Porous Polymeric Membranes with Engineered Surfaces for Water Remediation

Abstract

Access to safe drinking water is one of the greatest challenges that have afflicted people across the globe. Approximately 1.2 billion people do not have access to safe drinking water while 2.6 billion have no access to sanitation. Around 4,000 children die per day due to communicable diseases transmitted through contaminated drinking water. Rising population, the burden on agriculture and technological growth has triggered rapid industrialization leading to overexploitation and contamination of freshwater aquifers that have declined the groundwater table. Energy efficient, low cost and effective methodology for water purification has to be devised in order to address this challenge and reutilize the available resources. To address this challenge, researchers have turned towards membrane-based separation technology. Various membrane-based separation processes like microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) have been extensively used in water purification. Although these membranes are highly efficient, they lose their performance due to bacterial and protein fouling i.e. undesirable deposition or accumulation of contaminants such as bacteria and protein on the membrane surface and/or inside the pores of the membrane. This thesis entitled “Porous polymeric membranes with engineered surfaces for water remediation” addresses these key issues using surface engineering of polymeric surfaces and by the fabrication of new biocidal and foul release materials using polymerization techniques. Like MF and UF based membranes, RO membranes are also susceptible to fouling and have limited salt rejection and heavy metal removal capabilities. To address these concerns, the concept of multilayered membranes was used wherein an antibacterial polymer will be the active layer, mixed metal organic framework (MMOF) is the interlayer and RO membrane will be the support layer. This is discussed in Chapter 5. To optimize the best antibacterial polymer, different polymer tool boxes were tailored by reversible addition-fragmentation chain-transfer (RAFT) polymerization from quaternary ammonium compound, hyperbranched amine and phosphonium-based homo/copolymers. The result reflected that one specific polymer was exemplary in terms of its overall performance but there was a scope of improvement of the rejection capabilities. This was achievable by changing the interlayer material prudently. Hence, in Chapter 6 and Chapter 7, the polymer active layer was kept as is and the interlayer was varied from MMOF to molybdenum disulfide tethered magnetospheres and graphene oxide anchored MOF, respectively. This mitigated fouling and yielded efficient and excellent performance for desalination and heavy metal removal. Finally, Chapter 8 sums up the major conclusions from each chapter and highlights the outcome of the works. It also discusses the future work that can be undertaken in this research area and new strategies that can be devised for novel antibacterial and antifouling membranes that can yield unimpeded flow to water