SYNTHESIS OF PHOTOCATALYTIC ACTIVE TITANIUM DIOXIDE NANOTUBES AND THE EFFECT OF CALCINATION

Photocatalytic active, well-ordered TiO2 nanotubes (TNTs) were synthesized using electrochemical anodization of a Ti substrate. A third generation electrolyte comprising mixture of ethylene glycol and ammonium fluoride in water was used to grow the TNTs at 60 V and 2 h deposition time. The effect of post-annealing on the physical properties and the photocatalytic activity of the TNT samples at two different temperatures, 300 degrees C and 400 degrees C was investigated. Further, the effect of pre-annealing of Ti substrate foil before growth of TNTs between 250 degrees C and 650 degrees C was investigated. Calcining at 300 degrees C and 400 degrees C for 1 h transformed the TNTs from amorphous to anatase phase. SEM images reveal dense and self-organization of TNTS for Ti foils annealed at 350 degrees C and 440 degrees C. The photodegradation rate of MB was twice as high for samples annealed at 400 degrees C compared to those annealed at 300 degrees C. The length of the TNT reached a maximum of 8.85 mu m on Ti foils pre-annealed to 440 degrees C for 1 h, after which a drastic reduction to 4.87 mu m and 4.24 mu m was observed on Ti foils pre-annealed to 525 degrees C and 625 degrees C respectively. The wall thickness systematically decreased as 32 nm, 31 nm, 29 nm, 21 nm, and 20 nm, respectively, when TNTs were grown on Ti foils heated at 250 degrees C, 350 degrees C, 440 degrees C, 525 degrees C, and 625 degrees C.