The Carbon-Water Interface: Modeling Challenges and Opportunities for the Water-Energy Nexus

Abstract

Providing clean water and sufficient affordable energy to all without compromising the environment are key priorities of the scientific community. Many recent studies have focused on carbon--based devices in the hope of addressing these grand challenges, justifying and motivating detailed studies of water in contact with carbonaceous materials. Such studies are becoming increasingly important because of the miniaturization of newly proposed devices, with ubiquitous nano--pores, large surface--to--volume ratio, and many, perhaps most of the water molecules at contact with a carbon--based surface. In this brief review we discuss some recent advances obtained by simulations and experiments in the development of carbon--based materials for applications in water desalination. We suggest possible ways forward, with particular emphasis on the synergistic combination of experiments and simulations, with simulations now sometimes offering sufficient accuracy to provide fundamental insights. We also point the interested reader to recent works that complement our short summary on the state of the art of this important and fascinating field. 2 Introduction: the importance of reverse osmosis in water desalinationThe scientific community is facing the challenge of providing technological solutions for the water--energy nexus while preserving the environment. Carbon--based devices have been developed both for desalinating water and for storing energy. Such devices are characterized by vast carbon--water interfaces, due to the ubiquity of nano--pores. It is indeed possible that many, perhaps most water molecules within such devices come in contact with the carbon surface. Hence, a detailed understanding of water--carbon interfaces is necessary to ensure progress. Here, we review some recent advances obtained by atomistic simulations and experiments on this field. Traditional water desalination approaches such as multi--flash distillations are widely used, but require large amounts of energy. As such, they are not sustainable in the long run. Reverse osmosis (RO) has become the technology of choice for most new installations. Two innovations are considered to be responsible for the wide application of RO. The first was the introduction of thin film composite membranes; the other was the implementation of energy recovery devices that re--use part of the energy present in pressurized brine (i.e., pressure exchangers and efficient pumps) (1, 2). Although RO is mature and reliable, it remains energy intensive (3--5). At its core are membranes permeable to water and impermeable to salt. The state--of--the art membranes, based on polyamide thin film composites, degrade in the presence of chlorine (which makes disinfection difficult) and are prone to fouling (6). Many believe that 'in order for desalination to live up to the water challenges of the 21 st century a step--change is needed in RO membrane technology' (7). Although high mechanical strength as well as resistance to degradation and fouling are prerequisites to practical appli...

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