Optofluidic synthesis of metal/semiconductor Janus nanoparticles by laser photochemical deposition

During the last decade, there has been a tremendous interest in Janus particles with more than a thousand publications on synthesis, assembling, manipulation and active particle applications. Among the different associations, metal/semiconductors particles are scarce. Additionally, most of the syntheses are time consuming and produce rather low quantities of particles. To circumvent these difficulties, we present a general and flexible optofluidic strategy. Our method consists in exciting optically semiconductor nanoparticles (NPs) within their band gap to generate electron-hole pairs and use the electrons to photoactivate the redox transformation of an active ion present in the solution. Flow in a microchannel ensures continuous production. Considering its extensive application field, we choose TiO2 NPs as semiconductor. The NPs, are made dissymmetric by laser photodeposition of metals (Ag, Au) and the dissymmetry is investigated by varying chemical (morphology of the TiO2, metal precursor, pH of the solution, reagent concentration) and physical (beam power, flow rate of NPs) parameters. The generalization to other types of semiconductors such as ZnO is also demonstrated.