Scalable diafiltration process for the purification of a colloidal dispersion of ultrasmall iron (oxyhydr)oxide-based nanoparticles

The process description for large-scale production of iron (oxyhydr)oxide nanoparticles is currently receiving greater attention, with cost-effective industrial production usually crucial for economic application. In this context, the purification step is often price-determining in the production process. Dialysis as membrane-assisted purification is one of the most widely used methods in the case of iron (oxyhydr)oxide nanoparticles but has very limited suitability for large-scale production. This study aims to demonstrate for the first time that cross–flow filtration is a suitable alternative for the industrial production of ultrasmall iron (oxyhydr)oxide nanoparticles. This study includes the development of a concentration and diafiltration process for ultrasmall iron (oxyhydr)oxide nanoparticles on a laboratory scale, upscaling for the purification of 75 kg nanoparticle suspension, and comparison with dialysis purification. In summary, the optimized filtration process is characterized by a consistent and high product quality and high product yield, comparable to dialysis purification and suitable for pilot-scale production. Finally, the results demonstrated that the developed process is an economically attractive alternative to dialysis. The processing time is reduced by 79 %, the water consumption is 96 % lower, and 66 % of the material costs are saved.