Ceramic membrane technology, whether applied as a stand-alone separation technology or in combination with energy-intensive approaches like distillation, is a promising solution for lower energy alternatives with minimal carbon footprints. To improve the separation of solutes in the nanofiltration range from industrial wastewater streams, ceramic nanofiltration (NF) membranes with reproducible sub-nanometre pore sizes are required. To achieve this, the emerging technique of molecular layer deposition (MLD) is employed to develop ceramic NF membranes, and its efficiency and versatility make it a powerful tool for preparing uniform nanoscale high-porosity membranes. Our work, which involved vapor-phase titanium tetrachloride as a precursor and ethylene glycol as a co-reactant, followed by calcination in air at 350 °C, resulted in NF membranes with pore sizes (radii) around ~0.8 ± 0.1 nm and a demineralized water permeability of 13 ± 1 L·m⁻²·h⁻¹·bar⁻¹.The high-water flux with >90% rejection of polyethylene glycol molecules with a molecular size larger than 380 ± 6 Dalton indicates the efficiency of the MLD technique in membrane functionalization and size-selective separation processes, and its potential for industrial applications.

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).