PAPERmaking! FROM THE PUBLISHERS OF PAPER TECHNOLOGY Volume 2, Number 1, 2016
Fig. 5 N 2 adsorption – desorption isotherms and pore size distribution of the anatase and rutile prepared pigment UV – Vis and photoluminescence spectroscopy Figure 6 shows the UV – visible absorption spectra of the TiO 2 nanopigments of the three prepared samples. The spectra reveal that the rutile sample shows the most narrow intensive peak at wavelength of 320nm which is consistent with its known high refractive index and high brightness. In the case of anatase and brookite samples, the peak obtained at wavelength equal to 280nm is broader than the other peak due to the appearance of the two phases as confirmed by XRD analysis. The anatase sample obtained less intensive peak than rutile peak at approximate wavelength of 300nm. The band gap energies (E g ) of TiO 2 nanopigments were calculated using the equation: E g = hC / λ int (2) where h is Planck’s constant (4.135 x 10 -6 eV nm); C, the velocity of light (3 x 10 8 ms -1 ), and λ is the wavelength (in nm) corresponding to the intersection of extension of linear parts of the spectrum of y-axis and x-axis. From Fig. 6, the energy gaps for anatase, mixture of anatase and brookite and rutile are 3.36, 3.30 and 3.37eV, respectively. Bulk titanium oxide has a band gap in the range of ~3eV. For low dimensional nanostructured TiO 2 materials, electrons and holes are expecting to move shorter distances approximated by the indirect band gap between highest occupied and lowest unoccupied states. However, due to the large surface-to-volume ratio, lower dimensional TiO 2 nanostructures tend to have larger band gaps.
Fig. 6 UV-Vis absorption spectra of TiO2 nanopigments a Anatase, b Mixture of brookite and anatase and c rutile samples
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Article 3 – Titanium Coating Pigments
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