Unveiling dialysis effects on carbon dots via FTIR spectroscopy

Carbon dots (CDs) synthesized from piperazine/phthalic acid (P:PhA) and urea/citric acid (U:CA) precursor systems were investigated in order to clarify how dialysis affects their surface chemistry and optical response. FTIR spectra acquired before and after dialysis revealed changes in several vibrational bands associated with O–H/N–H, C=O, and C–N/C–O functional groups. These spectral variations suggest that dialysis mainly removes residual molecular species with weights higher than cutoff of dialysis membranes highlighting the chemical features of the carbon dots obtained. A FTIR analysis of the representative P: PhA 2:1 sample showed that dialysis is associated with changes in the relative intensity of O–H/N–H, C=O, and C–N/C–O-related contributions. Complementary photoluminescence measurements indicated that these chemical changes were accompanied by modifications in the optical response, while representative TEM observations suggested improved particle dispersion after purification. These results support the view that dialysis acts primarily by separating undesired reaction byproducts, highlighting the importance of post-synthetic purification in defining the final properties of these nanomaterials.