Cysteine-grafted nonwoven geotextile: a new and efficient material for heavy metals sorption--part A

Cysteine is an interesting biomolecule in the heavy metals trapping field, thanks to its amino, thiol and carboxylic groups. This amino acid is indeed present in some natural chelating agents: glutathione, phytochelatins and metallothioneins. However, cysteine has never been used in remediation processes. When immobilized on a polypropylene nonwoven (PP) geotextile, an innovative and eco-friendly material is obtained, with potential use in drainage and filtration of wastewaters and sediments. PP was first functionalized with acrylic acid using a low pressure cold plasma process to bring reactive carboxylic functions onto the surface (PP-g-AA). Cysteine was then covalently grafted on this modified PP. The cysteine grafting on PP-g-AA was optimized using response surface methodology, which allowed concluding that the best conditions of immersion without heating consist in: a solution containing 0.229 mol/L of cysteine for 28 h. The materials were characterized by Scanning Electron Microscopy, InfraRed Spectroscopy and X-ray Photoelectron Spectroscopy: evidence of covalent cysteine grafting was given. Preliminary sorption tests at 20 °C and pH = 4.5 with artificially polluted solutions give promising results for divalent heavy metal ions: 95 mg Cu (II) (CuSO4 solution), 104 mg Cu (II) and 135 mg Pb(II) (with NO3(-) counter-ion) per gram of PP are trapped.