Assembling of nanoparticles using ice crystals

This article introduces a method to assemble nanoparticles into the form of fibers and monolithic microhoneycombs using unidirectional freezing. The nanoparticles used were of TiO2, high SiO2 Y-type zeolite, and graphite. A silica hydrogel was used as the binder, and an array of needle-shaped ice crystals formed during the unidirectional freezing of the particle–hydrogel complex was used as the template. It was found that such particle–hydrogel complexes can be easily molded into the form of fibers and monolithic microhoneycombs like hydrogels which do not include particles. The morphology can be changed by adjusting the firmness of the silica hydrogel. The strength of the microhoneycombs was found to decrease with the inclusion of nanoparticles, but could be recovered through calcination. The fibers and monolithic microhoneycombs are expected to have the combined functions of the particles and binder included within them. They are also equipped with a network of nanopores and macropores which reach to the surface of the nanoparticles, therefore various fluids can gain access to the surface of the nanoparticles quite easily. Due to this high accessibility, it is expected that the included nanoparticles can show their maximum performances.