Alkali-resistant nanofiltration membranes: materials, mechanisms, applications, and perspectives

Industrial alkaline solutions, characterized by complex compositions and large treatment volumes, pose significant challenges for purification and resource recovery. Nanofiltration (NF) offers an effective and economically advantageous for separating and purifying alkaline solutions. However, the polyamide layer of traditional NF membranes is susceptible to nucleophilic attack by OH^– ions in alkaline environments, causing performance degradation over time. Recent advancements in alkali-resistant NF membranes have demonstrated stable separation under such harsh conditions. Despite this progress, comprehensive analyses addressing monomer selection, design principles, preparation methods, process coupling, economic evaluation, and application requirements remain insufficiently addressed, creating confusion in membrane design, selection, and application. This paper provides a thorough overview of the materials and performance of current alkali-resistant NF membranes, delving into the underlying mechanisms of alkali resistance. Additionally, it summarizes the preparation techniques and industrial applications of these membranes, while also highlighting the broader application requirements. Finally, the paper outlines the challenges and future research directions of material upgrading and process optimization for alkali-resistant NF membranes. The goal is to provide valuable insights to guide further advancements in this field, paving the way for more efficient and durable membrane technologies for separation, purification and resource recovery of alkaline solutions.