Synthesis of highly luminescent cobalt(II)-bis(8-hydroxyquinoline) nanosheets as isomeric aromatic amine probes

Highly luminescent and water-soluble cobalt(II)-bis(8-hydroxyquinoline) (CoQ₂) nanosheets have been successfully synthesized via a simple, rapid sonochemical method. The water-soluble CoQ₂ nanosheets were characterized by luminescence spectroscopy, UV–vis spectroscopy, FT-IR spectroscopy and transmission electron microscopy (TEM). The CoQ₂ nanosheets allow highly sensitive and selective determination of p-nitroaniline via fluorescence quenching. Under optimal conditions, the relative fluorescence intensities of nanosheets decreased linearly with increasing p-nitroaniline. However, the sensitivity of CoQ₂ nanosheets toward other aromatic amines including o-diaminobenzene, m-diaminobenzene, p-diaminobenzene, p-toluidine, o-nitroaniline, m-nitroaniline, p-chloroaniline and aniline is negligible. It is found that p-nitroaniline can quench the luminescence of CoQ₂ nanosheets in a concentration-dependent manner that is best described by a Stern–Volmer-type equation. The possible underlying mechanism is discussed.