Co ₃ O ₄ Nanoparticles Decorated with Pd and PdO Nanoparticles for the Reduction of 4-Nitrophenol

The Co3O4@Pd/PdO nanocomposites were prepared through an oxygen ion implantation process with metal–organic frameworks (MOFs) as the precursor, and their catalytic reduction reactions of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by NaBH4 under room temperature were investigated in this work. It has been discovered that the reaction time was only 17 s, the turnover frequency (TOF) is about 934 mol4-NP molPd–1 h–1, and the first order rate constant κ could reach 6.97 × 10–2 s–1, which was outperformed most PdO or Pd catalysts. Besides their high void structure and more ultrafine catalyst particles, the unique composite interfaces of Pd and PdO made them have super high catalytic activity. It made the electrons of Pd 4d orbitals be easily transferred to the interface of Pd and PdO and combined with the unsaturated oxygen leading to the formation of more catalytic active sites, and the interface electron transfer effects of Pd and PdO based on the 4d orbitals theory was proposed. Furthermore, the density functional theory calculations (DFT) demonstrated that Co3O4@Pd/PdO nanocomposites had a larger negative adsorption energy (about −2.46 eV) compared with the Co3O4@PdO nanocomposites (about −1.37 eV), which were prepared by the most conventional annealing method in air at different temperature. The Co3O4@Pd/PdO nanocomposites also had a more obvious charge transfer phenomenon to 4-NP molecules during the process of reactive adsorption from the charge density difference results, which made them have super high catalytic activity. This study will not only provide an efficient quick and simple method to dispose MOFs precursor with unique structure, but also a strategy to design catalyst materials with excellent catalytic performance.