Biosorption of methylene blue dye by rice (Oryza sativa L.) straw: adsorption and mechanism study

In this work, rice (Oryza sativa L.) straw biosorbent (RSB) was evaluated as natural, renewable, and low-cost biosorbent for removal of methylene blue (MB) dye from aqueous solution. The structural characterization of the RSB was performed through pore structural analysis (Brunauer-Emmett-Teller), scanning electron microscopy and energy dispersive X-ray analysis, X-ray diffraction, Fourier transform infrared, point of zero charge method, and proximate analysis. Batch adsorption experiments were conducted to study the influence of adsorbent dosage (0.05-0.30 g), solution pH (2-12), initial dye concentration (20-100 mg/L), and contact time (0-240 min) on the adsorption of the MB. The kinetic uptake results were well described by the pseudo-second-order kinetic. The experimental data at equilibrium fitted well with the Langmuir model at 303 degrees K, and the maximum adsorption capacity of MB on the RSB surface was found to be 158 mg/g. The mechanism of adsorption included mainly electrostatic attractions, n-pi stacking interaction, and hydrogen bonding interaction. The results indicate the potential use of RBS as natural, renewable, and low-cost biosorbent for the removal of MB dye as a model of cationic dye.