Fabrication of Stimuli-Responsive Electrospun Nanofiber Structures for Environmental and Energy Application: Adsorption-based Water Harvesting

Abstract

Atmospheric water is a potential source of an abundant amount of freshwater that is available across the globe. The capture and release of water from atmospheric humidity by using sorbent enables sustainable water delivery without disruption of the hydrological cycle. Exploring efficienf novel water sorbents for adsorption-based water harvesting, this dissertation covers research tasks to fabricate a temperature-responsive hydrogel nanofiber that has a switchable phase transition in response to a small temperature change. The series of studies in this dissertation demonstrates that the electrospinning technique is facilely used to fabricate nanofibrous water sorbents from the perspectives of research in material (polymer, inorganic, organic-inorganic polymeric hybrids) and structure (fiber shape and morphology), as well as in water sorption properties. As the first step in understanding water vapor adsorption properties in silica materials, silica nanofibers (SNFs) with different mesoporosity degrees, achieved by controlling the electrospinning parameter, are synthesized. The pore arrangement in the formation of SNFs describes how environmental humidity during electrospinning affects the micellar assembly of nanostructured porous fibers, resulting in the development of water uptake properties. Next, poly (N-vinyl caprolactam-co-acrylic acid) (P(VCL-co-AA)) nanofiber with switchable wettability within a narrow temperature range shows excellent water uptake and release in thermally simulated systems. The detailed mechanism underlying the superior water uptake properties of a core/shell-structured temperature-responsive nanofiber is elucidated. In the last strategy, a deliquescent salt incorporated in the hydrophilicity-switchable polymeric network of P(VCL-co-AA) to induce water uptake even at a low humidity level appears to function at all humidity levels and temperature ranges. This hybrid nanofiber composite enables effective water desorption to promote water evaporation at a relatively low temperature assisted by solar heat. Through a review of advanced in water harvesting applications, this dissertation identifies and clarifies the progress and expectations of atmospheric water harvesting. From the understanding of the structural and interfacial properties of electrospun nanofibers in the series of research tasks, stimuli-responsive wettability switching with an interconnected nanofiber network has been presented for a fundamental and systematic study of adsorption-based water harvesting. Further exploration of the fabrication of electrospun nanostructured materials will provide new insights into sorption-based applications from the environmental and energy points of view.