Environmentally friendly adsorbent derived from rock melon skin for effective removal of toxic brilliant green dye: linear versus non-linear analyses

Abstract

ABSTRACT This present study investigated the adsorption characteristics of rock melon skin (RMS) as a promising adsorbent for the removal of toxic brilliant green (BG) dye. The functional group and surface morphology analyses were carried out to characterise the adsorbent. The RMS-BG equilibrated within 30 minutes of contact time and showed stability under the pH range (4–10) studied. Adsorption of BG was not only unaffected but was enhanced in the presence of NaCl. Adsorption isotherm data analysed using six isotherm models, namely Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, Redlich-Peterson and Sips, pointed to the Freundlich being the best model. The maximum adsorption capacity (qmax ) of 118.0 mg g−1, based on the Langmuir model, was higher when compared to some reported natural and chemically modified adsorbents. Adsorption of BG onto RMS obeyed the pseudo second order kinetics (R 2 = 0.9976). Thermodynamics studies indicated the adsorption process was endothermic in nature. The spent RMS was able to be regenerated and reused whilst maintaining high adsorption of >95% BG even at the 5th cycle when base treatment was used. Comparison of linear and non-linear analyses indicated that the kinetics data fitted better with non-linear regression method whilst adsorption isotherm was better suited using linear regression method. The above findings demonstrate the potential application of RMS as a low-cost effective adsorbent for the removal of BG dye in wastewater treatment.