Highly effective adsorption of xanthene dyes (rhodamine B and erythrosine B) from aqueous solutions onto lemon citrus peel active carbon: characterization, resolving analysis, optimization and mechanistic studies

Abstract

The aim of this work is to study the adsorption of xanthene dyes, erythrosine B (EB) and rhodamine B (RB), in aqueous binary dye solution. A novel adsorbent powder was prepared by heating lemon citrus peels impregnated with phosphoric acid at 500 °C; the adsorbent was characterized by scanning electron microscopy (SEM), FT-IR spectroscopy, and surface potential studies. A speciation method was developed for two dyes that have overlapping spectral peaks using ratio derivative UV-visible spectrophotometry. The experiments were designed and optimized by experimental design and response surface methodology (RSM). The optimized adsorption conditions in the batch system were pH 4, an adsorbent dose of 0.3 g L⁻¹, and an extraction time of 21 min. The isotherm adsorption capacities for EB and RB were 296 and 254 mg g⁻¹, respectively. The adsorption rate studies showed that the removal of the dyes obeyed pseudo-second order kinetics. Thermodynamic studies showed that removal of the dyes from the binary solution was endothermic and spontaneous.