Generation of Titanium Dioxide Parts using Cellulose Nanocrystal Aerogel Hard Templates
This project studies the generation of crystalline mesoporous structured titanium dioxide (TiO2) using cellulose nanocrystal (CNC) aerogel hard templates for photocatalytic and biomaterial applications. Suspensions of CNCs in water varying in solid loading from 20 mg/mL to 100 mg/mL were prepared and frozen at three different temperatures (-20 °C, -40 °C, or -80 °C) using four combinations of hollow cylindrical molds and mold plates with different thermal conductivities (stainless-steel or glass) placed on different heat conductive and insulative substrates (aluminum, polystyrene foam and cardboard). Frozen samples were then freeze dried to sublimate the ice and render a multiscale and mesoporous structure with a variety of microstructural features, including lamellar sheeting, flakes, ribbons, or striations. Ceramic green bodies are then produced by reacting Titanium isopropoxide with water through several different processes to generate amorphous TiO2 either in-situ in the CNC aerogel or as a suspension for infiltration under varying pressure. Green bodies are dried at room temperature, and the extent of ceramic coating of the template is visually determined using SEM imaging. Once dried, crystalline TiO2 are produced through a two-step heat treatment with a CNC burnout at 270 °C and crystallization and sintering at 500 °C, 600 °C, or 1000 °C. The final crystallinity and phase composition is examined using XRD, and the final porosity is determined using BET. Results have shown the ability to satisfactorily coat aerogels under 10 mm in one dimension with TiO2. These samples have been successfully heat-treated to produce both anatase and rutile phase TiO2 while maintaining the macrostructure of the CNC aerogel. Multiscale porosity has been achieved, and samples heat treated at 1000 °C have achieved structural integrity.