Adsorption of rhodamine B by Pleurotus eryngii: growth, modification, characterization, adsorption isotherms, kinetics and thermodynamics

The fungus Pleurotus eryngii (PE) was modified with six different methods. The modified Pleurotus eryngii (MPE) and PE fungi samples were characterized by (Fourier transform infrared) FTIR technique and thermogravimetry to understand the mechanism of modifications. Surface analysis of the fungi samples were compared with scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), and Brunauer–Emmett–Teller (BET) characterizations. Cetyltrimethylammonium bromide (CTAB) modification enhanced the adsorption capacity of PE for rhodamine B from 12.4 to 19.2 mg.g⁻¹ that is the maximum at pH 8. The adsorption capacity of the CTAB-modified Pleurotus eryngii (CMPE) was reduced to 8.55 mg.g⁻¹, 3.80 mg.g⁻¹, and 5.80 mg.g⁻¹ in aqueous solutions of Na₂CO₃, NaCl, and NaNO₃, respectively, as well as the effect of the aqueous solutions of Pb²⁺ and Ni²⁺ on adsorption capacity were limited. The adsorption capacity of the CTAB-modified Pleurotus eryngii for rhodamine B was compared with Aspergillus niger (10.3 mg.g⁻¹). The biosorption of CMPE was relatively high for reactive black 5 (96.0 mg.g⁻¹) and reactive red 120 (98.5 mg.g⁻¹) at about five times for rhodamine B. The adsorption isotherm was fitted well for the Langmuir model for PE and CMPE with a favorable adsorption. The kinetics of the adsorption process was pseudo-second order for PE and CMPE. The decrease of the adsorption capacity was observed for fungi samples with an exothermic adsorption process.