Process for preparing graphene nanoplatelets
Process for producing graphene nanoplatelets, comprising expanding flakes of intercalated graphite and collection of the same in a dispersing medium with forming of a dispersion that is subjected to exfoliation and size reduction treatment carried out by high pressure homogenization in a high shear homogenizer. A dispersion of graphene is obtained in the form of nanoplatelets, at least 90% of which have a lateral size (x, y) from 50 to 50,000 nm and a thickness (z) from 0.34 to 50 nm.
1. A process for producing graphene nanoplatelets having a C/O ratio ≥100:1, comprising the steps of:
a) expanding flakes of intercalated graphite having a lateral size of ≤500 μm by exposing said flakes to a temperature from 1300 to 12000° C. for a time of less than 2 seconds and obtaining an expanded graphite,
b) dispersing said expanded graphite in a dispersing medium,
wherein said dispersing medium is water and said dispersion of said expanded graphite is carried out in the absence of a surfactant or in the presence of a surfactant in an amount not higher than 1% by weight of the weight of said expanded graphite, and
said dispersion of said expanded graphite in said dispersing medium is carried out directly after said step of expansion at high temperature by collecting said expanded graphite in said dispersing medium just after its formation:
c) subjecting said expanded graphite obtained from step b) to exfoliation and size reduction treatment by high pressure homogenization in a homogenizer in which the dispersion of said expanded graphite is pumped at a pressure above 35 MPa through one or more microchannels or necks having a transverse section of 500 μm or less, whereby the particles of said expanded graphite are subjected to shear stresses and are caused to collide at an energy level from 10 to 200 Wh/g, and
d) obtaining a dispersion of said graphene nanoplatelets in said dispersing medium, wherein at least 90% of said graphene nanoplatelets have a lateral size (x, y) from 50 to 50,000 nm and a thickness (z) from 0.34 to 50 nm, the lateral size being greater than the thickness (x,y>z).
2. The process of claim 1 , wherein said size reduction treatment by high pressure homogenization of said step c) is carried out in a homogenizer in which the dispersion of expanded graphite is pumped at a pressure from 100 to 500 MPa.
3. The process of claim 1 , wherein said size reduction treatment by high pressure homogenization of said step c) is carried out in a homogenizer in which the dispersion of expanded graphite is pumped at a pressure from 150 to 500 MPa.
4. The process of claim 1 , wherein said high pressure homogenization treatment is carried out in a homogenizer in which the dispersion of said expanded graphite is pumped through one or more micro-channels or necks having a transverse section ≤250 μm.
5. The process of claim 1 , wherein said high pressure homogenization pumped through one or more micro-channels or necks having a transverse section ≤100 μm.
6. The process of claim 1 , wherein the process is carried out in a continuous manner by continuously feeding said graphite flakes to said high temperature expansion step, continuously discharging the so-obtained expanded graphite in said dispersing medium and continuously subjecting said expanded graphite dispersed in said dispersing medium to said exfoliation and size reduction treatment carried out by high pressure homogenization.
7. The process of claim 1 , further comprising:
e) concentrating or drying said dispersion obtained after said exfoliation and size reduction treatment.
8. The process of claim 1 , wherein said step a) of expanding said intercalated graphite flakes at a temperature from 1300 to 12000° C. for a time of less than 2 seconds is carried out by means of an electric arc, a microwave oven, a high frequency induction oven, or by forming plasma.