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 NaHCO 3 or (NH 4 )(H 2 PO 4 ). The freeze-drying method sublimates ice, and nanoparticles of NaHCO 3 or (NH 4 )(H 2 PO 4 ) 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 NaHCO 3 or (NH 4 )(H 2 PO 4 ) 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.