Mixed TiO2 Research Articles

Transverse ridge cracking in tensile fragmentation tests of thin brittle coatings on polymer substrates

Thin brittle coatings on polymers can be used to improve barrier properties. The interfacial adhesion is known to affect cracking of the coating under deformation. It is therefore desirable to experimentally quantify the adhesive properties. For thin coating systems, this can be done e.g. by tensile fragmentation tests or nanoindentation techniques. For crack opening, an alternative method presents itself in a secondary damage mechanism typically found in tensile fragmentation tests. At large strains, the transverse compressive strains can give rise to ridge cracks, which may be observed in high-resolution scanning electron microscopy. It is shown that such observations can be used to estimate the critical energy release rate in interfacial crack growth. The method is exemplified for 20 nm thick coatings of TiO2 and coatings of mixed oxide TiO2 and Al2O3 on polyethylene terephthalate films. The experiments gave values of 2.5 J/m2 and 1.6 J/m2 for these interfaces, respectively. Energy release rates from a micromechanical model based on beam theory were found to be comparable with non-linear finite element predictions for the present crack configurations. Direct measurement of the transverse strains from digital image correlation resulted in predictions closer to the more exact numerical results as compared with predictions based on an assumed linear elastic Poisson contraction. The effects of the non-linear stress-strain behavior of the polymer film could thus be dealt with by measuring the compressive strains giving rise to the ridge cracks. Overall, this work shows how the ridge cracking can provide insight in interfacial crack growth in predominantly opening mode, and possibly be used to roughly estimate fracture toughness even for ultrathin coatings in this investigation.

Correlation between microstructural defects and photoelectrochemical performance of 1D Ti–Nb composite oxide photoanodes for solar water splitting

We report on the optimized fabrication of ultrathin wall nanotubes grown on Ti–Nb alloy via anodization in organic-based electrolytes. The nanotubes are vertically aligned with wall thicknesses of 5–8 nm, diameters of 180–200 nm, and lengths of 2–2.8 μm. Raman spectroscopy and glancing angle x-ray diffraction (GAXRD) measurements indicated the formation of composite oxides of anatase TiO2 and monoclinic Nb2O5. The composite oxides showed better stability at elevated temperatures up to 650 ᵒC and with much smaller induced microstrain compared to the TiO2 counterpart. X-ray photoelectron spectroscopy (XPS) analysis confirmed the composition of the fabricated nanotubes as a mixed TiO2–Nb2O5 composite. Upon their use as photoanodes to split water, the composite TiO2–Nb2O5 NTs showed almost 2-fold increase in the obtained photocurrent compared to that of bare TiO2 NTs prepared under the same conditions. Moreover, the incident photon to current efficiency (IPCE) of the mixed oxide nanotubes was higher than that of bare TiO2 with a positive shift towards longer wavelengths, indicating improved electron mobility and charge collection. Hence, the addition of Nb resulted in the formation of thermally stable and photoactive photoanodes for solar fuel production.

Microstructural evolution and high-temperature oxidation mechanisms of a Ti-Mo-Si composite

The objective of this study was to improve the safety working temperature of Ti alloy by developing a new Ti-Mo-Si composite. After SPS sintering, the Ti-Mo-Si composite in situ formed β-Ti, α-Ti, Ti5Si3, and TiC phases. During oxidation, the composite followed parabolic oxidation kinetics. A dense multi-layered structured oxide layer that consists of TiO2(I)/mixed SiO2 and TiO2(II) was formed on the surface of the matrix with a grain size that gradually decreased after 120 h of oxidation. The amorphous SiO2 sealed the clearances between the TiO2 grains, which provided the oxide layer with a self-healing ability. This type of oxide layer caused an increase in the antioxidant temperature of the matrix to 900 °C for 120 h.

Ambient temperature ZrO2-doped TiO2 crystalline photocatalysts: Highly efficient powders and films for water depollution

In this paper, several TiO2 materials doped with zirconia precursor (0.7, 1.4, 1.6 and 2.0 mol%) were synthesized by an easy aqueous sol-gel synthesis at ambient temperature. This method consists in the peptization of the TiO2 colloid in presence of HNO3. The corresponding pure TiO2 material was also synthesized for comparison. The performances and the physico-chemical properties of these materials were compared to the well-known Evonik P25 photocatalyst.The physico-chemical characterizations showed that nano-crystalline anatase-brookite particles were produced with the sol-gel process, with higher specific surface area than P25 (∼200 m2 g-1 vs. 47 m2 g-1). All samples presented a higher visible absorption than P25. The XPS spectra showed that all the samples were doped with nitrogen and that mixed TiO2–ZrO2 oxide materials were obtained when doping with zirconia precursor.Photoactivity was evaluated through the degradation of p-nitrophenol in water. On the one hand, under UV/visible light, the ZrO2 doping increased the degradation efficiency of the pure TiO2 catalyst due to a better charge separation in the mixed TiO2–ZrO2 oxides. The activity of the sample with the highest dopant content was even higher than the one of P25. On the other hand, under visible light, all samples were much more efficient than P25. This activity shift towards visible range was due to the N-doping of the catalysts, with a slight improvement for the doped ones.Finally, the feasibility of producing films starting from an aqueous suspension of the photocatalyst was assessed on P25, pure TiO2 and the best doped material. The photoactivity of these films, evaluated on the degradation of methylene blue under UV-A light, showed that the sample with the highest dopant concentration had an efficiency 4 times higher than pure TiO2 and 20 times higher than P25.

Fabrication and characterization of perovskite solar cells with ZnGa2O4 mixed TiO2 photoelectrode

Perovskite solar cells are easily decomposed by ultraviolet rays. In order to limit the function of TiO2 as a photocatalyst, ZnGa2O4 nanoparticles were mixed into a mesoporous TiO2 layer. The bandgap of the mixed layer increased by 0.1 eV and the efficiency of perovskite solar cell increased by 0.5%. However, it acts as a resistive element and lowers the current. Since ZnGa2O4 emits absorbed ultraviolet rays in blue, a thin film is additionally formed on the glass substrate to convert ultraviolet rays into electric current in a perovskite solar cell. When an ultraviolet ray is irradiated, an additional current of 100 μA cm−2 can be obtained.

In-situ synthesis of mixed phase electrospun TiO2 nanofibers: a novel visible light photocatalyst

TiO2 nanofibers were synthesized by electrospinning method using mixed titanum isopropoxide and polyvinylpyrrolidone precursors in ethanol followed by calcination at high temperature. The obtained TiO2 e-spun nanofibers were characterized by FESEM, TEM, XRD, XPS and BET surface area analytical techniques. XRD result shows that the nanofibers contain both anatase and rutile mixed phases. FESEM and TEM study indicates the development of precise fine tiny nanoparticles with diameter in the range of 10–20 nm, which are oriented along one dimensional direction to form the fibrous structure with diameter in the range of 300–500 nm. The mixed phase TiO2 nanofibers were used as photocatalysts for degradation of Rhodamine-B and Methyl orange under solar light irradiation and also under visible light irradiation. More than 99% degradation was achieved within 90 min of irradiation time for both the dyes. Furthermore, it is observed that the TiO2 photocatalyst is efficiently degrading (98%) the tetracycline hydrochloride solution within 70 min of contact time. The excellent visible light photocatalytic activity may be attributed to the combine factors of hetero-conjunction at anatase–rutile interface and immediate charge transfer due to 1D structure, which inhibit the electron–hole recombination. Rutile-Anatase dual phase TiO2 nanofibers exhibit excellent visible light photocatalytic activity due to the combine factors of hetero-conjunction at anatase-rutile interface and immediate charge transfer due to 1D structure, which inhibits the electron-hole recombination.

Rapid gas-liquid detonation synthesis of core-shell structural graphite coated TiO2 nanoparticles

Here we demonstrate a simple, rapid for the controlled synthesis of core-shell structural graphite coated TiO2 nanoparticle (TiO2@G), which are directly prepared by detonation chemical decomposition of the gas-liquid mixture of CH4, O2, C6H6 and TiCl4 in milliseconds. Various techniques, including XPS, TEM, XRD and Raman were employed to investigate the products. It is found that the sphere, good disperse mixed crystal TiO2 nanoparticles with crystal size of 10–30 nm were coated with thick graphite layers. Based on Zeldovich Neuman-Doring (ZND) model, the detonation synthesis mechanism of core-shell structure TiO2@G is discussed. This rapid synthesis method can be extended to the preparation of other core-shell materials.

Electrochemical synthesis of porous Ti-Nb alloys for biomedical applications

Porous titanium‑niobium alloys of composition Ti-24Nb, Ti-35Nb and Ti-42Nb were synthesised by electro-deoxidation of sintered oxide discs of mixed TiO2 and Nb2O5 powders in molten CaCl2 at 1173 K, and characterised by XRD, SEM, EDX and residual oxygen analysis. At the lower Nb content a dual-phase α/β-alloy was formed consisting of hexagonal close-packed and body-centred cubic Ti-Nb, whereas at the higher Nb contents a single-phase β-alloy was formed of body-centred cubic Ti-Nb. The corrosion behaviour of the alloys prepared was assessed in Hanks' simulated body fluid solution at 310 K over extended periods of time. Potentiodynamic polarisation studies confirmed that the alloys exhibited passivation behaviour, and impedance studies revealed that the passive films formed on the surface of the alloys comprised a bi-layered structure. XPS analysis further proved that this contained hydroxyapatite at the top and native metal oxide underneath. The mechanical properties of the alloys were evaluated, and the elastic moduli and the Vickers hardness were both found to be in the range of that of bone. Overall, Ti-35Nb is proposed to be the best-suited candidate of the materials studied in regard to biomedical applications.

Early oxidation behavior of Si-coated titanium

Oxidation of pure Ti coated with a thin Si layer was investigated to clarify the role of titanium silicide phases in improving oxidation resistance of titanium alloys. The system initially reacted to form a two-layer structure with Ti5Si3 and SiO2. Oxidation proceeded by upward diffusion of Ti to form TiO2 wedge-like crystals on the surface and inward oxidation of Ti5Si3 into a mixed nanocrystalline TiO2 and SiO2 internal scale that was locally layered. The Ti5Si3 phase inhibited oxygen inward diffusion, thereby limiting oxygen ingress into Ti and retarding inward Ti oxidation until the silicide layer was completely oxidized.

C-dots dispersed macro-mesoporous TiO2 phtocatalyst for effective waste water treatment

Synthesis of macro-mesoporous Titania (Titanium dioxide-TiO2) nanospheres was successfully achieved using a modified template-free methodology to incorporate macroporous channels into a mesoporous TiO2 framework to form mixed macro-mesoporous TiO2 spheres (MMPT), which were doped with carbon dots (C-dots) to form improved nanocomposites (C-dots@MMPT). Elemental composition, surface bonding and optical properties of these nanocomposites were characterized by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR) and ultraviolet-visible absorption spectroscopy (UV-VIS). Evaluation of photocatalytic activity for each (C-Dots@MMPT) sample was performed via degrading the Methylene Blue (MB) dye compared with bare samples (MMPT) under visible light irradiation using 300 Watt halogen lamp.

Increasing the Efficiency of Organic Dye‐Sensitized Solar Cells over 10.3% Using Locally Ordered Inverse Opal Nanostructures in the Photoelectrode

Abstract3D inverse opal (3D‐IO) oxides are very appealing nanostructures to be integrated into the photoelectrodes of dye‐sensitized solar cells (DSSCs). Due to their periodic interconnected pore network with a high pore volume fraction, they facilitate electrolyte infiltration and enhance light scattering. Nonetheless, preparing 3D‐IO structures directly on nonflat DSSC electrodes is challenging. Herein, 3D‐IO TiO2 structures are prepared by templating with self‐assembled polymethyl methacrylate spheres on glass substrates, impregnation with a mixed TiO2:SiO2 precursor and calcination. The specific surface increases from 20.9 to 30.7 m2 g−1 after SiO2 removal via etching, which leads to the formation of mesopores. The obtained nanostructures are scraped from the substrate, processed as a paste, and deposited on photoelectrodes containing a mesoporous TiO2 layer. This procedure maintains locally the 3D‐IO order. When sensitized with the novel benzothiadiazole dye YKP‐88, DSSCs containing the modified photoelectrodes exhibit an efficiency of 10.35% versus 9.26% for the same devices with conventional photoelectrodes. Similarly, using the ruthenium dye N719 as sensitizer an efficiency increase from 5.31% to 6.23% is obtained. These improvements originate mainly from an increase in the photocurrent density, which is attributed to an enhanced dye loading obtained with the mesoporous 3D‐IO structures due to SiO2 removal.

Surfactant Effect on the Synthesis of Mesoporous TiO<sub>2</sub>-SiO<sub>2</sub> Coatings Using Sol-Gel Technology

The aim of the research was to develop the area of mesoporous thin films of a binary TiO2–SiO2 system. Sol was synthesized from tetraethylorthosilicate as the silica source and titanium isopropoxide solution as the TiO2 source, while triblock copolymer surfactant (Pluronic F 127 (10% solution in water, (P))) was used as the mesostructure-directing agent. In this paper we present sol-gel obtained TiO2–SiO2 with a mesoporous structure. The effects of added titanium on the mesostructure and on the porosity are presented and discussed. Four different molar percentage ratios of Ti: Si were used for the synthesis of mixed TiO2–SiO2 mesoporous thin films on glass substrate. The mesoporous structure of thin films was characterized by X-ray diffraction (XRD) patterns, atomic force microscopy (AFM), scanning electron microscopy (SEM) and the water contact angle. These mesoporous TiO2–SiO2 thin films could have many potential applications in many areas such as separation membranes, catalysis, optics, and self-cleaning surfaces.

Evaluation of the Antimicrobial Efficacy of Titanium Dioxide Nanoparticles on the Surfaces of Public Toilets

The infection control in surfaces of public toilets environment is a matter of great concern and a major challenge, especially during mass gatherings. The present study aimed to evaluate the antimicrobial efficacy of titanium dioxide nanoparticles coating on environmental surfaces of public toilets during Hajj time. A pilot study has been designed to evaluate the antimicrobial efficacy of titanium dioxide nanoparticles on the surfaces of public toilets. The results showed a significant reduction in colony-count of the test samples. Maximum average reduction count of test microbes of the seats and walls reached (99.7%) while that of the doors reached (99.1%) which was statistically significant (P value = 0.001). It was concluded that there was a marked effect of a mixed TiO2 coating on reducing the microbial count at the surfaces of public toilets environments. Further research on efficacy against specific organisms, intestinal parasites, fungi, viruses and bacteriophage is recommended.

Influence of growth parameters on the properties of TiO2 films prepared by anodic spark oxidation method and photocatalytic degradation of methylene blue

Porous titanium dioxide (TiO2) coatings were prepared on the pure titanium substrate by anodic spark oxidation (ASO) method in electrolytes containing various concentrations of sulfuric acid. The crystal phase, surface morphology, chemical composition, and optical property of the TiO2 films were analyzed by using XRD, SEM, XPS, and UV-vis spectroscopy. The photocatalytic activity is evaluated by the decomposition of methylene blue (MB) aqueous solution under UV light irradiation. It is found that the electrolyte concentration plays an important role in the properties and characteristics of the TiO2 coatings. The results show that TiO2 films consist of primarily the rutile phase with altering fraction depending on the electrolyte concentration without any heat treatment. The results demonstrated that there were formed too many sub-micron and nanopores of TiO2 neighboring to the micropores. TiO2 layer anodized in 0.75 M H2SO4 exhibited much higher photocatalytic activity than the other films. The results imply that anatase-rutile mixed TiO2 coatings can be successfully used for the photocatalytic degradation of organic pollutants.

Hydrogen absorption by Ti-implanted Zr-1Nb alloy

This paper describes the hydrogenation behavior of Zr-1Nb alloy Ti-implanted by plasma immersion ion implantation (PIII). Hydrogen sorption kinetics of the Ti-modified alloy was investigated under gas-phase hydrogenation at 400 °C for 1 h. The influence of implantation time on the protective properties of the modified layer was shown. The lowest hydrogen absorption as well as the highest hydrogen trapping efficiency was achieved after PIII for 30 min. The main contribution to the reduction of hydrogen permeation is the formation of an oxide layer consisting of mixed TiO2 and ZrO2 on the modified surface of the alloy. X-ray photoelectron spectroscopy (XPS) revealed that PIII titanium oxide exists on the surface in the form of TiO2, which transforms to mixed Ti2O3 and TiO2 after hydrogenation. The thickness of the modified layer increases with implantation time that improves the efficiency of hydrogen trapping. All the absorbed hydrogen is gradually distributed in the modified layer and no hydrides are formed after hydrogenation in Ti-modified Zr-1Nb for 15 and 30 min.

Low-Temperature Sol-Gel Synthesis of Nitrogen-Doped Anatase/Brookite Biphasic Nanoparticles with High Surface Area and Visible-Light Performance

Nitrogen doping in combination with the brookite phase or a mixture of TiO2 polymorphs nanomaterials can enhance photocatalytic activity under visible light. Generally, nitrogen-dopedanatase/brookite mixed phases TiO2 nanoparticles obtained by hydrothermal or solvothermal method need to be at high temperature and with long time heating treatment. Furthermore, the surface areas of them are low (<125 m2/g). There is hardly a report on the simple and direct preparation of N-doped anatase/brookite mixed phase TiO2 nanostructures using sol-gel method at low heating temperature. In this paper, the nitrogen-doped anatase/brookite biphasic nanoparticles with large surface area (240 m2/g) were successfully prepared using sol-gel method at low temperature (165 °C), and with short heating time (4 h) under autogenous pressure. The obtained sample without subsequent annealing at elevated temperatures showed enhanced photocatalytic efficiency for the degradation of methyl orange (MO) with 4.2-, 9.6-, and 7.5-fold visible light activities compared to P25 and the amorphous samples heated in muffle furnace with air or in tube furnace with a flow of nitrogen at 165 °C, respectively. This result was attributed to the synergistic effects of nitrogen doping, mixed crystalline phases, and high surface area.

Influence of energy band alignment in mixed crystalline TiO2 nanotube arrays: good for photocatalysis, bad for electron transfer

Despite the wide application ranges of TiO2, the precise explanation of the charge transport dynamic through a mixed crystal phase of this semiconductor has remained elusive. Here, in this research, mixed-phase TiO2 nanotube arrays (TNTAs) consisting of anatase and 0–15% rutile phases has been formed through various annealing processes and employed as a photoelectrode of a photovoltaic cell. Wide ranges of optoelectronic experiments have been employed to explore the band alignment position, as well as the depth and density of trap states in TNTAs. Short circuit potential, as well as open circuit potential measurements specified that the band alignment of more than 0.2 eV exists between the anatase and rutile phase Fermi levels, with a higher electron affinity for anatase; this can result in a potential barrier in crystallite interfaces and the deterioration of electron mobility through mixed phase structures. Moreover, a higher density of shallow localized trap states below the conduction band with more depth (133 meV in anatase to 247 meV in 15% rutile phase) and also deep oxygen vacancy traps have been explored upon introducing the rutile phase. Based on our results, employing TiO2 nanotubes as just the electron transport medium in mixed crystalline phases can deteriorate the charge transport mechanism, however, in photocatalytic applications when both electrons and holes are present, a robust charge separation in crystalline anatase/rutile interphases will result in better performances.

Dependence of kinetics and pathway of acetaminophen photocatalytic degradation on irradiation photon energy and TiO2 crystalline

Degradation kinetics and pathway of acetaminophen (APAP) on anatase TiO2, rutile TiO2 and anatase–rutile mixed TiO2 were investigated at UVC 254nm and UVA 366nm in a wide photon flux region in the present work. Hydroxyl radicals (OH) induced hydroxylation is the predominant pathway for the degradation of APAP on anatase or anatase containing TiO2 particularly under UVC irradiation, which accounted for more than 50% of total degradation. Valance band hole (hVB) induced one electron oxidation contributed approximately 70% of the degradation of APAP on rutile TiO2 under UVA 366nm irradiation, while direct photolysis contributed more than rutile TiO2 photocatalysis under UVC 254nm irradiation because of competition for irradiation photon between APAP and rutile TiO2. These results showed that contribution of OH and hVB on anatase TiO2 is independent of irradiation photon energy, while irradiation photon energy significantly influences the contribution of OH, hVB and direct photolysis to the degradation of APAP on rutile or rutile containing TiO2. Therefore, degradation patterns of APAP and maybe other phenols in TiO2 photocatalysis process could be controlled through changing irradiation photon energy and TiO2 crystalline, which will make TiO2 photocatalysis a selective oxidation system.

Study of 2-Propanol Photocatalytic Degradation on Surface of Phase-Ratio-Controlled TiO2 Nanoparticles

The crystal form of TiO2 is a crucial focus of research on the photocatalytic degradation of gaseous pollutants by TiO2-based composite photocatalysts. To explore the synergistic effect of mixed crystalline TiO2 on gaseous organic-pollutant photocatalytic degradation, we synthesized a series of TiO2 nanoparticles with controllable phase ratios. We explored the role of the TiO2 phase ratio on the photocatalytic activity and degradation pathway in the photodegradation of 2-propanol (IPA). We estimated the crystallite size and crystal proportions of anatase and rutile by X-ray diffraction. We used the Brunauer–Emmett–Teller method to calculate the specific surface area and Fourier transform infrared spectroscopy to characterize the surface chemistry of the samples. Our results show the photocatalytic activities of pure anatase and the sample with 8.6% rutile to be much better than those of the samples with a phase junction and pure rutile. As such, anatase is the better option for the study of photodegradation design and preparation of gas-phase organic pollutants.

Simultaneous H2 production and pollutant removal from biodiesel wastewater by photocatalytic oxidation with different crystal structure TiO2 photocatalysts

This work was performed to test the feasibility of hydrogen (H2) production simultaneously with pollutant removal from biodiesel wastewater by the photocatalytic oxidation via different crystal structure TiO2 photocatalysts at ambient temperature (∼ 30 °C) and pressure. It was found that the simultaneous H2 production and pollutant removal could not be achieved using a fresh biodiesel wastewater, but proceeded well when the wastewater was diluted around 3.3-fold. The crystal structure of TiO2 markedly affected the rate of H2 production and pollutant removal. The mixed anatase–rutile phase crystal structure TiO2 photocatalysts exhibited a higher photocatalytic activity than that in the single rutile crystal structure, probably due to the co-presence of rutile and anatase phases of TiO2. The properties of the mixed crystal structure TiO2 photocatalyst, including the crystallite size, BET surface area, pore volume, band gap energy and point of zero charge (PZC) value affected the photocatalytic activity more than the phase composition. Among the evaluated mixed crystal structure, the TiO2 photocatalyst treated at 400 °C (T400) showed a great potential to produce H2 simultaneously with pollutant removal of approximately 19.83%, 83.13% and 84.13% of COD, BOD and oil & grease, respectively, with a H2 production rate of 67.4 µmol/h.