Immobilized heterogeneous catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalytic materials, and particularly relates to an immobilized heterogeneous catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) dissolving chitosan in an acetic acid aqueous solution to form a colloid; (2) mixing nickel salt and ferric salt with the colloid to obtain a precursor solution; (3) dropwise adding the precursor solution into an alkali solution, carrying out a cross-linking reaction, washing, and drying to obtain an immobilized heterogeneous catalyst; the concentration of the alkali liquor is greater than 0.6 mol / L, and the alkali liquor contains glutaraldehyde. According to the invention, the immobilized heterogeneous catalyst is prepared by adopting a specific in-situ growth method, is a photocatalyst for efficiently removing OTC through cooperation of PMS / Vis, and has the advantages of low cost and high environmental tolerance. The immobilized heterogeneous catalyst provided by the invention also has good cyclic catalytic performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of catalytic materials, and particularly relates to a kind of immobilized heterogeneous catalyst and its preparation method and application. BACKGROUND

[0002] Tetracycline antibiotics (TCs) are widely present in water bodies and are difficult to degrade, and traditional processes (such as adsorption, biodegradation and membrane filtration, etc.) have low removal efficiency. The advanced oxidation process (PS-AOPs) based on persulfate is an effective means to degrade TCs due to its ability to generate strong oxidizing free radicals. Among them, persulfate monosulfate (PMS) can be activated by various ways, but it is difficult to achieve the highest activation efficiency due to limitations such as incomplete oxidation and unstable efficiency, which restricts its practical application. Photocatalysis is an economical and environmentally friendly water treatment method, but it has problems such as insufficient catalytic efficiency due to the rapid recombination of photo-generated electrons and holes. In recent years, the photocatalytic process has been introduced into heterogeneous PS-AOPs to construct a peroxymonosulfate / visible light (PMS / Vis) synergistic system, which has the advantages of high efficiency, mild conditions, and economic affordability. Layered double hydroxides (LDHs) with NiFe LDH, due to its narrow band gap, environmental friendliness and double transition metal synergistic activation effect, are considered to be an efficient catalyst for PMS / Vis synergistic system. However, this catalyst material still faces problems such as easy agglomeration of powder and fast recombination rate of photo-generated carriers in practical application, which seriously limits the performance of the catalyst.

[0003] Therefore, there is an urgent need to develop a new type of catalyst with low cost, high efficiency, easy recovery and environmental friendliness. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a kind of immobilized heterogeneous catalyst and its preparation method and application.

[0005] The present application synthesizes an immobilized heterogeneous catalyst by in-situ growth method, which is chitosan / NiFe layered double hydroxide composite aerogel beads (CS / NiFe LDH), and is used for PMS / Vis synergistic degradation of oxytetracycline (OTC), solving the problems of easy agglomeration, difficult recovery and fast recombination rate of photo-generated carriers of powder state layered double hydroxide. The immobilized heterogeneous catalyst described in the present application is a kind of photocatalyst for efficient PMS / Vis synergistic removal of OTC, which has low cost and high environmental tolerance. The immobilized heterogeneous catalyst described in the present application also has good cyclic catalytic performance.

[0006] That is, the immobilized heterogeneous catalyst described in the present application at least solves any of the following problems: (1) solving the problems of easy agglomeration and difficult recovery of powder LDH catalyst; (2) inhibiting metal ion leaching; (3) improving PMS / Vis synergistic activation efficiency, and realizing efficient degradation of tetracycline antibiotics.

[0007] The first aspect of the application provides a preparation method of an immobilized heterogeneous catalyst.

[0008] The preparation method of the immobilized heterogeneous catalyst comprises the following steps: (1) dissolving chitosan in an aqueous acetic acid solution to form a colloid; (2) mixing a nickel salt and an iron salt with the colloid to obtain a precursor solution; (3) dropping the precursor solution into a lye to perform a cross-linking reaction, washing, drying, and obtaining the immobilized heterogeneous catalyst; The concentration of the lye is greater than 0.6 mol / L, and the lye contains glutaraldehyde.

[0009] Preferably, in step (1), the mass fraction of the aqueous acetic acid solution is 2-5%, and is further preferably 4-5%.

[0010] Preferably, in step (1), the use amount ratio of chitosan to the aqueous acetic acid solution is 1.5 g:(40-60) mL, and is further preferably 1.5 g:(50-60) mL.

[0011] Preferably, in step (2), the nickel salt is nickel nitrate or hydrated nickel nitrate.

[0012] Preferably, in step (2), the iron salt is ferric nitrate or hydrated ferric nitrate.

[0013] Preferably, in step (2), the molar ratio of the nickel salt to the iron salt is (2-4):1, and is further preferably 3:1.

[0014] Preferably, in step (2), the mass ratio of the nickel salt to the colloid is (0.3-1.4):51.5, for example, 0.7674:51.5.

[0015] Preferably, in step (2), the volume ratio of the precursor solution to the lye is (40-60):301 mL, for example, 50:301.

[0016] Preferably, in step (2), the lye comprises a sodium hydroxide solution or a potassium hydroxide solution.

[0017] Preferably, in step (2), the concentration of the lye is 0.6-1.2 mol / L, and is further preferably 1-1.1 mol / L.

[0018] Preferably, in step (2), the cross-linking reaction is performed for 20-24 h.

[0019] Preferably, in step (2), the cross-linking reaction is performed at a temperature of 20-30℃.

[0020] Preferably, in step (2), the washing is performed using deionized water.

[0021] The above preparation method uses chitosan (CS) aerogel beads as a carrier, and NiFe LDH nanosheets are fixed by in-situ growth to form a three-dimensional porous composite catalyst (CS / NiFe LDH), i.e., a fixed heterogeneous catalyst. The -NH2 / -OH functional groups of CS can coordinate with metal ions to stabilize the NiFe LDH active center. Synergistic mechanism: the three-dimensional porous structure promotes PMS capture and electron transport, and the photo-generated electrons under visible light excitation activate PMS to generate reactive oxygen species (ROS); Degradation path: through the synergistic approach of free radicals (·SO4 - , ·OH) and non-free radicals (O2, h 1 ) + ), the antibiotic is degraded.

[0022] The second aspect of the present application provides a fixed heterogeneous catalyst.

[0023] A fixed heterogeneous catalyst is prepared by the above preparation method.

[0024] Preferably, the fixed heterogeneous catalyst comprises NiFe LDH and a carrier, the carrier is chitosan, and the NiFe LDH is loaded on the carrier.

[0025] Preferably, in the fixed heterogeneous catalyst, the mass fraction of the NiFe LDH is 10-30%, further preferably 20-25%, and more preferably 20%.

[0026] The third aspect of the present application provides an application of a fixed heterogeneous catalyst.

[0027] The fixed heterogeneous catalyst prepared by the above preparation method is applied in catalytic degradation of antibiotics.

[0028] Preferably, the antibiotic comprises terramycin.

[0029] Compared with the prior art, the present application has the following beneficial effects: (1) The immobilized heterogeneous catalyst is prepared by a specific in-situ growth method, is a high-efficiency PMS / Vis synergistic OTC removal photocatalyst, has low cost and high environmental tolerance, and has good cyclic catalytic performance.

[0030] (2) The immobilized heterogeneous catalyst has high degradation performance: the degradation rate of oxytetracycline (OTC) reaches 94.99%, and the reaction rate (k = 0.1012 min -1 ) is 4.77 times and 5.30 times of that of a single PMS system (k = 0.0212 min -1 ) and a visible light system (k = 0.0191 min -1 ). Strong stability: the degradation rate still reaches 89.71% after 5 cycles; Low metal leaching: the CS network inhibits the dissolution of metal ions (the Ni / Fe leaching concentration is significantly lower than that of the powder LDH); Universality: suitable for various antibiotics (TC, NOR, LVX) and dyes (MB, RR120), and maintains high efficiency in pH = 3-11 and different water qualities (tap water, lake water). BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 XRD patterns of the CS beads, NiFe powder and the immobilized heterogeneous catalyst prepared in Example 1; Figure 2 SEM of the immobilized heterogeneous catalyst prepared in Example 1; Figure 3 OTC PMS / Vis synergistic catalytic degradation curves of the immobilized heterogeneous catalysts prepared in Examples 1-5; Figure 4 Degradation curves of the immobilized heterogeneous catalyst prepared in Example 1 on different pollutants; Figure 5 Cyclic degradation curves of the immobilized heterogeneous catalyst prepared in Example 1 on OTC; Figure 6 Comparison results of degradation rates and metal ion leaching concentrations in solution of CS+NiFe LDH and the immobilized heterogeneous catalyst prepared in Example 1; Figure 7 OTC PMS / Vis synergistic catalytic degradation curves of the immobilized heterogeneous catalysts prepared in Example 1 and Comparative Examples 1-5. DETAILED DESCRIPTION

[0032] In order to make the skilled in the art more clearly understand the technical solutions described in the present application, the following examples are listed for illustration. It should be pointed out that the following examples do not constitute a limitation on the scope of protection required by the present application.

[0033] The raw materials, reagents or devices used in the following examples, unless otherwise specified, can be obtained from conventional commercial channels, or can be obtained by existing known methods.

[0034] The molar ratio of Ni(NO3)2·6H2O and Fe(NO3)3·9H2O in Examples 2-5 below is 3:1. Example 1

[0035] A preparation method of an immobilized heterogeneous catalyst, comprising the following steps: (1) Dissolve 1.5 g of chitosan (CS) in 50 mL of 5 wt% acetic acid aqueous solution to form a CS colloid; (2) Dissolve Ni(NO3)2·6H2O and Fe(NO3)3·9H2O in the CS colloid in a ratio of 3:1 by molar ratio under mechanical stirring to obtain a precursor solution, wherein the mass ratio of Ni(NO3)2·6H2O to the CS colloid is 0.7674:51.5; (3) Drop 50 mL of the precursor solution into a mixed solution of 300 mL of 1 mol / L NaOH solution and 1 mL of glutaraldehyde through a peristaltic pump, and cross-link for 24 h. After cross-linking, the hydrogel beads are washed with deionized water until neutral, and then freeze-dried to obtain an immobilized heterogeneous catalyst, which is denoted as CS / NiFe LDH composite beads.

[0036] The mass fraction of NiFe LDH in the immobilized heterogeneous catalyst prepared in this example is 20%, which is denoted as CS / NiFe20. Example 2

[0037] Compared with Example 1, the difference between Example 2 is that the mass ratio of Ni(NO3)2·6H2O to the CS colloid is 0.3401:51.5, and the other processes are the same as those of Example 1.

[0038] The mass fraction of NiFe LDH in the immobilized heterogeneous catalyst prepared in this example (denoted as CS / NiFe10) is 10%. Example 3

[0039] Compared with Example 1, the difference between Example 3 is that the mass ratio of Ni(NO3)2·6H2O to the CS colloid is 0.5436:51.5, and the other processes are the same as those of Example 1.

[0040] The immobilized heterogeneous catalyst prepared in this example (denoted as CS / NiFe15) has a mass fraction of 15% of NiFe LDH. Example 4

[0041] Compared with Example 1, the difference of Example 4 is that the mass ratio of Ni(NO3)2·6H2O to CS colloid is 1.0261:51.5, and other processes are the same as Example 1.

[0042] The immobilized heterogeneous catalyst prepared in this example (denoted as CS / NiFe25) has a mass fraction of 25% of NiFe LDH. Example 5

[0043] Compared with Example 1, the difference of Example 5 is that the mass ratio of Ni(NO3)2·6H2O to CS colloid is 1.3168:51.5, and other processes are the same as Example 1.

[0044] The immobilized heterogeneous catalyst prepared in this example (denoted as CS / NiFe30) has a mass fraction of 30% of NiFe LDH.

[0045] Comparative Example 1 Compared with Example 1, the difference of Comparative Example 1 is that the concentration of NaOH solution in step (3) is 0.6 mol / L, and other processes are the same as Example 1.

[0046] Comparative Example 2 Compared with Example 1, the difference of Comparative Example 2 is that the concentration of NaOH solution in step (3) is 0.8 mol / L, and other processes are the same as Example 1.

[0047] Comparative Example 3 Compared with Example 1, the difference of Comparative Example 3 is that 50 mL of 2 wt% acetic acid aqueous solution is used instead of 50 mL of 5 wt% acetic acid aqueous solution, and other processes are the same as Example 1.

[0048] Comparative Example 4 Compared with Example 1, the difference of Comparative Example 4 is that 50 mL of 3 wt% acetic acid aqueous solution is used instead of 50 mL of 5 wt% acetic acid aqueous solution, and other processes are the same as Example 1.

[0049] Comparative Example 5 Compared with Example 1, the difference of Comparative Example 5 is that 50 mL of 4 wt% acetic acid aqueous solution is used instead of 50 mL of 5 wt% acetic acid aqueous solution, and other processes are the same as Example 1.

[0050] Product Effect Test 1. Structure Characterization Figure 1 XRD pattern of CS beads, NiFe powder, immobilized heterogeneous catalyst prepared in Example 1. Figure 1 In the figure, “Intensity” represents intensity, “2 Theta (degree)” represents 2 theta (°). “PDF #40-0215” represents the XRD card number corresponding to the nickel-iron hydrotalcite structure, and (003), (006), (012), (113) represent the peaks at 2 theta = 11.41°, 23.97°, 34.42° and 61.25°, which can be respectively corresponding to (003), (006), (012) and (113) crystal planes. Among them, (003), (006) and (012) crystal planes represent the layered structure of hydrotalcite, and (113) crystal plane represents the stacking order of hydrotalcite layer.

[0051] Figure 2 SEM image of immobilized heterogeneous catalyst prepared in Example 1.

[0052] 2. Catalytic degradation performance evaluation 30 mg of immobilized heterogeneous catalyst prepared in Example and 5 mM PMS were dispersed into 100 mL of 10 mg / L OTC (or TC tetracycline, MB methylene blue, RR120 reactive red 120, NOR norfloxacin, LVX levofloxacin) solution, a 300 W xenon lamp (wavelength λ = 320-720 nm) was used as a simulated light source, and a cooling circulating water machine was used to control the system reaction temperature to be 10°C, and the light source was about 15 cm away from the liquid surface. The results are shown in Figure 3 , Figure 4 .

[0053] Figure 3 OTC PMS / Vis synergistic catalytic degradation curve of immobilized heterogeneous catalyst prepared in Examples 1-5; Figure 3 In the figure, “Time” represents time, “C t / C0” represents the OTC concentration at a certain time divided by the initial OTC concentration, and Figure 3 It can be seen that the removal rate of immobilized heterogeneous catalyst prepared in Example 1 for OTC is 94.99% after 30 min of reaction.

[0054] Figure 4 Degradation curve of immobilized heterogeneous catalyst prepared in Example 1 for different pollutants; Figure 4 In the figure, “Degradation efficiency” represents degradation efficiency, “TCs” represents tetracycline antibiotics, “Dyes” represents dyes, and “FQs” represents fluoroquinolone antibiotics, and Figure 4It can be seen that the degradation of different pollutants by the immobilized heterogeneous catalyst prepared in Example 1 is as follows: the degradation efficiency is in the order of RR120 (99.66%) > MB (98.55%) > TC (95.09%) > OTC (94.99%) > NOR (85.48%) > LVX (84.35%), all of which are more than 80%.

[0055] 3. Cycle performance test After the end of each degradation experiment, the beads were fished out with a filter screen and washed with deionized water before being used in the next experiment. The absorbance was measured at the same time point for each reaction to evaluate the changes in degradation performance.

[0056] Figure 5 Cycle degradation curve of OTC by the immobilized heterogeneous catalyst prepared in Example 1; Figure 5 In the table, “Degradation efficiency” represents the degradation efficiency, and “Cycles” represents the number of cycles, from Figure 5 It can be seen that the degradation efficiency of OTC after five cycles still reaches 89.71%.

[0057] 4. Metal ion leaching test The sample was accurately weighed into a digestion tube, and aqua regia 5 mL, hydrogen peroxide 1 mL, and hydrofluoric acid 1 mL were added. The digestion tank and support cup were placed in a digestion instrument for digestion, with a digestion temperature of 150°C for 120 min and a digestion temperature of 210°C for 120 min. After digestion, the digestion solution was transferred to a beaker, 5 mL of nitric acid was added, and the acid was chased to near dryness. The volume was made up to the mark in a volumetric flask with ultrapure water, and the instrument was used for determination.

[0058] Figure 6 Comparison of degradation rate and leaching concentration of metal ions in solution of the mixture of CS (24 mg) + NiFe LDH (6 mg) directly mixed and the immobilized heterogeneous catalyst prepared in Example 1. Figure 6 In the table, “Leaching concentration” represents the leaching concentration, and “Degradation efficiency” represents the degradation efficiency, from Figure 6 It can be seen that the concentrations of Ni and Fe ions in the CS / NiFe / PMS / Vis system are much lower than those in the powdered CS+NiFe / PMS system. This is mainly due to the millimeter-level structure of the aerogel beads, which can selectively permeate PMS molecules and pollutants, and effectively block H + from directly contacting the NiFe active center. In addition, in-situ growth enhances the anchoring effect of the metal active center.

[0059] ReferenceFigure 3 The corresponding experimental conditions, the immobilized heterogeneous catalyst prepared by test example 1 and comparative examples 1-5 were tested for OTC PMS / Vis synergistic catalytic degradation effect, and the results were as follows Figure 7 As shown in the following table, Figure 7 The immobilized heterogeneous catalyst prepared by test example 1 and comparative examples 1-5 were tested for OTC PMS / Vis synergistic catalytic degradation curve. From Figure 7 It can be seen that the degradation rate of OTC by example 1 is 94.99%, comparative example 1 is 91.82%, comparative example 2 is 86.83%, comparative example 3 is 83.18%, comparative example 4 is 90.33%, and comparative example 5 is 87.28%.

Claims

1. A method for the preparation of an immobilized heterogeneous catalyst, characterized by, The method comprises the following steps: (1) dissolving chitosan in an acetic acid aqueous solution to form a colloid; (2) mixing a nickel salt and an iron salt with the colloid to obtain a precursor solution; (3) dropping the precursor solution into a lye to perform a cross-linking reaction, washing, drying, and obtaining the immobilized heterogeneous catalyst. The concentration of the lye is greater than 0.6 mol / L, and the lye contains glutaraldehyde.

2. The production method according to claim 1, characterized by, In step (1), the mass fraction of the acetic acid aqueous solution is 2-5%.

3. The preparation method according to claim 1, characterized in that, In step (1), the ratio of the use amount of chitosan to the acetic acid aqueous solution is 1.5 g:(40-60) mL.

4. The method of claim 1, wherein, In step (2), the nickel salt is nickel nitrate or hydrated nickel nitrate; and / or, the iron salt is ferric nitrate or hydrated ferric nitrate.

5. The preparation method according to claim 1, characterized in that, In step (2), the molar ratio of the nickel salt to the iron salt is (2-4):1; and / or, in step (2), the mass ratio of the nickel salt to the colloid is (0.3-1.4):51.

5.

6. The method of claim 1, wherein, In step (2), the volume ratio of the precursor solution to the lye is (40-60):301 mL; and / or, the lye comprises a sodium hydroxide solution or a potassium hydroxide solution; and / or, the concentration of the lye is 0.6-1.2 mol / L.

7. An immobilized heterogeneous catalyst characterized in that, The immobilized heterogeneous catalyst is prepared by the preparation method of any one of claims 1-6.

8. The immobilized heterogeneous catalyst of claim 7, wherein, The immobilized heterogeneous catalyst comprises a NiFe LDH and a carrier, the carrier is chitosan, and the NiFe LDH is loaded on the carrier.

9. The immobilized heterogeneous catalyst of claim 8, wherein, In the immobilized heterogeneous catalyst, the mass fraction of the NiFe LDH is 10-30%.

10. The application of the immobilized heterogeneous catalyst prepared by the preparation method of any one of claims 1-6 in catalytic degradation of antibiotics.

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