Engineering Ni-MOF/g-C3N4 Composite-Infused Polysulfone Membranes with Optimal Rejection, Flux, Antifouling, and Photocatalytic Properties for Wastewater Treatment

Nickel-based metal–organic frameworks (MOFs) with different ligands (terephthalic acid and 2-amino terephthalic acid) were developed and integrated with g-C₃N₄ (GCN) to construct a heterojunction-based composite photocatalyst. This composite was further incorporated into the polysulfone (PSF) at varying concentrations (3, 5, and 7 wt %) to fabricate photocatalytic membranes for the separation and degradation of dyes (rhodamine B/RhB and Congo red/CR) in wastewater. Structural and physiochemical investigations of the developed composites revealed that the Ni-MOF exhibits ligand-dependent properties, influencing both the membrane and photocatalytic properties of the system. Particularly, the Ni-MOF with 2-amino terephthalic acid/g-C₃N₄ (NATP/GCN) composite-infused membranes (NGM-5) demonstrated improved rejection, flux, antifouling, and photocatalytic degradation properties due to the favorable physiochemical features of the NATP/GCN composite. As a result, the NGM-5 showed an enhanced water flux of around 30.9 L/m²/h, while it is ∼25 L/m²/h in the case of bare membrane. The dye (RhB and CR) rejection efficacy of this NGM-5 is around 92 and 88%, respectively, which is double the times higher than that of the bare. Similarly, the RhB/CR dye solution flux of NGM-5 is around 42.3/55.4%, respectively, while it is only around 18.7/14.2% in the case of the bare-membrane. In addition, all modified-membranes showed enhanced fouling resistance compared to bare membranes, estimated through reversible and irreversible-fouling estimations. Furthermore, the photocatalytic efficiency of NGM-5 is appreciable, which degraded around 13.3/6.1% of RhB/CR dye, respectively, under sunlight. This included favorable chemical/electrostatic interactions of the composite with the membrane, leading to a rough surface with improved pore features and channels for effective separation of dyes and suitable band structure to perform effective redox reactions for efficient degradation of the dye molecules under sunlight. These observed results demonstrate that modifying membranes with rationally engineered photocatalysts can have a significant impact on developing multifaceted and dynamic photocatalytic membranes for sustainable applications in membrane-based wastewater treatment technologies.