RESUMO
Understanding the colloidal stability and aggregation behavior of TiO2 nanoparticles in aqueous suspension is a prerequisite to tune supracolloidal structure formation. While the aggregation mechanism for dried TiO2 nanopowders is well documented, there is still work to be done to understand TiO2 nanoparticle aggregation in suspension. Therefore, this work focuses on the colloidal stability and aggregation mechanism of TiO2 nanoparticle aqueous suspensions prepared using a straightforward one-step sol-gel-based approach over a concentration range of 0.5-5 wt %. Fully crystalline nanoparticles consisting primarily of anatase were obtained. After assessing the colloidal stability of the as-prepared suspensions, small-angle X-ray scattering coupled with fractal analysis was carried out. This analysis showed, for the first time, how the TiO2 nanoparticle aggregation mechanismâpredicted by the diffusion limited cluster-cluster aggregation (DLCA) and diffusion limited particle-cluster aggregation (DLA) theoriesâdepends directly on the starting concentration in the aqueous suspensions. We found that concentrated suspensions favored DLA, while dilute suspensions tend to follow the DLCA mechanism. The effect of the aggregation mechanism on the aggregate shape is also discussed.
RESUMO
Crosslinked PVDF-membranes are demonstrated to offer a viable alternative for centrifugation in the preparation of MOF-particles, thus realising new opportunities at lab-scale and continuous production at large-scale. The membranes combine extreme-pH with solvent stability, thus enabling application in any MOF synthesis, demonstrated here for ZIF-8, ZIF-67, HKUST-1, UiO-66 and MIL-53(Al).
