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The discovery of novel materials that are stable at ambient conditions with emergent functionalities is a pressing need of the 21st century to keep the pace of social and technological advancement in a sustainable manner. Nanotechnology and nanomaterials are one of this kind and the current era has already witnessed several groundbreaking discoveries of materials and disruptive technological advancements. Starting from 0D fullerene, the invention of 1D carbon nanotubes, and most recently 2D graphene, all are allotropes of carbon, have brought a lot of research opportunities to understand different physical and chemical phenomena at atomic and molecular scales and to convert such properties into useful applications. Among them, 2D materials find special attention due to unique properties such as ballistic carrier transport, immunity from substrate effects and commendable in plane mechanical robustness. However, the library of such materials is limited, and one can see that most of the technically viable materials that are already industrialized in a large scale belong to the class of non-van der Waals materials. The effect of confinement in one dimension on non-van der Waals materials remains unexplored owing to the difficulty in fabricating these materials to the ultra-thin limit with large lateral size or area. Recent advancement of cleaving non-van der Waals bulk materials to their ultra-thin counter parts through the state-of-the-art liquid phase exfoliation approach leads to renewed research interest among scientific community. The existence of cleaving/parting planes in certain directions of non-van der Waals materials, where the bonding strength is relatively weak compared to other crystallographic directions of the bulk crystal, facilitate smooth exfoliation when subjected to shear force through suitable methods. Herein, we attempt to discuss the rationale of such methods in the synthesis of non-van der Waals 2D materials that possess cleavage/parting planes with a special attention to natural ores, and to review the recent progress made in non-van der Waals two-dimensional materials with a special emphasis on emergent magnetism, catalysis, energy storage, and optoelectronics and related applications.

Steel corrosion has been a major perpetual issue of concern for durability and structural integrity of steel and reinforced concrete infrastructure. Polymeric, zinc-galvanic and chromate conversion coatings are commonly applied to protect typical steel materials such as structural steel, reinforcing steel bar (rebar), mild steel and light gauge steel used in infrastructure. Yet, due to physical integrity, long-term performance and environmental concerns, their applications have been limited. In recent years, graphene has garnered considerable attention in the field of anti-corrosive coatings and substantial progress has been achieved in the development of particular graphene-based monolithic (single/few-layer graphene and graphene oxides) as well as laminate and nanocomposite coatings. Despite considerable efforts dedicated towards fundamental research, the laboratory to industry transition of graphene-based anti-corrosive coatings remains challenging. To this end, this report reviews the state-of-the-art on graphene-based coating technology with application to steel surfaces and discusses, both, experimental studies and theoretical aspects. Specifically, this review presents (i) production of different forms of graphene-based materials and the coating process; (ii) corrosion resistance and anti-corrosive coating performance of graphene-coated steel materials, (iii) key potential areas and challenges pertaining to the application of graphene-based coating to structural steel and rebar; and (iv) potential future directions towards corrosion protection and smart coatings.

Despite decades of research, metallic corrosion remains a long-standing challenge in many engineering applications. Specifically, designing a material that can resist corrosion both in abiotic as well as biotic environments remains elusive. Here we design a lightweight sulfur-selenium (S-Se) alloy with high stiffness and ductility that can serve as a universal corrosion-resistant coating with protection efficiency of ~99.9% for steel in a wide range of diverse environments. S-Se coated mild steel shows a corrosion rate that is 6-7 orders of magnitude lower than bare metal in abiotic (simulated seawater and sodium sulfate solution) and biotic (sulfate-reducing bacterial medium) environments. The coating is strongly adhesive and mechanically robust. We attribute the high corrosion resistance of the alloy in diverse environments to its semi-crystalline, non-porous, anti-microbial, and viscoelastic nature with superior mechanical performance, enabling it to successfully block a variety of diffusing species., Comment: 22 pages, 4 figures

International audience; In this work, the tribological behavior of ultrathin-MoS2 was investigated to understand the independent roles of water and oxidation. Water adsorption was identified as the primary interfacial mechanism for both SiO2/pristine-MoS2 and SiO2/graphene interfaces, however, tribological behavior of pristine-MoS2 was observed to be more sensitive to presence of water due to stronger MoS2-water interaction. Comparison of pristine-MoS2 and oxidized-MoS2 revealed that the oxidation of MoS2 significantly increased its friction and sensitivity to water by play a more detrimental role. The specific effect of oxygen on friction via chemical interactions was studied in isolation through density functional theory (DFT) simulations of a tip sliding on MoS2 basal planes and over edges before and after oxidation. The maximum change in energy, or energy barrier correlating with friction, as the tip moved across the surface, increased after oxidation by up to 66% for the basal plane and by 25% at the edge. Charge density analysis suggests that the more localized and non-uniform interfacial charge distribution on oxygen rich surfaces, as compared to pristine surfaces, leads to higher resistance to sliding. This confirms that oxygen presence alone increases friction and when coupled with the presence of water, both effects are additive in increasing friction.

We review recent friction measurements on ordered superstructures performed by atomic force microscopy. In particular, we consider ultrathin KBr films on NaCl(001) and Cu(001) surfaces, single and bilayer graphene on SiC(0001), and the herringbone reconstruction of Au(111). Atomically resolved friction images of these systems show periodic features spanning across several unit cells. Although the physical mechanisms responsible for the formation of these superstructures are quite different, the experimental results can be interpreted within the same phenomenological framework. A comparison between experiments and modeling shows that, in the cases of KBr films on NaCl(001) and of graphene films, the tip-surface interaction is well described by a potential with the periodicity of the substrate which is modulated or, respectively, superimposed with a potential with the symmetry of the superstructure