Self-cleaning photocatalytic membranes in oil-water separation: Design strategies and sustainability challenges

The increasing discharge of oily wastewater demands innovative solutions to avert environmental and health crises. Photocatalytic membranes, integrating membrane filtration with photocatalysis, provide an efficient, self-cleaning, and sustainable remediation of oil-contaminated water. This review provides an integrated perspective on substrate stability, catalyst efficiency-stability trade-offs, and immobilization strategies in photocatalytic membranes, highlighting the urgency of adopting life cycle assessments to guide sustainable membrane innovation. First, the characteristics, stability, and modification of commonly used membrane substrates (metal meshes, polymers, and ceramics) are critically examined, with particular attention to environmental risks such as polymer degradation and PFAS release. Then, the performance and limitations of representative photocatalysts-including TiO₂, ZnO, g-C₃N₄, MOFs, MXene, and LDHs-are discussed, along with strategies for enhancing photocatalytic activity and long-term stability. Various immobilization techniques are compared in terms of compatibility with photocatalysts and substrates, highlighting the trade-offs between catalytic efficiency and stability. Additionally, the influence of operational parameters (e.g., oil type, surfactant, transmembrane pressure) on separation performance is systematically reviewed. This review critically evaluates emerging environmental concerns such as nanoparticle leaching and toxic intermediate formation, and advocates for the integration of life cycle assessment (LCA) to evaluate the sustainability of photocatalytic membranes for oil-water separation. By unifying material design with an environmental impact analysis, this work provides in-depth guidance for the development of safer and more sustainable photocatalytic membranes for oily wastewater treatment.