Jul 8, 2020
A team of scientists at the University of Science and Technology of China has developed an efficient and sustainable hierarchical steam generator that, with the help of bacterial cellulose nanocomposites, harnesses solar energy to purify water.
The wood-based hierarchical solar steam generator: CNT – carbon nanotubes, BC – bacterial cellulose, GB – glass bubbles. Image credit: Guan et al, doi: 10.1021/acs.nanolett.0c01088.
Water scarcity is a major global challenge in modern society. Nowadays, almost one-fifth of the world’s population lives in water-deficient areas.
Therefore, it is urgently required to develop efficient, low-cost, sustainable, and easily accessible technologies and devices to generate clean water, especially for people living in off-grid areas.
Since solar energy is one of the most abundant resources on Earth, water purification by solar distillation is considered as a promising technology to produce clean water from a variety of undrinkable water resources, including seawater, river/lake water, and contaminated water.
“A solar steam generator is a device that uses the abundant energy of the Sun to separate water and contaminants in solar distillation process,” said study senior author Dr. Shu-Hong Yu and colleagues.
“Many different versions of these devices have been developed, with varying efficiencies.”
“To design better solar steam generators, researchers must find ways to improve light absorption, heat management, water transport and evaporation.”
Dr. Yu and co-authors wanted to combine all four improvements in a single device.
The scientists chose wood as the basis of their generator because of its sustainability and porous structure, which allows rapid water transport.
They made their device with the help of bacteria that produced long cellulose nanofibers, which bound the layers of the device together.
They added bacteria to the surface of a block of wood and allowed them to ferment.
Then, they sprayed an aerosol of glass bubbles — tiny hollow spheres that provide excellent thermal insulation — onto the surface.
The glass bubbles became embedded in the cellulose nanofibers produced by the bacteria, forming a hydrogel.
Finally, the team added carbon nanotubes, which tangled with the cellulose nanofibers to form a light-absorbing, water-evaporating top layer.
“The device works by transporting water upward through the wood to the light-absorbing layer, which is heated by the Sun,” the authors said.
“The water evaporates, and the steam is collected and condensed to produce pure water.”
“The insulating layer of glass bubbles keeps heat from being transferred downward through the device and lost, and the nanoscale structures lower the energy required for water vaporization.”
“As a result, the new device has a higher evaporation rate and efficiency than most existing solar steam generators.”
The team’s solar steam generator is described in a paper published today in the journal Nano Letters.
Qing-Fang Guan et al. Sustainable Wood-Based Hierarchical Solar Steam Generator: A Biomimetic Design with Reduced Vaporization Enthalpy of Water. Nano Lett, published online July 8, 2020; doi: 10.1021/acs.nanolett.0c01088
This article is based on text provided by the American Chemical Society.
Thanks to: http://www.sci-news.com