Surface characterization and electrochemical studies of nylon 6-based manganese phosphate composite membrane for efficient brackish and industrial wastewater treatment

Abstract

The nylon 6-based manganese phosphate (NMP) composite membrane was synthesized using the die-mold casting process. This cation exchange membrane is designed to improve electrochemical behavior and stability. To attain a membrane with superior stability and selectivity, various polymer-to-inorganic salt ratios were evaluated through comparative analysis of ion exchange capacity, porosity, membrane potential, and chemical stability. Nylon 6 polymer and NMP inorganic material were combined in a ratio of 25% and 75%, respectively, to create the synthetic composite membrane. The inorganic material was created using the sol-gel method of material synthesis. Comprehensive characterization of the membrane was performed using SEM, XRD, FTIR, and EDX to confirm its surface morphology, crystalline structure, functional groups, elemental composition, ion transport behavior, etc. The synthesized membrane showed appropriate porosity (0.012%), ion-exchange capacity (0.8 mmol/g), high stability, reproducibility, and selectivity for salts and heavy metal ions. The electrical potentials measured across the composite membrane in contact with 1:1 electrolytes (KNO₃, NaNO₃, and LiNO₃) showed that LiNO₃ had the highest membrane potential values, followed by NaNO₃ and KNO₃ (LiNO₃ > NaNO₃ > KNO₃). The transport numbers and mobility ratio increased with decreasing concentration of electrolytes and followed the order KNO₃ > NaNO₃ > LiNO₃. Based on the excellent results, the developed membrane is cost-effective, environmentally friendly, and can be effectively used for the separation of brackish water and for industrial wastewater treatment applications.

Graphical Abstract