How an environmental issue could turn into useful high-valued products: The olive mill wastewater case

Carbon-based nanomaterials have been directly synthesized from olive mill wastewaters (OMWWs) for the first time, using expedite and simple environmental-friendly procedures. The OMWWs collected from a mill operating by a two-phase centrifugation system, after being heated (150-300 °C) solely or in the presence of additives for 2-12 h, furnished nanostructured materials in high yields. Under an optimised set of reaction conditions here described, the resultant as-synthetized aqueous dispersions of carbon nanoparticles exhibit outstanding fluorescence emission properties, which encompass an astonishing quantum yield (Φ_F > 0.4). The as-prepared carbon nanomaterials show excitation-dependent emissions covering the whole visible spectrum, with a predominant high glow in the blue-green region, and a remarkable photostability. The relevant features attained by the nanomaterials here reported, allied to their easy synthesis and carbon source affordability, render them with unique capabilities to be used in several current and emerging technological applications, namely in bioimaging and nanomedicine, sensorial analysis, (photo)catalysis and optoelectronics. The as-synthesized nanoparticles show a remarkable high sensitivity and selectivity towards haemoglobin.