SnO₂–MWCNT and SnO₂–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 SnO 2 with reduced graphene oxide (rGO) led to the formation of small, uniform SnO 2 nanoparticles, measuring 10–20 nm in size, whereas the inclusion of multiwalled carbon nanotubes (MWCNT) resulted in the formation of (200) oriented SnO 2 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 SnO 2 –rGO and SnO 2 –MWCNT display high peak current density and small Δ E in comparison to SnO 2, 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 Cd 2+, Pb 2+, Cu 2+, and Hg 2+, respectively. The high selectivity of SnO 2 –rGO for Cd 2+ and Pb 2+ ions and SnO 2 –MWCNT for Hg 2+ and Cu 2+ 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.