A scalable, cost-effective and salt-rejecting MoS2/SA@melamine foam for continuous solar steam generation. (September 2021) - Xiao, Juanxiu
Abstract: Solar steam generation (STG) has been regarded as a promising strategy to relieve concerns on water shortage. Though great progresses have been made to improve the efficiency, salt deposition in the STG evaporator presents vital issues to an effective and continuous water production. Here, A MoS2 -sodium alginate hydrogel wrapped melamine foam (MoS2 /SA@MF) hybrid sponge is developed through simple, scalable and low-cost dipping–drying–crosslinking process. In this work, a 4 × 4 cm MoS2 /SA@MF evaporator shows an evaporation rate of 1.92 kg/m 2 .h in 3.5 wt% NaCl solution under 1 kW.m −2, achieving a solar-thermal conversion efficiency of 90%. Additional to bimodal porous structure of the MF skeleton, thanks to meticulous designs, including drilling through-holes and cutting water-channels on the STG evaporator, the water transportation and salt ions convection are fully accelerated. It is systematically illustrated that a significant improvement in salt rejecting performance is achieved with a 1.81 kg/m 2 .h evaporation rate even after 100 h in a brine salinity up to 20 wt% under 1 kW.m −2 . In addition, a consistent and effective solar-thermal conversion efficiency of 84.8% is also achieved superior to most reported works. Furthermore, this work also reveals that, in case of putting the evaporator float on the brine solution, Marangoni effect stemming from the temperature gradient and salinity concentration gradient at saltwater-air interface, plays an important role in salt deposition in the edge of PS foam and the side of MoS2 /SA@MF hybrid sponge. The study also provides an effective strategy of isolating the evaporator from brine water to prevent Marangoni flow and enable its sustainable and practical applications. Graphical Abstract: The scalable, flexible and cost-effective MoS2 /SA@MF hybrid sponge realizes an excellent salt-rejecting performance by hindering the Marangoni flow at the saltwater-air interface. ga1 Highlights: Robust mechanical stability and excellent adhesion ability is achieved. An evaporation rate of 1.92 kg/m 2 .h with an efficiency of 90% are realized. No salt deposition even after 100 h in a 20 wt% brine water. The efficiency is up to 99.96% for removing Pb 2+ ions.