Hydrothermal Synthesis of Functionalized Carbon Nanodots and Their Clusters as Ionic Probe for High Sensitivity and Selectivity for Sulfate Anions with Excellent Detection Level

Abstract

Nitrogen-doped carbon nanodots (CNDs) were synthesized and utilized as sensing probes to detect different anions and metallic ions within aqueous solutions. The pristine CNDs were developed through a one-pot hydrothermal synthesis. <i>o</i>-Phenylenediamine was used as the precursor. A similar hydrothermal synthesis technique in the presence of polyethylene glycol (PEG) was adopted to form the PEG-coated CND clusters (CND-100k). Through photoluminescence (PL) quenching, both CND and PEG-coated CND suspensions display ultra-high sensitivity and selectivity towards HSO₄^&minus; anions (Stern&ndash;Volmer quenching constant (<i>K</i>_SV) value: 0.021 ppm^&minus;1 for CND and 0.062 ppm^&minus;1 for CND-100k) with an ultra-low detection limit (LOD value: 0.57 ppm for the CND and 0.19 ppm for CND-100k) in the liquid phase. The quenching mechanism of N-doped CNDs towards HSO₄^&minus; ions involves forming the bidentate as well as the monodentate hydrogen bonding with the sulfate anionic moieties. The detection mechanism of metallic ions analyzed through the Stern&ndash;Volmer formulation reveals that the CND suspension is well suited for the detection of Fe³⁺ (<i>K</i>_SV value: 0.043 ppm^&minus;1) and Fe²⁺ (<i>K</i>_SV value: 0.0191 ppm^&minus;1) ions, whereas Hg²⁺ (<i>K</i>_SV value: 0.078 ppm^&minus;1) sensing can be precisely performed by the PEG-coated CND clusters. Accordingly, the CND suspensions developed in this work can be employed as high-performance PL probes for detecting various anions and metallic ions in the liquid phase.