Scalable fabrication of thin α-Al₂O₃ microfiltration membranes via reverse dip-coating and in situ phase transformation for semiconductor wastewater treatment

Semiconductor packaging wastewater typically contains large amounts of suspended solids and submicron abrasive particles, posing a major challenge to precise and stable solid–liquid separation. Ceramic microfiltration (MF) membranes are promising for such applications because of their excellent chemical stability, mechanical robustness, and tolerance to aggressive cleaning conditions. However, conventional particle-sintering fabrication routes often produce structurally heterogeneous separation layers with broad pore-size distributions and high transport resistance. Herein, we report a scalable strategy for the fabrication of thin α-Al₂O₃ MF membranes by integrating sol–gel deposition, reverse dip-coating (RDC) and controlled in situ phase transformation. In this approach, RDC facilitates stable deposition of a boehmite-derived precursor layer, while the subsequent phase transformation is associated with grain rearrangement and the formation of intergranular MF pores. As a result, thin and uniform α-Al₂O₃ separation layers can be constructed without relying on conventional particle-packing routes. The optimized membrane exhibited an average pore size of 118 ± 4 nm and a high pure water permeance of 2636 ± 102 L m⁻² h⁻¹ bar⁻¹. When tested using a SiO₂-particle-containing model wastewater, it achieved particle rejection above 98% and a flux recovery ratio above 79% after backwashing during cyclic filtration tests. Importantly, the fabrication strategy was further extended to 1 m-long single-channel and 19-channel ceramic membranes, demonstrating the proof-of-concept feasibility of scale-up fabrication. This work establishes an RDC-enabled, phase-transformation-driven route for engineering high-permeance α-Al₂O₃ MF membranes, and provides a promising basis for the scalable treatment of particulate wastewater streams relevant to semiconductor packaging processes.