Oxygen Vacancies In TiO2 Research Articles

Semi-carbonized fluorinated polyimide-assisted preparation of TiO2 with strikingly boosted photocatalytic CO2 reduction performance

In this study, oxygen vacancies (OVs)-enriched TiO2 photocatalysts were facilely obtained using a hydrothermal synthesis with the assistance of semi-carbonized fluorinated polyimide (FPI). Addition of FPI has influenced the crystal growth of TiO2, promoting the formation of abundant OVs in TiO2. OVs enhance separation of photogenerated charges and light absorption of TiO2. Moreover, photocatalytic CO2 reduction experiments demonstrate that CO conversion on the 6 % sample (mass ratio of FPI to TiO2 is 6 %) is 2.9 times higher than that on the reference TiO2 under a xenon lamp illumination for 4 h Even after 4 cycles of photocatalytic CO2 reduction, the 6 % sample still has a high CO conversion rate. This work provides a viable pathway for the development of highly performance TiO2-based photocatalysts to promote the conversion of CO2 into high-valent carbon-containing compounds.

A Photo-Assisted Zinc-Air Battery with MoS2/Oxygen Vacancies Rich TiO2 Heterojunction Photocathode.

Converting solar energy into electrochemical energy is a sustainable strategy, but the design of photo-assisted zinc-air battery (ZAB) with efficient utilization of sunlight faces huge challenges. Herein, a photo-assisted ZAB of a three-electrode system using MoS2/oxygen vacancies-rich TiO2 heterojunction as charge cathode and Fe, N-doped carbon matrix (FeNC) as discharge cathode is constructed, where MoS2 is chosen as solar light-responsive catalytic material and TiO2 acts as electron transport layer and hole blocking layer, arising from a train of thought for efficient charging under sunlight irradiation and light-independent discharging. The introduction of oxygen vacancies in TiO2 facilitates the temporary trapping of carriers and triggers rapid carrier transfer at the interface of the heterojunction, which hinders the recombination of photogenerated holes, thereby facilitating their further participation in the oxygen evolution reaction. Moreover, FeNC exhibits superior oxygen reduction reaction performance due to strong d-π interactions. As a result, the well-built ZABs deliver a low charge voltage (0.71 V) under illumination at 0.1 mA cm-2, and a high power density (167.6mW cm-2) in dark. This work paves a special way for the development of ZABs by directly harvesting solar energy in charging and efficiently discharging regardless of lighting conditions.

Density functional theory (DFT) analysis of the effect of oxygen vacancies in TiO2 for the binding of oxides

Abstract Challenges in the environment, particularly the rise in atmospheric pollution, entail the development of new methods to assist in sustainable development. Earlier studies have proven that oxygen vacancies (OVs) occur as the most prevalent defect in transition metal oxides, which play an essential role in gaseous pollutant degradation. Titanium dioxide (TiO2), a naturally occurring semiconductor, is widely employed in pollutant removal. It is significant to examine the effects of oxygen vacancies on the adsorption characteristics of surfaces since O deficiencies are common on metal oxide surfaces. To date, earlier studies have centred on the reaction mechanism of TiO2, leaving the observation of OVs largely unexplored. The purpose of this study was to measure the effects of OV in TiO2 on the binding of oxides. In this case, the CP2K software performed DFT calculations to determine the effect of OVs on the overall binding of oxides and identify the TiO2 energy correlated with computational analysis. As a result, having OVs in the anatase TiO2 structure decreased the formation energy, thereby increasing its adsorption affinity for oxide binding. Therefore, it is significant to study the OVs in TiO2 and to further modify TiO2 to improve oxide binding for the removal of pollutants.

A novel kind of hollow SiO2@g-C3N4@TiO2 microspheres for rapid removal of dyes and antibiotics in water under sunlight

In this paper, using PVP-modified polystyrene microspheres as template, tetrabutyl titanate (TEOT), tetraethyl orthosilicate (TEOS) and melamine as precursor, we developed a facile one-pot two-step method to preparing a novel kind of mesoporous hollow SiO2@TiO2@g-C3N4 ternary composite microspheres with plush surface, in which highly active black titanium dioxide (TiO2) was formed by simple calcination without further chemical reduction treatment. The structure and morphology of the composite microspheres were detailed characterized for understanding the formation mechanism. Research results indicated that the hollow SiO2 microspheres can promote the formation of oxygen vacancies in TiO2, and the ternary combination narrowed the bandgap width of the black hollow composite microspheres to 1.43 eV, thus endowing it with excellent broad-spectrum catalytic performance for rapid photo-degradation of persistent organic pollutants (POPs) such as dyes and antibiotics in water under sunlight. The removal rates of dyes reached more than 70 %, as well as that of antibiotics more than 50 % within one hour. Finally, a plausible catalytic degradation mechanism was discussed.

Enhanced vanadium redox reaction catalytic properties enabled by tunning oxygen vacancy in rutile tio2 coated graphite felt electrodes

Abstract Catalyzing vanadium redox reactions in VRFBs with transition metal oxides is an effective and affordable approach. In this study, the surface electron distribution of TiO2 was regulated by introducing oxygen vacancies into its lattice, enabling the electrode to exhibit outstanding catalytic efficacy in VO2 +/VO2+ and V3+/V2+ redox transformations and suppress the detrimental side reaction (HER and OER) simultaneously. Benefiting from the enhanced catalytic activity and selectivity, the 1000-TiO2-GF electrode sustained a stable operation for 100 cycles at 120 mA cm−2 with no discernible efficiency degradation. The DFT results indicate that oxygen vacancy in TiO2 provides more extra electrons to its neighboring titanium, further strengthening the interaction between the electron-rich titanium and oxygen in VO2 +/VO2+, thus enhancing its catalytic performance. The enhanced catalytic activity for V3+/V2+ on oxygen vacancy-rich TiO2 coating can be attributed to the effective suppression of hydrogen evolution reaction, which can occupy active sites exclusively and produce detrimental H2 bubbles. This insight provides valuable guidance for the innovative design of catalysts in vanadium redox flow batteries.

Role of nitrogen and tantalum in the high-temperature oxidation behavior of AlCoCr0.5NiTaxTi(N) alloys synthesized by laser in situ synthesis

Laser cladding was used to synthesize the coatings of the AlCoCr0.5NiTaxTi (N) alloys on a Ti–6Al–4 V substrate. As the Ta content increased, the alloy evolved from columnar crystals composed of dendritic face-centered cubic (FCC)/L12 phases and interdendritic Laves phases to a eutectic structure. The high-valence state of Ta diminished oxygen vacancies in TiO2, which reduced the diffusion rate, so an appropriate Ta content improved high-temperature oxidation resistance. In the cladding process, nitrogen from the protective gas was partially dissolved in the alloy and partially formed Ti2N, both of which act as diffusion barriers for titanium, inhibiting the formation of titanium oxide and promoting the formation of continuous single aluminum oxide, thereby improving oxidation resistance at high temperatures.

Unraveling the evolution of oxygen vacancies in TiO2−x/Cu and its role in CO2 hydrogenation

Unraveling the evolution of oxygen vacancies in TiO2−x/Cu and its role in CO2 hydrogenation

Cu doping enhanced ZnIn2S4/TiO2(VO) Z-scheme heterojunction for efficient photocatalytic overall water splitting

The design and synthesis of efficient photocatalysts for overall water splitting is a promising research topic. By reasonable modification, the hydrogen evolution photocatalyst can have the ability for overall water splitting. Both ZnIn2S4 and TiO2 have shown great potential in the field of photocatalytic hydrogen evolution, but their use for efficient overall water splitting is challenging. In this work, a Z-scheme heterojunction material of Cu-doped ZnIn2S4 composite TiO2 with rich oxygen vacancies was synthesized. Cu doping enhanced the light absorption, reduced the bandgap, and improved photocatalytic activity. In addition, the oxygen vacancies in TiO2 were conducive to the separation and migration of electron-hole pairs, and the construction of a Z-scheme heterojunction between ZnIn2S4 and TiO2 can also effectively promote the separation and migration of carriers. Therefore, the photocatalytic activity of this material was significantly improved and exhibited excellent overall water splitting activity without any sacrificial agents and co-catalysts. The optimized hydrogen and oxygen evolution rates were 589.64 μmol/g/h and 292.75 μmol/g/h, respectively. This work provided favorable evidence for metal element doping to promote the photocatalytic activity of composite heterojunction materials and provided a new strategy for the development of heterojunction photocatalysts for overall water splitting.

Preparation of AC-TiO2 by One-Step Activation Method and the Degradation Properties of Tetracycline Hydrochloride

A one-step activation technique for preparing activated carbon/titanium dioxide (AC-TiO2) photocatalyst was developed in this study, which achieved the expansion of activated carbon and the crystallization transition of titanium dioxide in one step. The properties of the generated materials were examined utilizing photocatalytic degradation of tetracycline hydrochloride (TC). The optimized sample (10%AC-TiO2) has a photocatalytic efficiency of 99.8% in 60 minutes and a degradation efficiency of more than 90% after 5 cycles. According to the experiment results, the combination of AC with TiO2 at high temperatures can induce a considerable number of oxygen vacancies in TiO2, hence increasing the reaction activation site, resulting in improved photocatalytic performance. A strong C-Ti chemical bond can be formed between AC and TiO2. Simultaneously, using AC as the substrate decreases the aggregation problem induced by the small nano size of TiO2 and increases dispersion uniformity. The unique carbon structure with a amount of pore structure can considerably improve the catalystand#39;s adsorption efficacy. Because of the synergistic effect of adsorption-degradation and the perfect photocatalytic activity of TiO2, the composite photocatalyst has exceptional photocatalytic efficiency, opening new possibilities for TiO2 modification.

Introducing oxygen vacancies in TiO2 lattice through trivalent iron to enhance the photocatalytic removal of indoor NO

Introducing oxygen vacancies in TiO2 lattice through trivalent iron to enhance the photocatalytic removal of indoor NO

A high performance TiO2 anode modified by germanium and oxygen vacancies for lithium-ion batteries

A TiO2 anode modified by germanium and oxygen vacancies was fabricated using a hydrothermal method with an autoclave at 180 °C, followed by reduction sintering at 600 °C for 5 h in a reducing atmosphere. Germanium was obtained and distributed uniformly on the surface of the anatase TiO2 particles. Oxygen vacancies were identified on the TiO2 surface by electron paramagnetic resonance and X-ray photoelectron spectroscopy. The specific capacity of the Ge@TiO2−x anode was 510 mAh g−1 after 550 charge-discharge cycles. The charge transfer and electrolyte impedance of Ge@TiO2−x were smaller than those of the initial TiO2. The lithium-ion diffusion coefficient in Ge@TiO2−x was 7.87 × 10−13 cm2·s−1, which was significantly higher than that of a commercial TiO2 anode. The germanium and oxygen vacancies in TiO2 provided more active sites for the transport of lithium ions and electrons, thereby reducing the energy barrier, accelerating the charge transfer of lithium ions and enhancing the conductivity and capacity of the Ge@TiO2−x anode.

Surface‐Redox Pseudocapacitance‐Dominated Charge Storage Mechanism Enabled by the Reconstructed Cathode/Electrolyte Interface for High‐Rate Magnesium Batteries

AbstractTh all phenyl complex (APC) electrolyte is generally accepted to be compatible with Mg metal anodes, offering excellent plating/stripping reversibility. However, the large Cl desolvation penalty of the MgCl+ solvation structure in APC electrolyte causes a high reaction energy barrier at the cathode/electrolyte interface, resulting in unsatisfactory rate performance. Herein, the interface reconstruction strategy of an anatase TiO2 cathode is proposed by the combination of ultrathin carbon coating and oxygen vacancies, which realizes the fast surface‐redox pseudocapacitance charge storage mechanism via MgCl+, circumventing the sluggish solid‐phase migration of Mg2+. Theoretical calculations verify that the introduction of oxygen vacancies in TiO2, not only increases the intrinsic electronic conductivity, but also improves the adsorption capability for MgCl+, which enhances the surface‐redox pseudocapacitance of TiO2. Moreover, in situ Raman measurements, ex situ XPS spectra and XRD patterns demonstrate the structural integrity of TiO2 without undergoing phase change and the rapid reversible storage of MgCl+. Furthermore, in situ electrochemical impedance spectra reveal that the reconstructed cathode/electrolyte interface promotes the kinetics of active cations and induces the less potential‐dependent charge storage process. Consequently, TiO2 exhibits a remarkable rate performance (discharge capacity of 68.9 mAh g−1 at 1 A g−1) and long‐lifespan over 3000 cycles at 0.5 A g−1.

TiO2–x@C/MoO2 Schottky junction: Rational design and efficient charge separation for promoted photocatalytic performance

Limited solar light harvesting, sluggish charge transfer kinetics, and inferior affinity for adsorbed hydrogen species (H*) severely restrict the photocatalytic hydrogen generation activity of TiO2 photocatalysts. Herein, we present a novel TiO2–x@C/MoO2 Schottky junction prepared via a simple one-step in situ phase-transition-regulation strategy. Crucially, the abundant oxygen vacancies in TiO2–x@C/MoO2 narrow the bandgap and introduce defects to improve the photoresponse. The strongly bonded carbon layer not only serves as a fast charge-transport channel to improve the interlayer charge transfer efficiency but also protects oxygen vacancies from oxidation. Moreover, the Schottky barrier effectively impairs the recombination of electrons and holes and promotes the utilization of photogenerated electrons. Furthermore, the MoO2 cocatalyst optimizes the Gibbs free energy for H2 evolution. As a result of the favorable synergy, the resulting TiO2–x@C/MoO2 presents a significantly enhanced photocatalytic H2 production rate of 506 μmol g−1 h−1 compared to those of TiO2–x and TiO2–x@C (125.5- and 15.8-times larger, respectively). Moreover, outstanding stability over 27 h was achieved because of the protection provided by the surface carbon layer. This ingenious design and facile synthetic strategy offer exciting avenues for the design of strongly coupled Schottky junction photocatalysts for efficient solar-to-chemical conversions.

Doping-induced Ti3+ state and oxygen vacancies in TiO2: A single-chip combinatorial investigation

TiO2 is widely recognized as a high performance photocatalyst for photocatalytic applications. Oxygen vacancies (VO) and titanium defects are known to make a significant contribution to the enhanced photocatalytic efficiency of TiO2, accordingly control of these two centers is pivotal to optimizing the surface photochemical activity. In this work, the formation of VO and Ti3+ ions induced by n-type doping of TiO2 with Nb is demonstrated using a combinatorial investigation approach. Chemical Beam Vapour Deposition (CBVD) is used to fabricate Nb concentration-graded (NbxTi1-x)O2 anatase films with 0.009 ≤ x ≤ 0.033 over a 5 mm length on a single chip. Cathodoluminescence (CL) microanalysis shows the luminescence intensity decreases with increasing Nb concentration; however, the presence of a self-trapped exciton (STE) emission, characteristic of anatase TiO2, indicates that the Nb incorporation does not affect the structural properties of TiO2. Notably, the introduction of Nb donors induces the formation of the signature luminescence bands of VO and Ti3+ at 2.05 and 2.60 eV at 80 K, respectively, and their intensities rise by up to 28% with increasing Nb content. The formation of VO and Ti3+ is attributed to the effect of excess electrons locally produced by Nb donor doping. The thermal activation energies for the STE and defect-related emissions are found to be identical at 32 ± 4 meV, suggesting that the recombination kinetics is mediated by Nb donors. Significantly, we demonstrate that the near-surface VO density can be further increased by two different post-growth treatment approaches: (i) remote hydrogen plasma and (ii) low-energy electron beam irradiation (LEEBI), without effecting the valence state of Ti. Our results open opportunities to optimize the photocatalytic properties of TiO2 by defect engineering.

Defect-anchored single-atom-layer Pt clusters on TiO2−x/Ti for efficient hydrogen evolution via photothermal reforming plastics

Hydrogen generation from plastics waste is a promising strategy to solve the plastic pollution crisis. Making full use of infrared energy of solar spectrum is an important subject for efficient solar photocatalysis. Herein, single-atom-layer Pt (SAL-Pt) clusters anchored on TiO2−x/Ti was used as photothermal catalyst to generate hydrogen from plastic in liquid conditions. The confinement effect of laser-regulated oxygen vacancies in TiO2−x/Ti plays an important role in anchoring SAL-Pt under mildly temperature and pressure condition. The obtained Pt/TiO2−x/Ti possesses excellent photothermal catalytic hydrogen evolution performance from reforming plastic waste under infrared light (273.12 μmol cm−2 h−1). The enhanced photothermal activity of Pt/TiO2−x/Ti is due to enhanced infrared light absorption via plasmonic effect and hot electron aggregation on SAL-Pt from TiO2−x/Ti. The practical applicability is further verified by photothermal catalytic reforming plastics to H2 under ambient sunlight irradiation, which possesses high performance (25.5 μmol cm−2 h−1) and stability (in consecutive week).

Defective TiO2 Nanotube Arrays for Efficient Photoelectrochemical Degradation of Organic Pollutants.

Oxygen vacancies (OVs) are one of the most critical factors that enhance the electrical and catalytic characteristics of metal oxide-based photoelectrodes. In this work, a simple procedure was applied to prepare reduced TiO2 nanotube arrays (NTAs) (TiO2-x) via a one-step reduction method using NaBH4. A series of characterization techniques were used to study the structural, optical, and electronic properties of TiO2-x NTAs. X-ray photoelectron spectroscopy confirmed the presence of defects in TiO2-x NTAs. Photoacoustic measurements were used to estimate the electron-trap density in the NTAs. Photoelectrochemical studies show that the photocurrent density of TiO2-x NTAs was nearly 3 times higher than that of pristine TiO2. It was found that increasing OVs in TiO2 affects the surface recombination centers, enhances electrical conductivity, and improves charge transport. For the first time, a TiO2-x photoanode was used in the photoelectrochemical (PEC) degradation of a textile dye (basic blue 41, B41) and ibuprofen (IBF) pharmaceutical using in situ generated reactive chlorine species (RCS). Liquid chromatography coupled with mass spectrometry was used to study the mechanisms for the degradation of B41 and IBF. Phytotoxicity tests of B41 and IBF solutions were performed using Lepidium sativum L. to evaluate the potential acute toxicity before and after the PEC treatment. The present work provides efficient PEC degradation of the B41 dye and IBF in the presence of RCS without generating harmful products.

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.

Impact of Postprocessing Approaches and Interface Cocatalysts Regulation on Photocatalytic Hydrogen Evolution of Protonic Titanate Derived TiO2 Nanostructures

TiO2–based photocatalysis system for splitting water into hydrogen offers a sustainable and green technology to produce clean hydrogen energy. However, pristine TiO2 still exists inherent shortcomings restricting its practical applications. Herein, the impact of postprocessing approaches of protonic titanate on engineering of oxygen vacancy and photocatalytic hydrogen evolution of TiO2−x is studied. Subsequently, interfacial cocatalysts are successfully involved in the optimized TiO2−x for enhanced photocatalytic hydrogen evolution. TiO2−x with the highest photocatalytic hydrogen evolution performance of 3112.09 μmol g−1 h−1, denoted as TiO2–C, is selected to adjust the interface with Cu and MoS2 respectively. Cu–TiO2–C and MoS2–TiO2–C composites are synthesized to enhance the separation ability of photogenerated electron‐hole pairs and significantly improve the photocatalytic hydrogen evolution performance. The photocatalytic hydrogen evolution rates of 5 wt% Cu–TiO2–C and 40 wt% MoS2–TiO2–C are 9225.75 and 5765.48 μmol g−1 h−1, respectively. It is proved that different postprocessing methods can tune the content of oxygen vacancy in TiO2−x and regulate the photocatalytic hydrogen evolution performance of TiO2−x materials. The interface regulation of the cocatalyst also contributes to the separation of photogenerated electron‐hole pairs and serves as active sites to enhance hydrogen evolution performance.

Fabrication of Bi2O3 QDs decorated TiO2/BiOBr dual Z-scheme photocatalysts for efficient degradation of gaseous toluene under visible-light

Weak visible-light capture ability, ultrahigh charge recombination rate, and poor redox ability are crucial constraints to improve the photocatalytic performance for toluene degradation under visible-light. Hence, a dual Z-scheme of Bi2O3 quantum dots decorated TiO2/BiOBr photocatalysts (Bi2O3 QDs@TiO2/BiOBr) were prepared by a two-step hydrothermal method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) were performed to identify the existence of Bi2O3 QDs and TiO2 that loaded on the surface of BiOBr. The introducing of oxygen vacancies in TiO2 broadened its light absorption region to the visible-light. The constitutes of Bi2O3 QDs and BiOBr were regulated and the optimized photocatalyst BT1-B10 exhibited 94.1 % of removal rate for gaseous toluene degradation after 150 min irradiation of visible-light (>420 nm) as well as good recoverability and durability. This result was obviously superior to other comparison samples. In-situ DRIFTs spectra and Gas Chromatography-Mass Spectrometry (GC-MS) were carried out to provide a possible pathway for the toluene degradation. Additionally, a dual-channel electron transfer model based on the Z-scheme was proposed, which presented desirable visible-light response region, efficient charge separation efficiency, and enhanced redox ability. Notably, hydroxyl radicals (•OH) served as the dominant active species was confirmed by electron spin resonance (ESR) and gas-phase capture tests, that was beneficial to the ring-opening of toluene degradation. This dual Z-scheme heterojunction of Bi2O3 QDs@TiO2/BiOBr photocatalyst showed great potential for the degradation of toluene under visible-light irradiation.

Atom-Precise Heteroatom Core-Tailoring of Nanoclusters for Enhanced Solar Hydrogen Generation.

While core-shell nanomaterials are highly desirable for realizing enhanced optical and catalytic properties, their synthesis with atomic-level control is challenging. Here, the synthesis and crystal structure of [Au12 Ag32 (SePh)30 ]4- , the first example of selenolated Au-Ag core-shell nanoclusters, comprising a gold icosahedron core trapped in a silver dodecahedron, which is protected by an Ag12 (SePh)30 shell, is presented. The gold core strongly modifies the overall electronic structure and induces synergistic effects, resulting in high enhancements in the stability and near-infrared-II photoluminescence. The Au12 Ag32 and its homometal analog Ag44 , show strong interactions with oxygen vacancies of TiO2 , facilitating the interfacial charge transfer for photocatalysis. Indeed, the Au12 Ag32 /TiO2 exhibits remarkable solar H2 production (6810µmolg-1 h-1 ), which is ≈6.2 and ≈37.8 times higher than that of Ag44 /TiO2 and TiO2 , respectively. Good stability and recyclability with minimal catalytic activity loss are additional features of Au12 Ag32 /TiO2 . The experimental and computational results reveal that the Au12 Ag32 acts as an efficient cocatalyst by possessing a favorable electronic structure that aligns well with the TiO2 bands for the enhanced separation of photoinduced charge carriers due to the relatively negatively charged Au12 core. These atomistic insights will motivate uncovering of the structure-catalytic activity relationships of other nanoclusters.