Two-Dimensional (2D) Nanomaterials in Separation Science

This chapter defines the two-dimensional (2D) nanomaterials that have been used in separation science. Then, chapter summaries can be found at the end of this chapter.

The environment is continuously threatened with various kind of pollutants, which have detrimental effects not only on human health, but also on eco-systems. In general, the water body is an easy route to wastewater disposal where many contaminants of emerging concerns, such as pharmaceuticals and personal care products etc. are present. Very recently, other classes of novel water pollutants occur which include nanoplastics and nanoparticles. Here, we discuss both classical and newly emerging water pollutants categories with their possible consequences. In addition, treatments and tackling techniques of these water pollutants are summarized. Ten different areas of concern to solve these problems and challenges of emerging water pollutants are highlighted.

Membrane-based treatments are superior to conventional processes in water purification and desalination in terms of final water quality and smaller footprint. In addition, there are inherent weaknesses of state-of-the-art membranes in reverse osmosis (RO) technology, thus there is pressing constraints for next-generation membranes. Nano-porous graphene membranes as the mother of novel 2D materials have attracted tremendous attention in the last decade in this regard, and many theoretical and experimental attempts have been made towards the realization of these membranes for water desalination. Advancements and challenges facing this approach, research gaps and prospects that shed light on this field are explored in this chapter.

Graphene oxide (GO) is one of the most prominent nanoscaled membranes for water purification. Thanks to a combination of massive theoretical and experimental efforts, large-scale production of both three-dimensional (3D) and lamellar GO membranes is at hand. Countless methods to synthesize, functionalize, and characterize GO membranes are available, which inspire tremendous excitement about the possibilities of increasing the efficiency of current reverse osmosis (RO) desalination plants. Here, we reveal some of the main physical–chemical insights as well as manufacturing techniques of GO, reduced GO, and related material-based separation techniques.

Graphene, the thinnest material known to science, is a very promising candidate for separation membranes with ultra-high molecular permeance. It has been widely demonstrated that nanoporous graphene membranes have a great potential for solute separation. In this chapter, the recent advances on the nanoporous graphene membranes for the application in water purification via reverse osmosis and electrodialysis are both reviewed. The separation mechanisms and fabrication methods of this atomically thick membrane are especially discussed by highlighting the representative theoretical and experimental works. Currently, the studies on the porous graphene membranes via electrodialysis are relatively limited comparing to those of reverse osmosis. It is expected that more and more researchers are attracted to this frontier research field to make the two-dimensional membranes for water purification a reality by overcoming the challenges faced currently.

Thanks to rapid progress in the investigation of two-dimensional (2D) substances, hexagonal boron nitride (h-BN) has shown outstanding properties as filtration membrane and adsorbent for water purification applications. In this chapter, we explain the synthesis methods of h-BN including exfoliation and chemical vapor deposition. And then, the computer simulations in the field of h-BN nanosheets are described, and several recent studies of the membrane filtration of h-BN and pollutant adsorption of h-BN are reviewed from molecular dynamics insights. All findings suggest the promising potential of h-BN for water purification. We further reveal a brief experimental works which investigated the performance of h-BN for separation of solutes. The h-BN not only shows considerable adsorption potential for a wide range of oils, model dyes, and various metallic ions but also reveals high recoverability. To this end, several other new fabrication techniques are described. Despite several researches in this field, there are still research gaps which have been mentioned in the last section of this chapter.

Beyond graphene-based membranes, for water desalination, a vast horizon of new materials has been discovered for solutes separation from water. In this realm, the transition-metal dichalcogenides (TMDs) molybdenum and tungsten disulfide (MoS₂ and WS₂, respectively) stand as promising two-dimensional (2D) materials. Their tailoring for nanofluidics as well as the emerging synthesis and production methods unfold the possibility of applying MoS₂ and WS₂ in modern desalination processes based on 2D membranes. We present here an overview from their theoretical conception to their state-of-the-art applications, highlighting the challenges and opportunities associated with measuring water flow and ionic rejection rates at nanoscale. In a world full of environmental concerns, both the theoretical gaps and experimental perspectives point toward a promising use of MoS₂ and WS₂ as green components in separation technologies, contributing to increase the availability of clean, potable water.

Freshwater crisis is an ever-increasing severe twenty-first-century problem. Scientists, experts, and engineers are exploring various strategies to meet the freshwater desire. Membranes with high ion rejections and adsorptive capability are playing important roles in desalination and/or wastewater treatment. Many 2D membranes have been demonstrated great potential in water purification, such as metal–organic frameworks (MOF), MXenes, and zeolite nanosheets. In this chapter, applications of these 2D nanosheets in desalting and heavy metal ions removal are discussed from the point of computer simulations, synthesis procedures, and experimental works.