In the absence of a dopant or precursor modification, anatase to rutile transformation in synthetic TiO 2 usually occurs at a temperature of 600 ºC to 700 ºC. Conventionally, metal oxide dopants (e.g. Al 2 O 3 and SiO 2 ) are used to tune the anatase to rutile transformation. A simple methodology is reported here to extend the anatase rutile transformation by employing various concentrations of urea.XRD and Raman spectroscopy were used to characterize various phases formed during thermal treatment. A significantly higher anatase phase (97%) has been obtained at 800 ºC using a 1:1 (Ti (OPr) 4 : urea) composition and 11% anatase composition is retained even after calcining the powder at 900 ºC. On comparison a sample which has been prepared without urea showed that rutile phases started to form at a temperature as low as 600 °C. The effect of smaller amounts of urea such as 1:0.25 and 1:0.5 (Ti (OPr) 4 :urea) has also been studied and compared. The investigation concluded that the stoichiometric modification by urea 1:1 (Ti (OPr) 4 :urea) composition is most effective in extending the anatase to rutile phase transformation by 200 ºC compared to the unmodified samples. In addition, BET analysis carried out on samples calcined at 500 °C showed that the addition of urea up to 1:1 (Ti (OPr) 4 :urea) increased the total pore volume (from 0.108 cm 3 /g to 0.224 cm 3 /g) and average pore diameter (11 nm to 30 nm) compared to the standard sample. Samples prepared using 1:1 (Ti (OPr) 4 :urea) composition calcined at 900 ºC show significantly higher photocatalytic activity compared to the standard sample prepared under similar conditions. Kinetic analysis shows a marked increase in the photocatalytic degradation of rhodamine 6G on going from the standard sample (0.016 min , decoloration in 50 mins).

Kevlar–nanotube composite fibers of high strength and toughness are demonstrated. Commercially available Kevlar fibers are soaked in a suspension of nanotubes in the solvent N‐methylpyrrolidone, resulting in swelling of the fibers, and allowing the nanotubes to diffuse into the interior of the fiber (see image). The resulting composites are stronger and tougher than the original Kevlar fibers.

No abstract

No abstract