Study on Controllable Assembly of Stearic Acid within Interlayer Spacing of Montmorillonite and Its Energy Storage Performance

Inclusion of organic species in exfoliated montmorillonite nanolayers towards hierarchical functional inorganic-organic nanostructures

Montmorillonite (Mt) can readily undergo spontaneous delamination or exfoliation into nanolayers by various physical and chemical processes, which allow various strategies to engineer hierarchical functional inorganic-organic nanostructures. This review aims to discuss the recent progress in the liquid-phase exfoliation of Mt into individual nanolayers and the inclusion chemistry of functional organic species, ions, or molecules into the exfoliated Mt nanolayers to produce hierarchical functional inorganic-organic nanostructures. The exfoliation methods include mechanical force, ultrasonication, and intercalation-assisted exfoliation. Techniques for quickly assessing the quality of the exfoliated Mt nanolayers are still needed. Layer-by-layer (LbL) deposition, template, and evaporation-induced inclusions are examined to fabricate hierarchical Mt-organic species nanocomposites with unique functionalities and properties. The nanocomposites can be produced as multilayered porous films, brick-and-mortar coatings, hydrogels with a house-of-cards structure, core-shell materials, and hollow and mesoporous spherical nanocomposites, which exhibit significant potential for adsorption, catalysis, targeted delivery and controlled drug release, highly sensitive sensors, flame retardant coatings, and thermal energy storage and release (i.e. phase change materials). Finally, the challenges and prospects for the future development of hierarchical nanocomposites of exfoliated Mt nanolayers and organic species, particularly in hierarchical supramolecular nanostructured composites, are highlighted.

Confinement Effect of Graphene Interface on Phase Transition of n-Eicosane: Molecular Dynamics Simulations

Phase change materials (PCMs) are widely used in thermal management and energy storage systems. Investigations on the thermophysical properties enhancement of organic PCMs by introducing carbon-based frameworks have received much attention in recent years. Studies of the phase transition in nanoconfinement are still in controversy with divergent opinions among researchers. In this article, the phase transition behavior of n-eicosane in slit-shaped pores between sheets of graphene is investigated by molecular dynamics simulation. It is found that the graphene interface makes the phase transition temperature of n-eicosane increase, under the initial slit widths of 1.5-5.3 nm. Impacted by interaction and size effects, the distribution and orientation of n-eicosane molecules are quite different from those of the bulk state. In the confinement of graphene, the molecules turn to a reversible layered distribution parallel to the graphene sheets after solidification. The contact layers are found in all the confined systems, which is harder to melt and easier to solidify compared with the main part of the systems. The melting points of different systems are obtained by analysis of the liquid ratio. Finally, the relationship between the dimensionless phase transition point and slit width is discussed.

Clay Composites for Thermal Energy Storage: A Review

The development of novel materials and approaches for effective energy consumption and the employment of renewable energy sources is one of the current trends in modern material science. With this respect, the number of researches is focused on the effective harvesting and storage of solar energy for various applications. Phase change materials (PCMs) are known to be able to store thermal energy of the sunlight due to adsorption and release of latent heat through reversible phase transitions. Therefore, PCMs are promising as functional additives to construction materials and paints for advanced thermoregulation in building and industry. However, bare PCMs have limited practical applications. Organic PCMs like paraffins suffer from material leakage when undergoing in a liquid state while inorganic ones like salt hydrates lack long-term stability after multiple phase transitions. To avoid this, the loading of PCMs in porous matrices are intensively studied along with the thermal properties of the resulted composites. The loading of PCMs in microcontainers of natural porous or layered clay materials appears as a simple and cost-effective method of encapsulation significantly improving the shape and cyclic stability of PCMs. Additionally, the inclusion of functional clay containers into construction materials allows for improving their mechanical and flame-retardant properties. This article summarizes the recent progress in the preparation of composites based on PCM-loaded clay microcontainers along with their future perspectives as functional additives in thermo-regulating materials.

Surface Functionalization of Montmorillonite with Chitosan and the Role of Surface Properties on Its Adsorptive Performance: A Comparative Study on Mycotoxins Adsorption

Understanding surface and interfacial information, which has a close relationship to the structures and properties of materials, helps guide the design of materials for specific applications. This study focuses on the surface functionalization of montmorillonite (Mt) with chitosan (CTS) and exploring the role of surface properties on its adsorptive performance. Two prototypical products, namely, 180-Htc@Mt and 250-Htc@Mt, were fabricated via the hydrothermal method at 180 and 250 °C, respectively. Field emission scanning electron microscopy revealed that hydrothermal carbon (Htc) derived from CTS anchored on the surface of Mt uniformly with a spherical morphology. The introduction of Htc endowed the surface of Mt with abundant hydroxy, amine, and amide groups; organic carbon; developed porosity; and hydrophobic interfacial property. Hydrothermal temperature has huge impacts on the surface system, and smaller particles (average size of 27 vs 53 nm) with deeper carbonization, higher content of carbonaceous and nitrogenous functional groups, more developed porosity (66.149 vs 39.434 m²/g of specific surface area, 0.115 vs 0.090 cm³/g of pore volume), and slightly decreased hydrophobicity can be readily achieved at a higher temperature. The incoming surface protonated amine and amide functional groups show an ion-dipolar interaction to polar aflatoxin B₁ (AFB₁), and the increased organic carbon content as well as interfacial hydrophobicity generate a hydrophobic interaction to weak polar zearalenone (ZER). Consequently, the surface functionalization affords Mt enhanced adsorption capacity for AFB₁, approximately two times compared with Mt, and superior adsorption ability for ZER (10 mg/g). The present work provides sufficient evidence of "surface directs application" of Mt, which encourages researchers to focus on studies of the surface science of clay minerals.