Silica-pillared lamellar boron nitride membranes for ultrahigh-flux oil-water separation

Two-dimensional lamellar membranes offer precise nanochannel control for oil–water separation, yet structural instability and interlayer restacking often compromise long-term permeability and selectivity. Herein, a mechanism-driven strategy is proposed to engineer silica-pillared partially oxidized boron nitride (SiO₂@BNox) lamellar membranes with stabilized nanochannels for high-performance oil-water separation. Partial oxidation introduces hydroxyl functionalities that enhance surface polarity and provide anchoring sites for in-situ silica intercalation, while rigid SiO₂ pillars enlarge and stabilize the interlayer spacing to suppress restacking under hydraulic pressure. Molecular dynamics simulations reveal increased fractional free volume and regulated transport pathways in the pillared architecture, corroborating experimental observations. The optimized SiO₂@BNox/MCE membrane exhibits an ultrahigh pure water flux of 14,300 L m⁻² h⁻¹ at 2 bar (7150 L m⁻² h⁻¹ bar⁻¹ normalized) while maintaining up to 99.9% rejection for diesel-in-water emulsions. Stable separation performance was sustained over 20 filtration cycles with flux recovery ratios exceeding 95%, demonstrating strong resistance to irreversible fouling. The membrane further achieves rejection efficiencies of 99.5% and 99.3% for crude oil and vegetable oil emulsions, respectively, demonstrating its effectiveness across diverse oil-contaminated wastewater streams. This work establishes a rational interlayer engineering strategy that integrates surface activation and silica pillaring to stabilize lamellar nanochannels for sustained oil–water separation and provides a viable alternative to conventional MXene and graphene-based membranes.