Girls of Rice: Shining a Light on Nano-Distillation

Rice University researchers have exposed an extraordinary route to light-driven distillation, using nano-particles. The applications of this new technology have barely been imagined.

People in developing countries will be among the first to see the benefits of solar steam. Rice engineering undergraduates have already created a solar steam-powered autoclave that’s capable of sterilizing medical and dental instruments at clinics that lack electricity. Halas also won a Grand Challenges grant from the Bill and Melinda Gates Foundation to create an ultra-small-scale system for treating human waste in areas without sewer systems or electricity.

“Solar steam is remarkable because of its efficiency,” said Neumann, the lead co-author on the paper. “It does not require acres of mirrors or solar panels. In fact, the footprint can be very small. For example, the light window in our demonstration autoclave was just a few square centimeters.”

Another potential use could be in powering hybrid air-conditioning and heating systems that run off of sunlight during the day and electricity at night. Halas, Neumann and colleagues have also conducted distillation experiments and found that solar steam is about two-and-a-half times more efficient than existing distillation columns. _Rice University_via_New Energy & Fuel

Solar illumination of broadly absorbing metal or carbon nanoparticles dispersed in a liquid produces vapor without the requirement of heating the fluid volume. When particles are dispersed in water at ambient temperature, energy is directed primarily to vaporization of water into steam, with a much smaller fraction resulting in heating of the fluid. Sunlight-illuminated particles can also drive H2O-ethanol distillation, yielding fractions significantly richer in ethanol content than simple thermal distillation. These phenomena can also enable important compact solar applications such as sterilization of waste and surgical instruments in resource-poor locations. _ACS_via_Brian Westenhaus

Girls of Rice: Neuman & Halas

Using sunlight to distill water (or ethanol etc.) at the nano-scale illustrates the counter-intuitive potential of nano-particles. Human science has barely tapped the potential of nano-particles for chemical, biomedical, and physical purposes. And nano-particles are the most primitive type of nanotechnology. Imagine the disruptive influence of true nano-machines and nano-assemblers.

The key in the research is the technology has an overall energy efficiency of 24 percent. Photovoltaic solar panels, by comparison, typically have an overall energy efficiency around 15 percent. Bear in mind that about half of the solar energy arriving to earth’s surface is in the infrared range. Halas’ team set out to design a particle that would interact with the widest possible spectrum of sunlight energy. Their new nanoparticles are activated by both visible sunlight and shorter wavelengths that humans cannot see.

...The efficiency of the solar steam technology is due to the light-capturing nanoparticles that convert sunlight into heat. When submerged in water and exposed to sunlight, the particles heat up so quickly they instantly vaporize water and create steam. The nanoparticles are so effective they can even produce steam from icy cold water. Halas said the solar steam’s overall energy efficiency can probably be increased as the technology is refined.

The technology is going to be on a very different scale. Halas explains, “We’re going from heating water on the macro scale to heating it at the nanoscale. Our particles are very small – even smaller than a wavelength of light – which means they have an extremely small surface area to dissipate heat. This intense heating allows us to generate steam locally, right at the surface of the particle, and the idea of generating steam locally is really counter intuitive.” _New Energy & Fuel

More on this story from Brian Wang