| Summary: | Water is essential for all living things to sustain life and carry out daily activities. With the increasing demands on freshwater and the deterioration of the availability of freshwater sources, reserve osmosis (RO) has been classified as one of the viable technologies that are able to produce safe and clean quality water for every living thing to consume. However, the performance of polyamide (PA) thin-film composite (TFC) RO membranes is often restricted by poor antifouling and anti-chlorine properties, as well as the trade-off between water flux and salt rejection over a period of time. The surface modification of PA TFC membrane with zwitterionic material such as amino acid offers multiple functionalities that not only can ameliorate the fouling and chlorine attack issues, but also maintain satisfactory separation performances in terms of water flux and salt rejection. This study aimed to introduce a dipeptide which is known as a derived from two zwitterionic amino acids onto the surface of the PA TFC membrane through surface grafting. The dipeptide was synthesized by arginine ethyl ester dihydrochloride (Arg-OEt) with the presence of trypsin as a catalyst in this process to become arginyl-arginine (Arg-Arg) dipeptide. The grafting of Arg monomer and Arg-Arg dipeptide made a membrane surface thinner, smoother, more hydrophilic, and less negative charge evidenced from characterization through field emission scanning electron microscopy, atomic force microscopy, contact angle, and zeta potential measurements, respectively. The additional amine groups and extra guanidinium groups formed in the Arg-Arg dipeptide-modified membranes was analysed using Fourier transforms infrared spectroscopy and nuclear magnetic resonance. The RO water flux and salt rejection were enhanced by the modified membranes when tested in a lab scale dead-end filtration setup. Compared to the neat TFC membrane which exhibited a water flux of 10.50L/m²h and salt rejection of 96.20%, it was observed that the Arg-modified membrane showed an improvement in water flux and salt rejection at 13.36 L/m²h (improved by 27.28%) and 96.83% respectively, while the Arg-Arg dipeptide-modified membrane recorded 12.96L/m²h (improved by 23.43%) and 98.00% respectively. Besides that, Arg-Arg dipeptide-modified membranes showed high fouling resistance when tested using 2000 ppm bovine serum albumin as a model foulant. The results indicated that the final flux after four cycles of filtration was restored almost to the same value as the initial water flux. Also, the chlorine resistance for Arg-Arg dipeptide-modified membranes showed an improvement in which high separation performances were retained even after exposure to 500 ppm of sodium hypochlorite compared to the Arg-modified membranes and neat TFC membrane. It is concluded that Arg-Arg dipeptide has enhanced the surface properties of the membrane. Dipeptide can be used for industry-scaled membrane surface modification as it offers a simple and straightforward technique for membrane modification. Hence, Arg-Arg dipeptide promotes sustainable development goals in membrane development, especially in water desalination and water treatment industries.
|
|---|
