High throughput manufacturing of nanoparticles by membrane emulsification-precipitation processes

• Main Author: Medina Llamas, Maria
• Other Authors: Mattia, Davide
• Published: University of Bath 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.767591

The large-scale production of nanomaterials with fine control over their shape, size and properties remains a major obstacle towards their further use in a wide range of industrial applications. Therefore, the aim of the present PhD thesis is to assess the manufacturing of metal oxide NPs at large-scale using a membrane emulsification (ME)-precipitation process. In the project, flat and ring-shaped anodic alumina membranes (AAMS) were fabricated and their synthesis conditions optimised to obtain membranes with a narrow pore size distribution. Flat AAMs were used to produce oil-in-water nanoemulsions (NEs) in a dead-end stirred cell ME setup for the first time. Results show the regular pore structure and narrow pore size distribution of the AAMs enabled the formation of NEs with narrow droplet size distributions. The results demonstrated that rotational speed and membrane pore size were the key parameters in controlling the droplet size, with droplets as small as 144 ± 18 nm obtained, when Dpore = 58 ± 6 nm. Low proportionality values, Ddroplet/Dpore, ranging from 1.8 to 3.5, were obtained. Ring-shaped AAMs (Dp = 77 ± 9 nm) were synthetized for the first time with the purpose of producing oil-in-water NEs using a commercial stirred ME setup operating in a dead-end configuration. A systematic investigation of process parameters showed that narrow NEs were produced, obtaining proportionality constant values, as small as 2.8. Then, it was first reported the production of metal oxide NPs using an oil-in-water ME-precipitation process that can be easily scaled-up. For instance, we synthesized hematite NPs in a commercial dead-end ME setup fitted with a ring-shaped AAM and operating in a semi-continuous mode. The average primary particle size was 4.2 ± 0.5 nm and 18 ± 4 nm for the as-synthetized and calcined hematite NPs, respectively. Nevertheless, drying and calcination of the NPs leads to the formation of clusters in the micrometre range. Calculations of the emulsion production rate demonstrate the potential of the ME setup to produce up to 1.4 kg of per hour per metre square of membrane. Then, TiO2 NPs were synthesized in a continuous ME setup operating in a crossflow configuration, with the intention to produce NPs in a larger scale, with an average primary particle size ranging from 9.7 to 13.4 nm. The results show this manufacturing method can produce up to 2.8 kg NPs per hour per metre square of membrane. Non-metal doping was investigated, the results demonstrated the successful incorporation of interstitial nitrogen and carbon in the TiO2 lattice and showing a reduction of 1.05 eV in the band gap, which results in the formation of TiO2 NPs with photocatalytic response in the visible light spectrum.