Ferrocenyl metal–organic framework hollow microspheres for in situ loading palladium nanoparticles as a heterogeneous catalyst

Abstract

The preparation of hollow metal–organic framework (MOF) structures through a stepped dissolution–regrowth method avoids the troublesome template removal and etching process, although it still faces several challenges due to its intrinsic limitations. In this work, we reported the preparation of ferrocenyl MOF hollow microspheres by coordinating Fc(COOH)₂ with Zn²⁺ assisted by polyvinyl pyrrolidone (PVP). It was found that PVP was beneficial for the growth of well-defined MOF hollow microspheres (2–4 μm). Both the internal and exterior morphology could be regulated by controlling the dose of PVP (0–30 equiv.). In addition, the crystallinity, thermal stability of hollow MOFs and repeatability of synthesis were improved by PVP. Owing to the excellent redox properties of the ferrocenyl ligand (1,1′-ferrocenedicarboxylic acid), the prepared MOF hollow microspheres exhibited good redox properties, and were able to reduce the Pd²⁺ precursor into Pd nanoparticles (diameter = 3–5 nm) under mild conditions (25 °C, aqueous solution) without extra reducing agents. The Pd-loaded MOF hollow microspheres showed remarkable catalytic activity in the reduction of 4-nitrophenol to 4-aminophenol with a reaction rate constant k of 1.82 × 10⁻² s⁻¹.