Mesostructure control in monoliths 3D-printed using industry-grade SiO2 powder for CO2 capture

Abstract

Direct ink writing (DIW) enables the fabrication of silica monoliths with hierarchical porosity, offering potential for liquid and gas adsorption applications. Although silica and silanized silica are widely employed in such processes, control over mesoporous architecture in DIW-printed structures remains limited. In this study, mesoporosity was tuned using inks formulated from industry grade silica powders and a colloidal binder. Rheological behavior relevant to printability was characterized, and the porous architecture of extruded filaments was evaluated via nitrogen sorption. Pore size distributions ranging from 4 to 50 nm were achieved by adjusting powder characteristics. Narrow distributions were observed in inks with high colloidal silica content, while broader distributions resulted from bimodal particle blends. Depending on the particle size and agglomeration state, porosity arose either from intrinsic powder features or from interparticle voids formed during ink preparation. Post-printing silanization with 3-aminopropyl(triethoxysilane) consistently reduced both specific surface area and pore volume. A direct correlation was identified between surface area and the density of amine groups. CO2 adsorption measurements confirmed functional group accessibility across all formulations, with an average uptake of 0.2 mmol CO₂ per mmol NH₂. This work provides a predictive framework linking ink formulation to mesostructure and surface reactivity in printed silica monoliths.