Poly(N-isopropylacrylamide)-based microgels and their assemblies for organic-molecule removal from water

We review our recent efforts utilizing poly(N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgels and their assemblies for the removal of an azo-dye molecule, 4-(2-Hyrodxy-1-napthylazo) benzenesulfonic acid sodium salt (Orange II), from aqueous solutions. First, the ability of dispersed, single microgels to remove Orange II from aqueous solutions at room temperature is discussed. Uptake efficiency (i.e., the amount of Orange II removed from water) increased with AAc composition in the microgels, yielding a maximum uptake efficiency of 29.5% for pNIPAm microgels with 10% AAc. Assemblies of microgels (aggregates) were also investigated for their removal efficiency, which yielded a maximum uptake efficiency of 44.1% at room temperature. Removal efficiencies for the microgels and their aggregates were also monitored at elevated temperatures, and a maximum of 56.6% removal efficiency was achieved for unaggregated microgels, while aggregates were able to remove 73.1% Orange II. To further explore the impact of the microgel system's structure on function, we investigated the role microgel size in the aggregates plays on the uptake efficiency. Initial observations showed that the aggregates composed of microgels with large diameter yielded improved uptake efficiency over the aggregates composed of small diameter microgels. Langmuir sorption isotherms were fit to the data for the dye removal by the unaggregated and aggregated microgels, which showed good fits in all cases.