Facile Fabrication of Highly Dispersed Pd@Ag Core–Shell Nanoparticles Embedded in Spirulina platensis by Electroless Deposition and Their Catalytic Properties

Microorganisms are widely used as the biotemplates for producing micro/nanomaterials owing to their unique features, such as exquisite morphology, renewable, and environmentally friendly. However, mass intracellular synthesis of uniformly dispersed nanoparticles (NPs) inside microorganisms is still challenging, especially in a predictable and controllable manner. Here, a facile and efficiency strategy is proposed to controllably produce highly dispersed and surfactant-free Pd@Ag core–shell NPs within the Spirulina platensis (Sp.) cells. In this approach, the Sp. cells' permeability is enhanced by the hydrochloric acid treatment first, which enables the Pd NPs penetrate the cell envelope and distribute uniformly inside the cells, and then they can work as the catalytic seeds for the following electroless silver deposition, resulting in the intracellular fabrication of Pd@Ag core–shell NPs with no agglomeration. The Pd@Ag NPs show excellent catalytic activity (turnover frequency is up to 2893 h⁻¹ for the 6.32 nm Pd@Ag NPs), good stability, and recyclability toward the 4-nitrophenol reductions. The excellent properties are attributed to the asymmetrical core–shell structure, small size, and good dispersion of Pd@Ag NPs. Due to its facility, cost-effectiveness, and versatility, this method can be expanded to other microorganisms, so it opens tremendous opportunities for various metallic nanoparticles intracellular synthesis as well as the practical application.