Creating Nanopores by Calcination of Titanicone Layers Grown by Atmospheric-Pressure Molecular Layer Deposition, for Application in Ceramic Nanofiltration Membranes

To improve the size-selective separation by ceramic membranes of solutes in the nanofiltration range from industrial wastewater streams, such membranes require reproducible sub-nm pore size tuning (1-4). To achieve this, the emerging technique of molecular layer deposition (MLD) is employed to coat and further tune ceramic NF membranes. Our work involved MLD using vapor-phase titanium tetrachloride as a precursor and ethylene glycol as a co-reactant, followed by calcination in air at 350 o C of the porogen titanicone layers grown inside. This resulted in nanofiltration membranes with pore radii of ~0.8 ± 0.1 nm, a water permeability of 13 ± 1 L⸳m − 2 ⸳h − 1 ⸳bar − 1 and a high water flux with >90 % rejection of polyethylene glycol molecules with a molecular size larger than 380 ± 6 Dalton. This indicates the potential of the MLD technique as a powerful tool for preparing nanoscale high-porosity membranes with excellent thermal stability and permeability-selectivity trade-off, by membrane functionalization and size-selective tuning. In separation technology such membranes offer a promising solution as lower energy alternative with reduced carbon footprints as opposed to conventional alternatives based on energy-intensive approaches like distillation and crystallization. References 1. M. Chen, et al. , Atmospheric-Pressure ALD : recent applications and new emerging applications in high porosity/ 3D materials , Dalton Transactions, 52 (10), 10254–10277 (2023), and references therein. 2. M.P. Nijboer, et al., Tuning Nanopores in Tubular Ceramic Nanofiltration Membranes with Atmospheric-Pressure ALD : Prospects for Pressure-Based In-line Monitoring of Pore Narrowing , Separations, 11 (1), 24 (2024). 3. H. Sondhi, et al. , Increasing hydrophobicity of ceramic membranes by post-deposition nitrogen annealing of MLD grown hybrid layers , Applied Surface Science, Part A, 683 , 161790 (2025). 4. H. Sondhi, et al., Ceramic nanofiltration membranes: creating nanopores by calcination of atmospheric-pressure MLD grown titanicone layers, Membranes, 15 (3) 86 (2025).