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, V 5+ and V 3+ , 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 V 3+ : V 5+ 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 V 4+ oxidation state is derived from the vanadium 2p 3/2 peak, besides V 3+ and V 5+ . The ratio of peak area among V 3+ : V 4+ : V 5+ is 0.35 : 0.85 : 1. Apparently, the ratio of V 3+ 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 À1 ), VIT-3 (0.552 min À1 ), VIT-2 (0.891 min À1 ), and VIT-1(1.23 min À1 ) is in the ratio of 0.28 : 0.49 : 0.73 : 1. The experimental results show that the incorporation of vanadium oxide in TiO 2 enhances the photo-degradation efficiency for SA. Moreover, the photodegradation rate of the sample with the lowest V/Ti ratio (VIT-1) is B2 times faster than that of the one with the highest V/Ti ratio (VIT-3). The high ratio of V 3+ existing in VIT-1 is due to the dominated reductionthe kinetic priority to take place at the active center of VIT. Thus, the V 4+ is created and keeps growing quickly. Accordingly, the ratio of V 3+ existing in vanadium oxide is an important indicator to monitor the photocatalytic behavior of VIT.
The purposes of this study were: (1) to review the preparation and characterization of the intergrowth between goethite and hematite crystals; and (2) to propose a schematic diagram of the epitaxial relationships among three sets of (100) goethite twin crystals associated with the (001) orientation of the hexagonal prism of hematite. The Fe(ClO4)3 solution was prepared and aged at 70°C, which precipitated goethite initially and produced hematite later with prolonged aging. Goethite and hematite aged for 20 days were observed as star-shaped and hexagonal prisms, respectively. The results suggest that hematite could form later using goethite as a template surface. A selected area electron diffraction (SAED) pattern showed the epitaxial relationship among three sets of (100) goethite intergrowth crystals and hexagonal prisms with the (001) orientation of hematite. Goethite can be produced as lath-, X-, K-, or star-shaped crystals on the (100) orientation, depending on the Fe(ClO4)3 concentrations and the addition of HClO4 to Fe solution samples which were aged for a prolonged period at room temperature. The initial solubility products [(Fe3+)(OH–)3] of the sample solution, rather than the nature of the nuclei, are the key factors governing the formation of goethite or hematite. The addition of acids and high concentrations of iron solutions extend the secondary hydrolysis and induction period (IP) and favor the formation of hematite. The index of the SAED pattern of the star-shaped goethite intergrowth twin crystal has a (100) plane parallel to this basal plane and rotates at a 60° angle between two or three sets of lath-shaped goethite crystals, which share the (011) plane and form goethite twins with ‘interpenetrated’ crystal growth. Stereoscopic viewing using Oak Ridge Thermal Ellipsoid Plot (ORTEP) and CrystalMaker software was deployed to explore the relationship and configuration of oxygen atoms between pseudo-hexagonal (100) goethite associated with hexagonal (001) hematite lattice planes. A schematic diagram of the epitaxial relationship between star-shaped (100) goethite, which is acting as a template facilitating later precipitation of (001) hexagonal prisms of hematite on it, is presented.
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