Replacement/Etching Route to ZnSe Nanotube Arrays and Their Enhanced Photocatalytic Activities

Well-aligned ZnSe nanotube arrays with diameters of 300-400 nm and wall thicknesses of 60-70 nm have been controllably prepared based on a replacement/etching method, with ZnO nanorod arrays on zinc substrate as sacrificial templates. An obvious difference of the solubility product (K-sp) between the ZnSe wall and ZnO core materials is crucial for the direct replacement of one type of anions by the other. Ammonia as the chemical etching agent is also important for dissolving ZnO nanorod core. The photocatalytic activities of the as-prepared ZnSe nanotube arrays have been studied for the degradation of methyl orange aqueous solution and compared with those of ZnO nanorod arrays and the intermediates including ZnO/ZnSe core/sheath nanorod arrays and partially dissolved ZnO core/ZnSe sheath nanorod arrays, respectively. The results indicate that ZnSe nanotube arrays exhibit superior photocatalytic performance to the other three nanostructured arrays, which can be mainly attributed to their full hollow interior nanotubes providing more accessibility to the dye molecules and more reactive adsorption/desorption sites for photocatalytic reactions. Furthermore, the ZnSe nanotube arrays have successfully overcome the shortcomings related to photocatalyst recovery and stability, which the powder-form photocatalysts usually face. ZnSe nanotube arrays as photocatalysts are expected to be promising in sewage water treatment.