Highly Selective and Sensitive Recognition of Cobalt(ll) Ions Directly in Aqueous Solution Using Carboxyl-Functionalized CdS Quantum Dots as a Naked Eye Colorimetric Probe; Applications to Environmental Analysis

摘要

Quantum dots (QDs) are usually used as fluorescent probe, and they are difficult to use in colorimetric detection. However, in this report carboxyl-functionalized CdS (COF-CdS) QDs were synthesized in aqueous solution for colorimetric detection following a classic method. On the basis of inducing the aggregation of COF-CdS QDs, a simple naked eye colorimetric method with high sensitivity and selectivity was developed for the sensing of Co~(2+) ions in aqueous solutions. The Co ions induced COF-CdS QDs results in a marked enhancement of the UV—vis absorption spectra at 360 nm, and the process was accompanied by a visible color change from colorless to yellowish brown within 5 min, which proves a sensitive detection of Co~(2+) ions. The sensing of Co~(2+) ions can therefore be easily achieved by a UV—vis spectrophotometer or even by the naked eye. Under the optimized circumstances, this method yields excellent sensitivity (LOD ~ 0.23 μg mL~(-1)) and selectivity toward Co~(2+) ions. The calibration plot of (A — A_O) at 360 nm against concentration of Co~(2+) ions was linear over the range from 0.S to 14 μg mL~(-1) with a correlation coefficient of 0.9996. The accuracy and reliability of the method were further ascertained by recovery stuthes via standard addition method with percent recoveries in the range of 99.63—102.46%. The plausible mechanism for the color change reaction has also been discussed. Our attempt may provide a cost-effective, rapid, and simple solution for the inspection of Co~(2+) ions in the presence of a complex matrix from environmental aqueous samples.