In-situ Ti doping induces distortion of mullite whiskers in fly ash-based ceramic membranes for enhanced oil-water separation performance

Oil-in-water emulsions in oily wastewater effluents and accumulation of fly ash pose environmental issues. Mullite ceramic membranes, prepared leveraging the Al₂O₃ and SiO₂ components in fly ash, offer potential for wastewater treatment. However, the impact of TiO₂ impurities in fly ash on the microstructure and oil-water separation performance of ceramic membranes remains uncertain. This study analyzed the effects of in-situ TiO₂ doping on the crystal phase composition, pore structure, wettability, and oil-water separation performance of whisker-structured mullite ceramic membranes. Ti^4 + ions were successfully incorporated, achieving solid solution with 4 wt% TiO₂ within the mullite framework. TiO₂ doping induced lattice distortion in mullite. This enhanced internal crystal defects, boosted porosity, and modified surface energy, thereby improving hydrophilicity. The mullite ceramic membrane doped with 4 wt% TiO₂ exhibited optimal hydrophilicity (WCA = 22°) and underwater oleophobicity (UOCA = 156°), which improved its selective permeability. The permeation flux of the ceramic membrane increased significantly, reaching 810.76 L·m⁻²·h⁻¹ when doped with 4 wt% TiO₂), while the oil rejection rate was 96.4 %. Notably, during the first five minutes, the oil rejection rate of the ceramic membrane doped with 4 wt% TiO₂ increased to 95.1 %. This study offers a theoretical foundation for preparing high-efficiency oil-water separating mullite ceramic membranes from fly ash, particularly aiding in optimizing ceramic membrane performance through structural design and regulation strategies.