In the present work, cysteine-modified orange peel (COP) for the removal of Cu(II) from aqueous solutions has been developed and comparatively studied with diethylenetriamine-modified orange peel (DOP). Both COP and DOP were systematically evaluated via their capabilities for adsorbing Cu(II), including the key influential parameters such as initial pH, contact time and initial Cu(II) concentration. Further studies suggest that the sorption of Cu(II) onto both COP and DOP fits well with the pseudo-second-order equation, and the corresponding sorption isotherm can be classified to a Langmuir isotherm model. COP appears more advantageous over DOP and far better than that of unmodified OP in removal of Cu(II) from aqueous system. The maximum capacities of COP and DOP for adsorbing Cu(II) are 95.23 and 83.68 mg/g, respectively, about three times higher than that of unmodified OP. The sorption efficiency of COP drops by merely about 3% after five cycles, implying a promising usage in the removal of Cu(II) from wastewater in practice.

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