Tannin-Based Spontaneous Adhesion Superhydrophilic Coatings for Efficient Oil-in-Water Emulsion Separation and Dye Removal

It is significant to explore green, convenient, and widely applicable superhydrophilic coatings. This study proposes a strategy of using covalent cross-linking of tannic acid and tetrabutyl titanate to prepare a superhydrophilic coating, which can be simply applied on the porous substrate surface by vacuum filtration and immersion without additional binders. The surfaces modified by coatings get intriguing superhydrophilicity and underwater superoleophobicity due to the synergistic effect of the high roughness and hydrophilic polyphenols. A permeation flux of up to 5663.57 L m–2 h–1 bar–1 with a filtrate total organic carbon content of only 41.95 ppm is obtained under 0.1 bar. The modified membranes also exhibit efficient purification of dye solutions and mixed wastewaters, with absorbance reductions of up to 99.4%. In addition, stability tests prove the coatings to be acid- and alkali-resistant as well as mechanically robust. The surface modification method developed in this work can be easily extended to various materials for industrial wastewater treatment.