Crystal Structure and Photocatalytic Activity of Al-Doped TiO2 Nanofibers for Methylene Blue Dye Degradation.

Al-TiO2 nanofibers were prepared using a sol-gel derived electrospinning by varying the Al/Ti molar ratio from 0 to 0.73 to investigate the effect of Al doping on the crystal structure and the photocatalytic activity of Al-TiO2 for methylene blue (MB) degradation. XRD results indicated that as the Al/Ti molar ratio rose, crystal structure of Al-TiO2 was changed from anatase/rutile (undoped), anatase (0.07-0.18), to amorphous phase (0.38-0.73), which was confirmed by XPS and Raman analysis. The degradation kinetic constant increased from 7.3 x 10(-4) min(-1) to 4.5 x 10(-3) min(-1) with the increase of Al/Ti molar ratios from 0 to 0.38, but decreased to 3.4 x 10(-3) min(-1) when the Al/Ti molar ratio reached 0.73. The Al-TiO2 catalyst doped with 0.38 Al/Ti molar ratio demonstrated the best MB degradation. Experimental results indicated that the Al doping in Al-TiO2 was mainly attributed to the crystal structure of TiO2 and the photocatalytic degradation of MB.

Effect of collector speed and flow rate on morphology of Er doped TiO2 nanofibers.

The 0.5 mol% Er3+ doped TiO2 (Er(3+)-TiO2) nanofibers were synthesized by a sol-gel derived electrospinning and subsequent calcination for 3 h at 500 degrees 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 Er(3+)-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 mLh 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 Er(3+)-TiO2 nanofibers. The Er(3+)-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 4I15/2 to 4F7/2, 2H11/2 and 4F9/2, respectively. The Er(3+)-TiO2 nanofibers showed enhanced photoresponses under visible light.

Photocatalytic Activity of W-Doped TiO2 Nanofibers for Methylene Blue Dye Degradation.

Photocatalytic degradation of methylene blue (MB) in water was examined using W-doped TiO2 nanofibers prepared by a sol-gel derived electrospinning and subsequent calcination for 4 h at 550 degrees C. Different concentrations of W dopant in the range of 0 to 8 mol% were synthesized to evaluate the effect of W concentration on the photocatalytic activity of TiO2. XRD results indicated that the undoped TiO2 is composed of anatase and rutile phases. The rutile phase was transformed to anatase phase completely with the W doping. Among W-TiO2 catalysts, the 2 mol% W-TiO2 catalyst showed the highest MB degradation rate. The degradation kinetic constant increased from 1.04 x 10(-3) min(-1) to 3.54 x 10(-3) min(-1) with the increase of W doping from 0 to 2 mol%, but decreased down to 1.77 x 10(-3) min(-1) when the W content was 8 mol%. It can be concluded that the degradation of MB under UV radiation was more efficient with W-TiO2 catalysts than with pure TiO2-

Effect of Al Doping on Optical Band Gap Energy of Al-TiO2 Thin Films.

Al-TiO2 thin films were prepared using a sol-gel derived spin coating by varying the Al/Ti molar ratio from 0 to 0.73 to investigate the effect of Al doping on the optical band gap energy (Eg) of the films. GAXRD results indicated that Al-TiO2 is composed of anatase and FTO phases when the Al/Ti molar ratio was less than 0.18. Above 0.38, no other peaks except FTO were found and transparency of the films was severely deteriorated. Eg of Al-TiO2 decreased from 3.20 eV to 2.07 eV when the Al/Ti ratio was raised from 0 to 0.38. Eg of 2.59 eV was found for the anatase Al-TiO2 films having the Al/Ti ratio of 0.18. The absorption band of Al-TiO2 coatings shifted dramatically from the UV region to the visible region with increasing the amount of Al dopant. The Al doping was mainly attributed to the optical band gap energy of Al-TiO2.