▎ 摘　　要

The issue of residual heavy metals in environmental and water sources is a global challenge. Among heavy metals, chromium is a very dangerous metal that is very harmful to humans and all living things. Exposure may occur from natural or industrial sources of chromium. Therefore, designing an optical sensor to monitor Cr3+ ions in an aqueous solution with selectivity, simplicity, and high sensitivity is of great importance. In the present work, free radical polymerization is used to synthesize a magnetic Fe3O4@Pectin-polymethacrylamide@graphene quantum dot (Fe3O4@Pectin-MAM@GQD) nanocomposite with a core-shell structure. It is used as an optical nanosensor for the detection of Cr3+ ions in aqueous solutions. This method is based on increasing the UV-vis absorbance intensity of Fe3O4@Pectin-MAM@GQD in the presence of Cr3+ ions. At optimal conditions, pH = 6 and adsorbent dose of 0.3 mg/ml, the synthesized nanosensor showed a good linear correlation between the absorbance intensity of the nanosensor and the concentrations of Cr3+ in the range from 4 to 100 mu M. Remarkably, the result showed that the LOD and LOQ of Fe3O4@Pectin-MAM@GQD nanocomposite are equal to 0.468 mu M and 1.419 mu M, receptively. Using this method can identify chromium in aqueous pollutants since a low limit of detection of chromium in aqueous solutions (MRL approximate to 1 mu M, WHO).