A Newly Constructed Cobalt-Organic Coordination Polymer and Its Two Carbon-Based Composites Demonstrating Electrochemical Sensing to NO2− and Cr (VI)

A novel cobalt-organic ionic coordination polymer, incorporating the multifunctional 2-iodo-4-sulfonatobenzoate anion (isba₂⁻) and the rigid nitrogen-containing ligand 4,4′-bipyridine (bipy) {[Co (bipy)(H₂O)₃(CH₃CH₂OH)]·isba·2H₂O}_n (Co-bipy), was synthesized via a straightforward solution evaporation method at room temperature. Two innovative carbon-based composite materials Co-bipy@MWCNTs and Co-bipy@GO were successfully fabricated through hybridization with multi-walled carbon nanotubes and graphene oxide, respectively. Experimental investigation indicates that the electrocatalytic ability of Co-bipy towards the NO₂⁻ oxidation and Cr (VI) reduction can be enhanced by MWCNTs and GO. Among the three glassy carbon electrodes (GCE) modified with Co-bipy, Co-bipy@MWCNTs, and Co-bipy@GO, the Co-bipy@MWCNTs/GCE exhibits optimal performance for NO₂⁻ oxidation sensing in 0.1 M PBS and Cr (VI) reduction sensing in 0.1 M H₂SO₄. The successful modification of Co-bipy@MWCNTs on the screen-printed electrode (SPE) further enhanced the electrocatalytic performance of Co-bipy@MWCNTs. The Co-bipy@MWCNTs/SPE shows the most efficient sensing to NO₂⁻ and Cr (VI). The limits of detection (LOD) reach 0.13 μM for NO₂⁻ and 0.25 μM for Cr (VI), respectively. Furthermore, the Co-bipy@MWCNTs/SPE was effectively employed for the accurate detection of NO₂⁻ and Cr (VI) in the actual samples. The sensing mechanisms for NO₂⁻ and Cr (VI) were illustrated with the aid of Hirshfeld surface analysis and density of states (DOS) calculations.