Enhanced both water flux and salt rejection of reverse osmosis membrane through combining isophthaloyl dichloride with biphenyl tetraacyl chloride as organic phase monomer for seawater desalination

The mixed organic monomers of isophthaloyl dichloride (IPC) and 3,3′,5,5′-biphenyl tetraacyl chloride (BTEC) were used to prepare polyamide thin film composite (PA TFC) membranes for seawater desalination. IPC and BTEC act as a linear monomer and a cross-linking agent, respectively. As a result, the ratio of linear portion to cross-linking portion of polyamide film can be controlled by adjusting the fraction of monomer. It was found that the chemical composition, chain segment relaxation property, and the surface morphology of polyamide films changed significantly with the ratio of IPC to BTEC increasing. The rougher surface is formed while less pendant carboxylic acid groups present at higher IPC concentrations or lower BTEC concentrations. As the fraction of IPC increases, the length of linear segment between two cross linking point is increased, hence the enlarged polyamide network pore is formed. When IPC weight percentage increases from 0% to 70%, the water flux of the TFC membrane increases from 30 to 43.7 L/m2 h and the salt rejection increases from 99.3% to 99.7% at 5.5 MPa, 32800 ppm NaCl, 25±3 °C testing condition. We demonstrated that both water flux and salt rejection of the polyamide membrane can be improved by the control of ratio of IPC to BTEC.