Correlating Structural, Morphological, and Optical Modifications of Semicarbazone Pyranoquinoline (PQMHC) and Its Cu(II) Complex for Enhanced Photocatalytic Efficiency

In this study, we present the first synthesis and comprehensive structure–property analysis of a semicarbazone pyranoquinoline (PQMHC) ligand and its newly developed Cu(II)-PQMHC complex. X-ray diffraction (XRD) reveals that Cu(II) coordination induces a complete crystalline phase transition from the orthorhombic Imma lattice of the ligand to a monoclinic P2₁/m structure in the complex, confirming the formation of a coordination-driven architecture. High-resolution transmission electron microscopy (HR-TEM) and field-emission scanning electron microscopy (FE-SEM) show that this coordination reorganizes the nanofibrous assemblies into a more compact and uniform morphology, accompanied by a reduction in fiber diameter. Diffuse-reflectance spectroscopy indicates a notable band-gap narrowing from 2.305 eV (PQMHC) to 1.896 eV (complex), reflecting enhanced electronic delocalization and low-energy charge-transfer transitions due to metal coordination. Porosity analysis demonstrates that the ligand exhibits well-defined mesoporosity, whereas the Cu(II) complex shows reduced N₂ uptake, pore volume, and mesopore population, indicating densification and partial pore blockage upon complexation. Functional testing with Imazapyr-contaminated wastewater highlights a unique dual behavior: the Cu(II)-PQMHC complex achieves high adsorption efficiency (92%), while the free ligand exhibits superior photocatalytic degradation under UV-A and UV-C illumination. This work introduces a novel Cu(II)-PQMHC complex and establishes clear structure–morphology–function relationships, providing valuable insights for designing advanced materials for adsorption and photocatalytic applications.