Mixed sp²–sp³ Nanocarbon Materials: A Status Quo Review

Carbon nanomaterials with a different character of the chemical bond—graphene (sp²) and nanodiamond (sp³)—are the building bricks for a new class of all-carbon hybrid nanomaterials, where the two different carbon networks with sp³ and sp² hybridization coexist, interacting and even transforming into one another. The extraordinary physiochemical properties defined by the unique electronic band structure of the two border nanoallotropes ensure the immense application potential and versatility of these all-carbon nanomaterials. The review summarizes the status quo of sp² – sp³ nanomaterials, including graphene/graphene-oxide—nanodiamond composites and hybrids, graphene/graphene-oxide—diamond heterojunctions, and other sp²–sp³ nanocarbon hybrids for sensing, electronic, and other emergent applications. Novel sp²–sp³ transitional nanocarbon phases and architectures are also discussed. Furthermore, the two-way sp² (graphene) to sp³ (diamond surface and nanodiamond) transformations at the nanoscale, essential for innovative fabrication, and stability and chemical reactivity assessment are discussed based on extensive theoretical, computational and experimental studies.