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Hydrated cation–π interactions at liquid–solid interfaces between hydrated cations and aromatic ring structures of carbon-based materials are pivotal in many material, biological, and chemical processes, and water serves as a crucial mediator in these interactions. However, a full understanding of the hydrated cation–π interactions between hydrated alkaline earth cations and aromatic ring structures, such as graphene remains elusive. Here, we present a molecular picture of hydrated cation–π interactions for Mg2+ and Ca2+ by using the density functional theory methods. Theoretical results show that the graphene sheet can distort the hydration shell of the hydrated Ca2+ to interact with Ca2+ directly, which is water–cation–π interactions. In contrast, the hydration shell of the hydrated Mg2+ is quite stable and the graphene sheet interacts with Mg2+ indirectly, mediated by water molecules, which is the cation–water–π interactions. These results lead to the anomalous order of adsorption energies for these alkaline earth cations, with hydrated Mg2+–π < hydrated Ca2+–π when the number of water molecules is large (n ≥ 6), contrary to the order observed for cation–π interactions in the absence of water molecules (n = 0). The behavior of hydrated alkaline earth cations adsorbed on a graphene surface is mainly attributed to the competition between the cation–π interactions and hydration effects. These findings provide valuable details of the structures and the adsorption energy of hydrated alkaline earth cations adsorbed onto the graphene surface. [ABSTRACT FROM AUTHOR]

Crystal materials can exhibit novel properties under high pressure, which are completely different from properties under ambient conditions. Water ice has an exceptionally rich phase diagram with at least 20 known crystalline ice phases from experiments, where the high-pressure ice X and ice XVIII behave as an ionic state and a superionic state, respectively. Thus, the ice structures stabilized under high pressure are very likely to possess other novel properties. Herein, we constructed a sequence of hypothetical high-pressure ices whose structures were generated according to the topological frameworks of common metal oxides. Based on density functional theory calculations, the pressure-induced phase transition sequence is in order that the known Ag2O-Pn3¯m structure (ice X) transformed into a previously undiscovered TiO2_brookite-Pbca structure at a pressure of 300 GPa, followed by a transition to a new NaO2-Pa3 structure at a pressure of 2120 GPa. Hitherto unreported NaO2-Pa3 ice with a cubic structure is in the ionic state, where the oxygen atoms in NaO2-Pa3 have a face-centered cubic (fcc) sublattice, and the coordination number of H atoms increases to 3. These two structures are dynamically stable according to phonon spectrum analysis and remain stable at temperature of 100 K based on ab initio molecular dynamics (AIMD) simulations. More importantly, the NaO2-Pa3 ice exhibits novel metallic properties with a closing band gap above a pressure of 2600 GPa, owing to the electron orbital coupling of oxygen atoms in close proximity induced by pressure. [ABSTRACT FROM AUTHOR]

Ripples on graphene play a crucial role in manipulating its physical and chemical properties. However, producing ripples, especially at the nanoscale, remains challenging with current experimental methods. In this study, we report that tiny ripples in graphene can be generated by the adsorption of a single metal cation (Na+, K+, Mg2+, Ca2+, Cu2+, Fe3+) onto a graphene sheet, based on the density functional theory calculations. We attribute this to the cation–π interaction between the metal cation and the aromatic rings on the graphene surface, which makes the carbon atoms closer to metal ions, causing deformation of the graphene sheet, especially in the out-of-plane direction, thereby creating ripples. The equivalent pressures applied to graphene sheets in out-of-plane direction, generated by metal cation–π interactions, reach magnitudes on the order of gigapascals (GPa). More importantly, the electronic and mechanical properties of graphene sheets are modified by the adsorption of various metal cations, resulting in opened bandgaps and enhanced rigidity characterized by a higher elastic modulus. These findings show great potential for applications for producing ripples at the nanoscale in graphene through the regulation of metal cation adsorption. [ABSTRACT FROM AUTHOR]

Self-powered wearable pressure sensors based on flexible electronics have emerged as a new trend due to the increasing demand for intelligent and portable devices. Improvements in pressure-sensing performance, including in the output voltage, sensitivity and response time, can greatly expand their related applications; however, this remains challenging. Here, we report on a highly sensitive piezoelectric sensor with novel light-boosting pressure-sensing performance, based on a composite membrane of copper phthalocyanine (CuPC) and graphene oxide (GO) (CuPC@GO). Under light illumination, the CuPC@GO piezoelectric sensor demonstrates a remarkable increase in output voltage (381.17 mV, 50 kPa) and sensitivity (116.80 mV/kPa, <5 kPa), which are approximately twice and three times of that the sensor without light illumination, respectively. Furthermore, light exposure significantly improves the response speed of the sensor with a response time of 38.04 µs and recovery time of 58.48 µs, while maintaining excellent mechanical stability even after 2000 cycles. Density functional theory calculations reveal that increased electron transfer from graphene to CuPC can occur when the CuPC is in the excited state, which indicates that the light illumination promotes the electron excitation of CuPC, and thus brings about the high polarization of the sensor. Importantly, these sensors exhibit universal spatial non-contact adjustability, highlighting their versatility and applicability in various settings. [ABSTRACT FROM AUTHOR]

Author(s): Liang Chen [1, 2, 3]; Guosheng Shi [2]; Jie Shen [4]; Bingquan Peng [1]; Bowu Zhang [2]; Yuzhu Wang [2]; Fenggang Bian [2]; Jiajun Wang [1]; Deyuan Li [1, [...]

The recovery of gold from water is an important research area. Recent reports have highlighted the ultrahigh capacity and selective extraction of gold from electronic waste using reduced graphene oxide (rGO). Here, we made a further attempt with the thermal rGO membranes and found that the thermal rGO membranes also had a similarly high adsorption efficiency (1.79 g gold per gram of rGO membranes at 1000 ppm). Furthermore, we paid special attention to the detailed selectivity between Au3+ and other ions by rGO membranes. The maximum adsorption capacity for Au3+ ions was about 16 times that of Cu2+ ions and 10 times that of Fe3+ ions in a mixture solution with equal proportions of Au3+/Cu2+ and Au3+/Fe3+. In a mixed-ion solution containing Au3+:Cu2+:Na+:Fe3+:Mg2+ of printed circuit board (PCB), the mass of Au3+:Cu2+:Na+:Fe3+:Mg2+ in rGO membranes is four orders of magnitude higher than the initial mass ratio. A theoretical analysis indicates that this selectivity may be attributed to the difference in the adsorption energy between the metal ions and the rGO membrane. The results are conducive to the usage of rGO membranes as adsorbents for Au capture from secondary metal resources in the industrial sector. [ABSTRACT FROM AUTHOR]

2D materials are promising nanomaterials for future applications due to their predominant quantum effects and unique properties in optics, electrics, magnetics, and mechanics. However, explorations in unique properties and potential applications of novel 2D materials have been hampered by synthesis and their stability under ambient conditions. Recently, in the graphene, 2D β‐CuI is observed experimentally under ambient conditions. Here, it is shown that this 2D β‐CuI@graphene possesses unexpected piezoresistive effect and room‐temperature ferromagnetism. Moreover, this 2D β‐CuI crystal is likely to be stable in a wide range of temperature, that is, below 900 K. Theoretical studies reveal that the unexpected piezoresistive effect is mainly attributable to the convergence of the electrons on Cu and I atoms to the Fermi level with increasing strain. There is a magnetic moment that is ≈0.97 μB on the edge of β‐CuI nanocrystal created by an iodine vacancy, which is considered the origin of such strong room‐temperature ferromagnetism. Clearly, the 2D β‐CuI@graphene provides a promising nanomaterial in the nano‐sensors with low power consumption pressure and magnetic nano‐devices with a size down to atomic scale. The discovery in the present work will evoke various new 2D nanomaterials with novel properties in nanotechnology, biotechnology, sensor materials, and technologies. [ABSTRACT FROM AUTHOR]

Understanding the configuration and properties of the simplest lithium‐ion crystal, the Li‐Cl crystal, is essential for developing Li‐based electrochemical energy storage and conversion devices. Under ambient conditions, LiCl in a 1:1 stoichiometry is the only known stable form of the Li‐Cl crystal, and the corresponding crystals are insulating. Here, using cryo‐electron microscopy (cryo‐EM) and X‐ray photoelectron spectroscopy (XPS), this work reports a novel abnormal 2D Li2Cl crystal in ultra‐thin reduced graphene oxide (rGO) membranes by simply soaking the rGO membrane in unsaturated LiCl solution under ambient conditions and showed its high‐resolution image. Unexpectedly, such Li2Cl crystal presents metallic properties rather than insulating properties. Using vacuum filtration of the unsaturated LiCl solution through rGO membranes, this work prepares the rGO membranes with high content Li2Cl, displaying a high areal capacitance of 220 mF cm−2. Remarkably, the Li2Cl‐rGO membranes also exhibit heterostructure property and piezoelectricity. For the excess Li and unique electrical characteristics, these Li2Cl‐rGO membranes can be used as a humidity sensor. These findings point to possibilities for creating new Li‐based materials and fabricating novel high‐performance electronic devices, transistors, and sensors. [ABSTRACT FROM AUTHOR]

The adsorption dynamics of double-stranded DNA (dsDNA) molecules on a graphene oxide (GO) surface are important for applications of DNA/GO functional structures in biosensors, biomedicine and materials science. In this work, molecular dynamics simulations were used to examine the adsorption of different length dsDNA molecules (from 4 bp to 24 bp) on the GO surface. The dsDNA molecules could be adsorbed on the GO surface through the terminal bases and stand on the GO surface. For short dsDNA (4 bp) molecules, the double-helix structure was partially or totally broken and the adsorption dynamics was affected by the structural fluctuation of short dsDNA and the distribution of the oxidized groups on the GO surface. For long dsDNA molecules (from 8 bp to 24 bp) adsorption is stable. By nonlinear fitting of the contact angle between the axis of the dsDNA molecule and the GO surface, we found that a dsDNA molecule adsorbed on a GO surface has the chance of orienting parallel to the GO surface if the length of the dsDNA molecule is longer than 54 bp. We attributed this behavior to the flexibility of dsDNA molecules. With increasing length, the flexibility of dsDNA molecules also increases, and this increasing flexibility gives an adsorbed dsDNA molecule more chance of reaching the GO surface with the free terminal. This work provides a whole picture of adsorption of dsDNA molecules on the GO surface and should be of benefit for the design of DNA/GO based biosensors. [ABSTRACT FROM AUTHOR]

Great efforts have been made to separate micro/nanoparticles in small-volume specimens, but it is a challenge to achieve the simple, maneuverable and low-cost separation of sub-microliter suspension with large separation distances. By simply adding trace amounts of cations (Mg2+/Ca2+/Na+), we experimentally achieved the size-dependent spontaneous separation of colloidal particles in an evaporating droplet with a volume down to 0.2 μL. The separation distance was at a millimeter level, benefiting the subsequent processing of the specimen. Within only three separating cycles, the mass ratio between particles with diameters of 1.0 μm and 0.1 μm can be effectively increased to 13 times of its initial value. A theoretical analysis indicates that this spontaneous separation is attributed to the size-dependent adsorption between the colloidal particles and the aromatic substrate due to the strong hydrated cation-π interactions. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials are widely used in various fields, among which the application prospect in filtering and purifying water resources is broad. An important factor in sieving water molecules and other substances is the interlayer spacing of 2D material membranes. The interlayer spacing of graphene oxide and graphene membranes can be controlled by hydrated cations because of hydrated cation–π interaction. Similarly, our simulations show that hydrated cations can also control the interlayer spacing between hexagonal boron nitride (h-BN) sheets, which are smaller than that of graphene oxide sheets and graphene sheets. The interlayer distances are 8.70, 8.62, 7.68, 8.21, 8.93, 8.11 and 8.18 Å for hydrated Li+, Na+, K+, Mg2+, Ca2+, Cu2+ and Zn2+, respectively. Both hydration energy and the radius of the hydrated cation are deciding factors for monovalent hydrated cations and divalent hydrated cations in affecting the h-BN layer spacing. Further calculations indicate that unlike graphene and graphene oxide dominated by the hydrated cation–π interaction, the interactions between h-BN sheets and hydrate cations are mainly hydrogen bonds. However, there is an obvious hydrated cation–π interaction between hydrated K+ and the h-BN sheets. Our results are helpful for future ion sieving applications using the h-BN membranes. [ABSTRACT FROM AUTHOR]

Histidine (His) is widely involved in the structure and function of biomolecules. Transition-metal ions, such as Zn2+ and Cu2+, widely exist in biological environments, and they are crucial to many life-sustaining physiological processes. Herein, by employing density function calculations, we theoretically show that the water affinity of His can be enhanced by the strong cation–π interaction between His and Zn2+ and Cu2+. Further, the solubility of His is experimentally demonstrated to be greatly enhanced in ZnCl2 and CuCl2 solutions. The existence of cation–π interaction is demonstrated by fluorescence, ultraviolet (UV) spectroscopy and nuclear magnetic resonance (NMR) experiments. These findings are of great importance for the bioavailability of aromatic drugs and provide new insight for understanding the physiological functions of transition metal ions. [ABSTRACT FROM AUTHOR]

A similarity was noted between the transient responses of electrorheological fluids to square-wave electric fields with high frequency and that to the field with very low frequency, or the sudden applied direct current field. A similarity was also observed in the stress rise processes in both cases. These were the results of an examination of transient responses of the fluids to the fields in steady shear, using computational simulation method.

Lithium plays an increasingly important role in scientific and industrial processes, and it is extremely important to extract lithium from a high Mg2+/Li+ mass ratio brine or to recover lithium from the leachate of spent lithium-ion batteries. Conventional wisdom shows that Li+ with low valence states has a much weaker adsorption (and absorption energy) with graphene than multivalent ions such as Mg2+. Here, we show the selective adsorption of Li+ in thermally reduced graphene oxide (rGO) membranes over other metal ions such as Mg2+, Co2+, Mn2+, Ni2+, or Fe2+. Interestingly, the adsorption strength of Li+ reaches up to 5 times the adsorption strength of Mg2+, and the mass ratio of a mixed Mg2+/Li+ solution at a very high value of 500 : 1 can be effectively reduced to 0.7 : 1 within only six experimental treatment cycles, demonstrating the excellent applicability of the rGO membranes in the Mg2+/Li+ separation. A theoretical analysis indicates that this unexpected selectivity is attributed to the competition between cationâ€" Ď€ interaction and steric exclusion when hydrated cations enter the confined space of the rGO membranes. [ABSTRACT FROM AUTHOR]

Cation–π interactions are essential for many chemical, biological, and material processes, and these processes usually involve an aqueous salt solution. However, there is still a lack of a full understanding of the hydrated cation–π interactions between the hydrated cations and the aromatic ring structures on the molecular level. Here, we report a molecular picture of hydrated cation–π interactions, by using the calculations of density functional theory (DFT). Specifically, the graphene sheet can distort the hydration shell of the hydrated K+ to interact with K+ directly, which is hereafter called water–cation–π interactions. In contrast, the hydration shell of the hydrated Li+ is quite stable and the graphene sheet interacts with Li+ indirectly, mediated by water molecules, which we hereafter call the cation–water–π interactions. The behavior of hydrated cations adsorbed on a graphene surface is mainly attributed to the competition between the cation–π interactions and hydration effects. These findings provide valuable details of the structures and the adsorption energy of hydrated cations adsorbed onto the graphene surface. [ABSTRACT FROM AUTHOR]

Orientation arrangement of hydration shells for hydrated cation plays an important role in solid–liquid interfaces. However, there is still poor understanding about the structure of the hydration shells formed at the solid–liquid interface. In this paper, we study the structures and interaction of typical hydrated alkali metal cation (Li+, Na+ and K+) on the flat polar material surface of the hexagonal boron nitride (h-BN) sheet by increasing the number of water molecules from n = 1 to n = 9 through the artificial bee colony (ABC) algorithm and density functional theory calculations. The hydration shell around alkali metal cation could be divided into two groups, one is Li+-(H2O)n and Na+-(H2O)n and the other is K+-(H2O)n. The orientation of hydration shell for K+-(H2O)n complexes exhibits stronger anisotropy behaviour than both Li+-(H2O)n and Na+-(H2O)n complexes on the h-BN sheet. It is found that the stronger orientation anisotropy of K+-(H2O)n originates from the weak cation-hydration energy and its weak influence upon the π-K+ interaction. Our findings provide valuable insights into the microscopic details of the structures and adsorption of hydrated cation on the h-BN sheet. [ABSTRACT FROM AUTHOR]