Design and construct alkali-responsive nanocontainers for self-healing thin-film composite reverse osmosis membranes

Poor chlorine resistance is a major factor affecting service life of aromatic polyamide reverse osmosis membranes. Herein, alkali-responsive polymer nanocontainers are designed and constructed via emulsified cross-linking and electrostatic self-assembly of sodium alginate, chitosan, and polyaspartic acid around chitosan nanoparticles, and the nanocontainer is integrated into polyamide layer of thin film composite membranes. The nanocontainer does not only provide more channels for water molecules to improve membrane permeability, but also during routine alkaline washing process, polyaspartic acid at the outer layer reacts with alkaline agent to release healing agents: sodium alginate and chitosan to heal damaged sites to restore membrane performances. For example, with the addition of 0.005 wt% nanocontainers, water flux was increased by 32.8% compared to pristine membranes without sacrificing NaCl rejection. After soaking in alkaline cleaning solution, NaCl rejection of the membrane degraded by 2000 ppm active chlorine can be recovered by 97.3%. Therefore, self-healing nanocontainers can greatly improve chlorine resistance, water flux, and stability of polyamide reverse osmosis membranes.