Understanding the adsorption of Reactive red 2 onto metal hydroxide sludge: analysis with physico-statistical steric and energetic perspectives.

This theoretical investigation delves into the analysis of Reactive red 2 (RR-2) adsorption isotherms on metal hydroxide employing a sophisticated double-layer model characterized by dual-energy levels within the realm of physical adsorption phenomena. An examination of five distinct statistical physics frameworks was undertaken to elucidate the modeling and interpretation of equilibrium data. Expression for the physico-chemical parameters involved in the adsorption phenomena was derived based on statistical physics treatment. Fitting experimental adsorption isotherms (308-333 K) to a DAMTBS has revealed the number of anchored molecules per site, occupied receptor site density, and the number of adsorbed layers. The steric parameter n varies between 0.92 and 1.05. More importantly, it is evidenced that the adhesion mechanism of (RR-2) onto metal hydroxide as determined by the estimated adsorption energies (< 40 kJ/mol) supports a spontaneous and exothermic physisorption process. Thermodynamic potential functions such as entropy, Gibbs free energy, and internal energy have been computed based on the most suitable model. This research advances our physical understanding of how metal hydroxide captures dye molecules RR-2 through adsorption reaction for water depollution treatment.

Modeling the removal of Reactive Red 120 dye from aqueous effluents by activated carbon.

The adsorption isotherms of Reactive Red 120 (RR-120) on Brazilian pine-fruit shell activated carbon, at six temperatures (298, 303, 308, 313, 318 and 323 K) and pH = 6, were determined and interpreted using a double layer model with one energy. A statistical physics treatment established the formulation of this model. Steric and energetic parameters related to the adsorption process, such as the number of adsorbed molecules per site, the receptor sites density and the concentration at half-saturation, have been considered. Thermodynamic potential functions such as entropy, internal energy and Gibbs free enthalpy are analyzed, and the choice of the models is based on assumptions in correlation with experimental conditions. By numerical fitting, the investigated parameters were deduced. The theoretical expressions provide a good understanding and interpretation of the adsorption isotherms at the microscopic level. We believe that our work contributes to new theoretical insights on the dye adsorption in order to know the physical nature of the adsorption process.