Simple preparation method of black titanium dioxide

Abstract

The invention discloses a simple preparation method of black titanium dioxide, which comprises the following steps: taking sodium chloride-potassium chloride-urea as a molten salt system, directly mixing sodium chloride-potassium chloride-urea with a titanium source (such as titanyl sulfate or P25 and the like), and performing one-step pyrolysis in a muffle furnace in a static air atmosphere to prepare the black titanium dioxide. The phase of the black titanium dioxide is a compound of C and N co-doped anatase phase TiO2 and TiO. In the pyrolysis process, the oxygen removal and pore forming effects of a sodium chloride-potassium chloride-urea molten salt system and the reduction effect in the urea pyrolysis process are fully exerted. The whole preparation process is in a static air atmosphere, only one pyrolysis process is needed, the preparation cost is low, the method is simple and convenient, and large-scale application is easy to achieve; the obtained black titanium dioxide can effectively degrade methylene blue organic pollutants under the irradiation of visible light of a 300W xenon lamp with an optical filter.

Description

Technical Field

[0001] The invention belongs to the technical fields of green chemistry and photocatalytic nanomaterials, and particularly relates to a simple preparation method of black titanium dioxide. Background Art

[0002] As the climate and energy crises become increasingly severe, renewable energy sources such as solar energy, wind energy, geothermal energy, biomass energy, hydropower, and tidal energy are gradually attracting people's attention. In particular, solar energy, as one of the most abundant and clean resources, has attracted particular attention. According to statistics, the amount of solar radiation reaching the earth's surface each year is 3.00×10 24 With solar energy exceeding 5,000 times global energy consumption in 2021, solar energy is expected to play a key role in the transition to a sustainable society. However, in the field of photocatalysis, developing materials with high solar radiation capture efficiency is crucial for fully utilizing solar energy. Due to its unique physicochemical properties, the "black" semiconductor material, black titanium dioxide (B-TiOx), holds promise as a broad-spectrum photocatalytic material with broad responsiveness from the ultraviolet to the visible region.

[0003] Black titanium dioxide was originally named for its "black" appearance. It is generally believed that if a material meets any of the following criteria, it is defined as black titanium dioxide: (i) titanium dioxide is not white, and its color can be black, gray, brown, dark blue, etc.; (ii) the band gap is narrower than that of original titanium dioxide, anatase titanium dioxide is 3.2eV, rutile titanium dioxide is 3.0eV, and the band gap of black titanium dioxide is 1.54eV; (iii) the light absorption wavelength is greater than 400nm; (iv) the surface and subsurface structure are disordered; (v) the chemical formula is TiOx, where (0 <x<2)。

[0004] Black titanium dioxide mainly includes four types: fully crystalline (such as TiO and Ti2O3), doped bodies where bulk lattice oxygen is replaced by other elements (such as N and C), face-doped crystals where the crystal faces are doped, and face-defect bodies with oxygen defects. Preparation often requires high-temperature treatment at 800-1400°C, and high-temperature treatment also requires the participation of gases such as H2 and NH3 in the reaction, or the synthesis process must be carried out through multiple steps.

[0005] CN118343829A discloses a method for preparing black titanium dioxide, comprising dissolving sulfur powder in oleylamine to obtain a sulfur-oleylamine solution; grinding tetrabutyl titanate in air for 1 to 3 hours to obtain a white powder; fully dissolving the white powder in the sulfur-oleylamine solution under stirring to obtain a reaction solution; placing the reaction solution in a closed reactor and subjecting it to a hydrothermal reaction at 160 to 220°C for 16 to 24 hours to obtain a gel; washing the gel with ethanol by centrifugation and drying to obtain a brown powder; and fully mixing the brown powder with sulfur powder, placing the mixture in a closed reactor and heat-treating it at 500 to 700°C for 40 to 150 minutes under argon protection, and then naturally cooling it to room temperature to obtain a black titanium dioxide product. The black titanium dioxide product was used for the photocatalytic degradation of rhodamine B with an initial concentration of 10 mg / L. After 150 minutes of degradation, the concentration of rhodamine B dropped to 8.78 mg / L, and the degradation rate reached 12.2%, indicating that black titanium dioxide has a certain ability to photocatalytically degrade rhodamine B in the visible spectrum region.

[0006] The preparation method of black titanium dioxide disclosed in CN111847503A is to mix high-purity titanium dioxide powder and high-purity titanium powder evenly, spread them flatly in an alumina crucible, calcine them at 1200-1450°C in an argon atmosphere and keep them warm for at least 6 hours, and remove the crucible after natural cooling in the furnace to obtain black titanium dioxide (B-TiOx).

[0007] CN113499762A discloses a simple method for preparing a blue / black titanium dioxide photocatalytic material. The method comprises wrapping P25 tightly with aluminum foil and pressing the P25 into a sheet to remove interstitial oxygen. The P25 is then heat treated in a tube furnace at 550-620°C for 8-12 hours under an inert gas pressure of 0.15 MPa. The aluminum foil is then used to in-situ reduce the P25 to obtain a blue / black titanium dioxide photocatalytic material. 2-x .

[0008] CN103962117A discloses a method for preparing color-adjustable titanium dioxide with high-efficiency photocatalytic activity. The method comprises mixing a flammable and explosive metal hydride (sodium borohydride, lithium aluminum hydride, sodium hydride, calcium hydride or titanium hydride) with titanium dioxide in an inert atmosphere (argon, helium or nitrogen), heating the mixture at 200-400°C for 5 minutes to 10 hours, washing with water and ethanol, and then vacuum drying at 30-100°C to produce titanium dioxide with a color ranging from light gray to blue and finally to black.

[0009] The preparation method of black titanium dioxide powder disclosed in CN110790305A is to mix ascorbic acid powder with titanium dioxide powder, keep the mixture at 400-500°C for 1-3 hours under an inert atmosphere (nitrogen), wash with water, and dry to obtain black titanium dioxide.

[0010] Lee et al. (E.Lee, C.Park, DWLee, G.Lee, H.-Y.Park, J.Jang, H.-J.Kim, Y.-E.Sung, Y.Tak and SJYoo, ACS Catal., 2020, 10, 12080–12090.) prepared N and C co-doped black titanium dioxide in a 5% H2 / Ar atmosphere at 800°C using urea as a dopant.

[0011] As can be seen from the above, most existing black titanium dioxide production processes involve a two-step process of low-temperature hydrothermal and heat treatment, or thermal reduction with hydrogen (or metal, metal hydride, or ascorbic acid) in an inert gas atmosphere. These processes are complex, time-consuming, and require the consumption of high-value gases such as argon and H2. This not only poses a threat to production safety but also increases production costs, limiting the large-scale practical application of black titanium dioxide. Summary of the Invention

[0012] The purpose of the present invention is to provide a simple preparation method of black titanium dioxide.

[0013] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: sodium chloride, potassium chloride, urea and titanium source are ground and mixed evenly, and then placed in a crucible, the crucible lid is covered, and a constant temperature of 200-250°C is first maintained in a static air atmosphere for 20-40 minutes, then the temperature is raised to 400-450°C and maintained for 20-40 minutes, and finally the temperature is raised to 600-700°C and calcined for 1-5 hours. After calcination, the mixture is naturally cooled to room temperature to obtain black titanium dioxide.

[0014] In the above preparation method, the mass ratio of the titanium source to sodium chloride, potassium chloride and urea is preferably 1:1-3:1.25-3.75:2.5-7.5, and the mass ratio of the total mass of sodium chloride and potassium chloride to urea is preferably 0.45-1.35.

[0015] In the above preparation method, it is further preferred that the mass ratio of the titanium source to sodium chloride, potassium chloride and urea is 1:2:2.5:5:1.

[0016] The titanium source is any one of titanyl sulfate and P25 or a mixture of the two.

[0017] Furthermore, in the above preparation method, it is preferred to first maintain a constant temperature of 200° C. for 30 minutes in a static air atmosphere, then increase the temperature to 450° C. and maintain for 30 minutes, and finally increase the temperature to 650° C. and calcine for 2 to 4 hours.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. The present invention directly mixes the titanium source with the low-melting-point eutectic salt and performs in-situ pyrolysis, giving full play to the oxygen-displacing effect of the ionic salt of the eutectic salt and the reducing effect of urea, so that anatase TiO2 and TiO are generated in one step, and C and N co-doped black titanium dioxide is directly obtained, which simplifies the preparation process of black titanium dioxide.

[0020] 2. The entire preparation process of the present invention has only one step of pyrolysis, and adopts a low-cost sodium chloride-potassium chloride-urea eutectic salt system. The sodium chloride-potassium chloride can be recycled and reused, which has the advantages of low preparation cost, simple method, and easy large-scale application.

[0021] 3. The black titanium dioxide prepared by the present invention can catalytically degrade organic pollutants (such as methylene blue, etc.) under visible light. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 These are the appearance colors of black titanium dioxide obtained at different calcination temperatures, where (a) is 600°C, (b) is 650°C, and (c) is 700°C.

[0023] Figure 2 This is the XRD pattern of black titanium dioxide obtained under different urea dosage conditions.

[0024] Figure 3 This is the adsorption diagram of methylene blue by black titanium dioxide obtained under different urea dosage conditions.

[0025] Figure 4 This is the XRD pattern of black titanium dioxide obtained under different potassium chloride-sodium chloride dosage conditions.

[0026] Figure 5 This is the adsorption diagram of methylene blue by black titanium dioxide obtained under different potassium chloride-sodium chloride dosage conditions.

[0027] Figure 6 is the XRD pattern of black titanium dioxide obtained at different calcination times.

[0028] Figure 7 This is a diagram showing the photocatalytic removal of methylene blue by black titanium dioxide obtained at different calcination times.

[0029] Figure 8 This is the first-order kinetic simulation diagram of the photocatalytic removal of methylene blue by black titanium dioxide obtained at different calcination times.

[0030] Figure 9 This is a diagram of the active species of black titanium dioxide photocatalytic degradation of methylene blue obtained by calcination for 2 hours.

[0031] Figure 10 This is an SEM image of black titanium dioxide obtained by calcining for 2 hours, where (a) is a partial image and (b) is a full image.

[0032] Figure 11 This is the energy spectrum of black titanium dioxide obtained by calcining for 2 hours.

[0033] Figure 12 This is the infrared spectrum of black titanium dioxide obtained by calcining for 2 hours.

[0034] Figure 13 This is the physical adsorption isotherm of N2 and the pore size distribution diagram of the black titanium dioxide obtained by calcination for 2 hours (inset).

[0035] Figure 14 This is the UV-visible absorption spectrum of the black titanium dioxide suspension (the solvent is water) obtained by calcining for 2 hours. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and examples, but the protection scope of the present invention is not limited to these examples.

[0037] Example 1

[0038] Preparation of black titanium dioxide at different calcination temperatures

[0039] 1g of titanium oxysulfate, 2.5g of urea, 2g of sodium chloride and 2.5g of potassium chloride were ground and mixed in an agate mortar, then transferred to a 40mL crucible, covered with a crucible lid, and placed in a muffle furnace. The temperature was first kept at 200°C for 30 minutes, then raised to 450°C and maintained for 30 minutes, and finally raised to 600°C, 650°C and 700°C for 1 hour respectively to complete the high-temperature treatment of the sample. After the muffle furnace naturally cooled to room temperature, the calcined product was taken out. The crude sample was washed with deionized water for 3 to 5 times to remove residual impurities. After separation of the solid and liquid by filtration, the filter cake was placed in an oven for drying, and finally black titanium dioxide was obtained, which was recorded as BT. T-600 , BT T-650 , BT T-700 .

[0040] Depend on Figure 1 As can be seen from the sample color chart, the sample calcined at 600°C is brown; the sample calcined at 650°C is brown-black; and the sample calcined at 700°C is gray-brown. In other words, the sample prepared at 650°C tends to be pure black. Therefore, 650°C is the optimal calcination temperature in all subsequent examples.

[0041] Example 2

[0042] Preparation of black titanium dioxide under different urea dosage conditions

[0043] Weigh 1g of titanium oxysulfate, 2g of sodium chloride and 2.5g of potassium chloride, and change the amount of urea (U) to 2.5g, 5.0g and 7.5g respectively. Grind and mix evenly in an agate mortar, then transfer to a 40mL crucible, cover the crucible lid, place in a muffle furnace, keep a constant temperature of 200℃ for 30 minutes, then heat to 450℃ and keep for 30 minutes, and finally heat to 650℃ and roast for 1 hour to complete the high temperature treatment of the sample. After the muffle furnace cools naturally to room temperature, take out the roasted product. Wash the crude sample with deionized water 3 to 5 times to remove residual impurities. After separating the solid and liquid by filtration, the filter cake is placed in an oven to dry, and finally black titanium dioxide is obtained, which is recorded as BT. U-2.5 , BT U-5.0 , BT U-7.5 .

[0044] Depend on Figure 2 It can be seen that with the increase of urea dosage, the characteristic diffraction peak corresponding to the anatase phase at 2θ of 25.3°(101) first becomes passivated and then enhanced; while the half-peak width of the characteristic diffraction peaks corresponding to the TiO phase at 2θ of 37.24°(111) and 43.19°(200) gradually becomes wider, indicating that the increase of urea dosage in a certain range promotes the transformation of anatase and TiO towards low crystallinity.

[0045] Depend on Figure 3 It can be seen that when the urea dosage increases from 2.5g to 5.0g and 7.5g, respectively, the equilibrium removal efficiency of the obtained black titanium dioxide for methylene blue increases from 53.3% to 92.7% and 98.6%, respectively. From the perspective of the increase in the equilibrium removal efficiency of methylene blue and the reduction in reagents, the present invention uses a urea dosage of 5.0g as the optimal sample preparation condition.

[0046] Example 3

[0047] Preparation of black titanium dioxide under different potassium chloride-sodium chloride dosage conditions

[0048] Weigh 1g of titanium oxysulfate and 5.0g of urea, change the total mass of sodium chloride and potassium chloride to 2.25g, 4.5g and 6.75g respectively (the mass ratio of sodium chloride and potassium chloride is 1:1.25), and the mass ratio of the total mass of sodium chloride-potassium chloride to urea to 0.45, 0.9 and 1.35 respectively. Grind and mix evenly in an agate mortar and transfer to a 40mL crucible. Cover the crucible lid and place it in a muffle furnace. Keep the temperature at 200℃ for 30 minutes, then heat it to 450℃ and keep it for 30 minutes, and finally heat it to 650℃ and roast it for 1 hour to complete the high-temperature treatment of the sample. After the muffle furnace cools naturally to room temperature, take out the roasting product. Wash the crude sample with deionized water 3 to 5 times to remove residual impurities. After separating the solid and liquid by suction filtration, the filter cake is placed in an oven to dry, and finally black titanium dioxide is obtained, which is recorded as BT.S-0.45 , BT S-0.9 , BT S-1.35 .

[0049] Depend on Figure 4 The XRD pattern shows that with the increase of the amount of potassium chloride-sodium chloride, the characteristic diffraction peak corresponding to the anatase phase at 2θ of 25.3° (101) shows an amorphous passivation state and has no obvious change. However, the characteristic diffraction peaks corresponding to the TiO phase at 2θ of 37.24° (111), 43.19° (200), 62.85° (220) are significantly enhanced, indicating that the concentration and crystallization degree of TiO are significantly enhanced.

[0050] Depend on Figure 5 It can be seen that as the mass ratio of the total amount of potassium chloride and sodium chloride to urea increases from 0.45 to 0.9 and 1.35, respectively, the equilibrium removal rate of dimethyl blue by the obtained black titanium dioxide increases from 45.6% to 79.8% and 97.7%, respectively. From the perspective of the increase in the equilibrium removal rate of dimethyl blue by the total amount of potassium chloride and sodium chloride and reagent savings, the present invention adopts a mass ratio of the total amount of potassium chloride and sodium chloride to urea of ​​0.90 as the optimal preparation condition.

[0051] Example 4

[0052] Preparation of black titanium dioxide at different calcination times

[0053] 1g of titanium oxysulfate, 5.0g of urea, 2g of sodium chloride and 2.5g of potassium chloride were ground and mixed evenly in an agate mortar, then transferred to a 40mL crucible, covered with a crucible lid, and placed in a muffle furnace. The temperature was kept constant at 200°C for 30 minutes, then raised to 450°C and maintained for 30 minutes, and finally raised to 650°C and roasted for 1 hour, 2 hours, 3 hours, 4 hours and 5 hours respectively to complete the high-temperature treatment of the sample. After the muffle furnace naturally cooled to room temperature, the roasted product was taken out. The crude sample was washed with deionized water for 3 to 5 times to remove residual impurities. After separation of the solid and liquid by filtration, the filter cake was placed in an oven for drying, and finally black titanium dioxide was obtained, which was recorded as BT. 1h , BT 2h , BT 3h , BT 4h , BT 5h .

[0054] like Figure 6As shown in the figure, the intensity of the characteristic diffraction peaks corresponding to the (101) and (200) crystal planes of anatase TiO2 at 2θ = 25.3° and 48.1° (JCPSD-No. 21-1272) increases significantly with increasing calcination time. However, the symmetry and peak intensity of the characteristic diffraction peaks corresponding to the TiO phase at 2θ = 37.24° (111), 43.19° (200), and 62.85° (220) decrease to a certain extent with increasing calcination time. This indicates that increasing calcination time promotes the transformation of TiO to TiO2 to a certain extent.

[0055] Figure 7 The photocatalytic degradation of methylene blue by black titanium dioxide prepared at different calcination times is shown in Figure 2. The photocatalytic reaction conditions are: methylene blue concentration 20 mg / L, black titanium dioxide dosage 0.02 g, reaction temperature 25°C, and light source: a 300W xenon lamp with a filter. Figure 7 It can be seen that with the increase of illumination time, the concentration of methylene blue shows a downward trend, indicating that black titanium dioxide with different calcination times has a photocatalytic degradation effect on methylene blue. 2h , BT 3h , BT 4h The concentration of methylene blue drops rapidly to 0 within 1 hour of illumination, so the appropriate calcination time is 2 to 4 hours.

[0056] Figure 8 It will Figure 7 The data in the figure are obtained by using the first-order kinetic model. It can be seen that the photocatalytic degradation rate constant k of black titanium dioxide with different calcination times for methylene blue is in the following order: BT 2h (0.03181)>BT 3h (0.01503)>BT 4h (0.01358)>BT 1h (0.01433)>BT 5h (0.0058), indicating that the black titanium dioxide prepared with a calcination time of 2 h has the best photocatalytic degradation effect on methylene blue.

[0057] Figure 9 After adding four quenchers (benzoquinone, histidine, isopropanol, EDTA-2Na), BT 2h The removal rate of methylene blue by photocatalytic degradation. Among them, isopropanol detects hydroxyl radicals (·OH), histidine detects singlet oxygen ( 1 O2), benzoquinone detection containing superoxide free radicals (·O2 - ), EDTA-2Na detection of photogenerated holes (h + ).Depend on Figure 9It can be seen that after adding the above quenchers, the addition of isopropyl alcohol has no significant effect on the photocatalytic process compared with the degradation rate without quenchers; the addition of benzoquinone, histidine and EDTA-2Na reduces the degradation rate of methylene blue by about 25%, 40% and 23% respectively. 2h The main active species in photocatalytic degradation of organic pollutants is singlet 1 O2, followed by photogenerated holes (h + ) and superoxide radicals (·O2 - ).

[0058] Figure 10 It's BT 2h From the SEM image, it can be seen that a large number of quasi-spherical particles are attached to the flaky structure, and these flaky structures are intertwined to form a porous structure.

[0059] Figure 11 It's BT 2h Energy spectrum. It can be seen that BT 2h The element composition of Ti is 55.14wt.%, and O is 18.21wt.%. The two elements constitute BT 2h In addition, BT 2h The carbon content is 12.70 wt.%, and the nitrogen content is 7.01 wt.%, indicating the formation of carbon- and nitrogen-codoped black titanium dioxide. Co-doping with carbon and nitrogen can alter the band structure of titanium dioxide, affecting properties such as photocatalysis. Furthermore, the sample contains small amounts of elements such as sodium, sulfur, chloride, and potassium, which may have originated from the raw materials, experimental water, reagents, or post-processing.

[0060] Figure 12 It's BT 2h Infrared spectrum, it can be seen from the figure that BT 2h At 619cm -1 The absorption peak of O-Ti-O appears at 1623 cm -1 The stretching and bending vibrations corresponding to the OH bonds of adsorbed water appear at 2156 cm -1 and 1317cm -1 The absorption peak at may be caused by the stretching vibration of COC of adsorbed CO2.

[0061] Figure 13 It's BT 2h The adsorption isotherm and pore size distribution of nitrogen. It can be seen that BT 2hThe physical adsorption of nitrogen shows a typical IV type adsorption isotherm. In the range of p / p0<0.1, the volume of N2 adsorbed increases with the increase of p / p0, indicating the presence of a certain amount of micropores; in the medium pressure region p / p0 (0.41~0.90), the amount of N2 adsorbed gradually increases with the increase of p / p0, corresponding to the presence of a large number of mesopores. The interpolated pore size distribution diagram further confirms that BT 2h It is a material with a multi-level porous structure of micropores, mesopores and macropores. 2h The BET specific surface area is 78.14 m 2 / g, pore volume is 0.1469cm 3 / g, and the maximum pore size is 2.419nm.

[0062] Figure 14 It's BT 2h The UV-visible absorption spectrum of the suspension shows that BT 2h The absorbance of the suspension is between 0.949 and 1.377, indicating that BT 2h It has good visible light response characteristics.

Claims

1. A simple preparation method of black titanium dioxide, characterized by: Sodium chloride, potassium chloride, urea and titanium source are ground and mixed evenly, then placed in a crucible, covered with a crucible lid, and kept at a constant temperature of 200-250°C for 20-40 minutes in a static air atmosphere, then heated to 400-450°C and maintained for 20-40 minutes, and finally heated to 600-700°C and calcined for 1-5 hours. After calcination, the mixture is naturally cooled to room temperature to obtain black titanium dioxide.

2. The simple preparation method of black titanium dioxide according to claim 1, characterized in that: The mass ratio of the titanium source to sodium chloride, potassium chloride and urea is 1:1-3:1.25-3.75:2.5-7.

5.

3. The simple preparation method of black titanium dioxide according to claim 2, characterized in that: The mass ratio of the total mass of the sodium chloride and potassium chloride to the mass of urea is 0.45 to 1.

35.

4. The simple preparation method of black titanium dioxide according to claim 1, characterized in that: The mass ratio of the titanium source to sodium chloride, potassium chloride and urea is 1:2:2.5:

5.

5. The simple preparation method of black titanium dioxide according to any one of claims 1 to 3, characterized in that: The titanium source is any one of titanyl sulfate and P25 or a mixture of the two.

6. The simple preparation method of black titanium dioxide according to claim 1, characterized in that: In a static air atmosphere, the temperature is first kept constant at 200°C for 30 minutes, then raised to 450°C and maintained for 30 minutes, and finally raised to 650°C and calcined for 2 to 4 hours.

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