In situ synthesis of silver nanoparticles in poly(vinyl) alcohol layer coated thin film membrane for seawater desalination

• Main Author: Jayavardhana D/o Balaji
• Other Authors: Wang Rong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Environmental engineering
• Online Access: https://hdl.handle.net/10356/163791
• Institution: Nanyang Technological University

Singapore has been searching for efficient ways to alleviate water scarcity. Such solutions include seawater desalination via membrane technologies. This project aims to develop an antimicrobial seawater reverse osmosis (SWRO) membrane by incorporating silver nanoparticles (AgNPs) into poly(vinyl) alcohol (PVA) coating layer that formed atop a thin film composite (TFC) membrane. Before incorporating Ag nanoparticles into the PVA layer, the PVA coating protocols were first optimised. A control TFC membrane with pure water permeability (PWP) of 3.47 L/m2 .h.bar and salt rejection of 98.33% in treating 35,000 ppm NaCl solution under operating pressure of 50 bar and crossflow velocity of 0.1 m/s was established. Then, the concentration and molecular weight of PVA used for hydrophilic coating layer formation atop the control TFC membrane were optimised. The best-performed PVA- coated membrane (MPVA1-0.2) was prepared using PVA with the lowest molecular weight of 13-23 kDa and at a concentration of 0.2 w/v%. The permeability of MPVA1-0.2 membrane reduced insignificantly by 8.4% compared to the control membrane without PVA coating layer, achieving PWP of 3.1 L/m2 .h.bar with excellent salt rejection of 99.28%. The observed improvement in the salt rejection of the PVA-coated membrane was owing to the additional selectivity and stability provided by the hydrophilic PVA layer. Last, AgNPs were synthesised in situ during the PVA coating step, and three synthesis approaches were investigated. Silver nitrate and sodium borohydride were reacted at different stages, and the effect in affecting membrane performance was studied. Membrane characterisation, including atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and contact angle measurement were also conducted in this project to understand the change of membrane properties during the in-situ formation of AgNPs.