Single-Layer vs Multilayer MXene Nanofillers: Comparing Their Influences on Poly(ether sulfone) NF Membrane Performance in Wastewater Treatment

This study examines the performance of single-layer and multilayer MXene nanosheets as nanofillers in poly(ether sulfone) (PES) nanofiltration membranes. The primary objective is to identify the optimal MXene morphology that enhances the membrane’s ability to effectively remove salts, heavy metals, dyes, and antibiotics from aqueous solutions, both individually and in complex mixtures. Single-layer and multilayer MXene nanosheets were synthesized using HCl/LiF and HF etching solutions, respectively. These nanosheets were then incorporated into the PES matrix by adding varying amounts (0.1-1%) of MXene nanosheets through the phase inversion method. The results showed that the single-layer 1% membrane was better than the multilayer membrane in most aspects except for mechanical strength. It achieved the highest pure water flux of 121.6 L/m² h and a flux recovery rate of 90%. This membrane also had the highest removal rate for Na₂SO₄ (82.3%), Pb²⁺ (73.7%), RB198 (99.4%), and azithromycin (85%). The better performance of single-layer MXene nanosheets over their multilayer counterparts comes from their higher surface area and greater negative surface charge, which enhances membrane hydrophilicity and improves removal efficiency for negatively charged contaminants such as salts and anionic dyes through Donnan exclusion and electrostatic repulsion. Furthermore, the significant presence of single-layer MXene nanosheets in the modified membrane matrix enhances the active sites for the adsorption mechanisms used to remove heavy metals and antibiotics. Further, complementary testing, including 48 h of continuous filtration, multiple filtration-recovery cycles, competitive removal tests, and cyclic fouling evaluations, consistently demonstrated the superior performance of the single-layer 1% membrane compared to the multilayer counterpart. These findings indicate that modifying PES NF membranes with single-layer MXene nanosheets presents a promising approach for effectively treating wastewater. This study provides valuable insights for researchers and developers in selecting the appropriate method for modifying nanofiltration membranes with MXene nanosheets.