Only-sp² nanocarbon superhydrophobic materials - Synthesis and mechanisms of high-performance

Superhydrophobic systems have fascinated the human kind since the earliest observations of the repellence of water droplets by biological systems. Currently, superhydrophobic materials (SHMs), often inspired by nature and engineered as thin coatings, become an important class of complex systems with numerous industrial implementations. The most important applications of SHMs cover waterproof, self-cleaning, anti-/deicing, anti-fogging, and catalytic systems/units, e.g., in textiles, civil and military engineering, automotive and space industry, and water-from-oil separating systems. In a few above areas, SHMs proved also to be tailorable as smart, i.e., reversibly stimuli-responsive and/or recyclable solutions. In all of those emerging fields, carbon - as the 'sixth element' - represents one of the most prospective components, also in the 'only‑carbon'-based systems. The versatility of carbon (nano)materials, supported by their surface and morphology/topology tunability at from the nano- to macroscale, is vital in the manufacturing of high-performance SHMs. Here, we review only-sp²-hybridized nanocarbon SHMs, i.e., materials exhibiting water contact angle (WCA) >150°, from molecular design to synthesis and evaluation of their application-oriented properties, including WCA. The nanocarbons - pristine/as-made, (non-)covalently functionalized and in a form of carbon‑carbon composites - are analyzed according to their dimensionality: 0D fullerenes, 1D carbon nanotubes (CNTs), 2D graphene, and 3D carbon nanofibers (CNFs). Importantly, this review intends to provide premises toward novel sp²-nanocarbon SHMs, indicating nanowettability and Hansen Solubility Parameters the key ones.