Anchoring Pd Nanoparticles on Fe3O4@SiO2 Core–Shell Nanoparticles by Cross-Linked Polyvinylpyrrolidone for Nitrite Reduction

A novel and environmentally benign approach was developed to create a Fe3O4@SiO2 core–shell structure supported Pd catalyst consisting of a superparamagnetic Fe3O4 nanosphere core, a SiO2 shell with a rough surface, Pd nanoparticles deposited on a SiO2 shell, and a cross-linked polyvinylpyrrolidone (PVP) layer. It was found that both adsorbed PVP and SiO2 shell with a rough surface from the surface-protected etching process were critical to obtain the uniform PdO deposition, while the cross-linked PVP layer could effectively anchor and protect active Pd nanoparticles to enhance their stability to resist detachment from the catalyst support and improve the reusability of the catalyst. Because of its superparamagnetic behavior, it could disperse well in aqueous solution without external magnetic field and be separated easily from aqueous solution when an external magnetic field was present. It demonstrated a high catalytic activity, desirable N2 product selectivity over 99.7%, and good reusability for the catalytic nitrite reduction in aqueous solution.