Zirconia nanocomposites with carbon and iron(iii) oxide for voltammetric detection of sub-nanomolar levels of methyl parathion

rGO/HfO2 nanocomposite-enabled electrochemical sensor for high-performance pesticide detection

This study applies a periodic table-guided approach to select and investigate hafnium oxide (HfO2), in conjunction with reduced graphene oxide (rGO), for the electrochemical determination of methyl parathion (MP), an organophosphate insecticide. MP poses significant ecological and health risks due to its high toxicity, and despite bans, illegal use has been reported, especially in the global south. To address these challenges, an electrode modified with a nanocomposite of rGO/HfO2 was first constructed for MP detection. Its analytical performance was evaluated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The rGO/HfO2 nanocomposite demonstrated effective adsorption of MP and facilitated electron transfer for enhanced sensitivity. Characterization via SEM and FT-IR confirmed the successful in-situ reduction of GO and the strong interaction between HfO2 and MP. The sensor exhibited superior electrocatalytic activity compared to those using individual materials. Various detection techniques, including DPV, amperometry, and stripping voltammetry, were employed for MP detection. In DPV and stripping voltammetry, the peak current at -0.6 V was used to establish the calibration curve, while a fixed potential of -0.6 V (vs. Ag/AgCl) was applied for amperometry. DPV exhibited the best performance, with a limit of detection of 2.36 ppb. Moreover, the sensor displayed excellent selectivity in the presence of potential interferents, and validation through MP detection in spiked real water samples demonstrated its potential applicability for environmental monitoring.

Electrochemical sensors modified with iron oxide nanoparticles/nanocomposites for voltammetric detection of Pb (II) in water: A review

Permissible limits of Pb2+ in drinking water are being reduced from 10 μgL-1 to 5 μgL-1, which calls for rapid, and highly reliable detection techniques. Electrochemical sensors have garnered attention in detection of heavy metal ions in environmental samples due to their ease of operation, low cost, and rapid detection responses. Selectivity, sensitivity and detection capabilities of these sensors, can be enhanced by modifying their working electrodes (WEs) with iron oxide nanoparticles (IONPs) and/or their composites. Therefore, this review is an in-depth analysis of the deployment of IONPs/nanocomposites in modification of electrochemical sensors for detection of Pb2+ in drinking water over the past decade. From the analyzed studies (n = 23), the optimal solution pH, deposition potential, and deposition time ranged between 3 and 5.6, -0.7 to -1.4 V vs Ag/AgCl, and 100-400 s, respectively. Majority of the studies employed square wave anodic stripping voltammetry (n = 16), in 0.1 M acetate buffer solution (n = 19) for detection of Pb2+. Limits of detection obtained (2.5 x 10-9 - 4.5 μg/L) were below the permissible levels which indicated good sensitivities of the modified electrodes. Despite the great performance of these modified electrodes, the primary source of IONPs has always been commercial iron-based salts in addition to the use of so many materials as modifying agents of these IONPs. This may limit reproducibility and sustainability of the WEs due to lengthy and costly preparation protocols. Steel and/or iron industrial wastes can be alternatively employed in generation of IONPs for modification of electrochemical sensors. Additionally, biomass-based activated carbons enriched with surface functional groups are also used in modification of bare IONPs, and subsequently bare electrodes. However, these two areas still need to be fully explored.