CN107601443B

CN107601443B - Preparation method of ultrathin tungsten selenide nanosheets

Info

Publication number: CN107601443B
Application number: CN201711099676.0A
Authority: CN
Inventors: 宋吉明; 张冰倩; 牛和林; 毛昌杰; 陈京帅
Original assignee: Anhui University
Current assignee: Anhui University
Priority date: 2017-11-09
Filing date: 2017-11-09
Publication date: 2020-01-14
Anticipated expiration: 2037-11-09
Also published as: CN107601443A

Abstract

The invention discloses a preparation method of an ultrathin tungsten selenide nanosheet, and particularly relates to a method for preparing tungsten selenide by an oil phase method, wherein the tungsten selenide material has the property of catalyzing benzylamine to be coupled to generate imine, and the preparation method belongs to the technical field of material preparation and application. A Schlenk line route is adopted, oleylamine, oleic acid, octadecene and N-dodecyl mercaptan are used as solvents, a selenium source and a tungsten source in a certain ratio are used as reactants, a feather-shaped ultrathin nanosheet with the thickness of less than 2 nanometers is prepared at a certain reaction temperature, the nanosheet has the effect of efficiently catalyzing benzylamine to be coupled into N-benzylidene benzylamine, and the yield of the N-benzylidene benzylamine obtained by coupling benzylamine in cyclohexane and acetonitrile solvents respectively reaches 95% and 96%. The catalyst has large specific surface area, high catalytic efficiency, no use of noble metal and low cost. The preparation method is simple in preparation process, easy to operate, free of organic templates and surfactants and suitable for industrial production; the prepared tungsten selenide has pure phase, large specific surface area and high reusability.

Description

Preparation method of ultrathin tungsten selenide nanosheets

Technical Field

The invention belongs to the technical field of material preparation and application, and particularly relates to an ultrathin tungsten selenide nanosheet prepared by an oil phase method, wherein the material has the property of catalyzing benzylamine to generate imine through coupling.

Background

Recently, selenide semiconductor nanomaterials have become the focus of current research due to their various physicochemical properties, including thermoelectric properties, dielectric properties, and their potential applications. Most of the materials have low energy band gap, high absorption coefficient, good light resistance, low toxicity and high photoelectric conversion efficiency. As one of the important compounds of the selenide family, tungsten selenide material consists of a layered structure of two-dimensional Se-W-Se, in which the W atomic plane is located in the middle of two hexagonal Se atomic planes. The tungsten selenide layers are bonded by strong covalent bonds and the layers are bonded by van der waals forces. Because interlayer bonding is weak, the single-layer tungsten selenide can be easily prepared by a micromechanical stripping method. Although the micro-mechanical stripping method can effectively prepare the single-layer tungsten selenide nano material with high quality and high flatness, the large-scale and controllable preparation cannot be realized, so that a new preparation method is urgently required to be explored. James, et al. (J. Am. chem, so, 2013, 135, 223) synthesizing a p-type tungsten selenide crystal by a chemical vapor transport method; zuo, et al (j. mater. chem. a 2015, 3, 18090-; and growing 3D dendritic tungsten selenide (J. mater. chem. A2015, 3, 12149-12153) on the conductive carbon nanofiber mat by a CVD method. The related patents are: (1) application No. CN201010572042.4, title: a preparation method of a tungsten diselenide nano inclusion compound is characterized in that the tungsten diselenide nano inclusion compound with a core-shell structure is obtained through solid phase synthesis, and the application is in the validity period; (2) application No. CN201210374547.9, title: a preparation method of high-orientation tungsten diselenide nanowires adopts a hydrothermal method to prepare WO₂The nanowire is selenized by high-purity selenium with the purity of more than 99.9 percent to obtain the tungsten diselenide nanowire with high orientation, and the application is in the validity period.

From the above description and examples, it can be seen that there are many methods for preparing tungsten selenide nanosheets, but most of them have high requirements for reaction conditions and great technical difficulties, and there are few reports on the synthesis of tungsten selenide nanosheets in a solution phase. Different from the reports in the documents, the inventor prepares the ultrathin tungsten selenide nanosheet by adopting an oil phase method, taking selenium powder and tungsten hexachloride as raw materials and taking oleylamine, oleic acid, octadecene and n-dodecyl mercaptan as solvents; the material has higher catalytic performance on the coupling of benzylamine to generate imine.

Disclosure of Invention

The invention aims to provide a preparation method of a material with catalytic property and application of the material in catalyzing benzylamine to generate imine. The method has simple preparation process and good repeatability, can be synthesized in large quantities, and is suitable for industrial production. The prepared ultrathin nanosheet has high catalytic performance, and the conversion rate of catalytic benzylamine is up to 96%.

The preparation method of the ultrathin nanosheet comprises the following steps:

A. 2.2 mmol of selenium powder (0.174 g) was added to a mixed solution of 2.4 ml of oleylamine and 2.4 ml of n-dodecylmercaptan, and magnetically stirred at room temperature until the selenium powder was completely dissolved.

B. 1 mmol of tungsten chloride (0.397 g) was added to a mixed solution of oleylamine (10 ml), oleic acid (10 ml) and octadecene (10 ml), and magnetic stirring was carried out while vacuum nitrogen was circulated three times to remove air and water vapor in the reaction system. Heating the reaction solution to 140 ℃, vacuumizing for 30 minutes, and removing low-boiling-point substances; the temperature was raised to 300 ℃.

C. Injecting the selenium source precursor A into the B, continuing to react for 60 minutes after the temperature is raised to 300 ℃, putting the reaction liquid into a 10 ml centrifuge tube after the reaction is finished, adding 3 ml of trichloromethane to disperse the reaction liquid, adding 3 ml of ethanol to wash, centrifuging for 5 minutes at the rotating speed of 6000 rpm, repeatedly washing 3 times by using the precipitate, and drying the product in a 60 ℃ vacuum drying oven.

The reactant selenium source is selenium powder;

the reactant tungsten source is tungsten hexachloride;

the reaction vessel is a 100 ml three-neck flask;

the reaction route is the Schlenk line route.

The coupling method of benzylamine catalyzed by the tungsten selenide nanosheets prepared by the invention comprises the following steps: 55 microlitres (0.1 millimole) of benzylamine were measured and dissolved in 500 microlitres of different solvents and the reaction conversion was tested after a while.

Five solvents of N-hexane, cyclohexane, N-N dimethylformamide, absolute ethyl alcohol and acetonitrile are selected for testing the catalytic performance.

The specific operation is as follows:

putting magnetons into a glass tube, adding 30 mg of tungsten selenide product serving as a catalyst, adding 55 microliters (0.1 mmol) of benzylamine into the glass tube by using a liquid transfer gun, then adding 500 microliters of solvent, carrying out magnetic stirring reaction for 30 hours at 60 ℃ in a closed environment, centrifugally separating the catalyst, and carrying out quantitative analysis on the product by using gas chromatography to obtain the conversion rate.

The solvents are all of chromatographically pure grade;

the amount of benzylamine used as the reactant is 0.1 mmol and the concentration is 2' 10^-4M；

The dosage of the tungsten selenide catalyst is 30 mg;

the gas chromatography is Katsumadu GC-2010 plus.

The tungsten selenide nanosheet prepared by the invention has good catalytic performance on benzylamine coupling reaction, and the preparation and detection methods of the material are simple, can be synthesized in a large amount, are low in dosage and can be repeatedly used.

Description of the drawings:

fig. 1 is a Scanning Electron Micrograph (SEM) of tungsten selenide nanoplates prepared in example 1;

fig. 2 is a Transmission Electron Micrograph (TEM) of tungsten selenide nanosheets prepared in example 1;

fig. 3 is a selected area electron diffraction pattern (SAED) and High Resolution Transmission Electron Micrograph (HRTEM) of tungsten selenide nanoplates prepared in example 1;

fig. 4 is an X-ray powder diffraction pattern (XRD) of tungsten selenide nanoplates prepared in example 1;

fig. 5 is a Raman plot (Raman) of tungsten selenide nanoplates prepared in example 1;

FIG. 6 is a bar graph of the conversion of catalytic benzylamine coupling in different solvents as in example 2;

the specific implementation mode is as follows:

the invention is illustrated in detail below with reference to the examples:

example 1: preparing tungsten selenide nanosheets:

2.2 mmol selenium powder (0.174 g) is added into a mixed solution of 2.4 ml oleylamine and 2.4 ml n-dodecyl mercaptan, and magnetic stirring is carried out at room temperature until the selenium powder is completely dissolved to obtain the selenium source precursor. 1 mmol of tungsten chloride (0.397 g) was added to a mixed solution of oleylamine (10 ml), oleic acid (10 ml) and octadecene (10 ml), and magnetic stirring was carried out while vacuum nitrogen was circulated three times to remove air and water vapor in the reaction system. Heating the reaction solution to 140 ℃, vacuumizing for 30 minutes, and removing low-boiling-point substances; and (3) injecting the selenium source precursor when the temperature is raised to 300 ℃, reacting for 60 minutes after the temperature is raised again, placing the reaction solution into a 10 ml centrifuge tube after the reaction is finished, adding about 3 ml of trichloromethane to disperse the reaction solution, adding 3 ml of ethanol to wash the reaction solution, centrifuging for 5 minutes at a rotating speed of 6000 rpm, repeatedly washing the precipitate for 3 times, and drying in a vacuum drying oven at 60 ℃ to obtain the final product.

The morphology of the obtained sample is characterized by adopting a Japanese electron JEM-2100 Transmission (TEM), selective area diffraction (SAED) and high-resolution transmission electron microscope (HRTEM), and the phase of the sample is characterized by adopting a SmartLab 9 KW X-ray diffractometer (XRD) and an inVia-Reflex laser Raman spectrometer (Raman).

As can be seen from the scanning electron micrograph of the sample in FIG. 1 and the transmission electron micrograph of the sample in FIG. 2, the sample is a flower-like picture composed of feather-like ultrathin nanosheets, and the thickness of the flower-like picture is less than 2 nm; from standard card JCPDS No: 38-1388, it can be seen that the selected-region electron diffraction pattern (SAED) of the tungsten selenide nanosheets in fig. 3 corresponds to the (100), (103), (006), (105), (110), (008), (002) crystal planes of tungsten selenide, respectively, and the lattice spacing in the high-resolution transmission electron microscopy (HRTEM) is 0.625 nm and 0.287 nm, respectively, to the (002) crystal planes and (100) crystal planes of tungsten selenide. The X-ray powder diffractogram (XRD) of the product of fig. 4, in comparison to PDF card JCPDS No: 38-1388 in agreement; 250 cm from the Raman spectrum of FIG. 5^-1The characteristic peaks of tungsten selenide can be seen clearly at the left and right,

example 2: catalytic coupling of tungsten selenide nanosheets to benzylamine:

the coupling method of benzylamine catalyzed by the tungsten selenide nanosheets prepared by the invention comprises the following steps: 55 microliter of benzylamine was measured and dissolved in 500 microliter of various solvents, and the reaction conversion was measured after a while.

The specific operation is as follows:

putting magnetons into a glass tube, adding 30 mg of tungsten selenide product as a catalyst, adding 55 microliters (0.1 mmol) of benzylamine into the glass tube by using a liquid transfer gun, then adding 500 microliters of solvent, carrying out magnetic stirring reaction for 30 hours at 60 ℃ in a closed environment, adding the same solvent for dilution, carrying out centrifugal separation on the catalyst, and carrying out quantitative analysis on the product by using gas chromatography to obtain the conversion rate.

As can be seen from the bar graph of FIG. 6, the coupling of benzylamine to N-benzylmethylenebenzylamine yields of up to 95% and 96% respectively when the solvents are cyclohexane and acetonitrile.

Claims

1. A preparation method of ultrathin tungsten selenide nanosheets comprises the specific steps of adding 2.2 millimole selenium powder (0.174 g) into a mixed solution of 2.4 ml oleylamine and 2.4 ml n-dodecyl mercaptan, and magnetically stirring at room temperature until the selenium powder is completely dissolved to obtain a selenium source precursor; adding 1 mmol of tungsten chloride (0.397 g) into a mixed solution of 10 ml of oleylamine, 10 ml of oleic acid and 10 ml of octadecene, magnetically stirring, and circulating vacuum nitrogen for three times to remove air and water vapor in a reaction system; heating the reaction solution to 140 ℃, vacuumizing for 30 minutes, and removing low-boiling-point substances; and (3) injecting the selenium source precursor when the temperature is raised to 300 ℃, continuing to react for 60 minutes after the temperature is raised to 300 ℃, putting the reaction solution into a 10 ml centrifuge tube after the reaction is finished, adding 3 ml of trichloromethane to disperse the reaction solution, adding 3 ml of ethanol to wash the reaction solution, centrifuging for 5 minutes at a rotating speed of 6000 rpm, repeatedly washing 3 times by using the remained precipitate, and drying in a 60 ℃ vacuum drying oven to obtain the final product.