Preparation, characterization, and electrochemical sensing performance of a novel pristine Cd-MOF and its composite...

A novel Cd(II)-organic framework (Cd-MOF) {[Cd(isba)(bbtz)₂(H₂O)]·H₂O} (1) and its composite with CNTs (Cd-MOF@CNTs), [H₂isba = 2-iodo-4-sulfobenzoicacid; bbtz = 1, 4-bis(1,2,4-triazolyl-1-methyl)benzene], were synthesized successfully under ambient conditions. The Cd-MOF is a 2D (4, 4) topological framework, further extending into a two-fold interpenetrated 3D supramolecular network via hydrogen bonding. The activation energy for proton transfer in the composite Cd-MOF@CNT/Nafion membrane is lower than that in pristine Cd-MOF/Nafion, leading to its more temperature-insensitive proton conductivity. Hence, the proton conduction of the composite Cd-MOF@CNT/Nafion membrane was greatly improved. Cyclic voltammograms indicate that the Cd-MOF/GCE only has an oxidation peak with the peak potential suitable for the oxidation of glucose in 0.1 M NaOH. The i-t current response demonstrates that the Cd-MOF/GCE exhibits sensitive and selective oxidative sensing of glucose in the linear range of 0-5 mM with a limit of detection (LOD) of 9.64 μM. Different from the pristine Cd-MOF, Cd-MOF@CNTs shows a pair of irreversible redox peaks with an anodic peak potential appropriate for the glucose oxidation and a cathodic peak potential suitable for the hydrogen peroxide reduction in 0.1 M NaOH. So, the Cd-MOF@CNTs/GCE can be used not only for the electrocatalytic oxidation of glucose, but also for the electrocatalytic reduction of H₂O₂. The current-time response curve demonstrates that the Cd-MOF@CNTs/GCE exhibits more sensitive and selective oxidative sensing for glucose exponentially in the 0-18.5 mM range with a lower LOD down to 2.63 μM. The reductive sensing of H₂O₂ increases linearly in the range of 0-14.0 mM (LOD = 33.70 μM). Moreover, the Cd-MOF@CNTs/GCE can detect glucose and H₂O₂ efficiently in real-world samples. Cd-MOF@CNTs may act as a dual non-enzymatic electrochemical sensory material for glucose and H₂O₂.