Synthesis, characterization and DFT studies of ZnO–phthalocyanine and triazine-based phthalonitrile polymers synthesized from 4-nitrophthalonitrile monomer

Abstract

Phthalonitrile-derived polymer materials were synthesised from 4-nitrophthalonitrile via two distinct synthetic strategies: thermal polymerization using aniline catalyst and ZnO-assisted macrocycle polymerisation. Nano ZnO was synthesized by a chemical precipitation method and subsequently combined into the phthalonitrile system to promote the formation of zinc–phthalocyanine molecule, whereas curing in the presence of amine catalyst generated a triazine-linked polymer network. The synthesized materials were thoroughly examined using UV–Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) in order to assess their structural, optical, morphological, and thermal characteristics. Spectroscopic investigations demonstrated that the nitrile group was transformed into triazine and phthalocyanine frameworks. XRD studies revealed the crystalline wurtzite phase of ZnO nanoparticles and amorphous character to the cured phthalocyanine molecule. SEM analysis shows the surface morphology and particle distribution of polymer systems. Thermal studies demonstrated that the ZnO-containing phthalocyanine molecule exhibited improved thermal resistance and superior char retention compared with the triazine-based polymer. The photocatalytic activity of the ZnO–phthalocyanine molecule was investigated through photoinduced degradation of methylene blue dye, where progressive reduction of the characteristic absorption band indicated efficient dye decomposition. Density functional theory (DFT) calculations further showed that the zinc–phthalocyanine assembly possesses greater thermodynamic stability than the zinc–triazine structure, this ensures the formation of phthalocyanine molecule with ZnO. Frontier molecular orbital studies revealed a lower HOMO–LUMO energy gap for the phthalocyanine molecule, indicating significant electronic delocalization and structural stabilization. The experimental findings reveal the possibility of ZnO–phthalocyanine molecule for photocatalytic and advanced high-temperature polymer applications.

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