Solar thermal desalination as a nonlinear optical process

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 27; pp. 13182 - 13187
• Main Authors: Dongare, Pratiksha D., Alabastri, Alessandro, Neumann, Oara, Nordlander, Peter, Halas, Naomi J.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 02.07.2019
• Subjects: Chemical reactions; Dependence; Desalination; Distillation; Distilled water; Drinking water; Earth surface; Energy requirements; Evaporation; Incident light; Light emitting diodes; Light intensity; Localization; Luminous intensity; Minerals; Nanoparticles; Nonlinear optics; Nonlinear systems; Nonlinearity; Organic chemistry; Photons; Photovoltaic cells; Physical Sciences; Reverse osmosis; Salinity; Salinity effects; Seawater; Solar energy; Solar heating; Sustainable development; Water purification; Water treatment; Water vapor; hot spots; thermal; desalination; solar; nonlinear
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1905311116

The ever-increasing global need for potable water requires practical, sustainable approaches for purifying abundant alternative sources such as seawater, high-salinity processed water, or underground reservoirs. Evaporation-based solutions are of particular interest for treating high salinity water, since conventional methods such as reverse osmosis have increasing energy requirements for higher concentrations of dissolved minerals. Demonstration of efficient water evaporation with heat localization in nanoparticle solutions under solar illumination has led to the recent rapid development of sustainable, solar-driven distillation methods. Given the amount of solar energy available per square meter at the Earth’s surface, however, it is important to utilize these incident photons as efficiently as possible to maximize clean water output. Here we show that merely focusing incident sunlight into small “hot spots” on a photothermally active desalination membrane dramatically increases—by more than 50%—the flux of distilled water. This large boost in efficiency results from the nearly exponential dependence of water vapor saturation pressure on temperature, and therefore on incident light intensity. Exploiting this inherent but previously unrecognized optical nonlinearity should enable the design of substantially higher-throughput solar thermal desalination methods. This property provides a mechanism capable of enhancing a far wider range of photothermally driven processes with supralinear intensity dependence, such as light-driven chemical reactions and separation methods.