Efficient capture and detoxification of mercury dichloride from wastewater by a PVDF/PEI adsorption membrane

Poly(vinylidene fluoride) (PVDF), as one of the halogenated alkanes, has excellent membrane performance. Polyethyleneimine (PEI), with excellent chelating performance and strong alkalinity, could enable halogenated alkanes to produce active C--C bonds, and subsequently, PEI can be grafted onto the C--C sites in-situ. In this paper, a novel adsorption membrane (PVDF/PEI) was fabricated via a one-step bulk grafting reaction of branched PEI to PVDF networks by non-solvent-induced phase inversion. This membrane showed highly efficient removal of Hg(II) ions, where 97% of Hg(II) from 20 mL of simulated wastewater solution containing 400 mg/L Hg(II) was removed in just 30 min using 20 mg of the adsorbent. The Langmuir isotherm model fitted the adsorption process well and gave a maximum adsorption capacity of 1036 mg/g at 30 degrees C, which agreed with the experimental saturation adsorption capacity of 1023 mg/g, suggesting that all binding sites on the membrane were involved in adsorption. After adsorption, Hg(II) was reduced to Hg2Cl2 with low toxicity to generate the crystals with a regular shape. Mechanisms studies implied that the adsorption of Hg(II) onto PVDF/PEI was an integrated chemical process that involved chemical chelation and a redox reaction due to the strong interactions between the mercury atoms and the active sites on the membrane. This novel PVDF/PEI adsorption membrane was resistant to acid and alkali, and can be separated and recovered directly from aqueous by fishing out. To the best of our knowledge, this is the first time to report on a PEI-functionalized PVDF adsorption membrane for the efficient removal of Hg(II).