Preparation method of TiO2 / carbon dot composite material, product and application thereof

Abstract

The application discloses a preparation method of TiO2 / carbon dot composite material, the obtained product and application, and relates to the following steps: adding an alcohol salt of titanium into ethanol to perform partial hydrolysis, then separating and precipitating, washing with water, and drying to obtain a titanium precursor; grinding the carbon dots, an ammonium salt and the titanium precursor in the presence of ethanol; calcining the ground mixture in air, then washing with water to remove soluble substances; treating the washed sample in acetic acid, then performing heating treatment to obtain the TiO2 / carbon dot composite material. The carbon dots which can absorb visible light are in-situ deposited on the anatase TiO2 photocatalyst, and hydrogen ions are introduced into the carbon dot interlayer, so that the separation efficiency of photo-generated carriers is further improved, and the obtained composite material can absorb ultraviolet and visible light, and the photocatalytic effect is greatly improved.

Description

Technical Field

[0001] The present invention relates to a method for preparing a TiO2 / carbon dot composite material, specifically to a method for loading carbon dots with visible light absorption on TiO2 nanopowder with ultraviolet light response to form a TiO2 / carbon dot composite material. The present invention also relates to the TiO2 / carbon dot composite material obtained according to the method and the application of the composite material as a photocatalyst, belonging to the field of new energy materials and application technology. Background Art

[0002] Titanium dioxide (TiO2) photocatalyst is a broadband semiconductor material with high chemical stability and is non-toxic and harmless, making it one of the most widely used photocatalytic materials. Titanium dioxide can be excited by ultraviolet light, exhibits high catalytic activity, and its photogenerated charges possess sufficiently strong redox capacity to catalyze the degradation and mineralization of most organic pollutants. It is inexpensive, readily available, safe, and non-toxic. However, because it primarily absorbs ultraviolet light, its utilization of visible light is low. The high recombination rate of photogenerated carriers and low quantum efficiency make it difficult to treat high-concentration and large-volume industrial and domestic wastewater. Although visible light response can be achieved through doping, the efficiency remains relatively low. Therefore, expanding the light absorption range of TiO2 photocatalysts has become a key focus of research. Carbon dots are a new type of zero-dimensional photoluminescent nanomaterial with a particle size of less than 100nm. They have adjustable fluorescence emission and excitation wavelengths, good photostability, water solubility and biocompatibility, low toxicity, and contain rich functional groups on the surface, such as amino, hydroxyl, and carboxyl groups. They are a metal-free, non-toxic and harmless luminescent material. Their adjustable visible light range absorption can make up for the shortcomings of TiO2 photocatalytic materials and improve the utilization rate of sunlight. Summary of the Invention

[0003] In response to the problems that existing TiO2 photocatalysts absorb sunlight in the ultraviolet region and have low sunlight utilization efficiency, the present invention provides a method for preparing a TiO2 / carbon dot composite material and the resulting product. This method in situ deposits carbon dots that can absorb visible light on anatase TiO2 photocatalyst, directly embeds high-quality carbon dots in situ into TiO2 nanopowder, and simultaneously introduces hydrogen ions between the carbon dot layers, further improving the separation efficiency of photogenerated carriers. The resulting composite material can absorb ultraviolet and visible light, and the photocatalytic effect is greatly enhanced.

[0004] The specific technical solutions of the present invention are as follows:

[0005] A method for preparing a TiO2 / carbon dot composite material, the method comprising the following steps:

[0006] (1) Add titanium alkoxide dropwise to ethanol for partial hydrolysis, then separate the precipitate, wash with water, and dry to obtain a titanium precursor;

[0007] (2) grinding carbon dots, ammonium salt, and titanium precursor in the presence of ethanol;

[0008] (3) calcining the ground mixture in air and then washing with water to remove soluble matter;

[0009] (4) The washed sample was treated in acetic acid and then heated to obtain a TiO2 / carbon dot composite material.

[0010] Furthermore, in step (1), the titanium alkoxide is tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate or tetrabutyl titanate.

[0011] Furthermore, in step (1), titanium alkoxide is added dropwise to ethanol to partially hydrolyze the titanium alkoxide to form an incompletely hydrolyzed titanium precursor. The volume ratio of titanium alkoxide to ethanol is 0.1-0.15:1, for example, 0.1:1, 0.11:1, 0.12:1, 0.13:1, 0.14:1, or 0.15:1. After the titanium alkoxide is added dropwise, the reaction is stirred for 1-2 hours.

[0012] Furthermore, in step (2), the ammonium salt is ammonia water, ammonium bicarbonate or ammonium chloride. The role of the ammonium salt is to prevent the entry of oxygen during the calcination process and to improve the interface properties between titanium dioxide and carbon dots.

[0013] Furthermore, in step (2), the carbon dots can be luminescent carbon dots of various colors, and the luminescent colors of the carbon dots are within the visible light range.

[0014] Furthermore, in step (2), the mass ratio of carbon dots to titanium precursor is 0.01-0.02:1, for example, 0.01:1, 0.011:1, 0.012:1, 0.013:1, 0.014:1, 0.015:1, 0.016:1, 0.017:1, 0.018:1, 0.019:1, and 0.02:1.

[0015] Furthermore, in step (2), the mass ratio of the ammonium salt to the titanium precursor is 0.8-1.2:1, for example, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1.

[0016] Furthermore, in step (2), grinding is performed in the presence of ethanol to ensure more complete and uniform grinding, and the grinding time is 4-5 h.

[0017] Furthermore, in step (2), the carbon dots, ammonium salt, and titanium precursor are ground in ethanol. The purpose of grinding is to allow the incompletely hydrolyzed Ti precursor to react with the carbon dots in the presence of ammonium salt, thereby improving the interfacial properties of titanium dioxide and carbon dots and increasing the photocatalytic efficiency. During the grinding process, the carbon dots can be anchored on the TiO2 surface to prevent oxidation. There is no special requirement for the mixing order of the carbon dots, ammonium salt, titanium precursor, and ethanol. The carbon dots can be dispersed in ethanol first, and then the ammonium salt and titanium precursor are added. Alternatively, the carbon dots, ammonium salt, and ethanol can be mixed first, and then mixed with the titanium precursor. Alternatively, they can be mixed together at the same time. The grinding time is generally 4-5 hours.

[0018] Furthermore, in step (3), the calcination temperature is 400-500°C, for example, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, or 500°C. Calcination can be performed in an air atmosphere, and the carbon dots are not oxidized during the calcination process. Preferably, the calcination time is 0.5-2 hours, for example, 0.5 hours, 1 hour, 1.5 hours, or 2 hours.

[0019] Furthermore, in step (4), the calcined sample is first washed with water to remove soluble matter to obtain a powder sample, and then the sample is treated in acetic acid. The purpose of the acetic acid treatment is to introduce hydrogen ions. The concentration of acetic acid is 1-2 mol / L, for example, 1 mol / L, 1.5 mol / L, or 2 mol / L. Preferably, the acetic acid treatment time is 10-20 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, or 20 hours.

[0020] Furthermore, in step (4), the purpose of the heat treatment is to allow hydrogen ions to enter the interlayers of the graphite phase carbon dots. The heat treatment temperature is 90-110°C, for example, 90°C, 95°C, 100°C, 105°C, or 110°C. Preferably, the treatment time is 1-3 hours, for example, 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours.

[0021] The present invention deposits carbon dots with visible light absorption in situ and uniformly on anatase TiO2 nanopowder during the synthesis of anatase TiO2. Due to the adjustable absorption range of the carbon dots, the light absorption of the composite material can be expanded to the entire visible light range, thereby obtaining a photocatalyst with good performance. During the preparation process, the composite material is soaked in acetic acid and then heat-treated, thereby introducing hydrogen ions between the carbon dot layers. The further insertion of hydrogen ions is beneficial to carrier transport, further enhancing the catalytic effect. The carbon dots used in the present invention are cheap and green. When combined with traditional TiO2 photocatalyst materials, they are inexpensive and have excellent photocatalytic effects. They are an efficient composite photocatalyst that is more conducive to industrial application. Therefore, the TiO2 / carbon dot composite material obtained according to the above method and its application as a photocatalyst are also within the scope of protection of the present invention.

[0022] Furthermore, the present invention also provides the use of the composite material as a NO removal catalyst.

[0023] The present invention has the following beneficial effects:

[0024] 1. The method of the present invention has simple process, good repeatability, and cheap and readily available raw materials, which is conducive to industrial production.

[0025] 2. The present invention compounds carbon dots with anatase titanium dioxide and introduces hydrogen ions at the same time. Since the carbon dots respond to visible light, the solar energy utilization efficiency of the TiO2 photocatalyst is increased. The introduction of hydrogen ions improves the separation efficiency of photogenerated carriers. The resulting composite material can absorb ultraviolet and visible light, greatly enhancing the photocatalytic effect. It is an efficient composite photocatalyst, and the composite material has good stability and stable photocatalytic performance after long-term use.

[0026] 3. The catalyst of the present invention can be used for photolysis of water to produce hydrogen, photocatalytic reduction of CO2, NO x It has high efficiency in catalytic oxidation, photocatalytic hydrogen peroxide production and chemical fuel conversion, especially in the photocatalytic oxidation of NO, and has good application prospects in the environmental field. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an electron microscope photograph of the sample obtained in Example 1.

[0028] Figure 2 This is a diagram showing the experimental results of using the sample obtained in Example 1 as a photocatalyst to treat NO.

[0029] Figure 3 This is a graph showing the experimental results of cyclic stability of the sample obtained in Example 1 as a photocatalyst for treating NO. DETAILED DESCRIPTION

[0030] The present invention will be further described below by way of examples. It should be understood that the following description is only for the purpose of explaining the present invention and does not limit its contents.

[0031] In the following examples, carbon dots were purchased from Nanjing Chico Biotechnology Co., Ltd., Beijing Beike Nanotechnology Co., Ltd., and other companies.

[0032] Example 1

[0033] 1.1 Add 2 ml of tetrabutyl titanate dropwise to 20 ml of ethanol, stir for 2 h, centrifuge, wash, and dry to obtain titanium precursor powder.

[0034] 1.2 Concentrate the commercially available ethanol solution of green-luminescent carbon dots to obtain 2 ml of carbon dot solution containing 0.015 g of green-luminescent carbon dots. Mix this carbon dot solution, 1 g of ammonium bicarbonate, and 1 g of the titanium precursor obtained in step 1.1. Grind in a mortar for 4 h. If the ethanol evaporates during the grinding process, add more ethanol. Grind to obtain a dry powder.

[0035] 1.3 The powder obtained by grinding in step 1.2 was heat-treated at 450°C in air atmosphere for 1.2 hours, and then the sample was washed with water three times to remove unreacted soluble matter;

[0036] 1.4 The sample obtained in step 1.3 was immersed in 1.5 M acetic acid solution for 15 hours, centrifuged and dried, and then treated at 100 degrees Celsius for 1.5 hours to obtain a TiO2 / carbon dot composite photocatalyst.

[0037] Figure 1 This is an electron microscope photo of the sample. It can be seen from the picture that the carbon dots are evenly distributed in the TiO2 nanopowder.

[0038] Example 2

[0039] 2.1 Add 2 ml of tetraethyl titanate dropwise to 13.5 ml of ethanol, stir for 1.5 h, centrifuge, wash, and dry to obtain titanium precursor powder.

[0040] 2.2 Concentrate the commercially available ethanol solution of red-luminescent carbon dots to obtain 2 ml of carbon dot solution containing 0.02 g of red-luminescent carbon dots. Mix this carbon dot solution, 1 g of 25 wt% ammonia water, and 1 g of the titanium precursor powder obtained in step 2.1. Grind in a mortar for 4 h. If the ethanol evaporates during the grinding process, add more ethanol. Grind to obtain a dry powder.

[0041] 2.3 The powder obtained in step 2.2 was heat-treated at 400°C in air atmosphere for 2 hours, and then the sample was washed with water three times to remove unreacted soluble matter;

[0042] 2.4 The sample obtained in step 2.3 was soaked in 1 M acetic acid solution for 20 hours, dried by centrifugation and then treated at 95 degrees Celsius for 3 hours to obtain TiO2 / carbon dot composite photocatalyst. The sample morphology was similar to that of Example 1, and the carbon dots were uniformly distributed in the TiO2nanopowder.

[0043] Example 3

[0044] 3.1 1.5 ml of tetramethyl titanate was added dropwise to 10 ml of ethanol, and after the dropwise addition was completed, the mixture was stirred for 1 h. After centrifugation, washing and drying, a titanium precursor powder was obtained.

[0045] 3.2 An ethanol solution of commercially available blue luminescent carbon dots was concentrated to obtain 2 ml of a carbon dot solution containing 0.01 g of blue luminescent carbon dots. The carbon dot solution, 1 g of ammonium chloride and 1 g of the titanium precursor powder obtained in step 3.1 were mixed and ground in a mortar for 4 h. If the ethanol evaporated during the grinding process, ethanol was added again. Finally, dry powder was obtained after grinding.

[0046] 3.3 The powder obtained in step 3.2 was heat treated at 500 degrees Celsius in an air atmosphere for 0.5 hours. After that, the sample was washed with water 3 times to remove unreacted soluble substances.

[0047] 3.4 The sample obtained in step 3.3 was soaked in 1.8 M acetic acid solution for 10 hours, dried by centrifugation and then treated at 110 degrees Celsius for 2 hours to obtain a TiO2 / carbon dot composite photocatalyst. The sample morphology was similar to that of Example 1, and the carbon dots were uniformly distributed in the TiO2nanopowder.

[0048] Example 4

[0049] 4.1 1 ml of tetrapropyl titanate was added dropwise to 8.5 ml of ethanol, and after the dropwise addition was completed, the mixture was stirred for 1.5 h. After centrifugation, washing and drying, a titanium precursor powder was obtained.

[0050] 4.2 An ethanol solution of commercially available green luminescent carbon dots was concentrated to obtain 2 ml of a carbon dot solution containing 0.015 g of green luminescent carbon dots. The carbon dot solution containing 0.015 g of green luminescent carbon dots, 1 g of ammonium bicarbonate and 1 g of the titanium precursor powder obtained in step 4.1 were mixed and ground in a mortar for 4 h. If the ethanol evaporated during the grinding process, ethanol was added again. Finally, dry powder was obtained after grinding.

[0051] 4.3 The powder obtained in step 4.2 was heat treated at 480 degrees Celsius in an air atmosphere for 2 hours. After that, the sample was washed with water 3 times to remove unreacted soluble substances.

[0052] 4.4 The sample obtained in step 4.3 was immersed in a 1.5 M acetic acid solution for 15 hours, centrifuged, dried, and then treated at 90°C for 2 hours to obtain a TiO2 / carbon dot composite photocatalyst. The sample morphology was similar to that of Example 1, with the carbon dots evenly distributed throughout the TiO2 nanopowder.

[0053] Comparative Example 1

[0054] The photocatalyst was prepared according to the steps of Example 1, except that ammonium bicarbonate was not added in step 1.2. The final product did not contain carbon dots.

[0055] Comparative Example 2

[0056] The photocatalyst was prepared according to the steps of Example 1, except that the acetic acid treatment was not performed and step 1.4 was omitted. The final product contained carbon dots.

[0057] Comparative Example 3

[0058] The photocatalyst was prepared according to the steps of Example 1, except that in step 1.3, the calcination temperature was 550 degrees Celsius. The final product contained fewer carbon dots.

[0059] NO photocatalytic oxidation experiment

[0060] NO photocatalytic oxidation tests were conducted under full-spectrum conditions (using a 300W Xe lamp as a light source). 100mg of the photocatalysts prepared in the above examples and comparative examples were anchored to a quartz glass plate on the bottom plate of a photocatalytic reactor. The reactor was bubbling with NO gas for 0.5 hours. The light source was then turned on and the reactor was connected to a NOx analyzer. NO concentrations were monitored and recorded every 1 minute. After 8 minutes of reaction, the NO removal efficiency was calculated.

[0061] NO removal efficiency = (1-C / C0) × 100%, where C0 represents the initial NO concentration and C represents the NO concentration at different time points.

[0062] The NO removal efficiency after 8 minutes of reaction is shown in Table 1 below, where the NO removal efficiency of the catalyst in Example 1 at different time points is shown in Table 1. Figure 2 shown.

[0063]

[0064] It can be clearly seen from the data in Table 1 that the photocatalyst obtained by the method of the present invention has a very good removal effect on NO, and a high removal rate can be achieved in 8 minutes.

[0065] The stability cycle test of the photocatalyst of Example 1 was carried out in the same manner as above for 4 times. Figure 3As shown in the figure, after four stability cycle experiments, the catalyst removal capacity of Example 1 did not decrease, indicating that the material has good stability.

Claims

1. A method for preparing a TiO2 / carbon dot composite material, characterized in that The following steps are involved: (1) Add titanium alkoxide dropwise to ethanol for partial hydrolysis, then separate the precipitate, wash with water, and dry to obtain a titanium precursor; (2) grinding carbon dots, ammonium compounds, and titanium precursors in the presence of ethanol; (3) calcining the ground mixture in air and then washing with water to remove soluble matter; (4) The washed sample is treated in acetic acid and then heated to obtain a TiO2 / carbon dot composite material; In step (2), the ammonium compound is ammonia water, ammonium bicarbonate or ammonium chloride, the mass ratio of carbon dots to titanium precursor is 0.01-0.02:1, and the mass ratio of ammonium compound to titanium precursor is 0.8-1.2:1; In step (3), the calcination temperature is 400-500°C and the calcination time is 0.5-2 hours; In step (4), the concentration of acetic acid is 1-2 mol / L, and the acetic acid treatment time is 10-20 hours; In step (4), the heating temperature is 90-110°C and the treatment time is 1-3 hours.

2. The preparation method according to claim 1, wherein: In step (1), the titanium alkoxide is tetramethyl titanate, tetraethyl titanate, tetrapropyl titanate or tetrabutyl titanate.

3. The preparation method according to claim 1 or 2, characterized in that: In step (1), the volume ratio of titanium alkoxide to ethanol is 0.1-0.15:

1.

4. The preparation method according to claim 1, wherein: In step (2), the grinding time is 4-5 hours.

5. A TiO2 / carbon dot composite material prepared according to the preparation method of any one of claims 1 to 4.

6. Use of the TiO2 / carbon dot composite material according to claim 5 as a photocatalyst.

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