A novel synthesis method to produce silver-doped CeO2 nanotubes based on Ag nanowire templates

Silver nanowires were used as templates to synthesize silver-doped CeO2 (Ag–CeO2) nanotubes by the precipitation method. The precipitated solid was dried at 100 °C for 24 h and calcined at 500 °C for 5 h. A TEM, HRTEM, LV-SEM and XRD study was carried out to determine the micro and nanostructural characteristics of the samples. LV-SEM analysis allowed us to observe microtubular empty structures constituted by Ce, O and Ag as indicated by EDS. These tubular structures, with an external diameter from 120 to 280 nm and an internal diameter from 40 to 80 nm, were mainly composed of 11 nm ceria nanoparticles. This kind of structures was obtained when CeO2 nanoparticles covered the Ag nanowires during the synthesis. Due to the presence of ammonium hydroxide used during the synthesis, a fraction of the silver nanowire reacts and Ag atoms begin to migrate outside the ceria microtube. When the sintering process is applied, the Kirkendall effect can occur. So, out-diffusion of the remnant Ag through the interface is faster than the in-diffusion of the shell material (CeO2), which eventually results in a coaxial nanotube on completion of the non-equilibrium interdiffusion, leaving the central core completely empty, driving the formation of hollow tubular Ag–CeO2 structures as a result.