Fullerenes and tree-shaped/fingerprinted carbon quantum dots for chromium adsorption via microwave-assisted synthesis

Background: Employing citric acid/dimethyl formamide (CA/DMF), two distinct types of carbon quantum dots (CQDs), tree-shaped/fingerprinted (TF-CQDs) and fullerene-like (F) were synthesized from both cellulose and carboxymethyl cellulose (CMC). Methods: Fluorescence microscopy revealed different emission colors: blue for TF-CQDs and green for F, highlighting the structural influence on light properties. Transmission electron microscopy (TEM) confirmed the intricate fingerprinted and tree-like morphology of TF-CQDs and the spherical nature of F derived from CMC. The adsorption behavior and kinetics of Cr(vi) removal from water by TF-CQDs and F were evaluated. Significant findings: Both samples demonstrated rapid Cr(vi) uptake; TF-CQDs reached equilibrium within 120 minutes compared to 240 minutes for F. Subsequent leaching led to decreased adsorption after these initial periods. Kinetic analysis revealed a first-order model for TF-CQDs, implying physical adsorption dominance. Conversely, F exhibited a better fit to pseudo-first and second-order models, suggesting combined chemical and physical mechanisms.