(754b) Molten Salt Hydrates As Solvent Media in the Synthesis of Mesoporous TiO2 Flakes

The importance of titanium dioxide is highlighted by its various potential applications in many fields encompassing but not limited to sensing, lithium ion batteries, dye-sensitized solar cells and catalysis. The reason behind the versatility of TiO₂ lies at its intrinsic properties such as low cost, nontoxicity, chemical stability, acidity, specific surface area and relatively good thermal stability. The manufacturing of TiO₂ from titanium containing ores still relies on the sulfate and chloride processes which are energy intensive as well as not environmentally friendly. TiO₂ in the form of thin flakes, films, nanosheets or even 2D structures have received considerable attention due to their enhanced reactivity in photocatalytic as well as in several heterogeneous catalytic reactions¹. Recently, the molten salt synthesis method has been reported to produce TiO₂ nanosheets that exhibit improved capacity as compared to the bare TiO₂ as well as better activity in dye-sensitized solar cells ^{2, 3}.

In this work, we report a simple synthesis strategy where Molten Salt Hydrates (MSH) are utilized as solvents for the production of TiO₂ flakes. We hypothesize that the ordered structure of the MSH medium is responsible for guiding the agglomeration of small TiO₂ nanoparticles (~5-8nm) to an apparent 2D-like morphology with large aspect ratio and tunable thickness. Specifically, aqueous lithium bromide (LiBr) solutions with various H₂O/salt molar ratio, always within the molten salt hydrate regime, have been tested in order to study possible morphological and structural changes of the TiO₂. This new synthesis strategy occurs at nearly ambient temperature and short reaction times due to the high reactivity between the TiO₂ precursor and water; calcination comprises the only post synthesis heat treatment. The prepared TiO2 flakes show an ordered mesoporous structure with a pore size distribution in the range of 3-8nm. We will thoroughly discuss the effect of salt/precursor as well as water/precursor on controlling the aspect ratio and thickness of the prepared TiO₂. We also use in-situ Raman measurements to follow the calcination steps as well as to evaluate the long-term thermal stability of the prepared materials.

1. T. Wang, L. Liu, G. Ge, M. Liu, W. Zhou, K. Chang, F. Yang, D. Wang and J. Ye, Journal of Catalysis, 2018, 367, 296-305.
2. M. V. Reddy, S. Adams, G. T. J. Liang, I. F. Mingze, H. Van Tu An and B. V. R. Chowdari, Solid State Ionics, 2014, 262, 120-123.
3. Z. Peining, W. Yongzhi, M. V. Reddy, A. Sreekumaran Nair, P. Shengjie, N. Sharma, V. K. Peterson, B. V. R. Chowdari and S. Ramakrishna, RSC Advances, 2012, 2.