Formation of Meso-Structured Multi-Scale Porous Titanium Dioxide by Combined Soft-Templating, Freeze-Casting and Hard-Templating Using Cellulose Nanocrystals

This thesis identifies a facile and versatile technique for creating multi-scale porous titania with tunable meso-scale morphology. Three templating approaches were simultaneously utilized in achieving this; namely, soft-templating by template-free self-assembly of an aligned macroporous structure, freeze-casting for the preservation of particle dispersion found in suspension, and hard-templating by the use of cellulose nanocrystals (CNCs) as sacrificial material. A systematic study was conducted wherein three synthesis parameters (water content, alcohol solvent content, and drying method) were varied in the hydrolysis of titanium tetra-isopropoxide (TTIP) by the sol-gel method to determine their contribution to the formation of multi-scale porous titania exhibiting aligned macrochannels and mesoporosity. The optimal synthesis settings for producing multi-scale porous titania were identified as H2O/TTIP molar ratio of 30, without any isopropanol (acting as solvent), and freeze-drying after freezing at -40°C. Subsequently, CNCs were added in various quantities (0-50vol%) to the hydrolysis of TTIP using these optimized settings to achieve more direct and precise control of the final titania meso-structure. Morphological studies revealed that the final titania bodies maintained the formation of macrochannels 1-3 μm in diameter as a result of hydrolysis in excess water in the absence of an organic solvent and exhibited successful templating mutually affected by CNC addition and freeze-casting. Freeze-drying preserved particle dispersion in the colloid suspension, hindering agglomeration otherwise found after oven-drying and enhanced the CNCs' role of disrupting titania aggregation and increasing interconnectivity. Thus, meso-structured multi-scale porous titania was prepared by a combined templating strategy using template-free self-assembly, freeze-casting, and CNC hard-templating.