Spatiotemporal-resolved nanoparticle synthesis via simple programmed microfluidic processes

The spatiotemporally splitting nanoparticle (NP) formation route is critical but extremely challenging in terms of methodology development for large-scale continuous production of NPs with defined sizes, structures and properties, particularly for magnetic and/or hybrid NPs. Herein, we present transparent, chip-based, simple programmed microfluidic processes (C-SPMPs) and sequentially developed, transparent micro-tubing based simple programmed microfluidic processes (MT-SPMPs). By C-SPMPs and MT-SPMPs, four stages including mixing/reaction, nucleation, growth and termination during NPs formation could be well-separated and observed by the changes of flow color along the microchannels for the first time using magnetic Co, Fe, Ni, CoFe and NiFe NPs as examples. A four-section mechanism was proposed and discussed for the development of these strategies by the in situ monitoring of the changes in the relative C=O and C-O bond content in the coordinating cyclic lactam groups in the bi-channel solvent (i.e., N-methy-2-pyrrolidone) and the stabilizer (i.e., polyvinylpyrrolidone) and UV-vis spectra of reaction solution using the formation of CoFe NPs as a model. These strategies are beneficial for optimizing each stage by tuning channel length, flow rate, reactant concentration, and reaction and termination temperatures for the synthesis of NPs with uniform sizes of less than 5 nm. Their magnetic and optical properties were further evaluated, and they exhibited spin-glass-like behavior and unique ultra-violet absorbance, respectively. The developed SPMPs themselves preserve a scale-out feature with a current productivity of at least 13.0 g/(day-line) according to the Fe, Co or Ni content.