Capability of novel ZnFe₂O₄ nanotube arrays for visible-light induced degradation of 4-chlorophenol.

Highly ordered ZnFe₂O₄ nanotube arrays were successfully prepared by anodic aluminum oxide templates from sol-gel solution. The results from environmental scanning electron microscopy and X-ray photoemission spectroscopy indicated that the as-prepared samples were vertically aligned spinel ZnFe₂O₄ nanotube arrays, and the nanotubes were uniform along the axial direction with an average diameter of approximately 200 nm. The absorption edge of ZnFe₂O₄ nanotube arrays shifted to a higher energy in the UV-Vis absorption spectrum compared with that of ZnFe₂O₄ nanoparticles film. The synthesized ZnFe₂O₄ nanotube arrays exhibited excellent photocatalytic capability for degradation of 4-chlorophenol under visible-light irradiation. The main intermediate degradation species of 4-chlorophenol identified by liquid chromatography-mass technique were benzoquinone, hydroquinone, hydroxybenzoquinone and 2-peroxy-o-dihydroxybenzene. The degradation pathways of 4-chlorophenol under visible-light irradiation was derived and discussed by interpreting the observations of the intermediate species in the photocatalytic reactions.