CN112811398A - Method for preparing hydrogen peroxide by using enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst - Google Patents
Method for preparing hydrogen peroxide by using enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst Download PDFInfo
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- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 title claims abstract description 133
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- C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
- C01B15/01—Hydrogen peroxide
- C01B15/022—Preparation from organic compounds
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/24—Nitrogen compounds
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- B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
- B01J31/02—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides
- B01J31/06—Catalysts comprising hydrides, coordination complexes or organic compounds containing organic compounds or metal hydrides containing polymers
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Abstract
The invention discloses a method for preparing hydrogen peroxide by using an enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst. The adopted composite photocatalyst has the advantages of multiple reactive active sites, wide light absorption range, low electron-hole pair recombination rate, good photocatalytic performance, good stability, environmental friendliness and the like, when the composite photocatalyst is used for preparing hydrogen peroxide, the yield can reach 880.494 mu mol/L within 1h, and can still reach 861.445 mu mol/L after five times of circulation, and the composite photocatalyst has the advantages of simple method, high preparation efficiency, high yield and the like, can be used for preparing the hydrogen peroxide on a large scale, and is beneficial to industrial application.
Description
Technical Field
The invention belongs to the technical field of material preparation and environmental catalysis, relates to a preparation method of hydrogen peroxide, and particularly relates to a method for preparing hydrogen peroxide by using an enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst.
Background
With the development of modern industry, the problems of energy crisis and environmental pollution become more serious, wherein the shortage of energy and environmental deterioration are major problems facing and urgently waiting for solving in 21 st century. Therefore, the utilization of new energy and the control of environmental pollution have important significance for the national sustainable development strategy. The photocatalysis technology has the advantages of low cost, no pollution, high efficiency and the like, and has wide application prospect in the aspects of energy storage, conversion and environmental protection.
The carbon nitride is composed of two elements of carbon and nitrogen, and has the advantages of abundant element reserves, wide sources, simple and convenient synthesis method, good economy and easy obtainment. In addition, carbon nitride has good visible light response capability and high stability, so that the application of the carbon nitride in the field of visible light photocatalysis is concerned. However, the monomer carbon nitride also has the non-negligible defects, and the photocatalytic performance is not remarkable due to the defects of small specific surface area, high electron-hole recombination rate, low quantum efficiency, low utilization rate of visible light and the like. Therefore, the large-scale application of graphite-phase carbon nitride semiconductors in the fields of energy and environmental photocatalytic research is severely limited.
In recent years, in order to expand the light absorption capacity of carbon nitride and improve the photocatalytic performance of carbon nitride, researchers modify carbon nitride by adopting different methods, and the traditional modification method mainly comprises doping of metal elements or nonmetal elements, morphology control, semiconductor heterojunction construction and the like. The method is a better modification method, mainly means that one or more semiconductors with proper band gaps are compounded through CN, the advantages of light absorption of respective energy band structures can be combined, and the response of the semiconductor heterojunction to a large-anode spectrum is widened and increased; and meanwhile, a binary or multi-element heterostructure is constructed, so that the potential of a valence band and a conduction band can be further improved. The non-metal semiconductor heterojunction has the advantages of low price, environmental protection and the like, so the non-metal semiconductor heterojunction is widely concerned, but the existing non-metal carbon nitride-based photocatalytic hydrogen peroxide production material still has the defects of difficult synthesis control, low yield and the like, and is not beneficial to large-scale production. For example, the prior patent discloses that the carbon fiber interpenetrating micro-heterojunction carbon nitride photocatalyst can be used for preparing hydrogen peroxide under visible light photocatalysis, the stripping process of the method by using oxygen etching is difficult to control, and flaky g-C with uniform appearance is difficult to obtain in large-scale production3N4And the yield is still low relative to the hydrogen peroxide production time of 6 h.
Covalent organic frameworks are a class of porous crystalline organic materials that can integrate customized organic monomers into extended crystalline frameworks like molecular edition "le gao" building blocks, thereby enabling their use in catalysis, environmental remediation, and biologically related applications. In the aspect of photoresponse, the two-dimensional COF material has the advantages of incomparable property, and the periodic two-dimensional single-molecule framework has obvious electronic stacking through long-range ordered uniaxial accumulation between planes, so that electrons can be transferred in covalent sheet layers and also can be transferred between layers, and the improvement of the photocatalytic performance is facilitated. By utilizing the excellent visible light response capability and photo-generated electron transfer capability of the photocatalyst, the photo-response range of the photocatalyst can be effectively expanded, the separation of photo-generated charges is promoted, and the photocatalyst has a good application prospect in the field of photocatalysis. However, the existing covalent organic framework/carbon nitride composite material has poor crystallinity, so the structure is easy to dissociate in the process of photocatalytic reaction. Therefore, how to effectively overcome the problems is to obtain the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst which has the advantages of more reaction active sites, wide light absorption range, low recombination rate of electron-hole pairs, good photocatalytic performance, good stability and environmental protection, and has important significance for improving the preparation efficiency and the yield of the hydrogen peroxide.
Disclosure of Invention
The invention aims to solve the technical problem of the prior art and provides a method for preparing hydrogen peroxide by using an enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, which has high preparation efficiency and high yield.
In order to solve the technical problems, the invention adopts the following technical scheme:
a method for preparing hydrogen peroxide by using an enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst comprises the following steps: mixing an enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst with an electron donor solution for photocatalytic reaction to obtain hydrogen peroxide; the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst comprises an enol-ketone covalent organic framework and graphite-phase carbon nitride, wherein the enol-ketone covalent organic framework is loaded on the surface of the graphite-phase carbon nitride.
In the method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst, the loading capacity of the enol-ketone covalent organic framework is 1-25% of the mass of the graphite-phase carbon nitride; the graphite phase carbon nitride is in a lamellar shape; the enol-ketone covalent organic framework is in a fiber stick shape.
In the method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst, the load capacity of the enol-ketone covalent organic framework is 3-15% of the mass of the graphite-phase carbon nitride.
In the above method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst is further improved, and comprises the following steps:
s1, ultrasonically dispersing graphite-phase carbon nitride into dimethyl sulfoxide to obtain graphite-phase carbon nitride dispersion liquid;
s2, mixing the graphite-phase carbon nitride dispersion liquid obtained in the step S1 with the enol-ketone covalent organic framework, performing ultrasonic treatment, and stirring to obtain the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst.
In step S1, the graphite-phase carbon nitride is prepared by calcining melamine as a precursor; the preparation method of the graphite phase carbon nitride comprises the following steps: heating melamine to 500-600 ℃ at the heating rate of 1-5 ℃/min, preserving heat for 3-6 h, cooling, and grinding to obtain the graphite phase carbon nitride.
In step S2, the enol-ketone covalent organic framework is prepared by taking melamine and 2,4, 6-trihydroxybenzene-1, 3, 5-trimethylaldehyde as raw materials and performing solvothermal reaction in a mixed solution system of N, N-dimethylacetamide and dimethylsulfoxide.
In the above method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst, the preparation method of the enol-ketone covalent organic framework is further improved, and comprises the following steps: dispersing melamine and 2,4, 6-trihydroxybenzene-1, 3, 5-trimethyl aldehyde in a mixed solution of N, N-dimethylacetamide and dimethyl sulfoxide, adding glacial acetic acid, carrying out solvothermal reaction at 100-150 ℃ for 1-4 d, and filtering to obtain an enol-ketone covalent organic framework; the molar ratio of the melamine to the 2,4, 6-trihydroxybenzene-1, 3, 5-trimethyl aldehyde is 2-1: 1-2; (ii) a The volume ratio of the N, N-dimethylacetamide to the dimethyl sulfoxide to the glacial acetic acid is 2: 1: 0.01-0.1; the concentration of the glacial acetic acid is 3M-6M.
In the above method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, the step S1 is further improved, wherein the ultrasonic dispersion is performed at a temperature of 20-45 ℃; the ultrasonic dispersion time is 0.5-3 h.
In the above method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, the further improvement is that in step S2, the ultrasonic treatment is performed at a temperature of 20 ℃ to 45 ℃; the ultrasonic time is 0.5 h-3 h; the stirring is carried out at the temperature of 20-45 ℃; the stirring time is 12-36 h.
In the method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst, the addition amount of the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst is further improved, and 0.5 g-1.5 g of the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst is added into each liter of the electron donor solution.
In the above method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, the electron donor solution is a mixed solution of an electron donor and water; the volume ratio of the electron donor to the water is 1: 5-9; the electron donor is at least one of isopropanol, triethanolamine, ethanol, benzyl alcohol, formic acid, methanol and ethylene diamine tetraacetic acid.
In the method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst, the volume ratio of the electron donor to the water is 1: 9.
The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst is further improved, and the time of the photocatalytic reaction is 45-65 min.
Compared with the prior art, the invention has the advantages that:
(1) the invention provides a method for preparing hydrogen peroxide by using an enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst, which comprises the steps of mixing the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst with an electron donor solution for carrying out photocatalytic reaction, and reducing O by 2 electrons2The preparation method of the hydrogen peroxide is to take isopropanol as an electron donor for example, and the preparation principle is shown in formulas (1) and (2), wherein the adopted enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst comprises an enol-ketone covalent organic framework and graphite-phase carbon nitride, the enol-ketone covalent organic framework is loaded on the surface of the graphite-phase carbon nitride, after the enol-ketone covalent organic framework and the graphite-phase carbon nitride form a heterojunction, oxygen on the enol-ketone covalent organic framework is charged with negative electricity, the graphite-phase carbon nitride is charged with positive electricity when the proton is lost, when the photon is generated by illumination, the electron can be transferred from the enol-ketone covalent organic framework to the graphite-phase carbon nitride, the flow of the electron is beneficial to the effective separation of the photon-hole pairs and the prolonging of the electron life, the generated electrons react with an electron donor in the solution to generate hydrogen ions, and the hydrogen ions react with the electrons on the surface of the catalyst and oxygen to generate hydrogen peroxide. In addition, the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst has higher crystallinity, and the existence of the enol-ketone isomeric tautomeric structure also enables the chemical thermal stability of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst to be stronger, so that the stability of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst under the illumination condition can be improved; meanwhile, an electron-rich electron-deficient conjugated structure existing in the introduced enol-ketone covalent organic framework is also beneficial to the improvement of the photocatalytic performance. In addition, the photocatalyst prepared by the invention is nontoxic, has a wide application prospect, and is particularly applicable to the field of photocatalysis. The enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst adopted in the invention has the advantages of multiple reaction active sites, wide light absorption range, low electron-hole pair recombination rate, good photocatalytic performance, good stability, environmental protection and the like, and is usedWhen the method is used for preparing the hydrogen peroxide, the yield of the hydrogen peroxide can reach 880.494 mu mol/L after 60min of photocatalytic reaction, compared with pure carbon nitride, the yield is improved by 49.49 times, and the yield of the hydrogen peroxide is still as high as 861.445 mu mol/L after five times of cycles.
CH3CHOHCH3+2h+→CH3COCH3+2H+ (1)
O2+2H++2e-→H2O2 (2)
(2) In the method, in the adopted enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst, the enol-ketone covalent organic framework can generate an internal electric field, has excellent visible light response capability and photo-generated electron transfer capability, expands the light absorption range of carbon nitride and improves the photo-generated electron-hole separation efficiency.
(3) In the method, in the adopted enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, electrons are converted from the enol-ketone covalent organic framework to the graphite phase carbon nitride and react with adsorbed oxygen to generate superoxide radical (O)2 -) And further converted into hydrogen peroxide (H) under illumination2O2) Compared with the pure carbon nitride, the activity of the hydrogen peroxide produced by photocatalysis is enhanced, and the method has great significance for promoting the practical application of the carbon nitride material in a wide range.
(4) In the invention, the enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst is adopted, the mass ratio of the graphite phase carbon nitride to the enol-ketone type covalent organic framework is optimized to be 1: 0.01-0.25, wherein for the enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst, the photocatalytic activity is firstly enhanced and then reduced along with the increase of the dosage of the enol-ketone type covalent organic framework. In the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, when the mass ratio of the graphite phase carbon nitride to the enol-ketone covalent organic framework is 1: 0.05, the photocatalytic property is optimal, the photocatalytic activity is enhanced probably because the composite enol-ketone covalent organic framework can improve the separation efficiency of the photo-generated electron hole pair of the enol-ketone covalent organic framework/graphite phase carbon nitride composite material, but the photocatalytic activity of the photocatalyst is gradually reduced along with the increase of the dosage of the enol-ketone covalent organic framework, because the content of the enol-ketone covalent organic framework loaded on the surface of the graphite phase carbon nitride is too much, although the addition of the enol-ketone covalent organic framework is beneficial to charge separation, the absorption of the graphite phase carbon nitride to visible light is reduced, and the generation of the electron-hole pair is reduced due to lower light collection amount, at the same time, also covers part of the active sites, so that an excess of enol-keto covalent organic framework leads to a reduction in the photocatalytic activity.
(5) According to the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, graphite phase carbon nitride and the enol-ketone covalent organic framework are used as raw materials, and the enol-ketone covalent organic framework is loaded on the graphite phase carbon nitride in dimethyl sulfoxide through pi-pi stacking to prepare the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst. In the invention, the enol-ketone covalent organic framework is loaded on the graphite-phase carbon nitride by ultrasonic stirring compounding for the first time, and the method has the advantages of simple process, convenient operation, easily obtained raw materials, low cost, high preparation efficiency, high yield and the like, is suitable for large-scale preparation, and is beneficial to industrial production.
(6) The enol-ketone covalent organic framework adopted in the invention takes melamine and 2,4, 6-trihydroxybenzene-1, 3, 5-triformal as the total organic framework building units, and-CH (is equal to N-and/or-CH)2N (OH) -is connected to form a porous skeleton with a periodic structure, on one hand, compared with a common covalent organic skeleton connected by imine bond, the enol-ketone covalent organic skeleton has higher stability, the structure is not easy to change in the light reaction, and the enol-ketone covalent organic skeleton is beneficial to the recycling of the catalyst; on the other hand, the enol-keto covalent organic framework has wide light absorption range (about 650 nm) and is beneficial to absorption and utilization of visible light, and meanwhile, the keto-enol organic framework contains electron-rich groups and electricity shortageThe sub-group can form an internal electric field, and is beneficial to electron hole separation and transmission after being compounded with carbon nitride to form a II-type heterojunction, thereby improving the yield of hydrogen peroxide.
Drawings
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention.
FIG. 1 is an XRD pattern of enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 25% TpMa/CN) and carbon nitride photocatalyst (CN) prepared in example 1 of the present invention.
FIG. 2 is a FT-IR chart of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 25% TpMa/CN) and the carbon nitride photocatalyst (CN) prepared in example 1 of the present invention.
FIG. 3 is a DRS diagram of enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 25% TpMa/CN) and carbon nitride photocatalyst (CN) prepared in example 1 of the present invention.
FIG. 4 is a PL diagram of enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN) and carbon nitride photocatalyst (CN) prepared in example 1 of the present invention.
FIG. 5 is a TEM image of enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN), carbon nitride photocatalyst (CN) and enol-ketone type covalent organic framework (TpMa) prepared in example 1 of the present invention, wherein (a) is CN, (b) is TpMa, and (c) is 5% TpMa/CN.
FIG. 6 is SEM pictures of enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN), carbon nitride photocatalyst (CN) and enol-ketone type covalent organic framework (TpMa) prepared in example 1 of the present invention, wherein (a) is CN, (b) is TpMa, and (c) is 5% TpMa/CN.
FIG. 7 is a graph showing the relationship between time and yield in the photocatalytic production of hydrogen peroxide by the enol-keto covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 15% TpMa/CN and 25% TpMa/CN) and the carbon nitride photocatalyst (CN) in example 1 of the present invention.
FIG. 8 is a histogram of cycle count-yield for the cyclic catalytic production of hydrogen peroxide by the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst in example 2 of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and specific preferred embodiments of the description, without thereby limiting the scope of protection of the invention.
In the following examples of the present invention, unless otherwise specified, materials and instruments used are commercially available, processes used are conventional, apparatuses used are conventional, and the obtained data are average values of three or more repeated experiments.
Example 1:
a method for preparing hydrogen peroxide by using an enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst comprises the following steps:
taking 100mg of enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 15% TpMa/CN, 25% TpMa/CN) and carbon nitride photocatalyst (CN), respectively adding the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst and the carbon nitride photocatalyst into 100mL of isopropanol aqueous solution with volume concentration of 10% (the isopropanol aqueous solution is mixed solution of isopropanol and ultrapure water, wherein the volume ratio of the isopropanol to the ultrapure water is 1: 9), magnetically stirring for one hour in a dark place (i.e. under the dark condition), turning on a light source after reaching adsorption equilibrium, and carrying out photocatalytic reaction for 60min under visible light (lambda is more than or equal to 420nm) to obtain hydrogen peroxide.
In this embodiment, the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst (1% TpMa/CN) used includes graphite-phase carbon nitride and an enol-ketone covalent organic framework, and the enol-ketone covalent organic framework is loaded on the graphite-phase carbon nitride, wherein the mass ratio of the graphite-phase carbon nitride to the enol-ketone covalent organic framework is 1: 0.01. The graphite phase carbon nitride is in a lamellar shape. The enol-ketone covalent organic skeleton is fibrous rod-shaped and 116nm in diameter.
In this embodiment, the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN) includes the following steps:
(1) putting 8g of melamine into a crucible, placing the crucible in a muffle furnace, heating the crucible to 550 ℃ at the heating rate of 2.3 ℃/min, preserving the heat at 550 ℃ for 4h, taking out the melamine after natural cooling, and grinding the melamine by using a mortar to obtain a yellow powder sample, namely the graphite-phase carbon nitride, which is named as CN.
(2) Dispersing melamine and 2,4, 6-trihydroxybenzene-1, 3, 5-trimethyl aldehyde in a mixed solution of N, N-dimethylacetamide and dimethyl sulfoxide, wherein the molar ratio of the melamine to the 2,4, 6-trihydroxybenzene-1, 3, 5-trimethyl aldehyde is 1: 1, adding 0.3mL of 3M glacial acetic acid serving as a catalyst, carrying out solvothermal reaction on the obtained mixed solution at 120 ℃ for 3d, and filtering after the reaction is finished to obtain an enol-ketone type covalent organic framework named TpMa.
(3) Dispersing 500mg of graphite-phase carbon nitride obtained in the step (1) into 50mL of dimethyl sulfoxide, performing ultrasonic treatment at 25 ℃ for 2h to obtain graphite-phase carbon nitride dispersion liquid, then adding 5mg of enol-ketone covalent organic framework obtained in the step (1), performing ultrasonic treatment at 25 ℃ for 2h, stirring for 24h, performing suction filtration, and drying to obtain the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst, which is named as 1% TpMa/CN.
In this example, the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN) used is substantially the same as the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN), and the difference is only: the mass ratio of the graphite phase carbon nitride to the enol-ketone type covalent organic framework in the enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst (5 percent TpMa/CN) is 1: 0.05.
In this embodiment, the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN) is basically the same as the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN), and the difference is that: the amount of enol-keto covalent organic skeleton used was 25 mg.
In this example, the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (25% TpMa/CN) used is substantially the same as the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN), and the difference is only: the mass ratio of the graphite phase carbon nitride to the enol-ketone type covalent organic framework in the enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst (25 percent TpMa/CN) is 1: 0.25.
In this embodiment, the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (25% TpMa/CN) is basically the same as the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN), and the difference is that: the amount of enol-keto covalent organic skeleton used was 125 mg.
In this example, the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (15% TpMa/CN) used is substantially the same as the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN), and the difference is only: the mass ratio of the graphite phase carbon nitride to the enol-ketone type covalent organic framework in the enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst (15 percent TpMa/CN) is 1: 0.15.
In this embodiment, the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (15% TpMa/CN) is basically the same as the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN), and the difference is that: the amount of enol-keto covalent organic skeleton used was 75 mg.
In this embodiment, the method for preparing the carbon nitride photocatalyst (CN) includes the following steps:
putting 8g of melamine into a crucible, placing the crucible in a muffle furnace, heating the crucible to 550 ℃ at the heating rate of 2.3 ℃/min, preserving the heat at 550 ℃ for 4h, taking out the melamine after natural cooling, and grinding the melamine by using a mortar to obtain a yellow powder sample, namely the carbon nitride photocatalyst, which is named as CN.
FIG. 1 is an X-ray diffraction pattern of enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 25% TpMa/CN) and carbon nitride photocatalyst (CN) prepared in example 1 of the present invention. As can be seen from fig. 1, two distinct XRD diffraction peaks ascribed to the (100) and (002) crystal planes of graphite phase carbon nitride appear at 13.0 ° and 27.5 °, confirming that the product produced is mainly carbon nitride. Meanwhile, a characteristic peak of the enol-ketone covalent organic framework is not seen, on one hand, the load is small, on the other hand, the characteristic peak of the enol-ketone covalent organic framework is partially overlapped with the carbon nitride, and the fact that the combination of the enol-ketone covalent organic framework has no influence on the structure of the carbon nitride is also shown. Compared with the carbon nitride photocatalyst (CN) of comparative example 1, the 27.5 ° peak intensity of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst prepared in examples 1 to 3 is weaker and weaker, which indicates that the crystal form of the composite photocatalyst is weakened and the thickness of the composite photocatalyst is reduced along with the increase of the loading amount of the enol-ketone covalent organic framework.
FIG. 2 is a FT-IR chart of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 25% TpMa/CN) and the carbon nitride photocatalyst (CN) prepared in example 1 of the present invention. As can be seen from FIG. 2, 3000-3500cm-1、1200-1600cm-1And 800cm-1Are respectively assigned to NH2And NH, and compared with the carbon nitride photocatalyst (CN) of the comparative example 1, the structure of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst is not obviously changed.
FIG. 3 is a DRS diagram of enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 25% TpMa/CN) and carbon nitride photocatalyst (CN) prepared in example 1 of the present invention. As can be seen from fig. 3, the absorption wavelength of the carbon nitride photocatalyst (CN) in comparative example 1 is about 462nm, the absorption wavelength band of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 25% TpMa/CN) prepared in examples 1-3 gradually shifts red with the loading amount of the enol-ketone covalent organic framework, the absorption wavelength is broadened to above 560nm, the absorption range of light is increased, and the utilization rate of light is improved. In addition, comparisonThe specific surface area of the carbon nitride photocatalyst (CN) prepared in example 1 was 11.9m2G, whereas the enol-keto covalent organic framework/graphite-phase carbon nitride composite photocatalyst prepared in example 2 (5% TpMa/CN) had a specific surface area of 15.5m2/g。
FIG. 4 is a PL diagram of enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN) and carbon nitride photocatalyst (CN) prepared in example 1 of the present invention. Photoluminescence (PL) spectroscopy is useful for studying the separation efficiency of electron-hole pairs. In the present invention, the PL emission spectrum is excited at a wavelength of 350nm, with a peak centered at about 453 nm. As can be seen from fig. 4, the carbon nitride photocatalyst (CN) in comparative example 1 exhibited a higher PL peak intensity, which means a high recombination rate between photo-generated electrons and holes. While the PL intensity of 5% TpMa/CN was lower than that of CN, indicating a lower rate of recombination of photo-generated charges in 5% TpMa/CN. In general, the rate of suppressed photogenerated charge recombination is always beneficial in increasing the photoactivity and quantum yield, thereby facilitating an increase in the photocatalysis.
FIG. 5 is a TEM image of enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN), carbon nitride photocatalyst (CN) and enol-ketone type covalent organic framework (TpMa) prepared in example 1 of the present invention, wherein (a) is CN, (b) is TpMa, and (c) is 5% TpMa/CN. FIG. 6 is SEM pictures of enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN), carbon nitride photocatalyst (CN) and enol-ketone type covalent organic framework (TpMa) prepared in example 1 of the present invention, wherein (a) is CN, (b) is TpMa, and (c) is 5% TpMa/CN. As can be seen from fig. 5 and 6, the carbon nitride photocatalyst (CN) prepared in comparative example 1 has a bulk aggregation structure and a small specific surface area, the enol-ketone covalent organic framework prepared in comparative example 2 has a fiber stick-shaped structure, and the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst prepared in example 3 has a fiber stick-shaped enol-ketone covalent organic framework on lamellar carbon nitride, which indicates that the enol-ketone covalent organic framework is successfully supported on a carbon nitride lamellar.
In this example, 100mL of 10% strength by volume isopropanol solution without any added material was used as a blank for comparison.
Determination of hydrogen peroxide production: absorbing the photocatalytic reaction solution in a reaction container of 3mL every 10min, and filtering by using an organic phase filter head of 0.22 mu m to obtain a transparent colorless solution to be detected. 1mL of a 0.1mol/L potassium hydrogen phthalate solution and 1mL of a 0.4mol/L potassium iodide solution were sequentially added dropwise to the solution to be measured, and the mixture was kept for 30 minutes for color development. And detecting the developed liquid to be detected on an ultraviolet-visible spectrophotometer instrument.
FIG. 7 is a graph showing the relationship between time and yield in the photocatalytic production of hydrogen peroxide by the enol-keto covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 15% TpMa/CN and 25% TpMa/CN) and the carbon nitride photocatalyst (CN) in example 1 of the present invention. As shown in FIG. 7, the carbon nitride photocatalyst (CN) prepared in comparative example 1 produced 17.79. mu. mol/L of hydrogen peroxide after 1 hour of light irradiation, while the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 15% TpMa/CN and 25% TpMa/CN) produced 124.659. mu. mol/L, 880.494. mu. mol/L, 686.486. mu. mol/L and 476.412. mu. mol/L, respectively.
The results show that: the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (5% TpMa/CN) in example 1 has the highest yield of hydrogen peroxide, and can generate 880.494 mu mol/L of hydrogen peroxide after 60min of photocatalytic reaction, while the carbon nitride photocatalyst (CN) can generate 17.79 mu mol/L of hydrogen peroxide after 60min of photocatalytic reaction. As can be seen from comparison, compared with the traditional carbon nitride monomer, the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst (1% TpMa/CN, 5% TpMa/CN, 15% TpMa/CN and 25% TpMa/CN) of the invention respectively improves the yield of hydrogen peroxide by 7.01, 49.49, 38.59 and 26.78 times, and the main reason of the phenomenon is that the enol-ketone covalent organic framework is loaded on the graphite phase carbon nitride, and the enol-ketone covalent organic framework effectively improves the separation efficiency of electron-hole and the light absorption efficiency in the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst, expands the light absorption range and enhances the photocatalytic efficiency of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst by utilizing the internal electric field of the enol-ketone covalent organic framework and the synergistic effect of the enol-ketone covalent organic framework and the graphite phase carbon nitride Activating and finally realizing the high-efficiency production of the hydrogen peroxide.
Example 2:
the method for investigating the reusability of the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst in the process of producing hydrogen peroxide by photocatalysis comprises the following steps:
(1) 100mg of the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst (5% TpMa/CN) prepared in example 1 was weighed and added to 100mL of an aqueous solution of isopropanol having a volume concentration of 10%, thereby obtaining a reaction system.
(2) And (2) placing the reaction system (the isopropanol solution added with 5% TpMa/CN) obtained in the step (1) on a magnetic stirrer, stirring for 1h in a dark place to achieve adsorption balance, taking 3mL of solution out of the magnetic stirrer to represent initial solution to be reacted, namely the solution with the reaction time of 0min, filtering and developing color, measuring the concentration of the solution by using an ultraviolet-visible spectrophotometer, and converting the concentration into yield.
(3) And (3) carrying out photocatalytic reaction on the solution remaining in the step (2) under visible light, taking 3mL of solution out of a reaction system (isopropanol solution added with 5% TpMa/CN) when the reaction time is 60min, filtering and developing color, measuring the concentration of hydrogen peroxide generated in the solution to be measured by using an ultraviolet-visible spectrophotometer, and converting the concentration into the yield.
(4) And (4) centrifugally separating the solution reacted in the step (3), pouring out supernatant, collecting 5% TpMa/CN after reaction, desorbing isopropanol and hydrogen peroxide by using ethanol, centrifugally drying, weighing, and adding into 100mL of 10% isopropanol water solution again.
(5) And (5) continuously repeating the steps (2) to (4) for four times.
FIG. 8 is a histogram of cycle count-yield for the cyclic catalytic production of hydrogen peroxide by the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst in example 2 of the present invention. In fig. 8, the hydrogen peroxide production is plotted on the ordinate and the cycle number is plotted on the abscissa, wherein the bar charts of 1, 2, 3, 4 and 5 correspond to the results of the cycle-yield of hydrogen peroxide production by photocatalysis of the first reaction, the second reaction, the third reaction, the fourth reaction and the fifth reaction, respectively. As can be seen from fig. 8, after five cycles, 5% TpMa/CN still exhibits high-efficiency photocatalytic performance, and the yield of hydrogen peroxide still reaches 861.445 μmol/L after five cycles, which indicates that the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst of the present invention has the advantage of stable photocatalytic performance, and is a novel visible light composite photocatalyst with high hydrogen peroxide yield and good reusability.
The results in fig. 1-8 show that the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst has the advantages of multiple reactive active sites, wide light absorption range, low electron-hole pair recombination rate, good photocatalytic performance, good stability, environmental friendliness and the like, is simple in method, high in preparation efficiency, high in yield and the like when being used for preparing hydrogen peroxide, can be used for preparing the hydrogen peroxide on a large scale, and is beneficial to industrial application.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-described embodiments. All technical schemes belonging to the idea of the invention belong to the protection scope of the invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention, and such modifications and embellishments should also be considered as within the scope of the invention.
Claims (10)
1. A method for preparing hydrogen peroxide by using an enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst is characterized by comprising the following steps: mixing an enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst with an electron donor solution for photocatalytic reaction to obtain hydrogen peroxide; the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst comprises an enol-ketone covalent organic framework and graphite-phase carbon nitride, wherein the enol-ketone covalent organic framework is loaded on the surface of the graphite-phase carbon nitride.
2. The method for preparing hydrogen peroxide by using the enol-ketone type covalent organic framework/graphite phase carbon nitride composite photocatalyst according to claim 1, wherein the loading amount of the enol-ketone type covalent organic framework is 1% -25% of the mass of the graphite phase carbon nitride; the graphite phase carbon nitride is in a lamellar shape; the enol-ketone covalent organic framework is in a fiber stick shape.
3. The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst according to claim 2, wherein the loading amount of the enol-ketone covalent organic framework is 3% -15% of the mass of the graphite-phase carbon nitride.
4. The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst according to claim 3, wherein the preparation method of the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst comprises the following steps:
s1, ultrasonically dispersing graphite-phase carbon nitride into dimethyl sulfoxide to obtain graphite-phase carbon nitride dispersion liquid;
s2, mixing the graphite-phase carbon nitride dispersion liquid obtained in the step S1 with the enol-ketone covalent organic framework, performing ultrasonic treatment, and stirring to obtain the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst.
5. The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst according to claim 4, wherein in the step S1, the graphite-phase carbon nitride is prepared by taking melamine as a precursor and calcining the melamine as the precursor; the preparation method of the graphite phase carbon nitride comprises the following steps: heating melamine to 500-600 ℃ at a heating rate of 1-5 ℃/min, preserving heat for 3-6 h, cooling, and grinding to obtain graphite-phase carbon nitride;
in step S2, the enol-ketone covalent organic skeleton is prepared by taking melamine and 2,4, 6-trihydroxybenzene-1, 3, 5-triformal as raw materials and performing solvothermal reaction in a mixed solution system of N, N-dimethylacetamide and dimethylsulfoxide; the preparation method of the enol-ketone covalent organic framework comprises the following steps: dispersing melamine and 2,4, 6-trihydroxybenzene-1, 3, 5-trimethyl aldehyde in a mixed solution of N, N-dimethylacetamide and dimethyl sulfoxide, adding glacial acetic acid, carrying out solvothermal reaction at 100-150 ℃ for 1-4 d, and filtering to obtain an enol-ketone covalent organic framework; the molar ratio of the melamine to the 2,4, 6-trihydroxybenzene-1, 3, 5-trimethyl aldehyde is 2-1: 1-2; (ii) a The volume ratio of the N, N-dimethylacetamide to the dimethyl sulfoxide to the glacial acetic acid is 2: 1: 0.01-0.1; the concentration of the glacial acetic acid is 3M-6M.
6. The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst according to claim 5, wherein in the step S1, the ultrasonic dispersion is performed at a temperature of 20 ℃ to 45 ℃; the ultrasonic dispersion time is 0.5-3 h;
in step S2, the ultrasound is performed at a temperature of 20 ℃ to 45 ℃; the ultrasonic time is 0.5 h-3 h; the stirring is carried out at the temperature of 20-45 ℃; the stirring time is 12-36 h.
7. The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst according to any one of claims 1 to 6, wherein the addition amount of the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst is 0.5g to 1.5g of the enol-ketone covalent organic framework/graphite-phase carbon nitride composite photocatalyst added to each liter of the electron donor solution.
8. The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst according to claim 7, wherein the electron donor solution is a mixed solution of an electron donor and water; the volume ratio of the electron donor to the water is 1: 5-9; the electron donor is at least one of isopropanol, triethanolamine, ethanol, benzyl alcohol, formic acid, methanol and ethylene diamine tetraacetic acid.
9. The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst according to claim 8, wherein the volume ratio of the electron donor to the water is 1: 9.
10. The method for preparing hydrogen peroxide by using the enol-ketone covalent organic framework/graphite phase carbon nitride composite photocatalyst according to claim 8 or 9, wherein the time of the photocatalytic reaction is 45-65 min.
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| CN113673086A (en) * | 2021-07-22 | 2021-11-19 | 湖南大学 | Method for analyzing reaction mechanism of photocatalytic production of hydrogen peroxide |
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| CN113673086B (en) * | 2021-07-22 | 2023-10-20 | 湖南大学 | Analysis method of reaction mechanism of photocatalytic hydrogen peroxide production |
| CN113735065A (en) * | 2021-09-27 | 2021-12-03 | 湖南大学 | Method for producing hydrogen peroxide by using modified amino functionalized zirconium-based metal organic framework composite photocatalyst |
| CN113877629A (en) * | 2021-09-27 | 2022-01-04 | 湖南大学 | Enol-ketone type covalent organic framework photocatalyst and preparation method and application thereof |
| CN113877629B (en) * | 2021-09-27 | 2023-09-19 | 湖南大学 | Enol-ketone covalent organic framework photocatalyst, and preparation method and application thereof |
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