Robocasting of ordered mesoporous silica-based monoliths: Rheological, textural, and mechanical characterization

Hierarchically porous, high-surface-area silica materials are excellent candidates for multiple applications like catalysis and environmental remediation. Shaping these materials with additive manufacturing (AM) techniques, like robocasting, could enable their use with the benefit of on-demand, customized shaping and maximizing performance. Herein, ordered mesoporous silica COK-12 slurries were robocasted into monoliths, containing different ratios of uncalcined COK-12 and sodium bentonite (0-25 wt.%). The rheology of the mixed slurries is characterized by lower flow indexes (0.69 vs. 0.32) and higher yield stresses (96 vs. 259 Pa) compared to pure COK-12 ones. Monoliths were printed in woodpile structures and calcined at 600 degrees C. Micro-CT measurements showed a linear shrinkage of 25% after calcination. Mechanical characterization showed increased uniaxial strength (0.20 +/- 0.07 to 1.0 +/- 0.3 MPa) with increasing binder/solids ratio from 13 to 25%. The amorphous, mesoporous structure of COK-12 was retained. The structures exhibited open porosities of 52 +/- 4% and showed higher specific mesopore volumes, and increased average mesopore size (6 vs. 8 nm) compared to COK-12. Small-angle x-ray scattering analysis revealed an increased lattice parameter (10.3 vs. 11.0 nm) and reduced wall thickness (3.1 nm vs. 4.1 nm) of the COK-12 in the monoliths. These properties indicate suitability for their application as porous supports and adsorbents.