A visible light responsive titanium dioxide photocatalyst, its preparation method and application

Abstract

This invention provides a visible light responsive titanium dioxide photocatalyst, its preparation method, and its application. The photocatalyst has a core-shell structure or a heterojunction interface structure and includes the following components: matrix material: modified nano-titanium dioxide; modifying material: chiral carbon quantum dots; the chiral carbon quantum dots are grown in situ or grafted onto the surface of the matrix material through Ti-O-C chemical bonds or strong electrostatic interactions; the photocatalyst utilizes the spin filtering effect generated by the CISS effect of the chiral carbon quantum dots, so that the photogenerated electrons injected into the matrix and the remaining holes are in a spin-forbidden state, thereby inhibiting recombination; this invention uses physical laws rather than simple energy level matching to inhibit recombination, significantly improving the quantum efficiency; the long-lived electrons and holes can continuously generate active free radicals, effectively overcoming the difficult-to-degrade VOCs containing benzene ring structures such as toluene, and reducing the generation of intermediate products; the raw materials used are all inexpensive chemical products, free from heavy metal pollution, and suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the field of nano-photocatalytic materials and environmental governance technology, specifically relating to a visible light responsive titanium dioxide photocatalyst, its preparation method, and its application. Background Technology

[0002] Indoor air pollution is mainly caused by volatile organic compounds (VOCs), with formaldehyde and toluene being the most representative. Formaldehyde is chemically reactive but has a long release period, while toluene has a stable benzene ring structure and is difficult to completely oxidize and decompose. Traditional titanium dioxide (TiO2) photocatalytic technology faces two major bottlenecks:

[0003] Narrow spectral response: It can only absorb ultraviolet light (<380nm), and its utilization rate of indoor visible light is extremely low.

[0004] Low quantum efficiency: Due to the physical characteristics of semiconductors, photogenerated electrons and holes are highly susceptible to radiative or non-radiative recombination after separation, with lifetimes typically only on the nanosecond scale. This results in an inability to maintain the sustained oxidation capacity required for toluene ring-opening, and the easy generation of intermediate products such as benzaldehyde, leading to catalyst poisoning and deactivation.

[0005] Existing improvement techniques, such as noble metal deposition (Pt / Au), are too expensive, while non-metallic doping (N / S), although broadening the spectrum, often increases recombination centers. In recent years, the chirality-induced spin selectivity (CISS) effect in spintronics has been discovered, where electrons undergo spin polarization as they pass through chiral molecules. However, there are currently no reports of mature technologies applying this effect to the treatment of gas-phase VOCs and the photocatalytic modification of TiO2. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a visible light responsive titanium dioxide photocatalyst, its preparation method, and its application, aiming to solve the technical problems of high electron-hole recombination rate and poor visible light activity in existing titanium dioxide photocatalysts.

[0007] The technical solution of this invention is: a visible light responsive titanium dioxide photocatalyst, wherein the photocatalyst has a core-shell structure or a heterojunction interface structure, and comprises the following components:

[0008] Matrix material: Modified nano-titanium dioxide;

[0009] Modifying material: chiral carbon quantum dots;

[0010] The chiral carbon quantum dots are grown in situ or grafted onto the surface of the matrix material through Ti-OC chemical bonds or strong electrostatic interactions;

[0011] The photocatalyst utilizes the spin filtering effect generated by the CISS effect of chiral carbon quantum dots, which puts the photogenerated electrons injected into the matrix and the remaining holes in a spin-forbidden state, thereby inhibiting recombination.

[0012] Furthermore, the chiral carbon quantum dots have a particle size of 1–10 nm, and their precursors include a carbon source and a chiral ligand.

[0013] Furthermore, the carbon source is selected from one or more of citric acid, glucose, ascorbic acid, and polyacrylic acid.

[0014] Furthermore, the chiral ligand is selected from L-cysteine, D-cysteine, L-glutathione, L-lysine, L-histidine, or their corresponding enantiomers.

[0015] Furthermore, the matrix material is one of nitrogen-doped titanium dioxide, hydrogenated black titanium dioxide, or titanium dioxide nanotube array.

[0016] The preparation method of the visible light responsive titanium dioxide photocatalyst as described in any of the preceding methods includes the following steps:

[0017] Step S1, preparing chiral carbon quantum dot precursor solution: dissolving carbon source and chiral ligand in solvent at a molar ratio of 1:0.5 to 1:2;

[0018] Step S2, Synthesis of chiral carbon quantum dots: The precursor solution is treated by hydrothermal or microwave-assisted method and purified by dialysis to obtain a chiral carbon quantum dot solution;

[0019] Step S3, Assembly of composite photocatalyst: The matrix material is dispersed in the solution obtained in step S2, and composited by stirring adsorption, solvothermal treatment or ultrasonic deposition.

[0020] Step S4, post-processing: The composite product is dried and then calcined at low temperature under an inert atmosphere to obtain the photocatalyst.

[0021] Furthermore, in step S3, the mass percentage of chiral carbon quantum dots to matrix material is 0.5% to 5.0%.

[0022] Furthermore, in step S4, the low-temperature calcination temperature is 200–450°C.

[0023] The application of the visible light responsive titanium dioxide photocatalyst as described in any of the preceding claims is for the photocatalytic degradation of volatile organic compounds in the air under visible light excitation, said volatile organic compounds including formaldehyde and / or toluene.

[0024] Furthermore, the wavelength range of the visible light is 400nm to 780nm.

[0025] The beneficial effects of this invention are:

[0026] (1) Extremely high electron utilization: Recombination is suppressed by physical laws (spin forbidden) rather than simple energy level matching, which significantly improves the photon efficiency.

[0027] (2) Deep degradation capability: Long-lived electrons and holes can continuously generate active free radicals (·O2-,·OH), effectively overcoming the difficult-to-degrade VOCs containing benzene ring structures such as toluene and reducing the generation of intermediate products.

[0028] (3) Low cost: The raw materials used (citric acid, cysteine, titanium source) are all inexpensive chemical products, with no heavy metal pollution, and are suitable for large-scale industrial production. Attached Figure Description

[0029] Figure 1 This is a flowchart of the preparation method of the visible light responsive titanium dioxide photocatalyst in this invention. Detailed Implementation

[0030] Various exemplary embodiments of the invention will now be described in detail with reference to the accompanying drawings. The descriptions of the exemplary embodiments are merely illustrative and are in no way intended to limit the invention or its application or use. The invention can be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to make the invention thorough and complete, and to fully express the scope of the invention to those skilled in the art. It should be noted that, unless otherwise specifically stated, the relative arrangement of components and steps, the composition of materials, numerical expressions, and values ​​set forth in these embodiments should be interpreted as merely exemplary and not as limiting.

[0031] The terms "first," "second," and similar words used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Words such as "including" or "comprising" mean that the element preceding the word encompasses the element listed after it, without excluding the possibility of encompassing other elements. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0032] Visible light responsive titanium dioxide photocatalysts, which have core-shell or heterojunction interface structures, include the following components:

[0033] Matrix material: Modified nano-titanium dioxide (TiO2);

[0034] Modifying material: Chiral carbon quantum dots (C-CDs);

[0035] Chiral carbon quantum dots are grown in situ or grafted onto the surface of a substrate material via Ti-OC chemical bonds or strong electrostatic interactions.

[0036] Photocatalysts utilize the CISS effect of chiral carbon quantum dots to generate spin filtering, which puts the photogenerated electrons injected into the matrix and the remaining holes in a spin-forbidden state, thereby inhibiting recombination.

[0037] Specifically, N-doped or oxygen-vacancy-type TiO2 is selected as the substrate, and the absorption edge is red-shifted to the visible light region by introducing defect energy levels, thus solving the problem of "not being able to see light"; citric acid / glucose is selected as the carbon source to provide graphitized sp 2 Conductive framework and oxygen-containing functional groups for anchoring; L-cysteine / glutathione and other chiral ligands are selected to impart chiral structure to carbon dots during synthesis, and N and S co-doping is achieved to adjust energy levels; Visible light trapping: C-CDs have excellent upconversion fluorescence properties and visible light absorption capabilities, serving as photosensitizers to broaden the photoresponse range of TiO2; Spin blocking mechanism: Due to the CISS effect, when photogenerated electrons transfer from chiral carbon dots to the conduction band of TiO2 (or in the opposite direction), their spin state is polarized (e.g., only electrons with spin up are allowed to pass through). At this time, the holes remaining in the valence band correspond to the spin down state. According to the Pauli exclusion principle, for electrons to return to the valence band and recombine with holes, spin flipping must occur. Since spin flipping is a quantum forbidden process, the rate is extremely slow, thus exponentially extending the lifetime of electron-hole pairs (reaching the microsecond or even millisecond level).

[0038] In some embodiments, the chiral carbon quantum dots have a particle size of 1–10 nm, and their precursors include a carbon source and a chiral ligand. Chiral carbon quantum dots (Chiral C-CDs) are the core modifying component of this invention, and their main function is as a "spin filter" and photosensitizer. The macroscopic or mesoscopic chiral structure of carbon dots induces the CISS effect (chirality-induced spin selectivity). The chiral potential field constructed by the carbon dots can spin polarize photoexcited electrons transported to TiO2 (e.g., only allowing electrons with spins parallel to momentum to pass through), physically blocking the recombination of electrons and holes. Simultaneously, carbon dots with a particle size less than 10 nm exhibit quantum size effects, making it easy to adjust the conduction band potential to be more negative than TiO2, ensuring smooth electron thermodynamic injection. Compared to metal complexes, carbon dots have excellent conductivity, biocompatibility, and resistance to photolysis, and can act as electron bridges to reduce local electron density.

[0039] In some embodiments, the carbon source is selected from one or more of citric acid, glucose, ascorbic acid, and polyacrylic acid; small molecules such as citric acid and glucose are selected as carbon sources, mainly for constructing graphitized cores (sp) through dehydration condensation during hydrothermal carbonization. 2The carbon dot framework of hybrid carbon provides a π-π conjugated system to ensure rapid electron transport. Citric acid has a moderate carbonization rate, which is beneficial for controlling particle size distribution. Moreover, its rich carboxyl groups (-COOH) and hydroxyl groups (-OH) can be retained on the carbon dot surface after synthesis. This not only gives the material excellent water solubility to adsorb polar formaldehyde molecules, but also allows it to undergo a condensation reaction with the hydroxyl groups on the TiO2 surface to form a stable Ti-OC chemical bond, ensuring unobstructed electron transport channels and preventing the modification agent from falling off.

[0040] In some embodiments, the chiral ligand is selected from L-cysteine, D-cysteine, L-glutathione, L-lysine, L-histidine, or their corresponding enantiomers. L-cysteine ​​and L-glutathione, when used as chiral ligands, primarily play a dual role as both "chiral inducers" and "heteroatom dopants." During the nucleation and growth of carbon dots, the ligand acts as a template, "imprinting" chiral information into the helical structure or surface defects of the carbon dots, endowing them with overall optical activity. Furthermore, the uniform L-configuration of the natural amino acid ensures the generation of a consistent spin polarization field. Simultaneously, the nitrogen (N) and sulfur (S) elements in the ligand achieve co-doping of the carbon dots, effectively regulating the Fermi level and introducing surface defect states as active adsorption sites. In particular, the thiol group (-SH) possesses extremely strong metal affinity, further enhancing the binding strength between the carbon dots and the TiO2 matrix.

[0041] In some embodiments, the matrix material is one of nitrogen-doped titanium dioxide (N-TiO2), hydrogenated black titanium dioxide (Black TiO2), or titanium dioxide nanotube arrays (TiO2 NTs). Nitrogen-doped titanium dioxide (N-TiO2) or black titanium dioxide is selected as the host and nanocarrier for the photocatalytic reaction. Its semiconductor band structure generates photogenerated electron-hole pairs, and the strong oxidizing power of the valence band hole up to +2.7 eV directly mineralizes formaldehyde and toluene. Modified TiO2 is chosen instead of pure TiO2 because pure TiO2 has an excessively wide band gap (~3.2 eV) and only responds to ultraviolet light. Introducing nitrogen atom doping or oxygen vacancy defects can form defect energy levels in the band gap, red-shifting the absorption edge to the visible light region of 400–500 nm, thus meeting the application requirements in low-light indoor environments. Furthermore, the excellent chemical stability of TiO2 allows it to withstand the erosion of slightly acidic intermediates (such as benzoic acid) generated during toluene degradation, ensuring the long lifespan of the catalyst.

[0042] In some embodiments, such as Figure 1 As shown, a method for preparing a visible light-responsive titanium dioxide photocatalyst as described in any of the preceding embodiments is disclosed, comprising the following steps:

[0043] Step S1, preparing chiral carbon quantum dot precursor solution: dissolving carbon source and chiral ligand in solvent at a molar ratio of 1:0.5 to 1:2;

[0044] Step S2, Synthesis of chiral carbon quantum dots: The precursor solution is treated by hydrothermal or microwave-assisted method and purified by dialysis to obtain a chiral carbon quantum dot solution;

[0045] Step S3, Assembly of composite photocatalyst: The matrix material is dispersed in the solution obtained in step S2, and composite is carried out by stirring adsorption, solvothermal treatment or ultrasonic deposition.

[0046] Step S4, post-processing: The composite product is dried and then calcined at low temperature under an inert atmosphere to obtain the photocatalyst.

[0047] Specifically, the hydrothermal method involves reacting in an aqueous solution environment at 160–220°C for 2–8 hours; the microwave-assisted method utilizes microwave heating equipment at a power of 500–800W for 5–20 minutes.

[0048] In some embodiments, the mass percentage of chiral carbon quantum dots to matrix material in step S3 is 0.5% to 5.0%.

[0049] In some embodiments, in step S4, the low-temperature calcination temperature is 200–450°C.

[0050] In some embodiments, the application of a visible light responsive titanium dioxide photocatalyst as in any of the preceding embodiments is disclosed for photocatalytic degradation of volatile organic compounds in the air under visible light excitation, the volatile organic compounds including formaldehyde and / or toluene.

[0051] In some embodiments, the wavelength range of visible light is 400 nm to 780 nm; more specifically, the wavelength range of visible light is 400 nm to 750 nm.

[0052] The technical solution of the present invention will be further described below through more specific embodiments.

[0053] Example 1

[0054] Preparation of chiral carbon dots (L-CDs): 1 g of citric acid and 1 g of L-cysteine ​​were dissolved in 10 mL of deionized water. The mixture was placed in a high-pressure reactor lined with polytetrafluoroethylene and hydrothermally reacted at 180 °C for 4 hours. After cooling, the mixture was dialyzed (molecular weight cutoff 1000 Da) for 24 hours to obtain the L-CDs solution.

[0055] Matrix preparation: N-TiO2 powder was prepared by using urea and tetrabutyl titanate as raw materials, followed by sol-gel and calcination at 450℃.

[0056] Composite: 0.5g N-TiO2 was dispersed in 50mL of a system containing 5mL L-CDs solution, stirred for 12 hours, dried by rotary evaporation, and then calcined at 300℃ for 2 hours under nitrogen protection.

[0057] Functional analysis: L-cysteine ​​provides the chiral source and S / N doping, citric acid provides the carbon framework, and N-TiO2 provides the visible light responsive substrate.

[0058] Example 2

[0059] Preparation: Chiral carbon dots were prepared by hydrothermal reaction at 200°C for 6 hours using 1g glucose as the carbon source and 1.5g L-glutathione (tripeptide) as the ligand. The remaining steps were the same as in Example 1.

[0060] Functional analysis: Macromolecular peptide ligands provide more surface functional groups and defect sites, enhancing adsorption capacity.

[0061] Example 3

[0062] Preparation: Carbon dots were prepared using ascorbic acid and L-lysine as raw materials.

[0063] Matrix: Black TiO2 obtained by high-pressure hydrogenation (450℃, 15 bar H2).

[0064] Composite: Ultrasonic deposition method is used to avoid high temperature damage to oxygen vacancies in black TiO2.

[0065] Analysis of its effects: Black TiO2 itself has extremely strong full-spectrum absorption capabilities, and combined with the CISS effect, it further reduces the recombination that is very easy to occur inside, achieving a "strong combination".

[0066] Example 4

[0067] Preparation: D-cysteine ​​(the enantiomer of L-cysteine) was used instead of L-cysteine, and the remaining steps were the same as in Example 1.

[0068] Analysis of effects: The preparation of catalysts with opposite optical rotations aims to demonstrate that spin polarization can be generated as long as a single chiral structure is present.

[0069] Example 5

[0070] Preparation: Citric acid and L-cysteine ​​solution were placed in a microwave digester and heated at 700W for 10 minutes to rapidly synthesize carbon dots.

[0071] Matrix: Commercial P25 (Degussa).

[0072] Composite: Same as Example 1.

[0073] Functional analysis: To verify the feasibility of the rapid preparation process and its modification effect on common commercial substrates.

[0074] Example 6

[0075] Substrate: TiO2 nanotube arrays are grown on titanium sheets by anodizing.

[0076] Composite: The nanotube sheet was immersed in an L-histidine-modified carbon dot solution for 24 hours and then dried by lifting.

[0077] Application Analysis: This demonstrates that the material can be fabricated into thin-film devices, which is beneficial for applications in air purifier filters.

[0078] Comparative Example 1

[0079] Chiral carbon dots were prepared using only citric acid and ethylenediamine (a non-chiral molecule) and loaded onto N-TiO2. This was used to exclude the conductivity enhancement brought by carbon dots and to verify the chiral CISS effect independently.

[0080] Comparative Example 2

[0081] N-TiO2 matrix without any carbon dots. Used as a performance baseline.

[0082] Comparative Example 3

[0083] L-cysteine ​​monomers were directly physically mixed with N-TiO2 without hydrothermal carbonization to form quantum dots. This was used to demonstrate the necessity of the "carbon quantum dot" structure.

[0084] Performance testing and results data: In a 1 cubic meter sealed chamber, a 300W xenon lamp (with a 420nm filter) was used to simulate indoor visible light, with an initial toluene concentration of 20ppm and a reaction time of 4 hours.

[0085] Table 1 Comparison of performance test results between the examples and comparative examples.

[0086] Group Core features Toluene removal rate (%) CO2 mineralization rate (%) Example 1 L-Cys / Cit / N-TiO2 94.5 88.2 Example 2 L-GSH / Glu / N-TiO2 92.1 85.4 Example 3 Black TiO2 substrate 95.8 89.1 Example 4 D-type chirality 93.9 87.5 Example 5 Microwave / P25 78.5 65.2 Example 6 Nanotube arrays 89.4 81.3 Comparative Example 1 nonchiral CDs 62.3 45.6 Comparative Example 2 Pure N-TiO2 38.1 18.5 Comparative Example 3 Physical mixing 41.2 22.4

[0087] Compared to Comparative Example 1, Example 1 showed an approximately 32% increase in toluene removal rate and nearly doubled mineralization rate, directly demonstrating that the CISS effect induced by the introduction of chiral structures can significantly promote electron-hole separation and deep oxidation reactions. Example 4 (Type D) showed comparable results to Example 1 (Type L), indicating that the direction of spin polarization does not affect the overall effect of suppressing recombination; the key lies in the presence of a single chirality. Comparative Example 3 showed extremely poor results, indicating that quantum dots with energy level structures must be formed and chemically bonded to achieve effective electron injection. This invention, through the above technical solutions, effectively solves the problem of low purification efficiency of existing photocatalysts for stubborn VOCs under visible light, and has broad prospects for industrial application.

[0088] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present application will now be described in detail with reference to the embodiments.

[0089] The various embodiments of the present invention have now been described in detail. To avoid obscuring the concept of the invention, some details known in the art have not been described. Those skilled in the art will fully understand how to implement the technical solutions disclosed herein based on the above description.

[0090] The embodiments described above only illustrate some implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A visible light responsive titanium dioxide photocatalyst, characterized by, The photocatalyst has a core-shell structure or a heterojunction interface structure, and comprises the following components: a base material: modified nanometer titanium dioxide; a modification material: chiral carbon quantum dots; The chiral carbon quantum dots are in-situ grown or grafted on the surface of the base material through Ti-O-C chemical bonds or strong electrostatic interactions; The photocatalyst utilizes the spin filtering effect generated by the CISS effect of the chiral carbon quantum dots, so that the photo-generated electrons injected into the base material and the remaining holes are in a spin-forbidden state, thereby inhibiting recombination. 2.The visible-light-responsive titanium dioxide photocatalyst according to claim 1, characterized by: The particle size of the chiral carbon quantum dots is 1-10 nm, and the precursors thereof include a carbon source and a chiral ligand. 3.The visible-light-responsive titanium dioxide photocatalyst according to claim 2, characterized by: The carbon source is selected from one or more of citric acid, glucose, ascorbic acid, and polyacrylic acid. 4.The visible-light-responsive titanium dioxide photocatalyst according to claim 2, characterized by: The chiral ligand is selected from one of L-cysteine, D-cysteine, L-glutathione, L-lysine, L-histidine, or a corresponding enantiomer thereof. 5.The visible-light-responsive titanium dioxide photocatalyst according to claim 1, characterized by: The base material is one of nitrogen-doped titanium dioxide, hydrogenated black titanium dioxide, or a titanium dioxide nanotube array.

6. A method for producing the visible light responsive titanium dioxide photocatalyst according to any one of claims 1 to 5, characterized by, The method comprises the following steps: Step S1: preparing a chiral carbon quantum dot precursor solution: dissolving a carbon source and a chiral ligand in a solvent at a molar ratio of 1:0.5 to 1:2; Step S2: synthesizing chiral carbon quantum dots: treating the precursor solution by a hydrothermal method or a microwave-assisted method, and purifying by dialysis to obtain a chiral carbon quantum dot solution; Step S3: assembling a composite photocatalyst: dispersing a base material in the solution obtained in step S2, and performing composite by stirring adsorption, solvothermal treatment, or ultrasonic deposition; Step S4: post-treatment: drying the composite product and performing low-temperature calcination under an inert atmosphere to obtain the photocatalyst.

7. The method of claim 6, wherein the method is characterized by: In step S3, the mass percentage of chiral carbon quantum dots to the base material is 0.5%-5.0%.

8. The method for preparing the visible light responsive titanium dioxide photocatalyst according to claim 6, characterized in that: In step S4, the low-temperature calcination temperature is 200-450°C.

9. Use of a visible light responsive titanium dioxide photocatalyst according to any one of claims 1 to 5, characterized in that: The photocatalyst is used for photocatalytic degradation of volatile organic compounds in air under visible light excitation, wherein the volatile organic compounds include formaldehyde and / or toluene.

10. The use of a visible light responsive titanium dioxide photocatalyst according to claim 9, characterized in that: The wavelength range of the visible light is 400-780 nm.

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