Floatable hydrophilic and hydrophobic heterojunction photocatalytic material and application thereof

Abstract

The invention relates to a floatable hydrophilic and hydrophobic heterojunction photocatalytic material and application thereof, and belongs to the technical field of preparation of photocatalytic materials.The preparation method of the heterojunction photocatalytic material includes the steps that TiO2 / g-C3N4, anhydrous potassium carbonate and tetrahydrofuran are mixed to be uniform, reflux condensation is conducted, TFMBB is added, a reaction is conducted under the illumination condition, and the floatable hydrophilic and hydrophobic heterojunction photocatalytic material is obtained. And after the reaction is finished, carrying out suction filtration and drying to prepare the floatable hydrophilic and hydrophobic heterojunction photocatalytic material. The heterojunction photocatalytic material provided by the invention has a special floatable hydrophilic and hydrophobic structure, is more beneficial to selective adsorption of CO2 and effective separation of carriers, and can effectively improve the efficiency of photocatalytic reduction of CO2.

Description

Technical Field

[0001] The present invention relates to the technical field of photocatalytic material preparation, and in particular to a floatable hydrophilic and hydrophobic heterojunction photocatalytic material and applications thereof. Background Art

[0002] Excessive emissions of carbon dioxide (CO2), a greenhouse gas, contribute to global climate change, becoming one of the major challenges facing the world today. Converting CO2 and H2O into high-value-added chemicals (such as CO and CH4) not only mitigates the greenhouse effect but also enables the recycling of carbon resources, which has important environmental and economic implications.

[0003] The photocatalytic CO2 reduction reaction is divided into a CO2 reduction half-reaction and an H2O oxidation half-reaction. These two half-reactions play a vital role in the photocatalytic CO2 reduction process. The CO2 reduction half-reaction refers to the process in which a photocatalyst uses photogenerated electrons to reduce CO2 to organic matter or carbon-based compounds under light conditions. This process involves multiple electron transfers and usually produces a series of intermediates, ultimately forming the desired product. The H2O oxidation half-reaction refers to the process in which a photocatalyst uses photogenerated holes to oxidize water molecules into oxygen under light conditions. The CO2 reduction half-reaction and the H2O oxidation half-reaction are interdependent and together constitute the full reaction of photocatalytic CO2 reduction. Both are indispensable, and a low reaction rate of either will affect the overall reaction.

[0004] Heterojunctions have attracted widespread attention as photocatalytic materials with high photogenerated electron-hole separation efficiency. TiO2 / g-C3N4 heterojunctions have been widely used in photocatalytic hydrogen evolution, pollutant degradation, and CO2 reduction due to their excellent photogenerated electron reduction and photogenerated hole oxidation capabilities. However, TiO2 / g-C3N4 heterojunctions are hydrophilic. During the CO2 reduction process in the liquid phase, most of the adsorption sites on the surface of the photocatalytic material are occupied by H2O molecules, forming a competitive reaction for photocatalytic hydrogen evolution, thereby reducing the photocatalytic reduction efficiency of CO2. In addition, the solubility of CO2 in aqueous solution is low (35 mg / mol at 1 atmosphere), which limits the improvement of the CO2 photocatalytic reduction efficiency. Therefore, how to improve the CO2 photocatalytic reduction efficiency of TiO2 / g-C3N4 heterojunctions is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] In view of the deficiencies in the above-mentioned prior art, the purpose of the present invention is to provide a floatable hydrophilic and hydrophobic heterojunction photocatalytic material and its application. The present invention utilizes 4-(trifluoromethyl)benzyl bromide (TFMBB) as a selective hydrophobic modification material, and selectively grafts CF2 hydrophobic groups onto the surface of one side of g-C3N4 in the TiO2 / g-C3N4 heterojunction by condensation reflux under light, thereby synthesizing a hydrophilic and hydrophobic TiO2 / CF2-C3N4 heterojunction material that can float on the water surface. The heterojunction photocatalytic material of the present invention has a special floatable hydrophilic and hydrophobic structure, which is more conducive to the selective adsorption of CO2 and the effective separation of carriers, and can effectively improve the efficiency of photocatalytic reduction of CO2.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect of the present invention, a floating hydrophilic and hydrophobic heterojunction photocatalytic material is provided, which is prepared by the following method:

[0008] TiO2 / g-C3N4, anhydrous potassium carbonate and tetrahydrofuran are mixed evenly, condensed and refluxed, TFMBB is added, and the reaction is carried out under light conditions. After the reaction is completed, it is filtered and dried to prepare a floating hydrophilic and hydrophobic heterojunction photocatalytic material.

[0009] The mass ratio of the added TFMBB and TiO2 / g-C3N4 is (1-7.5):0.5.

[0010] The present invention uses TFMBB as a hydrophobic material to modify TiO2 / g-C3N4, increasing the material's water contact angle and enabling it to float on the water surface. This reduces the material's adsorption of H2O, thereby avoiding competition for water adsorption sites and indirectly improving CO2 selectivity (especially in humid environments and liquid phase systems). The fluorinated hydrophobic groups can bind to CO2 through dipole-quadrupole interactions without significantly adsorbing H2O. Furthermore, they can be selectively grafted onto g-C3N4, allowing the hydrophobic side of the CF2-C3N4 to float above the water surface, thereby facilitating the photocatalytic reduction of CO2, while the hydrophilic side is below the water surface, further facilitating the separation of the photocatalytic reduction and photocatalytic oxidation half-reactions and improving their respective efficiencies.

[0011] Preferably, the ratio of the added amounts of TiO2 / g-C3N4, anhydrous potassium carbonate and tetrahydrofuran is 0.5g:1g:40ml.

[0012] The addition of anhydrous potassium carbonate is to remove moisture from the reaction system to prevent water molecules from affecting the reaction; tetrahydrofuran is used as a solvent to dissolve 4-(trifluoromethyl)benzyl bromide (TFMBB) in the solution.

[0013] Preferably, the condensation reflux temperature is 70-90°C.

[0014] Preferably, the reaction time under light conditions is 24 hours.

[0015] Preferably, the TiO2 / g-C3N4 is prepared by the following method:

[0016] g-C3N4 is dispersed in a TiCl4 solution to synthesize a TiO2 / g-C3N4 precursor solution; the TiO2 / g-C3N4 precursor solution is ultrasonically dispersed and then placed in a high-pressure reactor for reaction at 150°C for 24 hours. The solid is separated after natural cooling, washed, and dried to prepare TiO2 / g-C3N4.

[0017] Due to the combination of TiO2 and g-C3N4 semiconductor, the separation rate of TiO2 / g-C3N4 photogenerated carriers is increased, thereby improving the photocatalytic activity of the catalyst.

[0018] More preferably, the g-C3N4 is prepared by the following method:

[0019] Melamine was heated to 550°C at a rate of 5°C / min and calcined for 2h, and then cooled to room temperature to obtain g-C3N4.

[0020] A second aspect of the present invention provides the use of the above-mentioned floatable hydrophilic and hydrophobic heterojunction photocatalytic material in photocatalytic reduction of CO2.

[0021] In the above applications, the floatable hydrophilic and hydrophobic heterojunction photocatalytic material of the present invention can significantly improve the CO2 photocatalytic reduction efficiency.

[0022] Beneficial effects of the present invention:

[0023] The present invention selectively grafts CF2 hydrophobic groups onto the g-C3N4 of TiO2 / g-C3N4. The resulting floatable, hydrophilic and hydrophobic TiO2 / CF2-g-C3N4 photocatalyst can float in aqueous solution, effectively resolving the issues of selective CO2 adsorption and low reduction efficiency on the TiO2 / g-C3N4 catalyst surface. This floatable, hydrophilic and hydrophobic TiO2 / CF2-g-C3N4 heterojunction photocatalytic material exhibits superior photocatalytic activity compared to TiO2 / g-C3N4 in the photocatalytic CO2 reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 3 and 4 are X-ray diffraction (XRD) patterns of the materials prepared in Example 3 and Comparative Example 3 of the present invention.

[0025] Figure 2 It is the Fourier transform infrared spectrum (FTIR graph) of the materials prepared in Example 3 and Comparative Examples 1 to 3 of the present invention.

[0026] Figure 3 3 and 4 are the water contact angles and physical images of the materials prepared in Example 3 and Comparative Example 3 of the present invention.

[0027] Figure 4 1-3 are the water contact angles of the heterojunction photocatalytic materials prepared in Examples 1-3 of the present invention; in the figure, 1, 2, and 3 represent the heterojunction photocatalytic materials prepared in Example 1, Example 2, and Example 3, respectively.

[0028] Figure 5 This is a comparison of the effects of the materials prepared in Example 3 and Comparative Examples 1 to 3 of the present invention for photocatalytic CO2 reduction.

[0029] Figure 6 This is the effect of the heterojunction photocatalytic materials prepared in Examples 1-3 of the present invention for photocatalytic CO2 reduction; in the figure, 1, 2, and 3 represent the heterojunction photocatalytic materials prepared in Example 1, Example 2, and Example 3, respectively. DETAILED DESCRIPTION

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0031] The "room temperature" herein refers to a temperature of 15-30°C.

[0032] As mentioned above, the TiO2 / g-C3N4 heterojunction is not ideal for the photocatalytic reduction of CO2 in the aqueous phase due to its hydrophilicity.

[0033] In view of this, the present invention has carried out hydrophobic modification on the TiO2 / g-C3N4 heterojunction. The introduction of hydrophobic groups is one of the effective strategies to improve the selectivity of CO2, but it must be comprehensively evaluated in combination with the overall design of the material, the adsorption mechanism and the actual application environment. It is not the case that adding hydrophobic groups to the material can improve the adsorption of CO2 by the material. Some long-chain polymer materials, such as silanes and lipids, have hydrophobic properties, but they can also easily hinder the entry and exit channels of CO2 molecules. The present invention has found through research that the hydrophobic modified material TFMBB can reduce the adsorption of H2O by the material, thereby avoiding water competition for adsorption sites and indirectly improving the selectivity of CO2 (especially in humid environments and liquid phase systems). Its fluorinated hydrophobic groups can bind to CO2 through dipole-quadrupole interactions without significantly adsorbing H2O. By introducing the hydrophobic modified material TFMBB, the TiO2 / g-C3N4 heterojunction has hydrophilicity and hydrophobicity, so that it can float on the water surface.

[0034] More importantly, the fluorinated hydrophobic groups of TFMBB can be selectively grafted onto g-C3N4, allowing the hydrophobic side CF2-C3N4 to float on the water surface. g-C3N4 participates in the CO2 reduction half-reaction. Its floating on the liquid surface can fully contact with the CO2 in the air. Compared with the CO2 content in water, there is more CO2 in the air, which overcomes the problem of the low solubility of CO2 in aqueous solution leading to a lower rate of CO2 reduction half-reaction.

[0035] In summary, the present invention utilizes TFMBB to perform hydrophobic modification on the TiO2 / g-C3N4 heterojunction, making it hydrophilic and hydrophobic so that it can float on the water surface; allowing the hydrophobic side CF2-C3N4 to float above the water surface, which is more conducive to the photocatalytic reduction of CO2; and the hydrophilic side is below the water surface, which is more conducive to the separation of the photocatalytic reduction half-reaction and the photocatalytic oxidation half-reaction and the improvement of their respective efficiencies.

[0036] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below with reference to specific embodiments.

[0037] The test materials used in the examples and comparative examples of the present invention are all conventional test materials in the field and can be purchased through commercial channels.

[0038] CAS number of 4-(Trifluoromethyl)benzyl bromide (TFMBB) is 402-49-3.

[0039] Example 1: Preparation of Floating Hydrophilic and Hydrophobic Heterojunction Photocatalytic Material (TiO2 / CF2-g-C3N4)

[0040] (1) Preparation of g-C3N4

[0041] Melamine was placed in a tube furnace, heated to 550°C at a rate of 5°C / min, calcined for 2 hours, cooled to room temperature, and ground to obtain a light yellow powder, which is graphite phase carbon nitride (g-C3N4).

[0042] (2) Preparation of TiO2 / g-C3N4

[0043] 5.68g of TiCl4 (98% purity) was dropwise added to 100mL of ice water to obtain a TiCl4 solution. 0.5g of g-C3N4 was then dispersed in the TiCl4 solution to synthesize a TiO2 / g-C3N4 precursor solution. The TiO2 / g-C3N4 precursor solution was sonicated in a 300W ultrasonic machine for 0.5h, then placed in an autoclave and reacted at 150°C for 24h. After natural cooling, the solid was separated, washed, and dried at 60°C to prepare TiO2 / g-C3N4.

[0044] (3) Preparation of TiO2 / CF2-g-C3N4

[0045] 0.5g TiO2 / g-C3N4, 1g anhydrous potassium carbonate, and 40mL tetrahydrofuran were weighed and placed in a 100mL single-necked round-bottom flask. Ultrasonication was performed at 300W for 20 minutes. To remove dissolved air from the THF solution, N2 gas was bubbled through the flask for 5 minutes. The flask was placed in an 80°C oil bath with a condenser coil for reflux. Then, 2mL of a 0.5g / mL TFMBB solution in THF was added. An incandescent lamp was placed above the flask to simulate light conditions. The reaction was continued at 80°C for 24 hours. After the reaction, the precipitate was collected by filtration and dried in a vacuum oven at 60°C to obtain a floating hydrophilic / hydrophobic heterojunction photocatalytic material (TiO2 / CF2-g-C3N4).

[0046] Example 2: Preparation of Floating Hydrophilic and Hydrophobic Heterojunction Photocatalytic Material (TiO2 / CF2-g-C3N4)

[0047] The preparation methods of g-C3N4 and TiO2 / g-C3N4 are the same as those in Example 1.

[0048] 0.5g of TiO2 / g-C3N4, 1g of anhydrous potassium carbonate, and 40mL of tetrahydrofuran were placed in a 100mL single-necked round-bottom flask and sonicated at 300W for 20 minutes. N2 gas was bubbled through the flask for 5 minutes to remove dissolved air from the THF solution. The flask was placed in an 80°C oil bath with a condenser coil for reflux. Then, 10mL of a 0.5g / mL TFMBB solution in THF was added. An incandescent lamp was placed above the flask to simulate light conditions, and the reaction was continued at 80°C for 24 hours. After the reaction, the precipitate was collected by filtration and dried in a vacuum oven at 60°C to obtain a floating hydrophilic / hydrophobic heterojunction photocatalytic material (TiO2 / CF2-g-C3N4).

[0049] Example 3: Preparation of Floating Hydrophilic and Hydrophobic Heterojunction Photocatalytic Material (TiO2 / CF2-g-C3N4)

[0050] The preparation methods of g-C3N4 and TiO2 / g-C3N4 are the same as those in Example 1.

[0051] 0.5g of TiO2 / g-C3N4, 1g of anhydrous potassium carbonate, and 40mL of tetrahydrofuran were placed in a 100mL single-necked round-bottom flask and sonicated at 300W for 20 minutes. To remove dissolved air from the THF solution, N2 gas was bubbled through the flask for 5 minutes. The flask was placed in an 80°C oil bath with a condenser coil for reflux. Then, 15mL of a 0.5g / mL TFMBB solution in THF was added. An incandescent lamp was placed above the flask to simulate light conditions, and the reaction was continued at 80°C for 24 hours. After the reaction, the precipitate was collected by filtration and dried in a vacuum oven at 60°C to obtain a floating hydrophilic / hydrophobic heterojunction photocatalytic material (TiO2 / CF2-g-C3N4).

[0052] Comparative Example 1:

[0053] Melamine was placed in a tube furnace, heated to 550°C at a rate of 5°C / min, calcined for 2 hours, cooled to room temperature, and ground to obtain a light yellow powder, which is graphite phase carbon nitride (g-C3N4).

[0054] Comparative Example 2:

[0055] 5.68 g of TiCl₄ (98% purity) was dropwise added to 100 mL of ice water to obtain a TiCl₄ solution. The TiCl₄ solution was ultrasonicated in a 300 W ultrasonic machine for 0.5 h, placed in an autoclave, and reacted in an oven at 150°C for 24 h. After natural cooling, the solid was separated, washed, and dried at 60°C to obtain TiO₂.

[0056] Comparative Example 3:

[0057] 5.68 g of TiCl4 (98% purity) was dropwise added to 100 mL of ice water to obtain a TiCl4 solution, and then 0.5 g of g-C3N4 was dispersed in the TiCl4 solution to synthesize a TiO2 / g-C3N4 precursor solution. The TiO2 / g-C3N4 precursor solution was ultrasonicated in a 300 W ultrasonic machine for 0.5 h, placed in an autoclave, and reacted in an oven at 150°C for 24 h. After natural cooling, the solid was separated, washed, and dried at 60°C to prepare TiO2 / g-C3N4.

[0058] Test example:

[0059] 1. X-ray diffraction analysis:

[0060] The heterojunction photocatalytic material (TiO2 / CF2-g-C3N4) prepared in Example 3 and the TiO2 / g-C3N4 prepared in Comparative Example 3 were subjected to X-ray diffraction analysis. Figure 1 shown.

[0061] The results show that the XRD peaks of TiO2 / CF2-g-C3N4 are almost consistent with those of TiO2 / g-C3N4, indicating that the hydrophobic material will not affect the crystal structure of the material. The TiO2 in the material exists in anatase phase and rutile phase. The (101), (004), (200), (002) and (215) crystal planes indicate the presence of anatase phase; the (110), (101), (111), (211), (220), (204) and (301) crystal planes indicate the presence of anatase phase. The (001), (100) and (002) crystal planes indicate the presence of graphite carbon nitride (g-C3N4). The XRD peaks of TiO2 / CF2-g-C3N4 are almost consistent with those of TiO2 / g-C3N4.

[0062] 2. Fourier transform infrared spectroscopy analysis:

[0063] The heterojunction photocatalytic material (TiO2 / CF2-g-C3N4) prepared in Example 3, g-C3N4 prepared in Comparative Example 1, TiO2 prepared in Comparative Example 2, and TiO2 / g-C3N4 prepared in Comparative Example 3 were analyzed by Fourier transform infrared spectroscopy. The results are as follows: Figure 2 shown.

[0064] The results show that: at 3500-3000cm -1 The peaks of NH and OH are at 1650-1100 cm -1 The peak of CN is at 810cm -1 The above infrared peaks indicate the presence of g-C3N4 in the material. -1 The Ti-O peak is located in the center, indicating the presence of TiO2 in the material. Both TiO2 / g-C3N4 and TiO2 / CF2-g-C3N4 exhibit the aforementioned infrared peaks, demonstrating the successful synthesis of the composite materials. The presence of a CF peak in the shaded area of TiO2 / CF2-g-C3N4 indicates the successful grafting of hydrophobic groups.

[0065] 3. Water contact angle measurement:

[0066] The water contact angles of the heterojunction photocatalytic materials (TiO2 / CF2-g-C3N4) prepared in Examples 1-3 and the TiO2 / g-C3N4 prepared in Comparative Example 3 were measured using a water contact angle meter (JC2000DF, Shanghai Zhongchen Digital Technology Instrument Co., Ltd.). The results are as follows: Figure 3-4 As shown,

[0067] The results show that the water contact angle of TiO2 / g-C3N4 is 0°, which means it is a hydrophilic material and will disperse evenly in water; the water contact angle of TiO2 / CF2-g-C3N4 is 133°, which means it is a hydrophobic material and will float on the water surface. Figure 3 ). Figure 4 The water contact angle of the material increases gradually with the addition of 2 mL, 10 mL, and 15 mL of 0.5 g / mL TFMBB in tetrahydrofuran solution.

[0068] 4. Determination of the effect of photocatalytic CO2 reduction:

[0069] The heterojunction photocatalytic materials (TiO2 / CF2-g-C3N4) prepared in Examples 1-3, the g-C3N4 prepared in Comparative Example 1, the TiO2 prepared in Comparative Example 2, and the TiO2 / g-C3N4 prepared in Comparative Example 3 were placed in an aqueous phase and subjected to photocatalytic CO2 reduction measurements under the same conditions. The results are shown in FIG. Figure 5-6 shown.

[0070] The results show that the photocatalytic CO2 reduction of TiO2 / CF2-g-C3N4 is 4.18 times higher than that of TiO2 / g-C3N4, indicating that the photocatalytic CO2 reduction performance of the material is significantly improved after hydrophobic modification ( Figure 5 ). Figure 6 As shown, "1, 2, 3" represent the addition of 2 mL, 10 mL, and 15 mL of 0.5 g / mL TFMBB tetrahydrofuran solution, respectively. As the amount of 4-(trifluoromethyl)benzyl bromide (TFMBB) solution added increases, the photocatalytic CO2 reduction performance of the material gradually improves.

[0071] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A floating hydrophilic and hydrophobic heterojunction photocatalytic material, characterized in that: Prepared by the following method: TiO2 / g-C3N4, anhydrous potassium carbonate and tetrahydrofuran are mixed evenly, condensed and refluxed, TFMBB is added, and the reaction is carried out under light conditions. After the reaction is completed, it is filtered and dried to prepare a floating hydrophilic and hydrophobic heterojunction photocatalytic material. The mass ratio of the added TFMBB and TiO2 / g-C3N4 is (1-7.5):0.

5.

2. The heterojunction photocatalytic material according to claim 1, characterized in that: The ratio of the added amounts of TiO2 / g-C3N4, anhydrous potassium carbonate and tetrahydrofuran is 0.5g:1g:40ml.

3. The heterojunction photocatalytic material according to claim 1, characterized in that: The condensation reflux temperature is 70-90°C.

4. The heterojunction photocatalytic material according to claim 1, characterized in that: The reaction time under light conditions is 24 h.

5. The heterojunction photocatalytic material according to claim 1, characterized in that: The TiO2 / g-C3N4 is prepared by the following method: Dispersing g-C3N4 in TiCl4 solution to synthesize TiO2 / g-C3N4 precursor solution; The TiO2 / g-C3N4 precursor solution was ultrasonically dispersed and placed in a high-pressure reactor, reacted at 150°C for 24 hours, and then naturally cooled to separate the solid, wash, and dry to prepare TiO2 / g-C3N4.

6. The heterojunction photocatalytic material according to claim 5, characterized in that: The g-C3N4 is prepared by the following method: Melamine was heated to 550°C at a rate of 5°C / min and calcined for 2h, and then cooled to room temperature to obtain g-C3N4.

7. Use of the heterojunction photocatalytic material according to any one of claims 1 to 6 in photocatalytic reduction of CO2.

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