Laminar nanofiltration composite membranes based on two-dimensional aluminum-tetrakis(4-carboxyphenyl)porphyrin (Al-TCPP) nanosheets for efficient dye/salt wastewater treatment

With the increasing severity of environmental pollution and the growing demand for water resource recycling, the purification of industrial wastewater has become a pressing global challenge. At present, commercially available wastewater treatment membranes are limited by the intrinsic properties of their membrane-forming materials, resulting in permeance, rejection, and antifouling performance of the membranes could not meet the ideal requirements for industrial operation. Therefore, it is necessary to develop novel membrane fabrication materials to overcome these limitations. In this study, two-dimensional aluminum-tetrakis(4-carboxyphenyl)porphyrin (2D Al-TCPP) metal-organic framework (MOF) nanosheets were synthesized and employed in membrane fabrication. Benefiting from their small pore size (<1 nm) and unique physicochemical properties, Al-TCPP nanosheets enhanced both the permeance and rejection performance of nanofiltration membranes. Through vacuum filtration, Al-TCPP nanosheets were deposited onto a polyamide porous substrate to form laminar nanofiltration composite membranes. The 2D Al-TCPP nanosheets content in the dispersion used for vacuum-assisted deposition was systematically varied to regulate the microstructure of the membrane selective layer. The resulting membranes were evaluated for dye/salt wastewater separation. Nanofiltration tests revealed a high pure water permeance of 210.6 L m⁻² h⁻¹ bar⁻¹ (LMH/bar) and a methyl blue rejection exceeding 98 % using a 30 ppm nanosheet suspension. The distinctive physicochemical features of Al-TCPP nanosheets further impart strong antifouling capability to the membrane. Overall, the 2D Al-TCPP-based laminar composite membranes demonstrate strong potential for practical dye/salt wastewater nanofiltration. These findings further underscore the promise of 2D Al-TCPP MOF nanosheets as advanced building blocks for next-generation wastewater treatment membranes.