A persulfate-based pickering emulsion and a method for preparing benzaldehyde by selective oxidation of benzyl alcohol

Abstract

The present application relates to a kind of Pickering emulsion based on persulfate and the method for the selective oxidation of benzyl alcohol to prepare benzaldehyde, with persulfate as oxidant, hyperphil biochar as emulsifier and catalyst, while forming Pickering emulsion catalytic system based on persulfate, efficiently activate persulfate to produce active oxygen species, realize the efficient selective oxidation of benzyl alcohol to generate benzaldehyde.Hyperphil biochar is made of marine waste green algae, cheap and easy to get, not only reduces the production cost of emulsifier and catalyst, but also solves the ecological crisis of green algae faced by coastal cities;Catalyst is relatively easy to recover after reaction, and can be recycled after simple cleaning.

Description

Technical Field

[0001] This invention relates to a Pickering emulsion based on persulfate and a method for the selective oxidation of benzyl alcohol to prepare benzaldehyde, belonging to the field of selective oxidation of alcohols. Background Technology

[0002] Benzaldehyde is an important chemical raw material and intermediate that can be used to derive various chemical products. It is widely used in pharmaceuticals, fragrances, dyes, and other fields. It is the simplest and most commonly used aromatic aldehyde in industry. Currently, the commonly used methods for synthesizing benzaldehyde are benzyl chloride hydrolysis and toluene selective oxidation. The former limits the application of benzaldehyde because the final product contains chlorine, while the latter has the disadvantage of low benzaldehyde selectivity.

[0003] Benzyl alcohol oxidation is a promising alternative to the two traditional processes mentioned above. This method utilizes an oxidant to directly oxidize the alcohol to an aldehyde, resulting in a relatively simple process with high yield. Currently, various reaction routes have been developed based on different catalytic oxidation systems for the oxidation of benzyl alcohol to benzaldehyde. Among commonly used oxidants, chromates and manganates contain heavy metals, which can cause environmental pollution, while hydrogen peroxide is unstable and poses an explosion risk. From a green chemistry perspective, molecular oxygen offers economic and environmental advantages as an oxidant, but higher reaction temperatures or the addition of a co-catalyst are required to achieve higher reaction rates.

[0004] Persulfate (PMS, HSO5) - SO₄²⁻ is a chemically stable and inexpensive solid oxidant. In recent years, it has gained attention for its potential to be activated by light, electricity, heat, metal-based and non-metal-based catalysts, producing reactive oxygen species (such as ·OH, SO₄²⁻) with high redox potentials. ·- O2 ·- and 1 O2 is widely used to remove highly toxic, persistent, and recalcitrant organic pollutants from water bodies. However, its application in the fine synthesis of organic chemicals, particularly in the oxidation of alcohols to aldehydes, is relatively rare.

[0005] Because persulfate is a water-soluble inorganic salt, while most organic compounds are hydrophobic and lipophilic, the effect of directly using persulfate as an oxidant to oxidize alcohols to aldehydes is often poor due to the limited interfacial contact area. Although organic surfactants can act as emulsifiers to increase the contact area between the organic and aqueous phases and reduce the diffusion resistance at the liquid-liquid interface, organic surfactants are difficult to separate from the final product, which can cause secondary pollution.

[0006] If a catalyst can be synthesized that can not only efficiently activate persulfate to produce reactive oxygen species, but also emulsify immiscible oil and water phases, reduce interfacial diffusion resistance, and improve the efficiency of benzyl alcohol to benzaldehyde without the need for surfactants, it will have great guiding significance and application value. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a Pickering emulsion based on persulfate and a method for the selective oxidation of benzyl alcohol to prepare benzaldehyde.

[0008] The Pickering emulsion of the present invention uses persulfate as an oxidant and superamphilic biochar as an emulsifier and catalyst to form a persulfate-based Pickering emulsion catalytic system in an oil-water two-phase system.

[0009] In this Pickering emulsion catalytic system, the catalytic activity of the superamphilic biochar can be utilized to efficiently activate persulfate and generate a large amount of ·O2. - and 1 O2 and other active oxygen species oxidize benzyl alcohol, achieving one-step production of benzaldehyde without the need for surfactants or heating.

[0010] To achieve the above-mentioned objectives, the present invention is implemented through the following technical solution:

[0011] A persulfate-based Pickering emulsion comprises an aqueous phase, an oil phase, and an emulsifier, wherein the volume ratio of the aqueous phase to the oil phase is (0.25–4.0):1, the concentration of the emulsifier in the aqueous phase is 1–50 g / L, the emulsifier is superamphilic biochar, the aqueous phase is an aqueous persulfate solution, and the oil phase is a hexane solution.

[0012] According to a preferred embodiment of the present invention, the superamphilic biochar is prepared by the following method:

[0013] After pretreatment, the seaweed was pulverized to obtain seaweed powder. The seaweed powder was placed in a tube furnace and heated to 400-1000℃ under nitrogen protection, and then kept at that temperature for 30-180 minutes. After cooling to room temperature, a black solid powder was obtained. Then, it was ball-milled in a planetary ball mill for 1-5 hours, and then washed and dried to obtain superamphilic biochar.

[0014] According to a preferred embodiment of the present invention, the heating rate of the tube furnace is 3-10 °C / min, the nitrogen flow rate is 50-400 mL / min, and the rotational speed of the ball mill is 50-300 rpm.

[0015] According to a preferred embodiment of the present invention, the heating rate is 3-8℃ / min, the pyrolysis temperature is 500-800℃, the holding time is 30-60min, and the rotation speed of the ball mill is 100-200 rpm.

[0016] According to a preferred embodiment of the present invention, the concentration of the persulfate aqueous solution is 5-15 mM, and the persulfate is potassium peroxymonosulfate.

[0017] According to a preferred embodiment of the present invention, the molar number of persulfate is 1.7 to 3.4 times the molar number of alcohol hydroxyl groups.

[0018] According to a preferred embodiment of the present invention, the volume ratio of the aqueous phase to the oil phase is (0.4 to 2.0):1, and the concentration of the emulsifier in the aqueous phase is 1 to 10 g / L.

[0019] The above-mentioned method for preparing Pickering emulsion based on persulfate includes the following steps:

[0020] According to the ratio, use a pipette to take the oil phase and aqueous phase into brown glass bottles respectively, and then add the superamphilic biochar to the oil-water two-phase system, emulsify at a speed of 6000-9000 rpm for 1-10 minutes.

[0021] A method for the selective oxidation of benzyl alcohol to benzaldehyde using Pickering emulsion based on persulfate includes the following steps:

[0022] Benzyl alcohol was dissolved in n-hexane to obtain a benzyl alcohol-n-hexane solution, which was used as the oil phase. Persulfate aqueous solution was used as the aqueous phase. The oil phase and aqueous phase were respectively taken into brown glass bottles by pipetting. Then, superamphilic biochar was added to the oil-water two-phase system and emulsified at 6000-9000 rpm for 1-10 min. Finally, the glass bottle was sealed and placed at room temperature for 0.5-5 h to complete the selective oxidation of benzyl alcohol to benzaldehyde.

[0023] According to a preferred embodiment of the present invention, the concentration of benzyl alcohol in the benzyl alcohol-hexane solution is 1-5 mM.

[0024] According to a preferred embodiment of the present invention, the concentration of the persulfate aqueous solution is 5-15 mM, and the persulfate is potassium peroxymonosulfate.

[0025] According to a preferred embodiment of the present invention, the volume ratio of the aqueous phase to the oil phase is (0.25 to 4.0): 1, and the concentration of the super-amphiphilic biochar in the aqueous phase is 1 to 50 g / L.

[0026] According to a preferred embodiment of the present invention, after the selective oxidation of benzyl alcohol to benzaldehyde is completed, the mixed emulsion containing the catalytic oxidation product benzaldehyde is centrifuged to separate the Pickering emulsion and recover the superamphilic biochar. The superamphilic biochar recovered after centrifugation is washed with anhydrous ethanol and dried.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. This invention uses superamphilic biochar as an emulsifier and catalyst, and persulfate as an oxidant, to obtain a persulfate-based Pickering emulsion. For the first time, persulfate is directly used as an oxidant to achieve efficient oxidation of benzyl alcohol to benzaldehyde, which is non-toxic, harmless, highly stable, and easy to transport and store. Secondly, persulfate is currently mainly used for environmental pollution remediation. This invention broadens the application space of persulfate, enriches its application scenarios, and has high academic value.

[0029] 2. This invention uses super-amphiphilic biochar as both an emulsifier and a catalyst. First, it achieves the formation of a Pickering emulsion catalytic system based on persulfate, which expands the contact area between the organic and aqueous phases, reduces interfacial diffusion resistance, and improves the mass transfer efficiency of benzyl alcohol at the oil-water interface. Second, in the formed emulsion catalytic system, the super-amphiphilic biochar can efficiently activate persulfate to generate highly oxidizing reactive oxygen species, thereby achieving efficient and selective oxidation of benzyl alcohol to benzaldehyde in one step.

[0030] 3. This invention does not require the introduction of other substances as emulsifiers or catalysts, thus reducing the production cost of benzaldehyde; secondly, the operation process of this invention is simple, the reaction conditions are mild, and the equipment requirements are low. In some embodiments, benzyl alcohol can be 100% converted into benzaldehyde at room temperature.

[0031] 4. The super-amphiphilic biochar used in this invention is made from marine waste seaweed, which is inexpensive and readily available. This not only greatly reduces the production cost of emulsifiers and catalysts, but also provides a solution to the ecological crisis of seaweed faced by coastal cities. After the reaction is completed, the super-amphiphilic biochar can be separated from the emulsion through simple operations such as centrifugation or filtration, so as to achieve recycling and further reduce the production cost of benzaldehyde. Attached Figure Description

[0032] Figure 1 The results show the contact angle test results of water droplets (A) and oil droplets (B) obtained from Examples 1, 2, 3 and 4.

[0033] Figure 2 Optical microscope images of the Pickering emulsions formed in Examples 1(A), 2(B), 3(C), and 4(D).

[0034] Figure 3 For example, DMPO captures O2. - EPR spectrum of the subsequent product.

[0035] Figure 4 For the experimental example of TEMP capture 1 EPR spectrum of the product after O2. Detailed Implementation

[0036] The present invention will be further described below with reference to the embodiments.

[0037] Example 1

[0038] The method for the selective oxidation of benzyl alcohol to benzaldehyde using Pickering emulsion based on persulfate comprises the following steps:

[0039] Preparation of superamphilic biochar:

[0040] The collected *Ulva prolifera* was washed with deionized water, dried, pulverized, and sieved through an 80-mesh sieve. 10g of the *Ulva prolifera* powder was weighed into a Sigma tube furnace and heated to 600℃ at a rate of 5℃ / min under nitrogen protection, and held at that temperature for 60min. After cooling to room temperature, the resulting black solid powder was ball-milled in a planetary ball mill at a speed of 200 rpm for 2 hours. After ball milling, the black solid powder was washed with deionized water and then placed in a vacuum drying oven at 60℃ overnight to obtain the superamphilic biochar, designated SAB-600.

[0041] Selective oxidation of benzyl alcohol to prepare benzaldehyde:

[0042] 6 μL of benzyl alcohol was pipetted into 20 mL of n-hexane to obtain a 2.89 mM benzyl alcohol solution, which was used as the oil phase. 0.6148 g of potassium peroxymonosulfate was weighed and dissolved in 100 mL of deionized water to obtain a 10 mM potassium peroxymonosulfate solution, which was used as the aqueous phase. 10 mL of the oil phase and 5 mL of the aqueous phase were pipetted into brown glass bottles. Then, superamphilic biochar was added to the above oil-water two-phase system. The concentration of superamphilic biochar in the aqueous phase was 2 g / L. The mixture was emulsified using a homogenizer at 8000 rpm for 3 min to obtain a persulfate-based Pickering emulsion. Finally, the glass bottle was sealed and placed at room temperature for 2 h to complete the selective oxidation of benzyl alcohol to benzaldehyde.

[0043] Example 2

[0044] The method for the selective oxidation of benzyl alcohol to benzaldehyde using Pickering emulsion based on persulfate comprises the following steps:

[0045] Preparation of superamphilic biochar:

[0046] The collected *Ulva prolifera* was washed with deionized water, dried, pulverized, and passed through an 80-mesh sieve. 10g of *Ulva prolifera* powder was weighed into a Sigma tube furnace and heated to 700℃ at a rate of 5℃ / min under nitrogen protection, and held at that temperature for 60min. After cooling to room temperature, the resulting black solid powder was placed in a planetary ball mill and ball-milled at a speed of 200 rpm for 2 hours. After ball milling, the black solid powder was washed with deionized water and then placed in a vacuum drying oven at 60℃ overnight to obtain superamphilic biochar, denoted as SAB-700.

[0047] Selective oxidation of benzyl alcohol to prepare benzaldehyde:

[0048] 6 μL of benzyl alcohol was pipetted into 20 mL of n-hexane to obtain a 2.89 mM benzyl alcohol solution, which was used as the oil phase. 0.6148 g of potassium peroxymonosulfate was weighed and dissolved in 100 mL of deionized water to obtain a 10 mM potassium peroxymonosulfate solution, which was used as the aqueous phase. 10 mL of the oil phase and 10 mL of the aqueous phase were pipetted into separate brown glass bottles. Then, superamphilic biochar was added to the above oil-water two-phase system, with a concentration of 4 g / L in the aqueous phase. The mixture was emulsified using a homogenizer at 8000 rpm for 3 min to obtain a persulfate-based Pickering emulsion. Finally, the glass bottle was sealed and the mixture was allowed to react at room temperature for 2 h to complete the selective oxidation of benzyl alcohol to benzaldehyde.

[0049] Example 3

[0050] The method for the selective oxidation of benzyl alcohol to benzaldehyde using Pickering emulsion based on persulfate comprises the following steps:

[0051] Preparation of superamphilic biochar:

[0052] The collected *Ulva prolifera* was washed with deionized water, dried, pulverized, and passed through an 80-mesh sieve. 10g of *Ulva prolifera* powder was weighed into a Sigma tube furnace and heated to 800℃ at a rate of 5℃ / min under nitrogen protection, and held at that temperature for 60min. After cooling to room temperature, the resulting black solid powder was placed in a planetary ball mill and ball-milled at a speed of 200 rpm for 2 hours. After ball milling, the black solid powder was washed with deionized water and then placed in a vacuum drying oven at 60℃ overnight to obtain superamphilic biochar, denoted as SAB-800.

[0053] Selective oxidation of benzyl alcohol to prepare benzaldehyde:

[0054] 6 μL of benzyl alcohol was pipetted into 20 mL of n-hexane to obtain a 2.89 mM benzyl alcohol solution, which was used as the oil phase. 0.6148 g of potassium peroxymonosulfate was weighed and dissolved in 100 mL of deionized water to obtain a 10 mM potassium peroxymonosulfate solution, which was used as the aqueous phase. 10 mL of the oil phase and 15 mL of the aqueous phase were pipetted into separate brown glass bottles. Then, superamphilic biochar was added to the above oil-water two-phase system, with a concentration of 6 g / L in the aqueous phase. The mixture was emulsified using a homogenizer at 8000 rpm for 3 min to obtain a persulfate-based Pickering emulsion. Finally, the glass bottle was sealed and the mixture was allowed to react at room temperature for 2 h to complete the selective oxidation of benzyl alcohol to benzaldehyde.

[0055] Example 4

[0056] The method for the selective oxidation of benzyl alcohol to benzaldehyde using Pickering emulsion based on persulfate comprises the following steps:

[0057] Preparation of superamphilic biochar:

[0058] The collected *Ulva prolifera* was washed with deionized water, dried, pulverized, and passed through an 80-mesh sieve. 10g of *Ulva prolifera* powder was weighed into a Sigma tube furnace and heated to 900℃ at a rate of 5℃ / min under nitrogen protection, and held at that temperature for 60min. After cooling to room temperature, the resulting black solid powder was placed in a planetary ball mill and ball-milled at a speed of 200 rpm for 2 hours. After ball milling, the black solid powder was washed with deionized water and then placed in a vacuum drying oven at 60℃ overnight to obtain superamphilic biochar, denoted as SAB-900.

[0059] Selective oxidation of benzyl alcohol to prepare benzaldehyde:

[0060] 6 μL of benzyl alcohol was pipetted into 20 mL of n-hexane to obtain a 2.89 mM benzyl alcohol solution, which was used as the oil phase. 0.6148 g of potassium peroxymonosulfate was weighed and dissolved in 100 mL of deionized water to obtain a 10 mM potassium peroxymonosulfate solution, which was used as the aqueous phase. 10 mL of the oil phase and 20 mL of the aqueous phase were pipetted into separate brown glass bottles. Then, superamphilic biochar was added to the above oil-water two-phase system, with a concentration of 8 g / L in the aqueous phase. The mixture was emulsified using a homogenizer at 8000 rpm for 3 min to obtain a persulfate-based Pickering emulsion. Finally, the glass bottle was sealed and the mixture was allowed to react at room temperature for 2 h to complete the selective oxidation of benzyl alcohol to benzaldehyde.

[0061] Experimental Example 1

[0062] The surface wettability of the superamphilic biochar obtained in Examples 1-4 was characterized using a contact angle meter, and the morphology of the Pickering emulsions formed in Examples 1-4 was characterized using an optical microscope. After the reaction was completed, the Pickering emulsions containing catalytic oxidation products in Examples 1-4 were centrifuged and then the oil phase products were analyzed using a gas chromatograph.

[0063] The specific results are shown in Table 1. Figures 1-2 As shown.

[0064] Table 1. Comparison of the activities of superamphilic biochar-stabilized persulfate-based emulsion catalytic systems.

[0065] Test sample Benzyl alcohol conversion rate (%) Benzaldehyde selectivity (%) Example 1 62.66 73.80 Example 2 71.30 90.00 Example 3 77.58 100.00 Example 4 82.59 83.70

[0066] As shown in Table 1, the superamphilic biochar prepared in this invention, used as an emulsifier and catalyst, exhibited high catalytic activity in the Pickering emulsion catalytic system based on persulfate for the selective oxidation of benzyl alcohol. In Example 3, 100% selectivity for benzaldehyde was achieved.

[0067] from Figure 1 It can be seen that the superamphilic biochar prepared at different pyrolysis temperatures all exhibit a contact angle of 0° for both water and oil droplets, demonstrating superamphilicity. Therefore, it can be used as a solid emulsifier to stabilize Pickering emulsion catalytic systems based on persulfate, such as... Figure 2 As shown.

[0068] After the reaction was completed, the Pickering emulsion containing the catalytic oxidation products was placed in a centrifuge (taking Example 3 as an example) to recover the superamphilic biochar. The recovered superamphilic biochar was repeatedly washed with anhydrous ethanol, dried, and used in the next Pickering emulsion catalytic experiment. The results of the superamphilic biochar recycling experiment are shown in Table 2.

[0069] Table 2. Cyclic performance test results of superamphilic biochar

[0070] Loop count Benzyl alcohol conversion rate (%) Benzaldehyde selectivity (%) 1 79.52 100.00 2 80.65 98.62 3 79.64 97.66 4 75.61 97.50 5 72.33 98.87

[0071] As can be seen from Table 2, although the conversion rate of benzyl alcohol by the superamphiphilic biochar decreased with the increase of the number of cycles, it is clear that its selectivity for benzaldehyde remained above 97%, indicating that the Ulva-based superamphiphilic biochar synthesized in this invention has the ability to efficiently and selectively oxidize benzyl alcohol to prepare benzaldehyde.

[0072] Experimental Example 2

[0073] 1. In the emulsion catalytic system of this invention, to clarify the mechanism of selective oxidation of benzyl alcohol to benzaldehyde, reactive oxygen species quenching experiments were conducted. 50 mM tert-butanol (TBA), dimethyl sulfoxide (DMSO), furfuryl alcohol (FFA), and p-benzoquinone (p-BQ) were added as reactive oxygen species quenchers, respectively. The experimental results are shown in Table 3.

[0074] Table 3. Effects of different quenchers on benzyl alcohol conversion and benzaldehyde selectivity

[0075] quencher Benzyl alcohol conversion rate (%) Benzaldehyde selectivity (%) blank 92.38 100.00 TBA 92.15 100.00 DMSO 90.96 95.81 FFA 19.44 19.04 p-BQ 0.15 0.09

[0076] As shown in Table 3, compared to the control experiment, the addition of TBA and DMSO had negligible effects on the selective oxidation of benzyl alcohol to benzaldehyde, while the addition of FFA and p-BQ significantly inhibited the selective oxidation of benzyl alcohol to benzaldehyde, with the addition of p-BQ almost completely preventing the oxidation reaction from occurring. This indicates that in this emulsion catalytic system, singlet oxygen (… 1 The non-radical oxidation pathway dominated by O2 and the superoxide radical (·O2)-dominated pathway - The radical oxidation pathway dominated by ) drives the selective oxidation of benzyl alcohol to benzaldehyde.

[0077] 2. To further verify the results of the above reactive oxygen species quenching experiments, electron paramagnetic resonance (EPR) experiments were conducted using 5,5-dimethyl-1-pyrrolline-N-oxide (DMPO) and 2,2,6,6-tetramethyl-4-piperidinone (TEMP) as scavenging agents. The results are as follows: Figure 3 and Figure 4 As shown in the figure. It can be seen from the figure that DMPO and O2... - The signal peaks of the products after the reaction and TEMP and 1 The signal peaks of the products after the O2 reaction were all detected, and the intensity of the signal peaks continuously increased with the extension of reaction time, proving that a large amount of O2 was generated in the emulsion catalytic system of this invention. - and 1 Active oxygen species such as O2 are used to achieve the selective oxidation of benzyl alcohol to benzaldehyde.

[0078] Experimental Example 3

[0079] The effect of varying amounts of the amphiphilic biochar (SAB-800) prepared in Example 3 on the selective oxidation of benzyl alcohol to benzaldehyde is shown in Table 4.

[0080] Table 4. Effects of superamphilic biochar dosage on benzyl alcohol conversion and benzaldehyde selectivity.

[0081]

[0082] The results showed that as the SAB-800 dosage increased from 0.5 g / L to 2.0 g / L, the conversion rate of benzyl alcohol increased from 26.54% to 77.58%, and the selectivity of benzaldehyde increased from 53.24% to 100%. This is because with the increase in catalyst dosage, more Pickering emulsions, i.e., more micro / nano reactors, can be formed in the emulsion catalytic system, which accelerates the mass transfer and oxidation of benzaldehyde at the organic-water interface. At the same time, more catalyst can activate PMS to generate more reactive oxygen species, thereby producing more benzaldehyde.

[0083] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A persulfate-based Pickering emulsion, comprising an aqueous phase, an oil phase, and an emulsifier, wherein, The volume ratio of the aqueous phase to the oil phase is (0.25~4.0):1, the concentration of the emulsifier in the aqueous phase is 1~50g / L, the emulsifier is superamphilic biochar, the aqueous phase is a persulfate aqueous solution, and the oil phase is a hexane solution. Superamophilic biochar was prepared by the following method: After pretreatment, the seaweed was pulverized to obtain seaweed powder. The seaweed powder was placed in a tube furnace and heated to 400~1000℃ under nitrogen protection, and then held at that temperature for 30~180min. After cooling to room temperature, a black solid powder was obtained. Then, it was ball-milled in a planetary ball mill for 1~5h, and then washed and dried to obtain super-amphiphilic biochar. The heating rate of the tube furnace was 3~10℃ / min, the nitrogen flow rate was 50~400mL / min, and the rotation speed of the ball mill was 50~300 rpm.

2. The Pickering emulsion based on persulfate according to claim 1, characterized in that, The concentration of the persulfate aqueous solution is 5-15 mM, and the persulfate is potassium peroxymonosulfate.

3. The Pickering emulsion based on persulfate according to claim 1, characterized in that, The volume ratio of the aqueous phase to the oil phase is (0.4~2.0):1, and the concentration of the emulsifier in the aqueous phase is 1~10 g / L.

4. The method for preparing the Pickering emulsion based on persulfate according to claim 1, comprising the following steps: According to the ratio, use a pipette to take the oil phase and aqueous phase into brown glass bottles respectively, and then add the superamphilic biochar to the oil-water two-phase system, emulsify at a speed of 6000-9000 rpm for 1-10 minutes.

5. The method for selective oxidation of benzyl alcohol to benzaldehyde using a persulfate-based Pickering emulsion as described in claim 1, comprising the following steps: Benzyl alcohol was dissolved in n-hexane to obtain a benzyl alcohol-n-hexane solution, which was used as the oil phase. Persulfate aqueous solution was used as the aqueous phase. The oil phase and aqueous phase were respectively taken into brown glass bottles by pipetting. Then, superamphilic biochar was added to the oil-water two-phase system and emulsified at 6000-9000 rpm for 1-10 min. Finally, the glass bottle was sealed and placed at room temperature for 0.5-5 h to complete the selective oxidation of benzyl alcohol to benzaldehyde.

6. The method according to claim 5, characterized in that, The concentration of benzyl alcohol in a benzyl alcohol-hexane solution is 1-5 mM.

7. The method according to claim 5, characterized in that, The concentration of the persulfate aqueous solution is 5-15 mM, the persulfate is potassium peroxymonosulfate, the volume ratio of the aqueous phase to the oil phase is (0.25~4.0):1, and the concentration of the superamphilic biochar in the aqueous phase is 1~50 g / L.

8. The method according to claim 5, characterized in that, After the selective oxidation of benzyl alcohol to benzaldehyde is completed, the mixed emulsion containing the catalytic oxidation product benzaldehyde is centrifuged to separate the Pickering emulsion and recover the superamphilic biochar. The recovered superamphilic biochar is then washed with anhydrous ethanol and dried.

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