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Direct ink writing (DIW) method is a novel kind of ceramic fabrication approach which allows one to design and rapidly construct ceramic products in complex shapes without the need for any lithographic masks, dies or expensive moulds. A 40 wt.% water-based titanium dioxide (TiO₂) suspension was formulated. With the help of DIW technique, two-dimensional (2D) spiral structures, three-dimensional (3D) woodpile structures, cylindrical structures and half conical structures at micrometer scale were fabricated. According to the rheological test, the ink shows a shear-thinning behavior and appropriate viscoelastic properties, which ensures a feasible shaping process. The scanning electron microscopy (SEM) test shows that the samples sintered at 1050${}^{\circ }$C for 2 h have formed ceramics completely. The DIW method has merits to pattern ceramics into special-shaped structures into two and three dimensions with high precision and good designability, which provides new ideas and methods for structural, functional and biomedical applications.

A series of Ti${}_{1-x}$Co${}_x$O${}_{2-\delta }$ ($x$ = 0.01, 0.03, 0.05, 0.07) nanoparticles were synthesized by sol–gel method. The X-ray diffraction, transmission electron microscopy, Raman analysis and X-ray photoelectron spectroscopy ruled out the signatures of Ti${}^{3+}$, Co-clusters or any other oxides of Co. The ferromagnetic behavior was clearly observed at room temperature in doped samples with saturation magnetization $(M_s)$ of the order of 0.008–0.035 emu/g depending on doping concentrations. The saturation magnetization is found to be increased with the Co contents increasing from 1% to 7%. From the plot of the M–T curve, we obtain the $T_c$ as $\sim$515 K for 5% Co-doped TiO₂. Oxygen vacancies were detected from the photoluminescence (PL) measurement. Magnetic properties analyses and PL analyses showed that oxygen vacancies probably played a major role in ferromagnetism of the Ti${}_{1-x}$Co${}_x$O₂ system with Co substituting for Ti. The first-principles calculation was performed to investigate the magnetic properties of Co-doped TiO₂ nanoparticles. It can be found that the major magnetic moment is from the 3d electron of Co. The experiment results are consistent with the first-principles calculation. The ferromagnetism derived from the spin-split of O-2p and Co-3d electron states caused by p–d orbit hybridization.

In this study, zinc sulfide (ZnS)/titanium oxide(TiO₂) nanoparticles were prepared by a two-step facile hydrothermal method and then annealing at $400^{\circ }\mathrm{\text{C}}$ for 30 min. Also, the transient absorption measurement and photocatalytic activity of ZnS/TiO₂ before and after annealing were investigated. The characterization technique such as the scanning electron microscopy (SEM) and X-ray diffraction (XRD) and UV–Visible spectroscopy have been employed to study the surface morphology and structural details. The SEM image shows the change in the surface morphology due to annealing. The change of the crystal structure of ZnS–TiO₂ is revealed by XRD spectra. The femtosecond transient absorption measurement showed moderate decay over several hundred picoseconds for annealed ZnS/TiO₂. Moreover, improved photocatalytic activity of annealed ZnS/TiO₂ nanoparticles in visible light has been observed.

TiO₂ films of different thickness are deposited on silicon substrate at low temperature and pressure by a Helicon-PECVD reactor. The evolution of film morphology and topography is observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), meanwhile the spectroscopic ellipsometry (SE) measurements are performed to investigate the film growth mechanism and optical constants. The SEM and AFM observations show that all the films exhibit a columnar structure, moreover all the columns are vertical grown and well-organized when the thickness below $\sim$80 nm. As the thickness is increased to $\sim$150 nm, 250 nm and 450 nm, the column size is increased in the top layers, the whole film morphology becomes inhomogeneous, which leads to a decreased density and rougher surface. By fitting the SE measurements, a suitable gradient physical model is found to describe the film morphologies, the model consists of a native SiO₂ layer on Si substrate, a mediate layer mixed TiO₂ with void whose concentration gradient changed from bottom to top, and a top roughness layer. For thick films ($\ge \sim$450 nm), the absorption and scattering on the rough surface is considered in order to keep the precision of SE fits. It is found that the optical index is decreased with film thickness, which is related to the evolution of structure in the top layers.

Band structure of anatase ${\mathrm{\text{TiO}}}_2$ could be modified by doping foreign atoms. With ab-initio calculations, considering praseodymium, nitrogen and gadolinium as potential dopants, some mono-, co- and tri-doped models are introduced. The structure modification due to each model is compared with a standard ${\mathrm{\text{TiO}}}_2$ system. Pr doping reduced the band gap of ${\mathrm{\text{TiO}}}_2$ by introducing Pr 4f states below the conduction band, and the Fermi level appears below the conduction band minimum. The addition of nitrogen in Pr-doped ${\mathrm{\text{TiO}}}_2$ pushed back the Fermi level to its intrinsic position while reducing the band gap. The tri-doped system comprising of Pr, N and Gd as dopants provided a populated band gap. The impurity states associated with Gd appeared in the middle of the band gap. The density of states analysis reveals that Pr 4f states change the location of N 2p states in the band structure. Instead of appearing as isolated states, the N 2p states are mixed with O 2p states while the Pr 4f states are coupled with the Ti 3d states in Pr, N-${\mathrm{\text{TiO}}}_2$. The Pr, N, Gd tri-doped ${\mathrm{\text{TiO}}}_2$ system provided strong visible light absorption due to the stepwise transition of electrons by Gd f states. While providing reasonable visible light absorption, the Pr, N-${\mathrm{\text{TiO}}}_2$ is expected to provide strong visible light photoactivity due to the clear band gap. Due to the absence of isolated states, the generated photo-excited carriers would be efficiently utilized in the oxidation/reduction processes.

The TiO₂ thin film was grown on a $64^{\circ }$ Y-axis cut, X-axis propagation lithium niobate substrate by radio frequency magnetron sputtering to fabricate a surface acoustic wave device. The sputtering ratios of argon to oxygen at 20% and post-annealing temperature at $500^{\circ }$C for 3 h were controlled to improve the photocatalytic activity of TiO₂ thin film. The effects of work frequency and input voltage of the surface acoustic wave device on the methylene blue photocatalytic degradation efficiency of the TiO₂ thin film were investigated. The TiO₂ thin film was vibrated at radio frequency by surface acoustic wave device to increase the scattering and reactive frequency for methylene blue in liquid. The surface acoustic wave device operated at 28.65 MHz work frequency and 0.95 V input voltage revealed the highest photocatalytic degradation efficiency of methylene blue. Compared to the TiO₂ thin film combined with and without surface acoustic wave device, the surface acoustic wave device enhanced the TiO₂ thin film photocatalytic degradation efficiency to 46%.

The scattering layer in the TiO₂ photoanode (PAs) of dye-sensitized solar cells (DSSCs) is doped with single-layer graphene (G), and DSSC is prepared by doctor blade coating method. A small amount of graphene (0.0016 wt.%) in a graphene aqueous solution (G-AS) and a G-TiO₂ paste was prepared to make 2–20 wt.% of G-AS in the deionized water (DIW). The UV-Vis measurement results show that the TiO₂ scattering layers doped with graphene effectively improve the visible light absorption intensity of DSSC PAs and increase the current density (Jsc) from 13.84 mA/cm² to 16.20 mA/cm². The Electrochemical Impedance Spectroscopy (EIS) measurement showed that the internal structural impedance Rk $(\mathrm{\Omega })$ decreased from 12.086 $(\mathrm{\Omega })$ (without graphene doping) to 9.875 $(\mathrm{\Omega })$ at 5 wt.% of the graphene doping. The photoelectric conversion efficiency (PCE) increased from 6.56% of the original un-doped graphene to the maximum PCE value of 7.57% at 5 wt.%. The results show that the best PCE is obtained when the concentration of G-AS is 5 wt.%.

TiO₂ nanoparticles, as a typical inert metal oxide, were added into ${\text{Pb}}^{2+}$ plating solutions to prepare Ti/PbO₂+nano-TiO₂ composite coatings. The effect of TiO₂ nanoparticles on the electrodeposition process of PbO₂ was investigated by voltammetric studies. The composition, structure and morphology of the obtained composite coatings were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM), respectively. Cyclic voltammetry was employed to study the effect of nano-TiO₂ particles on the PbO₂ electrodeposition process. It is found that high doping (2–8 g/L) of TiO₂ nanoparticles significantly decreased the crystallite size which can be attributed to a crystallite-refining effect of nano-TiO₂ during the electrodeposition of PbO₂.

There is intensive research by the community to improve materials for renewable energy applications such as hydrogen production, photovoltaics and light-emitting diodes. Titanium dioxide (TiO₂) is an important material where we can improve its fundamental properties, through doping aiming to form more efficient devices. Here, we use electronic structure calculations based on density function theory (DFT) to explore the effect of dopants, such as boron (B), germanium (Ge), molybdenum (Mo), and tungsten (W), on the structural and electronic properties of TiO₂. We investigated both the interstitial and the oxygen substitutional positions, and for the minimized energy optimized structures, we used hybrid DFT calculations to predict the electronic properties through the density of states, which proved costly but not as much to outweigh their advantage in accuracy. For most cases considered, the dopants reduce the theoretical bandgap of TiO₂, while gap states form. The variation of the bandgap ranges from a very small increase of 0.04eV to a significant decrease of 0.8eV, while the exact “position” of new gap states differs for each type of dopant and for its “spot” in the crystalline structure. It is proposed that these states and the change of the bandgap contribute to the significant changes in the optical and electronic properties of TiO₂ and can be beneficial to the photovoltaic and photocatalytic applications of TiO₂ and its implementation for hydrogen production.