Sonochemical Synthesis of Cyclodextrin-Coated Quantum Dots for Optical Detection of Pollutant Phenols in Water

A simple, rapid sonochemical procedure for the preparation of highly fluorescent and water-soluble CdSe/ZnS quantum dots (QDs) using α-, β-, and γ-cyclodextrin (CD) as surface-coating agents is reported. The water-soluble QDs were characterized by luminescence spectroscopy, UV−vis spectroscopy, FT-IR spectroscopy, NMR spectroscopy, and transmission electron microscopy (TEM). The quantum yields (QYs) of α-CD-QDs, β-CD-QDs, and γ-CD-QDs in water were about 45, 39, and 27%, respectively. The n-CD-QDs allow highly sensitive determination of phenols by changing CD coating via fluorescence intensity quenching. The α-CD-QDs and β-CD-QDs are sensitive toward p-nitrophenol and 1-naphthol, respectively. Under optimal conditions, the relative fluorescence intensities of α-CD/CdSe/ZnS QDs and β-CD/CdSe/ZnS QDs both decreased linearly with increasing p-nitrophenol and 1-naphthol in the concentration range of 0.01−100 μM, with the corresponding detection limits (3σ) of 7.92 × 10⁻⁹ and 4.83 × 10⁻⁹ M, respectively. However, the sensitivity of n-CD-QDs toward other phenols, including o-nitrophenol, m-nitrophenol, 2-naphthol, o-cresol, m-cresol and p-cresol, are negligible. It is found that p-nitrophenol and 1-naphthol can quench the luminescence of α-CD-QDs and β-CD-QDs in a concentration-dependent manner that is best described by a Stern−Volmer-type equation. The possible underlying mechanism is discussed.