Manganese dioxide nanoclusters as a potential nano-sorbent for the removal of silver ion from water

Hydrous manganese dioxide nanoclusters are prepared by the oxidation of manganese (II) ions with ammonium persulfate and used as a new sorbent for Ag+ ion removal from aqueous medium. The synthesized compound is characterized using scanning electron microscopy, dynamic light scattering, energy dispersive analysis of X-rays, X-ray diffraction and BET surface measurements. Scanning electron microscopy images showed that the synthesized Hydrous manganese dioxide nanoclusters include cactus-shaped nanoclusters with uniform needles of average diameter of 36 nm and length of 1000 nm. X-ray diffraction data reveal that γ-MnO2 is formed in this method. Batch experiments are carried out to evaluate the Ag+ adsorption capacity of Hydrous manganese dioxide nanoclusters. The maximum adsorption capacity estimated by the Langmuir model was 81.97  mg g-1 for Ag+. Silver ion adsorption on Hydrous manganese dioxide nanoclusters is a fast process and the kinetics followed a pseudo-second-order rate equation. The removal efficiency of Ag+ depends on Hydrous manganese dioxide nanoclusters amount, pH and temperature of the solution. The presences of Na+, Ca2+ and Mg2+ ions in the concentrations lower than 200 ppm have no significant influence on silver ion removal. The adsorbed ions can easily eluted by the small volume of a solution consisting thiourea and hydrochloric acid. Finally, the experimental data show that the synthesized Hydrous manganese dioxide nanoclusters can quantitatively remove silver ions from real water samples.