Construction of tunable “silica molecular brush” on the polyamide membrane surface for enhancing water permeability and antifouling performance

Surface modification has been widely applied for improvement permeability and antifouling performance of polyamide (PA) reverse osmosis (RO) membrane. A low-cost and easily obtained organoalkoxysilane, γ-Aminopropyl triethoxysilane (APTES), was grafted on PA RO membrane surface via a second interfacial polymerization (SIP) process combined with the activation effect of n-decane solvent, thus to form an antifouling PA surface with different silica brush-like structures, which can effectively weaken the attractive forces between the membrane surface and organic foulants. Meanwhile, n-decane solvent during the SIP process plays a dual function, which can not only minimize hydrolysis of both APTES monomers and unreacted acyl chloride groups on PA surface but also enhance microporosity of the nascent PA (solvent activation of PA), thereby grafting APTES on PA surface via amidation reaction can achieve maximization, and the water permeability of APTES modified PA (APTES-PA) membranes is improved. These APTES-PA membranes showed high water permeability (above 3.47 LMH/bar) with competitive NaCl rejection (above 98.75%), as well as excellent stability during 70 h of cross-flow test. Moreover, the existence of silica brush-like structures via grafting APTES molecules on PA layer can significantly elevate the antifouling performance of membranes against both negatively and positively charged foulants.