Environmentally Friendly Engineering and Three-Dimensional Printing of TiO2 Hierarchical Mesoporous Cellular Architectures

Three-dimensional (3D) printing of hierarchically ordered cellular materials with tunable microstructures is a major challenge from both synthesis and scalable manufacturing perspectives. A simple, environmentally friendly, and scalable concept to realize morphologically and microstructurally engineered cellular ceramics is herein demonstrated by combining direct foam writing with colloidal processing. These cellular structures are widely applicable across multiple technological fields including energy harvesting, waste management/water purification, and biomedicine. Our concept marries sacrificial templating with direct foaming to synthesize multiscale porous TiO2 foams that can be 3D printed into planar, free-standing, and spanning hierarchical structures. The latter being reported for the first time. We show how by varying the foam-inks' composition and frothing conditions, the rheological properties and foam configurations (i.e., open- or closed-cell) are tuned. Furthermore, our printing studies indicate a synergy between intermediate extrusion pressures and low speeds for realizing spanning features. Additionally, the dimensional changes associated with the postprocessing of the different foam configurations are discussed. We investigate the effects of the foams' composition on their microstructure and surface area properties. Additionally, the foams' photocatalytic performance is correlated with their microstructure, improving for open-cell architectures. The proposed synthesis and scalable manufacturing method can be extended to fabricate similar structures from alternative ceramic foam systems, where control of the porosity and surface properties is crucial, demonstrating the great potential of our synthesis approach.