Structure Control of Fine Particles in the Gas Phase and Its Application to Advanced Materials Development

Abstract

Background and Aims: Gas-phase particle synthesis enables the formation of unique microparticles and nanoparticles due to specific formation mechanisms, including particle generation from microdroplets and formation under non-equilibrium conditions through rapid quenching. This approach allows for the synthesis of distinctive structures such as aggregated nanoparticles, spherical particles, amorphous particles, core–shell structures, porous particles, hollow particles, and heterogeneous material composites. The aim of this study was to develop functional nanoparticles with controlled structures using aerosol-based methods and evaluate their performance in energy, environmental, and life science applications.

Methods and Results: We employed spray-based synthesis methods, including flame spray pyrolysis and spray drying, to achieve structural control of functional nanoparticles. For porous structure formation, Nb-doped SnO₂ (NTO) nanoparticles were synthesized using flame spray pyrolysis with polymethyl methacrylate (PMMA) particles as pore-forming templates. The resulting macroporous NTO particles demonstrated enhanced gas diffusion properties and achieved power generation performance comparable to carbon nanoparticles in polymer electrolyte fuel cells, with porosity increased from 12% to 36%. Three-way catalyst particles with controlled pore sizes (61–381 nm) showed improved CO oxidation performance, with 90% CO conversion achieved at lower temperatures due to enhanced mass transfer within the porous structures. For composite material development, cellulose nanofiber/iron oxide hybrid particles were successfully synthesized via spray drying, enabling magnetic separation while maintaining high negative surface charge (−50 mV) and biocompatibility for life science applications. Temperature optimization studies revealed that porous catalyst particles achieved 100% CO conversion at 130°C, representing a 170°C reduction compared to conventional aggregate particles. The magnetic hybrid particles demonstrated excellent recyclability, maintaining both binding capacity and magnetic responsiveness over multiple separation cycles without structural degradation.

Conclusions and Outlooks: Gas-phase structuring of nanoparticles offers significant potential for advanced material development through precise control of particle morphology and internal structure. Future challenges include: (1) numerical understanding of colloidal arrangement during solvent evaporation, (2) quantitative control of particle structure and function-based design, (3) integration of experimental approaches with AI-driven process science, (4) development of nanostructured particle–resin composites, and (5) scale-up processes for enhanced productivity. Japan’s advantages in nanomaterial availability position it well for pioneering next-generation particle development for advanced applications.