Nanopartículas plasmônicas aplicadas para processos de destilação solar

Abstract

Metal nanoparticles (NPs), especially those of noble metals such as gold and silver, have attracted great attention from the scientific community due to the possibility of tuning and optimizing their optical properties, such as absorption and refraction, in a wide spectral region, through the localized surface plasmon (LSP) phenomenon. Such a tuning procedure can be achieved by controlling the shape and size of the metal NPs, as well as the conditions of the host medium, thus allowing their applications in various areas ranging from medicine, energy to the development of new technologies based on plasmonic devices. In this dissertation, plasmonic nanofluids constituted of gold NPs, with variable morphologies and sizes, were designed, synthesized, characterized and applied solar energy harvesting and harnessing systems. To analyze the solar thermal conversion efficiency, gold nanospheres and nanorods, coated with a silica shell, as well as silica-gold core-shell NPs were synthesized. Theoretical results show that the presence of the longitudinal LSP band, present in the rod-shaped anisotropic NPs, favors the matching with the solar irradiance spectrum, giving rise to more efficient solar collectors. However, the broadband absorption spectrum of the gold nanoshells allows DASC efficiencies of 98% to be achieved, even using thin solar collectors. The nanofluids were applied experimental studies on solar energy harvesting (using a solar simulator) and in real conditions, to monitor the influence of the NP´s morphology and size on the efficiency to heat fluids and generate steam. It was demonstrated that at low solar irradiance, plasmonic NPs behave as good nanoheaters for direct absorption solar collectors, reaching nanofluid temperature increases of 5 times higher than in typical base fluids. On the other hand, at high solar irradiances, control over the plasmonic NP geometry allows the generation of large steam amounts, making plasmonic nanofluids attractive for applications in direct solar distillation. Plasmonic NPs were tested to optimize the efficiency of an ethanol solar distillation system, carrying out experiments with a mixture of water and ethanol, as well as using fermented sugarcane juice (wine), donated by a plant located in the city of Cabo de Santo Agostinho - Pernambuco.The experiments carried out in this dissertation support the development of a new sustainable technology, with great potential to reduce the greenhouse gases emission, produced in the conventional distillation process of biofuels and alcoholic beverages.