Titanium dioxide particles doped with nitrogen and transition metals, methods for their preparation and use

Abstract

The present application provides nitrogen and transition metal doped titanium dioxide particles, a preparation method and application thereof. The nitrogen and transition metal doped titanium dioxide particles are composed of a core, an inner shell coating the core and an outer shell coating the inner shell, wherein the core is a magnetic carrier, the inner shell is silicon dioxide, and the outer shell is nitrogen and transition metal doped titanium dioxide, wherein the core and the inner shell constitute a composite magnetic carrier. Wherein, taking the mass of the surface elements of the nitrogen and transition metal doped titanium dioxide particles as 100%, the content of the nitrogen is 3.34% to 11.8%, and the content of the transition metal is 0.7% to 3%.

Description

Technical Field

[0001] This invention relates to the field of photocatalysis, and particularly to a nitrogen and transition metal-doped titanium dioxide particle, its preparation method, and its application. Background Technology

[0002] In recent years, with the rampant emission of organic dyes and the increasing severity of global pollution, photocatalytic materials for degradation have become a research hotspot. Domestic and international studies have shown that photocatalysis has excellent removal effects on hydrocarbons, carboxylic acids, dyes, nitrogen-containing organics, phenols, and chlorinated organics in water, especially for recalcitrant organic pollutants, where photocatalysis is of great significance. Among commonly used photocatalysts, TiO2 is currently the most valued. TiO2 is an excellent research subject due to its low cost, non-toxicity, large specific surface area, high catalytic activity, and corrosion resistance. TiO2 is an n-type semiconductor catalyst with a low-energy valence band and a high-energy conduction band, with a band gap of 3.2 eV in between. When the light energy is greater than or equal to the band gap width, electrons in the valence band transition to the conduction band, leaving holes (h) in the valence band. + This process generates highly active hole-electron pairs. During photocatalysis, holes (h...) + TiO2 has an extremely strong ability to acquire electrons; the redox potential of holes in its valence band is +2.7 eV. It can attract OH groups. - H2O molecules are converted into hydroxyl radicals ·OH with strong oxidizing power and high reactivity, while free oxygen in substances or solvents adsorbed on the TiO2 surface captures electrons to form highly active free radicals such as ·O2. Organic pollutants can be catalytically degraded into inorganic small molecules such as CO2 and H2O, and finally thoroughly purified. There are many reports on TiO2 as a photocatalyst at home and abroad, but in practical applications, several problems restrict the application of TiO2 photocatalysts: (1) Narrow spectral response range. The band gap of anatase TiO2 (E0 = 3.2 eV) can only absorb ultraviolet light with wavelengths less than or equal to 387 nm. Ultraviolet light accounts for only 3% to 4% of sunlight, which makes its light energy utilization rate low. (2) Difficult to recycle and low reusability. Therefore, how to develop a photocatalyst that can respond to visible light and is easy to recycle and reuse has become a research hotspot.

[0003] Doping is a common modification method for TiO2. Studies have shown that doping TiO2 with non-metallic or transition metal ions can alter the hybridization of the electron cloud, narrowing the band gap, redshifting the absorption band, and improving its visible light activity. TiO2 doping can be categorized into metal ion doping and non-metal ion doping. Doping with metal ions such as Sn(II), Nb(V), Co(II), Cu(II), and Ru(III) can improve its visible light activity, while non-metallic ions, primarily N, B, C, and S, are dominant. In recent years, research on metal-nonmetal N dual-doped TiO2 has gradually attracted attention, as the synergistic effect of metal and non-metal may increase its catalytic activity. Currently, research on metal-nonmetal N dual-doped TiO2 typically uses urea as the N source and the corresponding metal salt for preparation, but the visible light catalytic performance of the products is usually low. Summary of the Invention

[0004] One aspect of the present invention provides a nitrogen and transition metal doped titanium dioxide particle, which comprises a core, an inner shell covering the core, and an outer shell covering the inner shell, wherein the core is a magnetic carrier, the inner shell is silicon dioxide, and the outer shell is nitrogen and transition metal doped titanium dioxide, wherein the core and the inner shell constitute a composite magnetic carrier.

[0005] In one specific embodiment, the particle size of the composite magnetic carrier is 100 to 1000 nm.

[0006] In one specific embodiment, the particle size of the composite magnetic carrier is 200 to 500 nm.

[0007] In one specific embodiment, the transition metal is at least one of cobalt, iron, and copper.

[0008] In one specific embodiment, the nitrogen and transition metal doped titanium dioxide particles, taken as 100% by mass, contain 3.34% to 11.8% nitrogen and 0.7% to 3% transition metal. The nitrogen and transition metal doped titanium dioxide particles contain surface elements obtained by EDS elemental analysis, for example, surface elements obtained by EDS elemental analysis using a Hitachi SU8100 emission scanning electron microscope.

[0009] In one specific embodiment, the nitrogen and transition metal-doped titanium dioxide particles, by mass, constitute 100%, wherein the nitrogen content is 3.34% to 7.23% and the transition metal content is 0.9% to 3%. The nitrogen and transition metal-doped titanium dioxide particles are surface elements obtained by EDS elemental analysis, for example, surface elements obtained by EDS elemental analysis using a Hitachi SU8100 emission scanning electron microscope.

[0010] The second invention provides a method for preparing nitrogen and transition metal-doped titanium dioxide particles as described in any one of the first inventions, comprising the following steps:

[0011] 1) The composite magnetic carrier, the first solvent, and tetrabutyl titanate are mixed and dispersed to obtain the first dispersion;

[0012] 2) Mix the second solvent, the third solvent, and the surfactant, then mix with the first dispersant, and adjust the pH to acidic to obtain the second dispersion;

[0013] 3) Add a transition metal nitrate or a hydrate of a transition metal nitrate to the second dispersion to form a sol;

[0014] 4) Separate the solid components from the sol, wash and dry them to obtain a solid product;

[0015] 5) The solid product is calcined to obtain the nitrogen and transition metal doped titanium dioxide particles.

[0016] In one specific embodiment, the first solvent and the third solvent are independently anhydrous ethanol, and the second solvent is water.

[0017] In one specific embodiment, the surfactant is sodium dodecyl sulfate and / or sodium dodecylbenzenesulfonate.

[0018] In one specific embodiment, in step 1), the mass ratio of the composite magnetic carrier to tetrabutyl titanate is (0.1 to 1.2): 100.

[0019] In one specific embodiment, in step 2), the amount of surfactant added is such that the molar ratio of surfactant to titanium (element) is (2 to 3):50, for example, the molar ratio of surfactant to titanium (element) is 2.36:50.

[0020] In one specific embodiment, in step 3), the amount of transition metal nitrate or transition metal nitrate hydrate added is such that the molar ratio of transition metal ion to titanium (element) is (1 to 2):100, for example, the molar ratio of transition metal ion to titanium (element) is 1:100.

[0021] In one specific implementation, in step 2), the pH value is adjusted to 2 to 4.

[0022] In one specific embodiment, in step 1), the composite magnetic carrier and the first solvent are mixed, ultrasonically dispersed evenly, and then tetrabutyl titanate is added and stirred evenly to obtain the first dispersion.

[0023] In step 2), the second solvent, the third solvent, and the surfactant are mixed and then added dropwise to the first dispersant. The pH is adjusted to acidic with nitric acid to obtain the second dispersion.

[0024] In step 3), a transition metal nitrate or a transition metal nitrate hydrate is added to the second dispersion, and the mixture is stirred continuously at ambient temperature for 2 to 4 hours, and then left to stand at ambient temperature for 8 to 12 hours to form a sol.

[0025] In one specific embodiment, in step 4), the solid components are separated from the sol by centrifugation or magnetic adsorption.

[0026] In one specific embodiment, in step 5), the calcination temperature is 450 to 500°C, and the calcination time is 120 to 180 minutes.

[0027] The third invention provides the application of nitrogen and transition metal doped titanium dioxide particles according to any one of the first invention or the nitrogen and transition metal doped titanium dioxide particles prepared by the method according to any one of the second invention in the photocatalytic degradation of antibiotics and / or dyes.

[0028] In one specific embodiment, the application is for the photocatalytic degradation of ciprofloxacin and / or rhodamine B.

[0029] The beneficial effects of this invention are:

[0030] While introducing Fe3O4 magnetic cores facilitates catalyst recovery and redshifts the absorption band, reports indicate that directly coating TiO2 with Fe3O4 can lead to a decrease in catalytic efficiency. Therefore, this invention employs transition metal nitrates as both an N source and a transition metal ion source to dope TiO2 with N and transition metals, effectively increasing the transition metal / N content ratio and enhancing its visible light photocatalytic performance. Simultaneously, a SiO2 layer separates the Fe3O4 magnetic cores, preventing TiO2 from affecting the magnetic cores at high temperatures and acting as an adhesive to adsorb more TiO2, further improving the catalytic effect. Then, using chemical methods, a TiO2 layer with a high transition metal / N ratio and doped with transition metal elements, resulting in a visible light-responsive magnetic nanocatalyst with a double-shell core structure, is further coated onto the surface of the magnetic particles coated with a hydroxyl SiO2 layer. This magnetic nanocatalyst, through the surface coating of a doped TiO2 layer with a high transition metal / N ratio, introduces defect sites or alters the crystallinity of TiO2, reducing the energy required for electron excitation and improving visible light photocatalytic activity. Simultaneously, the introduction of Fe3O4 magnetic cores allows for easy catalyst recovery and reuse through the application of an external magnetic field. Furthermore, the introduction of a SiO2 layer on the surface of the Fe3O4 magnetic cores prevents damage to the magnetic cores from high temperatures and acidic environments, reducing the impact of the magnetic cores on the photocatalytic efficiency of the TiO2 layer.

[0031] The nitrogen- and transition metal-doped titanium dioxide particles of this invention exhibit high visible light photocatalytic efficiency for the catalytic degradation of antibiotic wastewater and the organic dye Rhodamine B under visible light conditions, achieving degradation efficiencies of 99.7% and 98.8% for antibiotic wastewater and Rhodamine dye solution, respectively. Furthermore, they are easy to separate, recover, and recycle, showing promising application prospects in catalyzing water and air pollution. Attached Figure Description

[0032] Figure 1 The XRD comparison diagrams of N / Co-TiO2@SiO2@Fe3O4 prepared in Example 1 with Fe3O4 particles and TiO2 particles are shown.

[0033] Figure 2 The EDS elemental analysis diagram of the N / Cu-TiO2@SiO2@Fe3O4 particles prepared in Example 3 is shown.

[0034] Figure 3 The kinetic curves of visible light photocatalytic degradation of ciprofloxacin aqueous solution by the particulate products prepared in Examples 1 to 3, as well as Comparative Examples 1 and 2, are shown.

[0035] Figure 4 The kinetic curves of visible light catalytic degradation of Rhodamine B aqueous solution in Examples 1, 1, and 2 are shown. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments. However, the embodiments of the present invention are merely illustrative examples and should not be construed as limiting the present invention under any circumstances.

[0037] Example 1

[0038] Preparation of N / Co-TiO2@SiO2@Fe3O4 particles

[0039] 1) Add 40 mL of anhydrous ethanol and 54 mg of 200-500 nm SiO2@Fe3O4 magnetic nanoparticles to a 250 mL three-necked flask, disperse them evenly in an ultrasonic cleaner, then add 0.05 mol of tetrabutyl titanate, and stir mechanically for 30 min to obtain the first dispersion.

[0040] 2) Mix 9 mL of deionized water, 25 mL of anhydrous ethanol and 2.36 mmol of SDS, then slowly add the mixture dropwise to the first dispersion. Adjust the pH to 3.0 with nitric acid to obtain the second dispersion.

[0041] 3) Add 0.5 mmol Co(NO3)2·6H2O to the second dispersion, stir continuously at ambient temperature for 2 hours, and then let stand at ambient temperature overnight to form a sol;

[0042] 4) Centrifuge the sol at 8000 rpm for 3 min. After centrifugation, remove the supernatant, wash three times with deionized water, then wash three times with anhydrous ethanol, and then dry at 100℃ for 4 h to obtain the solid product.

[0043] 5) The solid product was placed in a muffle furnace and calcined at 450°C for 120 min in an air atmosphere to obtain N / Co-TiO2@SiO2@Fe3O4 particles.

[0044] XRD analysis of N / Co-TiO2@SiO2@Fe3O4 particles was performed using a D8 ADVANCE X-ray powder diffractometer (Co target, Bruker, Germany), with Fe3O4 and TiO2 particles used as controls. Figure 1 .

[0045] Depend on Figure 1 The results show that the N / Co-TiO2@SiO2@Fe3O4 particles exhibit the corresponding anatase TiO2 diffraction peaks (101), (004), (200), and (105) at 2θ = 25.4°, 37.8°, 48.1°, 53.9°, 54.3°, and 62.8°, respectively. This indicates that TiO2 has been successfully coated on the outer layer of SiO2@Fe3O4, and the characteristic peaks of Fe3O4 at 2θ = 35.6° (311) and 57.2° (511) are significantly weakened.

[0046] The N / Co-TiO2@SiO2@Fe3O4 particle products were analyzed by EDS using a Hitachi SU8100 scanning electron microscope. The results showed that, based on the total mass of the surface elements of the N / Co-TiO2@SiO2@Fe3O4 particles analyzed by the Hitachi SU8100 scanning electron microscope as 100%, the N content was 7.23% and the Co content was 0.91%.

[0047] Example 2

[0048] Preparation of N / Fe-TiO2@SiO2@Fe3O4 particles

[0049] 0.14552g Co(NO3)2·6H2O was replaced with 0.20200g Fe(NO3)3·9H2O to obtain N / Fe-TiO2@

[0050] SiO2@Fe3O4 particles.

[0051] Everything else is the same as in Example 1.

[0052] The N / Fe-TiO2@SiO2@Fe3O4 particle products were analyzed by EDS using a Hitachi SU8100 scanning electron microscope. The results showed that, based on the total mass of the surface elements of the N / Fe-TiO2@SiO2@Fe3O4 particles analyzed by EDS using the Hitachi SU8100 scanning electron microscope as 100%, the N content was 3.34% and the Fe content was 2.98%.

[0053] Example 3

[0054] Preparation of N / Cu-TiO2@SiO2@Fe3O4 particles

[0055] 0.14552g Co(NO3)2·6H2O was replaced with 0.09378g Cu(NO3)2·xH2O to obtain N / Cu-TiO2@

[0056] SiO2@Fe3O4 particles.

[0057] Everything else is the same as in Example 1.

[0058] The N / Cu-TiO2@SiO2@Fe3O4 particle products were analyzed by EDS using a Hitachi SU8100 emission scanning electron microscope. The results are shown in the figure. Figure 2 ,Depend on Figure 2 It can be seen that, based on the total mass of the surface elements of N / Cu-TiO2@SiO2@Fe3O4 particles analyzed by EDS using a Hitachi SU8100 emission scanning electron microscope, the N content is 6.14% and the Cu content is 0.96%.

[0059] Comparative Example 1

[0060] 1) Mix 60 mg of SiO2@Fe3O4 magnetic nanoparticles with 40 mL of deionized water, add the mixture to a 250 mL three-necked flask, and disperse it evenly in an ultrasonic cleaner to obtain the first dispersion.

[0061] 2) Dissolve 0.84g of urea in 5mL of deionized water to obtain an aqueous urea solution;

[0062] 3) Add urea aqueous solution and 5 mL tetrabutyl titanate to the first dispersion by vigorous stirring, keep at 40°C for 2 hours, and then sonicate at 40°C for 40 min to obtain the second dispersion.

[0063] 4) Centrifuge the second dispersion at 8000 rpm for 3 min. After centrifugation, remove the supernatant, wash three times with deionized water, then wash three times with anhydrous ethanol, and then dry at 100℃ for 4 h to obtain the solid product.

[0064] 5) The solid product was placed in a muffle furnace and calcined at 450°C for 120 min in an air atmosphere to obtain TiO2@SiO2@Fe3O4 particles.

[0065] Comparative Example 2

[0066] 1) Mix 60 mg of SiO2@Fe3O4 magnetic nanoparticles with 40 mL of deionized water, add the mixture to a 250 mL three-necked flask, and disperse it evenly in an ultrasonic cleaner to obtain the first dispersion.

[0067] 2) Dissolve 0.84g of urea in 5mL of deionized water to obtain an aqueous urea solution;

[0068] 3) Dissolve 3.3g of CoCl2·6H2O in 5mL of water to obtain an aqueous solution of CoCl2;

[0069] 4) Add urea aqueous solution, CoCl2 aqueous solution and 5 mL tetrabutyl titanate to the first dispersion solution by slow and sequential addition, and maintain at 40°C for 2 hours. Then sonicate at 40°C for 40 min to obtain the second dispersion solution.

[0070] 5) Centrifuge the second dispersion at 8000 rpm for 3 min. After centrifugation, remove the supernatant, wash three times with deionized water, then wash three times with anhydrous ethanol, and then dry at 100℃ for 4 h to obtain the solid product.

[0071] 6) The solid product was placed in a muffle furnace and calcined at 450°C for 120 min in an air atmosphere to obtain N / Co-TiO2@SiO2@Fe3O4 particles.

[0072] The N / Co-TiO2@SiO2@Fe3O4 particle products were analyzed by EDS using a Hitachi SU8100 scanning electron microscope. The results showed that, based on the total mass of the surface elements of the N / Co-TiO2@SiO2@Fe3O4 particles analyzed by the Hitachi SU8100 scanning electron microscope as 100%, the N content was 21.84% and the Co content was 1.78%.

[0073] Performance testing

[0074] 1. Visible light photocatalytic degradation of ciprofloxacin

[0075] 3 mg of the granules prepared in Examples 1 to 3, as well as Comparative Examples 1 and 2, were added to 3 mL of 0.017 mmol / L solution, respectively. -1 In a ciprofloxacin aqueous solution, a xenon lamp was turned on while the stirrer was running for photocatalytic reaction. Samples were taken every half hour, and the reaction was completed after 3 hours. Each sample was centrifuged, and the supernatant was used to determine its ultraviolet spectrum. The results are shown below. Figure 4 .

[0076] Depend on Figure 3 It can be seen that when the particles prepared in Comparative Examples 1 and 2 were added to the ciprofloxacin aqueous solution, the degradation rates of ciprofloxacin were only 26.6% and 42.2%, respectively, after 3 hours of visible light irradiation. In contrast, after adding the particles prepared in Examples 1 to 3, the degradation rate of ciprofloxacin under visible light irradiation was significantly increased, and ciprofloxacin was basically completely degraded within 3 hours. The degradation rates of the particles prepared in Examples 1 to 3 reached 99.13%, 91.56%, and 99.67%, respectively. Among them, the particles prepared in Examples 1 and 3 showed a very fast degradation rate in the first hour, with ciprofloxacin degradation rates reaching 86.43% and 98.91%, respectively, demonstrating high visible light photocatalytic activity.

[0077] 2. Visible light photocatalytic degradation of Rhodamine B

[0078] 50g of the granules prepared in Example 1, Comparative Example 1, and Comparative Example 2 were added to 50mL of 4mg / L Rhodamine B aqueous solution, respectively. The xenon lamp was turned on simultaneously with the stirring device, and a timer was started for continuous irradiation. Samples were taken every half hour, and the reaction was stopped after 3 hours. Each sample was centrifuged, and the ultraviolet absorption of the supernatant was measured after centrifugation. The results are shown in [Figure number missing]. Figure 4 .

[0079] Depend on Figure 4 It can be seen that, after 3 hours of visible light irradiation, the degradation rates of Rhodamine B in Comparative Examples 1 and 2 were only 59.5% and 72.1%, respectively. In contrast, the particles prepared in Example 1 showed a significantly faster degradation rate of Rhodamine B under visible light irradiation. Furthermore, the particles prepared in Example 1 could essentially completely degrade Rhodamine B within 3 hours, achieving a degradation rate of 98.8%, thus exhibiting high visible light photocatalytic activity.

[0080] While the present invention has been described with reference to specific embodiments, those skilled in the art will understand that various changes can be made without departing from the true spirit and scope of the invention. Furthermore, numerous modifications can be made to the subject, spirit, and scope of the invention to suit specific situations, materials, material compositions, and methods. All such modifications are included within the scope of the claims of the present invention.

Claims

1. A nitrogen and transition metal-doped titanium dioxide particle, comprising a core, an inner shell covering the core, and an outer shell covering the inner shell, wherein, The core is a magnetic carrier, the inner shell is silicon dioxide, and the outer shell is nitrogen and transition metal-doped titanium dioxide, wherein the core and the inner shell constitute a composite magnetic carrier SiO2@Fe3O4; the transition metal is cobalt and / or copper; The nitrogen and transition metal-doped titanium dioxide particles, with a surface element content of 3.34% to 11.8% and a transition metal content of 0.7% to 3%, are calculated as 100% by mass. The nitrogen and transition metal-doped titanium dioxide particles are prepared according to the following method: 1) The composite magnetic carrier SiO2@Fe3O4, the first solvent, and tetrabutyl titanate were mixed and dispersed to obtain the first dispersion; 2) Mix the second solvent, the third solvent, and the surfactant, then mix with the first dispersion, and adjust the pH to acidic to obtain the second dispersion; 3) Add a transition metal nitrate or a hydrate of a transition metal nitrate to the second dispersion to form a sol; 4) Separate the solid components from the sol, wash and dry them to obtain a solid product; 5) The solid product is calcined to obtain the nitrogen and transition metal-doped titanium dioxide particles; The first solvent and the third solvent are independently anhydrous ethanol, and the second solvent is water; The surfactant is sodium dodecyl sulfate and / or sodium dodecylbenzenesulfonate.

2. The nitrogen- and transition metal-doped titanium dioxide particles according to claim 1, characterized in that, The nitrogen and transition metal doped titanium dioxide particles have a surface element content of 3.34% to 7.23% and a transition metal content of 0.9% to 3%, respectively, based on the mass of the surface elements.

3. The nitrogen- and transition metal-doped titanium dioxide particles according to claim 1, characterized in that, In step 1), the mass ratio of the composite magnetic carrier SiO2@Fe3O4 to tetrabutyl titanate is (0.1 to 1.2):100; and / or In step 2), the amount of surfactant added is such that the molar ratio of surfactant to titanium is (2 to 3):50; and / or In step 3), the amount of transition metal nitrate or transition metal nitrate hydrate added is such that the molar ratio of transition metal ions to titanium is (1 to 2):

100.

4. The nitrogen- and transition metal-doped titanium dioxide particles according to claim 1, characterized in that, In step 2), adjust the pH value to 2 to 4.

5. The nitrogen- and transition metal-doped titanium dioxide particles according to claim 1, characterized in that, In step 1), the composite magnetic carrier SiO2@Fe3O4 and the first solvent are mixed and ultrasonically dispersed evenly. Then, tetrabutyl titanate is added and stirred evenly to obtain the first dispersion. In step 2), the second solvent, the third solvent, and the surfactant are mixed and then added dropwise to the first dispersion. The pH is adjusted to acidic with nitric acid to obtain the second dispersion. In step 3), a transition metal nitrate or a transition metal nitrate hydrate is added to the second dispersion, and the mixture is stirred continuously at ambient temperature for 2 to 4 hours, and then allowed to stand at ambient temperature for 8 to 12 hours to form a sol.

6. The nitrogen- and transition metal-doped titanium dioxide particles according to claim 1, characterized in that, In step 4), the solid components are separated from the sol by centrifugation or magnetic adsorption; and / or In step 5), the calcination temperature is 450 to 500°C and the calcination time is 120 to 180 minutes.

7. The use of nitrogen and transition metal-doped titanium dioxide particles according to any one of claims 1 to 6 in the photocatalytic degradation of antibiotics and / or dyes.

8. The application according to claim 7, characterized in that, The application is for the photocatalytic degradation of ciprofloxacin and / or rhodamine B.

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