Mechanical Optimization of Diatomite Monoliths from Freeze Casting for High-Throughput Applications

The silica cell walls of diatoms, the abundant microalga 1-100 μm in size, show a highly ordered hierarchical porosity and are widely available through their fossilized form known as diatomite. The goal of this research was to use this cost-effective source of porous silica in a unidirectional freezing process called ice-templating, or freeze casting, to create a ceramic membrane with unidirectional lamellar walls of ∼15 μm channels, which allows for an efficient mass transport of fluids (i.e., low pressure drop), while maintaining the optimal mechanical properties. Control over the monoliths was explored by varying the mass ratio of diatomite and sodium carbonate and the solid ratio in the initial slurry before freeze casting. The resultant monolith properties were assessed using scanning electron microscopy, mercury intrusion porosimetry, and mechanical testing. The membranes then underwent an in-line vacuum filtration of methylene blue dye and monodisperse latex beads to quantify the membrane filtration performance through chemical adsorption and depth filtration capabilities, respectively. Control over the material properties of the biosourced ceramic monoliths allows for a cost-efficient and hierarchically porous ceramic template with efficient mass transfer capabilities that can be potentially functionalized with a variety of sophisticated nanomaterials for various adsorbent, filter, catalysis, and sensor applications.