Ammonium fluoride mediated mechano chemical synthesis of A2PdF6 (A = K, Rb) along with their catalytic role in environmental remediation

Abstract

To highlight the power of mechanochemistry to oxidize metal ions leading to the discovery of newer phases, ammonium fluoride mediated synthesis of A2PdF6 (A=Rb,K) has been carried out. Grinding reactions of ammonium fluoride with palladium (II) acetate and further cation exchange with AF (A=Rb,K) were closely monitored ex-situ characterizations such as high resolution powder X-ray diffraction (PXRD), fourier transform infrared (FT-IR) and Raman spectroscopy measurements. For the reaction involving RbF, Rb2PdF6 possessing K2PtCl6 type structure was confirmed from the Rietveld refinement of PXRD pattern, high resolution transmission emission microscopy (HR-TEM) and selected area electron diffraction (SAED) measurements. Elemental composition and oxidation state of palladium in Rb2PdF6 were examined using X-ray photoelectron spectroscopy (XPS) analysis. Ligand to metal charge transfer and d-d transitions of Pd (IV) were present in the UV–vis diffuse reflectance spectrum of Rb2PdF6 with a band gap of 2.67eV estimated using the Kubelka–Munk function. Its role as a catalyst to degrade the aqueous dye solutions (Methylene Blue, Malachite Green, Rhodamine-6G and Rhodamine-B) under UV–vis radiation has been evaluated along with their kinetics. The catalyst was active after four cycles of use. The reduction of Pd4+ to Pd0 by NaBH4 has been favourably used for the efficient and rapid conversion of highly carcinogenic, toxic, mutagenic Cr6+ to less toxic Cr3+. K2PdF6 possessing cubic K2PtCl6-type structure has also been synthesized for the first time by this method which presented yet another example for the alteration of reaction landscapes by mechanical forces.