Rapid Adsorption of Methylene Blue from Aqueous Solutions by Goethite Nanoadsorbents

Iron-oxide nanoadsorbents are attractive for wastewater treatment for two important reasons. First, nanoadsorbents can remove contaminants from wastewater rapidly. Second, iron oxide nanoadsorbents can be employed as catalysts for the decomposition of contaminants and thus eliminate sludge formation. This article investigates the use of iron-oxide nanoadsorbents to remove contaminants from wastewater. A later paper considers their use as catalysts for decomposition. In this study, goethite (a type of iron oxide) nanoparticles was employed for the removal of methylene blue from an aqueous solution, using a batch-adsorption technique. Effects of contact time, initial concentration of methylene blue, temperature, and solution pH on the adsorbed amount of methylene blue were investigated. Adsorption was rapid, as equilibrium was achieved within 20 minutes. An external mass transfer model fit adsorption kinetic results well and provided reasonable overall volumetric mass transfer coefficients. Increases in initial concentration, temperature, and pH favored the adsorption of methylene blue. Adsorption data fit both the Langmuir and Freundlich isotherm models well, with the better fit to the Langmuir model. Thermodynamic studies confirmed that the adsorption reaction was spontaneous and endothermic in nature.