Can you create 2D nanosheets from cat litter?

24 Mar 2017

What do talcum powder, beach sand and cat litter have in common? Surprisingly, they can all be used to create two-dimensional materials, known as nanosheets.

In what’s believed to be a world first, researchers from Trinity College Dublin and the University of Manchester used a technique called liquid phase exfoliation (LPE) to create 2D sheets from these unusual starting materials. They published their results this week in the journal 2D Materials.

Lead researcher Professor Jonathan Coleman, from Trinity College Dublin, said: “Two-dimensional materials have interesting properties and broad potential applications. For applications in fields such as composites, printed electronics and electrochemical devices, suspensions of nanosheets in liquids are needed. A number of methods exist to do this. However, they are all relatively limited, as they tend to apply only to a single material or family of materials. In contrast, LPE is quite versatile and widely applicable.”

In their study, the team aimed to find out exactly how versatile LPE is by using impure starting materials far removed from the pure powder or crystals from chemical suppliers normally used to create nanosheets.

Professor Coleman said: “LPE has been applied previously to graphene, boron nitride, and transition metal oxides, but these materials are nominally uncharged. Many layered oxides, hydroxides and silicates are charged.

“This means they must always be accompanied by charge balancing counter ions. The presence of these counter ions might suggest LPE cannot be used to exfoliate clays, for example. Additionally, the starting materials that have been exfoliated by LPE tend to be very pure. The question is whether LPE can be used to produce nanosheets from an impure starting material, or whether other components will dominate the exfoliated product.

The team put talcum powder bought from Boots (containing the layered compound talc), cat litter from Lidl (known to contain layered silicate compounds, notably palygorskite and montmorillonite/bentonite), and sand collected from a beach in Co. Kerry, Ireland (suspected to contain small amounts of layered clays), through a standard LPE procedure. This comprised placing the materials in a surfactant solution and using ultrasound to agitate the particles, which was then followed by centrifugation.

The team successfully produced nanosheets of talc, a bentonite/palygorskite mixture and mica from the three starting materials respectively.

Professor Coleman said: “Our results show that LP is an extremely versatile technique for producing nanosheets from layered precursors. It is possible to process naturally occurring materials such as talc, cat litter and a clay/sand mix using LPE and obtain purified nanosheets, while rejecting any unwanted non- 2D material.

“What is particularly surprising is that the bentonite and palygorskite layered crystals, contained in the cat litter as well as the mica in the beach sand, should both consist of charged layers with charge-balancing counter ions, yet could still be exfoliated by LPE.

“This shows LPE can potentially be applied to a much broader range of layered compounds than previously thought, opening the possibility of exfoliating a range of layered silicates as well as charged layered oxides and hydroxides.”