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In situ energy dispersive X-ray diffraction (EDXRD) has been used to monitor the crystallization of TiO2 nanoparticles from hydrothermal reactions of nitric acid (HNO3) peptized sol–gels at 210, 230, 250 and 270 °C. The EDXRD peaks revealed the formation of pure rutile phase TiO2 particles from all the hydrothermal reactions studied. The reaction kinetic data have been determined by monitoring changes in the integrated peak areas of the highest intensity diffraction peak (110). A kinetic and mechanistic analysis of the hydrothermal synthesis of TiO2 nanoparticles has been proposed based on the Avrami–Erofe'ev kinetic model. The Avrami exponent values obtained were within the range of around 0.5–1 for all the reactions studied, indicating that the hydrothermal crystallization of TiO2 nanoparticles involves a diffusion-controlled process mechanism. The as-synthesized TiO2 nanoparticles have been further characterized by powder X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD data are in good agreement with the EDXRD results and confirm the formation of pure rutile phase TiO2 particles. The TEM results showed that the TiO2 particles produced are below 100 nm in size and exhibit bi-modal size and morphology distribution. [ABSTRACT FROM AUTHOR]

Hydrothermal synthesis of titanium dioxide (TiO2) nanoparticles has been studied in situusing synchrotron radiation energy dispersive X-ray diffraction (EDXRD). The nanoparticles were produced from an acid (HNO3) and an alkaline (tetrabutylammonium hydroxide; TBA) peptized gel by hydrothermal treatment at 210 °C and 270 °C. The in situEDXRD spectra clearly showed that pure TiO2rutile phase nanoparticles were crystallized from HNO3peptized gel, whereas pure anatase phase nanoparticles were produced from the TBA peptized gel. The EDXRD data shows that the rate of the particle formation increases with an increase in the process temperature for both processes. The powder X-ray diffraction (XRD) and selected area electron diffraction (SAED) data confirms the in situEDXRD results. The TEM images show that the anatase nanoparticles have relatively homogeneous particle size and morphology distribution whereas the rutile nanoparticles exhibit bimodal size and morphology distribution attributed to Ostwald ripening effect during the hydrothermal treatment. [ABSTRACT FROM AUTHOR]

A novel magnetic SO 4 /Fe-Al-TiO 2 solid acid catalyst was synthesized for biodiesel production via the (trans)esterification of waste cooking oil (WCO). The nanocomposite catalyst was prepared by the sequential functionalisation of commercial rutile/anatase mixed phase TiO 2 nanoparticles (NPs) with alumina as a buffer layer, and subsequently hematite to impart magnetic character, prior to sulfation with chlorosulfonic acid to introduce Brønsted acidity. XRD showed that the SO 4 /Fe-Al-TiO 2 catalyst comprised titania (rutile and anatase phases), aluminium sulphate, and hematite nanoparticles, while electron microscopy revealed the layer-by-layer assembly of these components within the SO 4 /Fe-Al-TiO 2 catalyst. FTIR confirmed the presence of surface sulphate groups SO 4 2− and S 2 O 7 2− /S 3 O 10 2− , creating a predominantly Brønsted acid catalyst with high acid loading. The catalyst achieved 96% fatty acid methyl ester (FAME) yield from WCO after 2.5 h of reaction at 90 °C, using 3 wt% of the magnetic catalyst, and a methanol:oil molar ratio of 10:1. SO 4 /Fe-Al-TiO 2 was also effective for feedstocks containing up to 20 wt% of free fatty acid (FFA), and showed excellent stability for WCO (trans)esterification over 10 recycles. [ABSTRACT FROM AUTHOR]