Synthesis of a Metal Ion Adsorbent from Banana Fibers and Its Adsorption Properties for Rare Metal Ions

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The synthesis of metal ion adsorbents from modified banana fibers comprising a Schiff base was investigated. The adsorption properties of a metal ion adsorbent were evaluated, and banana fiber (BF)-g-(glycidyl methacrylate)(GMA)(BF-GMA) were synthesized. A Schiff base 2,2’-{iminobis[ethane-2,1-diylnitrilo(E)methylidine]}bisphenol was synthesized via a reaction of diethylenetriamine and 5-bromo-salicyialdehyde in methanol. A metal ion adsorbent (BF-GMA(Br)) was synthesized via a reaction of the Schiff base with BF-GMA. Over 90% of La³⁺, Gd³⁺, Tm³⁺, Pr³⁺, Tb³⁺, Yb³⁺, Nd³⁺, Dy³⁺, Lu³⁺, Sm³⁺, Ho³⁺, Eu³⁺, and Er³⁺ were adsorbed in a pH range of 6.0–6.6 by the synthesized metal ion adsorbent. Almost 100% of In³⁺ at a pH value of 3.0–4.0 and 95% of Ga³⁺ at a pH value of 3.9 were absorbed, thereby showing the maximum adsorption percentage. Almost 15% and 25% of In³⁺ was adsorbed at a pH value of 1.4–1.6 and 1.8, respectively. Adsorption of Ga³⁺ was barely observed in the pH range of 1.4–1.8. These results show that banana fibers can be utilized as metal ion adsorbents.