A high-efficiency recyclable amino black phosphorus / carbon dot / covalent organic framework ternary composite catalyst and a preparation method and application thereof

Abstract

The application discloses a high-efficiency recyclable amino black phosphorus / carbon dot / covalent organic framework ternary composite catalyst and a preparation method and application thereof, and belongs to the technical field of catalysts. The carbon dot is used as a reinforcing body, is loaded through a covalent organic framework, is mixed with amino black phosphorus nanosheets through a mechanical mixing electrostatic adsorption mode, and after a heterostructure is constructed, a nanocomposite catalyst with excellent photocatalytic effect can be prepared, and the nanocomposite catalyst is used as a photocatalyst. The composite catalyst is economic and environment-friendly, has excellent chemical stability and high-efficiency photodegradation performance, and is suitable for the field of photocatalysis.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to a high-efficiency recyclable aminated black phosphorus / carbon dot / covalent organic framework ternary composite catalyst as well as a preparation method and application thereof. BACKGROUND

[0002] In the field of industrial production, environmental friendliness and economic sustainability have always been the focus of attention, for example, photocatalytic hydrogen (H2) production and photocatalytic organic conversion, to generate value-added compounds in a sustainable and green way, avoid the consumption of non-renewable fossil fuels or high-energy reaction conditions, etc. As one of the most important intermediates in the synthesis of pesticides, drugs and bioactive molecules, imines have attracted the continuous attention and exploration of many researchers on their synthesis methods. However, in the traditional synthesis reaction of imines, acidic (or basic) and high-temperature reaction conditions are usually required to drive and catalyze, and the yield and product selectivity of these reactions are not ideal, there are various by-products, resulting in low imine yield, complex purification process and many other problems. The photocatalytic oxidative dehydrogenation coupling reaction of amines under pure oxygen (O2) atmosphere to prepare imines, which only requires light and pure oxygen environment, is more mild, lower cost and can greatly reduce the occurrence of side reactions, improve the yield of imines and reduce the difficulty of purification. The catalysts currently used for photocatalytic oxidative dehydrogenation coupling reaction of benzylamine mainly include metal-based photocatalysts (such as metal nanoparticles, metal oxides, metal sulfides, etc.), the preparation process of which often requires high temperature or strong acid and strong base environment, and the preparation process is complicated and dangerous, and the metal leaching phenomenon of the catalysts is inevitable during the subsequent long-term photocatalytic process, which makes the subsequent product utilization need to add an additional step of metal separation and purification. This not only further increases the cost, but also makes the catalyst difficult to recycle and difficult to handle, which is easy to cause metal pollution. Therefore, the design and development of non-metal-based photocatalysts with relatively high photocatalytic efficiency have important application prospects.

[0003] As a new type of semiconductor material, black phosphorus has a high theoretical specific capacity, fast carrier separation and migration rate, adjustable band gap, and low biological toxicity, and has good application prospects in energy storage batteries, catalysis, and medical carriers. Monolayer black phosphorus has two different directions in structure, armchair direction and zigzag direction. This special structure makes monolayer black phosphorus have significantly different physical properties in each direction. The layers of black phosphorus are fixed together by van der Waals force, which enables it to be exfoliated into a sheet structure of different thicknesses, and the band gap of black phosphorus can be adjusted from 0.3 eV to 2.0 eV by controlling the thickness of the black phosphorus sheet, so that it has an absorption range from visible light to infrared light. Thus, it has wide research and application potential in the fields of photocatalytic hydrogen production, photocatalytic nitrogen fixation, photocatalytic degradation of organic matter, and photocatalytic CO2 reduction. However, single black phosphorus material is easy to oxidize in the photocatalytic process, and the stability is poor, and the photo-generated electrons and holes are easy to recombine, which seriously limits the practical application of black phosphorus photocatalyst. Although researchers have proposed many methods to enhance the photocatalytic activity and improve the stability to solve the problem of easy recombination of photo-generated electrons and holes, including surface modification, covalent functionalization, etc., but it is still challenging to realize relatively efficient photocatalytic technology. As a carbon-based nanomaterial, carbon dots have low toxicity, simple and diverse preparation methods, strong light absorption capacity, and are an excellent charge transfer body, which has important application prospects in the field of photocatalysis. The size of carbon dots is usually less than 10 nm, and they are easily soluble in water or organic solvents, so single carbon dot material is difficult to separate in the photocatalytic process, which is not conducive to the purification of products and the recycling of carbon dots. Covalent organic framework is a kind of porous organic framework material polymerized by organic building units, which has a large specific surface area, a wide absorption spectrum range, and low biological harmfulness after design, and also has important application prospects in the field of photocatalysis. Single covalent organic framework has the problem of insufficient electrical conductivity, which limits the improvement of its photocatalytic efficiency.

[0004] In view of the above problems, it is necessary to study and prepare a non-metallic, low-toxicity, excellent photocatalytic performance, simple recycling process, and practical and green photocatalytic material.

[0005] Based on the above reasons, the present application is proposed. SUMMARY

[0006] Based on the above reasons, in view of the problems or defects in the prior art, the purpose of the present application is to provide an efficient recyclable aminated black phosphorus / carbon dots / covalent organic framework ternary composite catalyst and its preparation method and application, to solve or at least partially solve the above technical defects in the prior art: the novel aminated black phosphorus / carbon dots / covalent organic framework ternary composite catalyst prepared by the present application can be used for the oxidative dehydrogenation coupling reaction of benzylamine by aminating black phosphorus nanosheets and constructing a heterojunction structure between different materials to improve the stability and photocatalytic efficiency of the composite material.

[0007] In order to achieve one of the above purposes of the present application, the technical solution adopted by the present application is as follows:

[0008] A preparation method of an efficient recyclable aminated black phosphorus / carbon dots / covalent organic framework ternary composite catalyst, the method specifically comprises the following steps:

[0009] The aminated black phosphorus nanosheets, carbon dots and covalent organic framework are mixed according to the proportion, then a proper amount of anhydrous ethanol is added, the obtained mixture is mechanically ultrasonically compounded in an inert gas atmosphere and low temperature conditions for 1-2h, then centrifuged, washed and vacuum dried to obtain the aminated black phosphorus / carbon dots / covalent organic framework ternary composite catalyst.

[0010] Further, in the above technical solution, the mass ratio of the aminated black phosphorus nanosheets, carbon dots and covalent organic framework is 5:2:2-14:2:2.

[0011] Preferably, in the above technical solution, the mass ratio of the aminated black phosphorus nanosheets, carbon dots and covalent organic framework is 9:2:2.

[0012] Further, in the above technical solution, the amount of anhydrous ethanol is not specifically limited, as long as it can realize the complete and sufficient mixing of the solid mixture composed of aminated black phosphorus nanosheets, carbon dots and covalent organic framework. For example, in the preferred embodiment of the present application, the amount ratio of the solid mixture to anhydrous ethanol is (10-15) mass parts:5 volume parts; wherein the mass parts and volume parts are based on mg:mL.

[0013] Further, in the above technical solution, the inert gas includes any one of nitrogen or argon, etc. In the preferred embodiment of the present application, the inert gas used is nitrogen.

[0014] Further, in the above technical solution, in the preferred embodiment of the present application, the low temperature is preferably carried out in an ice water bath.

[0015] Further, in the above technical solution, the preparation method of the aminated black phosphorus nanosheets is as follows:

[0016] The black phosphorus nanosheet is uniformly dispersed in an N,N-dimethylformamide solution to obtain a black phosphorus nanosheet dispersion liquid; then, thionyl chloride and diethylenetriamine are sequentially added to the black phosphorus nanosheet dispersion liquid, and the obtained mixed reaction liquid is heated to 75-85 DEG C and kept constant temperature for 10-15 h under continuous stirring; after the reaction is completed, the obtained product is cooled to room temperature, centrifuged, washed, and vacuum dried to obtain the amino-functionalized black phosphorus nanosheet.

[0017] Preferably, in the above technical solution, the concentration of the N,N-dimethylformamide solution is 0.2-0.8 mg / mL.

[0018] Preferably, in the above technical solution, the concentration of the black phosphorus nanosheet dispersion liquid is 0.5-0.8 g / mL.

[0019] Preferably, in the above technical solution, the volume ratio of the black phosphorus nanosheet dispersion liquid to thionyl chloride and diethylenetriamine is 50:2:5.

[0020] Preferably, in the above technical solution, in the preferred embodiment of the present application, the reaction temperature is 80 DEG C, and the reaction time is 12 h.

[0021] Preferably, in the above technical solution, the black phosphorus nanosheet is prepared by sequentially ball milling black phosphorus crystals for 2-4 h, ultrasonic exfoliation for 4-8 h, centrifugation, and vacuum drying.

[0022] Further, in the above technical solution, the carbon dots are prepared by the following method:

[0023] The citric acid and ethylenediamine are mixed according to the ratio, then added to a polytetrafluoroethylene liner, and then transferred to a hydrothermal reaction kettle, the reaction kettle is heated to 180-200 DEG C and reacted for 5-6 h; after the reaction is completed, centrifugation, dialysis with a dialysis membrane with a molecular weight cutoff of 1-2 KDa, and drying are performed to obtain the carbon dots.

[0024] Preferably, in the above technical solution, the ratio of the amount of citric acid to ethylenediamine is (1-2) g:(335-670) μL.

[0025] Preferably, in the above technical solution, the dialysis time is 12-18 h.

[0026] Further, in the above technical solution, the covalent organic framework is prepared by the following method:

[0027] The benzotriazole, acrylic acid-N, N-dimethylaminoethyl ester, toluene, 1, 4-dioxane, and acetic acid solution are mixed according to the proportion, and the obtained mixed reactants are added into a polytetrafluoroethylene lining and then transferred into a hydrothermal synthesis reactor, and then the reactor is heated to 120-150 DEG C and reacted for 78-85 h; after the reaction is completed, the obtained product is centrifuged, washed, and vacuum dried, and then extracted for multiple times, and finally vacuum dried to obtain the covalent organic framework.

[0028] Preferably, in the technical scheme, the mass ratio of the benzotriazole to the acrylic acid-N, N-dimethylaminoethyl ester is (20-40):(27.4-54.8).

[0029] Preferably, in the technical scheme, the concentration of the acetic acid solution is 3-5 mol / L.

[0030] Preferably, in the technical scheme, the amount ratio of the benzotriazole to the toluene, 1, 4-dioxane, and acetic acid solution is (20-40) parts by mass:(0.5-1) parts by volume:(1.5-3) parts by volume:(0.2-0.4) parts by volume; wherein the mass and volume are based on mg:mL.

[0031] Preferably, in the technical scheme, the steps of centrifuging and washing include sequentially centrifuging and washing the obtained reaction product with deionized water, tetrahydrofuran, acetonitrile, and anhydrous ethanol.

[0032] Preferably, in the technical scheme, the step of extracting includes sequentially extracting with tetrahydrofuran, acetonitrile, acetone, and anhydrous ethanol, and each organic solvent extraction is performed for 3-4 h.

[0033] The second object of the present application is to provide an aminated black phosphorus / carbon dot / covalent organic framework ternary composite catalyst prepared by the above-mentioned method.

[0034] The third object of the present application is to provide an application of the aminated black phosphorus / carbon dot / covalent organic framework ternary composite catalyst prepared by the above-mentioned method in the oxidation dehydrogenation coupling reaction of benzylamine, the hydrogen production by photocatalysis, the CO2 reduction by photocatalysis, and the like.

[0035] The present application provides a photocatalyst for the oxidation dehydrogenation coupling reaction of benzylamine, which comprises the aminated black phosphorus / carbon dot / covalent organic framework ternary composite catalyst prepared by the above-mentioned method of the present application. The catalytic effect of the aminated black phosphorus / carbon dot / covalent organic framework ternary composite catalyst of the present application on the oxidation dehydrogenation coupling reaction of benzylamine can reach nearly complete catalysis within 12 h.

[0036] The roles of the raw materials used in the application are as follows:

[0037] (1) The role of the amino-modified black phosphorus nanosheet is: by controlling the exfoliation time to adjust the band gap of the black phosphorus nanosheet, the black phosphorus nanosheet has a light absorption range suitable for the wavelength of the light source; by modifying the surface of the black phosphorus nanosheet with amino groups, the active sites at the edges of the black phosphorus nanosheet are enhanced, and the black phosphorus nanosheet is prevented from reacting with oxygen or water, thereby enhancing the catalytic effect and the stability of the black phosphorus nanosheet, enhancing the quenching phenomenon of the carbon dots, inhibiting the energy loss caused by the emission of fluorescence by the carbon dots, and affecting the photocatalytic efficiency.

[0038] (2) The role of the carbon dots is: the carbon dots with high quantum yield form a heterojunction structure with the black phosphorus, inhibit the recombination of photo-generated electrons and holes of the black phosphorus, improve the photocatalytic efficiency, and have good photocatalytic efficiency themselves; the carbon dots form a synergistic effect with the black phosphorus to further improve the photocatalytic efficiency; and the good biocompatibility of the carbon dots facilitates the recycling and reuse of the catalyst.

[0039] (3) The role of the covalent organic framework is: a two-dimensional network structure is formed by connecting organic molecular units through covalent bonds; at least 8 organic molecular units are synthesized; a structure unit with a high nitrogen content is integrated into a covalent organic framework with the advantages of low framework density, high porosity, open pore structure, large specific surface area, etc.; the carbon dots can be loaded to more easily construct a better heterojunction structure, thereby promoting the photocatalytic reaction; and the covalent organic framework can form a P-N bond with the black phosphorus nanosheet to further maintain the stability of the black phosphorus nanosheet.

[0040] The application of the prepared efficient and environmentally friendly amino-modified black phosphorus / carbon dot / covalent organic framework ternary composite catalyst in the field of photocatalysis; the photocatalytic effect of the amino-modified black phosphorus nanosheet on the oxidative dehydrogenation coupling reaction of benzylamine in an acetonitrile system reaches 12.3% within 12 hours; the photocatalytic effect of the carbon dots on the oxidative dehydrogenation coupling reaction of benzylamine in an acetonitrile system reaches 41.2% within 12 hours; the photocatalytic effect of the covalent organic framework on the oxidative dehydrogenation coupling reaction of benzylamine in an acetonitrile system reaches 13.8% within 12 hours; and the catalytic effect of the amino-modified black phosphorus / carbon dot / covalent organic framework ternary composite catalyst is better than that of a single material, indicating that the heterojunction structure can effectively hinder the recombination of electrons and holes of the black phosphorus nanosheet and improve the photocatalytic performance thereof.

[0041] After the carbon dots are used as reinforcing bodies and loaded through the covalent organic framework, the carbon dots are mixed with the amino-modified black phosphorus nanosheet through mechanical mixing and electrostatic adsorption, and a nano-composite catalyst with excellent photocatalytic effect can be prepared after the heterojunction structure is constructed, and the nano-composite catalyst can be used as a photocatalyst.

[0042] Compared with the prior art, the application has the following beneficial effects:

[0043] (1) The high-efficiency recyclable amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst prepared by the method has the advantages that the amino black phosphorus nanosheet is aminoated through mechanical ultrasonic compounding, the stability of the amino black phosphorus nanosheet is enhanced, and the amino black phosphorus nanosheet, the carbon dots and the covalent organic framework are combined into a heterojunction structure through electrostatic and chemical bond effects, so that the recombination of photo-generated electrons and holes of the black phosphorus nanosheet in the photocatalysis process is reduced, the quenching phenomenon of the carbon dots is enhanced, the energy loss caused by fluorescence of the carbon dots is reduced, the utilization efficiency of the carbon dots and the black phosphorus nanosheet is increased through the loading of the covalent organic framework, and therefore the final conversion efficiency of 12 hours reaches 96.7%, which is much higher than that of a single component.

[0044] (2) The composite catalyst is prepared by loading the carbon dots on the covalent organic framework and then combining the amino black phosphorus nanosheet to form a heterojunction structure, and the amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst has the advantages of economy, environmental protection, excellent chemical stability and high photocatalytic performance, and is suitable for the field of photocatalysis.

[0045] (3) The carbon dots are well loaded on the covalent organic framework and attached to the surface of the amino black phosphorus nanosheet through mechanical mixing and electrostatic adsorption, so that the photocatalytic effect of the catalyst is improved, and the amino black phosphorus nanosheet is protected from excessive oxidation. The prepared photocatalyst is in a powder form, has a large number of active sites, strong adsorption energy, good reaction kinetics and extremely low biological toxicity, and is a composite catalyst with good catalytic efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the drawings needed in the following embodiment or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0047] Figure 1 It is a schematic diagram of the covalent organic framework structure prepared in Example 1.

[0048] Figure 2 It is an XRD graph of the black phosphorus nanosheet prepared in Example 1.

[0049] Figure 3 It is an SEM graph of the amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 1.

[0050] Figure 4 It is a photocatalytic cycle example graph of the amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 1.

[0051] Figure 5 The kinetic curve diagram of the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in application example 1. DETAILED DESCRIPTION

[0052] The purpose of the present application is to solve the problems of insufficient stability and easy recombination of photo-generated electrons and holes of existing black phosphorus-based photocatalysts. A preparation method of a ternary composite catalyst is proposed. The advantages of the catalyst are to improve the stability of black phosphorus nanosheets through surface modification and interfacial action, inhibit the recombination of photo-generated electrons and holes, improve the catalytic efficiency through the synergistic effect between different materials, and can be recycled and reused through a simple method. The specific preparation method is as follows:

[0053] The amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst is prepared. The composite catalyst uses covalent organic framework to load carbon dots and attach to the surface of black phosphorus nanosheets to form a heterojunction structure, thereby obtaining a high-efficiency and environmentally friendly photocatalyst product. Since no metal elements are introduced, metal toxicity and possible metal pollution in subsequent processing can be effectively avoided. At the same time, the elements used to prepare the composite catalyst are N, C, and P, which are abundant in nature. The raw materials are low-toxicity or non-toxic substances, which can minimize chemical pollution and recycling problems. The product meets the energy-saving and environmentally friendly requirements of photocatalysts, has high catalytic efficiency, and can be used for photocatalytic amine oxidation dehydrogenation coupling reaction in pure oxygen (O2) atmosphere, and can be recycled and reused after the catalytic reaction is completed.

[0054] The technical solutions of the present application are described in detail below through the accompanying drawings and specific examples. The following examples are further descriptions of the present application, but do not limit the scope of the present application.

[0055] The equipment and raw materials used in the present application can be purchased from the market or are commonly used in the art. The methods in the following examples are conventional methods in the art, unless otherwise specified.

[0056] Example 1

[0057] The preparation method of an amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst in this example is as follows:

[0058] Step one, the preparation method of amino-phosphorene nanosheets is as follows:

[0059] (1) Preparation of black phosphorus nanosheets

[0060] The black phosphorus crystal (99.998%) and stainless steel balls were loaded into a hardened steel bottle with a ball-to-powder mass ratio of 500:1 and sealed in an argon-filled glove box. The milling process used high-energy planetary milling at a speed of 500 r / min. After 3 h of ball milling, the powder was mixed with anhydrous ethanol in a volume ratio of 2:3 to prepare a black phosphorus powder dispersion. The black phosphorus powder dispersion was ultrasonically exfoliated below 5°C for 8 h by a cell crusher at a power of 200 W. After the exfoliation was completed, the dispersion was centrifuged at a speed of 2000 r / min for 20 min. The supernatant was again centrifuged at a speed of 8500 r / min for 30 min. The precipitate was vacuum dried at 60°C to obtain black phosphorus nanosheets in powder form.

[0061] (2) Preparation of amino-functionalized black phosphorus nanosheets

[0062] The black phosphorus nanosheets prepared in step (1) were dispersed in a N,N-dimethylformamide solution (prepared by adding N,N-dimethylformamide to anhydrous ethanol) with a concentration of 0.5 mg / mL to obtain a black phosphorus nanosheet dispersion. Then, thionyl chloride (2.0 mL) and diethylenetriamine (5.0 mL) were added to the above dispersion, respectively, with a volume ratio of black phosphorus nanosheet dispersion:thionyl chloride:diethylenetriamine of 50:2:5. The resulting mixed reaction solution was heated to 80°C and continuously stirred for 12 h. After the reaction was completed, the heating was stopped and the solution was cooled to room temperature. The resulting sample was collected and washed with N,N-dimethylformamide and anhydrous ethanol at 10000 r / min for 10 min, respectively, for three times until the supernatant was clear. The amino-functionalized black phosphorus nanosheets were obtained after vacuum drying at 60°C.

[0063] Step two, the preparation method of the covalent organic framework is as follows:

[0064] Take 20 mg of phenyltriazole (purity 99.9%), 27.4 mg of acrylic acid-N, N-dimethylamine ethyl ester (purity 99.9%), 0.5 mL of toluene (purity 99.9%), 1.5 mL of 1, 4-dioxane (purity 99.9%), 0.2 mL of 3 mol / L acetic acid solution (prepared by adding acetic acid to deionized water) in a polytetrafluoroethylene-lined hydrothermal synthesis reactor, mix well, then put the reactor into the oven and react at 120°C for 78h, after the reaction is completed, use deionized water, tetrahydrofuran (purity 99.9%), acetonitrile (purity 99.9%), anhydrous ethanol (purity 99.9%) respectively at 8000r / min speed centrifugation 8min, after centrifugation, vacuum drying of the sample, first using tetrahydrofuran by soxhlet extraction method extraction 6h, then using acetonitrile by soxhlet extraction method extraction 3h, then using acetone (purity 99.9%) by soxhlet extraction method extraction 3h, finally using anhydrous ethanol by soxhlet extraction method extraction 3h, the final extraction product after vacuum drying at 40°C to prepare covalent organic framework.

[0065] Step three, the preparation method of carbon dots is as follows:

[0066] Put 2g of citric acid and 670μL of ethylenediamine into a polytetrafluoroethylene-lined hydrothermal synthesis reactor, then put the reactor into the oven and react at 180°C for 6h, after the reaction is completed, take out the sample and centrifuge at 7000r / min for 10min, after centrifugation, the sample is dialyzed using a dialysis membrane with a molecular weight cutoff of 1KDa for 12h, then rotary evaporation at 80°C, finally vacuum drying at 60°C to obtain carbon dots.

[0067] Mix 10mg of the amino black phosphorus nanosheets prepared in step one, the covalent organic framework prepared in step two, and the carbon dots prepared in step three in a mass ratio of (9:2:2), and place them in 5mL of anhydrous ethanol. Under nitrogen protection and ice bath conditions, mechanically ultrasonic composite the sample at 200W for 1.5h, then centrifuge with a high-speed centrifuge and wash with anhydrous ethanol, then vacuum dry the precipitate and grind to obtain the sample.

[0068] Figure 1 The schematic diagram of the covalent organic framework structure prepared in Example 1; Figure 2 The XRD pattern of the black phosphorus nanosheets ultrasonically exfoliated in Example 1, the peak is sharp and narrow, indicating that the black phosphorus nanosheets have good crystallinity and high purity; Figure 3 The SEM image of the amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 1, the carbon dots loaded on the covalent organic framework form clusters on the black phosphorus nanosheets, indicating the successful construction of the heterojunction structure.

[0069] Example 2

[0070] The preparation method of the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst of this embodiment is as follows:

[0071] Step one, the preparation method of the amino-phosphorene nanosheet is as follows:

[0072] (1) Preparation of phosphorene nanosheet

[0073] Take phosphorene crystals (99.998%) and stainless steel balls with a ball-to-powder mass ratio of 500:1 and seal them in a hardened steel bottle filled with argon in a glove box. High-energy planetary milling is used in the milling process at a speed of 500 r / min. After ball milling for 3 h, the powder is mixed with anhydrous ethanol to form a phosphorene powder dispersion liquid with a volume ratio of 2:3. The phosphorene powder dispersion liquid is ultrasonically exfoliated below 5°C for 4 h by a cell crusher at a power of 200 W. After the exfoliation is completed, the dispersion liquid is centrifuged at a speed of 2000 r / min for 20 min. The supernatant is again centrifuged at a speed of 8500 r / min for 30 min. The precipitate is vacuum dried at 60°C to obtain the phosphorene nanosheet in powder form.

[0074] (2) Preparation of amino-phosphorene nanosheet

[0075] The phosphorene nanosheet prepared in step (1) is dispersed in a N,N-dimethylformamide solution (configuration method same as example 1) with a concentration of 0.5 mg / mL to obtain a phosphorene nanosheet dispersion liquid. Then, thionyl chloride and diethylenetriamine are added to the above dispersion liquid, respectively, with a volume ratio of 50:2:5. The obtained mixed reaction liquid is heated to 80°C and continuously stirred for 12 h. After the reaction is completed, the heating is stopped and the temperature is cooled to room temperature. The obtained sample is collected and washed with N,N-dimethylformamide and anhydrous ethanol under the condition of 10000 r / min for 10 min, respectively, and washed three times until the supernatant is clear. The amino-phosphorene nanosheet is obtained after vacuum drying at 60°C.

[0076] Step two, the preparation method of the covalent organic framework is as follows:

[0077] Take 20 mg of benzotriazole (purity 99.9%), 27.4 mg of acrylic acid-N, N- dimethylaminoethyl ester (purity 99.9%), 0.5 mL of toluene (purity 99.9%), 1.5 mL of 1,4-dioxane (purity 99.9%), 0.2 mL of acetic acid solution (concentration 3 mol / L, preparation method same as example 1) in a polytetrafluoroethylene lined hydrothermal synthesis reactor, mix well, then put the reactor into the oven and react at 120℃ for 78h, after the reaction is completed, use deionized water, tetrahydrofuran (purity 99.9%), acetonitrile (purity 99.9%), anhydrous ethanol (purity 99.9%) respectively at 8000-9000r / min speed centrifugation 8min, after centrifugation, vacuum drying of the sample, first using tetrahydrofuran by soxhlet extraction method extraction 6h, then using acetonitrile (purity 99.9%) by soxhlet extraction method extraction 3h, then using acetone (purity 99.9%) by soxhlet extraction method extraction 3h, finally using anhydrous ethanol (purity 99.9%) by soxhlet extraction method extraction 3h, the final extraction product after vacuum drying at 40℃ to prepare covalent organic framework.

[0078] Step three, the preparation method of carbon dots is as follows:

[0079] Put 2g of citric acid and 670μL of ethylenediamine into a polytetrafluoroethylene lined hydrothermal synthesis reactor, then put the reactor into the oven and react at 180℃ for 6h, after the reaction is completed, take out the sample and centrifuge at 7000r / min for 10min, after centrifugation, the sample is dialyzed using dialysis membrane with molecular weight cutoff of 1KDa for 12h, then rotary evaporation at 80℃, finally vacuum drying at 60℃ to obtain carbon dots.

[0080] Take 10mg of the aminated black phosphorus nanosheet prepared in step one, the covalent organic framework prepared in step two, and the carbon dots prepared in step three, mix them uniformly in a mass ratio of 9:2:2, and place them in 5mL of anhydrous ethanol. Under the conditions of nitrogen protection and ice bath, the sample is mechanically ultrasonicated at 200W for 1.5h, then centrifuged with a high-speed centrifuge and washed with anhydrous ethanol. After vacuum drying, grinding, the sample is prepared.

[0081] Example 3

[0082] The preparation method of the amino-phosphorene / carbon dot / covalent organic framework ternary composite catalyst of this embodiment, while keeping the preparation process of the amino-phosphorene nanosheet, covalent organic framework, and carbon dot of embodiment 1 unchanged, only changes the mass ratio of the amino-phosphorene nanosheet to prepare the catalyst by the same synthesis method. 10 mg of powder of the amino-phosphorene nanosheet, covalent organic framework, and carbon dot prepared in embodiment 1 are uniformly mixed in a mass ratio of (14:2:2), and then placed in 5 mL of anhydrous ethanol. The sample is mechanically ultrasonicated under nitrogen protection at a power of 200 W for 1.5 h, then centrifuged with a high-speed centrifuge, washed with anhydrous ethanol, and then the precipitate is vacuum dried. After grinding, the sample is prepared.

[0083] Embodiment 4

[0084] The preparation method of the amino-phosphorene / carbon dot / covalent organic framework ternary composite catalyst of this embodiment, while keeping the preparation process of the amino-phosphorene nanosheet, covalent organic framework, and carbon dot of embodiment 1 unchanged, only changes the mass ratio of the amino-phosphorene nanosheet to prepare the catalyst by the same synthesis method. 10 mg of powder of the amino-phosphorene nanosheet, covalent organic framework, and carbon dot prepared in embodiment 1 are uniformly mixed in a mass ratio of (5:2:2), and then placed in 5 mL of anhydrous ethanol. The sample is mechanically ultrasonicated under nitrogen protection at a power of 200 W for 1.5 h, then centrifuged with a high-speed centrifuge, washed with anhydrous ethanol, and then the precipitate is vacuum dried. After grinding, the sample is prepared.

[0085] Embodiment 5

[0086] The preparation method of the amino-phosphorene / carbon dot / covalent organic framework ternary composite catalyst of this embodiment, while keeping the preparation process of the amino-phosphorene nanosheet, covalent organic framework, and carbon dot of embodiment 1 unchanged, only changes the mass ratio of the amino-phosphorene nanosheet to prepare the catalyst by the same synthesis method. 10 mg of powder of the amino-phosphorene nanosheet, covalent organic framework, and carbon dot prepared in embodiment 1 are uniformly mixed in a mass ratio of (9:2:1), and then placed in 5 mL of anhydrous ethanol. The sample is mechanically ultrasonicated under nitrogen protection at a power of 200 W for 1.5 h, then centrifuged with a high-speed centrifuge, washed with anhydrous ethanol, and then the precipitate is vacuum dried. After grinding, the sample is prepared.

[0087] Embodiment 6

[0088] The preparation method of the amino-phosphorene / carbon dot / covalent organic framework ternary composite catalyst of the embodiment is prepared by changing only the mass ratio of the carbon dots through the same synthesis method without changing the preparation process of the amino-phosphorene nanosheet, the covalent organic framework, and the carbon dot of embodiment 1. 10 mg of the amino-phosphorene nanosheet, the covalent organic framework, and the carbon dot prepared in embodiment 1 are uniformly mixed in a mass ratio of (9:2:3), and are placed in 5 mL of anhydrous ethanol. The sample is mechanically ultrasonicated under nitrogen protection at a power of 200 W for 1.5 h, and then is centrifuged by using a high-speed centrifuge and is washed by using anhydrous ethanol. Subsequently, the precipitate is vacuum dried, and the sample is prepared after grinding.

[0089] Comparative example 1

[0090] The preparation method of the amino-phosphorene catalyst of the comparative example is prepared by using only the amino-phosphorene nanosheet through the same synthesis method without changing the preparation process of the amino-phosphorene nanosheet of embodiment 1. 10 mg of the amino-phosphorene nanosheet prepared in embodiment 1 is placed in 5 mL of anhydrous ethanol. The sample is mechanically ultrasonicated under nitrogen protection at a power of 200 W for 1.5 h, and then is centrifuged by using a high-speed centrifuge and is washed by using anhydrous ethanol. Subsequently, the precipitate is vacuum dried, and the sample is prepared after grinding.

[0091] Comparative example 2

[0092] The preparation method of the carbon dot catalyst of the comparative example is prepared by using only the carbon dot through the same synthesis method without changing the preparation process of the carbon dot of embodiment 1. 10 mg of the carbon dot prepared in embodiment 1 is placed in 5 mL of anhydrous ethanol. The sample is mechanically ultrasonicated under nitrogen protection at a power of 200 W for 1.5 h, and then is centrifuged by using a high-speed centrifuge and is washed by using anhydrous ethanol. Subsequently, the precipitate is vacuum dried, and the sample is prepared after grinding.

[0093] Comparative example 3

[0094] The preparation method of the covalent organic framework catalyst of the comparative example is prepared by using only the covalent organic framework through the same synthesis method without changing the preparation process of the covalent organic framework of embodiment 1. 10 mg of the covalent organic framework prepared in embodiment 1 is placed in 5 mL of anhydrous ethanol. The sample is mechanically ultrasonicated under nitrogen protection at a power of 200 W for 1.5 h, and then is centrifuged by using a high-speed centrifuge and is washed by using anhydrous ethanol. Subsequently, the precipitate is vacuum dried, and the sample is prepared after grinding.

[0095] Application example 1

[0096] The amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 1 was used for photocatalytic oxidation dehydrogenation coupling reaction of benzylamine, and the specific steps were as follows:

[0097] 10 mg of the catalyst sample prepared in Example 1 was placed in a 10 mL glass test tube, 20 μL of benzylamine and 4 mL of acetonitrile were added, and a magnetic sonicator was added. The mixture was mixed by ultrasonic at a power of 200 W at a water bath temperature of 50°C for 20 min. After mixing, the glass test tube was blown with oxygen for 1 min, the reaction system was kept closed, and then stirred and irradiated under a light source of 30 W power and 365 nm wavelength for 12 h.

[0098] Application Example 2

[0099] The application method used in this application example was basically the same as that used in Application Example 1, and the only difference was that the catalyst sample used in this application example was the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 2.

[0100] Application Example 3

[0101] The application method used in this application example was basically the same as that used in Application Example 1, and the only difference was that the catalyst sample used in this application example was the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 3.

[0102] Application Example 4

[0103] The application method used in this application example was basically the same as that used in Application Example 1, and the only difference was that the catalyst sample used in this application example was the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 4.

[0104] Application Example 5

[0105] The application method used in this application example was basically the same as that used in Application Example 1, and the only difference was that the catalyst sample used in this application example was the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 5.

[0106] Application Example 6

[0107] The application method used in this application example was basically the same as that used in Application Example 1, and the only difference was that the catalyst sample used in this application example was the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 6.

[0108] Comparative Application Example 1

[0109] The application method used in this comparative application example is basically the same as that used in application example 1, and the only difference is that the catalyst sample used in this comparative application example is the aminated black phosphorus catalyst prepared in comparative example 1.

[0110] Comparative application example 2

[0111] The application method used in this comparative application example is basically the same as that used in application example 1, and the only difference is that the catalyst sample used in this comparative application example is the carbon dot catalyst prepared in comparative example 2.

[0112] Comparative application example 3

[0113] The application method used in this comparative application example is basically the same as that used in application example 1, and the only difference is that the catalyst sample used in this comparative application example is the covalent organic framework catalyst prepared in comparative example 3.

[0114] Comparative example

[0115] 20 μL of benzylamine and 4 mL of acetonitrile were placed in a glass test tube, and a magnetic sub was added. The mixture was mixed by ultrasonic at a power of 200 W in a water bath at a temperature below 50 °C for 20 min. After mixing, the glass test tube was blown with oxygen for 1 min, and the reaction system was kept closed. The mixture was stirred and irradiated under a light source with a power of 30 W and a wavelength of 365 nm for 12 h.

[0116] Test result analysis:

[0117] The difference between application example 1 and application example 2 is that the ultrasonic time of the added aminated black phosphorus nanosheet is different. As shown in Table 1, the system in which the aminated black phosphorus nanosheet with an ultrasonic time of 8 h is added in application example 1 can effectively photocatalyze the oxidative dehydrogenation coupling reaction of benzylamine, while the degradation effect of the system in application example 2 in which the aminated black phosphorus nanosheet with an ultrasonic time of 4 h is added is greatly reduced. Therefore, it is concluded that the ultrasonic time of the aminated black phosphorus nanosheet has a great influence on the photocatalytic effect.

[0118] The difference between application example 1, application example 3 and application example 4 is that the content of the aminated black phosphorus nanosheet added in the composite catalyst. The purpose of formulating this scheme is to analyze the optimal aminated black phosphorus nanosheet ratio of the composite catalyst. By changing the content of the aminated black phosphorus nanosheet, the mass fraction of the other two materials is also changed. In addition to proving that 9 / 13 (specifically referring to the mass ratio of the aminated black phosphorus nanosheet in the composite catalyst) is the optimal aminated black phosphorus nanosheet ratio, it further proves that the ternary composite catalyst of aminated black phosphorus / carbon dots / covalent organic framework can effectively catalyze the oxidative dehydrogenation coupling reaction of benzylamine under the condition of 356 nm light irradiation.

[0119] The difference between application example 1, application example 5 and application example 6 is the content of carbon dots added in the composite catalyst. The purpose of this scheme is to analyze the optimal carbon dot ratio of the composite catalyst. By changing the content of carbon dots, the mass fraction of the other two materials is also changed. In addition to proving that 2 / 13 (specifically, the mass ratio of carbon dots in the composite catalyst) is the optimal carbon dot ratio, it is further proved that the amino black phosphorus / carbon dot / covalent organic framework ternary composite catalyst can effectively catalyze the oxidative dehydrogenation coupling reaction of benzylamine under the condition of 356 nm light irradiation.

[0120] The difference between comparative application example 1, comparative application example 2 and comparative application example 3 is the component of the catalyst. According to the data in Table 1, the catalytic effect of the three material monomers under the condition of 365 nm light irradiation for 12 h is not good, which is less than 50%. At the same time, it is further illustrated that the generation of heterojunction structure and the catalytic effect of the amino black phosphorus / carbon dot / covalent organic framework ternary composite catalyst.

[0121] The difference between the control example and other application examples and comparative application examples is whether to add a catalyst. By excluding the influence of a series of processes that may cause self-catalysis of benzylamine due to time, temperature, ultrasonic, stirring and the like, the credibility and accuracy of the results of other schemes are further increased.

[0122] The specific calculation formula of the benzylamine catalytic conversion rate recorded in Table 1 and Table 2 is as follows:

[0123]

[0124] Table 1 Benzylamine catalytic conversion rate in different application examples

[0125] Scheme Amount of benzylamine added before the reaction / μmol Amount of benzylamine remaining after the reaction / μmol Conversion / % Application Example 1 4.38 0.14 96.7 Application Example 2 4.38 2.12 51.7 Application Example 3 4.38 2.42 44.8 Application Example 4 4.38 2.03 53.6 Application Example 5 4.38 1.55 64.7 Application Example 6 4.38 1.42 97.6 Comparative Application Example 1 4.38 3.84 12.3 Comparative Application Example 2 4.38 2.58 41.2 Comparative Application Example 3 4.38 3.78 13.8 Comparative Example 4.38 4.09 6.7

[0126] Table 2 Kinetic test of benzylamine catalytic conversion rate in application example 1

[0127] Reaction time / h Amount of benzylamine added before the reaction / μmol Amount of benzylamine remaining after the reaction / μmol Conversion / % 2 4.38 3.07 29.9 4 4.38 2.56 41.6 6 4.38 1.79 59.1 8 4.38 1.19 72.8 10 4.38 0.63 85.6 12 4.38 0.15 96.7

[0128] Photocatalytic cycle stability test:

[0129] The photocatalytic cycle experiment is that after the first cycle experiment of the ternary composite catalyst sample of example 1 is completed, the sample is washed by centrifugation with anhydrous ethanol for three times, and then 10 mg of the sample is taken after vacuum drying at 60°C. The second cycle experiment is carried out under the reaction conditions of application example 1. Finally, the third cycle experiment is carried out by the same steps. Each cycle experiment is repeated to prepare multiple samples to ensure that enough samples can be provided for the next cycle experiment, and 4 samples are selected from the multiple samples to take out the reaction solution after the required time for testing by a liquid chromatograph to obtain experimental data.

[0130] Figure 4For the efficiency graph of the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in Example 1, it can be seen that after three cycles of experiments in the same step, the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst still has a catalytic effect of more than 60%, proving its good stability.

[0131] Figure 5 For the kinetic curve graph of the amino-phosphorene / carbon dots / covalent organic framework ternary composite catalyst prepared in Application Example 1; the experiment of Application Example 1 was repeated 6 times, and 6 groups of experiments were sampled at reaction times of 2h, 4h, 6h, 8h, 10h and 12h respectively and no repeated sampling, and the experimental data of the 6 samples were obtained by liquid chromatograph to draw the kinetic curve graph. It can be seen that the catalytic effect curve rises smoothly, the catalytic effect at 2h is 29.9%, the catalytic effect at 4h is 41.6%, the catalytic effect at 6h is 59.1%, the catalytic effect at 8h is 72.8%, the catalytic effect at 10h is 85.6%, and the catalytic effect at 12h is 96.7%, close to complete catalysis. The average catalytic rate in the first 6h is close to 9.9%, the average catalytic rate in the first 10h is close to 8.6%, and the average catalytic rate in 12h is close to 8.1%, proving that the decrease of the concentration of the reactants to a certain extent will lead to the decrease of the catalytic effect, but the average minimum catalytic effect per hour is still more than 8%, and the average maximum catalytic effect can reach more than 10%, proving its good catalytic effect.

[0132] For those skilled in the art, the present application is not limited to the details of the above exemplary embodiments, and changes, modifications, substitutions, etc. can be made to realize the manner of the present application in other equivalent forms without departing from the spirit or principle of the present application. Therefore, the embodiments of the present application are exemplary and non-limiting. The scope of the present application should be defined by the appended claims rather than the above description, and all modifications and improvements to the technical solutions of the present application falling within the meaning and scope of the equivalent elements of the claims should fall within the protection scope determined by the claims of the present application.

Claims

1. A method for preparing a highly efficient and recyclable ternary composite catalyst of aminated black phosphorus / carbon dot / covalent organic framework, characterized in that: The method specifically comprises the following steps: The amino black phosphorus nanosheet, carbon dots and covalent organic framework are mixed according to the proportion, then appropriate amount of anhydrous ethanol is added, the obtained mixture is mechanically ultrasonic compounded for 1-2 h under inert gas atmosphere and low temperature condition, and then centrifuged, washed and vacuum dried to obtain the amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst. The mass ratio of the amino black phosphorus nanosheet, carbon dots and covalent organic framework is 5:2:2-14:2:2, and the low temperature condition is ice water bath condition. The preparation method of the covalent organic framework is as follows: The benzotriazole, acrylic acid-N,N-dimethylaminoethyl ester, toluene, 1,4-dioxane and acetic acid solution are mixed according to the proportion, the obtained mixed reactants are transferred into a polytetrafluoroethylene liner and then into a hydrothermal synthesis reaction kettle, the reaction kettle is heated to 120-150 DEG C and reacted for 78-85 h, after the reaction, the obtained product is centrifuged for multiple times, washed, vacuum dried, extracted for multiple times in sequence and finally vacuum dried to obtain the covalent organic framework, and the mass ratio of the benzotriazole to the acrylic acid-N,N-dimethylaminoethyl ester is (20-40):(27.4-54.8).

2. The method of claim 1, wherein: The preparation method of the amino black phosphorus nanosheet is as follows: The black phosphorus nanosheet is uniformly dispersed in an N,N-dimethylformamide solution to obtain a black phosphorus nanosheet dispersion liquid, then the black phosphorus nanosheet dispersion liquid is sequentially added with thionyl chloride and diethylenetriamine, the obtained mixed reaction liquid is heated to 75-85 DEG C and continuously stirred for 10-15 h, after the reaction, the obtained product is cooled to room temperature, centrifuged, washed and vacuum dried to obtain the amino black phosphorus nanosheet.

3. The method of claim 2, wherein: The volume ratio of the black phosphorus nanosheet dispersion liquid to thionyl chloride and diethylenetriamine is 50:2:

5.

4. The method of claim 1, wherein: The preparation method of the carbon dots is as follows: The citric acid and ethylenediamine are uniformly mixed according to the proportion, then transferred into a polytetrafluoroethylene liner and then into a hydrothermal reaction kettle, the reaction kettle is heated to 180-200 DEG C and reacted for 5-6 h, after the reaction, centrifuged, dialyzed with a dialysis membrane with a molecular weight cut-off of 1-2 KDa and dried to obtain the carbon dots.

5. The method of claim 4, wherein: The dosage ratio of the citric acid to the ethylenediamine is (1-2) g:(335-670) μL.

6. The amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst prepared by the preparation method in any one of claims 1-5.

7. The application of the amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst prepared by the preparation method in any one of claims 1-5 in a photocatalytic oxidative dehydrogenation coupling reaction of benzylamine, photocatalytic hydrogen production or photocatalytic CO2 reduction.

8. A photocatalyst for photocatalytic oxidative dehydrogenative coupling of benzylamine, characterized by: The amino black phosphorus / carbon dots / covalent organic framework ternary composite catalyst prepared by the preparation method in any one of claims 1-5.

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