Thermally stable two-dimensional hexagonal mesoporous nanocrystalline anatase, meso-nc-TiO2:: Bulk and crack-free thin film morphologies

Herein a novel synthetic route is described for the production of thermally stable, structurally well-defined two-dimensional (2D) hexagonal mesoporous nanocrystalline anatase (meso-nc-TiO2), with a large pore diameter, narrow pore-size distribution, high surface area, and robust inorganic walls comprised of nanocrystalline anatase. The synthetic approach involves the evaporation-induced co-assembly of a non-ionic amphiphilic triblock-copolymer template and titanium tetraethoxide, but with a pivotal change in the main solvent of the system, where the commonly used ethanol is replaced with I-butanol. This seemingly minor modification in solvent type from ethanol to I-butanol turns out to be the key synthetic strategy for achieving a robust, structurally well-ordered meso-nc-TiO2 material in the form of either thick or thin films. The beneficial "solvent" effect originates from the higher hydrophobicity of 1-butanol than ethanol, enhancing microphase separation and templating, lower critical micelle concentration of the template in I-butanol, and the ability to increase the relative concentration of the inorganic precursor to template in the co-assembly synthesis. Moreover, thin films with dimensions of several centimeters that are devoid of cracks down to the length scale of the mesostructure itself, having high porosity, well-defined mesostructural features, and semi-crystalline pore walls were straightforwardly and reproducibly obtained as a result of the physicochemical property advantages of 1-butanol over ethanol within our synthesis scheme.