Nanometric titanium oxide (TiO2) has been widely investigated as an active material for the photodegradation of complex organic contaminants in water treatment. It is well known that the photoactivity of n-TiO2 depends largely on its crystallographic structure: Anatase is considerably more active than the more stable rutile form. However, using loose powders is not possible in large-scale applications due to the risk of leaching in the environment, making removal costs prohibitive.  A suitable alternative is represented by the realization of elements of sintered anatase presenting large surface areas and geometries allowing for efficient UV irradiation. Sintering of n-TiO2 maintaining the anatase crystal structure is particularly challenging. The stabilization of the anatase crystal structure is strictly related to the grain size of the material. Any attempt to produce significant densification of the nanopowders results in grain growth that produces the transition to the rutile form.

In this work, we present an innovative approach to the realization of objects with complex geometries maintaining the anatase crystal structure. This is achieved using a two-step process. The first step involves realizing a green body with a 3D printing process based on the material extrusion approach. A water-based colloid with the appropriate rheological properties is realized using water, anatase nanopowders and a small amount of an organic binder (Pluronic). After desiccation the green body undergoes very rapid thermal cycling in SPS, using heating rates above 200 °C/min at temperatures around 800 °C. Both pressure-assisted and pressureless approaches have been investigated. Using this approach, various highly porous geometries with an anatase crystal structure content above 80% have been obtained. Preliminary tests have shown that these materials can produce a significant photodegradation of complex organic molecules under a flow of 300 ml min-1 5W 254nm UV lamps.