Protonated niobate nanosheets, H1.8Bi0.2CaNaNb3O10 (BCNN), were synthesized using a new organic-free simultaneous ion exchange and exfoliation process from the Aurivillius phase Bi2CaNaNb3O12. Nanosheet/TiO2 composites were prepared by thermal treatment of physical mixtures of commercially available anatase TiO2 and the nanosheet suspension. Methylene blue (MB) dye degradation studies for the composite show a clear correlation between the MB surface adsorption and the degradation rate. The composite exhibits strongly enhanced photocatalytic activity as the calcination temperature increases, suggesting the possibility of charge transfer at the BCNN–TiO2 interface and the existence of Nb5+ and O2−acid–base pairs. Both phenomena are attributed to the processing approach, which includes topochemical dehydration of the BCNN nanosheets during heat treatment.

Titanium dioxide (TiO2) and mixed oxides, i.e., mixtures of magnesium oxide and titanium dioxide (MgO–TiO2) with different ratios were synthesized by two methods—flame synthesis and aerogel, for comparison of their properties. The samples were characterized by powder x-ray diffraction (pXRD), energy-dispersive x-ray spectroscopy, Fourier transform infrared spectroscopy, Brunauer-Emmet-Teller method of surface area measurements, ultraviolet-visible spectroscopy (UV-vis), and transition electron microscopic analysis. The pXRD patterns of different mixed oxides with different mole ratios revealed that there were formations of different compositions and phases. These mixed oxides were also used as photocatalysts in the UV-vis light to oxidize acetaldehyde, and carbon dioxide (CO2) was measured as a product. The mixed oxides with low content of MgO (∼1–2 mol%) were found to be more UV-active photocatalysts for the degradation of acetaldehyde than the degradation by Degussa P25 and as-synthesized TiO2, the highest by the MgO–TiO2 mixed oxides of 1:50 ratio when comparisons were carried out among the samples prepared by the same method. Furthermore, the mixed oxides prepared by the aerogel method were found to be superior photocatalysts compared with the mixed oxides of equal ratio prepared by flame synthesis. This effect of insulator, MgO, on the photocatalytic activity of semiconductor, TiO2, was found to be interesting and can be applied for other applications as environmentally friendly materials.

Nanosized graphitic carbon provides high selectivity and stability of catalysts. However, the carbon is very light when used as a support, even when loaded with metals. To counteract this problem, carbon/TiO2 core–shell structures were synthesized via chemical vapor deposition (CVD) using a single source precursor to increase its density, while maintaining a high surface area and stability of the materials. The diameter of the carbon/TiO2 spheres could be controlled from 2 μm to 200 nm by varying the flow rate of nitrogen. TEM analysis revealed that a fraction of the spheres exhibited a core–shell structure, with a faint carbon shell surrounding the TiO2 sphere. The density of the carbon/TiO2structures was 0.70 g/mL, which is four times higher than that of pure carbon nanotubes and spheres synthesized by CVD.

TiO2@C core–shell nanostructures with various crystal structures of TiO2-B, anatase, and rutile were successfully synthesized by a simple hydrothermal process and postheat treatments. As-synthesized precursor hydrogen titanate@carbonaceous nanoribbons transformed into TiO2-B@C nanoribbons at 400 °C and further transformed into anatase and rutile TiO2@C nanoribbons at 700 and 800 °C, respectively. The morphology of nanoribbons can be retained up to 800 °C. The transformation temperature (800 °C) from anatase to rutile phase is lower than that of TiO2 nanofibers without carbon layers and anatase TiO2@C nanoparticles. These results show that the carbon shell plays important roles in promoting the phase transition from anatase to rutile phase and protecting the nanoribbon-like morphology. The formation mechanism of the TiO2@C core–shell nanostructures with various crystal structures was discussed.

Carbothermal reduction of semiconducting TiO2 into highly conductive titanium oxycarbide (TiOxCy) was investigated. The thermally produced uniform carbon layer on TiO2 (Degussa P25) protects the TiO2 nanoparticles from sintering and, at the same time, supplies the carbon source for doping TiO2 with carbon. At low temperatures (e.g., 700 °C), carbon only substitutes part of the oxide and distorts the TiO2 lattice to form TiO2−xCx with only substitutional carbon. When the carbon-doped TiO2 is annealed at a higher temperature (1100 °C), x-ray diffraction and x-ray photoelectron spectroscopy results showed that TiOxCy, a solid solution of TiO and TiC, was formed, which displays different diffraction peaks and binding energies. It was shown that TiOxCy has much better oxygen revolution reaction activity than TiO2 or TiO2−xCx. Further studies showed that the TiOxCyobtained can be used as a support for metal electrocatalyst, leading to a bifunctional catalyst effective for both oxygen reduction and evolution reactions.

The development of substoichiometric TiO2-based nanostructured materials with high aspect ratios for future proton exchange membrane fuel cells is investigated. Nanostructures were manufactured using atomic layer deposition of TiO2 over both anodic aluminum oxide templates and silicon nanowires. It was observed in this work that nanostructures with aspect ratios of 100:1 can be fabricated using both methods. The conductivity of TiO2 films was enhanced following a postdeposition reducing anneal (at 450 °C in H2). Liquid phase-deposited Pt and plasma-enhanced atomic layer deposition of Pt were both found to be appropriate suited for metallization of TiO2 structures.

This work presents the preparation and characterization of N-doped TiO2 nanocrystals obtained by a solid-state reaction in vacuum with urea as the nitrogen source. The particle sizes of the products are smaller than 20 nm from the x-ray powder diffraction patterns and the transmission electron microscopy images. Different from the reported samples obtained in air or under dry N2 or NH3 gas flow, the doped nitrogen exists mainly as absorbed NOx groups but as smaller incorporated species in the nanocrystals, which is supported by the results from x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and ultraviolet–visible diffuse reflectance spectroscopy. Dependent on the nitrogen amount, the surface photovoltage (SPV) response reaches the maximum at the mediate molar ratio of 5:4 (urea to TiO2), which can be explained that proper nitrogen concentration can enhance the separation of the photogenerated carriers to improve the SPV intensity, but excess nitrogen can spread the impurity energy levels to narrow energy gaps, which reinforces the combination of the photogenerated electrons and holes and then decreases the SPV signal. The corresponding detailed discussion is also reported.

Nanosized anatase TiO2 nanosheets with highly exposed reactive {001} facets (∼80%) were prepared via hydrothermal reaction with the addition of hydrofluoric acid and characterized by various techniques including transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller. High-quality TiO2 nanosheets films with different thicknesses (∼5–20 μm) were fabricated by doctor blading, and the effect of film thickness on the performance of dye-sensitized solar cells (DSSCs) was investigated by I-V characterization and dark current potential scan. The results show that each parameter of DSSCs performance depends strongly on the thickness of the TiO2 nanosheets films. An optimized DSSCs performance of 8.39% was obtained by the TiO2nanosheets film with a thickness of ∼15 μm.

A novel hybrid titania paste comprising aqueous-synthesized anatase (A) nanocrystalites and submicrometer-sized “sea urchin”-like rutile (R) particles that enables the construction of thin (5–6 μm) single-layer photoanodes with competitive power conversion efficiency is described. Owing to the high surface area of the dye (N719)-coated anatase film, the scattering properties of the unique rutile particulates, and the incorporation of P25 particles, the constructed bifunctional electrode films exhibit excellent electron transport properties (long electron lifetime) and no electrolyte diffusion resistance. Dye-sensitized solar cell devices built with the thin (5–6 μm) hybrid electrodes showed greatly improved power conversion efficiency (PCE), namely 7.04%, when compared to devices based on single anatase (4.20%), double-layer (A + R), or double thickness commercial benchmark paste (6.74%). This is an impressive result as less than 1/2 material was used in a single printed layer. Thinner films as the ones built here may prove particularly advantageous in using new noniodide electrolytes associated with slow diffusion rates.

A binder-free titania paste was prepared by chemical modification of an acidic TiO2 sol with ammonia. By varying the ammonia concentration, the viscosity of the acidic TiO2 suspension increased, thereby allowing uniform films to be cast. The photoelectrochemical performance of TiO2 electrodes, cast as single layers, was dependent on the thermal treatment cycle. Fourier transform infrared spectroscopy was used to characterize the extent of residual organics and found that acetates from the TiO2precursor preparation were retained within the electrode structure after thermal treatment at 150 °C. Electrodes of nominal thickness 4 μm produced an energy conversion efficiency as high as 5.4% using this simple thermal treatment.

Hydrothermally grown TiO2 nanorod (NR) photoelectrodes were prepared by sensitizing CdS quantum dots to improve visible light activity of the TiO2. The CdS-sensitized photoelectrodes were heat-treated to obtain enhanced performance of the photoelectrode under visible light. Furthermore, performance of the TiO2 NR-based photoanodes was compared with those made of TiO2 nanotubes (NTs). Photocurrent measurement and overall cell efficiency of the NR-based solar cells showed higher efficiency compared to NT-based solar cell.

Ink-jet printing technique is used to prepare porous (ZnO)1−x(TiO2)x composite films on indium tin oxide-coated glass substrates. Dye-sensitized solar cells were fabricated using well-characterized printed films of thickness ∼20 and 30 μm, respectively. It is found that the photovoltaic performance of the cells is dependent on the film thickness and the concentrations of ZnO. The obtained results are compared with those of pure ZnO- and TiO2-based cells prepared by the same route to optimize the device efficiency. This study suggests that ink-jet printers promise an inexpensive and simple technology for manufacturing solar cell composite films.

ZnO/TiO2 heterojunction composite fibers were prepared via a physical route, i.e., first electrospinning titanium dioxide (TiO2) fibers, then pulse plating zinc (Zn) on the fibers, and at last thermal treating the fibers. The morphologies, phase structures, and photocatalytic property of the composite fibers were characterized by using field-emission gun scanning electron microscope, x-ray diffractometer, high-resolution transmission electron microscope, and ultraviolet–visible spectrophotometer. It was found that a full or partial lattice coherent heterojunction was formed between the TiO2 fibers and zinc oxide (ZnO) particles, due to thermal treatment at 400 °C, which simultaneously resulted in the phase transformations including Zn to ZnO and amorphous TiO2 to anatase TiO2. The experimental results demonstrated that the photocatalytic activity of the composite fibers was improved and exhibited a value more than two times higher than that of TiO2 fibers.

Simulations of TiO2(both rutile and anatase) nanoparticles with water, methanol, and formic acid were conducted using a ReaxFF reactive force field to investigate the characteristic behavior of reactivity to these organic solvents. The force field was validated by comparing water dissociative adsorption percentage and bond length between Na and O with density functional theory (DFT) and experimental results. In the simulations, 1-nm rutile and anatase nanoparticles with water, methanol, and formic acid were used, respectively. The numbers of attached hydroxyl with time and nanoparticles distortion levels are presented. We found that the rutile nanoparticle is more reactive than the anatase nanoparticle and that formic acid distorts nanoparticles more than water and methanol.

The effect of Al doping on the reflective properties of TiO2 nanoparticles, synthesized by sol–gel method, has been investigated. It has been observed that with Al doping, the phase transition temperature for anatase to rutile phase increases; however, no change in morphology has been observed. No additional absorption edge was found in the absorption spectra, but a weak luminescent peak was noticed in the photoluminescence spectra. TiO2nanoparticles with 0.1% Al doping show higher photostability with practically no change in reflectance. A coating material has been prepared by dispersing these synthesized nanoparticles in water solution of organic binder. Coating material parameters such as pigment to binder weight ratio, solvent ratio, pH of solution have been taken into care to make the coating material flowable with good ability to adhere. Their coating was applied on a plastic substrate with different coating thicknesses to design light reflectors. These reflectors have been found to have diffuse reflectance of 98.17–98.29% for the 0.25-mm-thick coating.

Observation of room temperature ferromagnetism (RTFM) is reported in polycrystalline thin films of Ti1−xMnxO2 (x = 0.10 and 0.15) synthesized by spray pyrolysis technique on fused quartz substrates. Our experimental results clearly suggest partial incorporation of manganese (Mn) in titanium dioxide (TiO2) lattice up to certain extent and rest of the Mn ions are consumed to form secondary Mn-related phase such as manganese oxide (Mn3O4). The observed weak ferromagnetic ordering at room temperature in the films is established to be due to incorporation of Mn in TiO2matrix rather than the presence of other secondary phases since none of the Mn or Ti/Mn oxide phase is ferromagnetic at room temperature. Bound magnetic polaron model is invoked to explain the observed ferromagnetism in these highly resistive films.

We report on the photovoltaic properties of polymer solar cells with an inverted structure wherein the electron-collecting electrode comprises an indium tin oxide (ITO) electrode coated with titanium dioxide (TiO2) nanoparticles dispersed into poly(N-vinylpyrrolidone) (PVP). The optimization of performance of polymer solar cells in which the TiO2 concentration in PVP was varied is presented. Pristine solar cells with the TiO2:PVP-coated ITO electrodes showed S-shape current-voltage characteristics. The S-shaped feature disappeared after the continuous exposure of the solar cells to light from an AM 1.5G solar simulator, leading to an improved device performance compared with solar cells that use an ITO or ITO/TiO2 electron-collecting electrodes.