Abstract:

Objective Cotton fabrics，as a natural cellulose material， are an ideal substrate for developing functional textiles due to its wide availability， biodegradability and rich hydroxyl groups for modification. Current strategies for creating superhydrophobic cotton fabrics often face challenges such as environmental concerns， complex processes， reliance on expensive equipment and insufficient durability. Thus， this study aims to develop an environmentally friendly， facile method for preparing durable superhydrophobic cotton fabrics with integrated functionalities for efficient oil-water separation.

Method The original fabric was ultrasonically cleaned in a mixed solution of deionized water and ethanol （1∶1 volume ratio） for 30 min， dried at 60 ℃ to obtain the original cleaned fabric （OCF）， and then cut into 5 cm × 5 cm pieces for further use. The OCF was then immersed in a solution of FeCl₃·6H₂O within an acetate buffer （pH=5.0）， leading to the in-situ formation and deposition of micro/nano-structured iron oxyhydroxide （FeOOH） particles on the fiber surfaces， constructing a hierarchical rough morphology. Subsequently， the fabric was treated with a hexadecyltrimethoxysilane （HDTMS） ethanol solution. The hydrolysis and condensation of HDTMS formed a low-surface-energy siloxane layer， covalently grafting onto the fabric and the deposited particles. The chemical composition， surface morphology， and crystalline structure of the modified fabrics （denoted as H-FeCF） were characterized using FTIR， SEM， EDS and XRD. The superhydrophobicity was evaluated by water contact angle （WCA） and sliding angle （SA） measurements. Durability was assessed through abrasion， washing and immersion in solutions with a wide pH range （1.0-13.0）. Furthermore， self-cleaning ability and oil-water separation performance were systematically investigated.

Results Characterizations confirmed the micro/nano-featured roughness with FeOOH and the formation of a low-surface-energy HDTMS coating. The fabricated H-FeCF fabric exhibited a static WCA as high as 162.5° and a SA of 6.06°， confirming excellent superhydrophobicity. The modified surface demonstrates remarkable selective wettability. Droplets of various liquids， including pure water， coffee， tea， milk， and reactive brilliant blue solution， maintained a perfect spherical shape on the surface， whereas oil droplets were rapidly absorbed. The superhydrophobic surface demonstrates remarkable durability. After 800 abrasion cycles， the WCA remained at （150.26±0.98）°； after 10 wash cycles， the WCA was （151.56±0.89）°； and even after 24 h of immersion in strong acid （pH=1.0） or alkali （pH=13.0） solutions， the WCA stayed above 150°. Additionally， the fabric displays effective self-cleaning performance. For oil-water separation， the H-FeCF achieved an initial efficiency of 98.9% and a high flux of 7 803 L/（m²·h）. After 10 separation cycles， the efficiency stayed above 97.4%， although the flux decreased by 21.8% due to minor pore clogging and oil-induced swelling of the coating.

Conclusion A synergistic strategy combining surface roughening with FeOOH and low-surface-energy modification with HDTMS is successfully applied to prepare multifunctional superhydrophobic cotton fabrics， the method for which is simple and fluorine-free. The resulting fabric integrates superior superhydrophobicity， excellent durability against physical and chemical challenges， high-efficiency oil-water separation， and self-cleaning stability. This work provides a highly potential and sustainable material choice for future applications in the field of oily wastewater treatment.

Key words: superhydrophobic, cotton fabric, iron（III） chloride hexahydrate, hexadecyltrimethoxysilane, oil-water separation, self-cleaning, hydrophobicity durability