Adsorption of Cationic Dyes Using Waste from Fruits of Eugenia umbelliflora Berg (Myrtaceae)

Waste of the fruits of Eugenia umbelliflora (the by-product of medicinal plant processing) (FEU-T) and untreated fruits of Eugenia umbelliflora (FEU-UT) was studied in a batch system, as alternative adsorbents for removing the dyes methylene blue (MB) and rhodamine B (RhB) from aqueous solution. The adsorbent was characterized by point of zero charge, type of functional groups, Fourier infrared spectroscopy and thermogravimetric analysis. The adsorption was analyzed, and the Sips equation was found to be the best model. The adsorption and maximum adsorption capacity obtained for the FEU-UT were 157.2 mg/g for the MB and 161.1 mg/g for the RhB, and for the FEU-T, these figures were 111.6 mg/g for the MB and 106.4 mg/g for the RhB. The adsorption of the dye followed the kinetic pseudo-first-order. The adsorption process was found to be exothermic and spontaneous. The removal of the dyes was optimized using a factorial Box-Behnken design, and the initial dye concentration proved to be more influential in dye adsorption than system temperature. These results demonstrate that waste from the fruits Eugenia umbelliflora is a promising adsorbent for removing MB and RhB from aqueous solutions.