Preparation of silica–ethylmaltol nanoparticles encapsulating europium (III) chelate compound and elution of ethylmaltol forming silica nanocapsules

Silica–ethylmaltol (EMA) nanoparticles (NPs) encapsulating {2,2′,2″,2‴-{4′-{[(4,6-dichloro-1,3,5-triazin-2-yl)amino]biphenyl-4-yl}-2,2′:6′,2″-terpyridine-6,6″-diyl}bis(methylenenitrilo)}tetrakis(acetate)–Eu3+ (DTBTA–Eu (III)) were prepared by the sol–gel method with the addition of EMA. The luminescence emission peak intensity of DTBTA–Eu (III) encapsulated in silica–EMA NPs increased with the amount of DTATB–Eu (III) from 0.4 to 9.6 µmol with the NP size maintained at 441 to 527 nm. The elution of EMA into distilled water led to the easy formation of silica nanocapsules (NCs) containing DTBTA–Eu (III) by controlling the immersion time. The remaining 12% of DTBTA–Eu (III) was bound to the interior of the silica NCs and the luminescence emission intensity of DTBTA–Eu (III) decreased from 293 to 32 at 614 nm after 2 days of immersion. The citrate ions added during the preparation of silica–EMA NPs encapsulating DTBTA–Eu (III) induced an electrostatic repulsion between silica NPs caused by negative charges of citrate ions on the silica NPs, resulting in a decrease in NP size from 616±22 to 329±15 nm, and the luminescence emission peak intensities of silica–EMA NPs encapsulating DTBTA–Eu (III) decreased from 950 to 250.