Enhancing loose nanofiltration membrane performance with strategic diethanolamine and polyquaternium-10 modifications for efficient dye desalination

In response to the critical challenge of managing dye wastewater in the textile industry, this research presents an economically viable modification approach to enhance the dye/salt separation efficacy and operational stability of polyamide (PA) based nanofiltration membranes. By incorporating diethanolamine (DEA) as piperazine-aqueous phase additive and polyquaternium-10 (PQ-10) as surface modifier, this technique significantly optimized the properties of loose nanofiltration membranes. Structural modifications resulted in a significant reduction in surface zeta potential at pH 7.0, from −28.9 mV to −2.0 mV, expanded the molecular weight cut-off (MWCO) and most probable pore radius from 360 to 2340 Da and 0.28 to 0.64 nm, respectively. These changes led to high water permeability of 420.4 L·m −2 ·h −1 ·MPa −1 and much low sodium sulfate (Na 2 SO 4 ) rejection of 10.3 %, while maintaining a 98.9 % rejection for dye Congo red (CR). Long-term operational tests demonstrated stable rejection of approximately 98 % for CR and 11 % for Na 2 SO 4 over 50.0 h, affirming the high separation efficiency and good durability of membranes. This enhancement in dye/Na 2 SO 4 separation not only optimizes the balance between permeability and selectivity but also shows significant potential for scaling to industrial applications. The findings provide a robust strategy for addressing critical demands in wastewater treatment within the industry.