Standards Development

Scope

The document describes methods for characterising the chemical properties of powders or liquid dispersions containing graphene-related two-dimensional materials, using a set of suitable measurement te chniques. The techniques detailed are X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), thermogravimetric analysis (TGA) and Fourier -transform infrared spectroscopy (FTIR). These determine the carbon-to-oxygen ratio, elemental composition, trace metal impurities, weight percentage of chemical species and the functional groups present. The sample preparation, protocols and data analysis for the different techniques are included.

Purpose

Graphene does or will impact many application areas including solar cells, biosensors, displays , composites, flexible electronics and energy storage due to its exceptional properties. However, it is not just graphene that is used but other variants such as reduced graphene oxide, graphene oxide and functionalised forms of graphene are commonly employed. These different graphene-related twodimensional materials (GR2Ms) may be suitable for different application areas and therefore a full understanding of the chemical properties of commercially available materials is required so the correct material can be selected for different application areas.

As these materials are increasingly used in different industries, international standardization is required to support commercialization. Reliable, accurate, and reproducible measurements are important due to t he multiple production routes and consequent potential variability in properties. Producers of the material require standards to maintain quality in manufacture.

This technical specification details methods to measure the chemical properties of powder and dispersions containing GR2M. The techniques covered are X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICP-MS), thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR).

X-ray photoelectron spectroscopy (XPS) is used to provide quantitative measurements of the surface chemical composition of graphene-related two-dimensional materials. It can measure every element except hydrogen and helium that are within approximately 10 nm of the surface an d at equivalent homogeneous concentrations above the XPS detection limit.

Inductively coupled plasma mass spectrometry (ICP -MS) is used to provide quantitative measurements of the amount of metal impurities in samples containing graphene related two dimensional materials. However, using conventional solution sample introduction ICP -MS, the sample has to be completely solubilized and hence digestion of the samples is required using harsh acid and microwave treatment before analysis using ICP-MS.

Thermogravimetric analysis (TGA) is a common material characterization technique available in research and industry labs, which offers rapid and simple characterization of bulk material properties providing useful qualitative and quantitative information. TGA is widely used for characterization of graphene materials to determine the amount of impurities (i.e., water, amorphous carbon, metals), presence of functional groups, traces of surfactants or other organic impurities from fabrication process or impurities f rom initial raw material (Graphite, silica, metal oxides etc).

Fourier-transform infrared spectroscopy (FTIR) is used to understand the functional groups that are present for different materials with significant non-carbon elements already identified using complementary techniques herein