Synthesis of Uniform Size Rutile TiO2 Microrods by Simple Molten-Salt Method and Its Photoluminescence Activity

Abstract

Uniform-size rutile TiO₂ microrods were synthesized by simple molten-salt method with sodium chloride as reacting medium and different kinds of sodium phosphate salts as growth control additives to control the one-dimensional (1-D) crystal growth of particles. The effect of rutile and anatase ratios as a precursor was monitored for rod growth formation. Apart from uniform rod growth study, optical properties of rutile microrods were observed by UV-visible and photoluminescence (PL) spectroscopy. TiO₂ materials with anatase and rutile phase show PL emission due to self-trapped exciton. It has been observed that synthesized rutile TiO₂ rods show various PL emission peaks in the range of 400 to 900 nm for 355 nm excitation wavelengths. All PL emission appeared due to the oxygen vacancy present inside rutile TiO₂ rods. The observed PL near the IR range (785 and 825 nm) was due to the formation of a self-trapped hole near to the surface of (110) which is the preferred orientation plane of synthesized rutile TiO₂ microrods.

Keywords: TiO2 microrod; anatase; molten-salt method; photoluminescence; rutile.

Figure 1

Typical XRD patterns of rutile TiO₂ microrod samples prepared by different precursor ratios of rutile and anatase TiO₂ (rutile, seed): TiO₂ (anatase) (a) 1:1, (b) 1:2, (c) 1:3, and (d) 1:4.

Figure 2

SEM images of rutile TiO₂ microrod samples prepared by different ratios of TiO₂ (rutile, seed): TiO₂ (anatase) as a precursor (a) 1:1, (b) 1:2, (c) 1:3, and (d) 1:4.

Figure 3

(a) TEM, (b) HRTEM and (c) SAED images of rutile TiO₂ microrod samples prepared with a 1:3 ratio of TiO₂ (rutile, seed): TiO₂ (anatase) as a precursor.

Figure 4

UV−visible absorbance spectra of rutile TiO₂ microrod samples prepared by different ratios of TiO₂ (rutile, seed): TiO₂ (anatase) as a precursor (black) 1:1, (red) 1:2, (blue) 1:3, and (green) 1:4.

Figure 5

Band gap energy calculation using Tauc plot method for rutile TiO₂ microrod samples prepared by different ratios of TiO₂ (rutile, seed): TiO₂ (anatase) as a precursor (black) 1:1, (red) 1:2, (blue) 1:3, and (green) 1:4.

Figure 6

Photoluminescence emission spectra of synthesized rutile TiO₂ prepared with different precursors ratio of rutile: anatase TiO₂ : (black) 1:1, (red) 1:2, (blue) 1:3, and (green) 1:4. (a) PL emission range from 400 to 675 nm and (b) PL emission range from 750 nm to 900 nm at excitation wavelength 355 nm.

Figure 7

FTIR spectra for rutile TiO₂ microrod samples prepared by different ratios of TiO₂ (rutile, seed): TiO₂ (anatase) as a precursor (black) 1:1, (red) 1:2, (blue) 1:3, and (green) 1:4.