Use of amino-modified cotton fibers loaded with copper ions for anionic dye removal under batch and fixed-bed systems: A comparative study

Amine-functionalized supports were prepared by chemical modification of cotton fibers using amino compounds namely diethylenetriamine (DET) and 1,4-diaminobutane (DB) in order to be loaded with copper ions. Evidence of attaching amine groups onto cellulosic fibers was confirmed through nitrogen and SEM analysis. Adsorption behavior of Acid Blue 25 from aqueous solutions onto [Cu(II)/DET-cotton] and [Cu(II)/DB-cotton] has been evaluated via batch and column mode systems. During the batch experiments, the effects of temperature and type of adsorbent on dye removal were investigated. Results revealed the formation of ternary complexes of the type [AB25/Cu(II)/adsorbent] with a [5/2:3:1] stoichiometry for DET-cotton and a [1:1:1] stoichiometry for DB-cotton at 20 °C. In the isotherm studies, Langmuir, Freundlich, and Jossens equations were applied and it was found that the experimental data conformed to Jossens model. Thermodynamic parameters such as change in free energy (ΔG 0), enthalpy (ΔH 0), and entropy (ΔS 0) have also been calculated in this paper, and it was found that the adsorption process was exothermic and spontaneous. The column experiments were conducted to study the effect of bed height on adsorption performance of both adsorbents. Results exhibited that the column capacity of [Cu(II)/DET-cotton] complex was found to be higher than that of [Cu(II)/DB-cotton] as was obtained in batch process. BDST model was applied to experimental data in order to predict the breakthrough curves and determine the characteristics parameters of the column useful for process design. Results revealed that the used model was appropriate to fit the experimental data. Desorption studies to recover the adsorbed dye from both adsorbents were performed with NaOH and NH4Cl solutions.