Researchers up ante in solar desalination

Scientists at Georgia Institute of Technology and Nanjing University have developed a solar thermal desalination process based on what the researchers claimed to be low-cost and durable treated aluminium oxide sheets that focus the sun’s energy.

Aluminium nano particles on the oxide membrane can absorb more than 96% of the energy from a broad spectrum of sunlight. The membrane floats on saline water and transfers about 90% of the solar energy to the water surface to vapourize it. The water vapour is condensed to reduce dissolved solids to 0.01% of their original concentration.

In a paper published in Nature Photonics, the researchers claim the membrane remains stable through repeated cycles of use and is cheap to make. “The durability of the devices has also been examined, indicating a stable performance over 25 cycles under various illumination conditions. The combination of the significant desalination effect, the abundance and low cost of the materials, and the scalable production processes suggest that this type of plasmon- enhanced solar desalination device could provide a portable desalination solution.” the researchers said.

The researchers were able to upgrade an established characteristic in aluminium to generate plasmons – where electrons in the aluminium ions are energised in concert by electromagnetic radiation such as solar energy. This characteristic had, however, been demonstrated only in limited solar radiation bandwidths.

The engineers enhanced the bandwidth in their desalination system by coating nanopore perforated sheets of alumina with aluminium nano particles which then assemble on the surface and with in the pores of the membrane. This assembly enhanced the plasmon generating capacity of the aluminium. “To enable efficient solar desalination, broadband and efficient light absorption is the critical first step,” the researchers said.

“Our plasmon-enhanced solar desalination device can significantly increase the energy transfer efficiency with not only enhanced light absorption, but also more localized heating,” they added.

The authors of the paper said the system was “highly scalable, especially compared
to traditional top down approaches,” and as such they “could therefore provide a portable solution for solar desalination with a minimal carbon footprint.”