The material, designated PPy-CS/PF@DDA, is constructed by confining dodecylamine inside a polypyrrole-coated chitosan/phenolic resin foam. Polypyrrole harvests incoming solar radiation, the porous foam structure transports water efficiently to the evaporation surface, and dodecylamine stores thermal energy at a relatively low transition temperature. That combination allows the system to sustain vapor generation even when solar input weakens or disappears entirely.
Under one-sun illumination, the evaporator achieved a rate of 1.862 kg m-2 h-1. After the light source was removed, it continued at 0.684 kg m-2 h-1 as stored phase-change heat was released. In 20 wt% sodium chloride solution -- representing hypersaline brine -- the device maintained 1.763 kg m-2 h-1 without observable salt accumulation on its surface.
The device also reached 95% solar absorption and demonstrated stability through repeated light-dark cycles, addressing durability concerns that have limited earlier phase change material designs.
Desalination plants worldwide produce large volumes of concentrated brine as a byproduct, a waste stream that can contain residual treatment chemicals, heavy metals, and elevated salt loads that pose ecological and disposal risks. Solar-driven interfacial evaporation has attracted attention as a low-carbon approach because it concentrates heat at the water-air interface rather than heating bulk liquid. Existing systems, however, have struggled with intermittent sunlight, high phase-change transition temperatures, and salt fouling under hypersaline conditions.
The new evaporator was designed to address those failure modes simultaneously. By selecting dodecylamine as the phase-change component, the team kept the thermal storage transition temperature low enough to be useful under typical solar intensities, while the polypyrrole coating provided broadband light absorption and the foam matrix resisted salt crystal formation.
In laboratory tests with model wastewater, the device reduced major seawater ion concentrations by two to three orders of magnitude, bringing them within World Health Organization drinking water guidelines. It also sharply lowered heavy metal concentrations and separated clean water from methyl orange dye solution without dye carryover, suggesting potential applications beyond seawater desalination.
An outdoor test on the Ocean University of China campus used natural sunlight over a 10-hour period. The system produced 9.229 kg m-2 of freshwater across that interval, with peak output between 11:00 and 13:00 local time. Performance held through the lower-irradiance morning and afternoon periods rather than collapsing as cloud cover or oblique sun angles reduced incoming energy.
The authors report a material cost of $0.54 m-2 and describe a straightforward fabrication procedure, factors they argue support realistic scale-up. Potential applications cited include zero-liquid-discharge brine treatment, brine concentration for resource recovery, and wastewater purification in water-scarce regions where solar energy is available but variable.
The work was supported by the National Natural Science Foundation of China and the National Natural Science Foundation of Shandong Province.
Research Report:Phase-change photothermal foam enables continuous hypersaline brine desalination
Related Links
Ocean University of China
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