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We report a simple synthesis route for producing ultrafine porous TiO2 nanofibers (∼10 nm diameters) from electrospun rice-shaped TiO2 nanostructures. The rice-shaped TiO2 obtained by annealing the as-spun TiO2–PVAc composite nanofibers was treated with concentrated alkali (with KOH under hydrothermal conditions) followed by acid treatment and low temperature sintering. The alkali treatment produces the titanate (K2Ti3O7) which undergoes exchange of ions (protons) during the acid treatment resulting in H2Ti3O7. The heat treatment of the protonated titanate (H2Ti3O7) results in their conversion to ultrafine TiO2 (titanate-derived TiO2) nanofibers. The rice-shaped TiO2 and the titanate-derived TiO2 nanofibers were characterized by SEM, TEM, XRD, XPS, Raman and BET measurements and the latter has ∼2.5 times higher surface area than the former. The TiO2 nanofibers showed superior photocatalytic applications than the commercial P-25 TiO2 .

The present study reports the electrospinning of TiO2-graphene composite nanofibers to develop conductive nano-fiber mats using polyvinylpyrrolidone as a carrier solution. This carrier solution was sublimated at 450 °C to attain a complete conducting continuous nanofibrous network. It was observed during the annealing that as the graphene content was increased to 1 wt% the continuous fiber morphology was lost. Annealing did not have any impact on the fiber diameter (∼150 nm) or morphology as the graphene content was maintained between 0.0–0.7 wt%. The surface porosity of these samples was found be in the range of 45–48%. The presence of graphene in TiO2 nanofibers was confirmed using Raman spectroscopy. Photoluminescence spectroscopy showed excitonic intensity to be lower in graphene-TiO2 samples indicating that the recombination of photo-induced electrons and holes in TiO2 can be effectively inhibited in the composite nanofibers. Fluorescence spectroscopy was used to confirm this phenomenon where blue and quenched emissions were observed for the electrospun TiO2 nanofibers and composite fibers, respectively. Conductivity measurements showed the mean specific conductance values obtained for TiO2-graphene composites to be about two times higher values than that of the electrospun TiO2 fibers. Assembling these TiO2-graphene fiber composites as photoanodes in dye sensitized solar cells, an efficiency of 7.6% was attained.