Effective Enrichment and Quantitative Determination of Trace Hg²⁺ Ions Using CdS-Decorated Cellulose Nanofibrils

Water pollution caused by metal contamination is of serious concern. Direct determination of trace metal ions in real water samples remains challenging. A sample preparation technique is a prerequisite before analysis. Herein, we report the facile water-based hydrothermal synthesis of cadmium sulfide nanoparticles on a cellulose nanofiber surface to prepare a new adsorbent material. Field emission scanning electron microscopy, high-resolution tunneling electron microscopy, elemental mapping and X-ray photoelectron microscopy were used to characterize the surface morphology, structural determination, elemental composition and nature of bonding. The nanoadsorbent (cadmium-sulfide-decorated cellulose nanofibrils (CNFs@CdS)) was employed for the solid-phase extraction and determination of trace Hg(II) from aqueous media. The experimental conditions were optimized systematically and the data show a good Hg(II) adsorption capacity of 126.0 mg g^-1. The CNFs@CdS adsorbent shows the selective removal of Hg(II) accordingly to the hard and soft acid-base theory of metal-ligand interaction. A high preconcentration limit of 0.36 µg L^-1 was obtained with a preconcentration factor of 580. The lowest level of trace Hg(II) concentration, which was quantitatively analyzed by the proposed method, was found to be 0.06 µg L^-1. No significant interferences from the sample matrix were observed in the extraction of Hg(II). Analysis of the standard reference material (SRM 1641d) was carried out to validate the proposed methodology. Good agreement between the certified and observed values indicates the applicability of the developed methodology for the analysis of Hg(II) in tap water, river water and industrial wastewater samples.