Non-van der Waals quasi-2D materials; recent advances in synthesis, emergent properties and applications

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.