In-situ ion-assisted sol-gel method for homogeneous CeO₂ mesopore membrane

To achieve precise separation of bioactive molecules, an innovative strategy combining sonochemistry and in-situ ion assistance process was proposed to fabricate CeO₂ mesopore membranes with narrow pore size around 3.7 nm. Under the ultrasound cavitation, the precursors and the precipitants react uniformly at molecular scale. The residual appropriate in-situ ions dispersed around the cluster form a double electric layer, thereby enhancing the stability of the sol. During sintering, ions between the clusters generate CeO₂, reinforcing particle neck connections while the confined space between particles restricts further CeO₂ particle growth. The resulting CeO₂ membranes possess characteristics of a single fluorite phase, high crystallinity, and narrow pore size distribution. The optimal membrane thickness of 380 nm could be formed by a 2x dilution of sol and a 30-second coating time, exhibiting a complete structure with no obvious defects. The membrane achieved a molecular weight cut-off (MWCO) of ∼4300 Da, a pure water permeance of 61 L·m^-2·h^-1·bar^-1, an average pore size of 3.7 nm and a roughness of 3.4 nm. In chitosan oligosaccharides (COS) preparation using cellulase, the CeO₂ membranes demonstrated 100% cellulase retention and ∼50% transmission of COS with the degree of polymerization (DP) ranging from 2 to 5, thus achieving precise separation.