3D Printing of Powder‐Based Inks into Functional Hierarchical Porous TiO₂ Materials

Abstract

Integrating multifunctional semiconducting metal oxide powders into a 3D printing technique to construct hierarchical porous structures is highly desirable and remains a significant challenge. Herein, an extrusion‐based 3D printing strategy is developed that can assemble TiO2 powders into hierarchical porous structures with multiscale pores at both the macro‐ and microscale. Powder‐based TiO2 inks with a significant shear‐thinning behavior and adequate storage modulus and yield stress are developed to meet the requirements of 3D printing of TiO2 in an air environment without the need for an additional solidification treatment, which provides good printing flexibility. The hierarchical porous structures with a relatively high compressive strength provide the 3D‐printed TiO2 structures with great potential for use in many applications, including filtration, thermal insulation, biomedical scaffolds, catalyst supports, and energy conversion. Compared with scaffolds with a compact morphology, the hierarchical porous TiO2 scaffold as a photoelectrode achieves a higher nitrogen photofixation yield due to its high surface adsorption and activation capacity caused by its porous morphology. Importantly, the powder‐based ink design and extrusion‐based 3D printing approach are readily extended to other semiconducting metal oxides such as ZnO and their composites.

Enhanced Fe-TiO2 Solar Photocatalysts on Porous Platforms for Water Purification

“…Concerning photocatalysts, TiO 2 is in the spotlight and the subject of intense research, due to its remarkable properties, which include a strong oxidation potential to decompose organic pollutants, physical and chemical stabilities, low cost, non-toxicity, and earth abundance [ 10 , 11 , 12 , 13 , 14 , 15 ]. TiO 2 is widely used in photocatalysis for the degradation of contaminants, in both aqueous and gaseous mediums [ 16 ].…”

Vertical 3D Printed Forest‐Inspired Hierarchical Plasmonic Superstructure for Photocatalysis

“…In recent years, a variety of 3D printing methods, such as electric‐field‐driven microscale 3D printing, [ 31 ] femtoliter ink meniscus guiding evaporation printing, [ 32 ] and direct‐ink‐writing (DIW) 3D printing, [ 33–35 ] have been developed to construct various 3D structures. Among these strategies, the DIW method has recently been developed into a promising 3D printing approach for printing various materials without the need for expensive tooling, molds, or lithographic masks.…”

“…Among these strategies, the DIW method has recently been developed into a promising 3D printing approach for printing various materials without the need for expensive tooling, molds, or lithographic masks. [ 33–36 ] For Direct‐Ink‐Writing 3D printing technology, the preparation of a printable ink with suitable rheological properties is a prerequisite for printing. [ 36–38 ] On one hand, the ink needs to have a pronounced shear‐thinning property to allow it to be extruded smoothly from the fine nozzle; on the other hand, an adequate storage modulus ( G ′) of ink enables the freshly extruded filament to maintain its shape and makes the printed 3D structures self‐supporting rather than collapsing, which is especially important for vertical printing of pillar structure.…”

“…And the submicron TiO 2 particles were anatase phase. In previous work, [ 34 ] it has been demonstrated that the incorporation of NPs can significantly enhance the viscosity and storage modulus of the TiO 2 ink, which is beneficial to maintain the shape of the vertical cylindrical structure and thus help to realize the vertical 3D printing. In addition, the small NPs can also increase the contact among TiO 2 particles to enhance the degree of solid‐state reaction in the heat treatment process, and thus help to achieve a relatively high structural strength.…”

“…The incorporation of NPs enables to the formation of a denser arrangement stacked together, which also facilitates the solid phase reaction during the heat treatment process and improves the mechanical strength of the sample. [ 34 ] High structural strength will allow the TiO 2 pillar arrays to remain structurally intact and unbroken in subsequent photocatalytic applications, which is required for its recovery and reuse.…”