Hydrophilic/underwater oleophobic hybrid separation column containing layered-double-hydroxides and layered-double-oxides for oil-water separation

Efficient and sustainable treatment of oily wastewater remains a significant challenge due to the high stability of emulsified oil droplets. In this work, a functionally differentiated dual-layer separation column is constructed based on MgAl layered double hydroxides (LDHs) and layered double oxides (LDOs) functionalized wastewater treatment sludge (WTS) via a waste-to-resource strategy. Unlike conventional single-function materials, the proposed system features a vertically structured packed column in which distinct separation functions are spatially organized to achieve cascade regulation of emulsion transport. The upper MgAl LDHs/WTS layer serves as an interfacial regulation zone, exhibiting superhydrophilicity and underwater oleophobicity, which promotes rapid water permeation and facilitates droplet destabilization and coalescence. The lower MgAl LDOs/WTS layer, characterized by a porous and defect-rich structure, acts as a confinement zone to intercept and retain residual micro-sized oil droplets through tortuous flow pathways. This layer-resolved functional differentiation enables a cascade separation mechanism dominated by interfacial demulsification and structural interception under gravity-driven conditions. As a result, the optimized column achieves a high separation efficiency of 99.95% with a permeation flux of 1816 L m−2 h−1. In addition, the column configuration allows flexible tuning of separation performance by adjusting the packing height. Compared with conventional pressure-driven membrane systems, the gravity-driven packed column demonstrates advantages in energy efficiency, operational simplicity, and tolerance to complex feed compositions. Overall, this work provides an effective strategy for simultaneous sludge valorization and oily wastewater treatment, while offering new insights into structure-oriented design of functionally integrated separation systems.