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While nanoporous graphene oxide (GO) is recognized as one of the most promising reverse osmosis desalination membranes, limited attention has been paid to controlling desalination performance through the large GO pores, primarily due to significant ion leakage resulting in the suboptimal performance of these pores. In this study, we employed a molecular dynamics simulation approach to demonstrate that Mg2+ ions, adhered to carboxylated GO nanopores, can function as gates, regulating the transport of ions (Na+ and Cl−) through the porous GO membrane. Specifically, the presence of divalent cations near a nanopore reduces the concentration of salt ions in the vicinity of the pore and prolongs their permeation time across the pore. This subsequently leads to a notable enhancement in salt rejection rates. Additionally, the ion rejection rate increases with more adsorbed Mg2+ ions. However, the presence of the adsorbed Mg2+ ions compromises water transport. Here, we also elucidate the impact of graphene oxidation degree on desalination. Furthermore, we design an optimal combination of adsorbed Mg2+ ion quantity and oxidation degree to achieve high water flux and salt rejection rates. This work provides valuable insights for developing new nanoporous graphene oxide membranes for controlled water desalination. [ABSTRACT FROM AUTHOR]

[Display omitted] Water dissociation is of fundamental importance in scientific fields and has drawn considerable interest in diverse technological applications. However, the high activation barrier of breaking the O H bond within the water molecule has been identified as the bottleneck, even for the water adsorbed on the graphene oxide (GO). Herein, using the density functional theory calculations, we demonstrate that the water molecule can be spontaneously dissociated on GO supported by the (1 1 1) surface of the copper substrate (Copper-GO). This process involves a proton transferring from water to the interfacial oxygen group, and a hydroxide covalently bonding to GO. Compared to that on GO, the water dissociation barrier on Copper-GO is significantly decreased to be less than or comparable to thermal fluctuations. This is ascribed to the orbital-hybridizing interaction between copper substrate and GO, which enhances the reaction activity of interfacial oxygen groups along the basal plane of GO for water dissociation. Our work provides a novel strategy to access water dissociation via the substrate-enhanced reaction activity of interfacial oxygen groups on GO and indicates that the substrate can serve as an essential key to tuning the catalytic performance of various two-dimensional material devices. [ABSTRACT FROM AUTHOR]

Context : Previous theoretical studies have suggested that two-dimensional (2D) MBene materials might display adequate monatomic catalytic activity for the hydrogen evolution reaction (HER). Recently, a study reported the experimental synthesis of a 2D MBene (Mo4/3B2), re-defined as boridene, albeit no effort has been devoted to explore the single-atom catalytic activity for HER of this experimentally synthesized 2D material. Therefore, we herein investigate the single-atom HER performance of the boridene. Interestingly, with Mo defects mixed with single Au and Zn atoms shows excellent hydrogen evolution performance, and the change in the Gibbs free energy ( Δ G H ) value is close to 0 eV, which can even match the performance of Pt-based materials. Through analysis of the charge density difference and density of states, the mechanism affecting the HER performance is explained at the electronic level. This work provides a new direction for the use of the Mo4/3B2 monolayer two-dimensional materials in the field of single-atom catalysis for HER. Methods: This study used the DFT calculations in Vienna ab initio simulation package. The GGA-Perdew-Burke-Ernzerhof functional with DFT-D2 correction is used to describe the exchange–correlation interactions. The projection augmented wave is used with the plane wave cutoff of 500 eV. The convergences of energy and force are 10−5 eV and 0.01 eV/Å, respectively. A vacuum layer with a height of 20 Å is set in the Z direction. For geometry optimization, self-consistent, and DOS calculations, the k-point grids sampled in Brillouin zones are 3 × 3 × 1, 9 × 9 × 1, and 9 × 9 × 1, respectively. The AIMD simulation is performed in the canonical ensemble (NVT), and the temperature was maintained at 300 K by Nosé-Hoover thermostats with a time step of 2.0 fs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The graphitic carbon nitride (g-C 3 N 4) shows unique geometrical characterizes to anchoring metal trimer clusters. • They have excellent catalytic performances for yielding NH 3 products with limiting potential of 0.02–0.50 V involving kinetic barrier of 0.03–0.46 eV. • The establish the relationship between surficial activities and electronic properties. As a cleaner and more energy-efficient alternative, the electrochemical reduction of N 2 to NH 3 under mild conditions has emerged as a promising avenue for environmental protection. However, developing catalysts with both high activity and selectivity has been a challenging task. The advent of atomically dispersed catalysts is revolutionizing the field of catalysis. Drawing inspiration from the successful fabrication of Ru trimer on graphitic carbon nitride (g-C 3 N 4) nanosheets, herein, we adopted a series of trimeric metal clusters anchored on g-C 3 N 4 monolayer (TM 3 @g-C 3 N 4 , TM = 3 d , 4 d and 5 d transition metal atom), as well as utilized the criteria range to describe the stability, activity, energy cost and selectivity of supported trimers for N 2 reduction reaction based on ab initio calculations combined with multi-level screening strategies. Finally, 5 candidate TM 3 @g-C 3 N 4 (TM = Rh, Ru, V, Mo, and Re) exhibits decent catalytic activity with limiting potential ranging of –0.50 – –0.02 V. These spatially confined triatomic metal centers demonstrated proficiency in activating N 2 molecules while exhibiting tunable surficial reactivity through modulation of the metal elements and interfacial electron coupling between trimers and underlying substrates. More importantly, a structure–activity relationship was established, which provides crucial insights for precise design of highly efficient atomically-precise catalysts at an atomic level for hydrogen fuel storage. [ABSTRACT FROM AUTHOR]

Bismuth-based compounds have been identified as a class of promising candidates for the realization of high-performance thermoelectrics, derived from their exceptional electrical conductivity and intrinsic low lattice thermal conductivity κ L. Here, we employed first-principles calculations, self-consistent phonon theory, and compressive sensing technique in conjunction with the Boltzmann transport equation to investigate the anharmonic thermoelectric properties of full-heusler bismuth compounds Cs x Rb 3 − x Bi. As the Cs content increases, the κ L of Cs x Rb 3 − x Bi decreases due to impurity scattering effects, and then increases. Among them, at 300 K, Rb 3 Bi has the largest κ L of 0.69 Wm−1K−1, while Cs 2 RbBi has the smallest κ L of 0.45 Wm−1K−1, both of which are lower than the κ L of traditional bismuth-based thermoelectric materials. The ultralow κ L originates from the strong lattice anharmonicity. In addition, the coexistence of high dispersion and flat band edges leads to high thermoelectric power factor at optimal doping concentration. As a result, the largest thermoelectric figure of merit ZT values of 2.59 (4.19) at 300 (500) K were obtained for CsRb 2 Bi at optimal hole doping level. These findings suggest that Cs x Rb 3 − x Bi compounds are superior for thermal management and thermoelectric applications. • At finite temperatures, Cs x Rb 3 − x Bi compounds are not only mechanically stable but also dynamically stable. • The κ L of Rb 3 Bi, CsRb 2 Bi, Cs 2 RbBi, and Cs 3 Bi are 0.69, 0.47, 0.45, and 0.56 Wm−1K−1, respectively, at 300 K. • The p-type doped CsRb 2 Bi exhibits a ZT value of 2.59, while at 500K, the ZT value reaches 4.19. • The ultra-low κ L of CsRb 2 Bi originates from the rattling vibration of Bi atoms, which manifests as an 'avoided crossing' phenomenon. [ABSTRACT FROM AUTHOR]

The friction at the liquid-solid interfaces is widely involved in various phenomena ranging from nanometer to micrometer scales. By the molecular dynamic (MD) simulation, the friction properties of liquid-solid interfaces at the molecular level are calculated via the Green-Kubo relation. It is found that the system size will influence the value of the friction coefficient, especially for the solid surfaces with the larger polar charge. The value of the friction coefficient decreases with the increase in the system size and converges at large system sizes. The large polar charge will lead to a significant friction coefficient. However, the diffusion of water molecules on this surface is almost a constant, indicating that the diffusion coefficient seems to be independent of the system size and polar charge. This work provides insights for the selection of the system size in modeling the frictional properties of hydrophobic/hydrophilic surfaces. [ABSTRACT FROM AUTHOR]

Generally, the interface friction on solid surfaces is regarded as consistent with wetting behaviors, characterized by the contact angles. Here using molecular dynamics simulations, we find that even a small charge difference (≤0.36 e) causes a change in the friction coefficient of over an order of magnitude on two-dimensional material and lipid surfaces, despite similar contact angles. This large difference is confirmed by experimentally measuring interfacial friction of graphite and MoS2 contacting on water, using atomic force microscopy. The large variation in the friction coefficient is attributed to the different fluctuations of localized potential energy under inhomogeneous charge distribution. Our results help to understand the dynamics of two-dimensional materials and biomolecules, generally formed by atoms with small charge, including nanomaterials, such as nitrogen-doped graphene, hydrogen-terminated graphene, or MoS2, and molecular transport through cell membranes. The interface friction on solid surfaces is generally regarded as consistent with the wetting behaviour. Here the authors use molecular dynamics simulations and experiments to show that a small surface charge difference causes a change in the solid/water friction coefficient of over an order of magnitude, while the contact angles stay similar. [ABSTRACT FROM AUTHOR]

[Display omitted] • The GO humidity sensor fabricated by a simple way. • The GO humidity sensor with ultrafast response and recovery time less than 0.3s. • Protons generated from oxygen-containing groups and water molecules revealed. • An array of sensors was successfully fabricated to demonstrate its application. • LEDs lighted up by power-generating device made from humidity sensors. Next-generation humidity sensor, as one of the smart devices in artificial skin or flexible electronics, will need to be self-powered, flexible, fast and accurately detecting in the microenvironment. Although various flexible humidity sensors have already been demonstrated, most of them rely on large external power sources to operate, and still suffer from slow response, poor selectivity in environmental stimuli, and expensive and complicated procedures. Here, we realize a self-powered humidity sensor with ultrafast response and recovery time of less than 0.3 s by flexible GO film. Importantly, of all state-of-the-art humidity sensors, this is the fastest response for humidity sensor. Moreover, the sensor has a high sensitivity within a wide range of RH from 33% to 98%, and an excellent selective response to humidity under multiple environmental stimuli, due to its moist-induced generator. Theoretical computations reveal that protons generated spontaneously from oxygen-containing groups and water molecules, have a fast diffusion behavior as Grotthuss hopping. In particular, we build four real-time measurement systems capable of respiration monitoring of human, smart leaf surface humidity sensor, and energy harvesting. Our work provides a simple way to fabricate next-generation self-powered sensor using GO film with outstanding humidity sensor performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A prior exploration of the potential biological effect of a carbon nitride (C 3 N 3). • The moderate adsorption of C 3 N 3 nanosheet to membrane. • The molecular insights and mechanism of the interaction between C 3 N 3 and membrane. • The specific attraction between C 3 N 3 pores and lipid heads. Recently, the novel hole-containing carbon nitride C 3 N 3 nanomaterial was successfully synthesized, featuring outstanding and unique mechanical and electrical properties. However, to fully exploit this nanomaterial in biomedical applications, information regarding its biocompatibility is necessary. Herein, by using all-atom molecular dynamics simulations, we evaluate the interactions between a C 3 N 3 nanosheet and a critical cellular component, that is, a lipid membrane bilayer. Our results indicate that the C 3 N 3 nanosheet is able to interact with the lipid bilayer surface without affecting the membrane's structural integrity. Moreover, our results showed that the C 3 N 3 nanosheet is adsorbed on the surface of the lipid bilayer without inflicting any structural damage to the membrane, regardless of the conditions of the system (that is, with and without restrains in the C 3 N 3 nanosheet). Also, we found that both energy contributions, namely vdW and Coulomb energies, conjointly mediated the C 3 N 3 adsorption process. In comparison and as expected, pristine graphene significantly disturbed the membrane structure. Perpendicularly-oriented-sheet simulations described the significance of the surface charges of the C 3 N 3 nanosheet in prohibiting its insertion into the membrane. Detailed analysis indicated that the electrostatic attraction between the pores in the C 3 N 3 structure and the lipid head amino groups stabilized the interaction restricting the insertion of the C 3 N 3 structure deeper into the membrane. Our results suggested the importance of the negatively charged C 3 N 3 pores when interacting with lipid membranes. Our findings shed light on the potential compatibility of C 3 N 3 with biomembranes and its underlying molecular mechanism, which might provide a useful foundation for the future exploration of this 2D nanomaterial in biomedical applications. [ABSTRACT FROM AUTHOR]