Production of rhenium nanoparticles by low-temperature aqueous-phase reduction of NH4ReO4 using NaBH4

The synthesis of refractory rhenium (Re) powders is significant for the production of rhenic products. In this work, the ultra-fine Re nanoparticles were synthesized via a combination of aqueous-phase reduction and rapid hydrogen reduction using NH 4 ReO 4 as Re source. The theoretical reduction route was determined by investigating the Eh-pH diagram of the Re -H 2 O system and conducting thermodynamic calculations. The optimal results were achieved by adjusting the experimental parameters like acid type, initial acidity, molar ratio of BH 4 − : ReO 4 − , feed rate of reductant, reaction temperature (T), and reaction time (t). The amorphous Re powders with minor oxide inclusions can be prepared under the optimized conditions of [HCl] = 1.35 mol L −1 , BH 4 − : ReO 4 − molar ratio = 5.32, feed rate = 15 mL min −1 , reaction temperature = 30 °C, and reaction time = 30 min. The maximum reduction efficiency reaches 99.5%. After annealing in hydrogen for 30 min, the crystalline Re nanoparticles with low oxygen content can be obtained. This work demonstrates the feasibility and efficacy of rapidly synthesizing ultra-fine Re nanoparticles in a solution-based approach.