3D Printing of Hierarchical Porous Structures for Oil/Water Separation and Absorption

Efficient separation of immiscible oil and water phases is crucial for mitigating environmental pollution from various industries and ensuring clean water availability in the future. Traditional separation methods, such as gravity settling, coalescence, and filtration, often rely on rigid materials with limited structural control, resulting in low efficiency. Membrane-based methods, while precise, require substantial energy and are prone to fouling. Recent research has focused on capillary-force-driven separation using porous materials with gradient porosity distribution, which offer selective absorption and repulsion properties. However, traditional manufacturing methods for producing porous structures face several challenges, such as limited design complexity, poor microstructure control, lengthy multistep processes, and significant material waste. Additive manufacturing, particularly video-projection-based stereolithography (VP-SL), offers a promising solution by enabling the creation of complex, hierarchically porous structures with tailored morphologies in a time-efficient manner. In this article, the VP-SL process is utilized to fabricate structures with porosity gradients for efficient and rapid oil–water separation. The influence of the VP-SL printing speed on the porosity distribution of printed structures was analyzed. The mechanism underlying the oil absorption and separation performance of the proposed heterogeneous porous structures is discussed, and the relationship between capillary forces and pore morphology is modeled. The oil/water separation capability of traditional homogeneous and heterogeneous structures was measured to understand the influence of geometric contrast on the selective oil absorption. Experimental results validated that the VP-SL process can effectively print porous structures with a spatially varied porosity distribution, which can be used to selectively absorb or separate oil from oil–water mixtures.