Rational Assemblyof Hydrophobic Particles on TubularSiC Membranes for Water-in-Diesel (W/D) Emulsions: Synchronized WettabilityReversal and Pore Narrowing

Janus ceramic membranes with asymmetric wettability have proven highly effective for preparing water-in-diesel (W/D) emulsions. Therefore, the fabrication of such tubular membranes for continuous emulsification processes is of significant interest. In this study, tetraethyl orthosilicate (TEOS) and methyltriethoxysilane (MTES) were used as precursors, with ammonia serving as the catalyst, to achieve the controlled synthesis of hydrophobic silica (SiO₂) particles. Subsequently, these hydrophobic SiO₂ particles were coated onto the inner walls of tubular silicon carbide (SiC) membranes (mean pore size = 1.2 μm) via a simple dip-coating process. Results indicate that controlling the ammonia concentration allows for the synthesis of SiO₂ particles with sizes that appropriately match the pore dimensions of the tubular SiC membranes. As the SiO₂ solid content was increased from 0.10 to 2.00 wt %, the average pore size of the tubular SiC membranes decreased from 1.2 to 0.52 μm. Concurrently, the apparent water contact angle on the inner walls increased significantly from 15° to 142°, while the outer surface remained hydrophilic. Among the membranes with various surface wettability, the configuration featuring a hydrophobic inner wall and a hydrophilic outer surface proved most effective for emulsion production, yielding W/D emulsions with smaller average droplet diameter and uniform size distribution. This work introduces an effective method for simultaneously tuning the surface wettability and pore structure of tubular SiC ceramic membranes, thereby establishing a foundation for the continuous membrane emulsification of diesel fuel.