Cd²⁺ Detection by an Electrochemical Electrode Based on MWCNT-Orange Peel Activated Carbon

This study reports the development of a new electrochemical sensor based on a carbon paste electrode (CPE) composed of biomass-based orange peel activated carbon (ACOP) and multiwalled carbon nanotubes (MWCNTs), and this composite is used for the electrochemical detection of cadmium ions (Cd²⁺). The ACOP/MWCNT composite was characterized by FTIR, Raman, and electrochemical impedance spectroscopy. The electrochemical evaluation of Cd²⁺ was performed using square wave and cyclic voltammetry. The ACOP/MWCNT-CPE electrochemical sensor exhibited a coefficient of determination r² of 0.9907, a limit of detection of 0.91 ± 0.79 μmol L^-1, and a limit of quantification of 3.00 ± 2.60 μmol L^-1. In addition, the developed sensor can selectively detect Cd²⁺ in the presence of different interferents such as Zn²⁺, Pb²⁺, Ni²⁺, Co²⁺, Cu²⁺, and Fe²⁺ with a relative standard deviation (RSD) close to 100%, carried out in triplicate experiments. The ACOP/MWCNT-CPE presented high sensitivity, stability, and reproducibility and was successfully applied for the detection of Cd²⁺ in river water samples with recovery rate values ranging from 97.33 to 115.6%, demonstrating to be a very promising analytical alternative for the determination of cadmium ions in this matrix.