Sorting Two-Dimensional Nanomaterials Using Density Differentiation

NU 2008-027B

Inventors

Alexander A Green 

Mark C Hersam*

Abstract

Two-dimensional nanomaterials are promising materials in field effect transistors, reinforced composites, sensors, and transparent conductors. Among them, monolayer graphene, a two-dimensional single atomic layer of carbon, has outstanding electronic, mechanical, and chemical properties. Other two-dimensional nanomaterials include those derived from boron nitride (BN), transition metal dichalcogenides, graphite oxide and molybdenum disulfide (MoS2). Despite the technological potential of two-dimensional nanomaterials, scalable methods of synthesizing and purifying such are absent. There remains a need for methods of preparing and purifying two-dimensional nanomaterials with controlled number of layers and isolation of graphene nanomaterials in particular. The present invention affords sorting two-dimensional (planar) nanomaterials by atomic layer thickness by dispersion of the nanomaterials in water employing surface active components that associate differentially with nanomaterials of different thickness, and exhibit different buoyant densities in a fluid medium. Separation is accomplished by density gradient ultracentrifugation (DGU), after which physically separated nanomaterials, grouped according to atomic layer thickness, can be recovered. Thus an isolated fraction containing 80% of graphene flakes of 1.2 nm, corresponding to single-layer graphene, was obtained using DGU. The thickness distributions of the sorted graphene with this process show a monotonic increase in the average flake thickness with increasing buoyant density. Graphene fractions produced superior performance as transparent conductors (high optical transmittance from ‚àº300 to 3300 nm) and improved conductivity versus films produced from sedimented graphene solutions. These results suggest that additional two-dimensional nanomaterials can also be sorted using density differentiation. 

Applications

• 2D semiconductors and devices

Advantages

• High purity 2D graphene monolayer production
• Scalable 2D material exfoliation / purification process
• Environmentally compatible solvents and condition

Publication

Green A, Hersam M (2009) Solution Phase Production of Graphene with Controlled Thickness via Density Differentiation. Nano Letters, 9(12), 4031-4036

IP Status

Issued US Patent Nos. 8,852,444; 9,114,405; 9,416,010; 10,179,841; and 10,265,646