About MX 3 and MX 2 (M n+ = Mg 2+, Al 3+, Ti 4+, Fe 3+; X p− = F −, O 2−, OH −) nanofluorides

Abstract

Several nanosized fluoro-compounds have been prepared by microwave-assisted solvothermal routes: Al 3+-, Fe 3+- and Ti 4+-based oxyfluorides with the hexagonal tungsten bronze (HTB) framework, Ti 4+-based fluorinated anatase, and rutile MgF 2. The structural features have been determined using XRD and TEM analyses. The presence of OH − groups substituted for F − ions has been demonstrated for all of these nanofluorides. In Al- and Mg-based nanofluorides, the OH rate can be reduced by F 2-direct fluorination. Furthermore, the higher the polarizing power of the cation, the higher the oxygen content. For cation with high formal charge, such as Ti 4+ stabilized in a distorted octahedral site, the occurrence of O 2−/OH −/F − anions in its vicinity as well as vacancies have to be mentioned. Finally coupling the microwave-assisted solvothermal route with the F 2-direct fluorination allow preparing high surface area metal fluorides where the amount of oxygen is noticeable and contribute to create under-coordinated cationic species at the surface which can induce high Lewis acidity.