Novel Photothermal Materials and Thermally Engineered Membranes for Solar Desalination

A WashU dissertation by: Sisi Cao

Abstract: Although 71% of earth surface is covered with water, more than 97% of it is saltwater, and freshwater is limited to only about 2.5%. The freshwater shortage has been exacerbated due to the environmental pollution, increased agriculture needs, socio-economic development, and population growth. Among various desalination technologies, membrane distillation has gained wide attention due to its ability to treat highly saline water utilizing waste heat from industrial processes. However, the implementation of conventional membrane distillation is hindered in the remote regions and disaster-struck communities where the low-grade thermal energy from industrial plants and electricity are not readily available. To address this problem, photothermal driven membrane distillation (PMD), where membrane distillation is integrated with photothermal materials that can effectively convert light to thermal energy, has been recognized as an attractive and sustainable technology for freshwater generation. The overall objective of this work is to overcome several fundamental scientific challenges in realizing efficient PMD by exploring two key components of photothermal membranes, namely, substrates and photothermal materials.In the first part of this work, we have designed and investigated environmentally benign substrates (hydroxyapatite (HA) nanowires) for efficient PMD. Their structure and properties of this novel substrate material have been systematically investigated to reveal their potential in replacing the widely used polymeric substrates for efficient PMD. In the second part, we have investigated high-performance photothermal materials (polydopamine (PDA), MXene and polypyrrole (PPy)) for efficient PMD. Their excellent photothermal property, abundant functional groups and facile processability make them highly appealing in achieving high-performance PMD membranes. Taken together, this work further our understanding of the structure, properties, stability and performance of these novel materials and open up novel avenues in designing and realizing highly efficient PMD systems.

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