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Rice University graduate student Oara Neumann and scientist Naomi Halas are co-authors of new research on a highly efficient method of turning sunlight into heat. They expect their technology to have an initial impact as an ultra-small-scale system to treat human waste in developing nations without sewer systems or electricity. Rice University graduate student Oara Neumann and scientist Naomi Halas are co-authors of new research on a highly efficient method of turning sunlight into heat. They expect their technology to have an initial impact as an ultra-small-scale system to treat human waste in developing nations without sewer systems or electricity. Jeff Fitlow/Rice University

Nanotechnology in Solar Sterilization Breakthrough

A recent breakthrough in steam generation - fueled entirely by the sun - shows promise in advancing medical waste and equipment sterilization, wastewater treatment and water purification.

In the less-developed world medical sterilization and water treatment are major barriers to healthy communities.  In the developed world, these issues are typically solved through energy-intensive processes and high capital infrastructure, such as wastewater treatment and desalination plants.  An innovation in solar-driven steam generation has created a buzz around the possibility of new, relatively simple methods of treating waste, sterilizing medical equipment and purifying water.

In a recent study published in ASC Nano, a scientific journal dedicated to nanotechnology, researchers from Rice University describe using sunlight to heat nanoparticles, floating in cold water, to create steam without any boiling.  Upon being exposed to sunlight, the nanoparticles begin generating steam at 150°C within seconds and at an efficiency of 24%.  This is achieved, they reason, because the nanoparticles are able to heat up so rapidly and to such a high temperature that the water molecules surrounding them immediately turn to vapor while transferring little heat to the remaining water.  This differs from boiling, which would require that all of the water reach 100°C, rather than only those molecules in contact with the nanoparticles.

These findings could have a significant impact in low-income countries, especially since, as the study suggests, they “open up a wide range of novel compact solar energy applications such as distillation, desalination, and sterilization and sanitation applications in resource poor locations.”  Indeed, that seems to be the first order of business.

Naomi Halas, lead investigator on the study, last year won a grant from the Bill and Melinda Gates Foundation’s Grand Challenges in Global Health initiative for a solar steam sterilizer to treat human waste.  Furthermore, Ms. Halas and couple of her co-authors on the study recently submitted a patent application for a small-scale device that would use this technology to sterilize medical waste or equipment.

The technology should be well suited to the task.  A medical autoclave, for instance, requires relatively low-pressure steam at temperatures of no more than 132°C, which the experimental results have already been able to achieve.  But the real advantage of this nanoparticle approach may be the potential for low-cost sterilization equipment without any need for fuel.

A boiler, the dominant steam generation technology, like that used for sterilizing medical equipment in an autoclave, uses a fuel, such as gas, or electricity to boil a tank of water.  This is an energy-intensive piece of equipment, and as our Health Clinic Load Calculations show, it can be among the most power hungry devices in a lab.  A more versatile, compact and fuel-free device could reach health clinics unable to support the energy needs of conventional autoclaves.

While low-cost, environmentally-friendly steam production using this new nanoparticle technology could one-day have a profound impact on a wide range of industries, from power generation to chemical distillation, there remains much work to be done by researchers and designers.  The promise shown by this nascent technology, however, should be encouraging, especially as it may make its first mark by improving healthcare for those who traditional technologies have yet to reach.

The Powering Health Stories blog brings you current trends in the worlds of health, energy and development, as well as features on current work being undertaken by USAID.  If you have a story that you would like us to cover or one that you would like to contribute, contact us This email address is being protected from spambots. You need JavaScript enabled to view it. !