Novel ricinoleic acid highly functionalized hierarchical SiO2 with switchable superwettability for removal of oils, heavy metal ions, and organic dyes from water

It remains a challenge to explore a low-cost and green approach to prepare stimuli-responsive materials that can meet increasingly complicated separation demands. Herein, we report a facile method to prepare pH-responsive silica particles modified by abundant carboxyl groups (SiO2-COOH), which are introduced from bio-based ricinoleic acid via an efficient and mild thiol-ene click reaction. The hierarchical structure of SiO2-COOH can easily construct roughness that is essential for special wettability, which is demonstrated by the robust superhydrophobicity achieved synergistically with non-pH-responsive binder on different substrates and no significant change after 100 peels or extrusions. We also present the efficient separation of different oil-water mixtures by modified fabrics and sponges, respectively, based on their fast wettability transition within seconds at different pH. More importantly, benefiting from the chelation of carboxyl and hydroxyl groups from ricinoleic acid molecules and large specific surface area provided by the hierarchical structure, SiO2-COOH and its different alkali treatment products exhibit outstanding adsorption capacity to heavy metal ions and organic dyes, of which up to 180 mg/g for Pb2+. It is believed that the proposed novel and eco-friendly method is a promising candidate for the simultaneous removal of multiple pollutants from oily wastewater.