(230a) Enhancing Adsorption of Heavy Metal Ions By L-Tryptophan Functionalized Graphene Oxide

Heavy metal ions caused water pollution has currently attracted much attention due to their toxic effect to human health and other organisms in the environment. Adsorption technique has considered as the most adopted removing metal ion method because its cost effective, simple operation and high efficiency. Graphene oxide has been widely used as adsorbent in wastewater treatment due to super large surface area and flat structure. However, low removal efficiency is exhibited under low pH values in existing adsorbents. Introducing amine and carboxyl groups，which show strong affinity for heavy metal ions, onto graphene oxide to strengthen adsorption, L-tryptophan can be a good candidate. Firstly, L-tryptophan functionalized graphene oxide was prepared and characterized by Fourier Transform Infrared Spectroscopy, X-ray diffraction, Raman Spectroscopy and transmission electron microscopy. L-tryptophan was chemically grafted on graphene oxide by the nucleophilic substitution reaction of amine groups with epoxy groups. Then, Pb(II) and Cu(II) were treated as target metal ions and L-tryptophan functionalized graphene oxide was adopted as adsorbent. The effects of some factors, including pH, contact time, ion concentration and adsorbent dosage, on adsorption of Pb(II) and Cu(II) were investigated. L-tryptophan functionalized graphene oxide sample, which has more ion interaction sites, presented high removal efficiency over 90% at pH 4 and 5 for Pb(II) and Cu(II). The adsorbent also demonstrates extremely fast Pb- and Cu-removal within 40min. Lastly, the adsorption kinetics of Pb(II) and Cu(II) onto L-tryptophan functionalized graphene oxide were examined and could be well fitted to pseudo-second-order model. The results suggest that the L-tryptophan functionalized graphene oxide was suitable for removal of Pb(II) and Cu(II) with low pH.