Size–strain line-broadening analysis of anatase/brookite (TiO₂)-based nanocom­posites with carbon (C): XRPD and Raman spectroscopic analysis

A size–strain line-broadening analysis of the XRPD patterns and Raman spectra for two anatase/brookite (TiO₂)-based nanocom­posites with carbon (C) was carried out and the results com­pared with those of a similar sample free of carbon. The crystal structures and microstructures of anatase and brookite, as well as their relative abundance ratio, have been refined from XRPD data by the Rietveld method (the low amount of carbon is neglected). The XRPD size–strain analysis resulted in reliable structure and microstructure results for both anatase and brookite. The experimental Raman spectra of all the samples in the region 100–200 cm⁻¹ are dominated by a strong feature primarily com­posed of the most intense modes of anatase (E_g) and brookite (A_1g). The anatase crystallite sizes of 14–17 nm, estimated by XRPD, suggest the application of the phonon confinement model (PCM) for the analysis of the anatase E_g mode, whereas the relatively large brookite crystallite size (27–29 nm) does not imply the use of the PCM for the brookite A_1g mode. Superposition of the anatase E_g mode profile, calculated by the PCM, and the Lorentzian shape of the brookite A_1g mode provide an appropriate simulation of the change in the dominant Raman feature in the spectra of TiO₂-based nanocom­posites with carbon. Raman spectra measured in the high-frequency range (1000–2000 cm⁻¹) provide information on carbon in the investigated nanocom­posite materials. The results from field-emission scanning electron microscope (SEM), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy and nitro­gen physisorption measurements support the XRPD and Raman results.