A Pt-doped TiO2 photocatalytic material and its preparation method

Abstract

The application discloses a Pt-doped TiO2 photocatalytic material and a preparation method thereof, and relates to the technical field of photocatalytic resource conversion. The application realizes in-situ deposition of Pt species on the surface of TiO2 by using the transient temperature gradient generated under an extreme temperature difference through the rapid cooling and heating impact technology, effectively inhibits the diffusion and agglomeration of metal atoms in the thermodynamic process, realizes efficient dispersion of Pt, promotes the rapid migration of photo-generated carriers to the active sites of Pt, and is short in time consumption, simple in operation and easy to control.

Description

Technical Field

[0001] This invention relates to the fields of materials science and photocatalytic resource conversion technology, and in particular to a simple Pt-doped TiO2 photocatalytic material and its preparation method. Background Technology

[0002] In recent years, with the rapid development of the global economy and society and the continuous advancement of industrialization, fossil fuels, as the primary energy source, have been consumed in large quantities, leading to increasingly serious energy crises and environmental pollution problems. There is an urgent need to explore renewable energy sources. Among the avenues for finding renewable and clean energy, hydrogen energy, due to its extremely high energy density and zero-pollution combustion products, is widely considered the most ideal energy carrier for the future. Among numerous hydrogen production technologies, semiconductor photocatalytic hydrogen production technology can directly convert solar energy into chemical energy, possessing immense application potential. For photocatalytic hydrogen production technology, introducing sacrificial agents, especially methanol, into the system for sacrificial reforming to produce hydrogen not only effectively consumes biomass derivatives but also significantly suppresses the recombination of photogenerated carriers. Currently, this has become a key focus in the field of new energy research. Therefore, developing an easy-to-synthesize and highly efficient green method for preparing photocatalytic materials has always been a research hotspot in this field.

[0003] The bottleneck of photocatalysis technology lies mainly in the easy recombination of photogenerated electron-hole pairs (i.e., photogenerated carriers) and the extremely low light conversion efficiency. To address this issue, researchers have widely adopted strategies such as morphology control, heterojunction construction, defect engineering, and metal doping. Among these strategies, noble metal surface modification, especially Pt doping, has proven to be an extremely effective modification method. Pt, as an excellent hydrogen evolution cocatalyst, can rapidly capture photogenerated electrons, greatly reducing the hydrogen evolution overpotential and thus effectively improving the photocatalytic hydrogen production efficiency. For example, invention patent CN120815555A discloses a Pt-deposited CdZnS nanorod prepared by a low-temperature vacuum reduction method, which effectively solves the problems of photogenerated electron and hole recombination and narrow bandgap. However, the Pt loading at its optimal performance is still relatively high, resulting in low utilization of unit Pt, increasing the economic cost of the material, and the reaction still needs to be carried out under conditions of λ≥420nm, failing to effectively utilize the high proportion of energy in sunlight. Therefore, there is still a lack of highly efficient photocatalytic systems that combine broad spectral response and high economic efficiency. Invention patent CN116037214A prepared PtNPs@CTF with lower noble metal loading through a two-step high-temperature process. 1. Composite photocatalyst, CTF support 1. The good alkali resistance of the composite material gives it a certain degree of stability. However, Oswald ripening inevitably occurs during its high-temperature preparation, causing metallic Pt to irreversibly grow into large-sized nanoparticles. A large number of Pt atoms within these nanoparticles fail to effectively participate in the catalytic reaction, reducing the utilization rate of the precious metal. Overall, traditional precious metal doping still faces problems such as easy aggregation of active sites, low metal utilization, and high cost. These drawbacks significantly limit its large-scale application in practical industry. Therefore, selecting suitable support materials and optimizing the doping process to achieve high dispersion after precious metal doping is particularly important.

[0004] Currently, titanium dioxide (TiO2) has been extensively studied in the field of photocatalysis due to its advantages such as non-toxicity, low cost, strong resistance to photocorrosion, and high chemical stability. To improve the hydrogen production performance of TiO2, various methods for preparing TiO2 composite materials have been developed. For example, invention patent CN116020507B describes a hydrothermal and post-heat treatment process for preparing Ti3C2T... x In-situ growth of TiO2 to prepare heterojunction Ti3C2T x / TiO2, and then in-situ deposition of noble metals under photoinduced effects, to prepare photocatalytic materials with noble metal loadings ranging from 0.05% to 2.0 wt%. However, heterojunction Ti3C2T x The preparation of TiO2 requires lengthy hydrothermal processes and subsequent treatments. The cumbersome experimental procedures and high energy consumption during preparation deviate from the original purpose of photocatalysis. Invention patent CN121775862A discloses another method for preparing TiO2-based heterojunction photocatalysts. Although this method effectively improves the photocatalytic activity and photoelectric performance of the catalyst, Cu species may undergo in-situ reduction during the catalytic process in its reaction system. This results in an unstable and slow induction period for hydrogen production. Simultaneously, the photodeposited MnO... x Photocorrosion, dissolution, or mechanical detachment easily occur during catalysis, affecting the stability of the catalyst. In summary, these methods generally suffer from drawbacks such as long processing time, cumbersome preparation procedures, and high energy consumption. Therefore, there is an urgent need to develop a simple, time-efficient preparation method that can effectively control the morphology and dispersion state of the doped metal.

[0005] Currently, although there are various methods for synthesizing Pt-doped TiO2, most of these methods face the dilemma of being time-consuming, prone to agglomeration, and difficult to achieve low-cost mass production. Summary of the Invention

[0006] To address the aforementioned shortcomings of existing technologies, this invention provides a Pt-doped TiO2 photocatalytic material, its preparation method, and its application in photocatalytic hydrogen production.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: A method for preparing Pt-doped TiO2 photocatalytic material is provided, which includes the following steps: S1: Take [PtCl6] 2- The solution, under continuous stirring, is added to [PtCl6]. 2- An organic dispersant was added to the solution and stirred until homogeneous to obtain a Pt precursor solution; the Pt precursor solution was then pre-cooled to 0~6℃. S2: Heat nano-sized TiO2 to 400~800℃, keep it at that temperature for 3~6h, and then immediately immerse it in a pre-cooled Pt precursor solution to achieve rapid cooling and thermal shock. After immersion, let it stand for 5~20min, and then centrifuge to obtain solid matter. S3: Washing and drying the solid material yields the Pt-doped TiO2 photocatalytic material.

[0008] Furthermore, the organic dispersant is polyvinylpyrrolidone, dodecyltrimethylammonium bromide, or sodium dodecyl sulfate.

[0009] Furthermore, the [PtCl6] 2- The Pt concentration in the solution is 0.01–0.05 mmol / L; and [PtCl6] 2- The ratio of solution to organic dispersant is 20~60mL:0.05~0.2g.

[0010] Furthermore, the [PtCl6] 2- The solution was obtained by uniformly dispersing Na2[PtCl6], K2[PtCl6] or H2PtCl6·6H2O in an alcohol solution; The alcohol solution is prepared by mixing anhydrous ethanol, anhydrous methanol or ethylene glycol with deionized water in a volume ratio of 5:25 to 1:29.

[0011] Furthermore, the nano-sized TiO2 is one or a combination of two of anatase, rutile, and brookite.

[0012] Furthermore, the nano-sized TiO2 and [PtCl6] 2- The volume ratio of the solution used is 0.5~1.5g : 20~60mL.

[0013] Furthermore, in step S2, the heating rate of nano-sized TiO2 is 3~8℃ / min.

[0014] The present invention also provides a Pt-doped TiO2 photocatalytic material prepared by the above-described preparation method.

[0015] The present invention also provides the application of the above-mentioned Pt-doped TiO2 photocatalytic material in the photocatalytic hydrogen production of methanol aqueous solution.

[0016] The beneficial effects of this invention are as follows: 1. This invention utilizes rapid cooling and thermal shock technology to deposit Pt species in situ onto the TiO2 surface using the transient temperature gradient generated under extreme temperature differences. This not only effectively suppresses the diffusion and aggregation of metal atoms during thermodynamic processes, achieving efficient dispersion of Pt and promoting the rapid migration of photogenerated carriers to Pt active sites, but also has a very short preparation time, is simple to operate, and is easy to control.

[0017] 2. Under the action of the rapid cooling and thermal shock technology, the present invention induces defects mainly composed of oxygen vacancies on the surface of TiO2 support and constructs a strong metal-support interaction, which endows Pt-doped TiO2 photocatalytic material with more excellent light-harvesting ability and photogenerated carrier separation activity.

[0018] 3. When the Pt-doped TiO2 photocatalytic material prepared in this invention is applied to the photocatalytic hydrogen production of the methanol sacrificial system, thanks to the efficient exposure of the active sites, the hydrogen evolution rate per unit mass and the utilization rate of noble metals are significantly improved. Moreover, it can still maintain excellent structural stability and hydrogen production activity in continuous photocatalytic cycle tests over a long period of time. Attached Figure Description

[0019] Figure 1 The image shows the X-ray powder diffraction pattern of the Pt / TiO2 photocatalytic material prepared in Example 1 of this invention. Figure 2 This is a transmission electron microscope (TEM) image of the Pt / TiO2 photocatalytic material prepared in Example 1 of this invention. Figure 3 The image shows the X-ray photoelectron spectrum of the Pt / TiO2 photocatalytic material prepared in Example 1 of this invention. Figure 4 The image shows the electron paramagnetic resonance (EPR) pattern of the Pt / TiO2 photocatalytic material prepared in Example 1 of this invention. Figure 5 This is a comparison of the photocatalytic hydrogen production rates of the Pt / TiO2 photocatalytic material prepared in Example 1 of this invention under a water-methanol system; Figure 6 The results show the photocatalytic cycle stability of the Pt / TiO2 photocatalytic material prepared in Example 1 of this invention. Detailed Implementation

[0020] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0021] Unless otherwise specified, all raw materials used in the embodiments of this invention are commercially available analytical grade.

[0022] Example 1 A method for preparing a Pt-supported TiO2 photocatalytic material includes the following steps: S1. At room temperature, add 30 mL of the prepared H₂PtCl₆·6H₂O aqueous solution to a reaction flask equipped with a stirrer. [PtCl₆] 2- A homogeneous Pt-containing precursor solution was obtained by adding 0.1 g of polyvinylpyrrolidone at a concentration of 0.02 mmol / L and stirring at 500 rpm for 30 min. The solution was then transferred to a low-temperature drying environment at 4 °C and refrigerated for 4 h for later use.

[0023] Among them, [PtCl6] 2- The aqueous solution refers to a homogeneous mixed solution with a Pt concentration of 0.02 mmol / L obtained by mixing 0.311 mg of H2PtCl6·6H2O with 25 ml of deionized water and 5 ml of anhydrous methanol at room temperature, first sonicating for 10-30 min to disperse it, and then magnetically stirring at 300-600 rpm for 20-60 min.

[0024] S2. Weigh 0.6 g of nano-sized TiO2 powder and place it in a crucible, then transfer it to a muffle furnace and heat it to 600 °C at a heating rate of 5 °C / min, and hold it at that temperature for 4 h. After heating, immediately remove the TiO2 at the high temperature and immerse it directly into the pre-cooled Pt-containing precursor solution. The rapid cooling and thermal shock effect promotes the accelerated deposition of Pt on the TiO2 surface, thus achieving Pt doping on the TiO2 surface. Then, maintain the solution for 10 min to obtain a mixture containing the product.

[0025] S3. Transfer the mixed solution to a centrifuge tube and centrifuge at 4000 rpm for 5 min to obtain a solid product. Wash the centrifuged product with deionized water 5 times, and then dry it at 60℃ for 12 h (or overnight) to obtain the Pt-supported TiO2 photocatalyst material.

[0026] X-ray powder diffraction (XRD) analysis was performed on the prepared Pt-supported TiO2 photocatalyst material (hereinafter referred to as Pt / TiO2 composite). The results are as follows: Figure 1 As shown, by Figure 1 It can be seen that the diffraction peak positions of the synthesized Pt / TiO2 composite are almost identical to those of the original TiO2, indicating that Pt doping did not destroy the original crystal structure of TiO2. It is also noteworthy that no characteristic diffraction peaks belonging to metallic Pt or its oxides were observed in the XRD pattern, indicating that Pt was introduced in an amorphous state. This phenomenon is mainly attributed to the extremely low Pt loading in the system (only 0.04 wt%), and the fact that under the effect of thermal shock, Pt species are highly dispersed on the support surface, possibly existing as extremely fine ultra-low-loading nanoclusters or even single atoms, exceeding the detection limit of XRD. Furthermore, the overall diffraction peak intensity of the Pt / TiO2 composite is significantly enhanced compared to the original TiO2, suggesting that the rapid thermal shock process may have promoted an increase in the local crystallinity of TiO2 or further exposed specific crystal planes.

[0027] The microstructure of the Pt / TiO2 composite prepared in Example 1 was also characterized and analyzed by transmission electron microscopy (TEM), and the results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the Pt / TiO2 composite maintains a substrate morphology similar to that of the original TiO2, and no obvious Pt nanoparticles or obvious metal aggregates were observed within the field of view. This result is highly consistent with the conclusion that no characteristic Pt peaks were found in the XRD pattern. This further confirms that the thermal shock method used in this invention successfully suppressed the long-distance migration and aggregation of noble metal atoms during high-temperature treatment, achieving extreme dispersion of Pt species at ultra-low loading. This extremely high dispersion not only provides denser catalytic active sites but also helps to maximize the atomic utilization efficiency of noble metals.

[0028] To investigate the chemical composition, valence states, and chemical bond interactions of the surface elements, X-ray photoelectron spectroscopy (XPS) analysis was performed on the Pt / TiO2 composite prepared in Example 1. The results are as follows: Figure 3 As shown, where, Figure 3 In the diagram, 'a' represents the high-resolution X-ray photoelectron spectrum of the Pt 4f orbital of the Pt / TiO2 complex. Figure 3 The upper part of b in the image is a high-resolution X-ray photoelectron spectrum of the O 1s orbital of the Pt / TiO2 composite. Figure 3 The lower part of b in the image is a high-resolution X-ray photoelectron spectrum of the O 1s orbital of TiO2. Depend on Figure 3 As can be seen from 'a', the Pt / TiO2 composite system contains a zero valence state (Pt). 0 ) and positive 2 valence state (Pt 2+The presence of Pt not only demonstrates the successful doping of Pt, but also indicates a strong metal-support interaction between Pt and the TiO2 support, which facilitates the acceleration of photogenerated electron transfer to Pt sites. Furthermore, combined with... Figure 3 The high-resolution fine spectrum of O 1s in the upper part of b is also clearly observable. The fine O 1s spectrum shows three distinct characteristic peaks at binding energies of 529.8, 531.2, and 532.4 eV, corresponding to lattice oxygen bound to the metal, oxygen vacancies, and adsorbed oxygen, respectively. Compared with the original TiO2, the area of ​​the vacancy oxygen characteristic peak in the Pt / TiO2 material is significantly increased, further verifying the existence of oxygen vacancies.

[0029] In summary, the XPS spectra strongly demonstrate that the thermal shock process not only achieves efficient Pt anchoring, but also induces a large number of oxygen vacancy defects on the TiO2 surface, which will greatly enhance the catalytic activity of the material itself.

[0030] To visualize the oxygen vacancy defects, electron paramagnetic resonance (EPR) tests were also performed on the material. The results are as follows: Figure 4 As shown, by Figure 4 It is evident that the Pt / TiO2 composite exhibits a distinct characteristic signal peak at a specific g value, which is clearly attributed to the presence of oxygen vacancies in the system. This result is entirely consistent with the increase in the area of ​​the defect oxygen peak in the XPS O 1s spectrum. This demonstrates that the material prepared in this invention successfully achieves a one-step construction of dual-defect engineering involving both Pt doping and oxygen vacancies. These abundant oxygen vacancies not only act as shallow traps for photogenerated electrons, suppressing carrier recombination, but also synergize with highly dispersed Pt to further optimize the catalytic reaction kinetics on the surface.

[0031] The photocatalytic hydrogen production performance of the prepared Pt / TiO2 composite in a methanol system was evaluated. Specifically, a 300W Xe lamp was used as the light source in the methanol system. 4 mg of the Pt / TiO2 composite was ultrasonically dispersed in 8 mL of a methanol-water solution (60 vol%) in a closed quartz reactor. High-purity N2 was introduced at room temperature and pressure for approximately 30 min, followed by irradiation. The gaseous products were then quantitatively analyzed using gas chromatography. The test results are as follows: Figure 5 As shown. By Figure 5It is known that the hydrogen production rate of this material is 2.43 mmol / g / h, far exceeding that of TiO2 itself, reaching 104 times that of TiO2. Although the absolute value of the hydrogen production rate of the catalyst material of this invention is not the highest level in this field, a crucial premise that cannot be ignored is that the loading of the noble metal Pt in this material is only a very small 0.04 wt%. Achieving such a hydrogen production rate with such a low noble metal loading means that the mass activity and conversion turnover frequency (TOF) of Pt atoms are at an extremely high level. This strategy of ultra-low loading and high dispersion achieves a considerable yield of hydrogen per unit of noble metal at a very low noble metal cost. This demonstrates that the preparation method of this invention, while ensuring green environmental protection, simplicity and efficiency, has important research value in terms of the economic feasibility and large-scale application potential of photocatalytic hydrogen production.

[0032] To verify the practical application performance of the catalyst and assess its application prospects, the prepared Pt / TiO2 composite underwent four rounds of continuous photocatalytic hydrogen production performance cycling tests, such as... Figure 6 As shown. By Figure 6 It can be seen that the hydrogen production rate in each reaction cycle is above 2050 μmol / g / h, and no significant activity decay is observed, indicating that the catalyst has excellent reusability and stability. This excellent stability is mainly due to the rapid cooling and thermal shock process, which effectively prevents the highly dispersed active sites from detaching, being lost, or secondary agglomerating in long-term light exposure and highly reducing systems.

[0033] Example 2 A method for preparing a Pt-supported TiO2 photocatalytic material includes the following steps: S1. At room temperature, add 30 mL of the prepared Na₂[PtCl₆] aqueous solution to a reaction flask equipped with a stirrer. 2- A homogeneous Pt-containing precursor solution was obtained by adding 0.1 g of dodecyltrimethylammonium bromide at a concentration of 0.02 mmol / L and stirring at 500 rpm for 30 min. The solution was then transferred to a low-temperature drying environment at 4 °C and refrigerated for 4 h for later use.

[0034] Among them, [PtCl6] 2- The aqueous solution refers to a homogeneous mixed solution with a Pt concentration of 0.02 mmol / L obtained by mixing 0.272 mg Na2[PtCl6] with 29 ml deionized water and 1 ml anhydrous ethanol at room temperature, first sonicating for 10 min to disperse it, and then magnetically stirring at 500 rpm for 40 min.

[0035] S2. Weigh 0.8 g of nano-sized TiO2 powder and place it in a crucible, then transfer it to a muffle furnace and heat it to 400 °C at a heating rate of 5 °C / min, and hold it at that temperature for 4 h. After heating, immediately remove the TiO2 at the high temperature and immerse it directly into the pre-cooled Pt-containing precursor solution. The rapid cooling and thermal shock effect promotes the accelerated deposition of Pt on the TiO2 surface, thus achieving Pt doping on the TiO2 surface. Then, hold the solution for 5 min to obtain a mixed solution containing the product.

[0036] S3. Transfer the mixed solution to a centrifuge tube and centrifuge at 4000 rpm for 5 min to obtain a solid product. Wash the centrifuged product with deionized water 5 times, and then dry it at 60℃ for 12 h (or overnight) to obtain the Pt-supported TiO2 photocatalyst material.

[0037] Using the hydrogen production experiment in Example 1, the catalyst was replaced with the Pt-supported TiO2 photocatalytic material prepared in this example, and the hydrogen production rate was measured to be 1.98 mmol / g / h.

[0038] Example 3 A method for preparing a Pt-supported TiO2 photocatalytic material includes the following steps: S1. At room temperature, add 30 mL of the prepared K2[PtCl6] aqueous solution to a reaction flask equipped with a stirrer. 2- A homogeneous Pt-containing precursor solution was obtained by adding 0.1 g of sodium dodecyl sulfate at a concentration of 0.04 mmol / L and stirring at 500 rpm for 30 min. The solution was then transferred to a low-temperature drying environment at 4 °C and refrigerated for 4 h for later use.

[0039] Among them, [PtCl6] 2- The aqueous solution refers to a homogeneous mixed solution with a Pt concentration of 0.04 mmol / L obtained by mixing 0.583 mg of K2[PtCl6] with 29 ml of deionized water and 1 ml of ethylene glycol at room temperature, first sonicating for 20 min to disperse it, and then magnetically stirring at 500 rpm for 40 min.

[0040] S2. Weigh 0.6 g of nano-sized TiO2 powder and place it in a crucible, then transfer it to a muffle furnace and heat it to 400 °C at a heating rate of 5 °C / min, and hold it at that temperature for 4 h. After heating, immediately remove the TiO2 at the high temperature and immerse it directly into the pre-cooled Pt-containing precursor solution. The rapid cooling and thermal shock effect promotes the accelerated deposition of Pt on the TiO2 surface, thus achieving Pt doping on the TiO2 surface. Then, maintain the solution for 10 min to obtain a mixed solution containing the product.

[0041] S3. Transfer the mixed solution to a centrifuge tube and centrifuge at 4000 rpm for 5 min to obtain a solid product. Wash the centrifuged product with deionized water 5 times, and then dry it at 60℃ for 12 h (or overnight) to obtain the Pt-supported TiO2 photocatalyst material.

[0042] Using the hydrogen production experiment in Example 1, the catalyst was replaced with the Pt-supported TiO2 photocatalytic material prepared in this example, and the hydrogen production rate was measured to be 1.93 mmol / g / h.

Claims

1. A method for preparing a Pt-doped TiO2 photocatalytic material, characterized in that, The following steps are used: S1: take [PtCl6] 2- solution, under the condition of continuous stirring, add organic dispersant to the [PtCl6] 2- solution, stir uniformly to obtain Pt precursor solution; and pre-cool the Pt precursor solution to 0-6℃; S2: Heat nano-sized TiO2 to 400~800℃, keep it at that temperature for 3~6h, and then immediately immerse it in a pre-cooled Pt precursor solution to achieve rapid cooling and thermal shock. After immersion, let it stand for 5~20min, and then centrifuge to obtain solid matter. S3: Washing and drying the solid material yields the Pt-doped TiO2 photocatalytic material.

2. The method according to claim 1, characterized in that, The organic dispersant is polyvinylpyrrolidone, dodecyltrimethylammonium bromide, or sodium dodecyl sulfate.

3. The method according to claim 2, characterized in that, The [PtCl6] 2- The Pt concentration of the solution is 0.01-0.05 mmol / L; and the [PtCl6] 2- The ratio of the use amount of the solution to the organic dispersant is 20-60 mL: 0.05-0.2 g.

4. The method according to claim 3, characterized in that, said [PtCl6] 2- The solution was obtained by uniformly dispersing Na2[PtCl6], K2[PtCl6] or H2PtCl6.6H2O in an alcohol solution. The alcohol solution is prepared by mixing anhydrous ethanol, anhydrous methanol or ethylene glycol with deionized water in a volume ratio of 5:25 to 1:

29.

5. The method according to claim 4, characterized in that, The nanoscale TiO2 and [PtCl6] 2- The dosage ratio of the solution is 0.5-1.5 g: 20-60 mL.

6. The method according to claim 1, characterized in that, In step S2, the heating rate of nano-sized TiO2 is 3~8℃ / min.

7. A Pt-doped TiO2 photocatalytic material prepared by any one of the preparation methods described in claims 1 to 6.

8. The application of the Pt-doped TiO2 photocatalytic material according to claim 7 in the photocatalytic hydrogen production of methanol aqueous solution.

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