Energy-efficient Preparation of Amino and Sulfhydryl Functionalized Biomass Carbon Dots via a Reverse Microemulsion for Specific Recognition of Fe and L-cysteine.

Amino- and sulfhydryl- functionalized biomass carbon dots (BCDs) were prepared by one-pot reverse microemulsion for specific recognition of ferric ions (Fe) and L-cysteine (L-Cys). Green grapefruit peel was used as the carbon source while aminosilane and mercaptosilane were used as N- and S-supplier. Following the adsorption of Fe on the surfaces of BCDs-NH and BCDs-SH, the fluorescence responses was quenched step by step, while adding L-Cys to the BCDs-NH/Fe system restored the fluorescence. The BCDs-NH and BCDs-SH system exhibited extremely low limits of detection for Fe of 3.2 and 3.0 nM, respectively, within a wide linear ranges of 0.006-200 μM and 0.004-200 μM, respectively. The BCDs-NH/Fe systems were used as an optosensor for L-Cys in the concentration ranges of 0.08-30 and 30-1000 μM with a detection limit of 65 nM. Developed BCDs-NH and BCDs-SH were able to respond to Fe in water samples with satisfactory recoveries of 100.1%-103.1% and 94.6%-108.5%, respectively, and the BCDs-NH/Fe system was also able to respond to BCDs-NH/Fe in actual lake water samples with recoveries from 87.3% to 98.8%. Meanwhile, The BCDs-NH exhibited good photoluminescence and stability, and the with a fluorescence quantum yield was as high as 25%. This work demonstrates the feasibility of using such materials to remove hazardous ions from water and employing the resulting complexes for optosensing in a sustainable manner.