Tailored design of nanofiltration membrane with MoS2 quantum dots for enhancing selectivity and scaling resistance

Abstract

Nanofiltration technology is a promising solution for water purification, yet membrane scaling remains a major challenge that compromises both durability and efficiency. In this work, a thin-film nanocomposite (TFN) membrane was fabricated by incorporating molybdenum disulfide quantum dots (MoS₂ QDs) into the aqueous phase of piperazine (PIP) monomers. Diffusion experiments and theoretical calculations demonstrated that the MoS₂ QDs effectively reduced the diffusion rate of PIP due to their hydrophilic and electrostatic properties. As a result, compared to the control membrane, the TFN membranes exhibited a thinner, more hydrophilic, and less dense polyamide selective layer with enhanced electronegativity. The optimal TFN-5 membrane with only 0.0025 wt% MoS₂ QDs doping displayed a water permeance of 17.6 L m⁻²·h⁻¹·bar⁻¹ and excellent selectivity for a CaCl₂/Na₂SO₄ ratio of 114.8, surpassing most previously reported nanofiltration membranes. Additionally, the TFN-5 membrane also maintained structure and performance stability in simulated mixed salt solution and 120 h continuous operation tests. These improvements endowed the TFN-5 membrane with superior scaling resistance, resulting in only a 12 % flux decline and minimal gypsum deposition after exposure to a high-salinity mixed salt solution. This work shed light on the design and fabrication of high-performance nanofiltration with enhanced scaling resistance for drinking water treatment applications.