ZnO Doped Silica Nanoparticles (ZnO@SiO2) for Enhanced Electrochemical Detection of Cd2+ Ions in Real Samples

Abstract

Pollution by heavy metal ions has a serious impact on human health and the environment, which is why the monitoring of heavy metal ions is of great practical importance. In this work, we describe the development of an electrochemical sensor for the detection of cadmium (Cd²⁺) involving the doping of porous SiO₂ spheres with ZnO nanoparticles. Zinc oxide is chosen as the central dopant in the composite material to increase the conductivity and thus improve the electrochemical detection of Cd²⁺ ions with the SiO₂ spheres. The resulting composite is characterized by electrochemical spectroscopic XRD and microscopic methods. As a result, the developed sensor shows good selectivity towards the targeted Cd²⁺ ions compared to other divalent ions. After optimization of the experimental conditions, the electrochemical sensor shows two different linear ranges between 2.5 × 10^-11 molL^-1 to 1.75 × 10^-10 molL^-1 and 2 × 10^-9 molL^-1 to 1.75 × 10^-9 molL^-1, indicating a change from diffusion-controlled to surface-controlled oxidation of Cd²⁺. A detection limit was reached at 4.4 × 10^-11 molL^-1. In addition, it offers good repeatability and recovery, and can detect accurate trace amounts of Cd²⁺ ions in real samples such as tap water or seawater by spiking these samples with known Cd²⁺ concentrations. This setup also provides satisfactory recovery rates in the range of 89-102%.