A comprehensive review of electrospray technique for membrane development: Current status, challenges, and opportunities

In recent years, the electrospray (ES) technique has emerged as a novel method to fabricate or modify membranes used in separation processes. The ES technique has the potential to prepare three-dimensional (3D) membrane structures via precision-controlled layer-by-layer deposition, micro-/nano-droplet production, and in situ polymerisation. This review tracks the fundamentals and development of the ES technique and catalogues the features of membranes mainly in liquid phase pressure-driven and vapour phase thermally-driven separation processes prepared by this technique. The ES technique in cone-jet mode is classified into four stages to demonstrate the mechanisms. Based on the materials and membrane formation mechanisms involved, the state-of-the-art publications of the ES technique for membrane preparation are classified into four categories: ES for polymer delivery, ES-assisted monomer polymerisation, ES-assisted interfacial polymerisation, and ES for nanoparticle deposition. The knowledge gaps in each category are identified, with a key emphasis on the need to understand membrane formation mechanisms and the role of ES operating parameters to improve performance. Comparison of the ES technique with conventional membrane fabrication methods reveals the advantages of the ES technique, such as sustainable fabrication and production of three-dimensional, multi-layered, multi-material membrane structures and the limitations in reproducibility and scalability associated with the current state-of-the-art. Notwithstanding the current limitations, future perspectives are highlighted including utilising multiple ES configuration options, advancing ES techniques to realise 3D printing of membranes, accommodating novel materials for membrane fabrication, and exploring different types of substrates.