During the last decade, two-dimensional materials (2DMs) have attracted great attention due to their unique chemical and physical properties, which make them appealing platforms for diverse applications in opto-electronic devices, energy generation and storage, and sensing. Among their various extraordinary properties, 2DMs possess high surface area-to-volume ratios and ultra-high surface sensitivity to the environment, which are key characteristics for applications in chemical sensing. Furthermore, 2DMs' superior electrical and optical properties, combined with their excellent mechanical characteristics such as robustness and flexibility, make these materials ideal components for the fabrication of a new generation of high-performance chemical sensors. Depending on the specific device, 2DMs can be tailored to interact with various chemical species at the non-covalent level, making them powerful platforms for fabricating devices exhibiting a high sensitivity towards detection of various analytes including gases, ions and small biomolecules. Here, we will review the most enlightening recent advances in the field of chemical sensors based on atomically-thin 2DMs and we will discuss the opportunities and the challenges towards the realization of novel hybrid materials and sensing devices.

Membrane-based processes such as water purification and harvesting of osmotic power deriving from the difference in salinity between seawater and freshwater, are two strategic research fields holding great promises for overcoming critical global issues like the world growing energy demand, the climate change and the access to clean water. Ultrathin membranes based on two-dimensional materials (2DMs) are particularly suitable for highly selective separation of ions and effective generation of blue energy, because of their unique physicochemical properties and novel transport mechanisms occurring at the nano-and sub-nanometer length scale. However, due to the relatively high costs of fabrication compared to traditional porous membrane materials, their technological transfer towards large-scale applications still remains a great challenge. Herein, we present an overview of the current state-of-the-art in the development of ultrathin membranes based on 2DMs for osmotic power generation and water purification. We discuss several synthetic routes to produce atomically-thin membranes with controlled porosity and we describe in detail their performances, with a particular emphasis on pressure retarded osmosis and reversed electrodialysis methods. In the last section, outlooks and current limitations as well as viable future developments in the field of 2DMs membranes are provided.3