WO2016026339A1 - 一种TiO2纳米晶的合成方法 - Google Patents

一种TiO2纳米晶的合成方法 Download PDF

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WO2016026339A1
WO2016026339A1 PCT/CN2015/080268 CN2015080268W WO2016026339A1 WO 2016026339 A1 WO2016026339 A1 WO 2016026339A1 CN 2015080268 W CN2015080268 W CN 2015080268W WO 2016026339 A1 WO2016026339 A1 WO 2016026339A1
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tio
synthesized
tetratitanate
nanocrystals
precursor
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French (fr)
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杨晓晶
杜意恩
杜德健
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北京师范大学
北京师大科技园科技发展有限责任公司
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Definitions

  • the invention relates to the field of crystal materials, in particular to a method for synthesizing TiO 2 nanocrystals.
  • TiO 2 (titanium dioxide) nanocrystals can decompose water to form H 2 and O 2 under ultraviolet light. Since then, TiO 2 nanocrystals have attracted the attention and research of researchers at home and abroad.
  • TiO 2 nanocrystals are characterized by high stability, non-toxicity, environmental friendliness, and low price. They are not only widely used in photolysis of water to produce hydrogen, but also widely used in dye-sensitized solar cells, photocatalytic degradation of toxic pollutants, Energy storage and conversion, electrochromism and sensing. Since the exposed crystal plane of TiO 2 nanocrystals strongly affects its photocatalytic performance and photovoltaic performance, it is very important to synthesize anatase TiO 2 nanocrystals with specific exposed crystal faces.
  • the ⁇ 010 ⁇ crystal plane exhibits the highest reactivity because of its superior surface atomic structure and electronic structure. Therefore, the preparation of highly reactive ⁇ 010 ⁇ crystal face anatase nanocrystalline materials is currently a hot spot in the field of photocatalysis and solar cells.
  • the titanium raw materials used are mainly organic titanates, and the hydrolysis rate is very high. Fast, difficult to control in the experimental process; and because it is liquid, easy to deliquesce, transportation and storage is very inconvenient, and its price is high, resulting in higher prices of the resulting products, difficult to industrial production.
  • the ⁇ 010 ⁇ crystal face anatase TiO 2 synthesized by these reported synthetic methods also has some disadvantages in catalytic applications.
  • some organic compounds or inorganic ions usually cover the ⁇ 010 ⁇ crystal plane of the synthesized anatase TiO 2 nanocrystals, which can significantly reduce the catalytic performance.
  • the proportion of the ⁇ 010 ⁇ crystal plane is small. This limits the large-scale production and application of the ⁇ 010 ⁇ crystal face anatase TiO 2 nanocrystals.
  • the embodiment of the invention discloses a method for synthesizing TiO 2 nanocrystals. Its technical solutions are as follows:
  • a method for synthesizing TiO 2 nanocrystals may include the following steps:
  • the colloidal suspension of tetratitanate nanosheets was used as the precursor to adjust the pH of the precursor to a pH between 5 and 13.
  • the precursor of pH between 5 and 13 was hydrothermally reacted.
  • TiO 2 nanocrystals TiO 2 nanocrystals.
  • the obtained product is separated, and then the obtained product is washed, filtered, and dried.
  • the precursor having a pH between 5 and 13 is subjected to a hydrothermal reaction, specifically:
  • the precursor having a pH between 5 and 13 is microwaved at 160 ° C to 200 ° C for 1 hour to 2 hours;
  • the precursor having a pH between 5 and 13 is heated to 140 ° C to 200 ° C and then held for 18 hours to 30 hours.
  • the concentration of the first hydrochloric acid solution is 1mol / L -3mol / L;
  • the concentration of the first tetramethylammonium hydroxide solution is from 0.5 mol/L to 2 mol/L.
  • the method for preparing a colloidal tetratitanate nanosheet colloidal suspension comprises the following steps:
  • Synthetic layered potassium tetratitanate K 2 CO 3 and anatase TiO 2 raw materials, k 2 CO 3 and anatase TiO 2 are mixed, and the temperature is raised to 800 ° C to 1000 ° C, and the reaction is carried out for 20 hours. 30 ⁇ , a layered potassium tetratitanate is prepared, wherein the molar ratio of the K 2 CO 3 and anatase TiO 2 is (1 to 1.1): 4;
  • step b) synthesizing tetratitanic acid: dissolving potassium tetratitanate synthesized in step a) in a second hydrochloric acid solution for proton exchange reaction, after completion of the reaction, separating the obtained product, and then washing, filtering and drying the obtained product To obtain tetratitanic acid;
  • step c) synthesizing a colloidal suspension of tetratitanate nanosheets: adding tetratitanate synthesized in step b) to a second tetramethylammonium hydroxide solution to obtain a mixed solution; the mixed solution is at 90 ° C to 110 Reaction at °C for 20 hours ⁇ After 30 hours, after completion of the reaction, the obtained reactant was mixed with water and stirred, and after standing, it was filtered to obtain a colloidal suspension of the precursor tetratitanate nanosheet.
  • the method further comprises: sufficiently grinding.
  • the rate of temperature increase is from 2 ° C / min to 8 ° C / min.
  • the concentration of the second hydrochloric acid solution in step b) is from 0.7 mol/L to 2 mol/L.
  • the potassium tetratitanate synthesized in the step a) is dissolved in the second hydrochloric acid solution in the step b) to carry out a proton exchange reaction, specifically:
  • the potassium tetratitanate synthesized in the step a) is dissolved in the second hydrochloric acid solution, stirred for 3 to 5 days, and the second hydrochloric acid solution is changed once a day.
  • the mass ratio of tetratitanate to tetramethylammonium hydroxide in step c) is 1: (1.2 to 3).
  • the invention provides a synthetic method for exposing ⁇ 010 ⁇ crystal face anatase TiO 2 nanocrystals, which has low cost, no pollution, simple preparation process, strong controllability, short production cycle and good repeatability. For industrial production.
  • Figure 1 is a potassium tetratitanate (K 2 Ti 4 O 9 ) synthesized in the step a) of the first embodiment, tetratitanic acid (H 2 Ti 4 O 9 ⁇ 0.25H 2 O) synthesized in the step b), step c Tetratitanic acid (TMA + ) inserted in the synthesis of tetragonal acid (TMA + -intercalated H 2 Ti 4 O 9 ) and tetra-titanate nanosheets in a colloidal suspension of stripped nanoribbons XRD spectrum of titanic acid (Nanoribbon);
  • Example 2 is an XRD spectrum of anatase TiO 2 nanocrystals synthesized in Example 1 and Example 2, wherein (a) is an XRD spectrum of the anatase TiO 2 nanocrystal synthesized in Example 1; b) an XRD spectrum of the anatase TiO 2 nanocrystal synthesized in Example 1;
  • Example 3 is an XRD spectrum of anatase TiO 2 nanocrystals synthesized in Examples 4 to 8, and (a) is an XRD spectrum of anatase TiO 2 nanocrystals synthesized in Example 4; The XRD spectrum of the anatase TiO 2 nanocrystal synthesized in Example 5; (c) the XRD spectrum of the anatase TiO 2 nanocrystal synthesized in Example 6; (d) the synthesis of Example 7. XRD spectrum of anatase TiO 2 nanocrystal; (e) XRD spectrum of anatase TiO 2 nanocrystal synthesized in Example 8;
  • FIG. 4 is a scanning electron micrograph of anatase TiO 2 nanocrystals synthesized in Examples 1 to 3, wherein (a) is a scanning electron micrograph of the TiO 2 nanocrystal synthesized in Example 1, and (b) is an example. 2 Scanning electron micrograph of the synthesized TiO 2 nanocrystal, (c) is a scanning electron micrograph of the TiO 2 nanocrystal synthesized in Example 3;
  • 5 is a scanning electron micrograph of anatase TiO 2 nanocrystals synthesized in Examples 4 to 8, wherein (a) is a scanning electron micrograph of the TiO 2 nanocrystal synthesized in Example 4, and (b) is an example. 5 Scanning electron micrograph of the synthesized TiO 2 nanocrystal, (c) is a scanning electron micrograph of the TiO 2 nanocrystal synthesized in Example 6; (d) is a scanning electron micrograph of the TiO 2 nanocrystal synthesized in Example 7; a scanning electron micrograph of the TiO 2 nanocrystal synthesized in Example 8;
  • Example 6 is a transmission electron microscope (TEM) image and a high-resolution transmission electron microscope (HR-TEM) image of anatase TiO 2 nanocrystals synthesized in Example 1 and Example 2, wherein (a) is a synthesis of Example 1. Transmission electron micrograph of TiO 2 nanocrystals, (b) high resolution transmission electron micrograph of TiO 2 nanocrystals synthesized in Example 1; (c) transmission electron micrograph of TiO 2 nanocrystals synthesized in Example 2 (d) is a high resolution transmission electron micrograph of the TiO 2 nanocrystal synthesized in Example 2;
  • TEM transmission electron microscope
  • HR-TEM high-resolution transmission electron microscope
  • Example 7 is a transmission electron microscope (TEM) image and a high-resolution transmission electron microscope (HR-TEM) image of the anatase-type TiO 2 nanocrystals synthesized in Example 5 and Example 6, wherein (a) is a synthesis of Example 5. Transmission electron micrograph of TiO 2 nanocrystals, (b) high resolution transmission electron micrograph of TiO 2 nanocrystals synthesized in Example 5; (c) transmission electron micrograph of TiO 2 nanocrystals synthesized in Example 6 (d) is a high resolution transmission electron micrograph of the TiO 2 nanocrystal synthesized in Example 6;
  • Example 8 is a graph showing degradation efficiency and illumination time characteristics of the TiO 2 nanocrystals synthesized in Example 1;
  • Example 9 is a graph showing degradation efficiency and illumination time characteristics of the TiO 2 nanocrystals synthesized in Example 2.
  • Example 10 is a photocurrent-voltage characteristic diagram of TiO 2 nanocrystals synthesized in Example 1;
  • Figure 11 is a graph showing the photocurrent-voltage characteristics of the TiO 2 nanocrystals synthesized in Example 2.
  • the water used is preferably deionized water or distilled water.
  • K 2 CO 3 Specification AR, purchased by Tianjin Komi Chemical Reagent Development Co., Ltd.;
  • Anatase TiO 2 Specification AR, purchased by Tianjin Komi Chemical Reagent Development Co., Ltd.;
  • Hydrochloric acid 36.5% (mass fraction), purchased by Tianjin Komi Chemical Reagent Development Co., Ltd.;
  • TMAOH Tetramethylammonium hydroxide
  • Synthetic layered potassium tetratitanate According to the ratio of the amount of the substance: 1:4, 13.821 g (0.1 mol) of K 2 CO 3 and 31.960 g (0.4 mol) of anatase TiO 2 were weighed and placed in an agate mortar. Medium, after mixing, fully grind. Then, it was transferred to a corundum crucible, placed in a muffle furnace and heated at 900 ° C for 24 hours at a heating rate of 5 ° C / min; and a layered fibrous potassium tetratitanate (K 2 Ti 4 O 9 ) was obtained.
  • step b) Synthesis of tetratitanic acid: Weigh 10.0 g of K 2 Ti 4 O 9 synthesized in step a), add to a large beaker containing 1000 mL of 1 mol/L of the second hydrochloric acid solution, and magnetically stir for three days at room temperature, and replace it once a day.
  • the second hydrochloric acid solution completely converts K 2 Ti 4 O 9 to H 2 Ti 4 O 9 .
  • the product was separated by centrifugation; washed four times with deionized water, centrifuged three times, and finally the obtained sample was freeze-dried to obtain H 2 Ti 4 O 9 ⁇ 0.25H 2 O.
  • the product in the reaction kettle was transferred to a beaker, and then added with 360 mL of deionized water, stirred at room temperature for 24 hours on a magnetic stirrer, and then allowed to stand still for 24 hours, and then suction filtered to obtain a tetratitanate nanosheet.
  • Synthetic layered potassium tetratitanate According to the amount of the substance, the ratio is 1.05:4, 14.512 g (0.105 mol) of K 2 CO 3 and 31.960 g (0.4 mol) of anatase TiO 2 are weighed and placed in an agate mortar. Medium, after mixing, fully grind. Then, it was transferred to a corundum crucible, placed in a muffle furnace and heated at 800 ° C for 30 hours at a heating rate of 2 ° C / min; and a layered fibrous potassium tetratitanate (K 2 Ti 4 O 9 ) was obtained.
  • tetratitanic acid Weigh 10.0 g of K 2 Ti 4 O 9 synthesized in step a), add it to a large beaker containing 1000 mL of 0.7 mol/L of the second hydrochloric acid solution, and magnetically stir for three days at room temperature and replace every day. A second hydrochloric acid solution was used to completely convert K 2 Ti 4 O 9 to H 2 Ti 4 O 9 . After three proton exchange reactions, the product was separated by centrifugation, washed four times with deionized water, and centrifuged three times. Finally, the obtained sample was freeze-dried to obtain H 2 Ti 4 O 9 ⁇ 1.9H 2 O.
  • the product in the reaction kettle was transferred to a beaker, and then added with 360 mL of deionized water, stirred at room temperature for 24 hours on a magnetic stirrer, and then allowed to stand still for 24 hours, and then suction filtered to obtain a tetratitanate nanosheet.
  • Synthetic layered potassium tetratitanate According to the ratio of the amount of the substance: 1.:4, weigh 15.203 g (0.11 mol) of K 2 CO 3 and 31.960 g (0.4 mol) of anatase TiO 2 and place it in an agate mortar. Medium, after mixing, fully grind. Then, it was transferred to a corundum crucible, placed in a muffle furnace and heated at 1000 ° C for 20 hours at a heating rate of 8 ° C / min; and a layered fibrous potassium tetratitanate (K 2 Ti 4 O 9 ) was obtained.
  • the product in the reaction kettle was transferred to a beaker, and then added with 360 mL of deionized water, stirred at room temperature for 24 hours on a magnetic stirrer, and then allowed to stand still for 24 hours, and then suction filtered to obtain a tetratitanate nanosheet.
  • Steps a) to c) are the same as in Embodiment 1,
  • Steps a) to c) are the same as in Embodiment 2,
  • Steps a) to c) are the same as in Embodiment 3,
  • the relevant parameters for centrifugal separation may be a centrifugal rotation speed of 8000 rpm and a centrifugation time of 10 minutes.
  • the lyophilization is specifically carried out by placing the sample in a glass bottle for freezing, then installing it in a freezer, and turning on a rotary button to make an aqueous solution containing the sample.
  • the temperature of the liquid in the freezer is -15 ° C ⁇ 30 ° C
  • the sample freezing time is generally 30 minutes, you can form ice, of course, when the amount of aqueous solution in the sample is large, the time is long some.
  • After freezing into ice turn off the spin button and freezer, take out the freezer bottle, install it on the dryer, turn on the vacuum pump, and evacuate until the gauge pressure is about -0.09Mpa, and let it dry under vacuum for 24 hours.
  • the relevant parameters of the freeze-drying used in the present embodiment are only for the person skilled in the art to better understand the synthesis process of the TiO 2 nanocrystals, and do not represent the only relevant parameters listed to achieve the present invention.
  • Technical solutions, those skilled in the art can adjust the parameters according to actual conditions, which is feasible.
  • the invention is not specifically limited herein.
  • step c) synthesis of tetramethyl ammonium ions (TMA +) inserting four titanate (TMA + -intercalated H 2 Ti 4 O 9) and four titanate nanosheet colloidal suspension
  • TMA + tetramethyl ammonium ions
  • TMA + -intercalated H 2 Ti 4 O 9 tetramethyl ammonium ions
  • TMA + -intercalated H 2 Ti 4 O 9 titanate
  • the stripped nanoribbon-like tetratitanium (Nanoribbon) was characterized by XRD, wherein the collected data diffraction angle (2 ⁇ ) ranged from 3 to 70°, the scanning speed was 5°/min, and the acceleration voltage and applied current were respectively 40kV and 30mA. The result is shown in Figure 1.
  • Example 3 Nanocrystalline TiO 2 synthesized in Example 1 and Example 2 Synthesis of Nanocrystalline TiO 2 the same embodiment, the XRD diffraction spectrum which can Referring to FIG 2, the present invention is not described herein.
  • the products synthesized in Examples 4 to 8 were all anatase TiO 2 corresponding to a standard card having a JCPDS of 21-1272. It can be seen from these five XRD diffraction patterns that as the pH increases, the measured diffraction peak intensity increases and the width becomes narrower, indicating that the synthesized TiO 2 nanocrystalline particles are larger and the crystallinity is higher.
  • the anatase-type TiO 2 nanocrystals synthesized in Example 1 have a square shape and a rhombus shape, and the average particle size thereof is about 50 nm.
  • the morphology of the anatase-type TiO 2 nanocrystals synthesized in Example 2 and Example 3 was a shuttle type, and the average particle size was about 150 nm and 480 nm, respectively.
  • the anatase type TiO 2 nanocrystals synthesized in Example 4 have a square shape and a rhombus shape, and the average particle size thereof is about 50 nm.
  • the morphology of the anatase TiO 2 nanocrystals synthesized in Examples 5 to 8 (PH > 5) is a shuttle type, and the average particle size also follows the pH. The increase is increasing. It shows that pH has an important influence on the morphology and size of the particles.
  • TEM Transmission electron microscopy
  • HR-TEM high-resolution transmission electron microscopy
  • TEM Transmission electron microscopy
  • HR-TEM high-resolution transmission electron microscopy
  • TEM Transmission electron microscopy
  • HR-TEM high-resolution transmission electron microscopy
  • TEM Transmission electron microscopy
  • HR-TEM high-resolution transmission electron microscopy
  • the interplanar spacing with Respectively corresponding to anatase TiO (101) and (002) crystal plane 2 the angle between the two crystal face is 68.3 °, in accordance with anatase TiO (101) and (002) planes of constant 2
  • the exposed crystal faces of the anatase-type TiO 2 nanocrystals synthesized by the present invention are all ⁇ 010 ⁇ crystal faces.
  • the ⁇ 010 ⁇ crystal face anatase TiO 2 nanocrystals can be synthesized by using the synthesis method provided by the present invention.
  • Example 8 Since the embodiment of the present invention in Examples 1 to Example 8 were synthesized in the diamond and square appearance anatase type TiO 2 and the spindle morphology of nanocrystalline anatase type TiO 2 nanocrystalline, therefore, where each of the two Characterization of anatase TiO 2 nanocrystals for performance analysis, wherein rhombohedral and square-shaped anatase TiO 2 nanocrystals are exemplified in Example 1, fusiform anatase TiO 2 nanocrystals are implemented
  • the anatase type TiO 2 nanocrystals synthesized in the other examples are the same as those in the first embodiment or the second embodiment, the properties thereof can be referred to in the first embodiment or the second embodiment.
  • the emission wavelength of the ultraviolet lamp was 365 nm, and the distance from the methyl blue solution was 80 cm.
  • 3 mL of the suspension was taken in each of the two conical flasks and centrifuged to remove the titanium dioxide nanocrystals.
  • the degradation rate of methyl blue was determined by measuring the concentration change of the methyl blue solution before and after the ultraviolet lamp irradiation using a TU-1901 spectrophotometer.
  • commercial Degussa P25 52.50 m 2 /g, 80% anatase and 20% rutile was measured under the same conditions. The test results are shown in Figures 8 and 9, respectively.
  • Example 8 is a graph showing the degradation efficiency and illumination time characteristics of the TiO 2 nanocrystals synthesized in Example 1. It can be seen from the figure that the degradation of methyl blue by an anatase TiO 2 nanocrystal synthesized at 120 minutes is performed. The efficiency is 99%, and the degradation efficiency of P25 to methyl blue is 86%. Therefore, the degradation efficiency of the synthesized anatase TiO 2 nanocrystals to methyl blue is much higher than that of Degussa P25 to methyl blue. Degradation efficiency.
  • Figure 9 is a graph showing the degradation efficiency and illumination time characteristics of the TiO 2 nanocrystals synthesized in Example 2. It can be seen from the figure that the degradation of methyl blue by the two anatase TiO 2 nanocrystals synthesized at 120 minutes was observed. The efficiency is 96%, and the degradation efficiency of P25 to methyl blue is 86%. Therefore, the degradation efficiency of the two synthesized anatase TiO 2 nanocrystals to methyl blue is much higher than that of Degussa P25 to methyl blue. Degradation efficiency.
  • the exposed ⁇ 010 ⁇ crystal face anatase TiO 2 nanocrystals synthesized in the examples of the present invention have high degradation efficiency to methyl blue regardless of the rhombohedral shape and the square shape or the fusiform morphology. Degradation efficiency of methyl blue in Degussa P25.
  • the exposed ⁇ 010 ⁇ crystal face anatase TiO 2 nanocrystal synthesized by the embodiment of the invention has good photocatalytic performance.
  • Example 1 and Example 2 0.5 g of anatase TiO 2 nanocrystals synthesized in Example 1 and Example 2 were weighed and added to glass bottles, respectively, and then 2.5 g of ethanol and 2.0 g of ⁇ -terpineol were added to the two glass vials.
  • the washed FTO glass was immersed in a 0.1 M Ti(OC 3 O 7 ) 4 organotitanium solution for several seconds and then calcined in a high temperature furnace for 60 min.
  • the porous titania film electrode was prepared by applying a TiO 2 slurry of Example 1 and Example 2 to the FTO tape guide glass by a doctor blade method. The thickness of the film is controlled by the thickness of the tape used.
  • Example 1 The TiO 2 slurry of Example 1 and Example 2 was separately coated on FTO conductive glass, and then calcined at 315 ° C for 15 min in a high temperature furnace, and this operation was repeated several times until the desired film thickness was obtained, and then 450 ° C in a high temperature furnace. Calcined for 30 min. After cooling to room temperature, it was again immersed in a 0.1 M Ti(OC 3 O 7 ) 4 organotitanium solution for several seconds and then calcined in a high temperature furnace for 60 min.
  • the Pt counter electrode was prepared by immersing the FTO conductive glass in an isopropanol solution containing 0.5 mM H 2 PtCl 6 , taking it out after several minutes, and then calcining at 400 ° C for 20 min in a high temperature furnace.
  • the electrolyte solution is injected into the gap between the two electrodes by capillary action to assemble a sandwich-structured dye-sensitized solar cell.
  • the photoanodes of Degussa P25TiO 2 prepared by the same method were assembled into batteries, which were compared with the above batteries. The test results are shown in Figures 10 and 11.
  • Fig. 10 is a graph showing the photocurrent-voltage characteristic of Example 1 at a film thickness of 13.8 ⁇ m.
  • the synthesized anatase TiO 2 nanocrystal photoelectric current preferentially exposing the ⁇ 010 ⁇ crystal plane is 12.6 mA/cm 2
  • the conversion efficiency was 5.09%, which was significantly better than the photoelectric current of P25 of 10.3 mA/cm 2 and the conversion efficiency was 4.37%.
  • Fig. 11 is a graph showing the photocurrent-voltage characteristic of Example 2 at a film thickness of 16.4 ⁇ m.
  • the synthesized anatase TiO 2 nanocrystal photoelectric current preferentially exposing the ⁇ 010 ⁇ crystal plane is 13.6 mA/cm 2
  • the conversion efficiency was 5.48%, which was significantly better than the photoelectric current of P25 of 10.3 mA/cm 2 and the conversion efficiency was 4.37%.
  • the invention adopts a new method for synthesizing anatase TiO2 nanocrystals preferentially exposing ⁇ 010 ⁇ crystal planes, which has low cost, no pollution, simple preparation process, strong controllability, short production cycle and good repeatability.
  • the requirements of "green chemistry" apply to industrial production.
  • the ⁇ 010 ⁇ crystal face anatase TiO2 nanocrystal prepared by the method provided by the invention has high purity and uniform particle size distribution, and is used for degrading methyl blue solution and dye sensitized solar cell, and commercial Deco Compared with P25TiO2 (52.50m 2 /g, 80% anatase and 20% rutile), both catalytic performance and photovoltaic performance were significantly improved.

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Abstract

提供一种TiO 2纳米晶的合成方法，包括：以四钛酸纳米片胶态悬浮液作为前驱体，调节前驱体的pH值在5~13之间；将前驱体进行水热反应，得到TiO 2纳米晶。本方法合成的TiO 2纳米晶为锐钛型，其暴露晶面为{010}晶面，本方法成本低、无污染、工艺简单、可控性强、生产周期短、可重复性好，适于工业化生产。

Description

一种TiO2纳米晶的合成方法 技术领域
本发明涉及晶体材料领域，特别涉及一种TiO2纳米晶的合成方法。
背景技术
1972年，日本Honda和Fujishima发现在紫外光照射下，TiO2(二氧化钛)纳米晶能够分解水生成H2和O2。自此以后，TiO2纳米晶引起了国内外研究者的高度重视和深入研究。
TiO2纳米晶具有高稳定性、无毒、对环境友好，以及价格低廉等显著特点，不仅广泛应用于光解水制氢，而且广泛应用于染料敏化太阳能电池、光催化降解毒性污染物、能量储存和转化、电致变色和传感领域等。由于TiO2纳米晶的暴露晶面强烈影响其光催化性能和光伏打性能，因此，合成具特定暴露晶面的锐钛型TiO2纳米晶是非常重要的。
近年来，由于{010}晶面具有优越的表面原子结构和电子结构，二者协同作用，使{010}晶面展示出了最高的反应活性。因此，制备高反应活性的{010}晶面的锐钛型纳米晶材料是目前光催化和太阳能电池领域研究的热点。
目前对优先暴露{010}晶面锐钛型TiO2纳米晶的合成方法已经有了一些报道，在这些已报道的合成方法中，其所用的钛原料主要是有机钛酸酯，其水解速度很快，在实验过程难以控制；而且由于其为液态，易潮解，运输和存储很不方便，而且其价格偏高，导致所得产品的价格较高，难以工业化生产。
利用这些已报道的合成方法合成的{010}晶面的锐钛型TiO2在催化应用上也具有一些缺点。
首先，一些有机化合物或无机离子通常覆盖着合成的锐钛型TiO2纳米晶的{010}晶面上，能够明显降低其催化性能。再次，合成的锐钛型TiO2纳米晶中，其{010}晶面所占的比例较小。这就限制了所制得的{010}晶面锐钛型TiO2纳米晶的大规模生产和应用。
因此，绿色合成具有较大比例的清洁{010}晶面的锐钛型TiO2纳米晶是非常必要的。
发明内容
为解决上述问题，本发明实施例公开了一种TiO2纳米晶的合成方法。其技术方案如下：
一种TiO2纳米晶的合成方法，可以包括以下步骤：
以四钛酸纳米片胶态悬浮液为前驱体，调节前驱体的pH值，使其pH值在5～13之间；将pH值在5～13之间的前驱体进行水热反应，得到TiO2纳米晶。
其中，水热反应后，分离所得产物，然后对所得产物进行洗涤、过滤及干燥操作。
在本发明的一种优选实施方式中，所述将pH值在5～13之间的前驱体进行水热反应，具体为：
将pH值在5～13之间的前驱体在160℃～200℃微波辐射1小时～2小时；
或者
将pH值在5～13之间的前驱体加热至140℃～200℃后，保温18小时～30小时。
在本发明的一种优选实施方式中，用第一盐酸溶液与第一四甲基氢氧化铵溶液调节前驱体的pH值，所述第一盐酸溶液的浓度为1mol/L-3mol/L；所述第一四甲基氢氧化铵溶液的浓度为0.5mol/L～2mol/L。
在本发明的一种优选实施方式中，前驱体四钛酸纳米片胶态悬浮液的制备方法包括以下步骤：
a)合成层状四钛酸钾：以K2CO3和锐钛型TiO2原料，将K2CO3和锐钛型TiO2混匀后，升温至800℃～1000℃，反应20小时～30小时，制得层状四钛酸钾，其中，所述K2CO3和锐钛型TiO2的摩尔比为(1～1.1)∶4；
b)合成四钛酸：将步骤a)中合成的四钛酸钾溶于第二盐酸溶液中，进行质子交换反应，反应结束后，分离所得产物，然后对所得产物进行洗涤、过滤及干燥操作，得到四钛酸；
c)合成四钛酸纳米片胶态悬浮液：将步骤b)中合成的四钛酸加入到第二四甲基氢氧化铵溶液中，得到混合液；将所述混合液在90℃～110℃下反应20小时～ 30小时，反应结束后，将所得反应物与水混合并搅拌，静止后过滤，得到前驱体四钛酸纳米片胶态悬浮液。
在本发明的一种优选实施方式中，在步骤a)中，将K2CO3和锐钛型TiO2混匀后，在升温至800℃～1000℃之前，还包括：充分研磨。
在本发明的一种优选实施方式中，在步骤a)中，所述升温的速率为2℃/分钟～8℃/分钟。
在本发明的一种优选实施方式中，步骤b)中的第二盐酸溶液的浓度为0.7mol/L～2mol/L。
在本发明的一种优选实施方式中，步骤b)中所述将步骤a)中合成的四钛酸钾溶解于第二盐酸溶液中，进行质子交换反应，具体为：
将步骤a)中合成的四钛酸钾溶解于第二盐酸溶液中，搅拌3～5天，并每天更换一次第二盐酸溶液。
在本发明的一种优选实施方式中，步骤c)中四钛酸与四甲基氢氧化铵的质量比为1∶(1.2～3)。
本发明为暴露{010}晶面的锐钛型TiO2纳米晶提供了一种合成方法，这种方法成本低、无污染、制备工艺简单、可控性强、生产周期短、可重复性好，适用于工业化生产。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为实施例1步骤a)中合成的四钛酸钾(K2Ti4O9)、步骤b)中合成的四钛酸(H2Ti4O9·0.25H2O)、步骤c)中合成的四甲基氨根离子(TMA+)***的四钛酸(TMA+-intercalated H2Ti4O9)及四钛酸纳米片胶态悬浮液中的剥离的纳米带状的四钛酸(Nanoribbon)的XRD谱图；
图2为实施例1及实施例2所合成的锐钛型TiO2纳米晶的XRD谱图，其中，(a)为实施例1所合成的锐钛型TiO2纳米晶的XRD谱图；(b)为实施例1 所合成的锐钛型TiO2纳米晶的XRD谱图；
图3为实施例4～实施例8所合成的锐钛型TiO2纳米晶的XRD谱图，(a)为实施例4所合成的锐钛型TiO2纳米晶的XRD谱图；(b)为实施例5所合成的锐钛型TiO2纳米晶的XRD谱图；(c)为实施例6所合成的锐钛型TiO2纳米晶的XRD谱图；(d)为实施例7所合成的锐钛型TiO2纳米晶的XRD谱图；(e)为实施例8所合成的锐钛型TiO2纳米晶的XRD谱图；
图4为实施例1～实施例3合成的锐钛型TiO2纳米晶的扫描电镜图，其中，(a)为实施例1合成的TiO2纳米晶的扫描电镜图，(b)为实施例2合成的TiO2纳米晶的扫描电镜图，(c)为实施例3合成的TiO2纳米晶的扫描电镜图；
图5为实施例4～实施例8合成的锐钛型TiO2纳米晶的扫描电镜图，其中，(a)为实施例4合成的TiO2纳米晶的扫描电镜图，(b)为实施例5合成的TiO2纳米晶的扫描电镜图，(c)为实施例6合成的TiO2纳米晶的扫描电镜图；(d)为实施例7合成的TiO2纳米晶的扫描电镜图；(e)为实施例8合成的TiO2纳米晶的扫描电镜图；
图6为实施例1及实施例2合成的锐钛型TiO2纳米晶的透射电子显微镜(TEM)图及高分辨透射电子显微镜(HR-TEM)图，其中，(a)为实施例1合成的TiO2纳米晶的透射电子显微镜图，(b)为实施例1合成的TiO2纳米晶的高分辨透射电子显微镜图；(c)为实施例2合成的TiO2纳米晶的透射电子显微镜图，(d)为实施例2合成的TiO2纳米晶的高分辨透射电子显微镜图；
图7为实施例5及实施例6合成的锐钛型TiO2纳米晶的透射电子显微镜(TEM)图及高分辨透射电子显微镜(HR-TEM)图，其中，(a)为实施例5合成的TiO2纳米晶的透射电子显微镜图，(b)为实施例5合成的TiO2纳米晶的高分辨透射电子显微镜图；(c)为实施例6合成的TiO2纳米晶的透射电子显微镜图，(d)为实施例6合成的TiO2纳米晶的高分辨透射电子显微镜图；
图8为实施例1合成的TiO2纳米晶的降解效率与光照时间特性曲线；
图9为实施例2合成的TiO2纳米晶的降解效率与光照时间特性曲线；
图10为实施例1合成的TiO2纳米晶的光电流-电压特征曲线图；
图11为实施例2合成的TiO2纳米晶的光电流-电压特征曲线图。
具体实施方式
为了进一步说明本发明，下面将结合具体实施例对本发明的技术方案进行描述，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
首先，需要说明的是，本发明实施例在合成TiO2纳米晶的过程中，所使用的水优选为去离子水或蒸馏水。
进一步需要说明的是，本发明实施例采用的所有试剂，对其来源没有特殊的限制，在市场上购得或自制均可；例如：
K2CO3：规格AR，天津市科密欧化学试剂开发公司购得；
锐钛型TiO2：规格AR，天津市科密欧化学试剂开发公司购得；
盐酸：规格36.5％(质量分数)，天津市科密欧化学试剂开发公司购得；
四甲基氢氧化铵(TMAOH)：规格AR，天津市科密欧化学试剂开发公司购得。
还需要说明的是，本发明实施例在合成TiO2纳米晶的过程中所采用的实验设备，均为本领域通用的设备，没有特殊的要求，均可在市场上购得。发明人相信，本领域技术人员完全可以通过对本发明技术方案的描述来选择适当的实验设备，本发明在此不对实验设备进行具体限制与说明。
一、TiO2纳米晶的合成
实施例1
a)合成层状四钛酸钾：按照物质的量之比为1∶4，称量13.821g(0.1mol)K2CO3和31.960g(0.4mol)锐钛型TiO2放置到玛瑙研钵中，混匀后，充分研磨。然后将其转移到刚玉坩埚中，放入马弗炉中于900℃加热24小时，升温速率为5℃/分钟；制得层状纤维状四钛酸钾(K2Ti4O9)。
b)合成四钛酸：称取10.0g步骤a)中合成的K2Ti4O9，加入盛有1000mL 1mol/L第二盐酸溶液的大烧杯中，室温下磁力搅拌三天，每天更换一次第二盐酸溶液，使K2Ti4O9完全转化为H2Ti4O9。三次质子交换反应后，产物通过离心分 离；用去离子水洗涤4次，重复离心三次，最后将所得到的样品冷冻干燥，得到H2Ti4O9·0.25H2O。
c)合成四钛酸纳米片胶态悬浮液：称取3.5g(约0.01mol)步骤b)中合成的H2Ti4O9·0.25H2O，加入到容积为70mL的四聚乙烯反应釜中，再向其中加入40g(质量分数为12.5％)第二四甲基氢氧化铵溶液，密封后，放入高温旋转反应炉中于100℃加热24小时。待冷却至室温后，将反应釜中的产物转移到烧杯中，再加入360mL去离子水，在磁力搅拌器上室温搅拌24小时后，再静止24小时，然后抽滤，得到四钛酸纳米片胶态悬浮液，即前驱体。
d)合成TiO2纳米晶：用3mol/L的第一盐酸溶液和1mol/L的第一四甲基氢氧化铵溶液调节步骤c)中合成的四钛酸纳米片胶态悬浮液的pH值为5.0。取40mL调节好pH值的纳米片悬浮液加入到内部容积为80mL的四聚乙烯反应釜中，放入微波炉中在180℃下微波辐射1.5小时。冷却至室温后，离心分离、用去离子水洗涤4次，然后冷冻干燥。得到暴露{010}晶面的锐钛型TiO2纳米晶，其形貌为菱形和方块形。
实施例2
a)合成层状四钛酸钾：按照物质的量之比为1.05∶4，称量14.512g(0.105mol)K2CO3和31.960g(0.4mol)锐钛型TiO2放置到玛瑙研钵中，混匀后，充分研磨。然后将其转移到刚玉坩埚中，放入马弗炉中于800℃加热30小时，升温速率为2℃/分钟；制得层状纤维状四钛酸钾(K2Ti4O9)。
b)合成四钛酸：称取10.0g步骤a)中合成的K2Ti4O9，加入盛有1000mL0.7mol/L第二盐酸溶液的大烧杯中，室温下磁力搅拌三天，每天更换一次第二盐酸溶液，使K2Ti4O9完全转化为H2Ti4O9。三次质子交换反应后，产物通过离心分离，用去离子水洗涤4次，重复离心三次，最后将所得到的样品冷冻干燥，得到H2Ti4O9·1.9H2O。
c)合成四钛酸纳米片胶态悬浮液：称取3.5g(约0.01mol)步骤b)中合成的H2Ti4O9·1.9H2O，加入到容积为70mL的四聚乙烯反应釜中，再向其中加入40g(质量分数为25％)第二四甲基氢氧化铵溶液，密封后，放入高温旋转反应炉中于90℃加热30小时。待冷却至室温后，将反应釜中的产物转移到烧杯中，再加入360mL去离子水，在磁力搅拌器上室温搅拌24小时后，再静止24小时，然后抽滤，得到四钛酸纳米片胶态悬浮液，即前驱体。
d)合成TiO2纳米晶：用2mol/L的第一盐酸溶液和0.5mol/L的第一四甲基 氢氧化铵溶液调节步骤c)中合成的四钛酸纳米片胶态悬浮液的pH值为7.0。取40mL调节好pH值的纳米片悬浮液加入到内部容积为80mL的四聚乙烯反应釜中，放入微波炉中在160℃下微波辐射2小时。冷却至室温后，离心分离、用去离子水洗涤4次，然后冷冻干燥。得到暴露{010}晶面的锐钛型TiO2纳米晶，其形貌为梭形。
实施例3
a)合成层状四钛酸钾：按照物质的量之比为1.1∶4，称量15.203g(0.11mol)K2CO3和31.960g(0.4mol)锐钛型TiO2放置到玛瑙研钵中，混匀后，充分研磨。然后将其转移到刚玉坩埚中，放入马弗炉中于1000℃加热20小时，升温速率为8℃/分钟；制得层状纤维状四钛酸钾(K2Ti4O9)。
b)合成四钛酸：称取10.0g步骤a)中合成的K2Ti4O9，加入盛有1000mL 2mol/L第二盐酸溶液的大烧杯中，室温下磁力搅拌三天，每天更换一次第二盐酸溶液，使K2Ti4O9完全转化为H2Ti4O9。三次质子交换反应后，产物通过离心分离，用去离子水洗涤4次，重复离心三次，最后将所得到的样品冷冻干燥，得到H2Ti4O9·3H2O。
c)合成四钛酸纳米片胶态悬浮液：称取3.5g(约0.01mol)步骤b)中合成的H2Ti4O9·3H2O，加入到容积为70mL的四聚乙烯反应釜中，再向其中加入50g(质量分数为15％)第二四甲基氢氧化铵溶液，密封后，放入高温旋转反应炉中于110℃加热20小时。待冷却至室温后，将反应釜中的产物转移到烧杯中，再加入360mL去离子水，在磁力搅拌器上室温搅拌24小时后，再静止24小时，然后抽滤，得到四钛酸纳米片胶态悬浮液，即前驱体。
d)合成TiO2纳米晶：用1mol/L的第一盐酸溶液和2mol/L的第一四甲基氢氧化铵溶液调节步骤c)中合成的四钛酸纳米片胶态悬浮液的pH值为13.0。取40mL调节好pH值的纳米片悬浮液加入到内部容积为80mL的四聚乙烯反应釜中，放入微波炉中在200℃下微波辐射1小时。冷却至室温后，离心分离(、用去离子水洗涤4次，然后冷冻干燥。得到暴露{010}晶面的锐钛型TiO2纳米晶，其形貌为梭形。
实施例4
步骤a)～步骤c)均与实施例1相同，
d)合成TiO2纳米晶：用3mol/L的第一盐酸溶液和1mol/L的第一四甲基氢氧化铵溶液调节步骤c)中合成的四钛酸纳米片胶态悬浮液的pH值为5.0。取40mL调节好pH值的纳米片悬浮液加入到内部容积为70mL的四聚乙烯反应釜中，，密封后，放入高温旋转反应炉中，在180℃下加热24小时。冷却至室温后，离心分离、用去离子水洗涤4次，然后冷冻干燥。得到暴露{010}晶面的锐钛型TiO2纳米晶，其形貌为菱形和方块形。
实施例5
除步骤d)中四钛酸纳米片胶态悬浮液的pH值为6.2外，其它均与实施例4相同，得到暴露{010}晶面的锐钛型TiO2纳米晶，其形貌为菱形和方块形。
实施例6
步骤a)～步骤c)均与实施例2相同，
d)合成TiO2纳米晶：用2mol/L的第一盐酸溶液和0.5mol/L的第一四甲基氢氧化铵溶液调节步骤c)中合成的四钛酸纳米片胶态悬浮液的pH值为7.0。取40mL调节好pH值的纳米片悬浮液加入到内部容积为70mL的四聚乙烯反应釜中，，密封后，放入高温旋转反应炉中，在200℃下加热18小时。冷却至室温后，离心分离、用去离子水洗涤4次，然后冷冻干燥。得到暴露{010}晶面的锐钛型TiO2纳米晶，其形貌为梭形。
实施例7
除步骤d)中四钛酸纳米片胶态悬浮液的pH值为9.0外，其它均与实施例6相同，得到暴露{010}晶面的锐钛型TiO2纳米晶，其形貌为梭形。
实施例8
步骤a)～步骤c)均与实施例3相同，
d)合成TiO2纳米晶：用1mol/L的第一盐酸溶液和2mol/L的第一四甲基氢氧化铵溶液调节步骤c)中合成的四钛酸纳米片胶态悬浮液的pH值为13.0。取40mL调节好pH值的纳米片悬浮液加入到内部容积为70mL的四聚乙烯反应釜中，，密封后，放入高温旋转反应炉中，在140℃下加热30小时。冷却至室温后，离心分离、用去离子水洗涤4次，然后冷冻干燥。得到暴露{010}晶面的锐钛型TiO2纳米晶，其形貌为梭形。
上述实施1～实施8在合成TiO2纳米晶的过程中，采用离心分离的相关参数可以为离心的转速为8000转/分钟，离心时间为10分钟。
需要说明的是，本发明实施例中所采用的离心的相关参数只是为了让本领域技术人员能够更好的理解TiO2纳米晶的合成方法，并不代表只能所列举的相关参数才能实现本发明的技术方案，本领域技术人员可以根据实际情况对该参数进行调整，这都是可行的。本发明在此不作具体限定。
上述实施1～实施8在合成TiO2纳米晶的过程中，采用的冷冻干燥具体为：将样品放在冷冻专用的玻璃瓶中，然后安装在冷冻机中，打开旋转按钮，使含样品的水溶液在冷冻机中旋转冷冻成冰，冷冻机中液体的温度为-15℃～30℃即可，样品冷冻时间一般为30分钟，即可结成冰，当然样品中水溶液的量多时，时间要长些。冷冻成冰后，关闭旋转按钮和冷冻机，将冷冻瓶取出，安装到干燥机上，打开真空泵，抽真空至压力表表压大约为-0.09Mpa，使其在真空条件下干燥24小时。
同理，本实施例中所采用的冷冻干燥的相关参数只是为了让本领域技术人员能够更好的理解TiO2纳米晶的合成过程，并不代表只能所列举的相关参数才能实现本发明的技术方案，本领域技术人员可以根据实际情况对该参数进行调整，这都是可行的。本发明在此不作具体限定。
二、TiO2纳米晶的表征
1、XRD(X-ray diffraction，X射线衍射)分析
(a)采用SHIMADZU XRD-6100衍射仪分别对本发明实施例1步骤a)中合成的四钛酸钾(K2Ti4O9)、步骤b)中合成的四钛酸(H2Ti4O9·0.25H2O)、步骤c)中合成的四甲基氨离子(TMA+)***的四钛酸(TMA+-intercalated H2Ti4O9)及四钛酸纳米片胶态悬浮液中的剥离的纳米带状的四钛酸(Nanoribbon)进行XRD表征，其中，收集数据衍射角(2θ)的范围是3～70°，扫描速度是5°/min，加速电压和应用的电流分别是40kV和30mA。结果如图1所示。
从图1中可以看出，K2Ti4O9的(200)晶面的层间距由0.87nm减小到H2Ti4O9·0.25H2O的0.77nm，表明K2Ti4O9成功的发生了质子化，随着TMA+离子的***，其(200)晶面的层间距增加到1.82nm，表明TMA+与H+发生了交换反应，成功***到四钛酸的层间。TMA+***的四钛酸溶于水中，搅拌3天后，得到其对应的纳米带胶态悬浮液。将TMA+***的四钛酸纳米带胶态悬浮液离心分离后，进行XRD表征，发现在2θ为20°～40°范围内出现了一个晕轮，表明层状H2Ti4O9成功发生了的剥离反应，剥离成了纳米带；于此同时，XRD衍射谱图中在层间距为0.78nm、0.58nm、0.29nm处出现了峰强度较弱的衍射峰，表明发生剥离形成的部分纳米带在离心后又发生了再配列，重新堆叠成四钛酸。由上述可知，实施例1步骤a)～步骤c)合成了相应的目标产物。由于实施例2～8中步骤a)～步骤c)所得到的产物与实施例1相同，其XRD衍射谱图参照图1即可，本发明在此不作赘述。
(b)采用SHIMADZU XRD-6100衍射仪分别对本发明实施例1～实施例2合成的TiO2纳米晶进行XRD表征，其中，收集数据衍射角(2θ)的范围是3～70°，扫描速度是5°/min，加速电压和应用的电流分别是40kV和30mA。结果如图2所示。
从图2中可以看出，实施例1和实施例2所合成的TiO2纳米晶都是锐钛型(anatase)TiO2，与JCPDS为21-1272的标准卡对应。从此XRD衍射谱图可以看出，在pH＝7.0时，测得的衍射峰强度较高，说明在pH＝7.0时，合成的TiO2纳米晶颗粒较大，结晶度较高。
由于实施例3所合成的TiO2纳米晶与实施例1和实施例2所合成的TiO2纳米晶相同，其XRD衍射谱图参照图2即可，本发明在此不作赘述。
终上所述，实施例1～实施例3所采用的方法可以合成出锐钛型TiO2纳米晶。
(c)采用SHIMADZU XRD-6100衍射仪分别对本发明实施例4～实施例8合成的TiO2纳米晶进行XRD表征，其中，收集数据衍射角(2θ)的范围是3～70°，扫描速度是5°/min，加速电压和应用的电流分别是40kV和30mA。结果如图3所示。
从图3中可以看出，实施例4～实施例8合成的产物都是锐钛型(anatase)TiO2，与JCPDS为21-1272的标准卡对应。从这五个XRD衍射谱图可以看出，随着pH的升高，测得的衍射峰强度增大，宽度变窄，说明合成的TiO2纳米晶颗粒较大，结晶度较高。
2、场发射扫描电镜(field emission scanning electron microscope，简称FE-SEM)分析
(a)采用HITACHI S-90X型号的场发射扫描电镜对本发明实施例1和实施例2及实施例3合成的TiO2纳米晶形貌和微观结构进行分析，样品的制备是将样品溶解到去离子水中，超声后，取一滴点滴在硅板上，测定时加速电压是15kV，应用电流是10μA。其结果如图4所示。
从图4中可以看出，实施例1所合成的的锐钛型TiO2纳米晶的形貌为方块形和菱形，其颗粒平均大小为50nm左右。实施例2及实施例3所合成的锐钛型TiO2纳米晶的形貌为梭型，其颗粒平均大小分别为150nm和480nm左右。
由图4可知，pH值对颗粒的形貌和大小都有着重要的影响。
(b)采用HITACHI S-90X型号的场发射扫描电镜对本发明实施例4～实施例8合成的TiO2纳米晶形貌和微观结构进行分析，样品的制备是将样品分散到去离子水中，超声后，取一滴点滴在硅板上，测定时加速电压是15kV，应用电流是10μA。其结果如图5所示。
从图5(a)可以看出，实施例4(pH＝5.0)所合成的锐钛型TiO2纳米晶的形貌为方块形和菱形，其颗粒平均大小为50nm左右。从图5(b)～(e)中可以看出，实施例5～8(PH＞5)所合成的锐钛型TiO2纳米晶的形貌为梭型，其颗粒平均尺寸也随着pH的升高在增大。说明，pH对颗粒的形貌和大小都有着重要的影响。
3、透射电子显微镜(TEM)分析
对实施例1合成的TiO2纳米晶进行透射电子显微镜(TEM)及高分辨透射电子显微镜(HR-TEM)测试，测试条件为：加速电压是300kV，样品准备在载有碳膜的标准铜网格上。其结果如图6(a)和图6(b)所示；
对实施例2合成的TiO2纳米晶进行透射电子显微镜(TEM)及高分辨透射电子显微镜(HR-TEM)测试，测试条件为：加速电压是300kV，样品准备在载有碳膜的标准铜网格上。其结果如图6(c)和图6(d)所示；
从图6(a)可以看出，在pH＝5.0的条件下，所合成的锐钛型TiO2纳米晶的形貌为方块形和菱形。图6(b)中，晶面间距3.51
Figure PCTCN2015080268-appb-000001
和
Figure PCTCN2015080268-appb-000002
，分别对应于锐钛型TiO2的(101)和(004)晶面，这两个晶面间的夹角为68.3°，与根据锐钛型TiO2的(101)和(004)晶面常数计算的结果相一致。从图6(c)可以看出，在pH＝7.0的条件下，所合成的锐钛型TiO2纳米晶的形貌为梭形。图6(d)中，晶面间距
Figure PCTCN2015080268-appb-000003
Figure PCTCN2015080268-appb-000004
和
Figure PCTCN2015080268-appb-000005
分别对应于锐钛型TiO2的(101)和(002)晶面，其夹角为68.3°。由图6(b)和6(d)可以看出，本发明所合成的锐钛型TiO2纳米晶的暴露晶面都为{010}晶面。
对实施例5合成的TiO2纳米晶进行透射电子显微镜(TEM)及高分辨透射电子显微镜(HR-TEM)测试，测试条件为：加速电压是300kV，样品准备在载有碳膜的标准铜网格上。其结果如图7(a)和图7(b)所示；
对实施例6合成的TiO2纳米晶进行透射电子显微镜(TEM)及高分辨透射电子显微镜(HR-TEM)测试，测试条件为：加速电压是300kV，样品准备在载有碳膜的标准铜网格上。其结果如图7(c)和图7(d)所示；
从图7(a)可以看出，在pH＝5.0的条件下，所合成的锐钛型TiO2纳米晶的形貌为方块形和菱形。图7(b)中，晶面间距
Figure PCTCN2015080268-appb-000006
和
Figure PCTCN2015080268-appb-000007
分别对应于锐钛型TiO2的(101)和(002)晶面，这两个晶面间的夹角为68.3°，与根据锐钛型TiO2的(101)和(002)晶面常数计算的结果相一致。从图7(c)可以看出，在pH＝6.2的条件下，所合成的锐钛型TiO2纳米晶的形貌为梭形。图7(d)中，晶面间距
Figure PCTCN2015080268-appb-000008
和
Figure PCTCN2015080268-appb-000009
分别对应于锐钛型TiO2的(101)和(002)晶面，其夹角为68.3°。由图7(b)和7(d)可以看出，本发明所合成的锐钛型TiO2纳米晶的暴露晶面都为{010}晶面。
综合上述表征分析可知，应用本发明所提供的合成方法可以合成出了暴露{010}晶面锐钛型TiO2纳米晶。
三、TiO2纳米晶的性能分析
由于本发明实施例1～实施例8分别在合成出了菱形和方块形貌的锐钛型TiO2纳米晶及梭形形貌的锐钛型TiO2纳米晶，因此，在这里分别对两种形貌的锐钛型TiO2纳米晶进行性能分析，其中，菱形和方块形貌的锐钛型TiO2纳米晶以实施例1为例，梭形形貌的锐钛型TiO2纳米晶以实施例2为例，由于其它实施例合成的锐钛型TiO2纳米晶，均与实施1或实施例2相同，所以它们的性能参考实施例1或实施例2即可。
1、光催化实验
称取50mg实施例1和实施例2合成的锐钛型TiO2纳米晶，分别加入到150mL的锥形瓶中，然后向每一个锥形瓶中加入100mL 10mg/L的甲基蓝溶液，超声2h以使两个样品均匀分散。在照射之前，将两个锥形瓶中的悬浮液在暗处剧烈搅拌30min，以使染料在二氧化钛纳米晶表面达到吸附/去吸附平衡，然后在搅拌的条件下将两个锥形瓶中悬浮液放在250W紫外灯下照射，紫外灯的发射波长365nm，距离甲基蓝溶液的距离是80cm。每隔20min，在两个锥形瓶中分别取3mL悬浮液，离心以除去二氧化钛纳米晶。甲基蓝的降解速率通过使用TU-1901分光光度计测定紫外灯照射前后甲基蓝溶液的浓度变化确定。作为对比，商业用的德固赛P25(52.50m2/g，80％锐钛矿和20％金红石)在同样的条件下测定。测试结果分别如图8和图9所示。
图8为实施例1合成的TiO2纳米晶的降解效率与光照时间特性曲线，由图可以看出，在120分钟时，实施1所合成的锐钛型TiO2纳米晶对甲基蓝的降解效率为99％，P25对甲基蓝的降解效率86％，因此，实施1所合成的锐钛型TiO2纳米晶对甲基蓝的降解效率要远高于德固赛P25对甲基蓝的降解效率。
图9为实施例2合成的TiO2纳米晶的降解效率与光照时间特性曲线，由图可以看出，在120分钟时，实施2所合成的锐钛型TiO2纳米晶对甲基蓝的降解效率为96％，P25对甲基蓝的降解效率86％，因此，实施2所合成的锐钛型TiO2纳米晶对甲基蓝的降解效率要远高于德固赛P25对甲基蓝的降解效率。
综上所述，本发明实施例所合成的暴露{010}晶面锐钛型TiO2纳米晶，无论 是菱形和方块形貌，还是梭形形貌，其对甲基蓝的降解效率均高于德固赛P25对甲基蓝的降解效率。说明本发明实施例所合成的暴露{010}晶面锐钛型TiO2纳米晶有着良好的光催化性能。
2、光伏打性能测试
称取0.5g实施例1和实施例2合成的锐钛型TiO2纳米晶，并将它们分别加入到玻璃瓶中，然后再向两个玻璃瓶中加入2.5g乙醇，2.0gα-松油醇，1.4g10w％的乙基纤维素10和1.1g 10w％的乙基纤维素45，然后对两个玻璃瓶均超声处理5min，在室温下球磨3天，最后在真空旋转蒸发仪旋转蒸发掉乙醇，制得实施例1的TiO2浆和实施例2的TiO2浆。
用去离子水超声处理FTO玻璃(长×宽×高＝50mm×50mm×2.2mm，表面电阻率～7Ω/sq，Aldrich公司生产)5min，然后再用乙醇超声处理5min。将洗涤好的FTO玻璃浸于0.1M Ti(OC3O7)4有机钛溶液中数秒钟，然后在高温炉中煅烧60min。多孔二氧化钛薄膜电极使用刮刀法将实施例1和实施例2的TiO2浆分别涂到FTO导带玻璃上制备。薄膜的厚度通过所使用的胶带的厚度控制。将实施例1和实施例2的TiO2浆分别涂抹在FTO导电玻璃上后，在高温炉中315℃煅烧15min，如此操作多次直至得到所需的膜厚后，再在高温炉中450℃煅烧30min。冷却至室温后，再次将其浸于0.1M Ti(OC3O7)4有机钛溶液中数秒钟，然后再在高温炉中煅烧60min。等温度降低到80℃时，将其取出，迅速浸没于含3×10-4mol/L N719的乙腈和叔丁醇的混合溶液中，在暗处室温下放置24h，以使染料吸附在二氧化钛电极上。Pt对电极通过将FTO导电玻璃浸于含0.5mM H2PtCl6的异丙醇溶液中，数分钟后取出，然后在高温炉中400℃煅烧20min制备。电解质溶液依靠毛细管作用注入到两电极之间的空隙中，组装成三明治结构的染料敏化太阳能电池。电解质溶液是由含0.60mol/L 1-丁基-3-甲基咪唑碘化物(1-Butyl-3-methylimidazolium iodide)，0.10mol/L硫氰酸胍(Guanidine Thiocyanate)，0.50mol/L 4-叔丁基吡啶(4-tert-Butylpyridine)的乙腈(Acetonitrile)和戊腈(Valeronitrile)的混合溶液(体积比＝85％∶15％)组成的。由同样方法制备的德固赛P25TiO2的光电阳极组装成电池，与上述电池进行对照。测试结果如图10及图11所示。
图10为在膜厚为13.8μm时，实施例1的光电流-电压特征曲线图，从图中 可以看出，合成的优先暴露{010}晶面的锐钛型TiO2纳米晶光电电流为12.6mA/cm2，转化效率为5.09％，明显优于P25的光电电流10.3mA/cm2，转化效率4.37％。
图11为在膜厚为16.4μm时，实施例2的光电流-电压特征曲线图，从图中可以看出，合成的优先暴露{010}晶面的锐钛型TiO2纳米晶光电电流为13.6mA/cm2，转化效率为5.48％，明显优于P25的光电电流10.3mA/cm2，转化效率4.37％。
本发明采用了一种新方法合成优先暴露{010}晶面的锐钛型TiO2纳米晶，这种方法成本低、无污染、制备工艺简单、可控性强、生产周期短、可重复性好，“绿色化学”的要求，适用于工业化生产。采用本发明所供的方法制备的{010}晶面的锐钛型TiO2纳米晶纯度高、粒径分布均匀，用于降解甲基蓝溶液和染料敏化太阳能电池中，与商业用的德固赛P25TiO2(52.50m2/g，80％锐钛矿和20％金红石)相比，催化性能和光伏打性能都得到了显著提高。
以上对本发明所提供的一种TiO2纳米晶合成方法进行了详细介绍。本文中应用了具体实施例对本发明的原理及实施方式进行了阐述，以上实施例的说明只是用于帮助理解本发明的方法及其中心思想。应当指出，对于本领域的普通技术人员来说，在不脱离本发明原理的前提下，还可以对本发明进行若干改进和修饰，这些改进和修饰也落入本发明权利要求的保护范围内。

Claims (10)

  1. 一种TiO2纳米晶的合成方法，其特征在于，包括以下步骤：
    以四钛酸纳米片胶态悬浮液为前驱体，调节前驱体的pH值，使其pH值在5～13之间；将pH值在5～13之间的前驱体进行水热反应，得到TiO2纳米晶。
  2. 如权利要求1所述的方法，其特征在于：水热反应后，分离所得产物，然后对所得产物进行洗涤、过滤及干燥操作。
  3. 如权利要求1所述的方法，其特征在于：所述将pH值在5～13之间的前驱体进行水热反应，具体为：
    将pH值在5～13之间的前驱体在160℃～200℃微波辐射1小时～2小时；
    或者
    将pH值在5～13之间的前驱体加热至140℃～200℃后，保温18小时～30小时。
  4. 如权利要求1所述的方法，其特征在于：用第一盐酸溶液与第一四甲基氢氧化铵溶液调节前驱体的pH值，所述第一盐酸溶液的浓度为1mol/L-3mol/L；所述第一四甲基氢氧化铵溶液的浓度为0.5mol/L～2mol/L。
  5. 如权利要求1所述的方法，其特征在于，前驱体四钛酸纳米片胶态悬浮液的制备方法包括以下步骤：
    a)合成层状四钛酸钾：以K2CO3和锐钛型TiO2原料，将K2CO3和锐钛型TiO2混匀后，升温至800℃～1000℃，反应20小时～30小时，制得层状四钛酸钾，其中，所述K2CO3和锐钛型TiO2的摩尔比为(1～1.1)∶4；
    b)合成四钛酸：将步骤a)中合成的四钛酸钾溶于第二盐酸溶液中，进行质子交换反应，反应结束后，分离所得产物，然后对所得产物进行洗涤、过滤及干燥操作，得到四钛酸；
    c)合成四钛酸纳米片胶态悬浮液：将步骤b)中合成的四钛酸加入到第二四甲基氢氧化铵溶液中，得到混合液；将所述混合液在90℃～110℃下反应20小时～30小时，反应结束后，将所得反应物与水混合并搅拌，静止后过滤，得到前驱体四钛酸纳米片胶态悬浮液。
  6. 如权利要求5所述的方法，其特征在于：在步骤a)中，将K2CO3和锐钛型TiO2混匀后，在升温至800℃～1000℃之前，还包括：充分研磨。
  7. 如权利要求5所述的方法，其特征在于：在步骤a)中，所述升温的速率为2℃/分钟～8℃/分钟。
  8. 如权利要求5所述的方法，其特征在于：步骤b)中的第二盐酸溶液的浓度为0.7mol/L～2mol/L。
  9. 如权利要求5所述的方法，其特征在于：步骤b)中所述将步骤a)中合成的四钛酸钾溶解于第二盐酸溶液中，进行质子交换反应，具体为：
    将步骤a)中合成的四钛酸钾溶解于第二盐酸溶液中，搅拌3～5天，并每天更换一次第二盐酸溶液。
  10. 如权利要求5所述的方法，其特征在于：步骤c)中四钛酸与四甲基氢氧化铵的质量比为1∶(1.2～3)。
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