One-Step Heat-Induced Surface Hydrophobization of Cellulosic Membrane by APTES for Oil–Water Emulsion Separation

Widespread discharge of oily wastewater from industrial processes, combined with accidental oil spills, poses a significant challenge to the environment and human health. Hence, the efficient separation of oil/water mixtures is a pressing issue for sustainable development. Hydrophobic/oleophilic materials based on cellulose fibers modified with silanes show increasing interest for the selective separation of oil and water, but it remains difficult to achieve simple processing while ensuring stability, durability, environmental friendliness, and low cost. Here, a hydrophobic membrane was produced via a simple one-step modification by immersing the paper substrate (UNPr) in hydrolyzed 3-aminopropyltriethoxysilane (APTES). Heat treatment at 120 °C promoted interfacial interactions between the NH₂-NH₂ and NH₂-OH groups via conformational rearrangements that oriented the -NH₂ groups toward the fiber surfaces (inward), resulting in a transition from hydrophilic to hydrophobic surfaces. This modified paper showed a water contact angle (WCA) of over 134° and oil spread immediately with an oil contact angle (OCA) of ∼0°; moreover, the average pore volume of the membrane was 246.75 ± 469.3 μm³, which improved its selectivity and enabled efficient separation of even small water droplets.