Facile surface modification by aldehydes to enhance chlorine resistance of polyamide thin film composite membranes

• This two-step aldehydes modification was proved to be a mild chemical process solely confined to the outmost surface of PA layers.
• The separation performance of the modified PA-TFC membranes for the NaCl aqueous solution was close to that of the pristine membranes.
• The modified PA-TFC membranes exhibited ameliorative chlorine resistance both in acidic and alkaline aging conditions.
• Reagents involved were all easy-to-get and reacted with each other via chemical covalent bonds.

A facile two-step surface modification by aldehydes was proposed to prepare chlorine resistant polyamide (PA) thin film composite (TFC) membranes simultaneously maintaining its high separation performance. Firstly formaldehyde was employed to reduce the chlorine sensitive N-H bonds of amide groups in PA layers into the chlorine resistant N-CH2OH bonds. Then glutaraldehyde was introduced to crosslink the newborn N-CH2OH groups via the stable ether bonds aimed to tighten the polyamide inter-chains. In the statically accelerating chlorination, the two-step modified PA-TFC membranes exhibited ameliorative chlorine resistance both in the acidic and alkaline aging conditions. More importantly, the sound retention of the typical ridge-valley polyamide structure after modification revealed that it was a mild surface modification solely confined to the outmost surface of the layers and succeeded to maintain the high separation performance. A more hydrophilic surface was also obtained after modification and resulted in a better antifouling performance towards protein. Reagents involved in were all easy-to-get and reacted with each other via chemical covalent bonds, which might open a promising way to commercialize a stable chlorine-resistant polyamide thin film composite membranes simultaneously of high separation performance.

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