Study On Adsorption Properties Of Modified Cellulose-graft-poly (Methyl Acrylate) For Heavy Metals

Water pollution caused by heavy metals has been a serious issue to environment and human health. Due to harmful effects of heavy metal ions contamination in water, there is a pressing need to find efficient methods to combat this kind of pollution. Adsorption is a practical and reliable technology owing to its operable, economic, efficient and renewable properties. It has been found that the adsorbent containing amine or carboxyl functional group is effective on removing heavy metal ions, so, development of the carboxyl or polyamino-modified adsorbent is significant.Methyl acrylate (MA) is a kind of bifunctional monomer, which is not only frequently used as an organic synthesis intermediate but also used to synthesize polymers. This study successfully polymerized Cell-g-PMA by grafting polymerization of MA from surface of microcrystalline cellulose using eerie ammonium nitrate (CAN) as initiator. Subsequently, the adsorbent Cell-g-P(AA-Na) have been prepared via hydrolysis of obtained Cell-g-PMA with NaOH. Furthermore, adsorption effects of Pb (Ⅱ) and Cu (Ⅱ) on Cell-g-P(AA-Na) in aqueous solution were simply characterized.Tetraethylenepentamine (TEPA) is a typical water-soluble polyamine, which possesses strong chelating ability for heavy metal ions. In this study, we successfully synthesized a tetraethylenepentamine-modified cellulose-based adsorbent Cell-g-PMA-TEPA by introducing polyamino groups to Cell-g-PMA via amidation reaction with TEPA. And we put forward to an optimum synthesis time by elemental analysis. Cell-g-PMA-TEPA was characterized by FTIR, solid-state 13C NMR, TG/DTG analysis and SEM. In order to investigate adsorption capacities of heavy metals on Cell-g-PMA-TEPA, modified cellulose was then used for removal of Pb(Ⅱ) and Cu(Ⅱ) from aqueous solution.The adsorption process, which was pH dependent, showed maximum removal at pH 5.0 for Pb(Ⅱ) and pH 4.5 for Cu(Ⅱ), respectively. Influence of adsorption time on adsorption behavior was investigated, which revealed that adsorption equilibrium between Pb(Ⅱ), Cu(Ⅱ) and Cell-g-PMA-TEPA could be established within 200 min. Data from adsorption kinetic experiments agreed well with pseudo-second-order model based on the assumption that the process may be a chemical adsorption process involving valence forces through sharing or exchange of electrons between the adsorbent and the adsorbate. Further study indicated that adsorption isotherm fit well with Langmuir model, from which maximum adsorption capacities of Cell-g-PMA-TEPA were derived to be 444.4 mg/g for Pb(II) and 168.35 mg/g for Cu(II), respectively.Regeneration tests were performed by dynamic adsorption method and 0.1 M HCl aqueous solution was used for desorption. The dynamic adsorption capacity at first adsorption time was 440.4 mg/g for Pb(II),170.6 mg/g for Cu(II), respectively, and there were not apparent loss in equilibrium adsorption capacities during five adsorption times, i.e., loss in adsorption capacities for Pb(II) and Cu(II) were less than 10%, proving the prepared adsorbent applicable for removal of lead and copper from aqueous solution.