Browsing by Author "Dongare, Pratiksha D."

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    Nanophotonics-enabled Solar Membrane Distillation for Off-grid Water Purification
    (2017-04-21) Dongare, Pratiksha D.; Halas, Naomi J
    With more than a billion people lacking accessible drinking water, there is a critical need to convert non-potable sources such as seawater to water suitable for human use. However, energy requirements of desalination plants account for half their operating costs, so alternative, lower-energy approaches are equally critical. Membrane distillation (MD) has shown potential due to its low operating temperature and pressure requirements, but the requirement of heating the input water makes it energy intensive. Here we demonstrate nanophotonics-enabled solar membrane distillation (NESMD), where highly localized photothermal heating induced by solar illumination alone drives the distillation process, entirely eliminating the requirement of heating the input water. Unlike MD, NESMD can be scaled to larger systems and shows increased efficiencies with decreased input flow velocities. Along with its increased efficiency at higher ambient temperatures, these properties all point to NESMD as a promising solution for household- or community- scale desalination.
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    Solar thermal desalination as a nonlinear optical process
    (National Academy of Sciences, 2019) Dongare, Pratiksha D.; Alabastri, Alessandro; Neumann, Oara; Nordlander, Peter; Halas, Naomi J.; Laboratory for Nanophotonics; Nanosystems Engineering Research Center for Nanotechnology-Enabled Water Treatment
    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.