(Digital Presentation) Wettability of Carbon Nanostructures – Hydrophobic or Hydrophilic?
Authors: Stando Grzegorz Jan , Liu Haitao , Li Lei , Janas Dawid 
Published: September 2023

Nanocarbon nanostructures have significant potential to be applied in: filtration[1], energy storying[2], thermogenerators[3], electronics[4], and part of composite materials due to their enormous properties[2]. They characterized magnificent electrical, thermal, and mechanical properties. Many people think their surface nature is hydrophobic. However, more and more scientific publications present the opposite statement about carbon nanotubes and graphene[5-7]. The reason for hydrophobicity is undefined hydrocarbons, which are adsorbed on the nanocarbon surface. The surface character is a crucial parameter for such applications as: electrode materials for storage energy and integration degree between a part of composites.
The surface of fullerene C60, high quality (ID/IG = 0.01) single-walled carbon nanotubes (SWCNTs), single-layer graphene (SLG) deposed on copper foil have been investigated to understand the phenomenon of hydrophobic surface and prove that there are intrinsic hydrophilic. A coating from C60 was deposed on glass by spin coating and free-standing film from SWCNTs by method described in previous work. SLG on Cu was synthesized by CVD method. The water contact angle (WCA) was used to define character of surface. The sample was annealed in atmosphere H2/Ar (C60 and SLG) and air (SWCNTs) to remove surface impurities. WCA was measured after/before annealing. Initial C60 and SWCNTs have hydrophobic (WCA >90), SLG has slightly hydrophilic (about 80 ºC). After annealing the surface, all of them have a strongly hydrophilic character, which was even superhydrophilic for C60 and SWCNTs. The nanomaterials were characterized after/before annealing by many techniques such as: Raman spectroscopy, X-ray photoelectron spectroscopy, Scanning electron microscopy, Atomic force microscopy, and Attenuated total reflectance-Fourier transform infrared spectroscopy. All of them showed that the nanostructures had not been damaged during the surface purification process. Moreover, after a month of exposure to air, the WCA has increased. The samples were again analyzed by the techniques mentioned before and the reason for changing the surface characters was hydrocarbons. To indeficate the them selected groups of organic compound was deposed onto nanocarbon surface and the experimental results manifested that aromatic hydrocarbons are the main reason of hydrophobicity of the surface.
References:
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Acknowledgment:
G.S. would like to thank the Ministry of Science and Higher Education of Poland for financial support of scientific work from budget funds for science in the years 2019–2023 as a research project under the “Diamond Grant” program (grant agreement 0036/DIA/201948) and National Agency for Academic Exchange of Poland (under the Iwanowska program, grant agreement PPN/IWA/2019/1/00017/UO/00001) for financial support during the stay at the University of Pittsburgh in the USA. Part of the work was finial support by NSF (CBET-2028826).