CN115970765B - Bionic floatable photocatalytic material with 3D three-phase interface, preparation method and application thereof in photocatalytic nitrogen reduction synthesis of ammonia - Google Patents
Bionic floatable photocatalytic material with 3D three-phase interface, preparation method and application thereof in photocatalytic nitrogen reduction synthesis of ammonia Download PDFInfo
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- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 122
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 61
- 230000001699 photocatalysis Effects 0.000 title claims abstract description 58
- 239000000463 material Substances 0.000 title claims abstract description 54
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 title claims abstract description 34
- 239000011664 nicotinic acid Substances 0.000 title claims abstract description 29
- 229910021529 ammonia Inorganic materials 0.000 title claims abstract description 17
- 230000015572 biosynthetic process Effects 0.000 title claims abstract description 11
- 238000002360 preparation method Methods 0.000 title claims abstract description 11
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- 239000002243 precursor Substances 0.000 claims description 14
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- HEDRZPFGACZZDS-UHFFFAOYSA-N Chloroform Chemical compound ClC(Cl)Cl HEDRZPFGACZZDS-UHFFFAOYSA-N 0.000 claims description 4
- 229920000877 Melamine resin Polymers 0.000 claims description 4
- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 claims description 4
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- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 claims description 4
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- 238000001548 drop coating Methods 0.000 claims description 2
- SNGREZUHAYWORS-UHFFFAOYSA-N perfluorooctanoic acid Chemical compound OC(=O)C(F)(F)C(F)(F)C(F)(F)C(F)(F)C(F)(F)C(F)(F)C(F)(F)F SNGREZUHAYWORS-UHFFFAOYSA-N 0.000 claims description 2
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- 238000004528 spin coating Methods 0.000 claims description 2
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- 238000004506 ultrasonic cleaning Methods 0.000 claims description 2
- 235000013870 dimethyl polysiloxane Nutrition 0.000 claims 1
- CXQXSVUQTKDNFP-UHFFFAOYSA-N octamethyltrisiloxane Chemical compound C[Si](C)(C)O[Si](C)(C)O[Si](C)(C)C CXQXSVUQTKDNFP-UHFFFAOYSA-N 0.000 claims 1
- 238000004987 plasma desorption mass spectroscopy Methods 0.000 claims 1
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- 238000002336 sorption--desorption measurement Methods 0.000 description 2
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- 241000196324 Embryophyta Species 0.000 description 1
- YCKRFDGAMUMZLT-UHFFFAOYSA-N Fluorine atom Chemical compound [F] YCKRFDGAMUMZLT-UHFFFAOYSA-N 0.000 description 1
- 238000009620 Haber process Methods 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
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- 241000209502 Pistia Species 0.000 description 1
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- 229910052797 bismuth Inorganic materials 0.000 description 1
- JCXGWMGPZLAOME-UHFFFAOYSA-N bismuth atom Chemical compound [Bi] JCXGWMGPZLAOME-UHFFFAOYSA-N 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
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Abstract
A bionic floatable photocatalytic material with a 3D three-phase interface, a preparation method and application thereof in photocatalytic nitrogen reduction synthesis of ammonia under mild conditions belong to the technical field of photocatalysis. According to the invention, the hydrophilic BiVO 4 is loaded on the foam modified by the hydrophobizing agent to prepare the bionic photocatalyst system with a hydrophilic/hydrophobic Janus floatable structure. When the photocatalyst floats on the air-water surface, a large amount of gas reactants can be directly diffused to BiVO 4 from the external gas environment through the MS hydrophobic part, so that the barriers of low solubility and low diffusion speed of gas phase reactants in liquid are eliminated, water can be transported upwards from below the water surface, a gas-solid-liquid three-phase interface is successfully constructed, the mass transfer of nitrogen and water is effectively ensured, the light absorption is improved, the three-phase interface is constructed in the gas environment above the water surface for the first time, a universal method is provided for optimizing the efficient mass transfer of the gas consumption reaction, and the photocatalysis efficiency can be effectively improved.
Description
Technical Field
The invention belongs to the technical field of photocatalysis, and particularly relates to a bionic floatable photocatalytic material with a 3D three-phase interface, a preparation method and application thereof in photocatalytic nitrogen reduction synthesis of ammonia under mild conditions.
Background
Ammonia is a major component of nitrogen fertilizer, and is also a recognized potential energy or hydrogen carrier, which is critical to ensuring grain safety and energy supply, thus making it a key element in the global economic chain. Currently, the production of industrial ammonia relies mainly on the well-known Haber-Bosch process, which is carried out under severe conditions (723-923K and 15-35 MPa), resulting in serious environmental and energy problems. Development of alternative materials and techniques for synthesizing ammonia by efficient nitrogen reduction under mild conditions is an urgent topic.
The photocatalysis nitrogen reduction technology is to drive the chemical reaction of nitrogen reduction and conversion into ammonia by using solar energy and a semiconductor photocatalyst and taking water as a proton source, and provides a clean Haber-Bosch technology which can be used for replacing energy sources. However, the photocatalytic nitrogen reduction technology still needs to be improved so as to meet the requirements of industrial production. Therefore, development of efficient photocatalytic materials has important significance for improving the absorption of visible light, the absorption and activation of nitrogen and the utilization efficiency of photo-generated carriers. Nitrogen is a raw material for photocatalytic nitrogen fixation, and the supply of nitrogen is also a key factor affecting the reaction efficiency. Conventional photocatalytic nitrogen fixation occurs at the two-phase interface of the semiconductor and water, with only a small amount of nitrogen dissolved in the water (solubility of nitrogen in water 20mg/L,20 ℃ C., 100 kpa) participating in the reaction. Therefore, how to increase the nitrogen concentration and mass transfer rate on the surface of the photocatalyst becomes a precondition for realizing high-efficiency nitrogen fixation. Recently, scientists have proposed methods for constructing three-phase interfaces that allow gaseous reactants to be supplied from the gas phase to the reaction center, which alleviates the low solubility and slow diffusion barrier of gaseous reactants in conventional liquid-solid two-phase systems, and do a great deal of innovation about "three-phase interface constrained catalysis" (Chem.Sci., 2020,11,3124;Adv.Mater.Interfaces,2021,8,2001636).
In previous photocatalytic nitrogen fixation efforts, researchers have typically supported catalysts on superhydrophobic substrates with micro/nano structured surfaces that can trap a number of gases to form gas pockets and soak the catalytic system in an aqueous solution to ensure water mass transfer (Adv.Funct.Mater., 2021,31,2106120;Adv.Mater, 2022,34, e 2201295). However, the gaseous reactants still need to diffuse slowly in the aqueous solution for a considerable distance to reach the air pockets near the catalytic layer and participate in the reaction. Furthermore, the three-phase interface constructed in the previous studies can only react on the two-dimensional interface formed between the catalytic layer and the gas diffusion layer, where only a small amount of catalyst can contact both the gas and the liquid reactants. Therefore, the construction of three-phase interface photocatalysts for effective mass transfer of nitrogen still needs to be continuously explored, and the technology for transferring three-phase interfaces from underwater to water by means of a floatable system for synthesizing ammonia by photocatalytic nitrogen fixation has not been reported yet.
Disclosure of Invention
The invention aims to provide a bionic floatable photocatalytic material with a 3D three-phase interface, a preparation method and application thereof in photocatalytic nitrogen reduction synthesis of ammonia under mild conditions (room temperature and normal pressure). We draw inspiration from Pistia (an aquatic plant, lotus, can obtain water, nutrition, oxygen and sunshine on the water surface) in special physiological functions, load hydrophilic BiVO 4 onto a foam (MS) modified by a hydrophobizing agent part to prepare a bionic photocatalyst system with a hydrophilic/hydrophobic Janus floatable structure. When the photocatalyst floats on the air-water surface, a large amount of gas reactants can be directly diffused to the BiVO 4 from the external gas environment through the MS hydrophobic part, so that the barriers of low solubility and low diffusion speed of the gas-phase reactants in liquid are eliminated, and water can be transported upwards from the lower part of the water surface, thereby successfully constructing a gas-solid-liquid three-phase interface. Meanwhile, the three-phase interface is constructed on the water surface, sunlight can directly irradiate the reaction interface, multiple scattering can be caused in the macropores of the MS, and the light utilization rate is improved. The floatable bionic photocatalytic material prepared by the method effectively ensures mass transfer of nitrogen and water and improves light absorption, which is a universal method for optimizing efficient mass transfer of gas consumption reaction by constructing a three-phase interface in a gas environment above water surface for the first time, and can effectively improve photocatalytic efficiency.
The invention relates to a preparation method of a bionic floatable photocatalytic material with a 3D three-phase interface, which comprises the following steps:
1) Cutting foam into cuboids of 1-3 cm multiplied by 1-3 cm, sequentially carrying out ultrasonic cleaning by deionized water and ethanol, and drying for later use;
2) Preparing a hydrophobic solution: dispersing a hydrophobizing agent with a solvent to form a hydrophobic solution, and selectively coating the hydrophobic solution on the foam obtained in step 1) to obtain a partially modified hydrophilic/hydrophobic Janus floatable material;
3) Preparation of a BiVO 4 precursor solution: 1 to 24mmol Bi (NO 3)3·5H2 O is completely dissolved in 5 to 60mL of 1M HNO 3 water solution and stirred at room temperature for 15 to 60min to form a uniform solution, then 2 to 12mmol NH 4VO3 is added into the solution and vigorously stirred for 1 to 3h to obtain BiVO 4 precursor solution;
4) Immersing the partially modified hydrophilic/hydrophobic Janus floatable material obtained in the step 2) into the BiVO 4 precursor solution obtained in the step 3), and uniformly adsorbing the BiVO 4 inorganic semiconductor precursor solution by the hydrophilic/hydrophobic Janus floatable material through ultrasound; and transferring the reaction system into a polytetrafluoroethylene high-pressure reaction kettle, keeping the temperature at 60-80 ℃ for 10-20 hours, cooling to room temperature, respectively washing the obtained partially modified hydrophilic/hydrophobic Janus floatable material with deionized water and ethanol for 3-5 times, and finally drying the obtained product at 50-70 ℃ for 10-20 hours, thereby obtaining the bionic floatable photocatalytic material with the 3D three-phase interface.
The foam in the step 1) is one of a commercial polymer foam or a natural foam with a porous structure, such as melamine foam, polyurethane foam and the like.
The hydrophobizing agent in the step 2) is one of fluorine-containing and silicon-containing low-surface free energy materials such as Nafion (perfluorosulfonic acid-polytetrafluoroethylene copolymer), PDMS (polydimethylsiloxane), PVDF (polyvinylidene fluoride), perfluorooctanoic acid and the like; the coating process may be one of drop coating, dip coating, spin coating, and the like. The solvent for dispersing the hydrophobizing agent may be one of organic solvents such as n-hexane, cyclohexane, chloroform, tetrahydrofuran, ethanol, and the like. The partially modified hydrophilic/hydrophobic Janus floatable material comprises the following components in percentage by volume: 1 to 16.
The hydrophilic photocatalyst BiVO 4 can be popularized to inorganic semiconductor materials such as other bismuth-based catalysts, metal oxides, metal sulfides, bimetallic hydrides and the like.
According to the invention, a hydrophilic semiconductor is used as a main photocatalyst, and is loaded on a porous foam substrate modified by a partial hydrophobizing agent, so that the bionic floatable photocatalytic material with a 3D three-phase interface is obtained. The invention has the characteristics of simple equipment, convenient use, low price and easy obtainment of the used chemical reagent and good repeatability, and the substrate has good expandability and plasticity and can be produced in a large scale. The bionic floatable photocatalytic material with the 3D three-phase interface, which is prepared by the invention, has excellent photocatalytic nitrogen fixation performance and good selectivity and cycle stability, and the ammonia synthesis rate of the system is 624.87 mu mol g cat - 1h-1, which is 1.67 times and 353 times that of a corresponding two-phase system (BiVO 4 @MS) and powder system (BiVO 4) respectively. At present, no technology for synthesizing ammonia by means of photocatalytic nitrogen fixation by transferring a three-phase interface from underwater to water surface through a floatable system is reported. The bionic floatable photocatalytic material has the characteristics of low cost, convenient manufacture, good circulation stability and good expandability, and has wide application prospect in the aspect of optimizing the efficient mass transfer of the gas consumption reaction.
Drawings
Fig. 1 (1): scanning electron microscope pictures of the floatable material BiVO 4@PDMS@MS1/1 prepared in example 1; FIG. 1 (2) is a high magnification view of FIG. 1 (1); FIG. 1 (3) is a high magnification of the hydrophobic portion of FIG. 1 (1); FIG. 1 (4) is a high magnification view of the hydrophilic portion of FIG. 1 (1);
Fig. 2: (a) Schematic representation of the floatable material BiVO 4@PDMS@MS1/1 prepared in example 1 floating on the water surface; (b) Schematic representation of the floatable material BiVO 4@PDMS@MS1/3 prepared in example 2 floating on the water surface.
Fig. 3: (a) Examples 1 and (b) schematic diagrams of the floatable materials BiVO 4@PDMS@MS1/1 and BiVO 4@PDMS@MS1/3 prepared in example 2 forming a three-phase interface on the water surface and a partially enlarged schematic diagram thereof; wherein, hydroslice refers to BiVO 4 @MS hydrophilic part, hydroslice refers to BiVO 4 @PDMS@MS hydrophobic part, bulk water refers to bulk water in the reactor; air layer refers to an air layer formed on the hydrophobic surface of BiVO 4 @PDMS@MS; photocatalyst refers to photocatalyst BiVO 4;N2 flow refers to the diffusion direction of nitrogen in a reaction system; CAPILLARY EFFECT refers to capillary action in the macroporous structure of MS; laplace pressure gradient refers to the Laplace pressure gradient that develops on the MS surface. air phase refers to a gas phase in a reaction system, and nitrogen can be directly transferred from the part to a reaction interface through macropores of a hydrophobic MS (MS); sol phase refers to the catalyst phase (BiVO 4 @ PDMS @ MS); liquid phase refers to the aqueous phase of the reaction solution.
Fig. 4: photo-catalytic nitrogen fixation performance comparison graphs of floatable materials BiVO 4@PDMS@MS1/1 and BiVO 4@PDMS@MS1/3 prepared in examples 1 and 2 under light intensity irradiation of 200 mW.cm -2 (lambda >400 nm). The first histogram of the photocatalytic nitrogen fixation efficiency of BiVO 4@PDMS@MS1/1 in an argon atmosphere, the second histogram of the photocatalytic nitrogen fixation efficiency of powder BiVO 4 under the same reaction conditions as BiVO 4@PDMS@MS1/1; third, four bar graphs correspond to the photocatalytic nitrogen fixation efficiencies of BiVO 4@PDMS@MS1/1 and BiVO 4@PDMS@MS1/3; the fifth histogram is the photocatalytic nitrogen fixation efficiency of the BiVO 4 supported on a fully hydrophilic MS substrate to form a two-phase system under the same reaction conditions as the BiVO 4@PDMS@MS1/1; the sixth histogram is the MS nitrogen fixation efficiency after hydrophobic modification; the seventh histogram is the nitrogen fixation efficiency of BiVO 4@PDMS@MS1/1 under no illumination; the eighth bar graph is nitrogen fixation efficiency with light but without catalyst.
Detailed Description
The technical solution of the present invention will be described in more detail with reference to specific examples, but the examples should not be construed as limiting the invention.
Example 1
1) Cutting commercially available melamine foam (MS) into cubes of 2cm multiplied by 2cm, sequentially ultrasonically cleaning with deionized water and ethanol, and drying for use;
2) Preparing a hydrophobic spraying solution: uniformly dispersing PDMS in 10mL of normal hexane solution to obtain a hydrophobic solution with the PDMS concentration of 2 wt%; and uniformly mixing a PDMS curing agent (the mass ratio of the PDMS curing agent to the PDMS is 1:10) with the solution to obtain the super-hydrophobic spraying solution. Uniformly spraying the prepared hydrophobic spraying solution on the foam obtained in the step 1) through a spray gun with autogenous pressure to obtain a partially modified hydrophilic/hydrophobic Janus floatable material (Janus PDMS@MS), wherein the ratio of the hydrophilic/hydrophobic part is 1:1.
3) Preparation of a BiVO 4 precursor solution: 6mmol Bi (NO 3)3·5H2 O was completely dissolved in 30mL, 1M HNO 3 aqueous solution and stirred at room temperature for 30min to form a homogeneous solution, then 6mmol NH 4VO3 was added to the solution and vigorously stirred for 2h to give a BiVO 4 precursor solution.
4) Immersing the partially modified hydrophilic/hydrophobic Janus floatable material (Janus PDMS@MS) obtained in the step 2) into the solution obtained in the step 3), and uniformly adsorbing the BiVO 4 precursor solution by the hydrophilic/hydrophobic Janus floatable material (Janus PDMS@MS) through ultrasonic treatment. The mixed solution and Janus PDSM@MS were transferred to a polytetrafluoroethylene autoclave for 15 hours at 70℃and then cooled to room temperature. Washing the obtained floatable material BiVO 4 @PDMS@MS with deionized water and ethanol for 3 times respectively, and finally drying at 60 ℃ for 12 hours to obtain the bionic floatable photocatalytic material with the 3D three-phase interface, which is recorded as BiVO 4@PDMS@MS1/1.
Example 1 Performance test
The photocatalytic nitrogen fixation reaction is carried out at ambient pressure and temperature. In a typical photocatalytic experiment, a quantity of photocatalytic material BiVO 4@PDMS@MS1/1 was charged into a double-walled quartz reactor containing 100mL of deionized water and evacuated for 30 minutes to eliminate air interference. To further remove dissolved oxygen and establish adsorption-desorption equilibrium, high purity N 2 was blown in the dark at a flow rate of 100mL -1min-1 for 60min. A300W xenon lamp (PLS-SXE 300D) with a power density of 200 mW.cm -2 (lambda >400 nm) was placed at the top of the reactor at a distance of 8cm to irradiate the reaction system. In the photocatalytic process, continuous magnetic stirring and nitrogen purging are employed. During the reaction, samples were taken with sterile syringes every 60min and filtered through a 0.45 μm syringe filter. The concentration of NH 3 in the aqueous solution was quantified using a colorimetry technique (SHIMAZU UV-2550) using an ultraviolet-visible spectrophotometer.
As shown in fig. 1, the floatable system BiVO 4@PDMS@MS1/1 bionic assembly material prepared in example 1 has a three-dimensional network structure (average pore diameter: 60 μm), and is composed of adjacent melamine fibers with average diameter of 2 μm continuously crossed through a joint (fig. 1 (1)); the BiVO 4 nano-particles are uniformly loaded on the surface of the partially modified melamine (figure 1 (2)); irregular protrusions formed by PDMS adhesion can be observed on the hydrophobic end surface of BiVO 4 @PDMS@MS (FIG. 1 (3)), and the hydrophilic end surface of BiVO 4 @PDMS@MS is smooth (FIG. 1 (4)), which proves that the organic coating is partially modified successfully.
As shown in fig. 2, the floatable system BiVO 4@PDMS@MS1/1 bionic assembly material prepared in example 1 is modified in PDMS part to obtain a structure with typical hydrophilic-hydrophobic "two-sided god" (Janus); by placing it in a liquid, the liquid can be rapidly transferred to the hydrophobic end by capillary action and laplace gradient pressure, and the process only needs 30s.
As shown in fig. 3 (a), in the application of BiVO 4@PDMS@MS1/1 to the photocatalytic nitrogen fixation reaction, biVO 4@PDMS@MS1/1 can float on the water surface by the synergistic effect of surface tension and buoyancy, wherein hydrophobic BiVO 4@PDMS@MS1/1 is fully exposed to the gas phase, while hydrophilic BiVO 4 @ms is immersed in water. A large number of air layers are formed on the hydrophobic surface of the BiVO 4@PDMS@MS1/1, nitrogen can be effectively transmitted from air to a reaction interface through macropores of the hydrophobic MS, the nitrogen concentration of the three-phase interface is increased, and the capillary effect and the Laplace pressure gradient of the hydrophilic MS macropore structure in the BiVO 4 @MS ensure the effective mass transfer of water from the other side. An N 2-BiVO4-H2 O three-phase coexisting interface formed in a gas phase is formed in the bionic floatable system, so that nitrogen and water reach reactive sites from diffusion paths in different directions, simultaneous mass transfer of the nitrogen and the water is effectively ensured, and improvement of photocatalytic nitrogen fixation performance is dynamically ensured.
As shown in fig. 4, the floatable system BiVO 4@PDMS@MS1/1 bionic assembly material prepared in example 1 can continuously synthesize ammonia under irradiation of visible light, and the photocatalytic nitrogen fixation efficiency is greatly improved due to the unique formation of a 3D three-phase reaction interface in a gas phase, and BiVO 4@PDMS@MS1/1 shows an ammonia synthesis rate of 624.87 mu mol g cat -1h-1 which is about 1.67 times and 353 times higher than that of a related two-phase system (BiVO 4 @ms) and a powder system (BiVO 4), respectively.
Example 2
1) Cutting commercially available melamine foam (MS) into cubes of 2cm multiplied by 2cm, sequentially ultrasonically cleaning with deionized water and ethanol, and drying for use;
2) Preparing a hydrophobic spraying solution: uniformly dispersing PDMS in 10mL of normal hexane solution to obtain a hydrophobic solution with the PDMS concentration of 2 wt%; and uniformly mixing a PDMS curing agent (the mass ratio of the PDMS curing agent to the PDMS is 1:10) with the solution to obtain the super-hydrophobic spraying solution. Uniformly spraying the prepared hydrophobic spray solution on the foam obtained in the step 1) through a spray gun with autogenous pressure to obtain a partially modified hydrophilic/hydrophobic Janus floatable material (Janus PDMS@MS), wherein the ratio of hydrophilic/hydrophobic is 1:3.
3) Preparation of a BiVO 4 precursor solution: 6mmol Bi (NO 3)3·5H2 O was completely dissolved in 30mL of 1M aqueous HNO 3 and stirred at room temperature for 30min to form a homogeneous solution, then 6mmol NH 4VO3 was added to the solution and vigorously stirred for 2h to yield a BiVO 4 precursor solution.
4) Immersing the partially modified hydrophilic/hydrophobic Janus floatable material (Janus PDMS@MS) of step 2) into the solution obtained in step 3), and allowing the BiVO 4 precursor solution to be uniformly adsorbed by the hydrophilic/hydrophobic Janus floatable material (Janus PDMS@MS) by means of ultrasound. The mixed solution and Janus PDSM@MS were transferred to a polytetrafluoroethylene autoclave for 15 hours at 70℃and then cooled to room temperature. Washing the obtained floatable material BiVO 4 @PDMS@MS with deionized water and ethanol for 3 times respectively, and finally drying at 60 ℃ for 12 hours to obtain the bionic floatable photocatalytic material with the 3D three-phase interface, which is recorded as BiVO 4@PDMS@MS1/3.
Example 2 Performance test
The photocatalytic nitrogen fixation reaction is carried out at ambient pressure and temperature. In a typical photocatalytic experiment, a quantity of photocatalytic material BiVO 4@PDMS@MS1/3 was charged into a double-walled quartz reactor containing 100mL of deionized water and evacuated for 30 minutes to eliminate air interference. To further remove dissolved oxygen and establish adsorption-desorption equilibrium, high purity N 2 was blown in the dark at a flow rate of 100mL -1min-1 for 60min. A300W xenon lamp (PLS-SXE 300D) with a power density of 200 mW.cm -2 (lambda >400 nm) was placed at the top of the reactor at a distance of 8cm to irradiate the reaction system. In the photocatalytic process, continuous magnetic stirring and nitrogen purging are employed. During the reaction, samples were taken with sterile syringes every 60min and filtered through a 0.45 μm syringe filter. The concentration of NH 3 in the aqueous solution was quantified using a colorimetry technique (SHIMAZU UV-2550) using an ultraviolet-visible spectrophotometer.
As shown in fig. 2 (b), the floatable system BiVO 4@PDMS@MS1/3 bionic assembly material prepared in example 2 is modified in PDMS part to obtain a structure with typical hydrophilic-hydrophobic "two-sided god" (Janus); by placing it in a liquid, the liquid can be rapidly transferred to the hydrophobic end by capillary action and laplace gradient pressure, and the process only needs 50s.
As shown in fig. 3 (b), in the application of BiVO 4@PDMS@MS1/3 to the photocatalytic nitrogen fixation reaction, biVO 4@PDMS@MS1/3 can float on the water surface by the synergistic effect of surface tension and buoyancy, wherein hydrophobic BiVO 4@PDMS@MS1/3 is fully exposed to the gas phase, while hydrophilic BiVO 4 @ms is immersed in water. A large number of air layers are formed on the hydrophobic surface of the BiVO 4@PDMS@MS1/3, nitrogen can be effectively transmitted from air to a reaction interface through macropores of the hydrophobic MS, the nitrogen concentration of the three-phase interface is increased, and the capillary effect and the Laplace pressure gradient of the hydrophilic MS macropore structure in the BiVO 4 @MS ensure the effective mass transfer of water from the other side. An N 2-BiVO4-H2 O three-phase coexisting interface formed in a gas phase is formed in the bionic floatable system, so that nitrogen and water reach reactive sites from diffusion paths in different directions, simultaneous mass transfer of the nitrogen and the water is effectively ensured, and improvement of photocatalytic nitrogen fixation performance is dynamically ensured.
As shown in fig. 4, the floatable system BiVO 4@PDMS@MS1/3 bionic assembly material prepared in example 2 can continuously synthesize ammonia under irradiation of visible light, and the photocatalytic nitrogen fixation efficiency is greatly improved due to the unique formation of a 3D three-phase reaction interface in a gas phase, and BiVO 4@PDMS@MS1/3 shows an ammonia synthesis rate of 524.56 mu mol g cat -1h-1 which is about 1.41 times and 296 times higher than that of a related two-phase system (BiVO 4 @ms) and a powder system (BiVO 4), respectively.
Claims (6)
1. A preparation method of a bionic floatable photocatalytic nitrogen fixation material with a 3D three-phase interface comprises the following steps:
1) Cutting foam into a cuboid with the length of 1-3 cm multiplied by 1-3 cm, sequentially carrying out ultrasonic cleaning by deionized water and ethanol, and drying for later use;
2) Preparing a hydrophobic solution: dispersing a hydrophobizing agent with a solvent to form a hydrophobic solution, and selectively coating the hydrophobic solution on the foam obtained in step 1) to obtain a partially modified hydrophilic/hydrophobic Janus floatable material; the hydrophobizing agent is Nafion, PDMS, PVDF or perfluoro caprylic acid; a partially modified hydrophilic/hydrophobic Janus floatable material wherein the hydrophilic moiety is present in a ratio of 1: 1-16;
3) Preparation of a BiVO 4 precursor solution: 1-24 mmol Bi (NO 3)3·5H2 O is completely dissolved in 5-60 mL HNO 3 aqueous solution of 1-M and stirred at room temperature for 15-60 min to form a uniform solution, then 2-12 mmol NH 4VO3 is added into the solution and vigorously stirred for 1-3 h to obtain BiVO 4 precursor solution;
4) Immersing the partially modified hydrophilic/hydrophobic Janus floatable material obtained in the step 2) into the BiVO 4 precursor solution obtained in the step 3), and uniformly adsorbing the BiVO 4 inorganic semiconductor precursor solution by the hydrophilic/hydrophobic Janus floatable material through ultrasound; and transferring the reaction system into a polytetrafluoroethylene high-pressure reaction kettle, maintaining the temperature at 60-80 ℃ for 10-20 hours, cooling to room temperature, respectively washing the obtained partially modified hydrophilic/hydrophobic Janus floatable material with deionized water and ethanol for 3-5 times, and finally drying the obtained product at 50-70 ℃ for 10-20 hours to obtain the bionic floatable photocatalytic nitrogen fixation material with the 3D three-phase interface.
2. The method for preparing the bionic floatable photocatalytic nitrogen fixation material with the 3D three-phase interface as recited in claim 1, wherein the method comprises the following steps: the foam in the step 1) is melamine foam or polyurethane foam.
3. The method for preparing the bionic floatable photocatalytic nitrogen fixation material with the 3D three-phase interface as recited in claim 1, wherein the method comprises the following steps: the coating process in step 2) is one of drop coating, dip coating or spin coating.
4. The method for preparing the bionic floatable photocatalytic nitrogen fixation material with the 3D three-phase interface as recited in claim 1, wherein the method comprises the following steps: the solvent for dispersing the hydrophobizing agent in the step 2) is one of normal hexane, cyclohexane, chloroform, tetrahydrofuran or ethanol.
5. A bionic floatable photocatalytic nitrogen fixation material with a 3D three-phase interface is characterized in that: is prepared by the method of any one of claims 1 to 4.
6. The application of the bionic floatable photocatalytic nitrogen fixation material with 3D three-phase interface in photocatalytic nitrogen reduction synthesis of ammonia under mild conditions.
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