Phytic acid-induced purple phosphorus-metal phosphide-silver nano material, preparation method and application in preparation of ethylene by photo-reduction of carbon dioxide

Abstract

The invention discloses a phytic acid induced purple phosphorus-metal phosphide-silver nano material, a preparation method thereof and application of the phytic acid induced purple phosphorus-metal phosphide-silver nano material in preparation of ethylene through selective photocatalysis reduction of carbon dioxide, and belongs to the field of inorganic nano materials. The phytic acid-induced purple phosphorus-metal phosphide-silver nano material is prepared by modifying phytic acid on the surface of purple phosphorus alkene through a hydrogen bond induced self-assembly method and then through an in-situ phosphating strategy of chelating cobalt ions at fixed points by phytic acid molecules and a photodeposition method. The method is easy to operate and good in sample uniformity. The invention discloses the application of the phytic acid-induced purple phosphorus-metal phosphide-silver nano material in selective photocatalytic reduction of carbon dioxide to prepare ethylene for the first time, and the obviously enhanced light absorption characteristic and the obvious charge localization distribution characteristic of metal active sites of the phytic acid-induced purple phosphorus-metal phosphide-silver nano material are utilized; and high-activity and high-selectivity conversion of carbon dioxide to a high-added-value ethylene product is realized.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic nanomaterials, and particularly relates to a phytic acid-induced violet phosphorus-metal phosphide-silver nanomaterial, a preparation method thereof, and an application thereof in the selective photocatalytic reduction of carbon dioxide to ethylene. Background Art

[0002] Phosphorus is abundant in the earth's crust and has a complex phase diagram, and is a large family of non-metallic elemental semiconductors. Photocatalytic conversion of carbon dioxide (CO2) into high-value-added chemicals has become a feasible way to overcome the energy crisis and global warming problems, and phosphorus-based semiconductor structures have received extensive attention in the photocatalytic CO2 reduction reaction. The surface electron distribution of phosphorus-based materials can regulate CO2 adsorption and activation, intermediate stability, and separation of photogenerated carriers, thus significantly affecting their activity and selectivity for reducing CO2. Different phosphorus-based nanostructures have different electron distributions and optoelectronic properties, and thus exhibit different photocatalytic CO2 reduction performances, especially the selectivity for different reduction products.

[0003] Currently, the reported CO2 reduction photocatalysts are mostly limited to the production of one-carbon products such as carbon monoxide and methane, and there are few reports on higher-value-added two-carbon products, especially ethylene (C2H4) which can be used as the raw material gas for a variety of fine chemicals. This is because the complexity of the multi-electron reaction and the inefficiency of carbon-carbon coupling in the process of photocatalytic CO2 reduction to produce ethylene pose a huge challenge to the selective generation of ethylene. Similarly, the research on photocatalytic CO2 reduction of phosphorus structures was initially also limited to one-carbon products, such as fibrous red phosphorus (ene), red phosphorus / g-C3N4, red phosphorus quantum dots / TiO2, amino-modified black phosphorus, hydroxyl-modified monolayer black phosphorus, black phosphorus / g-C3N4, black phosphorus-Co ([Ru] assisted), black phosphorus:La / InVO4:La, black phosphorus / Co2P, Co2P @ black phosphorus / g-C3N4, black phosphorus / Bi 19 Br3S 27 and other structures' carbon monoxide catalytic characteristics, and the methane catalytic characteristics of structures such as red phosphorus / graphitic carbon nitride, CsPbBr3 / black phosphorus. Recently, the research on the selectivity of photocatalytic CO2 reduction of two-carbon products by phosphorus structures has become a new hot spot. Among them, the red phosphorus structure anchored with single gold atoms shows unique selectivity for the two-carbon product ethane. In addition, in the patent application with the publication number 202410701364.6, the violet phosphorus-silver plasmonic nanostructure has been proven to have excellent selectivity for the two-carbon product ethylene. However, due to the poor ability of phosphorus-based materials themselves to adsorb and activate carbon dioxide and the lack of effective means to regulate the surface electron distribution of phosphorus-based materials, the ethylene yield and selectivity of existing phosphorus-based CO2 reduction photocatalysts are still low. Summary of the Invention

[0004] The object of the present invention is to provide a phytic acid-induced violet phosphorus-cobalt phosphide-silver nanomaterial, its preparation method and application in the selective photocatalytic reduction of carbon dioxide to ethylene, which overcomes the defect that the prior art cannot reduce CO2 to ethylene with high yield and high selectivity.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The first object of the present invention is to disclose a phytic acid-induced violet phosphorus-metal phosphide-silver nanomaterial, which is composed of violet phosphorus nanosheets, metal phosphide nanofragments and silver nanoparticles. The silver nanoparticles are loaded on the surface of the violet phosphorus nanosheets, and the metal phosphide nanofragments are evenly distributed on the surface of the violet phosphorus nanosheets. The metal phosphide nanofragments are connected to the violet phosphorus nanosheets through phytic acid. Preferably, the size of the metal phosphide nanofragments is 1-99 nm, and the average particle size of the silver nanoparticles is not more than 20 nm.

[0006] Preferably, the violet phosphorus nanosheets are stacked by two-dimensional violet phosphorusene thin sheets, and the stacking layers are 10-200 layers.

[0007] Preferably, the metal phosphide nanofragments are selected from phosphides of Co or Ni.

[0008] The second object of the present invention is to disclose a preparation method of a phytic acid-induced violet phosphorus-metal phosphide-silver nanomaterial, which includes the following steps: S1, performing liquid-phase exfoliation on the violet phosphorus crystal to obtain a dispersion of violet phosphorusene nanosheets; S2, adding phytic acid to the dispersion of violet phosphorusene nanosheets and mixing and stirring to obtain a dispersion of phytic acid-modified violet phosphorusene nanosheets; S3, adding a metal salt to the dispersion of phytic acid-modified violet phosphorusene nanosheets for solvothermal reaction, and performing suction filtration, washing and freeze-drying to obtain a phytic acid-induced violet phosphorus-metal phosphide powder; S4, dispersing the phytic acid-induced violet phosphorus-metal phosphide powder in a mixed solvent, adding a silver salt solution, and performing photodeposition to obtain a violet phosphorus-metal phosphide-silver nanomaterial.

[0009] Preferably, in the step 1), the solvent for liquid-phase exfoliation is N,N-dimethylacetamide or N,N-dimethylformamide, and the dosage ratio of violet phosphorus to the solvent is 0.5-2 mg / mL.

[0010] Preferably, in the step 2), the dosage ratio of phytic acid to the dispersion of violet phosphorusene nanosheets is 0.5-2 mg / mL; The specific process of mixing and stirring phytic acid and violet phosphorusene nanosheets is as follows: first, treat in a 500 W ultrasonic water bath for 0.2-1 hour, and then stir evenly for 8-16 hours.

[0011] Preferably, in the step 3), the solvothermal reaction temperature is 100°C to 200°C, and the treatment time is 2 to 8 hours.

[0012] Preferably, in the step 4), the components of the mixed solvent are water, and triethanolamine, methanol or ascorbic acid; the types of silver salts added are silver nitrate, silver fluoride or silver chlorate, and the mass of silver ions contained in the silver salt solution is 1 wt% to 3 wt% of the mass of the phytic acid-induced purple phosphorus-metal phosphide.

[0013] The third object of the present invention is to disclose the application of the above phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial, or the phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial prepared by the above preparation method in the selective photocatalytic reduction of carbon dioxide to ethylene.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention firstly discloses a phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial. In the case of the simultaneous presence of two phosphorus sources, purple phosphorus and phytic acid, the metal phosphide is connected to the surface of the phosphorene nanosheet through phytic acid molecules. The phytic acid molecules on the surface of purple phosphorus can preferentially anchor metal ions through chelation. The uniformity and dispersion of metal ions brought about by this site-directed chelation induce the in-situ synthesis of small-sized fragmented metal phosphides at the nanoscale and their uniform coating on the surface of phosphorene. This uniform coating enables the electron distribution on the surface of purple phosphorus to be more significantly optimized, different from the large-sized and unevenly distributed nanoparticle-like metal phosphides directly grown on the substrate of phosphorene nanosheets and on various other reported substrates. The in-situ grown nano-metal phosphide component broadens the light absorption range of the purple phosphorus-metal phosphide-silver nanomaterial from the light wavelength range less than 600 nanometers to the near-infrared region, significantly enhancing the light absorption ability of the phosphorene nanosheet. The purple phosphorus-metal phosphide-silver nanomaterial disclosed in the present invention can promote the generation of photogenerated electrons in silver particles and electron-rich phosphorene nanosheets in the photoexcited state, and quickly transfer them to the metal sites in the metal phosphide, forming an obvious charge localization distribution. This charge distribution characteristic can not only effectively promote the separation of photogenerated carriers and photoelectron conduction, but also greatly promote the adsorption and activation of CO2 molecules, overcoming the problem of insufficient CO2 adsorption of pure phosphorene nanosheets. At the same time, the electron-rich characteristics of the metal sites also promote the adsorption and rapid protonation of CO * intermediate, providing favorable thermodynamic conditions and kinetic basis for the subsequent carbon-carbon coupling to generate the key dicarbon product intermediate.

[0015] The present invention discloses a preparation method of phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterials. For the first time, phytic acid is modified on the surface of phosphorene through a hydrogen bond-induced self-assembly method, and then an in-situ phosphidation strategy of surface-site chelating metal ions by phytic acid-modified phosphorene, as well as a photodeposition method, are used to achieve the preparation of phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterials. At the same time, the phosphorene nanosheet substrate has higher environmental stability than other phosphorus allotropes, making the synthesis process of the purple phosphorus-metal phosphide-silver nanomaterials disclosed in the present invention simple, without the need for inert gas protection. This method is easy to operate, has high controllability, and good sample uniformity.

[0016] The present invention also discloses the application of the phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterials in the selective photocatalytic reduction to produce ethylene. Due to the dual cocatalytic structure of metal phosphide + silver in the purple phosphorus-metal phosphide-silver nanomaterials, the photocatalytic CO2 reduction activity of the phosphorene nanosheets and the selectivity for high-value ethylene products are significantly improved, thus achieving a transformation from the low-activity carbon monoxide production of pure purple phosphorus (1.32 μmol g -1 ·h -1 −1) to the high-activity ethylene production of phytic acid-induced purple phosphorus-metal phosphide-silver (14.6 μmol g -1 ·h -1 −1) in the application of photocatalytic carbon dioxide reduction. Description of the Drawings

[0017] Figure 1 are the morphology pictures of phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterials; among them, (a) is the SEM image; (b) is the TEM image; (c) is the HRTEM image; (d-g) are the TEM dark field images and element distribution images; Figure 2 are the XRD comparison diagrams of purple phosphorus, purple phosphorus-cobalt phosphide, purple phosphorus-cobalt phosphide-silver, and phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterials; Figure 3 are the Raman comparison diagrams of purple phosphorus, purple phosphorus-cobalt phosphide, purple phosphorus-cobalt phosphide-silver, and phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterials; Figure 4 are the UV comparison diagrams of purple phosphorus, purple phosphorus-cobalt phosphide, purple phosphorus-cobalt phosphide-silver, and phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterials; Figure 5 are the photocatalytic carbon dioxide reduction performance comparison bar charts of purple phosphorus, purple phosphorus-cobalt phosphide, purple phosphorus-cobalt phosphide-silver, and phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterials; Figure 6Optoelectronic test diagrams of purple phosphorus, purple phosphorus-cobalt phosphide, purple phosphorus-cobalt phosphide-silver, and phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterials; among them, (a) is the transient photocurrent response diagram; (b) is the impedance diagram; Figure 7 In-situ FT-IR diagrams of purple phosphorus-cobalt phosphide, purple phosphorus-cobalt phosphide-silver, and phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterials; among them, (a) is the in-situ FT-IR diagram of phytic acid-induced purple phosphorus-cobalt phosphide-silver; (b) is the in-situ FT-IR diagram of purple phosphorus-cobalt phosphide-silver; (c) is the in-situ FT-IR diagram of purple phosphorus-cobalt phosphide; Figure 8 In-situ XPS diagrams of phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterials; among them, (a) is the high-resolution spectrum diagram of phosphorus; (b) is the high-resolution spectrum diagram of cobalt; (c) is the high-resolution spectrum diagram of silver; Figure 9 Morphology picture comparison of directly grown and phytic acid-induced purple phosphorus-cobalt phosphide materials; among them, (a, b) are the TEM image and SEM image of directly grown purple phosphorus-cobalt phosphide materials; (c, d) are the TEM image and SEM image of phytic acid-induced purple phosphorus-cobalt phosphide materials; Figure 10 Morphology and photocatalytic performance pictures of purple phosphorus-nickel phosphide nanomaterials; among them, (a) is the TEM image; (b) is the bar chart comparing the photocatalytic carbon dioxide reduction performance of purple phosphorus-cobalt phosphide and purple phosphorus-nickel phosphide. Detailed implementation mode

[0018] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0019] Violet Phosphorus (or the corresponding layered violet phosphorene nanosheets) is a new allotrope of phosphorus and belongs to two-dimensional layered materials. With its moderate bandgap, high stability, and versatility, it shows great potential in the fields of energy, electronics, catalysis, etc. This new layered elemental semiconductor of violet phosphorus has been proven to be the most stable phosphorus allotrope, providing a simple environment for the synthesis and modification of violet phosphorus-based nanostructures without the need for inert gas protection. The electron-rich two-dimensional structure on the surface of violet phosphorus also offers more possibilities for the design and synthesis of violet phosphorus-based nanostructures and the regulation of photocatalytic selectivity characteristics. For example, by regulating the electron distribution on the surface of violet phosphorus, it is a new perspective for the design and development of a phosphorus-based nanostructure photocatalyst for enhancing the selective photocatalytic reduction of CO2 to ethylene.

[0020] Based on the understanding of the above-mentioned development progress of the prior art, the present invention discloses a phytic acid-induced violet phosphorus-metal phosphide-silver nanomaterial, which includes violet phosphorene nanosheets, metal phosphide nanosheet fragments connected by phytic acid molecules, and trace silver cocatalyst nanoparticles loaded on the surface of violet phosphorus. The metal phosphide nanosheet fragments are connected to the violet phosphorene nanosheets through phytic acid and are uniformly distributed on their surfaces. The induction of phytic acid molecules can achieve the control of the morphology and size of metal phosphides. Compared with directly growing metal phosphides on the violet phosphorus substrate, the size of metal phosphides can be changed from large-size particles to nano-sized fragments through phytic acid induction. This feature enables the nano-phosphide fragments to be more uniformly coated and in contact with the violet phosphorus substrate, maximizing the regulatory effect of the phosphide on the electron distribution on the surface of violet phosphorus. Such an electron distribution can achieve efficient regulation of active sites and improve the activity of reducing carbon dioxide to ethylene. In contrast, for the metal phosphides directly grown on the violet phosphorus substrate, due to the less and uneven contact interface with the violet phosphorus substrate, the regulation of the electron distribution of the large-area violet phosphorus substrate cannot be achieved, so the activity of reducing carbon dioxide to ethylene cannot be effectively improved.

[0021] In the phytic acid-induced violet phosphorus-metal phosphide-silver nanomaterial disclosed in the present invention, the violet phosphorene nanosheets are stacked by two-dimensional violet phosphorene thin sheets, and the stacking layer number is distributed from 10 to 200 layers, mostly concentrated in 100 layers.

[0022] In the embodiments of the present invention, the metal phosphide nanosheet fragments are connected to the surface of the violet phosphorene nanosheets through phytic acid molecules and are uniformly coated in the form of nano-sized fragments of several to dozens of nanometers. The metal phosphide is nano-sized fragments, which are more uniformly distributed on the surface of the substrate material and have a larger contact area than the metal phosphide particles directly grown on the substrate, and have a stronger regulatory effect on the electron distribution.

[0023] In some embodiments of the present invention, the chemical composition of the metal phosphide is Co2P or Ni2P.

[0024] In an embodiment of the present invention, silver nanoparticles are loaded on the surface of purple phosphorus nanosheets, and the average particle size is not greater than 20 nm.

[0025] In an embodiment of the present invention, silver nanoparticles are preferentially loaded on the surface of purple phosphorus nanosheets rather than the surface of metal phosphides. The silver nanoparticles also play a role in regulating the electron distribution on the surface of purple phosphorus nanosheets and cooperate with metal phosphide nanofragments for regulation. Although precise control of the size of silver nanoparticles is not required, when their size is too large and significantly exceeds the above range, the distribution of silver on the substrate is uneven, and the regulation effect on the electron distribution of the substrate becomes poor, thereby causing a decrease in the electron localization effect and electron transport kinetics of the double-assisted catalytic system formed by silver and metal phosphides on purple phosphorus nanosheets, resulting in a decrease in catalytic activity.

[0026] In an embodiment of the present invention, phytic acid (PA) refers to inositol hexaphosphate with the chemical formula C6H 18 O 24 P6, which is formed by the combination of cyclic inositol and six phosphate groups and has the ability to chelate metal ions.

[0027] In the phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial structure proposed in the present invention, the environmental stability of the purple phosphorus nanosheet substrate compared to other phosphorus allotropes makes the synthesis process simple and does not require inert gas protection. Metal phosphides are connected to the surface of purple phosphorus nanosheets through phytic acid molecules and are uniformly coated in the form of small fragments with a size of several to dozens of nanometers. This is attributed to the fact that in the presence of both purple phosphorus and phytic acid as two phosphorus sources, the phytic acid molecules on the surface of purple phosphorus can preferentially anchor the active metal ions through chelation, and the uniformity and dispersibility of the active metal ions brought about by this site-specific chelation induce the in-situ synthesis and uniform coating of small-sized fragmented metal phosphide nanofragments, which is different from the large-sized nanoparticle-like metal phosphides directly grown on purple phosphorus nanosheets and various other reported substrates.

[0028] The present invention also discloses a preparation method of the above phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial, including the following steps: Step 1), grinding purple phosphorus crystals into powder, performing liquid-phase exfoliation after treatment with liquid nitrogen, and then standing for 5 - 12 h to remove the bottom precipitate to obtain a dispersion of purple phosphorus nanosheets; Step 2), adding a certain amount of phytic acid to the dispersion of purple phosphorus nanosheets and stirring to mix to obtain a dispersion of phytic acid-modified purple phosphorus nanosheets; Step 3), adding a certain amount of metal salt to the dispersion of phytic acid-modified purple phosphorus nanosheets, transferring it to a reaction kettle for solvothermal treatment, and then performing suction filtration, washing, and freeze-drying to obtain phytic acid-induced purple phosphorus-metal phosphide powder.

[0029] Step 4), disperse the obtained purple phosphorus-metal phosphide powder in a mixed solvent, add a certain amount of silver salt solution, carry out photo-deposition, and then obtain the phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial photocatalyst through suction filtration, washing, and freeze-drying.

[0030] In some embodiments of the present invention, in Step 1), the solvent for liquid-phase exfoliation is N,N-dimethylacetamide or N,N-dimethylformamide, and the volume ratio of the added amount of purple phosphorus to the solvent is 0.5-2 mg / mL.

[0031] In some embodiments of the present invention, in Step 2), the volume ratio of the added amount of phytic acid to the volume of the purple phosphorene nanosheet dispersion is 0.5-2 mg / mL. The process of phytic acid modification is as follows: first, treat it in an ultrasonic water bath of 500 W for 0.2-1 hour, and then stir it evenly for 8-16 hours. The added amount of phytic acid molecules is 0.5-2 mg / mL. When the dosage of phytic acid is too small or too large, a uniform coating of metal phosphide cannot be formed on the surface of the purple phosphorene nanosheets, thereby affecting its photocatalytic reduction of carbon dioxide to produce ethylene. The metal phosphide particles in-situ grown on the purple phosphorene nanosheets without phytic acid molecule modification often agglomerate into larger-sized nanoparticles. The reduction and uneven distribution of active sites will weaken the adsorption and activation of carbon dioxide molecules by the catalyst, resulting in a decrease in catalytic activity. The catalytic product is mainly carbon monoxide, with a small amount of methane and ethylene.

[0032] In some embodiments of the present invention, in Step 3), the added metal source is a cobalt source, and the types of cobalt salts are one or more of cobalt chloride, cobalt nitrate hexahydrate, cobalt acetylacetonate, and cobalt acetate, and the added amount is 0.2-4 mmol.

[0033] In some embodiments of the present invention, in Step 3), the added metal source is a nickel source, and the types of the added nickel source are one or more of nickel chloride, nickel nitrate hexahydrate, nickel acetylacetonate, and nickel acetate, and the added amount is 0.2-4 mmol.

[0034] The addition amount of the cobalt source or nickel source is 0.2 to 4 millimoles, because the amount added will significantly affect the morphology, composition, and photocatalytic effect of the synthesized sample. Taking the addition of the cobalt source as an example: when the addition amount of the cobalt source is 0.2 millimoles, only a small amount of Co2P particles are generated, or the generated Co2P particles grow unevenly at some positions on the surface of the phosphorene nanosheets. The catalytic performance is improved compared to pure phosphorene nanosheets (only trace amounts of carbon monoxide products) and a small amount of ethylene products appear; when the addition amount of the cobalt source increases to 0.9 millimoles, the surface of the phosphorene nanosheets is basically coated with a Co2P layer, the catalytic performance is rapidly improved and a small amount of ethylene and methane products appear; when the addition amount of the cobalt source continues to increase to 1.5 millimoles, the surface of the phosphorene nanosheets is coated with a large amount of Co2P, the catalytic performance begins to decline, no ethylene products but some methane products; when the cobalt source is in excess to 4 millimoles, the phosphorene nanosheets have basically been completely converted to Co2P, and the catalytic performance continues to decline, no ethylene products but still some methane products.

[0035] In some embodiments of the present invention, in step 3), the solvothermal temperature is 100 °C to 200 °C, and the treatment time is 2 to 8 hours.

[0036] In some embodiments of the present invention, in step 4), the components of the mixed solvent are water, and triethanolamine, methanol or ascorbic acid. The types of silver salts added are silver nitrate, silver fluoride or silver chlorate. The mass of silver ions contained in the silver salt solution is 1 wt% to 3 wt% of the mass of the phytic acid-induced purple phosphorus-metal phosphide.

[0037] The present invention also discloses the application of the above phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial in the selective photocatalytic reduction of carbon dioxide to ethylene.

[0038] The method of the present invention will be further described below in conjunction with the drawings and examples. In the following examples, conventional instrument equipment in the art is used. For various raw materials and reagents used (such as solvents, mixed solvents, etc.), unless otherwise stated, commercially available products are used, and their specifications are conventional specifications in the art, or can be prepared or formulated by known methods or reagent instructions. The experimental methods without specific conditions stated in the following examples are usually carried out under conventional conditions, or according to the conditions recommended by the manufacturer.

[0039] The present invention will be further described in detail below with reference to the drawings: Example 1 The method for preparing the phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterial is as follows: 85 mg of purple phosphorus crystals were ground and treated with liquid nitrogen, and then liquid-phase exfoliated in an N,N-dimethylacetamide solvent. After standing overnight to remove the bottom precipitate, a dispersion of phosphorene nanosheets was obtained.

[0040] Subsequently, 75 mL of the dispersion of purple phosphorene nanosheets was taken, and 1 mg / mL of phytic acid was added. It was treated in an ultrasonic water bath at 500 W for 0.5 h and then stirred uniformly for 12 h to obtain a dispersion of phytic acid-modified purple phosphorene.

[0041] Then, 0.9 mM of cobalt acetylacetonate was added to the phytic acid-modified purple phosphorene dispersion, and it was transferred to a reaction kettle for solvothermal treatment at 180 °C for 4 h. After filtration, washing, and freeze-drying, phytic acid-induced purple phosphorus-cobalt phosphide powder was obtained.

[0042] 20 mg of the obtained powder was dispersed in a mixed solvent of 72 mL of water and triethanolamine, and an aqueous silver nitrate solution with a mass ratio of silver ions contained relative to the mass of the phytic acid-induced purple phosphorus-cobalt phosphide powder of 3 wt % was added for photodeposition. After filtration, washing, and freeze-drying, phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterial (hereinafter referred to as VP-PA-Co2P-Ag) was obtained.

[0043] The morphology and crystal structure of the prepared VP-PA-Co2P-Ag are as Figure 1 shown in the SEM, TEM, HRTEM, mapping images and Figure 2 XRD pattern. The purple phosphorene nanosheet substrate is in the shape of regular rectangular flakes, and the cobalt phosphide in-situ grown by phytic acid induction is uniformly coated on the surface of the purple phosphorene nanosheets in the form of small-sized fragments, with a chemical composition of Co2P and relatively low crystallinity. A small amount of spherical silver particles are dispersed and loaded on the surface of the purple phosphorene nanosheets, with an average particle size of less than 20 nm and relatively high crystallinity. Figure 1 、 Figure 2 shown prove that after phytic acid modification, in-situ growth of cobalt phosphide, and silver particle loading, in addition to the surface coating of these new components, the morphology and crystal structure of the purple phosphorene nanosheets themselves remain unchanged. The Raman and UV spectra of VP-PA-Co2P-Ag are as shown in Figure 3 、and Figure 4 respectively. It can be seen from them that the basic vibration mode of the purple phosphorene nanosheets remains unchanged, but there is a slight Raman blue shift due to the interaction with the surface-loaded components; while the in-situ grown cobalt phosphide component broadens the light absorption range from a light wavelength range of <600 nm to the near-infrared region, significantly enhancing the light absorption ability of the purple phosphorene nanosheets.

[0044] Photocatalytic carbon dioxide reduction application: The photocatalytic carbon dioxide reduction reaction is carried out in a gas-solid mode without the participation of a sacrificial agent. The process is as follows: Disperse approximately 5 mg of the VP-PA-Co2P-Ag photocatalyst in 3 ml of ethanol, drop-coat it on a glass fiber support membrane, air-dry it naturally, and place it on a quartz rack in the reactor. Without contacting the photocatalyst, put approximately 0.5 g of potassium bicarbonate at the bottom of the reactor. After the system (Labsolar-6A, Beijing Perfectlight) is evacuated, inject 1.7 mL of 6 M sulfuric acid aqueous solution and supplement carbon dioxide until the system pressure reaches 80 kPa. Use a 300 W xenon lamp with an intensity of 1000 mW cm -2 as the light source. Monitor the products by on-line gas chromatography (Fuli Instrument GC9720Plus) at intervals of 0.5 h for 2.5 h. See Figure 5 , and the tested products contain 14.6 μmol g -1 ·h -1 ethylene, 2.7 μmol g -1 ·h -1 methane, 27.0 μmol g -1 ·h -1 carbon monoxide. Generally speaking, the ethylene product increases from 0 of the VP photocatalyst to 0.6 μmol g -1 ·h -1 of the VP-Co2P photocatalyst (2.2%), and further increases to 4.17 μmol g -1 ·h -1 of the VP-Co2P-Ag photocatalyst (9.8%), and finally significantly increases to 14.6 μmol g -1 ·h -1 of the VP-PA-Co2P-Ag photocatalyst (33.0%).

[0045] It can be seen that the VP-PA-Co2P-Ag photocatalyst prepared by the present invention is significantly superior to the unloaded phosphorene nanosheets, the phosphorene nanosheets loaded only with cobalt phosphide, and the phosphorene nanosheets loaded with cobalt phosphide and silver without phytic acid modification directly in terms of catalytic performance, especially ethylene activity and selectivity, as shown in Figure 5 , Figure 6 . See Figure 7 In (a) therein, the in-situ FT-IR diagram of VP-PA-Co2P-Ag as a photocatalyst shows obvious CO2 * radicals (1710 cm -1 ), indicating that its adsorption and activation effects on CO2 molecules are obvious, overcoming the problem of insufficient CO2 adsorption of pure phosphorene nanosheets (almost no obvious peaks); in addition, obvious CO * radicals (2077, 1854 cm -1), and the key intermediate COCHO of the obvious ethylene product * radical (1481 cm -1 ), indicating that the CO * adsorption and protonation reactions on the VP-PA-Co2P-Ag photocatalyst are easy to carry out, and the subsequent asymmetric carbon-carbon coupling to form the key two-carbon intermediate has a low reaction energy barrier. The CO2 reduction reaction changes from a complete one-carbon product tendency to an obvious two-carbon product tendency.

[0046] The direction of electron transfer during the photocatalysis of VP-PA-Co2P-Ag can be obtained from the comparison of in-situ XPS spectra under dark and light conditions. See Figure 8 , under light illumination, the P 2p (including two forms of phosphorus in violet phosphorus and cobalt phosphide) ( Figure 8 (a) in Figure 8 ) and Ag 3d ( Figure 8 (b) in <x * The peak positions shift to higher values, while the Co 2p peak (

[0047] Example 2 The method for preparing the phytic acid-induced violet phosphorus-cobalt phosphide-silver nanomaterial is as follows: Grind 85 mg of violet phosphorus crystals and treat them with liquid nitrogen, then perform liquid-phase exfoliation in N,N-dimethylacetamide solvent, and let it stand overnight to remove the bottom precipitate to obtain a dispersion of violet phosphorus nanosheets.

[0048] Subsequently, 75 mL of the dispersion of black phosphorus nanosheets was taken, and 0.5 mg / mL of phytic acid was added. It was treated in a 500 W ultrasonic water bath for 0.2 h and then stirred evenly for 8 h to obtain a dispersion of phytic acid-modified black phosphorus.

[0049] Then, 0.9 mM of cobalt acetylacetonate was added to the phytic acid-modified black phosphorus dispersion, and it was transferred to a reaction kettle for solvothermal treatment at 200 °C for 6 h. After filtration, washing, and freeze-drying, phytic acid-induced black phosphorus-cobalt phosphide powder was obtained.

[0050] 20 mg of the obtained powder was dispersed in a mixed solvent of 72 mL of water and triethanolamine, and an aqueous silver nitrate solution with a mass ratio of silver ions contained relative to the mass of the phytic acid-induced black phosphorus-cobalt phosphide powder of 3 wt % was added for photodeposition. After filtration, washing, and freeze-drying, phytic acid-induced black phosphorus-cobalt phosphide-silver nanomaterial (hereinafter referred to as VP-0.5PA-Co2P-Ag) was obtained.

[0051] The morphology and crystal structure of the prepared VP-0.5PA-Co2P-Ag are similar to those of VP-PA-Co2P-Ag, but the size of cobalt phosphide is larger and the coating is relatively uneven. Because when the amount of phytic acid is insufficient, the morphology and aggregation degree of cobalt phosphide cannot be effectively regulated.

[0052] Photocatalytic carbon dioxide reduction application: The photocatalytic carbon dioxide reduction reaction was carried out in a gas-solid mode without the participation of a sacrificial agent, and the process was as follows: Approximately 5 mg of the VP-0.5PA-Co2P-Ag photocatalyst was dispersed in 3 ml of ethanol, drop-coated on a glass fiber support membrane, air-dried naturally, and placed on a quartz rack in a reactor. Without contacting the photocatalyst, approximately 0.5 g of potassium bicarbonate was placed at the bottom of the reactor. After the system (Labsolar-6A, Beijing Perfectlight) was evacuated, 1.7 mL of 6 M sulfuric acid aqueous solution was injected and carbon dioxide was supplemented to the system pressure of 80 kPa. A 300 W xenon lamp with an intensity of 1000 mW cm −2 was used as the light source. Product monitoring was carried out by on-line gas chromatography (Fuli Instrument GC9720Plus) at intervals of 0.5 h for 2.5 h. The measured products included 3.21 μmol g -1 ·h -1 ethylene, 1.26 μmol g -1 ·h -1 methane, 24.10 μmolg -1 ·h -1Carbon monoxide. Generally speaking, the ethylene production increases from 0 of the VP photocatalyst to 3.21 μmol g -1 ·h -1 (11.2%).

[0053] It can be seen that for the VP-0.5PA-Co2P-Ag photocatalyst prepared in the present invention, compared with the purple phosphorus nanosheets directly loaded with cobalt phosphide and silver without phytic acid modification, the improvement in catalytic performance, especially in ethylene activity and selectivity, is not significant. This indicates that cobalt phosphide with relatively large size and uneven coating has insufficient adsorption and activation effects on carbon dioxide molecules, resulting in insufficient improvement in catalytic activity and ethylene selectivity.

[0054] Example 3 The method for preparing the purple phosphorus-cobalt phosphide-silver nanomaterial is as follows: 85 mg of purple phosphorus crystals were ground and treated with liquid nitrogen, and then liquid-phase exfoliated in N,N-dimethylacetamide solvent. After standing overnight to remove the bottom precipitate, a dispersion of purple phosphorus nanosheets was obtained.

[0055] Subsequently, 75 mL of the purple phosphorus nanosheet dispersion was taken, 0.9 mM of cobalt acetylacetonate was added, and the mixture was transferred to a reaction kettle for solvothermal treatment at 180 °C for 4 h. After filtration, washing, and freeze-drying, purple phosphorus-cobalt phosphide powder was obtained.

[0056] 20 mg of the obtained powder was dispersed in a mixed solvent of 72 mL of water and triethanolamine, and an aqueous silver nitrate solution with a mass ratio of silver ions to the mass of the purple phosphorus-cobalt phosphide powder of 3 wt % was added for photodeposition. After filtration, washing, and freeze-drying, purple phosphorus-cobalt phosphide-silver nanomaterial (hereinafter referred to as VP-Co2P-Ag) was obtained.

[0057] The prepared VP-Co2P-Ag is similar to the phytic acid-induced purple phosphorus-cobalt phosphide-silver nanomaterial in terms of morphology and crystal structure ( Figure 2 XRD, Figure 3 Raman, Figure 4 UV), except that cobalt phosphide mostly exists as larger-sized nanoparticle aggregates. This is because purple phosphorus without phytic acid modification cannot be anchored by the site-specific chelation of cobalt ions by surface phytic acid molecules. Therefore, larger-sized nanoparticle-shaped cobalt phosphide grows directly on the purple phosphorus nanosheets ( Figure 9 in (a) TEM, Figure 9 in (b) SEM), which is different from the in-situ synthesis and uniform coating of small-sized fragment-shaped Co2P induced by phytic acid ( Figure 9 in (c) TEM, Figure 9In (d) SEM). The basic vibration mode of the phosphorene nanosheets remains unchanged, but there is a slight Raman blue shift due to the interaction with the surface-loaded components ( Figure 3 Raman); while the in-situ grown cobalt phosphide component broadens the light absorption range from the light wavelength range of <600 nm to the near-infrared region, significantly enhancing the light absorption ability of the phosphorene nanosheets ( Figure 4 UV).

[0058] Photocatalytic carbon dioxide reduction application: The photocatalytic carbon dioxide reduction reaction proceeds in a gas-solid mode without the participation of sacrificial agents. The process is as follows: Disperse about 5 mg of the VP-Co2P-Ag photocatalyst in 3 ml of ethanol, drop-coat it on a glass fiber support membrane, air-dry it naturally, and place it on a quartz rack in the reactor. Without contacting the photocatalyst, put about 0.5 g of potassium bicarbonate at the bottom of the reactor. After the system (Labsolar-6A, Beijing Perfectlight) is evacuated, inject 1.7 mL of 6 M sulfuric acid aqueous solution and supplement carbon dioxide to the system pressure of 80 kPa. Use a 300 W xenon lamp with an intensity of 1000 mW cm -2 as the light source. The products are monitored by on-line gas chromatography (Fuli Instrument GC9720Plus), at intervals of 0.5 h for 2.5 h. See Figure 5 , and the tested products contain 4.17 μmol g -1 ·h -1 ethylene, 0.85 μmol g -1 ·h -1 methane, 37.50 μmolg -1 ·h -1 carbon monoxide. Generally, in comparison, the ethylene product increases from 0 of the VP photocatalyst to 0.6 μmol g -1 ·h -1 of the VP-Co2P photocatalyst (2.2%), and further increases to 4.17 μmol g -1 ·h -1 of the VP-Co2P-Ag photocatalyst (9.8%).

[0059] It can be seen that the VP-Co2P-Ag photocatalyst prepared by the present invention has better catalytic performance, especially in terms of ethylene activity and selectivity, than the unloaded phosphorene nanosheets and the phosphorene nanosheets only loaded with cobalt phosphide, as shown in Figure 5 , Figure 6 . See Figure 7 In (b), the in-situ FT-IR diagram of VP-Co2P-Ag as a photocatalyst shows an obvious CO2 *Free radicals (1710 cm -1 ), indicating that its adsorption and activation of CO2 molecules are strong, overcoming the problem of insufficient CO2 adsorption of pure phosphorene nanosheets (almost no obvious peaks); in addition, the figure also shows a certain amount of CO * free radicals (2077, 1855 cm -1 ), and the key intermediate COCHO * free radicals (1481 cm -1 ) of a small amount of ethylene products, indicating that there is also a tendency of a small amount of two-carbon products in addition to one-carbon products on the VP-Co2P-Ag photocatalyst. As for the unloaded phosphorene nanosheets and the phosphorene nanosheets loaded only with cobalt phosphide as a comparison, the products of reducing carbon dioxide as catalysts are only a small amount of carbon monoxide and methane one-carbon products, and no ethylene products are detected.

[0060] Example 4 The method for preparing the purple phosphorus-cobalt phosphide nanomaterial is as follows: 85 mg of purple phosphorus crystals were ground and treated with liquid nitrogen, and then liquid-phase exfoliated in N,N-dimethylacetamide solvent. After standing overnight to remove the bottom precipitate, a dispersion of phosphorene nanosheets was obtained.

[0061] Subsequently, 75 mL of the dispersion of phosphorene nanosheets was taken, 0.9 mM of cobalt acetylacetonate was added, and the mixture was transferred to a reaction kettle for solvothermal treatment at 180 °C for 4 h. After filtration, washing, and freeze-drying, purple phosphorus-cobalt phosphide powder (hereinafter referred to as VP-Co2P) was obtained.

[0062] The prepared VP-Co2P is similar to the purple phosphorus-cobalt phosphide-silver nanomaterial in terms of morphology and crystal structure ( Figure 9 SEM in (a), Figure 9 TEM in (b), Figure 2 XRD, Figure 3 Raman, Figure 4 UV), except that there are no silver particles loaded on the surface. The basic vibration mode of the phosphorene nanosheets remains unchanged, but there is a slight Raman blue shift ( Figure 3 Raman) due to the interaction with the surface-loaded cobalt phosphide; while the in-situ grown cobalt phosphide component broadens the light absorption range from the light wavelength range of <600 nm to the near-infrared region, significantly enhancing the light absorption ability of the phosphorene nanosheets ( Figure 4 UV).

[0063] Photocatalytic carbon dioxide reduction application: The photocatalytic carbon dioxide reduction reaction is carried out in a gas-solid mode without the participation of a sacrificial agent, and the process is as follows: Approximately 5 mg of VP-Co2P photocatalyst was dispersed in 3 mL of ethanol, drop-coated onto a glass fiber support membrane, allowed to air dry, and placed on a quartz rack in the reactor. Approximately 0.5 g of potassium bicarbonate was placed at the bottom of the reactor without contact with the photocatalyst. The system (Labsolar-6A, Beijing Perfectlight) was evacuated, and 1.7 mL of 6 M aqueous sulfuric acid solution was injected, followed by carbon dioxide replenishment to a system pressure of 80 kPa. A full-spectrum 1000 mW cm -2 A 300 W xenon lamp with high intensity was used as the light source. Product monitoring was performed by online gas chromatography (Fulli Instruments GC9720Plus) with an interval of 0.5 h and a maintenance of 2.5 h. Figure 5 The product was tested to contain 1.49 μmol g -1 ·h -1 Methane, 25.3 μmol g -1 ·h -1 carbon monoxide, better than unsupported purple phosphorene nanosheets ( Figure 5 、 Figure 6 ). In situ FT-IR image of VP-Co2P as a photocatalyst ( Figure 7 Only a small amount of one-carbon intermediate CO was observed in (c). * Free radicals (2077, 1855 cm -1 ), no two-carbon product intermediates for the formation of ethylene appeared, indicating that only one-carbon products can be produced on the VP-Co2P photocatalyst.

[0064] Example 5 The method for preparing the purple phosphorus-nickel phosphide nanomaterial is as follows: 85 mg of purple phosphorus crystals were ground and treated with liquid nitrogen before liquid phase exfoliation in N,N-dimethylacetamide. The solution was allowed to stand overnight to remove the bottom precipitate, yielding a dispersion of purple phosphorene nanosheets. Subsequently, 75 mL of the dispersion was added with 0.9 mM nickel nitrate hexahydrate and transferred to a reactor for solvothermal heating at 180°C for 4 hours. Purple phosphorus-nickel phosphide powder (hereafter referred to as VP-Ni2P) was obtained after filtration, washing, and freeze-drying.

[0065] The morphology of the prepared VP-Ni2P is ( Figure 10 (a) TEM) In contrast to VP-Co2P, the purple phosphorene nanosheet substrate is in the form of regular rectangular flakes, while the in situ grown nickel phosphide is densely coated on the surface of the purple phosphorene nanosheet in the form of small particles.

[0066] Photocatalytic carbon dioxide reduction applications: The photocatalytic carbon dioxide reduction reaction is carried out in a gas-solid mode without the participation of a sacrificial agent. The process is as follows: Disperse approximately 5 mg of the VP-Ni2P photocatalyst in 3 ml of ethanol, drop-coat it on a glass fiber support membrane, air-dry it naturally, and place it on a quartz rack in the reactor. Without contacting the photocatalyst, place approximately 0.5 g of potassium bicarbonate at the bottom of the reactor. After the system (Labsolar-6A, Beijing Perfectlight) is evacuated, inject 1.7 mL of 6 M sulfuric acid aqueous solution and supplement carbon dioxide to a system pressure of 80 kPa. Use a 300 W xenon lamp with an intensity of 1000 mW cm -2 as the light source for the full spectrum. Monitor the products by on-line gas chromatography (Fuli Instrument GC9720Plus) at intervals of 0.5 h for 2.5 h. See Figure 5 , and the test shows that the products contain 3.8 μmol g -1 ·h -1 methane, 17.6 μmol g -1 ·h -1 carbon monoxide, lower than that of VP-Co2P under the same conditions ( Figure 10 in (b)). It shows that various other metal phosphides similar to cobalt and nickel may also be applicable to the in-situ synthesis on the purple phosphorusene substrate by this technical method to improve the photocatalytic carbon dioxide reduction performance.

[0067] In summary, the phytic acid-induced synthesis process of purple phosphorus-metal phosphide-silver nanomaterials described in this invention is simple, does not require inert gas protection, has high sample controllability and good uniformity. The phytic acid molecules on the surface of purple phosphorus chelate at fixed points, inducing the in-situ synthesis and uniform coating of small-sized fragmented metal phosphides. This structure significantly broadens the light absorption range of the purple phosphorusene nanosheet substrate, promotes the generation of photogenerated electrons on silver particles and electron-rich purple phosphorusene nanosheets and their rapid transfer to the metal active sites in the metal phosphide, forming an obvious charge localization distribution. Therefore, the electron-rich characteristics of the metal active sites also promote the adsorption and rapid protonation of CO * intermediates and subsequent carbon-carbon coupling, realizing the generation of 14.6 μmol g -1 ·h -1 (33.0%) of high-value-added ethylene products. The catalytic performance is not only significantly superior to that of unloaded purple phosphorusene nanosheets, purple phosphorusene nanosheets only loaded with metal phosphides, and purple phosphorusene nanosheets directly loaded with metal phosphide and silver without phytic acid modification, but also superior to most current photocatalysts.

[0068] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention fall within the protection scope of the claims of the present invention.

Claims

1. A phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial, characterized in that, It is composed of phosphorene nanosheets, metal phosphide nanofragments, and silver nanoparticles. The silver nanoparticles are loaded on the surface of the phosphorene nanosheets, and the metal phosphide nanofragments are uniformly coated on the surface of the phosphorene nanosheets. The metal phosphide nanofragments are connected to the phosphorene nanosheets through phytic acid.

2. The phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial according to claim 1, wherein The size of the metal phosphide nanofragments is 1 - 99 nm, and the average particle size of the silver nanoparticles is not greater than 20 nm.

3. The phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial according to claim 1, characterized in that, The phosphorene nanosheets are stacked by two-dimensional phosphorene thin sheets, and the number of stacked layers is 10 - 200 layers.

4. The phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial according to claim 1, wherein The metal phosphide nanofragments are phosphides of Co or Ni.

5. Preparation method of phytic acid-induced purple phosphorus-metal phosphide-silver nanoparticles, characterized in that, It includes the following steps: S1, performing liquid-phase exfoliation on purple phosphorus crystals to obtain a dispersion of phosphorene nanosheets; S2, adding phytic acid to the dispersion of phosphorene nanosheets and mixing and stirring to obtain a dispersion of phytic acid-modified phosphorene nanosheets; S3, adding a metal salt to the dispersion of phytic acid-modified phosphorene nanosheets for solvothermal reaction, and obtaining phytic acid-induced purple phosphorus-metal phosphide powder after filtration, washing, and freeze-drying; S4, dispersing the phytic acid-induced purple phosphorus-metal phosphide powder in a solvent, adding a silver salt solution, and obtaining a purple phosphorus-metal phosphide-silver nanomaterial after photodeposition.

6. The preparation method of phytic acid-induced purple phosphorus-metal phosphide-silver nanoparticles according to claim 5, characterized in that, In the step 1), the solvent for liquid-phase exfoliation is N,N-dimethylacetamide or N,N-dimethylformamide, and the dosage ratio of purple phosphorus to the solvent is 0.5 - 2 mg / mL.

7. The preparation method of the phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial according to claim 5, wherein In the step 2), the dosage ratio of phytic acid to the dispersion of phosphorene nanosheets is 0.5 - 2 mg / mL; The specific process of mixing and stirring phytic acid and phosphorene nanosheets is as follows: first, treat in an ultrasonic water bath at 500 W for 0.2 - 1 hour, and then stir evenly for 8 - 16 hours.

8. The preparation method of the phytic acid-induced violet phosphorus-metal phosphide-silver nanomaterial according to claim 5, wherein In the step 3), the solvothermal reaction temperature is 100°C - 200°C, and the treatment time is 2 - 8 hours.

9. The preparation method of the phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial according to claim 5, characterized in that, In the step 4), the components of the mixed solvent are water, and triethanolamine, methanol, or ascorbic acid; the types of silver salts added are silver nitrate, silver fluoride, or silver chlorate, and the mass of silver ions contained in the silver salt solution is 1 wt% - 3 wt% of the mass of the phytic acid-induced purple phosphorus-metal phosphide.

10. Application of the phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial according to any one of claims 1 to 4, or the phytic acid-induced purple phosphorus-metal phosphide-silver nanomaterial prepared by the preparation method according to any one of claims 5 to 9 in the selective photocatalytic reduction to produce ethylene.

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