Solid-State synthesis of transition nanometal oxides (MnO₂, Co₃O₄, NiO, and ZnO) for catalytic and electrochemical applications

Herein, novel transition metal complexes were successfully synthesized in an aqueous medium by reacting aminoguanidine (Amgu) bicarbonate and 2-hydroxynicotinic acid (2-OHnicH) with divalent metal ions [M = Mn²⁺ (1), Co²⁺ (2), Ni²⁺ (3), or Zn²⁺ (4)] having a general composition of (AmguH)₂[M(2-Onic)₂(H₂O)₂]. This study focuses on the solid-state synthesis of transition metal oxide nanoparticles (MO NPs) from their respective metal complexes as precursors, followed by the assessment of the catalytic and electrochemical properties of the resulting MO NPs for various applications. Comprehensive characterization confirmed the identity and similarity of the prepared metal complexes. The antibacterial and antioxidant abilities of the metal complexes were evaluated, and the Ni(II) complex demonstrated a noteworthy biological activity. The complexes were further utilized as solid precursors to synthesize corresponding nanometal oxides through thermal decomposition. Transmission electron microscopy studies revealed the mean nanoparticle diameters to be 12.4 nm (MnO₂), 9.5 nm (Co₃O₄), 6.2 nm (NiO), and 8.1 nm (ZnO). The as-prepared MO NPs were employed as catalysts to reduce 4-nitrophenol and as electrochemical sensor materials to detect histamine (HA) and pyridoxine (PY). The NiO NPs demonstrated excellent properties as catalysts and as sensor materials and a promising specific capacitance and were selected for supercapacitor applications.