A Strategy of End Anchoring to Poly(N-isopropylacrylamide) Chains for the Thermo-Driven Controllable Oil–Water Separation

Abstract

Poly(N-isopropylacrylamide) (PNIPAM) chain with catechol end group was designed and successfully synthesized by a reversible addition−fragmentation chain transfer (RAFT) procedure, and then, even via a simple one-step soaking method, it could be firmly grafted to many different substrates (e.g., a stainless-steel mesh, a nylon microfiltration membrane, an Al plate, and glass). Moreover, after the end anchoring, the formed thin and uniform coating of PNIPAM onto the surfaces of the stainless-steel mesh and the nylon microfiltration membrane would endow the surfaces with a valuable thermo-driven controllable separation ability for oil−water mixtures and emulsions, respectively. And below PNIPAM's lower critical solution temperature (LCST) (34 °C), the membranes exhibited hydrophilicity and underwater oleophobicity and thus can be used for the separation of a "light oil"/ water mixture and an O/W emulsion through a "removing water" process; meanwhile, above its LCST, the membranes show the opposite properties (hydrophobicity and oleophilicity) and thus are used to separate a "heavy oil"/water mixture and a W/O emulsion through a "removing oil" process. In addition, without changing the morphologies and pore sizes of the substrates, the membranes gave many excellent performances such as excellent recyclability, high separation efficiency and a thermo-driven controllable separation ability. So, the facile and effective strategy presented in this work that is suitable for the coupling of PNIPAM with various substrates would also supply an inspiration to the effect conjunction for heterogeneous materials of other functional polymers and substrates.

Buoyancy-Assisted Fabrication of Liquid Diode: Janus Nanofibrous Membrane for Efficient Wastewater Treatment

“…It facilitates the creation of ultrafine fibers with a large surface area and enables precise control over morphology and pore structure of the fibers, enabling customization of pore size, porosity, and interconnectivity. , Additionally, the uniform distribution of fibers enhances the membranes’ mechanical strength and stability, providing opportunities for further enhancements in performance through modifications. ,, Despite the advantages of polymeric nanofibrous membrane separation technology, traditional membranes with single wettability face significant challenges in effectively separating complex oil–water emulsions. , Most superwetting membranes with singular wettability are only effective to separate specific oil or water mixtures . Such membranes are known as “oil-removing” or “water-removing” membranes. , This restriction significantly limits the real-world implementation of membranes in complicated wastewater treatment processes. Typically, membranes with a single wettability feature often struggle to simultaneously separate water-in-oil (w-in-o) and oil-in-water (o-in-w) emulsions.…”