A sustainable bio-based benzoxazine porous organic polymer derived vanillin for synergistic catalysis: Green synthesis of Pd nanoparticles and enhanced nitro reduction

A novel bio-based porous organic polymer (Gu-V-BZ POP) is successfully synthesized through Schiff base condensation using a vanillin-derived benzoxazine dialdehyde and triaminoguanidinium chloride. This approach harnesses renewable vanillin as a sustainable aromatic precursor, while the incorporated benzoxazine units enhance thermal stability and provide additional coordination sites for metal ion binding. The resulting nitrogen-rich, amine-functionalized polymer serves as an effective platform for the reduction of Pd(II) ions to well-dispersed palladium nanoparticles (Pd NPs) without the need for hazardous reducing agents. Structural and chemical characterization confirms the formation of the porous polymer network covering a surface area of 32.79 m² g⁻¹ and the successful immobilization of ultrafine Pd NPs (∼2.5 nm) on its surface. The catalytic performance of the resulting Pd@Gu-V-BZ POP nanocomposite is evaluated using the model conversion of p-nitrophenol (p-NP) to p-aminophenol (p-AP) under excess NaBH₄. The catalyst demonstrates exceptional activity,with apparent rate constants reaching 0.390 min⁻¹ and normalized activity of 46.90 mg⁻¹ s⁻¹ for the composite with the highest Pd loading (0.458 wt%). Detailed kinetic analysis reveals a clear structure-activity relationship. Furthermore, comparative studies using p-fluoronitrobenzene suggest that the amine groups on the polymer support actively participate in substrate activation through specific interactions. This work integrates renewable feedstock chemistry, green nanoparticle synthesis, and functional benzoxazine design to create an efficient and durable catalytic material, offering a sustainable strategy for the development of high-performance heterogeneous catalysts for environmental and industrial engineering.