Narrow Results

In this study, TiO₂ coatings are deposited on Si(100) wafers by direct current pulsed magnetron sputtering technology. The crystal structure of TiO₂ coatings gradually transforms from the anatase phase to the amorphous phase when the sputtering power is decreased from 900W to 150W. Besides, the growth surface temperature of TiO₂ coatings decreases from 630${}^{\circ }$C to 241${}^{\circ }$C. The relationship between the growth behavior and growth surface temperature of TiO₂ coatings is investigated using the dynamic scaling theory. The results show that in the first stage, the growth behavior of TiO₂ coatings gradually transforms from the Frank–van der Merwe mode to the Volmer–Weber mode with decreasing sputtering power from 900W to 150W. In the second stage, the growth behavior of TiO₂ coatings gradually transforms from the Stranski–Krastanov mode to the Volmer–Weber mode. Transformation of the growth behavior of TiO₂ coatings in the second stage transforms the crystal structure of TiO₂ coatings from the anatase phase to the amorphous phase.

${\mathrm{\text{TiO}}}_2$ nanomaterials with different content of ${\mathrm{\text{Ce}}}^{4+}$ ion were synthesized by the chemical method from solutions and demonstrated improved photocatalytic and optical properties with significant redshift compared to pristine ${\mathrm{\text{TiO}}}_2$. According to X-ray phase analysis and transmission electron microscopy, all synthesized materials are characterized by anatase modification, which holds up to $800^{\circ }$C, the particle size for all materials is 12–21 nm. X-ray diffraction spectra revealed that the anatase to rutile phase transition for materials doped with ${\mathrm{\text{Ce}}}^{4+}$ ions begins at a higher temperature of $800^{\circ }$C compared to pristine ${\mathrm{\text{TiO}}}_2$. The influence of synthesis conditions and ${\mathrm{\text{Ce}}}^{4+}$ content (0.1–2 mol.%) on characteristics and photocatalytic activity were investigated. The Ce-doped ${\mathrm{\text{TiO}}}_2$ nanomaterial, containing 0.1% ${\mathrm{\text{Ce}}}^{4+}$ provides an extremely high degree of methylene blue decomposition by 93% within visible light irradiation for 3 h. The stability of the catalyst over four cycles has been shown, which makes it possible to use it in the purification of water resources from dyes or other pollutants.

The influence of mixed metal–organic decomposition (MOD) coating materials has been studied based on the crystal growth of TiO₂ and TiO₂–Nb₂O₅ mixed thin films. These thin films were grown on quartz substrates using a dip-coating method. The crystal structures of TiO₂ films are well known to depend on sintering temperature, whereas the surface morphologies are not significantly affected by sintering temperature. Nb₂O₅ was mixed with the TiO₂ source material as a possible electron donor. The Nb content of the TiO₂–Nb₂O₅ mixed thin film depended on the Nb mole ratio in the TiO₂–Nb₂O₅ mixed MOD coating material. Large crystal grains were observed with increasing Nb content in the TiO₂–Nb₂O₅ mixed thin film, although Nb was inactive as a donor. It can be concluded that Nb enhances the growth of TiO₂ by MOD. This enhancement of crystal growth by the intentional addition of an impurity can be expected to improve the characteristics of other semiconductor materials grown by wet processes.

Graphene and titanium dioxide (TiO₂) composite catalyst has been synthesized by hydrothermal synthesis method, and used for the degradation of Rhodamine B (Rh.B) in water. The photoelectrocatalytic activity of this composite was evaluated by decomposing of Rh.B in water under visible or UV light irradiation. The degradation results indicated that the photoelectrocatalytic performance of this composite catalyst was greatly enhanced due to the improved adsorption performance and separation efficiency of photo-generated carriers possibly. The composite with graphene content of 10 wt.% exhibited superior activity under UV light irradiation. After 30 min of reaction, the photoelectrocatalytic degradation ratio of Rh.B was about 96% when pH $=$ 6–7. The results of this work provide a good method for the treatment of organic wastewater with high performance.

Codopant is an effective approach to modify the bandgap and band edge positions of transition metal oxide. Here, the electronic structures as well as the optical properties of pristine, mono-doped (N/P/Sb) and codoped (Sb, N/P) anatase TiO₂ have been systematically investigated based on density functional theory calculations. It is found that mono-doped TiO₂ exhibits either unoccupied or partially occupied intermediate state within the energy gap, which promotes the recombination of electron-hole pairs. However, the presence of (Sb, N/P) codopant not only effectively reduces the width of bandgap by introducing delocalized occupied intermediate states, but also adjusts the band edge alignment to enhance the hydrogen evolution activity of TiO₂. Moreover, the optical absorption spectrum for (Sb, N/P) codoped TiO₂, which is favored under oxygen-rich condition, demonstrates the improvement of its visible light absorption. These findings will promote the potential application of (Sb, N/P) codoped TiO₂ photocatalysis for water splitting under visible light irradiation.

Surface modification has been used as a method to create defects on ${\mathrm{\text{TiO}}}_2$ materials, which can improve their desirable properties. In this paper, defected ${\mathrm{\text{TiO}}}_2$ nano-powder was successfully synthesized by chemical reduction using ${\mathrm{\text{NaBH}}}_4$ as the reducing agent at 300–400${}^{\circ }\mathrm{\text{C}}$ under argon atmosphere. High defect concentration can be produced by increasing process temperature. The modified ${\mathrm{\text{TiO}}}_2$ shows good visible light absorption and photocatalytic activity on degradation of Rhodamine B (4–9 times higher than the pristine ${\mathrm{\text{TiO}}}_2$) with the visible light irradiation. Further XPS analysis and theoretical studies using full potential linearized augmented plane wave (FP-LAPW) method as implemented in wien2k code revealed the existence of oxygen vacancy and ${\mathrm{\text{Ti}}}^{3+}$ in the modified samples. These types of defects were responsible for the modifications of the electronic and optical properties of ${\mathrm{\text{TiO}}}_2$, resulting in the improved photocatalytic activity in visible light irradiation.

Titanium dioxide (TiO₂) is one of the most promising photocatalysts for photoelectrochemical applications due to its high chemical as well as photochemical stability. Its efficiency in practical applications is limited due to its wide bandgap, a high rate of recombination of electron–hole pairs and the weak photo-carriers separation efficiency. In this computational study, a path was followed to find out the redshift of the TiO₂ light absorption edge via lead (Pb) doping. The density functional theory (DFT) results revealed that the doped TiO₂ bandgap was decreased to the lower edge (2.1 eV) in the visible region resulting in a relatively better optical absorption of the material. Furthermore, doped TiO₂ was found to absorb a large part of the solar spectrum. The improvement in optical absorption resulted in good photo response. The calculated results also showed a redshift in optical properties produced through the doping of Pb in TiO₂.

This study develops the Ni–Fe–P–TiO₂ nanocomposite coatings via an electroless deposition process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to determine the coating structures. Hardness and wear tests were conducted to measure the coating’s mechanical performance, and polarization curves were recorded to evaluate the corrosion behavior. The results show that the TiO₂ nanoparticles are incorporated into the coatings. The proper addition of TiO₂ refines the coating surface morphology without changing the coating phase constituents. The best mechanical and corrosion performance is obtained for the 0.5-g/L modified Ni–Fe–P–TiO₂ sample, owing to its compact surface feature and well-dispersed TiO₂ nanoparticles.

To understand plasmon-induced charge-transfer mechanisms between a photo-excited gold (Au) nanoparticle and a TiO₂ nanoparticle, a Monte Carlo random walk (MCRW) simulation was applied to reproduce the charge recombination kinetics in the nanocrystalline (Au/TiO${}_2)$ assemblies reported previously based on transient absorption spectroscopy. The Au/TiO₂ assemblies consist of a confined electron diffusion space within a tiny TiO₂ nanoparticle, making it possible to study electron diffusion transport through MCRW simulation. In this simulation algorithm, the electron diffusion starts at the coordinate origin of a rectangle, and the next direction of movement is obtained by calculating the coordinate matrix and random offset so that the electron is reflected on three boundaries and absorbed when it reaches the other boundary. By simulation programming, the histogram which indicates the occurrence frequency of the step accumulation number up to the right boundary was obtained. From 100 to 100000 steps under condition of 10000 iteration, that is, changing the steps but keeping the iteration times to ensure that all particles experience absorption in the simulation. Comparing the trace of 10⁶ particles position with that of 10⁴ under 1000 simulations, the electron density was found to saturate other than the region near the right boundary, where electrons disappear by the absorption process during the electron diffusion process. Finally, by fitting curves, it is confirmed that the tendency of the simulated response reproduced the transient absorption kinetics.

Organic inorganic-based perovskites solar cells (PSCs) are quite prominent as next generation solar cells as they exhibit excellent properties as well as high power conversion efficiency. In spite of the high cost, interfacial recombinations and instability in ambient environment limit their commercialization. Herein, TiO₂-based compact layer (c-TiO₂) with different thicknesses is employed (<50nm) to study the charge transportation at interface and recombination in PSCs fabricated under high humid conditions (R${}_{\text{H}}\sim$ 80%). The thickness of CL was varied from 7nm to 35nm and was optimized by changing the precursor concentration as well as spinning speed. The prepared c-TiO₂ and the mesoporous layer of TiO₂ (m-TiO₂) were thoroughly characterized using Raman spectroscopy, UV-Vis, cyclic voltammetry and electrochemical techniques. Furthermore, CuSCN was used as hole transporting layer (HTL) in PSCs owing to ease of handling and nominal cost. The optimized PSC is found to show that the power conversion efficiency (PCE) improved by 50% on varying the thickness of CL and is stable even under high humid conditions. The elevated performance of PSCs is ascribed to the appropriate thickness of CL which resulted in improved charge transportation and reduced electron hole recombinations.

The optical properties of TiO₂ are changed while doped with impurity atoms. This paper made a systematical calculation of the bandgap, the density-of-states (DOS), the optical properties for pure TiO₂, and Bi-doped anatase TiO₂ according to the first-principles plane wave ultrasoft pseudopotential method which is primarily based on the density functional theory (DFT). The calculation results exhibit that the bandgap decreased after doping, and the impurity energy level is produced into the bandgap of Bi-doped TiO₂, which makes red-shift for the absorption band edge of Bi-doped TiO₂ and the absorption is enhanced more in the visible light range.

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.