TiO2 Materials Research Articles

Omnidirectional High Reflectors Using Silica/Superconductor Fibonacci Photonic Crystal for Optical Communication Applications

Using the transfer matrix method and Fibonacci structure, an omnidirectional high reflector that covers the fiber optics wavelengths is searched. We aim to make the reflector covers the operating wavelengths of Plastic and Glass fiber optics (650, 850, 1300 and 1550nm). Firstly, an ordinary Fibonacci structure composed of TiO2 and SiO2 slabs materials was studied and for TE and TM polarization modes the reflectance spectra cover only the 850, 1300 and 1550 nm wavelengths and for a limited range of wave-angle of incidence. Secondly, the SiO2 slabs were replaced with the superconductor YBCO slabs which allows the extension of the reflectance bands to cover all fiber optics wavelengths for the entire angle of incidence interval [0-1.5 radian] and for both polarization modes. During that, the structure thickness was optimized by varying the iteration number and the optical thickness of Fibonacci sequence. Finally, the optical behavior of the reflector was tested when changing the ambient temperature.

Statistical Optimization Influence on High Permittivity Gate Spacer in 16nm DG-FinFET Device

In this paper, the effect of high permittivity gate spacer on short channel effects (SCEs) for the 16 nm double-gate finFET is investigated, with the output responses optimized using L9 orthogonal array (OA) Taguchi method. The determination is done through Signal-to-noise ratio to the effectiveness of the process parameters towards four output responses such as threshold voltage (VTH), drive current (ION), leakage current (IOFF) and Subthreshold Swing (SS). The virtual fabrication of the 16 nm double-gate fin FET was performed using ANTHENA module while the electrical characteristics of the device were simulated using ATLAS module. These two modules were combined with Taguchi method to aid in designing and optimizing the process parameters. The electrical characterization was performed and significant improvement could be seen on the TiO2 and HfO2 material in terms of the ION/IOFF ratio obtained at 4.03106 and 3.61106 respectively for 0.179±12.7% V of VTH. It can be observed that when approaching a higher value of dielectric constant (high-K), the ION increases while the SS and IOFF decreases. As conclusion, the output responses from high-K materials have been proven to meet the minimum requirement by International Technology Roadmap Semiconductor (ITRS) 2013 for high performance Multi-Gate technology for the year 2015.

A compendium and meta-analysis of flatband potentials for TiO2, ZnO, and SnO2 semiconductors in aqueous media

Semiconductor/electrolyte interfaces are of great interest to numerous scientific fields including renewable energy, (photo)electrochemistry, and energy storage. The semiconductor flatband potential is a key parameter in locating the conduction band minimum or valence band maximum of the semiconductor material in electrolyte. Despite its importance for quantifying the energetic location of the semiconductor bands, literature reports for the same material demonstrate significant variability in the flatband potential. In this compendium and meta-analysis, reported flatband potentials of the common semiconductor materials TiO2, SnO2, and ZnO in aqueous electrolyte were compiled and assessed to quantify the spread in literature flatband potentials as well as determine the factors that lead to the significant spread. For TiO2, SnO2, and ZnO, literature flatband potentials referenced to the reversible hydrogen electrode span a range of nearly 2 V each. Flatband potential tabulations were separated by variables such as the solution pH, the crystalline polymorph, the crystal facet, the morphology, and the dimensions or combinations of these variables to assess the factors that contribute to the observed spread. Important and surprising findings from these categorizations are summarized: (1) Even for the narrowest categorizations, the spread in flatband potential is still large. (2) Flatband potentials of TiO2 and SnO2 follow the expected Nernstian dependence with solution pH. ZnO materials deviate from this Nernstian dependence. (3) In the aggregate, there is no statistically significant difference in the reported flatband potentials of anatase and rutile TiO2. Single crystal tabulations were the only distributions to have statistically significant differences in the flatband potential between anatase and rutile TiO2. (4) Anatase TiO2 materials with a nanotube morphology appear to have a +400 mV difference in mean flatband potential compared to all other morphologies, but we argue that this is likely due to widespread misuse of the Mott–Schottky analysis. Other interesting findings are revealed within the spread of literature flatband potentials, and possible explanations are provided to generate discussion. We also briefly review and discuss common techniques that were used to determine the flatband potential and the pitfalls/criticisms of these techniques. Last, we discuss some ways in which future research on the determination of the flatband potential can be performed to improve the reliability of reported values and the quality of the work. In total, the results from this meta-analysis suggest multiple factors can affect the measured flatband potential and that an abundance of caution should be applied when attempting to quantify the flatband potential of complex or nanostructured systems.

Toward high‐efficiency stable 2D/3D perovskite solar cells by incorporating multifunctional CNT:TiO2 additives into 3D perovskite layer

AbstractThe power conversion efficiency (PCE) of 2D/3D perovskite solar cells (PSCs) is still significantly low compared with 3D PSCs due to the poor charge transport ability of 2D perovskite thin films and a large number of defects in 3D thin films. Herein, to address these two issues, multifunctional TiO2 nanoparticles (NPs)‐modified carbon nanotubes (CNT:TiO2) additives are incorporated into 3D perovskite layer for the first time, and demonstrate three positive effects for CNT:TiO2 material application: firstly, it passivates the defect state of the 3D perovskite layer and enhances the charge mobility of the 3D layer; secondly, its interaction with the 2D film increases the conductivity of the 2D layer and produces the interface polarization electric field to promote the hole extraction. As a consequence, not only the PCE of the optimized 2D/3D PSCs with the CNT:TiO2 is greatly improved to 22.7% from 19.8% of the control PSCs, but also the stability is significantly improved.image

Removal of chlorhexidine digluconate from aqueous solution by heterogenous photocatalysis using sunlight-driven Ni-doped TiO2 material

Photoactive Ni-TiO2 was synthesized through green hydrothermal method with preferential photocatalytic performance in visible and solar light for synthetic and formulated wastewater treatment. Incorporation of this transition metal into TiO2 was examined by XRD, FTIR, UV–visible DRS, XPS, SEM-EDS and HRTEM analysis. According to the Langmuir–Hinshelwood model, the photodegradation of the chlorhexidine digluconate under solar (R2=0.986) and simulated visible light (R2=0.982), follows a pseudo-first-order kinetics. The interaction of operational fractions, such as S/C ratio, irradiation time, and pH of the reaction mixture, were evaluated using the RSM. Although complete mineralization of CHD was not achieved using Ni-TiO2 under visible light, but the parent compound was mineralized to some extent, as demonstrated by TOC reduction (85.71%-synthetic wastewater and 61.17%-formulated wastewater), UV254 (89.91% synthetic wastewater and 55.39%-formulated wastewater) and UV280 (68.23%-synthetic wastewater and 68.23%-formulated wastewater) absorbance variations. Based on the identified transformed products, the possible degradation pathway was proposed and bacterial susceptibility test on Bacillus cereus DPAML065 was performed to evaluate the toxicity of oxidation intermediates. Comparative studies about energy consumption and removal efficiency during simulated visible light/Ni-TiO2 and sunlight/ Ni-TiO2 mediated treatment system for formulated wastewater revealed that sunlight/ Ni-TiO2 mediated treatment system was high energy efficient (1.67 kWhKg-1) system.

Smart Surfaces: Photocatalytic Degradation of Priority Pollutants on TiO2-Based Coatings in Indoor and Outdoor Environments-Principles and Mechanisms.

Heterogeneous photocatalysis using semiconductor oxides such as TiO2, provides an up-and-coming solution for the degradation of environmental pollutants compared with other technologies. TiO2-containing construction materials and paints activated by UV/solar light destroy the ozone precursors NO and NO2 up to 80% and 30%, respectively. The majority of TiO2 materials developed so far are primarily for outdoor use. In recent years, substantial efforts have been made to investigate further the photocatalytic activity of materials containing TiO2 toward priority air pollutants such as NO, NO2, and volatile organic compounds (VOCs) frequently accumulated at high concentration levels, particularly in indoor spaces. The intention of the investigations was to modify the titanium dioxide (TiO2), so that it may be activated by visible light and subsequently used as additive in building envelop materials and indoor paints. This has been achieved, to a high extent, through doping of TiO2 with transition metals such as V, Cr, Fe, Mn, Ni, Co, Cu, and Zn, which reduce the energy gap of TiO2, facilitating the generation of free electrons and holes, thus, extending the absorption spectral range of modified TiO2 to the area of visible light (bathochromic shift-redshift). A substantial problem using TiO2-containing paints and other building materials in indoor environments is the formation of byproducts, e.g., formaldehyde, through the heterogeneous photocatalytic reaction of TiO2 with organic matrices. This affects the air quality in confined spaces and, thus, becomes a possible risk for human health and wellbeing. This work describes the principles and mechanisms of the photocatalytic reactions at the air/catalyst interface of priority pollutants such as NO, benzene, and toluene as individual compounds or mixtures. Emphasis is placed on the reaction and recombination processes of the charge carriers, valence band positive holes (h+) and free electrons (e−), on the surface of TiO2, and on key factors affecting the photocatalytic processes, such as humidity. A hypothesis on the role of aromatic compounds in suppressing the recombination process (h+ and e−) is formulated and discussed. Furthermore, the results of the photocatalytic degradation of NO under visible light conditions using different admixtures of TiO2 and manganese doped (Mn–TiO2) are presented and discussed.

Photocatalytic Oxidation of 5-Hydroxymethylfurfural Over Interfacial-Enhanced Ag/TiO2 Under Visible Light Irradiation.

Photocatalytic conversion of biomass-derived 5-hydroxyfurfural (HMF) to value-added 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) is an environmentally friendly process. Here, Ag nanoparticle (NP) supported on TiO2 (Ag/TiO2 ) materials with different interfacial structures were fabricated via incipient wetness impregnation. In the photocatalytic oxidation of 5-HMF to HMFCA, low-temperature reduction (473 K) on Ag/TiO2 could improve the photoinduced charge separation efficiency and promote the reaction due to the "enhanced" localized surface plasmon resonance (LSPR) effects achieved through strong metal-support interaction (SMSI). In particular, 2.5 % Ag/TiO2 -LTR exhibited superior performance with an HMFCA selectivity of up to 96.7 % under visible-light illumination. In contrast, the photocatalytic efficiency was greatly reduced when the reduction temperature increased to 773 K because of the encapsulation of Ag NPs by a thicker TiOx overlay, which significantly weakened visible-light harvesting. Overall, these findings offer an efficient methodology for designing interfacial enhanced plasmonic photocatalysts for the valorization of biomass.

Chemically Engineered Porous Molecular Coatings as Reactive Oxygen Species Generators and Reservoirs for Long-Lasting Self-Cleaning Textiles.

Wearable personal protective equipment that is decorated with photoactive self-cleaning materials capable of actively neutralizing biological pathogens is in high demand. Here, we developed a series of solution-processable, crystalline porous materials capable of addressing this challenge. Textiles coated with these materials exhibit a broad range of functionalities, including spontaneous reactive oxygen species (ROS) generation upon absorption of daylight, and long-term ROS storage in dark conditions. The ROS generation and storage abilities of these materials can be further improved through chemical engineering of the precursors without altering the three-dimensional assembled superstructures. In comparison with traditional TiO2 or C3 N4 self-cleaning materials, the fluorinated molecular coating material HOF-101-F shows a 10- to 60-fold enhancement of ROS generation and 10- to 20-fold greater ROS storage ability. Our results pave the way for further developing self-cleaning textile coatings for the rapid deactivation of highly infectious pathogenic bacteria under both daylight and light-free conditions.

Low-cost composite ultrafiltration membrane made from TiO2 and nanocomposite clay materials over zeolite support for oily wastewater purification and heavy metals removal

Low-cost composite ultrafiltration membrane made from TiO2 and nanocomposite clay materials over zeolite support for oily wastewater purification and heavy metals removal

Features of Cyanine Dyes Aggregation on Differently Charged Tio2 Matrices

Features of Cyanine Dyes Aggregation on Differently Charged Tio2 Matrices

Structural, dielectric, and impedance spectroscopy investigation of titanium dioxide electronic system

Titanium dioxide (TiO2) is one of the famous metal oxides, which is explored for many potential applications because of having distinctive characteristics. This article demonstrates the detailed structural and electrical properties of TiO2 material which is processed and synthesized by a high-temperature low-cost solid-state method. Dielectric parameters (dielectric constant: εr and tangent loss: tanδ), and complex impedance spectrum are inspected to evaluate the conductive, capacitive, and resistive performance of the material. The investigated material TiO2 has a large dielectric constant and low tangent loss, which makes it a potential contender for device applications at high temperatures. The imperative physiochemical properties allied with this sample may be very much useful in future electronic devices.

Fabrication of Al2O3 supported TiO2 membranes for photocatalytic applications

A facile sol–gel spin coating process to synthesise mesoporous nanocrystalline Al2O3 supported TiO2 photocatalytic membranes performance has been reported. Titania sol containing lauryl lactyl lactate surfactant as a pore forming agent was employed to improve the porous structure of TiO2 materials. The sol was spin coated on Al2O3 support to synthesise TiO2/Al2O3 membranes. The composite membranes were dried and calcined. The above procedure was repeated for three times. The fabricated TiO2 composite membrane has been utilised for the photocatalytic degradation of methylene blue dye as a model pollutant. The highest percentage degradation of about 99.25% was observed at pH 12. Such membranes can be employed very efficiently in waste water treatment systems, separation of gases and liquid mixtures, treating microorganisms and also for self-antifouling action.

Comparison of Thin Films of Titanium Dioxide Deposited by Sputtering and Sol-Gel Methods for Waveguiding Applications

In this work, TiO2 thin films were deposited onto glass substrate by two different techniques: sol-gel dip-coating (SG) and reactive DC magnetron sputtering (Sput). The prepared samples have been characterized by means of micro-Raman, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) measurements, scanning electron microscopy (SEM), UV-Visible spectrophotometry, and M-Lines spectroscopy (MLS). The micro-Raman results showed an amorphous TiO2-SG phase and the vibrational mode of TiO2-Sput is anatase phase. DSC-TGA analysis was used to investigate the thermal properties of the TiO2 material. SEM spectroscopy has shown that TiO2-SG has a disordered and more porous surface, TiO2-Sput sample is homogeneous and shows uniform distribution of densely packed well-defined grains. The obtained films have an optical transmittance varying from 60 to 88% in the visible region. The optical band gaps deduced from the transmittance are 3.48 and 3.53 eV for TiO2-SG and TiO2-Sput, respectively. The optical waveguiding measurements carried out on TiO2-SG and TiO2-Sput films show single guided modes behavior (TE0 and TM0). These measurements have allowed deducing the refractive index and thickness values that are 2.06 at 216 nm for TiO2-SG and 2.26 at 204 nm for TiO2-Sput thin films. The analysis of waveguiding properties indicates that amorphous TiO2 may prove to be more efficient in photonic device as compared to crystalline TiO2. Keywords: TiO2, thin films, sol-gel, sputtering, anatase, waveguiding.

Fabrication of Dye-Sensitized Solar Cells Using Aqueous and Ethanolic Extracts of Ixora macrothyrsa Flowers

Dye-sensitized solar cells (DSSCs) are promising types of photovoltaic cells which have the capability to generate electrical energy at low fabricationcost in comparison to the silicon crystalline solar cells. Titanium dioxide (TiO2) nanoparticles were synthesized by solvothermal method. DSSCs using Ixora macrothyrsa flowers as dye-sensitizer were fabricated using water and ethanol as solvents. The structural and surface properties of TiO2 nanoparticles were characterized using X-ray diffraction and Field Emission Scanning Electron Microscopy. The synthesized TiO2 material had tetragonal crystal structure which was highly stable and crystalline. The extracted natural dyes were characterized by UV-visible absorption spectroscopy and Fourier transform infrared (FTIR). The bandgap energy of TiO2 photoanode was studied by using UV-visible spectra and the functional group by using FTIR spectra. The photo-electrochemical parameters and efficiency of DSSC were measured using J-V measurement system. The result of J-V characteristics showed that the efficiency of DSSC’s based on TiO2 nanoparticles extracted from Ixora flowers using ethanol solvent was better than water solvent.

Nanomaterials and Rare Earths Used To Evaluate the Photocatalytic Degradation of a Dye, with Potential Use in Decontaminating Water Bodies

In this work, nanomaterials and rare earths were obtained with application in the degradation of dyes since in the developing countries the decontamination of water bodies is essential. We used TiO2 for incorporation of rare earths applied to photocatalytic activity in degradation of methyl blue due to its high chemical stability and corrosion resistance. We obtain nanostructured materials of TiO2, TiO2: Ln3+ (Ln3+ = Sm3+, Gd3+ and Yb3+) by sol gel method, for decontamination of dye such as methylene blue in surface water bodies. Through x-ray diffraction, we found that anatase-rutile phase was achieved in TiO2 and tetragonal anatase phase in TiO2 : Ln3+. Size average in nanometres of 31, 37, 44 y 34 for TiO2, TiO2 : Sm3+, TiO2: Gd3+ and TiO2:Yb3+ respectively determinate by atomic force microscopy and by UV spectroscopy the energy gap (2.94, 2.87, 2.85 and 2.95) eV respectively. As for the degradation of the methylene blue dye, the best catalyst under UV radiation was TiO2 : Gd3+ with 54% degradation compared to TiO2 that presented 52%, 29% for TiO2 : Sm3+ and with 27% to TiO2 : Yb3+ determined by fluorimetry. These materials must be applied in industrial post-treatment processes using photo catalysis for the decontamination of bodies of water.

Modeling and optimization of CZTS kesterite solar cells using TiO2 as efficient electron transport layer

In this paper, a numerical simulation study via AMPS 1D simulator is carried out to investigate the degradation mechanisms occurred in hybrid Cu2(Zn,Sn)Se4 (CZTS) solar cells that use a nonporous n-type-TiO2 material as a window. The advantageous Spike-like conformation against recombination at the TiO2/CZTS interface, which is ensured by the band-engineering offset established using TiO2 material, is discussed. The influence of the geometrical and physical parameters on the device fundamental figures of merit is assessed. Besides, the degradation effect linked to both deep and tail states situated in the gap of the materials, and the effective working temperature, are taken into account. The results reveal that the actual defect type (donor or neutral) at the Cu2ZnSnS4 layer has a harsh influence on the device performance. This is attributed to the raised Shockley–Read–Hall (SRH) recombination highlighted by investigating the variation of the carrier density along the absorber layer. A low barrier height at the back contact (ϕbl = 0.1 eV) and a suitable doping level and thickness of both the window (ND = 4 × 1017 cm−3, WTiO2 = 0.02 µm) and the absorber (NA = 6.5 × 1016 cm−3, WCZTS = 3.2 µm) layers could efficiently improve the device performance.

Electrochemical fabrication and reductive doping of electrochemically reduced graphene oxide decorated with TiO2 electrode with highly enhanced photoresponse under visible light

The development of visible-light active TiO2 or TiO2-based composite materials has been extensively studied in recent years due to their wide range of applications in energy and photocatalysts. The present study reports a facile and environmentally friendly one-pot electrochemical method for the electrochemical fabrication and doping of the electrochemically reduced graphene oxide (ERGO) decorated with TiO2 nanoparticles. The electrochemical reductive doping of TiO2/ERGO composites was carried out in an aqueous solution of H2SO4, LiClO4, NaOH and KOH by a potential controlled electrochemical process. A significant shift of the absorption edge to a lower energy in the visible-light region for hydrogenated and doped TiO2/ERGO composites has been observed, which suggested that the bandgap energy of TiO2/ERGO was narrowed after electrochemical treatment. Photocurrent densities of H-, Li-, Na- and K- doped TiO2/ERGO composites were approximately 11, 12, 9 and 7 times higher than those of undoped TiO2/ERGO electrodes respectively, which indicated that the separation efficiency of photo-induced electrons and holes was improved dramatically after electrochemical hydrogenation and doping. This electrochemical reductive treatment appears to be an effective way to enhance the performance of photovoltaic devices in the visible range by improving the electrical conductivity and electron mobility.

Defective Grey TiO2 with Minuscule Anatase–Rutile Heterophase Junctions for Hydroxyl Radicals Formation in a Visible Light-Triggered Photocatalysis

The novelty of this work was to prepare a series of defect-rich colored TiO2 nanostructures, using a peroxo solvothermal-assisted, high-pressure nitrogenation method. Among these solids, certain TiO2 materials possessed a trace quantity of anatase–rutile heterojunctions, which are beneficial in obtaining high reaction rates in photocatalytic reactions. In addition, high surface area (above 100 m2/g), even when utilizing a high calcination temperature (500 °C), and absorption of light at higher wavelengths, due to the grey color of the synthesized titania, were observed as an added advantage for photocatalytic hydroxyl radical formation. In this work, we adopted a photoluminescent probe method to monitor the temporal evolution of hydroxyl radicals. As a result, promising hydroxyl radical formations were observed for all the colored samples synthesized at 400 and 500 °C, irrespective of the duration of calcination.

Single-step fabrication of highly stable amorphous TiO2 nanotubes arrays (am-TNTA) for stimulating gas-phase photoreduction of CO2 to methane

This study investigates the facile fabrication of interfacial defects assisted amorphous TiO2 nanotubes arrays (am-TNTA) for promoting gas-phase CO2 photoreduction to methane. The am-TNTA catalyst was fabricated via a one-step synthesis, without heat treatment, by anodization of Titanium in Ethylene glycol-based electrolyte in a shorter anodizing time. The samples presented a TiO2 nanostructured array with a nanotubular diameter of 100 ± 10 nm, a wall thickness of 26 ± 5 nm, and length of 3.7 ± 0.3 μm, resulting in a specific surface of 0.75 m2 g. The am-TNTA presented prolonged chemical stability, a high exposed surface area, and a large number of surface traps that can reduce the recombination of the charge carriers. The am-TNTA showed promising photoactivity when tested in the CO2 reduction reaction with water under UV irradiation with a methane production rate of 14.0 μmol gcat−1 h−1 for a pure TiO2 material without any modification procedure. This enhanced photocatalytic activity can be explained in terms of surface defects of the amorphous structure, mainly OH groups that can act as electron traps for increasing the electron lifetime. The CO2 interacts directly with those traps, forming carbonate species, which favors the catalytic conversion to methane. The am-TNTA also exhibited a high stability during six reaction cycles. The photocatalytic activity, the significantly reduced time for synthesis, and high stability for continuous CH4 production make this nanomaterial a potential candidate for a sustainable CO2 reduction process and can be employed for other energy applications.

Structural, Morphological, and Optical Investigation of Ag‐Doped TiO2/rGO Nanocomposite Synthesized by Ex Situ Route

AbstractIn the present paper, the modified properties of widely used TiO2 material by forming its Ag‐doped TiO2/rGO nanocomposite are studied. The structural investigation by X‐ray diffraction (XRD) reveals the formation of single anatase phase that do not altere even in composite with a decrement in crystallite size from 12 to 8 nm. The SEM micrographs confirm nanosheets formation of rGO while uniform grain shapes of TiO2 nanoparticles (NPs). Fourier transformed infrared spectroscopy (FTIR) remarkably deduce the specific bands to support individual characteristics. However, UV‐vis spectroscopy exposes absorption shift toward the visible side by the effect of silver doping and rGO nanocomposite formation. Similarly, the energy band gap calculation by Tauc plots reveals a reduction in band gap from 3.26 to 3.18 eV. So, these successfully tuned properties of TiO2 open the new path to utilize it in various forthcoming optoelectronic devices.