N O Gopal

Titanium dioxide (TiO2) nanomaterial, a semiconducting photocatalyst in which the light induced production of charge carriers is the basic process has became the benchmark semiconductor photocatalyst. In spite of its various favorable properties, the practical application of TiO2 is mired by two major drawbacks. One is the rapid recombination of photogenerated electron-hole pairs and the other is its high energy band gap (3.2 eV for anatase) that requires the UV light to activate it, which limits the sufficient utilization of the naturally available solar energy. These two drawbacks associated with TiO2 have fascinated the researchers to modify it by various methods to enhance the spatial separation of the photogenerated charge carriers and to extend its optical response from ultraviolet to visible region for the efficient utilization of naturally available solar energy. An ideal morphology and high crystallinity of TiO2 could bring its optical response to visible region and guarantee the high spatial separation of photogenerated electron-hole pairs. In this aspect, TiO2 nanomaterials obtained by sol-gel and hydrothermal methods were found to have well defined morphology, high crystallinity and high purity. In this report, we present the results of our studies on morphologically different TiO2 nanomaterials obtained by various methods. TiO2 nanoparticles codoped with phosphorus and boron (P,B- TiO2) prepared by sol–gel method exhibit visible light driven MB degradation, which is much better than that of photocatalytic activity of only P doped TiO2, and commercially available Degussa P25. TiO2 nano-wires (Ti-NWs) and nano-flakes (Ti-NFs) were obtained from phosphorus doped TiO2 nanoparticles (Ti-P) by hydrothermal method and by subsequent heat treatment respectively. FE-SEM micrograph of the as prepared sample depicts well formed, entangled and randomly oriented nano-wires morphology, which changes to nano-flakes morphology after heat treatment. Absorption edge of the Ti-NWs sample shows blueshift where as the Ti-NFs sample exhibit redshift compared to precursor sample as evidenced by UV-Visible absorption spectra. Methyleneblue degradation profiles depict very high activity of Ti-NFs sample compared to Ti-NWs and the precursor samples, which is due to the observed redshift in the absorption edge, change in morphology and high crystallinity of the sample which in turn increases the optical response and separation of photogenerated charge carriers as evidenced by the optical and EPR measurements respectively. Boron doped TiO2–CeO2 (B/TiO2–CeO2) nanocomposite has been synthesized using solution combustion technique, which shows the porous morphology with uniform distribution of nanoparticles in them.