Statistical physics analysis of the adsorption of reactive red 141 dye on residual avocado peel (Persea americana) chemically modified with H2SO4 and HNO3

Abstract

The preparation and adsorption properties of avocado peels treated with H2SO4 and HNO3 for the removal of reactive red 141 dye are reported in this manuscript. Equilibrium adsorption of this organic dye on the two adsorbents was experimentally quantified at pH 6.5 and 298.15–328.15 K. An advanced physical model that assumed the formation of a finite number of layers of the adsorbed pollutant molecules on the adsorption sites was used to estimate the steric and energetic parameters of the dye adsorption mechanism. The modeling results showed dye molecular aggregation, in which each adsorption site of avocado peels treated with H2SO4 and HNO3 adsorbed several dye molecules simultaneously at different temperatures. The results also demonstrated that dye adsorption on avocado peels treated with these acids was exothermic. The estimated adsorption energies for the dye-treated biomass and dye-dye interactions indicated a physisorption associated with van der Waals forces and hydrogen bonding. The outcomes of this study contribute with insights into the adsorption mechanisms of dye molecules using treated avocado peels with the aim of developing sustainable water treatment methods according with a circular economy approach.