A method for preparing an amphiphilic photocatalyst by loading metal oxide on carbon nitride and application thereof to a water-phase benzene hydroxylation reaction

Abstract

This invention discloses a method for preparing an amphiphilic photocatalyst using carbon nitride-supported metal oxides and its application in the aqueous-phase benzene hydroxylation reaction. This catalyst not only retains the unique amphiphilicity of carbon nitride, improving the interfacial contact and mass transfer process between the water / benzene phases and promoting the rapid and efficient transfer of •OH generated in the aqueous phase to benzene to participate in the reaction, but also forms a good interfacial contact between the metal oxide and carbon nitride phases during molten salt heat treatment. Under illumination, photogenerated electrons can efficiently migrate from carbon nitride to the surface of the metal oxide, driving the rapid photo-Fenton reaction. Therefore, this catalyst exhibits excellent catalytic performance in the photocatalytic aqueous-phase benzene hydroxylation reaction to prepare phenol. This invention does not require the addition of additional organic solvents and can achieve a highly efficient benzene hydroxylation reaction in a pure aqueous phase, conforming to the concept of green chemistry and showing good prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalysis and organic synthesis technology, specifically relating to a method for preparing amphiphilic photocatalysts by supporting metal oxides with carbon nitride and its application in aqueous benzene hydroxylation reaction. Background Technology

[0002] Phenol, as an important basic organic chemical raw material, is widely used in the chemical industry. Currently, industrially, benzene is mainly synthesized into phenol via a three-step cumene process. However, this process suffers from high energy consumption, low atom utilization, harsh conditions, and severe environmental pollution. Using hydrogen peroxide as an oxidant to hydroxylate benzene in a single step to produce phenol offers advantages such as simplicity and environmental friendliness, meeting the needs of sustainable development and making it an ideal phenol production route. However, the current process widely uses organic solvents, which pose problems such as toxicity, environmental pollution, and increased costs. Using pure water as a solvent can effectively reduce reaction costs, minimize the harm of organic solvents to human health and the environment, and improve reaction safety, aligning with the principles of green chemistry. However, the immiscibility of benzene and water hinders the mass transfer process between the two phases during the reaction. For example, hydroxyl radicals (•OH) generated in the aqueous phase are difficult to efficiently transfer to the benzene phase, leading to their accumulation and decomposition into H2O and O2 in the aqueous phase, reducing H2O2 utilization, thereby decreasing reactivity and increasing production costs. Therefore, achieving efficient benzene hydroxylation in a pure aqueous phase is particularly important. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for preparing an amphiphilic photocatalyst using carbon nitride-supported metal oxides and its application in the aqueous benzene hydroxylation reaction. This method leverages the unique amphiphilic properties of carbon nitride, employing molten salt-assisted heat treatment to load metal oxides, which serve as Fenton active sites, onto its surface. During molten salt heat treatment, the metal oxides dissolve and regenerate, allowing them to grow uniformly on the carbon nitride surface as smaller particles and forming good interfacial contact. This facilitates the rapid migration of photogenerated electrons from the carbon nitride to the metal oxide surface during the photocatalytic reaction, promoting the efficient decomposition of H₂O₂ into •OH to drive the benzene hydroxylation reaction. Simultaneously, the catalyst retains the amphiphilic properties of carbon nitride, enabling the formation of a stable microemulsion between water and benzene, significantly improving the interfacial contact between them, and allowing reactive oxygen species generated in the aqueous phase to rapidly and efficiently transfer to benzene to participate in the reaction. Therefore, in the pure aqueous phase benzene hydroxylation reaction to prepare phenol, the catalyst exhibits excellent hydrogen peroxide decomposition efficiency and utilization, significantly improving the efficiency of benzene hydroxylation to phenol. This method features a simple synthesis technique, mild reaction conditions, and no need to add additional organic solvents. It can achieve efficient benzene hydroxylation reaction in a pure aqueous phase, which is in line with the concept of green chemistry and has certain prospects for industrial application.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] The first objective of this invention is to protect a method for preparing amphiphilic photocatalysts using carbon nitride-supported metal oxides, specifically comprising the following steps:

[0006] (1) Carbon nitride is obtained by calcining carbon nitride precursors in a muffle furnace, wherein the carbon nitride precursors include any one of cyanamide, dimelamine, melamine, urea, thiocyanate and trithiocyanate;

[0007] (2) Grind and mix the metal oxide, carbon nitride and molten salt evenly, and anneal the mixture in a muffle furnace to obtain a mixture with close contact between the two phase interfaces;

[0008] (3) The mixture was first washed with deionized water to remove molten salt, then soaked in 1 mol / L HCl solution, and then washed with deionized water until the ion concentration was less than 10 ppm. Finally, it was dried under vacuum to obtain a carbon nitride supported metal oxide amphiphilic photocatalyst.

[0009] Furthermore, the calcination treatment in step (1) is carried out at a temperature of 400℃~600℃ for 2~4 hours.

[0010] Further, the mass ratio of the metal oxide to carbon nitride used in step (2) is 0.3 to 1:1. The metal oxide includes any one of ferric oxide, iron tetroxide, lanthanum oxide, vanadium pentoxide, copper oxide, titanium dioxide, tungsten trioxide, bismuth oxide, zinc oxide, and cobalt trioxide.

[0011] Further, the mass ratio of the molten salt used in step (2) to the mass of the carbon nitride used is 1 to 6:1, and the molten salt includes any one or more of lithium chloride, potassium chloride, sodium chloride, and zinc chloride.

[0012] Furthermore, the annealing treatment in step (2) is carried out at a temperature of 450℃~650℃ for 2~4 hours.

[0013] The second objective of this invention is to protect the application of a carbon nitride-supported metal oxide amphiphilic photocatalyst, which is used in a pure aqueous phase with benzene or substituted benzene as a substrate, hydrogen peroxide as an oxidant, and under visible light irradiation and stirring or ultrasonic conditions to drive a benzene ring hydroxylation reaction, thereby producing phenol or the corresponding derivative.

[0014] Furthermore, the molar ratio of hydrogen peroxide to the substrate is 1 to 3:1.

[0015] Furthermore, the volume ratio of water to substrate is 1 to 10:1.

[0016] Furthermore, the reaction temperature for preparing phenol by hydroxylation of benzene or substituted benzene is 20~60℃, and the time is 1 h~12 h.

[0017] Furthermore, the visible light includes any one of LED lights, xenon lamps, and sunlight in nature.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The carbon nitride-supported metal oxide amphiphilic photocatalyst described in this invention has unique amphiphilic properties, which can promote the formation of a stable microemulsion between water and benzene, optimize the interfacial contact between the two, and enable the active oxygen species generated in the aqueous phase to be rapidly and efficiently transferred to benzene to participate in the reaction. Therefore, this catalyst can achieve a highly efficient benzene hydroxylation reaction in a pure aqueous phase without the addition of any organic additives, truly following the concept of green chemistry.

[0020] (2) During the molten salt heat treatment process, the metal oxide is dissolved and regenerated, so that it grows uniformly on the surface of carbon nitride in smaller particles and forms a good interfacial contact. This is beneficial to the rapid migration of photogenerated electrons from carbon nitride to the surface of metal oxide during the photocatalytic reaction, and promotes the efficient decomposition of H2O2 into •OH to drive the benzene hydroxylation reaction.

[0021] (3) Based on the above advantages, the amount of hydrogen peroxide used in the reaction of benzene hydroxylation to prepare phenol is equal to or slightly excessive with the amount of substrate, which helps to reduce reaction costs and improve the potential application value of the invention.

[0022] (4) The carbon nitride supported metal oxide amphiphilic photocatalyst disclosed in this invention can also be applied to environmental pollution treatment and other fields according to actual needs. Attached Figure Description

[0023] Figure 1 The Fe2O3 / CCN prepared in Example 1 and the Fe2O3 / CCN prepared in Comparative Examples 1, 2, and 3 # XRD patterns of Fe2O3 and CCN;

[0024] Figure 2 The Fe2O3 / CCN prepared in Example 1 and the Fe2O3 / CCN prepared in Comparative Examples 1, 2, and 3 # FT-IR spectra of Fe2O3 and CCN;

[0025] Figure 3 Fe2O3 / CCN prepared in Example 1 and Fe2O3 / CCN prepared in Comparative Example 1 # SEM image;

[0026] Figure 4Optical micrograph of the microemulsion formed in the presence of Fe2O3 / CCN prepared in Example 1, representing a water / benzene two-phase system;

[0027] Figure 5 The Fe2O3 / CCN prepared in Example 1 and Comparative Examples 1, 2, and 3 are used for application. # Performance evaluation diagram of the hydroxylation reaction of benzene with Fe2O3 and CCN;

[0028] Figure 6 This is a graph showing the cyclic performance evaluation of the Fe2O3 / CCN hydroxylation reaction of benzene in Example 1.

[0029] Figure 7 This is a performance evaluation diagram of the La2O3 / CCN photocatalytic nitric oxide removal reaction in Example 2. Detailed Implementation

[0030] To make the content of this invention easier to understand, the technical solution described below will be further explained in conjunction with specific embodiments, but this invention is not limited thereto.

[0031] Example 1: Preparation of a carbon nitride-supported ferric oxide amphiphilic photocatalyst (Fe2O3 / CCN)

[0032] Melamine was calcined in a muffle furnace at 550℃ for 3 hours to obtain carbon nitride. 1 g of carbon nitride was thoroughly ground and mixed with 0.6 g of Fe₂O₃, 1.8 g of LiCl, and 2.2 g of KCl, and then annealed in a muffle furnace at 550℃ for 3 hours. The annealed solid was further washed with deionized water until the ion concentration was below 10 ppm to remove residual medium salts. It was then soaked in 1 mol / L HCl solution for 12 hours, and further washed with deionized water until the ion concentration was below 10 ppm. The resulting solid was dried in a 60℃ oven, cooled to room temperature, and then ground to obtain Fe₂O₃ / CCN.

[0033] Application Example 1: Test of Benzene Hydroxylation Performance of Fe2O3 / CCN in Aqueous Phase

[0034] 50 mg of Fe₂O₃ / CCN was added to a reactor containing 7 mL of water, followed by 1 mL of benzene and 1.2 mL of H₂O₂. The reaction was carried out at 25 °C for 4 h under simulated sunlight irradiation and magnetic stirring at a stirring rate of 600 rpm, with continuous stirring throughout the reaction. After the reaction was complete, 10 mL of methanol was injected into the mixture to quench the reaction and convert the two-phase system into a single phase. Toluene was then added as an internal standard, and the reaction products were analyzed by liquid chromatography.

[0035] Example 2: Preparation of a carbon nitride-supported lanthanum trioxide photocatalyst (La2O3 / CCN)

[0036] Melamine was calcined in a muffle furnace at 550℃ for 3 hours to obtain carbon nitride. 1 g of carbon nitride was thoroughly ground and mixed with 0.5 g of La₂O₃, 1.8 g of LiCl, and 2.2 g of KCl, and then annealed in a muffle furnace at 550℃ for 3 hours. The annealed solid was washed with deionized water until the ion concentration was below 10 ppm to remove residual medium salts. It was then soaked in a 1 mol / L HCl solution for 12 hours, and further washed with deionized water until the ion concentration was below 10 ppm. The resulting solid was dried in a 60℃ oven, cooled to room temperature, and then ground to obtain La₂O₃ / CCN.

[0037] Application Example 2: Performance Test of La2O3 / CCN Photocatalytic Nitric Oxide Removal

[0038] A 0.02 g sample of La₂O₃ / CCN was loaded into a dedicated quartz reactor. A 50 W LED lamp was used as the visible light source, and a long-pass cutoff filter was used to control the wavelength of the incident light (λ≥420 nm). The lamp was introduced vertically from the top of the reactor at a distance of 20 cm. Standard air and NO (125 mg / m³) were then added. 3 Low-concentration NO was prepared by mixing the gas stream with NO gas to obtain an initial NO concentration of 520 mg / L. The diluted NO was then introduced into the reactor. After adsorption-desorption equilibrium was reached, the lamp was turned on. X The analyzer automatically samples every minute and records NO, NO2, and NO. X The concentration.

[0039] Comparative Example 1: Carbon nitride supported metal oxide photocatalyst (Fe2O3 / CCN) prepared by a simple heat treatment method # )

[0040] Melamine was calcined in a muffle furnace at 550℃ for 3 hours to obtain carbon nitride. 1 g of carbon nitride was thoroughly ground with 0.6 g of Fe₂O₃, and then annealed in a muffle furnace at 550℃ for 3 hours. After cooling to room temperature and grinding again, Fe₂O₃ / CCN was obtained. # .

[0041] Application Comparative Example 1: Fe2O3 / CCN # Benzene hydroxylation performance test in aqueous phase

[0042] Take 50 mg Fe2O3 / CCN #The mixture was added to a reactor containing 7 mL of water, followed by 1 mL of benzene and 1.2 mL of H₂O₂. Under simulated sunlight irradiation and magnetic stirring conditions, the reaction was carried out at 25 °C for 4 h with a stirring rate of 600 rpm. Stirring was maintained throughout the reaction. After the reaction was complete, 10 mL of methanol was injected into the mixture to quench the reaction and convert the two-phase system into a single phase. Toluene was then added as an internal standard, and the reaction products were analyzed by liquid chromatography.

[0043] Comparative Example 2: Preparation of Carbon Nitride (CCN)

[0044] Melamine was calcined in a muffle furnace at 550°C for 3 hours to obtain carbon nitride. 1 g of carbon nitride was thoroughly ground and mixed with 1.8 g of LiCl and 2.2 g of KCl, and then annealed in a muffle furnace at 550°C for 3 hours. The annealed solid was further washed with deionized water until the ion concentration was below 10 ppm to remove residual media salts. The resulting solid was dried in an oven at 60°C to obtain CCN.

[0045] Application Comparative Example 2: Test of Benzene Hydroxylation Performance of CCN in Aqueous Phase

[0046] 50 mg of CCN was added to a reactor containing 7 mL of water, followed by 1 mL of benzene and 1.2 mL of H₂O₂. The reaction was carried out at 25 °C for 4 h under simulated sunlight irradiation and magnetic stirring at a stirring rate of 600 rpm, with continuous stirring throughout the reaction. After the reaction was complete, 10 mL of methanol was injected into the mixture to quench the reaction and convert the two-phase system into a single phase. Toluene was then added as an internal standard, and the reaction products were analyzed by liquid chromatography.

[0047] Comparative Example 3: Ferric oxide (Fe2O3) and its performance in benzene hydroxylation in aqueous phase.

[0048] This sample is commercially available ferric oxide.

[0049] Application Comparative Example 3: Test of Benzene Hydroxylation Performance of Fe2O3 in Aqueous Phase

[0050] 50 mg of Fe₂O₃ was added to a reactor containing 7 mL of water, followed by 1 mL of benzene and 1.2 mL of H₂O₂. The reaction was carried out at 25 °C for 4 h under simulated sunlight irradiation and magnetic stirring at a stirring rate of 600 rpm, with continuous stirring throughout the reaction. After the reaction was complete, 10 mL of methanol was injected into the mixture to quench the reaction and convert the two-phase system into a single phase. Toluene was then added as an internal standard, and the reaction products were analyzed by liquid chromatography.

[0051] Chart Analysis

[0052] Figure 1 These are the X-ray diffraction (XRD) patterns of Example 1 and the comparative example. The Fe2O3 / CCN ratio can be observed in the images. # It has two phases, ferric oxide and carbon nitride, while Fe2O3 / CCN not only has these two phases, but also generates a small amount of iron oxide phase. This may be due to the efficient interfacial mass transfer between carbon nitride and ferric oxide during the molten salt process, and its ferromagnetism is beneficial to the recovery of the sample after the reaction.

[0053] Figure 2 The Fourier transform infrared spectra of Example 1 and the comparative example are shown in the figures. It can be seen from the figures that Fe2O3 / CCN... # The chemical structure of carbon nitride is not changed during molten salt or annealing.

[0054] Figure 3 Image a is a SEM image of Fe2O3 / CCN in Example 1. Fe2O3 particles were dissolved and regenerated on the CCN surface through molten salt heat treatment, and the particle size was about 30~50 nm. Some Fe2O3 particles can be observed embedded in CCN at the edge of carbon nitride. Figure 3 b is a comparative example of Fe2O3 / CCN # The SEM image shows that sintering is present in the sample after simple heat treatment, and the contact between Fe2O3 and CCN is insufficient. The particle size of Fe2O3 is about 200 nm.

[0055] Figure 4 In Example 1, the Fe2O3 / CCN phases of water and benzene are stably positioned at the interface between the benzene and aqueous phases. Furthermore, optical microscopy reveals that water and benzene form a stable microemulsion in an "oil-in-water" or "water-in-oil" manner. This optimizes the interfacial contact between the two, allowing reactive oxygen species generated in the aqueous phase to rapidly and efficiently transfer to the benzene to participate in the reaction, which is beneficial for the efficient conduct of the benzene hydroxylation reaction in the pure aqueous phase.

[0056] Figure 5 This is a comparison chart of the activity of Application Example 1 and Application Comparative Examples 1, 2, and 3. It is clear that Fe2O3 / CCN has the best photocatalytic performance, with a phenol yield of 31.6% within 4 hours, which is much higher than the other comparative examples.

[0057] Figure 6 This is a cyclic activity diagram of benzene hydroxylation of the Fe2O3 / CCN sample in Example 1. It can be seen that its photocatalytic activity is basically stable in the four rounds of reaction, and Fe2O3 / CCN shows excellent cycle stability.

[0058] Figure 7This is a performance evaluation graph of the photocatalytic removal of nitric oxide reaction in Example 2. It can be seen that after 30 minutes of oxidation reaction, La2O3 / CCN has a nitric oxide removal rate of 93.7%, showing excellent photocatalytic nitric oxide removal rate.

[0059] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. Use of a carbon nitride supported metal oxide amphiphilic photocatalyst, characterized in that: In a pure aqueous phase, using benzene or substituted benzene as a substrate and hydrogen peroxide as an oxidant, the benzene ring hydroxylation reaction is driven by the aforementioned carbon nitride-supported metal oxide amphiphilic photocatalyst under visible light irradiation and stirring or ultrasonic conditions, thereby producing phenol or the corresponding derivatives. The preparation method of the carbon nitride-supported metal oxide amphiphilic photocatalyst includes: calcining a carbon nitride precursor in a muffle furnace to obtain carbon nitride; grinding and mixing a metal oxide with carbon nitride and a molten salt in a certain proportion; annealing the mixture in a muffle furnace to obtain a crude product; washing the crude product with 1 mol / L HCl solution and deionized water respectively; and finally drying to obtain the carbon nitride-supported metal oxide amphiphilic photocatalyst; wherein the metal oxide includes any one of ferric oxide, iron(II,III) oxide, lanthanum oxide, vanadium pentoxide, copper oxide, titanium dioxide, tungsten trioxide, bismuth oxide, zinc oxide, and cobalt trioxide.

2. Use according to claim 1, characterized in that: The carbon nitride precursor includes any one or more of cyanamide, dicyanamide, melamine, urea, thiocyanate, and trithiocyanate.

3. Use according to claim 1, characterized in that: The carbon nitride precursor was calcined in a muffle furnace at a temperature of 400℃~600℃ for 2~4 hours.

4. Use according to claim 1, characterized in that: The mass ratio of the metal oxide to carbon nitride used is 0.3 to 1:1; the mass ratio of the molten salt to the carbon nitride used is 1 to 6:1, and the molten salt includes any one or more of lithium chloride, potassium chloride, sodium chloride, and zinc chloride.

5. Use according to claim 1, characterized in that: The annealing temperature is 450℃~650℃, and the time is 2~4 h.

6. Use according to claim 1, characterized in that: The volume ratio of water to substrate is 1 to 10:1; the molar ratio of hydrogen peroxide to substrate is 1 to 3:

1.

7. Use according to claim 1, characterized in that: The reaction temperature for preparing phenol by hydroxylation of benzene is 20~60℃, and the time is 1 h~12 h; the visible light includes any one of LED lamps, xenon lamps and sunlight.

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