Growth behavior of titanium dioxide thin films at different precursor temperatures

The hydrophilic TiO2 films were successfully deposited on slide glass substrates using titanium tetraisopropoxide as a single precursor without carriers or bubbling gases by a metal-organic chemical vapor deposition method. The TiO2 films were employed by scanning electron microscopy, Fourier transform infrared spectrometry, UV-Visible [UV-Vis] spectroscopy, X-ray diffraction, contact angle measurement, and atomic force microscopy. The temperature of the substrate was 500°C, and the temperatures of the precursor were kept at 75°C (sample A) and 60°C (sample B) during the TiO2 film growth. The TiO2 films were characterized by contact angle measurement and UV-Vis spectroscopy. Sample B has a very low contact angle of almost zero due to a superhydrophilic TiO2 surface, and transmittance is 76.85% at the range of 400 to 700 nm, so this condition is very optimal for hydrophilic TiO2 film deposition. However, when the temperature of the precursor is lower than 50°C or higher than 75°C, TiO2 could not be deposited on the substrate and a cloudy TiO2 film was formed due to the increase of surface roughness, respectively

Small Polarons in Transition Metal Oxides

The formation of polarons is a pervasive phenomenon in transition metal oxide compounds, with a strong impact on the physical properties and functionalities of the hosting materials. In its original formulation the polaron problem considers a single charge carrier in a polar crystal interacting with its surrounding lattice. Depending on the spatial extension of the polaron quasiparticle, originating from the coupling between the excess charge and the phonon field, one speaks of small or large polarons. This chapter discusses the modeling of small polarons in real materials, with a particular focus on the archetypal polaron material TiO2. After an introductory part, surveying the fundamental theoretical and experimental aspects of the physics of polarons, the chapter examines how to model small polarons using first principles schemes in order to predict, understand and interpret a variety of polaron properties in bulk phases and surfaces. Following the spirit of this handbook, different types of computational procedures and prescriptions are presented with specific instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure

Photodegradation of Selected PCBs in the Presence of Nano-TiO2 as Catalyst and H2O2 as an Oxidant

Photodegradation of five strategically selected PCBs was carried out in acetonitrile/water 80:20. Quantum chemical calculations reveal that PCBs without any chlorine on ortho-positions are closer to be planar, while PCBs with at least one chlorine atoms at the ortho-positions causes the two benzene rings to be nearly perpendicular. Light-induced degradation of planar PCBs is much slower than the perpendicular ones. The use of nano-TiO2 speeds up the degradation of the planar PCBs, but slows down the degradation of the non-planar ones. The use of H2O2 speeds up the degradation of planar PCBs greatly (by >20 times), but has little effect on non-planar ones except 2,3,5,6-TCB. The relative photodegradation rate is: 2,2′,4,4′-TCB > 2,3,5,6-TCB > 2,6-DCB ≈ 3,3′,4,4′-TCB > 3,4′,5-TCB. The use of H2O2 in combination with sunlight irradiation could be an efficient and “green” technology for PCB remediation

Synthesis and Characterization of Rutile TiO2Nanopowders Doped with Iron Ions

Titanium dioxide nanopowders doped with different amounts of Fe ions were prepared by coprecipitation method. Obtained materials were characterized by structural (XRD), morphological (TEM and SEM), optical (UV/vis reflection and photoluminescence, and Raman), and analytical techniques (XPS and ICP-OES). XRD analysis revealed rutile crystalline phase for doped and undoped titanium dioxide obtained in the same manner. Diameter of the particles was 5–7 nm. The presence of iron ions was confirmed by XPS and ICP-OES. Doping process moved absorption threshold of TiO2into visible spectrum range. Photocatalytic activity was also checked. Doped nanopowders showed normal and up-converted photoluminescence

TiO2 Nanoparticles Are Phototoxic to Marine Phytoplankton

Nanoparticulate titanium dioxide (TiO2) is highly photoactive, and its function as a photocatalyst drives much of the application demand for TiO2. Because TiO2 generates reactive oxygen species (ROS) when exposed to ultraviolet radiation (UVR), nanoparticulate TiO2 has been used in antibacterial coatings and wastewater disinfection, and has been investigated as an anti-cancer agent. Oxidative stress mediated by photoactive TiO2 is the likely mechanism of its toxicity, and experiments demonstrating cytotoxicity of TiO2 have used exposure to strong artificial sources of ultraviolet radiation (UVR). In vivo tests of TiO2 toxicity with aquatic organisms have typically shown low toxicity, and results across studies have been variable. No work has demonstrated that photoactivity causes environmental toxicity of TiO2 under natural levels of UVR. Here we show that relatively low levels of ultraviolet light, consistent with those found in nature, can induce toxicity of TiO2 nanoparticles to marine phytoplankton, the most important primary producers on Earth. No effect of TiO2 on phytoplankton was found in treatments where UV light was blocked. Under low intensity UVR, ROS in seawater increased with increasing nano-TiO2 concentration. These increases may lead to increased overall oxidative stress in seawater contaminated by TiO2, and cause decreased resiliency of marine ecosystems. Phototoxicity must be considered when evaluating environmental impacts of nanomaterials, many of which are photoactive

Investigating the effect of artists’ paint formulation on degradation rates of TiO2-based oil paints

This study reports on the effect of artists’ paint formulation on degradation rates of TiO2-based oil paints. Titanium white oil paint exists in a multitude of different recipes, and the effect of the formulation on photocatalytic binder degradation kinetics is unknown. These formulations contain, among others, one or both titanium dioxide polymorphs, zinc oxide, the extenders barium sulfate or calcium carbonate and various additives. Most research performed on the photocatalytic degradation process focusses on pure titanium white-binder mixtures and thus does not take into account the complete paint system. Since photocatalytic oil degradation is a process initiated by the absorption of UV light, any ingredient or combination of ingredients influencing the light scattering and absorption properties of the paint films may affect the degradation rate. In this study three sets of experiments are conducted, designed using the design of experiments (DoE) approach, to screen for the most important formulation factors influencing the degradation rate. The benefits of using DoE, compared to a more traditional ‘one factor at a time approach’ are robustness, sample efficiency, the ability of evaluate mixtures of multiple components as well as the ability to evaluate factor interactions. The three sets of experiments investigate (1) the influence of the TiO2 type, (2) the impact of different mixtures of two types of TiO2, ZnO and the additive aluminum stearate and (3) the influence of common extenders in combination with photocatalytic TiO2, on the photocatalytic degradation of the oil binder. The impact of the formulation on the degradation rate became apparent, indicating the shortcoming of oversimplified studies. The protective effect of photostable TiO2 pigments, even in a mixture with photocatalytic TiO2 pigments, as well as the negative effect of extenders was demonstrated. Furthermore, the ambiguous role of ZnO (photocatalytic or not) and aluminum stearate is highlighted. Neither can be ignored in a study of degradation behavior of modern oil paints and require further investigation