Novel hierarchically-packed tin dioxide sheets for fast adsorption of organic pollutant in aqueous solution

Aunique porous tin dioxide (SnO2) sheet, which simultaneously possesses a porous exterior composed of nanoparticles and a hierarchical interior composed of nanoflakes, was reported for the first time. It was prepared via a facile solvothermal route combined with an annealing process. The as-prepared hierarchically-packed nanostructures were characterized by X-ray diffraction (XRD), field emission scanning electronic microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The elemental mapping and the line scans were also performed in the high-angle annular dark-field (HAADF) mode on the same HRTEM. The novel SnO2 nanostructures were further employed to adsorb methylene blue which was used as the probe of organic pollutants in aqueous solution. The results show that the hierarchically-packed SnO2 sheets exhibit a fast adsorption rate to the absorbate. The removal efficiency reaches 98.5% in 5 min, which is significantly faster than that of commercial active carbon and some traditional nanostructures. As for the mechanism for such a fascinating adsorbing performance, a special adsorbate-depleted region formed inside the sheet is proposed, which is also supported by the study of the kinetic processes of gas adsorption and desorption. Moreover, the influence of pH, maximum adsorption capacity, and recyclability of the SnO2 sheets are also investigated. Our findings indicate that the novel hierarchically-packed SnO2 nanostructures could be a promising absorbent applied for rapid removal of organic pollutants in water.