Mechanism and performances of methyl orange and Congo red adsorption by MnO2–PVP composite

Abstract

Azo dyes are commonly used in textile industries; however, when these dyes cross the permissible limit set by the World Health Organization, they produce many health issues related to the brain, liver, kidneys, respiration, and sexual system. Herein, polyvinyl pyrrolidone (PVP)-supported manganese oxide (MnO2) was studied for azo dye removal from an aqueous medium. The adsorption mechanism study demonstrated that the dye adsorption by MnO2–PVP composite was not only due to the electrostatic force of attraction but also involved the ion exchange amid the hydroxide group and dye molecules. The surface area of the composite (120 m2 g−1) was larger than that of metal oxide (102 m2 g−1). The point of zero charge and surface area were improved from 5.2 and 102 to 5.6 and 120 m2 g−1, respectively. The dye removal capacity of MnO2–PVP composite was significantly higher than that of plain MnO2. The film diffusion control adsorption kinetic mechanism and the kinetic data were well fitted to the pseudo-second-order equation. Experiments were conducted as a function of initial dye concentration (5–200 mg L−1), pH (3–10), temperature (298–328 K), and adsorbent dosage (0.05–0.4 g) in batch adsorption systems. The thermodynamic investigations confirm that the dye adsorption process was endothermic in nature.