The lack of readily available sterilization processes for medicine and dentistry practices in the developing world is a major risk factor for the propagation of disease. Modern medical facilities in the developed world often use autoclave systems to sterilize medical instruments and equipment and process waste that could contain harmful contagions. Here, we show the use of broadband light-absorbing nanoparticles as solar photothermal heaters, which generate high-temperature steam for a standalone, efficient solar autoclave useful for sanitation of instruments or materials in resource-limited, remote locations. Sterilization was verified using a standard Geobacillus stearothermophilus-based biological indicator.nanoscience | nanoshells | plasmon | energy conversion

Nanoparticles that both absorb and scatter light, when dispersed in a liquid, absorb optical energy and heat a reduced fluid volume due to the combination of multiple scattering and optical absorption. This can induce a localized liquid-vapor phase change within the reduced volume without the requirement of heating the entire fluid. For binary liquid mixtures, this process results in vaporization of the more volatile component of the mixture. When subsequently condensed, these two steps of vaporization and condensation constitute a distillation process mediated by nanoparticles and driven by optical illumination. Because it does not require the heating of a large volume of fluid, this process requires substantially less energy than traditional distillation using thermal sources. We investigated nanoparticle-mediated, light-induced distillation of ethanol-H2O and 1-propanol-H2O mixtures, using Au-SiO2 nanoshells as the absorber-scatterer nanoparticle and nanoparticle-resonant laser irradiation to drive the process. For ethanol-H2O mixtures, the mole fraction of ethanol obtained in the light-induced process is substantially higher than that obtained by conventional thermal distillation, essentially removing the ethanol-H2O azeotrope that limits conventional distillation. In contrast, for 1-propanol-H2O mixtures the distillate properties resulting from light-induced distillation were very similar to those obtained by thermal distillation. In the 1-propanol-H2O system, a nanoparticle-mediated, light-induced liquid-liquid phase separation was also observed.

Conventional bioethanol for transportation fuel typically consumes agricultural feedstocks also suitable for human consumption and requires large amounts of energy for conversion of feedstock to fuel. Alternative feedstocks, optimally those not also in demand for human consumption, and off-grid energy sources for processing would both contribute to making bioethanol far more sustainable than current practices. Cellulosic bioethanol production involves three steps: the extraction of sugars from cellulosic feedstock, the fermentation of sugars to produce ethanol, and the purification of ethanol through distillation. Traditional production methods for extraction and distillation are energy intensive and therefore costly, limiting the advancement of this approach. Here we report an initial demonstration of the conversion of cellulosic feedstock into ethanol by completely off-grid solar processing steps. Our approach is based on nanoparticle-enabled solar steam generation, in which high-efficiency steam can be produced by illuminating light-absorbing nanoparticles dispersed in H 2 O with sunlight. We used solar-generated steam to successfully hydrolyze feedstock into sugars; we then used solar steamdistillation to purify ethanol in the final processing step. Coastal hay, a grass grown for livestock feed across the southern United States, and sugar cane as a control are successfully converted to ethanol in this proof-of-concept study. This entirely off-grid solar production method has the potential to realize the long-dreamed-of goal of sustainable cellulosic bioethanol production.