Flux-enhanced Α-alumina tight ultrafiltration membranes for effective treatment of dye/salt wastewater at high temperatures

α-Alumina tight ultrafiltration (UF) membranes maintain high thermal and chemical resistances and show great potential for application to the treatment and reuse of dye/salt in wastewater under harsh conditions. However, the development of alpha-alumina UF membranes with small pores is challenging. In this study, alumina nanoparticles (AlNPs) were added to boehmite sol as seeds to promote the formation of a single phase α-alumina membrane at low sintering temperature while maintaining a small pore diameter of ∼4.6 nm. The prepared ultra-high purity α-alumina membranes could withstand harsh conditions in the pH range 1–14. Furthermore, this AlNPs doping method increased the porosity and filtration areas of the alpha-alumina UF membranes, significantly enhancing their permeability. The alumina UF membrane displayed a high rejection of the dye molecules and passage of salts. This would allow the reuse of the salts and dyes present in the dye wastewater. When the temperature of the dye wastewater reached 60 °C, the permeability of the UF membrane could be greatly enhanced while maintaining a stable separation efficiency. Overall, this study offers a tight UF membrane (containing ultra-high purity α-alumina) that allows the reuse of the salts and dyes present in wastewater, thereby promoting a sustainable chemical process.