A proficient magnetic nano-platform with covalently assembled methyl red indicator for the dual recognition of pH and Hg2+

Abstract

This article embodies the synthesis, photophysical and complexation properties of a multifarious sensory probe based on ‘one-pot thioesterification’ of an established acid-base indicator viz. methyl red (MR) with 3-mercaptopropylsilatrane (MPS). The formulated silatrane (MR-OS) has been thoroughly characterized by elemental analysis; FTIR, UV–vis and NMR (1H and 13C) spectroscopy; and mass spectrometry. The spectral properties in different solvents were studied by UV–vis spectroscopy and highlighted with the Kamlet-Taft approach. The skeleton methyl red endowed inevitable acid sensing ability in the molecule, while an intriguing response to basic pH conditions has also been revealed. Furthermore, when screened for the sensorial aptitude towards various transition metal ions, colorimetric as well as UV–vis absorption analysis substantiate the selective binding with Hg2+. A protocol was also developed for the immobilization of MR-OS onto the surface of magnetic silica nanoparticles, whose features are the specific objectives of the present work. The resultant organic-inorganic hybrid nanoparticles (H-NPs) have been characterized by physicochemical techniques such as FT-IR, XRD, TEM, FE-SEM, EDX and TGA. The tethering of MR-OS with magnetic silica nanoparticles not only preserves the inherent fondness for both pH and Hg2+ ion but also renders a facile magnetic recovery which altogether make them apposite adsorbents for removal of Hg2+ as sketched by Langmuir adsorption isotherm.