Straightforward Synthesis of Metal Nanoparticles and Hierarchical Porous Metals Assisted by Partial Film Boiling Phenomena

The development of an eco-friendly and economical synthetic pathway of nanomaterials such as metal nanoparticles and nanoporous metals remains a challenging topic in the field of nanomaterials. Here we report a novel and eco-friendly series of synthetic methods from the preparation of metal nanoparticles to the fabrication of hierarchical porous metals by using partial film boiling phenomena established by a reactor with the inverse configuration of conventional Leidenfrost drop reactors, which is much more favorable to large-scale production than conventional Leidenfrost drop reactors. As a result, we have revealed two important facts, which can offer fresh vision to the field of metal nanoparticle and nanoporous metal synthesis. The first one is that Pd and Pt precursor can be reduced to neutral Pd and Pt nanoparticles under basic condition established by partial film boiling phenomena without reducing agents such as ethanol and citric acid. The second one is that when citric acid and ethanol as a mild reducing agent were added into the precursor aqueous solution, citric acid also plays an important role as a pore-forming agent, and ethanol facilitates the aggregation of as-prepared metal nanoparticles, resulting in the formation of nanoporous Pd and Pt. Our work is believed to suggest more eco-friendly and straightforward approaches for fabrication of metal nanoparticles and nanoporous metals. However, further research is required to explore whether our novel synthetic pathway is available to other metal systems.