Electrocatalytic activity of cobalt Schiff base complex immobilized silica materials towards oxygen reduction and hydrazine oxidation

Abstract

In this study, mesoporous silica spheres (MSS) are selected as a host framework to encapsulate Co(salen) and Co(salophen) (where Co(salen) is [N,N′-bis(salicylaldehyde) ethylenediimino cobalt(III)] and Co(salophen) is [N,N′-bis(salicylaldehyde)-1,2 phenylenediimino cobalt(III)]), represented as MSS–Co(salen) and MSS–Co(salophen) respectively. The prepared materials were characterized by various physicochemical methods such as diffuse reflectance, UV-vis, FT–IR and electrochemical techniques. Host–guest interactions with a feeble coordination bond (between one apical Si–O⁻ and the Co³⁺ metal ion) lead to the successful anchoring of Co(salen) and Co(salophen) to this silica framework. These constructed catalyst materials were applied to oxygen reduction studies as well as to the oxidative analytical determination of hydrazine (HZ). Both oxygen reduction (in 0.05 M HClO₄) and HZ oxidation (in neutral pH condition) showed significantly low overpotential on MSS–Co(salen) and MSS–Co(salophen) modified glassy carbon (GC) electrodes (GC/MSS–Co(salen) and GC/MSS–Co(salophen), respectively). Additionally, HZ was determined by two different electrochemical techniques, namely cyclic voltammetry (CV) and amperometry. From amperometry, GC/MSS–Co(salen) exhibits a linear calibration range from 10.0 to 210.0 μM for the HZ determination and GC/MSS–Co(salophen) exhibits two segmented linear calibration ranges from 10.0 to 310.0 μM. The CV technique demonstrates similar two segmented calibration plots (from 1.0 to 400.0 μM) for both GC/MSS–Co(salen) and GC/MSS–Co(salophen).