Carbon quantum dot sensitized TiO2 nanotube photo-anode material and preparation method and application thereof
By sensitizing TiO2 nanotube photoanode materials with carbon quantum dots, the problems of insufficient visible light absorption and electron-hole recombination of TiO2 photoanode materials were solved, realizing efficient photoelectrochemical synthesis of ammonia and improving photoelectrochemical activity and ammonia yield.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-19
- Publication Date
- 2026-04-03
AI Technical Summary
Existing TiO2 photoanode materials have limited absorption of visible light due to their wide bandgap characteristics. Photogenerated electron-hole pairs are prone to recombination, resulting in low light energy utilization and insufficient catalytic activity. Traditional organic dyes also have poor sensitization stability, which limits their application in photocatalytic ammonia synthesis.
By preparing a carbon quantum dot-sensitized TiO2 nanotube photoanode material, the light absorption range is broadened, the surface reactivity is enhanced, and carrier recombination is suppressed by combining carbon quantum dots with TiO2 nanotubes. Carbon quantum dots are loaded onto the TiO2 nanotube array by electrophoretic deposition.
It significantly improved the photoelectrochemical performance of the photoanode, increased the migration rate of photogenerated electrons and the light energy utilization rate, enhanced the absorption capacity of ultraviolet and visible light, suppressed electron-hole recombination, and increased the ammonia yield by 151.5%.
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Figure CN121781209A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrode material technology, specifically relating to a carbon quantum dot sensitized TiO2 nanotube photoanode material, its preparation method, and its application. Background Technology
[0002] Ammonia (NH3), a crucial raw material for modern industry and agriculture, plays a vital role in fertilizer production and energy storage. Due to its carbon-free, hydrogen-rich (17.7 wt%), high energy density (15.3 MJ / L), and lower storage and transportation costs compared to hydrogen, ammonia is considered an ideal next-generation hydrogen energy carrier, showing great promise in future clean energy systems. Currently, industrial ammonia synthesis mainly relies on the Haber-Bosch process. While widely used, this process has significant drawbacks: the reaction requires high temperature and pressure (300-550 ℃, 200-350 atm), resulting in high energy consumption, stringent operation, and the hydrogen it relies on largely originating from the "grey hydrogen" process, leading to substantial greenhouse gas emissions. Therefore, developing green ammonia synthesis technologies that operate under mild conditions and rely on renewable energy sources has significant research value and engineering implications. In photocatalytic ammonia synthesis research, TiO2 has become a commonly used photoanode material due to its non-toxicity, stability, and low cost. However, its wide bandgap limitation restricts its absorption of visible light, and the easy recombination of photogenerated electron-hole pairs leads to low light energy utilization and insufficient catalytic activity. Therefore, modifying TiO2 to improve its catalytic activity is particularly important.
[0003] Titanium dioxide nanotubes have attracted widespread attention due to their unique tubular structure. This structure not only possesses a high specific surface area, which facilitates the exposure of more reactive sites, but also promotes the directional migration of photogenerated carriers and effectively suppresses electron-hole recombination. Furthermore, the ordered nanotube arrays allow for precise modification at specific locations on the tube walls, enabling controllable regulation of properties such as doping, recombination, or defects. Surface sensitization technology, by loading visible light-responsive materials, can effectively broaden the light absorption range of TiO2 and promote charge separation. While traditional organic dye sensitization can extend the spectral response, it suffers from poor stability and easy dissociation, limiting its practical application. In recent years, carbon quantum dots (CQDs), as an emerging inorganic nanomaterial, have become an ideal choice for TiO2 sensitization modification due to their advantages such as upconversion effect, broad spectral absorption, high stability, low toxicity, and low cost. The combination of carbon quantum dots and TiO2 nanotubes can not only extend the light response range but also enhance surface reactivity and suppress carrier recombination, thereby significantly improving the photoelectrochemical performance of photoelectrodes.
[0004] Based on the above advantages, this study proposes to construct a TiO2 nanotube photoanode sensitized by carbon quantum dots, so as to synergistically leverage the structural characteristics of nanotubes and the sensitization effect of carbon quantum dots, providing a new approach to achieve efficient photoelectrocatalytic reactions. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention proposes a carbon quantum dot-sensitized TiO2 nanotube photoanode material, its preparation method, and its applications.
[0006] The technical solution of this invention is as follows: A method for preparing a carbon quantum dot-sensitized TiO2 nanotube photoanode material includes the following steps: S1. Preparation of TiO2 nanotube array: Using pretreated titanium sheet as anode and graphite as cathode, the titanium sheet is anodized, cleaned, and then calcined to obtain TiO2 nanotube array; S2. Preparation of carbon quantum dots: Carbon quantum dots are obtained by mixing citric acid and diethylenetriamine and reacting them hydrothermally. S3. Preparation of carbon quantum dot-sensitized TiO2 nanotube photoanode material: The TiO2 nanotube array prepared in S1 is immersed in the carbon quantum dot solution prepared in S2 for electrophoretic deposition to obtain the carbon quantum dot-sensitized TiO2 nanotube photoanode material.
[0007] Furthermore, the specific technical parameters for the titanium sheet anodizing treatment in step S1 are: anodizing for 2-6 hours at a voltage of 35-45V.
[0008] Furthermore, the specific technical parameters for calcination in step S1 are as follows: calcination at 450°C for 3-5 hours in an air atmosphere, with a heating rate of 4-8°C / min.
[0009] Further, the molar ratio of citric acid to diethylenetriamine in step S2 is 1:(2-5).
[0010] Furthermore, the technical parameters of the hydrothermal reaction in step S2 are as follows: hydrothermal reaction at 160-180℃ for 1-3 hours.
[0011] Furthermore, the specific technical parameters for electrophoretic deposition in step S3 are as follows: applying a potential of -2V to -5V on the TiO2 nanotube array for 60-100s.
[0012] The carbon quantum dot-sensitized TiO2 nanotube photoanode material was prepared according to the preparation method described above.
[0013] Application of the carbon quantum dot-sensitized TiO2 nanotube photoanode material in the photoelectrochemical reduction of nitrogen-containing substances to prepare ammonia.
[0014] Furthermore, the nitrogen-containing substance is nitrogen gas, nitrate, or nitrite.
[0015] Furthermore, the method for preparing ammonia by photoelectrochemical reduction of nitrogen-containing substances using the carbon quantum dot-sensitized TiO2 nanotube photoanode material specifically includes the following steps: using CQDs@TNA as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode; the electrolyte in the anode chamber is 1 M methanol and 0.1 M KOH solution; the electrolyte in the cathode chamber is 10 mM KNO3 and 0.1 M KOH solution; and the light intensity is 100 mW / cm². 2 The potential range is from -1.0 V to 0.5 V, and the reaction is carried out at a constant potential of 0.5 V vs. Ag / AgCl for 2-4 hours.
[0016] Compared with the prior art, the present invention has at least the following advantages: This invention relates to a carbon quantum dot-sensitized TiO2 nanotube photoanode material, its preparation method, and its applications. First, TiO2 nanotube arrays are prepared by anodizing and annealing TiO2. Then, the TiO2 nanotube arrays are electrophoretically deposited in a carbon quantum dot solution to obtain the carbon quantum dot-sensitized TiO2 nanotube photoanode material. The preparation method is simple, the raw materials are widely available, and the price is low. The photoanode material prepared by the method of this invention has a one-dimensional ordered tubular structure, a larger reactive surface area, and can improve the migration rate of photogenerated electrons. The ordered tubular pore structure can promote photon transmission and improve light energy utilization. Compared with TiO2 nanotube photoanodes without carbon quantum dot sensitization, the sensitized photoanode exhibits higher light absorption in both the ultraviolet and visible light regions. Since carbon quantum dots can act as charge carriers, photogenerated charge carriers migrate to the carbon quantum dots, thereby suppressing electron-hole recombination inside the photoanode and further increasing the charge carrier concentration. Therefore, the carbon quantum dot-sensitized TiO2 nanotube photoanode exhibits superior photoelectrochemical activity. Experiments have shown that the ammonia yield is increased by 151.5% compared to the traditional photoanode. Attached Figure Description
[0017] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below.
[0018] Figure 1 These are scanning electron microscope images of the surface and cross-section of CQDs@TNA prepared in Example 1 of this invention; Figure 2 This is a high-resolution scanning spectrum of C1s of CQDs@TNA prepared in Example 1 of the present invention; Figure 3 The UV-Vis absorption spectra of CQDs@TNA and pure TNA prepared in Example 1 of this invention are shown. Figure 4 The PL emission spectra of CQDs@TNA and pure TNA prepared in Example 1 of this invention; Figure 5 The system ammonia yields of different materials: TiO2, TNA, CQDs@TiO2, and CQDs@TNA. Detailed Implementation
[0019] The present invention will now be described in further detail. It should be noted that the following specific embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above application content.
[0020] This invention provides a general and / or specific description of the materials and experimental methods used in the experiments. Unless otherwise specified, all experimental or testing methods are conventional methods; all reagents or instruments used, unless otherwise specified, are commercially available conventional products prepared or used using conventional methods.
[0021] Example 1: Preparation method of carbon quantum dot-sensitized TiO2 nanotube photoanode material S1. Pretreatment: Place the titanium sheet in a 1:1 mixture of ethanol and acetone and ultrasonically clean it for 30 minutes, then ultrasonically clean it with deionized water for 10 minutes to remove surface contaminants, and then dry it under a nitrogen atmosphere for later use. S2. Preparation of TiO2 nanotube array (TNA): Using pretreated titanium sheet as anode and graphite sheet as cathode, anodize at 40V for 3 hours. After oxidation, immerse the sample in pure ethylene glycol for 12 hours, then ultrasonically clean it with deionized water for 1 minute and air dry at room temperature. Calcine the sample in air at 450℃ for 3 hours with a heating rate controlled at 5℃ / min to obtain a crystallized TiO2 nanotube array. S3. Preparation of carbon quantum dots (CQDs): Weigh 2g of anhydrous citric acid and dissolve it in 20 mL of deionized water. Add diethylenetriamine at a molar ratio of 1:4 and stir the solution for 10 min to mix thoroughly. Pour the mixture into a polytetrafluoroethylene (PTFE) liner, place it in a reaction vessel, and put it in a hydrothermal drying oven. Keep it at 170℃ for one hour. After the hydrothermal drying oven cools to room temperature, take out the yellow solution in the PTFE liner and add it into a biomembrane dialysis bag cut to a length of about 10cm. Seal the bag opening with a sealing clip and place it in a beaker. Add enough deionized water to the beaker until the biomembrane dialysis bag is completely submerged. Filter for 24 hours, changing the deionized water once every 12 hours. The carbon quantum dot solution can be obtained by filtration. S4. Carbon quantum dot sensitization to obtain photoanode material (CQDs@TNA): 50 mL of carbon quantum dot solution was poured into an electrolytic cell. A circuit was formed using TiO2 nanotube photoanode and platinum sheet as counter electrode. A potential of -3V was applied to the TiO2 nanotube photoanode for 60 s. The deposition process was repeated twice to finally obtain carbon quantum dot sensitized TiO2 nanotube photoanode material.
[0022] Example 2: Preparation method of carbon quantum dot-sensitized TiO2 nanotube photoanode material S1. Pretreatment: Place the titanium sheet in a 1:1 mixture of ethanol and acetone and ultrasonically clean it for 30 minutes, then ultrasonically clean it with deionized water for 10 minutes to remove surface contaminants, and then dry it under a nitrogen atmosphere for later use. S2. Preparation of TiO2 nanotube array (TNA): Using pretreated titanium sheet as anode and graphite sheet as cathode, anodize at 40V for 3 hours. After oxidation, immerse the sample in pure ethylene glycol for 12 hours, then ultrasonically clean it with deionized water for 1 minute and air dry at room temperature. Calcine the sample in air at 450℃ for 5 hours with a heating rate controlled at 5℃ / min to obtain a crystallized TiO2 nanotube array. S3. Preparation of carbon quantum dots (CQDs): Weigh 2g of anhydrous citric acid and dissolve it in 20 mL of deionized water. Add diethylenetriamine at a molar ratio of 1:5 and stir the solution for 10 min to mix thoroughly. Pour the mixture into a polytetrafluoroethylene (PTFE) liner, place it in a reaction vessel, and put it in a hydrothermal drying oven. Keep it at 180℃ for 3 hours. After the hydrothermal drying oven cools to room temperature, take out the yellow solution in the PTFE liner and add it into a biomembrane dialysis bag cut to a length of about 10cm. Seal the bag opening with a sealing clip and place it in a beaker. Add enough deionized water to the beaker until the biomembrane dialysis bag is completely submerged. Filter for 24 hours, changing the deionized water once every 12 hours. The carbon quantum dot solution can be obtained by filtration. S4. Carbon quantum dot sensitization to obtain photoanode material (CQDs@TNA): 50 mL of carbon quantum dot solution was poured into an electrolytic cell. A circuit was formed using TiO2 nanotube photoanode and platinum sheet as counter electrode. A potential of -3V was applied to the TiO2 nanotube photoanode for 100 s. The deposition process was repeated twice to finally obtain carbon quantum dot sensitized TiO2 nanotube photoanode material.
[0023] Example 3: Preparation method of carbon quantum dot-sensitized TiO2 nanotube photoanode material S1. Pretreatment: Place the titanium sheet in a 1:1 mixture of ethanol and acetone and ultrasonically clean it for 30 minutes, then ultrasonically clean it with deionized water for 10 minutes to remove surface contaminants, and then dry it under a nitrogen atmosphere for later use. S2. Preparation of TiO2 nanotube array (TNA): Using pretreated titanium sheet as anode and graphite sheet as cathode, anodize at 40V for 3 hours. After oxidation, immerse the sample in pure ethylene glycol for 12 hours, then ultrasonically clean it with deionized water for 1 minute and air dry at room temperature. Calcine the sample in air at 450℃ for 4 hours with a heating rate controlled at 5℃ / min to obtain a crystallized TiO2 nanotube array. S3. Preparation of carbon quantum dots (CQDs): Weigh 2g of anhydrous citric acid and dissolve it in 20 mL of deionized water. Add diethylenetriamine at a molar ratio of 1:2 and stir the solution for 10 min to mix thoroughly. Pour the mixture into a polytetrafluoroethylene (PTFE) liner, place it in a reaction vessel, and put it in a hydrothermal drying oven. Keep it at 160℃ for 2 hours. After the hydrothermal drying oven cools to room temperature, take out the yellow solution in the PTFE liner and add it into a biomembrane dialysis bag cut to a length of about 10cm. Seal the bag opening with a sealing clip and place it in a beaker. Add enough deionized water to the beaker until the biomembrane dialysis bag is completely submerged. Filter for 24 hours, changing the deionized water once every 12 hours. The carbon quantum dot solution can be obtained by filtration. S4. Carbon quantum dot sensitization to obtain photoanode material (CQDs@TNA): 50 mL of carbon quantum dot solution was poured into an electrolytic cell. A circuit was formed using TiO2 nanotube photoanode and platinum sheet as counter electrode. A potential of -5V was applied to the TiO2 nanotube photoanode for 80 s. The deposition process was repeated twice to finally obtain carbon quantum dot sensitized TiO2 nanotube photoanode material.
[0024] Example 4: Material Morphology and Structural Characterization Taking the sample prepared in Example 1 as an example, the morphology of its surface and cross-section was observed, and the scanning electron microscope images are shown below. Figure 1 As shown, from Figure 1 As can be seen from ab, the photoanode material maintains a highly ordered, vertically arranged one-dimensional nanotube array structure with uniform tube diameter, indicating that applying voltage and the carbon quantum dot deposition process do not destroy the tubular structure framework of TiO2 nanotubes, and the one-dimensional tubular structure has a larger reactive area.
[0025] Figure 2 The high-resolution scanning spectrum of C 1s for the carbon quantum dot-sensitized TiO2 nanotube photoanode material is shown in the figure. Characteristic peaks appear at 284.1 eV, 285.6 eV, and 287.8 eV, corresponding to CC / C=C, CO, and C=O, respectively. These results demonstrate that carbon quantum dots have been successfully loaded onto the TNA photoanode.
[0026] Example 5: Optical Properties and Charge Separation Efficiency Test To verify the improvement of light absorption and electron-hole pair separation efficiency by carbon quantum dot sensitization, the sample prepared in Example 1 was used as an example to perform ultraviolet-visible absorption spectroscopy and photoluminescence spectroscopy tests.
[0027] The results are as follows Figure 3-4 As shown, Figure 3 The images show the UV-Vis absorption spectra of carbon quantum dot-sensitized TiO2 nanotube photoanodes (CQDs@TNA) and nanotube (TNA) photoanodes. It can be seen that both CQDs@TNA and TNA photoanodes exhibit strong absorption in the UV region. However, compared to pure TNA, the CQDs@TNA sample shows a significant increase in absorbance across the entire visible light region (400-800 nm), indicating that the sensitization effect of carbon quantum dots effectively broadens the photoresponse range of TiO2 and improves light energy utilization.
[0028] Figure 4 The figures show the photoluminescence (PL) emission spectra of CQDs@TNA photoanode and TNA photoanode. Lower PL emission intensity indicates better separation of photogenerated carriers. The figures show that the emission intensity of the CQDs@TNA photoanode is significantly lower than that of the TNA photoanode, indicating that carbon quantum dot sensitization can act as an effective electron acceptor, rapidly capturing and transferring photogenerated electrons from the TiO2 conduction band, thereby suppressing their recombination with holes and effectively improving the electron-hole separation rate.
[0029] Example 6: Photoelectrochemical Ammonia Synthesis Performance Test To quantitatively evaluate the catalytic activity of the prepared photoanode in photoelectrochemical ammonia synthesis, the electrochemical testing method is as follows: TiO2, TNA, CQDs@TiO2 (prepared in the same way as in Example 1, except that TNA is replaced with TiO2), and CQDs@TNA (using the sample prepared in Example 1 as an example) were used as working electrodes, Pt sheet as counter electrode, and Ag / AgCl (saturated KCl) as reference electrode. The anolyte was a mixed solution of 1 M methanol + 0.1 M KOH, and the catholyte was 10 mM KNO3 + 0.1 M KOH. The test was conducted at room temperature and pressure, with a light intensity of 100 mW / cm². 2 The potential range was -1.0 V to 0.5 V (vs. Ag / AgCl), the anode potential was set to 0.5 V (vs. Ag / AgCl), and the generated ammonia was quantitatively detected by indophenol blue spectrophotometry.
[0030] The results are as follows Figure 5As shown in the figure, the system ammonia yield is different for different photoanodes. It can be seen from the figure that both the one-dimensional tubular structure of nanotubes and carbon quantum dot sensitization can improve the ammonia yield. The CQDs@TNA photoanode formed by carbon quantum dot sensitized TNA combines the advantages of both and shows superior performance, indicating that the CQDs@TNA photoanode has better photoelectrochemical performance.
[0031] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.
Claims
1. A method for preparing a carbon quantum dot-sensitized TiO2 nanotube photoanode material, characterized in that, Includes the following steps: S1. Preparation of TiO2 nanotube array: Using pretreated titanium sheet as anode and graphite as cathode, the titanium sheet is anodized, cleaned, and then calcined to obtain TiO2 nanotube array; S2. Preparation of carbon quantum dots: Carbon quantum dots are obtained by mixing citric acid and diethylenetriamine and reacting them hydrothermally. S3. Preparation of carbon quantum dot-sensitized TiO2 nanotube photoanode material: The TiO2 nanotube array prepared in S1 is immersed in the carbon quantum dot solution prepared in S2 for electrophoretic deposition to obtain the carbon quantum dot-sensitized TiO2 nanotube photoanode material.
2. The preparation method according to claim 1, characterized in that, The specific technical parameters for the titanium sheet anodizing treatment in step S1 are: anodizing for 2-6 hours at a voltage of 35-45V.
3. The preparation method according to claim 2, characterized in that, The specific technical parameters for calcination in step S1 are as follows: calcination at 450°C for 3-5 hours in an air atmosphere, with a heating rate of 4-8°C / min.
4. The preparation method according to any one of claims 1-3, characterized in that, The molar ratio of citric acid to diethylenetriamine in step S2 is 1:(2-5).
5. The preparation method according to claim 4, characterized in that, The specific technical parameters for the hydrothermal reaction in step S2 are: hydrothermal reaction at 160-180℃ for 1-3 hours.
6. The preparation method according to claim 5, characterized in that, The specific technical parameters for electrophoretic deposition in step S3 are as follows: apply a potential of -2V to -5V on the TiO2 nanotube array for 60-100s.
7. The carbon quantum dot-sensitized TiO2 nanotube photoanode material prepared by the preparation method according to any one of claims 1-6.
8. The application of the carbon quantum dot-sensitized TiO2 nanotube photoanode material as described in claim 7 in the photoelectrochemical reduction of nitrogen-containing substances to prepare ammonia.
9. The application according to claim 8, characterized in that, The nitrogen-containing substance is nitrogen gas, nitrate, or nitrite.
10. The application according to claim 9, characterized in that, The method for preparing ammonia by photoelectrochemical reduction of nitrogen-containing substances using the carbon quantum dot-sensitized TiO2 nanotube photoanode material specifically includes the following steps: using CQDs@TNA as the working electrode, a Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode; the electrolyte in the anode chamber is 1 M methanol and 0.1 M KOH solution; the electrolyte in the cathode chamber is 10 mM KNO3 and 0.1 M KOH solution; and the light intensity is 100 mW / cm². 2 The potential range is from -1.0 V to 0.5 V, and the reaction is carried out at a constant potential of 0.5 V vs. Ag / AgCl for 2-4 hours.