Magnetic nano titanium dioxide composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of nano materials, and particularly discloses a magnetic nano titanium dioxide composite material as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing a Fe < 2 + > / Fe < 3 + > mixed solution with a titanium source to form a uniform mixed solution; (2) dropwise adding a dispersing agent into the mixed solution, and stirring and mixing to obtain a reaction system; (3) carrying out heating and ultrasonic treatment on the system, adding an alkali source to adjust the pH value of the reaction system, and continuing the reaction; (4) after the reaction is finished, separating magnetic particles by adopting an external magnetic field, washing, and carrying out vacuum drying to obtain a Fe3O4 / TiO2 composite material; and the dispersing agent is a cocamidopropyl betaine or polyaspartic acid aqueous solution. The particle size of the prepared particles can be as low as 130 nm, PDIlt; 0.3 part; the saturation magnetization is greater than or equal to 40 emu / g, and the magnetic recovery efficiency within 30 seconds is greater than or equal to 90%; the degradation rate of visible light to organic pollutants within 50 minutes is greater than or equal to 57.8%, and the particle size change 1t within 72 hours under the condition that the pH value is 7-11; 15%; the magnetic nano titanium dioxide composite material disclosed by the invention has important application potential in the fields of photocatalysis and industrial wastewater treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nanomaterials, and relates to the preparation of a magnetic nanocomposite material, in particular to a Fe3O4 / TiO2 magnetic nanocomposite material, a preparation method thereof and application of the Fe3O4 / TiO2 magnetic nanocomposite material in the photocatalytic degradation of organic pollutants. BACKGROUND

[0002] Titanium dioxide (TiO2) nanoparticles have been widely used in the degradation of environmental pollutants due to their excellent photocatalytic performance. However, traditional TiO2 photocatalysts have significant technical limitations. Firstly, they have weak visible light response and can only utilize a small proportion (about 4%) of solar energy, resulting in low light energy utilization. Secondly, the particles tend to agglomerate, leading to a decrease in specific surface area and a decline in catalytic activity. Thirdly, it is difficult to recover the catalyst, and it is easy to be left in wastewater after treatment, causing resource waste and secondary pollution.

[0003] To solve the problem of recovery, the existing technology often uses magnetic Fe3O4 as a carrier to combine with TiO2 to form a Fe3O4 / TiO2 magnetic composite material. However, this composite process still has some core problems. Firstly, it is difficult to control the particle size, and the particles tend to agglomerate during the composite process, resulting in a product particle size often exceeding 500 nm, which makes it difficult to achieve nanoscale dispersion, leading to insufficient specific surface area and limited photocatalytic activity. Secondly, the dispersant has poor adaptability, and traditional dispersants (such as sodium silicate and citric acid) can only inhibit agglomeration through a single action, which can easily lead to loss of magnetism or secondary agglomeration (for example, when sodium silicate is used as a dispersant, the product particle size can reach more than 1000 nm). Thirdly, the process lacks synergy, and the existing technology lacks research on the synergistic regulation mechanism of “dispersant-reaction temperature-pH-reaction mode”, which cannot simultaneously achieve the performance balance of “small particle size-high dispersibility-strong magnetism”, and some processes (such as the sol-gel method) have problems such as high energy consumption, the use of organic solvents, and difficulty in large-scale production.

[0004] In summary, there is an urgent need in the current industry for a preparation technology that can precisely control the particle size of Fe3O4 / TiO2, balance high dispersibility and strong magnetism, and is green, low-cost and scalable, in order to break through the industry bottleneck of “high activity and easy recovery”. SUMMARY

[0005] In view of the deficiencies of the existing technology, the purpose of the present application is to provide a preparation method of a magnetic nanometer titanium dioxide composite material. The preparation method of the present application is green, low-cost and easy to scale, and the magnetic nanometer titanium dioxide composite material prepared has the advantages of high catalytic activity and convenient recovery.

[0006] The present application is achieved by the following technical solutions: A preparation method of a magnetic nanometer titanium dioxide composite material, comprising the following steps: (1) Fe3O4 nanoparticles are prepared by a chemical co-precipitation method; 2+ / Fe 3+ The mixed solution is mixed with the titanium source to form a uniform metal ion-precursor mixed solution; (2) adding a dispersing agent dropwise into the mixed solution and stirring to obtain a reaction system; (3) heating and ultrasonic treating the system, and adding an alkali source to adjust the pH of the reaction system to 9-11, and continuing the nucleation reaction under the condition; (4) after the reaction is completed, magnetic particles are separated by an external magnetic field, and Fe3O4 / TiO2 magnetic nano-titania composite material is obtained after washing and vacuum drying; The dispersing agent is cocamidopropyl betaine (CAB35) or a 10wt%-50wt% polyaspartic acid aqueous solution.

[0007] Further improved schemes of the present application are as follows: The Fe 2+ / Fe 3+ The molar ratio of divalent iron to trivalent iron in the mixed solution is 1: (1.5-2.5), and the Fe 2+ / Fe 3+ The total concentration of iron salt in the mixed solution is 0.05-0.4mol / L.

[0008] Further, the titanium source is one or more than two kinds of mixture of tetrabutyl titanate, titanium isopropanol or nano-titania powder.

[0009] Further, the TiO2 in the titanium source is 1: (1-2) of the Fe 2+ / Fe 3+ The molar ratio of iron ions in the mixed solution is 1: (1-2).

[0010] Further, the amount of the dispersing agent is 1-3% of the mass of the mixed solution.

[0011] Further, the alkali source is 20%-30% ammonia water or 0.1mol / L-0.5mol / L NaOH solution; and the alkali source is added dropwise or atomized and uniformly fed into the reaction system.

[0012] Further, the heating temperature in step (3) is 40-70℃; the ultrasonic treatment power is 150-450W, and the time is 10-30min; and the nucleation reaction time is 20-40min.

[0013] Further, the strength of the external magnetic field is 0.1-0.5T; the vacuum drying temperature is 50-70℃, and the time is 3-6h.

[0014] Further improved schemes of the present application are as follows: A magnetic nano-titania composite material prepared by the above preparation method.

[0015] The composite material has a particle size of 70-150nm, a polydispersity index PDI <0.3, a saturation magnetization intensity ≥40emu / g, and a magnetic recovery efficiency ≥90% within 30s under an applied magnetic field of 0.1-0.5T.

[0016] A further improved scheme of the present application is: The application of the magnetic nanometer titanium dioxide composite material in the degradation of organic pollutants is provided, wherein the organic pollutants include methylene blue, methyl orange and the like, and the degradation rate of the organic pollutants is ≥60% within 50min under visible light irradiation, so that the magnetic nanometer titanium dioxide composite material can be applied to industrial wastewater treatment or a photocatalytic reactor.

[0017] Compared with the prior art, the present application has the following beneficial effects: (1) Precise control of particle size: through the synergistic regulation of dispersants and process parameters, the particle size of Fe3O4 / TiO2 is reduced from the micron level (>800nm) of traditional processes to the nanometer level (70-150nm), the polydispersity index is <0.3, and the specific surface area and photocatalytic activity are significantly improved; (2) High-efficiency catalysis and recovery: the small particle size structure improves the quantum effect and the contact area of pollutants, the degradation rate of organic pollutants is ≥60% within 50min, which is more than 40% higher than that of traditional processes; the saturation magnetization intensity is ≥40emu / g, and the magnetic recovery efficiency is ≥90% within 30s, solving the problems of difficult recovery and easy residue; (3) Green and low cost: the co-precipitation method is used instead of the traditional sol-gel method, the energy consumption is reduced by more than 10%, no organic solvent is needed, environmental pollution is avoided, the raw materials (CAB35, polyaspartic acid and iron salt) are easy to obtain, the cost is reduced by 40% compared with the microemulsion method, and the method is suitable for large-scale production; (4) Wide application range: it can be adapted to the degradation of different types of organic pollutants (dyes, phenols, etc.), and is suitable for industrial wastewater treatment, photocatalytic reactor design and other scenes, and has significant industrialization potential. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a schematic diagram of the influence of CAB35 dosage on the particle size of the magnetic nanometer titanium dioxide; Figure 2 It is a schematic diagram of the influence of ammonia dosage on the particle size of the magnetic nanometer titanium dioxide; Figure 3 It is a photocatalytic degradation rate curve of methylene blue by the magnetic nanometer titanium dioxide prepared in Example 1.

[0019] Wherein, the vertical axis is the degradation rate (%), the horizontal axis is the degradation time (min); the degradation rate is 0% at 0 min, about 20% at 10 min, about 45% at 30 min, and 57.8% at 50 min. DETAILED DESCRIPTION

[0020] The application will be described in detail below with specific examples.

[0021] Example 1: Preparation of magnetic nano-titanium dioxide composite material using CAB35 as dispersant (1) Take 2g of ferrous chloride tetrahydrate (FeCl2·4H2O) and 3.3g of ferric chloride (FeCl3), dissolve in 25mL of deionized water to form a Fe 2+ / Fe 3+ mixed solution; (2) Take 0.05g of titanium dioxide powder (particle size 5~10nm), dissolve in 25mL of deionized water to form a TiO2 solution; (3) Take 1mL of the Fe 2+ / Fe 3+ mixed solution and 1mL of the TiO2 solution into a beaker, stir uniformly, and then ultrasonically treat for 5min under a power of 180W to form a precursor mixed system; (4) Add 300μL of CAB35 to the mixed system, and keep ultrasonic treatment under a power of 180W for 10min to ensure that the dispersant is uniformly adsorbed on the surface of the particles; (5) Increase the temperature of the system to 50℃, turn on the ultrasonic treatment under a power of 180W for 10-30min, drop 400μL of 25% ammonia water to adjust the pH of the reaction system to 9-11, and continue the ultrasonic treatment under a power of 180W for 30min to complete the hydrolysis and composite reaction; wrap the beaker with tin paper, and stand for 15min to observe the sedimentation; (6) Separate the magnetic particles using a 0.3T external magnetic field, wash with deionized water and ethanol alternately for 3 times, and dry in a 60℃ vacuum drying oven for 4h to obtain the target product Fe3O4 / TiO2 magnetic nano-composite material.

[0022] Example 2: Preparation of magnetic nano-titanium dioxide composite material using polyaspartic acid as dispersant (1) Preparation of the Fe 2+ / Fe 3+ mixed solution is the same as the operation of Example 1; (2) Take analytical pure tetrabutyl titanate, dissolve in anhydrous ethanol to prepare a 0.2mol / L solution; (3) Take 1mL of the above Fe 2+ / Fe 3+ mixed solution into a 10mL beaker, and protect for 5min by introducing high-purity nitrogen gas (flow rate 50mL / min) to prevent Fe2+ The above system was oxidized and then stirred for 5 min under 200 W ultrasonic to ensure homogeneity; 1 mL of tetrabutyl titanate ethanol solution was added dropwise into the above system under nitrogen protection and 200 W ultrasonic, and stirring was continued for 15 min to form a uniform mixture of "iron ion-titanium precursor"; (4) 200 μL of 30 wt% polyaspartic acid (PASP, industrial grade, biodegradable) aqueous solution was added dropwise into the mixture, and stirring was continued for 10 min under 55°C constant temperature water bath, 200 W ultrasonic, so that the PASP molecules were fully adsorbed on the particle surface to inhibit the initial agglomeration.

[0023] (5) Ammonia water (25 wt%, liquid droplet diameter 10-50 μm) was introduced at a rate of 0.8 mL / min to adjust the pH of the system to 10±0.5, and the reaction was continued for 30 min under 55°C and 200 W ultrasonic to promote the synergistic crystallization of Fe3O4 and TiO2; (6) The magnetic particles were separated by using a 0.3T external magnetic field, washed with deionized water and ethanol alternately for 4 times to remove the unreacted PASP and byproducts, and then dried in a 60°C vacuum drying oven for 5 h to obtain Fe3O4 / TiO2 magnetic nanocomposite material.

[0024] Example 3

[0025] In this example, the amount of CAB35 was 100 μL, 200 μL and 400 μL respectively, and other operations were substantially the same as those in Example 1, which will not be repeated here. The particle size and catalytic degradation performance of the obtained material were compared with those of the composite material obtained in Example 1, and the process and results are as follows: Methylene blue solution preparation: 50 mL of methylene blue aqueous solution with a concentration of 50 mg / L and 30 mL of methylene blue solution with a concentration of 30 mg / L were prepared as simulated pollutants. The initial absorbance (A0) was calibrated at 664 nm using a spectrophotometer.

[0026] Dark adsorption equilibrium: 0.05 g of magnetic nanometer titanium dioxide prepared in Example 3 and Example 1 was added into 50 mL of methylene blue solution, and the pollutant molecules were adsorbed on the surface of the catalyst under the condition of no light, and the adsorption-desorption equilibrium was reached after ultrasonic treatment for 30 min.

[0027] Photocatalytic reaction: 5 mL of reaction solution was taken every 10 min, and the catalyst was immediately separated by centrifuge or external magnetic field to obtain clear supernatant. After dilution by 5 times, the absorbance A(t) was measured at 664 nm using a spectrophotometer. After the degradation test was completed, the magnetic nanometer titanium dioxide could be recovered by an external magnetic field. The magnet was placed at the bottom of the beaker, and the magnetic catalyst was attracted to the bottom of the beaker. After the supernatant was poured off, the substrate was washed to obtain the recovery.

[0028] Degradation rate formula:

[0029] If there is a dark adsorption stage, the adsorption contribution needs to be deducted:

[0030] In the formula, A0: initial absorbance A dark : absorbance after dark adsorption A t : absorbance of every ten minutes sampling The detection and characterization results are shown in Table 1 and Figure 1 .

[0031] Table 1 Comparison of performance indicators of CAB35 dosage on the optimization of magnetic nano titanium dioxide CAB35 dosage (μL) Average particle size (nm) Photocatalytic performance (% methylene blue degradation within 50 min) Dispersion stability (particle size change rate after 24 h) 100 350 48~50 Particle size change rate 20%~22% 200 220 58~60 Particle size change rate 12%~14% 300 130 66 Particle size change rate < 8% 400 280 60~62 Particle size change rate 15%~17% Example 4

[0032] In this embodiment, 100 μL of tetrabutyl titanate is mixed in 8 mL of anhydrous ethanol to form a titanium source solution; the amount of 25% ammonia water is 300 μL, 500 μL, 600 μL, 700 μL, and 800 μL, respectively. The solution preparation and reflection process need to be carried out under 40°C, 180W ultrasonic treatment, and other operations are basically the same as those in Example 1, which will not be repeated here. The particle size and catalytic degradation performance of the obtained material are compared with those of the composite material obtained in Example 1, and the results are shown in Table 1 and Figure 2 .

[0033] Table 2 Comparison of performance indicators of different ammonia water dosage on the optimization of magnetic nano titanium dioxide Ammonia dosage (μL) Average particle size (nm) Reaction completeness Magnetic recovery efficiency (% within 30 s) Photocatalytic performance (% methylene blue degradation within 50 min) 300 409 Incomplete reaction (solution turbidity) <80 / 400 130 Complete reaction (solution uniformity) ≥92 57 500 322 Complete reaction ≥90 51 600 585 Complete reaction ≥88 38 700 816 Complete reaction ≥85 25 800 - Excessive hydrolysis (solution turbidity) <82 / Example 5

[0034] In this embodiment, the amount of 30wt% polyaspartic acid is 100 μL and 300 μL, respectively, and other operations are basically the same as those in Example 2, which will not be repeated here. The obtained material is compared with the composite material obtained in Example 2, and the results are shown in Table 3.

[0035] Table 3 Comparison of performance indicators of Fe3O4 / TiO2 magnetic nanocomposite prepared by using PASP as dispersant Performance parameters PASP dosage 100 μL group PASP dosage 200 μL group PASP dosage 300 μL group Average particle size (nm) 185.6 128.3 162.5 Polydispersity index (PDI) 0.26 0.22 0.28 Saturation magnetization (emu / g) 42.3 45.1 43.8 Magnetic recovery efficiency (within 30 s, 0.3T) 91.2% 95.6% 93.5% Photocatalytic degradation rate (50 min, methylene blue) 61.5% 67.2% 63.8% Dispersion stability (particle size change rate after 72 h at pH 7-11) 12.3% 7.8% 10.5% Biodegradability of dispersant Easily degradable (degradation rate > 80% in 90 days) Easily degradable (degradation rate > 80% in 90 days) Easily degradable (degradation rate > 80% in 90 days) Comparative Example 1

[0036] In this comparative example, 400 μL of 0.1 mol / L sodium silicate solution is used instead of CAB35, and other operations are basically the same as those in Example 1, which will not be repeated here.

[0037] Comparative Example 2 In this comparative example, the reaction temperature of step (5) was room temperature (20-25°C), and other operations were substantially the same as those of Example 1, which will not be repeated here.

[0038] The composite materials obtained from Comparative Examples 1 and 2 and Example 1 were compared, and the results are shown in the table below.

[0039] Performance parameters Example 1 Comparative Example 1 Comparative Example 2 Average particle size (nm) 130 1091.5 570.79 Polydispersity index (PDI) 0.25 >0.4 0.36 Saturation magnetization (emu / g) 44.5 38.2 40.8 Magnetic recovery efficiency (within 30 s, 0.3T) 95.0% 85-88% 91.5% Photocatalytic degradation rate (50 min, methylene blue) 66.0% 45.3% 52.2% Dispersion stability (particle size change rate after 72 h at pH 7-11) 8.0% 25.6% 18% Biodegradability of dispersant recalcitrant (90-day degradation rate < 30%) recalcitrant (90-day degradation rate < 20%) recalcitrant (90-day degradation rate < 30%) The above description of the embodiments is only for illustrating the technical concepts and characteristics of the present application, and the purpose is to enable those skilled in the art to understand the content of the present application and implement it. Those skilled in the art can obviously easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without having to undergo creative labor, and therefore, the above embodiments cannot be used to limit the protection scope of the present application. Any improvements and modifications made by those skilled in the art based on the disclosure of the present application without departing from the scope of the present application shall be covered within the protection scope of the present application.

Claims

1. A method for preparing a magnetic nanometer titanium dioxide composite material, characterized in that, The method comprises the following steps: (1) Fe 2+ / Fe 3+ The mixed solution is mixed with a titanium source to form a uniform metal ion-precursor mixed solution; (2) adding a dispersing agent into the mixed solution and stirring to obtain a reaction system; (3) heating and ultrasonic treating the system, and adding an alkali source to adjust the pH of the system to 9-11, and then continuing the nucleation reaction under the condition; (4) after the reaction, separating the magnetic particles by an external magnetic field, and then washing and vacuum drying to obtain the Fe3O4 / TiO2 magnetic nano-titanium dioxide composite material; The dispersing agent is cocamide propyl betaine or a 10wt%-50wt% polyaspartic acid aqueous solution.

2. The method according to claim 1, wherein the method comprises the following steps: 1) preparing a magnetic nano-Ti02 composite material by a sol-gel method. The Fe 2+ / Fe 3+ The molar ratio of divalent iron to trivalent iron in the mixed solution is 1: (1.5-2.5), and the Fe 2+ / Fe 3+ The total concentration of iron salt in the mixed solution is 0.05-0.4 mol / L.

3. The method according to claim 1, wherein the method is characterized by: The titanium source is one or more than two of tetrabutyl titanate, titanium isopropanol or nano-titanium dioxide powder.

4. The method according to claim 1, wherein the method is characterized by: The TiO2 in the titanium source and Fe 2+ / Fe 3+ The molar ratio of iron ions in the mixed solution is 1:(1-2).

5. The method according to claim 1, wherein the method is characterized by: The amount of the dispersing agent is 1-3% of the mass of the mixed solution.

6. The method according to claim 1, wherein the method is characterized by: The alkali source is 20%-30% ammonia water or a 0.1mol / L-0.5mol / L NaOH solution; the alkali source is added into the reaction system by dripping or atomization.

7. The method according to claim 1, wherein the method is characterized by: In step (3), the heating temperature is 50-70℃; the ultrasonic treating power is 150-450W, and the time is 10-30min; and the nucleation reaction time is 20-40min.

8. The method for preparing a magnetic nano-titanium dioxide composite material according to claim 1, characterized in that: The strength of the external magnetic field is 0.1-0.5T; the vacuum drying temperature is 50-70℃, and the time is 3-6h.

9. A magnetic nano-titanium dioxide composite material prepared by the method of any one of claims 1-8.

10. The application of the magnetic nano-titanium dioxide composite material of claim 9 in the degradation of organic pollutants.

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