Irregularly Shaped Zn_0.6Mn_2.4O₄ Nanoparticles for Supercapacitors and Nitroaromatics Detection

This work reports a coordination polymer-derived nanosized Zn0.6Mn2.4O4 as the electrode material for supercapacitor and sensing material for nitroaromatics in an aqueous medium. A bimetallic coordination polymer of formula {(H2pip)3[ZnxMn(3–x)(pydc-2,5)6(H2O)3]·6H2O} {where x = 0.6}, 1, was prepared through a hydrothermal process and utilized as a template. The structural information and phase information of 1 were examined by comparing the PXRD pattern of the compound with that of the pure Mn-based compound, 1a, simulated from the single-crystal X-ray data. Zn0.6Mn2.4O4 nanoparticles were synthesized by calcining the bimetallic coordination polymer, 1, at 350 °C for 1 h. The as-obtained Zn0.6Mn2.4O4 nanoparticles were thoroughly identified using PXRD, TEM, and EDX analyses. Scherrer’s formula gives the average particle size of about 25 nm for Zn0.6Mn2.4O4. Nanostructured Zn0.6Mn2.4O4 was operated as a pseudocapacitor electrode in 2 M KOH solution, which shows a specific capacitance of 1334 F g–1 at a scan rate of 5 mV s–1 in a three-electrode cell configuration. CV study exhibits long-term cycling performance with 90.5% retention of its original capacitance after 1500 cycles. On the other hand, upon excitation at 295 nm, the aqueous dispersion of nanosized Zn0.6Mn2.4O4 displays a strong emission peak centered at 410 nm and was utilized to trace a very low concentration of nitroaromatics in the water medium. Among the nitroaromatics, the addition of 50 μM of TNP quenches around 90% of the luminescence intensity of the aqueous suspended Zn0.6Mn2.4O4. The observed detection limit for TNP is 70 ppb. This outstanding sensitivity of Zn0.6Mn2.4O4 nanoparticles toward nitroaromatics inspired us to use it as a nitroaromatics detector. These results demonstrate that the nanostructured Zn0.6Mn2.4O4 could be a potential supercapacitor as well as a nitroaromatics detector with striking sensitivity for commercial purposes.