Bifunctional Sr(<scp>ii</scp>)-based coordination polymer for sensing of Ba(<scp>ii</scp>)/nitroaromatic compounds and supercapacitor applications

Main group element-based coordination polymers (CPs) are being widely studied for energy storage and sensing applications because of their structural versatility and electropositive properties. In this work, Sr(II)-CP, namely (SA2), was fabricated utilizing 3,5-pyridine dicarboxylic acid (PDC). The formation of SA2 was confirmed by single-crystal X-ray diffraction (SC-XRD). The topological rod net representation showed that SA2 followed a <b><i>(6</i>,<i>3) lla</i></b> underlying net. However, to enhance the electrochemical properties of SA2, a rGO@SA2 composite was fabricated by introducing reduced graphene oxide (rGO) using a sonication approach. The structures of SA2, rGO and rGO@SA2 were confirmed by spectroscopic and microscopy techniques (PXRD, FT-IR, TGA, UV-vis, SEM, and HR-TEM, respectively). SA2 served as an excellent sensor for Ba²⁺ (92%) metal ions and showed notable fluorescence selectivity for picric acid (PA-95%) compared with 1,4-nitroaniline (NA-83%) and benzoic acid (BA-49%). Furthermore, electrochemical analysis was performed using galvanostatic charge-discharge (GCD) and cyclic voltammetry (CV) techniques which showed good specific capacitances of 153.57 F g^-1 and 383.38 F g^-1 for SA2 and rGO@SA2 at a current density of 0.5 A g^-1, respectively. After 2000 cycles, rGO@SA2 showed a retention capacitance of 96.32%.