About MX3 and MX2 (M~(n+) = Mg~(2+), Al~(3+), Ti~(4+), Fe~(3+); X~(p-) = F~-, O~(2-), OH~-) nanofluorides

摘要

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 fiuorinated 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 F2-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 F2-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.