Metallic bismuth nanoparticles: Towards a robust, productive and ultrasound assisted synthesis from batch to flow-continuous chemistry.

Bismuth is a highly biocompatible and inexpensive metal with a high atomic number, which confers an important X-rays opacity. While bismuth oxide or bismuth sulphide have been extensively studied in imaging, little is known about metallic bismuth nanoparticles. The latter are more attractive for X-rays imaging because they contain neither oxygen nor sulfur, so that a high amount of metal atoms is contained within the nanoparticles. We report here a robust, efficient and green ultrasound assisted synthesis to obtain metallic bismuth NPs. The procedure, which has been optimized to get a reproducible synthesis, will also tend to minimize chemical hazards to health and environment. By applying the green chemistry principles, several experimental parameters have been studied such as reaction time, reactants stoichiometry, temperature, starting material quantities and purification steps number. Two energy delivery system (classical heating and sonication) were compared. The production of small metallic bismuth NPs on a large scale by flow chemistry coupled to sonication was showed for the first time. These optimizations of the process were completed by a comparison of two purification methods (centrifugation and ultrafiltration) to isolate purified thin black powders of d-glucose-coated bismuth NPs. Several analytical techniques were used to characterize products (structures, sizes and morphology) such as Fourier Transform InfraRed (FT-IR) spectroscopy, Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), Energy-dispersive X-ray spectrometry (EDX) and X-Ray Diffraction (XRD). All these analyses corroborated well with the structure of metallic bismuth NPs coated with a d-glucose shell.