Superwettable porous spheres prepared by recyclable Pickering emulsion polymerization for multifarious oil/water separations

Abstract

Green technologies, environmental protection, and sustainable development are some of the most important issues in today's world. Herein, a low-cost, environment-friendly, and sustainable strategy for fabricating a superwettable porous polymer sphere is reported for the treatment of various kinds of oil-in-water and water-in-oil emulsions. A thermoresponsive 2-hydroxy-3-butoxypropyl starch (HBPS) was synthesized as a representative natural material by simple chemical modification with butyl glycidyl ether, and was used as an effective stabilizer for Pickering emulsion formation. The state of the resulting emulsions could be switched by adjusting the temperature, with emulsification at low temperatures (lower than the lower critical solution temperature (LCST) of HBPS) and demulsification at high temperatures (higher than the LCST of HBPS). Based on this temperature-switchable emulsion system, a straightforward recyclable Pickering emulsion polymerization was designed and used for the fabrication of polymer spheres. A Pickering emulsion polymerization is an emulsion polymerization process in which the colloidal stability of the produced polymer dispersion is supported by solid particles. The distinct superwettability (superlipophilicity and under-oil superhydrophobicity), porosity, and small pore size of polymer spheres achieved resulted in an excellent performance in separating oil-in-water and water-in-oil emulsions with separation efficiencies over 99.9%. This work not only achieved a highly energy-efficient green recyclable Pickering emulsion polymerization system and provided a valuable strategy for the green synthesis process but also resulted in the fabrication of novel spheres with outstanding properties for separating various types of emulsions, with attractive prospects for advanced applications in separating complex emulsions, wastewater treatment, and environmental protection.