Supported carbon dots serve as high-performance adsorbent for the retention of trace cadmium

Carbon dots were prepared via a one-pot hydrothermal route, and a new solid-phase extraction (SPE) adsorbent was developed by immobilizing the carbon dots on the microcarrier cytopore, shortly termed as C-dots@cytopore. The C-dots@cytopore composites were characterized by means of FT-IR, SEM, XPS and fluorescence spectrometry. The performance of the composites for the adsorption of heavy metals was thoroughly evaluated by using cadmium as a model. The binding of cadmium on C-dots@cytopore fits Langmuir adsorption, and the adsorption dynamic follows pseudo-second-order adsorption kinetics model. The binding of cadmium was pH-dependent, with a maximum adsorption capacity of 2420μgg^-1 obtained at pH 4-7. A novel separation and preconcentration procedure was thus developed for trace cadmium using the C-dots@cytopore composites as SPE sorbent. The retained cadmium could be readily eluted and recovered by a 0.1molL^-1 HNO₃ solution and further quantified with graphite furnace atomic absorption spectrometry (GFAAS). With a sample volume of 1.0mL, an enrichment factor of 17.85 was obtained with a detection limit of 1.8ngL^-1 and a RSD value of 2.6% at 0.1μgL^-1 (n = 9). The procedure was further validated by analyzing cadmium in certified reference materials and a series of environmental water samples.