Plasma-Made Graphene Nanostructures with Molecularly Dispersed F and Na Sites for Solar Desalination of Oil-Contaminated Seawater with Complete In-Water and In-Air Oil Rejection

Abstract

Solar desalination that exploits interfacial evaporation represents a promising solution to global water scarcity. Real-world feedstocks (e.g., natural seawater and contaminated water) include oil contamination issues, raising a compelling need for desalination systems that offer anti-oil-fouling capability; however, it is still challenging to prepare oil-repellent and meanwhile water-attracting surfaces. This work demonstrates a concept of molecularly dispersing functional F and Na sites on plasma-made vertically oriented graphene nanosheets to achieve an in-air and in-water oleophobic, hydrophilic surface. The graphene architecture presents high in-air (138°) and in-water (145°) oil contact angles, with simultaneously high water affinity (0°). Such surface wettability is enabled by oleophobic, hydrophobic −CF x , and hydrophilic −COONa groups of the molecules that disperse on graphene surfaces; low-dispersion (0.439 mJ m −2 ) and high-polarity (95.199 mJ m −2 ) components of the solid surface tension; and increased surface roughness produced by graphene edges. The graphene nanostructures pump water upward by capillary action but repel oil from the surface, leading to complete in-water and in-air oil rejection and universal anti-oil-fouling capability for solar desalination. Consequently, stable solar−vapor energy efficiency of more than 85% is achieved regardless of whether the feedstock is pure or oil-contaminated water (e.g., a mixture of oil floating on water, an oil-in-water emulsion), resulting in the efficient production of clean water over several days. This outstanding performance is attributed to the universal (both in-water and in-air) oleophobic wettability, together with high light absorptance contributed by nanotraps, fast interfacial heat transfer enhanced by finlike nanostructures, and accelerated evaporation enabled by sharp graphene edges.

Complete System to Generate Clean Water from a Contaminated Water Body by a Handmade Flower-like Light Absorber

“…Traditional heating methods lose their efficiency because of heat dissipation in bulk water, leading to neglectable or meager evaporation rates . In contrary to conventional heating behaviors, the interfacial localized heating technique has gotten a huge appreciation recently. − This technique has the perk of localizing solar heat energy at the air–water interface, ultimately resulting in much better evaporation rates. , Recently, extensive efforts have been made to fabricate efficient, low-cost, and reliable solar light absorbers, such as solar-trackable super-wicking black metal panels, plasma-made graphene nanostructures, carbon nanotube composite polyacrylamide hydrogel, and so forth. − Especially, the fabrication of 3D geometric shapes with a rough exterior to increase exposed surface area, which ultimately leads to better solar light absorption and evaporation rates, such as 3D dyed black cotton towel, 3D hemispheric steam generator composed of nanocarbon, 3D spherical carbonized Platanus fruit, and so forth. − However, most of the designed solar light absorbers reported recently are still costly and composed of rare components with complex manufacturing processes . Interfacial localized heating systems are needed in rural areas, so it is better to be simple and low-cost because the local economy, technical training, and resources of rural areas are limited.…”

Self-contained Janus Aerogel with Antifouling and Salt-Rejecting Properties for Stable Solar Evaporation

“…First, the CS exhibits a low thermal conductivity of 0.053 W m −1 k −1 , which is comparable to the outstanding thermal insulator-expanded polystyrene foam (0.034−0.04 W m −1 k −1 ), to localize the solar heat at the air/ water interface (Figure 2e). 33 The infrared image displayed in Figure 2f manifests the heat localization on the top CCS layer. The coefficient of thermal conductivity can be elevated via the carbonization process.…”

Metal Oxy-Hydroxides with a Hierarchical and Hollow Structure for Highly Efficient Solar-Thermal Water Evaporation

“…The measured concentrations of Na + , K + , Mg 2+ , and Ca 2+ in the condensed water were 6.05, 1.70, 0.55, and 3.50 ppm, respectively, which were significantly reduced by 3 or 4 orders of magnitude compared to pristine seawater, meeting the World Health Organization drinking water standards. 30 At the same time, the COD of the natural seawater and the condensed water were analyzed as well (Figure 6a). The COD decreased from ∼700 ppm to ∼5 ppm, indicating a significant reduction in the content of organic contaminations.…”