Dr. Naomi Halas MA ’84, Ph.D ’87 on Solar Steam Generation

On Thursday September 22, Dr. Naomi Halas MA’84, Ph.D’87 gave a public talk on her research in solar steam technology and its applications in energy, sterilization, clean water, and medical treatment. Halas is currently Rice University’s Stanley C. Moore Professor in Electrical and Computer Engineering, Professor of Chemistry, Professor of Physics and Astronomy, Professor of Bioengineering, Founding Director of the Laboratory for Nanophotonics, and Founding Director of the Smalley Curl Institute.14433167_10154936952557923_1114709992413827004_n

Halas first started to explain how her solar steam sterilization system works by introducing the audience to the basic physics and chemistry behind her design. One fundamental question was established: how do you make steam? Simple. Just boil water. This leads to the next fundamental question: how can you convert this method into energy most efficiently? There are many answers to that.

Halas explained how her research team excited gold coated aluminum nanoshells in a water solution. Aluminum was used because it is more abundant, practical, and manufacturable than gold or silver. When sunlight hits the solution, the nanoparticles react and absorb light. This canonical ensemble (yes, I’m citing terminology I learned this semester in my PHYS 303 Thermodynamics & Statistical Mechanics class!) acts similarly to a very large optical field. Each particle acts as an optic lens that focuses light very intensely– more intensely than a molecule. Once the nanoshells capture light as a light wave, the electrons in the nanoparticles are excited, which then heats its local water reservoir (the water molecules) and then energy is captured. Halas’s team tested different concentrations of nanoparticle-water solutions to get the optimal energy scattering localized at the air-liquid interface. The rest of the volume of water remains not as heated because the energy is concentrated only at the surface. The optimal concentration was found to be 5*10^10 particles per mL.

This process has many applications. One relevant application is to photothermal cancer therapy where incident laser radiation on a tumor is concentrated only on the tumor so as to not affect healthy tissue. Another application is using a compact solar autoclave enabled by nanoparticle solution steam generation to sterilize medical devices. A third application is using a solar steam sterilizer for treatment of human waste. A company founded out of MIT in Nairobi called Sanergy franchises out clean latrines to entrepreneurs who then send the waste back to the company to sterilize and convert to fertilizer. Another application is using this technology to enhance the energy efficiency of solar panels by coating the solar panels with the nanoparticle solutions. The final application of her solar steam generator Halas presented was its use in distillation. According to Halas, this is the biggest energy challenge you’ve never heard of. Distillation, or the process of separating products into chemicals, can expend up to 70-85% of fuel costs for chemical industries who distill bioethanol. Halas even jokingly pointed out that beer companies must distill their beer.

This technology is valuable in aiding the developing countries where there is often poor water treatment. With direct solar distillation, the nanoparticle steam generator can produce steam so hot and so fast on as little energy as a car battery. One of the most needed equipment for medical trips to developing countries is sterilization equipment. The solar steam generator provides an attractive alternative to sanitizing medical equipment, water, and waste.
This event was sponsored by the Office of the President.
More information on Dr. Halas’s research can be found here and here and here.