New Insights into Crystal Defects, Oxygen Vacancies, and Phase Transition of Ir-TiO₂

Abstract

The impact of iridium (Ir) doping on the oxygen vacancies, relative stability, crystallite size, surface area, and anatase-to-rutile transition of TiO 2 was comprehensively investigated in this study. Ir-doped TiO 2 (Ir-TiO 2 ) was synthesized through a sol−gel technique, and the samples were annealed in the temperature range of 400−700 °C. Density functional theory calculations showed that the energy cost of an oxygen vacancy formation for Ir-TiO 2 was lower, as compared to that of the pristine TiO 2 , with the formation of Ir 3+ states in the band gap. Ir could provide more rutile nucleation sites and accelerate the rutile formation through the crystal strain relaxation. The entropy of mixing was reduced by the incorporation of Ir, which could induce the rutile formation with an increase in Gibbs free energy at temperatures below the normal phase transition temperature for pure TiO 2 . The rutile formation of Ir-TiO 2 could take place at a low annealing temperature (400 °C) compared to pristine TiO 2 (600 °C), indicating that the activation energy for phase transition could be decreased by incorporating Ir. XPS revealed the spin−orbit coupling of Ir 4f peaks, Ir 4f 7/2 (61.96 eV) and Ir 4f 5/2 (64.77 eV), due to the presence of Ir 3+ . Raman studies indicated the formation of charge-compensating oxygen vacancies and the presence of d states by Ir doping. It is concluded that the defects originated because the incorporation of Ir could facilitate rutile nucleation sites and thereby accelerate the phase transition through strain relaxation.

Macroporous TiO2 and Graphite-like Carbon Hybrid Hierarchical Interfaces for Improved Photocatalytic Activity Derived from Particle-Stabilized Emulsions

“…The phase transition from anatase to rutile occurs at about 600 °C. 71,72 However, we found that the phase composition of the catalyst was sustained even when the calcination temperature increased up to 800 °C. It can be speculated that the graphite-like carbon layers suppress the phase transition temperature from anatase to rutile of more than 200 °C.…”

Unravelling the Impact of Ta Doping on the Electronic and Structural Properties of Titania: A Combined Theoretical and Experimental Approach

“…The anatase grains act as nucleation sites to facilitate the phase transformation to rutile . However, there are no significant changes in the BJH adsorption pore size, which implicates the uniform dispersion of dopants on the TiO 2 surface …”

“…41 However, there are no significant changes in the BJH adsorption pore size, which implicates the uniform dispersion of dopants on the TiO 2 surface. 42 3.5. XPS.…”

Coumarin–Ir(III) Complex Anchored on Polymer Film as Photosensitizer for Efficient, Long-Term Photocatalytic Hydrogen Evolution

“…As shown in Figure 2a, the high-resolution Ir 4f XPS spectrum of complex 1 is centered at 61.74 eV (Ir 4f 7/2 ) and 64.76 eV (Ir 4f 5/2 ), which can be attributed to metallic Ir species. 27,28 Similarly, 1@NWF-g-MAH exhibits two peaks at 61.97 eV (Ir 4f 7/2 ) and 64.79 eV (Ir 4f 5/2 ), manifesting the existence of Ir(III) complexes on the substrate. Furthermore, the high-resolution N 1s XPS spectrum of complex 1 can be divided into three peaks (Figure 2b), corresponding to C− N�C (398.8 eV), tertiary nitrogen (N−(C) 3 ) (399.7 eV), and amino functional groups (−NH 2 ) (399.2 eV).…”