Modular 3D printed flow system for efficient one-step synthesis of phenyl-functionalised silica-coated superparamagnetic iron oxide nanoparticles†

Iron oxide nanoparticles (IONPs) are used in various applications, including magnetic solid phase extraction (MSPE), due to advantages such as excellent adsorption efficiency and easy separation from varied matrices using an external magnet. Here we introduce a low-cost 3D-printed modular flow system for the automated synthesis of phenyl-functionalised silica-coated iron oxide nanoparticles. This system consists of 3D-printed polypropylene (PP) reactors with varying geometries connected in series to synthesise bare IONPs, silica-coated IONPs, or phenyl-functionalised silica-coated IONPs using laminar flow regimes. The simplicity, affordability, robustness, and customisability of the system were illustrated. The synthesised IONPs were characterised using Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), zeta potential, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). The continuous flow system resulted in fast reactions under ambient conditions, with a production rate of approximately 5 mg min⁻¹. The produced IONPs were small (∼10 nm), resulting in a larger surface-to-volume ratio. Furthermore, the synthesised IONPs retained large enough saturation magnetisation values, which together with larger surface-to-volume ratios, is ideal for MSPE.