Abstract:
Rhodamine 6G functionalized mesoporous silica (RFMS) has been used for the selective sensing of Al3+,
Cr3+ and Fe3+ ions. RFMS has been characterized via FT-IR spectroscopy, PXRD, N2-adsorption/
desorption, TEM, 13C and 29Si solid state NMR, and absorption and fluorescence spectroscopy studies.
The amount of organic moieties incorporated into the silica matrix has been ascertained via TGA. RFMS
shows no absorption band in the visible region in the absence of any other cations, but in the presence
of Al3+, Cr3+ and Fe3+, it exhibits a band at 528 nm. The intensity of this peak increases with the increase
in the metal ion concentration. The fluorescence intensity of RFMS at 550 nm is enhanced significantly
in the presence of Al3+, Cr3+ and Fe3+ ions in water/ethanol (14 : 1, v/v) (lex = 500 nm). No other metal
ion is able to induce any enhancement in the emission intensity. The quantum yield and lifetime of
RFMS increase considerably in the presence of these trivalent cations. The naked eye detection of these
cations is possible through monitoring the color change of RFMS from colorless to pinkish orange
under visible light, while under UV light the color change occurs from bluish to fluorescent greenish.
The opening of the spirolactam ring of RFMS is induced by interactions with these cations, which results
in the pink color and strong fluorescence. RFMS has been utilized to separate Al3+, Cr3+ and Fe3+ ions
from an aqueous medium with very high removal efficiency (B90%). Its maximum uptake capacities
have been determined to be 11.20, 19.72 and 21.55 mg/g for Al3+, Cr3+ and Fe3+ ions, respectively.
