Adsorption and Removal of Methylene Blue from Aqueous Solution Using Sterile Bract of Araucaria angustifolia as Novel Natural Adsorbent

The aim of this work was to study the adsorption and removal of methylene blue from aqueous solution using sterile bract of Araucaria angustifolia as novel natural adsorbent. Raw and boiling-treated sterile bract samples were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and point of zero charge. The contents of humidity, ash, total extractive content, lignin and cellulose were 13.20, 3.30, 7.12, 44.45 and 30.92%, respectively. The methylene blue adsorption mechanism in the sterile bract was evaluated using non-linear Langmuir, Freundlich, Redlich-Peterson and Sips isotherm models, whereas the adsorption kinetic was evaluated using pseudo-first- and pseudo-second-order kinetic models. The methylene blue removal efficiencies of the raw and boiling-treated bracts were 98.59 +/- 0.01 and 99.90 +/- 0.01%, respectively, after 480 min. The best adsorption efficiency was found within 480 min of contact, 5.0 g of adsorbent with 500 mesh granulometry, pH = 6, initial adsorbate concentration of 150 mg L-1 and temperature of 292 K. The maximum methylene blue adsorption capacities of the raw and boiling-treated bracts according to the non-linear Langmuir isotherm model were 125.34 and 138.65 mg dye per gram bract, respectively. The kinetic fit depends on the solution pH, determination coefficient and Chi square test statistic. From thermodynamic results, it was concluded that the adsorption process is favorable, spontaneous (Delta G < 0), exothermic (Delta H < 0) and disordered at the solid-solution interface (Delta S > 0). Overall, the sterile bract of Araucaria angustifolia could be applied as low-cost alternative adsorbent for the treatment of textile industry wastewater.