Relevance of Anethum graveolens to remove Rhodamine B in aqueous solution: characterization, kinetic and isotherm study

Abstract

In the present study, we reported the feasibility to exploit the low cost, and renewable biomass Anethum graveolens (AG) as adsorbent to remove Rhodamine B (RhB) dye from aqueous solutions. The capacity of A. graveolens to absorb the dye was investigated by using batch adsorption procedure with examination of different operational factors such as pH (2–10), stirring speed (100–400 ppm), adsorbent concentration (0.5–5 mg L⁻¹) and the initial dye concentration (10–50 mg L⁻¹). The RhB removal efficiency increased from ~ 63 to 95%, depending on the operating conditions; the optimal conditions are 300 rpm for stirring speed, 6 and 7 for pH, 3 g L⁻¹ for biomass dosage and 10 mg L⁻¹ for dye’s concentration. In order to estimate the equilibrium parameters, the experimental data were analyzed using the nonlinear forms of different kinetic models (pseudo-first order kinetic model, pseudo-second order kinetic model, Elovich and intra-particle diffusion models), also different isotherm models (Langmuir, Freundlich, Dubinine and Temkin models) were studied. The results indicated that the RhB sorption follows the pseudo second order model; under the optimum conditions, the maximum biosorption capacity (q_max) of AG was (52–56 mg g⁻¹). Langmuir and Freundlich model could fit the data better than Dubinin–Radushkevich and Temkin models. Scanning electron microscopy (SEM–EDX), X-ray fluorescence, attenuated total reflectance and X-ray diffraction analyses have been used to evaluate the morphological changes and the mechanisms of dye interaction with biomass. The chemical modification of functional groups of biomass institute the major contribution of hydroxyl groups for effective dye decolorization through complexation and electrostatic interactions due to the interactions of dye molecules of RhB with the functional groups, of adsorbent such as OH, COOH, CN, and CH groups.