Naphthalimide-based organic nanoparticles for aluminium recognition in acidic soil and aqueous media

Abstract

An organic compound 1 was prepared using 1,8-naphthalimide and diethylenetriamine, and the resultant receptor showed interesting potential for metal recognition. The chemosensor activity of the naphthalimide-based receptor was evaluated following the synthesis of the organic nanoparticles (ONPs) using a reprecipitation method. The organic nanoparticles were evaluated for their photophysical properties, mainly using fluorescence spectroscopy in aqueous media, and the studies revealed that the ONPs selectively recognized aluminium ions in aqueous media. The sensor showed competitive binding for Al3+ and none of the other metal ions tested caused any interference in the detection of Al3+. Titrations were performed with aluminium ions, and the lowest detection limit calculated was 677 nM. The sensor was used to determine the Al3+ content of river water and acidic soils; results were validated using existing methods and the performance of the ONPs was found to be in a satisfactory error range. Finally, the mechanism of fluorescence recognition was further confirmed using DFT calculations, which showed that the aluminium, upon addition to receptor 1, takes away the excess electrons i.e. a lone pair from the central nitrogen of the diethylenetriamine part of receptor 1. This causes a reduction in photo-induced electron transfer (PET) and an increase in fluorescence intensity, which was authenticated using NMR and UV-Visible spectroscopic titrations of receptor 1 with Al3+ ions.