Janus layered nanofibrous aerogels with switchable wettability for targeted emulsion separation
Muhammed Ziauddin Ahmad Ebrahim, Darshana U. Malusare, Anurodh Tripathi, Tahira Pirzada, Saad A. Khan
Abstract
• Solid-templating of nanofibers into functional aerogels. • Stratified aerogels of hydrophobic and oleophilic layers enable oil–water separation. • Gravity-driven emulsion separation with >95 % efficiency over multiple cycles. • Surface energy model supports experimental separation/sorption findings. • a priori prediction for solvent sorption that could be pertinent in chemical spills. This study introduces an innovative bioinspired bilayered nanofibrous aerogel (NFA) fabrication approach to create asymmetric porosity and wettability in mechanically robust aerogels without the use of complicated processing steps and harsh chemical modifiers. Combining cellulose acetate-silica (CA-Sil) and polyacrylonitrile/polyvinylpyrrolidone (PAN/PVP) nanofiber layers, the hybrid NFA is assembled via a directional layer-by-layer freezing technique, resulting in a mechanically robust, 3D hierarchical porous structure. To provide responsive functionality, we also embed magnetic iron oxide (Fe 3 O 4 ) nanoparticles in the PAN/PVP nanofibers. The CA-Sil layer is hydrophobic (water contact angle (WCA) 129°), while the PAN/PVP-Fe layer is amphiphilic, enabling efficient, gravity-driven emulsion separation with over 95% removal efficiency across multiple cycles without significant loss of performance. Further insights into NFA’s selective sorption of various solvents, is obtained by examining its wettability through surface energy calculations using Zisman’s theory and Fowkes’ model validated by experiments. The surface energy values of 52.5 mN/m and 72.38 mN/m shown for the CA-Sil and PAN/PVP-Fe layers respectively corroborate selective permeability/separation, introducing a robust approach for emulsion separation. These layered NFAs with controlled selectivity establish a versatile framework for sustainably developing Janus porous materials using hybrid nanofibers meeting critical needs for tailored performance in diverse applications.