Performance of graphene-zinc oxide nanocomposite coated-glassy carbon electrode in the sensitive determination of para-nitrophenol

Graphene: zinc oxide nanocomposite (GN:ZnO NC) platform was tried for the sensitive determination of para-nitrophenol (p-NP) through the electrochemical method. ZnO nanoparticles (NPs) were synthesized by the modified wet-chemical method where in potassium hydroxide and zinc nitrate were used as precursors and starch as a stabilizing agent. A green and facile approach was applied to synthesize GN:ZnO NC in which glucose was employed as a reductant to reduce graphene-oxide to graphene in the presence of ZnO NPs. The synthesized NC was characterized using scanning and high-resolution transmission electron microscopy, energy dispersive x-ray analysis, X-ray diffraction and Raman spectroscopic techniques to examine the crystal phase, crystallinity, morphology, chemical composition and phase structure. GN:ZnO NC layer deposited over the glassy carbon electrode (GCE) was initially probed for its electrochemical performance using the standard 1 mM K3[Fe(CN)6] model complex. GN:ZnO NC modified GCE was monitored based on p-NP concentration. An enhanced current response was observed in 0.1 M phosphate buffer of pH 6.8 for the determination of p-NP in a linear working range of 0.09 × 10-6 to 21.80 × 10-6 M with a lower detection limit of 8.8 × 10-9 M employing square wave adsorptive stripping voltammetric technique at a deposition-potential and deposition-time of - 1.0 V and 300 s, respectively. This electrochemical sensor displayed very high specificity for p-NP with no observed interference from some other possible interfering substances such as 2, 4-di-NP, ortho-NP, and meta-NP. The developed strategy was useful for sensitive detection of p-NP quantity in canals/rivers and ground H2O samples with good recoveries.

First Electrochemical Method of Nitrothal-Isopropyl Determination in Water Samples

The aim of the research was the use of square wave adsorptive stripping voltammetry (SWAdSV) in conjunction with a hanging mercury drop electrode (HMDE) for the determination of nitrothal-isopropyl. It was found that optimal SW technique parameters were frequency, 200 Hz; amplitude, 50 mV; and step potential, 5 mV. Accumulation time and potential were studied to select the optimal conditions in adsorptive stripping voltammetry: 45 s at 0.0 V, respectively. The calibration curve (SWSV) was linear in the nitrothal-isopropyl concentration range from 2.0 × 10−7 to 2.0 × 10−6 mol L−1 with detection limit of 3.46 × 10−8 mol L−1. The repeatability of the method was determined at a nitrothal-isopropyl concentration level equal to 6.0 × 10−7 mol L−1 and expressed as RSD = 5.5% (n=6). The proposed method was successfully validated by studying the recovery of nitrothal-isopropyl in spiked environmental samples.