Are Graphitic Surfaces Hydrophobic?

Abstract

Graphitic carbons are important solid materials with myriad applications including electrodes, adsorbents, catalyst support, and solid lubricants. Understanding the interaction between water and graphitic carbons is critically important for both fundamental material characterization and practical device fabrication because the water-graphitic interface is essential to many applications. Research interests in graphene and carbon nanotubes over the past decades have brought renewed interest to elucidate wettability of graphitic carbons and understand their interaction with the surrounding environment. Research on this topic can be traced back to the 1940s, and the prevailing notion has been that graphitic carbons are hydrophobic. Though there have been different voices, this conclusion is supported by many previous water contact angle tests and well accepted by the community since sp carbon is nonpolar in nature. However, recent results from our groups showed that graphitic surfaces are intrinsically mildly hydrophilic and adsorbed hydrocarbon contaminants from the ambient air render the surface hydrophobic. This unexpected finding challenges the long-lasting conception and could completely change the way graphitic materials are made, modeled, and modified. With several other research groups reporting similar findings, it is important for the community to realize the importance of airborne contamination on the surface-related properties of graphitic materials and revisit the intrinsic water-graphite interaction. This Account aims to summarize our recent work on water wettability of graphitic surfaces and discuss future research directions toward understanding the intrinsic water-graphite interaction. Historical perspective will first be provided highlighting the long accepted notion that graphite is hydrophobic along with a few reports suggesting otherwise. Next, our recent experimental data will be presented showing that pristine graphene and graphite are mildly hydrophilic; chemical analysis showed that hydrocarbons adsorb onto the clean surfaces thus rendering them hydrophobic. These results are further rationalized by analyzing the change in surface energy of the graphitic surfaces before and after hydrocarbon contamination. Facile methods to remove hydrocarbons from a contaminated surface will be discussed along with a convenient water treatment method that we developed to inhibit hydrocarbon adsorption onto a pristine graphitic surface. Implications of contamination will be illustrated through comparing the electrochemical activity of pristine and contaminated graphite. Lastly, consequences of these findings and future research directions to address a few important unanswered questions will be discussed.

Graphene‐Assisted Growth of Patterned Perovskite Films for Sensitive Light Detector and Optical Image Sensor Application

“…Inspired by the above studies, we herein put forward a hydrophilic/hydrophobic surface‐induced large‐scale growth of high‐quality patterned Cs‐doped FAPbI 3 perovskite films with high yield through one‐step spin‐coating process assisted by CVD‐grown graphene films. As we all know, CVD‐graphene possesses a natural hydrophobic surface due to airborne contaminants and moisture adsorption, and it can also be transferred onto arbitrary substrates in principle . Therefore, the proposed technique is compatible not only with a variety of spin‐coated perovskite materials and perovskite manufacturing process but also with many substrates enabling some specific applications like next‐generation flexible and deformable optoelectronics.…”

Influence of removing PMMA residues on surface of CVD graphene using a contact-mode atomic force microscope

“…8 Aer transfer, PMMA cannot be removed completely, and the residue of PMMA degrades intrinsic electric and optical properties of 2D materials. [9][10][11][12] To address this issue, solutions such as annealing, [13][14][15][16][17] chemicals, 14 current-induced 18,19 atomic force microscope (AFM) cleaning, [20][21][22][23] rubbing cloth to induce electrostatic force, 24 inductively coupled plasma, 25 stencil mask patterning, 26,27 andCO 2 cluster 28 are usually employed.…”

Hydration layers at the graphite-water interface: Attraction or confinement

“…[36] exhibit a notable oscillatory behavior. Experimental water contact angle measurements recently prompted the following question: "Are graphitic surfaces hydrophobic" [37]?…”