Surface-modified ultrafiltration and nanofiltration membranes for the selective removal of heavy metals and inorganic groundwater contaminants: a review

Abstract

Groundwater contamination due to heavy metals and inorganic contaminants is a growing concern worldwide. Exposure to toxic elements, such as arsenic, chromium, copper, cadmium, fluoride, and nitrate, can pose significant health risks to humans and wildlife. Owing to its low footprint, cost-effectiveness, and automation, membrane technology has emerged as an effective technique for removing these contaminants. However, membrane fouling and the trade-off between membrane selectivity and permeability for charge-specific contaminants remain key challenges. To address these issues, this study comprehensively reviews various membrane surface modification techniques for the selective removal of heavy metals and inorganic contaminants. This review starts with the surface modification methods for ultrafiltration and nanofiltration membranes, including strategies, such as pore tuning, nanocomposites-based surface modifications, and membrane surface charge modifications by blending, coating, and chemical grafting. Furthermore, different metal/metal-oxide nanoparticles, hybrid nanomaterials, carbon nanotubes, graphene oxide, and metal–organic framework-based nanofillers in membrane blends and coats are also explored. Thereafter, it highlights the mechanisms behind removing different contaminants. The last section discusses the challenges and future prospects of such surface-modified membranes, which highlighted the area requiring extensive research, including the cost-economics, scale-up, and application of membranes in a real-time groundwater matrix, and how new-generation surface modification methods of membranes have shown promising results. This review provides valuable insights into the current state of knowledge in the membrane technology field, and its findings can guide future research and development efforts to address the challenges in heavy metals and inorganic contaminants from groundwater.