Selective inclusion of polycyclic aromatic hydrocarbons (PAHs) on calixarene coated silica nanospheres englobed with CdTe nanocrystals

Abstract

Highly luminescent and stable calixarene (CA[n], n = 4, 7) coated silica nanospheres englobed with CdTe nanocrystals were prepared via a sol–gel technique in aqueous media, and were characterized by luminescence spectroscopy, ultraviolet-visible spectroscopy (UV-vis), FT-IR spectroscopy, transmission electron microscopy (TEM), etc. The nanocomposites (CA[n]@SiO₂@CdTe) showed higher fluorescence intensity and were more stable in comparison with the previous SiO₂@CdTe nanoparticles (NPs). The CA[n]@SiO₂@CdTe NPs allowed highly sensitive determinations of PAHs by changing the calixarene coating via enhancement of the response of the fluorescence intensity of the CA[n]@SiO₂@CdTe NPs. The CA[4]@SiO₂@CdTe and CA[7]@SiO₂@CdTe NPs turned out to be sensitive to the presence of anthracene and pyrene, respectively. Under optimal conditions, the relative fluorescence intensities of CA[4]@SiO₂@CdTe and CA[7]@SiO₂@CdTe NPs both increased linearly with increasing anthracene and pyrene concentration in the range 0.1–50 µM, with the corresponding detection limits (3α) of 2.45 × 10⁻⁸ M and 2.94 × 10⁻⁸ M, respectively, while the fluorescence of CA[n]@SiO₂@CdTe NPs in response to other PAHs (including acenaphthene, anthracene, 9,9-diflurofluorene, carbazole, fluoranthene, phenanthrene, biphenyl, fluorene, pyrene) were negligible. It was found that anthracene enhanced the luminescence of the CA[4]@SiO₂@CdTe and pyrene enhanced that of CA[7]@SiO₂@CdTe nanocomposites in a concentration dependence that is best described by a Langmuir binding isotherm equation. The possible mechanism is discussed.