Continuous production of metal oxide nanoparticles via membrane emulsification-precipitation

A continuous and scalable method to produce metal oxide nanoparticles (NPs) with control of both particle size and composition via membrane emulsification (ME) is reported for the first time using an oil-in-water emulsion and a tubular ceramic membrane (Dpore = 100 nm). Using titania (TiO2) NPs as a model material, a systematic investigation of different process parameters allowed minimizing the emulsion droplet size, yielding a low droplet diameter to membrane pore diameter ratio of less than 3, compared to literature values of up to 10. After calcination, TiO2 NPs as small as 10 ± 2 nm were obtained. The particles' composition was changed via nonmetal doping, with the incorporation of interstitial nitrogen and carbon in the TiO2 lattice, confirmed by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS). The TiO2 NPs showed to be active for the photocatalytic degradation of phenol under both UV and visible light. Productivity calculations showed that it is possible to obtain ∼2 kg of NPs per hour per meter square of the membrane, opening the way to the large-scale production of NPs with fine control over their size and composition.