Effective adsorption of toxic brilliant green from aqueous solution using peat of Brunei Darussalam: isotherms, thermodynamics, kinetics and regeneration studies

Abstract

Peat, a natural adsorbent, has been successfully used for the removal of the hazardous water-soluble cationic dye, brilliant green (BG). Characterization of peat was carried out by determining its physical and chemical compositions such as moisture, ash, carbon%, hydrogen%, nitrogen%, and sulphur% (CHNS), crude protein and crude fat. X-ray fluorescence (XRF) was used for the determination of the percentage of elements present in peat. Functional groups present in peat were analyzed using Fourier transform infra-red (FTIR). Changes in the surface morphology of peat before and after treatment with BG were studied using Scanning Electron Microscopy (SEM). The optimization time required for establishment of an adsorption equilibrium is determined to be 2.0 h. The ambient pH of BG was used throughout the study. Adsorption isotherm models such as Langmuir, Freundlich, Halsey, Temkin, Redlich–Peterson (R–P) and Sips were simulated to fit with the experimental equilibrium data. Based on linear regression, simulated isotherm models and error analyses, the R–P isotherm fitted well for the adsorption of BG by peat. Adsorption kinetics was found to follow the pseudo second order model, with a rate constant of 0.39 g mmol⁻¹ min⁻¹. BG-loaded peat was successfully regenerated using 0.01 M sodium hydroxide (NaOH) solution for up to 5 consecutive cycles, while maintaining high adsorption ability of 98% even after the 5^th cycle.