meso-Porfirina e seus análogos metalados de Zinco e Paládio: propriedades anticorrosivas e fotocatalíticas

Abstract

Macromolecules are large and complex structures that play essential roles in the structure and function of all living organisms. Porphyrins, whether of natural or synthetic origin, belong to this class and are known for their structural variations based on their symmetry and metal coordination, which can present as symmetric, asymmetric, free-base, or metalated forms. In this context, the present work involved the synthesis and characterization of meso-porphyrin-type macromolecules and their metal complexes with Zinc (Zn) and Palladium (Pd). These compounds were synthesized using cardanol, the major component of Cashew Nut Shell Liquid (CNSL), and vanillin (a lignin-derived compound), both sourced from regional biomass. The macromolecules were characterized using a set of experimental techniques, including UV-Vis, FTIR, TGA, and 1H and 13C NMR. The synthesized compounds were applied in two main areas: (1) as anticorrosive coatings, by incorporating the macromolecule into alkyd resins, and (2) in heterogeneous photocatalysis, through the development of a hybrid compound combining meso-metalloporphyrins with graphitic carbon nitride (g-C₃N₄). The anticorrosion study aimed to investigate the protection of metals against corrosion using alkyd coatings, which was assessed through analyses of electrochemical properties, adhesion, hardness, and chemical resistance. The zinc-based derivative showed superior performance as a barrier coating, offering enhanced corrosion resistance and prolonging the lifespan of the protected materials. The catalytic aspect involved the photoreduction of 4-nitrophenol, a common pollutant found in wastewater. Among the tested materials, the g-C₃N₄/PdP hybrid exhibited the highest efficiency in the reduction process, following a first-order kinetic model. The newly synthesized meso-porphyrins proved to be effective, with the Zn meso-porphyrin incorporated into alkyd resins significantly increasing the durability of metal surfaces by shielding them from environmental degradation. Meanwhile, the metalloporphyrins (Zn and Pd) hybridized with g-C₃N₄ demonstrated strong potential as heterogeneous photocatalysts for the reduction of 4-nitrophenol in aqueous media.