Preparation method and application of titanium dioxide with disordered layer surface

Abstract

The invention discloses a preparation method of titanium dioxide with a disordered layer surface, which is characterized in that based on the reduction effect and the acid etching effect of oxalic acid, the reduction effect and the acid etching effect of oxalic acid are enhanced through a hydrothermal condition, and a TiO2 photocatalytic material with different disordered layer thicknesses is prepared by regulating and controlling the hydrothermal temperature. The formation of the disorder layer on the surface of TiO2 not only expands the visible light response range of the material, but also improves the ability of TiO2 to catalyze and degrade organic matters by visible light, shows good visible light catalytic activity, and has a removal rate of 94.77% and a mineralization rate of 61.74% after being irradiated by visible light for 6 hours. The method is simple in process and low in cost, and the prepared material has a good application prospect in the field of environmental pollutant treatment.

Description

Technical Field

[0001] The present invention relates to a preparation method and application of titanium dioxide with a disordered layer surface, belonging to the fields of material preparation and environmental chemistry. Background Art

[0002] Photocatalytic technology uses sunlight to drive photocatalysts to generate active species with strong oxidation ability, gradually degrading refractory organic compounds into non-toxic and harmless carbon dioxide and water. It has the advantages of mild reaction conditions, long-lasting performance, and complete degradation, and is considered one of the ideal environmental pollution treatment technologies. In the photocatalytic oxidation technology, photocatalytic materials play a key role. Among many photocatalytic materials, titanium dioxide (TiO2) is one of the most widely studied semiconductor materials in basic research and practical application research. It has a relatively high photon efficiency (up to 10% at most), and has characteristics such as non-toxicity, low price, good chemical stability, and light corrosion resistance. On the other hand, the valence band position of TiO2 is about 2.91 eV, and the band gap is 3.2 eV, which has strong oxidation ability under ultraviolet light. However, ultraviolet light only accounts for about 5% of sunlight, which greatly limits the practical application of TiO2. Therefore, researchers have adopted various means to modify TiO2 to improve its visible-light photocatalytic activity.

[0003] In 2011, researchers prepared TiO2 with a disordered layer by high-pressure hydrogenation, expanding the visible-light response range of TiO2 and inhibiting the recombination of photo-generated electron-hole pairs, thus greatly improving the photocatalytic degradation performance of the material for pollutants. There are also other methods such as zinc (aluminum) metal reduction method, NaBH4 reduction method, electrochemical reduction method, ultrasonic radiation method, vacuum calcination method, etc. Using these methods can also prepare black or blue TiO2, which shows excellent visible-light response characteristics and photocatalytic activity. It is reported that an amorphous layer is also formed on the surface of anatase or rutile TiO2 through the acid etching action of sulfuric acid and hydrochloric acid, which can significantly improve its photocatalytic activity for degrading pollutants. However, less attention has been paid to the mineralization performance of TiO2 with a disordered layer. Based on the acid etching action and reduction properties of oxalic acid, the present invention strengthens the acid etching and reduction of oxalic acid on TiO2 under hydrothermal conditions, and forms disordered layers with different thicknesses on the surface of TiO2 by controlling the hydrothermal temperature. The disordered layer on the surface of TiO2 can not only expand the visible-light response range of the material, but also promote the separation of photo-generated electron-hole pairs, greatly improving the performance of the material for photocatalytic removal and mineralization of phenol. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method and application of titanium dioxide with a disordered layer surface.

[0005] I. Preparation of Titanium Dioxide with a Disordered Layer Surface (1) Dissolve oxalic acid in water to prepare an oxalic acid solution with a concentration of 0.5 - 2 mol / L; (2) Add commercial titanium dioxide (P25 type TiO2) to the oxalic acid solution, stir and ultrasonically treat for 10 - 20 minutes; (3) Transfer the mixed solution to a hydrothermal reactor and react at 25 - 190 °C for 10 - 15 hours; (4) After the reaction, cool down. The product is filtered by suction, washed until neutral, dried at 60 - 80 °C and then ground to obtain a titanium dioxide material with a disordered layer structure on the surface.

[0006] Based on the acid etching effect and reduction property of oxalic acid, the present invention strengthens the acid etching and reduction effects of oxalic acid on TiO2 through hydrothermal conditions, forms disordered layers with different thicknesses on the surface of TiO2 by regulating the hydrothermal temperature, thereby expanding the visible light response range of the material, promoting the separation of photogenerated electron - hole pairs at the same time, and greatly improving the performance of the material in photocatalytic removal and mineralization of phenol.

[0007] II. Characterization and properties of titanium dioxide with a disordered layer surface 1. XRD pattern Use an XRD diffractometer to test the crystal form of the material. The test conditions are Cu Kα ray, tube voltage of 40 kV, tube current of 100 mA, scanning range of 5 - 80°, and scanning speed of 10° / min. Figure 1 It is the XRD pattern of titanium dioxide with different disordered layer surfaces. As Figure 1 can be seen, the untreated material DP - 0 mainly consists of anatase (JCPCD 21 - 1276) and rutile (JCPCD 21 - 1272). The crystal phases of the materials (DP - 25, DP - 100, DP - 130, DP - 160, DP - 190) prepared by treatment with an oxalic acid solution at different hydrothermal temperatures still mainly consist of anatase and rutile, no new diffraction peaks appear, and at the same time, the diffraction peaks of the anatase and rutile crystal phases do not show obvious shifts. When the hydrothermal temperature increases to 190 °C, the characteristic diffraction peak angles of anatase and rutile shift slightly towards larger angles. The reason may be that a large number of oxygen defects are formed in the material at a higher hydrothermal temperature, and the formation of a large number of oxygen defects causes changes in the crystal structure of TiO2.

[0008] 2. TEM images The TEM test is carried out on a Talos F200X G2 type transmission electron microscope (TEM) of FEI Company in the United States, and the morphology of the material is observed at an acceleration voltage of 200 kV. Figure 2 a, b, c, d are the TEM images of DP - 0, DP - 25, DP - 100, DP - 190 respectively. As Figure 2It can be observed that untreated DP-0 has clear lattice fringes with a lattice spacing of 0.355 nm, corresponding to the (101) crystal plane of anatase, and the crystal surface is relatively flat and smooth. The lattice fringes of DP-25 are relatively clear, corresponding to the (101) crystal plane of anatase, but the lattice fringes show discontinuity, and there is a disordered layer of about 0.3 nm on the material surface, indicating that the surface structure of the material is severely damaged, thus forming an ultrathin disordered structure on the material surface layer. As the hydrothermal temperature increases, the thickness of the disordered layer gradually increases. The thickness of the disordered layer on the surface of the DP-100 material prepared at a hydrothermal temperature of 100 °C is about 0.9 nm. When the hydrothermal temperature increases to 190 °C, the thickness of the disordered layer of the material is about 1.6 nm, and it can be clearly seen that the surface of the material is a core-shell structure wrapped by a disordered layer structure. According to the analysis of the HRTEM images, we have prepared TiO2 nanomaterials with disordered layer structures of different thicknesses by regulating the hydrothermal reaction temperature of TiO2 in an oxalic acid aqueous solution.

[0009] 3. UV-Vis Spectra Figure 3 The UV-Vis spectra of different materials are shown. Compared with the untreated DP-0, the absorption in the visible light region of several materials is significantly enhanced. Among them, the visible light response ranges of the materials treated at lower temperatures are relatively close. The DP-190 material has a large number of defects on its surface and subsurface, has a relatively thick disordered layer, and shows a wide visible light response range.

[0010] 4. Photocatalytic Degradation Performance of Phenol The photocatalytic performance test experiment was carried out on a multi-channel photocatalytic reaction system with a 420 nm LED light source. 0.05 g of the photocatalytic material was added to 50 mL of an aqueous phenol solution with an initial concentration of 10 mg / L for the adsorption and photocatalytic performance test experiments. Under dark conditions, it was stirred for 30 minutes to make the adsorption of phenol by the material reach equilibrium. After 30 minutes of adsorption, 5 mL of the sample was taken, and the concentration of phenol was measured by a high-performance liquid chromatograph to calculate the adsorption performance of the material for phenol. Then, the LED light source was turned on, and 5 mL of the sample was taken every 30 min or 60 min. After centrifugation, the supernatant was taken, filtered through a 0.22 μm filter membrane, and the concentration of phenol was measured by a high-performance liquid chromatograph.

[0011] Figure 4 The photocatalytic performance of different materials for the removal of phenol under visible light is shown. Figure 4It can be seen that several materials all have certain photocatalytic activity towards phenol. Under visible light irradiation for 6 h, the removal rates of phenol by DP-25, DP-100, DP-130, DP-160, and DP-190 reach 91.02%, 94.77%, 87.65%, 76.03%, and 56.90% respectively. The photocatalytic activity of the materials can be judged according to the reaction rate constants fitted by the first-order kinetic equation. The photocatalytic degradation rate constants of DP-25, DP-100, DP-130, and DP-160 materials towards phenol are 0.00637 min -1 、0.00778 min -1 、0.00555 min -1 、0.00383 min -1 , which are higher than the photocatalytic degradation rate constant of untreated DP-0 (0.00328 min -1 ) (see Table 1). In particular, the photocatalytic degradation rate constant of DP-100 is 2.37 times that of DP-0, showing the best photocatalytic activity. When the hydrothermal temperature rises to 190 °C, the performance of photocatalytic degradation of phenol (0.00227 min -1 ) decreases significantly, lower than that of unmodified TiO2 (DP-0). The reason may be that the too thick disordered layer increases the recombination of some photogenerated electron-hole pairs, thus slightly decreasing the photocatalytic degradation performance.

[0012] Meanwhile, based on the organic carbon content in the supernatant after 6 h of photocatalytic reaction, the photocatalytic mineralization performance of different materials towards phenol was evaluated, and the results are shown in Figure 5 . As can be seen from Figure 5 , the mineralization rates of phenol by several treated materials DP-25, DP-100, DP-130, DP-160, and DP-190 under visible light irradiation for 6 h reach 49.28%, 61.74%, 55.68%, 36.31%, and 25.37% respectively, all higher than the mineralization rate of pure TiO2 towards phenol, showing good mineralization performance. The experimental results show that the mineralization ability of TiO2 treated by this method has been significantly improved.

[0013] Beneficial effects of the present invention compared with the prior art: (1) Using oxalic acid as a single reagent to simultaneously achieve the dual effects of reduction and acid etching, simplifies the traditional complex process that requires multiple steps / multiple reagents (such as hydrogenation method, metal reduction method) and high energy consumption. By controlling the hydrothermal temperature (25 - 190 °C), the thickness of the disordered layer (0.3 - 1.6 nm) can be accurately regulated. Compared with methods such as high-pressure hydrogenation and vacuum calcination, there are no harsh conditions such as high temperature and high pressure, with lower energy consumption and a simple process flow, and it is safer and more controllable.

[0014] (2) Significantly improved visible-light photocatalytic degradation performance: The formation of the disordered layer expands the visible-light response range of the material, increases the number of photo-generated electrons participating in the photocatalytic reaction, and thus improves the photocatalytic degradation performance of phenol. Among them, the removal rate of phenol by the DP-100 sample under visible light (the main wavelength of the LED lamp is 420 nm) reaches 94.77%, and the photocatalytic reaction rate constant is 0.00778 min -1 , which is 2.4 times that of the untreated DP-0 material (0.00328 min -1 ); at the same time, it has good mineralization ability, and the mineralization rate of phenol reaches 61.74%, which is more than 3 times that of the untreated DP-0 material (19.51%). The experimental results confirm that the formation of the disordered layer promotes the deep mineralization of organic pollutants.

[0015] (3) Significantly reduced raw material cost and operation cost: The price of oxalic acid is only 1 / 5 of that of reducing agents such as NaBH4. The temperature required for the preparation process is lower than 200 °C, with lower energy consumption. The required energy is much lower than that of the hydrogenation method and the vacuum calcination method (400 - 600 °C), reducing the production cost of the material from aspects such as raw material selection and process operation.

[0016] (4) Structural controllability: The surface structure of titanium dioxide is regulated by the temperature of the reaction system containing oxalic acid, thereby affecting the photocatalytic performance of the material. A quantitative relationship between "disordered layer thickness - photocatalytic performance" is established. The experimental results show that 100 °C → 0.9 nm disordered layer → optimal photocatalytic performance, 190 °C → 1.6 nm → decreased photocatalytic performance, revealing the relationship between the reaction temperature, the disordered layer thickness, and the photocatalytic performance. Description of the Drawings

[0017] Figure 1 is the XRD pattern of titanium dioxide with a disordered layer surface.

[0018] Figure 2 is the TEM image of titanium dioxide with a disordered layer surface.

[0019] Figure 3 is the ultraviolet-visible absorption spectrum (UV-Vis spectrum) of titanium dioxide with a disordered layer surface Figure 4 is the visible-light photocatalytic phenol removal performance of titanium dioxide with a disordered layer surface.

[0020] Figure 5 is the visible-light catalytic phenol mineralization performance of titanium dioxide with a disordered layer surface. Detailed Embodiments

[0021] The preparation and performance of titanium dioxide with a disordered layer surface of the present invention are further described below through specific examples.

[0022] Example 1 Weigh 5.04 g of oxalic acid dihydrate, add 50 mL of water to completely dissolve it to obtain a 1 mol / L oxalic acid solution. Add 1.00 g of commercial TiO2 (P25), stir and ultrasonicate for 10 - 20 minutes, then place it in a hydrothermal reaction kettle, heat it to 100 °C at a rate of 2 °C / min, keep it warm for 12 hours, cool it, filter the product by suction and wash it until neutral, and then dry it at 60 °C and grind it to obtain the product. The final product is obtained and labeled as DP - 100. The thickness of the disordered layer on the surface of the DP - 100 material is about 0.9 nm. The removal rate of phenol under visible light irradiation for 6 h is 94.77%, and the reaction rate constant is 0.00778 min -1 , and the mineralization rate is 61.74%.

[0023] Example 2 Weigh 5.04 g of oxalic acid dihydrate, add 50 mL of water to completely dissolve it to obtain a 1 mol / L oxalic acid solution. Add 1.00 g of commercial TiO2 (P25), stir and ultrasonicate at room temperature (25 °C) for 12 hours, and obtain the material treated by oxalic acid impregnation at room temperature through washing, drying and grinding, which is labeled as DP - 25. The thickness of the disordered layer on the surface of the DP - 25 material is about 0.3 nm. The removal rate of phenol under visible light irradiation for 6 h is 91.02%, and the reaction rate constant is 0.00637 min -1 , and the mineralization rate is 49.28%.

[0024] Example 3 The hydrothermal temperature is 130 °C, and other steps are the same as in Example 1. The product is labeled as DP - 130. The removal rate of phenol under visible light irradiation for 6 h is 87.65%, and the reaction rate constant is 0.00555 min -1 , and the mineralization rate is: 55.68%.

[0025] Example 4 The hydrothermal temperature is 160 °C, and other steps are the same as in Example 1. The product is labeled as DP - 160. The removal rate of phenol under visible light irradiation for 6 h is 76.03%, and the reaction rate constant is 0.00383 min -1 , and the mineralization rate is: 36.31%.

[0026] Example 5 The hydrothermal temperature is 190 °C, and other steps are the same as in Example 1. The product is labeled as DP - 190. The thickness of the disordered layer on the surface of the DP - 190 material is about 1.6 nm. The removal rate of phenol under visible light irradiation for 6 h is 56.90%, and the reaction rate constant is 0.00227 min -1, the mineralization rate is: 25.37%.

Claims

1. A preparation method of titanium dioxide with a disordered layer surface, characterized in that, It includes the following steps: (1) Dissolve oxalic acid in water to prepare an oxalic acid solution with a concentration of 0.5 - 2 mol / L; (2) Add commercial titanium dioxide to the oxalic acid solution, stir and ultrasonically treat for 10 - 20 minutes; (3) Transfer the mixed solution to a hydrothermal reactor and react at 25 - 190 °C for 10 - 15 hours; (4) After the reaction, cool it. The product is filtered by suction, washed until neutral, dried at 60 - 80 °C and then ground to obtain a titanium dioxide material with a disordered layer structure on the surface.

2. The preparation method of titanium dioxide with a disordered layer surface according to claim 1, characterized in that: The commercial titanium dioxide is P25 type TiO2, and its crystal form is a mixed phase of anatase and rutile.

3. The preparation method of titanium dioxide with a disordered layer on the surface according to claim 1, characterized in that: The disordered layer surface structure is formed by the acid etching and reduction of oxalic acid. The thickness of the disordered layer is positively correlated with the hydrothermal temperature, and the thickness of the disordered layer is 0.3 nm - 1.6 nm.

4. A titanium dioxide material with a disordered layer surface prepared by any of the methods according to claims 1 to 3, characterized in that: The surface of the material is a core-shell structure wrapped by a disordered layer. The inner core is a TiO2 material with an anatase or rutile crystal phase. The thickness of the disordered layer is 0.3 - 1.6 nm, and the light absorption ability in the visible light region is significantly enhanced.

5. Application of titanium dioxide with a disordered layer surface prepared by the method according to claim 1 or titanium dioxide with a disordered layer surface according to claim 4 in photocatalytic degradation of organic pollutants.

6. The application according to claim 5, wherein: The organic pollutants include phenolic compounds. The photocatalytic reaction is carried out under visible light conditions. When the thickness of the disordered layer is 0.9 nm, the removal rate of phenol by the material is as high as 94.77%, and the mineralization rate is as high as 61.74%.

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