Effect of Collector Speed and Flow Rate on Morphology of Er Doped TiO₂ Nanofibers

The 0.5 mol% Er³⁺ doped TiO₂ (Er³⁺-TiO₂) nanofibers were synthesized by a sol–gel derived electrospinning and subsequent calcination for 3 h at 500 °C in air. The calcined fibers were examined to evaluate the effect of collector speed and flow rate on morphology of the fibers. The dynamic viscosity and surface tension of precursor solution were 34 cP and 22.7 mN/m, respectively. The Er³⁺-TiO₂ nanofibers were electrospun horizontally on the drum rotated at 100∼500 rpm and flow rate of 0.2∼0.5 mL/h under a DC voltage of 10 kV. The grounded collector is a stainless mandrel placed 12 cm away from the tip of the needle. Beads were observed for the nanofibers prepared at flow rates from 0.2 mL/h to 0.5 mL/h when the collector speed was 100 rpm. The nanofibers increased in diameter slightly from 150 nm to 190 nm as the flow rate was raised from 0.2 mL/h to 0.5 mL/h. No beads were found at the collector speed of above 300 rpm when the flow rate was 0.2 mL/h. The optimized flow rate and collector speed of the nanofibers were determined to be in the range of 0.2∼0.3 mL/h and 300∼400 rpm, respectively. Uniform, smooth and continuous fibers with diameters of 150 to 170 nm were detected. Crystallite size determined by the Scherrer formula was about 6 nm. It can be concluded that the collector speed and the flow rate are influential on the morphology of the Er³⁺-TiO₂ nanofibers. The Er³⁺-TiO₂ nanofibers, prepared at 0.2 mL/h and 300 rpm, had typical absorption peaks located at 490, 523 and 654 nm, corresponding to the transitions from ⁴I_15/2 to ⁴F_7/2, ²H_11/2 and ⁴F_9/2, respectively. The Er³⁺-TiO₂ nanofibers showed enhanced photoresponses under visible light.