Nanocomposite hydrogel engineered hierarchical membranes for efficient oil/water separation and heavy metal removal

The contaminants of oily sewage and heavy metal ions have been increasingly released into the aquatic environment, which causes a severe threat to both ecosystem and human health. However, it is still difficult to use a single separation technology to effectively deal with such a complex hazardous system to ensure the water safety and environmental remediation. Herein, a novel nanocomposite hydrogel-coated membrane was designed by one-step dip-coating of tannic acid (TA)/sodium alginate (SA)/3-aminopropyltriethoxysilane (APTES) co-depositing strategy, which combines the robust adhesion of TA, the hierarchical architecture induced by APTES and the strong hydration ability of SA. The as-prepared membrane exhibits excellent hydrophilicity and underwater superoleophobicity, which achieves efficient separation for various oil/water emulsions and outstanding anti-oil fouling performance. Meanwhile, the excellent heavy metal adsorption capacity was realized due to the abundant adsorption sites (-COO-, –NH2 and phenolic hydroxyl) and large surface area caused by hierarchical structures. Most interestingly, the fabricated membrane also presented strong chemical stability over a wide pH range 3–11, high salt tolerance and good resistance to anhydrous ethanol corrosion. The designed superwetting membranes show great potential for the purification of oil/water emulsion and the removal of heavy metal ions to effectively remediate the aquatic environment by the concept of 'killing two birds by one stone'.