Extraction-like removal of organic dyes from polluted water by the graphene oxide/PNIPAM composite system

Graphene oxide (GO)/poly(N-isopropylacrylamide) (PNIPAM) composite materials have been widely applied in waste water treatment by working as free adsorbents with thermoresponsiveness. In this work we report a novel GO/PNIPAM composite system that has been rationally designed for removal of organic dyes from polluted water in a new mechanism, that is, an extraction-like mechanism. The system gives a phase transition to produce a solution phase and a gel phase at temperatures above the lower critical solution temperature (LCST) of PNIPAM, during which the GO sheets are fully transferred into the gel phase. More interestingly, dyes can be efficiently adsorbed and enriched in the gel phase, which can then be conveniently separated from water in an extraction-like process. Compared to conventional extractive separation systems, the GO/PNIPAM composite system gives two phases triggered by temperature change, which have a clear phase boundary and are much easier for separation. Moreover, the system can protect GO from reduction and flocculation so as to retain high stability. PNIPAM and GO can also work synergistically for dye adsorption to give high adsorption capacity and efficiency. This study will provide a new perspective for design and fabrication of novel, safe and effective systems for dye removal and nanomaterial management.