A novel carbon paste electrode modified with ZnO nanorods and 2-(4-oxo-3-phenyl-3,4-dihydroquinazolinyl)-N′-phenyl-hydrazinecarbothioamide (2PHCZNCPE) was fabricated and employed to study the electrocatalytic oxidation of droxidopa, using cyclic voltammetry, chronoamperometry and square wave voltammetry as diagnostic techniques. It has been found that the oxidation of droxidopa at the surface of modified electrode occurs at a potential of about 435 mV less positive than that of an unmodified carbon paste electrode. Square wave voltammetry exhibits a linear dynamic range from 7.0 × 10^–8 to 3.0×10⁻⁴ M and a detection limit of 45.0 nM for droxidopa. Finally this modified electrode was used for simultaneous determination of droxidopa and carbidopa.

The potential use of novel iron based mineral catalysts as an effective and available material for electrocatalytic oxidation of refractory contaminants by heterogeneous electro-Fenton (HEF) process was studied for the first time. For this purpose, four natural catalysts, namely ilmenite (FeTiO₃), pyrite (FeS₂), chromite (FeCr₂O₄), and chalcopyrite (CuFeS₂) were selected as the source of ferrous iron (Fe²⁺) ions. The catalyst samples were appropriately characterized by X-ray diffraction (XRD) and RAMAN analysis. The degradation kinetics and mineralization rate of 0.2 mM antibiotic cefazolin (CFZ), as a contaminant of emerging concern, were comparatively investigated by HEF using the catalysts mentioned above. The effect of important experimental parameters such as catalysts loading and current on the process efficiency was investigated. Moreover, the performance of these new mineral catalysts was compared in term of CFZ degradation kinetics, mineralization power, mineralization current efficiency and electrical energy consumption. A greater enhancement in degradation/mineralization of CFZ was obtained when using chalcopyrite as the catalyst in HEF. The stability and reusability experiments demonstrated negligible decrease in catalytic activity of chalcopyrite after five consecutive runs. Besides, the rate constant for CFZ oxidation by hydroxyl radicals was estimated according the pseudo-first-order reaction kinetics. The empirical assessment, in addition to economic evaluation, confirmed that iron based mineral catalysts and specifically chalcopyrite could be an appropriate and cost-effective alternative catalyst for HEF due to its high catalytic activity, availability, eco-friendly nature and low energy consumption compared to other synthesized catalysts.