Facile synthetic route to transition metal oxyfluorides via reactions between metal oxides and PTFE

Abstract

Inorganic oxyfluorides have significant importance in the development of new functionalities for energy production and storage, photonics, catalysis, etc. In order to explore a simple preparation route that avoids the use of toxic HF or F 2 gas as a reaction reagent, we have employed polytetrafluoroethylene (PTFE). Five oxyfluorides including Nb 5 O .8 were synthesized by reactions between PTFE and transition metal oxides in sealed quartz ampules. The reaction mechanism was studied by means of gas analysis, which detected SiF 4 as a main product gas during the reaction. A possible reaction mechanism between the PTFE and transition metal oxides is discussed.

A Fluorination Method for Improving Cation‐Disordered Rocksalt Cathode Performance

“…For example, the successful fluorination of monoclinic‐structured Nb 2 O 5 by PTFE was achieved at 950 °C, enabled by the favorable presence of Nb–F environment. [ 31 ] Here, the optimal temperature that allows for simultaneously degradation of PTFE and the formation of the phase‐pure cation‐disordering structure was investigated. A series of DRX materials with varying level of F content, including Li 1.2 Mn 0.6 Nb 0.2 O 2 (F0), Li 1.2 Mn 0.625 Nb 0.175 O 1.95 F 0.05 (F2.5), Li 1.2 Mn 0.65 Nb 0.15 O 1.9 F 0.1 (F5), Li 1.2 Mn 0.7 Nb 0.1 O 1.8 F 0.2 (F10), Li 1.2 Mn 0.725 Nb 0.75 O 1.75 F 0.25 (F12.5), Li 1.2 Mn 0.75 Nb 0.05 O 1.7 F 0.3 (F15), and Li 1.2 Mn 0.8 O 1.6 F 0.4 (F20) that correspond to an F content of 0 at%, 2.5 at%, 5 at%, 10 at%, 12.5 at%, 15 at%, and 20 at%, respectively, were prepared after experimenting with synthesis temperatures.…”

Solid State Fluorination on the Minute Scale: Synthesis of WO3−xFx with Photocatalytic Activity

“…The SPS synthesis of WO 3−x F x yielded significantly higher degrees of fluorination than conventional methods using the same ball-milled precursor mixture, because heating to T > 550 °C in quartz ampules led to loss of fluorine or even the formation of reduced tungsten oxides. [22][23][24] In SPS, the increase of the reaction temperature to 600 °C still led to an increase of the fluorine content (indicated by an increase of the lattice parameter of the cubic unit WO 3−x F x cell for large PTFE excess), while samples dwelled at 600 °C for more than 10 min showed a lower fluorine content ( Figure S2, Supporting Information). Optimization of the reaction protocol led to the temperature program shown Figure 1B.…”

“…High‐temperature approaches using binary fluorides (like MF 2 or MF 3 (M = alkaline‐earth or lanthanide metal) have limitations because of the stability of the starting compounds compared to the intended products 18. Therefore, alternate fluorination routes have been developed for obtaining oxyfluorides 19–24…”

“…[18] Therefore, alternate fluorination routes have been developed for obtaining oxyfluorides. [19][20][21][22][23][24] Fluorination using a powder of the fluorinated polymers as a source of fluorine in a reductive fluorination process relies on their solid form, chemical stability at room temperature and their relatively low decomposition temperature compared with most inorganic compounds. [21][22][23][24] This allows to perform a reductive fluorination of oxides easily and safely.…”

Synthesis of Nb2O5 Nanoplates and their Conversion into NbO2F Nanoparticles by Controlled Fluorination with Molecular Fluorine

“…[3a], , These solution based methods have environmental implications on one hand, and on the other hand, give resulting materials which are high HF contaminated (HF as high as 14 atomic %) and lacking control over the nanostructured particles . It is worth noting that recent work of Hirai et al, devoted to the fluorination of Nb 2 O 5 by reaction with PTFE (polytetrafluoroethylene) above 500 °C showed the formation of two niobiumoxyfluorides i.e., Nb 5 O 12 F and Nb 3 O 7 F . Two other studies described the synthesis of NbO 2 F using NbF 5 with Nb 2 O 5 in one side and with SiO 2 in another side , .…”