A Microstructured Graphene/Poly(N‐isopropylacrylamide) Membrane for Intelligent Solar Water Evaporation

Abstract

Intelligent solar water evaporation (iSWE) was achieved with at hermally responsive and microstructured graphene/poly(N-isopropylacrylamide) (mG/PNIPAm) membrane.A st he solar intensity varies,t he water evaporation is tuned through reversible transformations of microstructures reminiscent of the stomatal opening and closing of leaves. Consequently,t his mG/PNIPAm membrane displays ah igh water evaporation rate change (DWER) of 1.66 kg m À2 h À1 under weak sunlight (intensity < 1sun) and al ow DWER of 0.24 kg m À2 h À1 under intense sunlight (1 sun < intensity < 2sun). Because of the double-layer structure with predictable shape and dynamics,t he leaf-like membrane can further autonomously modulate the water evaporation by self-curling under intense solar irradiation in accordance with simulation results.T his mG/PNIPAm membrane provides as mart material platform with self-adaptability in response to changing environments.Innature,avariety of plants take advantage of solar energy and water for photosynthesis,and equip themselves with selfadaptive functions to survive in various environments. [1] Examples of botanical phenomena include the stomatal opening/closing of plant leaves to regulate the water transpiration rate, [2] cactus leaves degenerating into thorns to adapt to ad esert environment, [3] and the self-curling of leaves of gramineous plants to reduce water loss at summer noon. [4] All of these responses of plants to changing environments play an important role in sustaining life.O nt he other hand, various materials with excellent photothermal conversion have been explored for solar steam generation. [5] However,the development of leaf-like smart materials with self-adaptive functions for intelligent solar water evaporation (iSWE) is challenging and has not been reported thus far.Herein, we explored the iSWE concept by developing at hermally responsive and microstructured graphene/ poly(N-isopropylacrylamide) (mG/PNIPAm) membrane that switches itself on and off depending on the intensity of the sunlight irradiation. Thesynergism between the excellent photothermal conversion of graphene and the fast thermal response of PNIPAm provides the mG/PNIPAm membrane with reversibly opening/closing microstructures for iSWE, which is reminiscent of the stomatal opening/closing of natural leaves.A dapting to varying sunlight, the mG/ PNIPAm membrane shows ah igh water evaporation rate change (DWER) of 1.66 kg m À2 h À1 under weak solar irradiation (intensity < 1sun), and al ow DWER of 0.24 kg m À2 h À1 under intense solar irradiation (1 sun < intensity < 2sun). Because of its double-layer leaf or flower structure generated by laser-processing technology,the intelligent membranes can proactively curl or fold themselves to modulate the water loss under intense sunlight. This work demonstrates the concept of iSWE and provides af undamental approach to the development of other intelligent materials that adapt in response to their environment.Stomata are small pores on the surfaces of leaves and stalks,w hich play an i...

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