Surface Heterogeneity of SiO2 Polymorphs: An XPS Investigation of α-Quartz and α-Cristobalite

Abstract

Silica minerals, one of the most abundant mineral species on the earth, play important roles in geochemistry and environment processes. The diversity of the SiO4 tetrahedron polymerization style might result in the heterogeneity of the surface microstructures and properties of SiO2 polymorphs. The surface properties of two common crystalline SiO2 polymorphs, i.e., α-quartz and α-cristobalite, have been investigated by the surface site density measurement, batch methylene blue (MB) adsorption, and X-ray photoelectron spectroscopy (XPS). The Langmuir adsorption isotherms suggest the formation of monolayer MB on both α-quartz and α-cristobalite surfaces. The adsorption capacity of α-quartz toward MB is larger than that of α-cristobalite, which positively correlates with the density of surface site. XPS spectra reveal that the adsorption takes place between the nitrogen atom of the dimethylamino groups in MB and silanols on α-quartz and α-cristobalite surfaces. The O/Si atom ratio related with adsorption of α...