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Surface modification of rubber ( Hevea brasiliensis ) leaves for the adsorption of copper ions: kinetic, thermodynamic and binding mechanisms
Author(s) -
Ngah Wan Saime Wan,
Hanafiah Megat Ahmad Kamal Megat
Publication year - 2009
Publication title -
journal of chemical technology and biotechnology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.64
H-Index - 117
eISSN - 1097-4660
pISSN - 0268-2575
DOI - 10.1002/jctb.2024
Subject(s) - adsorption , copper , chemistry , langmuir , freundlich equation , langmuir adsorption model , enthalpy , gibbs free energy , aqueous solution , natural rubber , endothermic process , inorganic chemistry , hevea brasiliensis , thermodynamics , organic chemistry , physics
BACKGROUND: This research describes the adsorption of copper ions from aqueous solutions following the modification of rubber ( Hevea brasiliensis ) leaves with formaldehyde solution. The main objectives of this research were to identify the binding mechanisms of copper ions on the chemically modified rubber leaves by spectroscopic techniques and to investigate the effects of several important physicochemical parameters such as pH, copper concentration, contact time, adsorbent dose and temperature on copper removal. RESULTS: Based on a kinetic study, the pseudo‐second‐order model was found to fit the experimental results well, while the Boyd kinetic model indicated that the rate‐determining step was due to film diffusion. Adsorption isotherms were modelled by the Langmuir and Freundlich isotherm equations, with the former providing a better fit for the data. Based on the Langmuir model, the maximum adsorption capacities of Cu(II) ions at 300, 310 and 320 K were 8.36, 8.61 and 8.71 mg g −1 , respectively. Thermodynamic parameters such as the Gibbs free energy (Δ G °), enthalpy (Δ H °) and entropy changes (Δ S °) were calculated. The adsorption process was spontaneous as the values of Δ G ° were negative, and endothermic as higher adsorption capacities were recorded at higher temperatures. More than 80% of copper ions bound on the adsorbent were able to be desorbed using 0.02 mol L −1 HCl, HNO 3 and EDTA solutions. Besides ion exchange, surface complexation could also play a major role in copper binding. CONCLUSION: Due to its relative abundance and satisfactory adsorption capacity, the modified rubber leaves can be considered as a good low‐cost adsorbent for removing copper ions from dilute aqueous solutions. Copyright © 2008 Society of Chemical Industry