Photo-catalytic behavior of vanadia incorporated titania nanoparticles

Abstract

Vanadium oxide incorporated titania nanoparticles (VIT), with an adjustable V/Ti ratio from 8.61% to 28.19%, are prepared to monitor the influence of the oxidation state of vanadium on the redox behavior of VIT. Two oxidation states of vanadium, V⁵⁺ and V³⁺, are deconvoluted from the vanadium 2p_3/2 peak of X-ray photoemission spectra (XPS) of VIT-1 (V/Ti = 8.61%) and VIT-2 (V/Ti = 18.84%), respectively. The ratio of V³⁺ : V⁵⁺ decreases 5.46 times from VIT-1 (4.97 : 1) to VIT-2 (0.91 : 1). As the V/Ti ratio increased to 28.19% (VIT-3), a new V⁴⁺ oxidation state is derived from the vanadium 2p_3/2 peak, besides V³⁺ and V⁵⁺. The ratio of peak area among V³⁺ : V⁴⁺ : V⁵⁺ is 0.35 : 0.85 : 1. Apparently, the ratio of V³⁺ in VIT samples decreases as the ratio of V/Ti increases. In the photo-degradation of salicylic acid (SA), the rate constant (k_cat) for P-25 (0.345 min⁻¹), VIT-3 (0.552 min⁻¹), VIT-2 (0.891 min⁻¹), and VIT-1 (1.23 min⁻¹) is in the ratio of 0.28 : 0.49 : 0.73 : 1. The experimental results show that the incorporation of vanadium oxide in TiO₂ enhances the photo-degradation efficiency for SA. Moreover, the photo-degradation rate of the sample with the lowest V/Ti ratio (VIT-1) is ∼2 times faster than that of the one with the highest V/Ti ratio (VIT-3). The high ratio of V³⁺ existing in VIT-1 is due to the dominated reduction reaction (V⁵⁺–O–V⁵⁺)O₄ → (:V³⁺–O–V⁵⁺)O₃ in the low V/Ti ratio environment. If the V/Ti ratio is increased to 28.19%, the polymerization reaction, (V⁵⁺–O–V⁵⁺)O₄ + (:V³⁺–O–V⁵⁺)O₃ → (V⁵⁺–O–V⁴⁺–O–V⁴⁺–O–V⁵⁺)O₆, has the kinetic priority to take place at the active center of VIT. Thus, the V⁴⁺ is created and keeps growing quickly. Accordingly, the ratio of V³⁺ existing in vanadium oxide is an important indicator to monitor the photocatalytic behavior of VIT.