Bioinspired superwetting materials for oil–water separation: mechanisms, limitations and engineering solutions

Abstract

Industrial sewage discharge and oil spills from ships into the ocean are becoming increasingly serious. Therefore, how to effectively solve the problem of oil pollution in water resources for secondary water recycling has become an issue of growing concern. Inspired by bionics, numerous superwetting materials have been developed for oil–water separation. This review argues that the field is currently transitioning from static wettability-based designs (e.g., superhydrophobic/superoleophilic, and Janus materials) to dynamic, stimulus-responsive systems. However, a critical gap remains between laboratory-scale separation efficiency (>99% in most cases) and real-world durability under complex conditions such as high-viscosity crude oil, surfactants, and mechanical abrasion. Rather than merely cataloging reported materials, five representative classes are critically analyzed: superhydrophilic/underwater superoleophobic, superhydrophilic/superoleophobic, superhydrophobic/superoleophilic, Janus, and stimulus-responsive smart materials. For each class, a specific unresolved paradox is identified (e.g., water-film instability, fluorochemical dependency, pore clogging, interfacial delamination, and response-speed/energy trade-offs). Based on this critical analysis, persistent technical bottlenecks across all five material classes are identified and a set of standardized evaluation metrics is proposed to facilitate a fair cross-comparison, aiming to guide the design of next-generation oil–water separation technologies that are not only efficient but also durable and scalable.