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Solar-thermal evaporation is a promising technology for energy-efficient desalination, but salt accumulation on solar absorbers and system longevity are the major challenges that hinder its widespread application. In this study, we present a sustainable Janus wood evaporator that overcomes these challenges and achieves a record-high evaporation efficiencies in hypersaline water, one of the most difficult water sources to treat via desalination. The Janus wood evaporator has asymmetric surface wettability, where the top layer acts as a hydrophobic solar absorber with water blockage and salt resistance, while the bottom hydrophilic wood layer allows for rapid water replenishment and superior thermal insulation. An evaporation efficiency of 82.0% is achieved for 20% NaCl solution under 1 sun, and persistent salt-resistance is observed during a 10-cycle long-term test. To ensure the environmental impact of the Janus wood evaporator, for the first time, a life cycle assessment (LCA) is conducted to compare this Janus wood evaporator with the emerging Janus evaporators, indicating a functional and more sustainable opportunity for off-grid desalination and humanitarian efforts. 

Aggregation significantly influences the transport, transformation, and bioavailability of engineered nanomaterials. Two–dimensional MoS2 nanosheets are one of the most well-studied transition-metal dichalcogenide nanomaterials. Nonetheless, the aggregation behavior of this material under environmental conditions is not well understood. Here, we investigated the aggregation of single-layer MoS2 (SL-MoS2) nanosheets under a variety of conditions. Trends in the aggregation of SL-MoS2 are consistent with classical Derjaguin–Landau–Verwey–Overbeek (DLVO) colloidal theory, and the critical coagulation concentrations of cations follow the order of trivalent (Cr3+) < divalent (Ca2+, Mg2+, Cd2+) < monovalent cations (Na+, K+). Notably, Pb2+ and Ag+ destabilize MoS2 nanosheet suspensions much more strongly than do their divalent and monovalent counterparts. This effect is attributable to Lewis soft acid–base interactions of cations with MoS2. Visible light irradiation synergistically promotes the aggregation of SL-MoS2 nanosheets in the presence of cations, which was evident even in the presence of natural organic matter. The light-accelerated aggregation was ascribed to dipole–dipole interactions due to transient surface plasmon oscillation of electrons in the metallic 1T phase, which decrease the aggregation energy barrier. These results reveal the phase-dependent aggregation behaviors of engineered MoS2 nanosheets with important implications for environmental fate and risk. 

Layer-stacked graphene oxide (GO) membranes, in which unique two-dimensional (2D) water channels are formed between two neighboring GO nanosheets, have demonstrated great potential for aqueous phase separation. Subjects of crucial importance are to fundamentally understand the interlayer spacing ( i.e. channel height) of GO membranes in an aqueous environment, elucidate the mechanisms for water transport within such 2D channels, and precisely control the interlayer spacing to tune the membrane separation capability for targeted applications. In this investigation, we used an integrated quartz crystal mass balance (QCM-D) and ellipsometry to experimentally monitor the interlayer spacing of GO, reduced GO and crosslinked GO in aqueous solution and found that crosslinking can effectively prevent GO from swelling and precisely control the interlayer spacing. We then used molecular dynamics simulations to study the mass transport inside the 2D channels and proved that the chemical functional groups on the GO plane dramatically slow down water transport in the channels. Our findings on GO structure and water transport provide a necessary basis for further tailoring and optimizing the design and fabrication of GO membranes in various separation applications.