Synthesis of graphene oxide/polyethyleneimine sponge and its performance in the sustainable removal of Cu(II) from water

Modification of graphene oxide (GO) with polyethyleneimine (PEI) has been studied to develop a GO/PEI sponge material that not only performs well in the adsorption of Cu(II) but also is easily separated from water. The results showed that GO had excellent affinity for PEI, and GO/PEI prepared at pH 9.0 using PEI with a MW of 70,000 was shown to be a good adsorbent for Cu(II). This GO/PEI was characterized with SEM, XRD, XPS, FTIR and TG analyses and was investigated for Cu(II) adsorption further. The adsorption isotherm data of Cu(II) were fitted well with the Langmuir model, from which the maximum adsorption of GO/PEI was calculated to be 150.9 mg/g at pH 5.5. This was much higher than that of GO and two commercial resins. GO/PEI showed high selectivity towards Cu(II). In GO/PEI, the contributions of amino groups on PEI and negative charges on GO were 79.2% and 20.8%, respectively. Cu(II) adsorption on GO/PEI decreased with decreasing pH, and 1 M HCl caused nearly complete desorption of the adsorbed Cu(II). Experimental results of five cycles of adsorption-desorption indicated that this material could be reused. Column studies showed that GO/PEI performed well in terms of both Cu(II) adsorption and stability in water.