Abstract

Unusual structure of low-density carbon nanofoam, different from the commonly observed micropearl morphology, was obtained by hydrothermal carbonization (HTC) of a sucrose solution where a specific small amount of naphthalene had been added. Helium-ion microscopy (HIM) was used to obtain images of the foam yielding micron-sized, but non-spherical particles as structural units with a smooth foam surface. Raman spectroscopy shows a predominant sp2 peak, which results from the graphitic internal structure. A strong sp3 peak is seen in X-ray photoelectron spectroscopy (XPS). Electrons in XPS are emitted from the near surface region which implies that the graphitic microparticles have a diamond-like foam surface layer. The occurrence of separated sp2 and sp3 regions is uncommon for carbon nanofoams and reveals an interesting bulk-surface structure of the compositional units.

Highlights

  • A large variety of nanomaterials can be formed from elemental carbon

  • When sp3 bonds are dominating, the materials are named diamond-like carbons. Their properties depend on the relative abundance of the sp2 - and sp3 - hybridized carbon atoms [1]. Carbon materials with both graphite- and diamond-like bonds were realized by various synthetic methods, e.g., laser ablation, chemical vapor deposition or hydrothermal carbonization [2]

  • We focus on hydrothermal carbonization (HTC) for the synthesis of carbon nanofoam with separated regions of sp2 - and sp3 -hybridized carbon atoms

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Summary

Introduction

Amorphous carbon materials with a high fraction of sp bonds are named graphite-like carbons. When sp bonds are dominating, the materials are named diamond-like carbons. Their properties depend on the relative abundance of the sp2 - and sp3 - hybridized carbon atoms [1]. Carbon materials with both graphite- and diamond-like bonds were realized by various synthetic methods, e.g., laser ablation, chemical vapor deposition or hydrothermal carbonization [2]. A material containing graphene sheets and diamond-like structures has been observed after catalytic carbonization of wood charcoal [3]. We focus on hydrothermal carbonization (HTC) for the synthesis of carbon nanofoam with separated regions of sp2 - and sp3 -hybridized carbon atoms

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