From Stable Water-based Titania Colloidal Suspension Preparation to Film Formation from Drying Droplets

Despite the limitations associated with titania regarding its unsustainable production and potential toxicity, this material is still used in a wide range of applications thanks to its unique properties. While titania can be replaced by components such as zinc oxide in some applications, in others, titania is likely to prevail until suitable alternatives are found, if there ever are. In the meantime, one can still take advantage of the properties of titania in a safer and more sustainable manner. This begins with better understanding titania, the goal of this thesis.This thesis starts with a meta-analysis of literature data (Chapter 3) where key synthesis parameters for the most sustainable titania production approaches, namely sol-gel and hydrothermal methods, are identified, analyzed, and categorized. This resulted in ranking reaction parameters depending on their impact on the properties of the resulting titania nanoparticles. Chapter 4 takes a more pragmatic approach by focusing on the impact of acid catalyst type on the water-based sol-gel synthesis of these nanoparticles. This study enabled to identify the reaction conditions leading to the optimum trade-off of sample purity and nanoparticle crystallinity. The colloidal stability of the resulting titania nanoparticle suspensions is investigated in Chapter 5. This investigation was conducted using several methods, including synchrotron small angle X-ray scattering, leading to elucidating the shape of fractal aggregates formed inside the as-prepared aqueous titania suspensions as a function of their concentration. The added value of Chapter 5 is to explicate these fractal structures and the aggregation mechanism for titania nanoparticles in aqueous suspensions. Aware of this aggregation mechanism, Chapter 6 studied the drying behavior of titania nanoparticle aqueous suspensions. The most important result in this chapter is showing that the quasi-steady state diffusion based solute transfer models, which have largely been successfully applied to describe drying dynamics and pattern formation for highly stable nanoparticle suspensions, are also valid for aggregation-prone suspensions like aqueous suspensions of titania nanoparticles.Although titania has been extensively studied from various perspectives and for a broad range of applications, this thesis shows that there is still more left to be understood from this transition metal oxide. In the perspective of delivering more sustainable solutions for titania production, this thesis focused on water-based systems prepared at room temperature. Of course, working under such mild conditions has shortcomings like the mixed crystalline phases for the resulting titania nanoparticles, instead of the typical higher purity from less sustainable processes. However, for applications which do not require a high level of crystalline phase purity, these mild conditions could be an alternative to a more sustainable titania production. Regarding the safer alternatives, this dissertation dealt with never dried suspensions prepared in situ from titania precursor. This never dried aspect looks like an alternative to the common manner of preparing titania dispersions from dispersing titania powders in liquid formulations.

Publication year:2022

Accessibility:Embargoed