Detection and Quantification of Graphene-Family Nanomaterials in the Environment

Abstract

An increase in production of commercial products containing graphene-family nanomaterials (GFNs) has led to concern over their release into the environment. The fate and potential ecotoxicological effects of GFNs in the environment are currently unclear, partially due to the limited analytical methods for GFN measurements. In this review, the unique properties of GFNs that are useful for their detection and quantification are discussed. The capacity of several classes of techniques to identify and/or quantify GFNs in different environmental matrices (water, soil, sediment, and organisms), after environmental transformations, and after release from a polymer matrix of a product is evaluated. Extraction and strategies to combine methods for more accurate discrimination of GFNs from environmental interferences as well as from other carbonaceous nanomaterials are recommended. Overall, a comprehensive review of the techniques available to detect and quantify GFNs are systematically presented to inform the state of the science, guide researchers in their selection of the best technique for the system under investigation, and enable further development of GFN metrology in environmental matrices. Two case studies are described to provide practical examples of choosing which techniques to utilize for detection or quantification of GFNs in specific scenarios. Because the available quantitative techniques are somewhat limited, more research is required to distinguish GFNs from other carbonaceous materials and improve the accuracy and detection limits of GFNs at more environmentally relevant concentrations.

Figure 1

A selection of unique graphene-family nanomaterial (GFN) properties and the analytical techniques that can be used to measure these properties.

Figure 2

Degradation of GFN/polymer nanocomposites by environmental processes such as UV-weathering, rain, acid rain, alkaline conditions, microbial activity, and mechanical wear can lead to the release of a heterogeneous mixture of polymer fragments, polymer fragments containing GFNs, GFNs coated in polymer, and free GFNs.

Figure 3

The thermal stability as a function of mass loss for graphene, graphene oxide^{, , , ,} and reduced graphene oxide^{, ,} relative to polymer matrices (LCPU = liquid crystalline polyurethane, PS = polystyrene, PMMA = poly(methyl methacrylate), PEST = polyester, and epoxy),^–, other carbonaceous nanomaterials, and plant material (lignin), soils or soil materials,^– and sediments. An asterisk (*) indicates that clay was not included as part of the thermal gravimetric analysis (TGA) profile while a double asterisk (**) indicates that clay was included as part of the TGA profile. The plot shows where overlap can occur between the thermal profile of the CNM and the thermal profile of the matrix. Ranges provided are the most dramatic change(s) observed with TGA under inert conditions (N₂ or Ar) with ramp rates ranging from 5 °C/min to 20 °C/min.

Figure 4

The availability of different techniques for GFN quantification. Techniques are compared based on their availability for purchase and their availability in environmental testing laboratories