CN116371435B - A single cluster dispersed wheel-shaped polyacid composite material and preparation method thereof - Google Patents

Abstract

The present invention provides a single cluster dispersed wheel-shaped polyacid composite material, which is formed by mixing carbon nitride nanosheets and wheel-shaped polyacid. The single cluster dispersed wheel-shaped polyacid composite material provided by the present invention utilizes an electrostatic adsorption method to disperse functionalized wheel-shaped polyacid into carbon nitride nanosheets, constructs a composite two-dimensional nanomaterial of wheel-shaped polyacid CuPOM single cluster dispersion, and reduces the recombination rate of photogenerated electrons and holes.

Description

A single cluster dispersed wheel-shaped polyacid composite material and preparation method thereof

Technical Field

The invention belongs to the technical field of photocatalysis, and in particular relates to a single cluster dispersed wheel-shaped polyacid composite material and a preparation method thereof.

Background Art

The oxidation reaction of olefins is one of the important reactions for the industrial production of high-value chemicals. Traditional industrial oxidation processes usually use strong oxidants such as peracids, HNO ₃ , HIO ₄ , which can cause a variety of problems such as deep oxidation of reactants, resulting in poor selectivity, difficulty in product separation, low conversion rate, and the generation of a large amount of environmentally harmful waste. Therefore, olefin oxidation catalysts with the characteristics of low price, green and non-toxic, easy to separate and recyclable have always been a hot topic for researchers.

Polyoxometalates (POMs) are polyoxometalates with excellent redox properties, unique photoelectric properties, and precise structures that can design single-atom-level active sites. They have attracted much attention in photocatalysis in recent years. Among them, the wheel-shaped tungstophosphate P ₈ W ₄₈ , as one of the large POM clusters, has high thermal stability and photocatalytic activity. In particular, the cavity of about 1 nm inside the wheel-shaped P ₈ W ₄₈ can introduce a variety of metal cations to form a "catalytic platform" with high catalytic activity. Therefore, the wheel-shaped POM containing metal ions inside can be used as an effective "catalytic reactor". The advantage of the functionalized wheel-shaped polyoxometalate catalyst is that the external "shell" has good adaptability to the reaction environment, which can ensure that the microenvironment in the cavity - the metal ions constructing the high active sites are not easily destroyed. However, the low specific surface area of the block P ₈ W ₄₈ , especially the high negative charge itself, makes the polyoxometalate molecules easy to agglomerate during the reaction, and the catalytic performance is seriously affected.

Inspired by the dispersion of single atoms in carbon nitride nanosheets, and taking advantage of the periodic structure and two-dimensional material characteristics of carbon nitride nanosheets, a two-dimensional composite material with functionalized wheel-shaped polyacid CuPOM single cluster dispersion was designed. The monodispersed CuPOM can greatly expose the active sites of the quadruple copper constructed in the cavity and can be used for efficient catalytic reactions. Carbon nitride nanosheets generate photogenerated electrons and holes under light. The photogenerated electrons are transferred to the polyacid CuPOM, and the holes remain on the surface of the carbon nitride nanosheets to oxidize organic matter. The composite material is more conducive to the photooxidation catalytic reaction.

Based on the above situation, the present invention provides a method for preparing a composite material based on monodispersed wheel-shaped polyacid CuPOM to carbon nitride nanosheets, which successfully uses molecular oxygen to highly selectively oxidize cyclohexene to epoxycyclohexane in a room temperature photocatalytic reaction, greatly improving the utilization efficiency of solar energy and expanding new ideas for the goal of green and low-carbon production of chemical products.

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Summary of the invention

The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, a single cluster dispersed wheel-shaped polyacid composite material is provided. The catalyst uses molecular oxygen as an oxygen source under room temperature illumination conditions to efficiently photo-oxidize cyclohexene to generate cyclohexene oxide.

The present invention provides a method for preparing a single cluster dispersed wheel-shaped polyacid composite material, the steps of which are:

(1) preparing wheel-shaped CuPOM, the specific method is as follows: adding CuCl ₂ ·2H ₂ O and K ₂₈ Li ₅ [H ₇ P ₈ W ₄₈ O ₁₈₄ ] ·92H ₂ O to a buffer solution of LiCH ₃ COO under stirring, then heating the solution to 80°C for 1 hour, cooling to room temperature and filtering, evaporating the filtrate at room temperature until the wall of the beaker is covered with blue crystals, then collecting and air-drying the blue crystals to obtain polyacid K ₁₂ Li ₁₆ {[Cu(H ₂ O)] ₂ [Cu ₄ (OH) ₄ (H ₂ O) ₈ ] ₂ P ₈ W ₄₈ O ₁₈₄ }·55H ₂ O, i.e., CuPOM;

(2) Preparation of carbon nitride nanosheets; the specific method is as follows: urea is heated to 793K in air at a heating rate of 5°C/min, and then the temperature is maintained for further heating for 240min, and the obtained bulk gC ₃ N ₄ solid is used to prepare carbon nitride nanosheets (CNNS) by thermal oxidation etching;

(3) Mixing the CuPOM prepared in step (1) with a carbon nitride solution to obtain a CNNS/CuPOM two-dimensional composite nanomaterial.

Furthermore, in the step (1), the molar ratio of CuCl ₂ ·2H ₂ O to K ₂₈ Li ₅ [H ₇ P ₈ W ₄₈ O ₁₈₄ ]·92H ₂ O is 24:1.

Furthermore, in the step (1), the pH value of the LiCH ₃ COO buffer solution is 5.

Moreover, in the step (2), the thermal oxidation etching is to heat the obtained bulk gC ₃ N ₄ to 773K at a rate of 5°C/min and heat for 120min, and grind the obtained light yellow powder in a quartz mortar to obtain carbon nitride nanosheets after thermal oxidation etching.

Moreover, in the step (3), a certain amount of carbon nitride nanosheets are first dispersed in a HCl solution with a pH of 3, and after ultrasonic treatment for 10 minutes, the powdered ring-shaped polyacid CuPOM is added to the solution of protonated carbon nitride nanosheets and stirred for 10 hours, then washed with deionized water until neutral, and freeze-dried to obtain CNNS/CuPOM.

The present invention also provides an application of the above-mentioned single-cluster dispersed wheel-shaped polyacid composite material, wherein the single-cluster dispersed wheel-shaped polyacid composite material is used as a photocatalyst for the photooxidation of cyclohexene with molecular oxygen to generate cyclohexene oxide with high selectivity, which is specifically achieved by the following technical scheme:

A method for photocatalytically catalyzing cyclohexene to generate cyclohexene oxide with high selectivity comprises the following steps: adding cyclohexene and isobutyraldehyde to the above-mentioned single cluster dispersed wheel-shaped polyacid composite material, photooxidizing the cyclohexene under light with 1,2-dichloroethane (DEC) as solvent, and generating cyclohexene oxide with high selectivity.

Moreover, the dosage ratio of the single cluster dispersed wheel-shaped polyacid composite material is 0.2-0.8 mmol: 4 mg.

Moreover, the catalytic reaction temperature is 20-25°C, and the catalytic reaction atmosphere is oxygen.

Furthermore, the catalytic reaction illumination condition may be a full spectrum wavelength.

Compared with the prior art, the present invention has the following beneficial effects:

(1) The single-cluster dispersed wheel-shaped polyacid composite material provided by the present invention utilizes an electrostatic adsorption method to disperse the functionalized wheel-shaped polyacid into carbon nitride nanosheets, thereby constructing a composite two-dimensional nanomaterial of a single-cluster dispersed wheel-shaped polyacid CuPOM, thereby reducing the recombination rate of photogenerated electrons and holes.

(2) Compared with the prior art, the present invention disperses the functionalized wheel-shaped polyacid CuPOM single cluster into carbon nitride nanosheets to form a Z-type heterojunction. The active sites of the tetranuclear copper constructed inside the wheel-shaped polyacid help activate oxygen molecules. Under light irradiation, the photogenerated electrons generated by the carbon nitride nanosheets are transferred to Cu ^Ⅱ inside the wheel-shaped polyacid to become Cu ^Ⅰ , and Cu ^Ⅰ activates the oxygen molecules into superoxide radicals. The photogenerated holes generated by the carbon nitride nanosheets oxidize cyclohexene to epoxycyclohexane.

(3) The synthesis steps of carbon nitride nanosheets in the preparation process of the composite two-dimensional nanomaterials of the present invention are simple and efficient. The raw materials are widely available and can be synthesized in large quantities with low cost and simple operation, which provides a simple synthesis strategy for designing functionalized polyacid single cluster dispersed nanomaterials.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is the XRD pattern of CNNS/CuPOM.

Figure 2 is the TEM image of CNNS/CuPOM.

DETAILED DESCRIPTION

The technical solution of the present invention is further described below in conjunction with specific embodiments.

Example 1

The present invention provides a composite nanomaterial, and the preparation method thereof comprises the following steps:

1) CuCl ₂ ·2H ₂ O (0.10 g, 0.60 mmol) and K ₂₈ Li ₅ [H ₇ P ₈ W ₄₈ O ₁₈₄ ]·92H ₂ O (0.37 g, 0.025 mmol) were added to a buffer solution of LiCH ₃ COO (20 mL, pH=5) under stirring. The solution was then heated to 80°C for 1 hour, cooled to room temperature and filtered. The filtrate was allowed to evaporate in an open beaker at room temperature. After 3-4 days, a blue crystalline product, solid A, began to appear.

2) 1 g of urea was heated to 793 K in air at a heating rate of 5 °C/min, and then the temperature was maintained and heated for 240 min to obtain a blocky gC ₃ N ₄ solid B;

3) After grinding solid B into powder, the temperature was raised to 773K at a rate of 5°C/min and heated for 120min to obtain carbon nitride solid B1 after thermal etching;

4) Disperse B1 powder into 35 mL of hydrochloric acid solution with pH = 3, and form solution C after ultrasonic treatment for 10 min;

5) adding 200 mg of the synthesized solid A powder to solution C and stirring for 10 h to form solution D;

6) After centrifuging solution D, the solid E was washed until the solution was neutral, and freeze-dried for 12 h to obtain a composite two-dimensional nanomaterial (labeled as CNNS/CuPOM).

Structural characterization:

The structure and morphology of the CuPOM polyacid prepared in step 1), the carbon nitride nanosheets prepared in step 3), and the CNNS/CuPOM obtained in step 6) were characterized, and the results are as follows:

1)CuPOM polyacid

The XRD pattern of CuPOM polyacid is shown in Figure 1.

2)CNNS

The XRD pattern of CNNS is shown in Figure 1. As shown in Figure 1, CNNS/CuPOM does not show the diffraction peak of CuPOM polyacid because the content of CuPOM polyacid is lower than the detection line, and it also shows that CuPOM polyacid has not aggregated into large volume particles on carbon nitride.

3)CNNS/CuPOM

The TEM image of CNNS/CuPOM is shown in Figure 2. As shown in Figure 2, there are obvious polyacid cluster particles on CNNS/CuPOM that are evenly dispersed on the carbon nitride nanosheets.

In summary, the wheel-shaped CuPOM single clusters are dispersed on the two-dimensional carbon nitride nanosheets.

Example 2

The present invention also applies the above-prepared CNNS/CuPOM to photo-oxidation of cyclohexene to generate cyclohexene oxide with high selectivity. The specific method is as follows:

4mg of CNNS/CuPOM photocatalyst, cyclohexene (0.50mmol), isobutyraldehyde (1.0mmol) and 6mL1,2-dichloroethane were added to a 25mL round-bottom flask. The reaction flask was capped and equipped with a balloon filled with oxygen to provide an oxygen source. After 8h of direct light reaction under a 300W xenon lamp without any filter, the supernatant was analyzed by GC-MS (GC-9790Plus), and the generated cyclohexene oxide was quantitatively measured and the yield of cyclohexene oxide was calculated. The yield of cyclohexene oxide was 96.5%.

CNNS/CuPOM is used for the photooxidation of cyclohexene to prepare cyclohexene oxide. CNNS/CuPOM has good catalytic activity and high selectivity for the photocatalytic oxidation of cyclohexene. For pure polyacid CuPOM, it is easy to agglomerate during the reaction, which is not conducive to the efficient use of active sites in the polyacid.

The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims (7)

1. A method for preparing a single cluster dispersed wheel-shaped polyacid composite material, characterized in that it comprises the following steps: (1) Preparing wheel-shaped CuPOM, the specific method is as follows: CuCl ₂ ·2H ₂ O and K ₂₈ Li ₅ [H ₇ P ₈ W ₄₈ O ₁₈₄ ] ·92H ₂ O are added to a buffer solution of LiCH ₃ COO under stirring, then the solution is heated to 80°C for 1 hour, cooled to room temperature and filtered, the filtrate is evaporated at room temperature until the wall of the beaker is covered with blue crystals, which are then collected and air-dried to obtain K ₁₂ Li ₁₆ {[Cu(H ₂ O)] ₂ [Cu ₄ (OH) 4 (H 2 O) ₈ ] _{2 P 8} W 48 O 184 } ·55H 2 O, i.e. CuPOM; the molar ratio of CuCl ₂ ·2H 2 O to K 28 Li 5 [H 7 P 8 W ₄₈ O ₁₈₄ ] ·92H ₂ O is 24: ₁ , the LiCH 3 COO buffer solution is heated to 80°C for 1 hour, cooled to room temperature and filtered, the filtrate is evaporated at room temperature until the wall of the beaker is covered with blue crystals, and then collected and air-dried to obtain K ₁₂ Li ₁₆ {[Cu(H 2 O)] 2 [Cu _{4 ( OH) 4 (H 2 O) 8 ] 2 P 8 W 48 O 184 } ·} 55H ₂ O, i.e. CuPOM. The pH value of COO buffer solution = 5; (2) Preparation of carbon nitride nanosheets; the specific method is as follows: urea is heated to 793K in air at a heating rate of 5°C/min, and then the temperature is maintained for further heating for 240min, and the obtained bulk gC ₃ N ₄ solid is used to prepare carbon nitride nanosheets (CNNS) by thermal oxidation etching; (3) Mixing the CuPOM prepared in step (1) with a carbon nitride solution to obtain a CNNS/CuPOM two-dimensional composite nanomaterial. 2. The method for preparing a single-cluster dispersed wheel-shaped polyacid composite material according to claim 1, characterized in that: in the step (2), the thermal oxidation etching is to heat the obtained bulk gC ₃ N ₄ to 773K at a rate of 5°C/min and heat for 120min, and grind the obtained light yellow powder in a quartz mortar to obtain carbon nitride nanosheets after thermal oxidation etching. 3. The method for preparing a single-cluster dispersed wheel-shaped polyacid composite material according to claim 1 is characterized in that: in the step (3), a certain amount of carbon nitride nanosheets are first dispersed in a pH=3 HCl solution, and after ultrasonic treatment for 10 minutes, the wheel-shaped polyacid CuPOM ground into powder is added to the solution of protonated carbon nitride nanosheets and stirred for 10 hours, and then washed with deionized water until neutral, and freeze-dried to obtain CNNS/CuPOM. 4. An application of a single-cluster dispersed wheel-shaped polyacid composite material as a photocatalyst, characterized in that: the single-cluster dispersed wheel-shaped polyacid composite material prepared by the single-cluster dispersed wheel-shaped polyacid composite material according to any one of claims 1 to 3 is used for the molecular oxygen photooxidation of cyclohexene to generate cyclohexene oxide with high selectivity, and the specific method is: A method for photocatalytically catalyzing cyclohexene to generate cyclohexene oxide with high selectivity comprises the following steps: adding cyclohexene and isobutyraldehyde to the above-mentioned single cluster dispersed wheel-shaped polyacid composite material, photooxidizing the cyclohexene under light with 1,2-dichloroethane (DEC) as solvent, and generating cyclohexene oxide with high selectivity. 5. The use of the single-cluster dispersed wheel-shaped polyacid composite material as a photocatalyst according to claim 4, characterized in that the dosage ratio of the single-cluster dispersed wheel-shaped polyacid composite material is: 0.2-0.8 mmol: 4 mg. 6. Use of the single-cluster dispersed wheel-shaped polyacid composite material as a photocatalyst according to claim 4, characterized in that the catalytic reaction temperature is 20-25°C, and the catalytic reaction atmosphere is oxygen. 7. The use of the single-cluster dispersed wheel-shaped polyacid composite material as a photocatalyst according to claim 4, characterized in that the illumination condition of the catalytic reaction can be a wavelength of the full spectrum.