Noble metal nanoparticles, such as Au and Ag, are typically synthesized via solution-phase reduction using chemical reductants, which can lead to size and shape inconsistencies and may involve toxic agents. We developed a reductant-free method that utilizes the solid–liquid interface to synthesize these nanoparticles. This approach eliminates the need for both reductants and surfactants, enabling stable dispersion over extended periods. Recently, we have also successfully immobilized nanoparticles onto various substrates, thereby expanding their potential for material applications.

Macropores, defined as pores larger than 50 nm, facilitate the easy flow of gases and liquids when they are interconnected. In ceramics, templates or pore-forming agents are typically used to create such structures. We discovered that the thermal decomposition of carbonates in water vapor spontaneously forms oxide particles with interconnected macroporous networks. These structures can physically trap nanoparticles, enabling applications such as composite anode materials for Li-ion batteries when combined with conductive particles. Recently, we successfully synthesized magnetic macroporous particles, which accelerate research toward applications in environmental remediation and biomedical fields.

To achieve carbon neutrality by 2050, advanced technologies for clean energy conversion and storage are essential. These technologies rely on critical elements like Li and Ni, making recycling vital due to geopolitical risks. We are developing a novel circular process to directly and selectively extract and separate elements from used solid materials. Furthermore, the solid-to-solid transformation, mediated by vapor, also enables the fabrication of porous materials with 3D hierarchical structures through shape-controlled conversion. Our approach contributes to upcycling in the circular economy.