Graphene oxide (GO) was covalently attached to glassy carbon (GC) electrode (GC-O-GO) for fabricating nanosensors to determine trace Pb 2+ and Cd 2+ using differential pulse anodic stripping voltammetry (DPASV). Surface characterization of the nanofilm-covered electrode was performed via electrochemical cyclic voltammetry (CV), transmission electron microscopy (TEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) techniques. Surface pKa of the GO covalent attached GC (GC-O-GO) was calculated via CV. Under optimal conditions, a linear response was found for Pb 2+ and Cd 2+ in the range from 1×10 −8 to 1×10 −12 M. The limit of detections (LODs) of Pb 2+ and Cd 2+ were 0.25 pM and 0.28 pM, respectively. The method shows good reproducibility, and stability was successfully applied to measure Pb 2+ and Cd 2+ levels in rice, soya, milk, and tap water samples, with good agreement with those obtained by the standard inductively coupled plasma optical emission spectrometry (ICP-OES) method. The method was evaluated by application with the simultaneous determination of the ions in food samples (n=6) using the standard addition method. The recoveries of the Pb 2+ and Cd 2+ were up to 98 %.

Carbonized electrode materials were prepared from carbonization of graphene nanoribbon (GNR) / coal tar pitch (CTP) composite (m% of GNR: 1%, 3%, 5% and 10%). The carbonized materials were denoted as follows: CTP-GNR1, CTP-GNR2, CTP-GNR3 and CTP-GNR4. Characterization included cyclic voltammetry (CV), infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). CTP-GNR1 was obtained as the nanocoil structure via SEM. Electrocatalytic activity for some redox probes, such as ferrocene and ferric/ferrous (K3Fe(CN)6 and K4Fe(CN)6) probe on the CTP-GNR1 modified glassy carbon (GC/CTP-GNR1) was found to be greater than others. The nanocoil material (CTP-GNR1) was used in the determination of dopamine (DA) and uric acid (UA) by differential pulse voltammetry (DPV). The electrode exhibits linear responses to DA and UA in the ranges of 2 μM–20 μM in the presence of 300 μM of L-ascorbic acid (AA). The detection limits (S/N = 3) for DA and UA are 3 nM and 6 nM, respectively.

Manganese dioxide (MnO 2 ) decorated graphene oxide was modified on the glassy carbon (GC) surface. The nanofilm covered electrode was used for determination of Pb 2+ and Cd 2+ via differential pulse anodic stripping voltammetry. Characterization of the modified electrode was performed via cyclic voltammetry, TEM, XPS, and XRD. The limit of detection (S/N = 3) of the method was calculated as 1.24 pM for Pb 2+ and 0.14 pM for Cd 2+ with the linear calibration curves ranged from 1 × 10 −11 M to 1 × 10 −7 M for Pb 2+ and Cd 2+ . The method shows good reproducibility and stability and was successfully applied to measure trace Pb 2+ and Cd 2+ in seawater samples from Turkey. The recoveries of the Pb 2+ and Cd 2+ response of the method were up to 96%.

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