Crystallization of silica promoted by residual hydrogen bonding interactions at high temperature

A novel approach to prepare crystalline silica through calcination of the composite of silica and highly fluorinated graphene at a relatively low temperature is demonstrated. Silica and its composites with graphene and its derivatives (graphene, graphene oxide and graphene with various degrees of fluorination) were synthesized and then calcined at 900 °C in an air atmosphere. The results of X-ray-diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy reveal that cristobalite was produced through calcining composites of silica and highly fluorinated graphene under ambient air at a relatively low temperature (900 °C), while for the composites of silica and graphene and its derivatives, the calcined products are all amorphous. Thermal gravimetric analysis results indicate that the maximum decomposition temperature of functional groups in highly fluorinated graphene at air temperature is 457 °C, which is higher than that in medium fluorinated graphene, lower fluorinated graphene and graphene oxide (411.3 °C, 313.4 °C and 238.9 °C). A high degradation temperature of highly fluorinated graphene contributes to strong residual hydrogen bonding interactions at high temperature. FTIR results further illustrate that many residual hydrogen bonding interactions in composites of silica and highly fluorinated graphene at higher temperature result in enough linear structures. As a consequence, stronger residual hydrogen bonding interactions at high temperature in composites of silica and highly fluorinated graphene restrain the self-condensation of Si-OH groups and promote the formation of crystalline structures.