Dye adsorption kinetics of organoamine-templated hollow silica microspheres with different porous structures

Abstract

As-synthesized hollow silica microspheres with micropores and thermally treated ones with mesopores were used as adsorbents. The two types of hollow microspheres have the same particle sizes and hollow centers, but with different pore sizes, surface areas, and pore volumes. The adsorption of rhodamine 6G and methyl blue on both hollow SiO2 microspheres was investigated and compared. The time-dependent adsorption data were fitted with different kinetic models. The results indicate that the charges of the adsorbents and the dyes in water, the relative sizes of nanopores, and dye molecules played important roles in the adsorption capacity and the kinetics besides the surface area and pore volume of the adsorbents. As expected, an electrostatic attraction between the oppositely charged adsorbents and adsorbates, a large surface area and pore volume helped to increase the adsorption. More important is that the results evidence that when nanopores are relatively small compared with the size of dye molecules, dye molecules may have limited access and rate to go inside the hollows, resulting in a slow adsorption kinetics and low adsorption capacity.