Additive manufacturing of polymer-derived titania for one-step solar water purification

Solar disinfection of drinking water (SODIS) is an approach for water purification widely used in households with limited access to fresh water. SODIS relies on microorganism inactivation triggered by sunlight energy in the UV spectrum and requires processing times of up to 48 h. Water treatment rate is drastically increased by using photocatalytic materials, such as TiO2, which can harvest sunlight to promote generation of reactive oxygen species (ROS) that inactivate bacteria within few hours. One main challenge that impedes the insertion of photocatalysts in most water treatment approaches is the need to populate the catalyst particles on a three-dimensional (3D) structure with a high-surface area that is stable under water flow. We develop an additive manufacturing (AM) process for titania and propose an efficient design of a solar water disinfection device based on architected TiO2 that does not require expensive filtering of the catalyst. We synthesize titanium monomers using a ligand exchange reaction between titanium alkoxide and acrylic acid and utilize these to prepare a pre-ceramic titania photoresist. We then use this photoresist in a commercial stereolithography apparatus to define complex 3D architectures, which are then pyrolyzed to remove organic content. The resulting structure has similar to 40% reduced dimensions compared with its as-fabricated counterpart and has a chemical composition of 46 wt% Ti, 31 wt% O, and 23 wt% C, as measured at the surface by Energy-Dispersive Spectroscopy (EDS). Using this methodology, we fabricated 3D structures with periodic cubic and octet geometries whose unit cells range from 0.65 to 1.14 mm, beam lengths of 115-170 mu m, and relative densities of 11-31%. Transmission Electron Microscopy (TEM) analysis reveals the microstructure of these lattices is nanoscrystalline titania (rutile) with a mean grain size of similar to 60 nm. Mechanical experiments reveal that these cubic titania microlattices, whose density is 350-365 kg/m(3), achieve compressive strengths of up to 4.3 MPa, which is several times stronger than what is reported for titania foams with comparable density. We finally demonstrate how the developed AM process can be modified to reduce carbon content and produce > 99 wt% titania parts. This work demonstrates that the proposed titania AM process can be used to create safe, efficient and cost-effective photocatalytic reactors for household water disinfection, as well as for applications in photocatalytic hydrogen production, CO2 conversion, and tissue engineering.