Today's extensive use of inorganic fertilizers in agricultural techniques has increased the concentration of nitrate in drinking water beyond safety limits, causing serious health problems in humans such as thyroidism and methemoglobinemia. Therefore, the present work describes the synthesis of a benzimidazolium salt-based fluorescent chemosensor (KG3) via a multistep synthesis which detects nitrate ions in aqueous medium. This was validated using various analytical techniques such as fluorescence spectroscopy, UV-visible spectroscopy, and electrochemical studies with a detection limit of 0.032 μM without any interference from other active water pollutants. Subsequently, KG3 is further modified with the help of iron oxide nanoparticles (Fe3O4 NPs) and silica to obtain the SiO2@Fe3O4-KG3 nanocomposite, which was immobilized over a polyether sulfone membrane and evaluated for removal of nitrate ions from groundwater with a removal efficiency of 96%. Moreover, the engineered composite membrane can serve as a solid-state fluorescence sensor to detect NO3- ions, which was demonstrated through a portable mobile-based prototype employing a hue, saturation, and value parameter model.
Keywords: ionic salts; iron oxide nanoparticles; membrane filtration; naked-eye detection; nitrate removal.