Modulating the Sensing Behavior of Functionalized Mesoporous Silica towards Metal Ions in Aqueous Medium

Abstract

A rhodamine‐bisphenol A incorporated mesoporous silica (RBA‐IMS) has been synthesized as a turn‐on chemosensor for selective sensing of Al3+, Cr3+ and Fe3+. It has been observed that the presence of an ethylenediamine unit instead of hydrazine, as reported previously, is significant, changing the sensing behavior altogether. The probe does not show any color or absorption band in the visible region and fluorescence in the absence of most of the cations except Al3+, Cr3+ and Fe3+. RBA‐IMS becomes pink with these cations, shows strong absorption at 530 nm and strong fluorescence at 550 nm in 10 mM HEPES buffer in water/methanol=14 : 1 (v/v) (pH 7.0). This is in contrast to the hydrazine‐containing material, which could sense Hg2+ and Cu2+ in aqueous media but not Al3+, Cr3+ and Fe3+. A small change of the linkage in the material suppresses the detection of the divalent cations while enabling the sensing of the trivalent cations in aqueous media.

Structure–metal ion selectivity of rhodamine-based chemosensors

“…Replacement of hydrazine with ethylenediamine changes the properties of silica based material. 120 Now the ethylenediamine linked probe was able to sense Al 3+ , Fe 3+ and Cr 3+ in water/methanol (14 : 1, v/v) where the cation catalyzed the breaking of imine bonds, leading to the detachment of the bisphenol–rhodamine unit from the silica framework. Thus, the selection of medium plays a significant role in determining metal ion selectivity and the reaction pathway.…”

Imaging of Al3+in plant roots by the interaction with a bisphenol A-based chemosensor

“…14 Bisphenol A has also been used to anchor fluorophoric platforms for sensing and separation of variuos metal ions. 15,16 Thus, there is plenty of opportunity to tune the spectral properties of bisphenol A by attaching different controlling units as it contains two aldehyde groups.…”