Zero-dimensional nano-carbons: Synthesis, properties, and applications

Zero-dimensional (0D) nano-carbons, including graphene quantum dots, nanodiamonds, and carbon dots, represent the new generation of carbon-based nanomaterials with exceptional properties arising from diverse quantum phenomena, such as the surface, size, and edge effects, which strongly depend on the carbon–carbon bond configuration (sp2, sp3, and a mixture of sp2 and sp3) and particle size. Their unique physicochemical properties, including the optical, electronic, magnetic, reactivity, and catalytic properties, are valuable for energy conversion and storage, sensing, catalysis, optoelectronic devices, modern nanotechnologies, biomedical, and many other applications. This review aims to provide insights into the distinctive effects of 0D nano-carbon microstructures on their physicochemical properties that are crucial for cutting-edge fundamental studies and a broad range of multifunctional applications. The key synthesis methods for different types of 0D nano-carbons and current advances of characterization and computational techniques to study the structures of 0D nano-carbons and their structure–property relationships are also discussed. The review concludes with the current status, challenges, and future opportunities in this rapidly developing research field.