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Use of Polyalthia longifolia based alumina composites for the removal of reactive dyes from aqueous medium

Present study is aimed at the synthesis and use of Polyalthia longifolia based alumina composites for the adsorption of Methylene blue (MB, cationic dye) and Alizarin Red S (ARS, anionic dye) from wastewater generated at laboratory scale. The characterization of modified adsorbent through Fourier transformation infrared spectroscopy revealed the presence of hydroxyl, amino, and carbonyl groups. Scanning electron microscopy analysis showed the roughness on the surface of the modified biosorbent that favors the adsorption process. The point of zero charge was also determined. Adsorption of dyes was studied over several experimental factors such as dose of adsorbent, time of contact, initial solution concentration, solution pH, and temperature. The equilibrium data was evaluated by non-linear form of adsorption isotherms models (Langmuir and Freundlich) using different initial solutions concentrations (10–90 ppm). Langmuir model was followed for the adsorption of MB while for the adsorption of ARS, Freundlich model was followed. Maximum monolayer adsorption capacity (qm) of adsorbent for MB and ARS was 74.63 and 25.06 mg/g, respectively. Equilibrium data was also evaluated by adsorption kinetic models (Pseudo-first-order and Pseudo-second-order). The studied process followed Pseudo-second-order model with (R2 = 0.9929) and (R2 = 0.9993) for MB and ARS, respectively. Thermodynamic parameters (ΔG°, ΔS°, and ΔH°) were also estimated. The negative values of ΔG° for MB specified the spontaneous while positive values of ΔG° for ARS indicated non-spontaneous nature of the reaction. Positive values of ΔS° and ΔH° for both dyes indicated that the adsorption process is feasible and endothermic in nature. Thus, the modified biomass of P. longifolia branches can be used effectively for the treatment of dyes in wastewater.