The Use of Different Templates for the Synthesis of Reproducible Mesoporous Titania Thin Films and Small Pore Ultrafiltration Membranes

Abstract

State-of-the-art commercial membranes are made with the sol-gel method. But the pore size is somewhat restricted to control in a reproducible way. Furthermore, the synthesis of uniform pores via the sol-gel method is challenging, and therefore the resulting membranes often exhibit a limited selectivity. In contrast, the template-assisted method (evaporation-induced self-assembly) described herein is able to form defect-free membranes and thin films with more narrow pore size distributions and thus sharper cutoff curves in a more reproducible way. Moreover, the effect of different templates (Brij 58, Brij 56, Brij 78, Brij 76) and concentrations on the porosity of the titania top layer and separation performance is thoroughly investigated. The pore formation mechanism of the template-assisted method is discussed. Under the synthesis conditions described herein, the Brij templates act as a separator, whereby the final pore size can be easily controlled by adjusting the amount of template used. Furthermore, the pores obtained with this template-assisted method are more uniform. Such defect-free, reproducible small pore ultrafiltration membranes with controllable pore size and narrow pore size distribution can open the path to further process intensification and more sustainable production by separating molecules with a small difference in molecular weight.

Microstructure analysis of porous lead zirconate–titanate films

“…A different mechanism of porous structure formation is expected for Brij‐type solutions. Brij with different molecular weights (C n H 2 n +1 [EO] m OH) has been used as a structure‐directing agent in the self‐assembly of silicates, titania, zirconia, or other transition‐metal oxides, including in the EISA method 36,38,39,49 . Brij surfactants are hydrophilic nonionic block copolymer surfactants with hydroxyl groups 38 .…”

“…Of course, confirming this speculation would require additional detailed experiments using different experimental techniques and is, therefore, outside the scope of this study. Another possible reason is that the low combustion temperature of Brij (250-350°C) 36,38,39,49,81 and low dimensionality of the organic template make the porous media less resistant to densification during condensation and crystallization.…”

“…The other structure‐directing agents used in the present work are nonionic block copolymer surfactants: polyethylene glycol dodecyl ether (Brij 30 or Brij L4) and polyoxyethylene (10) stearyl ether (Brij 76) (Table 1). These surfactants have been used to prepare various mesoporous materials, including silicates, titania, zirconia, and hybrid organic–inorganic materials, via the self‐assembly process 36,38,39,49,50 . In the present work, porous films are deposited using the EISA method via the spin‐on coating technique.…”

Aggregate-Free Micrometer-Thick Mesoporous Silica Thin Films on Planar and Three-Dimensional Structured Electrodes by Hydrodynamic Diffusion Layer Control during Electrochemically Assisted Self-Assembly

“…Ordered mesoporous materials (i.e., pore size 2–50 nm) have numerous applications in the fields of biomedicine, drug delivery, catalysis, , separation, , energy storage, photonics, nanodevices, and sensors. , The ability to control and tailor the nanopore structure and material properties during synthesis is a critical aspect to tune the materials for the desired application. In this regard, the templated sol–gel synthesis has seen considerable evolution since the development in the 1990s − as a result of the use of structure-directing agents (e.g., surfactants or polymers) and the large number of controllable synthesis parameters (e.g., pH, temperature, and precursor type) that has led to a wide variety of porous materials with unique structures and properties .…”

“…Ordered mesoporous materials (i.e., pore size 2−50 nm) have numerous applications in the fields of biomedicine, 1 drug delivery, 2 catalysis, 3,4 separation, 5,6 energy storage, 7 photonics, 8 nanodevices, 9 and sensors. 10,11 The ability to control and tailor the nanopore structure and material properties during synthesis is a critical aspect to tune the materials for the desired application.…”