Preparation method of core-shell structure material for efficient removal of insoluble vocs

Abstract

This invention discloses a method for preparing a core-shell structured material for the efficient removal of sparingly soluble VOCs, comprising the following steps: a) preparing iron oxide particles by a hydrothermal method; b) placing the iron oxide particles in a mixed solution of acetic acid and citric acid, and performing light etching and surface modification on the surface of the iron oxide particles; c) dispersing the iron oxide particles obtained after reacting with the mixed solution of acetic acid and citric acid in methanol, adding a mixed methanol solution of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone dropwise, and then adding triethylamine to obtain a core-shell structured material with a surface coated with polyphosphazene; d) calcining the polyphosphazene-coated core-shell structured material under a nitrogen protective atmosphere to obtain a core-shell structured material with a multi-element composite shell coating. This method achieves efficient removal of sparingly soluble VOCs by coating iron oxide particles with a composite shell and utilizing the synergistic effect of mass transfer-adsorption-catalysis in the Fenton system for removing sparingly soluble VOCs.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of environmental governance, and particularly relates to a preparation method of a core-shell structure material for efficient removal of insoluble VOCs. BACKGROUND

[0002] Atmospheric pollution is one of the environmental problems to be solved at present. The volatile organic compounds (VOCs) in the exhaust gas discharged in the process of industrial production seriously endanger the ecological environment and human health. Therefore, it is urgent to develop materials and methods for efficient treatment of VOCs.

[0003] Fenton oxidation method is concerned due to its simple operation, fast reaction speed, high degradation rate and other advantages. Since the process of degrading VOCs by Fenton method is carried out in aqueous solution, the solubility of insoluble VOCs in water is low, and the transfer rate from gas phase to liquid phase is slow, which limits the process of entering the Fenton system to participate in the degradation reaction, resulting in low degradation efficiency and greatly affecting the overall degradation efficiency of VOCs. And in this process, a large amount of iron ions as catalyst are introduced into the reaction system and are difficult to recover and utilize, thereby causing secondary pollution. After replacing with ferroferric oxide particles, although it is easy to recover, the ferroferric oxide particles are unstable in the reaction system and are prone to aggregation and iron ion leaching in the reaction process.

[0004] The carbon coating on the catalyst can prevent the aggregation of ferroferric oxide particles and the leaching of iron. Meanwhile, the coating of the surface carbon layer also improves the mass transfer efficiency of insoluble VOCs. However, the simple carbon coating has limited improvement on the mass transfer efficiency, and to some extent, reduces the number of active sites on the catalyst surface, which has limited improvement on the degradation efficiency of insoluble VOCs, and still cannot meet the needs of industrial production. SUMMARY

[0005] One object of the present application is to provide a core-shell structure material for efficient removal of insoluble volatile organic compounds (VOCs) in Fenton system and a preparation method thereof. The core-shell structure material is stable in structure, easy to recover, and has significantly improved degradation efficiency of insoluble VOCs when used in Fenton system.

[0006] The preparation method of the core-shell structure material for efficient removal of insoluble VOCs comprises the following steps:

[0007] a) dissolving ferric chloride, sodium citrate and sodium acetate in ethylene glycol, pouring into a reaction kettle, heating to 200℃ and keeping for 10h to obtain ferroferric oxide particles;

[0008] b) reacting the ferroferric oxide particles in a mixed solution of acetic acid and citric acid to obtain ferroferric oxide particles with slightly etched and modified surfaces;

[0009] c) dispersing the Fe3O4 particles obtained after reacting with the mixed solution of acetic acid and citric acid in methanol, dropping the mixed methanol solution of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone into the solution, and adding a basic capturing agent triethylamine to obtain a core-shell structure material of Fe3O4 particles coated with polyphosphazene on the surface;

[0010] d) calcining the core-shell structure material of Fe3O4 particles coated with polyphosphazene on the surface in a nitrogen protective atmosphere to obtain a core-shell structure material of Fe3O4 coated with a multi-element composite shell of carbon, nitrogen, phosphorus and sulfur on the surface.

[0011] Preferably, in step a), the iron trichloride, sodium citrate and sodium acetate are dissolved in ethylene glycol by at least one of stirring, ultrasonic and heating.

[0012] Preferably, in step a), after the reaction is completed, the reaction product is washed with ethanol and deionized water for 3 times respectively, and then freeze-dried.

[0013] Preferably, in step a), the diameter of the Fe3O4 particles is 150 nm to 300 nm.

[0014] Preferably, in step b), the concentration of acetic acid in the mixed solution is 10 -5 ~ 10 -4 mol / L, and the concentration of citric acid is 10 -7 ~ 2 x 10 -5 mol / L.

[0015] Preferably, in step b), the reaction time is 3 min to 5 min.

[0016] Preferably, in step c), 1 g of the Fe3O4 particles is ultrasonically dispersed in 150 to 300 mL of methanol; the concentration of hexachlorocyclotriphosphazene in the mixed methanol solution of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone is 10 -1 ~ 10 - 2 mol / L; the volume of the mixed methanol solution of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone added in the suspension containing 1 g of the Fe3O4 particles is 5 mL to 50 mL; the dropping process is carried out under mechanical stirring, and the volume of triethylamine added is 1 mL to 5 mL.

[0017] Preferably, in step c), the molar ratio of hexachlorocyclotriphosphazene to 4,4'-dihydroxydiphenyl sulfone in the mixed methanol solution of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone is 1:(5.5~8). Thus, elements of carbon, nitrogen, phosphorus and sulfur are introduced on the surface of the Fe3O4 particles.

[0018] Preferably, in step c), after adding triethylamine, the reaction is stirred for 4-6 hours, then the reaction is ended, and the product is separated by magnetic separation, washed with deionized water for 3 times, and then freeze-dried.

[0019] Preferably, in step d), the calcination temperature is 450-600 DEG C, and the calcination time is 1-5 hours.

[0020] Preferably, in step d), the thickness of the carbon, nitrogen, phosphorus, and sulfur multi-element composite shell layer is 18-22 nm, and the mass ratio of the four elements in the composite shell layer is carbon:nitrogen:phosphorus:sulfur = 1:(0.05-0.15):(0.05-0.3):(0.2-0.3). The applicant has found that when the thickness of the shell layer of the core-shell structure material is 18-22 nm, the mass transfer enhancement efficiency for the insoluble VOCs is much higher than that of other thicknesses. The mass ratio of the four elements in the composite shell layer not only affects the mass transfer enhancement efficiency for the insoluble VOCs, but also determines the electronic structure of the active sites on the material surface, thereby affecting the catalytic degradation efficiency of the insoluble VOCs.

[0021] Another object of the present application is to provide a core-shell structure material prepared by the above method.

[0022] The present application has the following advantages:

[0023] The core-shell structure material preparation method for efficient removal of insoluble VOCs according to the present application coats a carbon, nitrogen, phosphorus, and sulfur multi-element composite shell layer on the surface of the ferroferric oxide particles, and the removal efficiency for the insoluble VOCs is obviously improved. The core-shell structure material prepared by the preparation method has uniform particle size, stable structure, and is not easy to agglomerate in the Fenton system. After being used for a period of time, it can be recovered from the system by magnetic separation, and when it is used in the Fenton system again, the removal efficiency for the insoluble VOCs does not decrease obviously. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Figure 1 is a schematic diagram of the preparation process of the core-shell structure material with a carbon, nitrogen, phosphorus, and sulfur multi-element composite shell layer coated on the surface of the ferroferric oxide particles.

[0025] In the figure, 1 is the preparation process of the ferroferric oxide particles, 2 is the process of slightly etching and modifying the surface of the ferroferric oxide particles, 3 is the process of coating the surface of the ferroferric oxide particles with polyphosphazene after surface etching and modification, and 4 is the process of obtaining the core-shell structure material with a carbon, nitrogen, phosphorus, and sulfur multi-element composite shell layer coated on the surface of the ferroferric oxide particles after calcination.

[0026] Figure 2 Figure 2 is a schematic diagram of a bubble reaction device for VOCs degradation.

[0027] In the diagram: 1 is the air inlet, 2 is the bubble generator, 3 is the VOC-containing bubble, 4 is the core-shell structure material with a multi-element composite shell of carbon, nitrogen, phosphorus and sulfur coated on the surface of iron oxide, and 5 is the air outlet.

[0028] Figure 3 The image shows an electron microscope (EM) image of the core-shell structured material prepared in Example 2, which has a multi-element composite shell of carbon, nitrogen, phosphorus, and sulfur coated on the surface of iron oxide. Detailed Implementation

[0029] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be described in detail below with reference to specific embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of the invention.

[0030] Example 1:

[0031] The specific process of the method is as follows: Figure 1 As shown, 1.6 g of ferric chloride, 1.4 g of sodium citrate, and 5.0 g of sodium acetate were dissolved in 60 mL of ethylene glycol, poured into a stainless steel reactor lined with polytetrafluoroethylene, and heated to 200 °C in an oven for 10 h. After magnetic separation of the product, it was washed and dried to obtain iron oxide particles.

[0032] Prepare a mixed solution of acetic acid and citric acid, wherein the concentration of acetic acid is 2 × 10⁻⁶. -5 mol / L, citric acid concentration is 5×10 -6 mol / L. 1g of the above iron oxide particles were poured into 100mL of the above mixed solution, mechanically stirred, and reacted for 4min. The mixture was then removed, washed, and dried to obtain iron oxide particles that had undergone slight etching and surface modification with mixed acid.

[0033] 1 g of the above-mentioned mixed acid-treated iron oxide particles were dispersed in 180 mL of anhydrous methanol to obtain an iron oxide suspension. 0.4 g of hexachlorocyclotriphosphazene and 1.8 g of 4,4'-dihydroxydiphenyl sulfone were dissolved in 40 mL of anhydrous methanol to obtain a mixed methanol solution. This mixed methanol solution was added dropwise to the suspension. Then, 3 mL of triethylamine was added dropwise to the mixed suspension. The mixture was stirred for 6 h, and the product was collected, washed, and dried to obtain a core-shell structured material with polyphosphazene coated on the surface of the iron oxide particles.

[0034] The core-shell structured material with polyphosphazene coated on the surface of the above-mentioned iron oxide particles was heated to 600°C and held at that temperature for 4 hours in a nitrogen atmosphere, resulting in a core-shell structured material with a multi-element composite shell of carbon, nitrogen, phosphorus, and sulfur coated on the surface of iron oxide. Elemental analysis results showed that the mass ratio of the four elements was carbon:nitrogen:phosphorus:sulfur = 1:0.12:0.08:0.20.

[0035] The core-shell structured material with a multi-element composite shell of carbon, nitrogen, phosphorus, and sulfur coated on the surface of the aforementioned iron oxide was applied to the Fenton-bubbling reactor, such as... Figure 2 As shown. Before the reaction begins, the toluene concentration at the inlet is adjusted and maintained stably at 0.8 g / m³. 3 A certain amount of deionized water, 8.6 mL of 30% H₂O₂, and 1 g of the core-shell structured material prepared under the above conditions, coated with a multi-element composite shell of carbon, nitrogen, phosphorus, and sulfur on the surface of iron oxide, were added to the bubbling reaction apparatus. The pH of the solution was adjusted to 5 using sulfuric acid and sodium hydroxide solutions, both with a concentration of 0.1 mol / L. The concentration of toluene at the inlet and outlet was measured using gas chromatography. The results showed that the degradation rate of toluene was higher than 96% within the first 3 hours after the start of the reaction. In the system using the uncoated iron oxide particles described in this invention, the degradation rate of toluene was less than 30% after the start of the reaction.

[0036] Example 2:

[0037] Dissolve 1.6 g of ferric chloride, 1.4 g of sodium citrate, and 5.0 g of sodium acetate in 80 mL of ethylene glycol. Pour the solution into a stainless steel reactor lined with polytetrafluoroethylene (PTFE), and heat in an oven to 200 °C for 10 h. After magnetic separation, the product is washed and dried to obtain iron oxide (Fe3O4) particles.

[0038] Prepare a mixed solution of acetic acid and citric acid, wherein the concentration of acetic acid is 5 × 10⁻⁶. -5 mol / L, citric acid concentration is 8×10 -6 mol / L. 1g of the above iron oxide particles were poured into 100mL of the above mixed solution, mechanically stirred, and reacted for 3min. The mixture was then removed, washed, and dried to obtain iron oxide particles that had undergone slight etching and surface modification with mixed acid.

[0039] 1 g of the above-mentioned mixed acid-treated iron oxide particles were dispersed in 200 mL of anhydrous methanol to obtain an iron oxide suspension. 0.5 g of hexachlorocyclotriphosphazene and 2.5 g of 4,4'-dihydroxydiphenyl sulfone were dissolved in 50 mL of anhydrous methanol to obtain a mixed methanol solution. This mixed methanol solution was then added dropwise to the suspension. 4 mL of triethylamine was then added dropwise to the mixed suspension. The mixture was stirred for 6 h, and the product was collected, washed, and dried to obtain a core-shell structured material with polyphosphazene coated on the surface of the iron oxide particles.

[0040] The core-shell structure material with polyphosphazene coated on the surface of the above-mentioned iron oxide particles was heated to 550°C in a nitrogen atmosphere and kept at that temperature for 3 hours to obtain a core-shell structure material with a multi-element composite shell of carbon, nitrogen, phosphorus and sulfur coated on the surface of iron oxide.

[0041] Transmission electron microscopy (TEM) results showed that the surface of the aforementioned iron oxide (Fe3O4) was coated with a multi-element composite shell of carbon, nitrogen, phosphorus, and sulfur, with a thickness of approximately 20 nm. Elemental analysis revealed that the mass ratio of the four elements was carbon:nitrogen:phosphorus:sulfur = 1:0.13:0.14:0.21. The TEM image of this material is shown below. Figure 3 As shown, a core-shell structure is formed, in which the opaque part is the core layer, namely iron oxide particles; and the transparent part is the shell layer, namely a polyphosphazene coating layer containing four elements: carbon, nitrogen, phosphorus and sulfur.

[0042] The above materials are applied to a Fenton-bubbling reaction apparatus, such as Figure 2 As shown. Before the reaction begins, the concentration of n-octane at the inlet is adjusted and maintained stably at 1.0 g / m³. 3 A certain amount of deionized water, 8.6 mL of 30% H₂O₂, and 1 g of the core-shell structured material prepared under the above conditions, coated with a multi-element composite shell of carbon, nitrogen, phosphorus, and sulfur on the surface of iron oxide, were added to the bubbling reaction apparatus. The pH of the solution was adjusted to 5 using sulfuric acid and sodium hydroxide solutions, both with a concentration of 0.1 mol / L. The concentration of n-octane at the inlet and outlet was measured using gas chromatography. The results showed that the degradation rate of n-octane remained at 85% after 3 hours of reaction. In the system containing the uncoated iron oxide particles described in this invention, the degradation rate of n-octane was less than 24% after 3 hours of reaction.

[0043] The core-shell structure material in the Fenton-bubbling reactor was magnetically recovered, washed, and freeze-dried before being reused in the Fenton system to degrade insoluble VOCs. After being recycled five times according to the above steps, the system's degradation efficiency for n-octane was still more than 95% higher than that of the first use.

[0044] Comparative Example 1

[0045] Dissolve 1.6 g of ferric chloride, 1.4 g of sodium citrate, and 5.0 g of sodium acetate in 80 mL of ethylene glycol. Pour the solution into a stainless steel reactor lined with polytetrafluoroethylene (PTFE), and heat in an oven to 200 °C for 10 h. After magnetic separation, the product is washed and dried to obtain iron oxide (Fe3O4) particles.

[0046] 1.0 g of the above-mentioned iron(III) oxide particles were dispersed in a solution containing 80 mL of water, 32 mL of anhydrous ethanol, and 0.4 mL of ammonia, and sonicated for 1 h to obtain a homogeneous suspension. Then, 0.25 g of resorcinol was added to the solution. After mechanical stirring at room temperature for 30 minutes, 0.4 mL of 38 wt% formaldehyde solution was added, and polymerization was carried out for 24 hours. The resulting Fe3O4@phenolic resin composite material was obtained. After magnetic separation, washing, and drying, the Fe3O4@phenolic resin composite material was carbonized at 650 °C under a nitrogen atmosphere for 2 h. A core-shell structured material with a carbon shell was obtained; transmission electron microscopy showed that the C-shell thickness was 20 nm. The above material was applied in a Fenton-bubbling reactor, such as... Figure 2 As shown.

[0047] Compared to the core-shell structure material with a carbon, nitrogen, phosphorus and sulfur multi-element composite shell coated on the surface of iron oxide described in Example 2, the degradation efficiency of n-octane in the Fenton-bubbling reaction system using the above material was reduced by 46%.

[0048] Comparative Example 2:

[0049] Dissolve 1.6 g of ferric chloride, 1.4 g of sodium citrate, and 5.0 g of sodium acetate in 80 mL of ethylene glycol. Pour the solution into a stainless steel reactor lined with polytetrafluoroethylene (PTFE), and heat in an oven to 200 °C for 10 h. After magnetic separation, the product is washed and dried to obtain iron oxide (Fe3O4) particles.

[0050] Prepare a mixed solution of acetic acid and citric acid, wherein the concentration of acetic acid is 5 × 10⁻⁶. -5 mol / L, citric acid concentration is 8×10 -6 mol / L. 1g of the above iron oxide particles were poured into 100mL of the above mixed solution, mechanically stirred, and reacted for 3min. The mixture was then removed, washed, and dried to obtain iron oxide particles that had undergone slight etching and surface modification with mixed acid.

[0051] 1 g of the above-mentioned mixed acid-treated iron oxide particles were dispersed in 200 mL of anhydrous methanol. 0.5 g of hexachlorocyclotriphosphazene and 1.2 g of 4,4'-dihydroxydiphenyl sulfone were dissolved in 50 mL of anhydrous methanol and added dropwise to the above solution. Then, 4 mL of triethylamine was added dropwise. The mixture was stirred for 6 h, and the product was collected, washed, and dried to obtain a core-shell structured material with polyphosphazene coated on the surface of the iron oxide particles.

[0052] The core-shell structure material with polyphosphazene coated on the surface of the above-mentioned iron oxide particles was heated to 800°C in a nitrogen atmosphere and kept at that temperature for 3 hours to obtain a core-shell structure material with a multi-element composite shell of carbon, nitrogen, phosphorus and sulfur coated on the surface of iron oxide.

[0053] Compared to Example 2, the ratio of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone and the calcination temperature were changed, thereby altering the shell element ratio and the shell thickness. Transmission electron microscopy results showed that the surface of the above-mentioned iron oxide was coated with a multi-element composite shell of carbon, nitrogen, phosphorus, and sulfur, with a thickness of approximately 11 nm. Elemental analysis results showed that the mass ratio of the four elements was carbon:nitrogen:phosphorus:sulfur = 1:0.10:0.003:0.06.

[0054] The above materials are applied to a Fenton-bubbling reaction apparatus, such as Figure 2 Compared to Example 2, the system's degradation efficiency for n-octane decreased by 42%.

[0055] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this invention, and these modifications or substitutions should all be covered within the scope of protection of this invention. Therefore, the scope of protection of this invention should be determined by the scope defined in the claims.

Claims

1. An application of core-shell structured materials for the efficient removal of sparingly soluble VOCs, characterized in that, The preparation method of the core-shell structure material includes the following steps: a) Dissolve ferric chloride, sodium citrate and sodium acetate in ethylene glycol, pour into a reaction vessel, heat to 200°C and keep warm for 10 hours to obtain iron oxide particles; b) The iron oxide particles were placed in a mixed solution of acetic acid and citric acid to react and obtain iron oxide particles with light surface etching and surface modification. c) The iron oxide particles obtained after reacting with the mixed solution of acetic acid and citric acid are dispersed in methanol, and a mixed methanol solution of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone is added dropwise. Then, the alkaline scavenging agent triethylamine is added to obtain a core-shell structured material with polyphosphazene coated on the surface of the iron oxide particles. d) The core-shell structure material with polyphosphazene coated on the surface of the iron oxide particles is calcined in a nitrogen protective atmosphere to obtain a core-shell structure material with a multi-element composite shell of carbon, nitrogen, phosphorus and sulfur coated on the surface of iron oxide. In step a), the diameter of the iron oxide particles is 150 nm to 300 nm; In step d), the thickness of the carbon, nitrogen, phosphorus and sulfur multi-element composite shell is 18nm to 22nm, and the mass ratio of the four elements in the composite shell is carbon:nitrogen:phosphorus:sulfur = 1:(0.05 to 0.15):(0.05 to 0.3):(0.2 to 0.3).

2. The application according to claim 1, characterized in that, In step b), the acetic acid concentration in the mixed solution is 10. -5 ~10 -4 mol / L, citric acid concentration is 10 -7 ~2×10 -5 mol / L.

3. The application according to claim 1, characterized in that, In step b), the reaction time is 3 min to 5 min.

4. The application according to claim 1, characterized in that, In step c), each 1g of the iron oxide particles is ultrasonically dispersed in 150-300mL of methanol; the concentration of hexachlorocyclotriphosphazene in the mixed methanol solution of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone is 10. -1 ~10 -2 mol / L; to each suspension containing 1g of the above iron oxide particles, the volume of the mixed methanol solution of hexachlorocyclotriphosphazene and 4,4'-dihydroxydiphenyl sulfone added is 5mL to 50mL; the dropwise addition process is carried out under mechanical stirring, and the volume of triethylamine added is 1mL to 5mL.

5. The application according to claim 1, characterized in that, In step c), the molar ratio of hexachlorocyclotriphosphazene to 4,4'-dihydroxydiphenyl sulfone in the mixed methanol solution is 1:(5.5-8).

6. The application according to claim 1, characterized in that, In step c), triethylamine is added and the mixture is stirred for 4 to 6 hours. After the reaction is completed, magnetic separation is performed.

7. The application according to claim 1, characterized in that, In step d), the calcination temperature is 450–600°C and the calcination time is 1–5 h.

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