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•The OH stretch is mainly dependent on the local hydrogen-bonded networks.•Temperature decrease mainly leads to a structural transition from DA to DDAA.•A local statistical ...interpretation of the water structure is proposed.
In this Letter, Raman spectroscopy is employed to study supercooled water down to a temperature of 248K at ambient pressure. Based on our interpretation of the Raman OH stretching band, decreasing temperature mainly leads to a structural transition from the single donor–single acceptor (DA) to the double donor–double acceptor (DDAA) hydrogen bonding motif. Additionally, a local statistical interpretation of the water structure is proposed, which reveals that a water molecule interacts with molecules in the first shell through various local hydrogen-bonded networks. From this, a local structure order parameter is proposed to explain the short-range order and long-range disorder.
Hydrophobic interactions are involved in and believed to be the fundamental driving force of many chemical and biological phenomena in aqueous environments. This review focuses on our current ...understanding on hydrophobic effects. As a solute is embedded into water, the interface appears between solute and water, which mainly affects the structure of interfacial water (the topmost water layer at the solute/water interface). From our recent structural studies on water and air-water interface, hydration free energy is derived and utilized to investigate the origin of hydrophobic interactions. It is found that hydration free energy depends on the size of solute. With increasing the solute size, it is reasonably divided into initial and hydrophobic solvation processes, and various dissolved behaviors of the solutes are expected in different solvation processes, such as dispersed and accumulated distributions in solutions. Regarding the origin of hydrophobic effects, it is ascribed to the structural competition between the hydrogen bondings of interfacial and bulk water. This can be applied to understand the characteristics of hydrophobic interactions, such as the dependence of hydrophobic interactions on solute size (or concentrations), the directional natures of hydrophobic interactions, and temperature effects on hydrophobic interactions.
Atomic clusters, consisting of a few to a few thousand atoms, have emerged over the past 40 years as the ultimate nanoparticles, whose structure and properties can be controlled one atom at a time. ...One of the early motivations in studying clusters was to understand how the properties of matter evolve as a function of size, shape, and composition. Over the past few decades, more than 200 000 papers have been published in this field. These studies have not only led to a considerable understanding of this evolution from clusters to crystals, but also have revealed many unusual size-specific properties that make cluster science an interdisciplinary field on its own, bridging physics, chemistry, materials science, biology, and medicine. More importantly, the possibility of creating a new class of materials, composed of clusters instead of atoms as building blocks, has fueled the hope that one can synthesize materials from the bottom-up with unique and tailored properties. This Review focuses on the properties that set clusters apart from their corresponding bulk. Furthermore, this Review describes how different electron-counting rules can lead to the design of stable clusters, mimicking the chemistry of atoms. We highlight the potential of these “superatoms” as building blocks of cluster-assembled materials. Specifically, we emphasize cluster-inspired materials for energy applications. The concluding section includes a summary of the salient features of clusters, potential challenges that remain, and an outlook for the future of cluster science.
In this work, from the discussion on water structure and clusters, it can be deduced that the OH stretching vibration is closely related to local hydrogen-bonded network for a water molecule, and ...different OH vibrations can be assigned to OH groups engaged in various hydrogen bonding. At ambient condition, the main local hydrogen bonding for a molecule can be classified as DDAA (double donor–double acceptor), DDA (double donor–single acceptor), DAA (single donor–double acceptor) and DA (single donor–single acceptor) and free OH vibrations. As for water at 290
K and 0.1
MPa pressure, the OH stretching region of the Raman spectrum can be deconvoluted into five sub-bands, which are located at 3014, 3226, 3432, 3572, and 3636
cm
−1, and can be assigned to
ν
DAA-OH,
ν
DDAA-OH,
ν
DA-OH,
ν
DDA-OH, and free OH
2 symmetric stretching vibrations, respectively.
Raman spectroscopy was utilized to investigate the effects of dissolved NaCl on water structure. For aqueous NaCl solutions, the difference spectra indicate a clear isosbestic point at 3345cm−1 and a ...weak isosbestic point around 3625cm−1. According to our explanation on Raman OH stretching band of water, it can be inferred that the addition of NaCl primarily breaks the tetrahedral hydrogen bonding and promotes formation of the donor hydrogen bonding in water, and slightly lowers the amount of free OH bonds. This is different from the effects of pressure and temperature on water structure. For liquid water, a water molecule interacts with neighboring water molecules through various local hydrogen bonded networks. Additionally, the enthalpy change of hydrogen bonding in water can be determined to be 11.35kJ/mol.
The increasing concentration of CO2 in the atmosphere, and the resulting environmental problems, call for effective ways to convert CO2 into valuable fuels and chemicals for a sustainable carbon ...cycle. In such a context, CO2 electrocatalytic reduction has been hotly studied due to the merits of ambient operational conditions and easy control of the reaction process by changing the applied potential. Among the various systems studied, Cu and Au are found to possess the highest Faradaic efficiency toward cathodic electrocatalytic conversion of CO2 to hydrocarbons and CO, respectively. However, both of them suffer from large overpotentials owing to the limitations imposed by the scaling relations between the carbonaceous adsorbates. Therefore, establishing how to break the scaling relations for effective electrochemical conversion of CO2 has become an urgent research topic. The recent advances in breaking the adsorption energy scaling relations to reduce the overpotential, improve the catalytic activity and suppress the side reaction, are summarized. The origin of the scaling relations, their negative effects on CO2 electrocatalysis, and the strategies for breaking the limitations are discussed. Some suggestions for future study are also proposed.
The origin of the scaling relations, their negative effects on CO2 electrocatalysis, and the strategies for breaking their limitations to reduce the overpotential, improve the catalytic activity and suppress the side reaction, are discussed.
In recent years, microwave mechanical rock breaking—an energy-saving technology with environmental benefits and high efficiency—is increasingly being used to improve the rock-breaking efficiency of ...geothermal well drilling. Herein, we studied the evolution of different types of cracks in gabbro under uniaxial loading using the acoustic emission (AE) technique. The results show that, after microwave heating, the number of microcracks in gabbro increases and AE becomes more and more active. During the loading process, AE characteristics can be divided into three typical periods: the peak period, silent period, and active period, which are closely related to the deformation process of the rock. When the heating power exceeds 3.3 kW, the proportion of shear cracks increases with increases in irradiation energy. With an increase in stress level, the proportion of tensile cracks increases, but near failure, shear fracture is still dominant. Under the same irradiation energy, the combination of high heating power and low heating time is more conducive to rock failure. Further, when the heating power is greater than 3.3 kW, the damage to rock is more obvious. The test results provide a theoretical and experimental basis for determining the optimal microwave irradiation conditions to improve rock-breaking efficiency in geothermal development.
A two-dimensional (2D) periodic Fe phthalocyanine (FePc) single-layer sheet has very recently been synthesized experimentally (Abel, M.; et al. J. Am. Chem. Soc. 2011, 133, 1203), providing a novel ...pathway for achieving 2D atomic sheets with regularly and separately distributed transition-metal atoms for unprecedented applications. Here we present first-principles calculations based on density functional theory to investigate systematically the electronic and magnetic properties of such novel organometallics (labeled as TMPc, TM = Cr–Zn) as free-standing sheets. Among them, we found that only the 2D MnPc framework is ferromagnetic, while 2D CrPc, FePc, CoPc, and CuPc are antiferromagnetic and 2D NiPc and ZnPc are nonmagnetic. The difference in magnetic couplings for the studied systems is related to the different orbital interactions. Only MnPc displays metallic d xz and d yz orbitals that can hybridize with p electrons of Pc, which mediates the long-range ferromagnetic coupling. Monte Carlo simulations based on the Ising model suggest that the Curie temperature (T C) of the 2D MnPc framework is ∼150 K, which is comparable to the highest T C achieved experimentally, that of Mn-doped GaAs. The present study provides theoretical insight leading to a better understanding of novel phthalocyanine-based 2D structures beyond graphene and BN sheets.
Salt weathering has considerable effects, and it has recently become the subject of interest among researchers and engineers, especially in terms of sandstone heritage buildings and sandstone ...monuments. However, the impacts of salt weathering on sandstone after wetting-drying cycles have been neglected in the literature. Under the conditions of the long-term or gradual underground seepage of water into sandstone heritage buildings and monuments, salt accumulation and recrystallization occur in sandstone when the rate of evaporation is sufficiently high, and they reduce rock stability. In view of this problem, experiments subjecting sandstone to up to 50 wetting-drying cycles were conducted using water and solutions containing concentrations of 4%, 6% or 8% magnesium sulfate (MgSO4). The physical and mechanical properties were tested after different wetting-drying cycles. The results show that the wetting-drying cycles impacted the sandstone samples soaked in a salt solution more than the samples that were soaked in only water. Thirty cycles is the threshold number in terms of changes in P-wave velocity, thermal conductivity and tensile strength. A correlation analysis was conducted, and it showed that both color lightness and thermal conductivity are good parameters for evaluating tensile strength. The results contribute to the evaluation process and protection of sandstone heritage buildings and monuments against salt weathering.
•A combined experiment was designed and conducted for studying salt weathering of sandstone heritage.•Cyclic wetting and drying cycles substantially accelerate the weathering process.•Thirty cycles is the threshold in our results after which the sandstone begins to deteriorate.•Color and thermal conductivity were introduced for evaluating tensile strength.
In addition to spintronics another motivation for exploring ferromagnetic two-dimensional materials is for biomedical applications such as magnetic labeling and hyperthermia treatment of tumors. ...Unfortunately, the widely studied Mn-containing monolayer is not biocompatible, although it is ferromagnetic. Here using first principles calculations combined with Monte Carlo simulations based on the Ising model, we systematically study a class of 2D ferromagnetic monolayers CrX3 (X = Cl, Br, I). The feasibility of exfoliation from their layered bulk phase is confirmed by the small cleavage energy and high in-plane stiffness. Spin-polarized calculations, combined with self-consistently determined Hubbard U that accounts for strong correlation energy, demonstrate that CrX3 (X = Cl, Br, I) monolayers are ferromagnetic and that Cr is trivalent and carries a magnetic moment of 3 μ(B); the resulting Cr(3+) ions are biocompatible. The corresponding Curie temperatures for CrCl3, CrBr3 and CrI3 are found to be 66, 86, and 107 K, respectively, which can be increased to 323, 314, and 293 K by hole doping. The biocompatibility and ferromagnetism render these Cr-containing trihalide monolayers unique for applications.
