Title: Hydrothermal rutile to anatase reverse phase transformation

Authors: C. McNicoll; T. Kemmitt; V. Golovko

Addresses: Advanced Materials, Callaghan Innovation Ltd, 69 Gracefield road, P.O. Box 31-310, Lower Hutt 5040, New Zealand; MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand; Department of Chemistry, Canterbury University, Private Bag 4800, Christchurch 8140, New Zealand ' Advanced Materials, Callaghan Innovation Ltd, 69 Gracefield Road, P.O. Box 31-310, Lower Hutt 5040, New Zealand; MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand ' MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, P.O. Box 600, Wellington 6140, New Zealand; Department of Chemistry, Canterbury University, Private Bag 4800, Christchurch 8140, New Zealand

Abstract: TiO₂ sols peptised with oxalic acid were synthesised with oxalic acid ratios from 0.25 to 1.0 oxalic acid per titanium. The resulting transparent colloidal sols of TiO₂ contained a mixture of phases and sizes of TiO₂ particles depending on the oxalic acid content. The sols were hydrothermally treated at different temperatures ranging from 85°C to 275°C. Treatment below 100°C produced mostly anatase, while the decomposition of the oxalic acid between 120°C and 170°C allowed a phase change to rutile, with a rapid crystallite size increase from around 10 nm to 40 nm. AT-FTIR confirmed the complete decomposition of organic acids within the sols treated at 220°C. Very limited rutile crystallite growth was observed above this temperature. However, sols produced with the lower oxalic acid content remained as rutile while those produced using higher initial oxalic: Ti ratios (0.5 and 1.0 M equivalents) induced a reverse phase transformation back to anatase phase TiO₂. High resolution SEM showed that the anatase phase TiO₂ crystallites grew to around 30 nm at the highest temperature used (275°C) having indistinct morphology, while the rutile phase TiO₂ were elongated rods growing up to 100 nm.

Keywords: TiO2 sols; hydrothermal treatment; reverse phase change; anatase; rutile crystallite growth; oxalic acid; nanotechnology; reverse phase transformation; titanium dioxide; titania; transparent colloidal sols.

DOI: 10.1504/IJNT.2014.060570

International Journal of Nanotechnology, 2014 Vol.11 No.5/6/7/8, pp.493 - 501

Published online: 15 Dec 2014 *

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