The incorporation of bismuth(III) into metal-organic frameworks for electrochemical detection of trace cadmium(II) and lead(II).

The first example of metallic bismuth encapsulated into a mesoporous metal-organic framework of the type MIL-101(Cr) matrix is presented. Bi(III)-impregnated MIL-101(Cr) (Bi(III)/MIL-101(Cr)) was dropped onto a conductive carbon cloth electrode (CCE). Then, bismuth was generated by electrochemical reduction of the Bi(III)/MIL-101(Cr) supported on CCE (Bi/MIL-101(Cr)/CCE). The resulting Bi/MIL-101(Cr)/CCE display impressive performance in terms of peak currents for the ions Cd(II) and Pb(II) when compared to the single-component counterparts. Differential pulse anodic stripping voltammetry (DPASV) enabled sensing of the two ions over linear working range of 0.1 to 30 μg L-1 and 30 to 90 μg L-1. The parameters are refined before the detection of two metal ions, including the amount of bismuth in MIL-101(Cr), optimum pH (5.0), deposition potential (-1.2 V) and deposition time (600 s). The respective detection limits are 60 and 70 ng L-1 (at S/N = 3). This is strikingly lower than the guideline values of domestic water given by the WHO which are 3 μg L-1 for Cd(II) and 10 μg L-1 for Pb(II). The Bi/MIL-101(Cr) onto CCE is fairly specific for Cd(II) (at around -0.76 V) and Pb(II) (at around -0.54 V), well reproducible and has excellent recovery in real water analysis. Graphical abstract Schematic illustration of the preparation of a Bi(III)/MIL-101(Cr) metal-organic framework, its deposition on a carbon cloth electrode (CCE), and its application for detection of Cd(II) and Pb(II) by differential pulse adsorptive stripping voltammetry (DPASV).