Insights into the morphological and structural particularities of highly sensitive porous bismuth-carbon nanocomposites based electrochemical sensors

Porous bismuth-carbon xerogels (Bi-CX) and aerogels (Bi-CA) were investigated as electrode materials for heavy metals ions (CdII, PbII) detection below the maximum limits allowed in drinking water. The new materials were prepared by using the sol-gel method followed by drying in ambient atmosphere (CX) or under supercritical conditions using liquid CO2 (CA), and finally, pyrolysis in inert atmosphere. The morphological and structural characterization, performed by using SEM, EDX, N2 adsorption/desorption, TEM, XRD, and XPS techniques, revealed for both investigated materials the presence of a porous carbon structure, embedded with Bi nanoparticles of various sizes. It was noticed that the dimensions and structural features of the Bi nanoparticles are strongly influenced by the drying conditions. Bi-CX and Bi-CA powders, dispersed in chitosan solution, were deposited on the surface of glassy carbon (GC) electrodes and the resulted modified electrodes, GC/Chi-(Bi-CA) and GC/Chi-(Bi-CX), were used for PbII and CdII simultaneous detection by using square wave anodic stripping voltammetry. The obtained results were rationalized considering the structural differences between Bi-CX and Bi-CA. To the best of our knowledge, the sensitivity (20.9 μA/ppb) and the detection limit (0.02 ppb; S/N 3), estimated for CdII detection at GC/Chi-(Bi-CA) electrode, were the highest and the lowest ever reported, respectively. At the same time, excellent detection limit (0.16 ppb; S/N 3) and sensitivity (7.04 μA/ppb) were found for PbII detection at GC/Chi-(Bi-CX) electrode.