Photoswitchable Ti3 + species in photochromic TiO2 nanoparticles for efficient photooxidation of C-H bonds

Abstract

The invention discloses a photochromic TiO2-PEG200 (Polyethylene Glycol 200) nano particle and an application of the photochromic TiO2-PEG200 nano particle in photocatalytic oxidation of a C-H bond. The catalyst is synthesized through a solvothermal method, PEG200 is used as a solvent and a modifier, and self-doped Ti < 3 + > and surface oxygen vacancies are introduced into TiO2. Under the irradiation of blue light (405nm), the catalyst generates a photochromic effect, Ti < 4 + > is reduced into high-concentration Ti < 3 + > in situ, and meanwhile, a large amount of superoxide free radicals (O < 2 + >) are generated. A photo-generated hole directly activates an ethylbenzene alpha-C-H bond to generate a benzyl free radical, and the benzyl free radical reacts with a superoxide free radical (O2.) and is finally converted into acetophenone. The catalyst has excellent visible light response and charge separation efficiency, and the acetophenone yield is up to 56 mmol.g <-1 >. H <-1 > and is 10 times that of traditional TiO2. The reversible circulation of Ti < 3 + > / Ti < 4 + > enables the catalyst to maintain good stability, and the activity is still maintained at 95% or above after five times of circulation. The operation conditions are mild (room temperature and normal pressure), a strong oxidant is not needed, an efficient, stable and environment-friendly photocatalysis solution is provided for C-H bond activation, and the method has important application value in the field of fine chemical synthesis.

Description

Technical Field

[0001] This invention relates to a photocatalytic oxidation of C(sp) 3 This paper describes the preparation method of TiO2-PEG200 nanoparticles with photochromic properties due to their α-H bonds and their application in the photocatalytic oxidation of ethylbenzene to acetophenone. This research falls under the fields of organic synthesis, environmental remediation, and energy conversion. Background Technology

[0002] The catalytic oxidation of ethylbenzene to acetophenone represents a key shift in modern chemical industry, as acetophenone is an important raw material for the production of perfumes, dyes, agrochemicals, and pharmaceuticals. However, due to C(sp... 3 The high bond dissociation energy of the -H bond and its weak adsorption on catalyst surfaces mean that traditional oxidation processes are mostly carried out under harsh conditions of high temperature, high pressure, and corrosive reagents, leading to serious environmental problems. Heterogeneous photocatalysis offers a promising alternative strategy for the activation and oxidation of CH bonds, as it can even be carried out under mild conditions by utilizing renewable solar energy as a driving force. Unfortunately, many potential heterogeneous catalysts are still limited by low photocatalytic efficiency due to severe recombination of charge carriers, a lack of active sites in the reaction process, and an unclear surface reaction mechanism for CH bond oxidation. Therefore, there remains a need for highly efficient heterogeneous catalysts for CH bond activation to produce high-value-added chemicals.

[0003] Among various semiconductors, titanium dioxide (TiO2) is widely recognized as one of the most promising photocatalysts due to its high photoactivity, stability, low cost, and non-toxicity. Currently, TiO2 has been extensively studied as a heterogeneous photocatalyst, including applications in air / water purification, pollutant removal, organic compound degradation, building surface self-healing, and toluene oxidation. However, due to the high recombination rate of photogenerated charges and the limited number of active sites, reported TiO2 photocatalysts for CH bond photooxidation still suffer from low conversion efficiency and poor selectivity. Furthermore, due to its wide bandgap (~3.2 eV), traditional TiO2 only reacts to ultraviolet (UV) light. Therefore, it is highly desirable to develop efficient TiO2 photocatalysts for visible light-driven aerobic photocatalytic oxidation under mild conditions. To this end, this invention is proposed. Summary of the Invention

[0004] In this study, we report a Ti with significant optical switchability 3+Photochromic TiO2-PEG200 nanoparticles were developed for the efficient photocatalytic oxidation of ethylbenzene to acetophenone under visible light. This study is the first to explore the influence of photochromism on the mechanism of improving the photocatalytic oxidation efficiency of ethylbenzene to acetophenone, and provides insights into the design of photochromic catalysts and the photocatalytic oxidation of C(sp...)... 3 In-depth insights into the -H bond.

[0005] The technical solution of the present invention is as follows: A method for photocatalytic oxidation of C(sp) 3 The preparation method of photochromic TiO2 nanoparticles with α-H bonds and their application in the photocatalytic oxidation of ethylbenzene to acetophenone is based on titanium tetrachloride (TiCl4) as a substrate and polyethylene glycol (PEG) as a solvent, and is synthesized via a solvothermal method, including the following steps: TiCl4 was dissolved in PEG under magnetic stirring. After continuous stirring at room temperature, the mixture was transferred to a PTFE-lined stainless steel autoclave (50 mL) and subjected to a solvothermal reaction in an oven. After natural cooling to room temperature, the precipitate was collected by centrifugation and washed with a small amount of acetone.

[0006] According to the present invention, preferably, the molecular weight of the polyethylene glycol in step (1) is 200.

[0007] According to the present invention, preferably, the room temperature stirring time in step (1) is 10 min.

[0008] According to the present invention, preferably, the volume ratio of titanium tetrachloride to polyethylene glycol in step (1) is 1:60.

[0009] According to the present invention, preferably, the titanium source in step (1) is titanium tetrachloride (TiCl4).

[0010] According to the present invention, preferably, the solvothermal reaction in the oven in step (1) is carried out at a temperature of 190°C for a time of 12 hours.

[0011] According to the present invention, the application of the above-mentioned photochromic material in the photocatalytic activation of ethylbenzene; More preferably, the method for photocatalytic oxidation of C(sp) 3 The method for preparing photochromic TiO2 nanoparticles with α-H bonds can be applied to the degradation of organic matter and dyes, or to the synthesis of organic matter.

[0012] The technical features and beneficial effects of this invention are as follows: This invention provides a TiO2-PEG200 nanoparticle photocatalyst with photochromic properties. Approximately 5 nm anatase-phase TiO2 nanoparticles were synthesized in PEG200 via a solvothermal method. This catalyst has three significant technical features: First, it achieves photochromic properties through PEG coordination and self-doping of Ti... 3+ The synergistic effect of surface oxygen vacancies enabled visible light response (bandgap reduced to 2.80 eV); secondly, high-concentration Ti could be dynamically generated under blue light (405 nm) irradiation. 3+ And accompanied by a noticeable color change (light yellow → black); third, Ti 3+ / Ti 4+ The reversible cycle can continuously generate superoxide radicals (O2). ·− Simultaneously, photogenerated holes activate the C(sp) group of ethylbenzene. 3 The H-bonds form benzyl radicals. These radicals then react with O2. •− The interaction leads to the formation of peroxy radicals, which is crucial for the synthesis of acetophenone. This photochromic enhancement mechanism significantly improves the overall efficiency of the photocatalytic oxidation process. Its beneficial effects are reflected in three aspects: in terms of catalytic performance, the yield of acetophenone reaches as high as 56 mmol·g. -1 ·h -1 It boasts 10 times the activity of traditional TiO2, with a selectivity exceeding 99%. In terms of stability, it retains over 95% activity after 5 cycles, and XRD confirms its structural stability. Regarding environmental friendliness, it requires only room temperature and atmospheric pressure conditions and visible light drive, eliminating the need for high temperature, high pressure, or strong oxidants, thus meeting the requirements of green chemistry. This technology solves the problems of low visible light utilization, high charge recombination rate, and other drawbacks associated with traditional TiO2 photocatalysts. 3+ Addressing key issues such as poor stability, this study provides an efficient, stable, and environmentally friendly photocatalytic solution for CH bond activation, which has significant application value in the synthesis of pharmaceutical intermediates, fragrances, and other fine chemicals. Attached Figure Description

[0013] Figure 1 The image shows the XRD pattern of TiO2-PEG200.

[0014] Figure 2 Transmission electron microscope image of TiO2-PEG200.

[0015] Figure 3 High-resolution transmission electron microscope image of TiO2-PEG200.

[0016] Figure 4 UV-vis diffuse absorption spectra of TiO2 and TiO2-PEG200 nanoparticles Figure 5XPS spectra of TiO2 and TiO2-PEG200 nanoparticles (Ti 2p).

[0017] Figure 6 XPS spectra of TiO2 and TiO2-PEG200 nanoparticles (O 1s).

[0018] Figure 7 ESR spectra of TiO2 and TiO2-PEG200 nanoparticles.

[0019] Figure 8 Rate diagram of photocatalytic production of acetophenone from TiO2-PEG200 nanoparticles Figure 9 This is a schematic diagram illustrating the photocatalytic oxidation mechanism of TiO2-PEG200 nanoparticles. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0021] In addition, the experimental methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified. Example

[0022] A method for photocatalytic oxidation of C(sp) 3 The preparation method of photochromic TiO2 nanoparticles with H-bonds includes the following steps: (1) Dissolve 0.5 mL TiCl4 in 30 mL PEG under magnetic stirring. After stirring continuously for 10 minutes at room temperature, transfer the mixture to a Teflon-lined stainless steel autoclave (50 mL) and heat at 190 °C for 12 hours. After naturally cooling to room temperature, collect the precipitate by centrifugation and wash with a small amount of acetone.

[0023] The XRD pattern of the TiO2-PEG200 nanoparticles prepared in this embodiment is shown below. Figure 1 The XRD pattern of TiO2-PEG200 showed sharp diffraction peaks corresponding to the anatase phase TiO2, indicating that the product has high crystallinity. No other impurity characteristic peaks were observed in the XRD pattern, indicating that the TiO2-PEG200 nanoparticles have high purity.

[0024] The transmission electron microscope images of the TiO2-PEG200 nanoparticles prepared in this embodiment are as follows: Figure 2 As shown, the sample is composed of small nanoparticles. The selected area electron diffraction (SAED) pattern can be clearly indexed as the (200), (004) and (101) crystal planes of the anatase phase TiO2, indicating that the sample has good crystallinity.

[0025] High-resolution transmission electron microscope images of the TiO2-PEG200 nanoparticles prepared in this embodiment are shown below. Figure 3 As shown, the lattice spacing is 0.35 nm, corresponding to the (101) crystal plane of the anatase phase TiO2. Furthermore, the images show that the TiO2-PEG200 nanoparticles consist of irregular nanoparticles with a size of approximately 5.0 nm. These results are consistent with the XRD analysis results.

[0026] The UV-vis diffuse absorption spectra of TiO2 and TiO2-PEG200 nanoparticles prepared in this embodiment are as follows: Figure 4 As shown, the white TiO2 nanoparticles exhibit strong light absorption in the 200-390 nm range. The UV-Vis diffuse reflectance absorption spectrum shows that the absorption band edge of the TiO2-PEG200 nanoparticles is redshifted compared to that of the TiO2 nanoparticles, and there is a distinct absorption shoulder in the 405-700 nm range, consistent with its pale yellow appearance. This is because Ti... 3+ And the increase in oxygen vacancies. Using the Kubelka-Munk function, the band gaps (Eg values) of TiO2 and TiO2-PEG200 nanoparticles were calculated to be 2.95 eV and 2.80 eV, respectively. Figure 4 As shown in the illustration, the Eg value of TiO2-PEG200 nanoparticles is lower than that of TiO2, which may be due to the presence of Ti in TiO2 nanoparticles. 3+ This mechanism enables a wider range of visible light absorption.

[0027] The XPS spectra of TiO2 and TiO2-PEG200 nanoparticles (Ti 2p) prepared in this embodiment are as follows: Figure 5 As shown, for TiO2-PEG200 nanoparticles, the Ti 2p spectrum has two peaks at 463.51 eV and 457.74 eV, corresponding to Ti 2p, respectively. 1 / 2 and Ti 2p 3 / 2 By fitting with a multi-Gaussian function, the Ti signal can be decomposed into Ti 3+ (463.37 eV and 457.92 eV) and Ti 4+ (464.11 eV and 458.25 eV) species, indicating that the TiO2 nanoparticles contain Ti 4+ Reduced to Ti 3+ There exists Ti 3+ And it is accompanied by oxygen vacancies. TiO2-PEG200 nanoparticles contain Ti 3+ The signal strength of TiO2 is much stronger than that of TiO2, indicating that Ti 3+ The concentration of the species increased significantly. Furthermore, the Ti 2p of the TiO2-PEG200 nanoparticles... 3 / 2 and Ti 2p1 / 2 The peak shifted by 0.53 eV towards higher binding energies, which may be due to Ti 3+ The increase in species and the enrichment of oxygen vacancies enhance the attraction to surrounding electrons.

[0028] The XPS spectra of TiO2 and TiO2-PEG200 nanoparticles prepared in this embodiment are shown below. Figure 6 As shown, the O 1s spectrum of TiO2-PEG200 nanoparticles has four peaks at 529.28, 530.17, 531.17, and 532.31 eV, which are attributed to the Ti-O bond, CO-Ti, oxygen in the surface hydroxyl groups, and oxygen vacancies, respectively. In TiO2-PEG200 nanoparticles, the bonding process is typically achieved through Ti... 3+ Replace Ti 4+ To compensate for charge imbalance, oxygen vacancies are induced. Compared to TiO2, the O1s peak of TiO2-PEG200 nanoparticles shifts by 0.25 eV towards higher binding energies, mainly due to the increased surface electron density caused by oxygen vacancies. Furthermore, it is noteworthy that the relative intensity of the peak attributable to oxygen vacancies in TiO2-PEG200 nanoparticles is higher than that in TiO2, consistent with its pale yellow appearance. The increase in oxygen vacancies further enhances the separation and transfer efficiency of photogenerated charges in TiO2-PEG200 nanoparticles.

[0029] The ESR spectra of the TiO2 and TiO2-PEG200 nanoparticles prepared in this embodiment are as follows: Figure 7 As shown, the presence of oxygen vacancies in TiO2-PEG-200 nanoparticles was confirmed using electron spin resonance (ESR) spectroscopy. An ESR signal appeared in the TiO2-PEG-200 nanoparticles at a g value of 1.997, which is attributed to the surface TiO2 within the particles. 3+ Species. In contrast, the relative intensity of its ESR signal increased, indicating that there is more Ti in the TiO2-PEG-200 nanoparticles. 4+ Reduced to Ti 3+ . Example

[0030] 1 mL of ethylbenzene, 2 mL of acetonitrile, and 10 mg of the TiO2 nanoparticle photocatalyst from Example 1 were added to a 5 mL dry quartz flask. The resulting mixture was stirred for 10 minutes to maintain adsorption-desorption equilibrium and to completely dissolve oxygen in the solution. Then, at room temperature and under an oxygen atmosphere, the photocatalyst was applied using a 405 nm LED (100 mW / cm²). 2The mixture was irradiated for 6 hours. After the specified time, the mixture was centrifuged at 12,000 rpm for 3 minutes to obtain a solid sample. The liquid phase product was analyzed using ultramass spectrometry, with 0.1 mmol / L 1,3,5-trimethoxybenzene as an internal standard. The formation rate of acetophenone was determined by proton nuclear magnetic resonance spectroscopy. The formation rate of acetophenone was 56 mmol·g⁻¹. -1 ·h -1 .

[0031] The rate curve for the photocatalytic production of acetophenone from TiO2-PEG200 nanoparticles in the examples (reaction conditions: 25 °C, O2, 2 mL acetonitrile, 1 mL ethylbenzene, 10 mg TiO2-PEG200 nanoparticle catalyst, blue light). Figure 8 As shown.

[0032] The reaction mechanism diagram in this embodiment is as follows: Figure 9 As shown, under 405nm blue light irradiation, due to the coordination polyol and self-doped Ti... 3+ The synergistic integration with surface oxygen vacancies resulted in a significant photochromic effect, where the trapped electrons transferred Ti... 4 + In-situ restoration to Ti 3+ Promotes Ti enrichment under radiation 3+ The generation of this state significantly improves charge separation efficiency and extends light absorption into the visible spectrum. Crucially, in an aerobic environment, Ti... 3+ Reversible oxidation to Ti 4+ It will produce a large number of superoxide radicals (O2) ·− ) as the driver C (sp 3 The key oxide species activated by the -H bond. The resulting superoxide radical (O2) ·− It is expected that benzyl radicals generated through photogenerated hole oxidation will form peroxy radicals, which will further hydrolyze to produce acetophenone as the final product. This significant activity is attributed to the photochromic effect, which stabilizes Ti. 3+ / Ti 4+ The cycle continues, and superoxide radicals (O2) are maintained during long-term reactions. ·− The generation of ).

Claims

1. A method for photocatalytic oxidation of C(sp) 3 The method for preparing photochromic TiO2 nanoparticles with α-H bonds includes the following steps: (1) Dissolve 0.5 mL of TiCl4 in 30 mL of PEG under magnetic stirring. After stirring continuously for 10 minutes at room temperature, transfer the mixture to a 50 mL stainless steel autoclave lined with polytetrafluoroethylene. (2) Heat at 190°C for 12 hours. After naturally cooling to room temperature, collect the precipitate by centrifugation and wash with a small amount of acetone.

2. The method for photocatalytic oxidation of C(sp) according to claim 1 3 A method for preparing photochromic TiO2 nanoparticles with α-H bonds, characterized in that, The molecular weight of the polyethylene glycol is 200.

3. The method for photocatalytic oxidation of C(sp) according to claim 1 3 A method for preparing photochromic TiO2 nanoparticles with α-H bonds, characterized in that, The stirring time at room temperature is 10 minutes.

4. The method for photocatalytic oxidation of C(sp) according to claim 1 3 A method for preparing photochromic TiO2 nanoparticles with α-H bonds, characterized in that, The volume ratio of titanium tetrachloride to polyethylene glycol is 1:

60.

5. The method for photocatalytic oxidation of C(sp) according to claim 1 3 A method for preparing photochromic TiO2 nanoparticles with α-H bonds, characterized in that, The titanium source is titanium tetrachloride (TiCl4).

6. The method for photocatalytic oxidation of C(sp) according to claim 1 3 A method for preparing photochromic TiO2 nanoparticles with α-H bonds, characterized in that, The solvothermal reaction in the oven is carried out at a temperature of 190°C for 12 hours.

7. The application of photochromic TiO2 nanoparticles prepared according to claim 1 in the photocatalytic oxidation of ethylbenzene to acetophenone.

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