Semi-continuous production of iron oxide nanoparticles via membrane emulsification

The large-scale production of nanomaterials with fine control over their shape, size and properties remains a major obstacle towards their further use. Here, the semi-continuous production of metal oxide nanoparticles (NPs) via membrane emulsification (ME) is reported for the first time, using an oil-in-water emulsion and a commercial stirred ME setup fitted with a novel ring-shaped anodic alumina membrane (AAM). A systematic investigation of process parameters showed that the narrow pore size distribution of AAMs resulted in a narrow size distribution of both droplets and particles, with D_droplet/D_pore as small as 2.8, compared to typical literature values of 10 or more. The average particle size was 4.2 ± 0.5 nm and 18 ± 4 nm for the as-synthetized and calcined NPs, respectively. Calculations of the emulsion production rate demonstrate the potential of the ME setup to produce up to 1 kg of NP per hour per metre squared of membrane.