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The first one pot gel combustion synthetic strategy towards ‘black TiO2−x’ using Ti butoxide, diethylene glycol and water as the only precursors.

Sodium-ion hybrid capacitors are attracting great attention and are emerging as promising energy storage devices, with their remarkable footsteps in energy and power densities. However, the development of efficient electrode materials that result in a minimum trade-off between their energy and power densities, and that allow long-term cycling stability, still remains a challenge for realizing their full potential as an alternate energy storage system for commercial applications. Herein, for the first time, we study the sodium-ion intercalation pseudocapacitance behavior of brown TiO2 nanotubes for their application as an efficient anode material for Na-ion hybrid capacitors. We synthesized semicrystalline and crystalline anatase brown TiO2 nanotubes, aggregated in a flowerlike morphology, through a hydrothermal route, and performed detailed electrochemical studies. The kinetic studies reveal that semicrystalline brown TiO2 exhibits a Na-ion intercalation pseudocapacitive behavior with 57% of capacitive storage at 1.0 mV s–1, whereas crystalline brown TiO2 is more faradaic in nature. Further, hybrid Na-ion capacitors are fabricated with brown TiO2 materials as an anode and activated carbon as a cathode, and the fabricated device showed an excellent electrochemical performance with a high energy density of ∼68 Wh kg–1 and a high power density of ∼12.5 kW kg–1 and with a good cycling stability up to 10 000 cycles with ∼80% capacitive retention. The obtained results represent a promising approach toward developing efficient electrodes for hybrid Na-ion capacitors.

Green and rapid microwave syntheses of 'yellow oxygen rich' (YAT-150) and 'black oxygen vacancy rich' (BAT-150) anatase TiO2 nanoparticles are reported for the first time. YAT-150 was synthesized using only titanium(iv) butoxide and water as precursors. The in situ precursor modification by Mn(ii) acetate switched anatase TiO2 from YAT-150 to BAT-150. The entry of Mn(2+) into the crystal lattice of anatase TiO2 paved the way for peak texturing in the existing peak orientations along with the origin of three new anatase TiO2 peaks in the (103), (213) and (105) directions. The as synthesized ultra-small (∼5 nm) yellow and black anatase TiO2 nanoparticles were found to be two fold and four fold more photoactive than the commercially available photocatalyst Degussa-P25 under sunlight illumination.

Dopant free, solar active ZnO photocatalysts with oxygen vacancy richness were achieved by a solution processing strategy followed by calcination at various temperatures 300, 500, 700, 800, and 900 °C. All the ZnO nanocrystals possessed defective structures with copious surface oxygen vacancies directed toward notable visible light absorption around λ = 480 nm (band gap = 3.05−3.09 eV). The photocatalytic efficiencies of all ZnO samples were systematically examined under sunlight and UV illumination using methylene blue (MB) as a model system. ZnO calcined at 500 and 700 °C demonstrated microrod morphology with band gap energies of 3.08 and 3.09 eV respectively have shown the highest solar photocatalytic activity revealed the synergistic effect between oxygen vacancy and the rod morphology. ZnO calcined at 500 °C, having maximum surface oxygen vacancy sites degraded MB within 10 min whereas the commercial photocatalyst Degussa-P25 has taken 20 min under solar illumination.

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This review focuses on the recent developments of high temperature stable anatase TiO2 photocatalyst. Eventhough TiO2 exists in different forms anatase, rutile and brookite, anatase phase stabilization is often the key to obtain the highest photocatalytic performance for TiO2, particularly for the use as an antibacterial and self-cleaning coatings in high temperature processed ceramics. Different methods available for the anatase stabilization in literature are critically reviewed and emphasis is placed on relatively recent developments. Currently available methods of anatase stabilizations are classified in to four categories viz (i) doping with metal ions (ii) doping with non-metal ions (iii) co-doping with metal and non-metal ions and (iv) dopant free stabilization by oxygen richness. Further to this, the application of these high temperature stabilized anatase TiO2 photocatalyst on various ceramics substrates such as tile, glass and sanitary wares as self-cleaning and antibacterial coatings are also been briefly discussed.

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