Oxidation-Modulated CQDs Derived from Covalent Organic Frameworks as Enhanced Fluorescence Sensors for the Detection of Chromium(VI) and Ascorbic Acid

Abstract

High-performance sensors for the selective and sensitive identification of chromium(VI) [Cr(VI)] with high toxicity and carcinogenicity are urgently demanded. Carbon quantum dots (CQDs) as outstanding fluorescence sensors were widely applied to detect Cr(VI). Herein, the covalent organic frameworks (COFs) were utilized as a homogeneous precursor to prepare CQDs with N heteroatom by microwave-assisted chemical tailoring. The oxidation degree of COFQDs was adjusted by controlling the amount of sodium persulfate. The results showed that the oxidation degree has a significant influence on the fluorescence performance of COFQDs. In particular, the obtained COFQDs, which possess unique C−N conjugated structures and controllable oxidation degree, displayed a high quantum yield (QY) of up to 26%. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) results indicated that the cutting mechanism involved the breaking of hydrogen bonds and imine bonds, accompanied by partial hydrolysis. In addition, the COFQDs demonstrated promise as efficient "on−off" photoluminescence sensors to detect Cr(VI), providing great advantages including rapid response, large-scale monitoring, and high selectivity. Also, the COFQDs−Cr(VI) system was also used as an "off−on" fluorescence sensor for the detection of ascorbic acid (AA). This study is expected to open an avenue for preparing CQDs with excellent properties using suitable precursors and optimizing oxidation degree.

A water-soluble conjugated polyelectrolyte for selective and sensitive detection of carcinogenic chromium(vi)

“…Thus, recently various advanced materials such as polymers, 12,13 small organic compounds, 14 nanocomposites, [15][16][17][18][19] gold nanoclusters, 20 metal-organic frameworks (MOFs), [21][22][23][24][25] carbon dots, etc. [26][27][28][29][30][31] have been developed as fluorescent probes for Cr(VI) detection. However, most of them further lack superior sensing ability and/or economical on-site usage.…”

Fluorescence Quenching and Highly Selective Adsorption of Ag+ Using N-Doped Graphene Quantum Dots/Poly(vinyl alcohol) Composite Membrane

“…In the past decade, quantum dots (QDs) have received considerable attention in research fields, including analytical sensing, , immune sensing, energy storage, and catalytic oxidation owing to their excellent photochemical stability, long fluorescence lifetime, good water solubility, and good optical properties, including a tunable band gap, narrow emission bandwidth, and high efficiency . Thus, the excellent affinity and fluorescence selectivity of QDs to heavy metal ions in the above studies attracted our attention.…”