Bioinspired Angstrom-Scale Heterogeneous MOF-on-MOF Membrane for Osmotic Energy Harvesting.

Membrane-based salinity gradient energy generation from the osmotic potential at the interface of a river and seawater through reverse electrodialysis is a promising route for realizing clean, abundant, and sustainable energy. Membrane permeability and selective ion transport are crucial for efficient osmotic energy harvesting. However, balancing these two parameters in the membrane design and synthesis remains challenging. Herein, a hybridized bilayer metal-organic frameworks (MOF-on-MOF) membrane is fabricated for efficient transmembrane conductance for enhanced osmotic power generation. The heterogeneous membrane is constructed from imidazolate framework-8 (ZIF-8) deposited on a UiO-66-NH2 membrane intercalated with poly(sodium-4-styrenesulfonate) (PSS). The angstrom-scale cavities in the ZIF-8 layer promote ion selectivity by size exclusion, and the PSS-intercalated UiO-66-NH2 film ensures cation permeability. The synergistic effect is a simultaneous improvement in ion transport and selectivity from an overlapped electric double layer generating 40.01 W/m2 and 665 A/m2 permeability from a 500-fold concentration gradient interface at 3 KΩ and 9.20 W/m2 from mixing of real sea-river water. This work demonstrates a rational design strategy for hybrid membranes with improved ion selectivity and permeability for the water-energy nexus.

Multifunctionality through Embedding Patterned Nanostructures in High-Performance Composites.

Despite being a pillar of high-performance materials in industry, manufacturing carbon fiber composites with simultaneously enhanced multifunctionality and structural properties has remained elusive due to the lack of practical bottom-up approaches with control over nanoscale interactions. Guided by the droplet's internal currents and amphiphilicity of nanomaterials, herein, a programmable spray coating is introduced for the deposition of multiple nanomaterials with tailorable patterns in composite.  It is shown that such patterns regulate the formation of interfaces, damage containment, and electrical-thermal conductivity of the composites, which is absent in conventional manufacturing that primarily rely on incorporating nanomaterials to achieve specific functionalities. Molecular dynamics simulations show that increasing the hydrophilicity of the hybrid nanomaterials, which is synchronous with shifting patterns from disk to ring, improves the interactions between the carbon surfaces and epoxy at the interfaces,manifested in enhanced interlaminar and flexural performance. Transitioning from ring to disk creates a larger interconnected network  leading to improved thermal and electrical properties without penalty in mechanical properties. This novel approach introduces a new design , where the mechanical and multifunctional performance is controlled by the shape of the deposited patterns, thus eliminating the trade-off between properties that are considered paradoxical in today's manufacturing of hierarchical composites.

Aqueous Dispersion of Carbon Nanomaterials with Cellulose Nanocrystals: An Investigation of Molecular Interactions.

Dispersing carbon nanomaterials in solvents is effective in transferring their significant mechanical and functional properties to polymers and nanocomposites. However, poor dispersion of carbon nanomaterials impedes exploiting their full potential in nanocomposites. Cellulose nanocrystals (CNCs) are promising for dispersing and stabilizing pristine carbon nanotubes (pCNTs) and graphene nanoplatelets (pGnP) in protic media without functionalization. Here, the underlying mechanisms at the molecular level are investigated between CNC and pCNT/pGnP that stabilize their dispersion in polar solvents. Based on the spectroscopy and microscopy characterization of CNCpCNT/pGnP and density functional theory (DFT) calculations, an additional intermolecular mechanism is proposed between CNC and pCNT/pGnP that forms carbonoxygen covalent bonds between hydroxyl end groups of CNCs and the defected sites of pCNTs/pGnPs preventing re-agglomeration in polar solvents. This work's findings indicate that the CNC-assisted process enables new capabilities in harnessing nanostructures at the molecular level and tailoring the performance of nanocomposites at higher length scales.

Designing Angstrom-Scale Asymmetric MOF-on-MOF Cavities for High Monovalent Ion Selectivity.

Biological ion channels feature angstrom-scale asymmetrical cavity structures, which are the key to achieving highly efficient separation and sensing of alkali metal ions from aqueous resources. The clean energy future and lithium-based energy storage systems heavily rely on highly efficient ionic separations. However, artificial recreation of such a sophisticated biostructure has been technically challenging. Here, a highly tunable design concept is introduced to fabricate monovalent ion-selective membranes with asymmetric sub-nanometer pores in which energy barriers are implanted. The energy barriers act against ionic movements, which hold the target ion while facilitating the transport of competing ions. The membrane consists of bilayer metal-organic frameworks (MOF-on-MOF), possessing a 6 to 3.4-angstrom passable cavity structure. The ionic current measurements exhibit an unprecedented ionic current rectification ratio of above 100 with exceptionally high selectivity ratios of 84 and 80 for K+ /Li+ and Na+ / Li+ , respectively (1.14 Li+ mol m-2 h-1 ). Furthermore, using quantum mechanics/molecular mechanics, it is shown that the combined effect of spatial hindrance and nucleophilic entrapment to induce energy surge baffles is responsible for the membrane's ultrahigh selectivity and ion rectification. This work demonstrates a striking advance in developing monovalent ion-selective channels and has implications in sensing, energy storage, and separation technologies.

Mechanical hydrolysis imparts self-destruction of water molecules under steric confinement.

Decoding behavioral aspects associated with the water molecules in confined spaces such as an interlayer space of two-dimensional nanosheets is key for the fundamental understanding of water-matter interactions and identifying unexpected phenomena of water molecules in chemistry and physics. Although numerous studies have been conducted on the behavior of water molecules in confined spaces, their reach stops at the properties of the planar ice-like formation, where van der Waals interactions are the predominant interactions and many questions on the confined space such as the possibility of electron exchange and excitation state remain unsettled. We used density functional theory and reactive molecular dynamics to reveal orbital overlap and induction bonding between water molecules and graphene sheets under much less pressure than graphene fractures. Our study demonstrates high amounts of charge being transferred between water and the graphene sheets, as the interlayer space becomes smaller. As a result, the inner face of the graphene nanosheets is functionalized with hydroxyl and epoxy functional groups while released hydrogen in the form of protons either stays still or traverses a short distance inside the confined space via the Grotthuss mechanism. We found signatures of a new hydrolysis mechanism in the water molecules, i.e. mechanical hydrolysis, presumably responsible for relieving water from extremely confined conditions. This phenomenon where water reacts under extreme confinement by disintegration rather than forming ice-like structures is observed for the first time, illustrating the prospect of treating ultrafine porous nanostructures as a driver for water splitting and material functionalization, potentially impacting the modern design of nanofilters, nanochannels, nano-capacitators, sensors, and so on.

Orbital Overlapping through Induction Bonding Overcomes the Intrinsic Delamination of 3D-Printed Cementitious Binders.

3D printing of cementitious materials holds a great promise for construction due to its rapid, consistent, modular, and geometry-controlled ability. However, its major drawback is low cohesion in the interlayer region. Herein, we report a combined experimental and computational approach to understand and control fabrication of 3D-printed cementitious materials with significantly enhanced interlayer strength using multimaterial 3D printing, in which the composition, function, and structure of the materials are programmed. Our results show that the intrinsic low interlayer cohesion is caused by excess moisture and time lag that block the majority of valuable interactions in the interlayer zone between the adjacent cement matrices. As a remedy, a thin epoxy layer is introduced as an intermediator between the adjacent extruded layers, both to improve the interlayer cohesion and to extend the possible time delay between printed adjacent layers. Our ab initio calculations demonstrate that an orbital overlap between the calcium ions, as the main electrophilic part of the cement structure, and the hydroxyl groups, as the nucleophilic part of the epoxy, create strong interfacial absorption sites. These electronic absorptions lead to several iono-covalent bonds between the cement matrix and epoxy, leading to significant improvements in tensile, shear, and compressive strengths as well as ductility of the 3D-printed composites. This is verified by our experimental data, which showed an average of 84% improvement in interlayer bonding. The upward augmentation of interlayer bonding helps 3D printing cementitious material to overcome their intrinsic limitation of weak interlayer cohesion, thereby mitigating/eliminating the key bottleneck of additive manufacturing in constructing materials.

Tunable, Multifunctional Ceramic Composites via Intercalation of Fused Graphene Boron Nitride Nanosheets.

Ternary two-dimensional (2D) materials such as fused graphene-boron nitride (GBN) nanosheets exhibit attractive physical and tunable properties far beyond their parent structures. Although these features impart several multifunctional properties in various matrices, a fundamental understanding on the nature of the interfacial interactions of these ternary 2D materials with host matrices and the role of their individual components has been elusive. Herein, we focus on intercalated GBN/ceramic composites as a model system and perform a series of density functional theory calculations to fill this knowledge gap. Propelled by more polarity and negative Gibbs free energy, our results demonstrate that GBN is more water-soluble than graphene and hexagonal boron nitride (h-BN), making it a preferred choice for slurry preparation and resultant intercalations. Further, a chief attribute of the intercalated GBN/ceramic is the formation of covalent C-O and B-O bonds between the two structures, changing the hybridization of GBN from sp2 to sp3. This change, combined with the electron release in the vicinity of the interfacial regions, leads to several nonintuitive mechanical and electrical alterations of the composite such as exhibiting higher young's modulus, strength, and ductility as well as sharp decline in the band gap. As a limiting case, though both tobermorite ceramic and h-BN are wide band gap materials, their intercalated composite becomes a p-type semiconductor, contrary to intuition. These multifunctional features, along with our fundamental electronic descriptions of the origin of property change, provide key guidelines for synthesizing next generation of multifunctional bilayer ceramics with remarkable properties on demand.

Mechanical and electromechanical properties of functionalized hexagonal boron nitride nanosheet: A density functional theory study.

Hydroxylation as a technique is mainly used to alter the chemical characteristics of hexagonal boron nitride (h-BN), affecting physical features as well as mechanical and electromechanical properties in the process, the extent of which remains unknown. In this study, effects of functionalization on the physical, mechanical, and electromechanical properties of h-BN, including the interlayer distance, Young's modulus, intrinsic strength, and bandgaps were investigated based on density functional theory. It was found that functionalized layers of h-BN have an average distance of about 5.48 Å. Analyzing mechanical properties of h-BN revealed great dependence on the degree of functionalization. For the amorphous hydroxylated hexagonal boron nitride nanosheets (OH-BNNS), the Young's modulus moves from 436 to 284 GPa as the coverage of -OH increases. The corresponding variations in the Young's modulus of the ordered OH-BNNS with analogous coverage are bigger at 460-290 GPa. The observed intrinsic strength suggested that mechanical properties are promising even after functionalization. Moreover, the resulted bandgap reduction drastically enhanced the electrical conductivity of this structure under imposed strains. The results from this work pave the way for future endeavors in h-BN nanocomposites research.