A series of spinel solid solutions Li4x/3Co2−2xTi1+2x/3O4 (LCT, 0.2 ≤ x ≤ 0.8) were synthesized and their structures and microwave dielectric properties were characterized in detail. The distribution of cations at A and B sites in the lattice has been analyzed by using Rietveld refinement. The microstructure and dielectric properties were studied by scanning electron microscope and microwave network analyzer. The solid solutions undergo a discontinuous B-site, Li/Ti order–disorder phase transition from a disordered cubic phase to an ordered cubic phase with increasing x values from 0.4 to 0.6. With increasing the A-site lithium content, the LCT ceramics exhibit improved dielectric permittivity er (20.3–26.5), high Q × f value (≥29 400 GHz) and a tailored temperature coefficient of resonant frequency τf from −40 to 10 ppm per °C. Optimized microwave dielectric properties were achieved for the composition with x = 0.8: er = 26.5, Q × f ≈ 29 400 GHz and τf ≈ 10 ppm per °C. A correlation between the cation distribution and microwave dielectric loss is discussed in detail.

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTDefect Engineered g-C3N4 for Efficient Visible Light Photocatalytic Hydrogen ProductionQiuling Tay†, Pushkar Kanhere†, Chin Fan Ng‡, Shi Chen‡, Sudip Chakraborty§, Alfred Cheng Hon Huan‡∥, Tze Chien Sum‡, Rajeev Ahuja§, and Zhong Chen*†View Author Information† School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore‡ Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371, Singapore§ Department of Physics and Astronomy, Uppsala University, Box 516, Uppsala 75120, Sweden∥ Institute of High Performance Computing, Agency for Science, Technology and Research, 1 Fusionopolis Way, #16-16 Connexis North, Singapore 138632, Singapore*(Z.C.) E-mail: [email protected]Cite this: Chem. Mater. 2015, 27, 14, 4930–4933Publication Date (Web):July 13, 2015Publication History Received20 June 2015Revised3 July 2015Published online14 July 2015Published inissue 28 July 2015https://doi.org/10.1021/acs.chemmater.5b02344Copyright © 2015 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views8560Altmetric-Citations362LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (927 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Atmospheric chemistry,Defects,Defects in solids,Electrical conductivity,Hydrogen Get e-Alerts

Mechanically robust coatings that display both superhydrophobic and superoleophobic behavior are of great interest for a wide range of applications including sports facilities, automobile and aircraft, solar panels, and wind turbine blades. In this study, a novel method of combining both low and high surface energy SiO2 nanoparticles was employed to prepare superhydrophobic and superoleophobic coating by sol–gel method. The hydrophobicity and oleophobicity of the coatings were analyzed by various liquid droplets with surface energy ranging from 72.4 to 29.5mJ/m2. Pencil scratch test, cross-cut tape adhesion test, nano-indentation, and PosiTest Pull-Off adhesion test were carried out for the coating mechanical properties. Tuning of surface topology was carried out by controlling molar ratio of low and high surface energy SiO2 nanoparticles. It is observed that with the molar ratio at 2:4 between the low and high surface energy SiO2 nanoparticles, the coating gives rise to the best superoleophobicity and mechanical properties. Such coatings hold good promise for self-cleaning and anti-icing applications under mechanically erosive/abrasive environment.

Self-cleaning coatings are of immense importance for various technological applications. In this work, we report the formulation and characterization of erosion-resistant self-cleaning coatings. Hydroxyl-terminated polydimethyl siloxane (PDMS) was added to tetraethylorthosilicate (TEOS) based sol–gel network as a functional additive. The coatings showed a low sliding angle (less than 10°) when the static water contact angle was around 112°. Spectrophotometric measurement was used to quantify the self-cleaning efficiencies after subjecting the samples to artificial dirt spray and water cleaning. The effect of filler content on the self-cleaning efficiency was discussed. The mechanical properties and durability of the coatings were also studied. Based on the current work, we have successfully demonstrated the concept of self-cleaning coatings without forming superhydrophobic surfaces.

Electronic and optical properties of CH3NH3Pb1−xSnxI3 are determined using DFT. Sn doping narrows band gap allowing 850 nm absorption. Delocalized Sn-5p induced electronic states increase mobility. 50% Sn doping is revealed as optimum composition.

Self-cleaning coatings with excellent water-repellence and good mechanical properties are in high demand. However, producing such coatings with resistance to mechanical abrasion and environmental weathering remains a key challenge. Mechanically robust coatings based on tetraethylorthosilicate (TEOS) and glycidoxypropyltriethoxysilane (Glymo) have been prepared using a sol-gel method. Emphasis is given to the addition of Glymo, an epoxy silane which creates an organic matrix that blends with the inorganic Si-O-Si matrix formed from the TEOS. The combination of the blended matrix produced coatings with good adhesion to substrates and improved mechanical properties. Fluoroalkylsilane (FAS) and silica fillers were introduced to increase the hydrophobicity of the coating. It was found that the water contact angle (CA) of these coatings increases from 115 degrees to 164 degrees upon decreasing filler size from 1-5 mu m to 10-20 nm. The sliding angle (SA) for coatings with 15 wt.% loading of 10-20 nm silica is around 2 degrees. UV weathering does not show significant effect on the properties of the coatings. Mechanical properties and performances including hardness, Young's modulus, coating adhesion and abrasion resistance were systematically analyzed. In the current work, a simple self-cleaning test, which measures the extent of dirt accumulation and subsequent removal by water spray, was performed. The coatings with 15 wt.% loading of 10-20 nm silica particles show the best self-cleaning performance both before and after mechanical abrasion. The developed coating process is simple and can be easily scaled-up for large surfaces that require self-cleaning function. (C) 2015 Elsevier B.V. All rights reserved.

Sol-gel coatings with different roughness and surface energy were prepared on glass substrates. Methyl triethoxysilane (MTEOS), 3-Glycidyloxypropyl trimethoxysilane (GLYMO) and fluoroalkylsilane (FAS) were used to obtain a mechanically robust icephobic coating. Different amount of hydrophobic silica nano particles was added as fillers to introduce different roughness and surface energy to the coatings. The microstructure, roughness, and surface energy, together with elemental information and surface chemical state, were investigated at room temperature. The contact angle and sliding angle were measured at different temperatures to correlate the wetting behavior at low temperature with the anti-icing performance. The ice adhesion shear strength was measured inside an ice chamber using a self-designed tester. The factors influencing the ice adhesion were discussed, and the optimum anti-icing performance found in the series of coatings. It was found that lower surface energy leads to lower ice adhesion regardless of the roughness, while the roughness plays a more complicated role. The wetting behavior of the droplet on surface changes as temperature decreases. The anti-icing performance is closely related to the antiwetting property of the surfaces at subzero temperatures.

Perovskite-based photocatalysts are of significant interest in the field of photocatalysis. To date, several perovskite material systems have been developed and their applications in visible light photocatalysis studied. This article provides a review of the visible light (λ > 400 nm) active perovskite-based photocatalyst systems. The materials systems are classified by the B site cations and their crystal structure, optical properties, electronic structure, and photocatalytic performance are reviewed in detail. Titanates, tantalates, niobates, vanadates, and ferrites form important photocatalysts which show promise in visible light-driven photoreactions. Along with simple perovskite (ABO3) structures, development of double/complex perovskites that are active under visible light is also reviewed. Various strategies employed for enhancing the photocatalytic performance have been discussed, emphasizing the specific advantages and challenges offered by perovskite-based photocatalysts. This review provides a broad overview of the perovskite photocatalysts, summarizing the current state of the work and offering useful insights for their future development.

Electronic structures of doped NaTaO3 compounds are of significant interest to visible light photocatalysis. This work involves the study of the band gap, band edge potentials, and thermodynamic stability of certain mono-doped and co-doped NaTaO3 systems, using DFT-PBE as well as hybrid (PBE0) functional calculations. Doping of certain non-magnetic cations (Ti, V, Cu, Zn, W, In, Sn, Sb, Ce, and La), certain anions (N, C, and I), and certain co-dopant pairs (W-Ti, W-Ce, N-I, N-W, La-C, Pb-I, and Cu-Sn) is investigated. Our calculations suggest that substitutional doping of Cu at the Ta site, Cu at the Na site, and C at the O site narrows the band gap of NaTaO3 to 2.3, 2.8, and 2.1 eV, respectively, inducing visible light absorption. Additionally, passivated co-doping of Pb-I and N-W narrows the band gap of NaTaO3 to the visible region, while maintaining the band potentials at favorable positions. Hybrid density of states (DOS) accurately describe the effective band potentials and the location of mid-gap states, which shed light on the possible mechanism of photoexcitation in relation to the photocatalysis reactions. Furthermore, the thermodynamic stability of the doped systems and defect pair binding energies of co-doped systems are discussed in detail. The present results provide useful insights into designing new photocatalysts based on NaTaO3.

On page 2932, Tze Chien Sum, Shuzhou Li, Zhili Dong, Zhong Chen, and co-workers report an efficient Ag@AgCl cubic cage photocatalyst with well-defined hollow interior, prepared using a watersoluble sacrificial salt-crystal-template process. The photocatalyst shows excellent photocatalytic degradation performance, which is attributed to the significant light confinement and enhancement around the Ag/AgCl interfacial plasmon hot spots, multilight-reflection inside the cage structure, and the observed ultrafast electron transfer from Ag nanoparticles to AgCl.

Phase formation and photophysical properties of bismuth doped sodium tantalum oxide (perovskite, defect pyrochlore) nanoparticles prepared by a hydrothermal method were studied in detail. It was revealed that the synthesis conditions like NaOH concentration and bismuth precursor (NaBiO3·2H2O) markedly affect the crystal structure of sodium tantalum oxide. At low NaOH concentration and high bismuth precursor (NaBiO3·2H2O) content, Bi doped Na2Ta2O6 (defect pyrochlore) phase was predominantly formed, while at higher NaOH concentration, Bi doped NaTaO3 (perovskite) phase was formed. It was observed that the defect pyrochlore (Bi doped Na2Ta2O6) phase was formed and stabilized by the presence of dopant precursor (NaBiO3·2H2O). The chemical analysis of the samples confirmed the doping of Bi3+ cations in both phases. Doping of bismuth enabled visible light absorption up to 500 nm in perovskite and defect pyrochlore type sodium tantalum oxide. Bi doped NaTaO3 samples showed better performance for the photocatalytic degradation of rhodamine B than that of Bi doped Na2Ta2O6, under visible light irritation (λ>420 nm). The present results shed light on phase formation of sodium tantalate and these results are useful in understanding properties of NaTaO3 based compounds, synthesized by the hydrothermal method.

Photon‐coupling and electron dynamics are the key processes leading to the photocatalytic activity of plasmonic metal‐semiconductor nanohybrids. To better utilize and explore these effects, a facile large‐scale synthesis route to form Ag@AgCl cubic cages with well‐defined hollow interiors is carried out using a water‐soluble sacrificial salt‐crystal‐template process. Theoretical calculations and experimental probes of the electron transfer process are used in an effort to gain insight into the underlying plasmonic properties of the Ag@AgCl materials. Efficient utilization of solar energy to create electron‐hole pairs is attributed to the significant light confinement and enhancement around the Ag/AgCl interfacial plasmon hot spots and multilight‐reflection inside the cage structure. More importantly, an ultrafast electron transfer process (≤150 fs) from Ag nanoparticles to the AgCl surface is detected, which facilitates the charge separation efficiency in this system, contributing to high photocatalytic activity and stability of Ag@AgCl photocatalyst towards organic dye degradation.

In this paper, we have employed DFT and HSE06 methods to study the doping effects on the NaTaO3 photocatalyst. N, S, C, and P monodoping and N–N, C–S, P–P, and N–P codoping have been studied. The redopants’ formation energies have been calculated, and we find S monodoping is energetically more favorable than any other elemental doping. The mechanism of anion doping on the electronic properties of NaTaO3 is discussed. We find the band gap reduces significantly if we dope with anionic elements whose p orbital energy is higher than the O 2p orbitals. N and S can shift the valence band edge upward without losing the ability to split water into H2 and O2. Double-hole-mediated codoping can decrease the band gap significantly. On the basis of our calculations, codoping with N–N, C–S, and P–P could absorb visible light. However, they can only decompose water into H2 when the valence band edge is above the water oxidation level.

The coexistence of low-index facets with a highly photoactive {001} facet in anatase TiO2 nanocrystals has been recently found beneficial to enhance the photocatalytic performance of TiO2 via a synergistic effect. In this paper, this synergistic effect has been further extended from a single crystal to interconnected nanocrystals with dominating {001} or {010} facet in intact hierarchical TiO2 nanostrucutre. The particles synthesized at the optimal condition showed outstanding photocatalytic hydrogen production of 364.2 mu mol.g(-1).h(-1), which is about four times as much as that of commercial P25 (96.5 mu mol-g(-1).h(-1)). Femtosecond transient spectroscopy and density functional theory (DFT) study indicates that effective electron-hole separation takes place within these nanostructures. This new prototype of synergy, which we denote as quasi-heterojunctions, shows that enhanced photocatalytic performance could be derived in the same anatase phase by synthesizing appropriate faceted nanostructures. This work provides a new dimension to facet engineering of TiO2 and other semiconductor photocatalysts.

The coexistence of low-index facets with a highly photoactive {001} facet in anatase TiO2 nanocrystals has been recently found beneficial to enhance the photocatalytic performance of TiO2 via a synergistic effect. In this paper, this synergistic effect has been further extended from a single crystal to interconnected nanocrystals with dominating {001} or {010} facet in intact hierarchical TiO2 nanostrucutre. The particles synthesized at the optimal condition showed outstanding photocatalytic hydrogen production of 364.2 μmol·g–1·h–1, which is about four times as much as that of commercial P25 (96.5 μmol·g–1·h–1). Femtosecond transient spectroscopy and density functional theory (DFT) study indicates that effective electron–hole separation takes place within these nanostructures. This new prototype of synergy, which we denote as quasi-heterojunctions, shows that enhanced photocatalytic performance could be derived in the same anatase phase by synthesizing appropriate faceted nanostructures. This work provid...

Three-dimensional TiO2 microspheres with different hierarchical nanostructures were synthesized by the synergistic strategies of ultrafast electrochemical spark discharge spallation process followed by thermal treatment. The morphology, crystal structure, surface area, and photocatalytic activity of the hierarchical nanostructures were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, surface area analysis, and UV-vis spectroscopy respectively. The nanostructure of hierarchical microspheres undergoes three evolution steps, which includes the change from nanosheets into hybrid nanoflakes/nanoparticles and finally to nanoparticles as calcination temperature increases, in line with the predicable trend of increase in crystallinity and decrease in specific surface area. Compared to other forms of calcined TiO2 samples (nanosheets and na.noparticles), the hybrid TiO2 nanoflake/nanoparticle hierarchical porous structure exhibits a higher photocatalytic activity for the degradation of organic compounds (methyl orange and bisphenol A). This is attributed to their larger specific surface area (similar to 116 m(2)/g), more abundant porosity, and good crystallinity. On the basis of this hybrid structure, a visible light sensitive Ag/TiO2 microsphere photocatalyst is designed which shows faster degradation rate under the visible light illumination (>420 nm). The porous microspheric photocatalyst does not lose its activities after recycled use, showing great potential for practical application in environmental cleanup.

A solid solution photocatalyst, Na1-xLaxFe1-xTaxO3 (x up to 0.06), was prepared by the conventional solid-state method. The photophysical properties of the samples were studied by various experimental techniques and the electronic structures were investigated by using screened hybrid density functional (HSE06) calculations. The solid solution photocatalyst showed absorption of visible light extending up to 450 nm. Upon loading of platinum nanoparticles cocatalyst, the photocatalytic hydrogen evolution of 0.81 mu.mol.h(-1).g(-1) was obtained for 2% doping of LaFeO3 in NaTaO3, under visible radiation (lambda > 390 nm; 20% methanol solution). The photocatalytic properties of the solid solution were found to be better than Fe doped NaTaO3 compounds on account of the suitable band structure. The electronic structure analysis revealed that, in the case of Fe doping at the Ta site, unoccupied electronic states in between the band gap appear that are responsible for the visible-light absorption. However, in the case of La and Fe codoping (passivated doping) the mid-gap electronic states are completely filled, which makes the band structure suitable for the visible-light photocatalysis. The present solid solution of perovskites (LaFeO3 and NaTaO3) sheds light on the interesting photophysical properties and photocatalytic activities which could be beneficial for the photocatalysts derived from these compounds.

Novel cationic quaternary chalcohalide nanobelts were found in Hg4In2Q3Cl8 (Q = S, Se, Te), obtained by solid-state reaction. Due to the effects of dimensional reduction, both theoretical and experimental results demonstrate that their bandgaps are remarkably increased compared to those of the zinc-blende structure HgQ (Q = S, Se, Te).

Visible light active Bismuth doped NaTaO3 powders were synthesized by the conventional solid state route for different Bi concentrations (2.5%, 5.0%, and 7.5% by moles). The optical properties of the doped samples were tuned by changing the molar ratio of Na and Ta in the initial reactants. The doped samples prepared with Na/Ta ratio close to unity (1.01-1.03) resulted in the highest band gap narrowing compared to the other synthesis conditions. It was shown that the photocatalytic hydrogen evolution occurred from these samples under the visible light irradiation (lambda > 390 nm) after loading of appropriate amount of platinum co-catalyst. The other synthesis conditions (Na/Ta = 1/1-x; x = 0.025, 0.05, 0.075 and Ta/Na = 1/11-x; x = 0.025, 0.05, 0.075; x is bismuth content) were not useful for the photocatalytic hydrogen evolution. The structural characterization suggested that the samples prepared with Na/Ta ratio close to unity, contain Bi ions located at both Na and Ta sites in the lattice. The Mott-Schottky plots revealed that the flat band potential of the pristine NaTaO3 is highly negative to the H-2/H2O reduction potential (-1.19 eV vs. SCE, pH = 7) and for all Bi doped NaTaO3 samples, the flat band potential was sufficient for the hydrogen generation. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.