Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO2 Using DRS,PL, and EPR

The electronic structure and photoactivation process in N‐doped TiO₂ is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat‐ and photoinduced N‐doped TiO₂ catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti³⁺ states are formed to enhance the optical absorption in the visible‐light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N‐doped TiO₂, the DRS absorption and PL emission in the visible spectral region of 450–700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N_s^.), oxygen vacancies with one electron (V_o^.), and Ti³⁺ ions are produced with light irradiation and the intensity of N_s^. species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO₂ corresponding to the main absorption band at 410 nm of N‐doped TiO₂, but oxygen vacancies and Ti³⁺ states as defects contribute to the visible‐light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N‐doped TiO₂ is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen‐vacancy‐related defects leads to quenching of paramagnetic N_s^. species but they stabilize the active nitrogen species N_s^?.     

Synthesis and Characterization of Europium‐exchanged Titanate Nanoporous Phosphors

Eu_x(NH₄)_2‐2xTi₃O₇ nanoporous phosphor was prepared by ion exchange method. (NH₄)₂Ti₃O₇ nanotubes were employed as the host structure by treating H₂Ti₃O₇ with NH₄OH solution and the activator, Eu²⁺, was introduced into the host via ion exchange. This is an easy and feasible way to prepare a phosphor. The synthesized samples were characterized using TEM, XRD, N₂ adsorption‐desorption isotherm, TPR, and fluorescence spectrophotometer. Experimental results showed that a portion of Eu²⁺ ions was oxidized into Eu³⁺ ions during ion exchange, resulting in the present phosphor with blue‐emitting and red‐emitting. Moreover, the tubular structure of Eu_x(NH₄)_2‐2xTi₃O₇ was distorted as Eu²⁺ was placed into the host structure. This distortion is attributed to the electrostatic interaction between Eu²⁺ and the electric field of the host structure.     

Room‐Temperature and Aqueous‐Phase Synthesis of Plasmonic Molybdenum Oxide Nanoparticles for Visible‐Light‐Enhanced Hydrogen Generation

A straightforward aqueous synthesis of MoO_3?x nanoparticles at room temperature was developed by using (NH₄)₆Mo₇O₂₄?4 H₂O and MoCl₅ as precursors in the absence of reductants, inert gas, and organic solvents. SEM and TEM images indicate the as‐prepared products are nanoparticles with diameters of 90–180 nm. The diffuse reflectance UV‐visible‐near‐IR spectra of the samples indicate localized surface plasmon resonance (LSPR) properties generated by the introduction of oxygen vacancies. Owing to its strong plasmonic absorption in the visible‐light and near‐infrared region, such nanostructures exhibit an enhancement of activity toward visible‐light catalytic hydrogen generation. MoO_3?x nanoparticles synthesized with a molar ratio of Mo^VI/Mo^V 1:1 show the highest yield of H₂ evolution. The cycling catalytic performance has been investigated to indicate the structural and chemical stability of the as‐prepared plasmonic MoO_3?x nanoparticles, which reveals its potential application in visible‐light catalytic hydrogen production.     

Sulfur and Ti3+ co‐Doping of TiO2 Nanotubes Enhance Photocatalytic H2 Evolution Without the Use of Any co‐catalyst

TiO₂ nanotubes were successfully co‐doped with sulfur and Ti³⁺ states using a facile annealing treatment in H₂/H₂S gas mixture. The obtained nanotubes were investigated for their photocatalytic performance and characterized by SEM, XRD, XPS, EPR, IPCE, IMPS and Mott‐Schottky measurements. The synthesized co‐doped TiO₂ nanotubes show an enhanced photocatalytic hydrogen production rate compared to tubes that were treated only in pure H₂ or H₂S atmosphere—this without the presence of any co‐catalyst. It was found that sulfur in co‐doped TiO₂ exists in the form of S^2? and a small quantity of S⁴⁺/S⁶⁺, which leads to a narrowing of the band gap. However, the enhanced absorption of light in the visible range is not the key reason for the improved photocatalytic performance. We ascribe the enhanced photocatalytic activity to a synergetic effect of S mid‐gap states and disordered Ti³⁺ defects that facilitate photo generated electron transfer.     

A Hybrid Assembly of MXene with NH2−Si Nanoparticles Boosting Lithium Storage Performance

A facile hybrid assembly between Ti₃C₂T_x MXene nanosheets and (3‐aminopropyl) triethoxylsilane‐modified Si nanoparticles (NH₂?Si NPs) was developed to construct multilayer stacking of Ti₃C₂T_x nanosheets with NH₂?Si NPs assembling together (NH₂?Si/Ti₃C₂T_x). NH₂?Si/Ti₃C₂T_x exhibits a significantly enhanced lithium storage performance compared to pristine Si, which is attributed to the robust crosslinking architecture and considerably improved electrical conductivity as well as shorter Li⁺ diffusion pathways. The optimized NH₂?Si/Ti₃C₂T_x anode with Ti₃C₂T_x: NH₂?Si mass ratio of 4 : 1 displays an enhanced capacity (864 mAh g^?1 at 0.1 C) with robust capacity retention, which is significantly higher than those of NH₂?Si NPs and Ti₃C₂T_x anodes. Furthermore, this work demonstrates the important effect of the MXene‐based electrode architecture on the electrochemical performance and can guide future work on designing high‐performance Si/MXene hybrids for energy storage applications.     

Structural and Electrochemical Study of Vanadium‐Doped TiO2 Ramsdellite with Superior Lithium Storage Properties for Lithium‐Ion Batteries

Titanium‐oxide‐based materials are considered attractive and safe alternatives to carbonaceous anodes in Li‐ion batteries. In particular, the ramsdellite form TiO₂(R) is known for its superior lithium‐storage ability as the bulk material when compared with other titanates. In this work, we prepared V‐doped lithium titanate ramsdellites with the formula Li_0.5Ti_1?xV_xO₂ (0≤x≤0.5) by a conventional solid‐state reaction. The lithium‐free Ti_1?xV_xO₂ compounds, in which the ramsdellite framework remains virtually unaltered, are easily obtained by a simple aqueous oxidation/ion‐extraction process. Neutron powder diffraction is used to locate the Li channel site in Li_0.5Ti_1?xV_xO₂ compounds and to follow the lithium extraction by difference‐Fourier maps. Previously delithiated Ti_1?xV_xO₂ ramsdellites are able to insert up to 0.8 Li⁺ per transition‐metal atom. The initial gravimetric capacities of 270 mAh g^?1 with good cycle stability under constant current discharge conditions are among the highest reported for bulk TiO₂‐related intercalation compounds for the threshold of one e^? per formula unit.     

熔融盐法制备富氧空位TiO2纳米片及其光催化性能

氧空位缺陷对半导体材料性能的积极作用引起人们越来越多的关注。本文中,以TiCl4在三氟乙酸中的水解产物为前驱体,通过一步熔融盐法成功合成了具有富氧空位的蓝色TiO2纳米片。由于熔融盐低的氧分压,使前驱体在煅烧过程中消耗了TiO2中的晶格氧从而产生大量的氧空位和Ti3+。紫外-可见漫反射光谱测试表明,蓝色TiO2纳米片的带隙宽度减小至2.69eV,光吸收范围从紫外光区拓宽到可见光区。所制备的蓝色TiO2纳米片表现出优异的光催化活性,在全光谱照射下,对若丹明B的光降解速率是纯TiO2的47.3倍。同时,形成的晶格氟掺杂能有效地稳定氧空位,极大地提高了光生载流子的分离效率。本工作为在半导体氧化物材料内构建氧空位提供了新的思路。     

In Situ Preparation of a Ti3+ Self‐Doped TiO2 Film with Enhanced Activity as Photoanode by N2H4 Reduction

A new synthetic method to fabricate Ti³⁺‐modified, highly stable TiO₂ photoanodes for H₂O oxidation is reported. With Ti foil as both the conducting substrate and the Ti³⁺/Ti⁴⁺ source, one‐dimensional blue Ti³⁺/TiO₂ crystals were grown by a one‐step hydrothermal reaction. The concentration of Ti³⁺ was further tuned by N₂H₄ reduction, leading to a greater photoelectrocatalytic activity, as evidenced by a high photocurrent density of 0.64 mA cm^?2 at 1.0 V vs RHE under simulated AM 1.5 G illumination. Electron paramagnetic resonance and Mott–Schottky plots reveal that higher charge‐carrier density owing to N₂H₄ reduction contributes to the observed improvement. The generality of this synthesis method was demonstrated by its effectiveness in improving the performance of other types of photoanodes. By integrating the advantages of the 1D TiO₂ architecture with those of Ti³⁺ self‐doping, this work provides a versatile tool toward the fabrication of efficient TiO₂ photoanodes.     

The investigation of Ag decorated double‐wall hollow TiO2 spheres as photocatalyst

In this paper, a novel TiO₂ nanosheets assembled double‐wall hollow sphere (DHS)has been prepared successfully via hydrothermal treatment of SiO₂@TiO₂ with the assistant of CTAB.The prepared samples are characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), electron spin resonance (ESR), X‐ray diffraction (XRD) and X‐ray photoelectron spectra (XPS), etc.Results show that redeposited silica species play a key role in the formation of the double‐wall structure. The as‐synthesized DHS nanostructure exhibits a large surface area (417.6 m² g^‐1) and excellent mechanical strength. Furthermore, after decoration of Ag and calcination treatment, the double‐shelled TiO₂/Ag heterostructures show an enhanced photocatalytic performance in the degradation of RhB under UV or visible light irradiations for the following reasons: the surface plasmon resonance effect of Ag, strong interaction between Ag and TiO₂ nanosheets, large surface area, excellent adsorption capacityand unique double‐wall structure. On the basis of the experimental results, a possible mechanism for pollutantdegradation under visual light irradiation has been proposed.     

Isoelectric points of plasma‐modified and aged silicon oxynitride surfaces measured using contact angle titrations

Acid‐base properties of metal oxides and polymers can control adhesion properties between materials, electrical properties, the physical structure of the material and gas adsorption behavior. To determine the relationships between surface isoelectric point, chemical composition and aging effects, plasma‐surface treatment of amorphous silicon oxynitride (SiO_xN_y) substrates was explored using Ar, H₂O vapor, and NH₃ inductively coupled rf plasmas. Overall, the Ar plasma treatment resulted in nonpermanent changes to the surface properties, whereas the H₂O and NH₃ plasmas introduced permanent chemical changes to the SiO_xN_y surfaces. In particular, the H₂O plasma treatments resulted in formation of a more ordered SiO₂ surface, whereas the NH₃ plasma created a nitrogen‐rich surface. The trends in isoelectric point and chemical changes upon aging for one month suggest that contact angle and composition are closely related, whereas the relationship between IEP and composition is not as directly correlated. Copyright © 2010 John Wiley & Sons, Ltd.     

Synthesis of Mixed-Phase TiO<Subscript>2</Subscript> Nanopowders Using Atmospheric Pressure Plasma Jet Driven by Dual-Frequency Power Sources

Mixed-phase TiO₂ nanopowders with different ratios of anatase and rutile have been successfully synthesized using atmospheric pressure plasma jet driven by dual-frequency power sources. The crystal structures of the TiO₂ nanopowders were characterized by X-ray diffraction, SAED, HRTEM, and Raman shift spectroscopy. These results indicated that samples possessed anatase and rutile structure, in addition, the crystallinity of the TiO₂ nanopowders increased and the chlorine contamination decreased with discharge RF power increasing. The photocatalytic activity of the TiO₂ nanopowders was evaluated by decomposition methylene blue solution. The TiO₂ nanopowders which were produced at the discharge RF power of 110 W had the highest photocatalytic activity. Optical emission spectroscopy (OES) was used to detect various excited species in the plasma jet. The results indicate that the various RF power significantly changes the intensities of emission lines (Ar, Ar⁺, Ti, Ti⁺, Ti²⁺, Ti³⁺ and O), which results in the TiO₂ nanopowders a mixture of anatase and rutile phases. The nonequilibrium chemical composition could be formed in one step without anneal. It may have potential applications for synthesizing nanosized particles of high crystallinity by reactive nonthermal plasma processing.     

Zinc‐Reduced Mesoporous TiOx Li‐Ion Battery Anodes with Exceptional Rate Capability and Cycling Stability

We demonstrate a unique synthetic route for oxygen‐deficient mesoporous TiO_x by a redox–transmetalation process by using Zn metal as the reducing agent. The as‐obtained materials have significantly enhanced electronic conductivity; 20 times higher than that of as‐synthesized TiO₂ material. Moreover, electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements are performed to validate the low charge carrier resistance of the oxygen‐deficient TiO_x. The resulting oxygen‐deficient TiO_x battery anode exhibits a high reversible capacity (～180 mA h g^?1 at a discharge/charge rate of 1 C/1 C after 400 cycles) and an excellent rate capability (～90 mA h g^?1 even at a rate of 10 C). Also, the full cell, which is coupled with a LiCoO₂ cathode material, exhibits an outstanding rate capability (>75 mA h g^?1 at a rate of 3.0 C) and maintains a reversible capacity of over 100 mA h g^?1 at a discharge/charge of 1 C/1 C for 300 cycles.     

Fullerol–Titania Charge‐Transfer‐Mediated Photocatalysis Working under Visible Light

The development of visible‐light‐active photocatalysts is being investigated through various approaches. In this study, C₆₀‐based sensitized photocatalysis that works through the charge transfer (CT) mechanism is proposed and tested as a new approach. By employing the water‐soluble fullerol (C₆₀(OH)_x) instead of C₆₀, we demonstrate that the adsorbed fullerol activates TiO₂ under visible‐light irradiation through the “surface–complex CT” mechanism, which is largely absent in the C₆₀/TiO₂ system. Although fullerene and its derivatives have often been utilized in TiO₂‐based photochemical conversion systems as an electron transfer relay, their successful photocatalytic application as a visible‐light sensitizer of TiO₂ is not well established. Fullerol/TiO₂ exhibits marked visible photocatalytic activity not only for the redox conversion of 4‐chlorophenol, I^?, and Cr^VI, but also for H₂ production. The photoelectrode of fullerol/TiO₂ also generates an enhanced anodic photocurrent under visible light as compared with the electrodes of bare TiO₂ and C₆₀/TiO₂, which confirms that the visible‐light‐induced electron transfer from fullerol to TiO₂ is particularly enhanced. The surface complexation of fullerol/TiO₂ induced a visible absorption band around 400–500 nm, which was extinguished when the adsorption of fullerol was inhibited by fluorination of the surface of TiO₂. The transient absorption spectroscopic measurement gave an absorption spectrum ascribed to fullerol radical cations (fullerol^.+) the generation of which should be accompanied by the proposed CT. The theoretical calculation regarding the absorption spectra for the (TiO₂ cluster+fullerol) model also confirmed the proposed CT, which involves excitation from HOMO (fullerol) to LUMO (TiO₂ cluster) as the origin of the visible‐light absorption.     

Synthesis of novel MnOx@TiO2 core-shell nanorod catalyst for low-temperature NH3-selective catalytic reduction of NOx with enhanced SO2 tolerance

In this study, a MnO_x@TiO₂ core-shell catalyst prepared by a two-step method was used for the low-temperature selective catalytic reduction of NO_x with NH₃. The catalyst exhibits high activity, high stability, and excellent N₂ selectivity. Furthermore, it displays better SO₂ and H₂O tolerance than its MnO_x, TiO₂, and MnO_x/TiO₂ counterparts. The prepared catalyst was characterized systematically by transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman, BET, X-ray photoelectron spectroscopy, NH₃ temperature-programmed desorption and H₂ temperature-programmed reduction analyses. The optimized MnO_x@TiO₂ catalyst exhibits an obvious core-shell structure, where the TiO₂ shell is evenly distributed over the MnO_x nanorod core. The catalyst also presents abundant mesopores, Lewis-acid sites, and high redox capability, all of which enhance its catalytic performance. According to the XPS results, the decrease in the number of Mn⁴⁺ active centers after SO₂ poisoning is significantly lower in MnO_x@TiO₂ than in MnO_x/TiO₂. The core-shell structure is hence able to protect the catalytic active sites from H₂O and SO₂ poisoning.     

Composition‐Tailored 2 D Mn1−xRuxO2 Nanosheets and Their Reassembled Nanocomposites: Improvement of Electrode Performance upon Ru Substitution

Composition‐tailored Mn_1?xRu_xO₂ 2 D nanosheets and their reassembled nanocomposites with mesoporous stacking structure are synthesized by a soft‐chemical exfoliation reaction and the subsequent reassembling of the exfoliated nanosheets with Li⁺ cations, respectively. The tailoring of the chemical compositions of the exfoliated Mn_1?xRu_xO₂ 2 D nanosheets and their lithiated nanocomposites can be achieved by adopting the Ru‐substituted layered manganese oxides as host materials for exfoliation reaction. Upon the exfoliation–reassembling process, the substituted ruthenium ions remain stabilized in the layered Mn_1?xRu_xO₂ lattice with mixed Ru³⁺/Ru⁴⁺ oxidation state. The reassembled Li–Mn_1?xRu_xO₂ nanocomposites show promising pseudocapacitance performance with large specific capacitances of approximately 330 F g^?1 for the second cycle and approximately 360 F g^?1 for the 500th cycle and excellent cyclability, which are superior to those of the unsubstituted Li–MnO₂ homologue and many other MnO₂‐based materials. Electrochemical impedance spectroscopy analysis provides strong evidence for the enhancement of the electrical conductivity of 2 D nanostructured manganese oxide upon Ru substitution, which is mainly responsible for the excellent electrode performance of Li–Mn_1?xRu_xO₂ nanocomposites. The results underscore the powerful role of the composition‐controllable metal oxide 2 D nanosheets as building blocks for exploring efficient electrode materials.     

Properties and Structure of Spinel Li‐Mn‐O‐F Compounds for Cathode Materials of Secondary Lithium‐ion Battery

The spinel Li‐Mn‐O‐F compound cathode materials were synthesized by solid‐state reaction from calculated amounts LiOH‐H₂O, MnO₂(EMD) and LiF. The results of the electrochemical test demonstrated that these materials exhibited excellent electrochemical properties. It's initial capacity is ‐ 115 mAh.g¹ and reversible efficiency is about 100%. After 60 cycles, its capacity is still around 110 mAh.g¹ with nearly 100% reversible efficiency. The spinel Li‐Mn‐O‐F compound possibly has two structure models: interstitial model [Li]‐[Mn³⁺_xMn⁴⁺_2‐x]O₄F_δ, in which the fluorine is located on the interstice of crystal lattice, and substituted model [Li]‐[Mn³⁺_xMn⁴⁺_2‐x]O_4‐δF_δ, which the fluorine atom substituted the oxygen atom. The electrochemical result supports the interstitial model [Li][Mn³⁺_xMn⁴⁺_2‐x]O₄F_δ.     

具有高可见光催化活性的Ti3+和碳共掺杂改性的TiO2光催化剂

以乙醇为碳源,采用操作简单的真空活化法一步实现对TiO₂的Ti³⁺与C的共掺杂改性,TiO₂用X衍线衍射、紫外-可见光谱、顺磁共振、X射线光电子能谱和红外光谱等手段表征了催化剂的结构、组成、光学性质. 结果表明, 经Ti³⁺与C共掺杂改性后的催化剂表现出高的可见光降解甲基橙活性. 复合在催化剂表面的石墨可以增强催化剂对可见光的响应范围,而Ti³⁺与氧缺陷形成的掺杂能级则可以提高光生电子的迁移效率. 实验表明,两者之间的协同作用促进了其可见光催化活性的提高.     

Enhanced Electrocatalytic N2 Reduction via Partial Anion Substitution in Titanium Oxide–Carbon Composites

The electrochemical conversion of N₂ at ambient conditions using renewably generated electricity is an attractive approach for sustainable ammonia (NH₃) production. Considering the chemical inertness of N₂, rational design of efficient and stable catalysts is required. Therefore, in this work, it is demonstrated that a C‐doped TiO₂/C (C‐Ti_xO_y/C) material derived from the metal–organic framework (MOF) MIL‐125(Ti) can achieve a high Faradaic efficiency (FE) of 17.8 %, which even surpasses most of the established noble metal‐based catalysts. On the basis of the experimental results and theoretical calculations, the remarkable properties of the catalysts can be attributed to the doping of carbon atoms into oxygen vacancies (OVs) and the formation of Ti?C bonds in C‐Ti_xO_y. This binding motive is found to be energetically more favorable for N₂ activation compared to the non‐substituted OVs in TiO₂. This work elucidates that electrochemical N₂ reduction reaction (NRR) performance can be largely improved by creating catalytically active centers through rational substitution of anions into metal oxides.     

Photocatalysis enhancement of CaAl<Subscript>2</Subscript>O<Subscript>4</Subscript>:Eu<Superscript>2+</Superscript>, Nd<Superscript>3+</Superscript>@TiO<Subscript>2</Subscript> composite powders

CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders were synthesized by a sol–gel method under mild conditions (i.e. low temperature and ambient pressure). The as-prepared powders were characterized by transmission electron microscopy (TEM) and analyzed by X-ray diffraction (XRD). The photocatalytic behavior of the TiO₂-base surfaces was evaluated by the degradation of nitrogen monoxide gas. It suggested that CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders were composed of anatase titania and that CaAl₂O₄:Eu²⁺, Nd³⁺. TiO₂ particles were deposited on the surface of CaAl₂O₄:Eu²⁺, Nd³⁺ to form uniform film. CaAl₂O₄:Eu²⁺, Nd³⁺@TiO₂ composite powders exhibited higher photocatalytic activity compared with pure TiO₂ under visible light. And the result also clearly indicated that the long afterglow phosphor absorbed and stored lights for the TiO₂ to remain photocatalytic activity in the dark.     

Gold(III) Complexes of Asymmetrically Aryl‐Substituted 1,2‐Dithiolene Ligands Featuring Potential‐Controlled Spectroscopic Properties: An Insight into the Electronic Properties of bis(Pyren‐1‐yl‐ethylene‐1,2‐dithiolato)Gold(III)

The electrochemical, UV/Vis–NIR absorption, and emission‐spectroscopic features of (TBA⁺)( 1 ⁻) and the corresponding neutral complex 1 were investigated (TBA⁺=tetrabutylammonium; 1 ⁻=[Au^III(Pyr,H‐edt)₂]⁻; Pyr,H‐edt²⁻=pyren‐1‐yl‐ethylene‐1,2‐dithiolato). The intense electrochromic NIR absorption (λ_max=1432 nm; ε=13000 M ⁻¹ cm⁻¹ in CH₂Cl₂) and the potential‐controlled visible emission in the range 400–500 nm, the energy of which depends on the charge of the complex, were interpreted on the grounds of time‐dependent DFT calculations carried out on the cis and trans isomers of 1 , 1 ⁻, and 1 ²⁻. In addition, to evaluate the nonlinear optical properties of 1 ^x− (x=0, 1), first static hyperpolarizability values β_tot were calculated (β_tot=78×10⁻³⁰ and 212×10⁻³⁰ esu for the cis isomer of 1 ⁻ and 1 , respectively) and compared to those of differently substituted [Au(Ar,H‐edt)₂]^x− gold dithiolenes [Ar=naphth‐2‐yl ( 2 ), phenyl ( 3 ); x=0, 1].