Effect of variable oxidation states of Mn+n ion impregnated TiO2 nanocomposites for superior adsorption and photoactivity under visible light

This paper deals with the importance of oxidation state and ionic size of Mn(II) and Mn(VII) co-catalyst impregnated TiO2 for the observed electrokinetic, adsorption and photocatalytic properties of Mn+n-TiO2 nanocomposites. Due to difference in net electronic charge and ionic size of Mn(II) and Mn(VII) ions, the zeta potential, streaming potential and surface charge demand of Mn(II)-TiO2 and Mn(VII)-TiO2 nanocomposites are greatly varied. The absorption edge of Mn+n-TiO2 nanocatalysts revealed the red shift (515-550 nm) with increased oxidation state (from II to VII) of Mn+n due to (6)A(1)(g) -> T-4(1g) g transition. The photoluminescence (404-530 nm) of Mn(II)-TiO2 is highly quenched relative to Mn(VID-TiO2 during 340 nm excitation. Further, the HRTEM analysis confirmed the presence of Mn(VII) (similar to 20-45 nm) and Mn(II) (similar to 40-60 nm) nanodeposits over TiO2 surface. Binding energies at 639.1 and 640.3 eV showed the presence of Mn in (0) and (II) oxidation state for Mn(II)-TiO2 and 646 eV alongwith a satellite peak for Mn(VII)-TiO2 co-catalyst. As a result, the adsorption and photocatalytic degradation of cationic (Fuchsin blue and methylene blue) and anionic (Salicylic acid and Salicylaldehyde) pollutants by Mn-+(n)-TiO2 nanocomposites are notably improved relative to bare TiO2 depending on their respective oxidation state and surface morphological features. (C) 2019 Elsevier B.V. All rights reserved.