Adsorption behavior and mechanism of alizarin yellow and rhodamine B dyes on water hyacinth (Eichhornia crassipes) leaves

Abstract

This work studied a low-cost water hyacinth biosorbent to remove alizarin yellow (AY) and rhodamine B (RB) from aqueous solutions. The physicochemical characterization of the water hyacinth leaf (WHL) was carried out by Brunauer-Emmett-Teller surface area analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy. Contact time, pH, initial dye concentration, and temperature on adsorption were investigated in batch mode. The maximum removal of AY and RB was detected at pH 2. The results showed that the adsorption of dyes was enhanced with increased contact time, initial dye concentration, and temperature. The contact time reached equilibrium within 120 min and 90 min for AY and RB, respectively. The Langmuir and Freundlich isotherm models were applied to the equilibrium data. The Langmuir isotherm model better described the equilibrium data, indicating the monolayer adsorption for all dyes. The maximum adsorption capacity values from the Langmuir model were 37.04 and 23.98 mg/g for AY and RB, respectively. The kinetic data of the adsorption were better described using the pseudo-second-order model. Thermodynamic studies showed that the adsorption of dyes was endothermic and spontaneous, and the adsorption was physisorption. The adsorption mechanisms involved H-bonding, Yoshida H-bonding, n−π, and π−π interactions for both dyes. Moreover, electrostatic interactions could form between the negative parts of AY and the positive surface of the water hyacinth leaf. In conclusion, the water hyacinth leaf could be employed as a low-cost adsorbent to remove AY and RB from wastewater.