CN114669328A - Composite material photocatalyst for nitrogen reduction, preparation and application thereof - Google Patents

Composite material photocatalyst for nitrogen reduction, preparation and application thereof Download PDF

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CN114669328A
CN114669328A CN202210138266.7A CN202210138266A CN114669328A CN 114669328 A CN114669328 A CN 114669328A CN 202210138266 A CN202210138266 A CN 202210138266A CN 114669328 A CN114669328 A CN 114669328A
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mof
aunps
photocatalyst
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CN114669328B (en
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殷安翔
王博
陈立伟
郝宇晨
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Beijing Institute of Technology BIT
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Abstract

The invention relates to a composite material photocatalyst for nitrogen reduction, and preparation and application thereof, and belongs to the technical field of photocatalytic nitrogen reduction reaction. The photocatalyst is a composite material consisting of a porous polymer film, MOF assembled on the porous polymer film and AuNPs encapsulated in MOF particle cavities, and can realize direct plasma catalysis at a gas-film-liquid three-phase reaction interface, so that the photocatalytic nitrogen reduction performance is greatly improved. In addition, the reaction device provided by the invention can force the nitrogen-containing gas to directly pass through the photocatalyst, and avoids the dissolution process of nitrogen in aqueous solution in the traditional photocatalytic design, thereby increasing the local concentration of nitrogen on the surface of AuNPs and further promoting the photocatalytic reaction.

Description

Composite material photocatalyst for nitrogen reduction, preparation and application thereof
Technical Field
The invention relates to a composite material photocatalyst for nitrogen reduction, and preparation and application thereof, and belongs to the technical field of photocatalytic nitrogen reduction reaction.
Background
Currently, composite catalysts composed of Plasmonic Metal Nanoparticles (PMNPs) and other materials have been applied to photocatalytic nitrogen reduction reactions, and thermal electrons generated on PMNPs can be transferred to an attached semiconductor or Metal promoter to remotely drive the nitrogen reduction reaction. They suffer from the following disadvantages: (1) the Schottky barrier between the PMNPs and the semiconductor carrier can block the transmission of hot electrons, thereby influencing the photoelectric conversion efficiency; (2) with the increase of the distance from PMNPs, the field intensity of the local surface plasma resonance field is exponentially attenuated, and the catalytic center of the catalyst is separated from the local surface plasma resonance field, so that the catalyst cannot fully participate in the activation of surface adsorbed nitrogen molecules; (3) in the conventional reaction system, a photocatalyst is immersed in an aqueous solution and nitrogen is blown into the aqueous solution, and because the solubility of nitrogen in water is extremely low (when 283K, 1 volume of water can dissolve about 0.02 volume of nitrogen), the concentration of nitrogen molecules and mass transfer diffusion of nitrogen molecules to an active center are limited by the reaction interface design, so that the total reaction efficiency is further limited. Therefore, advanced photocatalytic nitrogen reduction catalysts and reaction interface designs are highly needed to address the challenges of photoelectric conversion, nitrogen molecule activation and mass transfer.
Disclosure of Invention
Aiming at the problems of photoelectric conversion, nitrogen molecule activation and mass transfer existing when the existing plasma material is used as a nitrogen reduction reaction photocatalyst, one of the purposes of the invention is to provide a composite material photocatalyst for nitrogen reduction, which realizes direct plasma catalysis at a gas-film-liquid three-phase reaction interface, so that the photocatalytic nitrogen reduction performance is greatly improved, and a new design idea is provided for the plasma photocatalytic application scene of other gas molecules.
The invention also provides a preparation method of the composite material photocatalyst for nitrogen reduction, which has the advantages of simple process, easy operation and easily obtained raw materials.
The invention also provides application of the composite material photocatalyst for nitrogen reduction, and the composite material photocatalyst is designed into a reactor for photocatalytic nitrogen reduction, and can further promote the diffusion of heterogeneous reactants and promote photocatalytic reaction.
The purpose of the invention is realized by the following technical scheme.
A composite photocatalyst for nitrogen reduction is a composite material consisting of Gold Nanoparticles (AuNPs), an Organic Metal Framework (MOF) and a porous polymer film;
Wherein, AuNPs are limited in MOF (namely the AuNPs are encapsulated in the cavities of MOF particles), the mass fraction of the AuNPs on the MOF (abbreviated as Au @ MOF) loaded with the AuNPs is preferably 0.6-5.3%, and more preferably 1.5-3.5%; au @ MOF is assembled on the porous polymer film, and the loading of Au @ MOF on the porous polymer film is preferably 0.1mg/cm2～1.2mg/cm2More preferably 0.5mg/cm2～0.6mg/cm2。
Further, the particle size of AuNPs is preferably 1.5nm to 4.5 nm.
Further, the MOF is preferably a MOF material having no light absorption in the visible light region, the particle size of the MOF material is preferably 20nm to 800nm, more preferably 50nm to 350nm, and the MOF material is more preferably UiO-66.
Further, the porous polymer film is preferably a porous Polytetrafluoroethylene (PTFE) film.
A preparation method of a composite material photocatalyst for nitrogen reduction comprises the following steps:
(1) preparation of AuNPs @ MOF by dipping-reduction method
Adding MOF particles into water for ultrasonic dispersion, then dropwise adding a tetrachloroauric acid aqueous solution under stirring, then sealing and stirring and mixing for not less than 3 hours in the dark, collecting and washing precipitates, then dispersing the washed precipitates into the water, dropwise adding a sodium borohydride aqueous solution under stirring to reduce Au (III) in MOF pores, continuing stirring and reacting for more than 30 minutes after a reaction system turns red to fully react, then collecting solid substances and washing to obtain AuNPs @ MOF;
Further, the concentration of the dispersed MOF particles in water is preferably 1 g/L-10 g/L;
(2) assembling AuNPs @ MOF on porous polymer film by suction filtration method
Firstly, ultrasonically dispersing Au @ MOF in a solvent, then injecting a Nafion PFSA polymer and uniformly mixing, then pouring the mixed solution into a Buchner funnel paved with a porous polymer film, removing the solvent in the mixed solution through suction filtration, and finally drying to obtain an Au @ UiO-66/PTFE film composite material, namely the photocatalyst is obtained;
wherein the solvent plays a role of dispersion and does not react with Au @ UiO-66 and Nafion PFSA polymer, the solvent is preferably at least one of water with a boiling point below 100 ℃, an inorganic solvent and an organic solvent, and the solvent is more preferably water or/and absolute ethyl alcohol; the volume ratio of Nafion PFSA polymer to solvent was 1: (50-100); the dispersion concentration of Au @ MOF in the solvent is preferably 0.1g/L to 3 g/L.
Further, when the MOF is UiO-66, a solvothermal method can be adopted to prepare UiO-66 particles, and the specific steps are as follows: adding phthalic acid, zirconium tetrachloride, N-Dimethylformamide (DMF) and acetic acid (AcOH) into a reaction container, mixing, sealing the reaction container, reacting at 70-150 ℃ for 12-48 h, collecting white precipitate generated by the reaction, washing the collected white precipitate with DMF to remove unreacted precursors, performing solvent exchange with water within 2-4 days, and finally drying to obtain UiO-66 particles;
Wherein the molar ratio of zirconium tetrachloride to terephthalic acid is 3: 1-1: 3, the concentration of terephthalic acid in a reaction system is 3 mmol/L-40 mmol/L, and the volume ratio of DMF to acetic acid in the reaction system is 5: (0.1-0.5).
A device for realizing gas-film-liquid three-phase interface reaction comprises the photocatalyst, a reaction tank and a constant temperature system;
the reaction tank is a closed cavity cuboid structure, the photocatalyst is placed in the reaction tank and divides the reaction tank into an air chamber and a liquid chamber, a gas inlet is formed in one side face of the air chamber and used for introducing nitrogen-containing gas into the air chamber, an exhaust port is formed in the top of the liquid chamber and used for exhausting gas, a quartz window is formed in one side face of the liquid chamber and used for receiving illumination, a liquid inlet and a liquid outlet are formed in the liquid chamber, the liquid outlet, a constant temperature system and the liquid inlet are sequentially connected through a pipeline, and the constant temperature of the solution in the liquid chamber is ensured.
Furthermore, the solution in the liquid chamber mainly provides protons, and an aqueous solution with the pH value of 3.5-8.5 can be selected.
Further, the temperature of the solution in the liquid chamber is preferably 283 to 373K.
Has the advantages that:
(1) in the photocatalyst, AuNPs are not only light capture 'antennas' but also activation centers, and other photosensitizers or cocatalysts are not needed. Under the irradiation of visible light, thermal electrons generated by plasma excitation can be directly transferred to nitrogen molecules adsorbed on the surfaces of AuNPs. Because the nitrogen molecules are adsorbed on the surfaces of AuNPs, the nitrogen molecules are positioned in a strong local surface plasma resonance field, and the synergistic local surface plasma effect, including electron transfer, energy transfer and local electric field polarization effect, can participate in the activation process of the nitrogen molecules adsorbed on the surfaces and other reaction intermediates so as to promote the reaction process.
(2) In the photocatalyst, the MOF material is not only a stable substrate of AuNPs, but also ensures high stability and dispersibility of the AuNPs in the photocatalytic reaction process through the confinement effect, and promotes mass transfer of heterogeneous reactants (such as nitrogen and hydrated protons) to the surfaces of the AuNPs. In addition, the porous polymer film can promote mass transfer of multiphase reactants, thereby further promoting the plasma photocatalytic nitrogen reduction reaction.
(3) The device for realizing the gas-membrane-liquid three-phase interface reaction can force the nitrogen-containing gas to directly pass through the catalyst membrane, and avoids the dissolution process of nitrogen in aqueous solution in the traditional photocatalytic design, thereby increasing the local concentration of nitrogen on the surface of AuNPs and further promoting the photocatalytic reaction. The Au @ UiO-66/PTFE membrane composite material shows higher NH3The yield is increased, and the apparent quantum efficiency is increased and the apparent activation energy is reduced along with the increase of the optical power density, namely, the photocatalytic nitrogen reduction reaction efficiency can be improved by increasing the light intensity. For example: when the intensity of the 520nm monochromatic light is from 10mW/cm2Increased to 40mW/cm2When the quantum efficiency is increased from 0.58% to 0.97%.
Drawings
FIG. 1 is a Transmission Electron Microscope (TEM) and High-Angle Annular Dark-Field Scanning Transmission Electron microscope (HAADF-STEM) image of UO-66 particles prepared in example 1; wherein, the scale of the A graph is 100nm, and the scale of the B graph is 20 nm.
FIG. 2 is a TEM and HAADF-STEM of Au @ UiO-66 prepared in example 1; wherein the scale of the graph A is 100nm, and the scale of the graph B is 20 nm.
FIG. 3 is a plot of the spherical aberration corrected HAADF-STEM of a single AuNP encapsulated within UiO-66 in Au @ UiO-66 prepared in example 1; wherein the scale bar is 1 nm.
FIG. 4 is a graph of a spherical aberration corrected HAADF-STEM of one AuNP in Au @ UiO-66 prepared in example 1; wherein the scale bar is 1 nm.
FIG. 5 is TEM images of different rotation axis angles from +30 to-30 for one Au @ UiO-66 particle prepared in example 1; wherein the scale bar is 20 nm.
FIG. 6 is a graph showing the particle size distribution of AuNPs in Au @ UiO-66 prepared in example 1.
FIG. 7 is an Au 4f energy level spectrum of Au @ UiO-66 prepared in example 1.
FIG. 8 is a graph comparing the Zr 3d level spectra of Au @ UiO-66 and UiO-66 prepared in example 1.
FIG. 9 is a Scanning Electron Microscope (SEM) comparison of UiO-66 particles prepared in examples 1-4; wherein, the A-D pictures correspond to the embodiments 1-4 one by one in sequence, and the scale bar is 500 nm.
FIG. 10 is a graph comparing the particle size distribution of UiO-66 particles prepared in examples 1-4; wherein, the A-D diagrams correspond to the embodiments 1-4 one by one in sequence.
FIG. 11 shows the N at 77K of UiO-66 prepared in examples 1-42Adsorption isotherm comparison.
FIG. 12 is a graph comparing the pore size distribution of UiO-66 prepared in examples 1 to 4.
FIG. 13 is a Powder X-Ray Diffraction (PXRD) comparison graph of UiO-66 prepared in examples 1-4.
FIG. 14 is a comparison of Fourier Transform Infrared (FT-IR) spectra of UiO-66 prepared in examples 1-4.
FIG. 15 is a graph comparing the UV-vis absorption spectra (ultra violet and Visible, UV-vis) of UO-66 prepared in examples 1-4; wherein, the A-D diagrams correspond to the embodiments 1-4 one by one in sequence.
FIG. 16 is a HAADF-STEM comparison of Au @ UiO-66 prepared in examples 1-4; the images A to D correspond to the embodiments 1 to 4 one by one in sequence, the scale of the image A is 20nm, the scale of the image B and the image C is 50nm, and the scale of the image D is 100 nm.
FIG. 17 is a graph comparing the particle size distributions of AuNPs in Au @ UiO-66 prepared in examples 1 to 4; wherein, the A-D diagrams correspond to the embodiments 1-4 one by one in sequence.
FIG. 18 is a PXRD comparison graph of Au @ UiO-66 prepared in examples 1-4.
FIG. 19 is a comparison of UV-vis spectra of Au @ UiO-66 prepared in examples 1-4; wherein, the A-D diagrams correspond to the embodiments 1-4 one by one in sequence.
FIG. 20 is a comparative FT-IR spectrum of Au @ UiO-66 prepared in examples 1 to 4.
FIG. 21 is a graph comparing the ammonia production rates of Au @ UiO-66 prepared in examples 1 to 4; error bars represent standard deviations of three independent samples.
FIG. 22 is a TEM comparison of Au @ UiO-66 prepared in example 1 and examples 5-8; wherein, the graphs A to E correspond to the graphs in the embodiment 5, the embodiment 1 and the embodiments 6 to 8 one by one in sequence, and the scale bar is 40 nm.
FIG. 23 is a FT-IR comparison of the FT-IR spectra of Au @ UiO-66 prepared in example 1 and examples 5-8.
FIG. 24 is a comparison of UV-vis spectra of Au @ UiO-66 prepared in example 1 and examples 5-8.
FIG. 25 is a PXRD comparison graph of Au @ UiO-66 prepared in example 1 and examples 5-8.
FIG. 26 is a comparison graph of the adsorption isotherms of Au @ UiO-66 prepared in example 1 and examples 5-8 at 77K.
FIG. 27 is a graph comparing the photocatalytic ammonia production rates of Au @ UiO-66 prepared in example 1 and examples 5-8; error bars represent standard deviations of three independent samples.
FIG. 28 is a cross-sectional SEM comparison of Au @ UiO-66/PTFE membrane composites prepared in example 1 and examples 9-11; wherein, the graphs A to D correspond to the graphs in the embodiment 9, the embodiment 1 and the embodiments 10 to 11 in sequence one by one, and the scale bar is 30 μm.
FIG. 29 is a graph comparing the mass activity (left axis) and the area activity (right axis) of Au @ UiO-66/PTFE membrane composites prepared in example 1 and examples 9-11.
FIG. 30 shows Au @ UiO-66 and Au @ UiO-66/PTFE film composites, Au/SiO, prepared in example 12And Au-SiO2PTFE film composite material, Au/ZrO2With Au/ZrO2Ammonia production rate of the/PTFE membrane composite (left axis), and the ratio of the membrane composite to the ammonia yield of the corresponding powder catalyst (right axis) are plotted versus.
FIG. 31 is a graph comparing the apparent quantum efficiencies of Au @ UiO-66 and Au @ UiO-66/PTFE film composites prepared in example 1 at different wavelengths.
FIG. 32 is a graph comparing the results of stability testing of the Au @ UiO-66/PTFE membrane composite prepared in example 1.
FIG. 33 is a schematic structural view of an apparatus for carrying out a gas-membrane-liquid three-phase interfacial reaction according to an embodiment.
Detailed Description
The present invention is further illustrated by the following figures and detailed description, wherein the processes are conventional unless otherwise specified, and the starting materials are commercially available from a public source without further specification. In addition, in the description of the present invention, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
The following examples:
x-ray powder diffractometer: the instrument model is as follows: rigaku MiniFlex 600 diffractometer; radiation source: CuK α X-ray (λ ═ 0.154056 nm); voltage: 40 kV; current: 50 mA; scanning rate: 1 degree min–1。
Ultraviolet-visible spectrophotometer: the instrument model is as follows: a Shimadzu UV-2600 spectrophotometer; slit width: 2.0 nm; resolution ratio: 0.5 nm. The UV-vis diffuse reflectance spectrum was measured on a Shimadzu UV-2600 spectrophotometer (slit width: 5.0 nm; resolution: 1.0nm) equipped with an integrating sphere.
Fourier transform infrared spectrometer: the instrument model is as follows: bruker ALPHA spectrometer;resolution ratio: 4cm–1。
Nuclear magnetic resonance spectrometer: the instrument model is as follows: bruker Ascend 700(700MHz) spectrometer.
Ion chromatography: the instrument model is as follows: thermo Scientific Dionex Aquion chromatograph (cationic) and Thermo Scientific Dionex ICS-900 (anionic) ion chromatograph. The eluent in the cation column was 20mM methanesulfonic acid at a flow rate of 1.0mL min–1The eluent in the anion column was 3.5mM Na2CO3/1.0mM NaHCO3Flow rate of 1.2mL min–1. All measurements were performed at ambient temperature.
Inductively coupled plasma emission spectrometer: the instrument model is as follows: agilent ICP-OES 720 spectrometer. The parameters are set as follows: radio Frequency (RF) power of 1.20kW, plasma gas flow of 15.0L min –1The flow rate of the auxiliary gas is 1.50L min–1The flow rate of the atomizing gas is 0.75L min–1The ejection delay is 15s and the instrument settling delay is 15 s.
X-ray photoelectron spectroscopy: the instrument model is as follows: thermo Fisher Scientific ESCALAB 250Xi photoelectron spectrometer; radiation source: monochromatic Al K α radiation (h ν 1486.6 eV); analysis area: 500 μm; analyzing the depth: about 10 nm; calibration: the binding energy of the C1s peak at 284.8eV was used; prior to testing, the basic vacuum of the analysis chamber: 1X 10–9mBar。
A gas adsorption instrument: the instrument model is as follows: quantachrome ASiQMH 002-5. The pore size distribution is fitted by non-local density functional theory (NLDFT).
Field emission scanning electron microscope: the instrument model is as follows: hitachi S-4800 scanning electron microscope; testing voltage: 5 kV; testing current: 10 μ A.
Transmission electron microscope: the instrument model is as follows: JEOL JEM-2100 and JEOL JEM-2100F transmission electron microscopes; working voltage: 200 kV. The instrument model is as follows: FEI Tecnai G2F 30 transmission electron microscope, operating voltage: 300 kV.
High angle annular dark field scanning transmission electron microscope: the instrument model is as follows: FEI Tecnai G2F 30 transmission electron microscope; working voltage: 300 kV. The instrument model is as follows: JEOL JEM-2100F transmission electron microscope; working voltage: 200 kV.
Spherical aberration correction transmission electron microscope: the instrument model is as follows: JEM-ARM200F TEM equipped with spherical aberration corrector; working voltage: 200 kV.
When the composite material photocatalyst for nitrogen reduction prepared in the embodiment is adopted to carry out photocatalytic reaction, the related reaction device comprises the photocatalyst prepared in the embodiment, a reaction tank and a constant temperature system;
the reaction tank is of a closed cavity cuboid structure, the photocatalyst is placed in the reaction tank and divides the reaction tank into a gas chamber and a liquid chamber, a gas inlet is formed in one side face of the gas chamber and used for introducing nitrogen-containing gas into the gas chamber, an exhaust port is formed in the top of the liquid chamber and used for exhausting gas, a quartz window is formed in one side face of the liquid chamber and used for receiving illumination, a liquid inlet and a liquid outlet are further formed in the liquid chamber, and the liquid outlet, the constant temperature system and the liquid inlet are sequentially connected through a pipeline to ensure constant temperature of solution in the liquid chamber, as shown in figure 33.
Example 1
(1) Adding 62.3mg of terephthalic acid and 106mg of zirconium tetrachloride into 50mL of N, N-Dimethylformamide (DMF), carrying out ultrasonic treatment for 10min, and then subpackaging the solution into 10 glass vials with the same amount, wherein each glass vial contains 5mL of the solution; adding 200 μ L of acetic acid to each vial, sealing and shaking the vial, and then placing the vial in a constant temperature oven at 90 ℃ for reaction for 48 h; collecting a white precipitate formed by the reaction by centrifugation (8000rpm, 10min), washing the collected white precipitate 3 times with DMF to remove unreacted precursors, then performing solvent exchange with ultrapure water within 3 days, and replacing with fresh ultrapure water every day; finally, drying in a vacuum oven at normal temperature overnight to obtain UiO-66 particles;
(2) Grinding the dried UiO-66 particles into fine powder using an agate mortar, and then fully dispersing 10mg of the fine powder in 2mL of ultrapure water by ultrasonic treatment; after 40. mu.L of an aqueous tetrachloroauric acid solution with a concentration of 25.4mM was added to the dispersion of UiO-66 with stirring, it was sealed and vigorously stirred in the dark for 8h, after which the precipitate was collected by centrifugation (8000rpm, 10min) and washed 1 time with water; dispersing the washed precipitate in 2mL of ultrapure water, dropwise adding 102 mu L of ice-cold sodium borohydride aqueous solution with the concentration of 0.1M into the dispersion liquid of the precipitate under stirring, and continuously stirring for 4 hours in the dark to ensure that the reaction system fully reacts when the reaction system turns red; finally, collecting solid matters through centrifugation (8000rpm, 10min), washing the solid matters with water for 3 times, and finally drying the solid matters in dynamic vacuum at 150 ℃ for 12 hours to obtain Au @ UiO-66;
(3) dispersing 7mg of Au @ UiO-66 prepared in the step (2) in a mixed solvent consisting of 7mL of absolute ethyl alcohol and 1mL of ultrapure water through ultrasonic treatment, then injecting 100 mu L of Nafion PFSA polymer, quickly shaking for uniform mixing, pouring the mixed solution onto a porous PTFE membrane which is washed by ethanol in advance and placed in a sand core funnel (inner diameter: 3.5cm), removing the solvent in the mixed solution through suction filtration by using a vacuum pump, and placing the solid matter collected after suction filtration in an oven at 40 ℃ for drying overnight to obtain the Au @ UiO-66/PTFE membrane composite material, namely the composite material photocatalyst for nitrogen reduction.
Dispersing 15mg of Au @ UiO-66 powder obtained in the step (2) in 50mL of 0.5mol/L potassium sulfate aqueous solution, transferring the dispersion to a conventional photoreactor, and reacting the dispersion with high-purity N2(purity 99.999%) was bubbled for 30 minutes to remove air residue. In the test of catalytic Performance on Au @ UiO-66, a 300W Xe lamp equipped with a 400nm long pass filter was used as a visible light source, and the light intensity at the sample level was set at 100mW/cm2Mixing the dispersion with high purity N at a flow rate of 80mL/min2Bubbling was continued and magnetic stirring was applied, and the temperature of the reaction solution was maintained at (298. + -. 0.5) K by circulating cooling water. Measuring NH3Yield of (2) was 0.14mmol/gcat/h。
When the Au @ UiO-66/PTFE membrane composite material obtained in the step (3) is subjected to a photocatalytic reaction test, high-purity N is obtained2Firstly enters the gas chamber through a gas inlet of the gas chamber, then enters a liquid chamber through an Au @ UiO-66/PTFE membrane composite material (the diameter: 3.5cm) to form a gas-membrane-liquid three-phase reaction interface, the temperature of an aqueous solution (a potassium sulfate aqueous solution with the concentration of 0.5 mol/L) in the liquid chamber is kept at (25 +/-0.5) DEG C, the wavelength is 400-800 nm, and the light intensity is 100mW/cm2Under irradiation, NH3Yield of (2) was 0.36mmol/gcatThe highest apparent quantum efficiency was 1.54%.
As can be seen from FIGS. 1 and 2, the UiO-66 particles and the Au @ UiO-66 particles were prepared in a mainly octahedral shape with a size distribution having an average particle size of 146nm, indicating that encapsulation of AuNPs did not change the size or morphology of the UiO-66 particles. In addition, as can be seen from the HAADF-STEM graph (or B graph) of FIG. 2 and FIG. 6, the average particle size of AuNPs was 2.4 nm. As can be seen from fig. 3 and 4, the AuNP is mainly surrounded by (111) and (100) planes. As can be seen from the TEM image of FIG. 5 at different spindle angles, there are almost no AuNPs outside the UiO-66 particles, indicating that most AuNPs encapsulate the inside of the UiO-66 particles. The mass fraction of AuNPs in Au @ UiO-66 was 1.9 wt.% as measured by inductively coupled plasma emission spectroscopy.
The X-ray photoelectron spectroscopy (XPS) plots of FIGS. 7 and 8 show that the AuNPs in the Au @ UiO-66 particles are in the metallic state, while the XPS peak shift for the Zr species is negligible, indicating ZrOxThere was no observable charge transfer between the clusters and aunps.
Example 2
(1) UiO-66 granules were prepared by following the procedure of step (1) of example 1 except that the addition of 200. mu.L of acetic acid to each vial in example 1 was modified to 300. mu.L of acetic acid, and the other conditions were not changed;
(2) au @ UiO-66 was prepared according to the method of step (2) of example 1;
(3) An Au @ UiO-66/PTFE film composite was prepared according to the procedure of step (3) of example 1, i.e., a composite photocatalyst for nitrogen reduction was obtained accordingly.
The Au @ UiO-66 powder obtained in step (2) of this example was subjected to a photocatalytic reaction test under the same conditions as in example 1, and NH was measured3Yield of (2) was 0.12mmol/gcat/h。
Example 3
(1) UiO-66 granules were prepared by following the procedure of step (1) of example 1 except that the addition of 200. mu.L of acetic acid to each vial in example 1 was modified to 400. mu.L of acetic acid, and the other conditions were not changed;
(2) au @ UiO-66 was prepared according to the method of step (2) of example 1;
(3) an Au @ UiO-66/PTFE film composite was prepared in accordance with the procedure of step (3) of example 1, that is, a composite photocatalyst for nitrogen reduction was obtained accordingly.
The Au @ UiO-66 powder obtained in step (2) of this example was subjected to a photocatalytic reaction test under the same conditions as in example 1, and NH was measured3The yield of (a) was 0.076mmol/gcat/h。
Example 4
(1) UiO-66 granules were prepared by following the procedure of step (1) of example 1 except that the addition of 200. mu.L of acetic acid to each vial in example 1 was modified to 500. mu.L of acetic acid, and the other conditions were not changed;
(2) au @ UiO-66 was prepared according to the method of step (2) of example 1;
(3) An Au @ UiO-66/PTFE film composite was prepared in accordance with the procedure of step (3) of example 1, that is, a composite photocatalyst for nitrogen reduction was obtained accordingly.
The Au @ UiO-66 powder obtained in step (2) of this example was subjected to a photocatalytic reaction test under the same conditions as in example 1, and NH was measured3Yield of (2) was 0.064mmol/gcat/h。
FIGS. 9 and 10 show that the particle size of UiO-66 can be controlled by adjusting the amount of acetic acid added in step (1). As the amount of acetic acid added increases, the average particle size of the UiO-66 particles can gradually increase from 146nm to 650 nm. FIGS. 11 and 12 show that the N of the UiO-66 particles increases with the amount of acetic acid added in step (1)2The adsorption capacity is gradually increased, and the pore volume is gradually increased. FIGS. 13 and 14 show that the change in the amount of acetic acid added in step (1) has less influence on the topology and functional groups of the UiO-66 as a whole. FIG. 15 shows that changes in the size of the UiO-66 particles do not directly affect their absorption in the visible region. Therefore, AuNPs can be supported by the visible light inert carriers to explore the direct plasma photocatalytic nitrogen reduction reaction of the AuNPs under the irradiation of visible light.
FIGS. 16 and 17 show that changes in the size of UiO-66 do not greatly affect the particle size of AuNPs supported in step (2). According to the characterization results of FIGS. 18-20, although the sizes of the UiO-66 are different, the growth of AuNPs in the cavity of the UiO-66 in the step (2) can be realized, Au @ UiO-66 particles can be successfully obtained, and the crystal structure, the functional group and the local surface plasmon extinction properties of the obtained Au @ UiO-66 particles are similar.
The test results of fig. 21 show that as the size of the particles of the support UiO-66 increases, the ammonia production rate gradually decreases, demonstrating that diffusion of nitrogen molecules from the surface of the UiO-66 particles to the surface of the AuNPs within the pores is critical, while appropriately sized particles of UiO-66 will promote diffusion of nitrogen molecules, thereby promoting the reaction.
Example 5
(1) The UiO-66 particles were prepared according to the method of step (1) of example 1;
(2) au @ UiO-66 was prepared by the method of step (2) of example 1, except that 40. mu.L of an aqueous tetrachloroauric acid solution having a concentration of 25.4mM and 102. mu.L of a freshly prepared ice-cold aqueous sodium borohydride solution having a concentration of 0.1M in example 1 were respectively changed to 20. mu.L of an aqueous tetrachloroauric acid solution having a concentration of 25.4mM and 51. mu.L of a freshly prepared ice-cold aqueous sodium borohydride solution having a concentration of 0.1M, and the other conditions were not changed;
(3) an Au @ UiO-66/PTFE film composite was prepared in accordance with the procedure of step (3) of example 1, that is, a composite photocatalyst for nitrogen reduction was obtained accordingly.
The Au @ UiO-66 powder obtained in step (2) of this example was subjected to a photocatalytic reaction test under the same conditions as in example 1, and NH was measured3The yield of (a) was 0.079mmol/gcat/h。
Example 6
(1) UiO-66 granules were prepared according to the method of step (1) of example 1;
(2) Au @ UiO-66 was prepared by the same procedure as in step (2) of example 1, except that 40. mu.L of an aqueous tetrachloroauric acid solution having a concentration of 25.4mM and 102. mu.L of an ice-cold aqueous sodium borohydride solution having a concentration of 0.1M as those prepared in example 1 were respectively modified to 60. mu.L of an aqueous tetrachloroauric acid solution having a concentration of 25.4mM and 153. mu.L of an ice-cold aqueous sodium borohydride solution having a concentration of 0.1M, and other conditions were not changed;
(3) an Au @ UiO-66/PTFE film composite was prepared according to the procedure of step (3) of example 1, i.e., a composite photocatalyst for nitrogen reduction was obtained accordingly.
The Au @ UiO-66 powder obtained in step (2) of this example was subjected to a photocatalytic reaction test using the same conditions as in example 1, and NH was measured3Yield of (2) was 0.13mmol/gcat/h。
Example 7
(1) The UiO-66 particles were prepared according to the method of step (1) of example 1;
(2) au @ UiO-66 was prepared by the method of step (2) of example 1, except that 40. mu.L of an aqueous tetrachloroauric acid solution having a concentration of 25.4mM and 102. mu.L of a freshly prepared ice-cold aqueous sodium borohydride solution having a concentration of 0.1M in example 1 were respectively changed to 80. mu.L of an aqueous tetrachloroauric acid solution having a concentration of 25.4mM and 204. mu.L of a freshly prepared ice-cold aqueous sodium borohydride solution having a concentration of 0.1M, and the other conditions were not changed;
(3) An Au @ UiO-66/PTFE film composite was prepared in accordance with the procedure of step (3) of example 1, that is, a composite photocatalyst for nitrogen reduction was obtained accordingly.
The Au @ UiO-66 powder obtained in step (2) of this example was subjected to a photocatalytic reaction test under the same conditions as in example 1, and NH was measured3The yield of (1) was 0.087mmol/gcat/h。
Example 8
(1) UiO-66 granules were prepared according to the method of step (1) of example 1;
(2) au @ UiO-66 was prepared by following the procedure of step (2) of example 1 except that 40. mu.L of an aqueous tetrachloroauric acid solution having a concentration of 25.4mM and 102. mu.L of a freshly prepared ice-cold aqueous sodium borohydride solution having a concentration of 0.1M in example 1 were respectively changed to 100. mu.L of an aqueous tetrachloroauric acid solution having a concentration of 25.4mM and 255. mu.L of a freshly prepared ice-cold aqueous sodium borohydride solution having a concentration of 0.1M, and the other conditions were not changed;
(3) an Au @ UiO-66/PTFE film composite was prepared in accordance with the procedure of step (3) of example 1, that is, a composite photocatalyst for nitrogen reduction was obtained accordingly.
The Au @ UiO-66 powder obtained in step (2) of this example was subjected to the same conditions as in example 1Carrying out photocatalytic reaction test to obtain NH3The yield of (1) was 0.071mmol/gcat/h。
As can be seen from fig. 22, the size of the AuNPs is very small when the AuNPs loading is low (e.g., 0.9 wt.%), while larger AuNPs can be found outside the uo-66 particles when the AuNPs loading is high (e.g., 5.2 wt.%).
The test results in FIG. 23 show that the absorption peaks in the FT-IR spectrum of different AuNPs loaded Au @ UiO-66 particles have no significant change, indicating that the chemical structure of UiO-66 is hardly changed by the incorporation of AuNPs.
Combining the color changes of the different systems and the test results of fig. 24, it was found that the color of the aqueous dispersion of Au @ UiO-66 particles gradually changed from white to dark red as the AuNPs loading increased from 0 wt.% to 5.2 wt.%. In addition, for all the Au @ UiO-66 powders, a distinct localized surface plasmon resonance peak can be observed around 520nm, indicating that the UiO-66 substrate can prevent the agglomeration of small AuNPs, and can ensure their high dispersibility even in a dry solid form.
The test results in fig. 25 show that the loading of AuNPs does not have a significant effect on the framework structure of the UiO-66 particles. A weak and broad diffraction peak at 38.1 ° was not observed until the AuNPs loading increased to 4.1 wt.%, corresponding to the (111) crystallographic plane of fcc Au, which indirectly suggests that at relatively low AuNPs loadings, the small size of the AuNPs leads to poor crystallinity.
From the test results of FIG. 26 and the data in Table 1, it can be seen that as the loading of AuNPs increases, the surface area and pore volume of the Au @ UiO-66 particles gradually decrease, which also indicates that the AuNPs are wrapped inside the UiO-66 particles and partially occupy the pores of the UiO-66. Table 1 shows the pore volume and specific surface area test data for UiO-66 and Au @ UiO-66 prepared in example 1 and examples 5-8.
TABLE 1
Figure BDA0003505846720000101
The test results in fig. 27 show that no ammonia production was detected by the UiO-66 particles under visible light, whereas encapsulation of AuNPs in the UiO-66 particles showed a significant ammonia production rate. The ammonia production rate showed volcano-like dependence on the mass loading of AuNPs, with maximum activity at AuNPs loading of 1.9 wt.%.
Example 9
(1) UiO-66 granules were prepared according to the method of step (1) of example 1;
(2) au @ UiO-66 was prepared according to the method of step (2) of example 1;
(3) an Au @ UiO-66/PTFE membrane composite was prepared in accordance with the procedure of step (3) of example 1, except that 7mg of Au @ UiO-66 in example 1 was dispersed in a mixed solvent of 7mL of absolute ethanol and 1mL of ultrapure water and 100. mu.L of Nafion PFSA polymer was modified to 3.5mg of Au @ UiO-66 dispersed in a mixed solvent of 3.5mL of absolute ethanol and 0.5mL of ultrapure water and 50. mu.L of Nafion PFSA polymer, respectively, and other conditions were not changed, and a composite photocatalyst for nitrogen reduction was accordingly obtained.
The Au @ UiO-66/PTFE film photocatalyst prepared in the embodiment is subjected to a photocatalytic reaction test under the same conditions as in embodiment 1, and NH is measured3Yield of (2) was 0.38mmol/gcat/h。
Example 10
(1) UiO-66 granules were prepared according to the method of step (1) of example 1;
(2) Au @ UiO-66 was prepared according to the method of step (2) of example 1;
(3) an Au @ UiO-66/PTFE membrane composite was prepared in accordance with the procedure of step (3) of example 1, except that 7mg of Au @ UiO-66 in example 1 was dispersed in a mixed solvent of 7mL of absolute ethanol and 1mL of ultrapure water and 100. mu.L of Nafion PFSA polymer was modified to 10.5mg of Au @ UiO-66 dispersed in a mixed solvent of 10.5mL of absolute ethanol and 1.5mL of ultrapure water and 150. mu.L of Nafion PFSA polymer, respectively, and other conditions were not changed, and a composite photocatalyst for nitrogen reduction was obtained accordingly.
The Au @ UiO-66/PTFE film photocatalyst prepared in the example was subjected to a photocatalytic reaction test under the same conditions as in example 1 to obtain NH3Yield of (2) was 0.26mmol/gcat/h。
Example 11
(1) UiO-66 granules were prepared according to the method of step (1) of example 1;
(2) au @ UiO-66 was prepared according to the method of step (2) of example 1;
(3) an Au @ UiO-66/PTFE membrane composite was prepared in accordance with the procedure of step (3) of example 1, except that 7mg of Au @ UiO-66 in example 1 was dispersed in a mixed solvent of 7mL of absolute ethanol and 1mL of ultrapure water and 100. mu.L of Nafion PFSA polymer was modified to 14mg of Au @ UiO-66 dispersed in a mixed solvent of 14mL of absolute ethanol and 2mL of ultrapure water and 200. mu.L of Nafion PFSA polymer, respectively, and the other conditions were not changed, thereby obtaining a composite photocatalyst for nitrogen reduction accordingly.
The Au @ UiO-66/PTFE film photocatalyst prepared in the embodiment is subjected to a photocatalytic reaction test under the same conditions as in embodiment 1, and NH is measured3Yield of (2) was 0.16mmol/gcat/h。
As can be seen from FIG. 28, the loading of Au @ UiO-66 on the porous PTFE film was 0.28mg/cm2、0.56mg/cm2、0.84mg/cm2、1.12mg/cm2The thicknesses of the catalyst layers in the Au @ UiO-66/PTFE membrane were 7.1. mu.m, 14.7. mu.m, 21.3. mu.m, and 28.4. mu.m, respectively.
The results of the tests in FIG. 29 show that the mass activity increases from 20.0mmol/g with increasing Au @ UiO-66 layer thickness from 7.1 μm to 28.4. mu.mAuThe reaction time/h is reduced to 8.42mmol/gAuH (from 0.38 mmol/g)catThe/h is reduced to 0.16mmol/gcatH); the area activity showed volcano-like dependence at a catalyst loading of 0.84mg/cm2When the activity is 0.22 mu mol/cm2/h。
The test results in FIG. 30 show that under similar reaction conditions (nitrogen flow: 80mL/min, visible light intensity: 100 mW/cm)2) At this time, the yield of ammonia on Au @ UiO-66/PTFE membrane was as high as 0.36mmol/gcat/h(18.9mmol/gAuH) is 2.5 times of the Au @ UiO-66 powder in the solution. While at the same catalyst loading (0.56 mg/cm)2) In this case, from non-porous particles (1.9 wt.% Au/SiO)2，2.0wt.％Au/ZrO2) Composed of non-porous solidsThe ammonia production rate of the membrane can only be increased by about 40%. The difference in the rate of increase in ammonia production rate between porous MOF and non-porous solid membranes demonstrates their different mass transfer characteristics. For the Au @ UiO-66/PTFE membrane, nitrogen and water molecules diffuse through its pore structure to the highly dispersed active sites (i.e., AuNPs). For non-porous solid membranes, dense packing of solid powders would severely impede mass transfer of reactants, and most active sites would also be covered by nearby particles, thereby reducing accessibility of reactant molecules.
The test result of FIG. 31 shows that, compared with the photocatalytic reaction of Au @ UiO-66 powder material in solution, the apparent quantum efficiency of the Au @ UiO-66/PTFE film is remarkably improved, and the apparent quantum efficiency at 520nm is as high as 1.54%.
The Au @ UiO-66/PTFE film prepared in example 1 was subjected to cycle performance testing using the Au @ UiO-66/PTFE film for each cycle period for high purity N 22 hours of photocatalytic nitrogen reduction reaction (the test conditions refer to example 1), after one cycle period is finished, the Au @ UiO-66/PTFE film is soaked in ultrapure water and dried, and then the photocatalytic nitrogen reduction reaction of the next cycle is carried out. The test results in FIG. 32 show that the photocatalytic nitrogen reduction performance of the Au @ UiO-66/PTFE membrane shows high stability, showing about 17.4mmol/g in 24 hoursAu/h(0.33mmol/gcatThe ammonia production rate per hour).
In summary, the above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A composite photocatalyst for nitrogen reduction, characterized in that: the photocatalyst is a composite material consisting of AuNPs, MOF and a porous polymer film;
Wherein AuNPs are restricted in MOF to form Au @ MOF; au @ MOF is assembled on the porous polymer film to form Au @ UiO-66/PTFE film composite, namely the photocatalyst.
2. The composite photocatalyst for nitrogen reduction according to claim 1, characterized in that: the mass fraction of AuNPs in the Au @ MOF is 0.6-5.3%, and the loading capacity of the Au @ MOF on the porous polymer film is 0.1mg/cm2～1.2mg/cm2。
3. The composite photocatalyst for nitrogen reduction according to claim 1, characterized in that: the mass fraction of AuNPs in the Au @ MOF is 1.5-3.5%, and the loading capacity of the Au @ MOF on the porous polymer film is 0.5mg/cm2～0.6mg/cm2。
4. The composite photocatalyst for nitrogen reduction according to claim 1, characterized in that: in the Au @ MOF, the particle size of AuNPs is 1.5-4.5 nm, and the particle size of MOF materials is 50-350 nm.
5. The composite photocatalyst for nitrogen reduction according to claim 1, characterized in that: the MOF is made of MOF materials which do not absorb light in the visible light region.
6. A method for preparing the composite photocatalyst for nitrogen reduction according to any one of claims 1 to 5, characterized in that: the steps of the method are as follows,
(1) Preparation of AuNPs @ MOF by adopting impregnation-reduction method
Adding MOF particles into water for ultrasonic dispersion, then dropwise adding a tetrachloroauric acid aqueous solution under stirring, then sealing and stirring and mixing for not less than 3 hours in the dark, collecting and washing precipitates, then dispersing the washed precipitates into water, dropwise adding a sodium borohydride aqueous solution under stirring, continuing stirring and reacting for more than 30 minutes after the reaction system turns red, then collecting solid substances and washing to obtain AuNPs @ MOF;
(2) assembling AuNPs @ MOF on porous polymer film by suction filtration method
Firstly, ultrasonically dispersing Au @ MOF in a solvent, then injecting a Nafion PFSA polymer and uniformly mixing, then pouring the mixed solution into a Buchner funnel paved with a porous polymer film, removing the solvent in the mixed solution through suction filtration, and finally drying to obtain an Au @ UiO-66/PTFE film composite material, namely the photocatalyst;
wherein the solvent is at least one of water with a boiling point below 100 ℃, inorganic solvent and organic solvent, and does not react with Au @ UiO-66 and Nafion PFSA polymer; the volume ratio of Nafion PFSA polymer to solvent was 1: (50-100).
7. The method for preparing a composite photocatalyst for nitrogen reduction according to claim 6, characterized in that: in the step (1), the concentration of the dispersed MOF particles in water is 1 g/L-10 g/L; in the step (2), the dispersion concentration of Au @ MOF in the solvent is 0.1 g/L-3 g/L.
8. The method for preparing the composite photocatalyst for nitrogen reduction according to claim 6, characterized in that: when the MOF is UiO-66, preparing UiO-66 particles by a solvothermal method, which comprises the following steps:
adding phthalic acid, zirconium tetrachloride, DMF (dimethyl formamide) and acetic acid into a reaction container, mixing, sealing the reaction container, reacting at 70-150 ℃ for 12-48 h, collecting white precipitate generated by the reaction, washing the collected white precipitate with DMF (dimethyl formamide), performing solvent exchange with water within 2-4 days, and finally drying to obtain UiO-66 particles;
wherein the molar ratio of zirconium tetrachloride to terephthalic acid is 3: 1-1: 3, the concentration of terephthalic acid in a reaction system is 3 mmol/L-40 mmol/L, and the volume ratio of DMF to acetic acid in the reaction system is 5: (0.1-0.5).
9. An apparatus for realizing gas-film-liquid three-phase interface reaction is characterized in that: the device comprises the photocatalyst, a reaction tank and a constant temperature system of any one of claims 1 to 5;
the reaction tank is of a closed cavity cuboid structure, the photocatalyst is placed in the reaction tank and divides the reaction tank into an air chamber and a liquid chamber, a gas inlet is formed in one side face of the air chamber, an exhaust port is formed in the top of the liquid chamber, a quartz window is formed in one side face of the liquid chamber, a liquid inlet and a liquid outlet are formed in the liquid chamber, the liquid outlet, the constant temperature system and the liquid inlet are sequentially connected through pipelines, and the constant temperature system is used for ensuring the constant temperature of the solution in the liquid chamber.
10. The apparatus for realizing gas-membrane-liquid three-phase interface reaction according to claim 9, wherein: the solution in the liquid chamber is an aqueous solution with the pH value of 3.5-8.5; the temperature of the solution in the liquid chamber is 283K to 373K.
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