention.
Claims (9)
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| CN119056390A (en) * | 2024-09-29 | 2024-12-03 | 江苏海普功能材料有限公司 | Cesium extracting adsorbent and preparation method thereof and method for extracting cesium from salt lake brine |
| CN119236900A (en) * | 2024-11-08 | 2025-01-03 | 舟山新诺佳生物工程有限责任公司 | Application of PEG-modified MIL-101(Cr) in removing cholesterol from fish oil |
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| CN119056390A (en) * | 2024-09-29 | 2024-12-03 | 江苏海普功能材料有限公司 | Cesium extracting adsorbent and preparation method thereof and method for extracting cesium from salt lake brine |
| CN119236900A (en) * | 2024-11-08 | 2025-01-03 | 舟山新诺佳生物工程有限责任公司 | Application of PEG-modified MIL-101(Cr) in removing cholesterol from fish oil |
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