Photoinduced and Electrochemical Applications of Carbon-Based Nanoparticles from Spent Coffee Grounds

The interest of the scientific community toward carbon-based nanostructures is justified by the wide range of applications of such multifaceted structures. In the present work, carbon nanoparticles (CNPs) were synthesized, in mild conditions, by using spent coffee grounds as the carbon source. Green-emitting CNPs of about 40 nm were obtained, and they were characterized by X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, fluorescence spectroscopy, and Fourier transform infrared spectroscopy, highlighting that they are naturally doped with N, K, Mg, and P. Such intrinsic doping promotes the characteristic green emission; furthermore, the N- and P-doping prompted us to evaluate their ability to photoproduce O-1(2) for PDT applications. The presence of heteroatoms in the CNP structure was also used to electrochemically promote the oxygen reduction reaction and hydrogen evolution reaction catalysis.