Investigation On The Controllable Preparation Of Nb₂O₅Nanofibers And Their Photocatalytic Properties

Recently, semiconductor nanomaterials have exhibited great potential in the decomposition of organic pollutants, which is simple to realize in wide range without any secondary pollutants. However, semiconductor nanopowders are the mostly used photocatalyzers, which intend to agglomerate during the catalyst process and difficult to be recycled. The nanofibers synthesized by electrospinning process exhibited ultrahigh specific surface area with less agglomeration, which is easy to be recycled. Therefore, the electrospun nanofibers have been regarded as one of the best candidate of nanopowders in photocatalytic fields. Nb2O5is an important wide-band-gap semiconductor material with abundant phase structures and exhibited great potential in the photocatalytic applications. In this paper, the Nb2O5nanofibers have been prepared by electrospinning method. The influence of electrospinning process to the structure, morphology and microstructures have been studied. Based on that, the photocatalytic properties of the Nb2O5nanofibers in the decomposition of organic dye were investigated. The influence rule of the phase and structure to the photocatalytic efficiency was also studied. The main results were as follow:(1) The morphology-control of Nb2O5nanofibers. The nanofibers which prepared by electrospinning was annealed in elevated temperature. The electrical field between the tip and sample collector plate has shown great impact on the diameter of the ND2O5nanofibers. Due to the ejection of charged solution drops under the high electrical field, the increase of electrical field will lead to the enlargement of electrostatic force, and finally result in the decrease of the diameters. Moreover, the morphology of nanofibers was also influenced by the annealing temperature. As the temperature increased, the grain size increased and the surface of the nanofibers were smoother.(2) The structure-control of nanofibers. The structure control of the Nb2O5nanofibers can be realized by adjusting the annealing temperature and atmospheres. For samples annealed in air, the increasing of annealing temperature will lead to the phase transition from pseudo-hexagonal to orthorhombic Nb2O5nanofibers. For samples annealed in oxygen gas, the change of annealing temperature will lead to the formation of orthorhombic/monoclinic mixing-phase Nb2O5nanofibers. The relative content of monoclinic phase increases with the annealing temperature.(3) The optical absorption properties of nanofibers. The optical band gap of Nb2O5nanofibers with different structures were calculated by using the UV-Vis absorption spectrum. The results show that the band gap can be adjusted between2.51-2.77eV by changing the annealing temperature and atmospheres. The increase of temperature under the same atmosphere will result in the decrease of band gap.(4) The photocatalytic dye degradation performance of nanofibers. The photocatalytic degradation of methylene blue by the Nb2O5nanofibers was investigated. The results show that the hexagonal Nb2O5nanofibers with the highest band gap exhibited highest photocatalytic efficiency. Moreover, the monoclinic dominant mix phase samples exhibited lowest photocatalytic efficiency due to the decrease of band gap with the increasing of monoclinic content. The variation of photocatalytic efficiency with the phase of Nb2O5nanofibers may be attributed to the variation of optical absorption efficiency from the mercury lamp due to the change of band gap.