Equilibrium, kinetic and thermodynamic studies of a low-cost biosorbent for the removal of Congo red dye: Acid and CTAB-acid modified celery (Apium graveolens)

Abstract

This study introduces a new and bio-friendly adsorbent based on natural and cetyltrimethylammonium bromide (CTAB) modified adsorbent, celery (Apium graveolens) residue for removal of organic pollutants. The adsorbent was characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and pHpzc techniques. Removal applicability and efficiency of this biosorbent were studied using Congo red (CR) as a sample organic pollutant. To reach the best results, main parameters such as pH, adsorbent mass, contact time, initial dye concentration and temperature were optimized through the adsorption experiments in a batch system. The kinetic and isotherm of CR removal follow pseudo-second-order kinetic model and the Langmuir isotherm model, respectively for both acid modified celery residue (ACR) and CTAB-acid modified celery residue (CTAB-ACR). The maximum monolayer adsorption capacities are 238.09 and 526.32 mg/g for ACR and CTAB-ACR, respectively. Also, thermodynamic parameters such as ΔGo, ΔHo and ΔSo were evaluated. It was concluded that the celery residue was a promising eco-friendly adsorbent and its adsorption capacity was improved significantly via CTAB modification in comparison to unmodified celery residue.