Hypochlorite degrades 2D graphene oxide sheets faster than 1D oxidised carbon nanotubes and nanohorns. (December 2017)

• Record Type: Journal Article
• Authors: Newman, Leon; Lozano, Neus; Zhang, Minfang; Iijima, Sumio; Yudasaka, Masako; Bussy, Cyrill; Kostarelos, Kostas
• Is Part Of: Npj 2D materials and applications. Volume 1(2017)
• Page Start: 1
• Page End: 9
• Publication Date: 2017-12
• Subjects: Graphene -- Periodicals; Materials science -- Periodicals; Nanostructured materials -- Periodicals; 620.115
• DOI: 10.1038/s41699-017-0041-3
• Languages: English
• ISSNs: 2397-7132

Abstract

Abstract Carbon nanostructures are currently fuelling a revolution in science and technology in areas ranging from aerospace engineering to electronics. Oxidised carbon nanomaterials, such as graphene oxide, exhibit dramatically improved water dispersibility compared to their pristine equivalents, allowing their exploration in biology and medicine. Concomitant with these potential healthcare applications, the issue of degradability has been raised and has started to be investigated. The aim of the present study was to assess the potential of hypochlorite, a naturally occurring and industrially used ion, to degrade oxidised carbon nanomaterials within a week. Our main focus was to characterise the physical and chemical changes that occur during degradation of graphene oxide compared to two other oxidised carbon nanomaterials, namely carbon nanotubes and carbon nanohorns. The kinetics of degradation were closely monitored over a week using a battery of techniques including visual observation, UV–Vis spectroscopy, Raman spectroscopy, infra-red spectroscopy, transmission electron microscopy and atomic force microscopy. Graphene oxide was rapidly degraded into a dominantly amorphous structure lacking the characteristic Raman signature and microscopic morphology. Oxidised carbon nanotubes underwent degradation via a wall exfoliation mechanism, yet maintained a large fraction of the sp2 carbon backbone, while the degradation of oxidised carbon nanohorns was somewhat intermediate. The present study shows the timeline of physical and chemical alterations of oxidised carbon nanomaterials, demonstrating a faster degradation of 2D graphene oxide sheets compared to 1D oxidised carbon nanomaterials over 7 days in the presence of an oxidising species. Carbon nanomaterials: graphene oxide degrades rapidly when exposed to hypochlorite Oxidised carbon nanomaterials degrade into amorphous structures upon exposure to hypochlorite, a naturally occurring anion in human body. A team led by Kostas Kostarelos at the University of Manchester investigated the physical and chemical modifications occurring during degradation of graphene oxide and oxidised carbon nanotubes and nanohorns exposed to sodium hypochlorite, commonly known as bleach. The degradation pathways were followed over a week with the aid of advanced characterisation tools such as transmission electron microscopy, atomic force microscopy, and optical spectroscopy. Graphene oxide underwent a gradual reduction in dimensions followed by agglomeration and disintegration of its structure. Owing to its peculiar physicochemical features, graphene oxide degraded faster than the other two oxidized carbon nanostructures. These findings may help unveiling the toxicological profile of carbon nanomaterials.