Spec4DeSal · Transforming Interface Studies for Sustainable Desalination: The Development of Interface-Specific Heterodyne-Detected χ(4) Spectroscopy for the study of Molybdenum Disulfide Nanochannels

The world faces an escalating water crisis, with over two billion people lacking access to clean drinking water, which is further exacerbated by increased droughts due to global warming. Traditional desalination methods are notorious for their inefficiency and excessive energy consumption, which creates an urgent demand for sustainable alternatives. Interfacial solar vapor generation (SVG) serves as a promising solution to this problem. Molybdenum disulfide (MoS2) nanochannels are able to efficiently harness solar energy and have been identified as a transformative material for desalination in the SVG process. Despite this, the molecular-level mechanisms enhancing their SVG, particularly their interaction with water, remain unclear, necessitating the need for precise spectroscopic techniques to investigate their interfacial mechanisms. Second-order non-linear susceptibility (χ(2)) sum frequency generation (SFG) spectroscopy emerges as an exceptional tool for unraveling the intricate details of molecular interactions at interfaces. While χ(2) SFG has proven invaluable in deciphering interfacial molecular interactions, it has limitations when probing interfaces hidden beneath thick infrared absorbers like water. To overcome this obstacle, we turn to interface-specific, heterodyne detected (HD) fourth-order non-linear susceptibility (χ(4)) spectroscopy, which employs near-infrared (NIR) light instead of IR. This makes it suitable for interfaces buried within thick IR absorbers that are transparent in the NIR region. Herein, I present a cutting-edge proposal for the development of a new and innovative HD-χ(4) spectroscopic technique to study MoS2 nanochannels used for SVG. HD-χ(4) spectroscopy can not only aid in desalination optimization, but also expand into challenging areas like the battery and electrochemical industries. This ambitious project aims to enhance our interfacial understanding, facilitating sustainable solutions amid water scarcity.