TiO2 Anatase Crystals Research Articles

Facile one-pot synthesis of defective (001)-TiO2−x/h-BN photocatalyst for environmental applications

Various factors control the photocatalyst efficiency including the lifetime of photogenerated charge carriers, photocatalyst surface energy, and light harvesting efficacy. In this study, the defective (001)-TiO2-x/h-BN composite was synthesized by a facile one-pot method to merge the fantastic features of the reactive metastable (001) facet and self-defects in TiO2 anatase crystals with the 2D h-BN. Pure anatase phase of TiO2 was obtained by the suggested preparation method, which contains ∼33 % of the exposed (001) facet. The predominancy of oxygen vacancy in TiO2 crystals was proved experimentally and theoretically by the DFT calculations. The defects in TiO2 along with the incorporated h-BN caused better light harvesting and longer charge lifetime. The prepared defective (001)-TiO2-x/h-BN was applied efficiently for NO removal with very limited release of the toxic NO2 by-product as an environmental application. The detected oxygen vacancy in TiO2 along with h-BN were found to play a synergistic enhancement for NO removal. However, more defects reduced the overall activity because of rapid oxidation of oxygen vacancies on surface of the photocatalyst. To sum up, the defective (001)-TiO2-x/h-BN composite can be considered as a promising material for environmental applications.

Investigation of nickel slag waste as a modifier on graphene-TiO2 microstructure for sensing phenolic compound

In the present work, the potential of nickel slag waste (NSW) was performed as a modifier of graphene-TiO2 material for sensing phenolic compound under an electrochemical system. It was provided to produce variations of mineral components to improve electrochemical sensing in its application for a sensor device. Preparation of composite material (slag-graphene-TiO2) was prepared through solid-state reaction by mixing of NSW, graphene, and TiO2 anatase crystal. Based on these results, we discover the composition of NSW with various mineral contents and produced anatase TiO2 crystal prepared via thermal method at 500 °C for 3 h. Subsequently, the slag-G-TiO2 composite has been homogeneous and characterized using SEM–EDX shows the microstructure formed with the variation of elements content. Moreover, the electrochemical test for sensing phenol compound exhibits the exceptionally sensitivity towards phenol detection in electrolyte solution by the limit of detection (LoD) is 0.0367 ppm and % RSD value of 0.016%. The electrode also produce excellent stability properties by repeatability of 1 to 21 times and the average of oxidation current at 183.57 µA. Finally, we test with a real sample to obtain the ability of phenol detection.

Enhanced Visible Light Photocatalytic Activity of N and Ag Doped and Co-Doped TiO2 Synthesized by Using an In-Situ Solvothermal Method for Gas Phase Ammonia Removal

Single doping and co-doping of N and Ag on TiO2 were successfully prepared by using an in-situ solvothermal method and their structural properties and chemical compositions were characterized. The results indicated that all photocatalysts displayed in TiO2 anatase crystal phase, and a small mesoporous structure was observed in the doped materials. The main roles of N and Ag on the property and photocatalytic activity of TiO2 were different. The N doping has significantly enhanced homogenous surface morphology and specific surface area of the photocatalyst. While Ag doping was narrowing the band gap energy, extending light absorption toward a visible region by surface plasmon resonance as well as delaying the recombination rate of electron and hole of TiO2. The existence of N in TiO2 lattice was observed in two structural linkages such as substitutional nitrogen (Ti-O-N) and interstitial nitrogen (O-Ti-N). Silver species could be in the form of Ag0 and Ag2O. The photocatalytic performance of the photocatalysts coated on stainless steel mesh was investigated by the degradation of aqueous MB and gas phase NH3 under visible LED light illumination for three recycling runs. The highest photocatalytic activity and recyclability were reached in 5% N/Ag-TiO2 showing the efficiency of 98.82% for methylene blue (MB) dye degradation and 37.5% for NH3 removal in 6 h, which was 2.7 and 4.3 times, respectively. This is greater than that of pure TiO2. This was due to the synergistic effect of N and Ag doping.

Zirconium doped mesoporous TiO2 multilayer thin films: Influence of the zirconium content on the photodegradation of organic pollutants

Though applications of TiO2 thin films in environmental pollution remediation are promising, up to date, photocatalytic efficiency is still a challenge. Herein, we report enhanced photocatalytic activity of mesoporous TiO2 thin films towards degradation of organic pollutants in water due to their modification with zirconium. Highly stable, uniform transparent thin films were prepared using evaporation induced self-assembly via dip-coating. The effects of Zr addition on the morphology, structure, crystallinity and photoactivity of the catalyst were investigated. Incorporation of Zr to Ti lattice positions in the TiO2 anatase crystals increased stability of anatase phase and enhanced the charge separation as confirmed by photoluminescence measurements. X-ray diffraction analysis proved the formation of ZrO2 as additional phase for Zr/Ti ratios above 0.1. The resulting nanocomposite formation influences the crystallite size as well as the N2 adsorption of the films.Optimized Zr doped TiO2 thin films with a Zr/Ti ratio of 0.05 showed almost complete photocatalytic degradation of chloridazon, phenol and 4-chlorophenol within 4 h of illumination; pure TiO2 thin films recorded much lower activities for all these pollutants.

Resin-gel incorporation of high concentrations of W6+ and Zn2+ into TiO2-anatase crystal to form quaternary mixed-metal oxides: effect on the a lattice parameter and photodegradation efficiency.

The search for a viable photocatalyst for water remediation is ongoing and in recent times the efforts have predominantly focused on improving the limitations of the TiO2 photocatalyst. This paper reports a dual strategy for improving the photocatalytic properties of TiO2. The first strategy is to dope up to 30% of W6+ and Zn2+ into the crystal lattice of TiO2 using the resin gel technique to synthesize quaternary mixed metal oxides (QMMOs). It was demonstrated by laser Raman spectroscopy, PXRD and various other strategies, including dislodging the dopants from the crystal lattice of TiO2, that these materials were successfully synthesized. More importantly, UV-DRS showed that these materials could absorb visible light. TiO2 and the QMMOs were also supported on 10% NCNTs synthesized from coal fly ash, by slightly modifying the resin gel technique. It was observed from TEM images that the NCNTs were uniformly coated with TiO2 and QMMO nanoparticles. These composites were observed to have lower photoluminescence emission spectra when compared to neat TiO2 and unsupported QMMOs. The two-part strategy employed in this project worked as the QMMOs supported on 10% NCNTs had higher visible light photodegradation efficiencies compared to neat TiO2 and the unsupported QMMOs.

Electroreduction as a viable strategy to obtain TiO2 nanotube films with preferred anatase crystal orientation and its impact on photoelectrochemical performance

Preferential orientation of anatase crystals in TiO2 nanotube (TNT) films was induced through an electroreduction pre-treatment prior to annealing at 450 °C in atmospheric air. This pre-treatment consisted of applying a cathodic potential between − 1 and −6 V vs. SCE, using either continuous or pulsed form. Relative to TNTs without pre-treatment, XRD characterization revealed that the ratio of intensities for anatase planes (004) and (101), I(004)/I(101), increased around five times when pulsed electroreduction was carried out at − 3 V versus SCE in a 0.1 M Na2SO4 solution, compared to that obtained without the pre-treatment. Since additional ions were not included in the electrolyte, this result demonstrated that pulsed electroreduction could be used as a simple strategy to preferentially orient TiO2 anatase crystals. However, it was also found that the induction of a preferred crystal orientation in the [001] direction negatively affected TNT photoelectrochemical performance. This response could be attributed to changes induced on the film during the electroreduction process, since electrochemical characterization showed that the electrical and semiconducting properties of the TNTs were drastically modified after pre-treatment. Therefore, these findings reveal that TNT preferential orientation in the [001] direction is not necessarily associated with improved photoelectrochemical behavior and that TNT photoresponse is strongly influenced by the methodology used to achieve such crystalline orientation.

Solvothermal synthesis and photocatalytic performance of Mg2+-doped anatase nanocrystals with exposed {0 0 1} facets

The photocatalytic activity of TiO2 and magnesium doped TiO2 nanocrystals in dopant range of 2–6.2at%, was studied. The doped and undoped nanocrystals with exposed {001} crystal facets were synthesized by a solvothermal method. Several studies have shown that the (001) surface of the TiO2 anatase crystal is more reactive than the thermodynamically stable (101) surface. The crystal structure as well as the shape of the TiO2 and Mg2+/TiO2 anatase nanoparticles were determined using two different techniques, such as X-ray powder diffraction (XRD) and transmission electron microscopy (TEM), which both lead to the agreeable conclusion that the nanocrystals are in the form of plates. Chemical analysis of the photocatalyst was carried out with X-ray photoelectron spectroscopy (XPS) and showed the presence of magnesium ions in the TiO2 nanoplates. UV–vis diffuse reflectance spectroscopy (DRS) showed that there is an adsorption shift for doped TiO2 to visible light region.The photocalaytic efficiency of the synthesized catalysts was investigated by the photocatalytic oxidation of the gaseous nitric oxide (NO) and decomposition of the gaseous acetaldehyde (CH3CHO) under UV irradiation. It was demonstrated that the low Mg2+ doped catalysts exhibited higher photocatalytic activity than the pure TiO2. The optimal concentration of dopant that is beneficial for the photocatalytic activity was studied.

Quantum chemical elucidation of the mechanism for hydrogenation of TiO2 anatase crystals

Hydrogenation of TiO2 is relevant to hydrogen storage and water splitting. We have carried out a detailed mechanistic study on TiO2 hydrogenation through H and∕or H2 diffusion from the surface into subsurface layers of anatase TiO2 (101) by periodic density functional theory calculations implementing on-site Coulomb interactions (DFT + U). Both H atoms and H2 molecules can migrate from the crystal surface into TiO2 near subsurface layer with 27.8 and 46.2 kcal∕mol energy barriers, respectively. The controlling step for the former process is the dissociative adsorption of H2 on the surface which requires 47.8 kcal∕mol of energy barrier. Both hydrogen incorporation processes are expected to be equally favorable. The barrier energy for H2 migration from the first layer of the subsurface Osub1 to the 2nd layer of the subsurface oxygen Osub2 requires only 6.6 kcal. The presence of H atoms on the surface and inside the subsurface layer tends to promote both H and H2 penetration into the subsurface layer by reducing their energy barriers, as well as to prevent the escape of the H2 from the cage by increasing its escaping barrier energy. The H2 molecule inside a cage can readily dissociate and form 2HO-species exothermically (ΔH = -31.0 kcal∕mol) with only 26.2 kcal∕mol barrier. The 2HO-species within the cage may further transform into H2O with a 22.0 kcal∕mol barrier and 19.3 kcal∕mol exothermicity relative to the caged H2 molecule. H2O formation following the breaking of Ti-O bonds within the cage may result in the formation of O-vacancies and surface disordering as observed experimentally under a high pressure and moderately high temperature condition. According to density of states analysis, the projected density of states of the interstitial H, H2, and H2O appear prominently within the TiO2 band gap; in addition, the former induces a shift of the band gap position notably towards the conduction band. The thermochemistry for formation of the most stable sub-surface species (2HO and H2O) has been predicted. These results satisfactorily account for the photo-catalytic activity enhancement observed experimentally by hydrogenation at high temperatures and high pressures.

Au/Y-TiO2 Catalyst: High Activity and Long-Term Stability in CO Oxidation

Gold catalysts supported on TiO2 doped with Y (1, 3, and 6 wt % of Y) were prepared by the deposition-precipitation with urea method. Two yttrium precursors were used: yttrium acetylacetonate and yttrium nitrate. The Y-TiO2 supports prepared by the sol–gel method allowed the formation of solids with high specific surface area. The incorporation of yttrium restricted the growth of TiO2 anatase crystals and hindered the transformation to the rutile phase. The average gold particle size was very similar in all the prepared catalysts (∼3 nm). Au/Y-TiO2 catalysts showed higher activity and stability at room temperature than Au/TiO2 in the CO oxidation reaction. This behavior is related to the strong anchoring of the gold particles on the structural defects and oxygen vacancies of the support caused by the doping of the anatase with yttrium. The variation of the yttrium precursor (acetylacetonate or nitrate) did not have an important effect on the catalytic activity or the temporal stability of the catalysts. I...

Anatase TiO2 Crystals with Exposed High‐Index Facets

Put your best face forward: The performance of TiO2 anatase crystals in energy and environmental applications is normally correlated with the TiO2 crystal facets exposed, and increasing the percentage of highly reactive surfaces is extremely important. A new gas-phase oxidation process using TiCl4 as precursor now yields anatase TiO2 single crystals with primarily high-index {105} facets, which can cleave water photocatalytically. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Preparation of a pristine TiO2 anatase (101) surface by cleaving

A natural TiO2 anatase crystal, cut to exhibit its (010) surface, was cleaved by breakingoff one of its corners. The resulting sample exhibited a small, flat area ca.2 mm2 in size with a (101) orientation as confirmed by LEED. The evolution of the surfacemorphology was monitored with UHV-STM. After one sputtering/annealing cycle the surfaceis characterized by periodic ridges that run parallel to the [010] direction. The ridges are ∼ 3 nm high and 10–15 nm wide and have a spacing of 30 nm. Interestingly, -oriented step edges are not observed, despite them having the lowest formationenergy. The ridges flatten with repeated sputter/annealing cycles. After atotal of three cycles a flat surface is achieved, which exhibits trapezoidalterraces that are typical for anatase (101). The importance of preparing sucha pristine surface for understanding the surface structure and chemistry ofTiO2 anatase is discussed.

Yttrium disilicate crystallites embedded porous sol-gel thin films for self-cleaning displays

We report on the preparation of self-cleaning and highly transparent yttrium disilicate phosphor host matrix. The yttrium disilicate crystallites were produced in titanosilicate thin films prepared by sol-gel and dip coating method. The thin film phosphor surface was maintained to be superhydrophilic by the synergic effect of the coproduced TiO2 anatase crystals and the high porosity of the film. The high porosity and the tuning of the pore size were attained by the “molecular footprint” technique. It was found that the film with higher contact fraction could retain the superhydrophilicity even in the absence of ultraviolet light. We successfully demonstrate the integration of this property to the films containing yttrium disilicate nanocrystals.