Iron-Based Oxides Anchored on the Catechol/Silane-Coated Polypropylene Nonwoven Fabrics for Effective Removal of Anionic Dyes

The dopamine modification strategy has received extensive attention in water treatment due to its simple and gentle preparation process, excellent adhesion, and good secondary reactivity. Further research has found that compounds containing the catechol groups can react with the amino-containing silane coupling agents under mild conditions to form dopamine-like hydrophilic coatings on the surface of hydrophobic membranes or fibers. This paper used cheap polypropylene melt-blown nonwovens as the substrate to prepare a large-capacity dye adsorbent PP-(CK-Fe). Specifically, catechol (CA) and (3-aminopropyl) triethoxysilane (KH550) were used to form a codeposited coating on the substrate. Then, we used the secondary reactivity of the coating to grow iron-based oxides in situ. The adsorbent had good adsorption performance on anionic dyes at the initial pH of the dye solution, including Orange II (380 mg/g), methyl orange (268 mg/g), Congo red (294 mg/g), and carmine (263 mg/g). However, it had almost no adsorption effect on cationic dyes at the initial pH, including methylene blue and Rhodamine B. We chose Orange II to explore the possible adsorption mechanism. The results confirmed that the adsorbent had good adsorption performance at pH 3–11. The adsorption process tended to be monolayer chemical adsorption. The maximum adsorption capacity (Qmax) of Orange II was 515.46 mg/g under optimal conditions. This study also confirmed that the codeposition coating constructed with polyphenol and amino-containing silane coupling agents had a secondary reactivity similar to the dopamine coating.