Route to Stabilization of Nanotechnetium in an Amorphous Carbon Matrix: Preparative Methods, XAFS Evidence, and Electrochemical Studies.

Abstract

Technetium-carbon nanophases are obtained by thermal decomposition of pertechnetates with large organic cations under an argon atmosphere. Parallel carbonization of organic cations (hexamethyleneiminium and triphenylguanidinium), which occurs during the thermal decomposition of their pertechnetates, leads to the formation of X-ray amorphous solid products. An X-ray absorption fine structure study revealed that they have a crystal structure containing technetium-carbon bonds with a length of 1.76 Å. After subsequent annealing treatment at 1073-1673 K, the synthesized technetium-carbon phase has a cubic lattice with an a of 4.01 ± 0.03 Å. The products of thermal decomposition of the same perrhenates are also X-ray amorphous; however, unlike that of pertechnetates, the distance between rhenium and carbon atoms in them is significantly greater (2.14 Å). After subsequent annealing, they have a hexagonal lattice. The electrochemical properties of technetium-carbon nanophases prepared by thermal decomposition of pertechnetates with large organic cations are different from the properties of those prepared with metallic technetium. The oxidation of technetium carbide to its oxides at the electrode surface observed in the first anodic scan of cyclic voltammograms can be used for the deposition of noble metal nanoclusters under open-circuit conditions to prepare composite catalysts for the hydrogen evolution reaction. Nanotechnetium in the amorphous carbon matrix can also be a prospective material for reactor transmutation of technetium to stable isotopically pure ruthenium-100.