About MX3 and MX2 (Mn+ = Mg2+, Al3+, Ti4+, Fe3+; Xp- = F-, O2-, OH-) nanofluorides

Several nanosized fluoro-compounds have been prepared by microwave-assisted solvothermal routes: Al3+ -, Fe3+- and Ti4+-based oxyfluorides with the hexagonal tungsten bronze (HTB) framework, Ti4+-based fluorinated anatase, and rutile MgF2. 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 Ti4+ stabilized in a distorted octahedral site, the occurrence of O2-/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. (C) 2011 Elsevier BM. All rights reserved.