Hygroscopic salt-hydrogel
composite sorbents have attracted increasing
attention for atmospheric water harvesting (AWH) applications but
suffer from the salting-out effect. To this end, this work, for the
first time, discovers that the salting-in effect possessed by a zwitterionic
hydrogel is able to facilitate water vapor sorption by the hygroscopic
salt under otherwise the same conditions. For demonstration, zwitterionic
hydrogel of poly-[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium
hydroxide (PDMAPS) was synthesized, and the hygroscopic salt of LiCl
was embedded into PDMAPS to produce the salt-hydrogel composite. LiCl
salt not only endows the sorbent with high water vapor sorption capacity
but also facilitates the dissociation of self-association between
cationic and anionic groups of PDMAPS. This salting-in effect was
evaluated and confirmed experimentally and via density functional
theory (DFT) calculation. The salting-in effect renders the zwitterionic
hydrogel matrix with enhanced swelling capacity, leading to the sorbent’s
high AWH performance. With a photothermal component of CNT integrated
into the sorbent, a fully solar energy-driven AWH process was demonstrated
outdoors. This study provides important guidance to the design of
hydrogel-based AWH sorbents.
Metal- and halide-free, solid-state water vapor sorbents are highly desirable for water-sorption-based applications, because most of the solid sorbents are suffering from low water sorption capacity or toxic metals, while...
Solar-assisted distillation
is considered promising to solve the
freshwater supply for off-grid communities. In this work, a passive
and flexible multistage membrane distillation (F-MSMD) device is devised
to produce freshwater via solar distillation with the latent heat
of vapor condensation being recycled to enhance its energy efficiency.
By designing a siphon effect, source water is continuously wicked
into the evaporation layer and the concentrated brine flows out of
the device before reaching saturation, which successfully solves the
otherwise challenge of salt accumulation inside the device. To achieve
such siphon flow, the recycled paper is prepared from spent copy paper
and used as the evaporation layer for efficient water delivery owing
to its large pore size and high hydrophilicity. An eight-stage F-MSMD
device exhibits a stable clean water production rate at 3.61 kg m–2 h–1 in the newly designed siphon-flow
mode. This work provides a green route for designing a solar-assisted
distillation device.
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