Carbon is one of the most abundant elements on Earth and is known for its ability to form a wide range of compounds. At the nanoscale, carbon can also form low-dimensional materials like graphene (2D), carbon nanotubes (1D), fullerenes (0D), and carbon dots (CDots) (0D), depending on how sp² and sp³ hybridized carbon atoms are arranged, which are featured for their unique properties and have become key in materials research.[1] While many carbon-based nanomaterials exhibit weak photoluminescence (PL), CDots are characterized by pronounced and tunable PL properties and are typically classified into four main types: carbon quantum dots (CQDs), graphene quantum dots (GQDs), carbon nanodots (CNDs), and carbonized polymer dots (CPDs).³ Despite extensive efforts towards defining these categories, accurately identifying the specific type of material remains a significant challenge due to the considerable overlap in their morphological and optical properties.[2] Among the challenges in characterizing CDots, a particularly notable feature is their PL dependence on the excitation wavelength. This behavior has been attributed to electronic transitions involving surface states, structural defects, or oxygen-containing functional groups, while others suggest it may result from a distribution of emissive sites or size-related effects.[3]

In this work, we present an ultrarapid microwave-assisted method (60 seconds) that enables the simultaneous synthesis of two distinct carbon-based nanomaterials. A specific purification procedure was developed, allowing their complete separation and revealing that each material exhibits unique physicochemical properties. Through this approach, we successfully obtained green-emissive CQDs with an average size of 7.0 ± 0.9 nm, along with non-emissive black carbon nanospheres of ca. 50 nm in diameter. To gain insight into their structural and functional behavior, an exhaustive characterization was carried out using complementary techniques, including Small-Angle X-ray Scattering (SAXS), Raman spectroscopy, Attenuated Total Reflectance – Fourier Transform Infrared Spectroscopy (ATR-FTIR), High resolution Transmission Electron Microscopy (HRTEM), X-ray Photoelectron Spectroscopy (XPS), and X-ray Diffraction (XRD). This comprehensive analysis provided a detailed understanding of the morphology, composition, and structural features of both nanomaterials. The photocatalytic activity of these materials was evaluated using as proof-of-concept the reduction of methyl viologen (MV²⁺) in aqueous media.