Lead‐based relaxor ferroelectrics are characterized by outstanding piezoelectric and dielectric properties, making them useful in a wide range of applications. Despite the numerous models proposed to ...describe the relation between their nanoscale polar structure and the large properties, the multiple contributions to these properties are not yet revealed. Here, by combining atomistic and mesoscopic‐scale structural analyses with macroscopic piezoelectric and dielectric measurements across the (100–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (PMN–xPT) phase diagram, a direct link is established between the multiscale structure and the large nonlinear macroscopic response observed in the monoclinic PMN‐xPT compositions. The approach reveals a previously unrecognized softening effect, which is common to Pb‐based relaxor ferroelectrics and arises from the displacements of low‐angle nanodomain walls, facilitated by the nanoscale polar character and lattice strain disorder. This comprehensive comparative study points to the multiple, distinct mechanisms that are responsible for the large piezoelectric response in relaxor ferroelectrics.
An anomalously large nonlinear piezoelectric response is identified in monoclinic (100–x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 compositions exhibiting relaxor‐ferroelectric behavior, revealing a previously unrecognized softening mechanism. This softening is observed in a number of relaxor‐based materials and arises from the high mobility of the low‐angle nanodomain walls, facilitated by the nanoscale polar character and lattice strain disorder, common to relaxors.
•Reducibility of Ni/ZSM-5 is lowered by the abundance of acid sites.•LA hydrogenation is favored by Ni/ZSM-5 with high Si/Al molar ratio.•Tailoring acidic and metallic function of Ni/ZSM-5 can steer ...the product distribution.•Investigation of catalytic mechanism of LA hydrogenation via microkinetics.•An innovative mathematical description of sorption energy barriers and (de)sorption kinetics.
The study examines Ni/ZSM-5 catalysts in vapor phase hydrogenation of levulinic acid (LA) under continuous flow conditions (ambient pressure, 210–250 °C). Advanced characterization revealed the interplay between Al and Ni. This was further reinforced by new approach of microkinetic modeling, which demonstrates a pioneering work on mathematical description of pulse H2 sorption, TPD kinetics, DRIFT-supported determination of sorption energy barriers and (de)sorption kinetics. The Ni/ZSM-5 (3.7 wt.% Ni, Si/Al = 28) emerged as the optimal choice for obtaining γ-valerolactone (GVL) as the desired product. Al-rich catalysts with high acid site amounts and low metallic Ni active site concentrations favored esterification, reducing hydrogenation activity, and impeding further hydrogenation of GVL to pentanoic/valeric acid (PA). To enhance PA formation, Ni/ZSM-5 (4 wt.% Ni, Si/Al = 750) with a high Si/Al ratio, was identified as crucial. The combination of described experiments and modelling is demonstrated beneficial for insightful investigation of the structure–activity relationship of Ni/ZSM-5 or any other mono/bi-functional catalysts.
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► Caffeine can be removed from aqueous solutions using composite photocatalysts. ► CNT have a positive effect on the photo-activity of larger TiO2 anatase particles. ► Photogenerated ...holes are preferential pathways for the photodegradation process. ► Photoexcited electrons are responsible for the higher activity of SA/CNTf-20. ► Films of SA/CNTf-20 are more active than films of P25.
The photocatalytic degradation of the psychoactive substance caffeine was studied using composites prepared with multi-walled carbon nanotubes and three different TiO2 materials: one synthesized by a modified sol–gel method and two others obtained from Evonik and Sigma–Aldrich. These materials were characterized by several techniques (e.g., DRIFT, XRD, N2 adsorption–desorption isotherms, TEM, SEM).
The tested materials increased the caffeine degradation rate and the oxygenated groups created by acid treatment on the surface of the carbon nanotubes were crucial for the photocatalytic activity of all prepared composites. In addition, the photocatalytic activity of TiO2 from Sigma–Aldrich markedly increased with the addition of functionalized carbon nanotubes, which seems to be related with the larger TiO2 crystallite sizes and the better contact of these TiO2 particles with carbon nanotubes.
Selective trapping of photogenerated holes and radicals by EDTA and tert-butanol shows that photogenerated holes are crucial on the photodegradation pathway but free radicals produced by photoexcited electrons do also participate in the mechanism and seem to be responsible for the higher activity observed for composites prepared with functionalized carbon nanotubes and TiO2 from Sigma–Aldrich in comparison to TiO2 alone. Films prepared with these composites revealed higher photocatalytic activity than films of TiO2 from Evonik.
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•High-Cr ferrous alloys are of great interest for future energy applications.•CP successfully designs the desired type of alloy.•SPEM and APT provide insight into the CP on atomic ...level.•CP provides new possibilities for materials processing for future energy applications.
Excellent properties (durability, wear and corrosion resistance) and long service life under extreme conditions are essential for the successful application of metallic materials in the energy sector. In particular, for future fusion applications, high Cr ferrous alloys (in our case Eurofer) are of great interest. Importantly, modified microstructure with higher dimensional stability improves corrosion and wear resistance properties. In this study, we successfully manipulate the desired type of microstructure, which could provide a solution to current challenges in such a high temperature, highly corrosive and highly irradiated environment, using a novel technique of cryogenic processing (CP). The research identifies the CP-driven changes not only to the microstructure, but also to the local chemistry and bonding state of the key alloying elements. The correlations and individual phenomena associated with CP have been evaluated using state-of-the-art techniques such as atom probe tomography and synchrotron-based in-situ scanning photoemission spectroscopy. This novel process and its novel microstructural manipulation opens up new possibilities for materials processing for future energy applications.
With the advancement of drug delivery systems based on mesoporous silica nanoparticles (MSNs), a simple and efficient method regulating the drug release kinetics is needed. We developed ...redox-responsive release systems with three levels of hindrance around the disulfide bond. A model drug (rhodamine B dye) was loaded into MSNs’ mesoporous voids. The pore opening was capped with β-cyclodextrin in order to prevent leakage of drug. Indeed, in absence of a reducing agent the systems exhibited little leakage, while the addition of dithiothreitol cleaved the disulfide bonds and enabled the release of cargo. The release rate and the amount of released dye were tuned by the level of hindrance around disulfide bonds, with the increased hindrance causing a decrease in the release rate as well as in the amount of released drug. Thus, we demonstrated the ability of the present mesoporous systems to intrinsically control the release rate and the amount of the released cargo by only minor structural variations. Furthermore, an in vivo experiment on zebrafish confirmed that the present model delivery system is nonteratogenic.
Zinc oxide particles were synthesized without the addition of water by autoclaving (anhydrous) zinc acetate/alcohol and zinc acetate/acetic acid/alcohol solutions at 160 °C. The solvothermal ...synthesis was performed in ethanol or octanol. The structural, optical and morphological characteristics of ZnO particles were investigated by X-ray diffraction (XRD), UV–Vis spectroscopy, FE-SEM and TEM/STEM microscopy. 13C NMR spectroscopy revealed the presence of ester (ethyl- or octyl-acetate) in the supernatants which directly indicate the reaction mechanism. The formation of ester in this esterification reaction generated water molecule in situ, which hydrolyzed anhydrous zinc acetate and initiated nucleation and formation of ZnO. It was found that the size and shape of ZnO particles depend on the type of alcohol used as a solvent and on the presence of acetic acid in solution. The presence of ethanol in the “pure” system without acetic acid favoured the formation of fine and uniform spherical ZnO nanoparticles (∼20 nm). With the addition of small amount of acetic acid the size of these small nanoparticles increased significantly up to a few hundred nanometers. The addition of small amount of acetic acid in the presence of octanol caused even more radical changes in the shape of ZnO particles, favouring the growth of huge rod-like particles (∼3 μm).
•ZnO particles were prepared via esterification reaction of anhydrous zinc acetate.•The formation of ZnO is initiated by water molecule generated in situ.•The results of 13C NMR spectroscopy confirmed the presence of acetate esters.•The size and morphology of ZnO particles depends on the alcohol used.•The uniform ZnO nanoparticles (∼20 nm) were obtained in the presence of ethanol.
A green, template‐free and easy‐to‐implement strategy was developed to access holey g‐C3N4 (GCN) nanosheets doped with carbon. The protocol involves heating dicyandiamide with β‐cyclodextrin (βCD) ...prior to polymerization. The local symmetry of the GCN skeleton is broken, yielding CxGCN (x corresponds to the initial amount of βCD used) with pores and a distorted structure. The electronic, emission, optical and textural properties of the best‐performing material, C2GCN, were significantly modified as compared to bulk GCN. The spectroscopic and luminescent features of C2GCN show the characteristic π–π* electronic transition of GCN, accompanied by much stronger n–π* electronic transitions owing to the porous and distorted network. These new electronic transitions, along with the presence of additional carbon synergistically contributed to enhanced visible light absorption and restrained recombination of electron–hole pairs. Steady‐state and time‐resolved photoluminescence showed an effective quench of the fluorescence emission, accompanied by a decrease of fluorescence lifetime of C2GCN (2.20 ns) in comparison with GCN (5.85 ns), owing to the delocalization of electron and holes to new recombination centers. The photocatalytic activity of C2GCN was attributed to efficient charge carrier separation and improved visible‐light absorbing ability. As result, C2GCN exhibited ∼5 times higher photocatalytic H2 generation under visible light than bulk GCN.
Holey gas! A green, simple and scalable strategy was used to prepare distorted C‐doped g‐C3N4 porous nanosheets. The synergetic effect between carbon doping and distortion enhanced the visible light absorption capacity and significantly reduced the recombination of the photogenerated charge‐carriers. The creation of a new electron transfer pathway promoted the efficient electron–hole separation, improving the photocatalytic performance for H2 generation in the visible light region.
We demonstrate formation of material consisting of three-dimensional Germanium nanowire network embedded in an insulating alumina matrix. A wide range of such nanowire networks is produced using a ...simple magnetron sputtering deposition process. We are able to vary the network parameters including its geometry as well as the length and width of the nanowires. The charge transport in these materials is shown to be related to the nanowire surface per unit volume of the material, α. For low values of α, transport is characterized by space charge limited conduction and a drift of carriers in the extended states with intermittent trapping-detrapping in the localized states. For large values of α, charge transport occurs through hopping between localized electronic states, similar to observations in disorder-dominated arrays of quantum dots. A crossover between these two mechanisms is observed for the intermediate values of α. Our results are understood in terms of an almost linear scaling of the characteristic trap energy with changes in the nanowire network parameters.
The production of spatially ordered arrays of nanopores in alumina is attracting considerable attention due to their valuable filtering and sensing applications. Here we investigate the production ...conditions of thin films consisting of a continuous 3D network of nanopores in alumina, with the network nodes arranged in a body-centered tetragonal lattice, and the pore size about 1 nm. The emphasis is on controlling the nanopores length, radius, and geometry of their network by the preparation parameters. The material is produced from 3D network of 1D Ge nanowires in alumina by a dedicated annealing treatment that causes Ge to evaporate. We show that the main limiting factors for the production of the nanopore networks are the fraction of Ge nanowires before annealing combined with the unit cell parameters of their network. The 3D networks of nanopores form easily when the Ge atomic fraction in the film is less than 40 %. For larger Ge percentages, the alumina matrix collapses because the interconnection to the neighbouring unit cells in the vertical direction is lost. The refractive index of the materials can be tuned in a wide range by varying the porosity, i.e. the parameters of the Ge nanowire network.
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•Material consisting of continuous 3D network of nanopores in alumina was produced by magnetron sputtering.•The nanopores have tunable radius and geometrical parameters of their network in a wide range of values.•The limiting factor for the material stability is the thickness of alumina walls between the pores.•The refraction index of the material is controllable by the nanopore radii and network parameters.
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•TNp and TN/Au catalysts were synthesized and tested in the CWPO of MO.•Obtained data showed predominant performance of TNp under ambient conditions.•TN/Au catalyst was active only at ...temperatures above 40°C.•Surplus of H2O2 enabled efficient degradation of MO and recovery of peroxo groups.
Titanium dioxide based nanotubes (TN) were synthesized through hydrothermal synthesis route followed by acid washing under ambient conditions. The as-prepared TN with high specific surface area and titanate layered structure were subsequently functionalized with titanium (IV) peroxo groups (TNp) and gold (TN/Au) to examine an influence of non-metal/metal presence in the CWPO of aqueous methyl orange (MO) solution under ambient conditions. The obtained results showed higher activity and mineralization extent of MO over TNp catalyst in comparison to TN/Au at ambient conditions. The 50ppm MO solution containing 2g/L of TNp catalyst and stoichiometric amount of hydrogen peroxide was purified up to 68% of TOC during 4h of CWPO process. As far as TN/Au is concerned, high TOC removal (83%) was only witnessed when the CWPO process was conducted at elevated temperatures (T=80°C). Moreover, comparing the simplicity of the synthesis routes and catalytic activities of obtained solids, the metal-free catalyst showed greater potential for the degradation of MO solution under ambient conditions without deprivation of its activity, as demonstrated in successive 4-cycle oxidation runs conducted in the presence of a surplus amount of H2O2.
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