Advanced Janus Aerogels Evaporator Featuring with Multiscale Architectures and Dual‐Layer Design for Efficient Oily Seawater Purification

Abstract The discharge of oily wastewater can severely disrupt aquatic ecosystem balance and threaten drinking water safety. Although superwetting membrane separation technology has become an effective means to address oily wastewater, there are still major challenges in the treatment of nano/submicron emulsions under specific conditions, such as high energy consumption, harsh separation conditions, and concentration polarization. Herein, a novel preparation of dual‐layer Janus‐structured nanofilament cellulose (JNC) aerogel photothermal evaporator is proposed that integrates solar‐assisted interfacial evaporation with high oil‐water selective separation to achieve the function of “coupled interception and evaporation”. The JNC aerogel evaporator is fabricated using a sequential bilayer gel molding strategy combined with directional freeze‐drying technology to form a vertically ordered cellular network structure with multi‐scale and multi‐level crosslinking, and precisely tunable hydrophilic and hydrophobic layer thicknesses. The as‐prepared evaporator possesses amphiphilicity, high compressibility, excellent desalting efficiency, and strong resistance to acids and alkalis. The evaporator can stably float on the water surface with a high evaporation rate of 2.86 kg Janus‐structured nanofilament cellulose (JNC)m ⁻² h ⁻¹ and oil removal efficiency exceeding 99.97% for various oil‐in‐water emulsions. Additionally, the emulsion separation mechanism of the evaporator is investigated through classical molecular dynamics simulations. This work provides an innovative approach to designing efficient evaporators for treating oily seawater.