Freeze-dissolving method: a fast green technology for producing nanoparticles and ultrafine powder

A new technology, a freeze-dissolving method, has been developed to isolate nanoparticles or ultrafine powder and is a more efficient and sustainable method than the traditional freeze-drying method. In this work, frozen spherical ice particles were produced with an aqueous solution of sodium bicarbonate or ammonium dihydrogen phosphate at various concentrations to generate nanoparticles of NaHCO₃ or (NH₄)(H₂PO₄). The freeze-drying method sublimates ice, and nanoparticles of NaHCO₃ or (NH₄)(H₂PO₄) in the ice templates remain. The freeze-dissolving method dissolves ice particles in a low freezing point solvent at temperatures below 0 °C, and then, nanoparticles of NaHCO₃ or (NH₄)(H₂PO₄) can be isolated after filtration. The freeze-dissolving method is 100 times faster with about 100 times less energy consumption than the freeze-drying method as demonstrated in this work with a much smaller facility footprint and produces the same quantity of nanoparticles with a more uniform size distribution.