Synthesis of α‑Quartz with Controlled Properties for the Investigation of the Molecular Determinants in Silica Toxicology

Many experimental studies about the harmful effects of crystalline silica on human health are present in the literature. However, the relationship between toxicological properties and surface functionalities of quartz is not yet fully explained because of the large intrinsic variability of natural samples. Specific surface properties are related to the surface structure: this implies that a reliable constraint on the crystal growth morphologies is necessary in order to control the behavior variability. With a view to understanding this relationship, a consistent, clean, and easy way to crystallize quartz is proposed. In this paper, α-quartz crystals with controlled morphology and properties were prepared by an unusual and accurate approach under mild hydrothermal conditions (200 °C, autogenic pressure) starting from silica gels prepared with different polymerizing agents. Gels and synthetic crystals were characterized using a wide range of experimental techniques: elemental analysis by ICP-OES, X-ray powder diffraction and Rietveld analysis, SEM and HR-TEM microscopies, BET surface analysis, differential centrifugal sedimentation, and FT-IR spectroscopy. Results are discussed in the light of the crystal growth mechanisms involved.