TiO2 Samples Research Articles

Effect of annealing temperature on the structural, electronic and magnetic properties of Co doped TiO2 nanoparticles: An investigation by synchrotron-based experimental techniques

The present study examines the effect of annealing temperature on the structural, electronic and magnetic properties of Co-doped TiO2 (TCO) nanoparticles (NPs) synthesized by the sol-gel method. X-ray powder diffractograms of TCO NPs annealed at 400, 600 and 800 °C exhibited the monophasic anatase, diphase (anatase and rutile) and monophasic rutile structures respectively. A morphological investigation using high-resolution scanning electron microscopy (HR-SEM) reveals the presence of nanoparticles with diameters ranging from ∼11 to ∼51 nm. The widening and shifting of the most intense Eg peak in Raman studies and SEM images of TCO NPs suggest Co incorporation in the TiO2 matrix and the formation of oxygen vacancies. Magnetic measurements of TCO at room temperature demonstrate ferromagnetic behaviour which is caused by the existence of oxygen vacancies and the doped Co content. Element specific technique, soft X-ray magnetic circular dichroism (XMCD) was used to study the magnetism in Co doped TiO2 samples. The estimated total magnetic moment by XMCD was in the range of ∼1.3 ± 0.1–2.3 ± 0.2 μB/Co. This huge magnetization was first time observed by the surface-sensitive Total Electron Yield (TEY) mode. The estimated saturation magnetic moment is in the range of 1.0–1.5 μB/Co, also consistent with XMCD analysis and cluster model calculation. The results obtained by XMCD recommend an intrinsic behaviour of ferromagnetism. The X-ray absorption spectra (XAS) of Co-doped TiO2 nanoparticles at Ti L2,3 and Co L2,3 -edge in TEY mode concludes that the valence states of Co and Ti ions are in 2 + and 4 + respectively. Cluster model calculation also confirmed that Co ions are in a 2 + valence state with D2 h high spin crystal-field symmetry at the surface while a random crystal field symmetry in bulk has been observed which is well consistent with experimental data.

Optimization of PEC and photocathodic protection performance of TiO2/CuInS2 heterojunction photoanodes

The establishment of heterojunction is a powerful strategy to enhance the photoresponse performance of photoanode. Here, TiO2/CuInS2 (T/CIS) composites were prepared via a two-step hydrothermal method, and their morphologies were controlled by adjusting the reaction time. The absorption spectra show that CuInS2 can significantly improve the absorption of visible light. The T/CIS2 (2 h reaction time) photoanode exhibited the most outstanding photoelectrochemical (PEC) performance, with a photocurrent density of 168% that of the pure TiO2 photoanode. Under simulated sunlight, this photoanode can supply a protective photocurrent of 0.49 mA cm−2 and a protective voltage of 0.36 V to stainless steel (304ss), which are about 4 and 2 times those of the TiO2 sample. The enhancement in the photocathodic protection performance is attributed to enlarged visible light absorbance and higher charge separation rate. This study demonstrates that the TiO2/CuInS2 photoanode is a promising candidate for application in photoinduced cathodic protection of metallic materials.

Ti3C2 MXene assembled with TiO2 for efficient photocatalytic mineralization of gaseous o-xylene

In the research of photocatalytic removal of VOCs, the mineralization rate of organic pollutants has been ignored. High mineralization rate means the reduction of intermediates, which is more conducive to environmental protection and photocatalysts stability. In this work, we successfully compounded conductive Ti3C2 with TiO2 for photocatalytic degradation of o-xylene. The production of CO2 by 1 % Ti3C2-TiO2 composite was about twice than that of pure TiO2. The results of PL and photocurrent response showed that 1 % Ti3C2-TiO2 composite had less carrier recombination and higher photocurrent response, which endows its stronger photocatalytic oxidation ability than TiO2. The in-situ infrared spectroscopy revealed that more aromatic anhydride species deposited on the TiO2 surface and led to the less mineralization degree for TiO2 sample. The four-cycle tests further confirmed the better stability of 1 % Ti3C2-TiO2 sample. This work disclosed the role of Ti3C2 in enhancing the mineralization of VOCs, which may provide a new perspective for the design of high-efficiency photocatalysts.

SYNTHESIS OF TITANIUM (IV) OXIDE AND PROSPECTS OF ITS APPLICATION IN ADSORPTION AND PHOTOCATALYTIC WATER TREATMENT PROCESSES

Pure titanium oxide (TiO2(ng)) and modified with potassium fluoride with different percentage of dopant: 2, 7, 15% (TiO2(2F), TiO2(7F), TiO2(15F), respectively) samples were synthesized by low-temperature sol-gel method. The morphology and particle size of pure titanium(IV) oxide (TiO2(ng)) and titanium(IV) oxide doped with potassium fluoride (TiO2(2F)) were investigated by scanning electron microscopy method. It was found that the doping with potassium fluoride does not have a significant effect on the shape of the particles, but allows to narrow the particle size distribution. X-ray phase and X-ray structural analyzes of the obtained TiO2 samples showed that the predominant phases of pure TiO2 were rutile and brookite, and only anatase contained in TiO2 doped with KF. The porous structure of the synthesized TiO2 samples was studied by the method of low-temperature nitrogen adsorption-desorption. It was found that the all obtained TiO2 samples belonged to porous adsorbents, the adsorption of which carried out monolayer. The adsorption properties of the obtained TiO2 samples were investigated using a model pollutant, phenol. It was found that the best adsorption properties showed TiO2(2F) sample at all three concentrations of pollutant. The maximum adsorption degree of phenol with an initial concentration of 3.125 mg/dm3 (18%) was achieved by TiO2(2F) sample; with an initial phenol concentration of 6.25 mg/dm3 was 21.5%, and at an initial phenol concentration of 12.5 mg/dm3 it was 42%. The highest photocatatical activity was shown by the sample of low-doped fluorine TiO2, in the presence of which phenol was decomposed by 68%.

Mechanistic Exploration of Visible Light-Activated Carbon/TiO2 Hybrid Dots Damaging Bacterial Cells

The carbon/TiO2 hybrid dots (C/TiO2-Dots) are structurally TiO2 nanoparticles (in the order of 25 nm in diameter from commercially available colloidal TiO2 samples) surface-attached by nanoscale carbon domains with organic moieties, thus equivalent to hybrids of individual TiO2 nanoparticles each decorated with many carbon dots. These hybrid dots with exposure to visible light exhibit potent antibacterial properties, similar to those found in neat carbon dots with the same light activation. The results from the use of established scavengers for reactive oxygen species (ROS) to “quench” the antibacterial activities, an indication for shared mechanistic origins, are also similar. The findings in experiments on probing biological consequences of the antibacterial action suggest that the visible light-activated C/TiO2-Dots cause significant damage to the bacterial cell membrane, resulting in higher permeability, with the associated oxidative stress leading to lipid peroxidation, inhibiting bacterial growth. The induced bacterial cell damage could be observed more directly in the transmission electron microscopy (TEM) imaging. Opportunities for the further development of the hybrid dots platform for a variety of antibacterial applications are discussed.

Performance of commercial titanium dioxide samples in terms of dye photodegradation assessed using smartphone-based measurements

The photocatalytic activity of four titanium dioxide samples (TiO2-P25 Degussa, PC105 Millennium, PC500 Millennium, and Anatase) was studied in the degradation of dyes (Congo Red (CR), Methyl Orange (MO), and Direct Red 23 (DR23)) using cost-effective smartphone-based analysis. The obtained kinetic curves are well described by the first-order kinetic model. It was established that the phase composition, the size of the particles, and the specific surface area of ​​the catalyst have a significant effect on the photocatalytic activity of the studied TiO2 samples. It was investigated that the Millennium PC500 sample is the most effective photocatalyst due to a large specific surface area and a small particle size (8 nm). TiO2-P25 Degussa and Anatase also demonstrate a high photocatalytic activity in the degradation of CR and DR23 dyes, which can be explained by the accelerated process of electron transfer between the anatase and rutile phases. For the PC105 sample, a higher CR photodegradation efficiency is observed compared to PC500. It can be concluded that heterogeneous photocatalysis is an effective method for the removal of toxic dyes from wastewater. With the use of smartphone-based analysis, it is possible monitoring the photodegradation kinetics in real-time.

Copper Oxide Coupled Titanium Dioxide (CuO/TiO<sub>2</sub>) Nanocomposite Photocatalyst for Degradation of Methyl Orange Dye

Titanium dioxide (TiO2) was utilized in photocatalysis applications due to their non- toxic, cheap and high photocatalytic activity. However, its photocatalytic reaction is limited by low surface area as well as the rapid recombination of photogenerated electron-hole pairs and only has ability to absorb a small fraction (<5%) of indoor light. In this study, copper oxide coupled titanium dioxide (CuO/TiO2) nanocomposite photocatalyst was synthesized using hydrothermal method. The synthesised photocatalyst was characterized by using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), Scanning electron microscopy(SEM), Brunauer, Emmett, teller (BET) and UV- Visible Spectroscopy. Spectra obtained from FTIR have proved that there are existence of O-H stretching, O-H vibration and metal-O bond that correlates to the functional groups of the samples. As affirmed by XRD analysis, highly crystalline rutile TiO2 phase was obtained for pure TiO2 samples. Rutile TiO2 phase is remained and additional peaks belong to copper oxide was observed for CuO/TiO2 nanocomposite photocatalyst sample. This finding suggesting that copper oxide was successfully loaded onto TiO2. Morphological study from SEM shows the presence of short rod-like particles of copper oxide and agglomerated TiO2 bulk particles. BET surface area for CuO, TiO2 and CuO/TiO2 nanocomposite photocatalysts were 20.50 m2/g, 15.26 m2/g and 17.13 m2/g, respectively. The photocatalytic degradation of methyl orange (MO) was found to be 85.0% using CuO/TiO2 nanocomposite photocatalyst, which is better than pure TiO2 and pure CuO after 3 hours reaction.

Photocatalytic degradation abilities of binary core-shell SiO2@mZrO2/TiO2 nanocomposites: Characterization, kinetic and thermodynamic study of metoclopramide (MCP) eradication for water purification

In this work, SiO2@ZrO2/TiO2 nanoparticles have been synthesized and characterized by FTIR, XRD, SEM-EDX, TEM, BET-BJH, TG-DTA and DRS analyses. In addition, the photocatalytic activity of the nanoparticles prepared has been investigated in the photodegradation and photomineralization of metoclopramide (MCP). In particular, hexadecylamine (HDA) was used in the coating process functions as the soft template for the preparation of silica@mesostructured metal oxide core-shell nanosphere. A band gap energy (Eg) of 2.94 eV was found for the SiO2@ZrO2/TiO2 sample, which corresponds to a 421.71 nm absorption edge wavelength. SiO2@ZrO2/TiO2 nanoparticles showed unusually smaller band gap energy in comparison with their parent oxides; namely, TiO2 (3.20 eV) and ZrO2 (5.02 eV), which could be due to the generation of heterojunctions between the two phases. The best photocatalytic activity was obtained at pH 5 (near the pHpzc: 4), 0.7 g/L of the catalyst, and 15 mg/L MCP. A Hinshelwood kinetic analysis of the photodegradation process yielded a rate constant of 0.033 min−1 with a t1/2 value of 21 min. When the photodegraded MCP solutions were subjected to the COD experiment k = 6.76 min−1 (t1/2 = 18.05 min) were obtained for the mineralized MCP molecules. An activation energy of 15.3 kJ/mol was obtained for the process using the Arrhenius equation. A negative ΔS‡ (-0.23 kJ/mol) with positive ΔH‡ and ΔG‡ values were obtained for the MCP photodegradation by the SiO2@ZrO2/TiO2 composite.

TiO2–CU Thin Film Material for Optical Hydrogen Gas Sensor Applications

Purpose: Several scientific researches are underway to investigate the possibility of using various green energies. Hydrogen gas is a candidate of such research, since its use as a fuel in automobiles releases pure water, a recyclable biproduct. But, the leakages of the gas are detrimental to its application due to its low auto ignition energy of 20 μj, wider air flame limit of 4-75 % and high flame velocity of 3.46 ms-1. This study involved fabrication of an optical gas sensor for sensing the leakage levels of hydrogen gas to a surrounding.
 Methodology: Titanium dioxide thin films of thicknesses 47.7, 56.2, 82.3, 100.4 and 120.5 nm were deposited on both microscope and FTO glass slides using DC magnetron sputtering technique and characterized as primate and annealed at 400 and 500oC. Copper (Cu) catalytic layers of 5.6, 10.2, 17.3 and 21.0 nm were deposited using EDWARDS AUTO 306 Magnetron sputtering system on an optimized 100.4 nm TiO2 sample, annealed at 400oC. Optical properties were deduced from transmittance and absorbance spectra measured using 1800 Shimadzu spectrophotometer in the optimum range of 280-800 nm through simulation. The optical behavior of the films was generated using SCOUT software and analyzed using ORIGIN 9.1 64-bit software.
 Results: The energy band gap decreased with material thickness from 4.2±0.05 eV for 47.7 nm film to 3.9±0.05 eV for 100.4 nm films. 120.5 nm films showed higher energy gap of 4.0±0.05 eV. Transmittance decreased with increase in thickness probably due to agglomeration of film particles. The energy gap of the 100.4 nm, TiO2 thin films annealed at 400oC was 3.9±0.05 eV. This is a material quality of the anatase phase. The copper surface layer increased absorption in the higher wavelength region. The energy band gaps were reduced from 3.9 to 3.8±0.05 eV with increased coverage. Self-limiting at 17.3 nm copper overlayer realized increased energy gap to 4.1±0.05 eV. A lower energy band gap range of 3.9-3.8±0.05 eV was realized when FTO substrates were used. The transmittance decreased with increased H2 gas concentration. The optical energy gap reduced from 4.1±0.05 eV in 0 ccm to 3.9±0.05 eV in 50 ccm of hydrogen gas concentration. The sensitivity increased from 0.3 % in 0ccm to 3.9 % in 50 ccm hydrogen gas concentration. An average sensitivity of 2.0 % was realized for films fabricated on FTO substrate. This is higher than 1.7 % reported earlier. The material gas sensing potential was done at room temperature. The fabricated sensor material showed higher sensitivity and lower temperature operation and is furthermore, expected to be cheaper and safer
 Unique Contribution to Theory, Policy and Practices: Though, in order to realize a more portable stand-alone gas sensor, an investigation on an ideal photon type source that incorporates the material is recommended. Further, extension of this study on structure and morphology of the film is essential to understand its sensing behavior.

Maintenance of initial lightness on mortars treated with TiO2 in the long term

The importance of colours is not limited to the aesthetic but also other parameters like thermal comfort. Painting light colours on the building's external surfaces increases its reflection of solar radiation, reducing the heat gains. In contrast, dark colours can increase solar heat gains by absorbing more radiation. Regarding the TiO2 answer to the lightness on the facade, different samples of TiO2 were tested. First, in the laboratory for methylene blue dye degradation and second in a natural environment using different forms of treatment (powder and suspension) on mortars, measured by a spectrophotometer over three years to determine the loss of lightness over time. The methylene blue test showed that the TiO2-P25p, TiO2-PC-S7s, and TiO2-E502s samples had the same effectiveness after exposure to artificial UV radiation, while the TiO2-PC105p sample presented the worst performance. Concerning the lightness, after thirty-seven months of the natural exposition, the white painted specimens had the best results than specimens with TiO2 suspensions and specimens with TiO2 in powder. Beyond the absorptivity, the white painted specimens could be considered with low absorptivity. In contrast, the specimens treated with TiO2 suspension and those treated with TiO2 powder could be medium absorptivity. Regarding the visual aesthetic perception, the study concludes that for the final user, there is no great difference in white painted specimens, while for the other (powder and suspension), the colour difference can be noticed well over three years of exposure.

Experimental optical and structural properties of ZnS, MgF2, Ta2O5, Al2O3 and TiO2 deposited by electron beam evaporation for optimum anti-reflective coating designs

MgF2, ZnS, Ta2O5, Al2O3 and TiO2 are some of the most common dielectric materials actually used in solar cells as anti-reflective coatings. For such purpose, they have been deposited by electron beam evaporation, which is one of the preferred technique in industrial settings. In this work we aim to understand the relationship between their optical and physical properties and deposition parameters and thicknesses, being spectroscopic ellipsometry the main technique used for such issue. MgF2 and ZnS have demonstrated rather good optical quality except for the thinnest samples. For Ta2O5, O2 flow during growth has been revealed as critical parameter for ensuring the proper composition of the layer. Al2O3 samples showed a very important amount of Al hydroxide, which is detrimental of the optical quality of these layers. TiO2 samples have also contamination problems, in this case due to oxygen species and Ti3+ oxide presence. For all these oxides, optical properties are clearly influenced by layer thickness. The layer optical parameters n and k have been determined as a function of wavelength (300–1800 nm) and validated against experimental reflectance and transmittance data. Finally, the impact that the proper knowledge of n and k values have when designing broad-band anti-reflective coatings for III-V multijunction solar cells is quantified in terms of short-circuit current relative increase.

Construction of an all-solid-state Z-scheme Ag@Ag3PO4/TiO2-(F2) heterostructure with enhanced photocatalytic activity, photocorrosion resistance and mechanism insight

Photocatalysis is still a promising technology to alleviate the antibiotic residual problem of wastewater in the ecological environment. Herein, an all-solid-state Z-scheme Ag@Ag3PO4/TiO2-(F2) (TFAP) heterojunction photocatalyst was constructed using the hydrothermal method for the first time. The photocatalytic performance of TFAP nanocomposites for tetracycline hydrochloride (TCH) degradation was evaluated under simulated sunlight. The prepared materials were characterized by XRD, FE-SEM, TEM, BET, FT-IR, UVvis DRS, XPS, PL, and ESR measurements. The TFAP nanocomposites showed high degradation efficiency and excellent repeatability to TCH destruction. Among them, the (TFAP 1–1) nanocomposite has a lower bandgap energy (1.80 eV), a larger specific surface area (53.48 m2/g), and a lower electron-hole recombination rate. After 2.5 h of simulated sunlight irradiation, the degradation rate of the 200 mg/L (TFAP 1–1) nanocomposite (k = 0.0154 min−1) to 10 mg/L TCH reached 94.14%, which was much higher than that of the pure TiO2, TiOF2, and Ag3PO4 samples. The experimental results demonstrated that TiO2 was generated as an intermediate product during the chemical reaction process between Ag3PO4 and TiOF2. Additionally, Ag nanoparticles were formed in the Ag3PO4/TiO2/TiOF2 heterojunction system. An electric field was formed between Ag3PO4 and Ag, enhancing the visible light absorption ability. Because of the Schottky potential difference, the electrons accumulate in Ag nanoparticles, thus enhancing the photocorrosion resistance of Ag3PO4. Additionally, the localized surface plasmon resonance (LSPR) effect of Ag nanoparticles greatly promoted the separation of carriers at the interface of the heterojunction. The LSPR effect leads to the co-oscillation of free electrons, which leads to the strong absorption of electromagnetic energy and enhances the photocatalytic performance of the heterojunction. The Ag@Ag3PO4 nanocomposites acted as electron transport media for an all-solid-state Z-scheme TFAP heterojunction system. This study provides some in-depth insights into the structural design of Z-scheme heterojunctions, which have certain implications for other catalytic systems.

Synthesis and photocatalytic potential of Nd-doped TiO2 under UV and solar light irradiation using a sol-gel ultrasonication method

Sol-gel ultrasonication process was used to synthesize doped TiO2 nanoparticles. Nd-doped TiO2 nanoparticles sample structures were characterized by X-ray powder diffraction (XRD) analysis, scanning electron microscopy (SEM), UV–Vis diffuse reflectance spectroscopy (DRS), FTIR, Energy dispersive spectroscopy (EDS). The photo-catalytic efficiency of the prepared sample was confirmed by the degradation of methylene blue in aqueous solution under ultraviolet (λ > 365) irradiation and solar light. According to XRD findings, virgin samples include anatase and rutile TiO2 (16.97 nm), while Nd-doped TiO2 (6.41 nm) samples contain anatase TiO2 solely. Doping of Nd on titanium dioxide resulted in a drop in the energy band gap from 3.23 eV to 3.16 eV. After modification, this transformation has resulted in a noticeable increase in photocatalyst activity. The photodegradation efficiency of Nd-doped TiO2 was found 99.11% under ultraviolet radiation in 60 min and 96.42% under solar light in 180 min, due to its smaller size, which provided a high surface area for the photocatalytic activity and enhanced the degradation efficiency of the photocatalyst.

Facile modification of TiO2 nanoparticles with H2O2 + NH4F for enhanced visible light photodegradation of rhodamine B and methylene blue

We report a facile modification method to increase the visible light activity of TiO2 samples. We use titanium isopropoxide (TTIP) as the raw Ti source, hydrolyzing in acidic and alkaline solutions, respectively, to fabricate different TiO2 samples as raw TiO2 together with P25-TiO2. Only hydrogen peroxide and ammonia fluoride are used for this facile modification method, and three TiO2 samples are modified for the visible light degradation. This method could promote the transformation of crystalline TiO2 from rutile to anatase, increase the specific surface area, and the bandgap of samples shift to lower energy (2.2 – 3.0 eV) after the modification. For the visible light photodegradation tests, all the three modified samples show a higher visible light photodegradation efficiency. The highest kinetic constant of Rhodamine B and methylene blue degradation is 7 and 2 times that of P25, respectively. Additionally, TiO2 fabricated by TTIP in alkaline solution and its as-modified sample show the highest adsorption of methylene blue dye, whose adsorption rate reaches 9 times that of P25. Thus, the present facile modification can effectively improve the photocatalytic ability of TiO2 under visible light.

The Role of Vacancies in a Ti2CTx MXene‐Derived Catalyst for Butane Oxidative Dehydrogenation

AbstractMXenes are a new family of 2D carbides or nitrides that have attracted attention due to their layered structure, tunable surface groups and high electrical conductivity. Here, we report for the first time that the Ti2CTx MXene catalyses the selective oxidative dehydrogenation of n‐butane to butenes and 1,3‐butadiene. This catalyst showed higher intrinsic activity compared to a commercial TiC and TiO2 samples in terms of C4 olefin formation rate. We propose that the stabilisation of structural vacancies and the change in composition (from a carbide to a mixed phase oxide) in the MXene causes its higher catalytic activity. These vacancies can lead to a higher concentration of unpaired electrons in the MXene‐derived material, enhancing its nucleophilic properties and favouring the production of olefins.

Visible-Light-Active Black TiO2 Nanoparticles with Efficient Photocatalytic Performance for Degradation of Pharmaceuticals.

Special attention has recently been paid to surface-defective titanium dioxide and black TiO2 with advanced optical, electrical, and photocatalytic properties. Synthesis of these materials for photodegradation and mineralization of persistent organic pollutants in water, especially under visible radiation, presents interest from scientific and application points of view. Chemical reduction by heating a TiO2 and NaBH4 mixture at 350 °C successfully introduced Ti3+ defects and oxygen vacancies at the surface of TiO2, with an increase in the photocatalytic degradation of amoxicillin—an antibiotic that is present in wastewater due to its intense use in human and animal medicine. Three TiO2 samples were prepared at different annealing temperatures to control the ratio between anatase and rutile and were subjected to chemical reduction. Electron paramagnetic resonance investigations showed that the formation of surface Ti3+ defects in a high concentration occurred mainly in the anatase sample annealed at 400 °C, contributing to the bandgap reduction from 3.32 eV to 2.92 eV. The reduced band gap enhances visible light absorption and the efficiency of photocatalysis. The nanoparticles of ~90 m2/g specific surface area and 12 nm average size exhibit ~100% efficiency in the degradation of amoxicillin under simulated solar irradiation compared with pristine TiO2. Mineralization of amoxicillin and by-products was over 75% after 48 h irradiation for the anatase sample, where the Ti3+ defects were present in a higher concentration at the catalyst’s surface.

Microwave-assisted reduction of Ti species in MgH2-TiO2 composite and its effect on hydrogen storage

The goal of this work is to shed light on the significant dehydrogenation behavior of MgH2-TiO2 composite exposed to microwave irradiation, and the changes in chemical state of titanium species that occur as a result. It is discovered that the reduced titanium oxide (TiO2-x) formed during ball milling can significantly absorb microwave radiation and act as “hot spots”, such that the MgH2 with 25 wt% TiO2 sample is nearly completed dehydrogenated at a constant temperature of 220 °C in a microwave field. Upon full dehydrogenation, the microwave irradiated sample significantly absorbs 1.25 wt% H2 within 600 sec and 4.25 wt% H2 within 10 h at 25 °C under 1 bar of hydrogen. Characterization results of these samples show that microwave irradiation assists the uniform dispersal of defective TiO2-x species around Mg/MgH2 particles and further promotes the reduction of Ti4+ to lower valence states, for better electron transfer between Mg2+ and H-. HRTEM images as well reveal that part of Mg grain size falls around 10 nm, which is believed to significantly enhance the hydrogen sorption as observed. Our findings show that the synergistic effects of microwave irradiation and heat may advance MgH2 further to practical applications.

Investigation of the Atomic Layer Deposition of the Titanium Dioxide (TiO2) Film as pH Sensor Using a Switched Capacitor Amplifier

The electrical and chemical properties of the titanium dioxide (TiO2) coated spirals grown by the atomic layer deposition (ALD) technique in two different temperatures of 150 °C and 300 °C are studied. The thickness of the TiO2 layers studied are 20, 40, and 80 nm. A switched capacitor amplifier is used to investigate the pH response and the capacitance of the samples. It is found that the performance of the TiO2 samples depends on either the thickness or the deposition temperature due to the differences in the physical properties of the oxide layer such as surface roughness and film density. The high temperature samples are more crystalline, whereas the low temperature samples are more amorphous. Since there is a low pass filter effect in the electrolyte–sample interface, the TiO2 coated samples show the better response to the pH change for the high temperature samples as the sensor surface area for binding the hydrogen ions is larger and the charge transfer resistance is smaller. Furthermore, more roughness on the surface can be obtained by increasing the thickness, which reduces the charge transfer resistance. In this study, the 80 nm sample deposited at 300 °C gives the best pH response of 40 mV/pH.

Computational assisted tuning of Co-doped TiO2 nanoparticles for ammonia detection at room temperatures

Improved gas sensors based on pure anatase TiO2 and Co-doped TiO2 nanoparticles were evaluated. A cobalt-doped TiO2 nanoparticle with a diameter of 40 nm was first synthesized. The morphology of the nanoparticles was analyzed by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The doped Co ion was confirmed to have entered the TiO2 lattice. Subsequently, gas sensors with different Co-doping concentrations were developed to investigate gas sensitivity to NH3. Compared with pure anatase TiO2 operating at 180 °C, Co-doped TiO2 samples were developed as NH3 gas sensors operating at room temperature. The 20% Co-doped sample exhibited the best performance, with a response value of 14 for 50 ppm NH3, which was 7 times higher than that of pure TiO2. The response and recovery times of the sensor were only 25 and 48 s, respectively, and exhibited both good stability and selectivity. Based on density functional theory (DFT), the calculated bandgap of Co-doped TiO2 decreased by 72% compared to pure TiO2. Structural simulation and mechanism analysis elucidated the good gas-sensing performance at room temperature and the property enhancement of the Co-doped TiO2 gas sensor.

Room-Temperature 181Ta(TiO2): An e-γ TDPAC Study

In this work, we report on the hyperfine parameters of the foreign 181Ta probe in the rutile structure of the single crystal TiO2 using the e−γ and γ−γ time differential perturbed angular correlation (TDPAC) technique. We implanted 181Hf ions into a sample of single crystal rutile TiO2 in the Bonn Isotope Separator. The implanted sample was then thermally annealed at a temperature of 873 K for 315 min in a vacuum. The 181Hf radioisotopes decayed by β− emission, followed by a cascade to the ground of γ rays or conversion electrons into a stable state 181Ta. The 181Ta probe substitutes the Ti lattice site with a unique nuclear quadrupole interaction, allowing for the precise measurement of the largest electric field gradient (Vzz) and asymmetry parameter (η). The hyperfine parameters obtained from the e−γ TDPAC spectroscopy agree with those of the γ−γ TDPAC spectroscopy at room temperature, apart from a calibration factor, both from our experiments and the literature. This suggests that the electronic recombination following the internal conversion of the L shell electron takes less time (ps) than the intermediate lifetime of the metastable 181Ta state (ns).