SnO<inf>2</inf>-MWCNT and SnO<inf>2</inf>-rGO Nanocomposites for Selective Electrochemical Detection in a Mixture of Heavy Metal Ions

Metal oxide-carbon nanocomposites offer an interesting platform for electrochemical sensing due to the synergistic effect of a highly active semiconducting surface and conducting carbon as the supporting backbone. In this work, the in situ synthesis of SnO2 with reduced graphene oxide (rGO) led to the formation of small, uniform SnO2 nanoparticles, measuring 10-20 nm in size, whereas the inclusion of multiwalled carbon nanotubes (MWCNT) resulted in the formation of (200) oriented SnO2 nanoplatelets of ∼200 nm. X-ray photoelectron spectroscopy (XPS) demonstrates a chemical interaction between Sn and C rather than physical adherence. The cyclic voltammograms (CVs) of SnO2-rGO and SnO2-MWCNT display high peak current density and small ΔE in comparison to SnO2, signifying fast electron transfer, reversibility, and enhanced electrochemically active sites. Under optimized experimental conditions of square wave anodic stripping voltammetry (SWASV), the nanocomposites demonstrate high sensitivity (3.9, 9.9, 45.5, and 25.4 mA cm-1 ppb-1) and a low detection limit (in ppb) toward Cd2+, Pb2+, Cu2+, and Hg2+, respectively. The high selectivity of SnO2-rGO for Cd2+ and Pb2+ ions and SnO2-MWCNT for Hg2+ and Cu2+ in a complex metal ion environment is encouraging and is probed by using density functional theory (DFT). Additionally, an artificial neural network (ANN)-based model justifies the sensor’s accuracy and precision for real-time, on-site detection of heavy metal ions directly in tap water.