A novel Ni–Schiff base complex for motivating glucose electrooxidation in alkaline solutions

Abstract

Many Schiff-base complexes of metal ions display enhanced catalytic activities toward redox reactions of many organic compounds; accordingly, application in electrocatalysis is a crucial issue. In this regard, a novel Ni–Schiff base complex (Ni(II)–SB) is synthesized by condensation of 4-(dimethylamino) benzaldehyde with amoxicillin and coordinated with Ni(II). Then, it is ink-cast onto a commercial carbon electrode to be used for electrooxidation of glucose in 0.5 M NaOH solution. Ni(II)–SB is inspected using an FTIR spectrometer and transmission electron microscopy (TEM). The elemental analysis and mapping for the Ni(II)–SB/C electrode surface are carried out using energy dispersive X-ray analyses (EDX) and scanning electron microscopy (SEM), respectively, and the phase structure is investigated using X-ray diffraction (XRD). Different electrochemical techniques are used to evaluate its electrochemical performance. The Ni(II)–SB/C electrode exhibits superior performance towards glucose electrooxidation due to its improved electron transfer ability, and the availability of its intrinsic redox couple of Ni²⁺/Ni³⁺. The cyclic voltammetric results indicate an electrochemically active surface area (ECSA) of 15.6 cm² mg⁻¹ and a surface coverage value of 4.4 × 10⁻⁷ mol cm⁻² for the Ni(II)–SB/C electrode in 0.5 M NaOH. An appreciable catalytic activity of 91 mA mg⁻¹ at 0.72 V is estimated for glucose electrooxidation. Moreover, a diffusion coefficient (D) of 1.34 × 10⁻⁵ cm² s⁻¹ and heterogeneous rate constant (K°) of 1.53 × 10⁵ cm³ mol⁻¹ s⁻¹ with a transfer coefficient (α) of 0.29 were determined for glucose oxidation on the Ni(II)–SB/C electrode. It displays a considerable stability with repeated cycling and with time due to its oxygen affinity. In addition, it shows a good reproducibility and sensitivity value of 42.3 μA cm⁻² mM⁻¹ in the linear range from 1.0 mM to 100 mM with a detection limit of 4 μM . A low charge transfer resistance value of 4.01 Ω cm² is achieved for glucose electrooxidation on the Ni(II)–SB/C electrode which confirms the fast electron transfer reaction compared with that in 0.5 M NaOH. The optimized geometry, molecular orbital and ground state properties of the SB and Ni(II)–SB catalyst were studied using Density Functional Theory (DFT). The spontaneity of the glucose adsorption on the Ni(II)–SB/C electrode surface is predicted from the values of E_interaction (−34105.4 eV) and E_binding (34105.4 eV).