Electrocatalytic effect of NiO supported onto activated carbon in oxidizing phenol at graphite electrode: Application in tap water and olive oil samples

The activated carbon doped by nickel oxide (NiO/AC) was prepared using solid reaction. The obtained powder was characterized using X-ray diffraction (XRD) and infrared spectroscopy (IR). The NiO/AC was also used to catalyze the electro-oxidation of phenol at carbon paste electrode (CPE) using electrochemical approaches. Kinetic parameters of phenol oxidation (as the electron transfer coefficient, diffusion coefficient and heterogeneous rate constant) were investigated. The results confirm that phenol oxidation is catalyzed by nickel oxide, due to resonance, steric and aggregation effects.

The experimental conditions were optimized by varying chemical and electrochemical parameters, which involve the oxidation of phenol. The electrode NiO/AC–CPE exhibits a good linear range from 1.0 × 10⁻⁶ mol L⁻¹ to 8.0 × 10⁻⁵ mol L⁻¹ and 1.0 × 10⁻⁴ mol L⁻¹ to 1.0 × 10⁻³ mol L⁻¹ with a limit of detection of 7.09 × 10^–7 mol L^–1 (signal (S) to noise (N) ratio, S/N = 3). This modified electrode NiO/AC-CPE offers a considerable improvement in voltammetric sensitivity toward phenol determination, compared to the unmodified electrode (CPE). The selectivity of the NiO/AC–CPE in detecting phenol was investigated for a number of ions (Cu²⁺, Cd⁺², Ag⁺_, Pb²⁺, Zn²⁺, Fe³⁺, Ni²⁺, Al³⁺, Mg²⁺, Ag²⁺ and Cr³⁺) and biomolecules (4-nitrophenol, dopamine, 2-nitrophenol, paracetamol, hydroquinone, catechol, resorcinol, 4-aminophenol and 3-aminophenol). The proposed method was successfully applied to phenol determination in tap water and olive oil.