Rapid Adsorption Methylene Blue from Aqueous Solution using Manganese Dioxide Nanowires: Facile Synthesis, Characterization, Kinetics, Thermodynamics and Mechanism Analysis

Abstract

Manganese dioxide nanomaterials with high crystallinity and purity was prepared quickly by a simple hydrothermal reaction, and the effect of hexadecyl trimethyl ammonium chloride (CTAC) on crystal form, morphology and pore structure of manganese dioxide was investigated. Removal of methylene blue from aqueous solution by adsorption onto two manganese dioxide adsorbents was studied. The material characterization results showed that manganese dioxides have (2×2) tunnel structure and nanowires morphology. BET surface area and pore volume of ɑ‐MnO2 (CTAC) was 58.99 m2/g and 0.2081 cm3/g, respectively. The adsorption results showed that pH value had a certain effect on the removal of methylene blue. The adsorption kinetics results indicated that the adsorption rate of ɑ‐MnO2 and ɑ‐MnO2 (CTAC) to methylene blue was very fast, most adsorption was completed within 5 minutes, and the adsorption equilibrium was reached after 2 hours. The removal efficiency of ɑ‐MnO2 and ɑ‐MnO2 (CTAC) was 71.27 % and 78.92 %, respectively. Pseudo‐second‐order kinetic model was better fitted with adsorption data than pseudo‐first‐order model, suggesting adsorption behavior is controlled by chemical processes. Additionally, the free energy change (ΔGΘ) was determined by Van′t Hoff equation is negative, which confirms the adsorption process is spontaneous and feasible. The adsorption mechanism involves a complex process of electrostatic attraction, charge‐independent adsorption, physical adsorption, hydrogen bonding and redox.