| dc.description.abstract | Safe drinking water for all is perhaps one of the prime nexus of the 21st century and one of the prime sustainable development goals. Around 1.2 billion people still lack access to safe potable water, while around 2.6 billion people still lack access to proper sanitation. Due to the rapid contamination of conventional freshwater aquifers and a decrease in the groundwater table, there is an urgent need to re-use the unconventional sources and remediate the contaminated aquifers. In this context, re-using desalinated water for practical applications seems a feasible solution since nearly 71 % of the earth is water, and 96.5 % of that water is occupied in oceans. Among techniques like thermal distillation, electro-dialysis, evaporation, membrane-based desalination is the most economical and cost-effective process. In this thesis a classical UCST system (PVDF/PMMA; polyvinylidene fluoride/poly (methyl methacrylate) is chosen to design a porous membrane for water remediation using crystallization induced phase separation. Membranes with varying pore sizes were obtained by varying the composition in the blend and etching the PMMA phase. A unique hierarchical architecture was developed by stitching different membranes using polyacrylic acid, as an adhesive, to achieve a gradient in pore size. The first working chapter (Chapter 3) illustrates the in-situ assembly of polyamide (PA) and PA-graphene oxide quantum dot (GQDs) framework supported on the templated hierarchical porous architecture to improve the rejection and fouling resistance. This strategy resulted in efficient salt rejection (more than 94% and 98% for monovalent salt and divalent salt respectively) studied through pressure enhanced osmosis process using 1000 ppm as draw solutions, and dye rejection (more than 90% and 85% for Methylene blue (MB) and Congo red (CR) respectively) studied through cross-flow experimental set up using 10 ppm as feed solution @ 60 psi pressure. Moreover, the antifouling properties of the PA-GQD modified membranes were superior (80%) as compared to the control PVDF membranes. In the next working chapter (Chapter 4), in order to further improve the antifouling and chlorine tolerance performance, a free-standing GO membrane was positioned in tandem with the PA layer formed in-situ on the surface of hierarchical porous membrane. This strategy resulted in rejection of more than 95% for monovalent ion and more than 97% for divalent ion using 1000 ppm draw solutions; fouling resistance was more than 85%; dye rejection was more than 96% and 90% for a model cationic dye (MB) and anionic dye (CR) @10 ppm feed. This particular membrane showed excellent chlorine tolerance performance @ 2000 ppm NaOCl solution as compared to the membranes described in Chapter 3. In the next chapter (Chapter 5), to arrest the swelling of GO, chemically crosslinked freestanding GO was sandwiched along with the porous membranes, followed by creating an active surface through the layer-by-layer assembly of Poly dopamine (PDA) and Poly styrene sulfonate (PSS) alternately. This strategy resulted in rejection more than 95% for monovalent ion and more than 97% for divalent ion using 2000 ppm draw solutions; fouling resistance was more than 90%; dye rejection was more than 99% and 98% for a model cationic dye (MB) and anionic dye (CR) @100 ppm feed. This particular membrane showed excellent chlorine tolerance performance @ 6000 ppm NaOCl solution. In the final working chapter (Chapter 6), a novel dense covalent organic framework (COFs) embedded PA layer was deposited on a highly stable crosslinked GO@COF membrane to enhance sieving efficacy. This modified membrane showed excellent rejection performance (more than 94%, 98% for monovalent ion, divalent ion, respectively using 2000 ppm draw solution, and near 100% for dyes @ 100 ppm feed) and resistance to fouling attack (more than 93%). Moreover, outstanding chlorine tolerance performance (@ 8000 ppm NaOCl solution) was obtained by this membrane as compared to all previous membranes described in the earlier chapters. The result presented in this thesis suggests the various modifications on PVDF membrane for the fabrication of thin film composite membranes as well as the approaches to maximize the rejection performance with excellent fouling resistance and stability. This study will further help guide the researchers working in the field from both academia and industry. | en_US |
