Adsorption of a Cationic Dye Crystal Violet onto a Binary Mixture of Forest Waste Biopolymer: Advanced Statistical Physics Studies

An eco-friendly and low cost modified mixture of both Wild Carob and Cupressus sempervirens with H3PO4 (Cupcar-H3PO4) was prepared to extract a cationic dye (Crystal Violet) from an aqueous solution in a batch reactor at the laboratory of chemical engineering, Department of Process Engineering, Faculty of Technology, Farhat Abbas Setif University-1. The pH effect, contact time, initial concentration of dye, ionic strength and temperature were investigated in this study. The Maximum adsorption capacity was found to be 117.26 mg/g at 25°C for a natural pH (ph =6.22). The active functional groups of Cupcar-H3PO4. These peak shifts indicated that especially the bonded –OH groups, C–O stretching of ether groups, and C=C group played a major role in CV adsorption onto Cupcar-H3PO4. The new bands of low intensity which appeared at 890 cm−1 and 813 cm-1 after CV adsorption and which could be attributed to a υ (CV-biosorbent) constituted the most striking result. Kinetics of biosorption of crystal violet (CV) was analyzed and the results showed that both pseudo order (PSO) and the pseud nth-order model (PNO) models gave most accurate fit than the pseudo-first-order model (PFO). Isotherm data were analyzed by four classical models, Langmuir and Freundlich with two parameters, Sips and Redlich-Peterson with three parameters. And for more information on the mechanism of CV uptake on the Cupcar-H3PO4 material, three advanced models are applied to isothermal data, Monolayer with one energy (M1), Monolayer with two energies (M2), and Double layer with one energy (M3). For the classical models and in the case of the two parameters models the Langmuir one gives a better fit for the data isotherm according to the R2. In the case of three parameters models, both Sips and Redlich-Peterson accurately described experimental data. Monolayer with two energy sites model (M2) was shown to be the most appropriate advanced statistical physics model for fitting CV biosorption onto the Cupcar-H3PO4 biosorbent, this model suggested that the CV pollutant was adsorbed at two different Cupcar-H3PO4 biosorbent sites, and that a variable number of CV molecules could be adsorbed at each site; from this, the CV dye was adsorbed with 2 different adsorption energies. The changes in the enthalpy, the standard free energy and the entropy were also evaluated and the reaction was found to be spontaneous, endothermic and physical in nature.