Interaction of toxic metals with penta variant functional groups decorated carbon quantum dots: An in-silico investigation using density functional theory calculations towards water remediation/quality monitoring applications

Using quantum chemical density functional theory, we have examined the detection ability of functionalized carbon quantum dots (CQDs) with different sizes and five functional groups (carboxyl (COOH), hydroxyl (OH), amino (NH2), thiol (S-H), and phosphono (H2PO3)) towards the toxic metals iron (Fe), chromium (Cr), selenium (Se), mercury (Hg), antimony (Sb), and cadmium (Cd) in both gas and solvent (water) phases. Preliminary screening through interaction studies has projected that the NH2-functionalized and COOH-functionalized CQDs had greater adsorption affinities toward the toxic metals. Further, the interaction of toxic metals with functionalized CQDs is qualitatively assessed through optical and magnetic transduction phenomena. The highest percentage of decrement in ultraviolet-visible absorption peaks is observed for Fe with COOH-functionalized CQD-C32H15O2 (69.91 %), Se with OH-functionalized CQD-C31O15H15 (44.56 %), Fe with NH2-functionalized CQD-C31H16N (98.42 %), Cr SH-functionalized CQD -C19H11S (39.16 %), Fe with H2PO3-functionalized CQDC31H16O3P (71.48 %). Furthermore, the appearance of new characteristic peaks in Raman spectra has confirmed the toxic metal complexation ability of the functionalized CQDs. Interestingly, the highest lifetime is observed in Fe with NH2-functionalized CQD C31H16N (31.52 ns). Finally, we can observe an increase in magnetic moment upon metal complexation with the functionalized CQDs. In summary, our investigations have proved that functionalized CQDs can act as adsorbents toward Fe, Cr, and Se while they can detect Hg and Sb in the drinking water making them as suitable candidates for water remediation as well as quality monitoring applications.