1.5 mL of Ti(IV)-isopropoxide, and 3 mL of acetic acid were added
to 10 mL of ethanol containing 0.45 g of polyvinyl pyrrolidone (PVP,
Aldrich, Mw 1,300,000) were used as the starting chemicals. The
mixture was vigorously stirred at room temperature to get a
homogeneous polymer solution. The solution was loaded into a
plastic syringe equipped with a 22-gauge stainless steel needle. The
needle was connected to a high-voltage supply (Gamma High Voltage
ES30) and the solution was fed at a constant rate (0.3 mL/h) using a
syringe pump (Top Syringe Pump Top-5300). A piece of flat aluminum
foil was placed below the tip of the needle to collect the nanofibers by
applying an electric field of 1, 1.25 and 2 kV/cm. The as-spun
nanofibers were heat treated at 600 °C for 3 h in order to remove
PVP and crystallize TiO2.
The prepared sol used in the electrospinning was dried at 100 °C
for 1 h and the obtained powder subjected to thermogravimetric
differential thermal analysis (DTA/TG) (Shimadzu DTG-60H). The
viscosity of the prepared sol was measured at 30 °C by using a
Brookfield DV-E model viscometer. The X-ray diffraction (XRD)
measurements were performed for crystal phase identification
(Rigaku D/Max-2200/PC) with CuKα radiation. The morphology and
average fiber diameter of nanofibers was characterized by scanning
electron microscope (JSM-6060 JEOL).