Core–Shell α‐Fe2O3@α‐MoO3 Nanorods as Lithium‐Ion Battery Anodes with Extremely High Capacity and Cyclability

α‐Fe₂O₃ nanoparticles are uniformly coated on the surface of α‐MoO₃ nanorods through a two‐step hydrothermal synthesis method. As the anode of a lithium‐ion battery, α‐Fe₂O₃@α‐MoO₃ core–shell nanorods exhibit extremely high lithium‐storage performance. At a rate of 0.1 C (10 h per half cycle), the reversible capacity of α‐Fe₂O₃@α‐MoO₃ core–shell nanorods is 1481 mA h g^?1 and a value of 1281 mA h g^?1 is retained after 50 cycles, which is much higher than that retained by bare α‐MoO₃ and α‐Fe₂O₃ and higher than traditional theoretical results. Such a good performance can be attributed to the synergistic effect between α‐Fe₂O₃ and α‐MoO₃, the small size effect, one‐dimensional nanostructures, short paths for lithium diffusion, and interface spaces. Our results reveal that core–shell nanocomposites have potential applications as high‐performance lithium‐ion batteries.     

LiMII(IO3)3 (MII=Zn and Cd): Two Promising Nonlinear Optical Crystals Derived from a Tunable Structure Model of α‐LiIO3

Excellent nonlinear optical materials simultaneously meet the requirements of large SHG response, phase‐matching capability, wide transparency windows, considerable energy band‐gap, good thermal stability and structure stability. Herein, two new promising nonlinear optical (NLO) crystals LiM^II(IO₃)₃ (M^II=Zn and Cd) are rationally designed by the aliovalent substitution strategy from the commercialized α‐LiIO₃ with the perfect parallel alignment of IO₃ groups. Compared with parent α‐LiIO₃ and related A^I₂M^IV(IO₃)₆, the title compounds exhibit more stable covalent 3D structure, and overcome the racemic twinning problem of A^I₂M^IV(IO₃)₆. More importantly, both compounds inherit NLO‐favorable structure merits of α‐LiIO₃ and show larger SHG response (≈14× and ≈12×KDP), shorter absorption edge (294 and 297 nm) with wider energy band‐gap (4.21 and 4.18 eV), good thermal stability (460 and 430 °C), phase‐matching behaviors, wider optical transparency window and good structure stability, achieving an excellent balance of NLO properties.     

Enhanced Photocatalytic Performance of ZnO Nanorods Coupled by Two‐Dimensional α‐MoO3 Nanoflakes under UV and Visible Light Irradiation

We exploit the utilization of two‐dimensional (2D) molybdenum oxide nanoflakes as a co‐catalyst for ZnO nanorods (NRs) to enhance their photocatalytic performance. The 2D nanoflakes of orthorhombic α‐MoO₃ were synthesized through a sonication‐aided exfoliation technique. The 2D MoO₃ nanoflakes can be further converted to substoichiometric quasi‐metallic MoO_3?x by using UV irradiation. Subsequently, 1D–2D MoO₃/ZnO NR and MoO_3?x/ZnO NR composite photocatalysts have been successfully synthesized. The photocatalytic performances of the novel nanosystems in the decomposition of methylene blue are studied by using UV‐ and visible‐illumination setup. The incorporated 2D nanoflakes show a positive influence on the photocatalytic activity of the ZnO. The obtained rate constant values follow the order of pristine ZnO NR<MoO₃/ZnO NR<MoO_3?x/ZnO NR composites. The enhancement of the photocatalytic efficiency can be ascribed to a fast charge carrier separation and transport within the heterojunctions of the MoO₃/ZnO NRs. In particular, the best photocatalytic performance of the MoO_3?x/ZnO NR composite can be additionally attributed to a quasi‐metallic conductivity and substoichiometry‐induced mid‐gap states, which extend the light absorption range. A tentative photocatalytic degradation mechanism was proposed. The strategy presented in this work not only demonstrates that coupling with nanoscale molybdenum oxide nanoflakes is a promising approach to significantly enhance the photocatalytic activity of ZnO but also hints at new type of composite catalyst with extended applications in energy conversion and environmental purification.     

Selective and Tunable Near‐Infrared and Visible Light Transmittance of MoO3−x Nanocomposites with Different Crystallinity

In this Communication, we report MoO_3−x nanocomposites in which the near‐infrared and visible light transmittance can be selectively modulated through the crystallinity. The MoO_3−x nanocomposites were fabricated by a hydrothermal method, and their optical properties were characterized by UV‐Vis spectrometer. The obtained results proved the possibility to tune the nanocomposite's optical properties in the UV/Visible spectral region: crystalline MoO₃ mainly regulates the near‐infrared range (800–2600 nm), and amorphous MoO_3−x mainly changes the visible range from 350 nm to 800 nm and MoO_3−x , with semi‐crystalline structures mainly modulating around 800–1000 nm. These kinds of optical modulations could be attributed to small polar absorption, free electron absorption and plasmon absorption according to different crystallinity. Our work may create new possibilities for future applications such as photochromism, photocatalysis, and electrochromism.     

Dye‐sensitized solar cells based on zinc(II) phthalocyanines bearing 3‐pyridin‐3‐ylpropoxy anchoring groups

In this study, nonperipherally tetra‐substituted ( 2 ), peripherally tetra‐substituted ( 3 ), and peripherally octa‐substituted ( 4 ) zinc(II) phthalocyanines were synthesized as sensitizers for dye‐sensitized solar cells (DSSCs) in which 3‐pyridin‐3‐ylpropoxy substituent acts as anchoring unit to bind TiO₂ surface. The optical results indicated that there is an interaction between the dyes and the TiO₂ surface. The photovoltaic performances of the DSSCs based on these dyes were found to depend on both the position and number of the substituents. Despite the more red‐shifted absorption, the DSSC based on 2 showed the conversion efficiency of 0.68%, which is lower than 1.36% and 0.92% for 3 and 4 , respectively, under one sun (AM 1.5G). The vertical orientation of the dye on TiO₂ surface could be the main reason for the higher photovoltaic performance of complex 3 , which is beneficial for not only injecting the electrons into the conduction band of TiO₂ but also reducing the charge recombination. Overall, these results demonstrate that the peripherally tetra‐substituted 3‐pyridin‐3‐ylpropoxy zinc(II) phthalocyanine complex ( 3 ) as a sensitizer can more efficiently utilize the photons in the red/near‐infrared region with respect to the other complexes studied.     

Visible‐Light‐Induced Efficient Selective Oxidation of Nonactivated Alcohols over {001}‐Faceted TiO2 with Molecular Oxygen

In the presence of molecular oxygen, a {001}‐faceted nanocrystalline anatase TiO₂ catalyst enabled the selective oxidation of nonactivated aliphatic alcohols to the corresponding aldehydes or ketones under visible light. The reaction shows excellent conversion and selectivity towards the formation of the carbonyl products without over‐oxidation to the corresponding carboxylic acids. The exceptional reactivity of the catalyst is possibly due to the absorption of visible light originating from a stronger interaction of alcohol with the {001} facet, which facilitates the modification of the band structure of TiO₂, thus facilitating the photogenerated hole transfer and subsequent oxidation processes. The experimental results have also been corroborated by first‐principles quantum chemical DFT calculations.     

Theoretical Study of α‐V2O5‐Based Double‐Wall Nanotubes

First‐principles calculations of the atomic and electronic structure of double‐wall nanotubes (DWNTs) of α‐V₂O₅ are performed. Relaxation of the DWNT structure leads to the formation of two types of local regions: 1) bulk‐type regions and 2) puckering regions. Calculated total density of states (DOS) of DWNTs considerably differ from that of single‐wall nanotubes and the single layer, as well as from the DOS of the bulk and double layer. Small shoulders that appear on edges of valence and conduction bands result in a considerable decrease in the band gaps of the DWNTs (up to 1 eV relative to the single‐layer gaps). The main reason for this effect is the shift of the inner‐ and outer‐wall DOS in opposite directions on the energetic scale. The electron density corresponding to shoulders at the conduction‐band edges is localized on vanadium atoms of the bulk‐type regions, whereas the electron density corresponding to shoulders at the valence‐band edges belongs to oxygen atoms of both regions.     

Photocatalytic properties of CuO/(001)‐TiO2 composites synthesized by the vapor–thermal method

Composites of (001)‐face‐exposed TiO₂ ((001)‐TiO₂) and CuO were synthesized in water vapor environment at 250°C with various Cu/Ti molar ratios (R_Cu/Ti). The resulting CuO/(001)‐TiO₂ composites were characterized using a variety of techniques. The synthesis under high‐temperature vapor allows close contact between CuO and (001)‐TiO₂, which results in the formation of heterojunctions, as evidenced by the shift of valence band maximum towards the forbidden band of TiO₂. An appropriate ratio of CuO can enhance the absorption of visible light and promote the separation of photogenerated carriers, which improve the photocatalytic performance. The degradation rate constant K_app increased from 5.5 × 10^?2 to 8.1 × 10^?2 min^?1 for R_Cu/Ti = 0.5. Additionally, the results showed that superoxide radicals (^?O₂^?) play a major role in the photocatalytic degradation of methylene blue.     

g-C3N4/SnS2 Heterostructure: a Promising Water Splitting Photocatalyst

Graphite-like carbon nitride (g-C₃N₄) based heterostrutures has attracted intensive attention due to their prominent photocatalytic performance. Here, we explore the g-C₃N₄/SnS₂ coupling effect on the electronic structures and optical absorption of the proposed g-C₃N₄/SnS₂ heterostructure through performing extensive hybrid functional calculations. The obtained geometric structure, band structures, band edge positions and optical absorptions clearly reveal that the g-C₃N₄ monolayer weakly couples to SnS₂ sheet, and forms a typical van der Waals heterojunction. The g-C₃N₄/SnS₂ heterostructure can effectively harvest visible light, and its valence band maximum and conduction band minimum locate in energetically favorable positions for both water oxidation and reduction reactions. Remarkably, the charge transfer from the g-C₃N₄ monolayer to SnS₂ sheet leads to the built-in interface polarized electric field, which is desirable for the photogenerated carrier separation. The built-in interface polarized electric field as well as the nice band edge alignment implys that the g-C₃N₄/SnS₂ heterostructure is a promising g-C₃N₄ based water splitting photocatalyst with good performance.     

Construction of hole‐transported MoO3‐x coupled with CdS nanospheres for boosting photocatalytic performance via oxygen‐defects‐mediated Z‐scheme charge transfer

The establishment of Z‐scheme charge transfer between semiconductors is an effective method to improve the performance of hybridized semiconductor photocatalysts. Herein, the novel photocatalysts consisting of MoO_3‐x and varying amounts of cadmium sulfide (CdS) nanospheres were successfully prepared via the one‐pot hydrothermal method in the presence of polyvinylpyrrolidone (PVP). It is indicated that the PVP not only served as the reducing agent for the formation of oxygen defects in MoO_3‐x, but also the cross‐linking agent for the coupling between MoO_3‐x and CdS. The CdS/MoO_3‐x composite allowed for higher visible‐light photocatalytic performance for enhanced removal of methylene blue and tetracycline with an efficiency of 97.6% and 85.5%, respectively. The improved performance of the CdS/MoO_3‐x composite was found to be mainly attributable to the remarkable charge carrier separation and transfer between CdS and MoO_3‐x based on the favorable hole‐transporting nature and oxygen deficiencies of MoO_3‐x. In addition, the hole‐oxidized photocorrosion of CdS was efficiently suppressed due to the presence of hole‐attractive MoO_3‐x. At the solid interface, an oxygen‐defects‐mediated Z‐scheme charge carrier transfer pathway was proposed as the underlying mechanism for the superior photocatalytic reaction.     

Extensive Reduction in Back Electron Transfer in Twisted Intramolecular Charge‐Transfer (TICT) Coumarin‐Dye‐Sensitized TiO2 Nanoparticles/Film: A Femtosecond Transient Absorption Study

We report the synthesis, characterization, and optical and electrochemical properties of two structurally similar coumarin dyes ( C1 and C2 ). These dyes have been deployed as sensitizers in TiO₂ nanoparticles and thin films, and the effect of molecular structure on interfacial electron‐transfer dynamics has been studied. Steady‐state optical absorption, emission, and time‐resolved emission studies on both C1 and C2 , varying the polarity of the solvent and the solution pH, suggest that both photoexcited dyes exist in a locally excited (LE) state in solvents of low polarity. In highly polar solvents, however, C1 exists in an intramolecular charge‐transfer (ICT) state, whereas C2 exists in both ICT and twisted intramolecular charge‐transfer (TICT) states, their populations depending on the degree of polarity of the solvent and the pH of the solution. We have employed femtosecond transient absorption spectroscopy to monitor the charge‐transfer dynamics in C1 ‐ and C2 ‐sensitized TiO₂ nanoparticles and thin films. Electron injection has been confirmed by direct detection of electrons in the conduction band of TiO₂ nanoparticles and of radical cations of the dyes in the visible and near‐IR regions of the transient absorption spectra. Electron injection in both the C1 /TiO₂ and C2 /TiO₂ systems has been found to be pulse‐width limited (<100 fs); however, back‐electron‐transfer (BET) dynamics has been found to be slower in the C2 /TiO₂ system than in the C1 /TiO₂ system. The involvement of TICT states in C2 is solely responsible for the higher electron injection yield as well as the slower BET process compared to those in the C1 /TiO₂ system. Further pH‐dependent experiments on C1 ‐ and C2 ‐sensitized TiO₂ thin films have corroborated the participation of the TICT state in the slower BET process in the C2 /TiO₂ system.     

Photoelectrochemical studies on aqueous suspensions of 3‐dodecyl 2–5 di‐thionyl pyrrole/metal oxide photoactive interfaces

Colloidal ZnO, Fe₂O₃ and Cu₂O solutions were used to explore photonic activities at metal oxides/organic semiconductors interfaces. Fluorescence spectroscopic and dynamic electrochemical techniques were performed on colloidal metal oxides articles modified with 3‐dodecyl 2–5 di‐thionyl pyrrole (3‐DODTh‐Py) to investigate the quantum absorbance efficiency at this inorganic/organic interface (IOI). The IOI assemblies were p‐n junction‐type interfaces, where 3‐DODTh‐Py) functions as electron donor. Results were interpreted using the optical and electrochemical parameters of the organic monomer such as IP (ionization potential), EA (electron affinity), and E_g (Energy band gap), and the barrier height at the IOI interface. One of the driving forces for great absorption at IOI was the great difference in electronegativity between inorganic and organic interface. Copyright © 2011 John Wiley & Sons, Ltd.     

Insights into the photocatalytic mechanism of the C4N/MoS2 heterostructure: A first-principle study

Constructing heterostructures by combining COFs and TMD is a new strategy to design efficient photocatalysts for CO₂ reduction reaction (CO₂RR) due to their good stability, tunable band gaps and efficient charge separation. Based on the synthesis of completely novel C₄N−COF in our previous reported work, a new C₄N/MoS₂ heterostructure was constructed and then the related structural, electronic and optical properties were also studied using first principle calculations. The interlayer coupling effect and charge transfer between the C₄N and MoS₂ layer are systematically illuminated. The reduced band gap of the C₄N/MoS₂ heterostructure is beneficial to absorb more visible light. For the formation of type-II band alignment, a built-in electric field appears which separates the photogenerated electrons and holes into different layers efficiently and produces redox active sites. The band alignment of the heterostructure ensures its photocatalytic activities of the whole CO₂ reduction reaction. Furthermore, the charge density difference and charge carrier mobility confirm the existence of the built-in electric field at the interface of the C₄N/MoS₂ heterostructure directly. Finally, the high optical absorption indicates it is an efficient visible light harvesting photocatalyst. Therefore, this work could provide strong insights into the internal mechanism and high photocatalytic activity of the C₄N/MoS₂ heterostructure and offer guiding of designing and synthesizing COF/TMD heterostructure photocatalysts.     

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^?.     

A Tandem Catalyst with Multiple Metal Oxide Interfaces Produced by Atomic Layer Deposition

Ideal heterogeneous tandem catalysts necessitate the rational design and integration of collaborative active sites. Herein, we report on the synthesis of a new tandem catalyst with multiple metal‐oxide interfaces based on a tube‐in‐tube nanostructure using template‐assisted atomic layer deposition, in which Ni nanoparticles are supported on the outer surface of the inner Al₂O₃ nanotube (Ni/Al₂O₃ interface) and Pt nanoparticles are attached to the inner surface of the outer TiO₂ nanotube (Pt/TiO₂ interface). The tandem catalyst shows remarkably high catalytic efficiency in nitrobenzene hydrogenation over Pt/TiO₂ interface with hydrogen formed in situ by the decomposition of hydrazine hydrate over Ni/Al₂O₃ interface. This can be ascribed to the synergy effect of the two interfaces and the confined nanospace favoring the instant transfer of intermediates. The tube‐in‐tube tandem catalyst with multiple metal‐oxide interfaces represents a new concept for the design of highly efficient and multifunctional nanocatalysts.     

The Role of Order in the Amplification of Light‐Energy Conversion in a Dye‐Sensitized Solar Cell Coupled to a Photonic Crystal

We investigate the cause of amplification of light‐energy conversion when coupling a nc‐TiO₂ film to a TiO₂ inverse opal by comparing it to an inverse TiO₂ glass (i‐TiO₂‐g) fabricated with the exact monodisperse air–hole size as an inverse opal with a stop band at 600 nm (600‐i‐TiO₂‐o). A significant twofold average gain in the photon‐to‐current conversion efficiency is measured to the red of the stop band at the 600‐i‐TiO₂‐o/nc‐TiO₂ bilayer under front‐wall and back‐wall illumination, greater than the gain within the stop band. A smaller amplification is measured under front‐wall illumination—and no gain is measured under back‐wall illumination—for i‐TiO₂‐g/nc‐TiO₂ at these energies. The photonic crystal therefore causes trapping of light through the bilayer, not only within the gap but also to the red, at frequencies within its dielectric band. This light‐trapping effect is found to be dependent on structural order, as a highly disordered inverse glass film with the same air–hole size and thickness does not yield the same gain. A drop in the transmission of light is measured within the same frequencies to the red of the stop band upon adding nc‐TiO₂ to 600‐i‐TiO₂‐o, consistent with light trapping in the bilayer.     

Understanding the Electronic Structures of Graphene Quantum Dot Physisorption and Chemisorption onto the TiO2 (110) Surface: A First‐Principles Calculation

We investigated the interfacial electronic structure and charge transfer properties of graphene quantum dot (GQD) physisorption and chemisorption on the TiO₂ (110) surface from density functional theory calculations. The simulations show that a slight charge transfer occurs in physisorption case while a significant charge transfer takes place in chemisorption configuration. We present a detailed comparison of the similarities and differences between the electronic structures. The similarities originate from the positive work function difference in both the physisorption and chemisorption configurations, which is able to drive electron transfer from GQD into TiO₂, leading to charge separation across the GQD–TiO₂ interface. The differences stem from the interaction between the GQD and TiO₂ substrate. For example, GQD bounds to TiO₂ surface through van der Waals interactions in the case of physisorption. In the chemisorption configuration, however, there exists strong covalent bonding between them. This leads to much more efficient charge separation for chemisorption than for physisorption. Furthermore, the GQD–TiO₂ composites show large band‐gap narrowing that could extend the optical absorption edge into the visible‐light region. This should imply that chemisorbed GQDs produce a composite with better photocatalytic and photovoltaic performance than composites formed through physisorption.     

BiVO4‐TiO2 Composite Photocatalysts for Dye Degradation Formed Using the SILAR Method

Composite photocatalyst films have been fabricated by depositing BiVO₄ upon TiO₂ via a sequential ionic layer adsorption reaction (SILAR) method. The photocatalytic materials were investigated by XRD, TEM, UV/Vis diffuse reflectance, inductively coupled plasma optical emission spectrometry (ICP‐OES), XPS, photoluminescence and Mott–Schottky analyses. SILAR processing was found to deposit monoclinic‐scheelite BiVO₄ nanoparticles onto the surface, giving successive improvements in the films′ visible light harvesting. Electrochemical and valence band XPS studies revealed that the prepared heterojunctions have a type II band structure, with the BiVO₄ conduction band and valence band lying cathodically shifted from those of TiO₂. The photocatalytic activity of the films was measured by the decolourisation of the dye rhodamine 6G using λ>400 nm visible light. It was found that five SILAR cycles was optimal, with a pseudo‐first‐order rate constant of 0.004 min^?1. As a reference material, the same SILAR modification has been made to an inactive wide‐band‐gap ZrO₂ film, where the mismatch of conduction and valence band energies disallows charge separation. The photocatalytic activity of the BiVO₄–ZrO₂ system was found to be significantly reduced, highlighting the importance of charge separation across the interface. The mechanism of action of the photocatalysts has also been investigated, in particular the effect of self‐sensitisation by the model organic dye and the ability of the dye to inject electrons into the photocatalyst′s conduction band.     

A Novel Way to Prepare TiO2 and γ‐Al2O3 Supported Catalysts with Large Surface Areas

Several TiO₂ and γ‐Al₂O₃ supported catalyst systems were prepared by a novel way and characterized by X‐ray diffraction, Raman spectroscopy and BET surface area measurement. The results show: (1) all the samples, including MoO₃/TiO₂, WO₃/TiO₂, V₂O₅/TiO₂, FeSO₄/γ‐Al₂O₃, Al₂ (SO₄)₃/γ‐Al₂O₃, K₂CO₃/‐Al₂O₃ and so on, prepared by impregnating TiO₂·H₂O or pseudo‐boehmite AlO(OH) with the active components then calcining at a high temperature exhibit much larger surface areas than that of pure TiO₂ or γ‐Al₂O₃ calcined at the same temperature; (2) the surface area of the sample increases with the increase in the coverage of active component on the surface of the support; (3) when the content of active component reaches its utmost monolayer dispersion capacity, the surface area of the sample is the largest, and then decreases when the content of active component exceeds its dispersion threshold.     

Synthesis of α‐diaminomethylenebutyrolactams by the reaction of α‐cyanobutyrolactams with n‐trimethylsilylamines

Successive treatment of α‐cyanobutyrolactams 1 with N‐trimethylsilylamines and water gave the corresponding α‐diaminomethylenebutyrolacatms 2 in good yields. In the NOESY spectra of 2 , the E isomer, the NOE observed between β‐CH₂ (butyrolactam) and N‐CH₂ (morpholine, pyrrolidine) or N‐CH₃ (dimethylamine) indicated a cis configuration of these groups.