Quantitative analysis of anatase-rutile mixtures of TiO2 employing X-ray diffractometry and visible-Raman spectroscopy at normal heating and superheating conditions- Implications and limitations of the Spurr-Mayers equation

초록

Titanium dioxide (TiO2) is a multifunctional material that has been extensively studied, mainly because of its superior optical, electronic, and photocatalytic properties. Since the invention of the Spurr and Mayers equation (Spurr et al., Anal. Chem. 1957, 29, 760-762), the proposed mathematical formulation based on the X-ray diffraction intensity ratio of anatase [Int(101)A] and rutile [Int(110)R] phases has been widely used to estimate the relative amounts of anatase (A) and rutile (R) in TiO2 mixtures. However, our findings reveal that this formula is valid only under conventional (steady-state) heating conditions-assisted synthesis of AR-TiO2 nano-particles (NPs). It becomes unreliable when applied to AR-TiO2 NPs synthesized under superheating conditions (e.g., unsteady-state involving acoustic shock waves). To support this claim, we present comparative XRD and Raman spectral results for AR-TiO2 NPs synthesized under both normal heating and superheating conditions. The X-ray intensity ratio of (101)A/(110)R remains constant in the superheating samples; however, the Raman spectral results demonstrate significant changes occurring in the intensity ratio of the anatase (B1g-399 cm-1) and rutile (Ag-447 cm-1) TiO2 NPs, which substantiates the changes occurring in the proportion of the anatase and rutile phases of AR-TiO2. Based on these findings, it is authenticated that the Spurr-Mayers equation has significant limits in its ability to provide the precise ratio of the anatase and rutile proportion in superheating-based synthesis of AR-TiO2 NPs. Its inaccuracy is attributed to the dominance of dynamic microstructure recrystallization processes and surface crystallographic changes, which were not accounted for in the original formulation.

키워드