Removal of TcO4− ions from solution: materials and future outlook
Technetium mainly forms during artificial nuclear fission; it exists primarily as TcO4− in nuclear waste, and it is among the most hazardous radiation-derived contaminants because of its long half-life (t1/2 = 2.13 × 105 years) and environmental mobility. The high water solubility of TcO4− (11.3 mol L−1 at 20 °C) and its ability to readily migrate within the upper layer of the Earth's crust make it particularly hazardous. Several types of materials, namely resins, molecular complexes, layered double hydroxides, and pure inorganic and metal–organic materials, have been shown to be capable of capturing TcO4− (or other oxoanions) from solution. In this review, we give a brief description about the types of materials that have been used to capture TcO4− and closely related oxyanions so far and discuss the possibility of using metal–organic frameworks (MOFs) as next-generation ion-exchange materials for the stated application. In particular, with the advent of ultra-stable MOF materials, in conjunction with their chemical tunability, MOFs can be applied to capture these oxyanions under real-life conditions.