Graphitic Carbon Nitride/MOFs Hybrid Composite as Highly Selective and Sensitive Electrodes for Calcium Ion Detection

The metal-organic framework (MOF) is a class of materials that exhibits a notable capacity for electron transfer. This unique framework design offers potential applications in various fields, including catalysis, gas storage, and sensing. Herein, we focused on a specific type of MOF called Ti-MOF. To enhance its properties and functionality, the composite material was prepared by incorporating graphitic carbon nitride (g-C₃N₄) into the Ti-MOF structure. This composite, known as g-C₃N₄@Ti-MOF, was selected as the active material for ion detection, specifically targeting calcium ions (Ca²⁺). To gain a comprehensive understanding of the structural and chemical properties of the g-C₃N₄@Ti-MOF composite, several analytical techniques were employed to characterize the prepared g-C₃N₄@Ti-MOF composite, including X-ray diffraction (XRD), SEM-EDX, and FT-IR. For comparison, different pastes were prepared by mixing Ti-MOF or g-C₃N₄@Ti-MOF, graphite, and o-NPOE as a plasticizer. The divalent Nernstian responses of the two best electrodes, I and II, were 28.15 ± 0.47 and 29.80 ± 0.66 mV decade^-1, respectively, with concentration ranges of 1 µM-1 mM and 0.1 µM-1 mM with a content 1.0 mg Ti-MOF: 250 mg graphite: 0.1 mL o-NPOE and 0.5 mg g-C₃N₄@Ti-MOF: 250 mg graphite: 0.1 mL o-NPOE, respectively. The electrodes showed high sensitivity and selectivity for Ca²⁺ ions over different species. The suggested electrodes have been successfully employed for Ca²⁺ ion measurement in various real samples with excellent precision (RSD = 0.74-1.30%) and accuracy (recovery = 98.5-100.2%), and they exhibited good agreement with the HPLC.