Metal-free few-layer phosphorous nanomaterial: method for its preparation and use thereof

Abstract

A method for preparing a metal-free few-layer phosphorous nanomaterial. The method comprises an ice-assisted exfoliation process (or solvent ice-assisted exfoliation process). The method allows for the preparation of a few-layer phosphorous nanomaterial with improved yield and reduced duration and exfoliation power. The few-layer phosphorous nanomaterial is used in the preparation of a photocatalyst. The photocatalyst exhibits a long-term stability, high photocatalytic H 2 evolution efficiency from water, and good stability under visible light irradiation.

1 . Method for preparing a few-layer phosphorous nanomaterial from a bulk layer-structured phosphorous material, comprising an ice-assisted exfoliation process or solvent ice-assisted exfoliation process. 
     
     
         2 . Method for preparing a few-layer phosphorous nanomaterial from a bulk layer-structured phosphorous material, comprising a combination of the following steps: grinding, dispersion in a solvent, freezing, melting, separation, purification. 
     
     
         3 . Method for preparing a few-layer phosphorous nanomaterial, comprising:
 (a) providing a bulk layer-structured phosphorous material;   (b) grinding the bulk phosphorous material;   (c) dispersing the grinded material into a first solvent to obtain a first dispersion;   (d) freezing the first dispersion for a period of time, preferably using liquid nitrogen;   (e) melting the frozen dispersion, preferably by sonication for a period of time to obtain a second dispersion; and   (f) submitting the second dispersion to a separation step, preferably involving centrifugation for a period of time, to obtain the nanomaterial.   
     
     
         4 . Method according to  claim 3 , further comprising a purification step; preferably the purification step comprises:
 (g) washing the nanomaterial using a second solvent, optionally repeating step (g) a number of time, preferably 2-6 times, or 3 times, or 4 times; and   (h) dispersing the nanomaterial into a third solvent,   
       wherein the second and third solvents are the same or different. 
     
     
         5 . Method according to  claim 3  or  4 , wherein steps (d) and (e) are repeated a number of time, preferably 2 to 6 times, or 3 times or 4 times. 
     
     
         6 . Method according to  claim 3 , wherein the freezing time period at step (d) is about 3-15 minutes, or about 4-14 minutes, or about 5-13 minutes, or about 5-12 minutes, or about 5-11 minutes, or about 5-10 minutes, or about 6-8 minutes. 
     
     
         7 . Method according to  claim 3 , wherein the sonication time period at step (e) is about 5-15 minutes, or about 6-14 minutes, or about 7-13 minutes, or about minutes 8-12 minutes, or about 9-11 minutes, or about 10 minutes. 
     
     
         8 . Method according to  claim 3 , wherein the centrifugation at step (f) is performed at 7000 rpm and the time period is about 10-20 minutes, or about 12-18 minutes, or about 14-16 minutes, or about 15 minutes. 
     
     
         9 . Method according to any one of  claims 1  to  8 , wherein the bulk layered structure phosphorous material is black phosphorous (BP), red phosphorous (RP), violet phosphorous (VP). 
     
     
         10 . Method according to any one of  claims 1  to  9 , wherein the bulk layer-structured phosphorous material is a black phosphorous (BP) material, and the few-layer phosphorous nanomaterial is a few-layer black phosphorous (BP) nanomaterial. 
     
     
         11 . Method according to  claim 1 , wherein the solvent is an organic solvent; preferably the organic solvent is selected from the group consisting of N-methyl-2-pyrrolidone (NMP), alcohols such as methanol, ethanol and isopropanol (IPA), diethyl ether, chloroform, tetrahydrofuran, cyclohexane, toluene, dimethylformamide, and combinations thereof; more preferably the solvent is N-methyl-2-pyrrolidone (NMP). 
     
     
         12 . Method according to  claim 3  or  4 , wherein:
 the first solvent is selected from the group consisting of N-methyl-2-pyrrolidone (NMP), alcohols such as methanol, ethanol and isopropanol (IPA), diethyl ether, chloroform, tetrahydrofuran, cyclohexane, toluene, dimethylformamide, and combinations thereof; 
 preferably the first solvent is N-methyl-2-pyrrolidone (NMP); 
 the second solvent is selected from the group consisting of isopropanol (IPA), other alcohols such as methanol and ethanol; diethyl ether, chloroform, tetrahydrofuran, cyclohexane, toluene, dimethylformamide, and combinations thereof; preferably the second solvent is isopropanol (IPA); and 
 the third solvent is selected from the group consisting of isopropanol (IPA), other alcohols such as methanol and ethanol; diethyl ether, chloroform, tetrahydrofuran, cyclohexane, toluene, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and combinations thereof; preferably the second solvent is isopropanol (IPA). 
 
     
     
         13 . Method according to any one  claims 1  to  12 , wherein substantially no oxidation occurs. 
     
     
         14 . Method according to any one  claims 1  to  12 , wherein the few-layer phosphorous nanomaterial is metal-free. 
     
     
         15 . A few-layer phosphorous nanomaterial obtained by the method as defined in any one of  claims 1  to  14 . 
     
     
         16 . A few-layer black phosphorous (BP) nanomaterial obtained by the method as defined in any one of  claims 1  to  14 . 
     
     
         17 . A few-layer phosphorous nanomaterial as defined in  claim 15  or  16 , having 4 to 10 layers, or 5 to 9 layers, or 6 to 8 layers, or 7 layers, or 6 layers. 
     
     
         18 . A few-layer phosphorous nanomaterial as defined in any one of  claims 15  to  17 , having a thickness which is less than about 12 nm, or less than about 10 nm; or which is about 9 nm, or about 8 nm, or about 7 nm, or about 6 nm, or about 5 nm. 
     
     
         19 . Use of a few-layer phosphorous nanomaterial as defined in any one of  claims 15  to  18 , in the development of photocatalysts, transistor devices, photodetector devices, solar cells, or in bio-imaging, or in phototherapy. 
     
     
         20 . A method for preparing a photocatalyst, comprising coupling the few-layer phosphorous nanomaterial as defined in any one of  claims 15  to  18 , with a 2D material; preferably the 2D material is selected from the group consisting of poly (methyl methacrylate), graphene or hexagonal boron nitride which may be nitrogen-doped, molybdenum disulfide, a carbon nitride nanomaterial; more preferably the 2D material is graphitic carbon nitride (g-C 3 N 4 ). 
     
     
         21 . A method for preparing a photocatalyst, comprising coupling the few-layer black phosphorous (BP) nanomaterial as defined in  claim 20 , with graphitic carbon nitride (g-C 3 N 4 ). 
     
     
         22 . Use of the few-layer phosphorous nanomaterial as defined in any one of  claims 15  to  18 , in the preparation of a photocatalyst. 
     
     
         23 . Use of the few-layer black phosphorous (BP) nanomaterial as defined in  claim 16 , in the preparation of a photocatalyst. 
     
     
         24 . A photocatalyst obtained by the method as defined in  claim 20  or  21 . 
     
     
         25 . A photocatalyst obtained by the method as defined in  claim 21 , which is few-layer black phosphorous nanomaterial/g-C 3 N 4 . 
     
     
         26 . Use of the photocatalyst as defined in  claim 24  or  25 , for water splitting (H 2  evolution).