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

• Published in: ACS applied materials & interfaces 2012-10, Vol.4 (10), p.5217-5226
• Main Authors: Gore, Anil H, Gunjal, Dattatray B, Kokate, Mangesh R, Sudarsan, Vasanthakumaran, Anbhule, Prashant V, Patil, Shivajirao R, Kolekar, Govind B
• Format: Article
• Language: English
• Subjects: Cadmium Compounds - chemistry; Cobalt - analysis; Colorimetry; Fluorescent Dyes - chemistry; Hydrogen-Ion Concentration; Ions - chemistry; Quantum Dots; Spectrophotometry, Ultraviolet; Sulfides - chemistry; Time Factors; Water - chemistry; Water Pollutants, Chemical - analysis
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/am301136q

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 Co2+ ions in aqueous solutions. The Co2+ 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 Co2+ ions. The sensing of Co2+ 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 Co2+ ions. The calibration plot of (A – A 0) at 360 nm against concentration of Co2+ ions was linear over the range from 0.5 to 14 μg mL–1 with a correlation coefficient of 0.9996. The accuracy and reliability of the method were further ascertained by recovery studies 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 Co2+ ions in the presence of a complex matrix from environmental aqueous samples.