Efficient shape transformation of palladium nanocrystals by biphasic oxidative etching and regrowth

Although great success has been achieved in shape-controlled synthesis of noble metal nanocrystals with optimal catalytic properties, the synthesis still needs perfecting for some specific noble metal nanocrystals, octahedral Pd nanocrystals for example, in terms of improved synthetic throughput and controllability for large-scale applications. Herein, we report a robust liquid-solid biphasic oxidative etching-regrowth strategy that can enable a rapid transformation of pre-synthesized Pd nanocubes into octahedrons at high concentrations. The key is to introduce HNO₂ into the polyol system, which not only serves as a strong oxidizing agent for efficient oxidative etching of Pd nanocubes into PdCl₄²⁻ but also produces active hydrogen to help reduce PdCl₄²⁻ back onto the Pd nanocrystals for their shape transformation. This liquid-solid biphasic system allows direct contact of Pd nanocubes with the oxidizing/reducing agents, both in high concentrations, and therefore can afford substantially more concentrated Pd octahedrons (0.86 mg mL⁻¹) than conventional synthesis. This synthesis requires a reaction time of only a few minutes, which is significantly more time-efficient than conventional strategies. Our approach is simple yet efficient and scalable for the shape-controlled synthesis of Pd and potentially other noble metal nanocrystals to extend their application in a broad range of fields.