Graphene oxide/polyethyleneimine aerogel for high-performance mercury sorption from natural waters

The development of effective sorbent materials to remove mercury (Hg) from real waters is a challenge. Here, we report the simple preparation of high-performance GOPEI aerogel for Hg remediation by self-assembly of high branched polyethyleneimine (PEI) with elevated molecular weight (Mw = 750 k) and graphene oxide (GO) under acidic conditions (pH < 3). Our studies revealed that the improved dimensional stability of GOPEI aerogels, critical for their use as sorbent materials, was obtained for a ratio GO:PEI 3:1. A small amount (10 mg L-1) of GOPEI proved a highly efficiency for Hg removal from natural waters (tap (91%), river (90%) and sea (81%)) under realistic environmental concentrations (50 mu g L-1), where the existence of co-ions and different Hg-speciation are usually inhibitory factors of a good removal efficiency. This excellent performance was attributed to the synergistic effect resultant from the interactions between GO and PEI, giving a high content of N-rich groups and negative zeta potential over a wide pH range (from 2 to 12). Kinetic modelling pointed to differences on the main mechanisms behind the Hg removal by GOPEI in ultrapure vs natural waters. In ultrapure water pseudo-first order, usually associated with physical sorption, showed to be the best fit according to Akaike's Information Criterion (99.8% of probability), while in natural waters pseudo-second order model performed better (51.5% to 99.9% of probability), suggesting that the sorption is likely to rely on chemical interactions between Hg ions and the functional groups of GOPEI. Furthermore, GOPEI showed to be easily regenerated, keeping its high removal performance after 3 successive sorption-desorption cycles.