Hybrid ZnO–porous graphene nanostructured electrode for the electrochemical detection of cadmium, lead and paraquat

Abstract

The threats posed by environmental pollution caused by heavy metals and pesticides, affecting ecosystems and human health, demand the on-site monitoring of these pollutants using sensitive electrochemical methods. In this work, we fabricated affordable and efficient hybrid ZnO–porous graphene (ZnGr_p) nanostructures from waste-derived cork using a simple and feasible direct laser writing technique. The successful fabrication of hybrid ZnGr_p was confirmed via microscopic and spectroscopic analyses. Under optimal conditions, the ZnGr_p nanostructured hybrid was utilized as an electrode material for the square wave anodic stripping voltammetry (SWASV) analysis of cadmium (Cd²⁺) and lead (Pb²⁺) ions in a 0.1 M acetate buffer solution. The calculated limits of detection (LODs) for Cd²⁺ and Pb²⁺ are 2.08 nM and 1.28 nM in a linear range of 1–25 μM, and the sensitivity values of ZnGr_p for these ions are 5.83 μM μA⁻¹ and 6.21 μM μA⁻¹, respectively. The ZnGr_p electrode accurately detects Cd²⁺ and Pb²⁺ in a linear range of 1–14 μM for spiked sea water samples, with a recovery rate of nearly 100%. Furthermore, the ZnGr_p electrode was utilized for the SWASV analysis of paraquat (PQ) in 0.1 M phosphate buffer solution (PBS) and the spiked wash water of Amaranthus leaves. Moreover, the LOD was found to be 0.09 μM in PBS in a linear range of 1–15 μM PQ. The standard addition calibration plot displays two linear ranges, a low-concentration range (2–6 μM) and a high-concentration range (6–15 μM), exhibiting a recovery rate of approximately 100%. The fabricated hybrid electrode is selective, reproducible and stable towards the real-time sensing of Cd, Pb and PQ.