Cadmium (Cd) and lead (Pb) in soil or water environment cause the ecological destruction and environmental deterioration when their contents exceed the natural background values. To trace the concentrations of Cd(II) and Pb(II), a sensitive and selective electrode was developed using disposable screen-printed carbon electrode (SPE) immobilized with a composite film of reduced graphene oxide/carboxylation multi-walled carbon nanotubes/gold nanoparticle hybrid (RGO-MWNT-AuNP) through π-π bind. This highly conductive nano-composite layer, "RGO-MWNT-AuNP," was characterized by scanning electron microscopy, UV-visible spectrometer, cyclic voltammetry, and electrochemical impedance spectroscopy. Square wave stripping voltammetry was applied to RGO-MWNT-AuNP/SPE to electroplate bismuth film and monitor the Cd(II) and Pb(II) simultaneously. To obtain high current responses, the detecting parameters were optimized. Under optimized conditions, the current responses showed a linear relationship with the concentrations of Cd(II) and Pb(II) in the range from 1.0 to 80.0 μg/L with a lower detection limit of 0.7 µg/L and 0.3 µg/L (S/N = 3), respectively. Finally, the prepared electrode was further employed to detect Cd(II) and Pb(II) in soil samples with good results.

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In this work, ammonium pyrrolidine dithiocarbamate (APDC) was used as a surface etchant to modify CdTe/CdS core-shell quantum dots (QDs). The APDC etchant combines with the cadmium ions (Cd2+) on the surface of the QDs, resulting in the formation of surface holes. The formation of these holes changes the QD surface structure, which leads to fluorescence quenching of the QDs. Newly added Cd2+ can selectively recognize and combine with these holes; thus, the fluorescence intensity of the QDs can be restored. The linear response of this turn-on fluorescent sensor was found to be 0–100 μg/L and 100–600 μg/L under the determined optimal conditions, and its limit of detection (LOD) for Cd2+ was 2.642 μg/L (23.5 nmol/L).

In this research, a novel hydroxyl functionalized covalent organic framework (COF) with fluorescent properties was rationally designed based on the reaction between 2,5-dihydroxy-terephthalic-dihydrazide (DHTPz) and 1,3,5-benzenetricarboxaldehyde (Bt) for the Zn2+...