Annealed TiO2 Research Articles

ZnO/TiO2 heterojunction nanorod array for efficient photoelectrochemical water splitting

This study presents a novel approach utilizing a simple, stable, reproducible CV (Cyclic Voltammetry) electrodeposition method to deposit varying amounts of ZnO onto ordered TiO2 (Rutile) nanorod arrays. Comprehensive investigations were conducted on the morphology, semiconductor band-gap structure of different ZnO/Rutile composites, and their performance in photocatalytic (PC) and photoelectrochemical (PEC) hydrogen production. Results demonstrate that the ZnO/TiO2 photoanodes fabricated in this manner exhibit outstanding PC/PEC hydrogen production capabilities. Particularly noteworthy is the Z/R-15 photoanode, showcasing superior PEC performance with a photocurrent density 3.5 times higher than that of the pristine TiO2 photoanode under equivalent conditions. Furthermore, it was observed that depositing ZnO onto highly crystalline, annealed TiO2 nanorods yields optimal photoelectrical properties. Incorporating oxygen-rich vacancies in ZnO significantly enhances the photoelectrocatalytic performance of TiO2 photoanodes. The CV electrodeposition method offers valuable insights for developing efficient photocatalytic hydrogen production catalysts.

Silver-infused TiO2 nanowires and unveiling their potential for superior wastewater dye remediations.

Silver infused ultrathin TiO2 nanowires (NWs) were synthesized via a single step solvothermal approach. The crystallinity, structure, and morphology were determined to understand the physicochemical nature of the nanocomposites. The catalytic efficiency of the newly synthesized nanocatalysts was tested for the textile waste treatment taking methylene blue (MB) as model pollutant under solar light irradiations. Nearly 96% photodegradation efficiency for MB was achieved within 20 min. Furthermore, the recyclability of the photocatalyst was also studied, and the material remained stable and effective up to four consecutive runs. RESEARCH HIGHLIGHTS: Precise size-controlled synthesis of Ag-incorporated titania nanowires (ATNWs) Controlled aspect ratios, with tunable lengths and diameters (100-3 nm) via precursor and surfactant optimization Demonstrated ATNWs' efficiency in degrading toxic dye, methylene blue (MB) 96% photodegradation efficiency for MB achieved within 20 min using 3 nm thick annealed TiO2 NWs Recyclability efficiency of photocatalyst, which remained stable and effective for up to four consecutive runs.

Nitrogen plasma-induced crystallization of anodic TiO2 nanotubes for solar photoelectrochemistry

Anodic TiO2 nanotubes have gained tremendous interest due to the high specific surface area and facile growth with potential in large scale production. Their geometric features such as length, diameter, wall thickness or spacing between adjacent nanotubes can be tailored through the processing parameters maintained during the anodization. However, the as-anodized nanotubes are amorphous and for practical applications they require phase transformation. Usually, it is realized via furnace annealing. Nonetheless, taking into account the heating and cooling stages the whole process can take several hours. Moreover, furnaces usually use resistive heating, hence crystallization in furnace can be recognized as a highly time- and energy-consuming process, and the size of the sample is limited by the dimensions of uniformly heated area in the furnace. Here we show fast 30-second nitrogen plasma-induced crystallization of TiO2 nanotubes depending on the position in the plasma flame. We found a comparable photoresponse to the furnace annealed TiO2 nanotubes without significant change in their ordered morphology. The proposed method shows promising results regarding the reproducibility and stability of the fabricated photoanodes. We anticipate that the present work will contribute to wider applications of plasma for modifications of functional materials, especially in terms of the phase transitions.

The formation mechanism of (001) preferred orientation for anatase TiO2 film prepared by DC pulsed magnetron sputtering

TiO2 films were deposited by DC pulsed magnetron sputtering with different sputtering power density (SPD). Then, as-deposited TiO2 films were annealed at 600 °C and the anatase TiO2 films were obtained. XPS results showed Ti/O atom ratio was kept at 1/(1.94 ± 0.04) for all as-deposited and annealed TiO2 films. XRD results showed that the annealed TiO2 films displayed obvious anatase (001) preferred orientation, which was deposited with SPD in 0.83 W/cm2. The cross-section TEM results showed that annealed TiO2 film with anatase (001) preferred orientation consisted of a small quantity of columnar crystals and a majority of equiaxed crystals, which [001] crystallographic axis was parallel to the normal direction of film. AFM results revealed that with SPD in 0.83 W/cm2, the dominated diffusion effect controlled TiO2 film growth process with Volmer-Weber mode, which contained the nano-size anatase crystal nuclei. The [001] crystal orientation of anatase crystal nuclei was uniform parallel to the normal direction of TiO2 film growth surface. During the annealing process, the nano-size anatase crystal nuclei grew and coalesced into the large anatase grains without the change of [001] crystal orientation, which resulted in TiO2 film with obvious (001) preferred orientation.

Blue TiO2 nanotube arrays as semimetallic materials with enhanced photoelectrochemical activity towards water splitting.

In the past years there has been a great interest in self-doped TiO2 nanotubes (blue TiO2 nanotubes) compared to undoped ones owing to their high carrier density and conductivity. In this study, blue TiO2 nanotubes are investigated as photoanode materials for photoelectrochemical water splitting. Blue TiO2 nanotubes were fabricated with enhanced photoresponse behavior through electrochemical cathodic polarization on undoped and annealed TiO2 nanotubes. The annealing temperature of undoped TiO2 nanotubes was tuned before cathodic polarization, revealing that annealing at 500 °C improved the photoresponse of the nanotubes significantly. Further optimization of the blue TiO2 nanotubes was achieved by adjusting the cathodic polarization parameters. Blue TiO2 nanotubes obtained at the potential of –1.4 V (vs. SCE) with a duration of 10 min exhibited twice more photocurrent response (0.39 mA cm-2) compared to the undoped TiO2 nanotube arrays (0.19 mA cm-2). Oxygen vacancies formed through the cathodic polarization decreased charge recombination and enhanced charge transfer rate; therefore, a high photoelectrochemical activity under visible light irradiation could be achieved.

Investigation of the Influences of Post-Thermal Annealing on Physical Properties of TiO2 Thin Films Deposited by RF Sputtering

For this study, titanium dioxide (TiO2) thin films were deposited on glass substrates at room temperature by the RF magnetron sputtering technique. The preparation parameters that offer better control and reproducibility of film fabrication were first optimized. Then, the effects of post-deposition annealing temperature at 350, 450, and 550°C on the microstructure, surface morphology, and optical properties of the prepared films were investigated using X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–Visible (UV–Vis) spectrophotometry. Interestingly, XRD analysis shows that as-deposited and annealed TiO2 film possess anatase crystal structure only with a preferential orientation along the (101) plane. The intensity of the (101) diffraction peak and crystallite size are found to increase with increasing annealing temperature, which indicates an improvement in the crystallinity of the films. Raman spectra confirm that all samples possess anatase phase and the crystallinity is enhanced with increasing thermal annealing. From the analysis of SEM and AFM images, it is revealed that the heat treatment significantly affects the morphology, grain size, and surface roughness of the TiO2 films. The UV–Vis spectroscopy analysis shows that as-deposited TiO2 thin film is highly transparent in the visible region with an average transmittance about 84%, whereas the transmission decreases slightly with an increase in annealing temperature. Moreover, the optical band gap energy shows a red shift with increasing the annealing temperature.

Robust TiO2 nanorods-SiO2 core-shell coating with high-performance self-cleaning properties under visible light

Photocatalytic SiO2–TiO2 composite coatings with excellent self-cleaning properties have attracted much attention in recent years due to their promising applications in many areas such as automobile windshields, window glasses, and solar cell panel covers, etc. However, most of these coatings are of low self-cleaning capability in the visible light region due to TiO2 only absorbing ultraviolet light, which limit their practical application. Here, highly transparent coatings of the rod-like TiO2–SiO2 nanoparticles on glass substrates were prepared by a simple dip-coating process. The photocatalytic activity and self-cleaning property of the coatings were evaluated by photocatalytic degradation of methylene blue (MB) and methyl stearate (MS) under visible light irradiation. It was found that the coatings exhibited ~4% enhancement in the optical transmission of glass and a good mechanical stability. The as-prepared and annealed rod-like TiO2–SiO2 nanoparticle coatings show excellent self-cleaning properties. The results mean that the coatings have a high potential for self-cleaning applications in removal of organic pollutants under visible light such as solar cell panels, architectural glasses and optical devices, etc.

Humidity sensing and breath analyzing applications of TiO2 slanted nanorod arrays

Humidity sensing devices are fabricated using titanium dioxide nanorod arrays and studied in this work. TiO2 slanted nanorods were grown by using electron beam assisted physical evaporation technique by keeping quartz substrates at a glancing angle of 80°. TiO2 slanted nanorod arrays were characterized using XRD, FESEM with EDS, HR-TEM, and Raman spectroscopy techniques. XRD characterization reveals that as-deposited nanorods are amorphous, and annealing at 500 ℃ for 6 h leads to anatase crystal structure. FESEM confirms the growth of uniformly distributed nanorods without any cracks throughout the substrate. Further, the humidity sensing property was analyzed for both as-deposited and annealed samples with bottom gap electrode configuration. The sensing towards a wide humidity range was tested for fabricated TiO2 devices of both as-deposited and annealed TiO2 nanorods in a homemade humidity sensing setup. Remarkably, the annealed TiO2 nanorod sensor is found to be having high sensitivity and fast response and recovery times of 145 and 210 ms, respectively, for 95 % humidity. Finally, to check the practical applicability, the TiO2 nanorod sensors were used to analyze the humidity level in exhaled human breath to determine the dehydration level.

The Role of Thickness Control and Interface Modification in Assembling Efficient Planar Perovskite Solar Cells.

Perovskite solar cells (PSCs) have achieved tremendous success within just a decade. This success is critically dependent upon compositional engineering, morphology control of perovskite layer, or contingent upon high-temperature annealed mesoporous TiO2, but quantitative analysis of the role of facile TiCl4 treatment and thickness control of the compact TiO2 layer has not been satisfactorily undertaken. Herein, we report the facile thickness control and post-treatment of the electron transport TiO2 layer to produce highly efficient planar PSCs. TiCl4 treatment of TiO2 layer could remove the surface trap and decrease the charge recombination in the prepared solar cells. Introduction of ethanol into the TiCl4 aqueous solution led to further improved open-circuit voltage and short-circuit current density of the related devices, thus giving rise to enhanced power conversion efficiency (PCE). After the optimal TiCl4 treatment, PCE of 16.42% was achieved for PSCs with TiCl4 aqueous solution-treated TiO2 and 19.24% for PSCs with TiCl4 aqueous/ethanol solution-treated TiO2, respectively. This work sheds light on the promising potential of simple planar PSCs without complicated compositional engineering and avoiding the deposition and optimization of the mesoporous scaffold layer.

Performance improvement of inverted perovskite solar cells using TiO2 nanorod array and mesoporous structure

Abstract In view of the low carrier mobility of organic materials, the carrier collection ability was suffered from the short transport length before carriers were recombined. To improve performances by enhancing carrier collection ability, the optimal period was 1.5 μm which was obtained by changing the period of titanium dioxide (TiO2) nanorod array in the inverted perovskite solar cells (IPSCs). The power conversion efficiency was improved to 11.96% from the 7.66% of the standard planar IPSCs. Besides, due to the inherent properties of high absorption surface area and high light scattering ability, the 150-nm-thick TiO2 mesoporous layer was embedded in the TiO2 electron transport layer. By changing the annealing temperature, the optimal crystallinity of anatase phase and the optimal porous distribution were obtained in the TiO2 mesoporous layers annealed at 500 °C for 30 min. Using the optimal annealed TiO2 mesoporous layers in the IPSCs, the power conversion efficiency was improved to 12.73%. The power conversion efficiency of 14.47% was obtained for the IPSCs embedded with the optimal 1.5-μm-periodic TiO2 nanorod array and the optimal 500 °C-annealed TiO2 mesoporous layer in the electron transport layer, simultaneously.

Effect of annealing on the photocatalytic activity of chemically prepared TiO2 thin films under visible light

Porous TiO2 thin film was fabricated onto glass substrate using a simplified chemical bath deposition method at moderately low temperature and the effects of thermal annealing on the structural, morphological, optical and photocatalytic properties were investigated. We report here that the as-prepared TiO2 thin films showed the amorphous phase while the little improvement in the crystallinity was observed after annealing. FESEM image of the as-deposited TiO2 thin film shows that the total surface of the substrate uniformly acquired by nearly spherical TiO2 clusters and a significant grain growth takes place and porous structure generates after the thermal annealing at 773 K. The average transmittance of the TiO2 films slightly decreases after annealing thus absorption band edge shifted towards higher wavelength. The decrease in bandgap value from 3.32 eV to 3.08 eV was observed after thermal annealing. The photocatalytic activity of the as-prepared and annealed TiO2 films was evaluated by photodegradation of congo red dye solution. After annealing, the photocatalytic activity of the TiO2 films was found to be increased because of the improvement of crystallization of anatase TiO2 thin films as evident from XRD and FESEM studies. The photocatalytic reaction for both as-deposited and annealed TiO2 thin film follows pseudo-first order kinetics.

Photoelectrochemical study of electrodeposited TiO2 thin films onto F:SnO2 substrates

TiO2 thin films have been effectively fused onto F:SnO2 (FTO) substrates via the electrodeposition method. The influence of deposition temperature on the synthesis of F:SnO2 substrates and relative information of as-deposited and annealed TiO2 thin films have been studied. Novel TiO2 microspheres are detected on F:SnO2 substrates at an optimized electrodeposition potential. Raman bands approve the creation of single-anatase-phase TiO2. The optimized deposition surroundings show a decrease in the band gap of F:SnO2 substrates and TiO2 thin films. The determined photoelectrochemical properties of annealed TiO2 thin films indicate a fill factor of 51% and power conversion efficiency of 0.15% for application in solar cells.

Effect of Y and Mn doping into rutile type TiO2/Ge stack structure by combinatorial synthesis

The effects of Y and Mn doping into the rutile TiO2 films on a (100) Ge substrate stack structure were investigated by combinatorial synthesis. Composition spread films were fabricated by combinatorial pulsed laser deposition. Regardless of the dopant concentration, the Mn-doped TiO2 film indicated an amorphous structure. In contrast, the Y-doped TiO2 film had a rutile-type crystal structure below an Y concentration of 11.0 at. %. The high Y concentration enhanced the amorphous structure and Ge diffusion into the TiO2 layer. Although both dopants reduced leakage currents, the effect of Y was greater than that of Mn. The post-deposition annealed Y-doped TiO2 indicated an improvement in the leakage current by three orders of magnitude and electron accumulation at a capacitor structure. The Y doping into TiO2 may provide beneficial effects of good interface control and effective dielectric material for Ge-based capacitors.

Evaluation of Crude Oil's Influence on Infochemicals Signalling Released by Ulvalactuca Using Ni-Cu / Nanotitania Sensor

Pollutions of seas and oceans by oil and crude oil are well thought-out as one of the most problems in environment. Owing to the existence of numerous types of algae in marine ecosystem, they contribute significantly to solve this problem through their ability to point out to the pollution via chemical signals so called infochemicals. Interestingly, the macroalgaeUlvaspp. release glucose as an infochemical into the environment to communicate with their bacterial symbionts. Therefore, it is hypothesized that the liberation of glucose will be affected quantitatively as a result of pollution. Occurrence of glucose possibly will detect through oxidation by electrochemical sensors and thus leads to the significant impact on the detection of pollution in the environment. Greatly, ordered annealed TiO2 nanoporous structure prepared and supplied by Ni-Cu nanoparticles was successfully prepared by linear sweep voltammetry. Their morphologies and chemical composition were characterized by HR-SEM and EDS analysis. The prepared Ni-Cu/nanoporous TiO2 electrode was employed for non-enzymatic glucose detection in alkaline electrolyte and showed a promising electro-catalytic activity for glucose that liberated as infochemicals. Cyclic voltammetry of U. lactuca growth media where glucose is supposed to be released in the absence and in the presence of crude oil with different concentrations (10, 20, 30 mg/l) was investigated using a potential range from +0.2 to +0.9 with a scan rate of 50 mV s-1 in 0.1 M NaOH. The result shows one oxidation peak at 0.73 V and one reduction peak at 0.33 V (vs. Ag/AgCl). The present study is considered as a first work combining between the infochemicals of algae and electrochemical sensors to indicate the degree of seawater pollution by crude oil under the condition used in this study. Further investigation is needed to proof the efficiency of U. lactucaas a bioindicatorand Ni-Cu/nanotitaniaas a sensor to detect the pollution in nature seawater.

Titanium Dioxide Thin Films as Methane Gas Sensors

TiO2 thin film was deposited onto n-Si substrate at 100 °C by using a sputtering method, and the film was annealed in air atmosphere at range of 500 °C–1000 °C. The structural and morphological properties of the all films were investigated by X-ray diffraction and atomic force microscope. The gas sensor with interdigitated platinum electrodes was fabricated with photolithographic techniques using the as-deposited and annealed TiO2 thin films as an active material. The sensitivity of the sensors was determined by altering the conductivity of the sensor material under methane gas with various concentrations at different working temperatures. It was determined that the fabricated sensor using as-deposited TiO2 thin film with 10-nm particle size has high sensitivity and fast response/recovery time. The sensor operated at 50 °C had also sensitive to the methane gas and its detection performance increased with temperatures. It was observed that the fabricated sensors exhibited reproducible and stable results.

Study of paramagnetic defect centers in as-grown and annealed TiO2 anatase and rutile nanoparticles by a variable-temperature X-band and high-frequency (236 GHz) EPR

Detailed EPR investigations on as-grown and annealed TiO2 nanoparticles in the anatase and rutile phases were carried out at X-band (9.6GHz) at 77, 120–300K and at 236GHz at 292K. The analysis of EPR data for as-grown and annealed anatase and rutile samples revealed the presence of several paramagnetic centers: Ti3+, O−, adsorbed oxygen (O2−) and oxygen vacancies. On the other hand, in as-grown rutile samples, there were observed EPR lines due to adsorbed oxygen (O2−) and the Fe3+ ions in both Ti4+ substitutional positions, with and without coupling to an oxygen vacancy in the near neighborhood. Anatase nanoparticles were completely converted to rutile phase when annealed at 1000°C, exhibiting EPR spectra similar to those exhibited by the as-grown rutile nanoparticles. The high-frequency (236GHz) EPR data on anatase and rutile samples, recorded in the region about g=2.0 exhibit resolved EPR lines, due to O− and O2− ions enabling determination of their g-values with higher precision, as well as observation of hyperfine sextets due to Mn2+ and Mn4+ ions in anatase.

Fabrication of Double-Walled Titania Nanotubes and Their Photocatalytic Activity

Double-walled titanium dioxide (TiO2) nanotubes have been successfully fabricated by electrochemical anodization at low temperature with subsequent annealing. The low temperature allows for suppression of the chemical etching. The as-fabricated and annealed TiO2 nanotubes are typically single-walled for tubes with diameters less than 150 nm. For nanotubes with diameters greater than 150 nm, it was observed that annealing initiated tube splitting of one to two and hence resulted in double-walled nanotubes. Raman spectroscopy analysis showed anatase phase for the nanotubes. Compared to the single-walled TiO2 nanotube, double-walled nanotubes have enlarged surface areas. This makes TiO2 nanotubes with a double-walled structure more effective for catalytic applications. Photocatalytic testing under ultraviolet (UV) radiation proved enhanced photocatalytic activity with a faster degradation rate of the organic chemical with double-walled nanotube film compared to the single-walled sample.

Enhanced photocatalytic activity of Bi2WO6/TiO2 nanotube array composite under visible light irradiation

Titania nanotube array (TiO2 NT) was fabricated by anodization of titanium in an electrolyte containing HF and NaHSO4. The as-anodized TiO2 NT was crystallized to anatase phase by a heat treatment at 500°C. Bi2WO6/TiO2 nanotube array composite (Bi2WO6/TiO2 NT) was synthesized by hydrothermal deposition of Bi2WO6 over the crystallized TiO2 NT. Bi2WO6 extended light absorption range of TiO2 NT, and the Bi2WO6/TiO2 exhibited stronger light absorption in both UV and visible light regions. In particular, the photoelectrochemical properties and photocatalytic activity of Bi2WO6/TiO2 NT under visible light irradiation were investigated. The photocurrent of Bi2WO6/TiO2 NT is four times as high as the bare annealed TiO2 NT was, which results from the enhanced photogenerated electron–hole pairs separation. The photocatalytic activity of Bi2WO6/TiO2 NT is two times as high as that of the pure TiO2 NT under visible light irradiation, and is about one and a half times as much as that over Bi2WO6. Moreover, the effect of pH on the photocatalytic activity of Bi2WO6/TiO2 NT was also investigated, and Bi2WO6/TiO2 NT showed highest photocatalytic activity at pH 6.0.

Quality Improvements of Titanium Oxide/Gallium Arsenide MOS Capacitors by Post-Metallization Annealing and Sulfur-Treatment

The characteristics of post-metallization annealed TiO2 with various thicknesses on (NH4)2S-treated GaAs were investigated. The electrical characteristics of TiO2 films grown on (NH4)2S-treated GaAs were improved due to the removal of native oxide. The post-metallization annealing treatment can further passivate the grain boundary of TiO2 film and interface of TiO2/GaAs. With both treatments, the leakage current densities of thick TiO2 (77nm)/GaAs are 1.4 × 10-7 and 2.3 × 10-5 A/cm2 at ± 1.5 MV/cm, and that of thin TiO2 (7.5 nm) are 1.7 × 10-6 and 4.5 × 10-5 A/cm2 at ± 2 V (2.7 MV/cm). The dielectric constant and equivalent oxide thickness can reach 52 and 0.53 nm, respectively. The lowest interface state density is 3.8 × 1012 cm-2eV-1 by the high-low frequency capacitance method.

Effect of Annealing Temperature on TiO2 Nanorod Films Prepared by dc Reactive Magnetron Sputtering for Dye-Sensitized Solar Cells

Anatase TiO2 nanorod films have been prepared on ITO coated glass substrates at room temperature by dc reactive magnetron sputtering technique. The nanorods are highly ordered and are perpendicular to the substrate. XRD measurements show that the anatase nanorods have a preferred orientation along the [110] direction. The prepared nanorods were annealed at different temperatures (200–500 °C) in air for 1 h. The dye-sensitized solar cells (DSSC) have been made using the as-deposited and annealed TiO2 nanorods as working electrodes. It has been found that annealing improves the efficiency of the DSSC. An optimum conversion efficiency of 2.13%, at 100 mW/cm2 light intensity has been achieved with TiO2 nanorods annealed at 300 °C.