Mo-Doped TiO<SUB>2</SUB> with Enhanced Visible Light Photocatalytic Activity: A Combined Experimental and Theoretical Study

Abstract

In this paper, the effects of Mo doping on the geometrical, electronic, optical, and photocatalytic properties of TiO2 have been investigated theoretically and experimentally. The density functional theory based calculations show that Mo doping creates impurity states (Mo 4d) below the conduction band of TiO2 and the Fermi level is pinned inside the conduction band verifying n-type doping nature of the Mo in TiO2, which enhances its visible light absorption. Anatase TiO2 particles with Mo contents of 0.08, 0.1, 0.5, 1.0, 1.5 and, 2.0 at.% were synthesized by hydrothermal method without any post heat treatment for crystallization. Experiment results show that Mo ions have been successfully doped into the TiO2 lattice. The morphology of TiO2 particles is nearly spherical and the grain size is uniformly distributed as about 10 nm. Synthesized sample with 0.1 at.% Mo doping concentration shows the best visible light photocatalytic activity due to the reduced band gap and improved electron-hole pairs separation. However, the photocatalytic activity of the sample with 2.0 at.% Mo is relatively low although its visible light absorption is the best among the samples. The enhanced recombination of electron-hole pairs caused by the excessive Mo doping concentration may account for it.

Mo doped TiO2: impact on oxygen vacancies, anatase phase stability and photocatalytic activity

“…For the stoichiometric system (figure 2(a)), Mo s-states emerge at the CBM of the TiO 2 host and the Mo d-states overlap with the titania CB. The emergence of Mo-derived defect states below the CBM was reported by the GGA studies of Mo-doped TiO 2 [36,63]. Mo dstates below the CBM were identified in these studies but there was no discussion of the Mo s-states.…”

“…The ionic radius of Mo 6+ is almost identical to that of Ti 4+ , being 0.062 nm and 0.068 nm, respectively, and, therefore, Mo 6+ ions could easily replace Ti 4+ ions in the anatase crystal lattice [34,35]. This kind of doping would minimise the lattice distortion [35,36]. Mo doping could also generate energy states within the band gap of TiO 2 to enhance the light absorption and minimise the electron-hole recombination [35][36][37].…”

“…This kind of doping would minimise the lattice distortion [35,36]. Mo doping could also generate energy states within the band gap of TiO 2 to enhance the light absorption and minimise the electron-hole recombination [35][36][37]. Khan and Berk suggested that an impurity level of Mo 6+ /Mo 5+ (Mo 6+ 4d 0 1e -→Mo 5+ 4d 1 ) could be generated below the conduction band (CB) of TiO 2 .…”

Photocatalytic reduction of NO2 and CO2 using molybdenum-doped titania nanotubes

“…Dieterle et al [38] indicated that the absorption bands from 0.55 to 3. [39,40]. This represented that the synthesis methods of precipitation and impregnation were both successful for doping Mo into the structure or depositing MoO x on the surface of TNTs.…”

Preparation of N-Doped TiO2-ZrO2Composite Films under Electric Field and Heat Treatment and Assessment of Their Removal of Methylene Blue from Solution

“…But the photocatalytic reactivity of TiO 2 under visible light condition (wavelength greater than 387.5 nm) still remains low after the addition of ZrO 2 to TiO 2 . In order to utilize the visible part of the solar spectrum, or under general illumination conditions, two approaches could be undertaken with one being doping transition metals into TiO 2 [4,5], and the other being forming defects of TiO catalyst compounds [6,7]. Although doping transition metals can improve the reactivity of TiO 2 under visible light, the TiO 2 reactivity under ultraviolet light would decrease correspondingly.…”