Efficient and sustainable preparation of fine particles by a bubble-assisted freeze-dissolving method

Abstract

The development of fine particles has enabled innovative solutions across energy, environmental, and biomedical applications, driving the demand for cleaner, more efficient, and environmentally friendly synthesis methods. In this study, we present a freeze-dissolving approach as a sustainable and energy-efficient alternative to conventional freeze-drying for the preparation of KHCO₃ and NH₄H₂PO₄ fine particles. By dripping aqueous solutions of KHCO₃ or NH₄H₂PO₄ into liquid nitrogen, ice-templated particles were rapidly formed and these ice particles were subsequently dissolved in ethanol below 273.15 K. As the ice quickly dissolved in ethanol, the fine particles formed within the ice templates were released into the solution and collected for characterization, including size distribution analysis, SEM imaging, and powder XRD. Compared with freeze-drying, the freeze-dissolving method yields significantly smaller particles while reducing energy consumption by 99%. Moreover, the first-time introduction of air bubbles during the freeze-dissolving step further reduces particle size and substantially limits agglomeration. This bubble-assisted freeze-dissolving technique proves more effective than non-bubbled methods across a range of initial solute concentrations and ice particle sizes, highlighting its potential as a scalable and eco-conscious strategy for fine particle production.