The interaction of water with TiO2 is crucial to many of its practical applications, including photocatalytic water splitting. Following the first demonstration of this phenomenon 40 years ago there ...have been numerous studies of the rutile single-crystal TiO2 (110) interface with water. This has provided an atomic-level understanding of the water-TiO2 interaction. However, nearly all of the previous studies of water/TiO2 interfaces involve water in the vapour phase. Here, we explore the interfacial structure between liquid water and a rutile TiO2 (110) surface pre-characterized at the atomic level. Scanning tunnelling microscopy and surface X-ray diffraction are used to determine the structure, which is comprised of an ordered array of hydroxyl molecules with molecular water in the second layer. Static and dynamic density functional theory calculations suggest that a possible mechanism for formation of the hydroxyl overlayer involves the mixed adsorption of O2 and H2 O on a partially defected surface. The quantitative structural properties derived here provide a basis with which to explore the atomistic properties and hence mechanisms involved in TiO2 photocatalysis.
Manipulating the surface energy, and thereby the wetting properties of solids, has promise for various physical, chemical, biological and industrial processes. Typically, this is achieved by either ...chemical modification or by controlling the hierarchical structures of surfaces. Here we report a phenomenon whereby the wetting properties of vermiculite laminates are controlled by the hydrated cations on the surface and in the interlamellar space. We find that vermiculite laminates can be tuned from superhydrophilic to hydrophobic simply by exchanging the cations; hydrophilicity decreases with increasing cation hydration free energy, except for lithium. The lithium-exchanged vermiculite laminate is found to provide a superhydrophilic surface due to its anomalous hydrated structure at the vermiculite surface. Building on these findings, we demonstrate the potential application of superhydrophilic lithium exchanged vermiculite as a thin coating layer on microfiltration membranes to resist fouling, and thus, we address a major challenge for oil-water separation technology.
Intelligent transport of molecular species across different barriers is critical for various biological functions and is achieved through the unique properties of biological membranes1-4. Two ...essential features of intelligent transport are the ability to (1) adapt to different external and internal conditions and (2) memorize the previous state5. In biological systems, the most common form of such intelligence is expressed as hysteresis6. Despite numerous advances made over previous decades on smart membranes, it remains a challenge to create a synthetic membrane with stable hysteretic behaviour for molecular transport7-11. Here we demonstrate the memory effects and stimuli-regulated transport of molecules through an intelligent, phasechanging MoS2 membrane in response to external pH. We show that water and ion permeation through 1T' MoS2 membranes follows a pH-dependent hysteresis with a permeation rate that switches by a few orders of magnitude. We establish that this phenomenon is unique to the 1T' phase of MoS2, due to the presence of surface charge and exchangeable ions on the surface. We further demonstrate the potential application of this phenomenon in autonomous wound infection monitoring and pH-dependent nanofiltration. Our work deepens understanding of the mechanism of water transport at the nanoscale and opens an avenue for the development of intelligent membranes.
ABSTRACTMarcos, MA, Koulla, PM, and Anthos, ZI. Preseason maximal aerobic power in professional soccer players among different divisions. J Strength Cond Res 32(2)356–363, 2018—The purpose of this ...study was to examine and compare the anthropometric, maximal oxygen uptake (VCombining Dot AboveO2max), and positional differences of first division (D1) professional football players from players of second (D2) and third (D3) divisions in Cyprus football leagues. Four hundred twenty-one professional male football players participated in this study. All subjects underwent anthropometric and body composition evaluation. In addition, they performed an incremental cardiopulmonary exercise testing (CPET) on a treadmill for VCombining Dot AboveO2max evaluation. The results were analyzed using 1-way analysis of variance, between subjects design revealing significant effects among the divisions. Tukeyʼs honest significant difference (HSD) tests demonstrated that players from D1 scored significantly higher on VCombining Dot AboveO2max and lasted significantly longer on the treadmill than participants of D2 and D3 (p ≤ 0.05). Similar findings were demonstrated when D2 was contrasted against D3 players. Goalkeepers, defenders, and forwards demonstrated significantly higher anthropometric measurements, whereas wingers and midfielders demonstrated significantly higher VCombining Dot AboveO2max (p ≤ 0.05) than goalkeepers and defenders. The findings of this study clearly demonstrated that cardiovascular fitness, as determined by CPET, is an important fitness parameter that differentiates professional football players who play at a more advanced level. This could be attributed to the different seasonal schedules that allow for longer transition time for lower division players and thus favoring greater detraining effects. Emphasis should be given by fitness professionals on transition period training to minimize the detraining effects especially in lower divisions.
Permanent-magnet motors with rare-earth magnets are among the best candidates for high-performance applications such as automotive applications. However, due to their cost and risks relating to the ...security of supply, alternative solutions such as ferrite magnets have recently become popular. In this paper, the two major design challenges of using ferrite magnets for a high-torque-density and high-speed application, i.e., their low remanent flux density and low coercivity, are addressed. It is shown that a spoke-type design utilizing a distributed winding may overcome the torque density challenge due to a simultaneous flux concentration and a reluctance torque possibility. Furthermore, the demagnetization challenge can be overcome through the careful optimization of the rotor structure, with the inclusion of nonmagnetic voids on the top and bottom of the magnets. To meet the challenges of a high-speed operation, an extensive rotor structural analysis has been undertaken, during which electromagnetics and manufacturing tolerances are taken into account. Electromagnetic studies are validated through the testing of a prototype, which is custom built for static torque and demagnetization evaluation. The disclosed motor design surpasses the state-of-the-art performance and cost, merging the theories into a multidisciplinary product.
Resolving the atomic structure of the surface of ice particles within clouds, over the temperature range encountered in the atmosphere and relevant to understanding heterogeneous catalysis on ice, ...remains an experimental challenge. By using first-principles calculations, we show that the surface of crystalline ice exhibits a remarkable variance in vacancy formation energies, akin to an amorphous material. We find vacancy formation energies as low as ~0.1-0.2 eV, which leads to a higher than expected vacancy concentration. Because a vacancy's reactivity correlates with its formation energy, ice particles may be more reactive than previously thought. We also show that vacancies significantly reduce the formation energy of neighbouring vacancies, thus facilitating pitting and contributing to pre-melting and quasi-liquid layer formation. These surface properties arise from proton disorder and the relaxation of geometric constraints, which suggests that other frustrated materials may possess unusual surface characteristics.
The study of catalytic behavior begins with one seemingly simple process, namely the hydrogenation of O to H2O on platinum. Despite the apparent simplicity its mechanism has been much debated. We ...have used density functional theory with gradient corrections to examine microscopic reaction pathways for several elementary steps implicated in this fundamental catalytic process. We find that H2O formation from chemisorbed O and H atoms is a highly activated process. The largest barrier along this route, with a value of ∼1 eV, is the addition of the first H to O to produce OH. Once formed, however, OH groups are easily hydrogenated to H2O with a barrier of ∼0.2 eV. Disproportionation reactions with 1:1 and 2:1 stoichiometries of H2O and O have been examined as alternative routes for OH formation. Both stoichiometries of reaction produce OH groups with barriers that are much lower than that associated with the O + H reaction. H2O, therefore, acts as an autocatalyst in the overall H2O formation process. Disproportionation with a 2:1 stoichiometry is thermodynamically and kinetically favored over disproportionation with a 1:1 stoichiometry. This highlights an additional (promotional) role of the second H2O molecule in this process. In support of our previous suggestion that the key intermediate in the low-temperature H2O formation reaction is a mixed OH and H2O overlayer we find that there is a very large barrier for the dissociation of the second H2O molecule in the 2:1 disproportionation process. We suggest that the proposed intermediate is then hydrogenated to H2O through a very facile proton-transfer mechanism.
It has long been known that the dielectric constant of confined water should be different from that in bulk. Recent experiments have shown that it is vanishingly small, however the origin of the ...phenomenon remains unclear. Here we used
ab initio
molecular dynamics simulations (AIMD) and AIMD-trained machine-learning potentials to understand water's structure and electronic properties underpinning this effect. For the graphene and hexagonal boron-nitride substrates considered, we find that it originates in the spontaneous anti-parallel alignment of the water dipoles in the first two water layers near the solid interface. The interfacial layers exhibit net ferroelectric ordering, resulting in an overall anti-ferroelectric arrangement of confined water. Together with constrained hydrogen-bonding orientations, this leads to much reduced out-of-plane polarization. Furthermore, we directly contrast AIMD and simple classical force-field simulations, revealing important differences. This work offers insight into a property of water that is critical in modulating surface forces, the electric-double-layer formation and molecular solvation, and shows a way to compute it.
Atomistic simulations explain recent experimental findings of dielectric polarization suppression in confined water, revealing it originates in an anti-ferroelectric order driven by spontaneous antiparallel alignment of water dipoles at surfaces.
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