Crystallographic phase stability of nanocrystalline polymorphs TiO2 by tailoring hydrolysis pH

Abstract

Nanocrystal TiO2 of high crystallinity (88.72 %) polymorphs have been synthesized by a unique simple route. At a low temperature under a measurable condition with differentiated hydrolysis pH of the reaction. Here titanium isopropoxide (TTIP) is used as a precursor, isopropyl alcohol (IP) is a peptizing agent and hydrolysis medium with variable pH (2.0, 2.5, 3.5, 4.5, 5.5, 7.0, 8.5, 9.5) acts as a promoter or catalyst of the reaction. We observed in the whole powder pattern fitting (WPPF) method, TiO2 consisting of 65.0 % anatase, 68.0 % brookite and 45.0 % rutile phase in weight fraction by tailoring different hydrolysis conditions with predominant crystal plane (101), (111), (110) for the individual polymorph anatase, brookite and rutile. The crystal lattice parameters, crystal structure, volume of the crystal lattice, crystal strain, asymmetry, d-spacing and average crystallite size were also studied for the polymorph. The percent of crystallinity dominating around 54.0 to 89.0 % of the titanium and oxygen atoms are arranged regularly and periodically observed for change in the molar ratio (r) tailoring the polymorph phase stability. TiO2 polymorph followed the blue shift at 319.00 to 336.00 nm and had good stability for the decreasing particle size (11.03 nm). This phenomenon has been revealed by transmission electron microscopy (TEM) into the polymorphs. Selected area electron diffraction (SAED) and nanobeam diffraction (NBD) showed the nanocrystal anatase with the prominent miller indices (101) and interplanar distance of 0.35 nm that was revealed by HR-TEM at the lowest pH. Nano anatase is ultrafine which was confirmed by EDS.

Keywords

• Brookite
• Crystal growth
• Polymorphs
• Rutile
• Ultrafine anatase