Compared to traditional water evaporation and condensation as a water treatment, solar steam generation by photothermal membranes dramatically enhances solar evaporation efficiency through photothermal conversion and heat localization at a membrane surface. As a two-dimensional transition-metal dichalcogenide (TMD) with a distinct band structure, environmentally abundant molybdenum disulfide (MoS2) has been employed for harvesting solar energy to produce hydrogen gas through water splitting. It has also been used in photovoltaic cells and in solar disinfection. In this study, for the first time, we explored the effects of MoS2’s crystal structure on solar steam generation. We compared the efficiencies of water evaporation using chemically exfoliated (ce) MoS2 and untreated bulk-MoS2. During Li-intercalation in ce-MoS2 synthesis, the phase of MoS2 transitions from the 2H phase (trigonal prismatic) to the 1T phase (orthogonal), where its narrow bandgap structure increases light absorption. The broad-band light absorption of ce-MoS2 in the solar spectrum drove efficient photothermal conversion and resulted in high solar evaporation efficiency. Further, ce-MoS2 nanosheets were incorporated into a bacterial nanocellulose (BNC) bilayer foam, achieving high mechanical stability as well as high solar evaporation efficiencies of ~76% and ~82% under 0.76 kW/m2 and 5.35 kW/m2 light intensities, respectively. These efficiencies are much higher than those of a bulk-MoS2/BNC bilayer aerogel (60% and 63% under the same light conditions). In addition to improved evaporation rates, the cytotoxicity of ce-MoS2 nanosheets was found to be lower than that of GO nanosheets with a similar size, a commonly suggested photothermal material. The results support that ce-MoS2 can be a highly efficient, scalable, and environmentally benign (low toxicity) photothermal material for use in solar evaporators to create fresh water. These findings also provide useful information about the environmental implications of ce-MoS2 after its utilization in other engineered applications, such as sensors, electronic devices, photothermal therapy, and solar sterilization.

Solar thermal water purification enabled by photothermal conversion using the 1T/2H phases of MoS2

2019 Fall National Meeting

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