Engineering 2,4,6-Triaminopyrimidine-Functionalized Fumed Silica for Highly Selective Hg2+ Detection: Spectroscopic and Theoretical Elucidations.

Hg2+ ions are highly toxic, persistent, and bioaccumulative heavy metal pollutants that pose a serious threat to human health, making the development of highly sensitive and selective chemosensors for their detection essential. In this research, a new hybrid material, fumed-Si-Pr-TAP, was prepared by stepwise functionalization of fumed-silica with 3-(chloropropyl)trimethoxysilane and 2,4,6-triaminopyrimidine (TAP). The prepared material was fully characterized using various techniques, including Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), N2 adsorption-desorption analysis, scanning electron microscopy (SEM), and energy dispersive X-ray spectrometry (EDX). The sensing studies revealed that this material can detect Hg2+ ions with good selectivity and an acceptable detection limit of 3 × 10-7 M in ethanolic media. This improved performance is attributed to the presence of nitrogen-rich TAP moieties on the fumed silica surface, which act as highly efficient coordination sites, making this hybrid compound outstanding for advanced chemosensor applications. Density functional theory calculations were carried out to better understand the interaction between the Pr-TAP ligand and Hg2+ ions at the molecular level. The optimized structures and electrostatic analyses reveal that nitrogen-rich regions serve as the primary binding sites, supporting strong coordination with mercury. Changes in the electronic structure, particularly the reduced HOMO-LUMO gap upon complex formation, highlight an increase in chemical reactivity that underpins the sensing behavior.