Synthesis of poly (hydroxamic acid) ligand for removal of Cu (II) and Fe (II) ions in a single component aqueous solution
Nozipho Nompumelelo Mzinyane, Augustine E. Ofomaja, Eliazer Bobby Naidoo
Abstract
Biosorbents are the alternatives for the removal of heavy metals because they are cheaper and more effective. This is attributed to the metallic elements interactions with the functional groups on the surface of the adsorbent. Additionally, the surface of biosorbents can further be improved by pretreatment and modification leading to the formation of functional derivatives onto the cellulose backbone. In this study pine cone powder was pretreated using Fenton reagent and modified by grafting with acrylic acid in order to enhance structural characteristics of the material. Grafting of acrylic acid onto Fenton treated pine cone powder was achieved by a free radical procedure in which ceric ammonium nitrate (CAN) was used as an initiator. Furthermore, a new poly (hydroxamic acid) ligand was synthesized from the poly(acrylic acid) grafted pine cone powder for heavy metal ions removal from aqueous media. The observed FTIR bands that shifted from 1727 cm −1 shifted to 1616 cm −1 confirmed that ester functional groups were converted to hydroxamic acid groups, which was further confirmed by elemental analysis results. The poly (hydroxamic acid) ligand was further characterized by TGA/DTA, XRD , SEM-EDS techniques. The TGA/DTA results revealed that the poly(acrylic acid) grafted pine cone powder had better thermal stability . The XRD spectra revealed that the structure of pine cone powder is composed mainly of crystalline cellulose. The SEM results indicated that the grafted pine cone powder showed a smooth surface, which is an indication that the acrylic acid was coated on the surface of the Fenton treated pine cone powder. It further revealed a coarse surface the poly (hydroxamic acid) ligand confirming the conversion of the carboxyl group to hydroxamic acid group. The linear Langmuir isotherm plot gave an R 2 values of 0.9997 for Cu (II), 0.9961 Fe (II) biosorption while Freundlich isotherm plot R 2 values were 0.9581 for Cu(II) and 0.9671 Fe (II) biosorption. These results demonstrate that the Freundlich isotherm was not a good fit to describe the process of adsorbed metal ions and their equilibrium concentration in solution. The theoretical values q e (mg g −1 ) of the pseudo second order model compared with those for the pseudo first order kinetic model agree with the experimental value q e (mg g −1 ). Therefore, these results confirm the chemisorption of Cu (II) and Fe (II) onto poly (hydroxamic acid) ligand.