Functionalized cellulose nanomaterials as a fluorescent 'turn-off' sensor for Ag+ ions in aqueous solutions and pharmaceutical samples

Abstract

A fluorescent chemosensor was effectively synthesized through the Schiff base condensation reaction between 2-amino-1-naphthol and 5-formylsalicylic acid, resulting in the formation of 2-[(2-hydroxy-1-naphthyl)imino]-5-hydroxybenzoic acid (HNHB). This compound was subsequently immobilized onto cellulose nanorods (CNRs) to create a hybrid nanocomposite sensor denoted as HNHB chemosensor. Structural and morphological characterization conducted via FTIR, XPS, and XRD validated the successful immobilization of the ligand while maintaining the crystallinity of the cellulose matrix. Transmission and scanning electron microscopy (TEM and SEM) images displayed a rod-like nanostructure characterized by a uniform distribution of the functional groups. The chemosensor presented a significant fluorescence quenching (turn-off) response solely in the presence of Ag⁺ ions, with this phenomenon attributed to photoinduced electron transfer instigated by Ag⁺ ions. The limits of detection and quantification were determined to be 0.0236 ppm and 0.0717 ppm, respectively. Density Functional Theory (DFT) calculations reaffirmed the formation of a stable Ag⁺-ligand complex, reporting reduction in the HOMO-LUMO energy gap upon coordination. The sensor demonstrated robust performance across real sample matrices, achieving recovery rates between 98.17 % and 99.77 % for Ag⁺ ions detection in pharmaceutical products and spiked tap water. These findings substantiate the HNHB chemosensor as a selective, stable, and cost-effective platform for the detection of trace amounts of Ag⁺ ions in aqueous environments and pharmaceutical samples.