Serendipity in solution-GQDs zeolitic imidazole frameworks nanocomposites for highly sensitive detection of sulfide ions

Abstract

An innovative and facile sensing approach for common inorganic anions present in aqueous media has been developed using nanocomposites of europium doped graphene quantum dots (GQDs:Eu) with zeolitic imidazole frameworks (ZIF-8). GQDs:Eu, prepared initially by solvothermal approach (at <10 nm in diameter), exhibited a strong and intense blue emission at 430 nm when dispersed in ethanol. ZIF-8 nanocubes, synthesized on a parallel basis, were in a fairly uniform size distribution (e.g., 185 nm in diameter). The formation of nanocomposites by surface adsorption (between GQDs:Eu and ZIF-8) led to significant increase in fluorescence intensity as observed through photo-luminescence spectroscopy. Their interactions with anions (e.g., in terms of variations in the fluorescence intensity) were initially checked against sulfide and other anionic species (e.g., Br-, Cl-, F-, and NO3-). Among the tested ions, GQDs:Eu-ZIF-8 were found to effectively and sensitively detect sulfide (S2-) with significantly high turn on fluorescence. The feasibility of this nanosensing system was explored further toward the detection of S2- ions. These nanocomposites were thus demonstrated to be feasible for solution-based sensing of S2- ions with high reproducibility and sensitivity at limit of detection (LOD) of 0.12 ppm.