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Stable seawater oxidation at a large current density of 500 mA cm−2 for 1000 h is achieved with a self-healing borate-intercalated nickel–cobalt–iron oxyhydroxide (NiCoFe-Bi) catalyst in highly alkaline artificial seawater at pH 14.95.

Covalent organic frameworks (COFs) have been used in cell imaging, but very rarely for imaging specific cell conditions. Herein, a β-ketoenamine-based fluorescent COF was post-synthetically modified to incorporate a hypoxia-targeting molecule. Fluorescence microscopy imaging shows that the material discriminates between HeLa cells grown under hypoxia and those cultured under normoxia.

The photocatalytic water splitting has a stupendous role to generate renewable hydrogen. However, the overall water splitting reaction is limited by the sluggish oxidation step. Bismuth vanadate (BiVO4) has been identified as one of the most promising n-type semiconductors for photocatalytic water oxidation due to its small energy gap and favorable band alignment. Thus, it is necessary to summarize the recent progress done on BiVO4 for the guidance of future research. In this review, we have discussed recent strategies that have been adopted to boost its photoconversion efficiency at three different levels: (1) facet control, (2) morphological control and, (3) interfacial control. The roles of high indexed facets, anisotropic morphologies, and mediator-based Z schemes are comprehensively discussed and the emphasis is given to find the suitable structural, morphological, and interfacial combination of BiVO4 for efficient water oxidation.

We explored the properties of the quasi-binary Bi2Se3–Bi2S3 system over a wide compositional range. X-ray diffraction analysis demonstrates that rhombohedral crystals can be synthesized within the solid solution interval 0–22 mol% Bi2S3, while at 33 mol% Bi2S3 only orthorhombic crystals are obtained. Core level photoemission spectroscopy reveals the presence of Bi3+, Se2− and S2− species and the absence of metallic species, thus indicating that S incorporation into Bi2Se3 proceeds prevalently through the substitution of Se with S. Spin- and angle-resolved photoemission spectroscopy shows that topological surface states develop on the surfaces of the Bi2Se3−ySy (y ≤0.66) rhombohedral crystals, in close analogy with the prototypical case of Bi2Se3, while the orthorhombic crystals with higher S content turn out to be trivial semiconductors. Our results connect unambiguously the phase diagram and electronic properties of the Bi2Se3–Bi2S3 system.

We used cathodoluminescence (CL) spectroscopy to characterize the oxygen vacancies (VO) in ceria (CeO2). The effects of the processing atmosphere and thermal quenching temperature on the nature and distribution of the intrinsic defects and on the spectroscopic behavior were investigated. The presence of polarons and associates of the polarons with the oxygen vacancies such as (VO••–CeCe′)• is demonstrated. CL intensity quenching above a critical concentration of VO has been shown. Even though the emission centers in all samples are the same, their concentration changes with the oxygen partial pressure of the processing atmosphere. Deconvolution of the observed CL spectra shows that the emissions originating from the F0 centers prevail over those of F+ centers of VO when the defect concentration is high.

Transition-metal (oxy)hydroxides with an abundance of redox metal sites are important for the development of electrochromic devices, rechargeable metal–air batteries, pseudo-capacitors, and industr...

Sensitive and remote areas have come under pressure from growing populations and tourism, often resulting in improper wastewater management. Efficiency, durability, the use of renewable construction materials, and the minimization of environmental impacts must be conformed to a sustainable paradigm. A life cycle assessment (LCA) was applied to compare three different decentralized wastewater treatment systems built at tourist facilities: a source separation sanitation system with a hybrid constructed wetland (S1), a sequential batch reactor (SBR) with a hybrid constructed wetland (S2), and a solar-powered composting toilet (S3). Benchmarking showed that S1 was preferred over S2. The differences were up to a factor of two, except for eutrophication, which was significantly higher for S2 (10×). S3 had the lowest environmental impact, but S3 treated only the blackwater fraction, i.e., urine, faeces, and toilet paper, and excluded greywater treatment, i.e., handwashing and/or kitchen wastewater. The scenario analysis showed that the environmental performance could be improved by installing solar panels, but this would increase the impact on the abiotic depletion of elements by 83% for S2. The LCA indicated the advantages, disadvantages, flexibility, and potential for design improvements to meet the environmental sustainability and market demands for system diversity.

We report on a hydrothermal synthesis of hexagonal ultra-thin Bi2Se3 platelets, which was performed without any organic reactants. The synthesis resulted in the particles with a surface, clean of any organic adsorbents, which was confirmed with a high-resolution transmission electron microscopy, zeta-potential measurements and thermogravimetric measurements coupled with a mass spectroscopy. Due to the absence of the adsorbed organic layer on the Bi2Se3 platelet surface, we were able to measure their inherent surface and optical properties. So far this has not been possible as it has been believed that such hexagonal Bi2Se3 platelets can only be prepared by a solvothermal synthesis, for which it was unable to avoid the organic surface layer. Here we explain the mechanism behind the successful hydrothermal synthesis and show a striking difference in zeta potential behaviour and UV-vis absorption characteristics caused by the adsorbed layer. The surface of the hydrothermally synthesized Bi2Se3 platelets was so clean to enable the occurrence of the localized surface plasmon resonance due to the bulk and topological surface electronic states.

Technologies for mass production require cheap and abundant materials such as ferrous chloride (FeCl

In this study, several biodegradable Mg alloys (Mg5Zn, Mg5Zn0.3Ca, Mg5Zn0.15Ca, and Mg5Zn0.15Ca0.15Zr, numbers in wt%) were investigated after thermomechanical processing via high-pressure torsion (HPT) at elevated temperature as well as after additional heat treatments. Indirect and direct analyses of microstructure revealed that the significant strength increases arise not only from dislocations and precipitates but also from vacancy agglomerates. By contrast with former low-temperature processing routes applied by the authors, a significant ductility was obtained because of temperature-induced dynamic recovery. The low initial values of Young’s modulus were not significantly affected by warm HPT-processing. nor by heat treatments afterwards. Also, corrosion resistance did not change or even increase during those treatments. Altogether, the study reveals a viable processing route for the optimization of Mg alloys to provide enhanced mechanical properties while leaving the corrosion properties unaffected, suggesting it for the use as biodegradable implant material.

Background: Studies on the formation of colloidal crystals in concentrated suspensions have mainly been based on dispersed suspensions with a repulsive inter-particle potential of hard or nearly hard spheres. The self-assembly in weakly-flocculated suspensions has still been unrealized. Here, we report on the formation of ordered structures in concentrated suspensions of nearly-hard spherical particles with weakly-attractive inter-particle interactions that are an order of magnitude higher than the particles’ thermal energy. Methods: In our case, the self-assembly in such suspensions is not thermodynamically driven, but an external shear force must be applied. The driving force for the particles’ ordering is an increase in the inter-particle interactions. This manifests itself in a decrease in the average angle between the interparticle interaction direction and the applied shear stress direction. Results: For a successful ordering into a large-scale closed packed assembly, the external shear force must not exceed the inter-particle attractive interaction for the minimum possible average angle (as in the closed packed structures) but be high enough to enable the particles to move in the highly loaded suspension. Conclusion: The developed method for the self-assembly of the weakly flocculated systems can be applied very generally e.g. a control over a composition of heterogeneous colloidal crystals, manufacturing of the large-scale photonic crystals or preparation of very densely packed compacts of particles needed for the production of sintered ceramics.

The perovskite LaFe0.5Mn0.5O3 synthesized in bulk form shows dielectric relaxation at two distinct temperature zones, whereas both the relaxations follow Arrhenius law. A sufficient coupling between the magnetic and dielectric order parameters in the presence of a magnetic field offers a large positive and negative magnetodielectric effect for LaFe0.5Mn0.5O3. A very large magnetodielectric coupling of +45% at 122 K, −18% at 147 K and −6.8% near room temperature is observed for the material in a comparatively low magnetic field of 5 kOe due to the influence of magnetoresistance on Maxwell-Wagner-Sillars polarization. Magnetoresistance of −5.6% is observed at 100 K for the material under 90 kOe.

© 2018 Elsevier Ltd The influence of different substitutional mechanisms on the electrocaloric effect of a lead-free SrBi2(Nb0.2Ta0.8)2O9Aurivillius phase was studied for application in electrocaloric cooling systems. The A-site substitution with barium efficiently reduced the temperature of maximum permittivity from about 300 °C to 100 °C. The A-site substitution induced phenomena that are typical of strong relaxor ferroelectrics such as significant broadening of the permittivity peak and an increase in its frequency dispersion and with a depolarization temperature below room temperature. These features directly influenced the electrocaloric effect. A direct measurement system, based on a modified-differential scanning calorimeter, was used to analyze the EC effect of the dense (Sr0.5Ba0.5)Bi2(Nb0.2Ta0.8)2O9ceramics. In accordance with the relaxor characteristics, the EC effect was found to increase continuously over a broad temperature range above the room temperature. This was attributed to the alignment of field induced polar nanodomains. Directions for optimization towards a high-performing EC ceramic were identified.

Following the advancements and diversification in synthetic strategies for porous covalent materials in the literature, the materials science community started to investigate the performance of covalent organic polymers (COPs) and covalent organic frameworks (COFs) in applications that require large surface areas for interaction with other molecules, chemical stability, and insolubility. Sensorics is an area where COPs and COFs have demonstrated immense potential and achieved high levels of sensitivity and selectivity on account of their tunable structures. In this review, we focus on those covalent polymeric systems that use fluorescence spectroscopy as a method of detection. After briefly reviewing the physical basis of fluorescence-based sensors, we delve into various kinds of analytes that have been explored with COPs and COFs, namely, heavy metal ions, explosives, biological molecules, amines, pH, volatile organic compounds and solvents, iodine, enantiomers, gases, and anions. Throughout this work, we discuss the mechanisms involved in each sensing application and aim to quantify the potency of the discussed sensors by providing limits of detection and quenching constants when available. This review concludes with a summary of the surveyed literature and raises a few concerns that should be addressed in the future development of COP and COF fluorescence-based sensors.

The coil to globule transition of the polypeptide chain is the physical phenomenon behind the folding of globular proteins. Globular proteins with a single domain usually consist of about 30 to 100 amino acid residues, and this finite size extends the transition interval of the coil-globule phase transition. Based on the pedantic derivation of the two-state model, we introduce the number of amino acid residues of a polypeptide chain as a parameter in the expressions for two cooperativity measures and reveal their physical significance. We conclude that the k2 measure, defined as the ratio of van ’t Hoff and calorimetric enthalpy is related to the degeneracy of the denatured state and describes the number of cooperative units involved in the transition, additionally, it is found that the widely discussed k2=1 is just the necessary condition to classify the protein as the two-state folder. We also find that Ωc, a quantity not limited from above and growing with system size, is simply proportional to the square of the transition interval. This fact allows us to perform the classical size scaling analysis of the coil-globule phase transition. Moreover, these two measures are shown to describe different characteristics of protein folding.

In the context of ionic transport in solids, the variation of a migration barrier height under electric fields is traditionally assumed to be equal to the classical electric work of a point charge that carries the transport charge. However, how reliable is this phenomenological model and how does it fare with respect to Modern Theory of Polarization? In this work, we show that such a classical picture does not hold in general as collective dipole effects may be critical. Such effects are unraveled by an appropriate polarization decomposition and by an expression that we derive, which defines the equivalent polarization-work charge. The equivalent polarization-work charge is not equal neither to the transported charge, nor to the Born effective charge of the migrating atom alone, but it is defined by the total polarization change at the transition state. Our findings are illustrated by oxygen charged defects in MgO and in SiO2., Ionic transport in solids is important for applications including rapid access memories and ion-based batteries. Here, the authors introduce polarization work contributions from the migrating ion and its environment, demonstrating the representative profile is given by a unique charge parameter.

Understanding the chemical processes at the interface between a metal and topological insulator (TI) is important when it comes to designing devices that exploit the peculiar topological surface states or studying the properties of TI heterostructures. In this paper we show that the interface between Ti and Bi2Se3 is unstable at RT and results in the formation of interfacial phases of titanium selenides and metallic Bi. The reaction has shown significant kinetics already at cryogenic temperatures, which is very surprising for a solid-state redox reaction. This can be explained with the possibility of electrons in the topological surface states playing a role in enhancing the Bi2Se3 surface reactivity due to the electron bath effect. For the Ti coverage above 40 nm, the interfacial processes cause compressive stress that triggers the morphological change (buckling) of the deposited film. The observed interface reaction, with all of its consequences, has to be considered not only in the design of devices, where the Ti adhesion layer is often used for contacts, but also for possible engineering of 2D TI heterostructures.

We present a method for high temperature stabilization of bulk amorphous aluminium oxide. The stabilization is achieved by dispersing polysilane dendritic molecules in aluminium hydroxide gel, which upon thermal treatment gives amorphous aluminium oxide stable up to 900 °C. The dispersed macromolecules covalently bind to the alumina matrix and induce homogeneously distributed strain fields that keep the alumina amorphous. The thermal conversion of the precursor system was followed by thermogravimetry with an evolved gas analysis, infrared spectroscopy and 29Si NMR. The amorphous structure of aluminium oxide was confirmed with an X-ray and electron diffraction. Additionally, the amorphous state was supported by presence of penta-coordinated aluminium detected by 27Al NMR and a low bandgap measured by a UV–visible absorption spectroscopy.

Understanding an interaction at an interface between a topological insulator and a metal is of critical importance when designing electronic and spintronic devices or when such systems are used in catalysis. In this paper, we report on a chemical instability of the interface between Bi2Se3 and Ag studied by X-ray powder diffraction and electron microscopy. We present strong experimental evidence of a redox solid-state reaction occurring at the interface with kinetics that is significant already at room temperature. The reaction yields Ag2Se, AgBiSe2, and Bi. The unexpected room-temperature chemical instability of the interface should be considered for all future theoretical and applicative studies involving the interface between Bi2Se3 and Ag.

We demonstrate RF sputtered Ni-doped ZnO nanostructures for detection of extremely low concentration (1 ppm) of hydrogen gas at moderate operating temperature of 75 °C. Structural, morphological, electrical and hydrogen sensing behavior of the Ni-doped ZnO nanostructures strongly depends on doping concentration. Ni doping exceptionally enhances the sensing response and reduces the operating temperature of the sensor as compared to undoped ZnO. The major role of the Ni-doping is to create more active sites for chemisorbed oxygen on the surface of sensor and, correspondingly, to improve the sensing response. The 4 at% of Ni-doped ZnO exhibits the highest response (∼69%) for 1% H 2 at 150 °C, which are ∼1.5 times higher than for the undoped ZnO. This is ascribed to lowest activation energy ∼6.47 KJ/mol. Diminishing of the relative response was observed in 6% Ni- doped ZnO due to separation of NiO phase.

Controllable atmospheric pressure CVD has been optimized to grow transition metal dichalcogenide MoSe2 with tunable morphology at 750 °C on a silicon substrate with a native oxide layer of 250 nm. Utilizing tetrapotassium perylene-3,4,9,10-tetracarboxylate (PTAS) as a seed promoter and varying the vertical distance between the substrate and the precursor MoO3, different morphologies of MoSe2 were achieved, including 2D triangles, hexagons, 3D pyramids and vertically aligned MoSe2 sheets. We find that the shape of MoSe2 is highly dependent upon the distance h between the substrate and the precursor. The change in the morphology is attributed to the confinement of vapor (MoO3 and Se) precursors and their concentrations due to the change in h. These results are helpful in improving our understanding about the factors which influence the morphology (shape evolution) and also the continuous growth of MoSe2 films.

Environmentally benign, algae-mediated biosynthesis of valuable copper-based materials in wastewater, combined with cupric ion (Cu2+) bioremediation, has the potential to reduce the cost of wastewater treatment and generate high quality biosolids. This study investigated the ability of a wild-type strain of Chlamydomonas reinhardtii to bioremediate free Cu2+ in wastewater-like nutrient media during the biosynthesis of copper nanoparticles (Cu NPs). The color of supernatants from treated Cu-polluted media provided a first indication of Cu-based NPs formation in the aqueous phase. Analysis by fluorescein diacetate hydrolysis, observations of cell morphology, and algal regrowth experiments after treatment showed that algal viability was crucial for efficient Cu2+ reduction to Cu NPs. UV–vis absorption spectroscopy demonstrated that sulfur-free medium, which enables sustained hydrogen photoproduction in alga, was not the most efficient in NPs formation. Dark-field scanning transmission electron microscopy (STEM) images overlapped with Cu signal map from energy dispersive X-ray spectrometry (EDS) and high-resolution transmission electron microscopy confirmed the presence of polydisperse, spherical, and well-dispersed sub-10 nm Cu NPs crystallites exclusively in algae-treated heavily Cu-polluted media (10 mg L−1). STEM and EDS also demonstrated the affinity of Cu NPs for carbon-rich (organic) objects. Overall, this study demonstrates the feasibility of Cu2+ bioremediation from the wastewater-like complex nutrient media and the simultaneous biosynthesis of Cu NPs by viable green microalga.

We present a systematic exploration of structural, electrical transport, thermomagnetic, and magneto–dielectric properties of polycrystalline perovskite, Pr2CuMnO6. Powder X-ray diffraction confirms the orthorhombic crystal structure with the Pbnm space group. The electrical transport studies reveal high resistivity (1.34 ×104 ohm–meter at 123 K) of the compound with semiconducting type temperature variation, and the conduction process follows the variable range hopping of polarons. Magnetization measurements reveal the magnetic ordering at 55 K followed by a cluster glass phase below 22 K. Frozen magnetic phase at lower temperature results from competing short-range FM/AFM interactions due to atomically disordered mixed valent B-site ions (Cu2+/3+ and Mn3+/4+). Inverse DC susceptibility reveals the observation of Griffiths phase above the glassy transition, extending up to 66 K. Magnetodielectric (MD) analysis reveals intrinsic MD effect (20 – 100 K) due to spin-lattice coupling followed by extrinsic MD effect (100 – 180 K) due to Maxwell–Wagner contribution.

Nanoparticles of Bi2Ti2O7 pyrochlore were synthesized by a coprecipitation method. They exhibit a high visible-light photoactivity for decolorization of a methyl-orange dye solution in the presence of a sacrificial agent, H2O2. The same pyrochlore system with an Ag co-catalyst showed even faster kinetics under only visible light and an unprecedentedly high photoactivity in the UV range.

The study is aimed at evaluating TiO2-SnS2 composites as effective solar-active photocatalysts for water treatment. Two strategies for the preparation of TiO2-SnS2 composites were examined: (i) in-situ chemical synthesis followed by immobilization on glass plates and (ii) binding of two components (TiO2 and SnS2) within the immobilization step. The as- prepared TiO2-SnS2 composites and their sole components(TiO2 or SnS2) were inspected for composition, crystallinity, and morphology using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analyses. Diffuse reflectance spectroscopy (DRS) was used to determine band gaps of immobilized TiO2-SnS2 and to establish the changes in comparison to respective sole components. The activity of immobilized TiO2-SnS2 composites was tested for the removal of diclofenac (DCF) in aqueous solution under simulated solar irradiation and compared with that of single component photocatalysts. In situ chemical synthesis yielded materials of high crystallinity, while their morphology and composition strongly depended on synthesis conditions applied. TiO2-SnS2 composites exhibited higher activity toward DCF removal and conversion in comparison to their sole components at acidic pH, while only in situ synthesized TiO2-SnS2 composites showed higher activity at neutral pH.