Carbon dots from agroindustrial residues: a critical comparison of the effect of physicochemical properties on their performance as photocatalyst and emulsion stabilizer

Carbon dots have been synthesized through a pyrolysis route with agroindustrial wastes of Yerba Mate (YM), Avocado Seed (AS), and Orange Peel (OP) as raw materials. The selection of the pyrolysis temperature was according to the thermogravimetric profile of the raw materials. A thorough characterization by transmission electron microscopy (TEM), ζ-potential, ultraviolet visible spectroscopy (UV/vis), Raman, Fourier transform infrared (FTIR) spectroscopy, and steady-state, and time-resolved area normalized emission spectroscopy (TRANES) suggest spherical nanomaterials with diameters lower than 5.0 nm and polyfunctional surfaces with an abundance of negatively charged surface groups. Regarding their application as photocatalyst and as Pickering emulsion stabilizers, all materials have different performances. In the first case, almost 100% and 40% of the photodecoloration of methylene blue was achieved in 2 h by the materials obtained from YM and AS, respectively. Nevertheless, different mechanisms were proposed for both cases. Regarding their performance as Pickering emulsion stabilizers, all materials show different performances. Interestingly, Raman spectroscopy results provide useful information to understand the observed results.