Robotic Deposition of TiO2 Films on Flexible Substrates from Hybrid Inks: Investigation of Synthesis-Processing-Microstructure-Photocatalytic Relationships

TiO2 is an important material widely used in optoelectronic devices clue to its semiconducting and photo catalytic properties, nontoxicity, and chemically inert nature. Some indicative applications include water purification systems and energy harvesting. The use of solution, water-based inks for the direct writing of TiO2 on flexible substrates is of paramount importance since it enables low-cost and low energy intensive large-area manufacturing, compatible with roll-to-roll processing. In this work we study,the effect of crystalline TiO2 and polymer addition on the rheological and direct writing properties of Ti-organic/TiO2 inks. We also report on the bridging crystallite formation from. the Ti-organic precursor into the TiO2 crystalline phase, under ultraviolet (UV) exposure or mild heat treatments up to 150 degrees C. Such crystallite formation is found to be enhanced by polymers with strong polarity and, plc such as polyacrylic acid (PAM. X-ray diffraction (XRD) coupled with Raman and X-ray photoelectron (XPS) spectroscopy are used to investigate the crystalline-phase transformation dependence based on the initial TiO2 crystalline-phase-concentration and polymer addition. Transmission electron microscopy imaging and selected area electron diffraction patterns confirm, the crystalline,nature,of such bridging printed structures. The obtained inks are patterned on flexible substrates using nozzle-based robotic deposition, a lithography free, additive manufacturing technique that allows the direct writing of material in specific, digitally predefined, substrate locations. Photocatalytic degradation of methylene blue solutions highlights the potential of the studied films for chemical degradation applications; from low-cost environmentally friendly materials systems.